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Why are marine magnetic anomalies suppressed over sedimented spreading centers?
NASA Astrophysics Data System (ADS)
Levi, Shaul; Riddihough, Robin
The absence of lineated marine magnetic anomalies over sedimented, recent spreading centers has been observed in several areas. We propose that magnetic anomalies can be suppressed as a result of pervasive hydrothermal reactions underneath thick blankets of sediment. The relatively impermeable sediment cover produces comparatively closed hydrothermal systems, which increase the residence time of the hot fluids in basaltic layer 2, causing more thorough leaching of the remanence-carrying iron-titanium oxides and diminishing the marine magnetic anomalies. This contrasts with lesser alteration at sparsely or unsedimented zones of extension with more open circulation. Conversely, spreading ridges and oceanic crust characterized by absent or subdued lineated anomalies may signal sites of extensive hydrothermal mineralization. This process might also provide an explanation for some magnetic ōquiet zones,ö such as in the Gulf of California, the Gulf of Aden, and the northern Red Sea. *Present address: Earth Physics Branch, Department of Energy, Mines and Resources, Ottawa, Ontario K2A 0Y3, Canada
A New Seafloor Spreading Model of the Red Sea: Magnetic Anomalies and Plate Kinematics
NASA Astrophysics Data System (ADS)
Dyment, J.; Tapponnier, P.; Afifi, A. M.; Zinger, M. A.; Franken, D.; Muzaiyen, E.
A high resolution aeromagnetic survey over the Saudi Arabian side of the Red Sea confirms the existence of consistent magnetic anomaly patterns, continuous from 16 to 24░N, and episodic up to 28░N, typical of slow to ultraslow spreading centers. The older Saudi-Sudanese aeromagnetic survey shows that these anomalies are symmetrical between 18 and 23░N. The strong, short-wavelength anomalies over the central trough south of 24░N have long been identified as Chrons 1 to 3 (0-5 Ma). By contrast, the weaker, longer-wavelength anomalies over adjacent sediment-covered areas do not fit standard magnetic anomaly models. The abrupt basement deepening from ~ 1.5 km in the central trough to ~ 5 km beneath the sediments partly accounts for the lower amplitude but not for the lack of short wavelengths. Other spreading centers also lack short-wavelength, high-amplitude magnetic anomalies where covered by thick sediments (Andaman Basin, Juan de Fuca Ridge). We interpret this to reflect the absence of a well-defined layer of pillow lavas, whose emplacement is hampered by rapid, abundant sedimentation. The formation of dykes and sills instead of extrusive lavas results in weaker, less coherent magnetization, generating longer-wavelength anomalies. We test this inference by removing the extrusive basalt contribution from a slow spreading center crustal magnetization model. The computed magnetic anomalies fit well with the shape and amplitude of the anomalies observed in the Red Sea. Two major long-wavelength anomalies are dated at 10-11 Ma (Chron 5) and 14-15 Ma (Chron 5B), implying seafloor spreading back to at least 15 Ma and constraining plate-kinematic reconstructions. Beyond being a key to the geological evolution of the Red Sea, these results emphasize that oceanic crust may exist without clear, short wavelength magnetic anomalies, particularly at the onset of seafloor spreading, when abundant sedimentation may preclude the formation of pillow lavas. The location of many inferred ocean-continent boundaries, particularly beneath thick evaporite sequences, should therefore be revisited, alleviating the need for 'transitional' crust and allowing for a tighter fit of continents in initial reconstructions.
Contribution of oceanic gabbros to sea-floor spreading magnetic anomalies.
Kikawa, E; Ozawa, K
The contribution of oceanic gabbros, representative rocks for layer 3 of the oceanic crust, to sea-floor spreading magnetic anomalies has been controversial because of the large variation in magnetic properties. Ocean Drilling Program (ODP) Leg 118 contains a continuous 500.7-meter section of oceanic gabbro that allows the relations between magnetization and petrologic characteristics, such as the degree of metamorphism and the magmatic evolution, to be clarified. The data suggest that oceanic gabbros, together with the effects of metamorphism and of magmatic evolution, account for a significant part of the marine magnetic anomalies. PMID:17777035
Investigation of spreading center ecolution by joint inversion of seafloor magnetic anomaly and tectonic fabric data
NASA Technical Reports Server (NTRS)
Shoberg, Tom; Stein, Seth
Spreading center segments that have experienced a complex tectonic history including rift propagation may have a complicated signature in bathymetric and magnetic anomaly data. To gain insight into the history of such regions, we have developed techniques in which both the magnetic anomaly patterns and seafloor fabric trends are predicted theoretically, and the combined predictions are compared numerically with the data to estimate best fitting parameters for the propagation history. Fitting functions are constructed to help determine which model best matches the digitized fabric and magnetic anomaly data. Such functions offer statistical criteria for choosing the best fit model. We use this approach to resolve the propagation history of the Cobb Offset along the Juan de Fuca ridge. In this example, the magnetic anomaly data prove more useful in defining the geometry of the propagation events, while the fabric, with its greater temporal resolution, is more useful for constraining the rate of propagation. It thus appears that joint inversion of magnetic and seafloor fabric data can be valuable in tectonic analyses.
Early India-Australia spreading history revealed by newly detected Mesozoic magnetic anomalies in the Perth Abyssal Plain
Granot, Roi
Early India-Australia spreading history revealed by newly detected Mesozoic magnetic anomalies the early spreading history between India and Australia during the Mesozoic breakup of Gondwana. However from Australia with Greater India during initial breakup at ~130 Ma, then rifted from India following
Continuous sea-floor spreading in Red Sea: an alternative interpretation of magnetic anomaly pattern
La Brecque, J.L.; Zitellini
The magnetic anomaly pattern over the Red Sea can be modeled as a continuous system of sea-floor spreading from the early Miocene to the present by using a timevarying process filter. The half spreading rate is approximately 1 cm/yr (0.4 in./yr) since initial rifting. The parameters that determine the process filter and development of the transition zone are the intrusion parameter (a measure of the dispersion of feeder dikes or horizontal strain about the rift axis), a flow parameter (a measure of the average flow width), and the effusion parameter (a measure of the volcanic effusion and thickness of layer 2). The authors estimate the flow parameter to be 2.7km(1.7 mi) and the intrusion parameter to be 7.5km(4.7 mi) at early rifting. These values suggest that a wide distribution of axial dikes or horizontal strain is the dominant factor in forming the magnetic anomaly pattern. Reduction in the width of the intrusion parameter and the effusion rate as rifting proceeded resulted in focusing of the strain, thinning of layer 2, and formation of the Red Sea deeps. Their modeling suggests that phase 2, or the stratoid phase, began about the time of anomaly 5C or chron C5C approximately 16 Ma. This age is compatible with geologic estimates of the initial rifting at the late Oligocene to early Miocene (Coleman, 1974; Gass, 1977). The opening rate for Africa-Arabia plate motion has remained relatively constant since early rifting although the African margin appears to be accreting faster than the Arabian plate.
Opening of the Gulf of Mexico and the Nature of the Crust in the Deep Gulf: New Evidence from Seafloor Spreading Magnetic Anomalies
NASA Astrophysics Data System (ADS)
Harry, D. L.; Eskamani, P. K.
The seafloor spreading history in the Gulf of Mexico is poorly constrained due to a lack of recognized seafloor spreading magnetic anomalies, a paucity of deep penetrating seismic data, and absence of drilling to constrain crystalline ocean floor composition and ages. We have identified lineated magnetic anomalies in the eastern Gulf on profiles collected during the Woods Hole R/V Farnella FRNL85-2 cruise that correlate with magnetic chrons M21R to M10. Forward modeling shows that these anomalies formed during creation of weakly magnetized new seafloor in the eastern Gulf between 149-134 Ma at an average half-spreading rate of 3.2 cm/yr. The oldest anomalies are located against stretched continental crust beneath the western Florida shelf on the east and the Yucatan shelf on the west. The youngest anomalies form a juxtaposed conjugate pair that mark the location of an extinct spreading ridge between Yucatan and Florida. Seismic velocities of the crust in the eastern Gulf and the amplitude of the magnetic anomalies are similar to the Iberian and Newfoundland rifted margins, where the early stages of continental breakup were accommodated by exhumation of subcontinental lithosphere rather than creation of new basaltic oceanic crust. We infer that the eastern Gulf of Mexico is underlain by exhumed sub-continental peridotitic mantle intruded by lesser volumes of basaltic igneous rocks generated by decompression melting of the asthenosphere during the late stages of opening of the Gulf. The long wavelength characteristics of the magnetic and gravity fields in the eastern Gulf, as well as the seismic velocity structure of the crust, differ from those in the central and western Gulf, which are more similar to typical magmatic rifted margins. This suggests that the character of the Gulf changes along strike, from a magmatic western portion to an amagmatic eastern portion. Paleogeographic restoration of the lineated magnetic anomaly pattern suggests a 4-phase model for opening of the Gulf. During phase 1 (Early Permian-Late Triassic), Yucatan and associated tectonic blocks that now comprise eastern Mexico were translated eastward from the Pacific realm into positions near the modern western Gulf. During phase 2 (Late Triassic-ca. 160 Ma) Yucatan and the South Florida block were translated southeastward relative to North America, rotating 6.7? counterclockwise about a pole located at 34?N, 74?W. This resulted in ca. 430 km of southeastward extension on the North American coastal plain, 120 km of southward extension on the northern Yucatan shelf, and displacement of the South Florida Block from a pre-rift position on the northwest Florida shelf to its modern position. During phase 3 (ca. 160-149 Ma), Yucatan rotated counterclockwise 46? relative to North America about a pole located at 27.6?N, 84.0?W. Phase 3 may have coincided with seafloor spreading in the central and western Gulf, but predated seafloor spreading in the eastern Gulf. During phase 4 (149-134 Ma), Yucatan moved southwestward relative to North America, rotating counterclockwise 2.2? about a pole located at 17.6?N, 74.2?W and completing opening of the Gulf.
Updated interpretation of magnetic anomalies and seafloor spreading stages in the South China Sea - Implications for the Tertiary tectonics of Southeast Asia
Anne Briais; Philippe Patriat; Paul Tapponnier
An updated interpretation of the magnetic data of the South China Sea is presented, and its implications for the evolution of the South China Sea spreading ridge are discussed. A new identification of magnetic lineations in the basin is described. The kinematic parameters of spreading are then computed from the fit of the magnetic isochrons, and the characteristics of the
Marine Magnetic Anomalies, Oceanic Crust Magnetization, and Geomagnetic Time Variations
NASA Astrophysics Data System (ADS)
Dyment, J.; Arkani-Hamed, J.
Since the classic paper of Vine and Matthews (Nature, 1963), marine magnetic anomalies are commonly used to date the ocean floor through comparison with the geomagnetic polarity time scale and proper identification of reversal sequences. As a consequence, the classical model of rectangular prisms bearing a normal / reversed magnetization has been dominant in the literature for more than 40 years. Although the model explains major characteristics of the sea-surface magnetic anomalies, it is contradicted by (1) recent advances on the geophysical and petrologic structure of the slow-spreading oceanic crust, and (2) the observation of short-term geomagnetic time variations, both of which are more complex than assumed in the classical model. Marine magnetic anomalies may also provide information on the magnetization of the oceanic crust as well as short-term temporal fluctuations of the geomagnetic field. The "anomalous skewness", a residual phase once the anomalies have been reduced to the pole, has been interpreted either in terms of geomagnetic field variations or crustal structure. The spreading-rate dependence of anomalous skewness rules out the geomagnetic hypothesis and supports a spreading-rate dependent magnetic structure of the oceanic crust, with a basaltic layer accounting for most of the anomalies at fast spreading rates and an increasing contribution of the deeper layers with decreasing spreading rate. The slow cooling of the lower crust and uppermost mantle and serpentinization, a low temperature alteration process which produces magnetite, are the likely cause of this contribution, also required to account for satellite magnetic anomalies over oceanic areas. Moreover, the "hook shape" of some sea-surface anomalies favors a time lag in the magnetization acquisition processes between upper and lower magnetic layers: extrusive basalt acquires a thermoremanent magnetization as soon as emplaced, whereas the underlying peridotite and olivine gabbro cool slowly and pass through serpentinization to bear a significant magnetization. Our analysis of the amplitude of Anomaly 25 shows a sharp threshold at the spreading rate of 30 km/Ma, which corresponds to the transition between oceanic lithosphere built at axial domes and axial valleys. The twice lower amplitudes are in agreement with a much disrupted and altered basaltic layer at slow rates and a significant contribution from the deeper layers. Oceanic lithosphere created at fast and slow spreading rates therefore exhibits contrasted magnetic structures. High resolution magnetic anomaly measurements carried out with deep tows and submersibles show that the magmatic (fast spreading and parts of the slow spreading) crust is a good recorder of short-term geomagnetic time variations, such as short polarity intervals, excursions, or paleointensity variations. Surface and deep-sea magnetic anomalies therefore help to confirm or infirm geomagnetic findings obtained by other means. Many excursions and paleointensity variations within Brunhes and Matuyama periods are confirmed, but the "saw tooth pattern" inferred from sediment cores - a possible candidate to explain the anomalous skewness - is not, which suggests a bias in the sedimentary approach.
Magnetic Anomalies from Satellite Magnetometer
Isidore Zietz; Gordon E. Andreasen; Joseph C. Cain
Proton magnetometer measurements were made from the USSR satellite Cosmos 49 during the period October 24 to November 3, 1964. A selected number of the 18,000 observations were fitted to a special field model; residual anomalies were less than 100 gammas and appear to be consistent with belts of broad anomalies that are known from surface and nearsurface magnetic measurements.
Magnetic Anomaly Lineations in the Gulf of Aden
NASA Astrophysics Data System (ADS)
Noguchi, Y.; Nakanishi, M.; Tamaki, K.; Fujimoto, H.; Huchon, P.; Leroy, S.; Styles, P.
We present the magnetic anomaly lineations in the Gulf of Aden to expose the seafloor spreading history. The Gulf of Aden is a young ocean basin formed by the rifting of Arabia Plate away from Somalia Plate. The Arabian plate moves away from Somalia Plate in an NE direction, at a rate of about 2 cm/yr. The rifting started from Oligocene (Bosworth et al., 2005). Seafloor spreading started at about 20 Ma in the eastern part of the Gulf of Aden (Fournier et al., 2010) and propagated westward into the Arabia-Africa continent (Manighetti et al., 1997). It reached the Afar hotspot area about 10 Ma (Audin et al., 2001). The spreading system continues to interact with the hotspot up to the present. Tamsett and Searle (1988) exposed that strike of segmentations of the spreading centers in the Gulf of Aden is NW-SE, although the trend of the spreading system is ENE. We examined magnetic anomaly data collected in the cruises by R/V L'Atalante in 1995 and R/V Hakuho-maru from 2000 to 2001 as well as those collected in other cruises. Elongated negative magnetic anomalies, which amplitude are more than 500 nT, are observed over the spreading centers. Most of the elongated anomalies are parallel with the spreading centers. The elongated magnetic anomalies west of 46 30'E have an E-W trend around the spreading centers. Several discontinuities in the magnetic anomaly contour map illustrate the position of the fracture zones concealed by sediments. Most of magnetic anomaly lineations east of 46 30'E have an N60-65 W strike. Our identification of magnetic anomaly lineations indicates a symmetric seafloor spreading with a spreading rate of about 1.0 cm/yr, although Leroy et al. (2004) showed an asymmetric seafloor spreading of the Sheba Ridge, east of our study area. The kinematics of the Arabia plate changed about 5 Ma, but our results did not show any coeval change in spreading rates of the spreading system in the Gulf of Aden.
Spreading rate dependence of gravity anomalies along oceanic transform faults.
Gregg, Patricia M; Lin, Jian; Behn, Mark D; Montķsi, Laurent G J
Mid-ocean ridge morphology and crustal accretion are known to depend on the spreading rate of the ridge. Slow-spreading mid-ocean-ridge segments exhibit significant crustal thinning towards transform and non-transform offsets, which is thought to arise from a three-dimensional process of buoyant mantle upwelling and melt migration focused beneath the centres of ridge segments. In contrast, fast-spreading mid-ocean ridges are characterized by smaller, segment-scale variations in crustal thickness, which reflect more uniform mantle upwelling beneath the ridge axis. Here we present a systematic study of the residual mantle Bouguer gravity anomaly of 19 oceanic transform faults that reveals a strong correlation between gravity signature and spreading rate. Previous studies have shown that slow-slipping transform faults are marked by more positive gravity anomalies than their adjacent ridge segments, but our analysis reveals that intermediate and fast-slipping transform faults exhibit more negative gravity anomalies than their adjacent ridge segments. This finding indicates that there is a mass deficit at intermediate- and fast-slipping transform faults, which could reflect increased rock porosity, serpentinization of mantle peridotite, and/or crustal thickening. The most negative anomalies correspond to topographic highs flanking the transform faults, rather than to transform troughs (where deformation is probably focused and porosity and alteration are expected to be greatest), indicating that crustal thickening could be an important contributor to the negative gravity anomalies observed. This finding in turn suggests that three-dimensional magma accretion may occur near intermediate- and fast-slipping transform faults. PMID:17625563
Spread spectrum magnetic resonance imaging
Puy, Gilles; Gruetter, Rolf; Thiran, Jean-Philippe; Van De Ville, Dimitri; Vandergheynst, Pierre; Wiaux, Yves; 10.1109/TMI.2011.2173698
We propose a novel compressed sensing technique to accelerate the magnetic resonance imaging (MRI) acquisition process. The method, coined spread spectrum MRI or simply s2MRI, consists of pre-modulating the signal of interest by a linear chirp before random k-space under-sampling, and then reconstructing the signal with non-linear algorithms that promote sparsity. The effectiveness of the procedure is theoretically underpinned by the optimization of the coherence between the sparsity and sensing bases. The proposed technique is thoroughly studied by means of numerical simulations, as well as phantom and in vivo experiments on a 7T scanner. Our results suggest that s2MRI performs better than state-of-the-art variable density k-space under-sampling approaches
Magnetic anomalies northeast of Shatsky Plateau
Risch, David Lawrence
MAGNETIC ANOMALIES NORTHEAST OF SHATSKY PLATEAU A Thesis by DAVID LAWRENCE RISCH Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE May 1982 Major Subject...: Oceanography MAGNETIC ANOMALIES NORTHEAST OF SHATSKY PLATEAU A Thesis by DAVID LAWRENCE RISCH Approved as to style and content by: C rman Committee Member Member Head of Department May 198Z ABSTRACT Magnetic Anomalies Northeast of Shatsky Plateau...
An impactor origin for lunar magnetic anomalies.
Wieczorek, Mark A; Weiss, Benjamin P; Stewart, Sarah T
The Moon possesses strong magnetic anomalies that are enigmatic given the weak magnetism of lunar rocks. We show that the most prominent grouping of anomalies can be explained by highly magnetic extralunar materials from the projectile that formed the largest and oldest impact crater on the Moon: the South Pole-Aitken basin. The distribution of projectile materials from a model oblique impact coincides with the distribution of magnetic anomalies surrounding this basin, and the magnetic properties of these materials can account for the intensity of the observed anomalies if they were magnetized in a core dynamo field. Distal ejecta from this event can explain the origin of isolated magnetic anomalies far from this basin. PMID:22403388
Anorthosites as Sources of Magnetic Anomalies
Laurie L. Brown; Suzanne A. McEnroe; William H. Peck; Lars Petter Nilsson
\\u000a Magnetic anomalies provide information about location, size and composition of earth structures, ore bodies and tectonic features\\u000a even in bodies containing only a few percent magnetic minerals. Here we investigate the magnetic properties and oxide mineralogy\\u000a of anorthosites, rocks rich in plagioclase (>90%), and compare their magnetic signatures to aeromagnetic anomaly maps of the\\u000a regions. Two of the anorthosite complexes
Marine Magnetic Anomalies and the Reconstruction of the World
NASA Technical Reports Server (NTRS)
Heirtzler, James R.; Smith, David E. (Technical Monitor)
Until the middle of the 20th century little was known about magnetic anomalies in the oceans. Then it was discovered that there are relatively large anomalies in most of the oceans and they were unrelated to any geological structure known at that time. In the early 1950's large anomalies had been found over the Mid-Atlantic Ridge, and linear anomalies over the eastern continental shelf of North America and, shortly after that, off the west coast. A survey of the ridge south of Iceland showed that the anomalies were linear, parallel to the ridge axis, and symmetrical about the axis. Using the theory that the anomalies were caused by geomagnetic field reversals and seafloor spreading it was possible to greatly extend the time scale of geomagnetic reversals, to determine the velocity of seafloor spreading and estimate the time of opening of the North Atlantic. Lamont had a world-wide collection of marine magnetic profiles. These were used, systematically, to determine the positions of most of the land masses of the world since the beginnings of the world's present oceans.
Regional magnetic anomaly constraints on continental rifting
NASA Technical Reports Server (NTRS)
Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.
Radially polarized MAGSAT anomalies of North and South America, Europe, Africa, India, Australia and Antarctica demonstrate remarkably detailed correlation of regional magnetic lithospheric sources across rifted margins when plotted on a reconstruction of Pangea. These major magnetic features apparently preserve their integrity until a superimposed metamorphoric event alters the magnitude and pattern of the anomalies. The longevity of continental scale magnetic anomalies contrasts markedly with that of regional gravity anomalies which tend to reflect predominantly isostatic adjustments associated with neo-tectonism. First observed as a result of NASA's magnetic satellite programs, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans. Accordingly, satellite magnetic observations provide a further tool for investigating continental drift to compliment other lines of evidence in paleoclimatology, paleontology, paleomagnetism, and studies of the radiometric ages and geometric fit of the continents.
The magnetic anomaly of the Ivreazone
NASA Technical Reports Server (NTRS)
Albert, G.
A magnetic field survey was made in the Ivreazone in 1969/70. The results were: significant anomaly of the vertical intensity is found. It follows the basic main part of the Ivrea-Verbano zone and continues to the south. The width of the anomaly is about 10 km, the maximum measures about +800 gamma. The model interpretation shows that possibly the anomaly belongs to an amphibolitic body, which in connection with the Ivrea-body was found by deep seismic sounding. Therefore, the magnetic anomaly provides further evidence for the conception that the Ivrea-body has to be regarded as a chip of earthmantle material pushed upward by tectonic processes.
Reduction of satellite magnetic anomaly data
NASA Technical Reports Server (NTRS)
Slud, E. V.; Smith, P. J.; Langel, R. A.
Analysis of global magnetic anomaly maps derived from satellite data is facilitated by inversion to the equivalent magnetization in a constant thickness magnetic crust or, equivalently, by reduction to the pole. Previous inversions have proven unstable near the geomagnetic equator. The instability results from magnetic moment distributions which are admissible in the inversion solution but which make only small contribution to the computed values of anomaly field. Their admissibility in the solution could result from noisy or incomplete data or from small poorly resolved anomalies. The resulting magnetic moments are unrealistically large and oscillatory. Application of the method of principal components (e.g. eigenvalue decomposition and selective elimination of less significant eigenvectors) is proposed as a way of overcoming the instability and the method is demonstrated by applying it to the region around the Bangui anomaly in Central Africa.
Satellite-altitude horizontal magnetic gradient anomalies used to define the Kursk Magnetic Anomaly
NASA Astrophysics Data System (ADS)
Taylor, P. T.; Kis, K. I.; Wittmann, G.
The Kursk Magnetic Anomaly (KMA), Russia, is one of the world's largest magnetic anomalies. We used satellite altitude horizontal gradient magnetic anomaly data to study this feature. There are two main objectives of our research; the first, to determine if the technique of the horizontal magnetic anomaly gradient analysis can be applied to CHAMP satellite altitude data to define the outline of the source of the Kursk Magnetic Anomaly (KMA). Another objective is to use the ten years of CHAMP data to reproduce the horizontal magnetic anomaly gradient data that will be measured by the two lower orbiting ESA/Swarm mission. We will be able to evaluate the application of these newer satellite altitude data for studying large areas with significant crustal magnetization. While we have acquired sufficient CHAMP orbital data to compute a horizontal gradient anomaly map from these ten years of data; the future ESA/Swarm mission will, however, allow us to compute directly the horizontal magnetic anomaly without orbital altitude and/or magnetic secular variations; however the east-west gradient that the Swarm is measuring will minimize, but not eliminate, the difference in external fields between the two lower satellites. One will still need to use relatively quiet data (e.g., Kp < 1) for crustal field mapping. Our results, developed from interpreting the satellite horizontal magnetic anomaly data, indicate that the source of the KMA is bowl shaped body open to the northwest covering an area of approximately 190,000 km2.
Understanding Magnetic Anomalies and Their Significance.
ERIC Educational Resources Information Center
Shea, James H.
Describes a laboratory exercise testing the Vine-Matthews-Morley hypothesis of plate tectonics. Includes 14 questions with explanations using graphs and charts. Provides a historical account of the current plate tectonic and magnetic anomaly theory. (MVL)
Arctic and Asia lithospheric satellite magnetic anomalies
Douglas Alsdorf; Patrick Taylor; Ralph von Frese; Robert Langel; James Frawley
The polar regions present special problems in magnetic studies because they are largely inaccessible and contain the most disturbed magnetic fields on earth (e.g., effects from auroral phenomena). A processing method, previously developed for south polar satellite magnetic data (e.g., Magsat), is applied to north polar data to separate the core and external fields from the lithospheric anomalies. The core
Inversion of marine magnetic anomalies by deconvolution
Harry, Dennis Lee
INVERSION OF MARINE MAGNETIC ANOMALIES BY DECONVOLUTION A Thesis by DENNIS LEE HARRY Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE December 1983 Maj... or Subject: Geophysics INVERSION OF MARINE MAGNETIC ANOMALIES BY DECONVOLUTION A Thesis by DENNIS LEE HARRY Approved as to style and content by: Phi p ~yrnowxtz (Co-Chairman of Committee) Richard L. Garison (Co-Chairman of Committee) Davis A...
Regional magnetic anomaly constraints on continental breakup
von Frese, R.R.B.; Hinze, W.J.; Olivier, R.; Bentley, C.R.
Continental lithosphere magnetic anomalies mapped by the Magsat satellite are related to tectonic features associated with regional compositional variations of the crust and upper mantle and crustal thickness and thermal perturbations. These continental-scale anomaly patterns when corrected for varying observation elevation and the global change in the direction and intensity of the geomagnetic field show remarkable correlation of regional lithospheric magnetic sources across rifted continental margins when plotted on a reconstruction of Pangea. Accordingly, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans.
The mineralogy of global magnetic anomalies
NASA Technical Reports Server (NTRS)
Haggerty, S. E. (principal investigator)
Experimental and analytical data on magnetic mineralogy was provided as an aid to the interpretation of magnetic anomaly maps. An integrated program, ranging from the chemistry of materials from 100 or more km depth within the Earth, to an examination of the MAGSAT anomaly maps at about 400 km above the Earth's surface, was undertaken. Within this framework, a detailed picture of the pertinent mineralogical and magnetic relationships for the region of West Africa was provided. Efforts were directed toward: (1) examining the geochemistry, mineralogy, magnetic properties, and phases relations of magnetic oxides and metal alloys in rocks demonstrated to have originated in the lower crust of upper mantle, (2) examining the assumption that these rocks portray the nature of their source regions; and (3) examining the regional geology, tectonics, gravity field and the MAGSAT anomaly maps for West Africa.
Deeptow magnetic survey of the Pacific Jurassic Quiet Zone: Implications for the marine magnetic anomaly timescale
NASA Astrophysics Data System (ADS)
Tivey, M. A.; Sager, W. W.; Lee, S.
We present results of a recently completed near-bottom magnetic survey of the Pacific Jurassic quiet zone located in Pigafetta Basin in the vicinity of ODP Hole 801C. A total of ~1550 km of tracklines were completed during 5 lowerings of the DSL120 sidescan sonar system of the National Deep Submergence Facility equipped with two magnetometer systems. The nominal altitude of the vehicle was 100 m above the seafloor with the average sediment thickness ~300 meters. We collected simultaneous vector magnetic data from a digital Honeywell HMR2300 magnetoresistor sensor and absolute total field using a Marine Magnetics Overhauser sensor provided by KORDI. The survey had four primary goals: 1) to investigate the presence or absence of magnetic lineations related to seafloor spreading around ODP Hole 801C, 2) to extend the magnetic anomaly mapping south to the Rough-Smooth (RS) boundary, thought to be the limit of the oldest Pacific crust, 3) to extend and confirm correlations of previously collected deeptow results, and 4) to investigate the M33-M34 sequence which can be clearly correlated with the timescale but also shows a period of rapid field reversal. The survey around Hole 801C was navigated within a transponder net whereas the remainder of the surveys were navigated using acoustic layback and bottom-lock doppler. From our results, we confirm that anomalies in the M33-M34 sequence are highly-lineated and well-correlated between adjacent lines with a high reversal rate. We found that anomalies older than M36 become harder to correlate to about M40 where there may be a possible change in trend of the anomaly strike. The anomaly record appears to become more linear again as Hole 801C is approached. Around Hole 801C the anomalies show a clear lineation with a strike direction of 25 degrees, although the correlation is not as consistent as the younger anomaly sequence. The decrease in anomaly amplitude that is seen from M21 through the M36 sequence appears to be low through anomaly M40 and then increases to a higher value thereafter with an average amplitude of 200 nT at deeptow altitude. South of Hole 801C towards the RS boundary we find that magnetic anomalies continue with short-wavelength anomalies superimposed on a longer wavelength anomalies making them difficult to correlate. High amplitude anomalies mark the RS boundary itself. In summary, we find evidence for seafloor spreading anomalies throughout the survey area although there are areas where correlation is difficult.
Continental magnetic anomaly constraints on continental reconstruction
NASA Technical Reports Server (NTRS)
Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.
Crustal magnetic anomalies mapped by the MAGSAT satellite for North and South America, Europe, Africa, India, Australia and Antarctica and adjacent marine areas were adjusted to a common elevation of 400 km and differentially reduced to the radial pole of intensity 60,000 nT. These radially polarized anomalies are normalized for differential inclination, declination and intensity effects of the geomagnetic field, so that in principle they directly reflected the geometric and magnetic polarization attributes of sources which include regional petrologic variations of the crust and upper mantle, and crustal thickness and thermal perturbations. Continental anomalies demonstrate remarkably detailed correlation of regional magnetic sources across rifted margins when plotted on a reconstruction of Pangea. Accordingly, they suggest further fundamental constraints on the geologic evolution of the continents and their reconstructions.
CHAMP Magnetic Anomalies of the Antarctic Crust
NASA Technical Reports Server (NTRS)
Kim, Hyung Rae; Gaya-Pique, Luis R.; vonFrese, Ralph R. B.; Taylor, Patrick T.; Kim, Jeong Woo
Regional magnetic signals of the crust are strongly masked by the core field and its secular variations components and hence difficult to isolate in the satellite measurements. In particular, the un-modeled effects of the strong auroral external fields and the complicated- behavior of the core field near the geomagnetic poles conspire to greatly reduce the crustal magnetic signal-to-noise ratio in the polar regions relative to the rest of the Earth. We can, however, use spectral correlation theory to filter the static lithospheric and core field components from the dynamic external field effects. To help isolate regional lithospheric from core field components, the correlations between CHAMP magnetic anomalies and the pseudo magnetic effects inferred from gravity-derived crustal thickness variations can also be exploited.. Employing these procedures, we processed the CHAMP magnetic observations for an improved magnetic anomaly map of the Antarctic crust. Relative to the much higher altitude Orsted and noisier Magsat observations, the CHAMP magnetic anomalies at 400 km altitude reveal new details on the effects of intracrustal magnetic features and crustal thickness variations of the Antarctic.
Equivalent magnetization over the World's Ocean and the World Digital Magnetic Anomaly Map
NASA Astrophysics Data System (ADS)
Dyment, Jerome; Choi, Yujin; Hamoudi, Mohamed; Thķbault, Erwan; Quesnel, Yoann; Roest, Walter; Lesur, Vincent
As a by-product of our recent work to build a candidate model over the oceans for the second version of the World Digital Magnetic Anomaly Map (WDMAM), we derived global distributions of the equivalent magnetization in oceanic domains. In a first step, we use classic point source forward modeling on a spherical Earth to build a forward model of the marine magnetic anomalies at sea-surface. We estimate magnetization vectors using the age map of the ocean floor, the relative plate motions, the apparent polar wander path for Africa, and a geomagnetic reversal time scale. We assume two possible magnetized source geometry, involving both a 1 km-thick layer bearing a 10 A/m magnetization either on a regular spherical shell with a constant, 5 km-deep, bathymetry (simple geometry) or following the topography of the oceanic basement as defined by the bathymetry and sedimentary thickness (realistic geometry). Adding a present-day geomagnetic field model allows the computation of our initial magnetic anomaly model. In a second step, we adjust this model to the existing marine magnetic anomaly data, in order to make it consistent with these data. To do so, we extract synthetic magnetic along the ship tracks for which real data are available and we compare quantitatively the measured and computed anomalies on 100, 200 or 400 km-long sliding windows (depending the spreading rate). Among the possible comparison criteria, we discard the maximal range - too dependent on local values - and the correlation and coherency - the geographical adjustment between model and data being not accurate enough - to favor the standard deviation around the mean value. The ratio between the standard deviations of data and model on each sliding window represent an estimate of the magnetization ratio causing the anomalies, which we interpolate to adjust the initial magnetic anomaly model to the data and therefore compute a final model to be included in our WDMAM candidate over the oceanic regions lacking data. The above ratio, after division by the magnetization of 10 A/m used in the model, represents an estimate of the equivalent magnetization under the considered magnetized source geometry. The resulting distributions of equivalent magnetization are further discussed in terms of mid-ocean ridges, presence of hotspots and oceanic plateaus, and the age of the oceanic lithosphere. Global marine magnetic data sets and models represent a useful tool to assess first order magnetic properties of the oceanic lithosphere.
Magnetic anomalies northeast of Cape Adare, northern Victoria Land (Antarctica), and their relation to onshore structures
Damaske, D.; Lõufer, A.L.; Goldmann, F.; M÷ller, H.-D.; Lisker, F.
An aeromagnetic survey was flown over the offshore region northeast of Cape Adare and the magnetic anomalies compared to onshore structures between Pennell Coast and Tucker Glacier. The magnetic anomalies show two nearly orthogonal major trends. NNW-SSE trending anomalies northeast of Cape Adare represent seafloor spreading within the Adare Trough. A connection of these anomalies to the Northern Basin of the Ross Sea is not clear. Onshore faults are closely aligned to offshore anomalies. Main trends are NW-SE to NNW-SSE and NE-SW to NNESSW. NNW-SSE oriented dextral-transtensional to extensional faults parallel the Adare Peninsula and Adare Trough anomalies. NE-SW trending normal faults appear to segment the main Hallett volcanic bodies.
Remanent magnetizations of oceanic basalts on the back-arc spreading axis in the southern Mariana
NASA Astrophysics Data System (ADS)
Mochizuki, N.; Nogi, Y.; Asada, M.; Yoshikawa, S.; Okino, K.
Magnetic anomaly high on a spreading axis has been a well-known character of the magnetic anomalies in the ocean, which is mainly related to magnetization intensity reduction with age due to low-temperature oxidation of titanomagnetite. Recently, a few deep-sea magnetic observations on the fast spreading axis showed that magnetization of the oceanic crust reflects relative paleointensity variation of the Brunhes Chron. These data suggest that the magnetization of oceanic basalt appears to reflect the geomagnetic intensity variation (i.e. the original thermoremanent magnetization (TRM) intensity variation) in spite of the alteration process (low-temperature oxidation of titanomagnetite). Previous studies discussed magnetization of oceanic crust on the basis of the natural remanent magnetization (NRM) itself. Therefore they cannot precisely estimate the alteration effect on magnetizations. In this study, we have reported progressive demagnetization results of NRM, anhysteretic remanent magnetization (ARM), and saturation isothermal remanent magnetization (SIRM) for the oceanic basalts on the back-arc spreading axis in the southern Mariana and discuss fundamental properties of magnetization of oceanic basalt.
Superconducting magnetic calibration source for magnetic anomaly detection MAD operations
M. Nisenoff; J. J. Kennedy; A. W. Webb
A superconducting solenoid was designed, built and tested to demonstrate the feasibility of using this type of device as a calibration source for Magnetic Anomaly Detection operations. A description of the dewar system required for such a solenoid is also described. The magnetic moment of the solenoid which was 48 cm in outer diameter, was 150,000 ampere-turns-meter squared.
Lunar magnetic anomalies and the Cayley formation
NASA Technical Reports Server (NTRS)
Strangway, D. W.; Gose, W. A.; Pearce, G. W.; Mcconnell, R. K.
It is proposed that magnetic anomalies such as found at the Apollo 16 site are associated with breccia flows which cooled in place from above 770 C. The required field at the time that this process took place is a few thousand gamma. It is suggested that the surface and orbital magnetic anomalies are caused by basins filled with Cayley-like breccia flows to a thickness of the order of a kilometer. These breccia blankets settled in place from temperatures above 770 C and a thickness on the order of 1 km was welded to a level of 2 to 4 on Warner's scale. A base surge caused by impact or by a volcanic event could be the mechanism by which these breccia blankets were deposited.
Spreading of Psoriatic Plaques: Alteration of Epidermal Differentiation Precedes Capillary Leakiness and Anomalies in Vascular Morphology
Dominique Parent; Bruno A. Bernard; Christiane Desbas; Michel Heenen; Michel Y. Darmon
To approach the temporal relationship between alterations in keratinization and capillary leakiness in psoriasis, we studied the topography of these anomalies in spreading psoriatic lesions- Histological and immunohistochemical studies were performed on skin biopsies obtained from normal individuals and from psoriatic patients. In the latter case, biopsies were taken in uninvolved skin, in the center of lesions, and at the
Paleo-Pole Positions from Martian Magnetic Anomaly Data
NASA Technical Reports Server (NTRS)
Taylor, Patrick T.; Frawley, James J.
Magnetic component anomaly maps were made from five mapping cycles of the Mars Global Surveyor s magnetometer data. Our goal was to find and isolate positive and negative anomaly pairs which would indicate magnetization of a single source body. From these anomalies we could compute the direction of the magnetizing vector and subsequently the location of the magnetic pole existing at the time of magnetization. We found nine suitable anomaly pairs and from these we computed four North and 3 South poles with two at approximately 60 degrees north latitude. These results suggest that during the existence of the Martian main magnetic field it experienced several reversals.
Paleo-Pole Positions from Martian Magnetic Anomaly Data
NASA Technical Reports Server (NTRS)
Frawley, James J.; Taylor, Patrick T.
Magnetic component anomaly maps were made from five mapping cycles of the Mars Global Surveyor's magnetometer data. Our goal was to find and isolate positive and negative anomaly pairs which would indicate magnetization of a single source body. From these anomalies we could compute the direction of the magnetizing vector and subsequently the location of the magnetic pole existing at the time of magnetization. We found nine suitable anomaly pairs and from these we computed paleo-poles that were nearly equally divided between north, south and mid-latitudes. These results suggest that during the existence of the martian main magnetic field it experienced several reversals and excursions.
A global magnetic anomaly map. [obtained from POGO satellite data
NASA Technical Reports Server (NTRS)
Regan, R. D.; Davis, W. M.; Cain, J. C.
A subset of POGO satellite magnetometer data has been formed that is suitable for analysis of crustal magnetic anomalies. Using a thirteenth order field model, fit to these data, magnetic residuals have been calculated over the world to latitude limits of plus 50 deg. These residuals averaged over one degree latitude-longitude blocks represent a detailed global magnetic anomaly map derived solely from satellite data. Preliminary analysis of the map indicates that the anomalies are real and of geological origin.
New Magnetic Anomaly Compilation Illuminates the Formation of the Aleutian Basin
NASA Astrophysics Data System (ADS)
Scheirer, D. S.; Barth, G. A.; Scholl, D. W.; Stern, R. J.
Aleutian Basin crust is deeply buried beneath 2 to 5 km of sediment, so magnetic data provide valuable insights into its structure and origin. A new compilation of marine magnetic anomalies, derived from one recent cruise (2011) and re-analysis of dozens of legacy cruises (primarily 1970's to 1980's), provides both a refined view of the magnetic field in the Bering Sea area and insights into the formation of the deep-water Aleutian and Bowers Basins. In the Aleutian Basin, the magnetic fabric can be divided into two similar-sized areas of distinct types. Type 1 magnetic fabric is characterized by north-south-oriented lineations in the southern Aleutian Basin. The lineations have irregular spacing, reminiscent of seafloor spreading stripes, and the amplitudes of the anomalies are also consistent with a magnetic source formed at spreading centers. Seismic reflection data show that the strongest magnetic lineations in the Type 1 area are not associated with basement relief, supporting an origin from remanent magnetization variations and consistent with their formation by seafloor spreading. This interpretation is consistent with OBS refraction results indicating that this is mafic crust ~8 km thick. The pattern of anomalies does not show an obvious symmetry about a possible fossil spreading axis, and attempts to assign the sequence of lineaments to the geomagnetic polarity timescale are not definitive. Thus, we cannot rule out either of the two hypotheses for the formation of the Aleutian Basin, as a Paleogene back-arc basin or as captured (old) plate trapped by formation of the Aleutian subduction zone at ~50 Ma. Type 2 magnetic fabric is characterized by higher-amplitude and more heterogeneous magnetic anomalies than Type 1 fabric, and it is located around the margins of the Aleutian Basin, to the north and west of the lineated fabric. Some features of the basement (e.g. Sounder Ridge) have corresponding magnetic anomalies in Type 2 areas, but other anomalies with little basement topography imply significant variations in the magnetic properties (susceptibility, remnant strength, or both) of the igneous crust. Seismic imaging and dredging near the Beringian Margin indicate that significant extensional deformation and subsidence of the margin has occurred seaward into the deep-water Aleutian Basin, and the boundary between Type 2 and Type 1 magnetic fabric may indicate the boundary between modified-continental crust and oceanic crust.
Continental and oceanic magnetic anomalies: Enhancement through GRM
NASA Technical Reports Server (NTRS)
Vonfrese, R. R. B.; Hinze, W. J.
In contrast to the POGO and MAGSAT satellites, the Geopotential Research Mission (GRM) satellite system will orbit at a minimum elevation to provide significantly better resolved lithospheric magnetic anomalies for more detailed and improved geologic analysis. In addition, GRM will measure corresponding gravity anomalies to enhance our understanding of the gravity field for vast regions of the Earth which are largely inaccessible to more conventional surface mapping. Crustal studies will greatly benefit from the dual data sets as modeling has shown that lithospheric sources of long-wavelength magnetic anomalies frequently involve density variations which may produce detectable gravity anomalies at satellite elevations. Furthermore, GRM will provide an important replication of lithospheric magnetic anomalies as an aid to identifying and extracting these anomalies from satellite magnetic measurements. The potential benefits to the study of the origin and characterization of the continents and oceans, that may result from the increased GRM resolution are examined.
Anomalies and Transport Coefficients: The Chiral Gravito-Magnetic Effect
Landsteiner, Karl; Pena-Benitez, Francisco
Axial anomalies give rise to interesting new transport phenomena such as the "chiral magnetic effect". We discuss how the associated transport coefficients can be studied via Kubo formulas at weak and strong coupling, the latter via gauge gravity duality. We argue for a new "chiral gravito-magnetic" (or vortical) effect sensitive to the presence of mixed gauge-gravitational anomalies.
Anomalies and Transport Coefficients: The Chiral Gravito-Magnetic Effect
Karl Landsteiner; Eugenio Megias; Francisco Pena-Benitez
Axial anomalies give rise to interesting new transport phenomena such as the "chiral magnetic effect". We discuss how the associated transport coefficients can be studied via Kubo formulas at weak and strong coupling, the latter via gauge gravity duality. We argue for a new "chiral gravito-magnetic" (or vortical) effect sensitive to the presence of mixed gauge-gravitational anomalies.
Influence of Impact Ejecta on Crustal Magnetic Field Anomalies.
NASA Astrophysics Data System (ADS)
Kuzmicheva, M.; Losseva, T.
A role of impact ejecta and post-impact atmospheric plume in providing magnetic anomalies is considered. It is shown that impact-ejecta generated magnetic field can provide both positive and negative anomalies. Geomagnetic field disturbances detected after the Tunguska bolide explosion are discussed.
Magnetic field anomaly detector using magnetoelectric composites
NASA Astrophysics Data System (ADS)
Bergs, Richard; Islam, Rashed A.; Vickers, Michael; Stephanou, Harry; Priya, Shashank
This study reports the low frequency magnetoelectric (ME) response of the sintered composites comprising of a piezoelectric phase Pb(Zr0.52Ti0.48)O3 (PZT) and magnetostrictive phases NiFe1.9Mn0.1O4 (NFM) and Ni0.8Zn0.2Fe2O4 (NZF) with varying ferrite contents of 3, 5, 10, 15, and 20mol%. It was found that the ME coefficient for the PZT-NZF samples shows considerably less scattering as a function of frequency and the composition 0.8PZT-0.2NZF exhibited a flat response in the range of 10-100Hz with a magnitude of 220mV /cmOe. This composition was used to design the magnetic field anomaly detector mounted in front of a global positioning system (GPS) controlled vehicle. The results from the vehicle test clearly demonstrate the feasibility of using sintered ME composites for magnetic field detection in the noisy environment.
Statistical analysis of the lithospheric magnetic anomaly data
NASA Astrophysics Data System (ADS)
Pavon-Carrasco, Fco Javier; de Santis, Angelo; Ferraccioli, Fausto; Catalßn, Manuel; Ishihara, Takemi
Different analyses carried out on the lithospheric magnetic anomaly data from GEODAS DVD v5.0.10 database (World Digital Magnetic Anomaly Map, WDMAM) show that the data distribution is not Gaussian, but Laplacian. Although this behaviour has been formerly pointed out in other works (e.g., Walker and Jackson, Geophys. J. Int, 143, 799-808, 2000), they have not given any explanation about this statistical property of the magnetic anomalies. In this work, we perform different statistical tests to confirm that the lithospheric magnetic anomaly data follow indeed a Laplacian distribution and we also give a possible interpretation of this behavior providing a model of magnetization which depends on the variation of the geomagnetic field and both induced and remanent magnetizations in the terrestrial lithosphere.
Axial anomaly of QED in a strong magnetic field and noncommutative anomaly
Sadooghi, N. [Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of); Institute for Studies in Theoretical Physics and Mathematics (IPM), School of Physics, P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of); Jafari Salim, A. [Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of)
The Adler-Bell-Jackiw (ABJ) anomaly of a 3+1 dimensional QED is calculated in the presence of a strong magnetic field. It is shown that in the regime with the lowest Landau level (LLL) dominance a dimensional reduction from D=4 to D=2 dimensions occurs in the longitudinal sector of the low energy effective field theory. In the chiral limit, the resulting anomaly is therefore comparable with the axial anomaly of a two-dimensional massless Schwinger model. It is further shown that the U{sub A}(1) anomaly of QED in a strong magnetic field is closely related to the nonplanar axial anomaly of a conventional noncommutative U(1) gauge theory.
The south-central United States magnetic anomaly
NASA Technical Reports Server (NTRS)
Hinze, W. J.; Braile, L. W. (principal investigators); Starich, P. J.
The South-Central United States Magnetic Anomaly is the most prominent positive feature in the MAGSAT scalar magnetic field over North America. The anomaly correlates with increased crustal thickness, above average crustal velocity, negative free air gravity anomalies and an extensive zone of Middle Proterozoic anorogenic felsic basement rocks. Spherical dipole source inversion of the MAGSAT scalar data and subsequent calculation of reduced to pole and derivative maps provide constraints for a crustal magnetic model which corresponds geographically to the extensive Middle Proterozoic felsic rocks trending northeasterly across the United States. These felsic rocks contain insufficient magnetization or volume to produce the anomaly, but are rather indicative of a crustal zone which was disturbed during a Middle Proterozoic thermal event which enriched magnetic material deep in the crust.
The south-central United States magnetic anomaly
NASA Technical Reports Server (NTRS)
Starich, P. J.
The South-Central United States Magnetic Anomaly is the most prominent positive feature in the MAGSAT scalar magnetic field over North America. The anomaly correlates with increased crustal thickness, above average crustal velocity, negative free-air gravity anomalies and an extensive zone of Middle Proterozoic anorogenic felsic basement rocks. Spherical dipole source inversion of the MAGSAT scalar data and subsequent calculation of reduced-to-pole and derivative maps provide additional constraints for a crustal magnetic model which corresponds geographically to the extensive Middle Proterozoic felsic rocks trending northeasterly across the United States. These felsic rocks contain insufficient magnetization or volume to produce the anomaly, but are rather indicative of a crustal zone which was disturbed during a Middle Proterozoic thermal event which enriched magnetic material deep in the crust.
Study of gravity and magnetic anomalies using MAGSAT data
NASA Technical Reports Server (NTRS)
Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (principal investigators)
The results of modeling satellite-elevation magnetic and gravity data using the constraints imposed by near surface data and seismic evidence shows that the magnetic minimum can be accounted for by either an intracrustal lithologic variation or by an upwarp of the Curie point isotherm. The long wavelength anomalies of the NOO's-vector magnetic survey of the conterminous U.S. were contoured and processed by various frequency filters to enhance particular characteristics. A preliminary inversion of the data was completed and the anomaly field calculated at 450 km from the equivalent magnet sources to compare with the POGO satellite data. Considerable progress was made in studing the satellite magnetic data of South America and adjacent marine areas. Preliminary versions of the 1 deg free-air gravity anomaly map (20 m gal contour interval) and the high cut (lambda approximately 8 deg) filtered anomaly maps are included.
Magnetic satellite anomalies and tectonostratigraphic terranes over Mexico
NASA Astrophysics Data System (ADS)
Hernßndez-Quintero, E.; Campos-EnrĒquez, O.
Satellite magnetic data from Magsat are described and correlated with surface or near surface magnetic studies between 10░ and 35░ north latitude and 85░ and 120░ west longitude. Mexico is featured by six satellite regional magnetic anomalies. Based in such results we made a detailed description of these magnetic anomalies (geographic extension, intensity, polarity). In order to approach our goal, filtering and enhancement of magnetic features were made (i.e., reduction to the pole, first and second vertical derivatives) resulting some maps where such features appear more clear. A first attempt to correlate these data with other studies such as gravimetry, geology, seismicity, heat flow, available in Mexico were developed in order to have a more basis to infer their origin. We found in some areas a high correlation between tectonostratigraphic Mexican terranes and magnetic satellite anomalies. According to our study there is evidence of magnetic material in the crust along the Gulf of Mexico coast plains with a degree of correlation with north Mayan terrane. Trans-Mexican Volcanic Belt (MVB) is divided in a more magnetic area to the east with a thick crust and low heat flow, meanwhile the west part is less magnetic with a thinner crust and high heat flow. Cochimi (ultramafic), Pericu and Yuma terranes are correlated with a magnetic anomaly to the south of Baja California peninsula. Magnetic anomaly observed in the Gulf of Mexico is well correlated with oceanic crust. Maya terrane is composed by magnetic crust. Likewise Mohave-Sonora Megashear seems to be southern limit of an anomaly located in the west part of Texas. The South of the studied area points that Mixteco, Zapoteco and Cuicateco terranes are underlied with magnetic material. Anomalies in Baja California peninsula and Middle America Trench, could be associated with pieces of the extinct oceanic Farallon plate. Our results seem to correlate with the existence of Oaxaquia terrane. Finally we present preliminary interpretation of three profiles.
Hematite Versus Magnetite as the Signature for Planetary Magnetic Anomalies?
NASA Technical Reports Server (NTRS)
Kletetshka, Gunther; Taylor, Patrick T.; Wasilewski, Peter J.
Crustal magnetic anomalies are the result of adjacent geologic units having contrasting magnetization. This magnetization arises from induction and/or remanence. In a planetary context we now know that Mars has significant crustal magnetic anomalies due to remanent magnetization, while the Earth has some anomalies where remanence can be shown to be important. This picture, however, is less clear because of the nature and the magnitude of the geomagnetic field which is responsible for superimposed induced magnetization. Induced magnetization assumes a magnetite source, because of its much greater magnetic susceptibility when compared with other magnetic minerals. We investigated the TRM (thermoremanent magnetization) acquisition of hematite, in weak magnetic fields up to 1 mT, to determine if the remanent and induced magnetization of hematite could compete with magnetite. TRM acquisition curves of magnetite and hematite show that multi-domain hematite reaches TRM saturation (0.3 - 0.4 A sq m/kg) in fields as low as 100 microT. However, multi-domain magnetite reaches only a few percent of its TRM saturation in a field of 100 microT (0.02 - 0.06 A sq m/kg). These results suggest that a mineral such as hematite and, perhaps, other minerals with significant remanence and minor induced magnetization may play an important role in providing requisite magnetization contrast. Perhaps, and especially for the Mars case, we should reevaluate where hematite and other minerals, with efficient remanence acquisition, exist in significant concentration, allowing a more comprehensive explanation of Martian anomalies and better insight into the role of remanent magnetization in terrestrial crustal magnetic anomalies.
Magnetic structure of a slow spreading ridge segment: Insights from near-bottom magnetic measurements
Paris-Sud XI, Universit├® de
Magnetic structure of a slow spreading ridge segment: Insights from near-bottom magnetic. Dyment, K. Tamaki, M. Ravilly, H. Horen, and P. Gente (2009), Magnetic structure of a slow spreading of the geomagnetic field and have proposed various constraints and models on the magnetic structure of the oceanic
The south-central United States magnetic anomaly
NASA Technical Reports Server (NTRS)
Starich, P. J.; Hinze, W. J.; Braile, L. W.
A positive magnetic anomaly, which dominates the MAGSAT scalar field over the south-central United States, results from the superposition of magnetic effects from several geologic sources and tectonic structures in the crust. The highly magnetic basement rocks of this region show good correlation with increased crustal thickness, above average crustal velocity and predominantly negative free-air gravity anomalies, all of which are useful constraints for modeling the magnetic sources. The positive anomaly is composed of two primary elements. The western-most segment is related to middle Proterozoic granite intrusions, rhyolite flows and interspersed metamorphic basement rocks in the Texas panhandle and eastern New Mexico. The anomaly and the magnetic crust are bounded to the west by the north-south striking Rio Grande Rift. The anomaly extends eastward over the Grenville age basement rocks of central Texas, and is terminated to the south and east by the buried extension of the Ouachita System. The northern segment of the anomaly extends eastward across Oklahoma and Arkansas to the Mississippi Embayment. It corresponds to a general positive magnetic region associated with the Wichita Mountains igneous complex in south-central Oklahoma and 1.2 to 1.5 Ga. felsic terrane to the north.
Study of magnetic anomalies over archaeological targets in urban environments
NASA Astrophysics Data System (ADS)
Eppelbaum, Lev V.
Magnetic prospecting is one of the most widely used methods for investigating archaeological sites in the world. It is often applied before and during various types of industrial development and in agricultural areas. In Israel, most potential archaeological targets are located in urban settings, which substantially complicate their geophysical signatures. Noise from natural factors such as the inclined magnetization (about 44░) complex geological structure of the sites, and uneven terrain relief as well as artificial sources such as modern iron-containing objects, power lines and underground communications can confound the interpretation of magnetic anomalies. For the quantitative analysis of magnetic anomalies from ancient targets in Israel nonconventional procedures ( Khesin et al., 1996; Eppelbaum and Khesin, 2001) were applied. In this paper the effects of power lines on the quantitative analysis of magnetic anomalies indicative of archaeological objects are investigated. The method was tested on two typical models of physical-archaeological ancient remains by using different distances to the power line.
Correlated Magnetic and Gravity Anomalies West of the Isidis Basin, Mars and Implications for Plains Magnetism
C. A. Raymond; S. E. Smrekar; G. E. McGill; A. M. Dimitriou
The magnetic field of Mars reflects strong crustal magnetism resulting from an ancient internal field. The crustal anomaly pattern parallels the geologic dichotomy in that most of the anomalies detected by the Mars Global Surveyor are located within the persumably older southern highlands while the northern lowlands has weak or no magnetic signature at satellite atltiudes. We have analyzed a
Magsat magnetic anomaly contrast across Labrador Sea passive margins
NASA Astrophysics Data System (ADS)
Bradley, Lauren M.; Frey, Herbert
Many passive margins not complicated by nearby anomalous crustal structure have satellite elevation crustal magnetic anomaly contrasts across them that are recognizable in reduced-to-pole versions of the Magsat and POGO data. In the Labrador Sea region this contrast is particularly well developed with strong positive anomalies overlying the continental crust of Greenland and eastern Canada and prominent negative anomalies situated over the Labrador Sea and Baffin Bay. In this work, forward modeling of the large-scale crustal bodies in this region (continental, oceanic, passive margin, several anomalous structures) was used to show that the Magsat anomaly contrast is due simply to the change in crustal susceptibility and thickness at the continental/oceanic crustal transition. Because the thickness varies more than the average susceptibility from continental to oceanic crust, the strong anomaly contrast is essentially an edge effect due mostly to the change in crustal structure.
Correlations of Lunar Magnetic Anomalies with Geologic Age and Material
NASA Astrophysics Data System (ADS)
Lawrence, K. P.; Johnson, C. L.
While the moon has is no present-day internally generated magnetic field, widespread coherently magnetized geologic units were observed with Apollo era surface and sub-satellite measurements and more recently with Lunar Prospector. However, unlike at Mars, magnetized lunar units show no clear-cut correlation with age: a few, but not all, basins of Nectarian age (3.92-3.85 Ga) exhibit magnetic anomalies within the basin; some, but not all, basins exhibit magnetic anomalies associated with their ejecta; and most of the crustal magnetization is in a spatially extensive region to the NW of South Pole Aitken. Recent paleomagnetic analyses have been performed on a range of sample types and ages including absolute and relative paleointensity and directional measurements. Collectively, these paleomagnetic results have been used to suggest the existence of a lunar dynamo during the period ~ 3.6 - 4.2 Ga. Various mechanisms that could have produced a dynamo spanning all or part of this time interval are being investigated, such as precession, nutation, and thermally or compositionally-driven core convection. It is also apparent that shock plays an important, although still poorly-understood, role in the magnetic history of the Moon: concentrations of magnetic anomalies correlate with the antipodes of four major impact basins; strong fields at Apollo 16 site those associated with the Reiner Gamma formation are attributed to basin ejecta; experiments have shown shock can demagnetize or remagnetize a material in the absence of a permanent magnetic field. Thus, despite significant recent work, no single data set, experiment, or model provides an unambiguous record of lunar magnetic evolution. A clear understanding regarding the timing of either a permanent global field or the existence of intermittent transient fields is not apparent. Here we focus on the issue of the correlation of crustal magnetic anomalies with geologic age (Copernican, Eratosthenian, Imbrian, Nectarian or Pre-Nectarian) and geologic unit (basin, crater, mare or dark, and terra materials) in an effort to place constraints on the source of magnetizations and the timing of acquisition of remanence. Previous studies have investigated the correlation of magnetization with individual basin age or particular formation units (e.g. Caley Formation) but this has not been extended to the global scale, covered all lunar ages, or expanded beyond correlation with basin materials. Statistical analyses using Lunar Prospector Magnetometer and Electron Reflectometer data quantify the correlation of geologic ages and units with magnetic anomalies. The majority of observable magnetic anomalies are associated with visible surface units having ages that are Imbrian or Nectarian. Magnetic anomalies are statistically more likely to occur in association with crater ejecta and highland material than with basin materials. We discuss whether this global interpretation is representative of magnetic anomalies found NW of South Pole Aitken (SPA) basin, to help determine whether the sources of circum-SPA magnetic anomalies are fundamentally different from those of magnetic anomalies elsewhere on the moon.
The mineralogy of global magnetic anomalies
NASA Technical Reports Server (NTRS)
Haggerty, S. E. (principal investigator)
The Curie Balance was brought to operational stage and is producing data of a preliminary nature. Substantial problems experienced in the assembly and initial operation of the instrument were, for the most part, rectified, but certain problems still exist. Relationships between the geology and the gravity and MAGSAT anomalies of West Africa are reexamined in the context of a partial reconstruction of Gondwanaland.
First high-resolution near-seafloor survey of magnetic anomalies of the South China Sea
NASA Astrophysics Data System (ADS)
Lin, J.; Xu, X.; Li, C.; Sun, Z.; Zhu, J.; Zhou, Z.; Qiu, N.
We successfully conducted the first high-resolution near-seafloor magnetic survey of the Central, Southwest, and Northern Central Basins of the South China Sea (SCS) during two cruises on board Chinese R/V HaiYangLiuHao in October-November 2012 and March-April 2013, respectively. Measurements of magnetic field were made along four long survey lines, including (1) a NW-SE across-isochron profile transecting the Southwest Basin and covering all ages of the oceanic crust (Line CD); (2) a N-S across-isochron profile transecting the Central Basin (Line AB); and (3) two sub-parallel NE-SW across-isochron profiles transecting the Northern Central Basin of the SCS (Lines D and E). A three-axis magnetometer was mounted on a deep-tow vehicle, flying within 0.6 km above the seafloor. The position of the tow vehicle was provided by an ultra-short baseline navigation system along Lines D and E, while was estimated using shipboard GPS along Lines AB and CD. To investigate crustal magnetization, we first removed the International Geomagnetic Reference Field (IGRF) of 2010 from the measured magnetic data, and then downward continued the resultant magnetic field data to a horizontal plane at a water depth of 4.5 km to correct for variation due to the fishing depth of the deep-tow vehicle. Finally, we calculated magnetic anomalies at various water depths after reduction-to-the-pole corrections. We also constructed polarity reversal block (PRB) models of crustal magnetization by matching peaks and troughs of the observed magnetic field anomaly. Our analysis yielded the following results: (1) The near-bottom magnetic anomaly showed peak-to-trough amplitudes of more than 2,500 nT, which are several times of the anomaly amplitudes at the sea surface, illustrating that deep-tow measurements acquired much higher spatial resolutions. (2) The deep-tow data revealed several distinctive magnetic anomalies with wavelengths of 5-15 km and amplitudes of several hundred nT. These short-wavelength anomalies were unrecognized in sea surface measurements. (3) Preliminary results showed that the study regions might have experienced several episodes of magnetic reversal events that were not recognized in existing models. (4) We are currently investigating the geomagnetic timing of these relatively short-duration events to determine the detailed spreading history of the sub-basins of the SCS. These high-resolution near-seafloor magnetic survey lines are located close to the planned drilling sites of IODP Expedition 349 scheduled for January-March 2014.
Lindsey, C. [NorthWest Research Associates, 3380 Mitchell Lane, Boulder, CO 80301 (United States); Cally, P. S. [School of Mathematical Sciences, Monash University, Victoria (Australia); Rempel, M. [High Altitude Observatory, National Center for Atmospheric Research, 3080 Center Green Drive CG1, Boulder, CO 80301 (United States)
Efforts to model sunspots based on helioseismic signatures need to discriminate between the effects of (1) a strong magnetic field that introduces time-irreversible, vantage-dependent phase shifts, apparently connected to fast- and slow-mode coupling and wave absorption and (2) a thermal anomaly that includes cool gas extending an indefinite depth beneath the photosphere. Helioseismic observations of sunspots show travel times considerably reduced with respect to equivalent quiet-Sun signatures. Simulations by Moradi and Cally of waves skipping across sunspots with photospheric magnetic fields of order 3 kG show travel times that respond strongly to the magnetic field and relatively weakly to the thermal anomaly by itself. We note that waves propagating vertically in a vertical magnetic field are relatively insensitive to the magnetic field, while remaining highly responsive to the attendant thermal anomaly. Travel-time measurements for waves with large skip distances into the centers of axially symmetric sunspots are therefore a crucial resource for discrimination of the thermal anomaly beneath sunspot umbrae from the magnetic anomaly. One-dimensional models of sunspot umbrae based on compressible-radiative-magnetic-convective simulations such as by Rempel et al. can be fashioned to fit observed helioseismic travel-time spectra in the centers of sunspot umbrae. These models are based on cooling of the upper 2-4 Mm of the umbral subphotosphere with no significant anomaly beneath 4.5 Mm. The travel-time reductions characteristic of these models are primarily a consequence of a Wilson depression resulting from a strong downward buoyancy of the cooled umbral medium.
Seismic Discrimination of Thermal and Magnetic Anomalies in Sunspot Umbrae
NASA Astrophysics Data System (ADS)
Lindsey, C.; Cally, P. S.; Rempel, M.
Efforts to model sunspots based on helioseismic signatures need to discriminate between the effects of (1) a strong magnetic field that introduces time-irreversible, vantage-dependent phase shifts, apparently connected to fast- and slow-mode coupling and wave absorption and (2) a thermal anomaly that includes cool gas extending an indefinite depth beneath the photosphere. Helioseismic observations of sunspots show travel times considerably reduced with respect to equivalent quiet-Sun signatures. Simulations by Moradi & Cally of waves skipping across sunspots with photospheric magnetic fields of order 3 kG show travel times that respond strongly to the magnetic field and relatively weakly to the thermal anomaly by itself. We note that waves propagating vertically in a vertical magnetic field are relatively insensitive to the magnetic field, while remaining highly responsive to the attendant thermal anomaly. Travel-time measurements for waves with large skip distances into the centers of axially symmetric sunspots are therefore a crucial resource for discrimination of the thermal anomaly beneath sunspot umbrae from the magnetic anomaly. One-dimensional models of sunspot umbrae based on compressible-radiative-magnetic-convective simulations such as by Rempel et al. can be fashioned to fit observed helioseismic travel-time spectra in the centers of sunspot umbrae. These models are based on cooling of the upper 2-4 Mm of the umbral subphotosphere with no significant anomaly beneath 4.5 Mm. The travel-time reductions characteristic of these models are primarily a consequence of a Wilson depression resulting from a strong downward buoyancy of the cooled umbral medium.
Lunar magnetic anomaly concentrations at the antipodal regions
NASA Astrophysics Data System (ADS)
Hemant Singh, Kumar; Kuang, Weijia; Singh, Raghav
The high resolution lunar-wide magnetic anomaly map derived from Lunar Prospector (LP) vector magnetometer data has revealed weak anomalies over the nearside large impact basins flooded by mare basalts. Stronger anomaly features are observed over many of the Nectarian and Pre-Nectarian aged lunar highlands. In particular, regions antipodal to some of the largest basin-forming impact craters show strong magnetic anomaly concentrations. Of the 43 basins investigated here, antipodal regions of 9 basins show these anomalous features with strengths in excess of 1-18 nT at LP's mapping altitude (30 km). These distinct anomalous concentrations were previously known to occur only at the antipodes of Imbrium, Orientale, Serenitatis, Crisium and Nectaris basins. The mean magnetic anomaly strength within each antipodal region, when plotted against increasing age of the antipodes, shows two age groupings with similar magnetic behavior. The first age grouping - (Imbrium, Orientale, Serenitatis, Crisium and Nectaris) is of Imbrium to Nectarian in age. This grouping is correlative with peak magnetic field enhancements between 3.6 and 3.9 Gyr, inferred from paleomagnetic data from the returned Apollo samples. The second age grouping (Lorentz, Coulomb-Sarton, Tranquillitatis and Cognitum) is of Mid to Early Pre-Nectarian age. This grouping has not been correlated to any known global magnetic field enhancement event, and needs further investigation to ascertain the origin of the anomalies. Although spatially adjacent, the magnetic field signatures of the Serenitatis and Imbrium antipodes exhibit distinct features, supporting the antipodal hypothesis. The absence of appreciable field enhancements at 34 other antipodes, however, indicates the importance of other processes, and superposition effects, that have operated on the Moon during its history.
Understanding the Tectonic Features in the South China Sea By Analyzing Magnetic Anomalies
NASA Astrophysics Data System (ADS)
Guo, L.; Meng, X.; Shi, L.; Yao, C.
The South China Sea (SCS) is surrounded by the Eurasia, Pacific and India-Australia plates. It formed during Late Oligocene-Early Miocene, and is one of the largest marginal seas in the Western Pacific. The collision of Indian subcontinent and Eurasian plate in the northwest, back-arc spreading in the centre and subduction beneath the Philippine plate along Manila trench in the east and along Palawan trough in the south had produced the complex tectonic features in the SCS that we can see today. In the past few decades, a variety of geophysical methods were conducted to study geological tectonics and evolution of the SCS. Here, we analyzed the magnetic data of this area using new data enhancement techniques to understand the regional tectonic features. We assembled the magnetic anomalies data with a resolution of two arc-minute from the World Digital Magnetic Anomaly Map, and then gridded the data on a regular grid. Then we used the method of reduction to the pole at low latitude with varying magnetic inclinations to stably reduce the magnetic anomalies. Then we used the preferential continuation method based on Wiener filtering and Green's equivalence principle to separate the reduced-to-pole (RTP) magnetic anomalies, and subsequently analyze the regional and residual anomalies. We also calculated the directional horizontal derivatives and the tilt-angle derivative of the data to derive clearer geological structures with more details. Then we calculated the depth of the magnetic basement surface in the area by 3D interface inversion. From the results of the preliminary processing, we analyzed the main faults, geological structures, magma distribution and tectonic features in the SCS. In the future, the integrated interpretation of the RTP magnetic anomalies, Bouguer gravity anomalies and other geophysical methods will be performed for better understanding the deep structure , the tectonic features and evolution of the South China Sea. Acknowledgment: We acknowledge the financial support of the SinoProbe project (201011039), the Fundamental Research Funds for the Central Universities (2010ZY26, 2011PY0184), and the National Natural Science Foundation of China (40904033, 41074095).
Low energy spread ion source with a coaxial magnetic filter
Leung, Ka-Ngo (Hercules, CA); Lee, Yung-Hee Yvette (Berkeley, CA)
Multicusp ion sources are capable of producing ions with low axial energy spread which are necessary in applications such as ion projection lithography (IPL) and radioactive ion beam production. The addition of a radially extending magnetic filter consisting of a pair of permanent magnets to the multicusp source reduces the energy spread considerably due to the improvement in the uniformity of the axial plasma potential distribution in the discharge region. A coaxial multicusp ion source designed to further reduce the energy spread utilizes a cylindrical magnetic filter to achieve a more uniform axial plasma potential distribution. The coaxial magnetic filter divides the source chamber into an outer annular discharge region in which the plasma is produced and a coaxial inner ion extraction region into which the ions radially diffuse but from which ionizing electrons are excluded. The energy spread in the coaxial source has been measured to be 0.6 eV. Unlike other ion sources, the coaxial source has the capability of adjusting the radial plasma potential distribution and therefore the transverse ion temperature (or beam emittance).
Relating crustal magnetization and satellite-altitude magnetic anomalies in the Ungava peninsula, northern Quebec, Canada
NASA Astrophysics Data System (ADS)
Pilkington, Mark; Percival, John A.
A prominent satellite-altitude magnetic anomaly (>6 nT) located over the Ungava peninsula, northern Quebec, is coincident with a region of intense aeromagnetic anomalies and high susceptibilities of exposed rocks. Inversion of a combined POGO-Magsat anomaly data set shows that the susceptibility levels required to satisfy the satellite-altitude anomaly range from 0.03 to 0.04 SI (assuming a 40-km-thick crust). These values are well within the range of measured surface susceptibilities in the Minto region and the anomaly can be explained if the measured values are representative of the average upper crustal magnetization. Therefore, the Ungava peninsula is one of the few areas on Earth where a direct relation between surface rock properties and satellite magnetic anomalies can be made.
The next generation Antarctic digital magnetic anomaly map
von Frese, R.R.B; Golynsky, A.V.; Kim, H.R.; Gaya-Piquķ, L.; Thķbault, E.; Chiappinii, M.; Ghidella, M.; Grunow, A.; ADMAP Working Group
S (Golynsky et al., 2001). This map synthesized over 7.1 million line-kms of survey data available up through 1999 from marine, airborne and Magsat satellite observations. Since the production of the initial map, a large number of new marine and airborne surveys and improved magnetic observations from the žrsted and CHAMP satellite missions have become available. In addition, an improved core field model for the Antarctic has been developed to better isolate crustal anomalies in these data. The next generation compilation also will likely represent the magnetic survey observations of the region in terms of a high-resolution spherical cap harmonic model. In this paper, we review the progress and problems of developing an improved magnetic anomaly map to facilitate studies of the Antarctic crustal magnetic field
New magnetic anomaly map of East Antarctica and surrounding regions
Golynsky, A.; Blankenship, D.; Chiappini, M.; Damaske, D.; Ferraccioli, F.; Finn, C.; Golynsky, D.; Goncharov, A.; Ishihara, T.; Ivanov, S.; Jokat, W.; Kim, H.R.; K÷nig, M.; Masolov, V.; Nogi, Y.; Sand, M.; Studing, M.; ADMAP Working Group
community over East Antarctica and surrounding regions, significantly upgrade the Antarctic Digital Magnetic Anomaly Project (ADMAP) compilation and lead to substantial improvements in magnetic anomaly pattern recognition. New data have been matched in one inverse operation by minimizing the data differences for the areas of overlap. The aeromagnetic data show many previously unknown magnetic patterns, lineaments and trends, defining the spatial extent of Ferrar volcanics and plutonic Granite Harbour Intrusives in the Transantarctic Mountains and previously unknown tectonic trends of the East Antarctic craton. Regional aeromagnetic investigations have successfully delineated Early Paleozoic inherited crustal features along the flanks of the West Antarctic Rift System and the southern boundary of the Archean Ruker Terrane in the Prince Charles Mountains. Magnetic records along the East Antarctic continental margin provide new constraints on the breakup of Gondwana.
Approximating edges of source bodies from magnetic or gravity anomalies.
Blakely, R.J.; Simpson, R.W.
Cordell and Grauch (1982, 1985) discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks. The final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes. Attempts to automate their final step. The method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources. The method applies to both local surveys and to continent-wide compilations of magnetic and gravity data.-from Authors
On the origin of the Bangui magnetic anomaly, central African empire
NASA Technical Reports Server (NTRS)
Marsh, B. D.
A large magnetic anomaly was recognized in satellite magnetometer data over the Central African Empire in central Africa. They named this anomaly the Bangui magnetic anomaly due to its location near the capital city of Bangui, C.A.E. Because large crustal magnetic anomalies are uncommon, the origin of this anomaly has provoked some interest. The area of the anomaly was visited to make ground magnetic measurements, geologic observations, and in-situ magnetic susceptibility measurements. Some rock samples were also collected and chemically analyzed. The results of these investigations are presented.
Homomorphic deconvolution of marine magnetic anomalies
Jones, Leo David
HOMOMORPIIIC DECONVOLUT ION OF MAR INE MAGNETIC ANOMAL I ES A Thesis by LEO DAVID JONES Submitted to the Graduate Colleoe of Texas Ahhi Unis ars i ty in partial fulfillment of the requirement for tne degree MASTEP, OF SCIENCE December 1975... Major Subject: Geophysics HOMOMORPHIC DECONVOLUT ION OF MARINE MAGNETIC ACNOMALIES A Thesis by LEO DAVID JONES Approved es to sty1e and content by: r"hi ~f C itt: Ch h~7 December 1976 ABSTRACT Homomorpi;ic Deconvolution of Marine Magnetic...
Macquarie island and the cause of oceanic linear magnetic anomalies.
Varne, R; Gee, R D; Quilty, P G
Macquarie Islands is formed of probably Pliocene oceanic crust. Intruded into pillow lavas is a belt of harzburgite and layered gabbro mnasses cut by dike swarms. Similar belt-like structures may cause the linear magnetic anomalies of the ocean. PMID:17731490
Plasma acceleration above martian magnetic anomalies.
Lundin, R; Winningham, D; Barabash, S; Frahm, R; Holmstr÷m, M; Sauvaud, J-A; Fedorov, A; Asamura, K; Coates, A J; Soobiah, Y; Hsieh, K C; Grande, M; Koskinen, H; Kallio, E; Kozyra, J; Woch, J; Fraenz, M; Brain, D; Luhmann, J; McKenna-Lawler, S; Orsini, R S; Brandt, P; Wurz, P
Auroras are caused by accelerated charged particles precipitating along magnetic field lines into a planetary atmosphere, the auroral brightness being roughly proportional to the precipitating particle energy flux. The Analyzer of Space Plasma and Energetic Atoms experiment on the Mars Express spacecraft has made a detailed study of acceleration processes on the nightside of Mars. We observed accelerated electrons and ions in the deep nightside high-altitude region of Mars that map geographically to interface/cleft regions associated with martian crustal magnetization regions. By integrating electron and ion acceleration energy down to the upper atmosphere, we saw energy fluxes in the range of 1 to 50 milliwatts per square meter per second. These conditions are similar to those producing bright discrete auroras above Earth. Discrete auroras at Mars are therefore expected to be associated with plasma acceleration in diverging magnetic flux tubes above crustal magnetization regions, the auroras being distributed geographically in a complex pattern by the many multipole magnetic field lines extending into space. PMID:16484488
Lunar magnetic anomalies detected by the Apollo substatellite magnetometers
Hood, L.L.; Coleman, P.J., Jr.; Russell, C.T.; Wilhelms, D.E.
Properties of lunar crustal magnetization thus far deduced from Apollo subsatellite magnetometer data are reviewed using two of the most accurate presently available magnetic anomaly maps - one covering a portion of the lunar near side and the other a part of the far side. The largest single anomaly found within the region of coverage on the near-side map correlates exactly with a conspicuous, light-colored marking in western Oceanus Procellarum called Reiner Gamma. This feature is interpreted as an unusual deposit of ejecta from secondary craters of the large nearby primary impact crater Cavalerius. An age for Cavalerius (and, by implication, for Reiner Gamma) of 3.2 ?? 0.2 ?? 109 y is estimated. The main (30 ?? 60 km) Reiner Gamma deposit is nearly uniformly magnetized in a single direction, with a minimum mean magnetization intensity of ???7 ?? 10-2 G cm3/g (assuming a density of 3 g/cm3), or about 700 times the stable magnetization component of the most magnetic returned samples. Additional medium-amplitude anomalies exist over the Fra Mauro Formation (Imbrium basin ejecta emplaced ???3.9 ?? 109 y ago) where it has not been flooded by mare basalt flows, but are nearly absent over the maria and over the craters Copernicus, Kepler, and Reiner and their encircling ejecta mantles. The mean altitude of the far-side anomaly gap is much higher than that of the near-side map and the surface geology is more complex, so individual anomaly sources have not yet been identified. However, it is clear that a concentration of especially strong sources exists in the vicinity of the craters Van de Graaff and Aitken. Numerical modeling of the associated fields reveals that the source locations do not correspond with the larger primary impact craters of the region and, by analogy with Reiner Gamma, may be less conspicuous secondary crater ejecta deposits. The reason for a special concentration of strong sources in the Van de Graaff-Aitken region is unknown, but may be indirectly related to the existence of strongly modified crustal terrain which also occurs in the same region. The inferred directions of magnetization for the several sources of the largest anomalies are highly inclined with respect to one another, but are generally depleted in the north-south direction. The north-south depletion of magnetization intensity appears to continue across the far-side within the region of coverage. The mechanism of magnetization and the origin of the magnetizing field remain unresolved, but the uniformity with which the Reiner Gamma deposit is apparently magnetized, and the north-south depletion of magnetization intensity across a substantial portion of the far side, seem to require the existence of an ambient field, perhaps of global or larger extent. The very different inferred directions of magnetization possessed by nearly adjacent sources of the Van de Graaff-Aitken anomalies, and the depletion in their north-south component of magnetization, do not favor an internally generated dipolar field oriented parallel to the present spin axis. A variably oriented interplanetary magnetizing field that was intrinsically strong or locally amplified by unknown surface processes is least inconsistent with the data. ?? 1979.
Global magnetic anomaly maps derived from POGO spacecraft data
NASA Astrophysics Data System (ADS)
Langel, Robert A.
Magnetic anomaly maps which are reduced to common elevation and to the pole are derived using data from the POGO spacecraft. The maps are global and are presented in both equatorial and polar projections. Reduction is accomplished using the equivalent source technique, including principal components analysis to deal with instabilities at and near the geomagnetic equator. Data reduction methods are discussed and average anomaly maps are presented together with their standard error. Such maps are derived for four distinct local time regions and intercompared in order to estimate the remaining effects of fields from ionospheric and magnetospheric sources.
Mesozoic Kinematic Evolution of the Central Atlantic Inferred From Regional Magnetic Anomalies
NASA Astrophysics Data System (ADS)
Labails, C.; Olivet, J.; Aslanian, D.; Sichler, B.; Roest, W.; Evain, M.
The magnetic anomaly signature of Central Atlantic margins is well defined by the gridded data published by Verhoef et al. (1996) on the North American region. However, a gridded dataset for the West African margin (South of the Canary Islands) was lacking. We have used magnetic data from the Geodas database, an Ifremer dataset and personnal communication from H.A. Roeser and W.J.M. Van der Linden in order to produce a gridded magnetic data of the Dakhla margin and to better constrain the kinematics of Central Atlantic early opening. Our model adopts the breakup timing of 195 Ma as proposed by Sahabi et al. (2004) - 20 myr earlier than what was generally proposed in previous models. According to our interpretation of the newly compiled magnetic data, the early opening of Central Atlantic was characterized by three distinct phases. In contrast to other models, we propose that for the first 30 myr (195-165 Ma, Lias-Dogger) the oceanic accretion was extremely slow (~0.8 cm/y). At the Blake Spur time, (around 165 Ma, Callovian basis), a drastic change occurred, both in the relative plate motions (initially NNW-SSE, it becomes NO-SE) and spreading rate (that increases up to ~ 4.8 cm/y). The BSMA (Blake Spur Magnetic Anomaly) is related to a great basement topographic change. From magnetic chron M22 (150 Ma, Tithonian basis) onwards, the spreading rate slowed down to about 2.6 cm/y and remained constant until magnetic chron M0 (125 Ma, Barremian-Aptian limit).
Manifestation of the petrogeneration zones of Northern and the Bering seas in ground magnetic anomalies and anomalies of satellite Champ
NASA Astrophysics Data System (ADS)
Litvinova, Tamara; Krasinsky, Egor; Petrova, Alevtina; Demina, Irina
The purpose of this paper are showed results of studying of specificity of a deep structure of zones of petrogeneration Northern and the Bering seas on aeromagnetic and satellite magnetometric datas. Research lateral and vertical heterogeneitys an earth's crust of Northern sea is carried out on the basis of the analysis of measurements of satellite Champ at height of 100 km and the digital database created on materials of sea shooting of a geomagnetic field, executed on non-magnetic schooner "Zarya". On sea measurements in Northern sea through large oil fields and gas ( Frigg, Ekofisk, Forties trough, Leman, etc.). Geomagnetic sections for an interval of depths from 1 up to 30 km are constructed. It has allowed to study character of distribution of magnetization of breeds of a cover, horizontal lamination intracore layers of an earth's crust and to allocate in zones petrogeneration synvertical fluidoconduct zones the channels described by alternation of not magnetic and low-magnetic layers. They were showed on geomagnetic sections as permeable zones quasi- laminated structures with the lowered magnetic properties in an interval of depths from 8 up to 28 km. Comparison to a map of the magnetic anomalies measured at height of 100 km by satellite Champ, has shown, that areas of the greatest petrocongestions North Sea ????? at height of 100 km are dated for a zone of gradients and a minimum of northeast displacement of regional anomalies of western and east blocks of Northern sea. It corresponds to representations about an orientation of a fissuring zone and the increased size of a geothermal gradient North Sea rift and is corresponded position allocated on hydromagnetic structures deep fluidoconduct channels. Thus, distribution to water areas of deposits of deposits is emphasized not only low-magnetic areas in a thickness of a sedimentary cover where they are directly located, but also by not magnetic lenses in breeds of the base spreading it in intervals of depths of 8-11 km and 15-18 km. The oil-gas-bearing province of the Bering Sea occupies uniform sedimentary megabasin. On aeromagnetic measurements at height of 300 m are constructed geomagnetic sections in an interval of depths from 0.5 km up to 25 km crossing the basic zones possible petrocongestions with traps structural and of structural - stratigraphic types. Distribution of magnetization in an interval of development of potentially productive sandy layers on depths from 1 up to 5 km is received. The most perspective zones possible petrocongestions are allocated in Ilpinsky, Olutorsky and Olutorsko-Komandorsky sedimentary basins. The deep permeable zone with system of low-magnetic lenses in intervals of depths 8-10, 12, 18-20 km, dated to Pilgin zone possible petrocongestions was most brightly showed. Comparison of ground supervision to the data received by results of measurements from satellite Champ at height of 100 km, shows, that large oil-gas-bearing Vertuhovskaya, Karaginskaya, Pahachiskaya and Pilginskaya zones are dated for a minimum isometric satellite magnetic anomaly. At height of 400 km this minimum keeps the form that speaks about stability of a condition of the permeable zones supervising oil-gas-bearing.
Deep-sea Vector Magnetic Anomalies over the Bayonnaise Knoll Caldera (Izu-Ogasawara Arc) (Invited)
NASA Astrophysics Data System (ADS)
Honsho, C.; Ura, T.; Kim, K.
The Bayonnaise Knoll caldera is located on the eastern margin of the backarc rift zone of the Izu-Ogasawara island arc. The caldera rim is ~3 km in diameter and 100-200 m high from the caldera floor 840-920 m deep. A large active hydrothermal field associated with sulfide deposit, called the Hakurei site, has been found at the foot of the southeastern caldera wall. We conducted deep-sea magnetic measurements using autonomous underwater vehicles to map ~75 % of an area 3 km by 4 km in the caldera. The magnetic vector field data were collected at 40-150 m altitude along the survey lines spaced 80-200 m apart. We improved the conventional correction method applied for removing the effect of vehicle magnetization, which greatly enhanced the precision of the resulting vector anomalies and allowed us to use the vector anomaly instead of the total intensity anomaly for inversion analysis. The magnetization distribution obtained using the vector anomaly was significantly different from the one obtained using the total intensity anomaly, especially in areas where the survey tracks were widely spaced. The aliasing effect appears in areas of sparse data distribution, and the magnetic field is more correctly calculated from the vector anomaly than the total intensity anomaly. The magnetization distribution in the caldera has two major features: a ~1.5-km wide belt of high magnetization, trending NNW-SSE through the caldera, and a clear low magnetization zone, ~300 m x ~500 m wide, extending over the Hakurei site. The high magnetization belt is considered to reflect basaltic volcanism associated with the backarc rifting that occurred after the formation of the Bayonnaise Knoll. The low magnetization zone is interpreted as the alteration zone resulting from the hydrothermal activity. Several zones of localized high magnetization are recognized within the high magnetization belt, some of them in the caldera wall adjacent to the low magnetization zone of the Hakurei site. We speculate that intensive magma intrusion occurred beneath the caldera wall and has provided the heat to generate hydrothermal fluid, which has been spouting out through the caldera wall faults. The surface expression of the vent field extends beyond the alteration zone inferred from the magnetization distribution, spreading upwards in the caldera wall. High-resolution topography around the Hakurei site indicates that the hydrothermal vents are generally distributed over a landform of slope failure. These observations would imply that hydrothermal fluid rising up in the up-flow zone moves laterally as well when it comes near the seafloor, probably along numerous fractures and fissures in the caldera wall. The distribution of pre-existing faults and fractures may rather control the fluid flow pathways in the shallow part and condition the surface extent of the vent field.
New frontiers in magnetic field interpretation and modeling: Examples from the World Digital Magnetic Anomaly Map
M. Purucker
The World Digital Magnetic Anomaly Map is a joint effort on the part of the marine, airborne, and satellite magnetic communities to stitch together a unified map of the earth's lithospheric magnetic field. Several preliminary versions of this map will be exhibited during AGU, and this presentation will highlight interpretations of data that have gone into making this map. Examples
Apparatus for detecting a magnetic anomaly contiguous to remote location by squid gradiometer and magnetometer systems
Overton, Jr., William C. (Los Alamos, NM); Steyert, Jr., William A. (Los Alamos, NM)
A superconducting quantum interference device (SQUID) magnetic detection apparatus detects magnetic fields, signals, and anomalies at remote locations. Two remotely rotatable SQUID gradiometers may be housed in a cryogenic environment to search for and locate unambiguously magnetic anomalies. The SQUID magnetic detection apparatus can be used to determine the azimuth of a hydrofracture by first flooding the hydrofracture with a ferrofluid to create an artificial magnetic anomaly therein.
ERIC Educational Resources Information Center
Online-Offline, 1999
This theme issue on anomalies includes Web sites, CD-ROMs and software, videos, books, and additional resources for elementary and junior high school students. Pertinent activities are suggested, and sidebars discuss UFOs, animal anomalies, and anomalies from nature; and resources covering unexplained phenonmenas like crop circles, Easter Island,ģ
A magnetic anomaly of possible economic significance in southeastern Minnesota
Zietz, Isidore
An aeromagnetic survey in southeastern Minnesota by the U. S. Geological Survey in cooperation with the State of Minnesota has revealed a high-amplitude, linear, and narrow magnetic feature that suggests a possible source of Precambrian iron-formation of economic value. For the past few years the U. S. Geological Survey has been conducting detailed geophysical studies of the midcontinent gravity anomaly--a broad, high-amplitude feature that extends from Lake Superior through the States of Minnesota, Iowa, Nebraska, and part of Kansas. As part of this study an aeromagnetic survey of the southern part of the State was made in cooperation with the State of Minnesota during the summer of 1963, in which a linear high-amplitude anomaly of the order of 4,000 gammas was discovered. Because of the high amplitude, the linearity, and the narrowness of the magnetic feature, it is believed the source may be Precambrian iron-formation of possible economic value. The anomalous area is in Fillmore County, approximately between the towns of Lanesboro and Peterson in the extreme southeastern part of the State. (See figures 1 and 2.) At the site of the anomaly, Cambrian sedimentary rocks occur in the valley of the Root River, and Ordovician rocks (nearly flat lying) mantle the upland areas. The uplands are largely covered by glacial deposits, which are relatively thin (Paul K. Sims, written communication, 1964). Depths to the Precambrian are estimated to range from 500 feet to 1,000 feet below the surface. The aeromagnetic map shown in figure 2 was compiled from continuous magnetic profiles made along east-west flight lines 1,000 feet above ground, and spaced approximately 1 mile apart. Contour intervals of 20, 100, and 500 gammas were used depending on the intensity. The instrument for the survey was a flux-gate type magnetometer (AN/ASQ-3A) which measures total-field variations. The contour map displays variations in magnetic pattern which are typical of shallow Precambrian rocks. Anomalies of the order of 1,000 gammas are shown along the east and west edges of the map. The outstanding feature is the previously mentioned linear positive anomaly that trends northeast and reaches a peak of 3,960 gammas. The positive anomaly is contoured from data on four consecutive profiles, but only two show high amplitudes. The high-amplitude anomalies along traverses 1 and 2 are shown in figure 3. Depth calculations suggest that the source of the anomaly lies about 1,000 feet below the surface. Assuming a dikelike source and magnetization resulting entirely from induction in the earth's field, several calculations were made in an attempt to fit the magnetic profile taken along the line AA' (see figs. 2 and 4), considered to be a typical cross-section of the magnetic anomaly. Comparisons are shown between observed and computed profiles. The fixed parameters used were (a) distance from detector to source of 2,000 ft; width of dike of 5,000 ft; dip of dike of 75?, 90?, 105? , and 120? , as shown. The best fit occurs when the dike is vertical or dips 75? to the southwest. For these cases, the susceptibility, k, is computed to be 0.016 c.g.s, units, and is comparable to k = 0.02+ calculated by Bath (1962) for the relatively unmetamorphosed iron-formation of the Main Megabi district in Minnesota where the induced magnetization was most likely the dominant magnetization. If the dominant magnetization for the anomaly in Fillmore County were remanent rather than induced, the economic importance of the anomaly would be greatly reduced. This anomaly seems sufficiently promising to warrant further geologic and geophysical investigation. Detailed ground magnetic and electrical studies would be useful to delineate the feature. In the final analysis, however, the presence of iron-formation can be determined only by the drill.
Regional magnetic anomalies of the Mediterranean in satellite and hydromagnetic measurements
Tamara Litvinova; Alevtina Petrova; Irina Demina
Observation of magnetic field using Champ satellite and compilation of digital maps of magnetic anomalies for altitudes 100 km and 400 km opens up new possibilities for a more reliable investigation of regional anomalies observed after airborne- and hydromagnetic surveys. For studying regional anomalies of the Mediterranean Sea basin, observed values of geomagnetic field measured along extended tacks for years
Thermal Sensitivity of MD Hematite: Implication for Magnetic Anomalies
NASA Technical Reports Server (NTRS)
Kletetschka, Gunther; Wasilewski, Peter J.; Taylor, Patrick T.
Magnetic remanence of crustal rocks can reside in three common rock-forming magnetic minerals: magnetite, pyrrhotite, and hematite. Thermoremanent magnetization (TRM) of magnetite and pyrrhotite is carried mostly by single domain (SD) grains. The TRM of hematite grains, however, is carried mostly by multidomain (NM) grains. This characteristic is illustrated by TRM acquisition curves for hematite of variable grainsizes. The transition between truly NM behavior and tendency towards SD behavior his been established between hematite grainsizes of 0. 1 and 0.05 mm. Coarse grainsize of lower crustal rocks and the large sensitivity of MD hematite grains to acquire TRM indicates that hematite could be a significant contributor to long-wavelength magnetic anomalies.
The prediction of lithospheric magnetic anomalies using the inversion of magnetisation data for vector spherical harmonics
S. Masterton; D. Gubbins; K. Hemant; D. Ivers; D. Muller; D. Winch
High resolution lithospheric magnetic field anomaly maps derived from satellite data now offer immense opportunities to interpret anomalies in terms of crustal magnetic properties such as susceptibility, magnetic crustal thickness, magnetisation type and intensity. We present a new method in which the magnetic field at satellite altitude is found by solving an inverse problem using our magnetisation estimates as data.
Numerical Simulations on Origin of Galilean Moons' Magnetic Anomalies
NASA Technical Reports Server (NTRS)
Jiao, LiQuo; Kuang, WeiJia; Ma, ShiZhuang
Galileo mission detected the magnetic anomalies originated from Galilean moons. These anomalies are likely generated in the moons interiors, under the influence of a strong ambient Jovian field. Among various possible generation mechanisms of the anomalies, we focus on magneto-convection and dynamos in the interiors via numerical simulation. To mimic the electromagnetic environment of the moons, we introduce in our numerical model an external uniform magnetic field B(sub 0) with a fixed orientation but varying field strength. Our results show that a finite B(sub 0) can substantially alter the dynamo processes inside the core. When the ambient field strength B(sub 0) increases to approximately 40% of the field generated by the pure dynamo action, the convective state in the core changes significantly: the convective flow decreases by 80% in magnitude, but the differential rotation becomes stronger in much of the fluid layer, leading to a stronger field generated in the core. The field morphologies inside the core tend to align with the ambient field, while the flow patterns show the symmetry-breaking effect under the influence of B(sub 0). Furthermore, the generated field tends to be temporally more stable.
Utility of Satellite Magnetic Observations for Estimating Near-Surface Magnetic Anomalies
NASA Technical Reports Server (NTRS)
Kim, Hyung Rae; vonFrese, Ralph R. B.; Taylor, Patrick T.; Kim, Jeong Woo; Park, Chan Hong
Regional to continental scale magnetic anomaly maps are becoming increasingly available from airborne, shipborne, and terrestrial surveys. Satellite data are commonly considered to fill the coverage gaps in regional compilations of these near-surface surveys. For the near-surface Antarctic magnetic anomaly map being produced by the Antarctic Digital Magnetic Anomaly Project (ADMAP), we show that near-surface magnetic anomaly estimation is greatly enhanced by the joint inversion of the near-surface data with the satellite observations relative to the conventional technique such as minimum curvature. Orsted observations are especially advantageous relative to the Magsat data that have order-of-magnitude greater measurement errors, albeit at much lower orbital altitudes. CHAMP is observing the geomagnetic field with the same measurement accuracy as the Orsted mission, but at the lower orbital altitudes covered by Magsat. Hence, additional significant improvement in predicting near-surface magnetic anomalies can result as these CHAMP data are available. Our analysis also suggests that considerable new insights on the magnetic properties of the lithosphere may be revealed by a further order-of-magnitude improvement in the accuracy of the magnetometer measurements at minimum orbital altitude.
Marine Magnetic Anomaly Compilations in the Indian Ocean for Plate Tectonics and Beyond (Invited)
NASA Astrophysics Data System (ADS)
Dyment, J.; Bhattacharya, G. C.; Vadakkeyakath, Y.; Bissessur, D.; Jacob, J.; Kattoju, K. R.; Ramprasad, T.; Royer, J.; Patriat, P.; Chaubey, A. K.; Srinivas, K.; Choi, Y.
The French territories in the western and southern parts of the Indian Ocean (i.e. Reunion and Mayotte islands, islands in the Mozambique Channel, Kerguelen and Crozet archipelagos, Saint Paul and Amsterdam islandsģ) have triggered significant scientific activities, including marine geophysics, by French scientists in this area. French marine magnetic data in this ocean span more than four decades, with records as old as 1966 and as recent as early 2009. Similarly, Indian scientists have collected a large amount of geophysical data in the northern Indian Ocean, with a focus on the Arabian Sea, the Bay of Bengal, the Central Indian Basin, and surrounding areas. To take advantage of the obvious complementarity of the French and Indian data sets for plate tectonics studies, we have conducted two projects funded by the Indo-French Centre for the Promotion of Advanced Research, the first one regarding the Arabian and eastern Somali basins, the second one the Central Indian, Madagascar and Crozet basins. These projects have been complemented by more localized work over the Mascarene Basin and Wharton basins, both characterized by an abandoned spreading centre. The purpose of this presentation is to show how such a compilation is being used to conduct plate tectonic studies, from the identification of the magnetic anomalies to their unambiguous picking using the analytic signal, the construction of isochrons and tectonic chart, and the paleogeographic reconstructions. Beyond this classical use, the compiled data can be used to produce magnetic anomaly grids and maps in areas with sufficient data coverage: such grids may help to improve and/or complement future versions of the World Digital Magnetic Anomaly Map (WDMAM).
The last frontier? High-resolution, near-bottom measurements of the Hawaiian Jurassic magnetic anomaly sequence
NASA Astrophysics Data System (ADS)
Tivey, M.; Tominaga, M.; Sager, W. W.
The Jurassic sequence of marine magnetic anomalies i.e. older than M29 remain the last part of the marine magnetic anomaly sequence of the geomagnetic polarity timescale (GPTS) that can be gleaned from the ocean crustal record. While Jurassic crust is present in several areas of the world's ocean basins, the oldest and arguably best preserved sequence is in the western Pacific where three lineations sets (Japanese, Hawaiian and Phoenix) converge on the oldest remaining ocean crust on the planet (i.e. crust that has not been subducted). The magnetic anomalies in these 3 lineation sets are marked by low amplitude, relatively indistinct anomalies (tiny wiggles) that collectively have been called the Jurassic quiet Zone (JQZ). Over the past 20 years we have been working on resolving the character and origin of these anomalies with various technologies to improve our resolution of this period. Following an aeromagnetic survey that revealed the possible presence of lineated anomalies older than M29 in the Japanese lineations, we conducted a deeptow magnetometer survey of the Japanese sequence in 1992. In 2002/03 we extended and confirmed this deeptow record with a deeptowed sidescan and magnetometer survey of the Japanese lineation sequence by tying in ODP Hole 801C and extending the anomaly sequence between M29 and M44. These surveys reveal remarkably fast reversals that are lineated and decrease in intensity back in time until M38, prior to which the sequence becomes somewhat confused (the LAZ or low amplitude zone) before recovering in both amplitude and lineated character around Hole 801C (M42). These results are partially supported by recently reported terrestrial magnetostratigraphy records that show the existence of reversals back to M38. A Jurassic GPTS was constructed from this Japanese anomaly sequence, but the overall global significance of the reversal sequence and systematic field intensity changes require confirmation from crustal records created at different spreading centers. In 2011, we undertook the next generation of near-bottom magnetic studies utilizing new autonomous underwater vehicle (AUV) technology (Sentry) and concurrent deeptow and seismic profiling surveys of the Hawaiian anomaly sequence. Preliminary results show a similar anomaly record to the Japanese sequence: an overall decrease in anomaly amplitude from M19 to M38 and a period of low amplitude, which in turn is preceded by a return to stronger amplitude anomalies. The magnetic anomaly correlations between Hawaiian and Japanese sea-surface level profiles confirm the reversal record back in time, at least, to M38. At the mid-water and near-bottom AUV levels, the magnetic data clearly show the short-wavelength anomaly character of the M29-M38 sequence, indicating that the fast reversals observed in the Japanese lineations are also present in the Hawaiian lineation set. The strong similarity of overall anomaly patterns between Japanese and Hawaiian sequences supports the preliminary conclusion that geomagnetic field behavior during the Jurassic was dynamic, with fast reversals and changing intensity, and certainly not "quiet". Finally, AUV surveys provide measurements of the marine magnetic anomaly record whose resolution is limited only by the crustal recording process and crustal magnetic architecture rather than spatial resolution.
Superconducting magnetic calibration source for magnetic anomaly detection (MAD) operations. Final report
M. Nisenoff; J. J. Kennedy; A. W. Webb
A superconducting solenoid was designed, built and tested to demonstrate the feasibility of using this type of device as a calibration source for Magnetic Anomaly Detection operations. A description of the dewar system required for such a solenoid is also described. The magnetic moment of the solenoid which was 48 cm in outer diameter, was 150,000 ampere-turns-meter squared.
Absolute Magnetization Distribution on Back-arc Spreading Axis Hosting Hydrothermal Vents; Insight from Shinkai 6500 Magnetic Survey
NASA Astrophysics Data System (ADS)
Fujii, M.; Okino, K.; Honsho, C.; Mochizuki, N.; Szitkar, F.; Dyment, J.
Near-bottom magnetic profiling using submersible, deep-tow, Remotely Operated Vehicle (ROV) and Autonomous Underwater Vehicle (AUV) make possible to conduct high-resolution surveys and depict detailed magnetic features reflecting, for instance, the presence of fresh lavas or hydrothermal alteration, or geomagnetic paleo-intensity variations. We conducted near-bottom three component magnetic measurements onboard submersible Shinkai 6500 in the Southern Mariana Trough, where five active hydrothermal vent fields (Snail, Yamanaka, Archean, Pica, and Urashima sites) have been found in both on- and off-axis areas of the active back-arc spreading center, to detect signals from hydrothermally altered rock and to distinguish old and new submarine lava flows. Fourteen dives were carried out at an altitude of 1-40 m during the R/V Yokosuka YK10-10 and YK10-11 cruises in 2010. We carefully corrected the effect of the induced and permanent magnetizations of the submersible by applying the correction method for the shipboard three-component magnetometer measurement modified for deep-sea measurement, and subtracted the IGRF values from the corrected data to obtain geomagnetic vector anomalies along the dive tracks. We then calculated the synthetic magnetic vector field produced by seafloor, assumed to be uniformly magnetized, using three dimensional forward modeling. Finally, values of the absolute magnetizations were estimated by using a linear transfer function in the Fourier domain from the observed and synthetic magnetic anomalies. The distribution of estimated absolute magnetization generally shows low values around the five hydrothermal vent sites. This result is consistent with the equivalent magnetization distribution obtained from previous AUV survey data. The areas of low magnetization are also consistent with hydrothermal deposits identified in video records. These results suggest that low magnetic signals are due to hydrothermal alteration zones where host rocks are demagnetized by hydrothermal circulation. The low magnetization zones around the off-axis vent sites are about ten times wider than those surrounding the on-axis sites, possibly reflecting the longer duration of hydrothermal circulation at these sites. Another interesting result is that the absolute magnetization shows extremely high intensities (>80 A/m) at the neo volcanic zones (NVZ) and relatively low intensities (<10 A/m) two to five kilometers away from the NVZ. These variations are quite consistent with those of the Natural Remanent Magnetization measured on basalt samples, suggesting that the low-temperature oxidation of host rock due to the reaction with seawater has completed within a few kilometers distance from the spreading axis. We conclude that the magnetization of the uppermost oceanic crust decreases with age due to the combination of the both hydrothermal rapid alteration and the low-temperature gradual alteration processes.
Magnetic Structure of Backarc Spreading Axis with Hydrothermal Vents; the Southern Mariana Trough
NASA Astrophysics Data System (ADS)
Fujii, M.; Okino, K.; Mochizuki, N.; Honsho, C.; Szitkar, F.; Dyment, J.; Nakamura, K.
Seafloor hydrothermal systems are important in relation to global heat and chemical fluxes as well as habitat of microbial communities. The substantial variation of hydrothermal systems in various tectonic settings has important implications for the magnetic structure of oceanic crust. It has been very difficult to detect the geophysical signature of hydrothermal systems from sea-surface data because the small scale of hydrothermal systems is below the limit of resolution. The advance of near-bottom survey methods using a submersible, deep-tow, ROV and AUV has made possible high-resolution geophysical mapping around hydrothermal areas. Near-bottom magnetic surveys can provide direct information on the magnetization of the shallower oceanic crust, implying hydrothermal alteration both in active and fossil vent sites. Near-bottom three component magnetic measurements on submersible Shinkai 6500 were carried out at hydrothermal fields in the Southern Mariana Trough, a slow spreading backarc basin. Fourteen dive surveys were conducted during cruises YK11-10 and YK10-11. We investigated the magnetic structure of four hydrothermal systems located at on- and off-axis to clarify how the geophysical and geological setting controls the fluid circulation at small scale. Recent researches at slow spreading ridges showed a relationship between crustal magnetic structure and host rock around hydrothermal vents (e.g. Tivey and Dyment, 2010), but no observation at backarc spreading axis has been reported so far. We carefully corrected the effects of induced and permanent magnetizations of the submersible by applying the method of Isezaki [1986] with dumped least-square method (Honsho et al., 2009). After subtracting the IGRF from the corrected observed data, we obtained geomagnetic vector anomalies in geographical coordinate. For three transects of the axis, we applied three methods; 2D inversion technique (Parker and Huestis, 1972), 2D forward modeling technique (Honsho et al, 2009) and 2D direct inversion technique (Hussenoeder et al., 1995). Transect 1 (T1) and transect 2 (T2) are parallel and very closely located, crossing the neo-volcanic zone near an on-axis hydrothermal site (Snail Site) at different altitude, 2m and 30m. Transect 3 (T3) also crosses a large on-axis volcanic mound on which another hydrothermal site (Yamanaka Site) is located. The equivalent magnetization calculated on T1 and T2 are similar although their resolutions are different. The one along T3 shows high values around the large volcanic mound and an area of low magnetization near a hydrothermal field recognized from high-resolution bathymetry (Yoshikawa et al., 2012). A similar reduction of magnetization above hydrothermal fields was also reported in basalt-hosted sites along the Mid Atlantic Ridge. The detailed bathymetry (2m grid) collected by AUV Urashima in the study area allows us to investigate the effect of three dimensional structure. We estimate magnetization using a new technique based on 3D forward modeling (Szitkar et al, this meeting). A preliminary result shows a similar but more detailed magnetic structure around the Yamanaka Site compared to results of the 2D methods.
Regional mapping of the lunar magnetic anomalies at the surface: Method and its application to strong and weak magnetic anomaly regions
NASA Astrophysics Data System (ADS)
Tsunakawa, Hideo; Takahashi, Futoshi; Shimizu, Hisayoshi; Shibuya, Hidetoshi; Matsushima, Masaki
We have developed a new method for regional mapping of the lunar magnetic anomalies as the vector field at the surface using the satellite observation, that is the surface vector mapping (SVM). The SVM is based on the inverse boundary value problem with a spherical boundary surface. There are two main procedures for reducing effects of bias and noise on mapping: (1) preprocessing the data to provide first derivatives along the pass, and (2) the Bayesian statistical procedure in the inversion using Akaike's Bayesian Information Criterion. The SVM was applied to two regions: the northwest region of the South Pole-Aitken basin as a strong magnetic anomaly region, and the southeast region of the lunar near side as a weak magnetic anomaly region. Since the results from the different datasets of the Kaguya and Lunar Prospector observations show good consistency, characteristic features of the lunar magnetic anomalies at the surface are considered to be well estimated except for components of wavelength shorter than about 1░. From the results by the SVM, both of the regions show elongation patterns of the lunar magnetic anomalies, suggesting lineated structures of the magnetic anomaly sources.
Deep-tow study of magnetic anomalies in the Pacific Jurassic Quiet Zone
Tominaga, Masako
The Jurassic Quiet Zone (JQZ) is a region of low amplitude, difficult-to-correlate magnetic anomalies located over Jurassic oceanic crust. We collected 1200 km of new deep-tow magnetic anomaly profiles over the Pacific JQZ that complement 2 deep...
On long-wavelength magnetic anomalies over Indian region
NASA Technical Reports Server (NTRS)
Srinivasan, S.; Carlo, L.; Rastogi, R. G.; Singh, B. P. (principal investigators)
A data set composed of vector magnetic measurements obtained by MAGSAT and very accurate altitude determinations made using Sun sensors and star cameras was used to obtain data for very quiet days over the Indian region at 10 S to 40 N and 60 E to 110 E in an effort to determine the validity of quantitative estimates made from aeromagnetic data obtained by removing the core field. To further account for the external effects, the ring current contributions estimated using both X and Z variations were subtracted from the observed values. Before this, the core contribution was eliminated through a spherical harmonic expansion with terms up to N=13. Analysis of the residual measurements using Fast Fourier techniques indicates that the anomalies contain substantial power for wavelengths of about 1500 kms. Because the ring current effect has a spatial structure of this dimension over India, efforts are being made to exactly eliminate these two interfering effects from the data.
An equivalent layer magnetization model for the United States derived from satellite altitude magnetic anomalies
NASA Technical Reports Server (NTRS)
Mayhew, M. A.
Long wavelength magnetic anomalies measured by the Pogo series satellites at altitudes 400-700 km over the United States and adjacent areas are inverted to an equivalent layer magnetization model based on an equal area dipole source array at the earth's surface. Minimum source spacing giving a stable solution and a physically meaningful magnetization distribution is 300 km, and a scheme is presented for effectively sampling the distribution on a grid twice as fine. The model expresses lateral variation in the vertical integral of magnetization and is a starting point for models of lateral variation in the form of the magnetization-depth curve in the magnetic crust. The magnetization model contours correlate with large-scale tectonic features, and in the western part of the country, probably reflect Curie isotherm undulations.
Sources of lunar magnetic anomalies and their bulk directions of magnetization - Additional evidence from Apollo orbital data
NASA Technical Reports Server (NTRS)
Hood, L. L.
A relatively high-amplitude magnetic anomaly directly detected with the Apollo 15 subsatellite magnetometer and centered near the crater Gerasimovich on the southeastern lunar far side is found to correlate with the location of a conspicuous Reiner Gamma-type swirl marking visible on a Zond 8 photograph. Examinations of available direct and indirect orbital magnetics measurements demonstrate that most strong anomalies occur in areas where morphologically similar markings are concentrated. Even though photogeologic studies indicate an impact-related origin for the swirls, both the swirls and their associated strong anomalies tend to exist preferentially in or near areas that have been seismically modified. Modeling of improved vector magnetic anomaly maps is used to infer 28 independent bulk directions of magnetization for relatively strong and isolated lunar magnetic anomaly sources.
Surveying the South Pole-Aitken basin magnetic anomaly for remnant impactor metallic iron
NASA Astrophysics Data System (ADS)
Cahill, Joshua T. S.; Hagerty, Justin J.; Lawrence, David J.; Klima, Rachel L.; Blewett, David T.
The Moon has areas of magnetized crust ("magnetic anomalies"), the origins of which are poorly constrained. A magnetic anomaly near the northern rim of South Pole-Aitken (SPA) basin was recently postulated to originate from remnant metallic iron emplaced by the SPA basin-forming impactor. Here, we remotely examine the regolith of this SPA magnetic anomaly with a combination of Clementine and Lunar Prospector derived iron maps for any evidence of enhanced metallic iron content. We find that these data sets do not definitively detect the hypothesized remnant metallic iron within the upper tens of centimeters of the lunar regolith.
Surveying the South Pole-Aitken basin magnetic anomaly for remnant impactor metallic iron
Cahill, Joshua T.S.; Hagerty, Justin J.; Lawrence, David M.; Klima, Rachel L.; Blewett, David T.
The Moon has areas of magnetized crust ("magnetic anomalies"), the origins of which are poorly constrained. A magnetic anomaly near the northern rim of South Pole-Aitken (SPA) basin was recently postulated to originate from remnant metallic iron emplaced by the SPA basin-forming impactor. Here, we remotely examine the regolith of this SPA magnetic anomaly with a combination of Clementine and Lunar Prospector derived iron maps for any evidence of enhanced metallic iron content. We find that these data sets do not definitively detect the hypothesized remnant metallic iron within the upper tens of centimeters of the lunar regolith.
Paleomagnetic and rock magnetic characterization of magnetic anomalies in the Central Iberian Arc (Iberian Peninsula)
NASA Astrophysics Data System (ADS)
Villalain, J.; Ayarza, P.; Martinez-Catalan, J. R.; ┴lvarez-Lobato, F.; G¾mez-Barreiro, J.; Sußrez Barrios, M.; Torres-L¾pez, S.
The Central Iberian Arc is one of the four oroclines delineated by the European Variscan Belt. It is located in NW and Central Iberia and characterized by a conspicuous magnetic response. The most intense magnetic anomaly within this arc is the so called Eastern Galicia Magnetic Anomaly (EGMA; Aller et al., 1994), located in the northern part of Spain and associated to the Lugo-Sanabria dome, an extensional structure in the inner part of arc. The aeromagnetic map of the Iberian Peninsula (Ardizone et al., 1989; Miranda et al., 1989) shows that the EGMA continues to Central Spain and turns back to the Atlantic Ocean, as a broad positive anomaly, delineating a tight fold at the core of the Central Iberian Arc. The source of the EGMA seems to be magnetite-bearing migmatites and inhomogeneous granites formed during an extensive late Carboniferous thermal event triggered by Variscan crustal thickening. These rocks were modeled as a lens-shaped body up to 12 km thick with magnetic susceptibility values between 0.02and 0.03 SI units, that underlie the whole dome extension and continues toward the west of it (Ayarza and MartĒnez Catalßn, 2007). However, this body crops out only in the deepest and northernmost part of the dome, in the Xistral Tectonic Window, and there, only its upper part is accessible. Migmatites and granitoids are abundant along the rest of the anomaly, but their magnetic susceptibility is low. Thus, the source of the magnetic anomaly should be buried there and its nature is unknown. Paleomagnetic and rock magnetic studies in the outcropping rocks responsible for the EGMA have been carried out, adding new constraints to the origin of this anomaly. Rock magnetic analysis as progressive acquisition of IRM, hysteresis loops, thermomagnetic experiments and X-ray indicate that the ferromagnetic fraction is dominated by multidomain magnetite and titanohematite. It is remarkable the unusual high anisotropy of magnetic susceptibility of these rocks, showing degree of anisotropy values 1.2
magnetic fabric shows Variscan affinity, related to an extensional ductile detachment that bounds the Lugo-Sanabria dome to the west. The paleomagnetic analysis consisting in thermal and alternating field demagnetization allows isolating a stable paleomagnetic component with high coercivity and maximum unblocking temperatures of about 630░C, that systematically shows reversed polarity. This component has been interpreted as a remagnetization because its mean direction match those of the Iberian Peninsula after anticlockwise rotation related to the opening of the Bay of Biscay during the Early Cretaceous. All these data must be included in the models in order to place new constraints on the origin, position, and shape of the source and to asses whether all the broad magnetic anomaly at the core of the Central Iberian Arc has the same origin as the EGMA, or a deeper source contributes to it and to the rest of the anomaly.
Airborne detection of magnetic anomalies associated with soils on the Oak Ridge Reservation, Tennessee
Doll, W.E.; Beard, L.P. [Oak Ridge National Lab., TN (United States). Environmental Sciences Div.; Helm, J.M. [Univ. of Utah, Salt Lake City, UT (United States). Dept. of Geology and Geophysics
Reconnaissance airborne geophysical data acquired over the 35,000-acre Oak Ridge Reservation (ORR), TN, show several magnetic anomalies over undisturbed areas mapped as Copper Ridge Dolomite (CRD). The anomalies of interest are most apparent in magnetic gradient maps where they exceed 0.06 nT/m and in some cases exceed 0.5 nT/m. Anomalies as large as 25nT are seen on maps. Some of the anomalies correlate with known or suspected karst, or with apparent conductivity anomalies calculated from electromagnetic data acquired contemporaneously with the magnetic data. Some of the anomalies have a strong correlation with topographic lows or closed depressions. Surface magnetic data have been acquired over some of these sites and have confirmed the existence of the anomalies. Ground inspections in the vicinity of several of the anomalies has not led to any discoveries of manmade surface materials of sufficient size to generate the observed anomalies. One would expect an anomaly of approximately 1 nT for a pickup truck from 200 ft altitude. Typical residual magnetic anomalies have magnitudes of 5--10 nT, and some are as large as 25nT. The absence of roads or other indications of culture (past or present) near the anomalies and the modeling of anomalies in data acquired with surface instruments indicate that man-made metallic objects are unlikely to be responsible for the anomaly. The authors show that observed anomalies in the CRD can reasonably be associated with thickening of the soil layer. The occurrence of the anomalies in areas where evidences of karstification are seen would follow because sediment deposition would occur in topographic lows. Linear groups of anomalies on the maps may be associated with fracture zones which were eroded more than adjacent rocks and were subsequently covered with a thicker blanket of sediment. This study indicates that airborne magnetic data may be of use in other sites where fracture zones or buried collapse structures are of interest.
An integrated geophysical study of the Beattie Magnetic Anomaly, South Africa
NASA Astrophysics Data System (ADS)
Scheiber-Enslin, Stephanie; Ebbing, J÷rg; Webb, Susan J.
The source of the Beattie Magnetic Anomaly (BMA) still remains unclear, with several competing hypotheses. Here we add a piece to the puzzle by investigating available potential field data over the anomaly. Filtered magnetic data show the BMA as part of a group of linear magnetic anomalies. As the linear anomaly north of the BMA is associated with exposed supracrustals, migmatites and shear zones within the Natal thrust terranes we assume a similar source for the BMA. This source geometry, constrained by seismic and MT data, fits potential field data over the BMA and other magnetic linear anomalies in the south-central and south-western Karoo. In these models the bodies deepen from ~ 5 km towards the south, with horizontal extents of ~ 20-60 km and vertical extents of ~ 10-15 km. Densities range from 2800 to 2940 kg/m3 and magnetic susceptibilities from 10 to 100 ū 10- 3 SI. These magnetic susceptibilities are higher than field values from supracrustal rocks (10-60 ū 10- 3 SI) but could be due to the fact that no remanent magnetisation was included in the model. The lithologies associated with the different linear anomalies vary as is evident from varying anomaly amplitudes. The strong signal of the BMA is linked to high magnetic susceptibility granulite facies supracrustals (~ 10-50 ū 10- 3 SI) as seen in the Antarctic, where the mobile belt continued during Gondwana times.
New frontiers in magnetic field interpretation and modeling: Examples from the World Digital Magnetic Anomaly Map
NASA Astrophysics Data System (ADS)
Purucker, M.
The World Digital Magnetic Anomaly Map is a joint effort on the part of the marine, airborne, and satellite magnetic communities to stitch together a unified map of the earth's lithospheric magnetic field. Several preliminary versions of this map will be exhibited during AGU, and this presentation will highlight interpretations of data that have gone into making this map. Examples to be discussed include 1) the Chicxulub impact structure, 2) geodynamical interpretations of dike swarms, 3) structural and tectonic interpretations of aeromagnetic maps over forearc basins with Cenozoic to Recent faulting, 4) heat flux beneath the Antarctic ice sheet, 5) the role of magnetic interpretations in identifying diamond-bearing kimberlites, and 6) structural inferences drawn from magnetic surveys over the West Siberian basin, and the Urengoy gas field.
Investigating tectonic and bathymetric features of the Indian Ocean using MAGSAT magnetic anomaly data
NASA Technical Reports Server (NTRS)
Sailor, R. V.; Lazarewicz, A. R. (principal investigators)
An equivalent source anomaly map and a map of the relative magnetization for the investigation region were produced. Gravimetry, bathymetry, and MAGSAT anomaly maps were contoured in pseudocolor displays. Finally, an autoregressive spectrum estimation technique was verified with synthetic data and shown to be capable of resolving exponential power spectra using small samples of data. Interpretations were made regarding the relationship between MAGSAT data spectra and crustal anomaly spectra.
Long-wavelength magnetic and gravity anomaly correlations on Africa and Europe
NASA Technical Reports Server (NTRS)
Vonfrese, R. R. B.; Olivier, R.; Hinze, W. J.
Preliminary MAGSAT scalar magnetic anomaly data were compiled for comparison with long-wavelength-pass filtered free-air gravity anomalies and regional heat-flow and tectonic data. To facilitate the correlation analysis at satellite elevations over a spherical-Earth, equivalent point source inversion was used to differentially reduce the magnetic satellite anomalies to the radial pole at 350 km elevation, and to upward continue the first radial derivative of the free-air gravity anomalies. Correlation patterns between these regional geopotential anomaly fields are quantitatively established by moving window linear regression based on Poisson's theorem. Prominent correlations include direct correspondences for the Baltic shield, where both anomalies are negative, and the central Mediterranean and Zaire Basin where both anomalies are positive. Inverse relationships are generally common over the Precambrian Shield in northwest Africa, the Basins and Shields in southern Africa, and the Alpine Orogenic Belt. Inverse correlations also presist over the North Sea Rifts, the Benue Rift, and more generally over the East African Rifts. The results of this quantitative correlation analysis support the general inverse relationships of gravity and magnetic anomalies observed for North American continental terrain which may be broadly related to magnetic crustal thickness variations.
Long-wavelength Magnetic and Gravity Anomaly Correlations of Africa and Europe
NASA Technical Reports Server (NTRS)
Vonfrese, R. R. B.; Hinze, W. J. (principal investigators); Olivier, R.
Preliminary MAGSAT scalar magnetic anomaly data were compiled for comparison with long-wavelength-pass filtered free-air gravity anomalies and regional heat-flow and tectonic data. To facilitate the correlation analysis at satellite elevations over a spherical-Earth, equivalent point source inversion was used to differentially reduce the magnetic satellite anomalies to the radial pole at 350 km elevation, and to upward continue the first radial derivative of the free-air gravity anomalies. Correlation patterns between these regional geopotential anomaly fields are quantitatively established by moving window linear regression based on Poisson's theorem. Prominent correlations include direct correspondences for the Baltic Shield, where both anomalies are negative, and the central Mediterranean and Zaire Basin where both anomalies are positive. Inverse relationships are generally common over the Precambrian Shield in northwest Africa, the Basins and Shields in southern Africa, and the Alpine Orogenic Belt. Inverse correlations also presist over the North Sea Rifts, the Benue Rift, and more generally over the East African Rifts. The results of this quantitative correlation analysis support the general inverse relationships of gravity and magnetic anomalies observed for North American continental terrain which may be broadly related to magnetic crustal thickness variations.
Magnetic Anomalies of the Fennoscandian Shield on a 2km resolution grid
NASA Astrophysics Data System (ADS)
Korhonen, Juha V.; Aaro, Sven; Reidar Skilbrei, Jan; All, Tarmo
Joint magnetic anomaly grid of the Fennoscandian Shield was released 2002, smoothed and used as data for the WDMAM2007. In comparison with MF5 this grid showed superior characteristics to other sets. The data will be released as a 2 km resolution grid for the WDMAM2011 with eventual updates of anomaly levels.
Geological modeling of the new CHAMP magnetic anomaly maps using a geographical information system technique
K. Hemant; S. Maus
Reliable global crustal field anomaly maps produced from magnetic measurements of the CHAMP satellite mission now allow for quantitative geological studies of crustal structure and composition. We have developed a GIS based forward modeling technique to model these anomaly maps. On the basis of the geologic and tectonic maps of the world, laboratory susceptibility values of the occurring rock types,
Random crustal magnetization and its effect on coherence of short-wavelength marine magnetic anomalies
Blakely, R.J.
Recent studies of DSDP samples from layer 2A of oceanic basement have found complex magnetic stratigraphies that seem incompatible with the frequent existence of linear short-wavelength anomalies caused by palaeomagnetic field behavior. Statistical models are developed for the lateral variation of the average magnetization of layer 2A: a Poisson series for reversals of the earth's field and a stairstep random series for discrete magnetic units. It is shown with the power-density spectra of these statistical models that lateral inhomogeneities must average out over distances of less than a few hundred meters. Specifically, individual magnetic units of the type seen at DSDP Site 332 cannot extend uniformly for distances greater than a few hundred meters. ?? 1979.
Structure and segmentation of the eastern Gulf of Aden basin and the Sheba ridge from gravity, bathymetric and magnetic anomalies: implications for accretion processes
NASA Astrophysics Data System (ADS)
D'Acremont, E.; Leroy, S.; Maia, M.; Gente, P.; Autin, J.
The eastern Gulf of Aden is a key place for investigating seafloor spreading processes and the evolution in space and time of the margin and ridge segmentation. The rifting of the Gulf that separated Arabia from Somalia started around 35 Ma ago followed by oceanic accretion from at least17.6 Ma. Bathymetric, gravity and magnetic data from the Encens-Sheba cruise are used to study the structure and segmentation of the eastern part of the basin and ridge, which have strong implications for accretion processes. The segmentation of the first oceanic spreading centre, which is dated at least 17.6 Ma by the magnetic anomaly (A5d) identification, seems to be directly related to the structural geometry of the margins. Then, magmatic processes governed the evolution of the segmentation. The segmentation of the oceanic crust evolved, by eastward propagation of the western segment, from three segments (from an5d to an5) to two segments (from an5). At 6 Ma (an3a) a third segment appeared by duplication of the Socotra transform fault, maybe due to a regional kinematics change. The Encens-Sheba oceanic domain is divided in two distinct areas trending NE-SW perpendicular to the Sheba ridge. (1) The Eastern area is characterized by a shorter wavelength variation of the axial segmentation with two spreading segments 30 to 40 km long, and by a thin crust particularly on the northern and southern ends of its flanks. (2) The Western zone, whose axial segment is more than 120 km long, is characterized by a thick crust and/or a hot mantle and no axial rift valley. This abnormal volcanic activity for a slow spreading ridge is emphasized by bathymetric highs with 5-10 km wide volcanic edifices, and by a negative anomaly of the MBA. These different results support the presence of an off-axis thermal anomaly located below the southern flank of the Sheba ridge. The magnetic anomalies and spreading asymmetry reveal that the location of this thermal anomaly might be relatively recent (~ 10 Ma). We propose that at 10 Ma the ridge jumped southwards as attracted by this thermal anomaly, which explains the asymmetry observed between the 5c and 5 anomalies (16 to 10 Ma).
Interpretation of the Gravity and Magnetic Anomalies of the Cappadocia Region, Central Turkey
a deep-seated magnetic anomaly which may be linked to the widespread volcanic activity at the surface potential and the presence of some undiscovered fields. FROGER et al. (1998) explored the hidden calderas
Specific heat anomalies at magnetic ordering temperatures of rare earth iron Laves compounds
M. P. Dariel; U. Atzmony; R. Guiser
The magnetic-ordering temperatures of rare earth and yttrium-iron Laves ; compounds have been determined by measuring the specific heat anomalies in a ; differential scanning calorimeter. The results are in general agreement with ; those deduced from magnetization measurements. The specific heat discontinuities ; at the magnetic-ordering temperatures are not consistent with the theoretical ; expressions derived for ferrites. (auth);
Paleomagnetic determinations on Lanzarote from magnetic and gravity anomalies: Implications for the early history of the Canary Islands
I. Blanco-Montenegro; F. G. Montesinos; A. GarcĒa; R. Vieira; J. J. VillalaĒn
The Bouguer and aeromagnetic anomaly maps of Lanzarote show a gravity high and a dipolar magnetic anomaly over the central part of the island, indicating one isolated source. Assuming that the structure responsible for both anomalies is the same, a methodology has been designed to estimate the total magnetization vector of the source, which is interpreted as a large intrusive
Equatorial Spread F in Relation to Post-Sunset Height Changes and Magnetic Activity
M. S. V. Gopal Rao; B. Ramchandra Rao
Equatorial spread F, magnetic activity, and post-sunset rise in h'F are studied in detail as three parameters, and correlations in the variations in each of the three pairs are ex- amined for all the seasons. Partial correlations are sought to examine the independent influence of magnetic activity and hF changes on spread F. It is observed that the time of
Magnetic structure of a slow spreading ridge segment: Insights from near-bottom magnetic measurements on board a submersible
Chie Honsho; Jķr¶me Dyment; Kensaku Tamaki; Morgane Ravilly; HķlĶne Horen; Pascal Gente
Near-bottom magnetic measurements on board submersible Nautile were carried out on the Mid-Atlantic Ridge 21░40?N segment, and deep-sea geomagnetic vector anomalies along 19 dive tracks were obtained by applying the processing method for shipboard three-component magnetometer data. A forward modeling technique using short-wavelength components of the anomalies arising from local topography and vertical motion of the submersible was designed to
Magnetic-field-induced dielectric anomaly and electric polarization in Mn4Nb2O9
NASA Astrophysics Data System (ADS)
Fang, Y.; Zhou, W. P.; Yan, S. M.; Bai, R.; Qian, Z. H.; Xu, Q. Y.; Wang, D. H.; Du, Y. W.
Magnetic, dielectric, and magnetoelectric properties have been investigated in the polycrystalline Mn4Nb2O9. Under zero magnetic fields, no dielectric anomaly and electric polarization are observed in this compound. When the sample is exposed in magnetic field, finite dielectric peaks and electric polarization are induced, which increase with increasing magnetic field, showing magneto-dielectric and magnetoelectric effects. The origin of magnetoelectric coupling of this compound has been discussed.
Magnetic Properties of Anorthosites: Possible Source Rocks for Planetary Magnetic Anomalies
NASA Astrophysics Data System (ADS)
Brown, L. L.; McEnroe, S. A.
Anorthosites, rocks composed of 90% plagioclase feldspar, are not uncommon on Earth, predominant on the Moon, and suspected units on both Mars and Mercury. Due to the minor amount of oxide minerals in most anorthosites, they have long been considered weakly-magnetic. We studied four related but distinct anorthosite units (Egersund-Ogna, Haland-Helleren, Ana-Sira and Garsaknatt) in the Rogaland Igneous Complex in Southern Norway, emplaced into Sveconorwegian basement around 930 Ma. Aeromagnetic maps of the region show moderate positive to large negative anomalies associated with the anorthosites. Measurements on 43 sites (279 samples) of susceptibility, natural remanent magnetization (NRM) and hysteresis properties provide a startling picture of the magnetic behavior of these rocks. Mean NRM values on each anorthosite range from a low of 0.6 A/m on the Egersund-Ogna body to 5.9 A/m on the Haland-Helleren, placing these rocks in similar NRM range to young basalts. Susceptibility varies widely from body to body, with a low of 4.88 x 10-4 SI on the Egersund-Ogna to 2.40 x 10-2 SI on the Haland-Helleren. All units have average Koenigsberger Ratio (Q) values greater than 1, ranging from 8 for the Garsaknatt to 61 for the Egersund-Ogna. With the exception of a few samples in the Garsaknatt, mean destructive fields for alternating field demagnetization for all bodies are greater than 40 mT. Most samples show considerable intensity remaining after thermal demagnetization to 560C and appreciable amounts above 580C. Hysteresis properties from the anorthosites show a wide range of Mr/Ms and Hcr/Hc values. Optical investigation of polished sections reveals the presence hemo-ilmenite in Ana Sira, Egersund-Ogna and Haland-Helleren anorthosites. Minor amounts of magnetite are restricted to the Garsaknatt and parts of the Haland-Helleren anorthosites. Although these four anorthosites have a wide range of magnetic properties, they all have appreciable remanent magnetization and all are capable of producing moderate to strong remanent-dominated anomalies. Because anorthosites are common on the Moon and suggested to exist on other planets, these rocks should be considered as possible sources for planetary paleomagnetism and/or magnetic anomalies.
Characterization of CHAMP magnetic data anomalies: magnetic contamination and measurement timing
NASA Astrophysics Data System (ADS)
Yin, Fan; L³hr, Hermann; Rauberg, Jan; Michaelis, Ingo; Cai, Hongtao
The CHAMP (CHAllenging Minisatellite Payload) mission ended after more than ten years in space on 19 September 2010. For achieving a high measurement accuracy of the magnetometers on CHAMP, detailed analyses of spacecraft magnetic characteristics in orbit are required. A decade of continuous magnetometer and housekeeping data are a good basis for evaluating some of the effects of variable spacecraft magnetic fields on the ambient field determination. It was found that some perturbations of FGM (FluxGate vector Magnetometer) or OVM (OVerhauser scalar Magnetometer) measurements are caused by stray fields induced by the power system, the ASC (advanced stellar compass) instrument or magneto-torquer currents. The magnetic effect of solar currents on FGM measurements varies with the local time of the orbit and amounts to 0.2 nT. In cases when one head of the ASC instrument was blinded by the sun, sometimes transient drops in instrument current strength occur, which were accompanied by magnetic disturbance signals (?0.3 nT) in FGM measurements. The magnetic residual contamination of OVM data by the torquer currents was of order 0.1 nT but still detectable. An improved torquer correction matrix is derived which eliminates this effect. In-flight scalar calibration parameters revealed some of the effects of timing anomalies. Time lags between FGM and OVM readings are misinterpreted by the scalar calibration as variations of the angles between some of the sensor axes. The resulting amplitudes of the anomalies presented here lie in the range of some 0.1 nT, but they are systematic in nature.
Magnetic properties of a massive hematite deposit and correlative magnetic anomaly
NASA Astrophysics Data System (ADS)
McEnroe, S.; Clark, D.; Schimdt, P. W.
Exploration samples from a Mid-Proterozoic massive hematite deposit in South Australia were examined in detail for magnetic properties. This deposit produces a large magnetic anomaly that can only be modeled with a significant remanent component. A gravity anomaly can be modeled using the density contrast between the massive hematite ore and the country gneiss rock. Exploration drill core samples show very high NRMs, up to 372 A/m, associated with high Q values. Based on susceptibilities, high- and low-field thermomagnetic curves, hysteresis loops and IRM acquisition/demagnetization curves, samples can be separated into two groups: 1) hematite-magnetite ores and 2) pure hematite ores. Low temperature demagnetization (cooling to liquid nitrogen temperatures and rewarming in zero field) of hematite-magnetite ores showed an 8 to 50% loss in magnetization. These samples have Mrs/Ms values 0.5 to 0.06 and Hcr/Hc from 3 to 8. AF demagnetization reveals MDFs of 50mT. The pure hematite samples all have Neel temperatures around 670░C. These samples show a 12-50% loss after low temperature demagnetization to below the Morin transition ( 80░C), but above the Verwey transition of magnetite, and only slight additional demagnetization at LN temperatures. Following low temperature demagnetization, AF demagnetization to 100mT produces an increase in intensity at low fields, followed by a small loss in magnetization up to 100mT. Mrs/Ms values range from 0.5 to 0.9, and Hcr/Hc is close to unity. SIRM acquisition shows that samples are between 3 to 15% saturated in the NRM state. The hematite ores are composed of well equilibrated hematite crystals all in the multidomain-size range. However, these samples are not saturated in the present day EarthÆs magnetic field and require a field of at least 0.2T to saturate.
Application of Magsat lithospheric modeling in South America. Part 1: Processing and interpretation of magnetic and gravity anomaly data
NASA Technical Reports Server (NTRS)
Hinze, W. J.; Braile, L. W.; Vonfrese, R. R. B. (principal investigators); Keller, G. R.; Lidiak, E. G.
Scalar magnetic anomaly data from MAGSAT, reduced to vertical polarization and long wavelength pass filtered free air gravity anomaly data of South America and the Caribbean are compared to major crustal features. The continental shields generally are more magnetic than adjacent basins, oceans and orogenic belts. In contrast, the major aulacogens are characterized by negative anomalies. Spherical earth magnetic modeling of the Amazon River and Takatu aulacogens in northeastern South America indicates a less magnetic crust associated with the aulacogens. Spherical earth modeling of both positive gravity and negative magnetic anomalies observed over the Mississippi Embayment indicate the presence of a nonmagnetic zone of high density material within the lower crust associated with the aulacogen. The MAGSAT scalar magnetic anomaly data and available free air gravity anomalies over Euro-Africa indicate several similar relationships.
Marine Magnetic Anomalies, Geomagnetic Field Reversals, and Motions of the Ocean Floor and Continents
J. R. Heirtzler; G. O. Dickson; E. M. Herron; W. C. Pitman; X. Le Pichon
This paper summarizes the results of the three previous papers in this series, which have shown the presence of a pattern of magnetic anomalies, bilaterally symmetric about the crest of the ridge in the Pacific, Atlantic, and Indian oceans. By assuming that the pattern is caused by a sequence of normally and reversely magnetized blocks that have been produced by
Automatic Detection of UXO Magnetic Anomalies Using Extended Euler Deconvolution Kristofer Davis*
estimates both location and, more importantly, the type of magnetic source that produced the anomaly. Any in exploration geophysics for rapidly estimating the location and depth to magnetic or gravity sources) where n is the degree of homogeneity. Carrying out simple differentiation, it can be shown from eq. (1
The intermediate wavelength magnetic anomaly field of the north Pacific and possible source distributions
NASA Technical Reports Server (NTRS)
Labrecque, J. L.; Cande, S. C.; Jarrard, R. D. (principal investigators)
A technique that eliminates external field sources and the effects of strike aliasing was used to extract from marine survey data the intermediate wavelength magnetic anomaly field for (B) in the North Pacific. A strong correlation exists between this field and the MAGSAT field although a directional sensitivity in the MAGSAT field can be detected. The intermediate wavelength field is correlated to tectonic features. Island arcs appear as positive anomalies of induced origin likely due to variations in crustal thickness. Seamount chains and oceanic plateaus also are manifested by strong anomalies. The primary contribution to many of these anomalies appears to be due to a remanent magnetization. The source parameters for the remainder of these features are presently unidentified ambiguous. Results indicate that the sea surface field is a valuable source of information for secular variation analysis and the resolution of intermediate wavelength source parameters.
Scalar magnetic anomaly maps of Earth derived from POGO and Magsat data
NASA Astrophysics Data System (ADS)
Arkani-Hamed, Jafar; Langel, Robert A.; Purucker, Mike
A new Polar Orbit Geophysical Observatory (POGO) scalar magnetic anomaly map at 400 km altitude is presented which consists of spherical harmonics of degree 15-60. On the basis of the common features of this map with two new Magsat anomaly maps, dawn and dusk, two scalar magnetic anomaly maps of the Earth are presented using two selection criteria with different levels of stringency. These selection criteria suppress the noncrustal components of the original maps by different amounts. The more stringent selection criteria seek to eliminate as much contamination as possible, at the expense of suppressing some anomaly signal. This map is represented by spherical harmonics of degree 15-60. The less stringent selection criteria seek to retain as much crustal signal as possible, at the expense of also retaining some contaminating fields. This map is represented by spherical harmonics of degree 15-65. The resulting two maps are highly correlated with degree correlation coefficients greater than 0.8.
Scalar magnetic anomaly maps of Earth derived from POGO and Magsat data
NASA Technical Reports Server (NTRS)
Arkani-Hamed, Jafar; Langel, Robert A.; Purucker, Mike
A new Polar Orbit Geophysical Observatory (POGO) scalar magnetic anomaly map at 400 km altitude is presented which consists of spherical harmonics of degree 15-60. On the basis of the common features of this map with two new Magsat anomaly maps, dawn and dusk, two scalar magnetic anomaly maps of the Earth are presented using two selection criteria with different levels of stringency. These selection criteria suppress the noncrustal components of the original maps by different amounts. The more stringent selection criteria seek to eliminate as much contamination as possible, at the expense of suppressing some anomaly signal. This map is represented by spherical harmonics of degree 15-60. The less stringent selection criteria seek to retain as much crustal signal as possible, at the expense of also retaining some contaminating fields. This map is represented by spherical harmonics of degree 15-65. The resulting two maps are highly correlated with degree correlation coefficients greater than 0.8.
The mineralogy of global magnetic anomalies. [rock magnetic signatures and MAGSAT geological, and gravity correlations in West Africa
NASA Technical Reports Server (NTRS)
Haggerty, S. E. (principal investigator)
Problems with the Curie balance, which severely hindered the acquisition of data, were rectified. Chemical analytical activities are proceeding satisfactorily. The magnetization characteristics of metamorphic suites were analyzed and susceptibility data for a wide range of metamorphic and igneous rocks. These rock magnetic signatures are discussed as well as the relationships between geology, gravity and MAGSAT anomalies of West Africa.
Application of magnetic resonance urography in diagnosis of congenital urogenital anomalies in children
Seyedmehdi Payabvash; Abdol-Mohammad Kajbafzadeh; Parisa Saeedi; Zhina Sadeghi; Azadeh Elmi; Mehrzad Mehdizadeh
Magnetic resonance urography (MRU) has become a useful adjuvant in evaluating urogenital anomalies. In present study, we evaluated\\u000a the ability of MRU in diagnosis of different congenital urogenital anomalies when the results of conventional imaging modalities\\u000a were inconclusive. A total of 90 children were included in this series. The children were evaluated with T2-weighted and contrast-enhanced\\u000a T1-weighted MRU sequences. The
MAGSAT investigation of crustal magnetic anomalies in the eastern Indian Ocean
NASA Technical Reports Server (NTRS)
Sailor, R. V.; Lazarewicz, A. R.
Crustal magnetic anomalies in a region of the eastern Indian Ocean were studied using data from NASA's MAGSAT mission. The investigation region (0 deg to 50 deg South, 75 to 125 deg East) contains several important tectonic features, including the Broken Ridge, Java Trench, Ninetyeast Ridge, and Southeast Indian Ridge. A large positive magnetic anomaly is associated with the Broken Ridge and smaller positive anomalies correlate with the Ninetyeast Ridge and western Australia. Individual profiles of scalar data (computed from vector components) were considered to determine the overall data quality and resolution capability. A set of MAGSAT ""Quiet-Time'' data was used to compute an equivalent source crustal magnetic anomaly map of the study region. Maps of crustal magnetization and magnetic susceptibility were computed from the equivalent source dipoles. Gravity data were used to help interpretation, and a map of the ratio of magnetization to density contrasts was computed using Poisson's relation. The results are consistent with the hypothesis of induced magnetization of a crustal layer having varying thickness and composition.
Study on crustal magnetic anomalies and Curie surface in Southeast Tibet
NASA Astrophysics Data System (ADS)
Gao, Guoming; Kang, Guofa; Bai, Chunhua; Wen, Limin
In this paper, the Potsdam model POMME-6.2 is used to investigate the distributions of crustal magnetic anomalies and Curie surface in Southeast Tibet. The Curie surface is compared with the regional heat flow, Bouguer anomaly, Moho depth, and seismicity. The results show that the magnetic anomalies and Curie surface are both consistent with the geological structure. Sichuan Basin exhibits a high positive anomaly, while orogenic belts such as the Longmenshan, northwestern Sichuan, and western Yunnan, exhibit weak positive or negative anomalies. The distribution of magnetic anomaly confirms that escape flow from east Tibet branches into northeastward part and southward part on west Sichuan Basin, due to resistance by the rigid basin. The depth of Curie surface ranges from 20 to 34 km. The Curie surface beneath the Longmenshan, Xiaojiang and Lijiang-Xiaojinhe faults is shallow, with the uplift strike consistent with the faults. The Curie surface beneath Sichuan Basin and the central Bayan Har massif is deep, with sheet-like depressions. Strong earthquakes primarily occurred in the areas with the uplift of Curie surface. The heat flow values near Tengchong, Lijiang, Dali and Kunming are high and the Curie surface there is shallow.
Interpretations of gravity and magnetic anomalies in the Songliao Basin with Wavelet Multi-scale Decomposition
NASA Astrophysics Data System (ADS)
Li, Changbo; Wang, Liangshu; Sun, Bin; Feng, Runhai; Wu, Yongjing
In this paper, we introduce the method of Wavelet Multi-scale Decomposition (WMD) combined with Power Spectrum Analysis (PSA) for the separation of regional gravity and magnetic anomalies. The Songliao Basin is situated between the Siberian Plate and the North China Plate, and its main structural trend of gravity and magnetic anomaly fields is NNE. The study area shows a significant feature of deep collage-type construction. According to the feature of gravity field, the region was divided into five sub-regions. The gravity and magnetic fields of the Songliao Basin were separated using WMD with a 4th order separation. The apparent depth of anomalies in each order was determined by Logarithmic PSA. Then, the shallow high-frequency anomalies were removed and the 2nd-4th order wavelet detail anomalies were used to study the basin's major faults. Twenty-six faults within the basement were recognized. The 4th order wavelet approximate anomalies were used for the inversion of the Moho discontinuity and the Curie isothermal surface.
Why are There So Few Magnetic Anomalies in Martian Lowlands and Basins?
NASA Technical Reports Server (NTRS)
Solomon, Sean C.; Aharonson, Oded; Banerdt, W. Bruce; Dombard, Andrew J.; Frey, Herbert V.; Golombek, Matthew P.; Hauck, Steven A., II; Head, James W., III; Johnson, Catherine L.; McGovern, Patrick J.
The discovery of large areas of strongly magnetized crust on Mars [1,2] provides important information on the timing of both crustal and deeper interior processes on that planet. Critical to an understanding of that timing, as well as to the processes that have contributed to the magnetization and demagnetization of crustal materials, is the geographical distribution of magnetic anomalies discernible from spacecraft orbit. The paucity of resolved magnetic anomalies in the northern lowlands and within and surrounding the best-preserved major impact basins has been noted since the crustal field was first globally mapped [1], but no straightforward explanation of that full pattern has yet been offered. Here we suggest that ancient hydrothermal alteration of magnetic carriers in Martian lowlands and basins may have contributed to the magnetization distribution observed today.
The Effect of Dissipation Mechanism on X-line Spreading in 3D Magnetic
NASA Astrophysics Data System (ADS)
Shepherd, L. S.; Cassak, P.; Phan, T.; Shay, M. A.; Gosling, J. T.
Naturally occurring magnetic reconnection generally begins in a spatially localized region and spreads in the direction perpendicular to the reconnection plane as time progresses. Reconnection spreading is associated with dawn-dusk asymmetries during substorms in the magnetotail and has been observed in two-ribbon flares (such as the Bastille Day flare) and laboratory experiments at the Versatile Toroidal Facility (VTF) and the Magnetic Reconnection eXperiment (MRX). It was suggested that X-line spreading is necessary to explain the existence of X-lines extending more than 390 Earth radii (Phan et al., Nature, 404, 848, 2006). Previous numerical studies exploring the spreading of localized magnetic reconnection exclusively addressed collisionless (Hall) reconnection. Here, we address the effect of dissipation mechanism has on X-line spreading with and without a guide field. We compare previous results with simulations using three alternate phases of reconnection - Sweet-Parker reconnection, collisional reconnection with secondary islands, and reconnection with anomalous resistivity. We present results from three-dimensional resistive magnetohydrodynamic numerical simulations to address the nature of X-line spreading. Applications to reconnection in the solar wind and corona will be discussed.
Electric/magnetic duality for chiral gauge theories with anomaly cancellation
Jan De Rydt; Torsten T. Schmidt; Mario Trigiante; Antoine Van Proeyen; Marco Zagermann
We show that 4D gauge theories with Green-Schwarz anomaly cancellation and possible generalized Chern-Simons terms admit a formulation that is manifestly covariant with respect to electric/magnetic duality transformations. This generalizes previous work on the symplectically covariant formulation of anomaly-free gauge theories as they typically occur in extended supergravity, and now also includes general theories with (pseudo-)anomalous gauge interactions as they may occur in global or local N=1 supersymmetry. This generalization is achieved by relaxing the linear constraint on the embedding tensor so as to allow for a symmetric 3-tensor related to electric and/or magnetic quantum anomalies in these theories. Apart from electric and magnetic gauge fields, the resulting Lagrangians also feature two-form fields and can accommodate various unusual duality frames as they often appear, e.g., in string compactifications with background fluxes.
First scalar magnetic anomaly map from CHAMP satellite data indicates weak lithospheric field
NASA Astrophysics Data System (ADS)
Maus, S.; Rother, M.; Holme, R.; L³hr, H.; Olsen, N.; Haak, V.
Satellite magnetic anomaly maps derived by different techniques from Magsat/POGO data vary by more than a factor of 2 in the deduced strength of the lithospheric magnetic field. Here, we present a first anomaly map from new CHAMP scalar magnetic field data. After subtracting a recent žrsted main and external field model, we remove remaining unmodeled large-scale external contributions from 120░ track segments by subtracting a best-fitting uniform field. In order to preserve N/S trending features, the data are not filtered along-track. Direct integration of the spherically gridded data yields the final degree 14-65 spherical harmonic expansion of the total intensity anomaly at the mean satellite altitude of 438 km. Apart from enhanced long wavelength features and a smoother general appearance, our initial map is strikingly similar to one of the lower strength Magsat/POGO maps.
Gravity and magnetic anomaly modeling and correlation using the SPHERE program and Magsat data
NASA Technical Reports Server (NTRS)
Braile, L. W.; Hinze, W. J. (principal investigators); Vonfrese, R. R. B.
The spherical Earth inversion, modeling, and contouring software were tested and modified for processing data in the Southern Hemisphere. Preliminary geologic/tectonic maps and selected cross sections for South and Central America and the Caribbean region are being compiled and as well as gravity and magnetic models for the major geological features of the area. A preliminary gravity model of the Andeas Beniff Zone was constructed so that the density columns east and west of the subducted plates are in approximate isostatic equilibrium. The magnetic anomaly for the corresponding magnetic model of the zone is being computed with the SPHERE program. A test tape containing global magnetic measurements was converted to a tape compatible with Purdue's CDC system. NOO data were screened for periods of high diurnal activity and reduced to anomaly form using the IGS-75 model. Magnetic intensity anomaly profiles were plotted on the conterminous U.S. map using the track lines as the anomaly base level. The transcontinental magnetic high seen in POGO and MAGSAT data is also represented in the NOO data.
Magnetic anomalies in east Pacific using MAGSAT data
NASA Technical Reports Server (NTRS)
Harrison, C. G. A. (principal investigator)
Methods for solving problems encountered in separating the core field from the crustal field are summarized as well as those methods developed for inverting total magnetic field data to obtain source functions for oceanic areas. Accounting for magnetization contrasts and the magnetization values measured in rocks of marine origin are also discussed.
Estimation of the direction of remanent magnetization: an inverse method using the phase spectrum of a magnetic anomaly
Moriarty, Thomas D.
in partial fidfillment of thc requirements for the degree of XIAS IER OF SOIL'NGF. December l988 iviajor Subject: Geophysics ES'I'llvlATION Ol' THV. DIIIECTION OF' RElvIANENT MACNETIZATION: AN INVERSE METHOD DSINC 'THE PIIASV. SPECTRIIM OV A MAGNETIC... ot Department) December 1988 ABSTRACT Estimation of Direction of Remanent Magnetization: An Inverse Method Using th~ Phase Spectrum ot a. Magnetic Anomaly. (December 1988) Thomas Daniel Moriarty, B. S. , Rensselaer Polytechnic Institute Co...
Craton vs. rift uppermost mantle contributions to magnetic anomalies in the United States interior
NASA Astrophysics Data System (ADS)
Friedman, S. A.; Feinberg, J. M.; Ferrķ, E. C.; Demory, F.; MartĒn-Hernßndez, F.; Conder, J. A.; Rochette, P.
The interpretation of satellite magnetic information (Magsat, Oersted, CHAMP, Swarm) requires the understanding of the mineralogy of crustal and mantle sources. Also, spectral analysis of magnetic data over forearcs and cratons calls for upper mantle contribution. The prospect of such a contribution contradicts the view that the mantle is too hot and its magnetism is too weak to influence magnetic anomalies. Here we examine the rock magnetic properties of fresh mantle xenoliths from four settings across the United States: phlogopite-spinel dunites from the Bearpaw Mountains, Montana, and lherzolites/harzburgites from San Carlos, Arizona; Kilbourne Hole, New Mexico; and Knippa, Texas. Paleomagnetic results show single-component natural remanent magnetizations (NRMs), which, combined with optical and secondary electron microscopy support the lack of post-eruption alteration and absence of host-rock contamination. The NRM carriers include magnetite at Bearpaw Mountain and San Carlos, and pyrrhotite at Kilbourne Hole and Knippa. These four areas show continental crust of distinct thicknesses and various geotherms. The potential mantle contribution to magnetic anomalies is forward modeled using crustal thickness, current geotherm and average magnetic properties of xenoliths. The San Carlos and Kilbourne Hole mantle, situated near the Rio Grande Rift is too hot and its magnetism is too weak to contribute to anomalies. The sulfide-dominated assemblage at Knippa does not support magnetization at mantle depths. In contrast, the Bearpaw Mountains combine a relatively cold geotherm (craton) and abundance of magnetite formed at mantle depth. This cratonic mantle, metasomatized by fluids from the Farallon plate, may contribute to long wavelength magnetic anomalies.
Processing and Analysis of Near-Seafloor Magnetic Anomalies around Futuna Island, SW Pacific Ocean
NASA Astrophysics Data System (ADS)
Szitkar, F.; Dyment, J.; Fouquet, Y.; Choi, Y.
In September 2010, cruise Futuna of R/V L'Atalante collected near-seafloor magnetic data with AUV Aster-X (70 m asf) and Deep-Sea Submersible (DSS) Nautile (2-20 m asf) on several volcanic systems around Futuna Island, SW Pacific Ocean. Here we present the data, the method of analysis, and a first geological interpretation. Unlike a ship, a submersible (or an AUV) cannot tow a magnetometer due to the close proximity of the seafloor. Instead, the magnetometer is rigidly fixed on the submersible, which magnetization affects the magnetic measurements. A vector magnetometer (i.e. three orthogonal fluxgate sensors) measures the field three components in a referential linked to the submarine, a requirement to determine and correct the magnetization of the submersible, The remanent magnetization vector (3 components) and the magnetic susceptibility tensor (9 coefficients) of the submersible are estimated by inverting magnetic data collected on calibration loops, far from both the ship and the seafloor, during the descent (ascent) of the submersible at the beginning (end) of the dives. For this estimation, the ambient field is assumed to be the IGRF, the departures from this assumption reflecting the magnetization of the submersible. The twelve coefficients are inverted from the loop data by a least square method, regularized by a dumping factor to account for the limited pitch and roll values sampled by the submersible. Once determined, these coefficients are used to reduce the magnetic data acquired during the whole dive for the magnetic effect of the submersible, the resulting three component anomalies being rotated to the geographic reference frame as well. The resulting anomalies acquired by the AUV on regularly-spaced tracks are gridded and reduced to the pole such as the resulting anomalies are located on the top of their causative sources. They are further inverted to equivalent magnetization using the high-resolution topography acquired by the AUV. The anomalies acquired by DSS Nautile on isolated and uneven tracks are cut and projected on linear segments. Synthetic anomalies are computed under the conditions of the experiment, assuming a unit magnetization. Observed and computed anomalies are compared on sliding windows, resulting in an estimate of the absolute magnetization of the seafloor. The data sets collected at 2-20 m (by DSS Nautile) and 70 m (by AUV Aster-X) jointly constrain the geological interpretation.
Remanent magnetization and three-dimensional density model of the Kentucky anomaly region
NASA Technical Reports Server (NTRS)
Existing software was modified to handle 3-D density and magnetization models of the Kentucky body and is being tested. Gravity and magnetic anomaly data sets are ready for use. A preliminary block model is under construction using the 1:1,000,000 maps. An x-y grid to overlay the 1:2,500,000 Albers maps and keyed to the 1:1,000,000 scale block models was created. Software was developed to generate a smoothed MAGSAT data set over this grid; this is to be input to an inversion program for generating the regional magnetization map. The regional scale 1:2,500,000 map mosaic is being digitized using previous magnetization models, the U.S. magnetic anomaly map, and regional tectonic maps as a guide.
Anomaly-induced quadrupole moment of the neutron in magnetic field
Kharzeev, D.E.; Yee, H.-U., Zahed, I.
Neutrons cannot possess a quadrupole moment in the vacuum. Nevertheless, we show that, in the presence of an external magnetic field, the neutrons acquire a new type of quadrupole moment Q{sup ij} = {chi}{sigma}{sup i} B{sup j} involving the components of spin and magnetic field. This 'chiral magnetic' quadrupole moment arises from the interplay of the chiral anomaly and the magnetic field; we estimate its value for the neutron in the static limit and find {chi} {approx_equal} 1.35 {center_dot} 10{sup -2} fm{sup 4}. The detection of the quadrupole moment of the neutron would provide a novel test of the role of the chiral anomaly in low-energy QCD and can be possible in the presence of both magnetic and inhomogeneous electric fields. The quadrupole moment of the neutron may affect, e.g., the properties of neutron stars and magnetars.
Magnetic properties of mantle xenoliths and implications for long wavelength magnetic anomalies
NASA Astrophysics Data System (ADS)
Friedman, Sarah A.
Unaltered peridotite xenoliths are broadly representative of the lithospheric mantle in both oceanic and continental domains. These peridotites are mainly lherzolites and harzburgites. Other rock types such as dunites, wehrlites and pyroxenites are generally not volumetrically significant. The respective contributions of rock-forming minerals to induced and remanent magnetization in these rocks are currently poorly constrained. This information can be used to assess the significance of long-wavelength magnetic anomalies. It can also provide insights, as an alternate approach to the spinel-olivine-pyroxene oxybarometer, into several important petrologic parameters of the lithospheric mantle including fO2. Forty-nine representative, uncontaminated and non-serpentinized xenoliths have been magnetically investigated. These specimens display contrasting remanent magnetic properties (NRM, Mr, Ms) depending on their tectonic settings, specifically oceanic hot-spot, continental mantle plume, island arc, and craton. The main paramagnetic silicates (olivine, clinopyroxene, orthopyroxene, etc...) typically account for most of the peridotite magnetic properties. The low-field bulk magnetic susceptibility of pristine, unaltered mantle xenoliths is ? 500 +/- 60 x 10-6 [SI] and displays limited variability. The total contribution of paramagnetic silicates to magnetic susceptibility (Kpara-silicates) can be determined from the high-field slope of a saturated hysteresis experiment. Kpara-silicates can also be calculated by adding the respective contributions of individual silicates based on their modes, chemical composition, and the Bohr magneton numbers of individual cations. Silicates account for between 56 and 97% (average ? 85%) of the magnetic susceptibility depending on rock composition. When present, the contribution of chrome spinel, which is paramagnetic in the absence of late-stage exsolution products, remains around 1%. Plagioclase-, spinel- and garnet-lherzolites share similar low-field magnetic properties. The remaining contribution to magnetic susceptibility arises from variable amounts of primary magnetite (and pyrrhotite to a minor extent). These mineral phases, although present in tens to hundreds of ppm only, contribute significantly to the rock magnetic properties because they have large intrinsic magnetic susceptibilities (? 1 to 4 [SI] for magnetite). Stoichiometric magnetite has been identified as microscopic exsolutions in the lattice of olivine and accounts for 2 to 43% (average ? 8%) of the magnetic susceptibility. Whether these pseudo-single domain magnetite grains are in equilibrium with other rock-forming minerals or not is still being investigated. Pyrrhotite (up to 600 ppm in some rare specimens), although detectable in low-temperature magnetic experiments, does not significantly contribute to magnetic susceptibility. The contribution of ferromagnetic minerals, such as magnetite and pyrrhotite, to remanent magnetization (Mr) is significant and varies greatly (over 250x between specimens) with tectonic setting. The fact that all specimens contain primary magnetite suggests that these assemblages equilibrated at least at or above the wustite-magnetite (WM) oxygen buffer and near the fayalite-magnetite-quartz (FMQ) oxygen buffer. The amount of magnetite present in the mantle peridotite assemblage seems to correlate with tectonic setting and may be linked to fO2 in the mantle. The timing of magnetite exsolution in olivine is still poorly understood and may depend on degree of partial melting, rate of cooling to ambient lithospheric temperature, or mantle metasomatic processes due to introduction of hydrous fluids.
The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates
NASA Astrophysics Data System (ADS)
Nadareishvili, M. M.; Kvavadze, K. A.
The low-temperature heat capacity in pure (y=0) and Zn-doped La1.84Sr0.16Cu1-yZnyO4 samples (y =0.033 and 0.06) have been performed in the temperature interval 1.8-60K by the method of high-precision pulsed differential calorimetry, providing measurements under the equilibrium conditions in contrast to commonly used differential scanning calorimeters. For these systems a new heat capacity anomaly was observed in the nonsuperconducting state, which is related with Zn impurities and has the form of single wide peak. The anomaly does not show a phonon character as it strongly shifts towards higher temperatures with increasing Zn content, as is characteristic for a magnetic anomaly. The anomaly increases almost linearly with the impurity concentration.
Influence of Martian crustal magnetic anomalies on the emission of energetic neutral hydrogen atoms
NASA Astrophysics Data System (ADS)
Wang, X.-D.; Barabash, S.; Futaana, Y.; Grigoriev, A.; Wurz, P.
We analyze the data on hydrogen energetic neutral atoms (ENAs) emissions from the dayside of Mars, recorded by a Neutral Particle Detector of the Analyzer of Space Plasmas and Energetic Atoms aboard Mars Express from 14 March to 9 July 2004. We first identify and analyze events of the ENA flux enhancement coinciding with the presence of the crustal magnetic anomalies on the dayside of Mars. We then backtrace the ENA emissions to the lower altitudes (source region) and build up an average map of the flux intensities in the geographic coordinates with all the available data. The map shows a peak-to-valley ENA flux enhancement of 40%-90% close to the crustal magnetic anomaly regions. These results suggest the influence of the magnetic anomalies on the ENA emission from the dayside of Mars. The enhancement may result from the deviation of the highly directional plasma flow above anomalies toward the detectors such that more charge exchange ENAs would be recorded. Alternatively, higher exospheric densities above the anomalies would also result in an increase of the charge exchange ENA flux.
A Study of Magnetic Reconnection: From 2D Energy Release to 3D Spreading and Localization
NASA Astrophysics Data System (ADS)
Shepherd, Lucas S.
Magnetic reconnection is a plasma process in which stored magnetic energy is converted into thermal and kinetic energies of the surrounding plasma. Oppositely directed magnetic field lines break and cross connect due to a dissipative mecha- nism. The now bent, reconnected field lines retreat from the X-line (the location of reconnection) at the Alfven speed due to the magnetic tension in the reconnected magnetic field, therefore generating outflows. This dissertation addresses three fundamental properties of magnetic reconnection. Solar flares are explosive events in the solar corona in which magnetic reconnection mediates the rapid release (on the order of minutes) of energy stored in magnetic fields into the surrounding plasma. The Sweet-Parker (collisional) model was the first self-consistent theory to explain magnetic reconnection, but is far too slow to explain observations. The formation of secondary islands make Sweet-Parker reconnection faster, but is it fast enough to explain energy release rates? Collisionless (Hall) reconnection leads to energy release rates fast enough to explain observations. Large-scale resistive Hall-Magnetohydrodynamics simulations of the transition from Sweet-Parker to Hall reconnection are presented; the first to separate secondary islands from collisionless effects. Three main results are described. There exists a regime with secondary islands but without collisionless effects entering, and the reconnection rate is faster than Sweet-Parker, but significantly slower than Hall reconnection. This implies that secondary islands do not cause the fastest reconnection rates. The onset of Hall reconnection ejects secondary islands from the vicinity of the X-line, implying that energy is released more rapidly during Hall reconnection. Early models of magnetic reconnection have treated reconnection as two- dimensional. However, naturally occurring magnetic reconnection often begins in a localized region and spreads in the direction perpendicular to the plane of reconnection. Theoretical arguments and large-scale two fluid simulations are used to study the spreading of reconnection X-lines localized in the direction of the current as a function of the strength of the out-of-plane (guide) magnetic field. It is found that the mechanism causing the spreading is different for weak and strong guide fields. In the weak guide field limit, spreading is due to the motion of the current carriers. However, spreading for strong guide fields is bidirectional and is due to the excitation of Alfven waves along the guide field. In general, we suggest that the X-line spreads bidirectionally with a speed governed by the faster of the two mechanisms for each direction. A prediction of the strength of the guide field at which the spreading mechanism changes is formulated and verified with three-dimensional simulations. In the solar wind, magnetic reconnection exhausts measuring 600 [Gosling et al. (2007)] and 390 [Phan et al. (2006)] Earth radii in length have been observed. The authors assumed that the extended exhaust was caused by an extended X-line. If this is the case, what mechanism is responsible for these large scale structures? It has been suggested these structures are formed by a small X-line forming near the sun and spreading as the X-line convects away from the sun. Another possibility is the X-line is localized in a small region and the exhaust expands into the out-of-plane direction. Theoretical arguments and large-scale simulations are used to study localized (not spreading) magnetic reconnection, and its three-dimensional structure. Localized reconnection may also be vital to the formation of supra-arcade downflows (SADs) in the corona. Both solar wind and coronal applications are discussed.
Gravity and magnetic anomalies and the deep structure of the Parnaiba cratonic basin, Brazil
Watts, A. B. "Tony"
Gravity and magnetic anomalies and the deep structure of the Parnaiba cratonic basin, Brazil A. B profile across the Parnaiba cratonic basin in NorthEast Brazil. The purpose of this project is to acquire margin of ParnaĒba Basin, Brazil. Geophysics 64: 337-356. Ussami N, Cogo de Sa N, Molina EC. 1993
Controls on Martian hydrothermal systems: Application to valley network and magnetic anomaly formation
Harrison, Keith
vents. There is also evidence for the past existence of hydrothermal systems on Mars (see Farmer [1996Controls on Martian hydrothermal systems: Application to valley network and magnetic anomaly December 2001; accepted 3 January 2002; published 3 May 2002. [1] Models of hydrothermal groundwater
Lunar Ion Transport Near Magnetic Anomalies: Possible Implications for Swirl Formation
NASA Technical Reports Server (NTRS)
Keller, J. W.; Killen, R. M.; Stubbs, T. J.; Farrell, W. M.; Halekas, J. S.
The bright swirling features on the lunar surface in areas around the Moon but most prominently at Reiner Gamma, have intrigued scientists for many years. After Apollo and later Lunar Prospector (LP} mapped the Lunar magnetic fields from orbit, it was observed that these features are generally associated with crustal magnetic anomalies. This led researchers to propose a number of explanations for the swirls that invoke these fields. Prominent among these include magnetic shielding in the form of a mini-magnetosphere which impedes space weathering by the solar wind, magnetically controlled dust transport, and cometary or asteroidal impacts that would result in shock magnetization with concomitant formation ofthe swirls. In this presentation, we will consider another possibility, that the ambient magnetic and electric fields can transport and channel secondary ions produced by micrometeorite or solar wind ion impacts. In this scenario, ions that are created in these impacts are under the influence of these fields and can drift for significant distances before encountering the magnetic anomalies when their trajectories are disrupted and concentrated onto nearby areas. These ions may then be responsible for chemical alteration of the surface leading either to a brightening effect or a disruption of space weathering processes. To test this hypothesis we have run ion trajectory simulations that show ions from regions about the magnetic anomalies can be channeled into very small areas near the anomalies and although questions remain as to nature of the mechanisms that could lead to brightening of the surface it appears that the channeling effect is consistent with the existence of the swirls.
Comparison of Magnetic Anomalies of Lithospheric Origin Measured by Satellite and Airborne Magnetometers over Western Canada
NASA Technical Reports Server (NTRS)
Langel, R. A.; Coles, R. L.; Mayhew, M. A.
Crustal magnetic anomaly data from the OGO 2, 4 and 6 (Pogo) satellites are compared with upward-continued aeromagnetic data between 50 deg -85 deg N latitude and 220 deg - 260 deg E longitude. Agreement is good both in anomaly location and in amplitude, giving confidence that it is possible to proceed with the derivation and interpretation of satellite anomaly maps in all parts of the globe. The data contain a magnetic high over the Alpha ridge suggesting continental composition and a magnetic low over the southern Canada basin and northern Canadian Arctic islands (Sverdrup basin). The low in the Sverdrup basin corresponds to a region of high heat flow, suggesting a shallow Curie isotherm. A ridge of high field, with two distinct peaks in amplitude, is found over the northern portion of the platform deposits and a relative high is located in the central portion of the Churchill province. No features are present to indicate a magnetic boundary between Slave and Bear provinces, but a trend change is evident between Slave and Churchill provinces. South of 60 deg latitude a broad magnetic low is located over very thick (40-50 km) crust, interpreted to be a region of low magnetization.
Interaction between Solar Wind and Lunar Magnetic Anomalies observed by Kaguya MAP-PACE
NASA Astrophysics Data System (ADS)
Saito, Yoshifumi; Yokota, Shoichiro; Tanaka, Takaaki; Asamura, Kazushi; Nishino, Masaki; Yamamoto, Tadateru; Uemura, Kota; Tsunakawa, Hideo
It is known that Moon has neither global intrinsic magnetic field nor thick atmosphere. Different from the Earth's case where the intrinsic global magnetic field prevents the solar wind from penetrating into the magnetosphere, solar wind directly impacts the lunar surface. Since the discovery of the lunar crustal magnetic field in 1960s, several papers have been published concerning the interaction between the solar wind and the lunar magnetic anomalies. MAG/ER on Lunar Prospector found heating of the solar wind electrons presumably due to the interaction between the solar wind and the lunar magnetic anomalies and the existence of the mini-magnetosphere was suggested. However, the detailed mechanism of the interaction has been unclear mainly due to the lack of the in-situ observed data of low energy ions. MAgnetic field and Plasma experiment - Plasma energy Angle and Composition Experiment (MAP-PACE) on Kaguya (SELENE) completed its ś1.5-year observation of the low energy charged particles around the Moon on 10 June, 2009. Kaguya was launched on 14 September 2007 by H2A launch vehicle from Tanegashima Space Center in Japan. Kaguya was inserted into a circular lunar polar orbit of 100km altitude and continued observation for nearly 1.5 years till it impacted the Moon on 10 June 2009. During the last 5 months, the orbit was lowered to ś50km-altitude between January 2009 and April 2009, and some orbits had further lower perilune altitude of ś10km after April 2009. MAP-PACE consisted of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). All the sensors performed quite well as expected from the laboratory experiment carried out before launch. Since each sensor had hemispherical field of view, two electron sensors and two ion sensors that were installed on the spacecraft panels opposite to each other could cover full 3-dimensional phase space of low energy electrons and ions. One of the ion sensors IMA was an energy mass spectrometer. IMA measured mass identified ion energy spectra that had never been obtained at 100km altitude polar orbit around the Moon. When Kaguya flew over South Pole Aitken region, where strong magnetic anomalies exist, solar wind ions reflected by magnetic anomalies were observed. These ions had much higher flux than the solar wind protons scattered at the lunar surface. The magnetically reflected ions had nearly the same energy as the incident solar wind ions while the solar wind protons scattered at the lunar surface had slightly lower energy than the incident solar wind ions. At 100km altitude, when the reflected ions were observed, the simultaneously measured electrons were often heated and the incident solar wind ions were sometimes slightly decelerated. At ~50km altitude, when the reflected ions were observed, proton scattering at the lunar surface clearly disappeared. It suggests that there exists an area on the lunar surface where solar wind does not impact. At ~10km altitude, the interaction between the solar wind ions and the lunar magnetic anomalies was remarkable with clear deceleration of the incident solar wind ions and heating of the reflected ions as well as significant heating of the electrons. Calculating velocity moments including density, velocity, temperature of the ions and electrons, we have found that there exists 100km scale regions over strong magnetic anomalies where plasma parameters are quite different from the outside. Solar wind ions observed at 10km altitude show several different behaviors such as deceleration without heating and heating in a limited region inside the magnetic anomalies that may be caused by the magnetic field structure. The deceleration of the solar wind has the same ?E/q (?E : deceleration energy, q: charge) for different species, which constraints the possible mechanisms of the interaction between solar wind and magnetic anomalies.
Joint geophysical investigation of a small scale magnetic anomaly near Gotha, Germany
NASA Astrophysics Data System (ADS)
Queitsch, Matthias; Schiffler, Markus; Goepel, Andreas; Stolz, Ronny; Guenther, Thomas; Malz, Alexander; Meyer, Matthias; Meyer, Hans-Georg; Kukowski, Nina
In the framework of the multidisciplinary project INFLUINS (INtegrated FLUid Dynamics IN Sedimentary Basins) several airborne surveys using a full tensor magnetic gradiometer (FTMG) system were conducted in and around the Thuringian basin (central Germany). These sensors are based on highly sensitive superconducting quantum interference devices (SQUIDs) with a planar-type gradiometer setup. One of the main goals was to map magnetic anomalies along major fault zones in this sedimentary basin. In most survey areas low signal amplitudes were observed caused by very low magnetization of subsurface rocks. Due to the high lateral resolution of a magnetic gradiometer system and a flight line spacing of only 50m, however, we were able to detect even small magnetic lineaments. Especially close to Gotha a NW-SE striking strong magnetic anomaly with a length of 1.5 km was detected, which cannot be explained by the structure of the Eichenberg-Gotha-Saalfeld (EGS) fault zone and the rock-physical properties (low susceptibilities). Therefore, we hypothesize that the source of the anomaly must be related to an anomalous magnetization in the fault plane. To test this hypothesis, here we focus on the results of the 3D inversion of the airborne magnetic data set and compare them with existing structural geological models. In addition, we conducted several ground based measurements such as electrical resistivity tomography (ERT) and frequency domain electromagnetics (FDEM) to locate the fault. Especially, the geoelectrical measurements were able to image the fault zone. The result of the 2D electrical resistivity tomography shows a lower resistivity in the fault zone. Joint interpretation of airborne magnetics, geoelectrical and geological information let us propose that the source of the magnetization may be a fluid-flow induced impregnation with iron-oxide bearing minerals in the vicinity of the EGS fault plane.
Magnetic Signatures of Impact Fractured Rocks from Sierra Madera, Texas, USA - Implications to Magnetic Anomalies on Mars
NASA Astrophysics Data System (ADS)
Adachi, T.; Kletetschka, G.; Wasilewski, P. J.; Mikula, V.
Mars Express Orbiter (sounding radar data) revealed that craters of ancient origin had been covered by thick sediments in northern hemisphere. Mars MOLA topography mission identified many crater on Mars surface. Thus despite the Mars dichotomy, both northern and southern hemisphere have been covered by impacts to similar density. Mars currently has no global magnetic field of internal origin. In southern hemisphere, magnetic field intensities due to anomalies of remanent origin are much lower over the gigantic impact craters (e.g. Hellas, Prometheus, and Argyre). Low magnetic field may not relate to the absence of internal dynamo but due to impacts. For example, the aerial survey over a two billion year old, largest crater on Earth, Vredefort in South Africa observed much lower magnetic intensity over the crater, despite of the strongly magnetized simgle domain (SD) magnetite in shocked granites. Randomized magnetic vector orientations caused by impact may be the origin of the lower magnetic field observed on both Vredefort and Mars. We conducted magnetic analysis for a suite of Sierra Madera Impact deformed rock sites with complete shatter cone structures and multiple striated joint set (MSJS), and the initial results were intriguing. NRM vector orientations, REM ratios, and AF demagnetization curves showed contrasted magnetic signatures between the sites as well as within the samples. The NRM signatures in small scale shatter cones and larger scale shatter cones indicated shock demagnetization (SDM). The peculiar signatures of the site with MSJS may be both SDM and shock magnetization (SRM). We characterized the complexity and distinct magnetic signatures of impact fractured rocks. The results suggest that the size of the shatter cones and structures may reflect the magnetic signatures of both intensity and directions. Also, the dimensional scale of shatter cones is indicative parameters for randomization of the magnetic vector orientations. Such variations may influence on overall magnetic intensity observed from a distance, which relates to magnetic anomalies on Mars and Moons.
Towards developing an analytical procedure of defining the equatorial electrojet for correcting satellite magnetic anomaly data
NASA Astrophysics Data System (ADS)
Ravat, Dhananjay; Hinze, William J.
Analysis of the total magnetic intensity MAGSAT data has identified and characterized the variability of ionospheric current effects as reflected in the geomagnetic field as a function of longitude, elevation, and time (daily as well as monthly variations). This analysis verifies previous observations in POGO data and provides important boundary conditions for theoretical studies of ionospheric currents. Furthermore, the observations have led to a procedure to remove these temporal perturbations from lithospheric MAGSAT magnetic anomaly data based on 'along-the-dip-latitude' averages from dawn and dusk data sets grouped according to longitudes, time (months), and elevation. Using this method, high-resolution lithospheric magnetic anomaly maps have been prepared of the earth over a plus or minus 50 deg latitude band. These maps have proven useful in the study of the structures, nature, and processes of the lithosphere.
Towards developing an analytical procedure of defining the equatorial electrojet for correcting satellite magnetic anomaly data
NASA Technical Reports Server (NTRS)
Ravat, Dhananjay; Hinze, William J.
Analysis of the total magnetic intensity MAGSAT data has identified and characterized the variability of ionospheric current effects as reflected in the geomagnetic field as a function of longitude, elevation, and time (daily as well as monthly variations). This analysis verifies previous observations in POGO data and provides important boundary conditions for theoretical studies of ionospheric currents. Furthermore, the observations have led to a procedure to remove these temporal perturbations from lithospheric MAGSAT magnetic anomaly data based on 'along-the-dip-latitude' averages from dawn and dusk data sets grouped according to longitudes, time (months), and elevation. Using this method, high-resolution lithospheric magnetic anomaly maps have been prepared of the earth over a plus or minus 50 deg latitude band. These maps have proven useful in the study of the structures, nature, and processes of the lithosphere.
Contribution of multidomain titanomagnetite to the intensity and stability of Mars crustal magnetic anomalies
NASA Astrophysics Data System (ADS)
Brachfeld, Stefanie; Cuomo, David; Tatsumi-Petrochilos, Lisa; Bowles, Julie A.; Shah, Deepa; Hammer, Julia
Two basalts with compositions relevant to the crusts of Mars and Earth were synthesized at igneous temperatures and held at 650░C for 21 to 257 days under quartz-fayalite-magnetite fO2 buffer conditions. The run products are germane to slowly cooled igneous intrusions, which might be a significant volumetric fraction of the Martian crust and carriers of magnetic anomalies in the Southern Highlands. Both basalts acquired intense thermoremanent magnetizations and intense but easily demagnetized anhysteretic remanent magnetizations carried by homogeneous multidomain titanomagnetite. Hypothetical intrusions on Mars composed of these materials would be capable of acquiring intense remanences sufficient to generate the observed anomalies. However, the remanence would be easily demagnetized by impact events after the cessation of the Mars geodynamo. Coercivity enhancement by pressure or formation of single domain regions via exsolution within the multidomain grains is necessary for long-term retention of a remanence carried exclusively by multidomain titanomagnetite grains.
Magnetic Anomaly Modeling of Volcanic Structure and Stratigraphy - Socorro Island, Eastern Pacific Ocean
NASA Astrophysics Data System (ADS)
Urrutia-Fucugauchi, Jaime; Escorza-Reyes, Marisol; Pavon-Moreno, Julio; Perez-Cruz, Ligia; Sanchez-Zamora, Osvaldo
Results of a magnetic survey of the volcanic structure of Socorro Island in the Revillagigedo Archipielago are presented. Socorro is part of a group of seamounts and oceanic islands built by volcanic activity at the northern end of the Mathematician ridge and intersection with the Clarion and Rivera fracture zones. Subaerial volcanic activity is characterized by alkaline and peralkaline compositions, marked by pre-, syn- and post-caldera phases of the Evermann volcano, and the Holocene mafic activity of the Lomas Coloradas. The magnetic survey conducted in the central-southern sector of the island permits to investigate the volcanic structure and subsurface stratigraphy. Regional fields for second- and third-degree polynomials show a magnetic low over the caldera, positive anomalies above the pre-caldera deposits and intermediate amplitude anomalies over Lomas Coloradas. Residual fields delineate the structural rim of the caldera, anomaly trends for the pre- and post-caldera deposits and a broad anomaly over Lomas Coloradas. Regional-residual anomalies, first vertical derivative, analytical upward and downward continuations, and forward four-layer modeling are used to construct the geophysical models. Rock magnetic properties were analyzed on samples collected at 24 different sites. Magnetic susceptibility showed wide range of variation from ~10 to ~500 10-3 SI, corresponding to the different lithologies from trachytes and glass-rich tuffs to alkali basalts. Data have been divided into groups with low, intermediate and high values. Rock magnetic analyses indicate that magnetite and titanomagnetites are the main magnetization carriers. Magnetic hysteresis loops indicate low coercivity minerals, with high saturation and remanent magnetizations and PSD domain states. Magnetic susceptibility versus temperature curves show irreversible behavior with Curie temperatures around 560-575 C, suggesting magnetite and Ti-poor titanomagnetites. Paleomagnetic directions determined on samples from one site in the pre-caldera flows and three sites in the post-caldera and Lomas Coloradas units, indicate normal polarity directions with mean declination of 350 and inclination of 37, close to the dipolar direction. Additional data on remanent magnetizations reported in Sbarbori et al. (2009) support dominant normal polarities for pre- and post-caldera units, with mean directions close to the dipolar and the present-day field directions. Implications for the magnetization contrasts used in modeling are to increase the intensities assigned for model units. The effective magnetizations assumed for the model units have dipolar inclinations and northward declinations. The magnetic anomaly shows a broad minimum over the caldera zone, a maximum over the caldera rim and a second maximum closely spaced, followed by a larger wavelength anomaly over the volcano slope and the pre-caldera deposits. The maximum is associated with the caldera rim and the minimum on the outer rim edge is associated with a fracture zone or a deep pre-caldera feature. Preferred models incorporate a topographic relief for the basaltic pre-caldera unit and post-caldera deposits. Top of the pre-caldera basaltic unit lies at depths of about 300 m and up to 600 and 800 m below sea level. The Lomas Coloradas Formation is modeled with thickness of about 200-350 m. Models allow evaluation of stratigraphic distribution and thickness of pre-, syn and post-caldera units and the Lomas Coloradas Formation. Preferred models for the southern flank incorporate a pre-caldera basaltic unit with abrupt relief and syn- and post-caldera silicic deposits with Lomas Coloradas alkaline basalts covering the volcano flanks. Relief for pre-caldera basaltic unit may be associated with the volcanic conduit system for Lomas Coloradas. The structure shown at the southern end of the profile is present in the reduction to the pole, residual field and analytical continuation fields. Models for Evermann volcano show structural features associated caldera collapse, the caldera rim and the pre-caldera morphology
Magnetic Anomalies and Rock Magnetic Properties Related to Deep Crustal Rocks of the Athabasca Granulite Terrane, Northern Canada
NASA Astrophysics Data System (ADS)
Brown, L. L.; Williams, M. L.
The Athabasca granulite terrane in northernmost Saskatchewan, Canada is an exceptional exposure of lower crustal rocks having experienced several high temperature events (ca 800C) during a prolonged period of deep-crustal residence (ca 1.0 GPa) followed by uplift and exhumation. With little alteration since 1.8 Ga these rocks allow us to study ancient lower crustal lithologies. Aeromagnetic anomalies over this region are distinct and complex, and along with other geophysical measurements, define the Snowbird Tectonic zone, stretching NE-SW across northwestern Canada, separating the Churchill province into the Hearne (mid-crustal rocks, amphibolite facies) from the Rae (lower crust rocks, granulite facies). Distinct magnetic highs and lows appear to relate roughly to specific rock units, and are cut by mapped shear zones. Over fifty samples from this region, collected from the major rock types, mafic granulites, felsic granulites, granites, and dike swarms, as well as from regions of both high and low magnetic anomalies, are being used to investigate magnetic properties. The intention is to investigate what is magnetic in the lower crust and how it produces the anomalies observed from satellite measurements. The samples studied reveal a wide range of magnetic properties with natural remanent magnetization ranging from an isolated high of 38 A/m to lows of 1 mA/m. Susceptibilities also range over several orders of magnitude, from 1 to 1 x10-4 SI. Magnetite is identified in nearly all samples using both low and high temperature measurements, but concentrations are generally very low. Hysteresis properties on 41 samples reveal nearly equal numbers of samples represented by PSD and MD grains, with a few samples (N=6) plotting in or close to the SD region. Low temperature measurements indicate that most samples contain magnetite, showing a marked Verway transition around 120K. Also identified in nearly half of the samples is pyrrhotite, noted by low temperature transitions at 30-35K. Preliminary results indicate that the same general lithologies can have very different magnetic properties with varying concentrations of magnetic minerals and with widely varying domain sizes and thus magnetic behavior. Additional work is needed to fully understand the magnetic signature causing the aeromagnetic anomalies, but with this information we will be able to better understand the varying rock types, compositions, and exposures in lower crustal rocks, be able to predict anomaly patterns, and eventually better understand the geologic history of this complex area.
Investigation of vehicle induced magnetic anomaly by triple-axis magnetoelectric sensors
NASA Astrophysics Data System (ADS)
Shen, Ying; Gao, Junqi; Hasanyan, Davresh; Wang, Yaojin; Li, Menghui; Li, Jiefang; Viehland, D.
This paper investigates magnetoelectric (ME) sensors for vehicle detection. We propose a novel triple-axis ME magnetic sensor system consisting of tri-layers of Metglas/ Pb(Zr, Ti)O3/Metglas laminates together with its fabrication and installation methods. This non-intrusive ME sensor system with a larger sensing range is viable for detection and recognition of vehicle induced magnetic signatures in an outdoor (open) environment. We also show a finite element simulation method capable predicting the magnetic anomaly projection in the geomagnetic field.
3D Inversion of magnetic data of grouped anomalies whith different magnetizations - study applied to Palmital intrusions
NASA Astrophysics Data System (ADS)
Ribeiro, V. B.; Louro, V. H.; Mantovani, M. S.
The southwest region of the Parecis Basin (Mato Grosso state, Brazil) is marked by the presence of a kimberlite alignment with high exploratory potential. Besides these intrusions, it is possible to notice several magnetic anomalies, associated to different igneous intrusions. In this work it will be studied the anomalies of Palmital 1 to 6, located between the kimberlitos of Jacarķ-01 and 02 (to the north) and Jauru-01 (to the south). The magnetic signatures of the anomalies from Palmital 1 to 6 are characterized by a wide variation in the direction of total magnetization that in association with the proximity of the bodies generates a complex scenario. For a better interpretation of these anomalies, techniques with low or none influence from the presence of the component of remanent magnetization were used. The Amplitude of the Analytic Signal (ASA) and the Enhanced Horizontal Derivative (EHD) allowed the delimitation of the lateral borders of the intrusions. The anomalous sources are fully covered by the Parecis Basin's sediments, without signs of outcropping. So, it was used the extrapolation of the EHD technique aiming to estimate the depth of the superior borders of these intrusions. In order to isolate the magnetic contribution associated to each sources before the 3D inversion, it was used the technique of the Amplitude of the Anomalous Magnetic Field (AAMF). The bodies recovered from the 3D inversion presented a good correlation with the results obtained by the ASA and the depths achieved by the EHD - between 150 and 350 meters for the shallow contrasts. The susceptibility contrast obtained between the anomalous sources and the embedding rock was 0.025 SI, matching with the average susceptibility values for igneous intrusions available in the literature.;
Modeling of the Central Magnetic Anomaly at Haughton Impact Structure, Canada
NASA Astrophysics Data System (ADS)
Quesnel, Y.; Gattacceca, J.; Osinski, G. R.; Rochette, P.
Located on Devon Island, Nunavut, Canada, the 23-km diameter Haughton impact structure is one of the best-preserved medium-size complex impact structures on Earth. The impact occurred ~39 Ma ago into a target formation composed of an ~2-km thick sequence of Lower Paleozoic sedimentary rocks of the Arctic Platform overlying Precambrian metamorphic basement of the Canadian Shield (Osinski et al., 2005). Clast-rich impact melt rocks line the crater and impact-induced hydrothermal activity took place, but since then no significant geological event has affected the area. In the 1980s, ground magnetic and gravity measurements were carried out within the central part of the crater (Pohl et al., 1988). A significant anomaly was discovered and coarsely modeled by a source body of simple geometry. More recently, an airborne magnetic survey delivered additional data that covered the whole crater but no modeling was done (Glass et al., 2002). Here, we present the results of a new ground magnetic survey accompanied by rock magnetic property measurements made on all samples of the crater. This has provided additional constraints to investigate the origin of this central magnetic anomaly. By conducting modeling, we have been able to reveal the geometry and volume of the source body as well as its magnetization properties. Our results suggest that the necessary magnetization intensity to account for this anomaly is too large to be associated with uplifted pre-impact target rocks. Therefore, we suggest that hydrothermal alteration could have enhanced the magnetization of the central part of this crater. References : Osinski, G. R. et al. 2005. MPS, 40:1759-1776 ; Pohl, J. et al. 1988. Meteoritics, 23:235-238 ; Glass, B. J. et al. 2002, Abstract #2008. 33th LPSC
Magsat equivalent source anomalies over the southeastern United States - Implications for crustal magnetization
NASA Technical Reports Server (NTRS)
Ruder, M. E.; Alexander, S. S.
The Magsat crustal anomaly field depicts a previously-unidentified long-wavelength negative anomaly centered over southeastern Georgia. Examination of Magsat ascending and descending passes clearly identifies the anomalous region, despite the high-frequency noise present in the data. Using ancillary seismic, electrical conductivity, Bouguer gravity, and aeromagnetic data, a preliminary model of crustal magnetization for the southern Appalachian region is presented. A lower crust characterized by a pervasive negative magnetization contrast extends from the New York-Alabama lineament southeast to the Fall Line. In southern Georgia and eastern Alabama (coincident with the Brunswick Terrane), the model calls for lower crustal magnetization contrast of -2.4 A/m; northern Georgia and the Carolinas are modeled with contrasts of -1.5 A/m. Large-scale blocks in the upper crust which correspond to the Blue Ridge, Charlotte belt, and Carolina Slate belt, are modeled with magnetization contrasts of -1.2 A/m, 1.2 A/m, and 1.2 A/m respectively. The model accurately reproduces the amplitude of the observed low in the equivalent source Magsat anomaly field calculated at 325 km altitude and is spatially consistent with the 400 km lowpass-filtered aeromagnetic map of the region.
NASA Technical Reports Server (NTRS)
Taylor, Patrick T.
Bangui anomaly is the name given to one of the Earth s largest crustal magnetic anomalies and the largest over the African continent. It covers two-thirds of the Central African Republic and therefore the name derives from the capitol city-Bangui that is also near the center of this feature. From surface magnetic survey data Godivier and Le Donche (1962) were the first to describe this anomaly. Subsequently high-altitude world magnetic surveying by the U.S. Naval Oceanographic Office (Project Magnet) recorded a greater than 1000 nT dipolar, peak-to-trough anomaly with the major portion being negative (figure 1). Satellite observations (Cosmos 49) were first reported in 1964, these revealed a 40nT anomaly at 350 km altitude. Subsequently the higher altitude (417-499km) POGO (Polar Orbiting Geomagnetic Observatory) satellite data recorded peak-to-trough anomalies of 20 nT these data were added to Cosmos 49 measurements by Regan et al. (1975) for a regional satellite altitude map. In October 1979, with the launch of Magsat, a satellite designed to measure crustal magnetic anomalies, a more uniform satellite altitude magnetic map was obtained. These data, computed at 375 km altitude recorded a -22 nT anomaly (figure 2). This elliptically shaped anomaly is approximately 760 by 1000 km and is centered at 6%, 18%. The Bangui anomaly is composed of three segments; there are two positive anomalies lobes north and south of a large central negative field. This displays the classic pattern of a magnetic anomalous body being magnetized by induction in a zero inclination field. This is not surprising since the magnetic equator passes near the center of this body.
True Polar Wander and Hotspot Fixity: A Paleomagnetic Investigation of the Skewness of Magnetic Anomaly 12r (32 Ma B.P.) on the Pacific Plate
NASA Astrophysics Data System (ADS)
Gordon, R. G.; Horner-Johnson, B. C.
Prior studies have shown that Pacific hotspots and Indo-Atlantic hotspots have moved in approximate unison relative to the spin axis since 65 Ma B.P. [Morgan, 1981; Gordon and Cape, 1981; Gordon, 1982] and since 56 Ma B.P. [Petronotis et al., 1994], which is most simply interpreted as true polar wander. In contrast, Pacific hotspots and Indo-Atlantic hotspots give conflicting results for 72 Ma B.P. and for 81 Ma B.P., which may indicate motion between Pacific hotspots and Indo-Atlantic hotspots [Tarduno and Cottrell, 1997; Petronotis et al., 1999; Tarduno et al., 2003]. Thus it is important to estimate Pacific plate apparent polar wander (APW) for more time intervals. From such estimates the APW of Pacific hotspots can be inferred and compared with that of Indo-Atlantic hotspots [e.g., Besse and Courtillot 2002]. Here we present a study of the skewness of anomaly 12r between the Galapagos and Clipperton and between the Clipperton and Clarion fracture zones. We chose this region for several reasons: First, numerical experiments, like those conducted by Acton and Gordon [1991], indicate that magnetic profiles between the Galapagos and Clarion fracture zones should contain the most information about the Pacific plate paleomagnetic pole for chron C12r (32 Ma B.P.). Second, in these two spreading rate corridors, spreading half rates range from 72 to 86 mm/a and therefore have negligible anomalous skewness, given that they exceed ?50 mm/a [Roest et al., 1992; Dyment et al. 1994]. Third, vector aeromagnetic profiles are available for analysis. One of the challenges to interpreting magnetic anomalies in low latitudes where the anomalies strike nearly north-south is the very low amplitude of the signal relative to the noise, the latter of which can be especially intense near the present magnetic equator due to the amplification of diurnal variation by the equatorial electrojet. Previously we showed that vector aeromagnetic profiles record low-latitude Pacific plate magnetic anomalies due to seafloor spreading with much greater clarity than do shipboard profiles in the same region [Horner-Johnson and Gordon, 2003]. The pole that we obtain has compact 95% confidence limits. We reduce the profiles to this pole and show that the appearance of the reduced-to-the-pole profiles is sensitive to the assumed pole position. The new pole shows that Pacific hotspots have moved significantly relative to the spin axis during the formation of the Hawaiian island and seamount chain, and is consistent with Pacific hotspots having moved in approximate unison with Indo-Atlantic hotspots relative to the spin axis since 32 Ma B.P.
Study of interaction between plasma flow and magnetic dipole field: Understanding plasma environment in lunar magnetic anomaly regions
NASA Astrophysics Data System (ADS)
Howes, C.; Wang, X.; Horanyi, M.; Robertson, S. H.
In-situ observations and modeling work have indicated strong interactions between the solar wind plasma and lunar crustal magnetic anomalies. These interactions will alter the near-surface plasma environment in the magnetic anomaly regions and be responsible for the formation of unusual albedo features, the so-called ';lunar swirls', and the production (or loss) of volatiles (e.g. hydroxyl), as well as electrostatic dust transport. We have done a series of laboratory experiments to study the fundamental physical processes governing the plasma (non-flowing) interactions with magnetic dipole fields above an insulating surface. The interactions were found very dynamic, including, for example, a highly non-uniform surface charge distribution. Here we present preliminary results of plasma flow interactions with the dipole fields with our newly developed large ion source (cross-section 24 cm in diameter, ion energy up to 30 eV, ion Mach number >>1). We will show the effects of ion energy and current on the plasma dynamics and surface charging. This study will enable us to better predict the plasma environment in the lunar magnetic anomaly regions, as well as associated geological features and possible dust activities.
On the origin of the magnetic susceptibility anomaly in nearly ferromagnetic alloys
NASA Astrophysics Data System (ADS)
de Coss, Romeo; Aguayo, Aar¾n; Ortiz-Chi, Filiberto
The magnetic susceptibility of the Ni-Rh and Ni-Cu alloys shows an anomaly near the transition from ferromagnetism to paramagnetism. In order to contribute to understand this phenomenon, we have studied the electronic and magnetic properties of the Ni1-xCux alloy by means of first principles calculations. The ground state properties were obtained using the Full-Potential Linear Augmented Plane Waves method. The alloying was modeled using the self-consistent virtual crystal approximation. The spin magnetic susceptibility is calculated from the total energy as a function of the spin moment, obtained using the Fixed Spin Moment methodology. We found that the calculations predict correctly the reduction of the magnetic moment with the Cu concentration and that the critical concentration where the magnetic moment goes to zero is xc = 0.5, in excellent agreement with the experimental data. The calculated magnetic susceptibility is in good agreement with the experimental data in the whole range of concentrations for the Ni1-xCux alloy, in particular the anomaly present at x 0.4 is reproduced by the calculations. This research was supported by Conacyt-M'exico under Grant No. 83604.
Circum-Arctic mapping project: new magnetic anomaly map of the Arctic (to 60 degrees N)
NASA Astrophysics Data System (ADS)
Gaina, Carmen
An international effort to compile Circum-Arctic geophysical and bedrock data has been conducted by several national agencies (Russia-VSEGEI and VNIIO, Sweden-SGU, Finland-GTK, Denmark-GEUS, USA-USGS, Canada-GSC, Germany-BGR and Norway-NGU) since 2005. This project aims to produce an atlas that will comprise geological and geophysical digital maps at a scale of 1: 5 million scale for the Arctic region limited by the 60 degree North latitude. New published and classified magnetic anomaly gridded data from each participant group were gathered and converted to a common datum (WGS84) and format. The Greenland region magnetic anomaly grid (Verhoef et al., 1996) has been updated with new aeromagnetic surveys performed in West Greenland between 1992-2001 (Rasmussen, 2002), and in the Nares Strait area (Damaske & Oakey, 2006; Oakey & Damaske, 2006). The oceanic area east of Greenland (NE Atlantic) contains most of the aeromagnetic data used in the Verhoef et al., (1996)'s compilation (pre-1990) plus new aeromagnetic surveys over offshore Norway collected up to 2007 (Olesen et al., 1997; Olesen et al., 2007; Gernigon et al., 2008). The gridded data has been upward continued to 1 km above ground or sea-level and trimmed around the areas of major overlaps. The Alaska USGS aeromagnetic compilation has been used as the "master grid" for merging the major gridded data sets together and the downward continued lithospheric magnetic field model MF6 derived from satellite data (Maus et al., 2008) has been used as a regional reference surface. We have used a blending function over the area of overlap in order to smooth the transition from one grid to the other (GridKnit, GEOSOFT). The resulting grid has been re-sampled to a 2 km grid cell. In order to construct the final Circum-Arctic magnetic anomaly grid (CAMP-M) we have adopted the approach used by several research groups for compiling the World Digital Magnetic Anomaly Map (WDMAM) and used near-surface magnetic data for the short wavelength component of the compilation and the satellite derived magnetic anomalies for the long wavelength (Hemant et al., 2007; Maus et al., 2007). MF6 extends to spherical harmonics degree 120 (333 km wavelength) and therefore it is able to provide consistent long wavelength information between 300 and 400 km. This information is mainly related to regional deeper and/or thicker portions of the magnetic sources within the crust. We have prepared two versions for the CAMP-M magnetic anomaly grid. The first one combines short wavelength components of regional grids (less than 400 km) with long wavelengths (400 km) of the MF6 model. The second one combines short wavelengths of regional datasets (obtained by filtering with a cosine squared taper to remove the wavelengths in the waveband between 307 and 333 km and larger, with the MF6 model (to degree 120). We have selected Model 1 as the new Circum-Arctic Magnetic Anomaly Map.
Multi-core Paralleled Design and Analysis for BP Inversion Algorithm of Magnetic Anomalies
XIA Jun-bao; LI Tao; WANG Qun
(Abstract)In the process of 3-D inversion of gravity and magnetic anomalies for physical properties with large scale data, the BP inversion algorithm produces huge storage and computation requirement. This paper offers an efficient solution based on the principle of storage equivalent and multi-core paralleled design. It mainly includes applying the principle of storage equivalent to the position function of physical
Berry Curvature, Triangle Anomalies, and the Chiral Magnetic Effect in Fermi Liquids
Dam Thanh Son; Naoki Yamamoto
In a three-dimensional Fermi liquid, quasiparticles near the Fermi surface may possess a Berry curvature. We show that if the Berry curvature has a nonvanishing flux through the Fermi surface, the particle number associated with this Fermi surface has a triangle anomaly in external electromagnetic fields. We show how Landau's Fermi liquid theory should be modified to take into account the Berry curvature. We show that the "chiral magnetic effect" also emerges from the Berry curvature flux.
Spherical Earth analysis and modeling of lithospheric gravity and magnetic anomalies. Ph.D. Thesis - Purdue Univ.
NASA Technical Reports Server (NTRS)
Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.
A comprehensive approach to the lithospheric analysis of potential field anomalies in the spherical domain is provided. It has widespread application in the analysis and design of satellite gravity and magnetic surveys for geological investigation.
Interaction between solar wind and lunar magnetic anomalies observed by MAP-PACE on Kaguya
NASA Astrophysics Data System (ADS)
Saito, Yoshifumi; Yokota, Shoichiro; Tanaka, Takaaki; Asamura, Kazushi; Nishino, Masaki N.; Yamamoto, Tadateru I.; Tsunakawa, Hideo
It is well known that the Moon has neither global intrinsic magnetic field nor thick atmosphere. Different from the Earth's case where the intrinsic global magnetic field prevents the solar wind from penetrating into the magnetosphere, solar wind directly impacts the lunar surface. MAgnetic field and Plasma experiment -Plasma energy Angle and Composition Experiment (MAP-PACE) on Kaguya (SELENE) completed its 1.5-year observation of the low energy charged particles around the Moon on 10 June 2009. Kaguya was launched on 14 September 2007 by H2A launch vehicle from Tanegashima Space Center in Japan. Kaguya was inserted into a circular lunar polar orbit of 100km altitude and continued observation for nearly 1.5 years till it impacted the Moon on 10 June 2009. During the last 5 months, the orbit was lowered to 50km-altitude between January 2009 and April 2009, and some orbits had further lower perilune altitude of 10km after April 2009. MAP-PACE consisted of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). Since each sensor had hemispherical field of view, two electron sensors and two ion sensors that were installed on the spacecraft panels opposite to each other could cover full 3-dimensional phase space of low energy electrons and ions. One of the ion sensors IMA was an energy mass spectrometer. IMA measured mass identified ion energy spectra that had never been obtained at 100km altitude polar orbit around the Moon. When Kaguya flew over South Pole Aitken region, where strong magnetic anomalies exist, solar wind ions reflected by magnetic anomalies were observed. These ions had much higher flux than the solar wind protons scattered at the lunar surface. The magnetically reflected ions had nearly the same energy as the incident solar wind ions while the solar wind protons scattered at the lunar surface had slightly lower energy than the incident solar wind ions. At 100km altitude, when the reflected ions were observed, the simultaneously measured electrons were often heated and the incident solar wind ions were sometimes slightly decelerated. At 50km altitude, when the reflected ions were observed, proton scattering at the lunar surface clearly disappeared. It suggests that there exists an area on the lunar surface where solar wind does not impact. At 10km altitude, the interaction between the solar wind ions and the lunar magnetic anomalies was remarkable with clear deceleration of the incident solar wind ions and heating of the reflected ions as well as significant heating of the electrons. Calculating velocity moments including density, velocity, temperature of the ions and electrons, we have found that there exists 100km scale regions over strong magnetic anomalies where plasma parameters are quite different from the outside. Solar wind ions observed at 10km altitude show several different behaviors such as deceleration without heating and heating in a limited region inside the magnetic anomalies that may be caused by the magnetic field structure. The deceleration of the solar wind has the same ?E/q (?E : deceleration energy, q: charge) for different species, which constraints the possible mechanisms of the interaction between solar wind and magnetic anomalies.
Martian meteorites and Martian magnetic anomalies: a new perspective from NWA 7034 (Invited)
NASA Astrophysics Data System (ADS)
Gattacceca, J.; Rochette, P.; Scozelli, R. B.; Munayco, P.; Agee, C. B.; Quesnel, Y.; Cournede, C.; Geissman, J. W.
The magnetic anomalies observed above the Martian Noachian crust [1] require strong crustal remanent magnetization in the 15-60 A/m range over a thickness of 20-50 km [2,3]. The Martian rocks available for study in the form of meteorites do contain magnetic minerals (magnetite and/or pyrrhotite) but in too small amount to account for such strong remanent magnetizations [4]. Even though this contradiction was easily explained by the fact that Martian meteorites (mostly nakhlites and shergottites) are not representative of the Noachian Martian crust, we were left with no satisfactory candidate lithology to account for the Martian magnetic anomalies. The discovery in the Sahara of a new type of Martian meteorite (NWA 7034 [5] and subsequent paired stones which are hydrothermalized volcanic breccia) shed a new light on this question as it contains a much larger amount of ferromagnetic minerals than any other Martian meteorite. We present here a study of the magnetic properties of NWA 7034, together with a review of the magnetic properties of thirty other Martian meteorites. Magnetic measurements (including high and low temperature behavior and M÷ssbauer spectroscopy) show that NWA 7034 contains about 15 wt.% of magnetite with various degrees of substitution and maghemitization up to pure maghemite, in the pseudo-single domain size range. Pyrrhotite, a common mineral in other Martian meteorites is not detected. Although it is superparamagnetic and cannot carry remanent magnetization, nanophase goethite is present in significant amounts confirming that NWA 7034 is the most oxidized Martian meteorite studied so far, as already indicated by the presence of maghemite (this study) and pyrite [5]. These magnetic properties show that a kilometric layer of a lithology similar to NWA 7034 magnetized in a dynamo field would be enough to account for the strongest Martian magnetic anomalies. Although the petrogenesis of NWA 7034 is still debated, as the brecciation could be either of volcanic or impact origin [5,6,7], it appears that pervasive (and possibly shock-induced) hydrothermalism affecting the uppermost crust in the presence of a dynamo field during the Noachian is a viable scenario to account for the observed magnetic anomalies. Such a scenario is supported by the Noachian or even pre-Noachian age of NWA 7034 [8,9] and its chemical and mineralogical compositions that match the ones of the inferred Noachian crust [5]. The natural remanent magnetization of the NWA 7034 samples studied so far had been obliterated by the strong magnets used by meteorite hunters, but work is underway to obtain samples that may have kept their original Martian magnetization. References [1] Acu±a M.H. et al. 1999. Science 284:790-793 [2] Langlais B. et al. 2004. JGR 109, doi: 10.1029/2003JE002048 [3] Quesnel Y. et al. 2007. Planet. Space Sci. 55:258-269 [4] Rochette P. et al. 2005 MAPS 40:529-540 [5] Agee C.B. et al. 2013. Science 339:780-785 [6] Hewins R.H. et al. 2013. 44th LPSC, abstract#2385 [7] Wittmann et al. 2013. 76th MetSoc meeting, abstract#5272 [8] Humayun et al. 2013. 76th MetSoc meeting, abstract#5198 [9] Nyquist et al. 2013. 76th MetSoc meeting, abstract#5318.
Chapter 3: Circum-Arctic mapping project: New magnetic and gravity anomaly maps of the Arctic
Gaina, C.; Werner, S.C.; Saltus, R.; Maus, S.; Aaro, S.; Damaske, D.; Forsberg, R.; Glebovsky, V.; Johnson, K.; Jonberger, J.; Koren, T.; Korhonen, J.; Litvinova, T.; Oakey, G.; Olesen, O.; Petrov, O.; Pilkington, M.; Rasmussen, T.; Schreckenberger, B.; Smelror, M.
New Circum-Arctic maps of magnetic and gravity anomalies have been produced by merging regional gridded data. Satellite magnetic and gravity data were used for quality control of the long wavelengths of the new compilations. The new Circum-Arctic digital compilations of magnetic, gravity and some of their derivatives have been analyzed together with other freely available regional and global data and models in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. Sharp, linear contrasts between deeply buried basement blocks with different magnetic properties and densities that can be identified on these maps can be used, together with other geological and geophysical information, to refine the tectonic boundaries of the Arctic domain. ?? 2011 The Geological Society of London.
Correlation between the Palaeozoic structures from West Iberian and Grand Banks margins using inversion of magnetic anomalies
NASA Astrophysics Data System (ADS)
Silva, Elsa A.; Miranda, J. M.; Luis, J. F.; Galdeano, A.
The Ibero-Armorican Arc (IAA) is a huge geological structure of Pre-Cambrian origin, tightened during hercynian times and deeply affected by the opening of the Atlantic Ocean and the Bay of Biscay. Its remnants now lie in Iberia, north-western France and the Canadian Grand Banks margins. The qualitative correlation between these three blocks has been attempted by several authors (e.g. Lefort, J.P., 1980. Un 'Fit' structural de l'Atlantique Nord: arguments geologiques pour correler les marqueurs geophysiques reconnus sur les deux marges. Mar. Geol. 37, 355-369; Lefort, J.P., 1983. A new geophysical criterion to correlate the Acadian and Hercynian orogenies of Western Europe and Eastern America. Mem. Geol. Soc. Am. 158, 3-18; Galdeano, A., Miranda, J.M., Matte, P., Mouge, P., Rossignol, C., 1990. Aeromagnetic data: A tool for studying the Variscan arc of Western Europe and its correlation with transatlantic structures. Tectonophysics 177, 293-305) using magnetic anomalies, mainly because they seem to preserve the hercynian zonation, in spite of the strong thermal and mechanical processes that took place during rifting and ocean spreading. In this paper, we present a new contribution to the study of the IAA structure based on the processing of a compilation of magnetic data from Iberia and Grand Banks margins. To interpret the magnetic signature, a Fourier-domain-based inversion technique was applied, considering a layer with a constant thickness of 10 km, and taking into account only the induced field. The digital terrain model was derived from ETOPO5 (ETOPO5, 1986. Relief map of the earth's surface. EOS 67, 121) and TerrainBase (TerrainBase, 1995. In: Row III, L.W., Hastings, D.A., Dunbar, P.K. (Eds.), Worldwide Digital Terrain Data, Documentation Manual, CD-ROM Release 1.0. GEODAS-NGDC Key to Geophysical Records. Documentation N. 30, April) databases. The pseudo-susceptibility distribution obtained was repositioned for the 156.5 Ma epoch, using the Srivastava and Verhoef [Srivastava, S.P., Verhoef, J., 1992. Evolution of Mesozoic sedimentary basins around the North Central Atlantic: a preliminary plate kinematic solution. In: Parnell, J. (Ed.), Basins on the Atlantic Seaboard: Petroleum Geology Sedimentology and Basin Evolution, Geological Society Special Publication No. 62, pp. 397-420] pole. Using this coherent magnetic framework, we can verify that the continuity between adjacent blocks is quite good, in terms of the amplitude, wavenumber and magnetic susceptibility pattern. If we accept that the magnetic properties can be taken as a marker of the hercynian zonation, as was verified in previous studies (Miranda, J.M., Galdeano, A., Rossignol, J.C., Mendes-Victor, L.A., 1989. Aeromagnetic anomalies in mainland Portugal and their tectonic implications. Earth Planet. Sci. Lett. 95, 161-177; Galdeano, A., Miranda, J.M., Matte, P., Mouge, P., Rossignol, C., 1990. Aeromagnetic data: A tool for studying the Variscan arc of Western Europe and its correlation with transatlantic structures. Tectonophysics 177, 293-305; Socias, I., 1994. Estudios de los Elementos del Campo Magnķtico en la Espa±a Peninsular a partir de Datos Aeromagmanķticos. Ph.D. thesis, University of Madrid), we can conclude that (1) the characteristic magnetic signature of Ossa Morena Zone is absent on the Iberian Margin and west of it; (2) no eastward continuation of the Collector Anomaly is found in Iberia; (3) only the inner zones of the Variscan Belt can be followed towards NW France; (4) there is a major (left lateral ?) strike-slip fault along the northern Portuguese shoreline that cuts the IAA and significantly displaces the once-contiguous variscan units.
Congenital Variants and Anomalies of the Pancreas and Pancreatic Duct: Imaging by Magnetic Resonance Cholangiopancreaticography and Multidetector Computed Tomography
Erden, Ay?e; T³rko?lu, Mehmet Akif; Yener, ųzlem
Though congenital anomalies of the pancreas and pancreatic duct are relatively uncommon and they are often discovered as an incidental finding in asymptomatic patients, some of these anomalies may lead to various clinical symptoms such as recurrent abdominal pain, nausea and vomiting. Recognition of these anomalies is important because these anomalies may be a surgically correctable cause of recurrent pancreatitis or the cause of gastric outlet obstruction. An awareness of these anomalies may help in surgical planning and prevent inadvertent ductal injury. The purpose of this article is to review normal pancreatic embryology, the appearance of ductal anatomic variants and developmental anomalies of the pancreas, with emphasis on magnetic resonance cholangiopancreaticography and multidetector computed tomography. PMID:24265565
EMAG2: A 2-arc min resolution Earth Magnetic Anomaly Grid compiled from satellite, airborne, and marine magnetic measurements
Maus, S.; Barckhausen, U.; Berkenbosch, H.; Bournas, N.; Brozena, J.; Childers, V.; Dostaler, F.; Fairhead, J.D.; Finn, C.; von Frese, R.R.B; Gaina, C.; Golynsky, S.; Kucks, R.; Lu, Hai; Milligan, P.; Mogren, S.; Muller, R.D.; Olesen, O.; Pilkington, M.; Saltus, R.; Schreckenberger, B.; Thebault, E.; Tontini, F.C.
A global Earth Magnetic Anomaly Grid (EMAG2) has been compiled from satellite, ship, and airborne magnetic measurements. EMAG2 is a significant update of our previous candidate grid for the World Digital Magnetic Anomaly Map. The resolution has been improved from 3 arc min to 2 arc min, and the altitude has been reduced from 5 km to 4 km above the geoid. Additional grid and track line data have been included, both over land and the oceans. Wherever available, the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids. Interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation, based on an oceanic crustal age model. The longest wavelengths (>330 km) were replaced with the latest CHAMP satellite magnetic field model MF6. EMAG2 is available at http://geomag.org/models/EMAG2 and for permanent archive at http://earthref.org/ cgi-bin/er.cgi?s=erda.cgi?n=970. ?? 2009 by the American Geophysical Union.
Computed tomography and magnetic resonance imaging of the coronary sinus: anatomic variants and congenital anomalies.
Chen, Yingming Amy; Nguyen, Elsie T; Dennie, Carole; Wald, Rachel M; Crean, Andrew M; Yoo, Shi-Joon; Jimenez-Juan, Laura
The coronary sinus (CS) is an important vascular structure that allows for access into the coronary veins in multiple interventional cardiology procedures, including catheter ablation of arrhythmias, pacemaker implantation and retrograde cardioplegia. The success of these procedures is facilitated by the knowledge of the CS anatomy, in particular the recognition of its variants and anomalies. This pictorial essay reviews the spectrum of CS anomalies, with particular attention to the distinction between clinically benign variants and life-threatening defects. Emphasis will be placed on the important role of cardiac CT and cardiovascular magnetic resonance in providing detailed anatomic and functional information of the CS and its relationship to surrounding cardiac structures. Teaching Points Ģ Cardiac CT and cardiovascular magnetic resonance offer 3D high-resolution mapping of the coronary sinus in pre-surgical planning.Ģ Congenital coronary sinus enlargement occurs in the presence or absence of a left-to-right shunt.Ģ Lack of recognition of coronary sinus anomalies can lead to adverse outcomes in cardiac procedures.Ģ In coronary sinus ostial atresia, coronary venous drainage to the atria occurs via Thebesian or septal veins.Ģ Coronary sinus diverticulum is a congenital outpouching of the coronary sinus and may predispose to cardiac arrhythmias. PMID:25048808
Insights into magmatic processes and hydrothermal alteration of in situ superfast spreading ocean crust at ODP/IODP site 1256 from a cluster analysis of rock magnetic properties
NASA Astrophysics Data System (ADS)
Dekkers, Mark J.; Heslop, David; Herrero-Bervera, Emilio; Acton, Gary; Krasa, David
analyze magnetic properties from Ocean Drilling Program (ODP)/Integrated ODP (IODP) Hole 1256D (6░44.1' N, 91░56.1' W) on the Cocos Plate in ś15.2 Ma oceanic crust generated by superfast seafloor spreading, the only drill hole that has sampled all three oceanic crust layers in a tectonically undisturbed setting. Fuzzy c-means cluster analysis and nonlinear mapping are utilized to study down-hole trends in the ratio of the saturation remanent magnetization and the saturation magnetization, the coercive force, the ratio of the remanent coercive force and coercive force, the low-field magnetic susceptibility, and the Curie temperature, to evaluate the effects of magmatic and hydrothermal processes on magnetic properties. A statistically robust five cluster solution separates the data predominantly into three clusters that express increasing hydrothermal alteration of the lavas, which differ from two distinct clusters mainly representing the dikes and gabbros. Extensive alteration can obliterate magnetic property differences between lavas, dikes, and gabbros. The imprint of thermochemical alteration on the iron-titanium oxides is only partially related to the porosity of the rocks. Thus, the analysis complements interpretation based on electrofacies analysis. All clusters display rock magnetic characteristics compatible with an ability to retain a stable natural remanent magnetization suggesting that the entire sampled sequence of ocean crust can contribute to marine magnetic anomalies. Paleointensity determination is difficult because of the propensity of oxyexsolution during laboratory heating and/or the presence of intergrowths. The upper part of the extrusive sequence, the granoblastic dikes, and moderately altered gabbros may contain a comparatively uncontaminated thermoremanent magnetization.
Magnetic anomaly map of North America south of 50 degrees north from Pogo data
NASA Technical Reports Server (NTRS)
Mayhew, M. A.
A magnetic anomaly map produced from Pogo data for North America and adjacent ocean areas is presented. At satellite elevations anomalies have wavelengths measured in hundreds of kilometers, and reflect regional structures on a large scale. Prominent features of the map are: (1) a large east-west high through the mid-continent, breached at the Mississippi Embayment; (2) a broad low over the Gulf of Mexico; (3) a strong gradient separating these features, which follows the Southern Appalachian-Ouachita curvature; and (4) a high over the Antilles-Bahamas Platform which extends to northern Florida. A possible relationship between the high of the mid-continent and the 38th parallel lineament is noted.
An attempt to obtain a detailed declination chart from the United States magnetic anomaly map
Alldredge, L.R.
Modern declination charts of the United States show almost no details. It was hoped that declination details could be derived from the information contained in the existing magnetic anomaly map of the United States. This could be realized only if all of the survey data were corrected to a common epoch, at which time a main-field vector model was known, before the anomaly values were computed. Because this was not done, accurate declination values cannot be determined. In spite of this conclusion, declination values were computed using a common main-field model for the entire United States to see how well they compared with observed values. The computed detailed declination values were found to compare less favourably with observed values of declination than declination values computed from the IGRF 1985 model itself. -from Author
Magnetic Anomaly of La1?xMxFeO3 (M = Ca, Sr, and Ba) around 100 K
NASA Astrophysics Data System (ADS)
Nakamae, Yuki; Ishida, Shu; Takemura, Wataru; Ohno, Masatoshi; Okada, Akimasa; Mitsui, Toshihiro; Kobayashi, Yoshihiko; Nakamura, Jin; Asai, Kichizo
A magnetic anomaly has been found around 100 K in La1?xMxFeO3 (M = Ca, Sr, and Ba) and Pr1?xSrxFeO3 with 0.05 ? x ? 0.4; the spontaneous magnetization of the weak ferromagnet increases below about 100 K after cooling in a magnetic field. We propose a model in which Fe4+ ions populated by doped holes preferentially occupy one magnetic sublattice of the antiferromagnetic structure in LaFeO3 and PrFeO3 as a result of charge ordering, which induces an inequality between the sublattice magnetizations and modifies the system from the antiferromagnet to a ferrimagnet. The magnetization below the magnetic anomaly temperature is explained as that of a weak ferromagnet with the canted sublattice magnetizations of the ferrimagnet.
Investigations of medium wavelength magnetic anomalies in the eastern Pacific using Magsat data
NASA Technical Reports Server (NTRS)
Harrison, C. G. A. (principal investigator)
The author has identified the following significant results. Three long total magnetic field profiles taken over ocean basins were analyzed. It is found that there is a significant signal in the wavelength range of 1500 to 150 km. This is too short a wavelength to be caused by the core field, which becomes insignificant at about a wavelength of 1500 km; this intermediate wavelength signal is not caused by a typical sea floor spreading process, which should give maximum power in the wavelength region about 50 km. It is shown that the external magnetic field contributes very little to this intermediate wavelength signal. Efforts to explain the cause of this signal have failed.
Investigation of source location determination from Magsat magnetic anomalies: The Euler method approach
NASA Technical Reports Server (NTRS)
Ravat, Dhananjay
The applicability of the Euler method of source location determination was investigated on several model situations pertinent to satellite-data scale situations as well as Magsat data of Europe. Our investigations enabled us to understand the end-member cases for which the Euler method will work with the present satellite magnetic data and also the cases for which the assumptions implicit in the Euler method will not be met by the present satellite magnetic data. These results have been presented in one invited lecture at the Indo-US workshop on Geomagnetism in Studies of the Earth's Interior in August 1994 in Pune, India, and at one presentation at the 21st General Assembly of the IUGG in July 1995 in Boulder, CO. A new method, called Anomaly Attenuation Rate (AAR) Method (based on the Euler method), was developed during this study. This method is scale-independent and is appropriate to locate centroids of semi-compact three dimensional sources of gravity and magnetic anomalies. The method was presented during 1996 Spring AGU meeting and a manuscript describing this method is being prepared for its submission to a high-ranking journal. The grant has resulted in 3 papers and presentations at national and international meetings and one manuscript of a paper (to be submitted shortly to a reputable journal).
Adaptive cancellation of geomagnetic background noise for magnetic anomaly detection using coherence
NASA Astrophysics Data System (ADS)
Liu, Dunge; Xu, Xin; Huang, Chao; Zhu, Wanhua; Liu, Xiaojun; Yu, Gang; Fang, Guangyou
Magnetic anomaly detection (MAD) is an effective method for the detection of ferromagnetic targets against background magnetic fields. Currently, the performance of MAD systems is mainly limited by the background geomagnetic noise. Several techniques have been developed to detect target signatures, such as the synchronous reference subtraction (SRS) method. In this paper, we propose an adaptive coherent noise suppression (ACNS) method. The proposed method is capable of evaluating and detecting weak anomaly signals buried in background geomagnetic noise. Tests with real-world recorded magnetic signals show that the ACNS method can excellently remove the background geomagnetic noise by about 21?dB or more in high background geomagnetic field environments. Additionally, as a general form of the SRS method, the ACNS method offers appreciable advantages over the existing algorithms. Compared to the SRS method, the ACNS algorithm can eliminate the false target signals and represents a noise suppressing capability improvement of 6.4?dB. The positive outcomes in terms of intelligibility make this method a potential candidate for application in MAD systems.
A Semiclassical Formulation of the Chiral Magnetic Effect and Chiral Anomaly in Even d+1 Dimensions
Omer F. Dayi; Mahmut Elbistan
In terms of the matrix valued Berry gauge field strength for the Weyl Hamiltonian in any even spacetime dimensions a symplectic form whose elements are matrices in spin indices is introduced. Definition of the volume form is modified appropriately. A simple method of finding the path integral measure and the chiral current in the presence of external electromagnetic fields is presented. It is shown that within this new approach the chiral magnetic effect as well as the chiral anomaly in even d+1 dimensions are accomplished straightforwardly.
Monitoring the evolution of Deception Island volcano from magnetic anomaly data (South Shetland Islands, Antarctica)
NASA Astrophysics Data System (ADS)
Catalßn, Manuel; Martos, Yasmina M.; Galindo-ZaldĒvar, Jes·s; Funaki, Minoru
Deception Island is a young and active volcano located in the south-western part of Bransfield back-arc basin. During the last twenty years the Royal Observatory of the Spanish Navy has carried out geophysical surveys in the area. In addition, an unmanned aerial vehicle flight was conducted in 2011 at 800 m height on the northern half of Deception Island. Analysing and comparing magnetic grids obtained in different periods and tie point readings allow us to detect temporal changes and isolate signals of volcanic origin. Magnetic survey cruises performed in Deception Island's inner bay (1988, 1999 and 2008), and the study of its outer area's magnetic anomaly changes, point to a period of high variations concentrated between December 1989 and December 1999 that may be related to the two main recent periods of seismic activity (1992 and January 1999). From December 1999 to December 2008, there were no significant changes in seismic activity; nevertheless, our data show some magnetic alterations, which might signal the slow progress of a volcanic environment towards equilibrium. Interpreting these magnetic changes called for the construction of several forward models. Additionally, we put forth this kind of study as a suitable, economical and easy method for monitoring an active volcanic system whenever it is possible to measure the magnetic field with accurate positioning, and if the external field components are removed correctly.
A permanent magnet electron beam spread system used for a low energy electron irradiation accelerator
NASA Astrophysics Data System (ADS)
Huang, Jiang; Xiong, Yong-Qian; Chen, De-Zhi; Liu, Kai-Feng; Yang, Jun; Li, Dong; Yu, Tiao-Qin; Fan, Ming-Wu; Yang, Bo
The development of irradiation processing industry brings about various types of irradiation objects and expands the irradiation requirements for better uniformity and larger areas. This paper proposes an innovative design of a permanent magnet electron beam spread system. By clarifying its operation principles, the author verifies the feasibility of its application in irradiation accelerators for industrial use with the examples of its application in electron accelerators with energy ranging from 300 keV to 1 MeV. Based on the finite element analyses of electromagnetic fields and the charged particle dynamics, the author also conducts a simulation of electron dynamics in magnetic field on a computer. The results indicate that compared with the traditional electron beam scanning system, this system boosts the advantages of a larger spread area, non-power supply, simple structure and low cost, etc., which means it is not only suitable for the irradiation of objects with the shape of tubes, strips and panels, but can also achieve a desirable irradiation performance on irregular constructed objects of large size.
The developing role of fetal magnetic resonance imaging in the diagnosis of congenital cardiac anomalies: A systematic review
Loomba, Rohit S; Chandrasekar, Suraj; Shah, Parinda H; Sanan, Prateek
Advances in the fetal magnetic resonance imaging (MRI) over the last few years have resulted in the exploring the use of fetal MRI to detect congenital cardiac anomalies. Early detection of congenital cardiac anomalies can help more appropriately manage the infant's delivery and neonatal management. MRI offers anatomical and functional studies and is a safe adjunct that can help more fully understand a fetusÆ cardiac anatomy. It is important for the obstetricians and pediatric cardiologists to be aware of the recent advancements in fetal MRI and it`s potential utility in diagnosing congenital cardiac anomalies. PMID:21976881
The developing role of fetal magnetic resonance imaging in the diagnosis of congenital cardiac anomalies: A systematic review.
Loomba, Rohit S; Chandrasekar, Suraj; Shah, Parinda H; Sanan, Prateek
Advances in the fetal magnetic resonance imaging (MRI) over the last few years have resulted in the exploring the use of fetal MRI to detect congenital cardiac anomalies. Early detection of congenital cardiac anomalies can help more appropriately manage the infant's delivery and neonatal management. MRI offers anatomical and functional studies and is a safe adjunct that can help more fully understand a fetus' cardiac anatomy. It is important for the obstetricians and pediatric cardiologists to be aware of the recent advancements in fetal MRI and it`s potential utility in diagnosing congenital cardiac anomalies. PMID:21976881
Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions
NASA Astrophysics Data System (ADS)
Ringer, S.; Vieth, M.; Bõr, L.; R³hrig, M.; Bayreuther, G.
The I -V characteristics of CoFeB/MgO/CoFeB magnetic tunnel junctions show pronounced nonlinearities which are relevant both for sensor applications and for the basic understanding of spin-dependent tunneling. To study the relation between the tunnel characteristics and the tunnel magnetoresistance (TMR) ratio, a series of CoFeB/MgO/CoFeB junctions was annealed with stepwise increasing annealing time at different temperatures. The related TMR ratio and the I -V characteristics were measured in the temperature range between 15 K and 300 K. This allowed the comparison of I -V characteristics of the same junction for TMR ratios between 25% and 150% at 300 K thus eliminating the influence of variations in the preparation process of separate individual samples. In addition to a zero bias anomaly observed in particular at low temperatures and for large TMR ratios, a conductance anomaly in the I -V curves was observed around a bias voltage of 350 mV. A general correlation between the deviation from Ohmic I -V characteristics and the TMR ratio was found both for parallel and antiparallel magnetizations of both ferromagnetic layers. This means that the shape of the I -V curves directly scales with the spin polarization of the tunneling current and the proportion of coherent electron tunneling. Both the 350 mV conductance anomaly and the correlation between non-Ohmic characteristics and the TMR ratio can be explained by considering the contributions of the relevant majority and minority spin bands of the ferromagnetic contacts.
Magnetic diffusion anomaly at the Nķel temperature of pyrrhotite, Fe1-xS.
William Herbert, F; Krishnamoorthy, Aravind; Rands, Lucy; Van Vliet, Krystyn J; Yildiz, Bilge
Cation diffusion is an important rate-limiting process in the growth of pyrrhotite (Fe1-xS) in passivating films on steels exposed to sulfidic environments, and for proposed synthetic applications of Fe1-xS, for example single-phase magnetic switching devices. Above the Nķel temperature TN of 315 ░C, where Fe1-xS is paramagnetic and structurally disordered, iron self-diffusivity *DFe predictably follows a standard, established Arrhenius law with temperature. However, we report (57)Fe tracer diffusion measurements below TN, obtained using secondary ion mass spectrometry (SIMS), that demonstrate a 100-fold reduction in diffusion coefficient as compared to the extrapolated, paramagnetic Arrhenius trend at 150 ░C. The results can be described by a magnetic diffusion anomaly, where the vacancy migration energy for the spontaneously-magnetized cation sublattice is increased by approximately 40% over the paramagnetic state. These constitute the first set of consistent diffusivity data obtained in magnetic pyrrhotite, allowing more accurate prediction of pyrrhotite growth rates and determination of magnetic properties for synthetic devices. PMID:25823983
First observation of a mini-magnetosphere above a lunar magnetic anomaly using energetic neutral atoms
NASA Astrophysics Data System (ADS)
Wieser, Martin; Barabash, Stas; Futaana, Yoshifumi; Holmstr÷m, Mats; Bhardwaj, Anil; Sridharan, R.; Dhanya, M. B.; Schaufelberger, Audrey; Wurz, Peter; Asamura, Kazushi
The Sub-keV Atom Reflecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 spacecraft has produced for the first time an image of a lunar magnetic anomaly in backscattered hydrogen atoms. The image shows that a partial void of the solar wind, a mini-magnetosphere, is formed above the strong magnetic anomaly near the Crisium antipode. The mini-magnetosphere is 360 km across at the surface and is surrounded by a 300-km-thick region of enhanced plasma flux that results from the solar wind flowing around the mini-magnetosphere. The mini-magnetosphere is visible only in hydrogen atoms with energy exceeding 150 eV. Fluxes with energies below 100 eV do not show corresponding spatial variations. While the high-energy atoms result from the backscattering process, the origin of the low-energy component is puzzling. These observations reveal a new class of objects, mini-magnetospheres, and demonstrate a new observational technique to study airless bodies, imaging in backscattered neutral atoms.
Observation of a lunar mini-magnetosphere above a magnetic anomaly using energetic neutral atoms
NASA Astrophysics Data System (ADS)
Wieser, Martin; Barabash, Stas; Futaana, Yoshifumi; Holmstr÷m, Mats; Bhardwaj, Anil; Sridharan, R.; Dhanya, M. B.; Schaufelberger, Audrey; Wurz, Peter; Asamura, Kazushi
The Sub-keV Atom Reflecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 spacecraft has resulted in a comprehensive data set about interaction of solar wind with the lunar surface. When solar wind hits the lunar surface, it is partly backscattered as energetic neutral atoms. The intensity of the backscattered energetic neutral atoms is a measure of the intensity of the solar wind reaching the surface. We report on the imaging of a lunar magnetic anomaly in backscattered neutral hydrogen atoms: The image shows the formation of a partial void of the solar wind, a mini-magnetosphere, above the strong magnetic anomaly near the Crisium antipode on the lunar farside. The mini-magnetosphere is 360 km across at the surface and surrounded by a 300-km-thick region of enhanced plasma flux that results from the solar wind flowing around the mini-magnetosphere. These observations demonstrate a new observational technique to study airless bodies, imaging in backscattered neutral atoms, and its application to a new class of objects, mini-magnetospheres.
A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications
NASA Technical Reports Server (NTRS)
Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.
Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While magnetic anomaly data represent the main focus of this study recently derived satellite gravity data are playing a major role in Arctic studies.
A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications
NASA Technical Reports Server (NTRS)
Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.
Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies. These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While Magnetic anomaly data represent the main focus of this study recently derived satellite gravity data (Laxon and McAdoo, 1998) are playing a major role in Arctic studies.
Energy Detection Based on Undecimated Discrete Wavelet Transform and Its Application in Magnetic Anomaly Detection
Nie, Xinhua; Pan, Zhongming; Zhang, Dasha; Zhou, Han; Chen, Min; Zhang, Wenna
Magnetic anomaly detection (MAD) is a passive approach for detection of a ferromagnetic target, and its performance is often limited by external noises. In consideration of one major noise source is the fractal noise (or called 1/f noise) with a power spectral density of 1/fa (0magnetic anomaly detection and UDWT are introduced in brief, while a possible detection system based on giant magneto-impedance (GMI) magnetic sensor is also given out. Then our proposed energy detection based on UDWT is described in detail, and the probabilities of false alarm and detection for given the detection threshold in theory are presented. It is noticeable that no a priori assumptions regarding the ferromagnetic target or the magnetic noise probability are necessary for our method, and different from the discrete wavelet transform (DWT), the UDWT is shift invariant. Finally, some simulations are performed and the results show that the detection performance of our proposed detector is better than that of the conventional energy detector even utilized in the Gaussian white noise, especially when the spectral parameter ? is less than 1.0. In addition, a real-world experiment was done to demonstrate the advantages of the proposed method. PMID:25343484
The analysis of ZTEM data across the Humble magnetic anomaly, Alaska
NASA Astrophysics Data System (ADS)
Sattel, Daniel; Witherly, Ken
ZTEM data acquired across the Humble magnetic anomaly of almost 30 000 nT were analysed for the presence of a magnetic gradient response and the effects from elevated magnetic susceptibilities. Mag3D inversion of the magnetic data indicates magnetic susceptibility values as high as 2.0 (SI). The response of moving the receiver coil through the magnetic-field gradient peaks at 0.01 Hz and drops off strongly with frequency. Lacking information about the field strength at the base station precludes the comparison of amplitudes between computed gradient responses and the survey data, but the comparison of response shapes suggests that the gradient responses are too small to have a noticeable effect on the survey data. ZTEM responses were forward modelled with a 3D algorithm developed at the University of British Columbia Geophysical Inversion Facility (UBC-GIF) that takes into account electric conductivities ? and magnetic susceptibilities ?, in order to assess the impact of the elevated ?-values derived from the Mag3D inversion. Computing the ZTEM response for these ?-values combined with resistive half-spaces indicates that the response amplitudes and shapes strongly depend on the background resistivities. Ignoring the elevated ?-values during an inversion can result in patterns that resemble crop circles. The approximate conductivity structure of the survey area was derived with a UBC-GIF 3D ZTEM inversion, which models ? = 0. Forward-model results of these conductivities combined with the elevated ?-values derived from the Mag3D inversion indicate that the conductivities are underestimated with the ? = 0 assumption. For an environment such as Humble, with deep-seated zones of elevated ?-values, the shallow inverted conductivity structure appears to be reliable, but the deeper structure should be interpreted with caution.
Circum-Arctic Magnetic Anomalies - Challenges of Compilation and the Value of Regional Interpretation in a Frontier Area
NASA Astrophysics Data System (ADS)
Saltus, R. W.; Gaina, C.; Brown, P. J.
Important societal issues are driving increased attention to polar regions. The arctic, in particular, is the focus of scientific studies relating to climate change as well as resource exploration and territorial claims. The news and entertainment media are picking up on polar themes and driving interest within popular culture. Part of the attraction and mystique of the ends of the Earth lies in their relative inaccessibility and harsh environment. These same attributes make it difficult to conduct even basic scientific investigation, and therefore, the arctic remains a scientific frontier in many respects. Delineation of a robust tectonic framework for the top of the world is an essential prerequisite to resource assessment. The difficulty of making direct geologic observations beneath ice and sea requires remote measurement. Regional magnetic anomaly mapping provides important constraining information for the development of tectonic models for this structurally complex region. In addition to the obvious logistical challenges to detailed magnetic field measurement in the high arctic, noise and instability in the magnetic field itself at high latitudes presents difficulties. Nevertheless, regional magnetic anomaly data have been collected over the past 50 years for much of the arctic. The available surveys are diverse in vintage and survey design; the amplitude and frequency content of measured anomalies are widely variable. Availability of metadata and other documentation are also inconsistent for these surveys. This leads to significant challenges in constructing accurate regional magnetic anomaly maps. Preliminary maps from a new international cooperation effort (CAMP-GM, under the direction of Carmen Gaina, Geological Survey of Norway) provide the most consistent view yet of magnetic anomalies for the tectonically complex arctic basins and surrounding continents. Careful attention to digital compilation details allows the new grids to be mathematically filtered to assist in the regional characterization of magnetic domains and boundaries. The frequency content, amplitudes, and patterns of regional magnetic anomalies provide a window into the tectonic character and structure of the crust. Continental, oceanic, and various types of transitional crust each have a distinctive magnetic anomaly signature that can be used to define a fundamental tectonic framework of the circum-arctic. Interpretation can be extended by including additional data such as regional bathymetry (an indicator of crustal buoyancy and isostatic equilibrium) and free air gravity (an independent indicator of crustal density balance and composition). Used together with magnetic domains these data reveal a composite geodynamic subdivision of the arctic. This subdivision provides a framework for investigations of mineral and energy resource potential, tectonic reconstruction, and long-term climate dynamics.
Investigation of the Crust of the Pannonian Basin, Hungary Using Low-Altitude CHAMP Horizontal Gradient Magnetic Anomalies
NASA Technical Reports Server (NTRS)
Taylor, Patrick T.; Kis, Karoly I.; Puszta, Sandor; Wittmann, Geza; Kim, Hyung Rae; Toronyi, B.
The Pannonian Basin is a deep intra-continental basin that formed as part of the Alpine orogeny. It is some 600 by 500 km in area and centered on Hungary. This area was chosen since it has one of the thinnest continental crusts in Europe and is the region of complex tectonic structures. In order to study the nature of the crustal basement we used the long-wavelength magnetic anomalies acquired by the CHAMP satellite. The SWARM constellation, scheduled to be launched next year, will have two lower altitude satellites flying abreast, with a separation of between ca. 150 to 200 km. to record the horizontal magnetic gradient. Since the CHAMP satellite has been in orbit for eight years and has obtained an extensive range of data, both vertically and horizontally there is a large enough data base to compute the horizontal magnetic gradients over the Pannonian Basin region using these many CHAMP orbits. We recomputed a satellite magnetic anomaly map, using the spherical-cap method of Haines (1985), the technique of Alsdorf et al. (1994) and from spherical harmonic coefficients of MF6 (Maus et aI., 2008) employing the latest and lowest altitude CHAMP data. We then computed the horizontal magnetic anomaly gradients (Kis and Puszta, 2006) in order to determine how these component data will improve our interpretation and to preview what the SW ARM mission will reveal with reference to the horizontal gradient anomalies. The gradient amplitude of an 1000 km northeast-southwest profile through our horizontal component anomaly map varied from 0 to 0.025 nT/km with twin positive anomalies (0.025 and 0.023 nT/km) separated by a sharp anomaly negative at o nT/km. Horizontal gradient indicate major magnetization boundaries in the crust (Dole and Jordan, 1978 and Cordell and Grauch, 1985). Our gradient anomaly was modeled with a twodimensional body and the anomaly, of some 200 km, correlates with a 200 km area of crustal thinning in the southwestern Pannonian Basin.
Modeling gravity and magnetic field anomalies at Tyrrhenus Mons and Syrtis Major, Mars: Evidence for polar wander, magnetic reversals, and the death of the dynamo
NASA Astrophysics Data System (ADS)
Milbury, C.; Raymond, C. A.; Schubert, G.; Smrekar, S. E.
Analysis of gravity and magnetic anomalies in the regions surrounding Tyrrhenus Mons and Syrtis Major provide insight into the activity and timing of the dynamo from the late Noachian through the Hesperian, the period when these volcanoes were geologically active. We model a collection of correlated gravity and magnetic anomalies distributed throughout the study areas. Our work differs from past studies in that we model a large number of magnetic anomalies, including relatively small anomalies and those that are contiguous with other anomalies. We select only anomalies that also have gravity signatures, which we use as inputs to the magnetic analysis to reduce the non-uniqueness in the horizontal position of the magnetic source. In contrast, most other studies have focused on the largest, most isolated magnetic anomalies. Our motivation is to constrain the continuous history of the magnetic field as recorded in the crust and to do so in a statistically robust manner. We find that two populations of paleomagnetic poles generally fit the data: paleopoles that cluster near the equator and near the geographic poles. Magnetic sources that favor low to middle latitude paleopoles are generally located below or immediately adjacent to Noachian surface units and sources that favor middle to high latitude paleopoles are located below or immediately adjacent to Hesperian features. The correlation of magnetic sources located below Noachian (Hesperian) aged crust with paleopoles distributions near the equator (geographic poles) supports the hypothesis that true polar wander occurred on Mars roughly consistent with the polar wander path near the 330░ E meridian determined by Perron et al. (2007). Both the equatorial and polar paleopole clusters have positive and negative polarities, which is evidence for reversals. The dipole moments associated with the two anomalies closest to Tyrrhenus Mons' caldera have opposite sign and are of similar geologic age, which is further evidence for reversals. Evidence of magnetization of Tyrrhenus Mons, Nili Patera, and Meroe Patera are presented. The Tharsis volcanic province and Elysium Mons were active in the Amazonian and are not significantly magnetized; this demonstrates that the dynamo likely ceased activity sometime in the late Hesperian to early Amazonian.
Examples of Models Fit to Magnetic Anomalies Observed Over Subaerial, Submarine, and Subglacial Volcanoes in the West Antarctic Rift System
NASA Astrophysics Data System (ADS)
Behrendt, J. C.; Finn, C. A.; Blankenship, D. D.
Aeromagnetic and marine magnetic surveys over the volcanically active West Antarctic rift system, constrained by seismic reflection profiles over the Ross Sea continual shelf, and radar ice sounding surveys over the West Antarctic Ice Sheet (WAIS) allowed calculation of models fit to very high-amplitude anomalies. We present several examples: exposed 2700-m high, subaerial erupted volcano Mt Melbourne; the 750-m high source of anomaly D (Hamilton submarine volcano) in the Ross sea; and the 600-m high edifice of Mt. CASERTZ beneath the WAIS. The character of these anomalies and their sources varies greatly, and is inferred to be the result of subaerial, submarine and subglacial emplacement respectively. Mt. Melbourne erupted through the WAIS at a time when it was grounded over the Ross Sea continental shelf. Highly magnetic volcanic flows inferred to have high remanent (normal) magnetization in the present field direction produce the 600-nT positive anomaly. The flows protected the edifice above the ice from erosion. Negligible amounts of probably subglacially erupted, apparently non-magnetic hyaloclastite exist in association with Mt. Melbourne. Mt. CASERTZ is nonmagnetic and the edifice is interpreted as consisting of a transient mound of unconsolidated hyaloclastite injected into the WAIS. However Mt. CASERTZ, about 8-km diameter, overlies a 200-m high, 40-km wide highly magnetic residual edifice modeled as the top of the source (an active subglacial volcano) of a 400-nT high positive anomaly. Any former edifices comprising hyaloclastite, pillow breccia or other volcanic debris injected into the moving WAIS apparently have been removed. About 400 other high- amplitude anomalies associated with low relief (80 percent less than 200 m) edifices at the base of the ice (the tops of the sources of these steep gradient anomalies) beneath the WAIS defined by radar ice sounding have been interpreted as having former hyaloclastite edifices, which were removed by the moving ice. The source of the -1300-nT negative anomaly D projecting 600 m above the Ross Sea continental shelf is enigmatic. We interpret models as either the result of reversed magnetization (less than 780 Ka) at a time of deglaciation of the continental shelf, or a hydrothermally altered central core surrounded by highly magnetic flows erupted beneath the Ross sea since deglaciation in Holocene time.
Remanent and Induced Magnetic Anomalies over the Bjerkreim-Sokndal Layered Intrusion: Effects from Crystal Fractionation and Magma Recharge
NASA Astrophysics Data System (ADS)
McEnroe, S. A.; Brown, L. L.; Robinson, P.
The Bjerkreim-Sokndal (BKS) norite-quartz mangerite layered intrusion is part of the early Neoproterozoic Rogaland Anorthosite Province intruded into the Fennoscandian shield in south Norway at ~930 Ma. The BKS is exposed over an area of 230 km2 with a thickness of ~7000m and is of economic interest for hemo-ilmenite, magnetite and apatite deposits. From the point of view of magnetic minerals, in the course of fractional crystallization and magma evolution, the ilmenite becomes less Fe3+-rich reflected by a change from ilmenite with hematite exsolution to nearly pure ilmenite. Magnetite starts to crystallize relatively late in the intrusive history, but its crystallization is interrupted by influxes of more primitive magma containing hemo-ilmenite. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the magnetic properties of NRM, susceptibility, and hysteresis. Magnetic properties are correlated with the oxide mineralogy and mineral chemistry. Early layers in the intrusion contain hemo-ilmenite. As the magma evolved and magnetite started to crystallize, this caused a distinct change over the layering from remanence-controlled negative anomalies to induced positive anomalies. When new, more primitive magma was injected into the system, hemo-ilmenite returned as the major oxide and the resulting magnetic anomalies are again negative. The most dramatic change in the magnetic signature is in the upper part of the intrusion in MCU IVe, where magnetite became a well established cumulate phase as indicated by susceptibility, but its induced magnetization is overcome by large NRM's associated either with hemo-ilmenite or with hemo-ilmenite and magnetite exsolved from pyroxenes. The average natural remanent magnetizations change from ~3 A/m in MCU IVd, to 15 A/m in MCU IVe, and back to 2 A/m in the overlying MCU IVf, producing a strong negative remanent anomaly that has been followed along strike for at least 20 km by ground-magnetic measurements. The highly varied magnetic properties of this intrusion, caused by varied magmatic crystallization of combinations of oxide minerals illustrate some of the possibilities to be considered in evaluating crustal magnetic anomalies.
Investigating tectonic and bathymetric features of the Indian Ocean using MAGSAT magnetic anomaly data
NASA Technical Reports Server (NTRS)
Lazarewicz, A. R.; Sailor, R. V. (principal investigators)
MAGSAT Investigator-B tapes were preprocessed by (1) removing all data points with obvious erroneous values and location errors; (2) removing smaller spikes (typically 15 nT or more), and deleting data tracks with fewer than 20 points; and (3) removing a linear trend from each track. The remaining data were recorded on tape for use by the equivalent source mapping (ESMAP) program which uses a least squares algorithm to fit the magnetization parameter of the grid of equivalent source dipoles in the crust to satellite data acquired at different times and locations. ESMAP was implemented on the TASC computing system and modified to read preprocessed MAGSAT tapes and interface with TASC plotting software. Some verification of the software was accomplished. Gridded 1-degree mean values of gravity anomaly and sea surface undulation computed from SEASAT radar altimeter were obtained and brought on line.
Electromagnetic particle-in-cell simulations of the solar wind interaction with lunar magnetic anomalies.
Deca, J; Divin, A; Lapenta, G; LembĶge, B; Markidis, S; Horßnyi, M
We present the first three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier magnetohydrodynamics and hybrid simulations, the fully kinetic nature of iPic3D allows us to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe for the first time the interaction of a dipole model centered just below the lunar surface under plasma conditions such that only the electron population is magnetized. The fully kinetic treatment identifies electromagnetic modes that alter the magnetic field at scales determined by the electron physics. Driven by strong pressure anisotropies, the mini-magnetosphere is unstable over time, leading to only temporal shielding of the surface underneath. Future human exploration as well as lunar science in general therefore hinges on a better understanding of LMAs. PMID:24785022
The role of magnetic resonance imaging in refining the diagnosis of suspected fetal renal anomalies
Abdelazim, Ibrahim Anwar; Belal, Maha Mohamed
Objective: This prospective study was designed to detect the role of magnetic resonance imaging (MRI) in refining the diagnosis of suspected fetal renal anomalies detected during screening sonography. Material and Methods: 54 pregnant women, with suspected fetal renal anomalies detected during routine ultrasound screening, were rescanned by MRI to refine the diagnosis of the suspected renal anomalies. The pregnancy outcome was examined externally and by postnatal ultrasonography. Results: Fifty-four cases of suspected renal anomalies detected during screening sonography of 8400 pregnant women (0.6%), were res-canned by MRI in this study. The MRI gave a similar diagnosis to postnatal ultrasound in 46 cases (16 cases of hydronephrosis, 14 cases of Polycystic Kidney Disease (PCKD), 9 cases of Multicystic Kidney Disease (MCKD), 2 cases of Renal Agensis (RA), 3 cases of single renal cyst and 2 cases of megacystis+hydroureter), while it gave a different diagnosis (false positive) in 6 cases (4 cases of hydronephrosis diagnosed by MRI confirmed to be PCKD by postnatal ultrasound, also, 1 case of MCKD diagnosed by MRI confirmed to be hydronephrosis by postnatal ultrasound and 1 case of RA diagnosed by MRI confirmed to be normal by postnatal ultrasound). The prenatal ultrasound gave a similar diagnosis to postnatal ultrasound in 43 cases (14 cases of hydronephrosis, 13 case of PCKD, 9 cases of MCKD, 2 cases of RA, 3 cases of single renal cyst and 2 case of megacystis+hydroureter), while it gave a different diagnosis (false positive) in 9 cases; 4 cases of hydronephrosis diagnosed by prenatal sonography confirmed to be PCKD by postnatal ultrasound, one case of PCKD+one case of MCKD, and one case of megacystis+hydroureter confirmed to be hydronephrosis by postnatal ultrasound, while one case of MCKD diagnosed by prenatal sonography was confirmed to be PCKD by postnatal ultrasound and one case of RA diagnosed by prenatal ultrasound was confirmed to be normal by postnatal ultrasound. Conclusion: The MRI can be used as a complementary adjunctive modality with excellent tissue contrast, especially in equivocal cases or inconclusive sonographic findings. PMID:24592062
Controls on Martian hydrothermal systems: Application to valley network and magnetic anomaly formation
NASA Astrophysics Data System (ADS)
Harrison, Keith P.; Grimm, Robert E.
Models of hydrothermal groundwater circulation can quantify limits to the role of hydrothermal activity in Martian crustal processes. We present here the results of numerical simulations of convection in a porous medium due to the presence of a hot intruded magma chamber. The parameter space includes magma chamber depth, volume, aspect ratio, and host rock permeability and porosity. A primary goal of the models is the computation of surface discharge. Discharge increases approximately linearly with chamber volume, decreases weakly with depth (at low geothermal gradients), and is maximized for equant-shaped chambers. Discharge increases linearly with permeability until limited by the energy available from the intrusion. Changes in the average porosity are balanced by changes in flow velocity and therefore have little effect. Water/rock ratios of ~0.1, obtained by other workers from models based on the mineralogy of the Shergotty meteorite, imply minimum permeabilities of 10-16 m2 during hydrothermal alteration. If substantial vapor volumes are required for soil alteration, the permeability must exceed 10-15 m2. The principal application of our model is to test the viability of hydrothermal circulation as the primary process responsible for the broad spatial correlation of Martian valley networks with magnetic anomalies. For host rock permeabilities as low as 10-17 m2 and intrusion volumes as low as 50 km3, the total discharge due to intrusions building that part of the southern highlands crust associated with magnetic anomalies spans a comparable range as the inferred discharge from the overlying valley networks.
Controls on Martian Hydrothermal Systems: Application to Valley Network and Magnetic Anomaly Formation
NASA Technical Reports Server (NTRS)
Harrison, Keith P.; Grimm, Robert E.
Models of hydrothermal groundwater circulation can quantify limits to the role of hydrothermal activity in Martian crustal processes. We present here the results of numerical simulations of convection in a porous medium due to the presence of a hot intruded magma chamber. The parameter space includes magma chamber depth, volume, aspect ratio, and host rock permeability and porosity. A primary goal of the models is the computation of surface discharge. Discharge increases approximately linearly with chamber volume, decreases weakly with depth (at low geothermal gradients), and is maximized for equant-shaped chambers. Discharge increases linearly with permeability until limited by the energy available from the intrusion. Changes in the average porosity are balanced by changes in flow velocity and therefore have little effect. Water/rock ratios of approximately 0.1, obtained by other workers from models based on the mineralogy of the Shergotty meteorite, imply minimum permeabilities of 10(exp -16) sq m2 during hydrothermal alteration. If substantial vapor volumes are required for soil alteration, the permeability must exceed 10(exp -15) sq m. The principal application of our model is to test the viability of hydrothermal circulation as the primary process responsible for the broad spatial correlation of Martian valley networks with magnetic anomalies. For host rock permeabilities as low as 10(exp -17) sq m and intrusion volumes as low as 50 cu km, the total discharge due to intrusions building that part of the southern highlands crust associated with magnetic anomalies spans a comparable range as the inferred discharge from the overlying valley networks.
Geophysical Surveying of Shallow Magnetic Anomalies Using the iPhone Magnetometer
NASA Astrophysics Data System (ADS)
Opdyke, P.; Dudley, C.; Louie, J. N.
This investigation examined whether the 3-axis Hall-effect magnetometer in the Apple iPhone 3GS can function as an effective shallow magnetic survey instrument. The xSensor Pro app from Crossbow Systems allows recoding of all three sensor components along with the GPS location, at a frequency of 1.0, 4.0, 16.0, and 32.0 Hz. If the iPhone proves successful in collecting useful magnetic data, then geophysicists and especially educators would have a new tool for high-density geophysical mapping. No-contract iPhones that can connect with WiFi can be obtained for about $400, allowing deployment of large numbers of instruments. iPhones with the xSensor Pro app surveyed in parallel with an Overhauser GEM system magnetometer (1 nT sensitivity) to test this idea. Anderson Bay, located on the Pyramid Lake Paiute Reservation, provided a rural survey location free from cultural interference. xSensor Pro, logged each component's intensity and the GPS location at a frequency of four measurements per second. Two Overhauser units functioned as a base unit and a roving unit. The roving unit collected total field at set points located with a handheld GPS. Comparing the total field computed from the iPhone components against that collected by the Overhauser establishes the level of anomalies that the iPhone can detect. iPhone total-field measurements commonly vary by 200 nT from point to point, so a spatial-temporal average over 25 seconds produces a smoothed signal for comparison. Preliminary analysis of the iPhone results show that the data do not accurately correlate to the total field collected by the Overhauser for any anomaly of less than 200 nT.
Three-Dimensional Mapping of Magnetic Strata From Aeromagnetic Anomalies: The Deformed Neroly Formation South of Mt. Diablo, Northern California
R. C. Jachens; R. W. Simpson; R. W. Graymer; C. M. Wentworth
We apply direct inversion of aeromagnetic anomalies to analyze the subsurface 3D shape of the highly magnetic Miocene Neroly Formation, which consists largely of medium to coarse-grained andesitic sandstones containing abundant magnetite. The Neroly Formation is widespread in the eastern San Francisco Bay region, and locally is tightly folded and disrupted by faulting in the compressional regime related to the
The history of Mars' dynamo as revealed by modeling magnetic anomalies near Tyrrhenus Mons and Syrtis Major
NASA Astrophysics Data System (ADS)
Milbury, C.; Schubert, G.; Raymond, C. A.; Smrekar, S. E.; Langlais, B.
The lack of magnetic anomalies within the major impact basins (Hellas, Argyre, and Isidis) has led many investigators to the conclusion that Mars' dynamo shut down prior to the time when these basins formed (ś4.0 Ga). We test this hypothesis by analyzing gravity and magnetic anomalies in the regions surrounding Tyrrhenus Mons and Syrtis Major, two volcanoes that were active during the late Noachian and Hesperian. We model magnetic anomalies that are associated with gravity anomalies and generally find that sources located below Noachian surface units tend to favor paleopoles near the equator and sources located below Hesperian surface features favor paleopoles near the geographical poles, suggesting polar wander during the Noachian-Hesperian. Both paleopole clusters have positive and negative polarities, indicating reversals of the field during the Noachian and Hesperian. Magnetization of sources below Hesperian surfaces is evidence that the dynamo persisted beyond the formation of the major impact basins. The demagnetization associated with the volcanic construct of Syrtis Major implies dynamo cessation occurred while it was geologically active approximately 3.6 billion years ago. Timing of dynamo activity is fundamentally linked to Mars' climate via the stability of its atmosphere, and is coupled to the extent and duration of surface geologic activity. Thus, the dynamo history is key for understanding both when Mars was most geologically active and when it may have been most hospitable to life.
Research for Key Techniques of Geophysical Recognition System of Hydrocarbon-induced Magnetic Anomalies Based on Hydrocarbon Seepage Theory
NASA Astrophysics Data System (ADS)
Zhang, L.; Hao, T.; Zhao, B.
Hydrocarbon seepage effects can cause magnetic alteration zones in near surface, and the magnetic anomalies induced by the alteration zones can thus be used to locate oil-gas potential regions. In order to reduce the inaccuracy and multi-resolution of the hydrocarbon anomalies recognized only by magnetic data, and to meet the requirement of integrated management and sythetic analysis of multi-source geoscientfic data, it is necessary to construct a recognition system that integrates the functions of data management, real-time processing, synthetic evaluation, and geologic mapping. In this paper research for the key techniques of the system is discussed. Image processing methods can be applied to potential field images so as to make it easier for visual interpretation and geological understanding. For gravity or magnetic images, the anomalies with identical frequency-domain characteristics but different spatial distribution will reflect differently in texture and relevant textural statistics. Texture is a description of structural arrangements and spatial variation of a dataset or an image, and has been applied in many research fields. Textural analysis is a procedure that extracts textural features by image processing methods and thus obtains a quantitative or qualitative description of texture. When the two kinds of anomalies have no distinct difference in amplitude or overlap in frequency spectrum, they may be distinguishable due to their texture, which can be considered as textural contrast. Therefore, for the recognition system we propose a new ōmagnetic spotsö recognition method based on image processing techniques. The method can be divided into 3 major steps: firstly, separate local anomalies caused by shallow, relatively small sources from the total magnetic field, and then pre-process the local magnetic anomaly data by image processing methods such that magnetic anomalies can be expressed as points, lines and polygons with spatial correlation, which includes histogram-equalization based image display, object recognition and extraction; then, mine the spatial characteristics and correlations of the magnetic anomalies using textural statistics and analysis, and study the features of known anomalous objects (closures, hydrocarbon-bearing structures, igneous rocks, etc.) in the same research area; finally, classify the anomalies, cluster them according to their similarity, and predict hydrocarbon induced ōmagnetic spotsö combined with geologic, drilling and rock core data. The system uses the ArcGIS as the secondary development platform, inherits the basic functions of the ArcGIS, and develops two main sepecial functional modules, the module for conventional potential-field data processing methods and the module for feature extraction and enhancement based on image processing and analysis techniques. The system can be applied to realize the geophysical detection and recognition of near-surface hydrocarbon seepage anomalies, provide technical support for locating oil-gas potential regions, and promote geophysical data processing and interpretation to advance more efficiently.
Inverse Dipolar Magnetic Anomaly Over the Volcanic Cone Linked to Reverse Polarity Magnetizations in Lavas and Tuffs - Implications for the Conduit System
NASA Astrophysics Data System (ADS)
Fucugauchi, J. U.; Perez-Cruz, L. L.; Trigo-Huesca, A.
A combined magnetics and paleomagnetic study of Toluquilla monogenetic volcano and associated lavas and tuffs from Valsequillo basin in Central Mexico provides evidence on a magnetic link between lavas, ash tuffs and the underground volcanic conduit system. Paleomagnetic analyses show that lavas and ash tuffs carry reverse polarity magnetizations, which correlate with the inversely polarized dipolar magnetic anomaly over the volcano. The magnetizations in the lava and tuff show similar southward declinations and upward inclinations, supporting petrological inferences that the tuff was emplaced while still hot and indicating a temporal correlation for lava and tuff emplacement. Conduit geometry is one of the important controlling factors in eruptive dynamics of basaltic volcanoes. However volcanic conduits are often not, or only partly, exposed. Modeling of the dipolar anomaly gives a reverse polarity source magnetization associated with a vertical prismatic body with southward declination and upward inclination, which correlates with the reverse polarity magnetizations in the lava and tuff. The study documents a direct correlation of the paleomagnetic records with the underground magmatic conduit system of the monogenetic volcano. Time scale for cooling of the volcanic plumbing system involves a longer period than the one for the tuff and lava, suggesting that magnetization for the source of dipolar anomaly may represent a long time average as compared to the spot readings in the lava and tuff. The reverse polarity magnetizations in lava and tuff and in the underground source body for the magnetic anomaly are interpreted in terms of eruptive activity of Toluquilla volcano at about 1.3 Ma during the Matuyama reverse polarity C1r.2r chron.
3D Electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies
NASA Astrophysics Data System (ADS)
Deca, J.; Lapenta, G.; Divin, A. V.; Lembege, B.; Markidis, S.
Unlike the Earth and Mercury, our Moon has no global magnetic field and is therefore not shielded from the impinging solar wind by a magnetosphere. However, lunar magnetic field measurements made by the Apollo missions provided direct evidence that the Moon has regions of small-scale crustal magnetic fields, ranging up to a few 100km in scale size with surface magnetic field strengths up to hundreds of nanoTeslas. More recently, the Lunar Prospector spacecraft has provided high-resolution observations allowing to construct magnetic field maps of the entire Moon, confirming the earlier results from Apollo, but also showing that the lunar plasma environment is much richer than earlier believed. Typically the small-scale magnetic fields are non-dipolar and rather tiny compared to the lunar radius and mainly clustered on the far side of the moon. Using iPic3D we present the first 3D fully kinetic and electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies. We study the behaviour of a dipole model with variable surface magnetic field strength under changing solar wind conditions and confirm that lunar crustal magnetic fields may indeed be strong enough to stand off the solar wind and form a mini-magnetosphere, as suggested by MHD and hybrid simulations and spacecraft observations. 3D-PIC simulations reveal to be very helpful to analyze the diversion/braking of the particle flux and the characteristics of the resulting particles accumulation. The particle flux to the surface is significantly reduced at the magnetic anomaly, surrounded by a region of enhanced density due to the magnetic mirror effect. Second, the ability of iPic3D to resolve all plasma components (heavy ions, protons and electrons) allows to discuss in detail the electron physics leading to the highly non-adiabatic interactions expected as well as the implications for solar wind shielding of the lunar surface, depending on the scale size (solar wind protons typically have gyroradii larger than the magnetic anomaly scale size) and magnetic field strength. The research leading to these results has received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013) under the grant agreement SWIFF (project 2633430, swiff.eu). Cut along the dipole axis of the lunar anomaly, showing the electron density structure.
A Preliminary, Full Spectrum, Magnetic Anomaly Grid of the United States with Improved Long Wavelengths for Studying Continental Dynamics
NASA Astrophysics Data System (ADS)
Ravat, Dhananjay; Korhonen, Juha
Under an initiative started by Thomas G. Hildenbrand of the U.S. Geological Survey, we have improved the long-wavelength (50-2,500 km) content of the regional magnetic anomaly compilation for the conterminous United States by utilizing a nearly homogeneous set of National Uranium Resource Evaluation (NURE) magnetic surveys flown from 1975 to 1981. The surveys were flown in quadrangles of 2░ of longitude by 1░ of latitude with east-west flight lines spaced 4.8 to 9.6 km apart, north-south tie lines variably spaced, and a nominal terrain clearance of 122 m. The NURE surveys were processed using the Comprehensive Magnetic Field Model (Sabaka et al. 2004) to remove the core field for the epochs of the surveys. Many of the surveys used base-station magnetometers to remove external field variations. This NURE magnetic anomaly field is merged with the short-wavelengths from the North American Magnetic Anomaly Map (ca. 2002) to create a full spectrum database called NURE_NAMAM2008. http://pubs.usgs.gov/of/2009/1258/
Three-Dimensional Mapping of Magnetic Strata From Aeromagnetic Anomalies: The Deformed Neroly Formation South of Mt. Diablo, Northern California
NASA Astrophysics Data System (ADS)
Jachens, R. C.; Simpson, R. W.; Graymer, R. W.; Wentworth, C. M.
We apply direct inversion of aeromagnetic anomalies to analyze the subsurface 3D shape of the highly magnetic Miocene Neroly Formation, which consists largely of medium to coarse-grained andesitic sandstones containing abundant magnetite. The Neroly Formation is widespread in the eastern San Francisco Bay region, and locally is tightly folded and disrupted by faulting in the compressional regime related to the left-stepping (restraining) connection between the strike-slip Greenville and Concord Faults. The inversion technique is based on the conversion of the anomalies produced by a magnetic layer to their equivalent magnetic potential (psuedogravity) anomalies, manipulation of these anomalies to produce anomalies that would result from a half-space with a variable-depth top having the shape of the top surface of the layer, and then inverting these pseudogravity anomalies for the shape of that top surface. Assumptions include a constant layer thickness, uniform magnetization which implies a constant pseudodensity contrast, and a surface that is single-valued (no recumbent folds or strata repeated with depth). Constraints on 3D position are applied where the layer crops out or is at a depth known from well or other information. Application of this inversion technique to aeromagnetic anomalies over the Neroly Formation yields a complex top surface characterized by elongate overlapping troughs and structural highs, including the well-known Tassajara anticline and adjacent Sycamore Valley syncline. Troughs are true synclinal lows whereas the structural highs may be fold crests, steep truncated strata, and/or fault duplicated strata. The strongest deformation is confined to within ~7 km of the near-vertical overturned Neroly beds that crop out along the NE margin of the valley, and is characterized by four laterally overlapping, margin parallel structural highs and intervening troughs, each between 10 and 20 km in length. A fifth possible structural high lies farther SW. Separation between the highs increases southwestward across strike away from the valley margin. The gross structure implied by the inferred shape of the Neroly layer is that of a 7 km wide, NW oriented doubly- plunging synform with internal, high-amplitude 'wrinkles'. The technique shows promise for application to deformed magnetic layers in other regions. Elsewhere in California these include the Purisima Formation of the Hollister Valley and Santa Cruz Mountains, the Etchegoin Formation along the San Andreas Fault near Parkfield, and the Coastal Belt of the Franciscan Complex.
A Preliminary Full Spectrum Magnetic Anomaly Database of the United States With Improved Long Wavelengths for Studying Continental Dynamics
NASA Astrophysics Data System (ADS)
Ravat, D.; Sabaka, T.; Elshayat, A.; Aref, A.; Elawadi, E.; Kucks, R.; Hill, P.; Phillips, J.; Finn, C.; Bouligand, C.; Blakely, R. J.
Under an initiative started by Thomas G. Hildenbrand of the U. S. Geological Survey, we have improved the long-wavelength (50-2500 km) content of the regional magnetic anomaly compilation for the conterminous United States by utilizing a nearly homogeneous set of National Uranium Resource Evaluation (NURE) magnetic surveys flown from 1975 to 1981. The surveys were flown in quadrangles of 2░ of longitude by 1░ of latitude with E-W flight-lines spaced 4.8 to 9.6 km, N-S tie-lines variably spaced, and a nominal terrain clearance of 122 m. Many of the surveys used base-station magnetometers to remove external field variations. NURE surveys were originally processed with IGRF core-field models, which left behind non- uniform residual trends in the data and discontinuities at survey boundaries. In this study, in place of the IGRF/DGRF, we used a spatially and temporally continuous model of the magnetic field known as the Comprehensive Model (CM), which allowed us to avoid discontinuities at survey boundaries. The CM simultaneously models the core magnetic field and long-wavelength ionospheric and magnetospheric fields, along with their induced components in the earth. Because of the availability of base-stations for removing external fields, we removed only the core-derived geomagnetic field based on CM4 (spherical harmonic degree 13) for our compilation. The NURE data have short-wavelength (less than 30 km) noise due to cultural sources, base-station offsets, and residual external field effects. It is possible to reduce and even remove these defects by identifying and editing them and by applying leveling and micro-leveling. There are also many high resolution individual surveys over the U.S. which could be incorporated into the improved NURE database; however, this could take a few years. Therefore, we have created a preliminary full spectrum magnetic anomaly database by combining short-wavelength magnetic anomalies from the North American Magnetic Anomaly Map (NAMAM) and long-wavelength anomalies from NURE using a Gaussian filter centered at 50-km wavelength. We call this product the NURE-NAMAM2008 magnetic database. NURE- NAMAM2008 is useful for analyzing geodynamic aspects of the crustal and mantle magnetic field that require precise long-wavelength information; e.g., estimating Curie-temperature depths and constraining lithospheric temperatures. Preliminary studies show that the corrected long-wavelength components in NURE- NAMAM2008 lead to more realistic Curie depths for the average western U.S. crust.
Magsat and POGO magnetic anomalies over the Lord Howe Rise Evidence against a simple continental crustal structure
NASA Technical Reports Server (NTRS)
Frey, H.
Magsat average scalar and POGO reduced-to-pole magnetic anomaly data both show prominent positive signatures over the Lord Howe Rise. Although generally assumed to be continental in nature, the Lord Howe Rise cannot simply be submerged ordinary continental crust, which would produce a negative anomaly contrast with respect to the surrounding higher susceptibility oceanic crust. Three-dimensional modeling of the plateau, using the known crustal structure and assuming an induced origin for the satellite elevation anomaly, leads to a model in which the lowest crustal layer in an otherwise 'continental' crustal structure has an unusually high susceptibility in the range cgs 0.008-0.010 (SI 0.10-0.13). Replacement or alteration of the lowest layer by a high-susceptibility rock type may be related to the subsidence of the plateau.
Analysis of the Nuevo Leon Magnetic Anomaly and its possible relation to the Cerro Prieto magmatic-hydrothermal system
Goldstein, N.E.; Corrigan, D.J.; Wilt, M.J.
The broad dipolar magnetic anomaly whose positive peak is centered near Ejido Nuevo Leon, some 5 km east of the Cerro Prieto I power plant, has long been suspected to have a genetic relationship to the thermal source of the Cerro Prieto geothermal system. This suspicion was reinforced after several deep geothermal wells, drilled to depths of 3-3.5 km over the anomaly, intersected an apparent dike-sill complex consisting mainly of diabase but with minor rhyodacite. A detailed fit of the observed magnetic field to a computer model indicates that the source may be approximated by a tabular block 4 x 6 km in area, 3.7 km in depth, 2.3 km thick, and dipping slightly to the north. Mafic dike chips from one well, NL-1, were analysed by means of electron microprobe analyses which showed them to contain a titanomagnetite that is paramagnetic at in situ temperature conditions. As the dike mineralogy does not account for the magnetic anomaly, the magnetic source is believed to be a deeper, magnetite-rich assemblage of peridotite-gabbro plutons. The suite of igneous rocks was probably emplaced at a shallow depth in response to crustal extension and thinning brought on by en echelon strike-slip faulting. The bottom of the magnetic source body, at an estimated depth of 6 km, is presumed to be at or near that of the Curie isotherm (575/sup 0/C) for magnetite, the principal ferromagnetic mineral in peridotiticgabbroic rocks. The geological model derived from the magnetic study is generally supported by other geophysical data. In particular, earthquake data suggest dike injection is occurring at depths of 6-11 km in an area beneath the magnetic source. Thus, it is possible that heat for the geothermal field is being maintained by continuing crustal extension and magmatic activity.
Analysis of the Nuevo Leon magnetic anomaly and its possible relation to the Cerro Prieto magmatic-hydrothermal system
Goldstein, N.E.; Wilt, M.J.; Corrigan, D.J.
The broad dipolar magnetic anomaly whose positive peak is centered near Ejido Nuevo Leon, some 5 km east of the Cerro Prieto I Power Plant, has long been suspected to have a genetic relationship to the thermal source of the Cerro Prieto geothermal system. This suspicion was reinforced after several deep geothermal wells, drilled to depths of 3 to 3.5 km over the anomaly, intersected an apparent dike-sill complex consisting mainly of diabase but with minor rhyodacite. A detailed fit of the observed magnetic field to a computer model indicates that the source may be approximated by a tabular block 4 by 6 km in area, 3.7 km in depth, 2.3 km thick, and dipping slightly to the north. Mafic dike chips from one well, NL-1, were analyzed by means of electron microprobe analyses which showed tham to contain a titanomagnetite that is paramagnetic at in-situ temperature conditions. As the dike mineralogy does not account for the magnetic anomaly, the magnetic source is believed to be a deeper, magnetite-rich assemblage of peridotite-gabbro plutons. the suite of igneous rocks was probably passively emplaced at a shallow depth in response to crustal extension and thinning brought on by strike-slip faulting. The bottom of the magnetic source body, at an estimated depth of 6 km, is presumed to be at or near that of the Curie isotherm (575/sup 0/C) for magnetite, the principal ferromagnetic mineral in peridotitic-gabbroic rocks. The geological model derived from the magnetic study is generally supported by other geophysical data. In particular, earthquake data suggest dike injection is occurring at depths of 6 to 11 km in an area beneath the magnetic source. Thus, it is possible that heat for the geothermal field is being maintained by continuing crustal extension and magmatic activity.
Middle atmospheric electrodynamic modification by particle precipitation at the South Atlantic magnetic anomaly
NASA Technical Reports Server (NTRS)
Gonzalez, W. D.; Dutra, S. L. G.; Pinto, O., Jr.
Evidence for a localized middle atmospheric electrodynamic modification at low latitudes (southern Brazilian coast) of the South Atlantic Magnetic Anomaly (SAMA), in association with enhanced geomagnetic activity, are presented in a unified way combining recent observational efforts and related numerical studies. They involve a distortion effect in the fair weather electric field at balloon altitudes. This effect is attributed to a local intensification of energetic electron precipitation through a related middle atmospheric ionization enhancement and is elucidated by numeric simulation. From the electric field measurements and the numeric simulation, the intensification of precipitation is considered to occur in fairly narrow regions at the observed low L values (around L = 1.13) of the SAMA, with horizontal extensions of the order of a few hundred kilometers. A physical mechanism that could be responsible for this sort of intensification is suggested. Furthermore, a comparison of the phenomenon of middle atmospheric electrodynamic modification at the SAMA with a similar one at auroral latitudes, in response to enhanced solar and geomagnetic activity, is also given.
Dielectric and magnetic anomalies and spin frustration in hexagonal RMnO3 (R=Y, Yb, and Lu)
T. Katsufuji; S. Mori; M. Masaki; Y. Moritomo; N. Yamamoto; H. Takagi
Single crystals of hexagonal RMnO3 (R=Y, Yb, and Lu), where Mn ions form the triangular lattice, were investigated, focusing on their dielectric\\/magnetic anomalies as well as geometrical spin frustration. It is found that the ratio of a Weiss temperature to TN is ~10 in RMnO3, indicating the dominant role of strong geometrical frustration. The effect of geometrical frustration also appears
Energetic neutral atom imaging of the moon: Observation of a mini-magnetosphere above a lunar magnetic anomaly
NASA Astrophysics Data System (ADS)
Wieser, Martin; Barabash, Stas; Futaana, Yoshifumi; Holmstr÷m, Mats; Bhardwaj, Anil; Sridharan, R.; Dhanya, B.; Schaufelberger, Audrey; Wurz, Peter; Asamura, Kazushi
The Sub-keV Atom Reecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 space-craft has resulted in a comprehensive data set about interaction of solar wind with the lunar surface. When solar wind hits the lunar surface, it is partly backscattered as energetic neutral atoms. The intensity of the backscattered energetic neutral atoms is a measure of the intensity of the solar wind reaching the surface. We report on the imaging of a lunar magnetic anomalies in backscattered neutral hydrogen atoms. At the example of the strong magnetic anomaly near the Crisium antipode on the lunar farside we show that a partial void of the solar wind, a mini-magnetosphere, is formed above the magnetic anomaly. The mini-magnetosphere is 360 km across at the surface and surrounded by a 300-km-thick region of enhanced plasma ux that results from the solar wind owing around the mini-magnetosphere. These observations demonstrate a new observational technique to study airless bodies, imaging in ackscattered neutral atoms, and its application to a new class of objects, mini-magnetospheres.
Interpretation of the Total Magnetic Field Anomalies Measured by the CHAMP Satellite Over a Part of Europe and the Pannonian Basin
NASA Technical Reports Server (NTRS)
Kis, K. I.; Taylor, Patrick T.; Wittmann, G.; Toronyi, B.; Puszta, S.
In this study we interpret the magnetic anomalies at satellite altitude over a part of Europe and the Pannonian Basin. These anomalies are derived from the total magnetic measurements from the CHAMP satellite. The anomalies reduced to an elevation of 324 km. An inversion method is used to interpret the total magnetic anomalies over the Pannonian Basin. A three dimensional triangular model is used in the inversion. Two parameter distributions: Laplacian and Gaussian are investigated. The regularized inversion is numerically calculated with the Simplex and Simulated Annealing methods and the anomalous source is located in the upper crust. A probable source of the magnetization is due to the exsolution of the hematite-ilmenite minerals.
High-resolution Measurement Of Magnetic Anomalies With An Unmanned Airship
NASA Astrophysics Data System (ADS)
Petzke, M.; Hofmeister, P.; Auster, H.; Hoerdt, A.; Glassmeier, K.
High-resolution magnetic mapping of areas is a suitable way to determine location, geometry and physical parameters of disturbing objects that cause magnetic anomalies. Areas are often difficult to walk and handheld measurements can become costly. It can also be dangerous to enter areas where ordnance is suspected. In these cases it may be advantageous to use an aircraft to perform the measurement. We use a 6.5 m long unmanned airship. Compared to helicopters or gyrocopters, an advantage is that the damage in case of hazards is almost negligible. We made considerable efforts to construct a system that is easy to control without intense training under moderate wind conditions (up to 2 m/s wind speed). The airship has a mass of 10 kg and is powered by four electric motors with a maximum total power of 4.8 kW. Two of the rotors are used to control the altitude of the ship; the other two can be used to control direction and speed. The required energy is provided by four 4S1P Lithium-Polymer battery packs. Batteries are designed to provide a maximum of 125 A at 14.8 V. They have a capacity of 0.3 kWh and can be recharged in 20 minutes. The airship carries a differential GPS receiver that measures the position of the airship at 100 Hz with a precision of 10 cm. The distance to the ground is measured with ultrasonic sensors. A fluxgate magnetometer measures the magnetic field with an accuracy of 1 nT, also at 100 Hz. The flight path does not follow a rigid measuring grid but is a random walk, with roughly constant altitude to achieve a mean sensor position of 2 m above the ground. Thus, near-surface disturbing bodies are well resolved if their distance from each other is greater than 4 m. First measurements demonstrate the feasibility of the system. Future applications will be mid-scale measurements which are too large or too cumbersome for handheld measurements, and too small to justify the use of a manned helicopter.
Magnetic Properties from the East Rift Zone of Kilauea: Implications for the Sources of Aeromagnetic Anomalies over Hawaiian Volcanoes
NASA Astrophysics Data System (ADS)
Rosenbaum, J. G.; Reynolds, R. L.; Trusdell, F.; Kauahikaua, J. P.
Aeromagnetic studies of the Island of Hawaiæi provide insights into geologic structure. High-amplitude short-wavelength anomalies occur along the southwest and east rift zones (ERZ) of Kilauea, the youngest volcano on the island. These anomalies have been attributed to contrast between highly magnetic intrusions at depth and less magnetic altered rocks. Anomalies along rift zones of the older volcanoes on the island have lower amplitude or are lacking. To better understand the origin of the high-amplitude anomalies, magnetic properties were obtained for samples from existing 1.7 - 2.0 km deep bore holes located on the ERZ 30 - 40 km east of the summit of Kilauea but not over associated aeromagnetic maxima. The bore holes penetrate subaerial flows, submarine flows, and intrusions. Average values of total magnetization (MT) based on measurements of magnetic susceptibility (?) and NRM range from ~5.5 A/m for terrestrial flows to ~10 A/m for pillow basalts. MT of intrusions varys with depth. In shallow intrusions (< ~850 m depth), MT averages ~12 A/m, whereas in deep intrusions MT averages ~9 A/m. In contrast, to flows and shallow intrusions, deep intrusions have unstable NRMs that commonly diminish >80% during AF demagnetization at a peak field of 10 mT. The NRMs of deep intrusions were probably affected by drilling, and consequently their laboratory MT values may be much larger than in situ values. Therefore, the deep intrusions are more likely to have relatively low magnetizations rather than the high magnetizations that were used in previous aeromagnetic models.Č The contrast in NRM stability for shallow and deep intrusions reflects differences in magnetic grain size. The average ARM/? for shallow intrusions is ~4 times that of deep intrusions. Also, deep intrusions have high Curie temperatures (TC>550 ░C) whereas shallow intrusions commonly have low TC, averaging ~165 ░C. The fine magnetic grain size and low TC of shallow intrusions are interpreted as the result of rapid crystallization after degassing. Limited oxygen in the subsurface environment would inhibit formation of ilmenite and thereby preserve high Ti-magnetite.Č After heating in air to ~300 ░C and above, TC and room-temperature saturation magnetization (MS) of shallow intrusions increase dramatically. On average, MS at ~25 ░C of shallow intrusions increases by a factor of 2.4 after heating to 600 ░C. Susceptibility increases similarly after heating in air but does not increase after heating in argon. In the presence of oxygen, Ti apparently separates even at moderate temperature, raising the TC and thereby MS and ?. If NRM increases in a similar manner (as is reasonable if the fine magnetic grain size is preserved), these rocks could attain MT in excess of 20 - 25 A/m. We speculate that this process occurs naturally in proximity to vents where repeated intrusions reheated (or maintained) these rocks to moderate temperatures. If such rocks are the source of anomalies along the Kilauea rift zones then destruction of the fine-grained titanomagnetite over time could explain the lack of prominent anomalies along older rift zones.
Ultralow frequency (ULF) magnetic field anomalies observed at Agra and their relation to moderate seismic activities in Indian region
Vinod Kushwah; Vikram Singh; Birbal Singh; M. Hayakawa
A three-component search coil magnetometer (f=0.01¢30Hz) has been employed to monitor the earthquake-induced magnetic field anomalies at Agra (Geograph. lat. 27.2░N, long. 78░E), India. The results show that the magnetic field amplitudes of the three components are normally low in the range of 0.03¢0.7nT, but they are occasionally enhanced to large values in the range of 0.3¢5nT (the X-component along
Airborne gamma-ray and magnetic anomaly signatures of serpentinite in relation to soil geochemistry, northern California
McCafferty, A.E.; Van Gosen, B. S.
Serpentinized ultramafic rocks and associated soils in northern California are characterized by high concentrations of Cr and Ni, low levels of radioelements (K, Th, and U) and high amounts of ferrimagnetic minerals (primarily magnetite). Geophysical attributes over ultramafic rocks, which include airborne gamma-ray and magnetic anomaly data, are quantified and provide indirect measurements on the relative abundance of radioelements and magnetic minerals, respectively. Attributes are defined through a statistical modeling approach and the results are portrayed as probabilities in chart and map form. Two predictive models are presented, including one derived from the aeromagnetic anomaly data and one from a combination of the airborne K, Th and U gamma-ray data. Both models distinguish preferential values within the aerogeophysical data that coincide with mapped and potentially unmapped ultramafic rocks. The magnetic predictive model shows positive probabilities associated with magnetic anomaly highs and, to a lesser degree, anomaly lows, which accurately locate many known ultramafic outcrops, but more interestingly, locate potentially unmapped ultramafic rocks, possible extensions of ultramafic bodies that dip into the shallow subsurface, as well as prospective buried ultramafic rocks. The airborne radiometric model shows positive probabilities in association with anomalously low gamma radiation measurements over ultramafic rock, which is similar to that produced by gabbro, metavolcanic rock, and water bodies. All of these features share the characteristic of being depleted in K, Th and U. Gabbro is the only rock type in the study area that shares similar magnetic properties with the ultramafic rock. The aerogeophysical model results are compared to the distribution of ultramafic outcrops and to Cr, Ni, K, Th and U concentrations and magnetic susceptibility measurements from soil samples. Analysis of the soil data indicates high positive correlation between magnetic susceptibilities and concentration of Cr and Ni. Although the study focused on characterizing the geophysical properties of ultramafic rocks and associated soils, it has also yielded information on other rock types in addition to ultramafic rocks, which can also locally host naturally-occurring asbestos; specifically, gabbro and metavolcanic rocks.
Small non-axisymmetric magnetic fields are known to cause serious loss of stability in tokamaks leading to loss of confinement and abrupt termination of plasma current (disruptions). The best known examples are the locked mode and the resistive wall mode. Understanding of the underlying field anomalies (departures in the hardware-related fields from ideal toroidal and poloidal fields on a single axis) and the interaction of the plasma with them is crucial to tokamak development. Results of both locked mode experiments and resistive wall mode experiments done in DIII-D tokamak plasmas have been interpreted to indicate the presence of a significant anomalous field. New measurements of the magnetic field anomalies of the hardware systems have been made on DIII-D. The measured field anomalies due to the plasma shaping coils in DIII-D are smaller than previously reported. Additional evaluations of systematic errors have been made. New measurements of the anomalous fields of the ohmic heating and toroidal coils have been added. Such detailed in situ measurements of the fields of a tokamak are unique. The anomalous fields from all of the coils are one third of the values indicated from the stability experiments. These results indicate limitations in the understanding of the interaction of the plasma with the external field. They indicate that it may not be possible to deduce the anomalous fields in a tokamak from plasma experiments and that we may not have the basis needed to project the error field requirements of future tokamaks.
A closer look at remanence-dominated aeromagnetic anomalies: Rock magnetic properties and magnetic mineralogy of the Russell Belt microcline-sillimanite gneiss, northwest Adirondack Mountains, New York
Suzanne A. McEnroe; Laurie L. Brown
A large, distinct negative aeromagnetic anomaly of over 2000 nT associated with microcline-sillimanite-quartz gneisses in the Russell area, northwest Adirondack Mountains, was previously shown to be remanence-dominated, although the carriers of remanence were not well documented. Russell Belt gneisses have a strong natural remanent magnetization with steep remanence directions, D=263░, I=-58░, an average intensity of 3.6 A\\/m, and typical susceptibilities
Analysis of isolated magnetic anomalies and magnetic signatures of impact craters: Evidence for a core dynamo in the early history of the Moon
NASA Astrophysics Data System (ADS)
Arkani-Hamed, Jafar; Boutin, Daniel
We investigate the possibility that a strong core dynamo of the Moon has magnetized the lunar crust. The magnetic data from two missions, Lunar Prospector and Kaguya, are used and the magnetic fields of two different features are examined: The isolated small magnetic source bodies with almost no topographic signatures, and the impact craters with diameters larger than 100 km. Five data sets are examined separately for each of the isolated magnetic anomalies: the r, ?, and ? components of the Lunar Prospector data, the r component of a 150-degree spherical harmonic model of the lunar magnetic field, and the r component of the Kaguya data. The r component of the Lunar Prospector data is also used to derive the magnetic field over the impact craters. We conclude that most of the ancient lunar far side crust is heterogeneously magnetized with coherency wavelength about a few hundred km. The paleomagnetic north poles determined from modeling the magnetic field of both features show some clustering whereas the source bodies are widely distributed, suggesting that the magnetizing field may have been a core dynamo field. Paleointensity data suggest that the core field intensity was at least 1 mT at the core mantle boundary. There is also evidence for core field reversals, because further clustering occurs when the south poles of some features are considered.
Pacific-North American plate motion from very long baseline interferometry compared with motion inferred from magnetic anomalies, transform faults, and earthquake slip vectors
NASA Technical Reports Server (NTRS)
Argus, Donald F.; Gordon, Richard G.
Geodetic VLBI measurements were used to test whether the Pacific-North American plate velocity averaged over several years of direct observation (1984-1987) equals that averaged over millions of years. It was also tested whether this velocity parallels the San Andreas fault, transform faults and earthquake slip vectors in the Gulf of California, and earthquake slip vectors along the Queen Charlotte fault, along the Alaskan peninsula, and along the Kamchatkan peninsula. The VLBI data provide an estimate of the direction of plate motion that is independent of estimates from fault azimuths and earthquake slip vectors. The Euler vector determined from VLBI was found to be nearly identical to the Euler vector of plate motion model NUVEL-1, which is based on the trends of transform faults, earthquake slip vectors, and spreading rates from marine magnetic anomalies that average motion since 3 Ma. The velocity between the Pacific and North American plates averaged over the past several years equals or nearly equals its velocity averaged over the past several million years, the difference along their boundary nowhere exceeding 4 + or - 7 mm/yr.
Direct evidence from anisotropy of magnetic susceptibility for lateral melt migration at superfast spreading centers
Robert J. Varga; Andrew J. Horst; Jeffrey S. Gee; Jeffrey A. Karson
Rare, fault-bounded escarpments expose natural cross sections of ocean crust in several areas and provide an unparalleled opportunity to study the end products of tectonic and magmatic processes that operated at depth beneath oceanic spreading centers. We mapped the geologic structure of ocean crust produced at the East Pacific Rise (EPR) and now exposed along steep cliffs of the Pito
Electromagnetic particle-in-cell simulations of the solar wind interaction with lunar magnetic anomalies
NASA Astrophysics Data System (ADS)
Deca, Jan; Divin, Andrey; Lapenta, Giovanni; LembĶge, Bertrand; Markidis, Stefano; Horßnyi, Mihßly
We present the first three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier MHD and hybrid simulations, the fully kinetic nature of iPic3D allows to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe the general picture of the interaction of a dipole model centred just below the lunar surface under various solar wind and plasma conditions and focus on the kinetic effects. It is shown that the configuration is dominated by electron motion, because the LMA scale size is small with respect to the gyroradius of the solar wind ions. Driven by strong pressure anisotropies, the mini-magnetosphere is also unstable over time, leading to only temporal shielding of the surface underneath. Our work opens new frontiers of research toward a deeper understanding of LMAs and is ideally suited to be compared with field or particle observations from spacecraft such as Kaguya (SELENE), Lunar Prospector or ARTEMIS. The ability to evaluate the implications for future lunar exploration as well as lunar science in general hinges on a better understanding of LMAs. This research has received funding from the European Commission's FP7 Program with the grant agreement SWIFF (project 2633430, swiff.eu) and EHEROES (project 284461, www.eheroes.eu). The simulations were conducted on the computational resources provided by the PRACE Tier-0 project 2011050747 (Curie supercomputer). This research was supported by the Swedish National Space Board, Grant No. 136/11. JD has received support through the HPC-Europa2 visitor programme (project HPC08SSG85) and the KuLeuven Junior Mobility Programme Special Research Fund.
Frequency of septum pellucidum anomalies in non-psychotic population: a magnetic resonance imaging study.
Aldur, M M; G³rcan, F; Ba?ar, R; Ak?it, M D
This prospective MRI investigation was performed to investigate septum pellucidum (SP) anomalies in 505 (242 male, 263 female) non-psychotic persons. The mean age of the population was 39.179 +/- 0.904 (40.461 +/- 1.395 male, 38 +/- 1.166 female). There was no significant difference between the means of age in the male and female groups (t-test, DF = 479, p > 0.05). The SP anomalies were classified as cavitation anomalies (Type I) and absence of the SP (Type II). Type I anomalies were subdivided into four groups as isolated cavum septi pellucidi (Ia), cavum septi pellucidi et cavum vergae (Ib), anterior small triangular cavities (Ic), and cysts of the SP (Id). The incidences of the anomalies (Type I + Type II) were 17.31%, 1.89%, 7.55%, 3.53%, 7%, 4.55%, 4.76% and 6.06% for the age groups of 0-9, 10-19, 20-29, 30-39, 40-49, 50-59, 60-69 and 70-79 years respectively. The anomalies were very significantly more frequent in the 0-9 years age group than in the other age groups (chi 2 = 9.7858, DF = 1, p < 0.05). The incidences of the anomalies (Type I + Type II) were 6.34%, 5.37%, 7.22% for the whole, male, and female populations, respectively. These values were 1.39%, 1.65% and 1.14% for Type Ia, 2.77%, 2.89% and 2.66% for Type Ib, and 1.78%, 0.83% and 2.66% for Type Ic. Both Type Id and II anomalies were determined in only one case for each group in females (0.2%). There was no significant difference between the incidences of the anomalies in both sexes (chi 2 = 0.45, DF = 1, p > 0.05). PMID:10399212
Deep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone and implications for the geomagnetic polarity reversal timescale and
., 113, B07110, doi:10.1029/2007JB005527. 1. Introduction [2] The Jurassic period appears to be a time of the Jurassic magnetic field. It was once suggested that this Jurassic ``Quiet Zone'' (JQZ) reflects a periodDeep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone and implications
Magnetic anomalies in the spin-chain system Sr3Cu1-xZnxIrO6
NASA Astrophysics Data System (ADS)
Niazi, Asad; Sampathkumaran, E. V.; Paulose, P. L.; Eckert, D.; Handstein, A.; M³ller, K.-H.
We report the results of ac and dc magnetization (M) and heat-capacity (C) measurements on the solid solution Sr3Cu1-xZnxIrO6. While the Zn end member is known to form in a rhombohedral pseudo-one-dimensional K4CdCl6 structure with an antiferromagnetic ordering temperature of (TN=)19 K, the Cu end member has been reported to form in a monoclinically distorted form with a Curie temperature of (TC=)19 K. The magnetism of the Zn compound is found to be robust to synthetic conditions and is broadly consistent with the behavior known in the literature. However, we find a lower magnetic ordering temperature (To) for the Cu compound with a slight variation in heat treatment conditions, thereby suggesting that To is sensitive to synthetic conditions. However, the Cu sample exhibits spin-glass-like behavior at low temperatures, judged by a frequency dependence of ac magnetic susceptibility and a broadening of the C anomaly at the onset of magnetic ordering, in sharp contrast to earlier proposals. We attempt to relate it to differences in crystallographic details. Small applications of magnetic field (H), however, drive this system to ferromagnetism unlike in Zn compound as inferred from the M data. Small substitutions for Cu/Zn (x=0.75 or 0.25) significantly depress magnetic ordering; in other words, To varies nonmonotonically with x (To~6,3, and 4 K for x=0.25, 0.5, and 0.67, respectively). These findings imply interesting x-T-H magnetic phase diagram for this compound. In addition, we conclude that the present solid-state solution may be well suited for future studies to probe magnetic competition phenomena in a chain system.
High-resolution near-bottom vector magnetic anomalies over Raven Hydrothermal Field, Endeavour Segment, Juan de Fuca Ridge
NASA Astrophysics Data System (ADS)
Tivey, Maurice A.; Johnson, H. Paul; Salmi, Marie S.; Hutnak, Michael
High-resolution, near-bottom vector magnetic data were collected by remotely operated vehicle Jason over the Raven hydrothermal vent field (47░57.3'N 129░5.75'W) located north of Main Endeavour vent field on the Endeavour segment of the Juan de Fuca Ridge. The survey was part of a comprehensive heat flow study of the Raven site using innovative thermal blanket technology to map the heat flux and crustal fluid pathways around a solitary hydrothermal vent field. Raven hydrothermal activity is presently located along the western axial valley wall, while additional inactive hydrothermal deposits are found to the NW on the upper rift valley wall. Magnetic inversion results show discrete areas of reduced magnetization associated with both active and inactive hydrothermal vent deposits that also show high conductive heat flow. Higher spatial variability in the heat flow patterns compared to the magnetization is consistent with the heat flow reflecting the currently active but ephemeral thermal environment of fluid flow, while crustal magnetization is representative of the static time-averaged effect of hydrothermal alteration. A general NW to SE trend in reduced magnetization across the Raven area correlates closely with the distribution of hydrothermal deposits and heat flux patterns and suggests that the fluid circulation system at depth is likely controlled by local crustal structure and magma chamber geometry. Magnetic gradient tensor components computed from vector magnetic data improve the resolution of the magnetic anomaly source and indicate that the hydrothermally altered zone directly beneath the Raven site is approximately 15 ū 106 m3 in volume.
An annular high-current electron beam with an energy spread in a coaxial magnetically insulated diode
Grishkov, A. A., E-mail: firstname.lastname@example.com; Pegel, I. V. [Russian Academy of Sciences, Institute of High Current Electronics, Siberian Branch (Russian Federation)] [Russian Academy of Sciences, Institute of High Current Electronics, Siberian Branch (Russian Federation)
An elementary theory of an annular high-current electron beam in a uniform transport channel and a coaxial magnetically insulated diode is generalized to the case of counterpropagating electron beams with a spread over kinetic energies. Expressions for the sum of the absolute values of the forward and backward currents in a uniform transport channel and for the flux of the longitudinal component of the generalized momentum in a coaxial magnetically insulated diode as functions of the maximum electron kinetic energy are derived for different values of the relative width of the energy distribution function. It is shown that, in a diode with an expanding transport channel and a virtual cathode limiting the extracted current, counterpropagating particle flows are established between the cathode and the virtual cathode within a certain time interval after the beginning of electron emission. The accumulation of electrons in these flows is accompanied by an increase in their spread over kinetic energies and the simultaneous decrease in the maximum kinetic energy. The developed model agrees with the results of particle-in-cell simulations performed using the KARAT and OOPIC-Pro codes.
SST Anomalies + Wind Anomalies
NSDL National Science Digital Library
Greg Shirah
Sea surface temperature (SST) anomalies and sea surface wind anomalies show the development of the 2002-2003 El Nino based on data from NASAs Aqua and QuikSCAT spacecraft. The wind data has been processed using the Variational Analysis Method (VAM).
Petrologic and geophysical study of the source of long wavelength crustal magnetic anomalies
NASA Technical Reports Server (NTRS)
Marsch, B.; Schlinger, C. M.
The magnetic mineralogy and magnetic signature of banded ion formations, diagenetic (unmetamorphosed) and low grade banded iron formations, high-grade mineralogy, and phase equilibria of magnetite inorogenic magmers are discussed.
Aeromagnetic anomalies and discordant lineations beneath the Niger Delta: Implications for new fracture zones and multiple sea-floor spreading directions in the meso-Atlantic' Gulf of Guinea cul-de-sac
Babalola, O.O.; Gipson, M. Jr. (Univ. of South Carolina, Columbia (United States))
An aeromagnetic contour map compiled over shallow water and onshore portions of the Nigerian continental margin, shows several elongate, long-wavelength anomaly closures with some alternating polarity, separated by steep gradient, NE lineations. The lineations are interpreted as new fracture zones or extensions of previously mapped ones. The NE trend in the western delta region is concordant with the fracture zone trends of the deeper Gulf of Guinea. Aeromagnetic lineations of the SE Niger Delta Basin however, discordantly trend ENE. Their termination against the former, is interpreted as evidence of early sea-floor spreading in a ENE-WSW direction in addition to the well documented NE-SW spreading of the Gulf of Guinea and the rest of the meso-Atlantic sea-floor; The geophysical crustal structure indicate the existence of two Early Cretaceous triple junctions beneath the Niger Delta Basin. The two triple-junctions further support the hypothesis that the African continent was a multi-plate system (in the Niger Delta region) during the early opening of the Atlantic.
The Longitudinal Variation of Night Airglow Intensity in the Region of the South Atlantic Magnetic Anomaly
J. A. Greenspan; C. A. Stone
Shipboard measurements made in the regions o.f the South Atlantic anomaly at a geomagnetic latitude corresponding to L -- 1.80 suggest the existence of a region of in- creased airglow activity near 6? ° geomagnetic longitude. We attempt to show that this anom- aly is not temporal in nature nor due to the effects of high-Mtitude nuclear tests carried out
Magnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5
NASA Astrophysics Data System (ADS)
Basu, Tathamay; Mohapatra, Niharika; Singh, Kiran; Sampathkumaran, E. V.
We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE) behaviour of a Haldane spin-chain compound containing light rare-earth ion, Nd2BaNiO5, in detail, as a function of temperature (T) and magnetic field (H) down to 2 K. In addition to the well-known long range antiferromagnetic order setting in at (TN = ) 48 K as indicated in dc magnetization (M), we have observed another magnetic transition near 10 K; this transition appears to be of a glassy-type which vanishes with a marginal application of external magnetic field (even H = 100 Oe). There are corresponding anomalies in dielectric constant (?') as well with variation of T. The isothermal M(H) curves at 2 and 5 K reveal the existence of a magnetic-field induced transition around 90 kOe; the isothermal ?'(H) also tracks such a metamagnetic transition. These results illustrate the MDE coupling in this compound. Additionally, we observe a strong frequency dependence of a step in ?'(T) with this feature appearing around 25-30 K for the lowest frequency of 1 kHz, far below TN. This is attributed to interplay between crystal-field effect and exchange interaction between Nd and Ni, which establishes the sensitivity of dielectric measurements to detect such effects. Interestingly enough, the observed dispersions of the ?'(T) curves is essentially H-independent in the entire T-range of measurement, despite the existence of MDE coupling, which is in sharp contrast with other heavy rare-earth members in this series.
Magnetic resonance imaging of cerebral anomalies in subjects with resistance to thyroid hormone
Leonard, C.M. [Univ. of Florida Health Science Center, Gainesville, FL (United States); Hauser, P.; Weintraub, B.D. [National Institute of Mental Health, Bethesda, MD (United States)]|[Baltimore VA Medical Center, MD (United States)] [and others
Resistance to thyroid hormone (RTH) is an autosomal dominant disease caused by mutations in the human thyroid receptor beta gene on chromosome 3. Individuals with RTH have an increased incidence of attention deficit hyperactivity disorder (ADHD). The purpose of this study was to search for developmental brain malformations associated with RTH. Forty-three subjects (20 affected males [AM], 23 affected females [AF]) with resistance to thyroid hormone and 32 unaffected first degree relatives (18 unaffected males [UM], 14 unaffected females [UF]) underwent MRI brain scans with a volumetric acquisition that provided 90 contiguous 2 mm thick sagittal images. Films of six contiguous images beginning at a standard sagittal position lateral to the insula were analyzed by an investigator who was blind with respect to subject characteristics. The presence of extra or missing gyri in the parietal bank of the Sylvian fissure (multimodal association cortex) and multiple Heschl`s transverse gyri (primary auditory cortex) were noted. There was a significantly increased frequency of anomalous Sylvian fissures in the left hemisphere in males with RTH (AM: 70%; AF: 30%; UM: 28% UF: 28%). Also, there was an increased frequency of anomalous Sylvian fissures on the left combined with multiple Heschl`s gyri in either hemisphere in males with RTH (AM: 50%; AF: 9%; UM: 6%; UF: 0%). However, RTH subjects with anomalies did not have an increased frequency of ADHD as compared with RTH subjects with no anomalies. Abnormal thyroid hormone action in the male fetus early during brain development may be associated with grossly observable cerebral anomalies of the left hemisphere. The effects of mutations in the thyroid receptor beta gene provide a model system for studying the complex interaction of genetic and non-genetic factors on brain and behavioral development. 19 refs., 2 figs., 2 tabs.
A closer look at remanence-dominated aeromagnetic anomalies: Rock magnetic properties and magnetic mineralogy of the Russell Belt microcline-sillimanite gneiss, northwest Adirondack Mountains, New York
NASA Astrophysics Data System (ADS)
McEnroe, Suzanne A.; Brown, Laurie L.
A large, distinct negative aeromagnetic anomaly of over 2000 nT associated with microcline-sillimanite-quartz gneisses in the Russell area, northwest Adirondack Mountains, was previously shown to be remanence-dominated, although the carriers of remanence were not well documented. Russell Belt gneisses have a strong natural remanent magnetization with steep remanence directions, D=263░, I=-58░, an average intensity of 3.6 A/m, and typical susceptibilities of 10-4SI. The remanence is thermochemical in origin, acquired during cooling from peak metamorphic conditions of 650░-750░C during the Ottawan Orogen (1050-1080 Ma). The reversed polarity of remanence reflects a reversed paleofield, rather than self-reversed, contrary to earlier suggestions. The gneisses contain up to 3% oxide, predominantly metamorphic titanohematite, which accounts for the low susceptibility values and highly stable remanence. Optical observations show titanohematite grains with multiple generations of ilmenite, pyrophanite, rutile, and spinel exsolution lamellae. Microprobe analyses confirm titanohematite compositions ranging from 72 to 97%Fe2O3, with hematite83 being most typical. In rare samples, inclusions of magnetite were identified. The ubiquitous presence of titanohematite, and the rare occurrence of magnetite, is supported by thermal and alternating field demagnetization studies, saturation magnetization measurements, hysteresis properties, temperature-hysteresis studies, and low-temperature remanence measurements. Numerous crustal granulites have titanohematite as part of the oxide assemblage, and this may contribute a strong remanent component to what have previously been considered to be solely induced anomalies.
GMinterp, A Matlab Based Toolkit for Gravity and Magnetic Data Analysis: Example Application to the Airborne Magnetic Anomalies of Biga Peninsula, NW Turkey
NASA Astrophysics Data System (ADS)
Ekinci, Y. L.; Yi?itba?, E.
The analysis of gravity and magnetic field methods is becoming increasingly significant for the earth sciences as a whole and these potential field methods efficiently assist in working out both shallow and deep geologic problems and play important role on modeling and interpretation procedures. The main advantage of some gravity and magnetic data processing techniques is to present the subtle details in the data which are not clearly identified in anomaly maps, without specifying any prior information about the nature of the source bodies. If the data quality permits, many analyzing techniques can be carried out that help to build a general understanding of the details and parameters of the shallower or deeper causative body distributions such as depth, thickness, lateral and vertical extensions. Gravity and magnetic field data are usually analyzed by means of analytic signal (via directional derivatives) methods, linear transformations, regional and residual anomaly separation techniques, spectral methods, filtering and forward and inverse modeling techniques. Some commercial software packages are commonly used for analyzing potential field data by employing some of the techniques specified above. Additionally, many freeware and open-source codes can be found in the literature, but unfortunately they are focused on special issues of the potential fields. In this study, a toolkit, that performs numerous interpretation and modeling techniques for potential field data, is presented. The toolkit, named GMinterp, is MATLAB-based consisting of a series of linked functions along with a graphical user interface (GUI). GMinterp allows performing complex processing such as transformations and filtering, editing, gridding, mapping, digitizing, extracting cross-sections, forward and inverse modeling and interpretation tasks. The toolkit enables to work with both profile and gridded data as an input file. Tests on the theoretically produced data showed the reliability of developed toolkit. Additionally some experiments on real data sets were performed to interpret the geological structure of Biga Peninsula, NW part of Anatolia, Turkey. Keywords: GMinterp, GUI, airborne magnetic data, geology, Biga Peninsula
Field induced changes in cycloidal spin ordering and coincidence between magnetic and electric anomalies in BiFeO3 multiferroic
NASA Astrophysics Data System (ADS)
Andrzejewski, B.; Molak, A.; Hilczer, B.; Budziak, A.; Bujakiewicz-Koro?ska, R.
The temperature dependences of ZFC and FC magnetization was measured for BiFeO3 ceramics in magnetic field up to ?0H=10 T and in temperatures from the range 2-1000 K. The antiferromagnetic order was detected from the hysteresis loops below the Nķel temperature TN=646 K. The anomaly in M(H), which occurred in the low magnetic field range, was ascribed to the field-induced transition from circular cycloid to the anharmonic cycloid. At high field limit, we observed the field-induced transition to the homogeneous spin order. From the M(H) dependence, we deduced that the spin cycloid becomes anharmonic above the field Ha that caused nonlinear magnetization. The cycloid vanished above the field Hc and the system again exhibited linear magnetization M(H). The anomalies in the electric properties, ??(T), tan?(T), and ?(T), which are manifested within the 635-670 K range, coincide with the anomaly in the temperature dependence of magnetization M(T), which occurs in the vicinity of TN=646 K. We propose that this coincidence can be explained by the critical behavior of chemical potential ?S, related to the magnetic phase transition.
Interpreting Mars ionospheric anomalies over crustal magnetic field regions using a 2-D ionospheric model
NASA Astrophysics Data System (ADS)
Matta, Majd; Mendillo, Michael; Withers, Paul; Morgan, Dave
spatially inhomogeneous, small-scale crustal magnetic fields of Mars influence the escape of planetary atmospheric species and the interaction of the solar wind with the ionosphere. Understanding the plasma response to crustal magnetic field regions can therefore provide insight to ionospheric structure and dynamics. To date, several localized spatial structures in ionospheric properties that have been observed over regions of varying magnetic field at Mars have yet to be explained. In this study, a two-dimensional ionospheric model is used to simulate the effects of field-aligned plasma transport in regions of strong crustal magnetic fields. Resulting spatial and diurnal plasma distributions are analyzed and found to agree with observations from several spacecraft and offer compelling interpretations for many of the anomalous ionospheric behaviors observed at or near regions of strong crustal magnetic fields on Mars.
Ocean-continent-transition at magma poor rifted margins, the magnetic signature of a magmatic breakup?
NASA Astrophysics Data System (ADS)
Bronner, A.; Sauter, D.; Manatschal, G.; Peron-Pinvidic, G.; Munschy, M.
Magnetic anomalies identified on the Zone of Exhumed Continental Mantle (ZECM) in the Iberia and Newfoundland margins have been interpreted as seafloor spreading anomalies. These magnetic anomalies do not lie on oceanic crust but within the transitional domain mainly composed of exhumed mantle intruded by magmatic bodies. The weakness of these anomalies, the absence of agreement about nature and depth of the sources and some inconsistencies between kinematic reconstructions and geological constraints suggest that these anomalies may not be standard seafloor spreading anomalies. Moreover, on both seaward edges of the ZECMs, seismic reflexion and refraction and ODP data show an unusual morphology characterized by a topographic high, a thicker crust and surface lava flows, all associated with a major sediment unconformity (dated at the Aptian/Albian transition). This structure called ½ outer high ╗ corresponds with the main magnetic anomaly (the J anomaly) observed in the transitional area of both margins. Here we present an alternative model based on forward modelling of magnetic anomaly constrained by seismic refraction and drill hole data. We show that the magnetic anomaly profiles across the ZECMs can be explained without inversions of the Earth magnetic field. We use only positive magnetizations assuming that magmatic and tectonic processes related to the J anomaly occur during the quiet Cretaceous magnetic period. Thus, we propose that the J anomaly results from an excess magma event associated with the emplacement of underplated magmatic bodies and surface lava flows respectively below and above the pre-existing exhumed mantle. The unusual high and variable amplitude of the J anomaly is then explained by the repartition of the magmatic and volcanic material in the serpentinized bedrock. We propose that this magmatic event is at the origin of continental breakup that occurred at about 112 Ma leading to the transition from the exhumation phase to seafloor spreading.
Spread-F during the magnetic storm of 22 January 2004 at low latitudes: Effect of IMF-Bz in relation to local sunset time
NASA Astrophysics Data System (ADS)
Rastogi, R. G.; Chandra, H.; Janardhan, P.; Hoang, Thai Lan; Condori, Louis; Pant, T. K.; Prasad, D. S. V. V. D.; Reinisch, B.
The paper describes the results of spread-F at low latitude stations around the world during the magnetic storm starting at 0130 UT on 22 January 2004. The storm can be divided into two phases, first phase up to 1000 UT when interplanetary magnetic field IMF-Bz was highly fluctuating around a small positive value and the second phase after a sudden large southward turning of IMF-Bz at 1030 UT. The first phase produced strong spread-F at Jicamarca, Sao Luis, and Ascension Island and caused complete inhibition of spread-F at Thumba and Waltair in India. It generated weak spread-F at Ho Chi Minh City in Vietnam and strong spread-F at Hainan and Chung Li. The strong spread-F at Hainan and Chung Li were caused by the positive IMF-Bz during the first phase of the storm and not by the negative pulse of IMF-Bz at 1000 UT.
The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies
NASA Astrophysics Data System (ADS)
Blakely, Richard J.; Sherrod, Brian L.; Weaver, Craig S.; Wells, Ray E.; Rohay, Alan C.
The Yakima fold and thrust belt (YFTB) in central Washington has accommodated regional, mostly north-directed, deformation of the Cascadia backarc since prior to emplacement of Miocene flood basalt of the Columbia River Basalt Group (CRBG). The YFTB consists of two structural domains. Northern folds of the YFTB strike eastward and terminate at the western margin of a 20-mGal negative gravity anomaly, the Pasco gravity low, straddling the North American continental margin. Southern folds of the YFTB strike southeastward, form part of the Olympic-Wallowa lineament (OWL), and pass south of the Pasco gravity low as the Wallula fault zone. An upper crustal model based on gravity and magnetic anomalies suggests that the Pasco gravity low is caused in part by an 8-km-deep Tertiary basin, the Pasco sub-basin, abutting the continental margin and concealed beneath CRBG. The Pasco sub-basin is crossed by north-northwest-striking magnetic anomalies caused by dikes of the 8.5 Ma Ice Harbor Member of the CRBG. At their northern end, dikes connect with the eastern terminus of the Saddle Mountains thrust of the YFTB. At their southern end, dikes are disrupted by the Wallula fault zone. The episode of NE-SW extension that promoted Ice Harbor dike injection apparently involved strike-slip displacement on the Saddle Mountains and Wallula faults. The amount of lateral shear on the OWL impacts the level of seismic hazard in the Cascadia region. Ice Harbor dikes, as mapped with aeromagnetic data, are dextrally offset by the Wallula fault zone a total of 6.9 km. Assuming that dike offsets are tectonic in origin, the Wallula fault zone has experienced an average dextral shear of 0.8 mm/y since dike emplacement 8.5 Ma, consistent with right-lateral stream offsets observed at other locations along the OWL. Southeastward, the Wallula fault transfers strain to the north-striking Hite fault, the possible location of the M 5.7 Milton-Freewater earthquake in 1936.
Earth's magnetic field anomalies that precede the M6+ global seismic activity
NASA Astrophysics Data System (ADS)
Cataldi, Gabriele; Cataldi, Daniele; Straser, Valentino
In this work has been analyzed the Earth's magnetic field variations and the M6+ global seismic activity to verify if M6+ earthquakes are preceded by a change of the Earth's magnetic field. The data of Earth's magnetic field used to conduct the study of correlation are provided by the induction magnetometer of Radio Emissions Project's station (Lat: 41░41'4.27"N, Long: 12░38'33,60"E, Albano Laziale, Rome, Italy), equipped with a ELF receiver prototype (with a vertically aligned coil antenna) capable to detect the variations of the intensity of the Earth's magnetic field on Z magnetic component. The M6+ global seismic activity data are provided in real-time by USGS, INGV and CSEM. The sample of data used to conduct the study refers to the period between 1 January 2012 and 31 December 2012. The Earth's magnetic field variations data set has been marked with the times (time markers) of M6+ earthquakes occurred on a global scale and has been verified the existence of disturbances of the Earth's geomagnetic field in the time interval that preceded the M6+ global seismic activity. The correlation study showed that all M6+ earthquakes recorded on 2012 were preceded by an increase of the Earth's magnetic field, detected in the Z magnetic component. The authors measured the time lag elapsed between the maximum increment of the Earth's magnetic field recorded before an earthquake M6+ and the date and time at which this occurred, and has been verified that the minimum time lag recorded between the Earth's magnetic field increase and the earthquake M6+ has been 1 minute (9 October 2012, Balleny Islands, M6,4); while, the maximum time lag recorded has been 3600 minutes (26 June 2012, China, M6,3). The average time lag has been 629.47 minutes. In addition, the average time lag is deflected in relation to the magnitude increase. Key words: Seismic Geomagnetic Precursor (SGP), Interplanetary Seismic Precursor (ISP), Earth's magnetic field variations, earthquakes, prevision.
Yves Gallet; Jeff Gee; Lisa Tauxe; John A. Tarduno
We document three short normal intervals in the natural remanent magnetization of sediments within the Matuyama Chron. These three anomalous zones of magnetization between the Jaramillo and Olduvai subchrons were identified from continuous measurements of archive halves from Hole 803 A using the pass-through 2G cryogenic magnetometer at Scripps. The U-channel samples were taken from the three intervals, analyzed using
The Mackenzie River magnetic anomaly, Yukon and Northwest Territories, Canada-Evidence for Early Proterozoic magmatic arc crust at the edge of the North American craton
Pilkington, M.; Saltus, R.W.
We characterize the nature of the source of the high-amplitude, long-wavelength, Mackenzie River magnetic anomaly (MRA), Yukon and Northwest Territories, Canada, based on magnetic field data collected at three different altitudes: 300??m, 3.5??km and 400??km. The MRA is the largest amplitude (13??nT) satellite magnetic anomaly over Canada. Within the extent of the MRA, source depth estimates (8-12??km) from Euler deconvolution of low-altitude aeromagnetic data show coincidence with basement depths interpreted from reflection seismic data. Inversion of high-altitude (3.5??km) aeromagnetic data produces an average magnetization of 2.5??A/m within a 15- to 35-km deep layer, a value typical of magmatic arc complexes. Early Proterozoic magmatic arc rocks have been sampled to the southeast of the MRA, within the Fort Simpson magnetic anomaly. The MRA is one of several broad-scale magnetic highs that occur along the inboard margin of the Cordillera in Canada and Alaska, which are coincident with geometric changes in the thrust front transition from the mobile belt to stable cratonic North America. The inferred early Proterozoic magmatic arc complex along the western edge of the North American craton likely influenced later tectonic evolution, by acting as a buttress along the inboard margin of the Cordilleran fold-and-thrust belt. Crown Copyright ?? 2008.
The Mackenzie River magnetic anomaly, Yukon and Northwest Territories, CanadaŚEvidence for Early Proterozoic magmatic arc crust at the edge of the North American craton
NASA Astrophysics Data System (ADS)
Pilkington, Mark; Saltus, Rick W.
We characterize the nature of the source of the high-amplitude, long-wavelength, Mackenzie River magnetic anomaly (MRA), Yukon and Northwest Territories, Canada, based on magnetic field data collected at three different altitudes: 300 m, 3.5 km and 400 km. The MRA is the largest amplitude (13 nT) satellite magnetic anomaly over Canada. Within the extent of the MRA, source depth estimates (8-12 km) from Euler deconvolution of low-altitude aeromagnetic data show coincidence with basement depths interpreted from reflection seismic data. Inversion of high-altitude (3.5 km) aeromagnetic data produces an average magnetization of 2.5 A/m within a 15- to 35-km deep layer, a value typical of magmatic arc complexes. Early Proterozoic magmatic arc rocks have been sampled to the southeast of the MRA, within the Fort Simpson magnetic anomaly. The MRA is one of several broad-scale magnetic highs that occur along the inboard margin of the Cordillera in Canada and Alaska, which are coincident with geometric changes in the thrust front transition from the mobile belt to stable cratonic North America. The inferred early Proterozoic magmatic arc complex along the western edge of the North American craton likely influenced later tectonic evolution, by acting as a buttress along the inboard margin of the Cordilleran fold-and-thrust belt.
Gravitational Anomaly and Transport
Landsteiner, Karl; Pena-Benitez, Francisco
Quantum anomalies give rise to new transport phenomena. In particular a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid.
Gravitational Anomaly and Transport
Karl Landsteiner; Eugenio Megias; Francisco Pena-Benitez
Quantum anomalies give rise to new transport phenomena. In particular a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid.
Spherical-earth Gravity and Magnetic Anomaly Modeling by Gauss-legendre Quadrature Integration
NASA Technical Reports Server (NTRS)
Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.; Luca, A. J. (principal investigators)
The anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical Earth for an arbitrary body represented by an equivalent point source distribution of gravity poles or magnetic dipoles were calculated. The distribution of equivalent point sources was determined directly from the coordinate limits of the source volume. Variable integration limits for an arbitrarily shaped body are derived from interpolation of points which approximate the body's surface envelope. The versatility of the method is enhanced by the ability to treat physical property variations within the source volume and to consider variable magnetic fields over the source and observation surface. A number of examples verify and illustrate the capabilities of the technique, including preliminary modeling of potential field signatures for Mississippi embayment crustal structure at satellite elevations.
Calculation of gravity and magnetic anomalies of finite-length right polygonal prisms.
Cady, J.W.
An equation is derived for the vertical gravity field due to a homogeneous body with polygonal cross?section and finite strike?length. The equation can be separated into the two?dimensional (2-D) terms of Talwani et al. (1959) and exact terms for the contributions of the ends of the prism. Equations for the magnetic field due to a similar body were derived by Shuey and Pasquale (1973), who coined the term ōtwo?and?a?half dimensionalö (2 1/2-D) to describe the geometry. Magnetic intensities are expressed as a vector sum, from which the common dot product formulation can be obtained by binomial expansion.
Particle-In-Cell Simulations of the Solar Wind Interaction with Lunar Crustal Magnetic Anomalies: Magnetic Cusp Regions
NASA Technical Reports Server (NTRS)
Poppe, A. R.; Halekas, J. S.; Delory, G. T.; Farrell, W. M.
As the solar wind is incident upon the lunar surface, it will occasionally encounter lunar crustal remanent magnetic fields. These magnetic fields are small-scale, highly non-dipolar, have strengths up to hundreds of nanotesla, and typically interact with the solar wind in a kinetic fashion. Simulations, theoretical analyses, and spacecraft observations have shown that crustal fields can reflect solar wind protons via a combination of magnetic and electrostatic reflection; however, analyses of surface properties have suggested that protons may still access the lunar surface in the cusp regions of crustal magnetic fields. In this first report from a planned series of studies, we use a 1 1/2-dimensional, electrostatic particle-in-cell code to model the self-consistent interaction between the solar wind, the cusp regions of lunar crustal remanent magnetic fields, and the lunar surface. We describe the self-consistent electrostatic environment within crustal cusp regions and discuss the implications of this work for the role that crustal fields may play regulating space weathering of the lunar surface via proton bombardment.
An Exercise on Magnetic-Anomaly Profiles and the Geomagnetic Polar-Reversal Time Scale.
ERIC Educational Resources Information Center
Shea, James Herbert
Develops an exercise in which students use magnetic-profile data gathered in the South Pacific to test the Vine-Matthews-Morley hypothesis. Uses the Eltanin 19N and 20N profiles. Relates the exercise to 20 current geology texts. (MVL)
Magnetic anomalies and tectonic fabric of marginal basins North of New Zealand
Alexander Malahoff; Robert H. Feden; Henry S. Fleming
Detailed airborne magnetic studies conducted over the region of the S. W. Pacific marginal basins extending from the Solomon Islands to New Zealand suggest that three major phases of basin formation and island arc development have occurred in this region. Development of the Tasman Sea took place during the Late Cretaceous-Paleocene. Development of the basins to the east of the
Three-dimensional interpretation of magnetic and gravity anomalies using the finite-difference similarity transform
, and Alan Reid4 ABSTRACT We present an automatic procedure for interpretation of mag- netic or gravity common fea- tures with the magnetic and gravity sounding based on the differ- ential similarity transform, Eastbourne, U.K. E-mail: firstname.lastname@example.com. ┬® 2010 Society of Exploration Geophysicists.All rights
The Gop Basin - A Possible Imprint of Early Oceanic Spreading Between Greater Seychelles and India
NASA Astrophysics Data System (ADS)
Bhattacharya, G. C.; Yatheesh, V.; Dyment, J.
The Arabian and its conjugate Eastern Somali basins were formed by the seafloor spreading at the Carlsberg Ridge since Early Tertiary (anomaly 28n; ~62.5 Ma). The reconstruction model at anomaly 28n suggested existence of a wide swath of deep offshore region (Gop and Laxmi basins) between the Laxmi Ridge and the India-Pakistan continental shelf. In the present study we focus on the Gop Basin, where the important constraints about the early geodynamic evolution of the Arabian Sea appear to exist. The nature of the crust underlying this basin remains a matter of debate, with views varying from volcanics-intruded thinned continental crust to oceanic crust formed by a now extinct spreading centre. Our interpretation of an updated compilation of marine geophysical data supports the oceanic nature of the crust underlying the Gop Basin, where the Palitana Ridge represents the extinct spreading centre related to an episode of early oceanic spreading between Greater Seychelles (Seychelles-Laxmi Ridge block) and India. Our magnetic modelling shows that the well correlatable, prominent but short sequence of magnetic anomalies in the Gop Basin does not allow a unique identification; it can be reasonably explained either as A31r - A25r (~69 - 56 Ma) or as A29r - A25r (~65 - 56 Ma) sequence. Both the models suggest that spreading in the Gop Basin was significantly affected by the nearby onset of the Reunion hotspot at ~65 Ma, which formed the Deccan Traps on the adjacent western Indian mainland.
Positive holes in magnesium oxide - Correlation between magnetic, electric, and dielectric anomalies
NASA Technical Reports Server (NTRS)
Batllo, F.; Leroy, R. C.; Parvin, K.; Freund, F.; Freund, M. M.
The present magnetic susceptibility investigation of high purity MgO single crystals notes an anomally at 800 K which is associated with increasing electrical conductivity, a rise in static dielectric constant from 9 to 150, and the appearance of a pronounced positive surface charge. These phenomena can be accounted for in terms of peroxy defects which represent self-trapped, spin-paired positive holes at Mg(2+) vacancy sites. The holes begin to decouple their spins above 600 K.
A real time index of geomagnetic background noise for the MAD (Magnetic Anomaly Detection) frequency band
NASA Astrophysics Data System (ADS)
Bernardi, A.; Fraser-Smith, A. C.; Villard, O. G.
An index of geomagnetic activity in the upper part of the ultra low frequency (ULF) range (less than 4.55 Hz) has been developed. This index will be referred to as the MA index (magnetic activity index). The MA index is prepared every half hour and is a measure of the strength of the geomagnetic activity in the Pc1-Pc3 pulsation frequency range during that half hour period. Activity in the individual Pc pulsation ranges can also be measured, if desired. The index is calculated from the running average of the full-wave rectified values of the band pass filtered geomagnetic signals and thus it provides a better indication of the magnitude of these band pass filtered magnetic pulsations than does the ap index, for example. Daily variations of the band pass filtered magnetic signals are also better captured by the MA index. To test this system we used analog tape recordings of wide-band geomagnetic signals. The indices for these tapes are presented in the form of plots, together with a comparison with the ap indices of the same time intervals. The MA index shows the daily variation of the geometric signals quite clearly during times when there is strong activity, i.e., when the ap index values are large. Because impulsive signals, such as lightning discharges, tend to be suppressed in the averaging process, the MA index is insensitive to impulsive noise. It is found that the time variation of the MA index is in general markedly different from the variation of the ap index for the same time intervals.
MAGSAT anomaly map and continental drift
NASA Technical Reports Server (NTRS)
Lemouel, J. L. (principal investigator); Galdeano, A.; Ducruix, J.
Anomaly maps of high quality are needed to display unambiguously the so called long wave length anomalies. The anomalies were analyzed in terms of continental drift and the nature of their sources is discussed. The map presented confirms the thinness of the oceanic magnetized layer. Continental magnetic anomalies are characterized by elongated structures generally of east-west trend. Paleomagnetic reconstruction shows that the anomalies found in India, Australia, and Antarctic exhibit a fair consistency with the African anomalies. It is also shown that anomalies are locked under the continents and have a fixed geometry.
Oxfordian magnetostratigraphy of Poland and its correlation to Sub-Mediterranean ammonite zones and marine magnetic anomalies
NASA Astrophysics Data System (ADS)
Przybylski, P. A.; G?owniak, E.; Ogg, J. G.; Zi¾?kowski, P.; Sidorczuk, M.; Gutowski, J.; Lewandowski, M.
A nearly continuous magnetostratigraphic polarity pattern was compiled from several ammonite-zoned carbonate successions of southern Poland and from a composite magnetostratigraphy from the Iberian Range of Spain. The array of sections spans the middle two-thirds of the Oxfordian within the Sub-Mediterranean Province (Cordatum through Bifurcatus ammonite zones). The average paleopole calculated from eight of these Polish sections is at 78.5░N, 184.9░E ( ?p = 2.6░, ?m = 3.5░). The Sub-Mediterranean polarity pattern is consistent with an independent polarity pattern derived from the Boreal-realm sections of the British Isles, and improves the inter-correlation between these faunal realms. Cycle stratigraphy published for these ammonite subzones from southern France enabled temporal scaling of the polarity pattern, thereby facilitating correlation to marine magnetic anomalies M28 through M33 as modeled from deep-tow magnetometer surveys in the Western Pacific. The bases of the Middle and Upper Oxfordian substages as defined in the Sub-Mediterranean zonation in Poland correspond approximately to chrons M33 and M29 of that Pacific M-sequence model.
Geologic structure of the northern New Caledonia ridge, as inferred from magnetic and gravity anomalies
Collot, J.-Y.; Rigolot, P.; Missegue, F.
Bathymetric, gravity, and magnetic data collected in the southwest Pacific Ocean over the northern New Caledonia ridge show that the main geological units known from the island of New Caledonia extend northward from this island, beneath the Grand Lagon Nord, the Grand Passage, and the d'Entrecasteaux reefs. These data support the model of tectonic evolution of the New Caledonia region proposed by Kroenke (1984). Differences in structure, geophysical signatures and morphology evident between areas north and those south of the Grand Passage, together with the nearness of the Le Noroit massif west of the Grand Passage, suggest that contemporaneously with Eocene to early Oligocene subduction along the western New Caledonia margin, an arc-ridge collision may have occurred near the northern termination of this subduction zone. -from Authors
Origin of the northern Indus Fan and Murray Ridge, Northern Arabian Sea: interpretation from seismic and magnetic imaging
Clift, Peter
deposited during the drift phase after the break-up of India┬Ł Seychelles┬ŁAfrica. A predrift sequence, magnetic anomalies and gravity field modeling indicate to be of continental character. The continental anomalies. From this study, thinned continental crust spreads between the northern Murray Ridge System
Reconstructing Coherent Networks from Electroencephalography and Magnetoencephalography with Reduced Contamination from Volume Conduction or Magnetic Field Spread
Drakesmith, Mark; El-Deredy, Wael; Welbourne, Stephen
Volume conduction (VC) and magnetic field spread (MFS) induce spurious correlations between EEG/MEG sensors, such that the estimation of functional networks from scalp recordings is inaccurate. Imaginary coherency [1] reduces VC/MFS artefacts between sensors by assuming that instantaneous interactions are caused predominantly by VC/MFS and do not contribute to the imaginary part of the cross-spectral densities (CSDs). We propose an adaptation of the dynamic imaging of coherent sources (DICS) [2] - a method for reconstructing the CSDs between sources, and subsequently inferring functional connectivity based on coherences between those sources. Firstly, we reformulate the principle of imaginary coherency by performing an eigenvector decomposition of the imaginary part of the CSD to estimate the power that only contributes to the non-zero phase-lagged (NZPL) interactions. Secondly, we construct an NZPL-optimised spatial filter with two a priori assumptions: (1) that only NZPL interactions exist at the source level and (2) the NZPL CSD at the sensor level is a good approximation of the projected source NZPL CSDs. We compare the performance of the NZPL method to the standard method by reconstructing a coherent network from simulated EEG/MEG recordings. We demonstrate that, as long as there are phase differences between the sources, the NZPL method reliably detects the underlying networks from EEG and MEG. We show that the method is also robust to very small phase lags, noise from phase jitter, and is less sensitive to regularisation parameters. The method is applied to a human dataset to infer parts of a coherent network underpinning face recognition. PMID:24349088
Gravity and magnetic anomalies used to delineate geologic features associated with earthquakes and aftershocks in the central Virginia seismic zone
NASA Astrophysics Data System (ADS)
Shah, A. K.; Horton, J.; McNamara, D. E.; Spears, D.; Burton, W. C.
Estimating seismic hazard in intraplate environments can be challenging partly because events are relatively rare and associated data thus limited. Additionally, in areas such as the central Virginia seismic zone, numerous pre-existing faults may or may not be candidates for modern tectonic activity, and other faults may not have been mapped. It is thus important to determine whether or not specific geologic features are associated with seismic events. Geophysical and geologic data collected in response to the Mw5.8 August 23, 2011 central Virginia earthquake provide excellent tools for this purpose. Portable seismographs deployed within days of the main shock showed a series of aftershocks mostly occurring at depths of 3-8 km along a southeast-dipping tabular zone ~10 km long, interpreted as the causative fault or fault zone. These instruments also recorded shallow (< 4 km) aftershocks clustered in several areas at distances of ~2-15 km from the main fault zone. We use new airborne geophysical surveys (gravity, magnetics, radiometrics, and LiDAR) to delineate the distribution of various surface and subsurface geologic features of interest in areas where the earthquake and aftershocks took place. The main (causative fault) aftershock cluster coincides with a linear, NE-trending gravity gradient (~ 2 mgal/km) that extends over 20 km in either direction from the Mw5.8 epicenter. Gravity modeling incorporating seismic estimates of Moho variations suggests the presence of a shallow low-density body overlying the main aftershock cluster, placing it within the upper 2-4 km of the main-fault hanging wall. The gravity, magnetic, and radiometric data also show a bend in generally NE-SW orientation of anomalies close to the Mw5.8 epicenter. Most shallow aftershock clusters occur near weaker short-wavelength gravity gradients of one to several km length. In several cases these gradients correspond to geologic contacts mapped at the surface. Along the gravity gradients, the aftershocks appear to cluster near areas with cross-cutting geologic features such as Jurassic diabase dikes. These associations suggest that local variations in rock density and/or rheology may have contributed to modifications of local stress regimes in a manner encouraging localized seismicity associated with the Mw5.8 event and its aftershocks. Such associations are comparable to results of previous studies recognizing correspondences between seismicity and features such as intrusive bodies and failed rifts in the New Madrid seismic zone and elsewhere. To explore whether similar correspondences may have occurred in the past, we use regional gravity and magnetic data to consider possible relations between historical earthquakes and comparable geologic features elsewhere in the central Virginia seismic zone.
Crustal thickness and Vp/Vs estimates near the Brunswick magnetic anomaly using receiver functions from the SESAME array
NASA Astrophysics Data System (ADS)
Parker, E. H.; Hawman, R. B.; Fischer, K. M.; Wagner, L. S.
The Southeastern Suture of the Appalachian Margin Experiment (SESAME) is designed to investigate lithospheric dynamics associated with the Paleozoic collision between the Suwanee terrane and Laurentia as well as subsequent Mesozoic rifting and passive margin formation. So far, we have deployed 63 broadband instruments along two N-S trending profiles across Georgia and northern Florida. A third NW-trending profile consisting of 19 stations extends across accreted terranes of the southern Appalachians from Augusta, GA to eastern TN. The N-S profiles are intended to provide constraints on variations in crustal structure across the Brunswick magnetic anomaly (BMA), a prominent magnetic low coinciding with south-dipping crustal-scale seismic reflectors evident on COCORP profiles in south Georgia. The seismic reflectivity is likely a consequence of suturing, but the BMA has been interpreted as an edge effect related to collision as well as an effect of mafic magmatism south of the suture zone. H-k stacking using 10 teleseismic receiver functions from station W27, located ~50-km north of the suture on the western N-S profile, suggests a crustal thickness (H) of 42-44 km and average crustal Vp/Vs (k) of 1.73-1.80. These estimates are in agreement with previous well-constrained stacking results from USNSN station GOGA, located ~70-km to the northeast, that suggest a crustal thickness of 41-43 km and average Vp/Vs 1.72-1.76. The proposed suture zone itself lies beneath sediments of the Atlantic Coastal Plain, and receiver functions from stations in this region appear to be strongly affected by high-amplitude reverberations within the sedimentary column. Therefore, preliminary H-k stacking results from stations directly over the BMA may be unreliable. However, receiver functions from station W23 near the Inner Piedmont-Coastal Plain boundary (near the north, up-dip end of the suture zone) display variations in Ps delay time and amplitude with event back-azimuth. Receiver functions from the S-azimuth (South American trench) display a relatively weak Ps conversion at ~4 seconds, while receiver functions from the NW-azimuth (Aleutian trench) show a more complex signal with an arrival at ~4 s followed by a higher-amplitude arrival at ~6 seconds. This may be indicative of compositional heterogeneity across the suture, anisotropy within the crust or mantle, or complexity at the crust-mantle interface related to collision of the Suwanee terrane. Forthcoming data from additional stations will provide improved constraints on crustal structure across the BMA.
Anomaly constraints on monopoles and dyons
Csaki, Csaba [Institute for High Energy Phenomenology Newman Laboratory of Elementary Particle Physics, Cornell University, Ithaca, New York 14853 (United States); Shirman, Yuri [Department of Physics, University of California, Irvine, California 92697 (United States); Terning, John [Department of Physics, University of California, Davis, California 95616 (United States); CERN, Physics Department, Theory Unit, Geneva (Switzerland)
Fermions with magnetic charges can contribute to anomalies. We derive the axial anomaly and gauge anomalies for monopoles and dyons, and find eight new gauge anomaly cancellation conditions in a general theory with both electric and magnetic charges. As a by-product, we also extend the Zwanziger two-potential formalism to include the {theta} parameter, and elaborate on the condition for CP invariance in theories with fermionic dyons.
Correlation analysis between the occurrence of ionospheric scintillation at the magnetic equator and at the southern peak of the Equatorial Ionization Anomaly
NASA Astrophysics Data System (ADS)
Lima, G. R. T.; Stephany, S.; Paula, E. R.; Batista, I. S.; Abdu, M. A.; Rezende, L. F. C.; Aquino, M. G. S.; Dutra, A. P. S.
Ionospheric scintillation refers to amplitude and phase fluctuations in radio signals due to electron density irregularities associated to structures named ionospheric plasma bubbles. The phenomenon is more pronounced around the magnetic equator where, after sunset, plasma bubbles of varying sizes and density depletions are generated by plasma instability mechanisms. The bubble depletions are aligned along Earth's magnetic field lines, and they develop vertically upward over the magnetic equator so that their extremities extend in latitude to north and south of the dip equator. Over Brazil, developing bubbles can extend to the southern peak of the Equatorial Ionization Anomaly, where high levels of ionospheric scintillation are common. Scintillation may seriously affect satellite navigation systems, such as the Global Navigation Satellite Systems. However, its effects may be mitigated by using a predictive model derived from a collection of extended databases on scintillation and its associated variables. This work proposes the use of a classification and regression decision tree to perform a study on the correlation between the occurrence of scintillation at the magnetic equator and that at the southern peak of the equatorial anomaly. Due to limited size of the original database, a novel resampling heuristic was applied to generate new training instances from the original ones in order to improve the accuracy of the decision tree. The correlation analysis presented in this work may serve as a starting point for the eventual development of a predictive model suitable for operational use.
A source-depth separation filter: Using the Euler method on the derivatives of total intensity magnetic anomaly data
Ravat, D.; Kirkham, K.; Hildenbrand, T.G.
An overview is given on the benefits of applying the Euler method on derivatives of anomalies to enhance the location of shallow and deep sources. Used properly, the method is suitable for characterizing sources from all potential-field data and/or their derivative, as long as the data can be regarded mathematically as "continuous". Furthermore, the reasons why the use of the Euler method on derivatives of anomalies is particularly helpful in the analysis and interpretation of shallow features are explained.
The Effects of Magnetic Anomalies Discovered at Mars on the Structure of the Martian Ionosphere and the Solar Wind Interaction as Follows from Radio Occultation Experiments
NASA Technical Reports Server (NTRS)
Ness, N. F.; Acuna, M. H.; Connerney, J. E. P.; Cloutier, P.; Kliore, A. J.; Breus, T. K.; Krymskii, A. M.; Bauer, S. J.
The electron density distribution in the ionosphere of nonmagnetic (or weakly magnetized) planet depends not only on the solar ultraviolet intensity, but also on the nature of the SW interaction with this planet. Two scenarios previously have been developed based on the observations of the bow shock crossings and on the electron density distribution within the ionosphere. According to one of them Mars has an intrinsic magnetosphere produced by a dipole magnetic field and the Martian ionosphere is protected from the SW flow except during "overpressure conditions, when the planetary magnetic field can not balance the SW dynamic pressure. In the second scenario the Martian intrinsic magnetic dipole field is so weak that Mars has mainly an induced magnetosphere and a Venus-like SW/ionosphere interaction. Today the possible existence of a sufficiently strong global magnetic field that participates in the SW/Mars interaction can no longer be supported. The results obtained by the Mars-Global-Surveyor (MGS) space-craft show the existence of highly variable, but also very localized magnetic fields of crustal origin at Mars as high as 400-1500 nT. The absence of the large-scale global magnetic field at Mars makes it similar to Venus, except for possible effects of the magnetic anomalies associated with the remnant crustal magnetization. However the previous results on the Martian ionosphere obtained mainly by the radio occultation methods show that there appears to be a permanent existence of a global horizontal magnetic field in the Martian ionosphere. Moreover the global induced magnetic field in the Venus ionosphere is not typical at the solar zenith angles explored by the radio occultation methods. Additional information is contained in the original extended abstract.
... genetic terms used on this page Learning About Poland Anomaly What is Poland anomaly? What are the ... Anomaly Additional Resources for Poland Anomaly What is Poland anomaly? Named after Sir Alfred Poland, Poland anomaly ( ...
M3 spectral analysis of lunar swirls and the link between optical maturation and surface hydroxyl formation at magnetic anomalies
Kramer, G.Y.; Besse, S.; Dhingra, D.; Nettles, J.; Klima, R.; Garrick-Bethell, I.; Clark, R.N.; Combe, J.-P.; Head, J. W., III; Taylor, L.A.; Pieters, C.M.; Boardman, J.; McCord, T.B.
We examined the lunar swirls using data from the Moon Mineralogy Mapper (M3). The improved spectral and spatial resolution of M3 over previous spectral imaging data facilitates distinction of subtle spectral differences, and provides new information about the nature of these enigmatic features. We characterized spectral features of the swirls, interswirl regions (dark lanes), and surrounding terrain for each of three focus regions: Reiner Gamma, Gerasimovich, and Mare Ingenii. We used Principle Component Analysis to identify spectrally distinct surfaces at each focus region, and characterize the spectral features that distinguish them. We compared spectra from small, recent impact craters with the mature soils into which they penetrated to examine differences in maturation trends on- and off-swirl. Fresh, on-swirl crater spectra are higher albedo, exhibit a wider range in albedos and have well-preserved mafic absorption features compared with fresh off-swirl craters. Albedoand mafic absorptions are still evident in undisturbed, on-swirl surface soils, suggesting the maturation process is retarded. The spectral continuum is more concave compared with off-swirl spectra; a result of the limited spectral reddening being mostly constrained to wavelengths less than ???1500 nm. Off-swirl spectra show very little reddening or change in continuum shape across the entire M3 spectral range. Off-swirl spectra are dark, have attenuated absorption features, and the narrow range in off-swirl albedos suggests off-swirl regions mature rapidly. Spectral parameter maps depicting the relative OH surface abundance for each of our three swirl focus regions were created using the depth of the hydroxyl absorption feature at 2.82 ??m. For each of the studied regions, the 2.82 ??m absorption feature is significantly weaker on-swirl than off-swirl, indicating the swirls are depleted in OH relative to their surroundings. The spectral characteristics of the swirls and adjacent terrains from all three focus regions support the hypothesis that the magnetic anomalies deflect solar wind ions away from the swirls and onto off-swirl surfaces. Nanophase iron (npFe0) is largely responsible for the spectral characteristics we attribute to space weathering and maturation, and is created by vaporization/deposition by micrometeorite impacts and sputtering/reduction by solar wind ions. On the swirls, the decreased proton flux slows the spectral effects of space weathering (relative to nonswirl regions) by limiting the npFe0 production mechanism almost exclusively to micrometeoroid impact vaporization/deposition. Immediately adjacent to the swirls, maturation is accelerated by the increased flux of protons deflected from the swirls. Copyright 2011 by the American Geophysical Union.
The Emerson Lake Body: A link between the Landers and Hector Mine earthquakes, southern California, as inferred from gravity and magnetic anomalies
Langenheim, V.E.; Jachens, R.C.
Gravity and magnetic data indicate a mafic crustal heterogeneity that lies between the Hector Mine 16 October 1999 (Mw 7.1) and Landers 28 June 1992 (Mw 7.3) epicenters. The aftershocks and ruptures of these two events avoided the interior of the body. Two- and three-dimensional modeling of the potential-field anomalies shows that the source, here named the Emerson Lake body (ELB), extends to a depth of approximately 15 km. The source of the gravity and magnetic anomaly is most likely Jurassic diorite because exposures of these rocks coincide with both gravity and magnetic highs west of Emerson Lake. Seismic tomography also shows higher velocities within the region of the ELB. We propose that the ELB was an important influence on the rupture geometry of the Landers and Hector Mine ruptures and that the ELB may have played a role in transferring of stress from the Landers earthquake to the Hector Mine hypocenter. Seismicity before the Landers earthquake also tended to avoid the ELB, suggesting that the ELB affects how strain is distributed in this part of the Mojave Desert. Thus, faults within the body should have limited rupture sizes and lower seismic hazard than faults bounding or outside this mafic crustal heterogeneity.
A Preliminary, Full Spectrum, Magnetic Anomaly Grid of the United States with Improved Long Wavelengths for Studying Continental Dynamics: A Website for Distribution of Data
Ravat, D.; Finn, C.; Hill, P.; Kucks, R.; Phillips, J.; Blakely, R.; Bouligand, C.; Sabaka, T.; Elshayat, A.; Aref, A.; Elawadi, E.
Under an initiative started by Thomas G. Hildenbrand of the U.S. Geological Survey, we have improved the long-wavelength (50-2,500 km) content of the regional magnetic anomaly compilation for the conterminous United States by utilizing a nearly homogeneous set of National Uranium Resource Evaluation (NURE) magnetic surveys flown from 1975 to 1981. The surveys were flown in quadrangles of 2 deg of longitude by 1 deg of latitude with east-west flight lines spaced 4.8 to 9.6 km apart, north-south tie lines variably spaced, and a nominal terrain clearance of 122 m. Many of the surveys used base-station magnetometers to remove external field variations.
Gravitational anomaly and transport phenomena.
Landsteiner, Karl; MegĒas, Eugenio; Pena-Benitez, Francisco
Quantum anomalies give rise to new transport phenomena. In particular, a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid. PMID:21797593
NSDL National Science Digital Library
In this simulation, learners explore how ocean currents spread all kinds of pollutionŚincluding oil spills, sewage, pesticides and factory wasteŚfar beyond where the pollution originates. Learners create an experimental "ocean" (water in a tray) and "continents" (rocks), then add melting ice cubes to create temperature-driven currents in the water. Learners observe how "pollution," represented by food coloring, spreads through the model ocean affected by both "currents" and "continents." This activity can be used with lessons on ocean science or environmental hazards.
Extravasation into brain and subsequent spread beyond the ischemic core of a magnetic resonance contrast agent following a step-down infusion protocol in acute cerebral ischemia
Background Limiting expansion of the ischemic core lesion by reinstating blood flow and protecting the penumbral cells is a priority in acute stroke treatment. However, at present, methods are not available for effective drug delivery to the ischemic penumbra. To address these issues this study compared the extravasation and subsequent interstitial spread of a magnetic resonance contrast agent (MRCA) beyond the ischemic core into the surrounding brain in a rat model of ischemia-reperfusion for bolus injection and step-down infusion (SDI) protocols. Methods Male Wistar rats underwent middle cerebral artery (MCA) occlusion for 3Āh followed by reperfusion. Perfusion-diffusion mismatched regions indicating the extent of spread were identified by measuring cerebral blood flow (CBF) deficits by arterial spin-labeled magnetic resonance imaging and the extent of the ischemic core by mapping the apparent diffusion coefficient (ADC) of water with diffusion-weighted imaging. Vascular injury was assessed via MRCA, gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) penetration, by Look-Locker T1-weighted MR imaging after either a bolus injection (n?=?8) or SDI (n?=?6). Spatial and temporal expansion of the MRCA front during a 25Āmin imaging period was measured from images obtained at 2.5Āmin intervals. Results The mean ADC lesion was 20?▒?7% of the hemispheric area whereas the CBF deficit area was 60?▒?16%, with the difference between the areas suggesting the possible presence of a penumbra. The bolus injection led to MRCA enhancement with an area that initially spread into the ischemic core and then diminished over time. The SDI produced a gradual increase in the area of MRCA enhancement that slowly enlarged to occupy the core, eventually expanded beyond it into the surrounding tissue and then plateaued. The integrated area from SDI extravasation was significantly larger than that for the bolus (p?=?0.03). The total number of pixels covered by the SDI at its maximum was significantly larger than the pixels covered by bolus maximum (p?=?0.05). Conclusions These results demonstrate that the SDI protocol resulted in a spread of the MRCA beyond the ischemic core. Whether plasma-borne acute stroke therapeutics can be delivered to the ischemic penumbra in a similar way needs to be investigated. PMID:25276343
Large-scale lithospheric magnetic anomalies in Europe as revealed by recorded geomagnetic storms at the observatory network
NASA Astrophysics Data System (ADS)
Dobrica, Venera; Demetrescu, Crisan
The magnetic field of the Earth, which extends in space as magnetosphere, is in permanent interaction with the solar electromagnetic, particle and magnetic flux outputs, i.e. the solar radiation, the solar wind, and, respectively, the heliospheric magnetic field. The variable current systems that develop as a result of these interactions create the so-called field of geomagnetic variations which, in turn, induces a response of the Earth's internal magnetic and conductive structures. In this study, the geomagnetic variations at storm timescales (minutes - days) provided by the network of European geomagnetic observatories have been used for modeling the magnetic structure of the European lithosphere. Large-scale magnetic structures in the lithosphere are evidenced by means of a magnetic induction model applied to geomagnetic observatory data recorded during several intense geomagnetic storm intervals (Dst<-200 nT) in the time period 2001-2005. The magnetic induction model assumes that the induced field is a linear combination of the components of the inducing field. As the inducing external source, the magnetic field of the ring current at each observatory location was used, inferred from the Dst geomagnetic index (minute). The lateral distribution of the lithosphere magnetic properties as described by the coefficients of the mentioned linear combination was derived and a comparison with distributions resulted in case of other variable sources (e.g. Sq) is discussed.
Bimodal distribution of blocking temperature for exchange-bias ferromagnetic/antiferromagnetic bilayers: a granular Monte Carlo study with less stable magnetic regions spread over the interface
NASA Astrophysics Data System (ADS)
Lhoutellier, G.; Ledue, D.; Patte, R.; Barbe, F.; Dieny, B.; Baltz, V.
In exchange bias based devices, ferromagnetic/antiferromagnetic disordered interfacial spins which exhibit low freezing temperatures contribute to the alteration of the exchange bias properties. In particular, the blocking temperature distributions earlier observed experimentally show two contributions: the common high-temperature peak due to the antiferromagnetic grain volume distribution and a less usual low-temperature contribution presumably attributed to disordered interfacial spins. Here, in order to test this assumption Monte Carlo simulations based on a granular level model are used to calculate blocking temperature distribution. Small magnetic grains with weaker anisotropy and interfacial coupling are introduced at the ferromagnetic/antiferromagnetic interface to account for the disordered interfacial spins. As a result, the bimodal character of blocking temperature distributions is reproduced and varying the amount of these smaller magnetic grains tunes the low-temperature contribution of the distribution. These simulations therefore validate the assumption that less stable magnetic regions spread over the ferromagnetic/antiferromagnetic interface may originate the bimodal character of blocking temperature distributions, as earlier brought forward by experimentalists to explain their results. In addition, because of the heterogeneities of the interface in the presence of less stable small grains, our simulations show that such bilayers cannot be described using a simple model of uniform rotation of the ferromagnetic layer interacting with an average interfacial coupling.
Gravitational Anomaly and Transport Phenomena
Karl Landsteiner; Eugenio MegĒas; Francisco Pena-Benitez
Quantum anomalies give rise to new transport phenomena. In particular, a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity
Antipodal Magnetic Anomalies on the Moon, Contributions from Impact Induced Currents Due to Positive Holes and Flexoelectric Phenomina and Dynamo
NASA Technical Reports Server (NTRS)
Kletetschka, G.; Freund, F.; Wasilewski, P. J.; Mikula, V.; Kohout, Tomas
Large impacts on the Moon generate large pressure pulses that penetrate the whole body. Several of these large impacts may have generated antipodal structure with anomalous magnetic intensity.These regions can be more than a thousand km across, with fields of the order of tens to hundreds of nT. This is the case of Orientale, Imbrium, Serenitatis, Crisium, and Nectaris impact basins. The production of large-scale magnetic fields and associated crustal magnetization due to lunar basin-forming impacts was hypothesized to have an origin in fields external to the impact plasma cloud that are produced by the magnetohydrodynamic interaction of the cloud with ambient magnetic fields and plasmas. During the period of compressed antipodal field amplification, seismic compressional waves from the impact converge at the antipode resulting in transient shock pressures that reach 2 GPa (20 kbar). This can produce conditions for shock magnetic acquisition of the crust antipodal to impact basins.
Ages and magnetic structures of the South China Sea constrained by deep tow magnetic surveys and IODP Expedition 349
NASA Astrophysics Data System (ADS)
Li, Chun-Feng; Xu, Xing; Lin, Jian; Sun, Zhen; Zhu, Jian; Yao, Yongjian; Zhao, Xixi; Liu, Qingsong; Kulhanek, Denise K.; Wang, Jian; Song, Taoran; Zhao, Junfeng; Qiu, Ning; Guan, Yongxian; Zhou, Zhiyuan; Williams, Trevor; Bao, Rui; Briais, Anne; Brown, Elizabeth A.; Chen, Yifeng; Clift, Peter D.; Colwell, Frederick S.; Dadd, Kelsie A.; Ding, Weiwei; Almeida, Ivßn. Hernßndez; Huang, Xiao-Long; Hyun, Sangmin; Jiang, Tao; Koppers, Anthony A. P.; Li, Qianyu; Liu, Chuanlian; Liu, Zhifei; Nagai, Renata H.; Peleo-Alampay, Alyssa; Su, Xin; Tejada, Maria Luisa G.; Trinh, Hai Son; Yeh, Yi-Ching; Zhang, Chuanlun; Zhang, Fan; Zhang, Guo-Liang
analyses of deep tow magnetic anomalies and International Ocean Discovery Program Expedition 349 cores show that initial seafloor spreading started around 33 Ma in the northeastern South China Sea (SCS), but varied slightly by 1-2 Myr along the northern continent-ocean boundary (COB). A southward ridge jump of ś20 km occurred around 23.6 Ma in the East Subbasin; this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the Southwest Subbasin, which propagated for about 400 km southwestward from ś23.6 to ś21.5 Ma. The terminal age of seafloor spreading is ś15 Ma in the East Subbasin and ś16 Ma in the Southwest Subbasin. The full spreading rate in the East Subbasin varied largely from ś20 to ś80 km/Myr, but mostly decreased with time except for the period between ś26.0 Ma and the ridge jump (ś23.6 Ma), within which the rate was the fastest at ś70 km/Myr on average. The spreading rates are not correlated, in most cases, to magnetic anomaly amplitudes that reflect basement magnetization contrasts. Shipboard magnetic measurements reveal at least one magnetic reversal in the top 100 m of basaltic layers, in addition to large vertical intensity variations. These complexities are caused by late-stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion. Deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0.5, which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and uniform magnetization. The primary contribution to magnetic anomalies of the SCS is not in the top 100 m of the igneous basement.
NSDL National Science Digital Library
In this activity, learners will investigate and try to explain various lunar anomalies. They will present hypotheses (both written and oral) and then debate the merits of each hypothesis, with no right or wrong answers. This activity is in Unit 2 of the teachers guide, Exploring the Moon, which is designed for use especially, but not exclusively, with the Lunar Sample Disk program.
Triangle Anomalies, Thermodynamics, and Hydrodynamics
Kristan Jensen
We consider 3+1-dimensional fluids with U(1)^3 anomalies. We use Ward identities to constrain low-momentum Euclidean correlation functions and obtain differential equations that relate two and three-point functions. The solution to those equations yields, among other things, the chiral magnetic conductivity. We then compute zero-frequency functions in hydrodynamics and show that the consistency of the hydrodynamic theory also fixes the anomaly-induced conductivities.
Age of the source of the Jarrafa gravity and magnetic anomalies offshore Libya and its geodynamic implications
Giuma Reeh; Tahar A'fa
The interpretation of the Jarrafa magnetic and gravity highs, NW Libyan offshore, suggests that it may be caused by a body of high-density and high magnetization. Analysis of their power spectra indicates two groups of sources at: (1) 2.7km depth, probably related to the igneous rocks, some of which were penetrated in the JA-1 borehole, (2) 5km depth, corresponding to
Aeromagnetic anomalies and discordant lineations beneath the Niger Delta - Implications for new fracture zones and multiple sea-floor spreading directions in the 'meso-Atlantic' Gulf of Guinea cul-de-sac
NASA Astrophysics Data System (ADS)
Babalola, Olufemi O.; Gipson, Mack, Jr.
An aeromagnetic map eliminating data gaps in the Nigerian continental margin is presented, and the implications of the mapped fracture zone structure and the interpretation of two triple junctions beneath the Niger Delta Basin for its early tectonic history are discussed. Sea-floor spreading was found to occur in two different directions, and not only the well-documented NE-SW spreading in the 'meso-Atlantic' ocean. The existence of two triple junctions located where the Niger Delta Basin abuts the southern ends of the Abakaliki and Anambra troughs is shown. The two newly interpreted triple junctions beneath the Niger Delta demonstrate the previously recognized structural complexity of the region, necessitating a review of models for its early tectonic history.
Lithospheric structure of a nascent spreading ridge inferred from gravity data: The western Gulf of Aden
NASA Astrophysics Data System (ADS)
HķBert, HķLĶNe; Deplus, Christine; Huchon, Philippe; Khanbari, Khaled; Audin, Laurence
The Aden spreading ridge (Somalia/Arabia plate boundary) does not connect directly to the Red Sea spreading ridge. It propagates toward the East African Rift through the Afar depression, where the presence of a hot spot has been postulated from seismological and geochemical evidence. The spreading direction (N37░E) is highly oblique to the overall trend (N90░E) of the ridge. We present and interpret new geophysical data gathered during the Tadjouraden cruise (R/V L'Atalante, 1995) in the Gulf of Aden west of 46░E. These data allow us to study the propagation of the ridge toward the Afar and to discuss the processes of the seafloor spreading initiation. We determine the lithospheric structure of the ridge using gravity data gathered during the cruise with the constraint of available refraction data. A striking Bouguer anomaly gradient together with the identification of magnetic anomalies defines the geographical extent of oceanic crust. The inversion of the Bouguer anomaly is performed in terms of variations of crustal thickness only and then discussed with respect to the expected thermal structure of the mantle lithosphere, which should depend not only on the seafloor spreading but also on the hot spot beneath East Africa. Our results allow us to define three distinct lithospheric domains in the western Gulf of Aden. East of 44░45'E the lithosphere displays an oceanic character (thermal subsidence recorded for the last 10 Ma and constant crustal thickness). Between 43░30'E and 44░10'E the lithosphere is of continental type but locally thinned beneath the axial valley. The central domain defined between 44░10'E and 44░45'E is characterized by a transitional lithosphere which can be seen as a stretched continental crust where thick blocks are mixed with thinned crust; it displays en echelon basins that are better interpreted as extension cells rather than accretion cells.
The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies
Blakely, Richard J.; Sherrod, Brian; Weaver, Craig; Wells, Ray E.; Rohay, Alan C.
Magnetic and gravity data, collected in south-central Washington near the Yakima Fold and Thrust Belt (YFTB) are used to model upper crustal structure, the extent of the late Columbia River Basalt flow named the Ice Harbor member, the vertical conduits (dikes) that the Ice Harbor erupted from, and whether the dikes are offset or affected by faulting on the Wallula Fault zone.
Photoluminescence anomalies of indirect excitons localized at interfaces in CdS/ZnSe MQWs in very high magnetic fields
NASA Astrophysics Data System (ADS)
Saito, H.; Akimoto, R.; Kindo, K.; Takeyama, S.
CdS/ZnSe multiple quantum wells (MQWs) shows very strong photoluminescence at low temperatures. The strong photoluminescence (PL) arises from the interface localization of the type-II excitons. A systematic study was attempted on the exciton density dependence of magneto-PL behavior up to 53 T by using a pulse magnet. We obtained a strong excitation density dependence of the type-II exciton Bohr radius trapped in interface roughness potentials.
Octahedral distortion induced magnetic anomalies in LaMn0.5Co0.5O3 single crystals
NASA Astrophysics Data System (ADS)
Manna, Kaustuv; Bhadram, Venkata Srinu; Elizabeth, Suja; Narayana, Chandrabhas; Anil Kumar, P. S.
Single crystals of LaMn0.5Co0.5O3 belonging to the ferromagnetic-insulator and distorted perovskite class were grown using a four-mirror optical float zone furnace. The as-grown crystal crystallizes into an orthorhombic Pbnm structure. The spatially resolved 2D Raman scan reveals a strain-induced distribution of transition metal (TM)-oxygen (O) octahedral deformation in the as-grown crystal. A rigorous annealing process releases the strain, thereby generating homogeneous octahedral distortion. The octahedra tilt by reducing the bond angle TM-O-TM, resulting in a decline of the exchange energy in the annealed crystal. The critical behavior is investigated from the bulk magnetization. It is found that the ground state magnetic behavior assigned to the strain-free LaMn0.5Co0.5O3 crystal is of the 3D Heisenberg kind. Strain induces mean field-like interaction in some sites, and consequently, the critical exponents deviate from the 3D Heisenberg class in the as-grown crystal. The temperature-dependent Raman scattering study reveals strong spin-phonon coupling and the existence of two magnetic ground states in the same crystal.
Phanerozoic stratigraphy of Northwind Ridge, magnetic anomalies in the Canada Basin, and the geometry and timing of rifting in the Amerasia Basin, Arctic Ocean
Grantz, A.; Clark, D.L.; Phillips, R.L.; Srivastava, S.P.; Blome, C.D.; Gray, L.-B.; Haga, H.; Mamet, B.L.; McIntyre, D.J.; McNeil, D.H.; Mickey, M.B.; Mullen, M.W.; Murchey, B.I.; Ross, C.A.; Stevens, C.H.; Silberling, N.J.; Wall, J.H.; Willard, D.A.
Cores from Northwind Ridge, a high-standing continental fragment in the Chukchi borderland of the oceanic Amerasia basin, Arctic Ocean, contain representatives of every Phanerozoic system except the Silurian and Devonian systems. Cambrian and Ordovician shallow-water marine carbonates in Northwind Ridge are similar to basement rocks beneath the Sverdrup basin of the Canadian Arctic Archipelago. Upper Mississippian(?) to Permian shelf carbonate and spicularite and Triassic turbidite and shelf lutite resemble coeval strata in the Sverdrup basin and the western Arctic Alaska basin (Hanna trough). These resemblances indicate that Triassic and older strata in southern Northwind Ridge were attached to both Arctic Canada and Arctic Alaska prior to the rifting that created the Amerasia basin. Late Jurassic marine lutite in Northwind Ridge was structurally isolated from coeval strata in the Sverdrup and Arctic Alaska basins by rift shoulder and grabens, and is interpreted to be a riftogenic deposit. This lutite may be the oldest deposit in the Canada basin. A cape of late Cenomanian or Turonian rhyodacite air-fall ash that lacks terrigenous material shows that Northwind Ridge was structurally isolated from the adjacent continental margins by earliest Late Cretaceous time. Closing Amerasia basin by conjoining seafloor magnetic anomalies beneath the Canada basin or by uniting the pre-Jurassic strata of Northwind Ridge with kindred sections in the Sverdrup basin and Hanna trough yield simular tectonic reconstructions. Together with the orientation and age of rift-marine structures, these data suggest that: 1) prior to opening of the Amerasia basin, both northern Alaska and continental ridges of the Chukchi borderland were part of North America, 2) the extension that created the Amerasia basin formed rift-margin graben beginning in Early Jurassic time and new oceanic crust probably beginning in Late Jurassic or early Neocomian time. Reconstruction of the Amerasia basin on the basis of the stratigraphy of Northwind Ridge and sea-floor magnetic anomalies in the Canada basin accounts in a general way for the major crustal elements of the Americasia basin, including the highstanding ridges of the Chukchi borderland, and supports S.W. Carye's hypothesis that the Amerasia basin is the product of anticlockwise rotational rifting of Arctic Alaska from North America.
Interpretation of CHAMP Magnetic Anomaly Data over the Pannonian Basin Region Using Lower Altitude Horizontal Gradient Data
NASA Technical Reports Server (NTRS)
Taylor, P. T.; Kis, K. I.; Wittmann, G.
The ESA SWARM mission will have three earth orbiting magnetometer bearing satellites one in a high orbit and two side-by-side in lower orbits. These latter satellites will record a horizontal magnetic gradient. In order to determine how we can use these gradient measurements for interpretation of large geologic units we used ten years of CHAMP data to compute a horizontal gradient map over a section of southeastern Europe with our goal to interpret these data over the Pannonian Basin of Hungary.
Anomalies in thermal expansion of rare-earth diborides in the temperature range of magnetic phase transformations
NASA Astrophysics Data System (ADS)
Novikov, V. V.; Chukina, T. A.; Verevkin, A. A.
The variations with temperature of the lattice parameters a(T) and c(T) and the thermal expansion coefficients of rare-earth diborides RB2( R=Tb, Dy, Ho, Er, Tm, Lu) have been investigated in the temperature range 4.2Ś300 K. It has been revealed that the dependences a(T) and c(T) exhibit an anomalous behavior in the vicinity of the ferromagnetic transformation temperatures T c which correlates with the temperature dependences of the heat capacity. It has been established that the magnetic contributions to the thermal expansion of the diborides ? a m( T) increase with increasing temperature and tend to constant values at T? T c and that the magnetic components ? c m(T) decrease for all the diborides studied, also tending to constant values at elevated temperatures. The exchange integrals Y a and Y c for the paramagnetic metal ions in the rare-earth diborides are determined from the dependences ? a m(T) and ? c m(T).
Elastic anomalies associated with structural and magnetic phase transitions in single crystal hexagonal YMnO3.
Thomson, R I; Chatterji, T; Howard, C J; Palstra, T T M; Carpenter, M A
Resonant ultrasound spectroscopy has been used to measure the elastic and anelastic behaviour through known structural and magnetic phase transitions in single crystal hexagonal YMnO3. Anomalous elastic behaviour is observed at the high temperature structural transition at ?1260 K, with a discontinuity in the elastic constants and nonlinear recovery below Tc, consistent with [Formula: see text] coupling. There is no change in dissipation associated with this high temperature transition, and no evidence in the elastic or anelastic behaviour for any secondary transition at ?920 K, thus supporting the thesis of a single high temperature transformation. Elastic stiffening is observed on cooling through TN, in accordance with previous studies, and the excess elastic constant appears to scale with the square of the magnetic order parameter. The strains incurred at TN are a factor of ?20 smaller than those at the structural transition, implying very weak [Formula: see text] coupling and a dominant contribution to the variation in the elastic constants from [Formula: see text]. The increased acoustic dissipation above TN is consistent with an order-disorder process. PMID:24390102
Estimation of hydrothermal deposits location from magnetization distribution and magnetic properties in the North Fiji Basin
NASA Astrophysics Data System (ADS)
Choi, S.; Kim, C.; Park, C.; Kim, H.
The North Fiji Basin is belong to one of the youngest basins of back-arc basins in the southwest Pacific (from 12 Ma ago). We performed the marine magnetic and the bathymetry survey in the North Fiji Basin for finding the submarine hydrothermal deposits in April 2012. We acquired magnetic and bathymetry datasets by using Multi-Beam Echo Sounder EM120 (Kongsberg Co.) and Overhouser Proton Magnetometer SeaSPY (Marine Magnetics Co.). We conducted the data processing to obtain detailed seabed topography, magnetic anomaly, reduce to the pole(RTP), analytic signal and magnetization. The study areas composed of the two areas(KF-1(longitude : 173.5 ~ 173.7 and latitude : -16.2 ~ -16.5) and KF-3(longitude : 173.4 ~ 173.6 and latitude : -18.7 ~ -19.1)) in Central Spreading Ridge(CSR) and one area(KF-2(longitude : 173.7 ~ 174 and latitude : -16.8 ~ -17.2)) in Triple Junction(TJ). The seabed topography of KF-1 existed thin horst in two grabens that trends NW-SE direction. The magnetic properties of KF-1 showed high magnetic anomalies in center part and magnetic lineament structure of trending E-W direction. In the magnetization distribution of KF-1, the low magnetization zone matches well with a strong analytic signal in the northeastern part. KF-2 area has TJ. The seabed topography formed like Y-shape and showed a high feature in the center of TJ. The magnetic properties of KF-2 displayed high magnetic anomalies in N-S spreading ridge center and northwestern part. In the magnetization distribution of KF-2, the low magnetization zone matches well with a strong analytic signal in the northeastern part. The seabed topography of KF-3 presented a flat and high topography like dome structure at center axis and some seamounts scattered around the axis. The magnetic properties of KF-3 showed high magnetic anomalies in N-S spreading ridge center part. In the magnetization of KF-2, the low magnetization zone mismatches to strong analytic signal in this area. The difference of KF-3 between the low magnetization zones and the analytic signals is considered that the submarine magnetic strength of KF-3 is lower than that of KF-1 and KF-2. The spreading ridges of the study areas showed common Central Anomaly Magnetization Highs (CAMH). As a whole, the previous studies on the structure of this study area (Auzende et al, 1990) support our results of the magnetic properties (Magnetic Anomaly and RTP). We can expect to have the better results by comparing with the other study like geophysics (seismic), geology, and geochemistry in this area. Reference Auzende, J.M., and 29 others, Active Spreading and Hydrothermalism in North Fiji Basin(SW Pacific). Results of Japanese French Cruise Kaiyo 87, Marine Geophysical Researches., 12, 269-283, 1990.
Spreading behaviour of the Pacific-Farallon ridge system since 83 Ma
NASA Astrophysics Data System (ADS)
Rowan, Christopher J.; Rowley, David B.
We present improved rotations, complete with uncertainties, for the Pacific-Farallon Ridge (PFR) between geomagnetic chrons 34y (83 Ma) and 10y (28.28 Ma). Despite substantial shortening since ś55 Ma, this ridge system and its remnants (e.g. the East Pacific Rise) have produced as much as 45 per cent of all oceanic lithosphere created since the Late Cretaceous, but reconstructions face the twin challenges of extensive subduction of Farallon crust-which precludes reconstruction by fitting conjugate magnetic anomaly and fracture zone (FZ) traces-and asymmetric spreading behaviour for at least the past 51 Myr. We have calculated best-fit `half'-angle stage rotations between nine geomagnetic chron boundaries (34y, 33y, 29o, 24.3o, 20o, 18.2o, 17.1y, 13y and 10y) using combined anomaly and FZ data from both the northern and southern Pacific Plate. For rotations younger than chron 24.3o, estimates for spreading asymmetry, derived using anomaly picks from yet-to-be subducted Farallon/Nazca crust in the south Pacific, allow full stage rotations to be calculated. Between 50 and 83 Ma, where no direct constraints on spreading asymmetry are possible, a `best-fit' full stage rotation was calculated based on the net Nazca:Pacific spreading asymmetry (Pacific spreading fraction fPAC = 0.44) over the past 50 Myr, with conservative lower and upper bounds, based on variability in the degree of spreading asymmetry over periods of <15 Myr, assuming fPACs of 0.5 and 0.36, respectively. Synthetic flowlines generated from our new stage rotation produce a better match to Pacific FZ trends than previously published rotations. With the exception of the chron 18o-20o rotation, the six stage poles for rotations between chrons 33y and 13y (74-33 Ma) all cluster tightly at 60-75░E, 60-68░N, consistent with the relatively constant trend of the major Pacific FZs. This stability spans at least one episode of Farallon Plate fragmentation caused by subduction of PFR segments beneath the Americas, at 55-48 Ma, which appears to have greatly accelerated divergence on the surviving ridge without significantly affecting the location of the instantaneous rotation pole. Together with quasi-periodic 15-20 Myr variations in the degree of spreading asymmetry that also appear to correlate with changes in spreading rate, this indicates that forces other than slab pull may be a factor in determining Pacific-Farallon Plate motions.
Wang, Xiaorui "Ray"
Events Anomaly Definition Main Theorem Application Conclusion Standard Methods Mahalanobis distance Mahalanobis Distance Mahalanobis distance generalizes the t-test normalizes distances according Anomalies as Rare Events Anomaly Definition Main Theorem Application Conclusion Mahalanobis Distance
Triangle anomaly in Weyl semi-metals
Gokce Basar; Dmitri E. Kharzeev; Ho-Ung Yee
Weyl semimetals possess massless chiral quasi-particles, and are thus affected by the triangle anomalies. We discuss the features of the chiral magnetic and chiral vortical effects specific to Weyl semimetals, and then propose three novel phenomena caused by the triangle anomalies in this material: 1) anomaly cooling; 2) charge transport by soliton waves as described by the Burgers' equation, and 3) the shift of the BKT phase transition of superfluid vortices coupled to Weyl fermions. In addition, we establish the conditions under which the chiral magnetic current exists in real materials.
Rifting to spreading in the southern Lau Basin: Variations within the transition zone
NASA Astrophysics Data System (ADS)
Watanabe, M.; Okino, K.; Kodera, T.
The Lau Basin and Havre Trough are back-arc basins related to Pacific-Australian plate convergence. Seafloor spreading occurs in the Lau Basin whereas the Havre Trough is in a rifting stage. At present, the spreading propagator's tip lies at the southern end of the Valu Fa Ridge (VFR) at 22░40'S. Studying this propagation process provides an opportunity to characterize the evolution of rifting to the initiation of seafloor spreading which is fundamental to back-arc basin development. New geophysical data of the southern Lau Basin reveals that as spreading propagates south, it evolves in a discrete style south of 22░40'S. The propagation axis lies along the eastern margin of the basin, where the well defined, linear VFR loses its identifying morphology. Topography in this eastern zone is characterized by grabens separated by short narrow ridges. High backscatter intensity indicates tectonic and magmatic activity in this eastern area. Mantle Bouguer anomalies (MBA) increase southwards from the VFR to form an elevated MBA area extending west from the currently active area. This indicates eastward migration of active rifting, during which the arc crust was extremely thinned. High magnetization is observed in a left-stepping pattern south of the VFR. We interpret this pattern as discrete segments that characterize the initiation of the spreading stage. There is no evidence of a single, continuous spreading axis like that which characterizes the central and northern Lau Basin. The magnetization highs are discrete and are observed in areas where deformation and magmatism are focused. They are offset relative to the VFR, though they generally follow the same north-south trend as the VFR.
Chiral anomalies and differential geometry
Zumino, B.
Some properties of chiral anomalies are described from a geometric point of view. Topics include chiral anomalies and differential forms, transformation properties of the anomalies, identification and use of the anomalies, and normalization of the anomalies. 22 references. (WHK)
High Occurrence of Aberrant Lymph Node Spread on Magnetic Resonance Lymphography in Prostate Cancer Patients With a Biochemical Recurrence After Radical Prostatectomy
Meijer, Hanneke J.M., E-mail: email@example.com [Department of Radiation Oncology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Lin, Emile N. van [Department of Radiation Oncology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Debats, Oscar A. [Department of Radiology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Witjes, J. Alfred [Department of Urology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Span, Paul N.; Kaanders, Johannes H.A.M. [Department of Radiation Oncology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Barentsz, Jelle O. [Department of Radiology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands)
Purpose: To investigate the pattern of lymph node spread in prostate cancer patients with a biochemical recurrence after radical prostatectomy, eligible for salvage radiotherapy; and to determine whether the clinical target volume (CTV) for elective pelvic irradiation in the primary setting can be applied in the salvage setting for patients with (a high risk of) lymph node metastases. Methods and Materials: The charts of 47 prostate cancer patients with PSA recurrence after prostatectomy who had positive lymph nodes on magnetic resonance lymphography (MRL) were reviewed. Positive lymph nodes were assigned to a lymph node region according to the guidelines of the Radiation Therapy Oncology Group (RTOG) for delineation of the CTV for pelvic irradiation (RTOG-CTV). We defined four lymph node regions for positive nodes outside this RTOG-CTV: the para-aortal, proximal common iliac, pararectal, and paravesical regions. They were referred to as aberrant lymph node regions. For each patient, clinical and pathologic features were recorded, and their association with aberrant lymph drainage was investigated. The distribution of positive lymph nodes was analyzed separately for patients with a prostate-specific antigen (PSA) <1.0 ng/mL. Results: MRL detected positive aberrant lymph nodes in 37 patients (79%). In 20 patients (43%) a positive lymph node was found in the pararectal region. Higher PSA at the time of MRL was associated with the presence of positive lymph nodes in the para-aortic region (2.49 vs. 0.82 ng/mL; p = 0.007) and in the proximal common iliac region (1.95 vs. 0.59 ng/mL; p = 0.009). There were 18 patients with a PSA <1.0 ng/mL. Ten of these patients (61%) had at least one aberrant positive lymph node. Conclusion: Seventy-nine percent of the PSA-recurrent patients had at least one aberrant positive lymph node. Application of the standard RTOG-CTV for pelvic irradiation in the salvage setting therefore seems to be inappropriate.
Sea-floor spreading during the past 10 million years on the East Pacific Rise between 35 p0 sS and 53 p0 sS, and the identification of short period pole reversal events
Woodward, Robert Joseph
15 DATA ACQUISITION AND PRELIMINARY ANALYSIS 16 Data Acquired Data Specifications Navigational Errors Aliasing Considerations Data Reduction Basic Processing of Magnetic Anomaly Profiles Normalization to the Spreading Axis Procedure Re... and ridge migration model 70 Page Figure 33. Map view of the study region as it i. s interpreted to have appeared 7 mybp 72 Figure 34. Map view of the study region as it is interpreted to have appeared 3. 5 mybp 73 Figure 35. Map view of the study...
Melt Anomalies in the South China Sea
NASA Astrophysics Data System (ADS)
Wang, T.; Lin, J.; Zhu, J.
We investigated melt anomalies and lithosphere dynamics of the South China Sea (SCS) through combined analysis of seafloor bathymetry, shipboard and satellite derived gravity, sediment thickness, and crustal age. Residual mantle Bouguer anomaly (RMBA) was calculated by removing from free-air gravity anomaly the predicted attractions of water-sediment, sediment-crust, and crust-mantle interfaces as well as the effect of lithospheric plate cooling. Gravity-derived crustal thickness model was then calculated from RMBA and was calibrated by comparison with seismically determined crustal thickness along multiple seismic refraction profiles in the SCS. Residual bathymetry anomaly (RBA) was obtained by subtracting from observed seafloor topography the predicted effects of plate cooling and the observed sediment load. Our analysis reveals several key observations: (1) Negative RMBA with an average amplitude of ~150 mGal is observed throughout the entire northwestern sub-basin, implying warmer mantle or thicker crust beneath this area. (2) Several isolated centers of negative RMBA (up to ~100 mGal in amplitude and 50-100 km in spatial dimension) are observed along the extinct spreading axis of the Central SCS Basin between 116░-119░E and at the eastern end of the Southwest SCS Basin just east of 115░E. These negative anomalies are associated with local topographic highs, reflecting areas of local thick crust. The extinct spreading center of the Southwest SCS Basin between 112░-115░E is associated with much more subduced negative RMBA and thus less melt anomalies. These local magmatic anomalies could reflect post-seafloor-spreading magmatism along the extinct spreading center from residual melts in the mantle. (3) There is obvious north-south asymmetry of RMBA and RBA. Between 16-25 Ma, the northern half of the SCS ocean basin is associated with more negative RMBA and positive RBA, indicating thicker crust or lighter mantle beneath the northern SCS than the southern counterpart. The average differences of RMBA and RBA are ~-20 mGal and 120 m, respectively. Moreover, the north-south asymmetry seems to generally increase with age, i.e., smaller near the extinct spreading axis while larger further off-axis. After 25 Ma, more negative RMBA and positive RBA is associated with the southern part. (4) Overall, the shape of the gravity-derived crustal thickness profiles broadly match that of seismically determined oceanic crustal thickness, although local discrepancies do exist. The crustal thickness of the SCS ocean basin is ~5.5 km on average from our gravity model, and can reach ~10 km locally.
Magnetic signature of large exhumed mantle domains of the Southwest Indian Ridge - results from a deep-tow geophysical survey over 0 to 11 Ma old seafloor
NASA Astrophysics Data System (ADS)
Bronner, A.; Sauter, D.; Munschy, M.; Carlut, J.; Searle, R.; Cannat, M.; Manatschal, G.
We investigate the magnetic signature of ultramafic seafloor in the eastern part of the Southwest Indian Ridge (SWIR). There, detachment faulting, continuous over 11 Myr, exhumed large areas of mantle-derived rocks. These exhumed mantle domains occur in the form of a smooth rounded topography with broad ridges locally covered by a thin highly discontinuous volcanic carapace. We present high-resolution data combining deep-tow magnetics, side-scan sonar images and dredged samples collected within two exhumed mantle domains between 62░ E and 65░ E. We show that, despite an ultra-slow spreading rate, volcanic areas within robust magmatic segments are characterized by well-defined seafloor spreading anomalies. By contrast, the exhumed mantle domains, including a few thin volcanic patches, reveal a weak and highly variable magnetic pattern. The analysis of the magnetic properties of the dredged samples and careful comparison between the nature of the seafloor, the deep-tow magnetic anomalies and the seafloor equivalent magnetization suggest that the serpentinized peridotites do not carry a sufficiently stable remanent magnetization to produce seafloor spreading magnetic anomalies in exhumed mantle domains.
Magnetic signature of large exhumed mantle domains of the Southwest Indian Ridge: results from a deep-tow geophysical survey over 0 to 11 Ma old seafloor
NASA Astrophysics Data System (ADS)
Bronner, A.; Sauter, D.; Munschy, M.; Carlut, J.; Searle, R.; Cannat, M.; Manatschal, G.
We investigate the magnetic signature of an ultramafic seafloor in the eastern part of the Southwest Indian Ridge (SWIR). There, detachment faulting, continuous over 11 Myrs, exhumed large areas of mantle derived rocks. These exhumed mantle domains occur in the form of a smooth rounded topography with broad ridges locally covered by a thin highly discontinuous volcanic carapace. We present high-resolution data combining deep-tow magnetics, side-scan sonar images and dredged samples collected within two exhumed mantle domains between 62░ E and 65░ E. We show that, despite an ultraslow spreading rate, volcanic areas within robust magmatic segments are characterized by well defined seafloor spreading anomalies. By contrast, the exhumed mantle domains, including a few thin volcanic patches, reveal a weak and highly variable magnetic pattern. The analysis of the magnetic properties of the dredged samples and careful comparison between the nature of the seafloor, the deep-tow magnetic anomalies and the seafloor equivalent magnetization suggest that the serpentinized peridotites do not carry a sufficiently stable remanent magnetization to produce seafloor spreading magnetic anomalies in exhumed mantle domains.
Magnetosheath Flow Anomalies in 3-D
NASA Technical Reports Server (NTRS)
Vaisberg, O. L.; Burch, J. L.; Smirnov, V. N.; Avanov, L. A.; Moore, T. E.; Waite, J. H., Jr.; Skalsky, A. A.; Borodkova, N. L.; Coffey, V. N.; Gallagher, D. L.; Rose, M. Franklin (Technical Monitor)
Measurements of the plasma and magnetic field with high temporal resolution on the Interball Tail probe reveal many flow anomalies in the magnetosheath. They are usually seen as flow direction and number density variations, accompanied by magnetic field discontinuities. Large flow anomalies with number density variations of factor of 2 or more and velocity variations of 100 km/s or more are seen with periodicity of about I per hour. The cases of flow anomalies following in succession are also observed, and suggest their decay while propagating through the magnetosheath. Some magnetospheric disturbances observed in the outer magnetosphere after the satellite has crossed the magnetopause on the inbound orbit suggest their association with magnetosheath flow anomalies observed in the magnetosheath prior to magnetopause crossing.
Quantum Spread Spectrum Communication
Humble, Travis S [ORNL
We show that communication of single-photon quantum states in a multi-user environment is improved by using spread spectrum communication techniques. We describe a framework for spreading, transmitting, despreading, and detecting single-photon spectral states that mimics conventional spread spectrum techniques. We show in the cases of inadvertent detection, unintentional interference, and multi-user management, that quantum spread spectrum communications may minimize receiver errors by managing quantum channel access.
SST Anomalies + Wind Anomalies (with dates)
NSDL National Science Digital Library
Greg Shirah
Sea surface temperature (SST) anomalies and sea surface wind anomalies show the development of the 2002-2003 El Nino based on data from NASAs Aqua and QuikSCAT spacecraft. The wind data has been processed using the Variational Analysis Method (VAM).
Magnetization of the oceanic crust: TRM or CRM?
NASA Technical Reports Server (NTRS)
Raymond, C. A.; Labrecque, J. L.
A model was proposed in which chemical remanent magnetization (CRM) acquired within the first 20 Ma of crustal evolution may account for 80% of the bulk natural remanent magnetization (NRM) of older basalts. The CRM of the crust is acquired as the original thermoremanent magnetization (TRM) is lost through low temperature alteration. The CRM intensity and direction are controlled by the post-emplacement polarity history. This model explains several independent observations concerning the magnetization of the oceanic crust. The model accounts for amplitude and skewness discrepancies observed in both the intermediate wavelength satellite field and the short wavelength sea surface magnetic anomaly pattern. It also explains the decay of magnetization away from the spreading axis, and the enhanced magnetization of the Cretaceous Quiet Zones while predicting other systematic variations with age in the bulk magnetization of the oceanic crust. The model also explains discrepancies in the anomaly skewness parameter observed for anomalies of Cretaceous age. Further studies indicate varying rates of TRM decay in very young crust which depicts the advance of low temperature alteration through the magnetized layer.
Hyperfine structure and hyperfine anomaly in Pb
J. R. Persson
The hyperfine structure in the 6p2-configuration in lead has been analysed and the results is compared with calculations. The hyperfine anomaly and improved values of the nuclear magnetic moment for four lead isotopes is obtained, using the results from the analysis. The results open up for new measurements of the hyperfine structure in unstable lead isotopes, in order to extract information of the hyperfine anomaly and distribution of magnetisation in the nucleus.
Lymphatic Malformation; Generalized Lymphatic Anomaly (GLA); Central Conducting Lymphatic Anomaly; CLOVES Syndrome; Gorham-Stout Disease ("Disappearing Bone Disease"); Blue Rubber Bleb Nevus Syndrome; Kaposiform Lymphangiomatosis; Kaposiform Hemangioendothelioma/Tufted Angioma; Klippel-Trenaunay Syndrome; Lymphangiomatosis
Anomalies of nuclear criticality
Clayton, E.D.
During the development of nuclear energy, a number of apparent anomalies have become evident in nuclear criticality. Some of these have appeared in the open literature and some have not. Yet, a naive extrapolation or application of existing data, without knowledge of the anomalies, could lead to potentially serious consequences. This report discusses several of these anomalies.
Analysis of spacecraft anomalies
NASA Technical Reports Server (NTRS)
Bloomquist, C. E.; Graham, W. C.
The anomalies from 316 spacecraft covering the entire U.S. space program were analyzed to determine if there were any experimental or technological programs which could be implemented to remove the anomalies from future space activity. Thirty specific categories of anomalies were found to cover nearly 85 percent of all observed anomalies. Thirteen experiments were defined to deal with 17 of these categories; nine additional experiments were identified to deal with other classes of observed and anticipated anomalies. Preliminary analyses indicate that all 22 experimental programs are both technically feasible and economically viable.
NASA Astrophysics Data System (ADS)
Arav, Igal; Chapman, Shira; Oz, Yaron
We analyse scale anomalies in Lifshitz field theories, formulated as the relative cohomology of the scaling operator with respect to foliation preserving diffeomorphisms. We construct a detailed framework that enables us to calculate the anomalies for any number of spatial dimensions, and for any value of the dynamical exponent. We derive selection rules, and establish the anomaly structure in diverse universal sectors. We present the complete cohomologies for various examples in one, two and three space dimensions for several values of the dynamical exponent. Our calculations indicate that all the Lifshitz scale anomalies are trivial descents, called B-type in the terminology of conformal anomalies. However, not all the trivial descents are cohomologically non-trivial. We compare the conformal anomalies to Lifshitz scale anomalies with a dynamical exponent equal to one.
M-anomaly Analyses and its implications for the architecture of the upper oceanic crust
Tominaga, Masako
My dissertation research consists of two themes: (a) the analysis of Middle Jurassic - Early Cretaceous marine magnetic anomalies (M-anomalies) in order to construct a comprehensive geomagnetic polarity timescale and (b) the investigation...
Anomalies in the polariton dynamics of a one-dimensional magnetic photonic crystal with antiferromagnetic interlayer ordering in an external DC electric field
D. V. Kulagin; A. S. Savchenko; S. V. Tarasenko; V. G. Shavrov
The effect of an external dc electric field on the electrodynamic properties of a one-dimensional magnetic photonic crystal (MPC) with antiferromagnetic interlayer ordering is analyzed within the effective-medium method with regard to the quadratic magneto-optical interaction. The magnetizations of adjacent tangentially magnetized ferromagnetic layers are antiparallel. In particular, the effect of a magnetic compensation point on the character of polariton
Anomalies in the polariton dynamics of a one-dimensional magnetic photonic crystal with antiferromagnetic interlayer ordering in an external DC electric field
NASA Astrophysics Data System (ADS)
Kulagin, D. V.; Savchenko, A. S.; Tarasenko, S. V.; Shavrov, V. G.
The effect of an external dc electric field on the electrodynamic properties of a one-dimensional magnetic photonic crystal (MPC) with antiferromagnetic interlayer ordering is analyzed within the effective-medium method with regard to the quadratic magneto-optical interaction. The magnetizations of adjacent tangentially magnetized ferromagnetic layers are antiparallel. In particular, the effect of a magnetic compensation point on the character of polariton dynamics in this type of MPCs is revealed.
Anomalies in the polariton dynamics of a one-dimensional magnetic photonic crystal with antiferromagnetic interlayer ordering in an external DC electric field
Kulagin, D. V.; Savchenko, A. S.; Tarasenko, S. V., E-mail: firstname.lastname@example.com [National Academy of Sciences of Ukraine, Galkin Institute of Physics and Technology (Ukraine); Shavrov, V. G. [Russian Academy of Sciences, Kotel'nikov Institute of Radio Engineering and Electronics (Russian Federation)
The effect of an external dc electric field on the electrodynamic properties of a one-dimensional magnetic photonic crystal (MPC) with antiferromagnetic interlayer ordering is analyzed within the effective-medium method with regard to the quadratic magneto-optical interaction. The magnetizations of adjacent tangentially magnetized ferromagnetic layers are antiparallel. In particular, the effect of a magnetic compensation point on the character of polariton dynamics in this type of MPCs is revealed.
Anomalies in the polariton dynamics of a one-dimensional magnetic photonic crystal with antiferromagnetic interlayer ordering in an external DC electric field
D. V. Kulagin; A. S. Savchenko; S. V. Tarasenko; V. G. Shavrov
The effect of an external dc electric field on the electrodynamic properties of a one-dimensional magnetic photonic crystal\\u000a (MPC) with antiferromagnetic interlayer ordering is analyzed within the effective-medium method with regard to the quadratic\\u000a magneto-optical interaction. The magnetizations of adjacent tangentially magnetized ferromagnetic layers are antiparallel.\\u000a In particular, the effect of a magnetic compensation point on the character of polariton
Bath, G.D.; Jahren, C.E.; Rosenbaum, J.G. [Geological Survey, Denver, CO (USA); Baldwin, M.J. [Fenix and Scisson, Inc., Mercury, NV (USA)
Air and ground magnetic anomalies in the Climax stock area of the NTS help define the gross configuration of the stock and detailed configuration of magnetized rocks at the Boundary and Tippinip faults that border the stock. Magnetizations of geologic units were evaluated by measurements of magnetic properties of drill core, minimum estimates of magnetizations from ground magnetic anomalies for near surface rocks, and comparisons of measured anomalies with anomalies computed by a three-dimensional forward program. Alluvial deposits and most sedimentary rocks are nonmagnetic, but drill core measurements reveal large and irregular changes in magnetization for some quartzites and marbles. The magnetizations of quartz monzonite and granodiorite near the stock surface are weak, about 0.15 A/m, and increase at a rate of 0.00196 A/m/m to 1.55 A/m, at depths greater than 700 m (2300 ft). The volcanic rocks of the area are weakly magnetized. Aeromagnetic anomalies 850 m (2800 ft) above the stock are explained by a model consisting of five vertical prisms. Prisms 1, 2, and 3 represent the near surface outline of the stock, prism 4 is one of the models developed by Whitehill (1973), and prism 5 is modified from the model developed by Allingham and Zietz (1962). Most of the anomaly comes from unsampled and strongly-magnetized deep sources that could be either granite or metamorphosed sedimentary rocks. 48 refs., 23 figs., 3 tabs.
Splenic Anomalies of Shape, Size, and Location: Pictorial Essay
Yildiz, Adalet Elcin; Ariyurek, Macit Orhan; Karcaaltincaba, Musturay
Spleen can have a wide range of anomalies including its shape, location, number, and size. Although most of these anomalies are congenital, there are also acquired types. Congenital anomalies affecting the shape of spleen are lobulations, notches, and clefts; the fusion and location anomalies of spleen are accessory spleen, splenopancreatic fusion, and wandering spleen; polysplenia can be associated with a syndrome. Splenosis and small spleen are acquired anomalies which are caused by trauma and sickle cell disease, respectively. These anomalies can be detected easily by using different imaging modalities including ultrasonography, computed tomography, magnetic resonance imaging, and also Tc-99m scintigraphy. In this pictorial essay, we review the imaging findings of these anomalies which can cause diagnostic pitfalls and be interpreted as pathologic processes. PMID:23710135
6d, N=(1,0) Coulomb Branch Anomaly Matching
Kenneth Intriligator
6d QFTs are constrained by the analog of 't Hooft anomaly matching: all anomalies for global symmetries and metric backgrounds are constants of RG flows, and for all vacua in moduli spaces. We discuss an anomaly matching mechanism for 6d N=(1,0) theories on their Coulomb branch. It is a global symmetry analog of Green-Schwarz-West-Sagnotti anomaly cancellation, and requires the apparent anomaly mismatch to be a perfect square, $\\Delta I_8={1\\over 2}X_4^2$. Then $\\Delta I_8$ is cancelled by making $X_4$ an electric / magnetic source for the tensor multiplet, so background gauge field instantons yield charged strings. This requires the coefficients in $X_4$ to be integrally quantized. We illustrate this for N=(2,0) theories. We also consider the N=(1,0) SCFTs from N small $E_8$ instantons, verifying that the recent result for its anomaly polynomial fits with the anomaly matching mechanism.
North Cascades Geology: Sea-Floor Spreading
NSDL National Science Digital Library
This site contains information about discoveries made after World War II when ocean-going geologists adapted sensitive magnetometers developed for antisubmarine warfare for use in seafloor research. This modern technology gave geologists their greatest boost in more than a century of field work and led to the idea of sea floor spreading. This site has animations showing sea-floor spreading and a magnetometer discovering magnetic strips. There are also diagrams showing the magnetic pattern on the ocean floor at the Juan de Fuca Ridge, Benioff-Wadati zones at continental margins, and an idealized representation of divergent plates with a resulting subduction zone.
NASA Technical Reports Server (NTRS)
Ross, Howard D.; Miller, Fletcher; Schiller, David; Sirignano, William
Recent reviews of our understanding of flame spread across liquids show that there are many unresolved issues regarding the phenomenology and causal mechanisms affecting ignition susceptibility, flame spread characteristics, and flame spread rates. One area of discrepancy is the effect of buoyancy in both the uniform and pulsating spread regimes. The approach we have taken to resolving the importance of buoyancy for these flames is: (1) normal gravity (1g) and microgravity (micro g) experiments; and (2) numerical modeling at different gravitational levels. Of special interest to this work, as discussed at the previous workshop, is the determination of whether, and under what conditions, pulsating spread occurs in micro g. Microgravity offers a unique ability to modify and control the gas-phase flow pattern by utilizing a forced air flow over the pool surface.
Kinematics of Jurassic ultra-slow spreading in the Piemonte Ligurian ocean
NASA Astrophysics Data System (ADS)
Vissers, Reinoud L. M.; van Hinsbergen, Douwe J. J.; Meijer, Paul Th.; Piccardo, Giovanni B.
The geological record of the western and northern Mediterranean region (Apennines, Alps, Carpathians) contains relics of an ocean basin of Jurassic age known as the Piemonte-Ligurian (PL), Alpine or Alpine Tethys ocean. We here reconstruct the age, direction and amount of extension in the PL basin by analyzing the differences in spreading rates based on marine magnetic anomalies and fracture zones in the Central Atlantic ocean between Africa and North America, and the North Atlantic Ocean between Iberia and North America. The difference in spreading rate must have been accommodated between Iberia and Adria, which we assume to be rigidly attached to the African plate in the late Jurassic. We compute a maximum of ś450 km of WSW-ENE extension between Iberia and Africa, largely between ś170 and ś150 Ma. Relative Adria (Africa)-Europe motion predicts up to 670 km of extension at the longitude of the western Alps - distributed over the PL and Valaisan basins - decreasing to ś315 km along the easternmost boundary of the PL basin formed by the Tornquist-Tesseyre line. We note that the Africa-Europe plate boundary in the late Jurassic was probably not discretely localized along the Tornquist-Tesseyre line, but distributed over several fault zones including the Severin oceanic basin to the west of the Moesian platform; the 315 km of PL extension in the east should hence be considered a maximum. It is unknown to what extent PL extension was accommodated by genuine ocean spreading, but full spreading rates in the western PL basin were slow, no more than 20 mm/yr. This ultraslow spreading is consistent with characteristics of western Mediterranean ophiolites, including exposure of upper mantle rocks at the sea floor, the alternation of volcanic and avolcanic segments, and the petrologic features of the pertinent magmas and peridotites.
Konstantinov, Igor E.
Taussig-Bing anomaly is a rare congenital heart malformation that was first described in 1949 by Helen B. Taussig (1898¢1986) and Richard J. Bing (1909¢). Although substantial improvement has since been achieved in surgical results of the repair of the anomaly, management of the Taussig-Bing anomaly remains challenging. A history of the original description of the anomaly, the life stories of the individuals who first described it, and the current outcomes of its surgical management are reviewed herein. PMID:20069085
Deep crustal structure of the northeastern Gulf of Mexico: Implications for rift evolution and seafloor spreading
NASA Astrophysics Data System (ADS)
Eddy, Drew R.; Van Avendonk, Harm J. A.; Christeson, Gail L.; Norton, Ian O.; Karner, Garry D.; Johnson, Christopher A.; Snedden, John W.
We image deep crustal structure using marine seismic refraction data recorded by a linear array of ocean-bottom seismometers in the Gulf of Mexico Basin Opening project (GUMBO Line 3) in order to provide new constraints on the nature of continental and oceanic crust in the northeastern Gulf of Mexico. GUMBO Line 3 extends ~524 km from the continental shelf offshore Pensacola, Florida, across the De Soto Canyon and into the central Gulf basin. Travel times from long offset, wide angle reflections and refractions resolve compressional seismic velocities and layer boundaries for sediment, crystalline crust, and upper mantle. We compare our results with coincident multichannel seismic reflection data. Our velocity model recovers shallow seismic velocities (~2.0-4.5 km/s) that we interpret as evaporites and clastic sediments. A Cretaceous carbonate platform is interpreted beneath the De Soto Canyon with seismic velocities >5.0 km/s. Crystalline continental crust thins seaward along GUMBO Line 3 from 23-10 km across the De Soto Canyon. High seismic velocity lower crust (>7.2 km/s) is interpreted as extensive syn-rift magmatism and possibly mafic underplating, common features at volcanic rift margins with high mantle potential temperatures. In the central Gulf basin we interpret thick oceanic crust (>8 km) emplaced at a slow full-spreading rate (~24 mm/yr). We suggest a sustained thermal anomaly during slow seafloor-spreading conditions led to voluminous basalt flows from a spreading ridge that overprinted seafloor magnetic anomalies in the northeastern Gulf of Mexico.
NASA Technical Reports Server (NTRS)
Collinson, G. A.; Sibeck, David Gary; Boardsen, Scott A.; Moore, Tom; Barabash, S.; Masters, A.; Shane, N.; Slavin, J.A.; Coates, A.J.; Zhang, T. L.; Sarantos, M.
We present a multi-instrument study of a hot flow anomaly (HFA) observed by the Venus Express spacecraft in the Venusian foreshock, on 22 March 2008, incorporating both Venus Express Magnetometer and Analyzer of Space Plasmas and Energetic Atoms (ASPERA) plasma observations. Centered on an interplanetary magnetic field discontinuity with inward convective motional electric fields on both sides, with a decreased core field strength, ion observations consistent with a flow deflection, and bounded by compressive heated edges, the properties of this event are consistent with those of HFAs observed at other planets within the solar system.
The anomaly data base of screwworm information
NASA Technical Reports Server (NTRS)
Giddings, L. E.
Standard statistical processing of anomaly data in the screwworm eradication data system is possible from data compiled on magnetic tapes with the Univac 1108 computer. The format and organization of the data in the data base, which is also available on dedicated disc storage, are described.
Table of hyperfine anomaly in atomic systems
Persson, J.R., E-mail: email@example.com
This table is a compilation of experimental values of magnetic hyperfine anomaly in atomic and ionic systems. The last extensive compilation was published in 1984 by B³ttgenbach [S. B³ttgenbach, Hyperfine Int. 20 (1984) 1] and the aim here is to make an up to date compilation. The literature search covers the period up to January 2011.
Magnetic effects of the substorm current wedge in a ōspread-out wireö model and their comparison with ground, geosynchronous, and tail lobe data
NASA Astrophysics Data System (ADS)
Sergeev, V. A.; Tsyganenko, N. A.; Smirnov, M. V.; Nikolaev, A. V.; Singer, H. J.; Baumjohann, W.
Although the substorm current wedge (SCW) is recognized as a basic 3-D current system of the substorm expansion phase, its existing models still do not extend beyond a cartoon-like sketch, and very little is known of how well they reproduce magnetic variations observed in the magnetosphere during substorms. A lack of a realistic quantitative SCW model hampers testing model predictions against large sets of spacecraft data. This paper (1) presents a computationally efficient and flexible model with a realistic geometry of field-aligned currents, conveniently parameterized by the SCW strength, longitudinal width, and position, all derived from ground-based midlatitude magnetic variations; and (2) tests the model against INTERMAGNET network observations during substorms and compares its predictions with space magnetometer data. The testing demonstrated significant and systematic discrepancies between the observed and predicted magnetic variations, depending on spacecraft location, concurrent magnetotail configuration, and substorm phase. In particular, we found that the net SCW current derived from the midlatitude field variations corresponds to only a relatively small and variable fraction of the distant 3-D substorm current, inferred from spacecraft data in the lobe and at geosynchronous distance. The discrepancy can be partly attributed to additional region 2 polarity field-aligned currents in the same longitudinal sector, associated with azimuthal diversion of the earthward plasma flow when it encounters the region of strong quasi-dipolar field in the inner magnetosphere.
Neuroimaging in craniovertebral anomalies as seen in the tropics.
Sankhe, Shilpa S; Kumar, S K Susheel
Craniovertebral junction (CVJ) disorders in the Occident are usually associated with systemic disorders. In contrast, in the Orient, a greater incidence of isolated CVJ anomalies is seen. Although these are developmental anomalies, they manifest late in life, with trauma and/or infection playing a promotive role. The most significant and common of these anomalies are basilar invagination and atlantodental dislocation, which also occur together. Accurate diagnosis of these anomalies is feasible using computed tomography and magnetic resonance imaging. Greater awareness of this subset of patients is essential for greater understanding and effective management of these ailments. PMID:22032505
NSDL National Science Digital Library
Activity and Starting Point page by R.M. MacKay. Clark College, Physics and Meteorology.
In this introductory Excel tutorial (Activity I) students use Excel to explore the geodynamics model equation for ocean depth around a sea-floor spreading center. For students with no prior Excel experience.
Characterization of potential sources of magnetic anomalies within the crust in a tectonically active region: Amphibolites and migmatites from Potrillo Maar, New Mexico
NASA Technical Reports Server (NTRS)
Spear, F. S.; Padovanni, E.
The purpose was to characterize the oxide mineralogy and petrology of samples collected from Potrillo Maar, New Mexico with the goal of explaining the magnetic anamoly that is observed over this region from remote sensing. Potrillo Maar is a diatreme that has brought rocks from all depths in the crust to the surface almost instantaneously. The samples are therefore thought to be representative of the crust as it exists today below this portion of the Rio Grande Rift. It is generally believed that oxide minerals (magnetite, hematite, etc.) are responsible for the magnetic signature of the crust. The samples from Portillo Maar therefore offer a unique opportunity to examine the magnetic mineralogy of the entire crust. The results indicate that the magnetic anamoly observed over Rio Grande Rift may be consequence of the tectonic activity that caused mylonitization of the rocks and allowed the infiltration of oxidizing fluids.
Isotopic Anomalies in CP Stars: Helium, Mercury, Platinum, and Calcium
C. R. Cowley; S. Hubrig; F. Castelli
We review the classical observational results for isotopic abundance variations for several elements in CP stars. We concentrate on the "newest" anomaly, in calcium. The cosmically very rare isotope, Ca-48 can rival and even dominate the more common, alpha nuclide, Ca-40. Relevant examples are found in the hot, non-magnetic HgMn stars, and the field horizontal-branch star, Feige 86. The calcium anomaly is also present in cool, magnetic stars, including the notorious HD 101065, Przybylski's star.
Tan F. Wong: Spread Spectrum & CDMA 2. Intro. Spread Spectrum Introduction to Spread Spectrum
Wong, Tan F.
Tan F. Wong: Spread Spectrum & CDMA 2. Intro. Spread Spectrum Chapter 2 Introduction to Spread Spectrum Communications As discussed in Chapter 0, a spread spectrum modulation produces a transmitted spectrum much wider than the minimum bandwidth required. There are many ways to generate spread spectrum
Crustal structure, accretionary processes and rift propagation: a gravity study of the intermediate-spreading Valu Fa Ridge, Lau Basin
NASA Astrophysics Data System (ADS)
Peirce, Christine; Turner, Ian M.; Sinha, Martin C.
The Valu Fa Ridge is an intermediate-spreading (full rate of 60mmyr-1) ridge located in the Lau Basin. In 1995 this ridge was surveyed using a multidisciplinary, geophysical approach to image crust and upper mantle structure, with the aim of investigating the processes of oceanic crustal accretion in a back-arc tectonic environment. As part of this experiment a network of gravity profiles was acquired, together with seismic, magnetic, swath bathymetry and controlled-source electromagnetic data. Presented in this paper are the results of forward modelling of a subset of the acquired gravity profiles, two oriented ridge-perpendicular and one ridge-parallel, using the preferred seismic models of Turner et al. (1999) as a basis of initial model construction. In addition, the gravity data set in its entirety has been used to calculate the mantle and residual mantle Bouguer anomalies with the aim of investigating variability in crustal structure, both density and layer thickness, and the nature of the underlying upper mantle. Of particular interest are the overlapping spreading centre between the Central and Northern Valu Fa Ridges, where seismic modelling implies a generally thickened crust and a magma chamber located beneath the overlap basin rather than separate chambers supplying each ridge, and the propagating rift tip and associated basin-bounding pseudo-fault. Modelling results suggest that the pre- and post-rift crusts have different compositional origins, with lower densities required >12km off-axis to fit the observed free-air gravity anomaly. The locations of the transitions into regions of lower density correspond with those of Turner et al. (1999) derived from seismic modelling, which in turn correspond in location to the rift-related pseudo-fault identified by Wiedicke & Collier (1993). Calculation and interpretation of the mantle and residual mantle Bouguer anomalies also confirms the lower off-axis densities and indicates a general increase in crustal thickness northwards towards the overlapping spreading centre between the Central and Northern Valu Fa Ridge segments. The presence of thicker crust, corresponding to a region of negative mantle and residual mantle Bouguer anomaly, implies that the region surrounding the overlapping spreading centre has been in the recent geological past, or is presently, the site of an increased magma supply. The residual mantle Bouguer anomaly also reveals features related directly to off-axis lateral variation in density and layer thickness, associated with the southward propagation of the Valu Fa Ridge into the Havre Trough. Modelling of the north-south variation in crustal thickness along-axis shows that the anomaly trend can be explained simply by thicker crust beneath each of the Valu Fa Ridge segments and the overlapping spreading centre between the Northern and Central Valu Fa Ridges. The observation of segment-centred crustal thickening is consistent with models of ridge segmentation that suggest that melt influx is located towards segment centres and that segment length is controlled by the maximum lateral extent to which this melt can flow (Macdonald et al. 1988; Tolstoy et al. 1993). However, the overlapping spreading centre remains anomalous from these models in that it also appears to be associated with thicker crust and an increased melt supply.
Hydrodynamics with Triangle Anomalies
Dam T. Son; Piotr Surowka
We consider the hydrodynamic regime of theories with quantum anomalies for global currents. We show that a hitherto discarded term in the conserve current is not only allowed by symmetries, but is in fact required by triangle anomalies and the second law of thermodynamics. This term leads to a number of new effects, one of which is chiral separation in a rotating fluid at nonzero chemical potential. The new kinetic coefficients can be expressed, in a unique fashion, through the anomalies coefficients and the equation of state. We briefly discuss the relevance of this new hydrodynamic term for physical situations, including heavy ion collisions.
Hydrodynamics with Triangle Anomalies
Son, Dam T. [Institute for Nuclear Theory, University of Washington, Seattle, Washington 98195-1550 (United States); Surowka, Piotr [Department of Physics, University of Washington, Seattle, Washington 98195-1560 (United States); Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow (Poland)
We consider the hydrodynamic regime of theories with quantum anomalies for global currents. We show that a hitherto discarded term in the conserved current is not only allowed by symmetries, but is in fact required by triangle anomalies and the second law of thermodynamics. This term leads to a number of new effects, one of which is chiral separation in a rotating fluid at nonzero chemical potential. The new kinetic coefficients can be expressed, in a unique fashion, through the anomaly coefficients and the equation of state. We briefly discuss the relevance of this new hydrodynamic term for physical situations, including heavy-ion collisions.
... terms: CAA, anomalous coronary artery (ACA), sudden cardiac arrest, sudden cardiac death A coronary artery anomaly (CAA) ... exercise Sudden cardiac death (also called sudden cardiac arrest) is the most dangerous symptom of a CAA. ...
Anomalies in vortex lattice dynamics driven by induced ac currents in superconducting films with magnetic arrays of two-fold symmetry
NASA Astrophysics Data System (ADS)
Moreno, A. J.; Chiliotte, C. E.; Pasquini, G.; Bekeris, V.; Gomez, A.; del Valle, J.; Gonzalez, E. M.; Prieto, J. L.; Vicent, J. L.
We study the dynamics of the vortex lattice driven by ac induced currents in the critical state regime, for T > 0.70 TC. The samples are superconducting films grown on top of two-fold symmetry array of magnetic dots. In these heterostructures, the induced ac currents flow parallel to the short and to the long side of the pinning array in different areas of the samples simultaneously. This behavior produces remarkable effects in the vortex lattice dynamics. First of all, periodic features are observed in the ac susceptibility versus applied magnetic field measurements which are related to matching effects between the vortex lattices and the magnetic array. However, the vortex lattice reconfiguration observed in magnetotransport experiments is absent. Some of these features are revealed as maxima instead of being minima, indicating higher mobility at certain matching fields. Competing unstable vortex configurations could lead to increase vortex mobility precluding the reconfiguration transition. At high temperatures, where the matching effects show up, the magnetic permeability of the dots is the mechanism that governs the JC(T) behavior. Moreover, the temperature dependence of the pinning force FP(T) shows a temperature crossover related to an unexpected enhancement in vortex mobility. Vortex¢vortex interaction and the interplay between trapped and interstitial vortices are a hint to explain these phenomena.
Long-wavelength aeromagnetic anomaly map of the conterminous United States
NASA Astrophysics Data System (ADS)
Sexton, John L.; Hinze, William J.; von Frese, Ralph R. B.; Braile, Lawrence W.
Total intensity magnetic anomaly unflltered and low-pass filtered profile and contour maps of the conterminous United States have been prepared from data provided by the U.S. Naval Oceanographic Office's Project MAGNET Survey. The maps are useful for regional geological investigations because the anomalies, particularly on the filtered maps that emphasize long-wavelength anomalies, can be correlated with known major geologic features. The most intense positive, long-wavelength anomaly occurs over Precambrian mafic basement rocks in eastern Tennessee and Kentucky. Other examples of prominent positive anomalies occur over the Great Valley of California and the Colorado Plateau and along the Appalachian fold belt. In contrast, prominent negative long-wavelength magnetic anomalies occur over the Cascade Mountains, Mississippi Embayment, and southern Rocky Mountains and marginally to the positive anomaly related to the Mid-continent Rift.
Edwin C. Gravereaux; Louis L. Nguyen; Leslie D. Cunningham
Opinion statementĀĀCongenital vascular anomalies are rare. The cardiovascular specialist should nevertheless be aware of the more common types\\u000a of vascular anomalies and understand the implications for patient treatment and the likelihood of associated morbidity. The\\u000a presentation of congenital arteriovenous malformations can range from asymptomatic or cosmetic lesions, to those causing ischemia,\\u000a ulceration, hemorrhage, or high-output congestive heart failure. Treatment of
de Diego, Jose A
Analysis of the radio-metric data from Pioneer 10 and 11 spacecrafts has indicated the presence of an unmodeled acceleration starting at 20 AU, which has become known as the Pioneer anomaly. The nature of this acceleration is uncertain. In this paper we give a description of the effect and review some relevant mechanisms proposed to explain the observed anomaly. We also discuss on some future projects to investigate this phenomenon.
Jose A. de Diego; Dario Nunez
Analysis of the radio-metric data from Pioneer 10 and 11 spacecrafts has indicated the presence of an unmodeled acceleration starting at 20 AU, which has become known as the Pioneer anomaly. The nature of this acceleration is uncertain. In this paper we give a description of the effect and review some relevant mechanisms proposed to explain the observed anomaly. We also discuss on some future projects to investigate this phenomenon.
NASA Astrophysics Data System (ADS)
Biance, Anne-Laure; Clanet, Christophe; Quere, David
When a spherical liquid droplet is brought in contact with a solid it wets totally, it tends to spread on the solid because of the driving capillary force. On the other hand, inertia and viscosity both resist to the motion. We studied the spreading of spherical millimetric water droplets and we observed that the spreading successively follows two dynamical laws: the solid-liquid contact first increases as t^1/2, and later as t^1/10. We interpreted the first regime as an inertial one and found a quantitative agreement with a recent theory by Eggers, Lister and Stone for a similar problem, namely, the coalescence of drops of low viscosity. The second regime is viscous as shown earlier by Tanner and Cazabat. We therefore measured the duration of the inertial regime, as a function of both the droplet radius and the liquid viscosity.
Equivalent magnetization over the World Ocean
NASA Astrophysics Data System (ADS)
Dyment, J.; Hamoudi, M.; Choi, Y.; Thebault, E.; Quesnel, Y.; Roest, W. R.; Lesur, V.
In another presentation (Hamoudi et al., this meeting), we present the construction of a new candidate for the World Digital Magnetic Anomaly Map (WDMAM) over oceanic areas. This map is based on: (a) a more realistic forward modeling of the marine magnetic anomalies which includes remanent magnetization vectors taking into account the age and motion of the oceanic lithosphere; (b) evaluation of the equivalent magnetization by comparison of the synthetic and observed anomalies along ship tracks; and (c) adjustment of the synthetic anomaly maps using this equivalent magnetization prior to merging with the observed anomalies. A by-product of this approach is a global distribution of equivalent magnetization over the World's Ocean. Note that, because no global basement map exists for the oceanic areas, we assume a uniform, 5 km-deep and 1 km-thick magnetized layer for the forward model. The resulting equivalent magnetization is therefore relative to this over-simplistic magnetic source. A first observation is that, within the hypotheses of the forward model, the average equivalent magnetization is about 3 A/m, a value which compares well with the Natural Remanent Magnetization (NRM) measured on ancient basalt samples. As expected, the mid-ocean ridges are marked by stronger equivalent magnetizations, an observation which reflects both the stronger NRM measured at ridge axes and their shallower bathymetry (not taken into account in our forward model). More interesting is the observation of significant along-axis variations. In the North Atlantic Ocean, the Kolbeinsey and Reykjanes ridges around Iceland are marked by a very strong equivalent magnetization and the Azores Plateau by a strong one as well.. Again this may reflect the combined effect of shallower seafloor, thicker and/or more magnetized basaltic layer at hotspots. In contrast, the areas between 45 and 55░N and between 0 and 10░N (Equatorial FZ) correspond to a weak equivalent magnetization. Further south, the Mid-Atlantic Ridge displays a more uniform signature, although off-axis variations seem associated to the Tristan and St Helena hotspots. In the Indian Ocean, a strong equivalent magnetization characterizes areas of hotspot-ridge interaction such as the Gulf of Aden, the Central Indian Ridge near Rodrigues Island, the Southwest Indian Ridge near Marion Island, and the Southeast Indian Ridge near St Paul and Amsterdam Islands. A weaker one is observed in colder area, at the Australian-Antarctic Discordance and around the Rodrigues Triple Junction. The Pacific Ocean is characterized by a generally stronger equivalent magnetization, both near ridges and in abyssal plains. Time variations, i.e. along seafloor spreading flowlines, are apparent across the Mid-Atlantic and Pacific-Antarctic ridges, with highs near the ridge axis (younger than 10 Ma) and between ~83 and 60 Ma, just after the Cretaceous Normal Superchron and lows between ~60 and 10 Ma. The Mesozoic basins of the Pacific and Atlantic oceans show a weaker equivalent magnetization before ~155 Ma and a stronger one after. Basins covered by thick sediments such as the Bengal Bay, Great Australian Bight, Nova Scotia Basin, and Western Somali Basin show a very weak equivalent magnetization, reflecting both a deeper basement and a possible thermal demagnetization. Some of these variations coincide with satellite magnetic anomalies.
Insights about the structure and evolution of the Scotia Arc from a new magnetic data compilation
NASA Astrophysics Data System (ADS)
Martos, Yasmina M.; Catalßn, Manuel; Galindo-ZaldĒvar, Jes·s; Maldonado, Andrķs; Bohoyo, Fernando
Analysis of a new regional compilation of magnetic anomalies from marine, aeromagnetic and satellite data reveals the main structural/tectonic elements of the Scotia Arc. The most relevant magnetic anomaly in the continental crust, the Pacific Margin Anomaly (PMA), is related to composite magmatic arc batholiths. It was emplaced by subduction processes along the Pacific continental margin of the Antarctic Peninsula and can be followed within the continental blocks of the South Scotia Ridge and South America. Four representative magnetic profiles also show the structure in depth, and allow us to characterize the main crustal elements of the region. The new compilation and models improve our knowledge of the Scotia Arc's development. The PMA is seen to have a roughly W-E orientation, decreasing in intensity eastwards from the Pacific Margin of the Antarctic Peninsula, and extending towards the South Scotia Ridge to Discovery Bank and even to Herdman Bank. However, the identification of the PMA in the North Scotia Ridge is uncertain, since the magnetic anomalies and the modeled profiles do not support the presence of an important batholithic body. This setting can be attributed to the kinematics of subduction, almost orthogonal to the Pacific margin of the Antarctic Peninsula and oblique along the South American margin. Based on the new magnetic anomaly map, magnetic modeling, and the continuity of the PMA along the Antarctic Peninsula and South Scotia Ridge, we propose a reconstruction of the initial distribution of the main continental blocks in the initial stages during the Cretaceous. The anomalies identified in the northern Scotia Sea are probably related to local basic and/or intermediate igneous rocks intruded in pull-apart basins that developed in the South America-Antarctica plate boundary deformation zone during the initial stages of South Atlantic Ocean and Weddell Sea spreading.
Spread spectrum for commercial communications
D. L. Schilling; L. B. Milstein; R. L. Pickholtz; M. Kullback; F. Miller
The authors describe how spread spectrum operates and explain why the FCC has allocated several spectral bands for spread spectrum. They examine what is wrong with the spectrum allocations the way they are now. They show who is using and will use spread spectrum and why. In particular, they discuss the use of spread spectrum for mobile cellular communications: the
Entry of solar-wind ions into the wake of a small body with a magnetic anomaly: A global Vlasov simulation
NASA Astrophysics Data System (ADS)
Umeda, Takayuki; Ito, Yosuke
The interaction between a plasma flow and a small dielectric body with a weak intrinsic global magnetic field is studied by means of a five-dimensional full electromagnetic Vlasov simulation with two configuration spaces and three velocity spaces. In the present study, entry processes of ions into the nightside wake tail are examined. The simulation result shows that the bow shock and the magnetopause are formed on the dayside. However, most of solar-wind ions are reflected at the dayside magnetopause and are picked up by the interplanetary magnetic field. Then, a small part of the reflected ions are taken into the deep wake tail near the body by the EūB cycloid motion.
Magnetic order and lattice anomalies in the J{sub 1}-J{sub 2} model system VOMoO{sub 4}
Bombardi, A. [Diamond Light Source Ltd., Rutherford Appleton Laboratory, Chilton-Didcot, OX11 0QX, Oxfordshire (United Kingdom); Chapon, L.C. [ISIS, CCLRC Rutherford Appleton Laboratory, Chilton-Didcot, OX11 0QX, Oxfordshire (United Kingdom); Margiolaki, I.; Mazzoli, C. [European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex 9 (France); Gonthier, S.; Duc, F. [Centre d'Elaboration des Materiaux et d'Etudes Structurales, CNRS, 31055 Toulouse Cedex (France); Radaelli, P.G. [ISIS, CCLRC Rutherford Appleton Laboratory, Chilton-Didcot, OX11 0QX, Oxfordshire (United Kingdom); Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)
High-resolution x-ray and neutron powder-diffraction measurements were performed on polycrystalline VOMoO{sub 4}. Below {approx_equal}40 K the system orders in a simple Neel antiferromagnetic state (propagation vector k-vector=0), indicating a dominant role of the nearest-neighbor interactions. The order is three dimensional but the reduced saturated magnetic moment m of 0.41 (1) {mu}{sub B}/V{sup 4+} at 2 K indicates strongly two-dimensional character and enhanced quantum fluctuations. On cooling, there is no evidence of a reduction of the crystal symmetry. However, neutron diffraction indicates an anomalous evolution of the lattice parameters, which can be related to the onset of magnetic correlations.
Octahedral distortion induced magnetic anomalies in LaMn{sub 0.5}Co{sub 0.5}O{sub 3} single crystals
Manna, Kaustuv, E-mail: firstname.lastname@example.com; Elizabeth, Suja; Anil Kumar, P. S. [Department of Physics, Indian Institute of Science, Bangalore 560012 (India); Bhadram, Venkata Srinu; Narayana, Chandrabhas [Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India)
Single crystals of LaMn{sub 0.5}Co{sub 0.5}O{sub 3} belonging to the ferromagnetic-insulator and distorted perovskite class were grown using a four-mirror optical float zone furnace. The as-grown crystal crystallizes into an orthorhombic Pbnm structure. The spatially resolved 2D Raman scan reveals a strain-induced distribution of transition metal (TM)¢oxygen (O) octahedral deformation in the as-grown crystal. A rigorous annealing process releases the strain, thereby generating homogeneous octahedral distortion. The octahedra tilt by reducing the bond angle TM-O-TM, resulting in a decline of the exchange energy in the annealed crystal. The critical behavior is investigated from the bulk magnetization. It is found that the ground state magnetic behavior assigned to the strain-free LaMn{sub 0.5}Co{sub 0.5}O{sub 3} crystal is of the 3D Heisenberg kind. Strain induces mean field-like interaction in some sites, and consequently, the critical exponents deviate from the 3D Heisenberg class in the as-grown crystal. The temperature-dependent Raman scattering study reveals strong spin-phonon coupling and the existence of two magnetic ground states in the same crystal.
Optimizing Hybrid Spreading in Metapopulations
Zhang, Changwang; Cox, Ingemar J; Chain, Benjamin M
Epidemic spreading phenomena are ubiquitous in nature and society. Examples include the spreading of diseases, information, and computer viruses. Epidemics can spread by \\textit{local spreading}, where infected nodes can only infect a limited set of direct target nodes and \\textit{global spreading}, where an infected node can infect every other node. In reality, many epidemics spread using a hybrid mixture of both types of spreading. In this study we develop a theoretical framework for studying hybrid epidemics, and examine the optimum balance between spreading mechanisms in terms of achieving the maximum outbreak size. In a metapopulation, made up of many weakly connected subpopulations, we show that one can calculate an optimal tradeoff between local and global spreading which will maximise the extent of the epidemic. As an example we analyse the 2008 outbreak of the Internet worm Conficker, which uses hybrid spreading to propagate through the internet. Our results suggests that the worm would have been eve...
Crustal structure and magnetic lineation along two geo-traverses from western continental margin of India to Eastern Somali Basin, NW Indian Ocean
NASA Astrophysics Data System (ADS)
Chaubey, A. K.; Anshu, A.; Sreejith, K.; Pandey, A.
Shipborne gravity and magnetic data along two parallel geo-traverses spanning from western continental margin of India to off Seychelles are used to delineate crustal structure and magnetic pattern of major structural features - western continental margin of India, Laxmi Basin, Laxmi Ridge, Arabian Basin, slow spreading Carlsberg Ridge and Eastern Somali Basin. The seismically constrained gravity models along the geo-traverses suggest considerable variation in crustal thickness - about 38 km on continental shelf of western India to about 4 km of the Eastern Somali Basin. The Eastern Somali Basin is characterized by thin oceanic crustal thickness (~3 to 4 km) as compared to its conjugate Arabian Basin where thickness varies from 5 to 6 km. The magnetic anomalies along the geo-traverse reveal three distinct zones: (i) a zone of relative high frequency short wavelength younger anomalies over the axial parts of the Carlsberg Ridge, (ii) a zone of well developed Early Tertiary magnetic anomalies in both the Arabian and Eastern Somali basins, and (iii) relative magnetic quiet zone, between the above two zones, representing a hiatus in spreading. Based on the results, we present a comparative analysis of crustal configuration and magnetic pattern of major structural features of the study area and discuss its tectonic evolution.
Astrometric solar system anomalies
Nieto, Michael Martin [Los Alamos National Laboratory; Anderson, John D [PROPULSION LABORATORY
There are at least four unexplained anomalies connected with astrometric data. perhaps the most disturbing is the fact that when a spacecraft on a flyby trajectory approaches the Earth within 2000 km or less, it often experiences a change in total orbital energy per unit mass. next, a secular change in the astronomical unit AU is definitely a concern. It is increasing by about 15 cm yr{sup -1}. The other two anomalies are perhaps less disturbing because of known sources of nongravitational acceleration. The first is an apparent slowing of the two Pioneer spacecraft as they exit the solar system in opposite directions. Some astronomers and physicists are convinced this effect is of concern, but many others are convinced it is produced by a nearly identical thermal emission from both spacecraft, in a direction away from the Sun, thereby producing acceleration toward the Sun. The fourth anomaly is a measured increase in the eccentricity of the Moon's orbit. Here again, an increase is expected from tidal friction in both the Earth and Moon. However, there is a reported unexplained increase that is significant at the three-sigma level. It is produent to suspect that all four anomalies have mundane explanations, or that one or more anomalies are a result of systematic error. Yet they might eventually be explained by new physics. For example, a slightly modified theory of gravitation is not ruled out, perhaps analogous to Einstein's 1916 explanation for the excess precession of Mercury's perihelion.
Orbital studies of lunar magnetism
NASA Technical Reports Server (NTRS)
Mcleod, M. G.; Coleman, P. J., Jr.
Limitations of present lunar magnetic maps are considered. Optimal processing of satellite derived magnetic anomaly data is also considered. Studies of coastal and core geomagnetism are discussed. Lunar remanent and induced lunar magnetization are included.
Survey and Interpretation Geophysical of Magnetic Isochrones 4n.2 a 2A.3 (7.9 3.6 Ma) in the Central Part of the Rivera Plate
NASA Astrophysics Data System (ADS)
Perez, D. A.; Mortera-Gutierrez, C. A.; Bandy, W. L.; Valle, S.
This study shows the results of six campaigns marine geophysics BABRIP06 in 2006, MAMRIV07 in 2007, MAMRIV08 in 2008, GUAYRIV10 in 2010, BATIBAJA11 in 2011 and MAMRIV12 in 2012, in the abyssal plain in the East Pacific Rise (EPR), on board the UNAM vessel, B/O El Puma. The oceanographic campaigns single beam bathymetric data collected and marine magnetic data. The results allow analyze and study the magnetic texture in the central north of the Rivera plate associated with geological structures and behavior of the seafloor to the isochronous 5A. The systematic survey of the magnetic data provided high resolution on the guidelines of the magnetic anomalies associated with cortical spreading between 7.9 and 3.6 Ma, generated by the northern segment of the East Pacific Rise (EPR), between the Rivera and Tamayo Oceanic Transformants. Multibeam bathymetry data and the acoustic reflectivity of the six campaigns are correlated with the geometry of the magnetic anomalies and seismic reflection profiles to understand the processes that formed the highlight recreational ocean in this area. The main results in this study is the identification of continuous magnetic isochrones 4n.2 to 2A.3, magnetic anomalies associated with seamounts, the geometry of the isochrones associated with a propagator and magnetic anomaly identification of isochronous 3n.3 had not been demonstrated by other oceanographic surveys. Possibly oceanic spreading rate was slower during these epochs and the identification of a cross anomaly was due to a fracture zone that generated the propagator.
MAGSAT anomaly field data of the crustal properties of Australia
NASA Technical Reports Server (NTRS)
Progress is reported in producing maps of Australia showing; crustal magnetic anomalies at constant elevation; bulk surface magnetization; and the geomagnetic field intensity, inclination and declination for the Australian region from global models of the geomagnetic field derived from MAGSAT data. The development of a data base management system is also considered.
Histopathology of vascular anomalies.
Aboutalebi, Amir; Jessup, Chad J; North, Paula E; Mihm, Martin C
Vascular anomalies may be appropriately classified into two broad categories, vascular tumors and vascular malformations, which are distinguished by the presence of cellular proliferation in contrast to aberrations in morphogenesis, respectively. This system of classification is based upon histological features that may in large part be differentiating, but nevertheless, may show morphological overlap. Advances in immunophenotyping allow for more precise diagnoses as well as further delineation of cell origins. In the discussion, we present the clinical, histological, and, when applicable, the immunophenotypic presentation of vascular anomalies commonly seen in infancy and early childhood. PMID:23188681
Phonon anomalies near the magnetic phase transitions in BiFeO3 thin films with rhombohedral R3c symmetry
NASA Astrophysics Data System (ADS)
Singh, Manoj K.; Katiyar, Ram S.
Raman spectra of epitaxal BiFeO3 thin films, grown on (111) SrTiO3 substrates, have been studied in temperature range 300-800 K. All four prominent A1-symmetry (81, 138, 170, and 214 cm-1) Raman modes show evolution with the temperature near the Nķel temperature (TN), which is interpreted due to spin lattice coupling and it could be also linked with the structural instability originated by octahedral tilting near TN as reported by A. Palewicz et al., Acta Cryst B 63, 537 (2007). As another evidence of spin-phonon coupling, softening of the 214 cm-1 stretching mode is observed near and below the magnetic ordering temperature.
Mars Crustal Remanent Magnetism: An Extinct Dynamo Leaves a Record of Field Reversals in the Heavily Cratered Highlands
NASA Technical Reports Server (NTRS)
Connerney, John E.; Acuna, Mario H.; Ness, Norman F.; Wasilewski, Peter J.
The Mars Global Surveyor spacecraft, in a highly elliptical polar orbit about Mars, obtained vector magnetic field measurements just above the surface of Mars (altitudes > 100 kilometers). Crustal magnetization, largely confined to the most ancient, heavily cratered Mars highlands, is frequently organized in east-west trending linear features, the largest of which extends over 2000 km. A representative set of survey passes are modeled using uniformly magnetized thin plates and a generalized inverse methodology. Crustal remanent magnetization exceeds that deduced for the largest terrestrial magnetic anomalies by more than an order of magnitude. Groups of quasi-parallel linear features of alternating magnetic polarity are found. They are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on Earth but with a much larger spatial scale.
Chiral anomaly and transport in Weyl metals
NASA Astrophysics Data System (ADS)
Burkov, A. A.
We present an overview of our recent work on transport phenomena in Weyl metals, which may be connected to their nontrivial topological properties, particularly to chiral anomaly. We argue that there are two basic phenomena, which are related to chiral anomaly in Weyl metals: anomalous Hall effect (AHE) and chiral magnetic effect (CME). While AHE is in principle present in any ferromagnetic metal, we demonstrate that a magnetic Weyl metal is distinguished from an ordinary ferromagnetic metal by the absence of the extrinsic and the Fermi surface part of the intrinsic contributions to the AHE, as long as the Fermi energy is sufficiently close to the Weyl nodes. The AHE in a Weyl metal is thus shown to be a purely intrinsic, universal property, fully determined by the location of the Weyl nodes in the first Brillouin zone. In other words, a ferromagnetic Weyl metal may be thought of as the only example of a ferromagnetic metal with a purely intrinsic AHE. We further develop a fully microscopic theory of diffusive magnetotransport in Weyl metals. We derive coupled diffusion equations for the total and axial (i.e. node-antisymmetric) charge densities and show that chiral anomaly manifests as a magnetic-field-induced coupling between them. We demonstrate that an experimentally-observable consequence of CME in magnetotransport in Weyl metals is a quadratic negative magnetoresistance, which will dominate all other contributions to magnetoresistance under certain conditions and may be regarded as a smoking-gun transport characteristic, unique to Weyl metals.
Chiral anomaly and transport in Weyl metals.
Burkov, A A
We present an overview of our recent work on transport phenomena in Weyl metals, which may be connected to their nontrivial topological properties, particularly to chiral anomaly. We argue that there are two basic phenomena, which are related to chiral anomaly in Weyl metals: anomalous Hall effect (AHE) and chiral magnetic effect (CME). While AHE is in principle present in any ferromagnetic metal, we demonstrate that a magnetic Weyl metal is distinguished from an ordinary ferromagnetic metal by the absence of the extrinsic and the Fermi surface part of the intrinsic contributions to the AHE, as long as the Fermi energy is sufficiently close to the Weyl nodes. The AHE in a Weyl metal is thus shown to be a purely intrinsic, universal property, fully determined by the location of the Weyl nodes in the first Brillouin zone. In other words, a ferromagnetic Weyl metal may be thought of as the only example of a ferromagnetic metal with a purely intrinsic AHE. We further develop a fully microscopic theory of diffusive magnetotransport in Weyl metals. We derive coupled diffusion equations for the total and axial (i.e. node-antisymmetric) charge densities and show that chiral anomaly manifests as a magnetic-field-induced coupling between them. We demonstrate that an experimentally-observable consequence of CME in magnetotransport in Weyl metals is a quadratic negative magnetoresistance, which will dominate all other contributions to magnetoresistance under certain conditions and may be regarded as a smoking-gun transport characteristic, unique to Weyl metals. PMID:25712419
Analysis and interpretation of MAGSAT anomalies over north Africa
NASA Technical Reports Server (NTRS)
Phillips, R. J.
Crustal anomaly detection with MAGSAT data is frustrated by inherent resolving power of the data and by contamination from external and core fields. Quality of the data might be tested by modeling specific tectonic features which produce anomalies that fall within proposed resolution and crustal amplitude capabilities of MAGSAT fields. To test this hypothesis, north African hotspots associated with Ahaggar, Tibesti and Darfur were modeled as magnetic induction anomalies. MAGSAT data were reduced by subtracting external and core fields to isolate scalar and vertical component crustal signals. Of the three volcanic areas, only the Ahaggar region had an associated anomaly of magnitude above error limits of the data. Hotspot hypothesis was tested for Ahaggar by seeing if predicted magnetic signal matched MAGSAT anomaly. Predicted model magnetic signal arising from surface topography of the uplift and the Curie isothermal surface was calculated at MAGSAT altitudes by Fourier transform technique modified to allow for variable magnetization. Curie isotherm surface was calculated using a method for temperature distribution in a moving plate above a fixed hotspot. Magnetic signal was calculated for a fixed plate as well as a number of plate velocities and directions.
Chiral Anomaly and Diffusive Magnetotransport in Weyl Metals
NASA Astrophysics Data System (ADS)
Burkov, A. A.
We present a microscopic theory of diffusive magnetotransport in Weyl metals and clarify its relation to the chiral anomaly. We derive coupled diffusion equations for the total and axial charge densities and show that the chiral anomaly manifests as a magnetic-field-induced coupling between them. We demonstrate that a universal experimentally observable consequence of this coupling in magnetotransport in Weyl metals is a quadratic negative magnetoresistance, which will dominate all other contributions to magnetoresistance under certain conditions.
Hybrid spread spectrum radio system
Smith, Stephen F. (London, TN) [London, TN; Dress, William B. (Camas, WA) [Camas, WA
Systems and methods are described for hybrid spread spectrum radio systems. A method, includes receiving a hybrid spread spectrum signal including: fast frequency hopping demodulating and direct sequence demodulating a direct sequence spread spectrum signal, wherein multiple frequency hops occur within a single data-bit time and each bit is represented by chip transmissions at multiple frequencies.
Gogan, Peter J.P.; Jessup, David A.; Barrett, Reginald H.
Antler anomalies were evident in tule elk (Cervus elaphus nannodes) within 1 yr of reintroduction to Point Reyes, California (USA). These anomalies are consistent with previously described mineral deficiency-induced anomalies in cervids. The elk were judged deficient in copper. Low levels of copper in soils and vegetation at the release site, exacerbated by possible protein deficiency due to poor range conditions, are postulated as likely causes of the antler anomalies.
Epidemiology: Understanding Disease Spread
NSDL National Science Digital Library
Marion Fass (Beloit College; Biology)
Factors that influence disease spread throughout populations can be explored with the program Epidemiology. Both population and disease characteristics can be modeled over different time periods. The Susceptible- Infected- Recovered (SIR) model enables us to make predictions based on significant variables such as the flow of new susceptibles in to the population, transmission rates, disease deaths, and the duration of the disease. Ebola is used as a model organism and epidemiology is presented from both a microbiological and social perspective. * build epidemiological models of different diseases, design strategies for disease control, and test the effectiveness of these strategies on virtual populations
Global Climate Highlights and Anomalies
NSDL National Science Digital Library
NOAA's Global Climate Highlights and Anomalies page offers weekly summaries of global climate highlights and anomalies (warm, cold, wet, dry). Areas experiencing climate anomalies are color-marked on a global map, followed by written summaries of each region's climate conditions. All weeks are posted for the year 2000 (to present), and a link points users to the complete 1999 archive.
Understanding Anomalies to Extract Vacuum Energy
Murad, P.A
Recent Russian literature contains some interesting speculations of potentially wide applicability regarding the physical vacuum. These investigations examined and applied a theory to various anomalies to try and understand what these events may represent. Data were collected by Dmitriev to quantify these events and identify commonalties that indicate the anomalies might have a natural origin. Dyatlov created theories on the Polarized Inhomogeneous Physical Vacuum where he claimed that each anomaly possessed a distinct boundary separate from its surroundings. Within this inhomogeneous boundary, the theory suggests that the magnetic, electric, gravitic, and spin fields would be different from its surroundings. From these findings, he developed equations that resemble the London equations for a superconductor and are somewhat similar to those developed later by Puthoff. The importance of these events is that with additional understanding, they may offer a means for extracting energy from the physical vacuum. Moreover, one may speculate that these anomalies may represent a gravitational vortex or even a portal or a wormhole to look into potential travel within other dimensions.
Illusory spreading of watercolor
Devinck, Frķdķric; Hardy, Joseph L.; Delahunt, Peter B.; Spillmann, Lothar; Werner, John S.
The watercolor effect (WCE) is a phenomenon of long-range color assimilation occurring when a dark chromatic contour delineating a figure is flanked on the inside by a brighter chromatic contour; the brighter color spreads into the entire enclosed area. Here, we determined the optimal chromatic parameters and the cone signals supporting the WCE. To that end, we quantified the effect of color assimilation using hue cancellation as a function of hue, colorimetric purity, and cone modulation of inducing contours. When the inner and outer contours had chromaticities that were in opposite directions in color space, a stronger WCE was obtained as compared with other color directions. Additionally, equal colorimetric purity between the outer and inner contours was necessary to obtain a large effect compared with conditions in which the contours differed in colorimetric purity. However, there was no further increase in the magnitude of the effect when the colorimetric purity increased beyond a value corresponding to an equal vector length between the inner and outer contours. Finally, L¢M-cone-modulated WCE was perceptually stronger than S-cone-modulated WCE for our conditions. This last result demonstrates that both L¢M-cone and S-cone pathways are important for watercolor spreading. Our data suggest that the WCE depends critically upon the particular spatiochromatic arrangement in the display, with the relative chromatic contrast between the inducing contours being particularly important. PMID:16881793
Rogers, Deborah S.; Deshpande, Omkar; Feldman, Marcus W.
The causes of socioeconomic inequality have been debated since the time of Plato. Many reasons for the development of stratification have been proposed, from the need for hierarchical control over large-scale irrigation systems to the accumulation of small differences in wealth over time via inheritance processes. However, none of these explains how unequal societies came to completely displace egalitarian cultural norms over time. Our study models demographic consequences associated with the unequal distribution of resources in stratified societies. Agent-based simulation results show that in constant environments, unequal access to resources can be demographically destabilizing, resulting in the outward migration and spread of such societies even when population size is relatively small. In variable environments, stratified societies spread more and are also better able to survive resource shortages by sequestering mortality in the lower classes. The predictions of our simulation are provided modest support by a range of existing empirical studies. In short, the fact that stratified societies today vastly outnumber egalitarian societies may not be due to the transformation of egalitarian norms and structures, but may instead reflect the more rapid migration of stratified societies and consequent conquest or displacement of egalitarian societies over time. PMID:21957457
Tan F. Wong: Spread Spectrum & CDMA 3. Spreading Sequences Spreading Sequences
Wong, Tan F.
of the spread spectrum signal in Chapter 2, we model the sequence elements as iid random variables. Based to approximate random sequences so that we are actually spreading the spectrum of the data signal. This explains # ; (3.3) where T = NT c 1 is the common period of the spreading signals and #28; 2 [0; T ) 2 . We
Yearly Arctic Temperature Anomaly
NSDL National Science Digital Library
Cindy Starr
This animation shows the yearly temperature anomaly over the Arctic region from 1981-82 through 2002-03. Years run from August 1 through July 31. Blue hues indicate cooling regions; red hues depict warming. Light regions indicate less change while darker regions indicate more. The temperature scale used ranges from -7.0 to +7.0 degrees Celsius in increments of .25 degrees. (See color bar below)
Magnetic vector data from the western Caribbean reveal possible origin
NASA Astrophysics Data System (ADS)
Barckhausen, U.; Engels, U.
During a cruise with RV Meteor in the spring of 2010, magnetic measurements were carried out in the central and western Caribbean with up to six magnetic sensors deployed at the same time. These were i) a towed gradiometer consisting of two Overhauser sensors, ii) two towed vector magnetometers, and iii) two shipboard oriented vector magnetometers. While the gradiometer data provide total field magnetic anomalies free from external variations, the vector data can be analyzed with different methods in the space and wavenumber domains. In the case of the towed vector data, attitude control is challenging whereas shipboard data require a very thorough compensation for the ship's magnetic field. The data were analyzed with the goal to gain insight into the origin of the basement rocks especially of the western Caribbean. Position and strike direction of magnetic anomalies in the Columbia basin possibly hold the key to distinguish between an origin of the crust in the Pacific ocean and an alternative in situ formation between the Americas. On six long profiles in the Columbia basin and adjacent regions we find consistently strike directions of the magnetic anomalies around N100░E which seems to be incompatible with a Pacific origin of the crust. Three Project Magnet aeromagnetic vector profiles crossing the research area at different angles were analyzed with the same method and yield very similar results. In our interpretation, the crust underlying the Columbia basin formed during the Cretaceous at a roughly E-W trending spreading center between the Americas. Since the crust likely formed during the Cretaceous Superchron (C 34), the strike direction we find in our data probably does not represent typical seafloor spreading anomalies. Instead we believe it is related to changes in the intensity of the Earth's magnetic field which are known to have left correlated traces in oceanic crust formed during this period. The analysis methods we used are sensitive to intensity changes just as well as to polarity changes. We can demonstrate that the data quality is high and that the strike direction signal is clear and well correlated between the different profiles and that it is also consistent between towed, shipboard, and aeromagnetic sensors.
QCD flux tubes and anomaly inflow
NASA Astrophysics Data System (ADS)
Xiong, Chi
We apply the Callan-Harvey anomaly-inflow mechanism to the study of QCD (chromoelectric) flux tubes, quark (pair) creation, and the chiral magnetic effect, using new variables from the Cho-Faddeev-Niemi decomposition of the gauge potential. A phenomenological description of chromoelectric flux tubes is obtained by studying a gauged Nambu-Jona-Lasinio effective Lagrangian, derived from the original QCD Lagrangian. At the quantum level, quark condensates in the QCD vacuum may form a vortexlike structure in a chromoelectric flux tube. Quark zero modes trapped in the vortex are chiral and lead to a two-dimensional gauge anomaly. To cancel it, an effective Chern-Simons coupling is needed and, hence, a topological charge density term naturally appears.
NSDL National Science Digital Library
University Corporation for Atmospheric Research Windows to the Universe team
This webpage is part of the University Corporation for Atmospheric Research (UCAR) Windows to the Universe program. It describes the nature and configuration of magnetic fields, which are the result of moving electric charges, including how they cause magnetic objects to orient themselves along the direction of the magnetic force points, which are illustrated as lines. Magnetic field lines by convention point outwards at the north magnetic pole and inward at the south magnetic pole. The site features text, scientific illustrations and an animation. Text and vocabulary are selectable for the beginning, intermediate, or advanced reader.
Spreading convulsions, spreading depolarization and epileptogenesis in human cerebral cortex
Major, Sebastian; Pannek, Heinz-Wolfgang; Woitzik, Johannes; Scheel, Michael; Wiesenthal, Dirk; Martus, Peter; Winkler, Maren K.L.; Hartings, Jed A.; Fabricius, Martin; Speckmann, Erwin-Josef; Gorji, Ali
Spreading depolarization of cells in cerebral grey matter is characterized by massive ion translocation, neuronal swelling and large changes in direct current-coupled voltage recording. The near-complete sustained depolarization above the inactivation threshold for action potential generating channels initiates spreading depression of brain activity. In contrast, epileptic seizures show modest ion translocation and sustained depolarization below the inactivation threshold for action potential generating channels. Such modest sustained depolarization allows synchronous, highly frequent neuronal firing; ictal epileptic field potentials being its electrocorticographic and epileptic seizure its clinical correlate. Nevertheless, LeŃo in 1944 and Van Harreveld and Stamm in 1953 described in animals that silencing of brain activity induced by spreading depolarization changed during minimal electrical stimulations. Eventually, epileptic field potentials were recorded during the period that had originally seen spreading depression of activity. Such spreading convulsions are characterized by epileptic field potentials on the final shoulder of the large slow potential change of spreading depolarization. We here report on such spreading convulsions in monopolar subdural recordings in 2 of 25 consecutive aneurismal subarachnoid haemorrhage patients in vivo and neocortical slices from 12 patients with intractable temporal lobe epilepsy in vitro. The in vitro results suggest that ?-aminobutyric acid-mediated inhibition protects from spreading convulsions. Moreover, we describe arterial pulse artefacts mimicking epileptic field potentials in three patients with subarachnoid haemorrhage that ride on the slow potential peak. Twenty-one of the 25 subarachnoid haemorrhage patients (84%) had 656 spreading depolarizations in contrast to only three patients (12%) with 55 ictal epileptic events isolated from spreading depolarizations. Spreading depolarization frequency and depression periods per 24?h recording episodes showed an early and a delayed peak on Day 7. Patients surviving subarachnoid haemorrhage with poor outcome at 6 months showed significantly higher total and peak numbers of spreading depolarizations and significantly longer total and peak depression periods during the electrocorticographic monitoring than patients with good outcome. In a semi-structured telephone interview 3 years after the initial haemorrhage, 44% of the subarachnoid haemorrhage survivors had developed late post-haemorrhagic seizures requiring anti-convulsant medication. In those patients, peak spreading depolarization number had been significantly higher [15.1 (11.4¢30.8) versus 7.0 (0.8¢11.2) events per day, P?=?0.045]. In summary, monopolar recordings here provided unequivocal evidence of spreading convulsions in patients. Hence, practically all major pathological cortical network events in animals have now been observed in people. Early spreading depolarizations may indicate a risk for late post-haemorrhagic seizures. PMID:22120143
Cortical Spreading Depression and Migraine
Katharina Eikermann-Haerter; Cenk Ayata
Cortical spreading depression, a slowly propagating wave of transient neuronal and glial depolarization, is widely accepted\\u000a as the electrophysiologic substrate of migraine aura and a trigger for headache. Recent clinical and experimental evidence\\u000a reinforces the putative role of cortical spreading depression in migraine pathophysiology. Imaging studies in migraineurs\\u000a demonstrated hemodynamic changes consistent with cortical spreading depression during aura, whereas recent
D. G. Singleton
An analysis has been made of reliable spread-F data obtained from IGY f plots for ionosonde stations grouped about longitudes 75°W and 120°E. The temporal variations of occurrence of the frequency-spreading component of spread F are found to change with lati- tude, these changes having a certain symmetry about the geomagnetic equator rather than about the geographic or dip equators.
Liquid spreading ASTP Science Demonstration
NASA Technical Reports Server (NTRS)
Bourgeois, S. V.; Facemire, B. R.
Wetting and spreading phenomena are significant in a wide variety of processes. This report discusses the results of an ASTP Science Demonstration, 'Liquid Spreading', and compares these results to theoretical predictions. On earth the initial spreading of large liquid drops on solid surfaces is always dominated by gravity; in this demonstration the effect of gravity is greatly reduced so that surface energy forces are the controlling factor.
9 CFR 319.762 - Ham spread, tongue spread, and similar products.
Code of Federal Regulations, 2010 CFR
... 2 2010-01-01 2010-01-01 false Ham spread, tongue spread, and similar products. 319.762 Section 319...OF IDENTITY OR COMPOSITION Meat Salads and Meat Spreads ¦ 319.762 Ham spread, tongue spread, and...
9 CFR 319.762 - Ham spread, tongue spread, and similar products.
Code of Federal Regulations, 2011 CFR
... 2 2011-01-01 2011-01-01 false Ham spread, tongue spread, and similar products. 319.762 Section 319...OF IDENTITY OR COMPOSITION Meat Salads and Meat Spreads ¦ 319.762 Ham spread, tongue spread, and...
Bevers, Stan; Amosson, Stephen H.; Waller, Mark L.; Dhuyvetter, Kevin C.
might be used when the marketer is bearish on a market to a point (i.e., the marketer believes the market has limited downside risk). An attractive feature of the bear put spread is that once the strike prices are selected and the premiums are known..., the maximum loss and net potential gain from the spread are also known. When to Use a Bear Put Spread A producer can use a bear put spread to hedge against a falling market. However, if the market falls below the strike price of the sold put op- tion...
Brain anomalies in velo-cardio-facial syndrome
Mitnick, R.J.; Bello, J.A.; Shprintzen, R.J. [Albert Einstein College of Medicine, Bronx, NY (United States)
Magnetic resonance imaging of the brain in 11 consecutively referred patients with velo-cardio-facial syndrome (VCF) showed anomalies in nine cases including small vermis, cysts adjacent to the frontal horns, and small posterior fossa. Focal signal hyperintensities in the white matter on long TR images were also noted. The nine patients showed a variety of behavioral abnormalities including mild development delay, learning disabilities, and characteristic personality traits typical of this common multiple anomaly syndrome which has been related to a microdeletion at 22q11. Analysis of the behavorial findings showed no specific pattern related to the brain anomalies, and the patients with VCF who did not have detectable brain lesions also had behavioral abnormalities consistent with VCF. The significance of the lesions is not yet known, but the high prevalence of anomalies in this sample suggests that structural brain abnormalities are probably common in VCF. 25 refs.
Physicochemical isotope anomalies
Esat, T.M. (Australian National Univ., Canberra)
Isotopic composition of refractory elements can be modified, by physical processes such as distillation and sputtering, in unexpected patterns. Distillation enriches the heavy isotopes in the residue and the light isotopes in the vapor. However, current models appear to be inadequate to describe the detailed mass dependence, in particular for large fractionations. Coarse- and fine-grained inclusions from the Allende meteorite exhibit correlated isotope effects in Mg both as mass-dependent fractionation and residual anomalies. This isotope pattern can be duplicated by high temperature distillation in the laboratory. A ubiquitous property of meteoritic inclusions for Mg as well as for most of the other elements, where measurements exist, is mass-dependent fractionation. In contrast, terrestrial materials such as microtektites, tektite buttons as well as lunar orange and green glass spheres have normal Mg isotopic composition. A subset of interplanetary dust particles labelled as chondritic aggregates exhibit excesses in {sup 26}Mg and deuterium anomalies. Sputtering is expected to be a dominant mechanism in the destruction of grains within interstellar dust clouds. An active proto-sun as well as the present solar-wind and solar-flare flux are of sufficient intensity to sputter significant amounts of material. Laboratory experiments in Mg show widespread isotope effects including residual {sup 26}Mg excesses and mass dependent fractionation. It is possible that the {sup 26}Mg excesses in interplanetary dust is related to sputtering by energetic solar-wind particles. The implication if the laboratory distillation and sputtering effects are discussed and contrasted with the anomalies in meteoritic inclusions the other extraterrestrial materials the authors have access to.
Gold anomalies and magnetometer profile data, Ester Dome area, Fairbanks district, Alaska
Stevens, D.L.; Forbes, Robert B.; Hawkins, D.B.
Gold analysis of grab and auger samples of bedrock taken along the new Ester Dome Road reveals that this road cuts several mineralized zones characterized by anomalous concentrations of gold. The results of a magnetometer traverse along this road indicate that the negative magnetic anomalies along the traverse may be correlative with the gold anomalies. The presence of previously unreported gold anomalies indicates that additional prospecting may be warranted.
Phenomenology of deflected anomaly-mediation
Riccardo Rattazzi; Alessandro Strumia; James D. Wells
We explore the phenomenology of a class of models with anomaly-mediated supersymmetry breaking. These models retain the successful flavor properties of the minimal scenario while avoiding the tachyons. The mass spectrum is predicted in terms of a few parameters. However various qualitatively different spectra are possible, often strongly different from the ones usually employed to explore capabilities of new accelerators. One stable feature is the limited spread of the spectrum, so that squarks and gluinos could be conceivably produced at TEVII. The lightest superpartner of standard particles is often a charged slepton or a neutral higgsino. It behaves as a stable particle in collider experiments but it decays at or before nucleosynthesis. We identify the experimental signatures at hadron colliders that can help distinguish this scenario from the usual ones.
Gravitational Anomaly and Hydrodynamics
Karl Landsteiner; Eugenio MegĒas; Luis Melgar; Francisco Pena-Benitez
We study the anomalous induced current of a vortex in a relativistic fluid via the chiral vortical effect, which is analogous to the anomalous current induced by a magnetic field via the chiral magnetic effect. We perform this analysis at weak and strong coupling. We discuss inequivalent implementations to the chemical potential for an anomalous symmetry. At strong coupling we
Zaleski, Witold A.; Houston, C. Stuart; Pozsonyi, J.; Ying, K. L.
The majority of abnormal sex chromosome complexes in the male have been considered to be variants of Klinefelter's syndrome but an exception should probably be made in the case of the XXXXY individual who has distinctive phenotypic features. Clinical, radiological and cytological data on three new cases of XXXXY syndrome are presented and 30 cases from the literature are reviewed. In many cases the published clinical and radiological data were supplemented and re-evaluated. Mental retardation, usually severe, was present in all cases. Typical facies was observed in many; clinodactyly of the fifth finger was seen in nearly all. Radiological examination revealed abnormalities in the elbows and wrists in all the 19 personally evaluated cases, and other skeletal anomalies were very frequent. Cryptorchism is very common and absence of Leydig's cells may differentiate the XXXXY chromosome anomaly from polysomic variants of Klinefelter's syndrome. The relationship of this syndrome to Klinefelter's syndrome and to Down's syndrome is discussed. ImagesFig. 1Fig. 2Fig. 3Fig. 4Fig. 5Fig. 6Fig. 7Fig. 8Fig. 9Fig. 10Fig. 11Fig. 12Fig. 13Fig. 14Fig. 15 PMID:4222822
NASA Astrophysics Data System (ADS)
Riofrio, L.
Independent experiments show a large anomaly in measurements of lunar orbital evolution, with applications to cosmology and the speed of light. The Moon has long been known to be slowly drifting farther from Earth due to tidal forces. The Lunar Laser Ranging Experiment (LLRE) indicates the Moon's semimajor axis increasing at 3.82 ▒ .07 cm/yr, anomalously high. If the Moon were today gaining angular momentum at this rate, it would have coincided with Earth less than 2 Gyr ago. Study of tidal rhythmites indicates a rate of 2.9 ▒ 0.6 cm/yr. Historical eclipse observations independently measure a recession rate of 2.82 ▒ .08 cm/yr. Detailed numerical simulation of lunar orbital evolution predicts 2.91 cm/yr. LLRE differs from three independent experiments by over12 sigma. A cosmology where speed of light c is related to time t by GM=tc^3 has been suggested to predict the redshifts of Type Ia supernovae, and a 4.507034% proportion of baryonic matter. If c were changing in the amount predicted, lunar orbital distance would appear to increase by an additional 0.935 cm/yr. An anomaly in the lunar orbit may be precisely calculated, shedding light on puzzles of 'dark energy'. In Planck units this cosmology may be summarized as M=R=t.Lunar Recession Rate;
Automated anomaly detection processor
NASA Astrophysics Data System (ADS)
Kraiman, James B.; Arouh, Scott L.; Webb, Michael L.
Robust exploitation of tracking and surveillance data will provide an early warning and cueing capability for military and civilian Law Enforcement Agency operations. This will improve dynamic tasking of limited resources and hence operational efficiency. The challenge is to rapidly identify threat activity within a huge background of noncombatant traffic. We discuss development of an Automated Anomaly Detection Processor (AADP) that exploits multi-INT, multi-sensor tracking and surveillance data to rapidly identify and characterize events and/or objects of military interest, without requiring operators to specify threat behaviors or templates. The AADP has successfully detected an anomaly in traffic patterns in Los Angeles, analyzed ship track data collected during a Fleet Battle Experiment to detect simulated mine laying behavior amongst maritime noncombatants, and is currently under development for surface vessel tracking within the Coast Guard's Vessel Traffic Service to support port security, ship inspection, and harbor traffic control missions, and to monitor medical surveillance databases for early alert of a bioterrorist attack. The AADP can also be integrated into combat simulations to enhance model fidelity of multi-sensor fusion effects in military operations.
Einstein, Entropy and Anomalies
NASA Astrophysics Data System (ADS)
Sirtes, Daniel; Oberheim, Eric
This paper strengthens and defends the pluralistic implications of Einstein's successful, quantitative predictions of Brownian motion for a philosophical dispute about the nature of scientific advance that began between two prominent philosophers of science in the second half of the twentieth century (Thomas Kuhn and Paul Feyerabend). Kuhn promoted a monistic phase-model of scientific advance, according to which a paradigm driven `normal science' gives rise to its own anomalies, which then lead to a crisis and eventually a scientific revolution. Feyerabend stressed the importance of pluralism for scientific progress. He rejected Kuhn's model arguing that it fails to recognize the role that alternative theories can play in identifying exactly which phenomena are anomalous in the first place. On Feyerabend's account, Einstein's predictions allow for a crucial experiment between two incommensurable theories, and are an example of an anomaly that could refute the reigning paradigm only after the development of a competitor. Using Kuhn's specification of a disciplinary matrix to illustrate the incommensurability between the two paradigms, we examine the different research strategies available in this peculiar case. On the basis of our reconstruction, we conclude by rebutting some critics of Feyerabend's argument.
NSDL National Science Digital Library
This radio broadcast discusses the history of magnetism from the time of its discovery by an apocryphal Greek sheperd until the late 16th century and the work of William Gilbert. There is also discussion of who pioneered the study of magnetism, what theories they constructed from its curious abilities, and how the power of the magnet was brought out of the realm of magic and into the service of science. The broadcast concludes with a discussion of why magnetism is still mysterious and how the modern search for the single magnetic pole, or magnetic monopole, could provide a fundamental unit of magnetism, essential for ultimate explanation. The broadcast is 41 minutes and 45 seconds in length.
Cryptographic Spread Spectrum Relay Communication
Zahoor Ahmed; J. P. Cances; V. Meghdadi
Spread spectrum (SS) is a technique of secure communication, which increases resistance to natural interference and jamming, and prevents detection. If a cryptographically secure pseudo random sequence is used, the communication becomes more secure. Generally some short pseudo-random sequences are used in Spread spectrum. In this paper we present comparatively a different technique of signal hiding where we use a
Lunar Magnetism: IRMs Normalization and Impact Related Magnetization
M. Fuller; J. Halekas; T. Adachi; G. Kletetschka; T. Kohout
Models of lunar magnetism need to explain: (1) strong Natural Remanent Magnetization (NRM), indicated by IRMs normalization, in some of the returned Apollo Mare Basalts and Melt Rocks with ages from about 3.85Ae to 3.65 Ae, (2) magnetic anomalies antipodal to the young basins of a similar age, (3) the absence of major magnetic anomalies over these same basins and
System for closure of a physical anomaly
Bearinger, Jane P; Maitland, Duncan J; Schumann, Daniel L; Wilson, Thomas S
Systems for closure of a physical anomaly. Closure is accomplished by a closure body with an exterior surface. The exterior surface contacts the opening of the anomaly and closes the anomaly. The closure body has a primary shape for closing the anomaly and a secondary shape for being positioned in the physical anomaly. The closure body preferably comprises a shape memory polymer.
First example of a reversible single-crystal-to-single-crystal polymerization-depolymerization accompanied by a magnetic anomaly for a transition-metal complex with an organic radical.
Ovcharenko, Victor I; Fokin, Sergey V; Kostina, Elvina T; Romanenko, Galina V; Bogomyakov, Artem S; Tretyakov, Eugene V
The reaction of copper(II) hexafluoroacetylacetonate [Cu(hfac)2] with the stable nitronyl nitroxide 2-(1-ethyl-3-methyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L(a)) resulted in a paired heterospin complex [[Cu(hfac)2]3(?-O,N-L(a))2][Cu(hfac)2(O-L(a))2]. The crystals of the compound were found to be capable of a reversible single-crystal-to-single-crystal (SC-SC) transformation initiated by the variation of temperature. At room temperature, the molecular structure of [[Cu(hfac)2]3(?-O,N-L(a))2][Cu(hfac)2(O-L(a))2] is formed by the alternating fragments of the pair complex. Cooling the crystals of the complex below 225 K caused considerable mutual displacements of adjacent molecules, which ended in a transformation of the molecular structure into a polymer chain structure. A reversible topotactic polymerization-depolymerization coordination reaction actually takes place in the solid during repeated cooling-heating cycles: [[Cu(hfac)2]3(?-O,N-L(a))2][Cu(hfac)2(O-L(a))2] ? Cu(hfac)2(?-O,N-L(a))]?. Polymerization during cooling is the result of the anomalously great shortening of intermolecular distances (from 4.403 ┼ at 295 K to 2.460 ┼ at 150 K; ?d = 1.943 ┼) between the terminal Cu atoms of the trinuclear fragments {[[Cu(hfac)2]3(?-O,N-L(a))2]} and the noncoordinated N atoms of the pyrazole rings of the mononuclear {[Cu(hfac)2(O-L(a))2]} fragments. When the low-temperature phase was heated above 270 K, the polymer chain structure was destroyed and the compound was again converted to the pair molecular complex. The specifics of the given SC-SC transformation lies in the fact that the process is accompanied by a magnetic anomaly, because the intracrystalline displacements of molecules lead to a considerable change in the mutual orientation of the paramagnetic centers, which, in turn, causes modulation of the exchange interaction between the odd electrons of the Cu(2+) ion and nitroxide. On the temperature curve of ?T, this shows itself as a hysteresis loop. The nontrivial character of the recorded spin transition during the cooling of the sample below 225 K lies in the fact that the magnetic moment abruptly increased. In contrast, heating the sample above 270 K led to a drastic decrease in ?T. This behavior of ?T is caused by a stepwise change in the character of the exchange interaction in the {>N-(Ģ)O-Cu(2+)-O(Ģ)-N<} fragments. The lengthening of distances between the paramagnetic centers on cooling below 225 K led to a transition from antiferromagnetic to ferromagnetic exchange and, vice versa, the shortening of distances between the paramagnetic centers during the heating of the heterospin polymer above 270 K led to a transition from ferromagnetic exchange to antiferromagnetic exchange. PMID:23134055
Revisiting Seafloor-Spreading in the Red Sea: Basement Nature, Transforms and Ocean-Continent Boundary
NASA Astrophysics Data System (ADS)
Tapponnier, P.; Dyment, J.; Zinger, M. A.; Franken, D.; Afifi, A. M.; Wyllie, A.; Ali, H. G.; Hanbal, I.
A new marine geophysical survey on the Saudi Arabian side of the Red Sea confirms early inferences that ~ 2/3 of the eastern Red Sea is floored by oceanic crust. Most seismic profiles south of 24░N show a strongly reflective, landward-deepening volcanic basement up to ~ 100 km east of the axial ridge, beneath thick evaporitic deposits. This position of the Ocean-Continent Boundary (OCB) is consistent with gravity measurements. The low amplitudes and long wavelengths of magnetic anomalies older than Chrons 1-3 can be accounted for by low-pass filtering due to thick sediments. Seafloor-spreading throughout the Red Sea started around 15 Ma, as in the western Gulf of Aden. Its onset was coeval with the activation of the Aqaba/Levant transform and short-cutting of the Gulf of Suez. The main difference between the southern and northern Red Sea lies not in the nature of the crust but in the direction and modulus of the plate motion rate. The ~ 30░ counterclockwise strike change and halving of the spreading rate (~ 16 to ~ 8 mm/yr) between the Hermil (17░N) and Suez triple junctions results in a shift from slow (? North Atlantic) to highly oblique, ultra-slow (? Southwest Indian) ridge type. The obliquity of spreading in the central and northern basins is taken up by transform discontinuities that stop ~ 40 km short of the coastline, at the OCB. Three large transform fault systems (Jeddah, Zabargad, El Akhawein) nucleated as continental transfer faults reactivating NNE-trending Proterozoic shear zones. The former two systems divide the Red Sea into three main basins. Between ~15 and ~5 Ma, for about 10 million years, thick evaporites were deposited directly on top of oceanic crust in deep water, as the depositional environment, modulated by climate, became restricted by the Suez and Afar/Bab-el-Mandeb volcano-tectonic 'flood-gates.' The presence of these thick deposits (up to ~ 8 km) suffices to account for the difference between the Red Sea and the Gulf of Aden. Widespread salt tectonics was triggered by the flow of large evaporite sheets and salt glaciers toward the ridge axis. Such flow was more pervasive in the north, where slower spreading resulted in a deeper trough, and was guided by the rugged topography of the oceanic seafloor. The Red Sea may represent the best model for comparably deep evaporitic basins along the Earth's passive margins, particularly in the South Atlantic.
Genetics of lymphatic anomalies
Brouillard, Pascal; Boon, Laurence; Vikkula, Miikka
Lymphatic anomalies include a variety of developmental and/or functional defects affecting the lymphatic vessels: sporadic and familial forms of primary lymphedema, secondary lymphedema, chylothorax and chylous ascites, lymphatic malformations, and overgrowth syndromes with a lymphatic component. Germline mutations have been identified in at least 20 genes that encode proteins acting around VEGFR-3 signaling but also downstream of other tyrosine kinase receptors. These mutations exert their effects via the RAS/MAPK and the PI3K/AKT pathways and explain more than a quarter of the incidence of primary lymphedema, mostly of inherited forms. More common forms may also result from multigenic effects or post-zygotic mutations. Most of the corresponding murine knockouts are homozygous lethal, while heterozygotes are healthy, which suggests differences in human and murine physiology and the influence of other factors. PMID:24590274
Modern test of chiral anomalies
Kramer, G.; Palmer, W.F.; Pinsky, S.S.
Chiral anomalies are calculated using an effective Lagrangian technique introduced for anomalies by Wess and Zumino and recently reformulated by Witten. Anomalous amplitudes for vector currents decaying into three pseudoscalars are tested by comparison with K/sub l4/ decay and eta ..-->.. ..pi../sup +/..pi../sup -/..gamma... 12 references.
Graph anomalies in cyber communications
Scott A Vander Wiel; Curtis B Storlie; Gary Sandine; Aric A Hagberg; Michael Fisk
Enterprises monitor cyber traffic for viruses, intruders and stolen information. Detection methods look for known signatures of malicious traffic or search for anomalies with respect to a nominal reference model. Traditional anomaly detection focuses on aggregate traffic at central nodes or on user-level monitoring. More recently, however, traffic is being viewed more holistically as a dynamic communication graph. Attention to
Isabella Anomaly: Lithospheric drip, delamination or fragment of the Farallon plate?
NASA Astrophysics Data System (ADS)
Forsyth, D. W.; Rau, C. J.
The Isabella Anomaly or Central Valley Anomaly in California is perhaps the best known example of a high seismic velocity anomaly that has been interpreted as a lithospheric instability. High P and S velocities extend to a depth of at least 150 km and perhaps to several hundred km in a nearly cylindrical region 100-150 km across. The amplitude of the anomaly in the upper 200 km is similar to that of the subducted Gorda plate. This anomaly has been variously interpreted as a convective drip or as a remnant of the lithosphere delaminated from beneath the eastern Sierra Nevada. We suggest instead that the Isabella anomaly may represent a fragment of the subducted Farallon plate that is still attached to the Pacific lithosphere. Directly seaward of the anomaly is the fossil Monterrey microplate, which is a remnant of the Farallon plate that was left when subduction ceased before the spreading center itself subducted. The microplate was then incorporated into the Pacific plate, but it is not clear how much of the subducting slab remained attached to the surface microplate. New Rayleigh wave tomographic images of Baja California show that there are still fragments of the Farallon plate remaining attached to the unsubducted Guadelupe and Magdelena microplate remnants, with anomalies extending down to at least 150 km. The geometry of these anomalies in relationship to the microplates is very similar to that of the Isabella anomaly. A major question with this interpretation is whether a bit of oceanic lithosphere extending down into the asthenosphere could be dragged along with the surface microplate/Pacific plate for 20 Ma since subduction ceased. Another anomaly similar to the Isabella anomaly begins in the shallow mantle beneath the northern end of San Francisco bay and dips to the west - another candidate for a lithospheric drip or convective instability?
The magnetic signature of ultramafic-hosted hydrothermal systems (Invited)
NASA Astrophysics Data System (ADS)
Szitkar, F.; Dyment, J.; Honsho, C.; Horen, H.; Fouquet, Y.
While the magnetic response of basalt-hosted hydrothermal sites is well known, that of ultramafic-hosted hydrothermal sites (UMHS) remains poorly documented. Here we present the magnetic signature of three of the six UMHS investigated to date on the Mid-Atlantic Ridge, i.e. sites Rainbow, Ashadze (1 and 2), and Logachev. Two magnetic signatures are observed. Sites Rainbow and Ashadze 1 are both characterized by a positive reduced-to-the-pole magnetic anomaly, i.e. a positive magnetization contrast. Conversely, sites Ashadze 2 and Logachev do not exhibit any clear magnetic signature. Rock-magnetic measurements on samples from site Rainbow reveal a strong magnetization (~30 A/m adding induced and remanent contributions) borne by sulfide-impregnated serpentinites; the magnetic carrier being magnetite. This observation can be explained by three (non exclusive) processes: (1) higher temperature serpentinization at the site resulting in the formation of more abundant / more strongly magnetized magnetite; (2) the reducing hydrothermal fluid protecting magnetite at the site from the oxidation which otherwise affects magnetite in contact with seawater; and (3) the formation of primary (hydrothermal) magnetite. We apply a new inversion method developed by Honsho et al. (2012) to the high-resolution magnetic anomalies acquired 10 m above seafloor at sites Rainbow and Ashadze 1. This method uses the Akaike Bayesian Information Criterion (ABIC) and takes full advantage of the near-seafloor measurements, avoiding the upward-continuation (i.e. loss of resolution) of other inversion schemes. This inversion reveals a difference in the intensity of equivalent magnetization obtained assuming a 100 m thick magnetic layer, ~30 A/m at site Rainbow and only 8A/m at site Ashadze, suggesting a thinner or less magnetized source for the latter. Hydrothermal sites at Ashadze 2 and Logachev are much smaller (of the order of 10 m) than the previous ones (several 100 m). These sites, known as "smoking craters", are episodically affected by explosions. The lack of any significant magnetic signature is explained by their small size and the random orientation of the (possibly magnetized) blocks spread out from the explosions. While basalt-hosted sites are characterized by a lack of magnetization, UMHS are characterized by a positive magnetization contrast, ranging from very strong (at site Rainbow) to negligible (at sites Ashadze 2 and Logachev) as a function of parameters such as the size of the deposit, the mode of discharge, and the fluid temperature, which effects remains to be carefully investigated.
Spatial resolution and repeatability of Magsat crustal anomaly data over the Indian Ocean
NASA Technical Reports Server (NTRS)
Sailor, R. V.; Lazarewicz, A. R.; Brammer, R. F.
Preliminary results from analysis of individual Magsat tracks in the eastern Indian Ocean demonstrate the resolution capability and repeatability of these data. Spectrum analysis indicates that 250 km is the absolute lower limit for resolving crustal magnetic anomalies in Magsat along-track data. Spectral coherence analysis of closely-spaced tracks shows that magnetic anomaly features with wavelengths greater than 700 km are highly repeatable from track to track.
A Model of Sea-Floor Spreading Teacher's Guide
NSDL National Science Digital Library
Ellen Metzger
This teacher's guide and activity uses a paper model to teach students about sea-floor spreading and the evolution of oceanic crust. It includes background information for teachers about plate boundaries, ocean floor features, and Earth's magnetic field, as well as procedures, materials needed, and discussion questions.
Effects of q-profile structure on turbulence spreading: A fluctuation intensity transport analysis
Yi, S.; Kwon, J. M. [National Fusion Research Institute, Eoeun-dong, Yuseong-gu, Daejeon 305-333 (Korea, Republic of); Diamond, P. H. [National Fusion Research Institute, Eoeun-dong, Yuseong-gu, Daejeon 305-333 (Korea, Republic of); Center for Astrophysics and Space Sciences and Department of Physics, University of California San Diego, La Jolla, California 92093-0429 (United States); Hahm, T. S. [Department of Nuclear Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of)
This paper studies effects of q-profile structure on turbulence spreading. It reports results of numerical experiments using global gyrokinetic simulations. We examine propagation of turbulence, triggered by an identical linear instability in a source region, into an adjacent, linearly stable region with variable q-profile. The numerical experiments are designed so as to separate the physics of turbulence spreading from that of linear stability. The strength of turbulence spreading is measured by the penetration depth of turbulence. Dynamics of spreading are elucidated by fluctuation intensity balance analysis, using a model intensity evolution equation which retains nonlinear diffusion and damping, and linear growth. It is found that turbulence spreading is strongly affected by magnetic shear s, but is hardly altered by the safety factor q itself. There is an optimal range of modest magnetic shear which maximizes turbulence spreading. For high to modest shear values, the spreading is enhanced by the increase of the mode correlation length with decreasing magnetic shear. However, the efficiency of spreading drops for sufficiently low magnetic shear even though the mode correlation length is comparable to that for the case of optimal magnetic shear. The reduction of spreading is attributed to the increase in time required for the requisite nonlinear mode-mode interactions. The effect of increased interaction time dominates that of increased mode correlation length. Our findings of the reduction of spreading and the increase in interaction time at weak magnetic shear are consistent with the well-known benefit of weak or reversed magnetic shear for core confinement enhancement. Weak shear is shown to promote locality, as well as stability.
Effects of q-profile structure on turbulence spreading: A fluctuation intensity transport analysis
NASA Astrophysics Data System (ADS)
Yi, S.; Kwon, J. M.; Diamond, P. H.; Hahm, T. S.
This paper studies effects of q-profile structure on turbulence spreading. It reports results of numerical experiments using global gyrokinetic simulations. We examine propagation of turbulence, triggered by an identical linear instability in a source region, into an adjacent, linearly stable region with variable q-profile. The numerical experiments are designed so as to separate the physics of turbulence spreading from that of linear stability. The strength of turbulence spreading is measured by the penetration depth of turbulence. Dynamics of spreading are elucidated by fluctuation intensity balance analysis, using a model intensity evolution equation which retains nonlinear diffusion and damping, and linear growth. It is found that turbulence spreading is strongly affected by magnetic shear s, but is hardly altered by the safety factor q itself. There is an optimal range of modest magnetic shear which maximizes turbulence spreading. For high to modest shear values, the spreading is enhanced by the increase of the mode correlation length with decreasing magnetic shear. However, the efficiency of spreading drops for sufficiently low magnetic shear even though the mode correlation length is comparable to that for the case of optimal magnetic shear. The reduction of spreading is attributed to the increase in time required for the requisite nonlinear mode-mode interactions. The effect of increased interaction time dominates that of increased mode correlation length. Our findings of the reduction of spreading and the increase in interaction time at weak magnetic shear are consistent with the well-known benefit of weak or reversed magnetic shear for core confinement enhancement. Weak shear is shown to promote locality, as well as stability.
Parametric dependencies of spontaneous hot flow anomalies
NASA Astrophysics Data System (ADS)
Omidi, N.; Zhang, H.; Chu, C.; Sibeck, D.; Turner, D.
Parametric dependencies of spontaneous hot flow anomalies at the quasi-parallel bow shock are investigated using global hybrid (kinetic ions and fluid electron) simulations with a variety of solar wind Mach numbers and directions of the interplanetary magnetic field (IMF). Simulations with solar wind Alfvķnic Mach number of 3 and small IMF cone angles (with the flow velocity) show sporadic formation of spontaneous hot flow anomalies (SHFAs). Increasing the Mach number shows the formation of copious number of SHFAs whose properties are examined in this study. It is shown that the duration of SHFAs does not show much variation with Mach number indicating that their size generally increases with Mach number. Additionally, the level of solar wind deceleration associated with SHFAs increases with Mach number as does the core ion temperature. It is also found that the edges of SHFAs are associated with jumps in magnetic field that increase with shock Mach number. The results also show that the rate of SHFA formation increases with increasing Mach number. Simulations with IMF cone angle of 90░ show that SHFAs form at the quasi-parallel bow shock provided the shock Alfvķn Mach number is ~>3. This shows that SHFAs may form at all cone angles.
Geophysical investigations of a geothermal anomaly at Wadi Ghadir, eastern Egypt
NASA Technical Reports Server (NTRS)
Morgan, P.; Boulos, F. K.; Hennin, S. F.; El-Sherif, A. A.; El-Sayed, A. A.; Basta, N. Z.; Melek, Y. S.
During regional heat flow studies a geothermal anomaly was discovered approximately 2 km from the Red Sea coast at Wadi Ghadir, in the Red Sea Hills of Eastern Egypt. A temperature gradient of 55 C/km was measured in a 150 m drillhole at this location, indicating a heat flow of approximately 175 mw/sqm, approximately four times the regional background heat flow for Egypt. Gravity and magnetic data were collected along Wadi Ghadir, and combined with offshore gravity data, to investigate the source of the thermal anomaly. Magnetic anomalies in the profile do not coincide with the thermal anomaly, but were observed to correlate with outcrops of basic rocks. Other regional heat flow and gravity data indicate that the transition from continental to oceanic type lithosphere occurs close to the Red Sea margin, and that the regional thermal anomaly is possibly related to the formation of the Red Sea.
Atmospheric and Surface Forcings on Recent Arctic Temperature Anomalies
NASA Astrophysics Data System (ADS)
Serreze, M. C.; Barrett, A. P.; Cassano, J. J.
The Arctic has seen outsized warming over the past decade (2000-2009) relative to lower latitudes. This reflects the combined effects of: 1) a general background warming interpreted as part of the planetÆs response to positive radiative forcing; 2) anomalies in atmospheric circulation; 3) changes in characteristics of the surface, in particular, reduced sea ice concentration and higher SSTs compared to climatology. Background radiative forcing is suggested from the widespread warming that is present for all seasons and for temperature anomalies stratified by each of the four cardinal wind directions. Anomalies in atmospheric circulation introduce spatial structure to seasonal temperature anomaly patterns. For example, strong positive anomalies centered between Svalbard and Novaya Zemlya in winter owe their existence in part to an anomalous southerly wind component. Circulation also explains local cooling, such as seen during spring over the quadrant from to date line eastward to 90 deg.W. The effects of reduced ice concentration are most apparent as regional ōhot spotsö in the temperature anomaly field. Surface forcing is evident from the stronger warming at the surface compared to the 925 hPa level. Processes can be mutually supporting. The best example is the region of positive temperature anomalies between Svalbard and Novaya Zemlya in winter - while both wind stress and warmth associated with anomalous southerly winds help to maintain open water, vertical heat fluxes from the open water help to keep the atmosphere warm. With regard to the trajectory of the Arctic system through the 21st century, an important issue is how the effects of atmospheric warming due to reduced sea ice concentration and higher SSTs will be spread out by winds to affect surrounding regions, acting as a feedback to foster more ice melt and reduce ice growth, or leading to enhanced warming over land affecting vegetation and soil temperature regimes. For the period 2000-2009, effects of winds in ōspreading out the heatö are most apparent over the Atlantic side of the Arctic in winter and over the central Arctic Ocean in autumn.
NSDL National Science Digital Library
David Stern
This overview of magnetism provides a brief history prior to 1600 and continues with the work of William Gilbert, Hans Christian Oersted, and Andre-Marie Ampere in describing and exploring the magnetosphere and learning the role that electric current plays in producing magnetism. Magnetic field lines are then discussed, citing the work of Michael Faraday. The work of James Clerk Maxwell and Heinrich Hertz is mentioned in a discussion of the relationship of light waves and radio waves as part of the electromagnetic spectrum.
Identifying solar wind structures related to Garuda 1 satellite anomaly by analyzing solar wind and IMF parameters
NASA Astrophysics Data System (ADS)
Rachman, Abdul; Herdiwijaya, Dhani
Understanding solar wind structures associated with anomalies experienced by a satellite can be useful in the prediction of satellite anomalies. This study uses solar wind and interplanetary magnetic field (IMF) parameters to identify the type of solar wind disturbances associated with the reported anomaly experienced by Garuda 1 satellite on April 5, 2005. By superposed epoch analysis we conclude that the corotating interaction region (CIR) with a stream interface at 6:30 UT of 4 April 2005 was associated with the anomaly. This CIR produced a moderate intensity magnetic storm with Dst = -90 nT.
Anomalies and graded coisotropic branes
NASA Astrophysics Data System (ADS)
Li, Yi
We compute the anomaly of the axial U(1) current in the A-model on a Calabi-Yau manifold, in the presence of coisotropic branes discovered by Kapustin and Orlov. Our results relate the anomaly-free condition to a recently proposed definition of graded coisotropic branes in Calabi-Yau manifolds. More specifically, we find that a coisotropic brane is anomaly-free if and only if it is gradable. We also comment on a different grading for coisotropic submanifolds introduced recently by Oh.
Tectonics of the failing spreading system associated with the 95.5░W Galapagos propagator
Martin C. Kleinrock; Roger C. Searle; R. N. Hey
The failing spreading system associated with the Galapagos 95.5░W propagator system comprises a complex set of volcanic and structural provinces. Data from detailed surveys using GLORIA SeaMARCII, Sea Beam, Deep-Tow, the submersible Alvin, magnetics, and bottom cameras constrain the plate boundary geometry and evolution of this area. Although the failing spreading system may involve diffuse spreading, the patterns of sedimentation,
Equatorial spread {ital F} effects on an HF path: Doppler spread, spatial coherence, and frequency coherence
Fitzgerald, T.J.; Argo, P.E.; Carlos, R.C. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)
In August 1990 we participated in the Equatorial Ionospheric Studies sounding rocket campaign near Kwajalein Atoll in the equatorial Pacific region. The campaign included measurements of plasma density using rocket probes and coherent and incoherent scatter radar. During the campaign we fielded high-frequency ionospheric sounders over a bistatic path between Maloelap Atoll and Bikini Atoll in the Marshall Islands. The distance between the transmitters and receivers was 700 km; the ionospheric-reflection region was at 10.18; {degree}N, 168.40;{degree}E, near the magnetic equator. We made three types of measurements: Doppler spread and spatial coherence for a single-frequency CW path; frequency coherence of multiple CW paths; and Doppler spread and time-delay spread for a 60-kHz bandwidth path. We obtained such data over a period of 2 weeks for approximately 2 hours each evening; during this period spread {ital F} was common. Fifty percent of the evenings showed Doppler spread of greater than 6 Hz at the {minus}10 dB level (relative to the peak signal power) and greater than 15 Hz at the {minus}30 dB level. Forty percent of the evenings showed spatial coherence distance of less than 180 m in the direction normal to the bistatic path; 40{percent} of the evenings showed spatial coherence of less than 75 m in the direction parallel to the path. Seventy-five percent of the evenings showed coherence bandwidths of less than 1.5 kHz. {copyright} 1999 American Geophysical Union
Magnetic potential and magnetization contrasts of Earth's lithosphere
NASA Astrophysics Data System (ADS)
Arkani-Hamed, J.; Dyment, J.
An inversion technique is developed in order to transform a global scalar magnetic anomaly map into a global magnetic susceptibility contrast map which delineates the magnetic characteristics of the lithosphere. The inversion involves two stages. In the first stage, a scalar magnetic anomaly map is transformed into a magnetic potential map. This stage requires no simplifying assumption, and it provides a means to upward/downward continue global scalar magnetic anomaly maps. In the second stage, the potential map is inverted into a magnetic susceptibility contrast map of the lithosphere based on the assumption that the magnetization is of induced origin. The magnetization of the continental crust that gives rise to satellite magnetic anomalies is largely of induced origin. It is also shown that the magnetization direction of the oceanic lithosphere does not differ significantly from the direction of the present core field, except in a few limited areas, supporting the assumption made about the induced magnetization of the lithosphere. The technique is applied to the scalar magnetic anomaly map of Earth derived using POGO and Magsat data. The resulting susceptibility contrasts directly correlate with geological features and better delineate small-scale features due to the enhancement of the higher-degree harmonics compared to the lower-degree ones.
Crustal Thickness on the Mid-Atlantic Ridge: Bull's-Eye Gravity Anomalies and Focused Accretion.
Tolstoy, M; Harding, A J; Orcutt, J A
Spreading segments of the Mid-Atlantic Ridge show negative bull's-eye anomalies in the mantle Bouguer gravity field. Seismic refraction results from 33 degrees S indicate that these anomalies can be accounted for by variations in crustal thickness along a segment. The crust is thicker in the center and thinner at the end of the spreading segment, and these changes are attributable to variations in the thickness of layer 3. The results show that accretion is focused at a slow-spreading ridge, that axial valley depth reflects the thickness of the underlying crust, and that along-axis density variations should be considered in the interpretation of gravity data. PMID:17812339
Lithospheric drift on early Mars: Evidence in the magnetic field
Daisuke Kobayashi; Kenneth F. Sprenke
The crustal magnetic anomalies on Mars may represent hot spot tracks resulting from lithospheric drift on ancient Mars. As evidence, an analysis of lineation patterns derived from the ?Br magnetic map is presented. The ?Br map, largely free of external magnetic field effects, allows excellent detail of the magnetic anomaly pattern, particularly in areas of Mars where the field is
Ocean-continent-transition and oceanic ridge structural evolution (eastern Gulf of Aden): Implications for rift to seafloor spreading processes
NASA Astrophysics Data System (ADS)
D'Acremont, E.; Leroy, S. D.; Beslier, M.; Autin, J.; Watremez, L.; Maia, M. A.; Gente, P.
The rifting between Arabia and Somalia, which started around 35 Ma ago, is followed by oceanic accretion from at least 17.6 Ma leading to the present Gulf of Aden. The transition between the thinned continental and the oceanic crusts is characterized, in space and time, by an ocean-continent transition (OCT). Here, we use bathymetry, gravity, seismic reflection and magnetism from the Encens-Sheba and Encens cruises in order to constrain the structure and segmentation of the conjugate OCT as well as the oceanic ridge between two main fracture zones (Alula-Fartak and Socotra-Hadbeen). The segmentation of the initial oceanic spreading centers seem directly related to the margin structure. Then, magmatic processes and kinematics change strongly influenced the evolution of the segmentation. The OCT and the oceanic domain can be divided into two distinct areas in the study area. The Eastern area is characterized by an extremely thin OCT and oceanic crusts (< 4km), a ~30 km wide and tectonized OCT with isolated continental blocks and short axial segments. In the western area, thicker OCT and oceanic crusts (>5km), a ~15 km wide OCT with a volcanic ridge, and a 6 km thick underplated mafic body in the northern margin suggest a high melt supply. The magmatic supply observed in the western domain is probably due to an off-axis thermal anomaly located below the southern flank of the Sheba ridge, at 75 km east of the major Alula-Fartak transform fault. This suggests that the OCT and the axial ridge morphology of this domain are perturbed by post-rift volcanism, which is due to a combination of the spreading rate, a thermal anomaly, and the cold edge effect of the Alula-Fartak transform fault. The presence of the inherited Mesozoic basins (Jezar-Qamar-Gardafui basin) located on this western domain can also explain, the difference in both the structure and the nature of the OCT between the two domains. The nature of the OCT could be either (or both) exhumed lower crust or exhumed serpentinized mantle. Locally in the western area, the OCT could be made of transitional crust intruded by magmatic bodies. A smaller deformation wavelength is observed on the northern margin, which is also steeper and narrower than the southern one. Detachment faults are observed on the southern margin attesting a simple shear rifting, where serpentinized peridotite could exhumed. Besides the influence of rifting obliquity, this structural asymmetry could be a consequence of the southern thermal anomaly or/and of the inherited Mesozoic basins and normal faults.
Prediction of the probability of occurrence of spread F over Brazil using neural networks
NASA Astrophysics Data System (ADS)
McKinnell, Lee-Anne; Paradza, Masimba; Abdu, Mangalathayil Ali
The probability of occurrence of spread F can be modelled and predicted using Neural Networks (NNs). This paper presents a feasibility study into the development of a NN based model for the prediction of the probability of occurrence of spread F over selected equatorial stations within the Brazilian sector. The input space included the day number (seasonal variation), hour (diurnal variation), sunspot number (measure of the solar activity), magnetic index (measure of the magnetic activity) and magnetic position. Twelve years of spread F data from Brazil measured (during 1978-1989) at the equatorial site Fortaleza and low latitude site Cachoeira Paulista are used in the development of an input space and NN architecture for the model. Spread F data that is believed to be related to plasma bubble developments (range spread F, RSF) and those associated with narrow spectrum irregularities that occur near the F layer (frequency spread F, FSF) were used in the model. The model results show the dependency of spread F probability occurrence as a function of local time, season and latitude. The model also illustrates some known characteristics of spread F such as the onset and peak occurrence of spread F as a function of distance from the equator. Results from this model will be presented in this paper and compared to those obtained with analytical models developed for the same purpose.
Kohn anomalies in graphene nanoribbons
Dresselhaus, Mildred
The quantum corrections to the energies of the ? point optical phonon modes (Kohn anomalies) in graphene nanoribbons (NRs) are investigated. We show theoretically that the longitudinal optical (LO) modes undergo a Kohn ...
Classifying sex biased congenital anomalies
Lubinsky, M.S. [Medical College of Wisconsin and Children`s Hospital, Milwaukee, WI (United States)] [Medical College of Wisconsin and Children`s Hospital, Milwaukee, WI (United States)
The reasons for sex biases in congenital anomalies that arise before structural or hormonal dimorphisms are established has long been unclear. A review of such disorders shows that patterning and tissue anomalies are female biased, and structural findings are more common in males. This suggests different gender dependent susceptibilities to developmental disturbances, with female vulnerabilities focused on early blastogenesis/determination, while males are more likely to involve later organogenesis/morphogenesis. A dual origin for some anomalies explains paradoxical reductions of sex biases with greater severity (i.e., multiple rather than single malformations), presumably as more severe events increase the involvement of an otherwise minor process with opposite biases to those of the primary mechanism. The cause for these sex differences is unknown, but early dimorphisms, such as differences in growth or presence of H-Y antigen, may be responsible. This model provides a useful rationale for understanding and classifying sex-biased congenital anomalies. 42 refs., 7 tabs.
Spacecraft environmental anomalies expert system
NASA Astrophysics Data System (ADS)
Koons, Harry C.; Groney, David J.
An expert system has been developed by The Aerospace Corporation, Space and Environment Technology Center for use in the diagnosis of satellite anomalies caused by the space environment. The expert system is designed to determine the probable cause of an anomaly from the following candidates: surface charging, bulk charging, single-event effects, total radiation dose, and space-plasma effects. Such anomalies depend on the orbit of the satellite, the local plasma and radiation environment (which is highly variable), the satellite-exposure time, and the hardness of the circuits and components in the satellite. The expert system is a rule-based system that uses the Texas Instrument's Personal Consultant Plus expert-system shell. The expert system's knowledgebase includes about 200 rules, as well as a number of databases that contain information on spacecraft and their orbits, previous spacecraft anomalies, and the environment.
Pacific Temperature Anomalies with Graph
NSDL National Science Digital Library
Greg Shirah
This animation shows the El Nino-La Nina Sea Surface Temperature Anomaly from January 1997 through July 1999. A graph inset shows the global average sea surface temperature fluctuation during this time period.
Gravitational Anomaly and Hydrodynamics
Landsteiner, Karl; Melgar, Luis; Pena-Benitez, Francisco
We study the anomalous induced current of a vortex in a relativistic fluid via the chiral vortical effect, which is analogous to the anomalous current induced by a magnetic field via the chiral magnetic effect. We perform this analysis at weak and strong coupling. We discuss inequivalent implementations to the chemical potential for an anomalous symmetry. At strong coupling we use a holographic model with a pure gauge and mixed gauge-gravitational Chern-Simons term in the action. We discuss the holographic renormalization and show that the Chern-Simons terms do not induce new divergences. Strong and weak coupling results agree precisely. We also point out that the holographic calculation can be done without a singular gauge field configuration on the horizon of the black hole.
Gravitational Anomaly and Hydrodynamics
Karl Landsteiner; Eugenio Megias; Luis Melgar; Francisco Pena-Benitez
We study the anomalous induced current of a vortex in a relativistic fluid via the chiral vortical effect, which is analogous to the anomalous current induced by a magnetic field via the chiral magnetic effect. We perform this analysis at weak and strong coupling. We discuss inequivalent implementations to the chemical potential for an anomalous symmetry. At strong coupling we use a holographic model with a pure gauge and mixed gauge-gravitational Chern-Simons term in the action. We discuss the holographic renormalization and show that the Chern-Simons terms do not induce new divergences. Strong and weak coupling results agree precisely. We also point out that the holographic calculation can be done without a singular gauge field configuration on the horizon of the black hole.
Anomaly detection on cup anemometers
NASA Astrophysics Data System (ADS)
Vega, Enrique; Pindado, Santiago; MartĒnez, Alejandro; Meseguer, Encarnaci¾n; GarcĒa, Luis
The performances of two rotor-damaged commercial anemometers (Vector Instruments A100 LK) were studied. The calibration results (i.e. the transfer function) were very linear, the aerodynamic behavior being more efficient than the one shown by both anemometers equipped with undamaged rotors. No detection of the anomaly (the rotorsÆ damage) was possible based on the calibration results. However, the Fourier analysis clearly revealed this anomaly.
Marine seismic refraction data indicate Mesozoic syn-rift volcanism and seafloor-spreading in the northwestern Gulf of Mexico
NASA Astrophysics Data System (ADS)
Eddy, Drew; van Avendonk, Harm; Christeson, Gail; Norton, Ian; Karner, Garry; Johnson, Chris; Kneller, Erik; Snedden, John
The Gulf of Mexico is a small ocean basin that formed by continental rifting and seafloor-spreading between North America and the Yucatan Block during the Jurassic to early Cretaceous. The lack of good, deeply-penetrating geophysical data in the Gulf of Mexico has precluded prior reconstructions of the timing and location of the transition from rifting to seafloor-spreading, as well as the degree to which magmatism influenced these geological processes. To illuminate the deep structure of this enigmatic region, we acquired four marine seismic refraction profiles in the northern Gulf of Mexico from the shelf to deep water as part of the Fall 2010 Gulf of Mexico Basin Opening (GUMBO) project. Here, we present the data and resulting seismic velocity structures of two GUMBO profiles in the northwestern Gulf of Mexico. GUMBO Line 1 extends ~330 km offshore south Texas from Matagorda Island across Alaminos Canyon to the central Gulf. GUMBO Line 2 extends ~400 km from the shelf offshore western Louisiana across the Sigsbee Escarpment. On both lines, ocean-bottom seismometers at 10-km spacing recorded 150m-spaced airgun shots over offsets up to 80 km. We use travel times from these long-offset reflections and refractions to image seismic velocities in the sediments, crystalline crust, and upper mantle using a tomographic inversion. On average, seismic velocities increase with depth from 2 km/s near the seafloor to 5 km/s near the interpreted base of salt. On both profiles we observe a large amount of lateral heterogeneity in the sediments due to salt tectonics. The deeper seismic velocity structure along GUMBO Line 1 also exhibits substantial lateral heterogeneity (4.5 km/s to 7 km/s) that may be consistent with crystallization of thin, ultraslow-spreading oceanic crust alternating with emplacement of exhumed mantle lithosphere. If the basement here is indeed oceanic, the prominent magnetic anomaly along the Texas coastline may represent the expression of synrift volcanism during the early opening of the Gulf of Mexico. In comparison, GUMBO Line 2 offshore from Louisiana displays higher seismic velocities that suggest thicker, slow- to normal-spreading oceanic crust with less-pronounced lateral variations in crustal structure than on GUMBO Line 1. Therefore, early seafloor spreading in the Gulf of Mexico may have been accompanied by more robust magmatism in the central portion of the basin compared to the west.
Two hydrothermal fields at the southern Central Indian Ridge (CIR) - structural and magnetic investigations
NASA Astrophysics Data System (ADS)
Bartsch, C.; Barckhausen, U.
With the research cruises INDEX in the years 2011 and 2012 we investigated the active ridge system of the southern Central Indian Ridge (CIR) in the Indian Ocean at the Rodriguez Triple Junction (RTJ) in terms of hydrothermal activities. Based on the analysis of structural/bathymetric and magnetic data we found indicators for the activity of hydrothermal vent sites which are related to the geometry of the ridge and the magma chambers. The CIR represents a typical slow spreading rift axis which strikes approximately north-south with an average spreading rate of 4.7 cm/a. An analysis of the spreading velocities from NW to SE illustrates a slight decrease from 4.7 cm/a to 4.5 cm/a at the RTJ. From 21░S to 25░30'S the ridge consists of six sections separated by discontinuities and one transform fault. The rift valley shows an asymmetric behaviour with steep slopes in the east and shallower slopes in the western part. The position of the center of magnetic Anomaly 1 is in some cases influenced by structural features like an overlapping spreading center and bending, along axis updoming, and an oceanic core complex. Furthermore, the spreading velocities show local changes near prominent structural features like the Knorr seamount. In this particular case, recent spreading was almost entirely confined to the western flank of the CIR. While the Knorr seamount blocks spreading in eastern direction. In general, in the mapped area a discrepancy between the center of magnetic Anomaly 1 and the bathymetric expression of the spreading center can be noticed in many places. In the northwestern part of the working area the active spreading axis lies west of the center of magnetic Anomaly 1, whereas in the southeastern part indications for a recent ridge jump to the east are observed. Such tectonic activities in combination with magmatic events are indicators for hydrothermal activity. In terms of structural geology normal faults and detachment faults represent pathways for the fluids to rise to the seafloor. Also a magma body as a heat source must be present in the vicinity of hydrothermal fields. It is necessary that the dimension of the magma source is relatively small, because too much volcanic activity might block the pathways for the fluids. The active vent fields known today from the CIR are characterized by sheet flow lavas. They are located at the eastern ridge flanks which are the steeper ones and close to non-transform discontinuities at the section ends. In that case the normal faults and limited volcanic activity are channelways for the hydrothermal fluids. At two hydrothermal vent fields a more detailed magnetic dataset shows a clear decrease in magnetic susceptibility of the basaltic rocks in the vicinity of the known vent sites. Responsible for that decrease is a process called metal leaching which is part of the hydrothermal vent site evolution circle. 3-D forward modeling provides insight into the dimensions of the hydrothermally altered rock bodies at the two locations.
Holographic description of gravitational anomalies
NASA Astrophysics Data System (ADS)
Solodukhin, Sergey N.
The holographic duality can be extended to include quantum theories with the broken coordinate invariance leading to the appearance of the gravitational anomalies. On the gravity side one adds the gravitational Chern-Simons term to the bulk action which is gauge invariant only up to the boundary terms. We analyze in detail how the gravitational anomalies originate from the modified Einstein equations in the bulk. As a side observation, we find that the gravitational Chern-Simons functional has the interesting conformal properties. It is invariant under the conformal transformations. Moreover, its metric variation produces a conformal tensor which is a generalization of the Cotton tensor to dimension d+1 = 4k-1, kinZ. We calculate the modification of the holographic stress-energy tensor that is due to the Chern-Simons term and use the bulk Einstein equations to find its divergence and thus reproduce the gravitational anomaly. The explicit calculation of the anomaly is carried out in dimensions d = 2 and d = 6. The result of the holographic calculation is compared with that of the descent method and an agreement is found. The gravitational Chern-Simons term originates by the Kaluza-Klein mechanism from a one-loop modification of M-theory action. This modification is discussed in the context of the gravitational anomaly in the six-dimensional (2,0) theory. The agreement with the earlier conjectured anomaly is found.
Repair of congenital 'disconnected uterus': a new female genital anomaly?
Kisu, Iori; Tanaka, Kyoko; Banno, Kouji; Okuda, Shigeo; Aoki, Daisuke
Congenital uterine anomaly is a female genital disorder caused by developmental anomaly of the M³llerian ducts. In this report, we present a case of repair of congenital 'disconnected uterus' between the cervix and the body of the uterus. The case did not correspond to the consensus classifications that have been proposed for congenital uterine anomaly. The patient was a young woman whose chief complaints were not having first menstruation and experiencing monthly severe lower abdominal pain. Magnetic resonance imaging showed that the uterine body was separated from the uterine cervix. Uteroplasty was conducted to anastomose the separated uterus. Periodic menstruation started 1 month after surgery and abdominal pain was improved. Performance of uteroplasty in this case was extremely significant and greatly improved the quality of life of the patient. PMID:25376460
A reexamination of the spreading center hypothesis for Ovda and Thetis regiones, Venus
NASA Technical Reports Server (NTRS)
Kiefer, Walter S.
Crumpler et al. (1987) proposed that Ovda and Thetis Regiones are spreading centers. The strong positive correlation between geoid and topography observed in ovda and Thetis is unlike that observed for terrestrial spreading centers. The maximum elevation expected for spreading centers on Venus is 1.5 km, and a cooling plate thermal model predicts a maximum geoid anomaly of 8 m, both much less than observed. Even if a spreading center is operative in Ovda and Thetis, most of the geoid and topography must be due to other mechanisms. Crumplet et al. also proposed the existence of 'cross-strike discontinuities', interpreted as transform fault zones, but the evidence for these structures is not conclusive.
Detonation spreading in fine TATBs
Kennedy, J.E.; Lee, K.Y.; Spontarelli, T.; Stine, J.R.
A test has been devised that permits rapid evaluation of the detonation-spreading (or corner-turning) properties of detonations in insensitive high explosives. The test utilizes a copper witness plate as the medium to capture performance data. Dent depth and shape in the copper are used as quantitative measures of the detonation output and spreading behavior. The merits of the test are that it is easy to perform with no dynamic instrumentation, and the test requires only a few grams of experimental explosive materials.
Shallow Drilling In The Salton Sea Region, The Thermal Anomaly
Newmark, R. L.; Kasameyer, P. W.; Younker, L. W.
During two shallow thermal drilling programs, thermal measurements were obtained in 56 shallow (76.2 m) and one intermediate (457.3 m) depth holes located both onshore and offshore along the southern margin of the Salton Sea in the Imperial Valley, California. These data complete the surficial coverage of the thermal anomaly, revealing the shape and lateral extent of the hydrothermal system. The thermal data show the region of high thermal gradients to extend only a short distance offshore to the north of the Quaternary volcanic domes which are exposed along the southern shore of the Salton Sea. The thermal anomaly has an arcuate shape, about 4 km wide and 12 km long. Across the center of the anomaly, the transition zone between locations exhibiting high thermal gradients and those exhibiting regional thermal gradients is quite narrow. Thermal gradients rise from near regional (0.09 C/m) to extreme (0.83 C/m) in only 2.4 km. The heat flow in the central part of the anomaly is >600 mW/m{sup 2} and in some areas exceeds 1200 mW/m{sup 2}. The shape of the thermal anomaly is asymmetric with respect to the line of volcanoes previously thought to represent the center of the field, with its center line offset south of the volcanic buttes. There is no broad thermal anomaly associated with the magnetic high that extends offshore to the northeast from the volcanic domes. These observations of the thermal anomaly provide important constraints for models of the circulation of the hydrothermal system. Thermal budgets based on a simple model for this hydrothermal system indicate that the heat influx rate for local ''hot spots'' in the region may be large enough to account for the rate of heat flux from the entire Salton Trough.
The North German Conductivity Anomaly revisited
NASA Astrophysics Data System (ADS)
Schõfer, A.; Houpt, L.; Brasse, H.; Hoffmann, N.
The North German Conductivity Anomaly was detected already in the early years of electromagnetic deep sounding. It refers to the reversal of induction arrows (as a graphical representation of the tipper transfer function, the ratio of vertical to horizontal magnetic field variations) at the northern and southern margins of the North German Basin. In spite of the many experiments carried out so far, its origin has remained ambiguous; explanations encompass a deep-crustal or even mantle source as well as the simple response to deepening of sedimentary sequences in the centre of the basin. Here, we report on modelling of new long-period magnetotelluric data collected along two profiles in NE Germany and S Sweden, with one transect crossing the Sorgenfrei-Tornquist Zone as the main boundary between Precambrian Baltica and the Palaeozoic belts of central Europe. With the exception of a few sites probably influenced by 3-D salt domes, the data allow a 2-D analysis. Resolution is reduced for large depths due to a well-conducting, saline aquifer, extending across the entire basin. The main result is that the reversal of induction arrows can largely be explained by the resistivity contrast between crystalline basement and sedimentary basin fill. Beneath R³gen island, a southward dipping conductor is interpreted to reflect an alum shale layer in Middle Cambrian-Lower Ordovician sediments. Beneath the southern basin, a moderately conductive upper mantle is modelled (although not very well resolved) which may reflect the thinning of the lithosphere as implied by seismic tomography. As the main anomalously inductive effect is primarily explained by the basin edges and numerous other anomalies exist inside the basin, we suggest not using the term 'North German Conductivity Anomaly' any longer.
Use of MAGSAT anomaly data for crustal structure and mineral resources in the US midcontinent
NASA Technical Reports Server (NTRS)
Carmichael, R. S.
Magnetic field data acquired by NASA's MAGSAT satellite is used to construct a long-wavelength magnetic anomaly map for the U.S. midcontinent. This aids in interpretation of gross crustal geology (structure, lithologic composition, resource potential) of the region. Magnetic properties of minerals and rocks are investigated and assessed, to help in evaluation and modelling of crustal magnetization sources and depth to the Curie-temperature isotherm.
NASA Technical Reports Server (NTRS)
Hood, L. L.; Sonett, C. P.; Srnka, L. J.
Aspects of lunar paleomagnetic and electromagnetic sounding results which appear inconsistent with the hypothesis that an ancient core dynamo was the dominant source of the observed crustal magnetism are discussed. Evidence is summarized involving a correlation between observed magnetic anomalies and ejecta blankets from impact events which indicates the possible importance of local mechanisms involving meteoroid impact processes in generating strong magnetic fields at the lunar surface. A reply is given to the latter argument which also presents recent evidence of a lunar iron core.
Pattern-based approach to fetal congenital cardiovascular anomalies using the transverse aortic arch view on prenatal cardiac MRI.
Dong, Su-Zhen; Zhu, Ming
Fetal echocardiography is the imaging modality of choice for prenatal diagnosis of congenital cardiovascular anomalies. However, echocardiography has limitations. Fetal cardiac magnetic resonance imaging (MRI) has the potential to complement US in detecting congenital cardiovascular anomalies. This article draws on our experience; it describes the transverse aortic arch view on fetal cardiac MRI and important clues on an abnormal transverse view at the level of the aortic arch to the diagnosis of fetal congenital cardiovascular anomalies. PMID:25149162
Congenital spinal cord anomalies: a pictorial review.
Gupta, Pankaj; Kumar, Atin; Kumar, Avneesh; Goel, Sandeep
Development of spinal canal and its contents occurs in a much regulated fashion. Aberration at any stage of development namely gastrulation, primary neurulation, secondary neurulation, and retrogressive differentiation can result in a specific abnormality. Spinal cord anomalies or spinal dysraphism is a heterogeneous group containing some entities that are obvious at birth and many that are discovered only after imaging for neurological symptoms or signs. Congenital spinal tumors are closely related and present either as an external mass or imaging abnormalities. Radiological imaging plays a crucial role in both diagnosis and postoperative evaluation of these patients. Magnetic resonance imaging is the modality of choice. Computed tomography is used in a limited fashion. Plain radiographs are the initial imaging in patients presenting with abnormal curvatures of spine. No other central nervous system abnormality requires as systematic an approach as spinal dysraphism. The authors present a review of both common and rare anomalies that they encountered for a 3-year period in their institute, a tertiary care level hospital. PMID:23332138
Spreading rate, spreading obliquity, and melt supply at the ultraslow spreading Southwest Indian Ridge
NASA Astrophysics Data System (ADS)
Cannat, Mathilde; Sauter, Daniel; Bezos, Antoine; Meyzen, Christine; Humler, Eric; Le Rigoleur, Marion
We use bathymetry, gravimetry, and basalt composition to examine the relationship between spreading rate, spreading obliquity, and the melt supply at the ultraslow spreading Southwest Indian Ridge (SWIR). We find that at regional scales (more than 200 km), melt supply reflects variations in mantle melting that are primarily controlled by large-scale heterogeneities in mantle temperature and/or composition. Focusing on adjacent SWIR regions with contrasted obliquity, we find that the effect of obliquity on melt production is significant (about 1.5 km less melt produced for a decrease of 7 mm/a to 4 mm/a in effective spreading rates, ESR) but not enough to produce near-amagmatic spreading in the most oblique regions of the ridge, unless associated with an anomalously cold and/or depleted mantle source. Our observations lead us to support models in which mantle upwelling beneath slow and ultraslow ridges is somewhat focused and accelerated, thereby reducing the effect of spreading rate and obliquity on upper mantle cooling and melt supply. To explain why very oblique SWIR regions nonetheless have large outcrops of mantle-derived ultramafic rocks and, in many cases, no evidence for axial volcanism (Cannat et al., 2006; Dick et al., 2003), we develop a model which combines melt migration along axis to more volcanically robust areas, melt trapping in the lithospheric mantle, and melt transport in dikes that may only form where enough melt has gathered to build sufficient overpressure. These dikes would open perpendicularly to the direction of the least compressive stress and favor the formation of orthogonal ridge sections. The resulting segmentation pattern, with prominent orthogonal volcanic centers and long intervening avolcanic or nearly avolcanic ridge sections, is not specific to oblique ridge regions. It is also observed along the SWIR and the arctic Gakkel Ridge in orthogonal regions underlain by cold and/or depleted mantle.
Further evidence of fracture-zone induced tectonic segmentation of the Antarctic Peninsula from detailed aeromagnetic anomalies.
Johnson, A.C.; Swain, C.J. [British Antarctic Survey, Cambridge (United Kingdom)] [British Antarctic Survey, Cambridge (United Kingdom)
Aeromagnetic anomaly data collected between 67{degrees}S and 70{degrees}S crossing the Antarctic Peninsula and adjacent offshore areas show a prominent NW-SE trend in the magnetic fabric. Apparent lateral offsets, previously recognized in the Pacific Margin Anomaly, have been mapped in detail and are shown to be much smaller than previously suggested. A 35 km wide zone of subdued magnetic anomalies at the Western edge of the Pacific Margin Anomaly, bounded by these apparent offsets, is interpreted as a downfaulted block of the mafic-intermediate batholith thought to be responsible for the Pacific Margin Anomaly. The trends of both fracture zones and magnetic lineaments strongly support the link between faulting in the Antarctic Peninsula magmatic arc and offshore tectonics. 20 refs., 3 figs.
Droplet spreading: Theory and experiments
NASA Astrophysics Data System (ADS)
Davis, Michael J.; Davis, Stephen H.
A hypothesis is presented that distinguishes the characteristics of spreading by hydrodynamic forces from those driven by molecular/kinetic effects, demarking the regimes by contact-line speeds and contact angles. Several applications of the criterion to experiments are discussed.
Dual polarized, heat spreading rectenna
NASA Technical Reports Server (NTRS)
Epp, Larry W. (Inventor); Khan, Abdur R. (Inventor); Smith, R. Peter (Inventor); Smith, Hugh K. (Inventor)
An aperture coupled patch splits energy from two different polarization components to different locations to spread heat. In addition, there is no physical electrical connection between the slot, patch and circuitry. The circuitry is located under a ground plane which shields against harmonic radiation back to the RF source.
NSDL National Science Digital Library
In this earth science activity (page 14 of the PDF), learners use layers of closed-cell foam to create their own model of the mid-ocean ridge in order to simulate seafloor spreading. Although this was created as a post-visit activity for a workshop about earth processes, it also makes an excellent stand alone activity.
Global Spread of Infectious Diseases
S. Hsu; A. Zee
We develop simple models for the global spread of infectious diseases, emphasizing human mobility via air travel and the variation of public health infrastructure from region to region. We derive formulas relating the total and peak number of infections in two countries to the rate of travel between them and their respective epidemiological parameters.
NSDL National Science Digital Library
Harry D. Johson
These excellent animations overlay animations of fire spread on 3D terrain that incorporates satellite imagery. A timeline shows the animation's current time relative to the fire occurrence, and an inset map provides an overhead view of the fire on a map that shows fuels by location. Animations are available for several wildfires that occurred in California.
Bevers, Stan; Amosson, Stephen H.; Waller, Mark L.; Dhuyvetter, Kevin C.
The Bull Call Spread can be used to hedge against or to benefit from a rising market. The user buys a call option at a particular strike price and sells a call option at a higher strike price. Margin requirements, advantages and disadvantages...
Magnetization Of Gabbroic Rocks and Peridotites Recovered From Mid Atlantic Ridge 14N - 16N, ODP Leg 209
NASA Astrophysics Data System (ADS)
Kikawa, E.; Garces, M.; Gee, J.
ODP Leg 209 was performed from May to July, 2004 at Mid Atlantic Ridge 14N - 16N. The precruise site survey studies performed by Alvine and Shinkai 6500 submersibles indicated the existence of fresh mantle peridotites for the drilling sites. However, the recovered rocks were basalts, gabbroic rocks and peridotites few of which were unaltered. Natural remanent magnetization (NRM) intensities calculated from ODP Leg 209 gabbroic rocks and peridotites indicated very large variations from 0.001 A/m to 50 A/m. Many of the rocks recovered were observed to have drilling-induced remanent magnetizations (DIRM). The DIRM was in general easily removed by alternating field (AF) demagnetization up to 20mT, so for most of the rocks recovered, it was possible to determine stable characteristic remanent magnetization vector directions. The DIRM which was unstable against AF demagnetization showed nearly vertical direction (downward). In many cases, the DIRMs possess more than 90 percent of NRMs of the rocks recovered. The existence of the DIRM in the rocks recovered made it difficult to obtain original natunal remanent magnetization intensities not altered by drilling. So care must be taken in considering in-situ magnetization of ODP Leg 209 gabbroic rocks and peridotites before recovered from the sea-floor, specially as remanent magnetization source for overlying sea-floor spreading magnetic anomalies, though some of the ODP Leg 209 gabbroic rocks and peridotites that were not affected by DIRM indicated reasonably high magnetization of 1 - 2 A/m to contribute to lineated marine magnetic anomalies . Similar DIRMs have been found to exist among gabbroic rocks and peridotites recovered during Legs 118, 147, and 176. Non-magnetic drilling tools including drill pipes, core barrels, BHA and so on would be essential to further studies for magnetizations for deep ocean crustal rcoks and mantle peridotites that contain relatively coarse grain magnetites easily affected by DIRM of essentially isothermal remanent magnetization (IRM) origin.
Graph anomalies in cyber communications
Vander Wiel, Scott A [Los Alamos National Laboratory; Storlie, Curtis B [Los Alamos National Laboratory; Sandine, Gary [Los Alamos National Laboratory; Hagberg, Aric A [Los Alamos National Laboratory; Fisk, Michael [Los Alamos National Laboratory
Enterprises monitor cyber traffic for viruses, intruders and stolen information. Detection methods look for known signatures of malicious traffic or search for anomalies with respect to a nominal reference model. Traditional anomaly detection focuses on aggregate traffic at central nodes or on user-level monitoring. More recently, however, traffic is being viewed more holistically as a dynamic communication graph. Attention to the graph nature of the traffic has expanded the types of anomalies that are being sought. We give an overview of several cyber data streams collected at Los Alamos National Laboratory and discuss current work in modeling the graph dynamics of traffic over the network. We consider global properties and local properties within the communication graph. A method for monitoring relative entropy on multiple correlated properties is discussed in detail.
Spacecraft environmental anomalies expert system
NASA Technical Reports Server (NTRS)
Koons, H. C.; Gorney, D. J.
A microcomputer-based expert system is being developed at the Aerospace Corporation Space Sciences Laboratory to assist in the diagnosis of satellite anomalies caused by the space environment. The expert system is designed to address anomalies caused by surface charging, bulk charging, single event effects and total radiation dose. These effects depend on the orbit of the satellite, the local environment (which is highly variable), the satellite exposure time and the hardness of the circuits and components of the satellite. The expert system is a rule-based system that uses the Texas Instruments Personal Consultant Plus expert system shell. The completed expert system knowledge base will include 150 to 200 rules, as well as a spacecraft attributes database, an historical spacecraft anomalies database, and a space environment database which is updated in near real-time. Currently, the expert system is undergoing development and testing within the Aerospace Corporation Space Sciences Laboratory.
Review on possible gravitational anomalies
Xavier Amador
This is an updated introductory review of 2 possible gravitational anomalies that has attracted part of the Scientific community: the Allais effect that occur during solar eclipses, and the Pioneer 10 spacecraft anomaly, experimented also by Pioneer 11 and Ulysses spacecrafts. It seems that, to date, no satisfactory conventional explanation exist to these phenomena, and this suggests that possible new physics will be needed to account for them. The main purpose of this review is to announce 3 other new measurements that will be carried on during the 2005 solar eclipses in Panama and Colombia (Apr. 8) and in Portugal (Oct.15).
Review on possible gravitational anomalies
NASA Astrophysics Data System (ADS)
Amador, Xavier E.
This is an updated introductory review of 2 possible gravitational anomalies that has attracted part of the Scientific community: the Allais effect that occur during solar eclipses, and the Pioneer 10 spacecraft anomaly, experimented also by Pioneer 11 and Ulysses spacecrafts. It seems that, to date, no satisfactory conventional explanation exist to these phenomena, and this suggests that possible new physics will be needed to account for them. The main purpose of this review is to announce 3 other new measurements that will be carried on during the 2005 solar eclipses in Panama and Colombia (Apr. 8) and in Portugal (Oct.15).
Anomalies and asymmetries in quark-gluon matter
Teryaev, O. V., E-mail: email@example.com [Joint Institute for Nuclear Research (Russian Federation)
The manifestations of axial anomaly and related effects in heavy-ion collisions are considered. Special role is played by various asymmetries. The azimuthal correlational asymmetries of neutron pairs at NICA/FAIR energy range may probe the global rotation of strongly interacting matter. The conductivity is related to the angular asymmetries of dilepton pairs. The strong magnetic field generated in heavy-ion collisions leads to the excess of soft dileptons flying predominantly in the scattering plane.
Plasmon mode as a detection of the chiral anomaly in Weyl semimetals
NASA Astrophysics Data System (ADS)
Zhou, Jianhui; Chang, Hao-Ran; Xiao, Di
Weyl semimetals are one kind of three-dimensional gapless semimetal with nontrivial topology in the momentum space. The chiral anomaly in Weyl semimetals manifests as a charge imbalance between the Weyl nodes of opposite chiralities induced by parallel electric and magnetic fields. We investigate the chiral anomaly effect on the plasmon mode in both intrinsic and doped Weyl semimetals within the random phase approximation. We prove that the chiral anomaly gives rise to a different plasmon mode in intrinsic Weyl semimetals. We also find the chiral anomaly leads to some exotic properties in the plasmon dispersion in doped Weyl semimetals. Consequently, the unconventional plasmon mode acts as a signature of the chiral anomaly in Weyl semimetals, by which the spectrum of plasmon provides a proper way to detect the Lifshitz transition.
Minerals in Martian meteorite illuminate magnetic mysteries
NASA Astrophysics Data System (ADS)
Wendel, JoAnna
Since magnetic anomalies on Mars were detected in Noachian-aged crust (about 4.4 billion years old) by the Mars Global Surveyor mission in the 1990s, scientists have been searching for their mineral origins. So far, meteorite samples from Mars have not yielded rocks with enough magnetic minerals to account for the anomalies.
Quantum spread spectrum multiple access
Juan Carlos Garcia-Escartin; Pedro Chamorro-Posada
We describe a quantum multiple access scheme that can take separate single photon channels and combine them in the same path. We propose an add-drop multiplexer that can insert or extract a single photon into an optical fibre carrying the qubits of all the other users. The system follows the principle of code division multiple access, a spread spectrum technique widely used in cellular networks.
Spreading dynamics of water droplets
NASA Astrophysics Data System (ADS)
Rieutord, F.; Rayssac, O.; Moriceau, H.
The spreading dynamics of water droplets on flat silicon surfaces is investigated. It is shown that, for situations close to complete wetting, the radius evolution with time can be described using a power law with a nonstandard exponent of 1/7. This dynamics is interpreted using a hydrodynamic model with an invariant dissipation profile. Such a description is also consistent with the slow dynamics observed for larger contact angles.
Fractal dimensions of wildfire spreading
NASA Astrophysics Data System (ADS)
Wang, S.-L.; Lee, H.-I.; Li, S.-P.
The time series data of 31 wildfires in 2012 in the US were analyzed. The fractal dimensions (FD) of the wildfires during spreading were studied and their geological features were identified. A growth model based on the cellular automata method is proposed here. Numerical study was performed and is shown to give good agreement with the fractal dimensions and scaling behaviors of the corresponding empirical data.
Monitoring smartphones for anomaly detection
Aubrey-derrick Schmidt; Frank Peters; Florian Lamour; Sahin Albayrak
In this paper we demonstrate how to monitor a smartphone running Symbian OS in order to extract features that de- scribe the state of the device and can be used for anomaly detection. These features are sent to a remote server, be- cause running a complex intrusion detection system (IDS) on this kind of mobile device still is not feasible,
Coral can have growth anomalies
Coral growth anomalies (GAs) are changes in the coral cells that deposit the calcium carbonate skeleton. They usually appear as raised areas of the skeleton and tissue that are different from the surrounding normal areas on the same colony. The features include abnormal shape a...
Lunar rocks and thermal anomalies
David Buhl
Recent microwave and infrared spectral observations of several of the large bright-rayed craters on the moon suggest that the thermal anomalies in these craters are produced by large rocks, boulders, and exposed rock strata. The data for the crater Tycho can be simulated by a surface consisting of 16% loose rocks of I-meter size and 4% exposed rock strata. A
Prenatal diagnosis of congenital anomalies
Todros, T; Capuzzo, E; Gaglioti, P
Up till the early 1970s, prenatal diagnosis of congenital anomalies was primarily aimed at detecting chromosomal abnormalities by amniocentesis.1. Over the last two decades, prenatal diagnosis has greatly benefited from advances in ultrasound technology and in our ability to detect microscopic and submicroscopic chromosome abnormalities as well as single gene disorders, leading to substantive improvements in detection of such congenital anomalies.2 At present, invasive prenatal diagnosis continues to be the gold standard for pregnancies at increased risk for chromosomal anomaly or other genetic disease, with chorionic villus sampling being the procedure of choice for the first trimester,3 whereas mid-trimester amniocentesis continues to be the most common form of invasive procedure for prenatal diagnosis.4 Still, invasive techniques are restricted to subgroups at risk for anomalies, for whom such time-consuming procedures are believed to be cost-effective, also accounting for procedure-related abortive risks. In the low-risk population prenatal diagnosis generally consists of screening procedures by means of ultrasound and maternal serum biochemistry. PMID:22368596
Development anomalies of the occiput
J. Wickenhauser; O. Hochberg
Four patients with classical features of bathrocephalism are described. Three further patients with developmental anomalies of the occiput are described and these are contrasted with those having classical bathrocephalism. The distinction between the two groups is emphasised. Reference is made to cases described in the pediatric literature which appears at times to depart from the traditional norms and classical notation.
Archaeological Anomalies in the Bahamas
Controversial claims have been made for the presence of anom- alous underwater archaeological sites in the Bahamas by a number of in- vestigators. The proponents emphasize extraordinary explanations for the anomalies and tend to bypass the scientific journals in favor of popular presentations with little scientific rigor. The skeptics debunk selected claims for some of the sites, do not adequately
Unusual Malignant Coronary Artery Anomaly: Results of Coronary Angiography, MR Imaging, and Multislice CT
Apitzsch, Jonas, E-mail: firstname.lastname@example.com [RWTH Aachen University, Department of Diagnostic Radiology (Germany); Kuehl, Harald P. [RWTH Aachen University, Department of Cardiology (Germany); Muehlenbruch, Georg; Mahnken, Andreas H. [RWTH Aachen University, Department of Diagnostic Radiology (Germany)
We report the case of a man with an uncommon anomaly of the origin and course of the left coronary artery. Clinical, coronary angiography, magnetic resonance imaging, and multislice computed tomography findings of this intermittently symptomatic 49 year-old patient with the rare anomaly of his left coronary artery stemming from the right sinus of Valsalva and taking an interarterial and intraseptal course are presented. The diagnostic value of the different imaging modalities is discussed.
Congenital anomalies of the male urethra
Terry L. Levin; Bokyung Han; Brent P. Little
The spectrum of congenital anomalies of the male urethra is presented. The embryologic basis of each anomaly, when known,\\u000a is discussed. Clinical and imaging features of each entity are presented.
The missing dimension in Magsat and POGO anomaly studies
NASA Astrophysics Data System (ADS)
Purucker, Michael E.; Sabaka, Terence J.; Langel, Robert A.; Olsen, Nils
The development of a comprehensive model of the near-Earth magnetic field in terms of sources in the core, ionosphere, and magnetosphere has allowed the isolation of heretofore unknown north-south trending anomalies of lithospheric origin. Previously, along-track filtering of satellite magnetic field data had been necessary in order to remove unmodeled magnetospheric and ionospheric magnetic fields. These fields change between adjacent passes by tens of nanoTeslas and have wavelengths which overlap the crustal spectrum. An example from Australia illustrates the additional information that can be extracted from the Magsat data set when this æmissing dimensionÆ is included. A north-south trending low covers most of eastern Australia, in agreement with the aeromagnetic map of Australia. This feature is seen in both the dawn and dusk subsets collected from Magsat. The center of this low is roughly coincident with the Eromanga Basin but extends for almost 2000 km in a N-S direction. The low corresponds to a region of almost featureless magnetic field on the aeromagnetic map. It is also consistent with an elevated geotherm previously proposed from studies of xenoliths in southeastern Australia. Filtering the new map in a north-south direction reproduces the previous best estimate of the Australian satellite anomaly field. We expect that this comprehensive model will provide a new window into the magnetic field of the earth's lithosphere. The model continues to be enhanced.
NASA Technical Reports Server (NTRS)
Taylor, Patrick T.; Ravat, D.; Frawley, James J.
Cosmos 49, Polar Orbit Geophysical Observatory (POGO) (Orbiting Geophysical Observatory (OGO-2, 4 and 6)) and Magsat have been the only low-earth orbiting satellites to measure the crustal magnetic field on a global scale. These missions revealed the presence of long- wavelength (> 500 km) crustal anomalies predominantly located over continents. Ground based methods were, for the most part, unable to record these very large-scale features; no doubt due to the problems of assembling continental scale maps from numerous smaller surveys acquired over many years. Questions arose as to the source and nature of these long-wave length anomalies. As a result there was a great stimulant given to the study of the magnetic properties of the lower crust and upper mantle. Some indication as to the nature of these deep sources has been provided by the recent results from the deep crustal drilling programs. In addition, the mechanism of magnetization, induced or remanent, was largely unknown. For computational ease these anomalies were considered to result solely from induced magnetization. However, recent results from Mars Orbiter Laser Altimeter (MOLA), a magnetometer-bearing mission to Mars, have revealed crustal anomalies with dimensions similar to the largest anomalies on Earth. These Martian features could only have been produced by remanent magnetization, since Mars lacks an inducing field. The origin of long-wavelength crustal anomalies, however, has not been completely determined. Several large crustal magnetic anomalies (e.g., Bangui, Kursk, Kiruna and Central Europe) will be discussed and the role of future satellite magnetometer missions (Orsted, SUNSAT and Champ) in their interpretation evaluated.
Lexical Ambiguity: Making a Case against Spread
ERIC Educational Resources Information Center
Kaplan, Jennifer J.; Rogness, Neal T.; Fisher, Diane G.
We argue for decreasing the use of the word "spread" when describing the statistical idea of dispersion or variability in introductory statistics courses. In addition, we argue for increasing the use of the word "variability" as a replacement for "spread."
An Opinion Spreading Model in Signed Networks
NASA Astrophysics Data System (ADS)
Li, Wei; Fan, Pengyi; Li, Pei; Wang, Hui; Pan, Yiguang
The opinion spreading process can be modeled as the spread of an epidemic through a network, which assumes homogeneous relationships between individuals. However, positive and negative relationships in signed networks play different roles in the opinion spreading process, following the general rule that the same opinion will diffuse through friends, while the opposite opinion will likely emerge out of interactions between enemies. In order to explore opinion spreading behavior in signed networks, we proposed a simple opinion spreading model based on the susceptible-infected-recovered (SIR) epidemic model. Under the assumption of homogeneous mixing, we also analyzed the phase transition of opinion spreading in signed networks and found that critical spreading rates were closely related to the fraction of positive relationships in signed networks. Finally, we confirmed the correctness of our solutions using numerical simulations of the opinion spreading model in signed networks.
Region Spherical Harmonic Magnetic Modeling from Near-Surface and Satellite-Altitude Anomlaies
NASA Technical Reports Server (NTRS)
Kim, Hyung Rae; von Frese, Ralph R. B.; Taylor, Patrick T.
The compiled near-surface data and satellite crustal magnetic measured data are modeled with a regionally concentrated spherical harmonic presentation technique over Australia and Antarctica. Global crustal magnetic anomaly studies have used a spherical harmonic analysis to represent the Earth's magnetic crustal field. This global approach, however is best applied where the data are uniformly distributed over the entire Earth. Satellite observations generally meet this requirement, but unequally distributed data cannot be easily adapted in global modeling. Even for the satellite observations, due to the errors spread over the globe, data smoothing is inevitable in the global spherical harmonic presentations. In addition, global high-resolution modeling requires a great number of global spherical harmonic coefficients for the regional presentation of crustal magnetic anomalies, whereas a lesser number of localized spherical coefficients will satisfy. We compared methods in both global and regional approaches and for a case where the errors were propagated outside the region of interest. For observations from the upcoming Swarm constellation, the regional modeling will allow the production a lesser number of spherical coefficients that are relevant to the region of interest
Minor Physical Anomalies, Intelligence, and Cognitive Decline
David Hope; Timothy Bates; Alan J. Gow; John M. Starr; Ian J. Deary
Background\\/Study Context: Minor physical anomalies are thought to be markers of development and increased frequency of such anomalies has been linked to lower levels of intelligence. Here the authors examine a finger curvature anomaly, and evaluate its potential as a marker of the causes of cognitive aging.Methods: Participants were members of the Lothian Birth Cohort 1921 (LBC 1921). Intelligence was
Anomaly Resolution in the International Space Station
NASA Technical Reports Server (NTRS)
Evans, William A.
Topics include post flight 2A status, groundrules, anomaly resolution, Early Communications Subsystem anomaly and resolution, Logistics and Maintenance plan, case for obscuration, case for electrical short, and manual fault isolation, and post mission analysis. Photographs from flight 2A.1 are used to illustrate anomalies.
Limb Body Wall Complex: A Rare Anomaly
Chikkannaiah, Panduranga; Dhumale, Hema; Kangle, Ranjit; Shekar, Rosini
We present autopsy findings of a case of limb body wall complex (LBWC). The fetus had encephalocele, genitourinary agenesis, skeletal anomalies and body wall defects. The rare finding in our case is the occurrence of both cranial and urogenital anomalies. The presence of complex anomalies in this fetus, supports embryonal dysplasia theory of pathogenesis for LBWC. PMID:24014975
Diagnosing network-wide traffic anomalies
Anukool Lakhina; Mark Crovella; Christophe Diot
Anomalies are unusual and significant changes in a network's traffic levels, which can often span multiple links. Diagnosing anomalies is critical for both network operators and end users. It is a difficult problem because one must extract and interpret anomalous patterns from large amounts of high-dimensional, noisy data.In this paper we propose a general method to diagnose anomalies. This method
Safeguarding SCADA Systems with Anomaly Detection
John Bigham; David Gamez; Ning Lu
This paper will show how the accuracy and security of SCADA systems can be improved by using anomaly detection to identify bad values caused by attacks and faults. The performance of invariant induction and n- gram anomaly-detectors will be compared and this paper will also outline plans for taking this work further by integrating the output from several anomaly- detecting
Correlates of spreading depolarization in human scalp electroencephalography
Drenckhahn, Christoph; Winkler, Maren K. L.; Major, Sebastian; Scheel, Michael; Kang, Eun-Jeung; Pinczolits, Alexandra; Grozea, Cristian; Hartings, Jed A.; Woitzik, Johannes
It has been known for decades that suppression of spontaneous scalp electroencephalographic activity occurs during ischaemia. Trend analysis for such suppression was found useful for intraoperative monitoring during carotid endarterectomy, or as a screening tool to detect delayed cerebral ischaemia after aneurismal subarachnoid haemorrhage. Nevertheless, pathogenesis of such suppression of activity has remained unclear. In five patients with aneurismal subarachnoid haemorrhage and four patients with decompressive hemicraniectomy after malignant hemispheric stroke due to middle cerebral artery occlusion, we here performed simultaneously full-band direct and alternating current electroencephalography at the scalp and direct and alternating current electrocorticography at the cortical surface. After subarachnoid haemorrhage, 275 slow potential changes, identifying spreading depolarizations, were recorded electrocorticographically over 694?h. Visual inspection of time-compressed scalp electroencephalography identified 193 (70.2%) slow potential changes [amplitude: ?272 (?174, ?375) ĄV (median quartiles), duration: 5.4 (4.0, 7.1) min, electrocorticography¢electroencephalography delay: 1.8 (0.8, 3.5) min]. Intervals between successive spreading depolarizations were significantly shorter for depolarizations with electroencephalographically identified slow potential change [33.0 (27.0, 76.5) versus 53.0 (28.0, 130.5) min, P?=?0.009]. Electroencephalography was thus more likely to display slow potential changes of clustered than isolated spreading depolarizations. In contrast to electrocorticography, no spread of electroencephalographic slow potential changes was seen, presumably due to superposition of volume-conducted electroencephalographic signals from widespread cortical generators. In two of five patients with subarachnoid haemorrhage, serial magnetic resonance imaging revealed large delayed infarcts at the recording site, while electrocorticography showed clusters of spreading depolarizations with persistent depression of spontaneous activity. Alternating current electroencephalography similarly displayed persistent depression of spontaneous activity, and direct current electroencephalography slow potential changes riding on a shallow negative ultraslow potential. Isolated spreading depolarizations with depression of both spontaneous electrocorticographic and electroencephalographic activity displayed significantly longer intervals between successive spreading depolarizations than isolated depolarizations with only depression of electrocorticographic activity [44.0 (28.0, 132.0) min, n?=?96, versus 30.0 (26.5, 51.5) min, n?=?109, P?=?0.001]. This suggests fusion of electroencephalographic depression periods at high depolarization frequency. No propagation of electroencephalographic depression was seen between scalp electrodes. Durations/magnitudes of isolated electroencephalographic and corresponding electrocorticographic depression periods correlated significantly. Fewer spreading depolarizations were recorded in patients with malignant hemispheric stroke but characteristics were similar to those after subarachnoid haemorrhage. In conclusion, spreading depolarizations and depressions of spontaneous activity display correlates in time-compressed human scalp direct and alternating current electroencephalography that may serve for their non-invasive detection. PMID:22366798
Optimization of network protection against virus spread
Van Mieghem, Piet
Optimization of network protection against virus spread Eric Gourdin Orange Labs, Issy Abstract--The effect of virus spreading in a telecommunication network, where a certain curing strategy in nature, to name a few: the spread of viruses and worms in the Internet, as well as social engineering
Simple Model for Thermal Spreading Impedance
Timo Veijola
A new method approximating the thermal spreading impedance in electri- cal components is presented. It is based on the dynamic temperature response of a heated sphere in a uniform, thermally linear medium. The frequency domain spreading impedance of a sphere can be expressed as a simple ana- lytic expression. For practical use, the thermal spreading impedance is synthesized approxi- mately
Coded Random CDMA with Partitioned Spreading
Lukasz Krzymien; Dmitri Truhachev; Christian Schlegel
A Code Division Multiple Access (CDMA) system is considered, where a number of concurrent users, distin- guished by random spreading waveforms, access the common additive white Gaussian noise (AWGN) channel. All users employ a regular low-density parity-check (LDPC) error con- trol code (ECC). Additionally, a method, called Partitioned Spreading (PS) is used. Each user's spreading waveform is divided into M
Modeling the Spread of Active Worms
Zesheng Chen; Lixin Gao; Kevin A. Kwiat
Active worms spread in an automated fashion and can flood the Internet in a very short time. Modeling the spread of active worms can help us understand how active worms spread, and how we can monitor and defend against the propagation of worms effectively. In this paper, we present a mathematical model, referred to as the Analytical Active Worm Propagation
Fit a Spread Estimator in Small Memory
MyungKeun Yoon; Tao Li; Shigang Chen; Jih-Kwon Peir
The spread of a source host is the number of distinct destinations that it has sent packets to during a measurement period. A spread estimator is a software\\/hardware module on a router that inspects the arrival packets and estimates the spread of each source. It has important applications in detecting port scans and DDoS attacks, measuring the infection rate of
Geopotential Field Anomaly Continuation with Multi-Altitude Observations
NASA Technical Reports Server (NTRS)
Kim, Jeong Woo; Kim, Hyung Rae; von Frese, Ralph; Taylor, Patrick; Rangelova, Elena
Conventional gravity and magnetic anomaly continuation invokes the standard Poisson boundary condition of a zero anomaly at an infinite vertical distance from the observation surface. This simple continuation is limited, however, where multiple altitude slices of the anomaly field have been observed. Increasingly, areas are becoming available constrained by multiple boundary conditions from surface, airborne, and satellite surveys. This paper describes the implementation of continuation with multi-altitude boundary conditions in Cartesian and spherical coordinates and investigates the advantages and limitations of these applications. Continuations by EPS (Equivalent Point Source) inversion and the FT (Fourier Transform), as well as by SCHA (Spherical Cap Harmonic Analysis) are considered. These methods were selected because they are especially well suited for analyzing multi-altitude data over finite patches of the earth such as covered by the ADMAP database. In general, continuations constrained by multi-altitude data surfaces are invariably superior to those constrained by a single altitude data surface due to anomaly measurement errors and the non-uniqueness of continuation.
Geopotential Field Anomaly Continuation with Multi-Altitude Observations
NASA Technical Reports Server (NTRS)
Kim, Jeong Woo; Kim, Hyung Rae; vonFrese, Ralph; Taylor, Patrick; Rangelova, Elena
Conventional gravity and magnetic anomaly continuation invokes the standard Poisson boundary condition of a zero anomaly at an infinite vertical distance from the observation surface. This simple continuation is limited, however, where multiple altitude slices of the anomaly field have been observed. Increasingly, areas are becoming available constrained by multiple boundary conditions from surface, airborne, and satellite surveys. This paper describes the implementation of continuation with multi-altitude boundary conditions in Cartesian and spherical coordinates and investigates the advantages and limitations of these applications. Continuations by EPS (Equivalent Point Source) inversion and the FT (Fourier Transform), as well as by SCHA (Spherical Cap Harmonic Analysis) are considered. These methods were selected because they are especially well suited for analyzing multi-altitude data over finite patches of the earth such as covered by the ADMAP database. In general, continuations constrained by multi-altitude data surfaces are invariably superior to those constrained by a single altitude data surface due to anomaly measurement errors and the non-uniqueness of continuation.
Cortical spreading depression: An enigma
NASA Astrophysics Data System (ADS)
Miura, R. M.; Huang, H.; Wylie, J. J.
The brain is a complex organ with active components composed largely of neurons, glial cells, and blood vessels. There exists an enormous experimental and theoretical literature on the mechanisms involved in the functioning of the brain, but we still do not have a good understanding of how it works on a gross mechanistic level. In general, the brain maintains a homeostatic state with relatively small ion concentration changes, the major ions being sodium, potassium, and chloride. Calcium ions are present in smaller quantities but still play an important role in many phenomena. Cortical spreading depression (CSD for short) was discovered over 60 years ago by A.A.P. LeŃo, a Brazilian physiologist doing his doctoral research on epilepsy at Harvard University, ōSpreading depression of activity in the cerebral cortex," J. Neurophysiol., 7 (1944), pp. 359-390. Cortical spreading depression is characterized by massive changes in ionic concentrations and slow nonlinear chemical waves, with speeds on the order of mm/min, in the cortex of different brain structures in various experimental animals. In humans, CSD is associated with migraine with aura, where a light scintillation in the visual field propagates, then disappears, and is followed by a sustained headache. To date, CSD remains an enigma, and further detailed experimental and theoretical investigations are needed to develop a comprehensive picture of the diverse mechanisms involved in producing CSD. A number of mechanisms have been hypothesized to be important for CSD wave propagation. In this paper, we briefly describe several characteristics of CSD wave propagation, and examine some of the mechanisms that are believed to be important, including ion diffusion, membrane ionic currents, osmotic effects, spatial buffering, neurotransmitter substances, gap junctions, metabolic pumps, and synaptic connections. Continuum models of CSD, consisting of coupled nonlinear diffusion equations for the ion concentrations, and a discrete lattice-Boltzmann method approach will be described. Also, we will describe some open problems and remaining challenges.
Hybrid spread spectrum radio system
Smith, Stephen F. (London, TN); Dress, William B. (Camas, WA)
Systems and methods are described for hybrid spread spectrum radio systems. A method includes modulating a signal by utilizing a subset of bits from a pseudo-random code generator to control an amplification circuit that provides a gain to the signal. Another method includes: modulating a signal by utilizing a subset of bits from a pseudo-random code generator to control a fast hopping frequency synthesizer; and fast frequency hopping the signal with the fast hopping frequency synthesizer, wherein multiple frequency hops occur within a single data-bit time.
Development and Congenital Anomalies of the Pancreas
Tadokoro, Hiroyuki; Takase, Masaru; Nobukawa, Bunsei
Understanding how the pancreas develops is essential to understand the pathogenesis of congenital pancreatic anomalies. Recent studies have shown the advantages of investigating the development of frogs, mice, and chickens for understanding early embryonic development of the pancreas and congenital anomalies, such as choledochal cysts, anomalous pancreaticobiliary junction, annular pancreas, and pancreas divisum. These anomalies arise from failure of complete rotation and fusion during embryogenesis. There are many theories in the et