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Wake fields and wake field acceleration
Bane, K.L.F.; Wilson, P.B.; Weiland, T.
In this lecture we introduce the concepts of wake fields and wake potentials, examine some basic properties of these functions, show how they can be calculated, and look briefly at a few important applications. One such application is wake field acceleration. The wake field accelerator is capable of producing the high gradients required for future very high energy e/sup +/e/sup -/ linear colliders. The principles of wake field acceleration, and a brief description of experiments in progress in this area, are presented in the concluding section. 40 references, 27 figures.
Collinear wake field acceleration
Bane, K.L.F.; Chen, P.; Wilson, P.B.
In the Voss-Weiland scheme of wake field acceleration a high current, ring-shaped driving bunch is used to accelerate a low current beam following along on axis. In such a structure, the transformer ratio, i.e., the ratio of maximum voltage that can be gained by the on-axis beam and the voltage lost by the driving beam, can be large. In contrast, it has been observed that for an arrangement in which driving and driven bunches follow the same path, and where the current distribution of both bunches is gaussian, the transformer ratio is not normally greater than two. This paper explores some of the possibilities and limitations of a collinear acceleration scheme. In addition to its application to wake field acceleration in structures, this study is also of interest for the understanding of the plasma wake field accelerator. 11 refs., 4 figs.
Conformal FDTD modeling wake fields
Jurgens, T.; Harfoush, F.
Many computer codes have been written to model wake fields. Here we describe the use of the Conformal Finite Difference Time Domain (CFDTD) method to model the wake fields generated by a rigid beam traveling through various accelerating structures. The non- cylindrical symmetry of some of the problems considered here requires the use of a three dimensional code. In traditional FDTD codes, curved surfaces are approximated by rectangular steps. The errors introduced in wake field calculations by such an approximation can be reduced by increasing the mesh size, therefore increasing the cost of computing. Another approach, validated here, deforms Ampere and Faraday contours near a media interface so as to conform to the interface. These improvements of the FDTD method result in better accuracy of the fields at asymptotically no computational cost. This method is also capable of modeling thin wires as found in beam profile monitors, and slots and cracks as found in resistive wall motions. 4 refs., 5 figs.
Vorticity Field from Successive Wake Vortices
NASA Technical Reports Server (NTRS)
The two-dimensional version of the Terminal Area Simulation System (TASS) was used to numerically simulate the interaction of wake vortices from closely separated aircraft. The aircraft parameters and separations are taken from observed data at an actual airport. The wake vortices are generated near the runway threshold for four successive aircraft. The ambient conditions are characterized by light crosswinds and stable stratification. This movie shows the time sequence of the vorticity field from the successive wake vortices. Apparent are the interactions between each pair of successive wake vortices and the ground.
Wake fields and energy spread for the ERHIC ERL
Fedotov, A.; Kayran, D.
Wake fields in high-current ERLs can cause significant beam quality degradations. Here we summarize effects of coherent synchrotron radiation, resistive wall, accelerating cavities and wall roughness for ERL parameters of the eRHIC project. A possibility of compensation of such correlated energy spread is also presented. An emphasis in the discussion is made on the suppression of coherent synchrotron radiation due to shielding and a possible reduction of wall roughness effects for realistic surfaces.
Coulomb field effect on plasma focusing and wake field acceleration
Amatuni, A.Ts.; Elbakian, S.S.; Sekhpossian, E.V. [Yerevan Physics Inst. (Armenia)
It is shown that the fields generated by relativistic electron (positron) bunches moving in overdense cold plasma have two components -- wake and Coulomb. The existence of the Coulomb component is caused by the absence of the Debay screening of the charge moving in plasma with the velocity greater than the thermal velocity of the plasma electrons. It is shown that at some conditions the contribution of the Coulomb component to focusing and self-focusing of the electron (positron) bunches, and wake field generation could be essential. This conclusion is valid for different descriptions of cold plasma-relativistic electron bunch system.
Vortex suppression of the cylinder wake by deflectors
S Ozono
The flow around a circular cylinder with a few interference elements shifted along the wake was investigated. This paper is mainly concerned with the case where a circular cylinder of the same diameter as that of the main cylinder was used as an interference element. In fact, this situation coincides with the flow around two circular cylinders in staggered arrangement
Collimator wake fields in the SLC final focus
Zimmermann, F.; Bane, K.L.F.; Ng, C.K.
The SLC final focus system accommodates 29 fixed or adjustable collimators for machine protection and background reduction. By amplifying pulse to pulse orbit variations and by generating emittance growth, collimator wake fields may degrade the beam quality at the interaction point (IP). In the SLC final focus, collimator half apertures are larger than the bunch length, so that the standard collimator wake formula of Bane and Morton does not apply. Numerical wake field calculations for SLC parameters agree quite well with the high frequency impedance of a step out transition. Due to the nature of a final focus system, the wake field kicks from all collimators add coherently, and the overall impact on luminosity can be significant. This paper suggests that collimator wake fields in the final focus provide a possible explanation for the 30% discrepancy between expected and measured luminosity in the 1994/95 SLC run.
Influence of fabrication errors on wake function suppression in NC X-band accelerating structures for linear colliders
R M Jones; C E Adolphsen; R H Miller; J W Wang; T Higo
Wake function suppression is effected by ensuring that the mode frequencies of an X-band normal conducting (NC) accelerating structure of multiple cells are detuned and moderately damped by waveguide manifolds attached to the outer wall of the accelerator. We report on the dilution in the wake function suppression that occurs due to errors resulting from the fabrication process. After diffusion
Wake Fields in the Super B Factory Interaction Region
Weathersby, Stephen; /SLAC; Novokhatski, Alexander; /SLAC
The geometry of storage ring collider interaction regions present an impedance to beam fields resulting in the generation of additional electromagnetic fields (higher order modes or wake fields) which affect the beam energy and trajectory. These affects are computed for the Super B interaction region by evaluating longitudinal loss factors and averaged transverse kicks for short range wake fields. Results indicate at least a factor of 2 lower wake field power generation in comparison with the interaction region geometry of the PEP-II B-factory collider. Wake field reduction is a consderation in the Super B design. Transverse kicks are consistent with an attractive potential from the crotch nearest the beam trajectory. The longitudinal loss factor scales as the -2.5 power of the bunch length. A factor of 60 loss factor reduction is possible with crotch geometry based on an intersecting tubes model.
Plasma wake field XUV radiation source
Prono, Daniel S. (Los Alamos, NM); Jones, Michael E. (Los Alamos, NM)
A XUV radiation source uses an interaction of electron beam pulses with a gas to create a plasma radiator. A flowing gas system (10) defines a circulation loop (12) with a device (14), such as a high pressure pump or the like, for circulating the gas. A nozzle or jet (16) produces a sonic atmospheric pressure flow and increases the density of the gas for interacting with an electron beam. An electron beam is formed by a conventional radio frequency (rf) accelerator (26) and electron pulses are conventionally formed by a beam buncher (28). The rf energy is thus converted to electron beam energy, the beam energy is used to create and then thermalize an atmospheric density flowing gas to a fully ionized plasma by interaction of beam pulses with the plasma wake field, and the energetic plasma then loses energy by line radiation at XUV wavelengths Collection and focusing optics (18) are used to collect XUV radiation emitted as line radiation when the high energy density plasma loses energy that was transferred from the electron beam pulses to the plasma.
Wake fields and energy spread for the eRHIC ERL
Fedotov, A.; Kayran, D.
Wake fields in high-current ERLs can cause significant beam quality degradations. Here we summarize effects of coherent synchrotron radiation, resistive wall, accelerating cavities and wall roughness for ERL parameters of the eRHIC project. A possibility of compensation of such correlated energy spread is also presented. An emphasis in the discussion is made on the suppression of coherent synchrotron radiation due to shielding and a possible reduction of wall roughness effects for realistic surfaces. In this report we discuss the wake fields with a focus on their effect on the energy spread of the beam. Other effects of wake fields are addressed elsewhere. An energy spread builds up during a pass though a very long beam transport in the eRHIC ERL under design. Such energy spread become important when beam is decelerated to low energy, and needs to be corrected. Several effects, such as Coherent Synchrotron Radiation (CSR), Resistive Wall (RW), accelerating RF cavities (RF) and Wall Roughness (WR) were considered. In this paper, we briefly summarize major contributions to energy spread from the wake fields for eRHIC parameters, and present possible energy spread compensation for decelerated beam. In the rest of the report we discuss effects which we believe are suppressed for the eRHIC parameters.
TRANSITION DYNAMICS OF THE WAKE FIELDS OF ULTRA SHORT BUNCHES A. Novokhatski, M. Timm and T and finite cell structures, ultra short bunches excite very high frequency electromagnetic fields. A frac leaves the structure. The rest part is chasing the bunch. In a time, this field will catch the bunch
Mariner 10 magnetic field observations of the Venus wake
NASA Technical Reports Server (NTRS)
Lepping, R. P.; Behannon, K. W.
Magnetic field measurements made over a 21-hour interval during the Mariner 10 encounter with Venus were used to study the down-stream region of the solar wind-Venus interaction over a distance of approximately 100 R sub v. For most of the day before closest approach the spacecraft was located in a sheath-like region which was apparently bounded by planetary bow shock on the outer side and either a planetary wake boundary or transient boundary-like feature on the inner side. The spacecraft made multiple encounters with the wake-like boundary during the 21-hour interval with an increasing frequency as it approached the planet. Each pass into the wake boundary from the sheath region was consistently characterized by a slight decrease in magnetic field magnitude, a marked increase in the frequency and amplitude of field fluctuations, and a systematic clockwise rotation of the field direction when viewed from above the plane of the planet orbit.
Evidence of photon acceleration by laser wake fields
Murphy, C.D.; Trines, R.; Vieira, J.; Reitsma, A.J.W.; Bingham, R.; Collier, J.L.; Divall, E.J.; Foster, P.S.; Hooker, C.J.; Langley, A.J.; Norreys, P.A.; Fonseca, R.A.; Fiuza, F.; Silva, L.O.; Mendonca, J.T.; Mori, W.B.; Gallacher, J.G.; Viskup, R.; Jaroszynski, D.A.; Mangles, S.P.D. [CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX (United Kingdom) and Blackett Laboratory, Imperial College, London, SW7 2BZ (United Kingdom); CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX (United Kingdom); GOLP/Centro de Fisica de Plasmas, Instituto Superior Tecnico, Lisbon (Portugal); Department of Physics, University of Strathclyde, Rottenrow, Glasgow, G4 0NG (United Kingdom); CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX (United Kingdom) and Department of Physics, University of Strathclyde, Rottenrow, Glasgow, G4 0NG (United Kingdom); CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX (United Kingdom); GOLP/Centro de Fisica de Plasmas, Instituto Superior Tecnico, Lisbon (Portugal); Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095-1547 (United States); Department of Physics, University of Strathclyde, Rottenrow, Glasgow, G4 0NG (United Kingdom); Blackett Laboratory, Imperial College, London, SW7 2BZ (United Kingdom)] (and others)
Photon acceleration is the phenomenon whereby a light wave changes color when propagating through a medium whose index of refraction changes in time. This concept can be used to describe the spectral changes experienced by electromagnetic waves when they propagate in spatially and temporally varying plasmas. In this paper the detection of a large-amplitude laser-driven wake field is reported for the first time, demonstrating photon acceleration. Several features characteristic of photon acceleration in wake fields, such as splitting of the main spectral peak and asymmetries between the blueshift and redshift for large shifts, have been observed. The experiment is modeled using both a novel photon-kinetic code and a three-dimensional particle-in-cell code. In addition to the wide-ranging applications in the field of compact particle accelerators, the concept of wave kinetics can be applied to understanding phenomena in nonlinear optics, space physics, and fusion energy research.
Modulation of continuous electron beams in plasma wake-fields
Rosenzweig, J.B.
In this paper we discuss the interaction of a continuous electron beam with wake-field generated plasma waves. Using a one-dimensional two fluid model, a fully nonlinear analytical description of the interaction is obtained. The phenomena of continuous beam modulation and wave period shortening are discussed. The relationship between these effects and the two-stream instability is also examined. 12 refs., 1 fig.
Fourier spectral simulations for wake fields in conducting cavities.
Min, M.; Chin, Y.-H.; Fischer, P. F.; Chae, Y.-Chul; Kim, K.-J.; KEK High Energy Accelerator Research Organization
We investigate Fourier spectral time-domain simulations applied to wake field calculations in two-dimensional cylindrical structures. The scheme involves second-order explicit leap-frogging in time and Fourier spectral approximation in space, which is obtained from simply replacing the spatial differentiation operator of the YEE scheme by the Fourier differentiation operator on nonstaggered grids. This is a first step toward investigating high-order computational techniques with the Fourier spectral method, which is relatively simple to implement.
High-Efficiency Absorber for Damping the Transverse Wake Fields
Novokhatski, A.; Seeman, J.; Weathersby, S.; /SLAC
Transverse wake fields generated by intense beams may propagate long distances in the vacuum chamber and dissipate power in different shielded elements such as bellows, vacuum valves or vacuum pumps. Induced heating in these elements may be high enough to deteriorate vacuum conditions. We have developed a broadband water-cooled bellows-absorber to capture and damp these harmful transverse fields without impacting the longitudinal beam impedance. Experimental results at the PEP-II SLAC B-factory demonstrate high efficiency of this device. This absorber may be useful in other machines like synchrotron light sources or International Linear Collider.
Control of wake and vortex shedding behind a porous circular obstacle by exerting an external magnetic field
NASA Astrophysics Data System (ADS)
Bovand, M.; Rashidi, S.; Dehghan, M.; Esfahani, J. A.; Valipour, M. S.
In this article the finite volume method (FVM) is carried out to simulate the flow around and through a two-dimensional porous cylinder. An external magnetic field is used to control the wake behind the bluff body and also to suppress the vortex shedding phenomena. The Darcy-Brinkman-Forchheimer model has been used for modeling the flow in the porous medium. Effects of Stuart (N), Reynolds (Re) and Darcy (Da) numbers on the flow behavior have been investigated. The results show that the critical Stuart number for suppress vortex shedding decreases with increasing the Darcy numbers. Also, the Stuart number for disappearance the re-circulating wake increases with increased Reynolds number for both porous and solid cylinders.
Two-Channel Rectangular Dielectric Wake Field Accelerator Structure Experiment
NASA Astrophysics Data System (ADS)
Sotnikov, G. V.; Marshall, T. C.; Shchelkunov, S. V.; Didenko, A.; Hirshfield, J. L.
A design is presented for a two-channel 30-GHz rectangular dielectric wake field accelerator structure being built for experimental tests at Argonne National Laboratory (ANL). This structure allows for a transformer ratio T much greater than two, and permits continuous coupling of energy from drive bunches to accelerated bunches. It consists of three planar slabs of cordierite ceramic (? = 4.7) supported within a rectangular copper block, forming a drive channel 12 mm�6 mm, and an accelerator channel 2 mm�6 mm. When driven by a 50 nC, 14 MeV single bunch available at ANL, theory predicts an acceleration field of 6 MeV/m, and T = 12.6. Inherent transverse wake forces introduce deflections and some distortion of bunch profiles during transit through the structure that are estimated to be tolerable. Additionally, a cylindrical two-channel DWFA is introduced which shares many advantages of the rectangular structure including high T, and the added virtue of axisymmetry that eliminates lowest-order transverse deflecting forces.
Particle Beam Stability in the Hollow Plasma Channel Wake Field Accelerator
Wurtele, Jonathan
Particle Beam Stability in the Hollow Plasma Channel Wake Field Accelerator Carl B. Schroeder1 structure is the transverse instability of the particle beam. INTRODUCTION Plasma-based accelerators have. The electromagnetic wake field response of a hollow plasma channel to a driver (laser or charged particle beam
A prescribed wake rotor inflow and flow field prediction analysis, user's manual and technical approach
NASA Technical Reports Server (NTRS)
Egolf, T. A.; Landgrebe, A. J.
A user's manual is provided which includes the technical approach for the Prescribed Wake Rotor Inflow and Flow Field Prediction Analysis. The analysis is used to provide the rotor wake induced velocities at the rotor blades for use in blade airloads and response analyses and to provide induced velocities at arbitrary field points such as at a tail surface. This analysis calculates the distribution of rotor wake induced velocities based on a prescribed wake model. Section operating conditions are prescribed from blade motion and controls determined by a separate blade response analysis. The analysis represents each blade by a segmented lifting line, and the rotor wake by discrete segmented trailing vortex filaments. Blade loading and circulation distributions are calculated based on blade element strip theory including the local induced velocity predicted by the numerical integration of the Biot-Savart Law applied to the vortex wake model.
On the field anomaly of near wakes in a collisionless plasma.
NASA Technical Reports Server (NTRS)
Liu, V. C.; Jew, H.
A variational approach is presented for determining the electric field induced by charge separation in the near wake of a large negatively charged body moving at mesothermal speeds in a tenuous plasma. It is shown that the presence of a potential well in the wake is due to the charge separation resulting from the unequal mass motions with which the ambient electrons and ions move into the wake.
Hirshfield, Jay L. [Omega-P, Inc.
Theory, computations, and experimental apparatus are presented that describe and are intended to confirm novel properties of a coaxial two-channel dielectric wake field accelerator. In this configuration, an annular drive beam in the outer coaxial channel excites multimode wakefields which, in the inner channel, can accelerate a test beam to an energy much higher than the energy of the drive beam. This high transformer ratio is the result of judicious choice of the dielectric structure parameters, and of the phase separation between drive bunches and test bunches. A structure with cm-scale wakefields has been build for tests at the Argonne Wakefield Accelerator Laboratory, and a structure with mm-scale wakefields has been built for tests at the SLAC FACET facility. Both tests await scheduling by the respective facilities.
Analysis of a high brightness photo electron beam with self field and wake field effects
Parsa, Z.
High brightness sources are the basic ingredients in the new accelerator developments such as Free-Electron Laser experiments. The effects of the interactions between the highly charged particles and the fields in the accelerating structure, e.g. R.F., Space charge and Wake fields can be detrimental to the beam and the experiments. We present and discuss the formulation used, some simulation and results for the Brookhaven National Laboratory high brightness beam that illustrates effects of the accelerating field, space charge forces (e.g. due to self field of the bunch), and the wake field (e.g. arising from the interaction of the cavity surface and the self field of the bunch).
Analysis of a high brightness photo electron beam with self field and wake field effects
Parsa, Z.
High brightness sources are the basic ingredients in the new accelerator developments such as Free-Electron Laser experiments. The effects of the interactions between the highly charged particles and the fields in the accelerating structure, e.g. R.F., Space charge and Wake fields can be detrimental to the beam and the experiments. We present and discuss the formulation used, some simulation and results for the Brookhaven National Laboratory high brightness beam that illustrates effects of the accelerating field, space charge forces (e.g. due to self field of the bunch), and the wake field (e.g. arising from the interaction of the cavity surface and the self field of the bunch).
Comparison of the plasma beat wave accelerator and the plasma wake field accelerator
Chen, P.; Ruth, R.D.
In this paper we compare the Plasma Beat Wave Accelerator and Plasma Wake Field Accelerator. We show that the electric fields in the plasma for both schemes are very similar, and thus the dynamics of the driven beams are very similar. The differences appear in the parameters associated with the driving beams. In particular to obtain a given accelerating gradient, the Plasma Wake Field Accelerator has a higher efficiency and a lower total energy for the driving beam. 7 refs., 2 tabs.
Silicon oxynitride: A field emission suppression coating
Nimel D. Theodore
We have studied coatings deposited using our inductively-coupled RF plasma ion implantation and desposition system to suppress field emission from large, 3-D electrode structures used in high voltage applications, like those used by Thomas Jefferson National Accelerator Facility in their DC-field photoelectron gun. Currently time and labor-intensive hand-polishing procedures are used to minimize field emission from these structures. Previous work
Silicon oxynitride: A field emission suppression coating
NASA Astrophysics Data System (ADS)
Theodore, Nimel D.
We have studied coatings deposited using our inductively-coupled RF plasma ion implantation and desposition system to suppress field emission from large, 3-D electrode structures used in high voltage applications, like those used by Thomas Jefferson National Accelerator Facility in their DC-field photoelectron gun. Currently time and labor-intensive hand-polishing procedures are used to minimize field emission from these structures. Previous work had shown that the field emission from polished stainless steel (27 muA of field-emitted current at 15 MV/m) could be drastically reduced with simultaneous deposition of sputtered silicon dioxide during nitrogen implantation (167 pA of field-emitted current at 30 MV/m). We have determined that this unique implantation and deposition procedure produces high-purity silicon oxynitride films that can suppress field emission from stainless steel regardless of their initial surface polish. However, when this implantation procedure was applied to large, 3-D substrates, arcs occurred, damaging the coating and causing unreliable and unrepeatable field emission suppression. We have developed a novel reactive sputtering procedure to deposit high-purity silicon oxynitride coatings without nitrogen ion implantation. We can control the stoichometry and deposition rate of these coatings by adjusting the nitrogen pressure and incident RF-power. Using profilometry, Auger electron spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Rutherford backscattering spectrometry, elastic recoil detection analysis, and current-voltage measurements, we have determined that the elemental composition, chemical bonding, density, and electrical properties of the reactively-sputtered silicon oxynitride coatings are similar to those produced by nitrogen implantation during silicon dioxide deposition. Furthermore, high voltage tests determined that both coatings similarly suppress field emission from 6" diameter, polished stainless steel electrodes. We determined a quantitative, predictive electron emission model to describe electron emission from our silicon oxynitride coatings. Although Fowler-Nordheim theory adequately describes field emission from metals, it does not apply to our dielectric coatings. Several models exist in the literature to describe electron emission from dielectrics. Based upon our high voltage field emission results, electron emission from our silicon oxynitride coatings is described by the Schottky and Poole-Frenkel emission models. These models predict that increasing the band gap, dielectric constant, and electron affinity of our silicon oxynitride coatings would further reduce field emission.
Electromagnetic wake fields and beam stability in slab-symmetric dielectric structures
NASA Astrophysics Data System (ADS)
Tremaine, A.; Rosenzweig, J.; Schoessow, P.
Several promising schemes for high-gradient acceleration of charged particles in slab-symmetric electromagnetic structures have been recently proposed. In this paper we investigate, by both computer simulation and theoretical analysis, the longitudinal and transverse wake fields experienced by a relativistic charged particle beam in a planar structure. We show that in the limit of an infinitely wide beam the net deflecting wake fields vanishes. This result is verified in the limit of a large aspect ratio (sheet) beam by finite beam analysis based on a Fourier decomposition of the current profile, as well as a paraxial wave analysis of the wake fields driven by Gaussian profile beams. The Fourier analysis forms the basis of an examination of flute instability in the sheet beam system. Practical implications of this result for beam stability and enhanced current loading in short-wavelength advanced accelerators are discussed.
Blunt body near wake flow field at Mach 6
NASA Technical Reports Server (NTRS)
Horvath, Thomas J.; McGinley, Catherine B.; Hannemann, Klaus
Tests were conducted in a Mach 6 flow to examine the reattachment process of an axisymmetric free shear layer associated with the near wake of a 70 deg. half angle, spherically blunted cone with a cylindrical after body. Model angle of incidence was fixed at 0 deg. and free-stream Reynolds numbers based on body diameter ranged from 0.5 x 10(exp 6) to 4 x 10(exp 6). The sensitivity of wake shear layer transition on reattachment heating was investigated. The present perfect gas study was designed to compliment results obtained previously in facilities capable of producing real gas effects. The instrumented blunted cone model was designed primarily for testing in high enthalpy hypervelocity shock tunnels in both this country and abroad but was amenable for testing in conventional hypersonic blowdown wind tunnels as well. Surface heating rates were inferred from temperature - time histories from coaxial surface thermocouples on the model forebody and thin film resistance gages along the model base and cylindrical after body. General flow feature (bow shock, wake shear layer, and recompression shock) locations were visually identified by schlieren photography. Mean shear layer position and growth were determined from intrusive pitot pressure surveys. In addition, wake surveys with a constant temperature hot-wire anemometer were utilized to qualitatively characterize the state of the shear layer prior to reattachment. Experimental results were compared to laminar perfect gas predictions provided by a 3-D Navier Stokes code (NSHYP). Shear layer impingement on the instrumented cylindrical after body resulted in a localized heating maximum that was 21 to 29 percent of the forebody stagnation point heating. Peak heating resulting from the reattaching shear layer was found to be a factor of 2 higher than laminar predictions, which suggested a transitional shear layer. Schlieren flow visualization and fluctuating voltage time histories and spectra from the hot wire surveys across the shear layer substantiate this observation. The sensitivity of surface heating to forebody roughness was characterized for a reattaching shear layer. For example, at R(sub infinity), d = 4 x 10(exp 6), when the shear layer was transitional, the magnitude of peak heating from shear layer impingement was reduced by approximately 24 percent when transition grit was applied to the forebody. The spatial location of the local peak, however, remained unchanged.
Autoinjection of electrons into a wake field using a capillary with attached cone
Mori, Y.; Kitagawa, Y. [Graduate School for the Creation of New Photonics, 1955-1 Kurematsu-cho, Hamamatsu, Shizuoka 431-1202 (Japan); Sentoku, Y. [Department of Physics, University of Nevada, 5625 Fox Avenue, Reno, Nevada 89506 (United States); Kondo, K.; Tsuji, K.; Nakanii, N.; Fukumochi, S.; Kashihara, M.; Kimura, K.; Tanaka, K. A.; Norimatsu, T.; Tanimoto, Tsuyoshi; Nakamura, H.; Kodama, R. [Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan); Graduate School of Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan); Takeda, K.; Tampo, M.; Mima, K. [Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan); Miura, E. [National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)
By using a cone attached to a capillary, electrons generated through a laser interaction were autoinjected and accelerated in a low-density wake field. The cone attached to the entrance of the capillary serves as an electron supplier. It increases the number of electrons from below the detection limit to 1.1 pC and the energy from 4 to 30 MeV. A two-dimensional particle-in-cell simulation reveals that a significant number of energetic electrons are extracted from the surface of the cone and are subsequently trapped in the wake field and accelerated in the capillary.
Autoinjection of electrons into a wake field using a capillary with attached cone
NASA Astrophysics Data System (ADS)
Mori, Y.; Sentoku, Y.; Kondo, K.; Tsuji, K.; Nakanii, N.; Fukumochi, S.; Kashihara, M.; Kimura, K.; Takeda, K.; Tanaka, K. A.; Norimatsu, T.; Tanimoto, Tsuyoshi; Nakamura, H.; Tampo, M.; Kodama, R.; Miura, E.; Mima, K.; Kitagawa, Y.
By using a cone attached to a capillary, electrons generated through a laser interaction were autoinjected and accelerated in a low-density wake field. The cone attached to the entrance of the capillary serves as an electron supplier. It increases the number of electrons from below the detection limit to 1.1 pC and the energy from 4 to 30 MeV. A two-dimensional particle-in-cell simulation reveals that a significant number of energetic electrons are extracted from the surface of the cone and are subsequently trapped in the wake field and accelerated in the capillary.
TE\\/TM alternating direction scheme for wake field calculation in 3D
Igor Zagorodnov; Thomas Weiland
In the future, accelerators with very short bunches will be used. It demands developing new numerical approaches for long-time calculation of electromagnetic fields in the vicinity of relativistic bunches. The conventional FDTD scheme, used in MAFIA, ABCI and other wake and PIC codes, suffers from numerical grid dispersion and staircase approximation problem. As an effective cure of the dispersion problem,
Laser wake-field acceleration and optical guiding in a hollow plasma channel
Wurtele, Jonathan
Laser wake-field acceleration and optical guiding in a hollow plasma channel T. C. Chiou and T underdenseplasmaareexamined.The evacuatedchannelin theplasmaservesasanoptical fiber to guidethe laserpulseover many morethanten Rayleighlengths.The acceleratinggradientson the axis of a channel of radiusC/C+,areof orderof one
Suppressive Surrounds of Receptive Fields In Monkey Frontal Eye Field
Cavanaugh, James; Joiner, Wilsaan M.; Wurtz, Robert H.
A critical step in determining how a neuron contributes to visual processing is determining its visual receptive field (RF). While recording from neurons in frontal eye field (FEF) of awake monkeys (Macaca mulatta), we probed the visual field with small spots of light and found excitatory RFs that decreased in strength from RF center to periphery. However, presenting stimuli with different diameters centered on the RF revealed suppressive surrounds that overlapped the previously determined excitatory RF, and reduced responses 84% on average. Consequently, in that overlap area, stimulation produced excitation or suppression, depending on the stimulus. Strong stimulation of the RF periphery with annular stimuli allowed us to quantify this effect. A modified Difference of Gaussians (DoG) model that independently varied center and surround activation accounted for the nonlinear activity in the overlap area. Our results suggest that: 1) the suppressive surrounds found in FEF are fundamentally the same as those in V1 except for the size and strength of excitatory and suppressive mechanisms, 2) methodically assaying suppressive surrounds in FEF is essential for correctly interpreting responses to large and/or peripheral stimuli and therefore understanding the effects of stimulus context, 3) regulating the relative strength of the surround clearly changes neuronal responses, and may therefore play a significant part in the neuronal changes resulting from visual attention and stimulus salience. PMID:22933810
The effect of space-charge and wake fields in the Fermilab Booster
Macridin, Alexandru; Spentzouris, Panagiotis; Amundson, James; /Fermilab; Spentzouris, Linda; McCarron, Daniel; /IIT, Chicago
We calculate the impedance and the wake functions for laminated structures with parallel-planes and circular geometries. We critically examine the approximations used in the literature for the coupling impedance in laminated chambers and find that most of them are not justified because the wall surface impedance is large. A comparison between the flat and the circular geometry impedance is presented. We use the wake fields calculated for the Fermilab Booster laminated magnets in realistic beam simulations using the Synergia code. We find good agreement between our calculation of the coherent tune shift at injection energy and the experimental measurements. In this paper we calculate the impedance and the wake functions for laminated structures with parallel-planes and circular geometries. First the coupling impedance is derived as a function of the wall surface impedance. Then the surface impedance is calculated by solving Maxwell's equations inside the lamination and the crack regions. We find that the commonly used resistive-wall approximations, good for metallic pipes with small surface impedance, are not valid in the laminated structures where the surface impedance is large. Realistic Synergia simulations of the Booster machine with wake fields predict transverse coherent tune shifts in good agreement with the experiment.
On the Production of Flat Electron Bunches for Laser Wake Field Acceleration
Kando, M.; Fukuda, Y.; Kotaki, H.; Koga, J.; Bulanov, S.V.; Tajima, T.; /JAERI, Kyoto; Chao, A.; Pitthan, R.; /SLAC; Schuler, K.-P.; /DESY; Zhidkov, A.G.; /CRIEPI, Tokyo; Nemoto, K.; /CRIEPI, Tokyo
We suggest a novel method for injection of electrons into the acceleration phase of particle accelerators, producing low emittance beams appropriate even for the demanding high energy Linear Collider specifications. In this paper we work out the injection into the acceleration phase of the wake field in a plasma behind a high intensity laser pulse, taking advantage of the laser polarization and focusing. With the aid of catastrophe theory we categorize the injection dynamics. The scheme uses the structurally stable regime of transverse wake wave breaking, when electron trajectory self-intersection leads to the formation of a flat electron bunch. As shown in three-dimensional particle-in-cell simulations of the interaction of a laser pulse in a line-focus with an underdense plasma, the electrons, injected via the transverse wake wave breaking and accelerated by the wake wave, perform betatron oscillations with different amplitudes and frequencies along the two transverse coordinates. The polarization and focusing geometry lead to a way to produce relativistic electron bunches with asymmetric emittance (flat beam). An approach for generating flat laser accelerated ion beams is briefly discussed.
Saturation of a longitudinal instability due to nonlinearity of the wake field
Krinsky, S.
Self-sustained synchrotron oscillations are observed in electron storage rings. In general the theoretical description of the saturation of an instability for large oscillation amplitude is a difficult problem, and techniques have not yet been developed which yield analytic approximations to the appropriate nonlinear Vlasov or Fokker-Planck equations. In this paper, a single point bunch interacting with the wake field from a single resonant mode of an rf cavity is considered, and the averaging method of Bogoliubov and Mitropolsky is used to study the saturation of the initial exponential growth of the oscillation amplitude, due to the nonlinearity of the wake field. The determination of the limiting amplitude of oscillation is discussed both in the presence and in the absence of radiation damping.
SELF: Fast Ion Surface Energy Loss in the Wake Fields of Solid Foils
NASA Astrophysics Data System (ADS)
Berry, Gordon; Nandi, Tapan; Haris, Kumar
We have measured the stopping powers of several fast, highly-ionized atoms passing through thin bi-layer targets made up of metals and non-conductors. We were surprised to find that the energy loss depends on the ordering of the target is significantly different on bi-layer reversal. We ascribe this new energy-loss (the SELF - the Surface Energy Loss Field) effect to the differing wake fields as the beam exits the target in the two cases. This finding is validated with several different bi-layer targets. Further, besides the highly charged ion beams, molecular ions also reveal similar results in the forward/backward coulomb explosions. We compare our energy loss results with those of previous theoretical predictions for the wake potential for fast ions in solids; lighter ions show better agreements: some theories show large discrepancies with our measurements. Further theoretical work is needed to better quantify our conclusions.
Quantum ring solitons and nonlocal effects in plasma wake field excitations
Fedele, R.; Tanjia, F. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', and INFN, Napoli (Italy); De Nicola, S. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', and INFN, Napoli (Italy); Istituto Nazionale di Ottica - C. N. R., Pozzuoli (Italy); Jovanovic, D. [Institute of Physics, University of Belgrade, Belgrade (Serbia); Shukla, P. K. [Center of Advanced Studies in Physical Sciences, Ruhr-Universitaet Bochum, Bochum (Germany)
A theoretical investigation of the quantum transverse beam motion for a cold relativistic charged particle beam travelling in a cold, collisionless, strongly magnetized plasma is carried out. This is done by taking into account both the individual quantum nature of the beam particles (single-particle uncertainty relations and spin) and the self consistent interaction generated by the plasma wake field excitation. By adopting a fluid model of a strongly magnetized plasma, the analysis is carried out in the overdense regime (dilute beams) and in the long beam limit. It is shown that the quantum description of the collective transverse beam dynamics is provided by a pair of coupled nonlinear governing equations. It comprises a Poisson-like equation for the plasma wake potential (driven by the beam density) and a 2D spinorial Schroedinger equation for the wave function, whose squared modulus is proportional to the beam density, that is obtained in the Hartree's mean field approximation, after disregarding the exchange interactions. The analysis of this pair of equations, which in general exhibits a strong nonlocal character, is carried out analytically as well as numerically in both the linear and the nonlinear regimes, showing the existence of the quantum beam vortices in the form of Laguerre-Gauss modes and ring envelope solitons, respectively. In particular, when the relation between the plasma wake field response and the beam probability density is strictly local, the pair of the governing equations is reduced to the 2D Gross-Pitaevskii equation that allows one to establish the conditions for the self focusing and collapse. These conditions include the quantum nature of the beam particles. Finally, when the relation between the plasma wake field response and the beam probability density is moderately nonlocal, the above pair of equations permits to follow the spatio-temporal evolution of a quantum ring envelope soliton. Such a structure exhibits small or violent breathing, but it remains very stable for long time.
Teaching Biology Field Courses in the Wake of Environmental Disasters.
ERIC Educational Resources Information Center
Baca, Bart J.
A biology field course organized to study the effects of the June 1979 Mexican oil spill on the marine biology of the shores of south Texas and Mexico is described, demonstrating how to effectively couple a biology classroom course with a natural or human caused environmental disaster. (Author/DC)
Investigation of Beam Instability Under the Effects of Long-Range Transverse Wake Fields in the Berkeley Future Light Source
Kur, Eugene; Zholents, Alexander A.
An ultra-relativistic charged particle bunch moving through a resonator cavity leaves behind a wake field that will affect subsequent bunches (if the bunch is not ultra-relativistic, the wake field will not be exclusively behind it). If the initial bunch enters the cavity off-axis, it will produce a transverse wake field that can then kick later bunches off the axis. Thus, even bunches that were initially traveling on axis could be displaced and, in turn, produce their own transverse wake fields, affecting following bunches. The offsets obtained by bunches could increase along the bunch train, leading to the so-called multi-bunch beam break-up instability [1]. The purpose of our investigation is to see whether such instability will occur in the superconducting, 1.3 GHz, 2.5GeV linac (see Table 1) planned for the Berkeley future light source (BFLS). We assume an initial steady-state situation established for machine operation; i.e. a continuous process where every bunch follows the same trajectory through the linac, with only small deviations from the axis of the rf structures. We will look at a possible instability arising from a bunch having a small deviation from the established trajectory. Such a deviation would produce a wake field that is slightly different from the one produced by the bunches following the established trajectory. This could lead to subsequent bunches deviating further from the established trajectory. We will assume the deviations are small (at first) and so the difference in the wake field caused by a bunch not traveling along the established trajectory is well approximated by a long-range transverse dipole wake. We are concerned only with deviations from the established trajectory; thus, in our models, a transverse position of zero corresponds to the bunch traveling along the established trajectory. Under this assumption, only the additional long-range transverse dipole wake remains in our models.
Analytical calculations of wake field generated by microwave pulses in a plasma filled waveguide for electron acceleration
Malik, Hitendra K. [Department of Physics, Indian Institute of Technology Delhi, New Delhi 110 016 (India)
Analytical expressions are obtained for the longitudinal field (wake field), density perturbation, and the potential behind microwave pulse propagating in a plasma filled rectangular waveguide with the pulse duration half of the electron plasma period. A feasibility study on wake field is carried out with rectangular pulse and its combination with Gaussian and triangular pulses under the effects of microwave pulse parameters and waveguide dimensions. It is inferred that the wake field in the waveguide cannot be attained when the length of rectangular microwave pulse is exactly equal to the plasma wavelength. A 1 ns short rectangular pulse with intensity of 250 kW/cm{sup 2} at the frequency of 5.03 GHz can excite the wake field of 1.0 MV/m in a waveguide with width of 6 cm and height of 4 cm. However, enhanced field is obtained when rectangular-triangular pulse (combination of rectangular and triangular pulses) is used. The field of wake gets weakened at higher microwave frequency and larger dimensions of the waveguide for other fixed parameters. However, a larger field is achieved when the pulse length of the microwave pulses is made shorter and/or intensity of the pulses is increased. A comparative study of the pulses shows that better results can be obtained with rectangular pulse (rectangular-Gaussian pulse: combination of rectangular and Gaussian pulses) if the microwave of shorter pulse duration (higher intensity) is available.
Comments on the impedances of the SSC shielded bellows at low frequencies due to the truncation of the wake fields
Ng, K.Y.
The behavior of the longitudinal impedance of the SSC shielded bellow at low frequencies depends very much on the length of the wake field used in the Fourier transformation. We show analytically and numerically that, regardless of the difference, single-bunch effects are independent of the actual shape of the impedance when the length of the wake used is bigger than the bunch length.
Field investigation of a wake structure downwind of a VAWT in a windfarm array
Liu, H.T.; Buck, J.W.; Germain, A.C.; Hinchee, M.E.; Solt, T.S.; LeRoy, G.M.; Srnsky, R.A.
The effects of upwind turbine wakes on the performance of a FloWind 17-m VAWT were investigated through a series of field experiments conducted at the FloWind windfarm on Cameron Ridge, Tehachapi, California. The field experiment was conducted within a VAWT array consisting of more than nine VAWTs with separations 3D crosswised by 8D downwind (where D is the turbine diameter) in a staggered configuration. The array is the upwind three rows of VAWTS in a total of six rows that are on top of the Cameron Ridge plateau. The terrain features in the vicinity are reasonably regular, with an upslope of 7 deg on the average; however, several local irregularities are present. The annual hourly averaged wind speed exceeds 8 m/s at the site. The wind field and the power-outputs of nine turbines within the array were measured with wind sensors and power transducers. Nine Gill propeller and 18 Maximum cup anemometers and one direction sensor were mounted on portable and stack-up towers installed upwind and within the turbine array. From the field measurements, the velocity and power/energy deficits were derived under various turbine on/off configurations. Much information was provided to characterize the structure of VAWT wakes and to assess their effects on the performance of downwind turbines. Recommendations are made for optimizing windfarm design and operations as well as for wind energy management.
High Fidelity Numerical Investigation of Rotor Wake Dynamics in the Near Field
NASA Astrophysics Data System (ADS)
Schroeder, Seth
The near wake of a notional submarine propeller was investigated computationally to identify the evolution and interaction of key flow structures as they travel downstream from the propeller plane. The time accurate flow field was solved using a high-fidelity large eddy simulation method with the boundary conditions on the propeller enforced through the immersed boundary method. A series of instantaneous solutions were generated for the unsteady analysis as well as to calculate the phase-averaged solution and turbulence statistics. Specific emphasis was placed on studying the stability of the helical tip vortices generated by each propeller blade. The vortices visually manifested instability modes were illustrated and the unstable behavior was quantified for a range of propeller operating conditions. A dependence on this operating condition was seen for the degree of instability and subsequent location of breakdown for the vortices. Particularly, the stronger vortices of the more highly loaded case were showing greater instabilities and faster breakdown than the weaker vortices of the lightly loaded case. The wakes at different operating conditions were analyzed in detail to investigate the underlying causes of instabilities in the vortices. A strong interaction was found between neighboring blade vortex sheets and tip vortices for the highly loaded case. This interaction was caused by differences in the wake alignment, or the helical pitch angles of the flow structures for each loading condition. Consequences of the instability and eventual breakdown of the tip vortices were illustrated and quantified through turbulence in the wake. Due to the unstable behavior and the breakdown process, the tip vortices become an additional source of turbulence downstream of the propeller plane while the rest of the wake is decaying. Finally, a realistic scenario of disturbed flow upstream of the propeller was studied through a coupled simulation. A notional appendage was designed based on model scale geometry of a submerged body and simulated upstream of the operating propeller. The dynamics of the propeller tip vortices were compared between the disturbed and undisturbed flow scenarios. The consequences of the upstream disturbance were quantified through both the global propeller force coefficients and the detailed evolution of the tip vortices. The appendage was found to have a measurable impact on the instability of the tip vortices while the location of vortex breakdown remained constant.
Fast wake measurements with LiDAR at Ris� test field
NASA Astrophysics Data System (ADS)
Bing�l, F.; Jos� Trujillo, J.; Mann, J.; Larsen, G. C.
The vast majority of wind turbines are today erected in wind farms. As a consequence, wake generated loads are becoming more and more important. We present a new and successful experimental technique, based on remote sensing, to measure instantaneously the flow in the wake of wind turbines. Downstream wind speed can be quantified spatially in one and two dimensions. Data analysis allows us to identify the wake transversal position, thus enabling us to quantify the wake meandering as well as the instantaneous wake expansion expressed in a meandering frame of reference. The experimental results are subsequently used in a preliminary verification of the basic conjecture of a wake meandering model that essentially considers the wake as a passive tracer.
Bachelor thesis: "Validation of an engineering model of the near wake wind field of wind turbines based on nacelle based lidar measurements"
Peinke, Joachim
Bachelor thesis: "Validation of an engineering model of the near wake wind field of wind turbines analysis are performed of near wake measurements of a 5 MW wind turbine at the offshore test field alpha, in an early stage of wind farm layout optimisation and wind turbine loading calculation in wind farms
Suppression and control of leakage field in electromagnetic helical microwiggler
Nobuhisa Ohigashi; Takayuki Ishida; Yoshiaki Tsunawaki; Kazuo Imasaki; Masayuki Fujita; Makoto Asakawa; Shin-Ichiro Kuruma; Chiyoe Yamanaka; Sadao Nakai; Kunioki Mima
An electromagnetic helical microwiggler with three poles in one period installing permanent magnets to suppress the leakage field has been designed and manufactured. The gap field of the wiggler is adjustable by controlling the position of an iron screw set in each retainer fixing the permanent magnet blocks. In a test wiggler with a period of 7.9 mm and magnetic
High-quality electron beam from laser wake-field acceleration in laser produced plasma plumes
Sanyasi Rao, Bobbili; Moorti, Anand; Rathore, Ranjana; Ali Chakera, Juzer; Anant Naik, Prasad; Dass Gupta, Parshotam [Laser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)] [Laser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)
Generation of highly collimated ({theta}{sub div}{approx}10 mrad), quasi-monoenergetic electron beam with peak energy 12 MeV and charge {approx}50 pC has been experimentally demonstrated from self-guided laser wake-field acceleration (LWFA) in a plasma plume produced by laser ablation of solid nylon (C{sub 12}H{sub 22}N{sub 2}O{sub 2}){sub n} target. A 7 TW, 45 fs Ti:sapphire laser system was used for LWFA, and the plasma plume forming pulse was derived from the Nd:YAG pump laser of the same system. The results show that a reproducible, high quality electron beam could be produced from this scheme which is simple, low cost and has the capability for high repetition rate operation.
Spatiotemporal Analysis of Local Field Potentials and Unit Discharges in Cat Cerebral Cortex during Natural Wake and
Destexhe, Alain
in the electroencephalogram (EEG) and local field potentials (LFPs) during slow-wave sleep (SWS). The distinction between these two sleep rhythms was demonstrated in intracellular studies from animals showing that the slow Natural Wake and Sleep States Alain Destexhe, Diego Contreras, and Mircea Steriade Laboratoire de
Comparison of observed plasma and magnetic field structures in the wakes of Mars and Venus
Dubinin, E. (Space Research Inst., Moscow (USSR)); Lundin, R. (Swedish Inst. of Space Physics, Kiruna (Sweden)); Riedler, W.; Schwingenschuh, K. (Space Research Inst., Graz (Austria)); Luhmann, J.G.; Russell, C.T. (Univ. of California, Los Angeles (USA)); Brace, L.H. (Univ. of Michigan, Ann Arbor (USA))
Plasma and magnetic field observations from the Phobos 2 spacecraft at Mars and the Pioneer Venus orbiter (PVO) at Venus show that there are some notable similarities in the structure of the low-altitude magnetotails at both of these weakly magnetized planets. In particular, it is found that when conditions in the interplanetary medium are steady and the orbit sampling geometry is appropriate, two magnetic tail lobes, with an intervening plasma sheet or central tail ray in the approximate location of the dividing current sheet, are present. This behavior is seen in both the Phobos 2 ASPERA plasma analyzer data and in the PVO Langmuir probe data. In the Phobos 2 data, the tail ray is found to be composed primarily of antisunward streaming oxygen (O{sup +}) plasma which has a bulk velocity consistent with an energy close to that of the upstream solar wind plasma. The PVO Langmuir probe experiment also detected two (or more) additional cold plasma structures flanking the central figure; Phobos 2 data, on the other hand, show a proton plasma boundary layer flanking the central (mostly O{sup +}) tail ray or plasma sheet, with sporadic fluxes or rays of O{sup +} ions. If the latter considered is to be the magnetosheath (solar wind plasma) at the tail boundary, it is mainly the common central tail O{sup +} features that suggest that there are common planetary ion acceleration and magnetotail formation processes at work in the low-altitude wakes of Mars and Venus. On the other hand, an important contribution from picked-up exospheric hydrogen in the wake at Mars cannot be ruled out.
Proper orthogonal decomposition of velocity gradient fields in a simulated stratified turbulent wake: analysis of vorticity and internal waves
NASA Astrophysics Data System (ADS)
Gurka, R.; Diamessis, P.; Liberzon, A.
The characterization of three-dimensional space and time-dependent coherent structures and internal waves in stratified environment is one of the most challenging tasks in geophysical fluid dynamics. Proper orthogonal decomposition (POD) is applied to 2-D slices of vorticity and horizontal divergence obtained from 3-D DNS of a stratified turbulent wake of a towed sphere at Re=5x103 and Fr=4. The numerical method employed solves the incompressible Navier-Stokes equations under the Boussinesq approximation. The temporal discretization consists of three fractional steps: an explicit advancement of the nonlinear terms, an implicit solution of the Poisson equation for the pseudo-pressure (which enforces incompressibility), and an implicit solution of the Helmholtz equation for the viscous terms (where boundary conditions are imposed). The computational domain is assumed to be periodic in the horizontal direction and non-periodic in the vertical direction. The 2-D slices are sampled along the stream-depth (Oxz), span-depth (Oyz) and stream-span planes (Oxy) for 231 times during the interval, Nt ? [12,35] (N is the stratification frequency). During this interval, internal wave radiation from the wake is most pronounced and the vorticity field in the wake undergoes distinct structural transitions. POD was chosen amongst the available statistical tools due to its advantage in characterization of simulated and experimentally measured velocity gradient fields. The computational procedure, applied to any random vector field, finds the most coherent feature from the given ensemble of field realizations. The decomposed empirical eigenfunctions could be referred to as "coherent structures", since they are highly correlated in an average sense with the flow field. In our analysis, we follow the computationally efficient method of 'snapshots' to find the POD eigenfunctions of the ensemble of vorticity field realizations. The results contains of the separate POD modes, along with the reconstructed vorticity and horizontal divergence fields based on the linear combination of the eigenfunctions. Similar to applications of POD to the characterization of coherent structures in turbulent boundary layers, characteristic geometrical features for each eigenmode of vorticity and horizontal divergence are deduced. The results show that in the Oxz plane at the wake centerline the first, most energetic, modes of vorticity reveal a structure similar of the forward-inclined vertical shear layers typical of late-time stratified wakes. In Oxz planes, off-set from the wake centerline, the signature of internal waves in the form of forward-inclined coherent beams extending into the ambient becomes evident. The angle of inclination becomes progressively vertical with increasing POD mode. Lower POD modes on the Oyz planes show a layered structure in the wake core with coherent beams radiating out into the ambient at angles spanning 0 to 75 degrees. The POD analysis of horizontal divergence on the Oxz and Oyz planes reveals similar features with the results for the vorticity field. Two notable exceptions at lower modes are the less organized structure of the wake core and the predominance of beam-like structures in laterally offset Oxz planes. Furthermore, these differences are confirmed through the relative energy spectra distribution of the eigenmodes for the vorticity and the horizontal divergence. Qualitative comparison of the reconstructed low-order velocity gradient fields and the computed flow fields shows the relative contribution of the different mode combinations, to the various flow features such as internal waves and vorticity. It is shown that POD analysis has provided a statistical description of the geometrical features previously observed in instantaneous flow fields of stratified turbulent wake.
The Role of Turbulence in Chemical and Dynamical Processes in the Near-Field Wake of Subsonic Aircraft
NASA Technical Reports Server (NTRS)
Lewellen, D. C.; Lewellen, W. Steve
During this grant, covering the period from September 1998 to December 2001, we continued the investigation of the role of turbulent mixing in the wake of subsonic aircraft initiated in 1994 for NASA's Atmospheric Effects of Aviation Project. The goal of the research has been to provide sufficient understanding and quantitative analytical capability to assess the dynamical, chemical, and microphysical interactions in the near-field wake that have the greatest potential to influence the global atmospheric impact of the projected fleet of subsonic aircraft. Through large-eddy simulations we have shown that turbulence in the early wake dynamics can have a strong effect on both the ice microphysics of contrail evolution and on wake chemistry. The wake vortex dynamics are the primary determinant of the vertical extent of the contrail; this together with the local wind shear largely determines the horizontal extent. The fraction of the initial ice crystals surviving the wake vortex dynamics, their spatial distribution, and the ice mass distribution are all sensitive to the aircraft type, assumed initial ice crystal number, and ambient humidity and turbulence conditions. Our model indicates that there is a significant range of conditions for which a smaller aircraft such as a B737 produces as significant a persistent contrail as a larger aircraft such as a B747, even though the latter consumes almost five times as much fuel. Large-eddy simulations of the near wake of a B757 provided a fine-grained chemical-dynamical representation of simplified NOx - HOx chemistry in wakes of ages from a few seconds to several minutes. By sampling the simulated data in a manner similar to that of in situ aircraft measurements it was possible to provide a likely explanation for a puzzle uncovered in the 1996 SUCCESS flight measurements of OH and HO2 The results illustrate the importance of considering fluid dynamics effects in interpreting chemistry results when mixing rates and species fluctuations are large, and demonstrate the feasibility of using 3D unsteady LES with coupled chemistry to study such phenomena.
Numerical simulations of a cylinder wake under a strong axial magnetic field
NASA Astrophysics Data System (ADS)
Dousset, Vincent; Poth�rat, Alban
We study the flow of a liquid metal in a square duct past a circular cylinder in a strong externally imposed magnetic field. In these conditions, the flow is quasi-two-dimensional, which allows us to model it using a two-dimensional (2D) model. We perform a parametric study by varying the two control parameters Re and Ha (Ha2 is the ratio of Lorentz to viscous forces) in the ranges [0�6000] and [0�2160], respectively. The flow is found to exhibit a sequence of four regimes. The first three regimes are similar to those of the non-magnetohydrodynamic (non-MHD) 2D circular wake, with transitions controlled by the friction parameter Re /Ha. The fourth one is characterized by vortices raising from boundary layer separations at the duct side walls, which strongly disturbs the K�rm�n vortex street. This provides the first explanation for the breakup of the 2D K�rm�n vortex street first observed experimentally by Frank, Barleon, and M�ller [Phys. Fluids 13, 2287 (2001)]. We also show that, for high values of Ha (Ha?1120), the transition to the fourth regime occurs for Re ?0.56Ha, and that it is accompanied by a sudden drop in the Strouhal number. In the first three regimes, we show that the drag coefficient and the length of the steady recirculation regions located behind the cylinder are controlled by the parameter Re /Ha4/5. Also, the free shear layer that separates the recirculation region from the free stream is similar to a free MHD parallel layer, with a thickness of the order of Ha-1/2 that is quite different to that of the non-MHD case, and therefore strongly influences the dynamics of this region. We also present one case at Re =3�104 and Ha =1120, where this layer undergoes an instability of the Kelvin-Helmholtz-type.
PIV Measurements of Cross-flow Velocity field in the Near Wake of a Pickup Truck
Al-Garni, Abdullah M.
normal to the freestream behind the cabin and tailgate have been obtained at four streamwise locations vortex structures that move randomly in space and time. The mean velocity in the near wake of the cabin pressure fluctuations at the tailgate edge as verified in the previous study. Moreover, the velocity data
Scaling of far-field wake angle of nonaxisymmetric pressure disturbance.
Moisy, F; Rabaud, M
It has been recently emphasized that the angle of maximum wave amplitude ? in the wake of a disturbance of finite size can be significantly narrower than the maximum value ?_{K}=sin^{-1}(1/3)?19.47^{?} predicted by the classical analysis of Kelvin. For axisymmetric disturbance, a simple argument based on the Cauchy-Poisson initial-value problem suggests that the wake angle decreases following a Mach-like law at large velocity, ??Fr_{L}^{-1}, where Fr_{L}=U/sqrt[gL] is the Froude number based on the disturbance velocity U, its size L, and gravity g. In this paper we extend this analysis to the case of nonaxisymmetric disturbances, relevant to real ships. We find that, for intermediate Froude numbers, the wake angle follows an intermediate scaling law ??Fr_{L}^{-2}, in agreement with the recent prediction of Noblesse et al. [Eur. J. Mech. B/Fluids 46, 164 (2014)]. We show that beyond a critical Froude number, which scales as A^{1/2} (where A is the length-to-width aspect ratio of the disturbance), the asymptotic scaling ??Fr_{B}^{-1} holds, where now Fr_{B}=A^{1/2}Fr_{L} is the Froude number based on the disturbance width. We propose a simple model for this transition, and provide a regime diagram of the scaling of the wake angle as a function of parameters (A,Fr_{L}). PMID:25019876
Electric field suppression of ultracold confined chemical reactions
Quemener, Goulven; Bohn, John L. [JILA, NIST and University of Colorado, Boulder, Colorado 80309-0440 (United States)
We consider ultracold collisions of polar molecules confined in a one-dimensional optical lattice. Using a quantum scattering formalism and a frame transformation method, we calculate elastic and chemical quenching rate constants for fermionic molecules. Taking {sup 40}K{sup 87}Rb molecules as a prototype, we find that the rate of quenching collisions is enhanced at zero electric field as the confinement is increased but that this rate is suppressed when the electric field is turned on. For molecules with 500 nK of collision energy, for realistic molecular densities, and for achievable experimental electric fields and trap confinements, we predict lifetimes for KRb molecules to be 1 s. We find a ratio of elastic to quenching collision rates of about 100, which may be sufficient to achieve efficient evaporative cooling of polar KRb molecules.
Dopaminergic control of sleep-wake states.
Dzirasa, Kafui; Ribeiro, Sidarta; Costa, Rui; Santos, Lucas M; Lin, Shih-Chieh; Grosmark, Andres; Sotnikova, Tatyana D; Gainetdinov, Raul R; Caron, Marc G; Nicolelis, Miguel A L
Dopamine depletion is involved in the pathophysiology of Parkinson's disease, whereas hyperdopaminergia may play a fundamental role in generating endophenotypes associated with schizophrenia. Sleep disturbances are known to occur in both schizophrenia and Parkinson's disease, suggesting that dopamine plays a role in regulating the sleep-wake cycle. Here, we show that novelty-exposed hyperdopaminergic mice enter a novel awake state characterized by spectral patterns of hippocampal local field potentials that resemble electrophysiological activity observed during rapid-eye-movement (REM) sleep. Treatment with haloperidol, a D2 dopamine receptor antagonist, reduces this abnormal intrusion of REM-like activity during wakefulness. Conversely, mice acutely depleted of dopamine enter a different novel awake state characterized by spectral patterns of hippocampal local field potentials that resemble electrophysiological activity observed during slow-wave sleep (SWS). This dopamine-depleted state is marked by an apparent suppression of SWS and a complete suppression of REM sleep. Treatment with D2 (but not D1) dopamine receptor agonists recovers REM sleep in these mice. Altogether, these results indicate that dopamine regulates the generation of sleep-wake states. We propose that psychosis and the sleep disturbances experienced by Parkinsonian patients result from dopamine-mediated disturbances of REM sleep. PMID:17035544
Generation and Suppression of E Region Artificial Field Aligned Irregularities
NASA Astrophysics Data System (ADS)
Miceli, R. J.; Hysell, D. L.; Munk, J.; Han, S.
Artificial field-aligned plasma density irregularities (FAIs) were generated in the E region of the ionosphere above the High Frequency Active Auroral Research Program (HAARP) facility during campaigns in May and August of 2012 and were quantified using a 30 MHz coherent scatter radar in Homer, Alaska. The purpose of the experiment was to analyze the X-mode suppression of FAIs generated from O-mode heating and to measure the threshold required to excite thermal parametric instabilities. The irregularities were excited by gradually increasing the power of a zenith pointing O-mode emission transmitted at a frequency of 2.75 MHz. To suppress the irregularities, a second X-mode emission at a higher frequency was added on alternating power cycles. The Homer radar measured the signal-to-noise ratio, Doppler shift, and spectral width of echoes reflected from the irregularities. We will calculate the threshold electric field required to excite the irregularities and compare with similar experiments in order to better understand the thermal parametric instability.
Wake flowfields for Jovian probe
NASA Technical Reports Server (NTRS)
Engel, C. D.; Hair, L. M.
The wake flow field developed by the Galileo probe as it enters the Jovian atmosphere was modeled. The wake produced by the probe is highly energetic, yielding both convective and radiative heat inputs to the base of the probe. A component mathematical model for the inviscid near and far wake, the viscous near and far wake, and near wake recirculation zone was developed. Equilibrium thermodynamics were used for both the ablation and atmospheric species. Flow fields for three entry conditions were calculated. The near viscous wave was found to exhibit a variable axial pressure distribution with the neck pressure approximately three times the base pressure. Peak wake flow field temperatures were found to be in proportion to forebody post shock temperatures.
Laser-doppler studies of the wake-effected flow field in a turbine cascade
Wittig, S.; Dullenkopf, K.; Schulz, A.; Hestermann, R.
The interaction between consecutive blade rows can be expected to have important effects on the heat transfer in cooled gas turbine cascades. In determining the local heat transfer under the influence of wake flow, nonintrusive optical measuring techniques were used to obtain the flow velocities and turbulence structures in the cascade inlet flow as well as along the test blade's surface. The main purpose of the measurements is to provide accurate experimental data for the development of predictive codes. The applicability primarily of the laser-Doppler technique is discussed and problems arising from the use of laser-dual-focus anemometry are reported. In simulating the effects of wake flow, a plane airfoil was traversed in front of the cascade.
Velocity field in the wake of a hydropower farm equipped with Achard turbines
A.-M. Georgescu; S. C. Georgescu; C. I. Cosoiu; N. Alboiu; Al Hamzu
The study consists of experimental and numerical investigations related to the water flow in the wake of a hydropower farm, equipped with three Achard turbines. The Achard turbine is a French concept of vertical axis cross-flow marine current turbine, with three vertical delta-blades, which operates irrespective of the water flow direction. A farm model built at 1:5 scale has been
Compression and Suppression of Shifting Receptive Field Activity in Frontal Eye Field Neurons
Cavanaugh, James; Wurtz, Robert H.
Before each saccade, neurons in frontal eye field anticipate the impending eye movement by showing sensitivity to stimuli appearing where the neuron's receptive field will be at the end of the saccade, referred to as the future field (FF) of the neuron. We explored the time course of this anticipatory activity in monkeys by briefly flashing stimuli in the FF at different times before saccades. Different neurons showed substantial variation in FF time course, but two salient observations emerged. First, when we compared the time span of stimulus probes before the saccade to the time span of FF activity, we found a striking temporal compression of FF activity, similar to compression seen for perisaccadic stimuli in human psychophysics. Second, neurons with distinct FF activity also showed suppression at the time of the saccade. The increase in FF activity and the decrease with suppression were temporally independent, making the patterns of activity difficult to separate. We resolved this by constructing a simple model with values for the start, peak, and duration of FF activity and suppression for each neuron. The model revealed the different time courses of FF sensitivity and suppression, suggesting that information about the impending saccade triggering suppression reaches the frontal eye field through a different pathway, or a different mechanism, than that triggering FF activity. Recognition of the variations in the time course of anticipatory FF activity provides critical information on its function and its relation to human visual perception at the time of the saccade. PMID:24227735
A Nondestructive Method for Measuring the RMS Length of Charge Bunches Using the Wake Field Radiation Spectrum
Shchelkunov, S.V.; Marshall, T.C. [Department of Applied Physics, Columbia University, New York City, NY 10027 (United States); Hirshfield, J.L. [Department of Physics, Yale University, New Haven, CT 06520-8120 (United States); Omega-P, Inc., New Haven, CT 06520 (United States); LaPointe, M.A. [Omega-P, Inc., New Haven, CT 06520 (United States); Department of Physics, Yale University, New Haven, CT 06520-8120 (United States)
We report progress in the development of a nondestructive technique to measure bunch rms-length in the psec range and below, and eventually in the fsec range, by measuring the high-frequency spectrum of wake field radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric. We demonstrate both experimentally and numerically that the generated spectrum is determined by the bunch rms-length, while the choice of the axial and longitudinal charge distribution is not important. Measurement of the millimeter-wave spectrum will determine the bunch rms-length in the psec range. This has been done using a series of calibrated mesh filters and the charge bunches produced by the 50MeV rf linac system at ATF, Brookhaven. We have developed the analysis of the factors crucial for achieving good accuracy in this measurement, and find the experimental data are fully understood by the theory. We point out that this technique also may be used for measuring fsec bunch lengths, using a prepared planar wake field microstructure.
Jay L. Hirshfield
The Phase I work reported here responds to DoE'ss stated need "...to develop improved accelerator designs that can provide very high gradient (>200 MV/m for electrons...) acceleration of intense bunches of particles." Omega-P'�?s approach to this goal is through use of a ramped train of annular electron bunches to drive a coaxial dielectric wakefield accelerator (CDWA) structure. This approach is a direct extension of the CDWA concept from acceleration in wake fields caused by a single drive bunch, to the more efficient acceleration that we predict can be realized from a tailored (or ramped) train of several drive bunches. This is possible because of a much higher transformer ratio for the latter. The CDWA structure itself has a number of unique features, including: a high accelerating gradient G, potentially with G > 1 GeV/m; continuous energy coupling from drive to test bunches without transfer structures; inherent transverse focusing forces for particles in the accelerated bunch; highly stable motion of high charge annular drive bunches; acceptable alignment tolerances for a multi-section system. What is new in the present approach is that the coaxial dielectric structure is now to be energized by-not one-�?but by a short train of ramped annular-shaped drive bunches moving in the outer coaxial channel of the structure. We have shown that this allows acceleration of an electron bunch traveling along the axis in the inner channel with a markedly higher transformer ratio T than for a single drive bunch. As described in this report, the structure will be a GHz-scale prototype with cm-scale transverse dimensions that is expected to confirm principles that can be applied to the design of a future THz-scale high gradient (> 500 MV/m) accelerator with mm-scale transverse dimensions. We show here a new means to significantly increase the transformer ratio T of the device, and thereby to significantly improve its suitability as a flexible and effective component in a future high energy, high gradient accelerator facility. We predict that the T of a high gradient CDWA can be increased by a substantial factor; this enhancement is dramatically greater than what has been demonstrated heretofore. This large enhancement in T that we predict arises from using a train of three or four drive bunches in which the spacing of the bunches and their respective charges are selected according to a simple principle that requires each bunch lose energy to the wakefields at the same rate, so as not to sacrifice drive beam efficiency�?¢�?�?�?�?as would be the case if one bunch exhausted its available energy while others had not. It is anticipated that results from the study proposed here can have a direct impact on design of the dielectric accelerator in a TeV-scale collider concept, and in the accelerator for an x-ray FEL.
NASA Astrophysics Data System (ADS)
Barney, Andrew; N�rk�r S�rensen, Jens; Ivanell, Stefan
The 44 papers in this volume constitute the proceedings of the 2015 Wake Conference, held in Visby on the island of Gotland in Sweden. It is the fourth time this conference has been held. The Wake Conference series started in Visby, where it was held in 2009 and 2011. In 2013 it took place in Copenhagen where it was combined with the International Conference on Offshore Wind Energy and Ocean Energy. In 2015 it is back where it started in Visby, where it takes place at Uppsala University Campus Gotland, June 9th�11th. The global yearly production of electrical energy by wind turbines has grown tremendously in the past decade and it now comprises more than 3% of the global electrical power consumption. Today the wind power industry has a global annual turnover of more than 50 billion USD and an annual average growth rate of more than 20%. State-of-the-art wind turbines have rotor diameters of up to 150 m and 8 MW installed capacity. These turbines are often placed in large wind farms that have a total production capacity corresponding to that of a nuclear power plant. In order to make a substantial impact on one of the most significant challenges of our time, global warming, the industry's growth has to continue for a decade or two yet. This in turn requires research into the physics of wind turbine wakes and wind farms. Modern wind turbines are today clustered in wind farms in which the turbines are fully or partially influenced by the wake of upstream turbines. As a consequence, the wake behind the wind turbines has a lower mean wind speed and an increased turbulence level, as compared to the undisturbed flow outside the farm. Hence, wake interaction results in decreased total production of power, caused by lower kinetic energy in the wind, and an increase in the turbulence intensity. Therefore, understanding the physical nature of the vortices and their dynamics in the wake of a turbine is important for the optimal design of a wind farm. This conference is aimed at scientists and PhD students working in the field of wake dynamics. The conference covers the following subject areas: Wake and vortex dynamics, instabilities in trailing vortices and wakes, simulation and measurements of wakes, analytical approaches for modeling wakes, wake interaction and other wind farm investigations. Many people have been involved in producing the 2015 Wake Conference proceedings. The work by the more than 60 reviewers ensuring the quality of the papers is greatly appreciated. The timely evaluation and coordination of the reviews would not have been possible without the work of the section editors: Christian Masson, �TS, Fernando Port�-Agel, EPFL, Gerard Schepers, ECN Wind Energy, Gijs Van Kuik, Delft University, Gunner Larsen, DTU Wind Energy, Jakob Mann, DTU Wind Energy, Javier Sanz Rodrigo, CENER, Johan Meyers, KU Leuven, Rebecca Barthelmie, Cornell University, Sandrine Aubrun-Sanches, Universit� d'Orl�ans and Thomas Leweke, IRPHE-CNRS. We are also immensely indebted to the very responsive support from the editorial team at IOP Publishing, especially Sarah Toms, during the review process of these proceedings. Visby, Sweden, June 2015 Andrew Barney, Jens N�rk�r S�rensen and Stefan Ivanell Uppsala University - Campus Gotland
Suppression of Rhizoctonia solani in potato fields. 1. Occurrence
G. Jager; H. Velvis
A search was made forRhizoctonia solani-suppressive soils by establishing many small experimental plots, half of which were planted withRhizoctonia-infected seed potatoes and the other half with disinfected seed stock. The sclerotium index of the harvested tubers was compared witht that of the seed potatoes. In suppressive soils, the sclerotium index of the harvest is much lower than that of the
Stratified wake of an accelerating hydrofoil
Ben-Gida, Hadar; Gurka, Roi
Wakes of towed and self-propelled bodies in stratified fluids are significantly different from non-stratified wakes. Long time effects of stratification on the development of the wakes of bluff bodies moving at constant speed are well known. In this experimental study we demonstrate how buoyancy affects the initial growth of vortices developing in the wake of a hydrofoil accelerating from rest. Particle image velocimetry measurements were applied to characterize the wake evolution behind a NACA 0015 hydrofoil accelerating in water and for low Reynolds number and relatively strong and stably stratified fluid (Re=5,000, Fr~O(1)). The analysis of velocity and vorticity fields, following vortex identification and an estimate of the circulation, reveal that the vortices in the stratified fluid case are stretched along the streamwise direction in the near wake. The momentum thickness profiles show lower momentum thickness values for the stratified late wake compared to the non-stratified wake, implying that the dra...
Towards a plasma wake-field acceleration-based linear collider 1 Work supported by U.S. Dept. of Energy grants DE-FG03-93ER0796, and the Alfred P. Sloan Foundation grant BR-3225. 1
J. Rosenzweig; N. Barov; A. Murokh; E. Colby; P. Colestock
A proposal for a linear collider based on an advanced accelerator scheme, plasma wake-field acceleration in the extremely nonlinear regime, is discussed. In this regime, many of the drawbacks associated with preservation of beam quality during acceleration in plasma are mitigated. The scaling of all beam and wake parameters with respect to plasma wavelength is examined. Experimental progress towards high-gradient
Study of the turbulent characteristics of the near-wake field of a medium-sized wind turbine operating in high wind conditions
Papadopoulos, K.H.; Helmis, C.G.; Soilemes, A.T.; Papageorgas, P.G.; Asimakopoulos, D.N. [Lab. of Meteorology, Athens (Greece)] [Lab. of Meteorology, Athens (Greece)
The near-wake turbulent structure that is downwind of a medium-sized, horizontal axis wind turbine at a distance of one rotor diameter is discussed. The experimental site is the Samos Island Wind Park comprising nine wind turbines installed on the top of a 400 m-high saddle. The analysis is based on experimental data obtained mainly under strong wind conditions by two masts erected upstream and downstream of a wind turbine. The field of wind turbulence is examined both in integral and spectral form. Consideration of the perturbation produced by the tower construction is crucial in the interpretation of results. Observations show that the turbulent field varies from the edge to the center of the wake and strongly depends on the incident wind speed. Increased turbulent levels are observed near the blade tips, with evidence of a similar trend around the hub height for all wind speeds. Decreases of wind turbulence are observed in mid frequencies inside the wake due to the reduced shear associated with the flat crosswind velocity profile. This effect seems to dominate in the variation of the integral values of the longitudinal wind component variance. The low frequency portion of wind spectra reverses behavior in high wind speeds, i.e., an increase in energy relative to background values is observed. This is probably due to the shape of the turbine characteristic power curve. Cross-wind profiles of turbulent shear stresses at the lower boundary of the wake are also discussed. 15 refs., 15 figs., 4 tabs.
Wake-field and space charge effects on high brightness beams calculations and measured results for the laser driven photoelectrons at BNL-ATF
Parsa, Z.
We discuss the formalism used to study the effects of the interactions between the highly charged particles and the fields in the accelerating structure, including space charge and wake fields. Some of our calculations and numerical simulation results obtained for the Brookhaven National Laboratory (BNL) high-brightness photoelectron beam at the Accelerator Test Facility (ATF) and the measured data at ATF are also included.
Jovian Plasmas Torus Interaction with Europa. Plasma Wake Structure and Effect of Inductive Magnetic Field: 3D Hybrid Kinetic Simulation
NASA Technical Reports Server (NTRS)
Lipatov, A. S.; Cooper, J F.; Paterson, W. R.; Sittler, E. C., Jr.; Hartle, R. E.; Simpson, David G.
The hybrid kinetic model supports comprehensive simulation of the interaction between different spatial and energetic elements of the Europa moon-magnetosphere system with respect to a variable upstream magnetic field and flux or density distributions of plasma and energetic ions, electrons, and neutral atoms. This capability is critical for improving the interpretation of the existing Europa flyby measurements from the Galileo Orbiter mission, and for planning flyby and orbital measurements (including the surface and atmospheric compositions) for future missions. The simulations are based on recent models of the atmosphere of Europa (Cassidy et al., 2007; Shematovich et al., 2005). In contrast to previous approaches with MHD simulations, the hybrid model allows us to fully take into account the finite gyroradius effect and electron pressure, and to correctly estimate the ion velocity distribution and the fluxes along the magnetic field (assuming an initial Maxwellian velocity distribution for upstream background ions). Photoionization, electron-impact ionization, charge exchange and collisions between the ions and neutrals are also included in our model. We consider the models with O� � and S� � background plasma, and various betas for background ions and electrons, and pickup electrons. The majority of O2 atmosphere is thermal with an extended non-thermal population (Cassidy et al., 2007). In this paper, we discuss two tasks: (1) the plasma wake structure dependence on the parameters of the upstream plasma and Europa's atmosphere (model I, cases (a) and (b) with a homogeneous Jovian magnetosphere field, an inductive magnetic dipole and high oceanic shell conductivity); and (2) estimation of the possible effect of an induced magnetic field arising from oceanic shell conductivity. This effect was estimated based on the difference between the observed and modeled magnetic fields (model II, case (c) with an inhomogeneous Jovian magnetosphere field, an inductive magnetic dipole and low oceanic shell conductivity).
Effect of wakes from moving upstream rods on boundary layer separation from a high lift airfoil
NASA Astrophysics Data System (ADS)
Volino, Ralph J.
Highly loaded airfoils in turbines allow power generation using fewer airfoils. High loading, however, can cause boundary layer separation, resulting in reduced lift and increased aerodynamic loss. Separation is affected by the interaction between rotating blades and stationary vanes. Wakes from upstream vanes periodically impinge on downstream blades, and can reduce separation. The wakes include elevated turbulence, which can induce transition, and a velocity deficit, which results in an impinging flow on the blade surface known as a ``negative jet.'' In the present study, flow through a linear cascade of very high lift airfoils is studied experimentally. Wakes are produced with moving rods which cut through the flow upstream of the airfoils, simulating the effect of upstream vanes. Pressure and velocity fields are documented. Wake spacing and velocity are varied. At low Reynolds numbers without wakes, the boundary layer separates and does not reattach. At high wake passing frequencies separation is largely suppressed. At lower frequencies, ensemble averaged velocity results show intermittent separation and reattachment during the wake passing cycle. Supported by NASA.
On the surface manifestations of ship wakes.
NASA Astrophysics Data System (ADS)
Kapustin, Ivan; Ermakov, Stanislav; Lazareva, Tatyana
During the field experiments on the Black Sea and on the Gorky Reservoir for the last 4 years the widening of the turbulent region generated by surface ships and the surface manifestations of the ship wakes has been studied. Measurements of currents in ship wakes have been made using ADCP (Acoustic Doppler Current Profiler) deployed from a motor boat. It was obtained that the time dependence of the wake width could be described approximately by a 0.4-power function, and the depth of wake remained constant at its initial stage, the latter allowed one to consider the wake widening as a one-dimensional process. We have developed a simple one-dimensional model of ship wake evolution using the semi-empirical theory of turbulence, and the initial stage of the wake widening (when neglecting dissipation) was described by the equation of turbulent energy balance with the pulse initial condition. We also observed in experiment mean circulating currents in the wake region resulting in the wind wave intensification on the boundaries of the wake region. It was shown that the later stage of the wake evolution is characterized by the presence of slicks bands on the edges of the wake. The slick bands formation is a result of the surfactants transport due to air bubbles in the turbulent wake and their compression by the mean currents. The work was supported by RFBR (projects 08-05-00634, 08-05-97011), the Program RAN Radiophysics, and the IPY THORPEX Project.
Detection of the electromagnetic field induced by the wake of a ship moving in a moderate sea state of finite depth
O. Yaakobi; G. Zilman; T. Miloh
The wake of a ship and ambient sea waves induce disturbances in the Earth�s geomagnetic field. Numerical simulations are used\\u000a to examine the feasibility of detecting these disturbances for moderate sea states. It is assumed that the electromagnetic\\u000a disturbances are sampled by an air-borne magnetometer moving steadily along a rectilinear path. Spectral analysis of the samples\\u000a is performed. Numerical simulations
A Limited Role for Suppression in the Central Field of Individuals with Strabismic Amblyopia
Barrett, Brendan T.; Panesar, Gurvinder K.; Scally, Andrew J.; Pacey, Ian E.
Background Although their eyes are pointing in different directions, people with long-standing strabismic amblyopia typically do not experience double-vision or indeed any visual symptoms arising from their condition. It is generally believed that the phenomenon of suppression plays a major role in dealing with the consequences of amblyopia and strabismus, by preventing images from the weaker/deviating eye from reaching conscious awareness. Suppression is thus a highly sophisticated coping mechanism. Although suppression has been studied for over 100 years the literature is equivocal in relation to the extent of the retina that is suppressed, though the method used to investigate suppression is crucial to the outcome. There is growing evidence that some measurement methods lead to artefactual claims that suppression exists when it does not. Methodology/Results Here we present the results of an experiment conducted with a new method to examine the prevalence, depth and extent of suppression in ten individuals with strabismic amblyopia. Seven subjects (70%) showed no evidence whatsoever for suppression and in the three individuals who did (30%), the depth and extent of suppression was small. Conclusions Suppression may play a much smaller role in dealing with the negative consequences of strabismic amblyopia than previously thought. Whereas recent claims of this nature have been made only in those with micro-strabismus our results show extremely limited evidence for suppression across the central visual field in strabismic amblyopes more generally. Instead of suppressing the image from the weaker/deviating eye, we suggest the visual system of individuals with strabismic amblyopia may act to maximise the possibilities for binocular co-operation. This is consistent with recent evidence from strabismic and amblyopic individuals that their binocular mechanisms are intact, and that, just as in visual normals, performance with two eyes is better than with the better eye alone in these individuals. PMID:22649494
Simulation studies on electron beam formation in high density plasmas in Laser Wake Field Acceleration
NASA Astrophysics Data System (ADS)
Patel, Bhavesh; Joshi, Chandrashekhar
In recent experimental work based on Laser Wakefield Acceleration, Rao et al. have demonstrated production of monoenergetic, 35 MeV electron bunch using 3 TW pulse and high density, 5.8 � 10 cm-3 plasma. The electron beam formation in such scenario relies greatly on physical processes like relativistic self-focusing and modulation instability. Further, in view of the fact that the laser pulse has a pulse-length several times the plasma wavelength, it may be surmised that the beam electrons may gain energy by direct laser acceleration in addition to that from the longitudinal fields. In present work, laser wakefield acceleration and electron bunch formation for this relatively low intensity laser pulse and a high density plasma is studied using particle-in-cell code OSIRIS. The objective here is to decipher the role of various physical mechanisms responsible for production of the surprisingly narrow energy electron bunch.The electrons are trapped only after the laser pulse is longitudinally compressed such that there is little overlap between the trapped electrons and the laser field. Thus the acceleration of beam electrons is due to the wakefield. This research is supported by DOE grant number DE-SC0010064 and the plan programme 11P-1401 ``Strong Field Science.''
Study of electron trapping by a transversely ellipsoidal bubble in the laser wake-field acceleration
Cho, Myung-Hoon [School of Natural Science, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of)] [School of Natural Science, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of); Kim, Young-Kuk; Hur, Min Sup [School of Electrical and Computer Engineering, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of)] [School of Electrical and Computer Engineering, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of)
We present electron trapping in an ellipsoidal bubble which is not well explained by the spherical bubble model by [Kostyukov et al., Phys. Rev. Lett. 103, 175003 (2009)]. The formation of an ellipsoidal bubble, which is elongated transversely, frequently occurs when the spot size of the laser pulse is large compared to the plasma wavelength. First, we introduce the relation between the bubble size and the field slope inside the bubble in longitudinal and transverse directions. Then, we provide an ellipsoidal model of the bubble potential and investigate the electron trapping condition by numerical integration of the equations of motion. We found that the ellipsoidal model gives a significantly less restrictive trapping condition than that of the spherical bubble model. The trapping condition is compared with three-dimensional particle-in-cell simulations and the electron trajectory in test potential simulations.
Suppression of magnetic relaxation by a transverse alternating magnetic field
Voloshin, I. F.; Kalinov, A. V.; Fisher, L. M. [All-Russia Electrical Engineering Institute (Russian Federation)], E-mail: email@example.com; Yampol'skii, V. A. [National Academy of Sciences of Ukraine, Institute of Radiophysics and Electronics (Ukraine)], E-mail: email@example.com
The evolution of the spatial distribution of the magnetic induction in a superconductor after the action of the alternating magnetic field perpendicular to the trapped magnetic flux has been analyzed. The observed stabilization of the magnetic induction profile is attributed to the increase in the pinning force, so that the screening current density becomes subcritical. The last statement is corroborated by direct measurements.
Airloads, wakes, and aeroelasticity
NASA Technical Reports Server (NTRS)
Johnson, Wayne
Fundamental considerations regarding the theory of modeling of rotary wing airloads, wakes, and aeroelasticity are presented. The topics covered are: airloads and wakes, including lifting-line theory, wake models and nonuniform inflow, free wake geometry, and blade-vortex interaction; aerodynamic and wake models for aeroelasticity, including two-dimensional unsteady aerodynamics and dynamic inflow; and airloads and structural dynamics, including comprehensive airload prediction programs. Results of calculations and correlations are presented.
Anisotropic Stark Effect and Electric-Field Noise Suppression for Phosphorus Donor Qubits in Silicon
A. J. Sigillito; A. M. Tyryshkin; S. A. Lyon
We report the use of novel, capacitively terminated coplanar waveguide (CPW) resonators to measure the quadratic Stark shift of phosphorus donor qubits in Si. We confirm that valley repopulation leads to an anisotropic spin-orbit Stark shift depending on electric and magnetic field orientations relative to the Si crystal. By measuring the linear Stark effect, we estimate the effective electric field due to strain in our samples. We show that in the presence of this strain, electric-field sources of decoherence can be non-negligible. Using our measured values for the Stark shift, we predict magnetic fields for which the spin-orbit Stark effect cancels the hyperfine Stark effect, suppressing decoherence from electric-field noise. We discuss the limitations of these noise-suppression points due to random distributions of strain and propose a method for overcoming them.
Emergence of spatially heterogeneous burst suppression in a neural field model of electrocortical activity
Bojak, Ingo; Stoyanov, Zhivko V.; Liley, David T. J.
Burst suppression in the electroencephalogram (EEG) is a well-described phenomenon that occurs during deep anesthesia, as well as in a variety of congenital and acquired brain insults. Classically it is thought of as spatially synchronous, quasi-periodic bursts of high amplitude EEG separated by low amplitude activity. However, its characterization as a �global brain state� has been challenged by recent results obtained with intracranial electrocortigraphy. Not only does it appear that burst suppression activity is highly asynchronous across cortex, but also that it may occur in isolated regions of circumscribed spatial extent. Here we outline a realistic neural field model for burst suppression by adding a slow process of synaptic resource depletion and recovery, which is able to reproduce qualitatively the empirically observed features during general anesthesia at the whole cortex level. Simulations reveal heterogeneous bursting over the model cortex and complex spatiotemporal dynamics during simulated anesthetic action, and provide forward predictions of neuroimaging signals for subsequent empirical comparisons and more detailed characterization. Because burst suppression corresponds to a dynamical end-point of brain activity, theoretically accounting for its spatiotemporal emergence will vitally contribute to efforts aimed at clarifying whether a common physiological trajectory is induced by the actions of general anesthetic agents. We have taken a first step in this direction by showing that a neural field model can qualitatively match recent experimental data that indicate spatial differentiation of burst suppression activity across cortex. PMID:25767438
Caught in the act: a field gone suppressive for common scab?
Technology Transfer Automated Retrieval System (TEKTRAN)
Potato varieties are evaluated for resistance to common scab (CS) in fields with high CS disease pressure. Occasionally, disease pressure naturally declines in a CS nursery; this is termed disease suppression. We have data on severity of potato CS in a scab nursery in Maine for 6 years between 2001...
Suppression of nematophagous fungi by enchytraeid worms: a field exclosure experiment
B. A. Jaffee; P. F. Santos; A. E. Muldoon
The feeding biology of Enchytraeus crypticus and other enchytraeids is poorly understood as is their effect on nematophagous fungi. Because enchytraeids had been associated\\u000a with nematophagous fungi in the field and had suppressed these fungi in soil microcosms, we tested the hypothesis that exclusion\\u000a of enchytraeids, largely E. crypticus, would improve establishment of certain nematophagous fungi in field plots. The
NASA Astrophysics Data System (ADS)
Lee, S.; Churchfield, M.; Sirnivas, S.; Moriarty, P.; Nielsen, F. G.; Skaare, B.; Byklum, E.
A team of researchers from the National Renewable Energy Laboratory and Statoil used large-eddy simulations to numerically investigate the merging wakes from upstream offshore wind turbines. Merging wakes are typical phenomena in wind farm flows in which neighboring turbine wakes consolidate to form complex flow patterns that are as yet not well understood. In the present study, three 6-MW turbines in a row were subjected to a neutrally stable atmospheric boundary layer flow. As a result, the wake from the farthest upstream turbine conjoined the downstream wake, which significantly altered the subsequent velocity deficit structures, turbulence intensity, and the global meandering behavior. The complexity increased even more when the combined wakes from the two upstream turbines mixed with the wake generated by the last turbine, thereby forming a �triplet� structure. Although the influence of the wake generated by the first turbine decayed with downstream distance, the mutated wakes from the second turbine continued to influence the downstream wake. Two mirror-image angles of wind directions that yielded partial wakes impinging on the downstream turbines yielded asymmetric wake profiles that could be attributed to the changing flow directions in the rotor plane induced by the Coriolis force. The turbine wakes persisted for extended distances in the present study, which is a result of low aerodynamic surface roughness typically found in offshore conditions.
Suppression of epileptiform activity by high frequency sinusoidal fields in rat hippocampal slices
Bikson, Marom; Lian, Jun; Hahn, Philip J; Stacey, William C; Sciortino, Christopher; Durand, Dominique M
Sinusoidal high frequency (20�50 Hz) electric fields induced across rat hippocampal slices were found to suppress zero-Ca2+, low-Ca2+, picrotoxin, and high-K+ epileptiform activity for the duration of the stimulus and for up to several minutes following the stimulus. Suppression of spontaneous activity by high frequency stimulation was found to be frequency (< 500 Hz) but not orientation or waveform dependent. Potassium-sensitive microelectrodes showed that block of epileptiform activity was always coincident with a stimulus-induced rise in extracellular potassium concentration during stimulation. Post-stimulus inhibition was always associated with a decrease in extracellular potassium activity below baseline levels. Intracellular recordings and optical imaging with voltage-sensitive dyes showed that during suppression neurons were depolarized yet did not fire action potentials. Direct injection of sinusoidal current into individual pyramidal cells did not result in a tonic depolarization. Injection of large direct current (DC) depolarized neurons and suppressed action potential generation. These findings suggest that high frequency stimulation suppresses epileptiform activity by inducing potassium efflux and depolarization block. PMID:11179402
Wind turbine wake aerodynamics
L. J. Vermeer; J. N. S�rensen; A. Crespo
The aerodynamics of horizontal axis wind turbine wakes is studied. The contents is directed towards the physics of power extraction by wind turbines and reviews both the near and the far wake region. For the near wake, the survey is restricted to uniform, steady and parallel flow conditions, thereby excluding wind shear, wind speed and rotor setting changes and yawed
Experimental evaluation of a flat wake theory for predicting rotor inflow-wake velocities
NASA Technical Reports Server (NTRS)
Wilson, John C.
The theory for predicting helicopter inflow-wake velocities called flat wake theory was correlated with several sets of experimental data. The theory was developed by V. E. Baskin of the USSR, and a computer code known as DOWN was developed at Princeton University to implement the theory. The theory treats the wake geometry as rigid without interaction between induced velocities and wake structure. The wake structure is assumed to be a flat sheet of vorticity composed of trailing elements whose strength depends on the azimuthal and radial distributions of circulation on a rotor blade. The code predicts the three orthogonal components of flow velocity in the field surrounding the rotor. The predictions can be utilized in rotor performance and helicopter real-time flight-path simulation. The predictive capability of the coded version of flat wake theory provides vertical inflow patterns similar to experimental patterns.
Development of a novel fouling suppression system in membrane bioreactors using an intermittent electric field.
Akamatsu, Kazuki; Lu, Wei; Sugawara, Takashi; Nakao, Shin-ichi
A novel membrane bioreactor system that uses an intermittent electric field was successfully developed to suppress membrane fouling, caused mainly by activated sludge. We found that the surface of the activated sludge is negatively charged, and propose the utilization of an electric repulsive force to move the sludge away from the membrane by applying an electric field only when the permeate flux has drastically declined because of membrane fouling. The experimental results showed that a field of 6 V cm(-1), switched on and off every 90 s, significantly improved the removal of the activated sludge from the membrane and accordingly improved the average permeate flux. PMID:19897224
Comparing satellite SAR and wind farm wake models
NASA Astrophysics Data System (ADS)
Hasager, C. B.; Vincent, P.; Husson, R.; Mouche, A.; Badger, M.; Pe�a, A.; Volker, P.; Badger, J.; Di Bella, A.; Palomares, A.; Cantero, E.; Correia, P. M. F.
The aim of the paper is to present offshore wind farm wake observed from satellite Synthetic Aperture Radar (SAR) wind fields from RADARSAT-1/-2 and Envisat and to compare these wakes qualitatively to wind farm wake model results. From some satellite SAR wind maps very long wakes are observed. These extend several tens of kilometres downwind e.g. 70 km. Other SAR wind maps show near-field fine scale details of wake behind rows of turbines. The satellite SAR wind farm wake cases are modelled by different wind farm wake models including the PARK microscale model, the Weather Research and Forecasting (WRF) model in high resolution and WRF with coupled microscale parametrization.
Near-Field Analysis of Bright and Dark Modes on Plasmonic Metasurfaces Showing Extraordinary Suppressed Transmission
Dobmann, Sabine; Ploss, Daniel; Peschel, Ulf
Plasmonic metasurfaces are investigated that consist of a sub wavelength line pattern in an ultrathin (~ 10 nm) silver film, designed for extraordinarily suppressed transmission (EOST) in the visible spectral range. Measurements with a near-field scanning optical microscope (NSOM) demonstrate that far field irradiation creates resonant excitations of antenna like (bright) modes that are localized on the metal ridges. In contrast, bound (dark) surface plasmon polaritons (SPPs) launched from an NSOM tip propagate well across the metasurface, preferentially perpendicular to the grating lines.
Critical magnetic field strength for suppression of the Richtmyer-Meshkov instability in plasmas.
Sano, Takayoshi; Inoue, Tsuyoshi; Nishihara, Katsunobu
The critical strength of a magnetic field required for the suppression of the Richtmyer-Meshkov instability (RMI) is investigated numerically by using a two-dimensional single-mode analysis. For the cases of magnetohydrodynamic parallel shocks, the RMI can be stabilized as a result of the extraction of vorticity from the interface. A useful formula describing a critical condition for magnetohydrodynamic RMI is introduced and is successfully confirmed by direct numerical simulations. The critical field strength is found to be largely dependent on the Mach number of the incident shock. If the shock is strong enough, even low-? plasmas can be subject to the growth of the RMI. PMID:24289690
Wavelength-dependent ionization suppression of diatomic molecules in intense circularly polarized laser fields
NASA Astrophysics Data System (ADS)
Kang, HuiPeng; Lin, ZhiYang; Xu, SongPo; Wang, ChuanLiang; Quan, Wei; Lai, XuanYang; Liu, XiaoJun; Jia, XinYan; Hao, XiaoLei; Chen, Jing; Chu, Wei; Yao, JinPing; Zeng, Bin; Cheng, Ya; Xu, ZhiZhan
We perform an experimental study on comparison between the ionization of homonuclear diatomic molecules (O2 and N2) and their companion atoms (Xe and Ar) radiated by circularly polarized intense laser fields. We find that the ionization of O2 shows suppression with respect to its companion atom Xe, which exhibits a clear wavelength and intensity dependence similar to that in linearly polarized laser field, while the ionization of N2 behaves like its companion atom Ar. With the help of S -matrix theoretical analysis, our observations can be attributed to both the molecular orbital and the two-center interference effect in molecular ionization process.
Vibrational phase imaging in wide-field CARS for nonresonant background suppression.
Zheng, Juanjuan; Akimov, Denis; Heuke, Sandro; Schmitt, Michael; Yao, Baoli; Ye, Tong; Lei, Ming; Gao, Peng; Popp, J�rgen
Coherent Anti-Stokes Raman Scattering (CARS) microscopy is a valuable tool for label-free imaging of biological samples. As a major drawback quantification based on CARS images is compromised by the appearance of a nonresonant background. In this paper we propose and demonstrate a wide-field CARS vibrational phase imaging scheme that allows for nonresonant background suppression. Several CARS images at a few consecutive planes perpendicular to the propagation direction were recorded to reconstruct a phase map utilizing the iteration phase retrieval method. Experimental results verify that the CARS background is efficiently suppressed by the phase imaging approach, as compared to traditional CARS imaging without background correction. The proposed background correction method is robust against environmental disturbance, since the experimental implementation of the suggested detection scheme requires no reference beam. PMID:25969113
A sidelobe suppressing near-field beamforming approach for ultrasound array imaging.
He, Zhengyao; Zheng, Fan; Ma, Yuanliang; Kim, Hyung Ham; Zhou, Qifa; Shung, K Kirk
A method is proposed to suppress sidelobe level for near-field beamforming in ultrasound array imaging. An optimization problem is established, and the second-order cone algorithm is used to solve the problem to obtain the weight vector based on the near-field response vector of a transducer array. The weight vector calculation results show that the proposed method can be used to suppress the sidelobe level of the near-field beam pattern of a transducer array. Ultrasound images following the application of weight vector to the array of a wire phantom are obtained by simulation with the Field II program, and the images of a wire phantom and anechoic sphere phantom are obtained experimentally with a 64-element 26?MHz linear phased array. The experimental and simulation results agree well and show that the proposed method can achieve a much lower sidelobe level than the conventional delay and sum beamforming method. The wire phantom image is demonstrated to focus much better and the contrast of the anechoic sphere phantom image improved by applying the proposed beamforming method. PMID:25994706
On the Suppression of Parametric Resonance and the Viability of Tachyonic Preheating after Multi-Field Inflation
Diana Battefeld; Thorsten Battefeld; John T. Giblin Jr
We investigate the feasibility of explosive particle production via parametric resonance or tachyonic preheating in multi-field inflationary models by means of lattice simulations. We observe a strong suppression of resonances in the presence of four-leg interactions between the inflaton fields and a scalar matter field, leading to insufficient preheating when more than two inflatons couple to the same matter field. This suppression is caused by a dephasing of the inflatons that increases the effective mass of the matter field. Including three-leg interactions leads to tachyonic preheating, which is not suppressed by an increase in the number of fields. If four-leg interactions are sub-dominant, we observe a slight enhancement of tachyonic preheating. Thus, in order for preheating after multi-field inflation to be efficient, one needs to ensure that three-leg interactions are present. If no tachyonic contributions exist, we expect the old theory of reheating to be applicable.
Status of wake and array loss research
Elliott, D.L.
In recent years, many projects have evaluated wind turbine wake effects and resultant array losses in both Europe and the United States. This paper examines the status of current knowledge about wake effects and array losses and suggests future research. Single-turbine wake characteristics have been studied extensively and are generally described well by existing theoretical models. Field measurements of wake effects in wind turbine arrays are largely limited to small arrays, with 2 to 4 rows of turbines. Few data have been published on wake effects within large arrays. Measurements of wake deficits downwind of large arrays that deficits are substantially larger and extend farther downwind than expected. Although array design models have been developed, these models have been tested and verified using only limited data from a few rows of wind turbines in complex terrain, whereas some of the largest arrays have more than 40 rows of wind turbines. Planned cooperative efforts with the wind industry will obtain existing data relevant to analyzing energy deficits within large arrays and identifying data sets for potential use in array model verification efforts. Future research being considered include a cooperative research experiment to obtain more definitive data on wake deficits and turbulence within and downwind of large arrays. 16 refs., 9 figs., 1 tab.
Wake Vortex Influence on Ambient Potential Temperature
NASA Technical Reports Server (NTRS)
The two-dimensional version of the Terminal Area Simulation System (TASS) was used to numerically simulate the interaction of wake vortices from closely separated aircraft. The aircraft parameters and separations are taken from observed data at an actual airport. The wake vortices are generated near the runway threshold for four successive aircraft. The ambient conditions are characterized by light crosswinds and stable stratification. This movie shows the effect that the vortices have upon the ambient potential temperature field.
Suppression of Entropy Perturbations in Multi--Field Inflation on the Brane
P. R. Ashcroft; C. van de Bruck; A. -C. Davis
At energies higher than the brane tension, the dynamics of a scalar field rolling down a potential are modified relative to the predictions of General Relativity. The modifications imply, among other things, that steeper potentials can be used to drive an epoch of slow--roll inflation. We investigate the evolution of entropy and adiabatic modes during inflation driven by two scalar fields confined on the brane. We show that the amount of entropy perturbations produced during inflation is suppressed compared to the predictions made by General Relativity. As a consequence, the initial conditions do not matter in multiple field inflation in brane worlds if inflation is driven at energies much higher than the brane tension.
A Graphene-Coated Ion Trap for Electric Field Noise Suppression
NASA Astrophysics Data System (ADS)
Eltony, Amira; Park, Hyesung; Wang, Shannon; Kong, Jing; Chuang, Isaac
Trapped ions have proven to be effective quantum bits; but increasing electric field noise as traps are miniaturized limits gate fidelity and progress towards a large-scale quantum computer. Removing contamination from surfaces is important for noise suppression; but cleaning techniques like argon ion bombardment are difficult to integrate with current systems and are too harsh for traps incorporating optical devices. We investigate an alternative solution: a protective coating against surface contamination. We fabricate copper traps with a graphene passivation layer and characterize them with single ions. Surprisingly, we find worse noise performance than for an uncoated metal trap.
Trailing edge wake flow characteristics of upper surface blown configurations. [noise generators
NASA Technical Reports Server (NTRS)
Reddy, N. N.
Mean and fluctuating flow characteristics in the wake of upper surface blown flap configurations are presented. Relative importance of the longitudinal and the transverse components of the wake flow turbulence for noise generation are evaluated using correlation between the near-field noise and the wake turbulence. Effects of the jet velocity, the initial turbulence in the jet, and the flap deflection angle on noise and wake flow characteristics are studied. The far-field noise data is compared with the existing empirical prediction method. The measured wake flow properties are compared with an analytical model used in the existing USB wake flow noise theory. The detailed wake flow profiles, wake flow turbulence space-time correlations, wake flow turbulence cross-power spectra, and near-field noise third octave band spectra are presented in the appendices.
Stebbins, A.; Veeraraghavan, S.; Silk, J.; Brandenberger, R.; Turok, N.
Accretion of matter onto wakes left behind by horizon-sized pieces of cosmic string is investigated, and the effects of wakes on the large-scale structure of the universe are determined. Accretion of cold matter onto wakes, the effects of a long string on fluids with finite velocity dispersion or sound speeds, the interactions between loops and wakes, and the conditions for wakes to survive disruption by loops are discussed. It is concluded that the most important wakes are those which were formed at the time of equal matter and radiation density. This leads to sheetlike overdense regions of galaxies with a mean separation in agreement with the scale of the bubbles of de Lapparent, Geller, and Huchra (1986). However, for the value of G(mu) favored from galaxy formation considerations in a universe with cold dark matter, a wake accretes matter from a distance of only about 1.5 Mpc, which is much less than the distance between the wakes. 39 references.
NASA Technical Reports Server (NTRS)
Stebbins, Albert; Veeraraghavan, Shoba; Silk, Joseph; Brandenberger, Robert; Turok, Neil
Accretion of matter onto wakes left behind by horizon-sized pieces of cosmic string is investigated, and the effects of wakes on the large-scale structure of the universe are determined. Accretion of cold matter onto wakes, the effects of a long string on fluids with finite velocity dispersion or sound speeds, the interactions between loops and wakes, and the conditions for wakes to survive disruption by loops are discussed. It is concluded that the most important wakes are those which were formed at the time of equal matter and radiation density. This leads to sheetlike overdense regions of galaxies with a mean separation in agreement with the scale of the bubbles of de Lapparent, Geller, and Huchra (1986). However, for the value of G(mu) favored from galaxy formation considerations in a universe with cold dark matter, a wake accretes matter from a distance of only about 1.5 Mpc, which is much less than the distance between the wakes.
Wind and Wake Sensing with UAV Formation Flight: System Development and Flight Testing
NASA Astrophysics Data System (ADS)
Larrabee, Trenton Jameson
Wind turbulence including atmospheric turbulence and wake turbulence have been widely investigated; however, only recently it become possible to use Unmanned Aerial Vehicles (UAVs) as a validation tool for research in this area. Wind can be a major contributing factor of adverse weather for aircraft. More importantly, it is an even greater risk towards UAVs because of their small size and weight. Being able to estimate wind fields and gusts can potentially provide substantial benefits for both unmanned and manned aviation. Possible applications include gust suppression for improving handling qualities, a better warning system for high wind encounters, and enhanced control for small UAVs during flight. On the other hand, the existence of wind can be advantageous since it can lead to fuel savings and longer duration flights through dynamic soaring or thermal soaring. Wakes are an effect of the lift distribution across an aircraft's wing or tail. Wakes can cause substantial disturbances when multiple aircraft are moving through the same airspace. In fact, the perils from an aircraft flying through the wake of another aircraft is a leading cause of the delay between takeoff times at airports. Similar to wind, though, wakes can be useful for energy harvesting and increasing an aircraft's endurance when flying in formation which can be a great advantage to UAVs because they are often limited in flight time due to small payload capacity. Formation flight can most often be seen in manned aircraft but can be adopted for use with unmanned systems. Autonomous flight is needed for flying in the "sweet spot" of the generated wakes for energy harvesting as well as for thermal soaring during long duration flights. For the research presented here formation flight was implemented for the study of wake sensing and gust alleviation. The major contributions of this research are in the areas of a novel technique to estimate wind using an Unscented Kalman filter and experimental wake sensing data using UAVs in formation flight. This has been achieved and well documented before in manned aircraft but very little work has been done on UAV wake sensing especially during flight testing. This document describes the development and flight testing of small unmanned aerial system (UAS) for wind and wake sensing purpose including a Ground Control Station (GCS) and UAVs. This research can be stated in four major components. Firstly, formation flight was obtained by integrating a formation flight controller on the WVU Phastball Research UAV aircraft platform from the Flight Control Systems Laboratory (FCSL) at West Virginia University (WVU). Second, a new approach to wind estimation using an Unscented Kalman filter (UKF) is discussed along with results from flight data. Third, wake modeling within a simulator and wake sensing during formation flight is shown. Finally, experimental results are used to discuss the "sweet spot" for energy harvesting in formation flight, a novel approach to cooperative wind estimation, and gust suppression control for a follower aircraft in formation flight.
Synergistic Effects of Turbine Wakes and Atmospheric Stability on Power Production at an Onshore Wind Farm
Wharton, S; Lundquist, J K; Marjanovic, N
This report examines the complex interactions between atmospheric stability and turbine-induced wakes on downwind turbine wind speed and power production at a West Coast North American multi-MW wind farm. Wakes are generated when the upwind flow field is distorted by the mechanical movement of the wind turbine blades. This has two consequences for downwind turbines: (1) the downwind turbine encounters wind flows with reduced velocity and (2) the downwind turbine encounters increased turbulence across multiple length scales via mechanical turbulence production by the upwind turbine. This increase in turbulence on top of ambient levels may increase aerodynamic fatigue loads on the blades and reduce the lifetime of turbine component parts. Furthermore, ambient atmospheric conditions, including atmospheric stability, i.e., thermal stratification in the lower boundary layer, play an important role in wake dissipation. Higher levels of ambient turbulence (i.e., a convective or unstable boundary layer) lead to higher turbulent mixing in the wake and a faster recovery in the velocity flow field downwind of a turbine. Lower levels of ambient turbulence, as in a stable boundary layer, will lead to more persistent wakes. The wake of a wind turbine can be divided into two regions: the near wake and far wake, as illustrated in Figure 1. The near wake is formed when the turbine structure alters the shape of the flow field and usually persists one rotor diameter (D) downstream. The difference between the air inside and outside of the near wake results in a shear layer. This shear layer thickens as it moves downstream and forms turbulent eddies of multiple length scales. As the wake travels downstream, it expands depending on the level of ambient turbulence and meanders (i.e., travels in non-uniform path). Schepers estimates that the wake is fully expanded at a distance of 2.25 D and the far wake region begins at 2-5 D downstream. The actual distance traveled before the wake recovers to its inflow velocity is dependent on the amount ambient turbulence, the amount of wind shear, and topographical and structural effects. The maximum velocity deficit is estimated to occur at 1-2 D but can be longer under low levels of ambient turbulence. Our understanding of turbine wakes comes from wind tunnel experiments, field experiments, numerical simulations, and from studies utilizing both experimental and modeling methods. It is well documented that downwind turbines in multi-Megawatt wind farms often produce less power than upwind turbine rows. These wake-induced power losses have been estimated from 5% to up to 40% depending on the turbine operating settings (e.g., thrust coefficient), number of turbine rows, turbine size (e.g., rotor diameter and hub-height), wind farm terrain, and atmospheric flow conditions (e.g., ambient wind speed, turbulence, and atmospheric stability). Early work by Elliott and Cadogan suggested that power data for different turbulent conditions be segregated to distinguish the effects of turbulence on wind farm power production. This may be especially important for downwind turbines within wind farms, as chaotic and turbulent wake flows increase stress on downstream turbines. Impacts of stability on turbine wakes and power production have been examined for a flat terrain, moderate size (43 turbines) wind farm in Minnesota and for an offshore, 80 turbine wind farm off the coast of Denmark. Conzemius found it difficult to distinguish wakes (i.e., downwind velocity deficits) when the atmosphere was convective as large amounts of scatter were present in the turbine nacelle wind speed data. This suggested that high levels of turbulence broke-up the wake via large buoyancy effects, which are generally on the order of 1 km in size. On the other hand, they found pronounced wake effects when the atmosphere was very stable and turbulence was either suppressed or the length scale was reduced as turbulence in this case was mechanically produced (i.e., friction forces). This led to larger reductions at downwind turbines and maximum ve
Unsteady wake measurements behind an airfoil and prediction of dynamic stall from the wake
Hamed Sadeghi; Mahmoud Mani; S. M. Hossein Karimian
Purpose � The primary purpose of this paper is to investigate the characteristics of the unsteady flow field in the wake of Eppler-361 airfoil undergoing harmonic pitch oscillation in both pre-stall and post-stall regimes. Design\\/methodology\\/approach � Experimental measurements were carried out to study the characteristics of the unsteady flow field within the wake of an airfoil. All of the experiments
Secondary energy growth and turbulence suppression in conducting channel flow with streamwise magnetic field
NASA Astrophysics Data System (ADS)
Dong, Shuai; Krasnov, Dmitry; Boeck, Thomas
The effects of a streamwise magnetic field on conducting channel flow are studied by analyzing secondary linear perturbations evolving on streamwise streaks and by direct numerical simulations of relaminarization. By means of an optimal perturbation approach, magnetic damping is found to increase the streamwise wavelength of the most amplified secondary perturbations and to reduce their amplification level. Complete suppression of secondary instability is observed at a critical magnetic interaction parameter that depends on the streak amplitude and on the Reynolds number when the transient evolution of the streaky basic flow is taken into account. Relaminarization in the direct numerical simulation occurs at lower values of the interaction parameter than the critical values from the stability computations for the streak amplitudes considered. The dependence of these threshold values of the interaction parameters on the Reynolds number is fairly similar between simulations and stability analysis. Relaminarization thresholds from the simulations are also in good agreement with experiments on pipe flow with streamwise magnetic field.
On the control and suppression of the Rayleigh-Taylor instability using electric fields
NASA Astrophysics Data System (ADS)
Cimpeanu, Radu; Papageorgiou, Demetrios T.; Petropoulos, Peter G.
It is shown theoretically that an electric field can be used to control and suppress the classical Rayleigh-Taylor instability found in stratified flows when a heavy fluid lies above lighter fluid. Dielectric fluids of arbitrary viscosities and densities are considered and a theory is presented to show that a horizontal electric field (acting in the plane of the undisturbed liquid-liquid surface), causes growth rates and critical stability wavenumbers to be reduced thus shifting the instability to longer wavelengths. This facilitates complete stabilization in a given finite domain above a critical value of the electric field strength. Direct numerical simulations based on the Navier-Stokes equations coupled to the electrostatic fields are carried out and the linear theory is used to critically evaluate the codes before computing into the fully nonlinear stage. Excellent agreement is found between theory and simulations, both in unstable cases that compare growth rates and in stable cases that compare frequencies of oscillation and damping rates. Computations in the fully nonlinear regime supporting finger formation and roll-up show that a weak electric field slows down finger growth and that there exists a critical value of the field strength, for a given system, above which complete stabilization can take place. The effectiveness of the stabilization is lost if the initial amplitude is large enough or if the field is switched on too late. We also present a numerical experiment that utilizes a simple on-off protocol for the electric field to produce sustained time periodic interfacial oscillations. It is suggested that such phenomena can be useful in inducing mixing. A physical centimeter-sized model consisting of stratified water and olive oil layers is shown to be within the realm of the stabilization mechanism for field strengths that are approximately 2 � 104 V/m.
Island Wake Dynamics and Wake Influence on the Evaporation Duct and Radar Propagation.
NASA Astrophysics Data System (ADS)
Burk, S. D.; Haack, T.; Rogers, L. T.; Wagner, L. J.
The conditions under which atmospheric island wakes form leeward of Kauai, Hawaii, are investigated using idealized numerical simulations and real data forecasts from the U.S. Navy's Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS). Nondimensional mountain height is varied in a series of idealized simulations by altering the island's terrain height; with increasing , the wake configuration varies from two small counterrotating vortices to a straight wake to a meandering wake to a von K�rm�n vortex street. In both the idealized and real data forecasts, stability changes across the wake alter the surface layer temperature and moisture profiles, thereby modifying the refractivity and evaporation duct height (EDH) fields. An electromagnetic (EM) propagation model and a radar clutter model are used to demonstrate that the alterations to the refractivity field created by the wake are capable of strongly affecting near-surface EM propagation. Substantial azimuthal variability in radar sea clutter was observed during radar performance tests conducted by the USS O'Kane leeward of Kauai in December of 1999; these anomalies were postulated to result from an island wake. Results from the linkage of COAMPS output with the two EM codes are compared with the radar returns collected aboard the O'Kane, and metrics are developed for comparing COAMPS forecast EDH values with those calculated directly from the shipboard observations.
Cancellation of the ion deflection due to electron-suppression magnetic field in a negative-ion accelerator
Chitarin, G., E-mail: firstname.lastname@example.com [Consorzio RFX, Association EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy); Dept. of Management and Engineering, University of Padova, Strad. S. Nicola 3, 36100 Vicenza (Italy); Agostinetti, P.; Aprile, D.; Marconato, N.; Veltri, P. [Consorzio RFX, Association EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy)] [Consorzio RFX, Association EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy)
A new magnetic configuration is proposed for the suppression of co-extracted electrons in a negative-ion accelerator. This configuration is produced by an arrangement of permanent magnets embedded in one accelerator grid and creates an asymmetric local magnetic field on the upstream and downstream sides of this grid. Thanks to the �concentration� of the magnetic field on the upstream side of the grid, the resulting deflection of the ions due to magnetic field can be �intrinsically� cancelled by calibrating the configuration of permanent magnets. At the same time, the suppression of co-extracted electrons can be improved.
NASA Technical Reports Server (NTRS)
A status report is presented on research directed at reducing the vortex disturbances of aircraft wakes. The objective of such a reduction is to minimize the hazard to smaller aircraft that might encounter these wakes. Inviscid modeling was used to study trailing vortices and viscous effects were investigated. Laser velocimeters were utilized in the measurement of aircraft wakes. Flight and wind tunnel tests were performed on scale and full model scale aircraft of various design. Parameters investigated included the effect of wing span, wing flaps, spoilers, splines and engine thrust on vortex attenuation. Results indicate that vortives may be alleviated through aerodynamic means.
An electronic device for artefact suppression in human local field potential recordings during deep brain stimulation
NASA Astrophysics Data System (ADS)
Rossi, L.; Foffani, G.; Marceglia, S.; Bracchi, F.; Barbieri, S.; Priori, A.
The clinical efficacy of high-frequency deep brain stimulation (DBS) for Parkinson's disease and other neuropsychiatric disorders likely depends on the modulation of neuronal rhythms in the target nuclei. This modulation could be effectively measured with local field potential (LFP) recordings during DBS. However, a technical drawback that prevents LFPs from being recorded from the DBS target nuclei during stimulation is the stimulus artefact. To solve this problem, we designed and developed 'FilterDBS', an electronic amplification system for artefact-free LFP recordings (in the frequency range 2-40 Hz) during DBS. After defining the estimated system requirements for LFP amplification and DBS artefact suppression, we tested the FilterDBS system by conducting experiments in vitro and in vivo in patients with advanced Parkinson's disease undergoing DBS of the subthalamic nucleus (STN). Under both experimental conditions, in vitro and in vivo, the FilterDBS system completely suppressed the DBS artefact without inducing significant spectral distortion. The FilterDBS device pioneers the development of an adaptive DBS system retroacted by LFPs and can be used in novel closed-loop brain-machine interface applications in patients with neurological disorders.
Development and testing of laser Doppler system components for wake vortex monitoring. Volume 1: Scanner development, laboratory and field testing and system modeling
NASA Technical Reports Server (NTRS)
Wilson, D. J.; Krause, M. C.; Coffey, E. W.; Huang, C. C.; Edwards, B. B.; Shrider, K. R.; Jetton, J. L.; Morrison, L. K.
A servo-controlled range/elevation scanner for the laser Doppler velocimeter (LDV) was developed and tested in the field to assess its performance in detecting and monitoring aircraft trailing vortices in an airport environment. The elevation scanner provides a capability to manually point the LDV telescope at operator chosen angles from 3.2 deg. to 89.6 deg within 0.2 deg, or to automatically scan the units between operator chosen limits at operator chosen rates of 0.1 Hz to 0.5 Hz. The range scanner provides a capability to manually adjust the focal point of the system from a range of 32 meters to a range of 896 meters under operator control, or to scan between operator chosen limits and at rates from 0.1 Hz to 6.9 Hz. The scanner controls are designed to allow simulataneous range and elevation scanning so as to provide finger scan patterns, arc scan patterns, and vertical line scan patterns. The development and testing of the unit is discussed, along with a fluid dynamic model of the wake vortex developed in a laser Doppler vortex sensor simulation program.
Crosswind Shear Gradient Affect on Wake Vortices
NASA Technical Reports Server (NTRS)
Proctor, Fred H.; Ahmad, Nashat N.
Parametric simulations with a Large Eddy Simulation (LES) model are used to explore the influence of crosswind shear on aircraft wake vortices. Previous studies based on field measurements, laboratory experiments, as well as LES, have shown that the vertical gradient of crosswind shear, i.e. the second vertical derivative of the environmental crosswind, can influence wake vortex transport. The presence of nonlinear vertical shear of the crosswind velocity can reduce the descent rate, causing a wake vortex pair to tilt and change in its lateral separation. The LES parametric studies confirm that the vertical gradient of crosswind shear does influence vortex trajectories. The parametric results also show that vortex decay from the effects of shear are complex since the crosswind shear, along with the vertical gradient of crosswind shear, can affect whether the lateral separation between wake vortices is increased or decreased. If the separation is decreased, the vortex linking time is decreased, and a more rapid decay of wake vortex circulation occurs. If the separation is increased, the time to link is increased, and at least one of the vortices of the vortex pair may have a longer life time than in the case without shear. In some cases, the wake vortices may never link.
Turbulent Plane Wakes Subjected to Successive Strains
NASA Technical Reports Server (NTRS)
Rogers, Michael M.
Six direct numerical simulations of turbulent time-evolving strained plane wakes have been examined to investigate the response of a wake to successive irrotational plane strains of opposite sign. The orientation of the applied strain field has been selected so that the flow is the time-developing analogue of a spatially developing wake evolving in the presence of either a favourable or an adverse streamwise pressure gradient. The magnitude of the applied strain rate a is constant in time t until the total strain e(sup at) reaches about four. At this point, a new simulation is begun with the sign of the applied strain being reversed (the original simulation is continued as well). When the total strain is reduced back to its original value of one, yet another simulation is begun with the sign of the strain being reversed again back to its original sign. This process is done for both initially "favourable" and initially "adverse" strains, providing simulations for each of these strain types from three different initial conditions. The evolution of the wake mean velocity deficit and width is found to be very similar for all the adversely strained cases, with both measures rapidly achieving exponential growth at the rate associated with the cross-stream expansive strain e(sup at). In the "favourably" strained cases, the wake widths approach a constant and the velocity deficits ultimately decay rapidly as e(sup -2at). Although all three of these cases do exhibit the same asymptotic exponential behaviour, the time required to achieve this is longer for the cases that have been previously adversely strained (by at approx. equals 1). These simulations confirm the generality of the conclusions drawn in Rogers (2002) regarding the response of plane wakes to strain. The evolution of strained wakes is not consistent with the predictions of classical self-similar analysis; a more general equilibrium similarity solution is required to describe the results. At least for the cases considered here, the wake Reynolds number and the ratio of the turbulent kinetic energy to the square of the wake mean velocity deficit are determined nearly entirely by the total strain. For these measures the order in which the strains are applied does not matter and the changes brought about by the strain are nearly reversible. The wake mean velocity deficit and width, on the other hand, differ by about a factor of three when the total strain returns to one, depending on whether the wake was first "favourably" or "adversely" strained. The strain history is important for predicting the evolution of these quantities.
Organization of suppression in receptive fields of neurons in cat visual cortex
G. C. Deangelis; J. G. Robson; I. Ohzawa; R. D. Freeman
1. The response to an optimally oriented stimulus of both simple and complex cells in the cat's striate visual cortex (area 17) can be suppressed by the superposition of an orthogonally oriented drifting grating. This effect is referred to as cross-orientation suppression. We have examined the spatial organization and tuning characteristics of this suppressive effect with the use of extracellular
Acceleration of nonmonoenergetic electron bunches injected into a wake wave
Kuznetsov, S. V., E-mail: firstname.lastname@example.com [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)
The trapping and acceleration of nonmonoenergetic electron bunches in a wake field wave excited by a laser pulse in a plasma channel is studied. Electrons are injected into the region of the wake wave potential maximum at a velocity lower than the phase velocity of the wave. The paper analyzes the grouping of bunch electrons in the energy space emerging in the course of acceleration under certain conditions of their injection into the wake wave and minimizing the energy spread for such electrons. The factors determining the minimal energy spread between bunch electrons are analyzed. The possibility of monoenergetic acceleration of electron bunches generated by modern injectors in a wake wave is analyzed.
Morley, R; Morley, C J; Lucas, P J; Lucas, A
Among 320 low birthweight infants seen at nine months post term those using a soft object, thumb, or fingers as comforter were significantly less likely to wake at night (9/96, 9%) than those with no comforter or using a dummy (66/224, 29%). Dummy users were as likely to wake (27/93, 29%) as those without a comforter (39/131, 30%). PMID:2604424
Study on the effects of ion motion on laser-induced plasma wakes
Zhou Suyun [Institute of Modern Optical Technologies, Key Lab of Advanced Optical Manufacturing Technologies of Jiangsu Province and Key Lab of Modern Optical Technologies of Education Ministry of China, Soochow University, Suzhou 215006 (China); School of Materials Sciences and Engineering, Jiangxi Science and Technology Normal University, Nanchang 330013 (China); Yu Wei [Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai 201800 (China); Yuan Xiao [Institute of Modern Optical Technologies, Key Lab of Advanced Optical Manufacturing Technologies of Jiangsu Province and Key Lab of Modern Optical Technologies of Education Ministry of China, Soochow University, Suzhou 215006 (China); Xu Han [National Laboratory for Parallel and Distributed Processing, School of Computer Science, National University of Defense Technology, Changsha 410073 (China); Cao, L. H.; Cai, H. B.; Zhou, C. T. [Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China)
A 2D analytical model is presented for the generation of plasma wakes (or bubbles) with an ultra-intense laser pulse by taking into account the response of plasma ions. It is shown that the effect of ion motion becomes significant at the laser intensity exceeding 10{sup 21} W/cm{sup 2} and plasma background density below 10{sup 19} cm{sup -3}. In this regime, ion motion tends to suppress the electrostatic field induced by charge separation and makes the electron acceleration less effective. As a result, the assumption of immobile ions overestimates the efficiency of laser wake-field acceleration of electrons. Based on the analytical model, the dynamics of plasma ions in laser-induced wake field is investigated. It is found that only one bubble appears as the plasmas background density exceeds the resonant density and the deposited laser energy is concentrated into the bubble, resulting in the generation of an ion bunch with extremely high energy density.
Engineering models for merging wakes in wind farm optimization applications
NASA Astrophysics Data System (ADS)
Machefaux, E.; Larsen, G. C.; Murcia Leon, J. P.
The present paper deals with validation of 4 different engineering wake superposition approaches against detailed CFD simulations and covering different turbine interspacing, ambient turbulence intensities and mean wind speeds. The first engineering model is a simple linear superposition of wake deficits as applied in e.g. Fuga. The second approach is the square root of sums of squares approach, which is applied in the widely used PARK program. The third approach, which is presently used with the Dynamic Wake Meandering (DWM) model, assumes that the wake affected downstream flow field to be determined by a superposition of the ambient flow field and the dominating wake among contributions from all upstream turbines at any spatial position and at any time. The last approach developed by G.C. Larsen is a newly developed model based on a parabolic type of approach, which combines wake deficits successively. The study indicates that wake interaction depends strongly on the relative wake deficit magnitude, i.e. the deficit magnitude normalized with respect to the ambient mean wind speed, and that the dominant wake assumption within the DWM framework is the most accurate.
Suppression of a charge-density-wave ground state in high magnetic fields: Spin and orbital mechanisms
D. Graf; J. S. Brooks; E. S. Choi; S. Uji; J. C. Dias; M. Almeida; M. Matos
The charge density wave (CDW) transition temperature in the quasi-one-dimensional (Q1D) organic material (Per)2Au(mnt)2 is relatively low (TCDW�12 K). Hence in a mean field BCS model, the CDW state should be completely suppressed in magnetic fields of order 30 40 T. To explore this possibility, the magnetoresistance of (Per)2Au(mnt)2 was investigated in magnetic fields to 45 T for 0.5 K
Evaluation of a Wake Vortex Upset Model Based on Simultaneous Measurements of Wake Velocities and Probe-Aircraft Accelerations
NASA Technical Reports Server (NTRS)
Short, B. J.; Jacobsen, R. A.
Simultaneous measurements were made of the upset responses experienced and the wake velocities encountered by an instrumented Learjet probe aircraft behind a Boeing 747 vortex-generating aircraft. The vortex-induced angular accelerations experienced could be predicted within 30% by a mathematical upset response model when the characteristics of the wake were well represented by the vortex model. The vortex model used in the present study adequately represented the wake flow field when the vortices dissipated symmetrically and only one vortex pair existed in the wake.
The effect of wake passing on turbine blade film cooling
James David Heidmann
The effect of upstream blade row wake passing on the showerhead film cooling performance of a downstream turbine blade has been investigated through a combination of experimental and computational studies. The experiments were performed in a steady-flow annular turbine cascade facility equipped with an upstream rotating row of cylindrical rods to produce a periodic wake field similar to that found
Low-mass Planets in Protoplanetary Disks with Net Vertical Magnetic Fields: The Planetary Wake and Gap Opening
NASA Astrophysics Data System (ADS)
Zhu, Zhaohuan; Stone, James M.; Rafikov, Roman R.
Some regions in protoplanetary disks are turbulent, while some regions are quiescent (e.g. the dead zone). In order to study how planets open gaps in both inviscid hydrodynamic disk (e.g. the dead zone) and the disk subject to magnetorotational instability (MRI), we carried out both shearing box two-dimensional inviscid hydrodynamical simulations and three-dimensional unstratified magnetohydrodynamical (MHD) simulations (having net vertical magnetic fields) with a planet at the box center. We found that, due to the nonlinear wave steepening, even a low mass planet can open gaps in both cases, in contradiction to the "thermal criterion" for gap opening. In order to understand if we can represent the MRI turbulent stress with the viscous ? prescription for studying gap opening, we compare gap properties in MRI-turbulent disks to those in viscous HD disks having the same stress, and found that the same mass planet opens a significantly deeper and wider gap in net vertical flux MHD disks than in viscous HD disks. This difference arises due to the efficient magnetic field transport into the gap region in MRI disks, leading to a larger effective ? within the gap. Thus, across the gap, the Maxwell stress profile is smoother than the gap density profile, and a deeper gap is needed for the Maxwell stress gradient to balance the planetary torque density. Comparison with previous results from net toroidal flux/zero flux MHD simulations indicates that the magnetic field geometry plays an important role in the gap opening process. We also found that long-lived density features (termed zonal flows) produced by the MRI can affect planet migration. Overall, our results suggest that gaps can be commonly produced by low mass planets in realistic protoplanetary disks, and caution the use of a constant ?-viscosity to model gaps in protoplanetary disks.
Near wake features of a flying European Starling
NASA Astrophysics Data System (ADS)
Kirchhefer, Adam; Kopp, Gregory; Gurka, Roi
A great deal of research focusing on flapping wings has been motivated by their high performance capabilities, especially in low Reynolds number configurations where static wing performance typically suffers. The approaches to studying flapping wings have taken different forms. One form has been the systematic investigation of the parameters that influence the relationship between flapping wings and their wake. The other form, and the approach used in the present work, is the investigation of flapping wings in nature. While the earliest work on the flapping wings of animals consists of observations of bird flight by Leonardo DaVinci, advances in technology have allowed for quantitative measurements of the wake. The near wake of a freely flying European starling has been measured using high speed, time-resolved, particle image velocimetry, simultaneously with high speed cameras which imaged the bird. These have been used to measure the near wake two-dimensional velocity field that can be associated with the bird's location and wing configuration in an avian wind tunnel. Time series of the velocities have been expressed as composite wake plots, which depict segments of the wing beat cycle for various spanwise locations in the wake. Measurements indicate that downwash is not produced during the upstroke, suggesting that the upstroke does not generate lift. As well, the wake velocities imply the presence of streamwise vortical structures, in addition to tip vortices. These two characteristics indicate similarities between the wake of a bird and the wake of a bat.
Effects of broad-spectrum monoamine oxidase inhibitors on the structure and ratio of stages in in the cat sleep-wake cycle
G. R. Akhvlediani; T. N. Oniani; M. G. Gvasaliya
Monoamine oxidase (MAO) inhibitors disturb the structure of the sleep-wake cycle and its ultradian rhythms by extending total slow-wave sleep, completely suppressing paradoxical sleep, and reducing total waking period considerably. Once the synchrony induced by MAO inhibitors has stopped, a rebound effect of increased waking occurs preceding and during partial restoral of paradoxical sleep. This fact is viewed as an
Harmonics suppression of vacuum chamber eddy current induced fields with application to SSC Low Energy Booster Magnets
Schlueter, R.D.; Halbach, K.
An expression for eddy currents induced in a thin-walled conductor due to a time-dependent electromagnet field excitation is formulated, allowing subsequent analytical development of a closed form expression predicting vacuum chamber eddy current induced field harmonics in iron-core multipole electromagnets. A passive technique for harmonics suppression is presented with specific application to the design of the Superconducting Super Collider (SSC) Low Energy Booster (LEB) Magnets.
PETRA III; K. Balewski; R. Wanzenberg; E. Gjonaj; T. Weiland
At DESY it is planned to convert the PETRA ring into a synchrotron radiation facility, called PETRA III. The wake fields of a tapered transition from the standard vacuum chamber to the small gap chamber of the insertion devices contribute significantly to the impedance budget of PETRA III. The computer codes MAFIA and PBCI have been used to determine the
Norman F. Ness
The possible detection of the lee wake of the magnetohydrodynamie interaction of the solar wind with the moon as observed by the Imp 1 satellite is discussed. The inter- planetary magnetic field was found to fluctuate very rapidly and reach anomalously large values when the satellite was approximately eclipsed by the moon in December 1963. Later data on the interplanetary
Characterization of an Actively Controlled Three-Dimensional Turret Wake
NASA Astrophysics Data System (ADS)
Shea, Patrick; Glauser, Mark
Three-dimensional turrets are commonly used for housing optical systems on airborne platforms. As bluff bodies, these geometries generate highly turbulent wakes that decrease the performance of the optical systems and the aircraft. The current experimental study looked to use dynamic suction in both open and closed-loop control configurations to actively control the turret wake. The flow field was characterized using dynamic pressure and stereoscopic PIV measurements in the wake of the turret. Results showed that the suction system was able to manipulate the wake region of the turret and could alter not only the spatial structure of the wake, but also the temporal behavior of the wake flow field. Closed-loop, feedback control techniques were used to determine a more optimal control input for the flow control. Similar control effects were seen for both the steady open-loop control case and the closed-loop feedback control configuration with a 45% reduction in the suction levels when comparing the closed-loop to the open-loop case. These results provide unique information regarding the development of the baseline three-dimensional wake and the wake with three different active flow control configurations.
Wake Vortex Advisory System (WakeVAS) Concept of Operations
NASA Technical Reports Server (NTRS)
Rutishauser, David; Lohr, Gary; Hamilton, David; Powers, Robert; McKissick, Burnell; Adams, Catherine; Norris, Edward
NASA Langley Research Center has a long history of aircraft wake vortex research, with the most recent accomplishment of demonstrating the Aircraft VOrtex Spacing System (AVOSS) at Dallas/Forth Worth International Airport in July 2000. The AVOSS was a concept for an integration of technologies applied to providing dynamic wake-safe reduced spacing for single runway arrivals, as compared to current separation standards applied during instrument approaches. AVOSS included state-of-the-art weather sensors, wake sensors, and a wake behavior prediction algorithm. Using real-time data AVOSS averaged a 6% potential throughput increase over current standards. This report describes a Concept of Operations for applying the technologies demonstrated in the AVOSS to a variety of terminal operations to mitigate wake vortex capacity constraints. A discussion of the technological issues and open research questions that must be addressed to design a Wake Vortex Advisory System (WakeVAS) is included.
ERIC Educational Resources Information Center
Vrdlovcova, Jill
All homes and schools produce waste. Children may have been astonished at how much people throw away, and this could be the "wake-up call" that arouses their interest. At Carymoor Environmental Centre (an Eco-Centre in South Somerset) getting children involved in active waste reduction and recycling is a priority. Carymoor tries to model waste�
Electromagnetic signature of human cortical dynamics during wakefulness and sleep
Destexhe, Alain
Electromagnetic signature of human cortical dynamics during wakefulness and sleep Signature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.5 Spatial reach of LFP & Electromagnetic Lead field . . . . . . . . . . . . . . . 35 2 Studies 45 4 Overview 47 4.1 Electromagnetic properties of the extracellular medium
Particle Access and Charging Environments in the Lunar Wake
NASA Technical Reports Server (NTRS)
Parker, Linda; Minow, Joseph; Singh, Nagendra; Araveti, Venkata S.; Venkiteswaran, Karthik
A plasma wake a region of low density, high temperature plasma forms on the far side of the Moon when solar wind, magnetosheath, and magnetotail plasma flows past the Moon [Manka, 1973; Ogilvie et al., 1996; Farrell et al., 1998; Halekas et al., 2005]. Ion populations in these flows typically have much smaller thermal velocity than bulk speed and are therefore excluded from the plasma wake while the large thermal electron velocity allows the lighter negatively charged particles to stream ahead of the ions into the wake. Charge separation due to electrons streaming ahead of the ions into the wake from the wake boundary establishes an ambipolar electric field which impedes the motion of electron flow and accelerates ions into the wake [Ogilvie et al., 1996; Farrell et al., 1997]. We have conducted a theoretical study of acceleration (and deceleration) of charged particles in lunar plasma environments, which investigated the mechanisms responsible for allowing solar wind entry into the lunar wake, and for producing energetic particle distributions observed within the lunar wake. To this end, the investigation utilized a macroscale 3D hybrid particle-in-cell numerical model of the interaction of the Moon with external plasma environments to compute electric fields in the lunar environment for a variety of external plasma conditions and interplanetary magnetic field orientations. Ion dynamics were attained from the hybrid code while electron dynamics were determined by considering electron test particle trajectories through the fields established in the hybrid code. Results from the code will be presented to evaluate charging environments within the lunar wake.
Suppression of thermopower of NaxCoO2 by an external magnetic field
Xiang, H. J. [North Carolina State University; Singh, David J [ORNL
We calculate the thermopower in Na{sub x}CoO{sub 2} using the standard Boltzmann transport theory and first principles electronic structures with spin polarization taken into account. The thermopower is found to be smaller when the system is polarized, which thereby provides an alternative reasonable explanation for the suppression of thermopower in a magnetic field. The role of the spin-orbit coupling on the thermoelectricity is also discussed.
First Lunar Wake Passage of ARTEMIS: Discrimination of Wake Effects and Solar Wind Fluctuations by 3D Hybrid Simulations
NASA Technical Reports Server (NTRS)
Wiehle, S.; Plaschke, F.; Motschmann, U.; Glassmeier, K. H.; Auster, H. U.; Angelopoulos, V.; Mueller, J.; Kriegel, H.; Georgescu, E.; Halekas, J.; Sibeck, D. G.; McFadden, J. P.
The spacecraft P1 of the new ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) mission passed the lunar wake for the first time on February 13, 2010. We present magnetic field and plasma data of this event and results of 3D hybrid simulations. As the solar wind magnetic field was highly dynamic during the passage, a simulation with stationary solar wind input cannot distinguish whether distortions were caused by these solar wind variations or by the lunar wake; therefore, a dynamic real-time simulation of the flyby has been performed. The input values of this simulation are taken from NASA OMNI data and adapted to the P1 data, resulting in a good agreement between simulation and measurements. Combined with the stationary simulation showing non-transient lunar wake structures, a separation of solar wind and wake effects is achieved. An anisotropy in the magnitude of the plasma bulk flow velocity caused by a non-vanishing magnetic field component parallel to the solar wind flow and perturbations created by counterstreaming ions in the lunar wake are observed in data and simulations. The simulations help to interpret the data granting us the opportunity to examine the entire lunar plasma environment and, thus, extending the possibilities of measurements alone: A comparison of a simulation cross section to theoretical predictions of MHD wave propagation shows that all three basic MHD modes are present in the lunar wake and that their expansion governs the lunar wake refilling process.
NSDL National Science Digital Library
Wake-Up_Brain - Fire up those synapses each Monday morning. It's Monday morning and caffeine is slowly percolating into your system but your brain is still covered with weekend sludge. You need something to get those synapses firing, a brain booster to stimulate those billions of gray matter cells. You need Good Morning Thinkers! ... an absolutely free brain wake-up service offered to you by the Innovative Thinking Network, a professional membership association of leaders forging the revitalization of organizations through the powerful use of Innovation, Creativity and Group Thinking Skills. Every Monday morning subscribers receive a short, light-hearted message designed to help wipe away the fog and open the door to more powerful, creative thinking.
Aircraft wake turbulence avoidance
NASA Technical Reports Server (NTRS)
Mcgowan, W. A.
Analytical studies and flight tests are used to describe the formation and severity of trailing vortices and the spatial extent of their influence. This information is then used to outline procedures for ready application by pilots, tower operators, and others concerned with the flow of traffic. The procedures provide the necessary appreciation of the physical attributes of trailing vortices, the potential hazards involved when encountering them, and how best to avoid the dangerous portions of the wake during flight operations.
Interplay between Kondo suppression and Lifshitz transitions in YbRh2Si2 at high magnetic fields.
Pfau, H; Daou, R; Lausberg, S; Naren, H R; Brando, M; Friedemann, S; Wirth, S; Westerkamp, T; Stockert, U; Gegenwart, P; Krellner, C; Geibel, C; Zwicknagl, G; Steglich, F
We investigate the magnetic field dependent thermopower, thermal conductivity, resistivity, and Hall effect in the heavy fermion metal YbRh2Si2. In contrast to reports on thermodynamic measurements, we find in total three transitions at high fields, rather than a single one at 10 T. Using the Mott formula together with renormalized band calculations, we identify Lifshitz transitions as their origin. The predictions of the calculations show that all experimental results rely on an interplay of a smooth suppression of the Kondo effect and the spin splitting of the flat hybridized bands. PMID:23829750
Evidence of Magnetic Breakdown on the Defects With Thermally Suppressed Critical Field in High Gradient SRF Cavities
Eremeev, Grigory [JLAB; Palczewski, Ari [JLAB
At SRF 2011 we presented the study of quenches in high gradient SRF cavities with dual mode excitation technique. The data differed from measurements done in 80's that indicated thermal breakdown nature of quenches in SRF cavities. In this contribution we present analysis of the data that indicates that our recent data for high gradient quenches is consistent with the magnetic breakdown on the defects with thermally suppressed critical field. From the parametric fits derived within the model we estimate the critical breakdown fields.
Wake Characterization of a Cross-Flow Turbine
NASA Astrophysics Data System (ADS)
Haegele, Chase
A cross-flow turbine wake is analyzed to better understand how these turbines affect the flow field in their immediate vicinity. Mean velocity, turbulence intensity, coherent turbulent kinetic energy, and Reynolds shear stresses are used to identify regions of turbulence and mixing. The shear layer between the turbine wake and bypass flow resembles a rectangular ring near the turbine which grows into a larger oval downstream. Mixing allows the wake to recover to roughly 70% of the free stream velocity at five diameters downstream. The results of this study gives future researchers a map to locate areas of interest for more in depth research.
Molecular wake shield gas analyzer
NASA Technical Reports Server (NTRS)
Hoffman, J. H.
Techniques for measuring and characterizing the ultrahigh vacuum in the wake of an orbiting spacecraft are studied. A high sensitivity mass spectrometer that contains a double mass analyzer consisting of an open source miniature magnetic sector field neutral gas analyzer and an identical ion analyzer is proposed. These are configured to detect and identify gas and ion species of hydrogen, helium, nitrogen, oxygen, nitric oxide, and carbon dioxide and any other gas or ion species in the 1 to 46 amu mass range. This range covers the normal atmospheric constituents. The sensitivity of the instrument is sufficient to measure ambient gases and ion with a particle density of the order of one per cc. A chemical pump, or getter, is mounted near the entrance aperture of the neutral gas analyzer which integrates the absorption of ambient gases for a selectable period of time for subsequent release and analysis. The sensitivity is realizable for all but rare gases using this technique.
Role of septal and entorhinal inputs in the generation of hippocampal electrical activity in the cat sleep-wake cycle
N. G. Nachkebiya; A. Ya. Nachkebiya; L. T. Oniani
The effects of septal lesion and entorhinal cortex section on hippocampal electrical activity during the cat sleep-wake cycle were investigated in chronic experiments. The medial portion of the septum only was found to participate in generation of this activity. Complete suppression of hippocampal theta rhythm during active wakefulness and paradoxical sleep were the main effects of septal lesion. In slow-wave
massive plasma refilling the lunar wake by Eath's bow shock
NASA Astrophysics Data System (ADS)
Xu, Xiaojun; Wong, Hon-Cheng; Ma, Yonghui
By using measurements from the "Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun" (ARTEMIS) spacecraft, we report the first observations of massive plasma refilling the near lunar wake (< 1 lunar radius from the surface), which is associated with a quasi-perpendicular bow shock (BS) of the Earth at the dusk side. As expected, the shock was greatly broadened into a magnetic ramp in the lunar wake. However, a small magnetic bifurcation in the shock ramp has been amplified remarkably in the lunar wake. Meanwhile, the local wake density increased so intensively that it surprisingly reached up to the value comparable to that in the solar wind. The density enhancement in the lunar wake is well associated with the magnetic ramp. Pitch angle distributions show that the refilling electrons are perpendicular to and the ions are quasi-parallel to the magnetic field. They are unlikely to enter the lunar wake via any known ways, i.e., drift or gyration. Analysis shows that they are most probably injected by the drift motion due to the magnetic strength gradient within the ramp of the BS outside the lunar wake.
Wake Vortex Research in the USA (WakeNet-USA)
NASA Technical Reports Server (NTRS)
Lang, Steve; Bryant, Wayne
This viewgraph presentation reviews the cooperative work that FAA and NASA are engaged in to safely increase the capacity of the National Airspace System by studying the wake vortex operations. Wake vortex avoidance is a limiting factor in defining separation standards in the airport terminal area and could become a reducing separation standards in en route airspace.
NASA Technical Reports Server (NTRS)
A 10% scale B-737-100 model was tested in the vicinity of a vortex wake generated by a wing mounted on a support in the forward section of the NASA-Langley 30 x 60 ft. Wind Tunnel. The wing span, angle of attack, and generating wing location were varied to provide vortex strengths consistent with a large variety of combinations of leader-follower aircraft pairs during vortex encounters. The test, conducted as part of the AST Terminal Area Productivity Program, will provide data for validation of aerodynamic models which will be used for developing safe separate standards to apply to aircraft in terminal areas while increasing airport capacity.
NSDL National Science Digital Library
Lisa Marie Rubin
The main character of this case is Denise, who we first meet in the early morning hours as she wakes up in a cold sweat, gasping for breath. But it is her husband, Jeremy, who has been diagnosed with heart disease, not her. What�s going on? In this interrupted case study, in which the other main character is Denise�s heart (who we get to know through a series of �interior� monologues), students learn about the risk factors, symptoms, and consequences of a heart attack. The case is suitable for a course in pathophysiology, first year nursing, enzymology, advanced biology or anatomy, or nutrition.
Chitin Amendment Increases Soil Suppressiveness toward Plant Pathogens and Modulates the Actinobacterial and Oxalobacteraceal Communities in an Experimental Agricultural Field
Cretoiu, Mariana Silvia; Korthals, Gerard W.; Visser, Johnny H. M.
A long-term experiment on the effect of chitin addition to soil on the suppression of soilborne pathogens was set up and monitored for 8 years in an experimental field, Vredepeel, The Netherlands. Chitinous matter obtained from shrimps was added to soil top layers on two different occasions, and the suppressiveness of soil toward Verticillium dahliae, as well as plant-pathogenic nematodes, was assessed, in addition to analyses of the abundances and community structures of members of the soil microbiota. The data revealed that chitin amendment had raised the suppressiveness of soil, in particular toward Verticillium dahliae, 9 months after the (second) treatment, extending to 2 years following treatment. Moreover, major effects of the added chitin on the soil microbial communities were detected. First, shifts in both the abundances and structures of the chitin-treated soil microbial communities, both of total soil bacteria and fungi, were found. In addition, the abundances and structures of soil actinobacteria and the Oxalobacteraceae were affected by chitin. At the functional gene level, the abundance of specific (family-18 glycoside hydrolase) chitinase genes carried by the soil bacteria also revealed upshifts as a result of the added chitin. The effects of chitin noted for the Oxalobacteraceae were specifically related to significant upshifts in the abundances of the species Duganella violaceinigra and Massilia plicata. These effects of chitin persisted over the time of the experiment. PMID:23811512
Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey
WAKE ISLAND AIRFIELD TERMINAL, BUILDING 1502 LOOKING SOUTHEAST AT NORTHWEST FA�ADE AND BLAST WALL, DATE UNKNOWN - Wake Island Airfield, Terminal Building, West Side of Wake Avenue, Wake Island, Wake Island, UM
Suppression of a Field Population of Aedes aegypti in Brazil by Sustained Release of Transgenic Male Mosquitoes
Garziera, Luiza; Lacroix, Renaud; Donnelly, Christl A.; Alphey, Luke; Malavasi, Aldo; Capurro, Margareth L.
The increasing burden of dengue, and the relative failure of traditional vector control programs highlight the need to develop new control methods. SIT using self-limiting genetic technology is one such promising method. A self-limiting strain of Aedes aegypti, OX513A, has already reached the stage of field evaluation. Sustained releases of OX513A Ae. aegypti males led to 80% suppression of a target wild Ae. aegypti population in the Cayman Islands in 2010. Here we describe sustained series of field releases of OX513A Ae. aegypti males in a suburb of Juazeiro, Bahia, Brazil. This study spanned over a year and reduced the local Ae. aegypti population by 95% (95% CI: 92.2%-97.5%) based on adult trap data and 81% (95% CI: 74.9-85.2%) based on ovitrap indices compared to the adjacent no-release control area. The mating competitiveness of the released males (0.031; 95% CI: 0.025-0.036) was similar to that estimated in the Cayman trials (0.059; 95% CI: 0.011 � 0.210), indicating that environmental and target-strain differences had little impact on the mating success of the OX513A males. We conclude that sustained release of OX513A males may be an effective and widely useful method for suppression of the key dengue vector Ae. aegypti. The observed level of suppression would likely be sufficient to prevent dengue epidemics in the locality tested and other areas with similar or lower transmission. PMID:26135160
Binocular Neurons in Parastriate Cortex: Interocular �Matching� of Receptive Field Properties, Eye Dominance and Strength of Silent Suppression
Wang, Chun; Dreher, Bogdan
Spike-responses of single binocular neurons were recorded from a distinct part of primary visual cortex, the parastriate cortex (cytoarchitectonic area 18) of anaesthetized and immobilized domestic cats. Functional identification of neurons was based on the ratios of phase-variant (F1) component to the mean firing rate (F0) of their spike-responses to optimized (orientation, direction, spatial and temporal frequencies and size) sine-wave-luminance-modulated drifting grating patches presented separately via each eye. In over 95% of neurons, the interocular differences in the phase-sensitivities (differences in F1/F0 spike-response ratios) were small (?0.3) and in over 80% of neurons, the interocular differences in preferred orientations were ?10�. The interocular correlations of the direction selectivity indices and optimal spatial frequencies, like those of the phase sensitivies and optimal orientations, were also strong (coefficients of correlation r ?0.7005). By contrast, the interocular correlations of the optimal temporal frequencies, the diameters of summation areas of the excitatory responses and suppression indices were weak (coefficients of correlation r ?0.4585). In cells with high eye dominance indices (HEDI cells), the mean magnitudes of suppressions evoked by stimulation of silent, extra-classical receptive fields via the non-dominant eyes, were significantly greater than those when the stimuli were presented via the dominant eyes. We argue that the well documented �eye-origin specific� segregation of the lateral geniculate inputs underpinning distinct eye dominance columns in primary visual cortices of mammals with frontally positioned eyes (distinct eye dominance columns), combined with significant interocular differences in the strength of silent suppressive fields, putatively contribute to binocular stereoscopic vision. PMID:24927276
Suppression of a Field Population of Aedes aegypti in Brazil by Sustained Release of Transgenic Male Mosquitoes.
Carvalho, Danilo O; McKemey, Andrew R; Garziera, Luiza; Lacroix, Renaud; Donnelly, Christl A; Alphey, Luke; Malavasi, Aldo; Capurro, Margareth L
The increasing burden of dengue, and the relative failure of traditional vector control programs highlight the need to develop new control methods. SIT using self-limiting genetic technology is one such promising method. A self-limiting strain of Aedes aegypti, OX513A, has already reached the stage of field evaluation. Sustained releases of OX513A Ae. aegypti males led to 80% suppression of a target wild Ae. aegypti population in the Cayman Islands in 2010. Here we describe sustained series of field releases of OX513A Ae. aegypti males in a suburb of Juazeiro, Bahia, Brazil. This study spanned over a year and reduced the local Ae. aegypti population by 95% (95% CI: 92.2%-97.5%) based on adult trap data and 81% (95% CI: 74.9-85.2%) based on ovitrap indices compared to the adjacent no-release control area. The mating competitiveness of the released males (0.031; 95% CI: 0.025-0.036) was similar to that estimated in the Cayman trials (0.059; 95% CI: 0.011 - 0.210), indicating that environmental and target-strain differences had little impact on the mating success of the OX513A males. We conclude that sustained release of OX513A males may be an effective and widely useful method for suppression of the key dengue vector Ae. aegypti. The observed level of suppression would likely be sufficient to prevent dengue epidemics in the locality tested and other areas with similar or lower transmission. PMID:26135160
Probing Neutrino Hierarchy and Chirality via Wakes
Hong-Ming Zhu; Ue-Li Pen; Xuelei Chen; Derek Inman
The relic neutrinos are expected to acquire a bulk relative velocity with respect to the dark matter at low redshifts, and downstream of dark matter halos neutrino wakes are expected to develop. We propose a method of measuring the neutrino mass based on this mechanism. The neutrino wake will cause a dipole distortion of the galaxy-galaxy lensing pattern. This effect could be detected by combining upcoming lensing surveys, e.g. the LSST and Euclid surveys with a low redshift galaxy survey or a 21cm intensity mapping survey which can map the neutrino flow field. The data obtained with LSST and Euclid should enable us to make positive detection if the three neutrino masses are Quasi-Degenerate, and a future high precision 21cm lensing survey would allow the normal hierarchy and inverted hierarchy cases to be distinguished, and even the right handed Dirac neutrinos may be detectable.
A circuit-level model of hippocampal place field dynamics modulated by entorhinal grid and suppression-generating cells.
Jayet Bray, Laurence C; Quoy, Mathias; Harris, Frederick C; Goodman, Philip H
Hippocampal "place cells" and the precession of their extracellularly recorded spiking during traversal of a "place field" are well-established phenomena. More recent experiments describe associated entorhinal "grid cell" firing, but to date only conceptual models have been offered to explain the potential interactions among entorhinal cortex (EC) and hippocampus. To better understand not only spatial navigation, but mechanisms of episodic and semantic memory consolidation and reconsolidation, more detailed physiological models are needed to guide confirmatory experiments. Here, we report the results of a putative entorhinal-hippocampal circuit level model that incorporates recurrent asynchronous-irregular non-linear (RAIN) dynamics, in the context of recent in vivo findings showing specific intracellular-extracellular precession disparities and place field destabilization by entorhinal lesioning. In particular, during computer-simulated rodent maze navigation, our model demonstrate asymmetric ramp-like depolarization, increased theta power, and frequency (that can explain the phase precession disparity), and a role for STDP and K(AHP) channels. Additionally, we propose distinct roles for two entorhinal cell populations projecting to hippocampus. Grid cell populations transiently trigger place field activity, while tonic "suppression-generating cell" populations minimize aberrant place cell activation, and limit the number of active place cells during traversal of a given field. Applied to place-cell RAIN networks, this tonic suppression explains an otherwise seemingly discordant association with overall increased firing. The findings of this circuit level model suggest in vivo and in vitro experiments that could refute or support the proposed mechanisms of place cell dynamics and modulating influences of EC. PMID:21151359
A Circuit-Level Model of Hippocampal Place Field Dynamics Modulated by Entorhinal Grid and Suppression-Generating Cells
Jayet Bray, Laurence C.; Quoy, Mathias; Harris, Frederick C.; Goodman, Philip H.
Hippocampal �place cells� and the precession of their extracellularly recorded spiking during traversal of a �place field� are well-established phenomena. More recent experiments describe associated entorhinal �grid cell� firing, but to date only conceptual models have been offered to explain the potential interactions among entorhinal cortex (EC) and hippocampus. To better understand not only spatial navigation, but mechanisms of episodic and semantic memory consolidation and reconsolidation, more detailed physiological models are needed to guide confirmatory experiments. Here, we report the results of a putative entorhinal-hippocampal circuit level model that incorporates recurrent asynchronous-irregular non-linear (RAIN) dynamics, in the context of recent in vivo findings showing specific intracellular�extracellular precession disparities and place field destabilization by entorhinal lesioning. In particular, during computer-simulated rodent maze navigation, our model demonstrate asymmetric ramp-like depolarization, increased theta power, and frequency (that can explain the phase precession disparity), and a role for STDP and KAHP channels. Additionally, we propose distinct roles for two entorhinal cell populations projecting to hippocampus. Grid cell populations transiently trigger place field activity, while tonic �suppression-generating cell� populations minimize aberrant place cell activation, and limit the number of active place cells during traversal of a given field. Applied to place-cell RAIN networks, this tonic suppression explains an otherwise seemingly discordant association with overall increased firing. The findings of this circuit level model suggest in vivo and in vitro experiments that could refute or support the proposed mechanisms of place cell dynamics and modulating influences of EC. PMID:21151359
An optically modulated zero-field atomic magnetometer with suppressed spin-exchange broadening
Jim�nez-Mart�nez, R. [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States) [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States); Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States); Knappe, S.; Kitching, J. [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States)] [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States)
We demonstrate an optically pumped {sup 87}Rb magnetometer in a microfabricated vapor cell based on a zero-field dispersive resonance generated by optical modulation of the {sup 87}Rb ground state energy levels. The magnetometer is operated in the spin-exchange relaxation-free regime where high magnetic field sensitivities can be achieved. This device can be useful in applications requiring array-based magnetometers where radio frequency magnetic fields can induce cross-talk among adjacent sensors or affect the source of the magnetic field being measured.
Strong Reduction of Tc Suppression by Magnetic Field in YBa2Cu3O7+x Films with Dispersed Nanoparticles
NASA Astrophysics Data System (ADS)
Cimpoiasu, E.; Feldmann, J. D.; Varanasi, C. V.; Haugan, T. J.; Barnes, P. N.; Levin, G. A.
Improvements in the critical current density Jc in applied magnetic fields are of great importance for applications of the YBa2Cu3O7-x coated conductors. Nanosize inclusions have shown to be effective in increasing Jc, but the precise physical mechanisms of their action remains elusive. A broader range of experiments is needed in order to elucidate the physics of this phenomenon. Here we discuss the magnetic field H- and temperature T-dependence of the resistivity of thin films in the normal state and near Tc. Pure YBCO films will be compared with those that contain either dispersed Y2O3 nanoparticles or BaSnO3 nanorods. The resistance of highly c-axis oriented YBCO films was measured by the Montgomery method in the range 20 K < T < 300 K and in fields up to 9 T. The films with inclusions show a much sharper and less broadened in-field transition (smaller Tc suppression by field) than pure YBCO. This correlates well with increased Jc measured by conventional methods and indicates increased pinning strength at all temperatures. In order to further identify the signatures of the nano-inclusions, the samples were annealed in air at 420 deg C. The changes induced by the annealing will be discussed. This work was partially supported by AFOSR and the AFRL Propulsion Directorate.
Wake Turbulence Mitigation for Arrivals (WTMA)
NASA Technical Reports Server (NTRS)
Williams, Daniel M.; Lohr, Gary W.; Trujillo, Anna C.
The preliminary Wake Turbulence Mitigation for Arrivals (WTMA) concept of operations is described in this paper. The WTMA concept provides further detail to work initiated by the Wake Vortex Avoidance System Concept Evaluation Team and is an evolution of the Wake Turbulence Mitigation for Departure concept. Anticipated benefits about reducing wake turbulence separation standards in crosswind conditions, and candidate WTMA system considerations are discussed.
On the estimation of swimming and flying forces from wake measurements.
Dabiri, John O
The transfer of momentum from an animal to fluid in its wake is fundamental to many swimming and flying modes of locomotion. Hence, properties of the wake are commonly studied in experiments to infer the magnitude and direction of locomotive forces. The determination of which wake properties are necessary and sufficient to empirically deduce swimming and flying forces is currently made ad hoc. This paper systematically addresses the question of the minimum number of wake properties whose combination is sufficient to determine swimming and flying forces from wake measurements. In particular, it is confirmed that the spatial velocity distribution (i.e. the velocity field) in the wake is by itself insufficient to determine swimming and flying forces, and must be combined with the fluid pressure distribution. Importantly, it is also shown that the spatial distribution of rotation and shear (i.e. the vorticity field) in the wake is by itself insufficient to determine swimming and flying forces, and must be combined with a parameter that is analogous to the fluid pressure. The measurement of this parameter in the wake is shown to be identical to a calculation of the added-mass contribution from fluid surrounding vortices in the wake, and proceeds identically to a measurement of the added-mass traditionally associated with fluid surrounding solid bodies. It is demonstrated that the velocity/pressure perspective is equivalent to the vorticity/vortex-added-mass approach in the equations of motion. A model is developed to approximate the contribution of wake vortex added-mass to locomotive forces, given a combination of velocity and vorticity field measurements in the wake. A dimensionless parameter, the wake vortex ratio (denoted Wa), is introduced to predict the types of wake flows for which the contribution of forces due to wake vortex added-mass will become non-negligible. Previous wake analyses are re-examined in light of this parameter to infer the existence and importance of wake vortex added-mass in those cases. In the process, it is demonstrated that the commonly used time-averaged force estimates based on wake measurements are not sufficient to prove that an animal is generating the locomotive forces necessary to sustain flight or maintain neutral buoyancy. PMID:16155224
Wind Turbine Wake Experiment - Wieringermeer (WINTWEX-W)
NASA Astrophysics Data System (ADS)
Kumer, Valerie; Reuder, Joachim; Svardal, Benny; Eecen, Peter
The Wind Turbine Wake Experiment - Wieringermeer (WINTWEX-W) is a cooperative wake measurement campaign conducted by the Norwegian Centre of Offshore Wind Energy (Norcowe) and the Energy Research Centre of the Netherlands (ECN). A scanning, four static Windcubes as well as a downstream looking nacelle LiDAR are placed for half a year downstream of one of five research wind turbines in ECNs' wind turbine test farm Wieringermeer. In order to capture wake characteristics under different weather conditions a 60� sector for three different elevations and two vertical cross-sections are scanned every minute with additional wind profile information every second at 2, 5 and 12 rotor diameter distances. Another static Windcube, a forward-looking nacelle LiDAR and three Sonics are placed upstream to measure the undisturbed approaching flow field. During the campaign several scanning algorithms are tested to capture most wake features. The aim of the campaign is a qualitative and quantitative description of single wind turbine wake evolution, propagation and persistency, as well as to improve CFD wake models by delivering a detailed data set of several real atmospheric conditions.
Hybrid Magnetic Tunnel Junction-MEMS High Frequency Field Modulator for 1\\/f Noise Suppression
Andr� Guedes; Samadhan B. Patil; Piotr Wisniowski; Virginia Chu; Jo�o P. Conde; Paulo P. Freitas
A dc to ac magnetic field transformer was developed using a magnetic tunnel junction (MTJ)\\/microelectromechanical system (MEMS) mixed device. A MEMS torsionator was fabricated with an incorporated magnetic flux guide, that when actuated by a gate electrode, modulates an external dc field into the same frequency of the micro-torsionator oscillation. Attached to it a MgO based MTJ was fabricated, performing
Suppression of electron-spin relaxation induced by magnetic fields in a Cd1-xMnxTe quantum well
NASA Astrophysics Data System (ADS)
Seo, K.; Kayanuma, K.; Aoshima, I.; Nishibayashi, K.; Souma, I.; Murayama, A.; Oka, Y.
Carrier-spin relaxation under a magnetic field has been studied in a diluted magnetic semiconductor quantum well (DMS-QW) of Cd0.95Mn0.05Te, by means of pump-probe absorption spectroscopy. With resonant excitation using a circularly polarized pump-pulse, dynamical spin-flip processes of an electron and heavy-hole (hh) are clearly observed in time dependences of the circularly polarized differential absorbance. In 0 T, time constants of 17 ps and 0.4 ps for the electron- and hh-spin relaxations in the Cd0.95Mn0.05Te QW are shorter than those of 46 ps and 1.0 ps in a non-magnetic CdTe QW, due to s-d exchange interactions between the carriers and Mn spins. The spin-flip time of the electron due to the exchange mechanism is determined as 27 ps. In an intense magnetic field of 5 T, the electron-spin relaxation due to the exchange mechanism is found to be strongly suppressed in the DMS-QW by magnetic-field-induced pinning of the Mn spins, exhibiting a longer time constant of 29 ps than that of 17 ps in 0 T. The role of LO-phonon is also discussed in the electron-spin relaxation under magnetic fields.
Sleep-wake syndrome - irregular ... routine during the day. The amount of total sleep time is normal, but the body clock loses ... have a different condition, such as shift work sleep disorder or jet lag syndrome.
Mach-like capillary-gravity wakes.
Moisy, Fr�d�ric; Rabaud, Marc
We determine experimentally the angle ? of maximum wave amplitude in the far-field wake behind a vertical surface-piercing cylinder translated at constant velocity U for Bond numbers Bo(D)=D/?(c) ranging between 0.1 and 4.2, where D is the cylinder diameter and ?(c) the capillary length. In all cases the wake angle is found to follow a Mach-like law at large velocity, ??U(-1), but with different prefactors depending on the value of Bo(D). For small Bo(D) (large capillary effects), the wake angle approximately follows the law ??c(g,min)/U, where c(g,min) is the minimum group velocity of capillary-gravity waves. For larger Bo(D) (weak capillary effects), we recover a law ???[gD]/U similar to that found for ship wakes at large velocity [Rabaud and Moisy, Phys. Rev. Lett. 110, 214503 (2013)]. Using the general property of dispersive waves that the characteristic wavelength of the wave packet emitted by a disturbance is of order of the disturbance size, we propose a simple model that describes the transition between these two Mach-like regimes as the Bond number is varied. We show that the new capillary law ??c(g,min)/U originates from the presence of a capillary cusp angle (distinct from the usual gravity cusp angle), along which the energy radiated by the disturbance accumulates for Bond numbers of order of unity. This model, complemented by numerical simulations of the surface elevation induced by a moving Gaussian pressure disturbance, is in qualitative agreement with experimental measurements. PMID:25215822
Impact of surface roughness on the turbulent wake flow of a turbine blade
NASA Astrophysics Data System (ADS)
Mulleners, Karen
Roughened aero engine blade surfaces lead to increased friction and reduced efficiency of the individual blades. The surface roughness also affects the wake flow of the blade and thus the inflow conditions for the subsequent compressor or turbine stage. To investigate the impact of surface roughness on a turbulent blade wake, we conducted velocity field measurements by means of stereo Particle Image Velocimetry (PIV) in the wake of a roughened turbine blade in a linear cascade wind tunnel. The turbine blade was roughened at different chord-wise locations. We examined the influence of the chord-wise location of the added surface roughness by comparing their impact on the width and depth of the wake, the positions and distribution of vortical structures and the overall circulation in the wake. The associated variations in the wake's turbulence characteristics including Reynolds stresses were also explored.
Gravitational wakes in Saturn's rings
H. Salo
Numerical simulations, including both gravitational interactions and dissipative impacts between particles, are used here to study realistic models for Saturn's rings. For the C-ring there is no instability, but for the B- and A-rings gravitational wakes form. In the A-ring these wakes are so strong that particles trapped in them from meter-sized aggregate particles, which themselves lead to further instability.
Wake potentials of the ILC Interaction Region
Novokhatski, A.; /SLAC
The vacuum chamber of the ILC Interaction Region (IR) is optimized for best detector performance. It has special shaping to minimize additional backgrounds due to the metal part of the chamber. Also, for the same reason this thin vacuum chamber does not have water cooling. Therefore, small amounts of power, which may be deposited in the chamber, can be enough to raise the chamber to a high temperature. One of the sources of 'heating' power is the electromagnetic field of the beam. This field diffracts by non-regularities of the beam pipe and excites free-propagating fields, which are then absorbed by the pipe wall. In addition we have a heating power of the image currents due to finite conductivity of the metallic wall. We will discuss these effects as updating the previous results. The conclusions of this report are: (1) The amount of the beam energy loss in IR is almost equal to the energy loss in one ILC (TESLA) accelerating cryo-module; (2) Addition energy spread at IR is very small; (3) Spectrum of the wake fields is limited 300 GHz; (4) Average power of the wake fields excited in IR is 30 W for nominal ILC parameters; and (5) Pulse power in this case is 6 kilowatts.
Wake Nonuniformity in AN MHD Channel.
NASA Astrophysics Data System (ADS)
Hruby, Vladimir J.
The influence of a wake type nonuniformity on the effective plasma electrical conductivity and Hall parameters ((sigma)(,eff) and (beta)(,eff)) was investigated experimentally and theoretically. The experimental device consisted of a combustion -driven 1 m long linear magnetohydrodynamic generator designated Mk VII and located at the Avco Everett Research Laboratory, Inc. (AERL). The reactants were oxygen-enriched air and No. 2 fuel oil. The combustion gases were seeded with potassium carbonate in a 50 percent water solution. The nominal thermal input was 10 MW, the inlet Mach number was 1.4 and the maximum magnetic field was B = 2.3 T. The channel was resistively Faraday loaded. The nonuniformity was produced by a flat plate (a vane) located in the supersonic nozzle, which created a wake lying in a plane parallel to the magnetic field. The vane removed approximately 1 percent of the channel thermal input, which resulted in a 6 percent stagnation enthalpy defect in its wake. Traversing optical probes at three locations along the channel detected little or no conductivity defect. The absence of conductivity defect was confirmed by the generator performance which remained the same with or without the vane, all other conditions being the same. An approximate analytical model showed that conductivity in the wake can be, under certain conditions, larger than that in the free stream. A traversing stagnation pressure probe however, did detect a velocity wake at the same conditions. A small amount of water (approximately 1 percent of the total mass flow) was then injected into the plasma from the trailing edge of the vane. That resulted in a strong initial conductivity defect which completely diffused and merged with boundary layers within 0.75 m. The conductivity ((TURN) thermal) profile was recorded by means of optical diagnostics. The stagnation pressure probe recorded both thermal and stagnation pressure defects. The generated power was reduced to a fraction of the power generated without the water injection. Electrical data together with the optical data were combined to evaluate the so -called plasma nonuniformity factor (G). The experimental G fell below that predicted by an approximate analytical expression derived by Rosa (G(,R)). Numerical investigation showed that the analytical approximations are not valid for large conductivity defects. A modified analytical expression resulted in better agreement between the theory and data. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI.
Efficient and stable transgene suppression via RNAi in field-grown poplars
Jingyi Li; Amy M. Brunner; Olga Shevchenko; Richard Meilan; Cathleen Ma; Jeffrey S. Skinner; Steven H. Strauss
The efficiency and stability of RNA interference (RNAi) in perennial species, particularly in natural environments, is poorly understood. We studied 56 independent poplar RNAi transgenic events in the field over 2 years. A resident BAR transgene was targeted with two different types of RNAi constructs: a 475-bp IR of the promoter sequence and a 275-bp IR of the coding sequence,
Complex geophysical wake flows. Madeira Archipelago case study
NASA Astrophysics Data System (ADS)
Caldeira, Rui Miguel A.; Sangr�, Pablo
Idealized studies of island wakes often use a cylinder-like island to generate the wake, whereas most realistic studies use a close representation of the oceanic bathymetry immersed in a complex representation of the "ambient" geophysical flows. Here, a system of multiple islands was placed into numerical and experimental channels, in order to focus on the complexity of the archipelago wake, including (a) the influence of small neighboring islands and (b) the role of the island-shelf. The numerical geostrophic and stratified channel was built using a three-dimensional primitive equation model, considering a realistic representation of the Madeira archipelago bathymetry, with prescribed initial and boundary conditions. Results from the simulations show that the neighboring islands alter the near-field wake. Small eddies generated by the neighboring islands lead to destabilization of the shear layers of the larger island. Laboratory experiments carried out in the Coriolis rotating tank corroborated this near-field disruptive mechanism. The neighboring island perturbation effect was present whatever the direction of the incoming flow, but under different regimes. North-south wakes produced geostrophic eddies (? R d), whereas west-east wakes produced (exclusively) ageostrophic submesoscale eddies (< < R d) which traveled offshore with wave-like motion. The archipelago shelf contributed to the asymmetric vertical migration of oceanic vorticity. Cyclonic vorticity dominated the surface dynamics, whereas anticyclonic circulation prevailed at the bottom part of the linearly stratified upper layer. This study identifies several likely wake scenarios induced by the Madeira archipelago, and may serve as guide for future multiscale numerical studies and in situ campaigns.
Coherent Pulsed Lidar Sensing of Wake Vortex Position and Strength, Winds and Turbulence in the Terminal Area
NASA Technical Reports Server (NTRS)
Brockman, Philip; Barker, Ben C., Jr.; Koch, Grady J.; Nguyen, Dung Phu Chi; Britt, Charles L., Jr.; Petros, Mulugeta
NASA Langley Research Center (LaRC) has field tested a 2.0 gm, 100 Hertz, pulsed coherent lidar to detect and characterize wake vortices and to measure atmospheric winds and turbulence. The quantification of aircraft wake-vortex hazards is being addressed by the Wake Vortex Lidar (WVL) Project as part of Aircraft Vortex Spacing System (AVOSS), which is under the Reduced Spacing Operations Element of the Terminal Area Productivity (TAP) Program. These hazards currently set the minimum, fixed separation distance between two aircraft and affect the number of takeoff and landing operations on a single runway under Instrument Meteorological Conditions (IMC). The AVOSS concept seeks to safely reduce aircraft separation distances, when weather conditions permit, to increase the operational capacity of major airports. The current NASA wake-vortex research efforts focus on developing and validating wake vortex encounter models, wake decay and advection models, and wake sensing technologies. These technologies will be incorporated into an automated AVOSS that can properly select safe separation distances for different weather conditions, based on the aircraft pair and predicted/measured vortex behavior. The sensor subsystem efforts focus on developing and validating wake sensing technologies. The lidar system has been field-tested to provide real-time wake vortex trajectory and strength data to AVOSS for wake prediction verification. Wake vortices, atmospheric winds, and turbulence products have been generated from processing the lidar data collected during deployments to Norfolk (ORF), John F. Kennedy (JFK), and Dallas/Fort Worth (DFW) International Airports.
Wake structure measurements at the Mod2 cluster test facility at Goodnoe Hills
P. B. S. Lissaman; T. G. Zambrano; G. W. Gyatt
A field measurement progam was carried out at the cluster of three MOD-2 wind turbines located at Goodnoe Hills, Washington, to determine the rate of decay of wake velocity deficit with downwind distance in various meteorological conditions. Measurements were taken at hub height (200 ft) between July 12 and August 1, 1982. Wake wind speeds were measured using a radiosonde
Wavy Wake Formation in the Absence of Submerged Bodies in Electrolyzed Salt Water
Hiroyuki Honji
It has been found experimentally that in electrolyzed salt water, a wavy wake forms in the absence of submerged bodies downstream of a localized region influenced by the magnetic field of permanent magnets moving at a constant velocity. The lower and upper critical numbers of a dimensionless current density (Q) for the formation region of the wavy wakes decrease with
Laminar forced convection wake above a series of vertical parallel plates
Zakaria Doulfoukar; Abderrahim Achiq
The study of a laminar forced convection wake above a series of vertical parallel plates is carried out. The development of momentum and energy fields in the near wake is studied analytically. Velocity, temperature and pressure gradient are presented in asymptotic expressions. Furthermore, the temperature in the immediate neighbourhood of the trailing edges, along the plates, is presented in a
TESLA Report 2003-19 THE SHORT-RANGE TRANSVERSE WAKE
TESLA Report 2003-19 THE SHORT-RANGE TRANSVERSE WAKE FUNCTION FOR TESLA ACCELERATING STRUCTURE T of a Free Electron Laser in TESLA project requires very short bunches. It results in a very long interaction calculate the short-range transverse wakefields of the TESLA linac accelerating structure. Wake fields
Efficient and stable transgene suppression via RNAi in field-grown poplars
Jingyi Li; Amy M. Brunner; Olga Shevchenko; Richard Meilan; Cathleen Ma; Jeffrey S. Skinner; Steven H. Strauss
The efficiency and stability of RNA interference (RNAi) in perennial species, particularly in natural environments, is poorly\\u000a understood. We studied 56 independent poplar RNAi transgenic events in the field over 2�years. A resident BAR transgene was targeted with two different types of RNAi constructs: a 475-bp IR of the promoter sequence and a 275-bp IR\\u000a of the coding sequence, each
Kirchhoff's Integral Representation and a Cavity Wake Potential
Novokhatski, Alexander; /SLAC
A method is proposed for the calculation of the short-range wake field potentials of an ultra-relativistic bunch passing near some irregularities in a beam pipe. The method is based on the space-time domain integration of Maxwell's equations using Kirchhoff's formulation. We demonstrate this method on two cases where we obtain the wake potentials for the energy loss of a bunch traversing an iris-collimator in a beam pipe and for a cavity. Likewise, formulas are derived for Green's functions that describe the transverse force action of wake fields. Simple formulas for the total energy loss of a bunch with a Gaussian charge density distribution are derived as well. The derived estimates are compared with computer results and predictions of other models.
Genetic approaches for target identification in sleep/wake systems.
Winrow, Christopher J; Turek, Fred W; Renger, John J
Attempts to therapeutically induce sufficient amounts of sleep have occurred since the advent of the medical arts, but the health implications of failing to maintain a correct balance of sleep/wake has only recently become widely appreciated both in the medical arena and among the general public. Inappropriate amounts of sleep have been linked to cognitive impairment, immune suppression and metabolic changes, as well as to the sequelae of reduced vigilance and increased likelihood of involvement in automobile accidents or other causes of fatalities. Currently approved treatments for insomnia and excessive sleepiness have suboptimal risk:benefit ratios; thus, opportunities exist for improved therapeutic approaches in the treatment of sleep/wake disorders through novel target identification. Until recently, the ability to link genes to sleep/wake behaviors has been limited to overt observations of sedation, stimulation, and narcoleptic or sleep 'attacks'. Recent research has been focused on approaches that combine measures of refined phenotypic electroencephalographic changes with chromosomal loci, in an attempt to identify novel targets that alter sleep/wake behaviors. PMID:18988125
Canopy wake measurements using multiple scanning wind LiDARs
NASA Astrophysics Data System (ADS)
Markfort, C. D.; Carbajo Fuertes, F.; Iungo, V.; Stefan, H. G.; Porte-Agel, F.
Canopy wakes have been shown, in controlled wind tunnel experiments, to significantly affect the fluxes of momentum, heat and other scalars at the land and water surface over distances of �O(1 km), see Markfort et al. (EFM, 2013). However, there are currently no measurements of the velocity field downwind of a full-scale forest canopy. Point-based anemometer measurements of wake turbulence provide limited insight into the extent and details of the wake structure, whereas scanning Doppler wind LiDARs can provide information on how the wake evolves in space and varies over time. For the first time, we present measurements of the velocity field in the wake of a tall patch of forest canopy. The patch consists of two uniform rows of 40-meter tall deciduous, plane trees, which border either side of the All�e de Dorigny, near the EPFL campus. The canopy is approximately 250 m long, and it is approximately 40 m wide, along the direction of the wind. A challenge faced while making field measurements is that the wind rarely intersects a canopy normal to the edge. The resulting wake flow may be deflected relative to the mean inflow. Using multiple LiDARs, we measure the evolution of the wake due to an oblique wind blowing over the canopy. One LiDAR is positioned directly downwind of the canopy to measure the flow along the mean wind direction and the other is positioned near the canopy to evaluate the transversal component of the wind and how it varies with downwind distance from the canopy. Preliminary results show that the open trunk space near the base of the canopy results in a surface jet that can be detected just downwind of the canopy and farther downwind dissipates as it mixes with the wake flow above. A time-varying recirculation zone can be detected by the periodic reversal of the velocity near the surface, downwind of the canopy. The implications of canopy wakes for measurement and modeling of surface fluxes will be discussed.
The Role of Mesopontine NGF in Sleep and Wakefulness
Ramos, Oscar V.; Torterolo, Pablo; Lim, Vincent; Chase, Michael H.; Sampogna, Sharon; Yamuy, Jack
The microinjection of nerve growth factor (NGF) into the cat pontine tegmentum rapidly induces rapid eye movement (REM) sleep. To determine if NGF is involved in naturally-occurring REM sleep, we examined whether it is present in mesopontine cholinergic structures that promote the initiation of REM sleep, and whether the blockade of NGF production in these structures suppresses REM sleep. We found that cholinergic neurons in the cat dorsolateral mesopontine tegmentum exhibited NGF-like immunoreactivity. In addition, the microinjection of an oligodeoxyribonucleotide (OD) directed against cat NGF mRNA into this region resulted in a reduction in the time spent in REM sleep in conjunction with an increase in the time spent in wakefulness. Sleep and wakefulness returned to baseline conditions 2 to 5 days after antisense OD administration. The preceding antisense OD-induced effects occurred in conjunction with the suppression of NGF-like immunoreactivity within the site of antisense OD injection. These data support the hypothesis that NGF is involved in the modulation of naturally-occurring sleep and wakefulness. PMID:21840513
Suppression of Amblyomma americanum (Ixodida: Ixodidae) for short-term field operations utilizing cypermethrin and lambda-cyhalothrin.
Hughes, Tony H; Richardson, Alec G; Hoel, David F; Mejeoumov, Tracy; Farooq, Mohammad; Stoops, Craig A
Tick-borne diseases pose significant risks to U.S. military personnel who conduct operations, both domestic and abroad. To determine the feasibility of protecting personnel from tick vectors during short-term field deployments, acaricides cypermethrin (Demon WP, Syngenta, Greensboro, NC) and lambda-cyhalothrin (Surrender Pestabs, CSI, Pasadena, TX) were applied to plots within two separate field sites on Camp Blanding Joint Training Center in Starke, FL, from May to June 2011. We analyzed their effectiveness in reducing tick counts for 6 wk after application. In total, 8,193 ticks were identified and counted, of which > 99% were a mix of nymphs and adult-stage Amblyomma americanum (L.). Our results indicate that both cypermethrin and lambda-cyhalothrin were effective in significantly reducing tick numbers and preventing entry into treated plots for 6 wk after application. Thus, these two acaracides can be used to effectively suppress tick populations and provide residual protection in small geographic areas of recreation or public health significance. PMID:24897866
Tomographic particle image velocimetry of desert locust wakes: instantaneous volumes combine to reveal hidden vortex elements and rapid wake deformation
Bomphrey, Richard J.; Henningsson, Per; Michaelis, Dirk; Hollis, David
Aerodynamic structures generated by animals in flight are unstable and complex. Recent progress in quantitative flow visualization has advanced our understanding of animal aerodynamics, but measurements have hitherto been limited to flow velocities at a plane through the wake. We applied an emergent, high-speed, volumetric fluid imaging technique (tomographic particle image velocimetry) to examine segments of the wake of desert locusts, capturing fully three-dimensional instantaneous flow fields. We used those flow fields to characterize the aerodynamic footprint in unprecedented detail and revealed previously unseen wake elements that would have gone undetected by two-dimensional or stereo-imaging technology. Vortex iso-surface topographies show the spatio-temporal signature of aerodynamic force generation manifest in the wake of locusts, and expose the extent to which animal wakes can deform, potentially leading to unreliable calculations of lift and thrust when using conventional diagnostic methods. We discuss implications for experimental design and analysis as volumetric flow imaging becomes more widespread. PMID:22977102
Improving actuator disk wake model
NASA Astrophysics Data System (ADS)
Costa Gomes, V. M. M. G.; Palma, J. M. L. M.; Silva Lopes, A.
The wind energy industry has traditionally relied on simple wake models for estimating Wind Turbine (WT) wake losses. Despite limitations, low requirements in terms of detailed rotor information makes their use feasible, unlike more complex models, such as Blade Element Method (BEM) or Actuator Line. Froude's Actuator Disk (AD) does not suffer the simpler model's limitation of prescribing the wake through a closed set of equations, while sharing with them the low rotor data requirements. On the other hand they require some form of parametrization to close the model and calculate total thrust acting on the flow. An Actuator Disk model was developed, using an iterative algorithm based on Froude's one-dimensional momentum theory to determine the WT's performance, proving to be successful in estimating the performance of both machines in undisturbed flow and in the wake of an upstream machines. Before Froude's AD limitations compared to more complex rotor models, load distributions emulating those of a BEM model were tested. The results show that little impact is obtained at 3 rotor diameters downstream and beyond, agreeing with common definition of a far-wake that starts at 1-2 diameters downstream, where rotor characteristics become negligible and atmospheric flow effects dominate.
Distributed control in a mean-field cortical network model: Implications for seizure suppression
NASA Astrophysics Data System (ADS)
Ching, ShiNung; Brown, Emery N.; Kramer, Mark A.
Brain electrical stimulation (BES) has long been suggested as a means of controlling pathological brain activity. In epilepsy, control of a spatially localized source, the seizure focus, may normalize neuronal dynamics. Consequently, most BES research has been directed at controlling small, local, neuronal populations. At a higher level, pathological seizure activity can be viewed as a network event that may begin without a clear spatial focus or in multiple sites and spread rapidly through a distributed cortical network. In this paper, we begin to address the implications of local control in a network scenario. To do so, we explore the efficacy of local BES when deployed over a larger-scale neuronal network, for instance, using a grid of stimulating electrodes on the cortex. By introducing a mean-field model of neuronal interactions we are able to identify limitations in network controllability based on physiological constraints that suggest the need for more nuanced network control strategies.
Distributed control in a mean-field cortical network model: implications for seizure suppression.
Ching, ShiNung; Brown, Emery N; Kramer, Mark A
Brain electrical stimulation (BES) has long been suggested as a means of controlling pathological brain activity. In epilepsy, control of a spatially localized source, the seizure focus, may normalize neuronal dynamics. Consequently, most BES research has been directed at controlling small, local, neuronal populations. At a higher level, pathological seizure activity can be viewed as a network event that may begin without a clear spatial focus or in multiple sites and spread rapidly through a distributed cortical network. In this paper, we begin to address the implications of local control in a network scenario. To do so, we explore the efficacy of local BES when deployed over a larger-scale neuronal network, for instance, using a grid of stimulating electrodes on the cortex. By introducing a mean-field model of neuronal interactions we are able to identify limitations in network controllability based on physiological constraints that suggest the need for more nuanced network control strategies. PMID:23005798
Numerical study on wake characteristics of high-speed trains
NASA Astrophysics Data System (ADS)
Yao, Shuan-Bao; Sun, Zhen-Xu; Guo, Di-Long; Chen, Da-Wei; Yang, Guo-Wei
Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of unsteady Reynold-averaged Navier-Stokes (URANS) and detached eddy simulation (DES) are utilized, respectively. Results reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.
Numerical study on wake characteristics of high-speed trains
NASA Astrophysics Data System (ADS)
Yao, Shuan-Bao; Sun, Zhen-Xu; Guo, Di-Long; Chen, Da-Wei; Yang, Guo-Wei
Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of unsteady Reynold-averaged Navier-Stokes (URANS) and detached eddy simulation (DES) are utilized, respectively. Results reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.
Study of a Wake Recovery Mechanism in a High-Speed Axial Compressor Stage
NASA Technical Reports Server (NTRS)
VanZante, Dale E.
This work addresses the significant differences in compressor rotor wake mixing loss which exist in a stage environment relative to a rotor in isolation. The wake decay for a rotor in isolation is due solely to viscous dissipation which is an irreversible process and thus leads to a loss in both total pressure and efficiency. Rotor wake decay in the stage environment is due to both viscous mixing and the inviscid strain imposed on the wake fluid particles by the stator velocity field. This straining process, referred to by Smith (1993) as recovery, is reversible and for a 2D rotor wake leads to an inviscid reduction of the velocity deficit of the wake. A model for the rotor wake decay process is developed and used to quantify the viscous dissipation effects relative to those of inviscid wake stretching. The model is verified using laser anemometer measurements acquired in the wake of a transonic rotor operated in isolation and in a stage configuration at near peak efficiency and near stall operating conditions. Additional insight is provided by a time-accurate 3D Navier-Stokes simulation of the compressor stator flow field at the corresponding stage loading levels. Results from the wake decay model exhibit good agreement with the experimental data. Data from the model, laser anemometer measurements, and numerical simulations indicate that for the rotor/stator spacing used in this work, which is typical of core compressors, rotor wake straining (stretching) is the primary decay process in the stator passage with viscous mixing playing only a minor role. The implications of these results on compressor stage design are discussed.
A digital photography and analysis system for estimation of root and shoot development in rice weed suppression studies in the field
Technology Transfer Automated Retrieval System (TEKTRAN)
Rice germplasm with an inherent ability to suppress weeds can potentially improve the economics and sustainability of weed control in rice. We devised a simple, rapid, and inexpensive digital imaging system to quantify several shoot and root growth characteristics in field-grown rice plants that ha...
Suppressing feedback in a distributed video coding system by employing real field codes
NASA Astrophysics Data System (ADS)
Louw, Daniel J.; Kaneko, Haruhiko
Single-view distributed video coding (DVC) is a video compression method that allows for the computational complexity of the system to be shifted from the encoder to the decoder. The reduced encoding complexity makes DVC attractive for use in systems where processing power or energy use at the encoder is constrained, for example, in wireless devices and surveillance systems. One of the biggest challenges in implementing DVC systems is that the required rate must be known at the encoder. The conventional approach is to use a feedback channel from the decoder to control the rate. Feedback channels introduce their own difficulties such as increased latency and buffering requirements, which makes the resultant system unsuitable for some applications. Alternative approaches, which do not employ feedback, suffer from either increased encoder complexity due to performing motion estimation at the encoder, or an inaccurate rate estimate. Inaccurate rate estimates can result in a reduced average rate-distortion performance, as well as unpleasant visual artifacts. In this paper, the authors propose a single-view DVC system that does not require a feedback channel. The consequences of inaccuracies in the rate estimate are addressed by using codes defined over the real field and a decoder employing successive refinement. The result is a codec with performance that is comparable to that of a feedback-based system at low rates without the use of motion estimation at the encoder or a feedback path. The disadvantage of the approach is a reduction in average rate-distortion performance in the high-rate regime for sequences with significant motion.
Comparing offshore wind farm wake observed from satellite SAR and wake model results
NASA Astrophysics Data System (ADS)
Bay Hasager, Charlotte
Offshore winds can be observed from satellite synthetic aperture radar (SAR). In the FP7 EERA DTOC project, the European Energy Research Alliance project on Design Tools for Offshore Wind Farm Clusters, there is focus on mid- to far-field wind farm wakes. The more wind farms are constructed nearby other wind farms, the more is the potential loss in annual energy production in all neighboring wind farms due to wind farm cluster effects. It is of course dependent upon the prevailing wind directions and wind speed levels, the distance between the wind farms, the wind turbine sizes and spacing. Some knowledge is available within wind farm arrays and in the near-field from various investigations. There are 58 offshore wind farms in the Northern European seas grid connected and in operation. Several of those are spaced near each other. There are several twin wind farms in operation including Nysted-1 and R�dsand-2 in the Baltic Sea, and Horns Rev 1 and Horns Rev 2, Egmond aan Zee and Prinses Amalia, and Thompton 1 and Thompton 2 all in the North Sea. There are ambitious plans of constructing numerous wind farms - great clusters of offshore wind farms. Current investigation of offshore wind farms includes mapping from high-resolution satellite SAR of several of the offshore wind farms in operation in the North Sea. Around 20 images with wind farm wake cases have been retrieved and processed. The data are from the Canadian RADARSAT-1/-2 satellites. These observe in microwave C-band and have been used for ocean surface wind retrieval during several years. The satellite wind maps are valid at 10 m above sea level. The wakes are identified in the raw images as darker areas downwind of the wind farms. In the SAR-based wind maps the wake deficit is found as areas of lower winds downwind of the wind farms compared to parallel undisturbed flow in the flow direction. The wind direction is clearly visible from lee effects and wind streaks in the images. The wind farm wake cases are modeled by various types of wake models. In the EERA DTOC project the model suite consists of engineering models (Ainslie, DWM, GLC, PARK, WASP/NOJ), simplified CFD models (FUGA, FarmFlow), full CFD models (CRES-flowNS, RANS), mesoscale model (SKIRON, WRF) and coupled meso-scale and microscale models. The comparison analysis between the satellite wind wake and model results will be presented and discussed. It is first time a comprehensive analysis is performed on this subject. The topic gains increasing importance because there is a growing need to precisely model also mid- and far-field wind farms wakes for development and planning of offshore wind farm clusters.
Content Analysis of Dreams and Waking Narratives
Alfio Maggiolini; Chiara Cagnin; Franca Crippa; Anna Persico; Pietro Rizzi
This study investigated the specificity of dream content and its continuity with waking life. For each subject (125 men and 125 women, between the ages of 19 and 29 years), a dream and a waking episode were collected according to \\
Numerical modeling of initially turbulent wakes with net momentum
NASA Astrophysics Data System (ADS)
Gourlay, Michael J.; Arendt, S. C.; Fritts, D. C.; Werne, J.
This paper presents results from the first fully three-dimensional direct numerical simulations of initially turbulent wakes with net momentum in unstratified and density stratified fluids. The initial conditions contain a super-position of an initially axisymmetric mean streamwise velocity profile plus a spectrally specified fluctuation velocity field with initially incoherent phases to model initial turbulence. To provide evidence in favor of their validity, we compare results from these simulations with previous measurements behind towed bodies in wind tunnels and towing tanks, and also compare with theories of turbulent wakes. Comparisons with laboratory flow experiments provide agreement, both with statistical quantities and vortex structures and evolution. We subsequently investigate open questions by analysis of the fully three-dimensional flow. Coherent vortices in stratified wakes have their origins in the vortex geometry of the mean wake flow, and do not require stratification or coherent seeding in the initial velocity fluctuations. We conclude that the simulations provide a trustworthy and valuable complement to wake research, and that the vortex structures result from a combination of the necessity that vortices form loops and diffusion of vorticity to smooth the loops into rings.
Prescribed wake methodologies for wind turbine design codes
Galbraith, R.A.M.; Coton, F.N.; Robison, D.J. [Univ. of Glasgow (United Kingdom). Dept. of Aerospace Engineering
Prescribed wake performance assessment models have been developed successfully for both vertical (VAWT) and horizontal (HAWT) axis wind turbines. In the case of the VAWT model the Beddoes and Leishman dynamic stall model has been incorporated. This has resulted in a fully unsteady 3-D code, establishing extremely accurate performance prediction across a wide range of operating conditions. Comparison of performance estimates from the prescribed wake model with those from free wake models have shown excellent correlation. To date, the HAWT model has been developed for the consideration of steady axial and yawed inflows. In the axial flow case comparisons of predicted power output with field data and free wake predictions have shown excellent agreement. Full validation of the yawed flow model is currently underway, with very encouraging initial results. The capabilities of the HAWT model are currently being extended by the inclusion of the Beddoes and Leishman dynamic stall model. Consideration of the significant unsteady aerodynamic influences acting on HAWTs while operating in yaw will significantly improve the models performance. The power of this modelling technique is the significant reduction in the computational overhead it offers. The prescribed wake models offer performance estimates of comparable detail and accuracy to those from free vortex analyses in minutes rather than hours. As such these models are highly suited to design assessment, with particular application to fatigue load analysis.
Numerical simulation of supersonic wake flow with parallel computers
Wong, C.C. [Sandia National Labs., Albuquerque, NM (United States); Soetrisno, M. [Amtec Engineering, Inc., Bellevue, WA (United States)
Simulating a supersonic wake flow field behind a conical body is a computing intensive task. It requires a large number of computational cells to capture the dominant flow physics and a robust numerical algorithm to obtain a reliable solution. High performance parallel computers with unique distributed processing and data storage capability can provide this need. They have larger computational memory and faster computing time than conventional vector computers. We apply the PINCA Navier-Stokes code to simulate a wind-tunnel supersonic wake experiment on Intel Gamma, Intel Paragon, and IBM SP2 parallel computers. These simulations are performed to study the mean flow in the near wake region of a sharp, 7-degree half-angle, adiabatic cone at Mach number 4.3 and freestream Reynolds number of 40,600. Overall the numerical solutions capture the general features of the hypersonic laminar wake flow and compare favorably with the wind tunnel data. With a refined and clustering grid distribution in the recirculation zone, the calculated location of the rear stagnation point is consistent with the 2D axisymmetric and 3D experiments. In this study, we also demonstrate the importance of having a large local memory capacity within a computer node and the effective utilization of the number of computer nodes to achieve good parallel performance when simulating a complex, large-scale wake flow problem.
Wakes of isolated Darrieus turbines
Akins, R.E.
A knowledge of the flow structure in the wake of a wind turbine is important in the design of arrays of units to be used in wind-farm applications. In order to better understand this structure, an experimental program to measure the wake structure downwind of a 17m Darrieus vertical-axis wind turbine was completed. Mean-velocity deficits have been measured as a function of tip-speed ratio and incident wind direction for several downstream locations. The results will allow verification and modification of existing models and improve the capability to predict performance of clusters of wind turbines.
Contrail Formation in Aircraft Wakes Using Large-Eddy Simulations
NASA Technical Reports Server (NTRS)
Paoli, R.; Helie, J.; Poinsot, T. J.; Ghosal, S.
In this work we analyze the issue of the formation of condensation trails ("contrails") in the near-field of an aircraft wake. The basic configuration consists in an exhaust engine jet interacting with a wing-tip training vortex. The procedure adopted relies on a mixed Eulerian/Lagrangian two-phase flow approach; a simple micro-physics model for ice growth has been used to couple ice and vapor phases. Large eddy simulations have carried out at a realistic flight Reynolds number to evaluate the effects of turbulent mixing and wake vortex dynamics on ice-growth characteristics and vapor thermodynamic properties.
Magnetic Fluctuations and Turbulence in the Venus Magnetosheath and Wake
Z. V�r�s; T. L. Zhang; M. P. Leubner; M. Volwerk; M. Delva; W. Baumjohann; K. Kudela
Recent research has shown that distinct physical regions in the Venusian induced magnetosphere are recognizable from the variations of strength and of wave/fluctuation activity of the magnetic field. In this paper the statistical properties of magnetic fluctuations are investigated in the Venusian magnetosheath, terminator, and wake regions. The latter two regions were not visited by previous missions. We found 1/f fluctuations in the magnetosheath, large-scale structures near the terminator and more developed turbulence further downstream in the wake. Location independent short-tailed non-Gaussian statistics was observed.
Diffraction of an impulsive line source with wake
NASA Astrophysics Data System (ADS)
Ayub, M.; Naeem, A.; Nawaz, Rab
The problem of diffraction due to an impulse line source by an absorbing half-plane with wake using Myres' impedance condition (Myers 1980 J. Sound Vib. 71 429-34) in the presence of a subsonic fluid flow is studied. The time dependence of the field requires a temporal Fourier transform in addition to the spatial Fourier transform. The solution of the problem in the presence of wake is obtained by using Greens' function method, Fourier transform, the Wiener-Hopf technique and the modified stationary phase method. Expressions for the total far field for the trailing edge (wake present) situation are given. It is observed that the field produced by the Kutta-Joukowski condition will be substantially in excess of the field when this condition is ignored. Finally, a simple procedure is devised to calculate the inverse temporal Fourier transform. The solution for the leading edge situation can be obtained if the wake, and consequently a Kutta-Joukowski edge condition, is ignored. This can also be seen from the numerical results.
Harmonics suppression of vacuum chamber eddy current induced fields with application to the Superconducting Super Collider (SSC) Low Energy Booster (LEB) Magnets
Schlueter, R.D.; Halbach, K.
This memo presents the formulation of an expression for eddy currents induced in a thin-walled conductor due to a time-dependent electromagnet field excitation. Then follows an analytical development for prediction of vacuum chamber eddy current induced field harmonics in iron-core electromagnets. A passive technique for harmonics suppression is presented with specific application to the design of the Superconducting Super Collider (SSC) Low Energy B (LEB) Magnets.
Wakes in Inertial Fusion Plasmas
NASA Astrophysics Data System (ADS)
Ellis, Ian Norman
Plasma wave wakes, which are the collective oscillatory response near the plasma frequency to the propagation of particles or electromagnetic waves through a plasma, play a critical role in many plasma processes. New results from backwards stimulated Raman scattering (BSRS), in which wakes with phase velocities much less than the speed of light are induced by the beating of counter-propagating light waves, and from electron beam stopping, in which the wakes are produced by the motion of relativistically propagating electrons through the dense plasma, are discussed. Both processes play important roles in Inertial Confinement Fusion (ICF). In BSRS, laser light is scattered backwards out of the plasma, decreasing the energy available to compress the ICF capsule and affecting the symmetry of where the laser energy hits the hohlraum wall in indirect drive ICF. The plasma wave wake can also generate superthermal electrons that can preheat the core and/or the ablator. Electron beam stopping plays a critical role in the Fast Ignition (FI) ICF concept, in which a beam of relativistic electrons is used to heat the target core to ignition temperatures after the compression stage. The beam stopping power determines the effectiveness of the heating process. This dissertation covers new discoveries on the importance of plasma wave wakes in both BSRS and electron beam stopping. In the SRS studies, 1D particle-in-cell (PIC) simulations using OSIRIS are performed, which model a short-duration (�500/?0 --1FWHM) counter-propagating scattered light seed pulse in the presence of a constant pump laser with an intensity far below the absolute instability threshold for plasma waves undergoing Landau damping. The seed undergoes linear convective Raman amplification and dominates over the amplification of fluctuations due to particle discreteness. The simulation results are in good agreement with results from a coupled-mode solver when special relativity and the effects of finite size PIC simulation particles are accounted for. Linear gain spectra including both effects are discussed. Extending the PIC simulations past when the seed exits the simulation domain reveals bursts of large-amplitude scattering in many cases, which do not occur in simulations without the seed pulse. These bursts can have amplitudes several times greater than the amplified seed pulse, and an examination of the orbits of particles trapped in the wake illustrates that the bursts are caused by a reduction of Landau damping due to particle trapping. This large-amplitude scattering is caused by the seed inducing a wake earlier in the simulation, thus modifying the distribution function. Performing simulations with longer duration seeds leads to parts of the seeds reaching amplitudes several times more than the steady-state linear theory results, similarly caused by a reduction of Landau damping. Simulations with continuous seeds demonstrate that the onset of inflation depends on the seed wavelength and incident intensity, and oscillations in the reflectivity are observed at a frequency equal to the difference between the seed frequency and the frequency at which the inflationary SRS grows. In the electron beam stopping studies, 3D PIC simulations are performed of relativistic electrons with a momentum of 10mec propagating in a cold FI core plasma. Some of the simulations use one simulation particle per real particle, and particle sizes much smaller than the interparitcle spacing. The wake made by a single electron is compared against that calculated using cold fluid theory assuming the phase velocity of the wake is near the speed of light. The results agree for the first wavelength of the wake. However, the shape of the wake changes for succeeding wavelengths and depends on the background plasma temperature, with the concavity pointing in the direction the electron is moving in cold plasmas and in the opposite direction as the plasma temperature increases. In the warm plasma the curvature is described by electrostatic Vlasov theory (for vparticle >> vth) and is due
Measuring bubbles in a bubbly wake flow
NASA Astrophysics Data System (ADS)
Lee, Seung-Jae; Kawakami, Ellison; Arndt, Roger E. A.
This paper presents measurements of the velocity and size distribution of bubbles in a bubbly wake. This was carried out by utilizing particle shadow velocimetry (PSV). This technique is a non-scattering approach that relies on direct in-line volume illumination by a pulsed source such as a light-emitting diode (LED). A narrow depth-of-field (DoF) is required for imaging a 2-dimensional plane within a flow volume. Shadows of the bubbles were collected by a high-speed camera. Once a reference image, taken when no bubbles were present in the flow, was subtracted from the images, the image was segmented using an edge detection technique. The Canny algorithm was determined to be best suited for this application. A curvature profile method was employed to distinguish individual bubbles within a cluster of highly overlapping bubbles. The utilized algorithm was made to detect partly overlapping bubbles and reconstruct the missing parts. The movement of recognized individual bubbles was tracked on a two dimensional plane within a flow volume. In order to obtain quantitative results, the wake of a ventilated hydrofoil was investigated by applying the shadowgraphy technique and the described bubble detection algorithm. These experiments were carried out in the high speed cavitation tunnel at Saint Anthony Falls Laboratory (SAFL) of the University of Minnesota. This research is jointly sponsored by the Office of Naval Re- search, Dr. Ron Joslin, program manager, and the Department of Energy, Golden Field Office.
Island wakes in the Southern California Bight
R. M. A. Caldeira; P. Marchesiello; N. P. Nezlin; P. M. DiGiacomo; J. C. McWilliams
Wind- and current-induced island wakes were investigated using a multiplatform approach of in situ, remote sensing, and numerical model simulations for the Southern California Bight (SCB). Island wind wakes are a result of sheltering from the wind, with weak wind mixing, strong heat storage, and consequent high sea surface temperature (SST). Wind wakes around Santa Catalina Island are most persistent
Spin dynamics in a diluted magnetic semiconductor quantum well studied by pump-probe absorption spectroscopy: Magnetic-field-induced suppression of electron-spin relaxation
NASA Astrophysics Data System (ADS)
Murayama, A.; Seo, K.; Nishibayashi, K.; Souma, I.; Oka, Y.
Exciton spin dynamics is studied in a diluted magnetic semiconductor quantum well of Cd0.95Mn0.05Te by pump-probe absorption spectroscopy under magnetic fields. The time dependences of the saturated absorbance for the higher- and lower-energy spin states of heavy-hole (hh) excitons clarify the following exciton-spin relaxation process in magnetic fields: ultrafast hh-spin relaxation with the formation of dark excitons and subsequent electron-spin relaxation. The electron-spin relaxation due to the s-d exchange mechanism involving Mn spins is suppressed in a high magnetic field by field-induced pinning of the Mn spins.
Effects of atmospheric stability on the evolution of wind turbine wakes: Volumetric LiDAR scans
NASA Astrophysics Data System (ADS)
Valerio Iungo, Giacomo; Port�-Agel, Fernando
Aerodynamic optimization of wind farm layout is a fundamental task to reduce wake effects on downstream wind turbines, thus to maximize wind power harvesting. However, downstream evolution and recovery of wind turbine wakes are strongly affected by the characteristics of the incoming atmospheric boundary layer (ABL) flow, like the vertical profiles of the mean wind velocity and the turbulence intensity, which are in turn affected by the ABL stability regime. Therefore, the characterization of the variability of wind turbine wakes under different ABL stability regimes becomes fundamental to better predict wind power harvesting and improve wind farm efficiency. To this aim, wind velocity measurements of the wake produced by a 2 MW Enercon E-70 wind turbine were performed with three scanning Doppler wind Light Detection and Ranging (LiDAR) instruments. One LiDAR was typically devoted to the characterization of the incoming wind, in particular wind velocity, shear and turbulence intensity at the height of the rotor disc. The other two LiDARs performed scans in order to characterize the wake velocity field produced by the tested wind turbine. The main challenge in performing field measurements of wind turbine wakes is represented by the varying wind conditions, and by the consequent adjustments of the turbine yaw angle needed to maximize power production. Consequently, taking into account possible variations of the relative position between LiDAR measurement volume and wake location, different LiDAR measurement procedures were carried out in order to perform 2-D and 3-D characterizations of the mean wake velocity field. However, larger measurement volumes and higher spatial resolution require longer sampling periods; thus, to investigate wake turbulence tests were also performed by staring the LiDAR laser beam over fixed directions and with the maximum sampling frequency. Furthermore, volumetric scans of the wind turbine wake were performed under different wind conditions via two simultaneous LiDARs. Through the evaluation of the minimum wake velocity deficit as a function of the downstream distance, it is shown that the stability regime of the ABL has a significant effect on the wake evolution; specifically the wake recovers faster under convective conditions. This result suggests that atmospheric inflow conditions, and particularly thermal stability, should be considered for improved wake models and predictions of wind power harvesting.
Electro-magnetic Feedback Control of Wake Flows
NASA Astrophysics Data System (ADS)
Chen, Zhihua; Aubry, Nadine
The purpose of this work is to develop a closed loop control algorithm for manipulating wake flows past a cylinder in an electrically low-conducting fluid (e.g. seawater). Our goal is to avoid flow separation from the surface of the body and fully suppress vortex shedding. For this purpose, we use arrays of electrodes and permanent magnets generating electro-magnetic body forces, i.e. Lorentz forces, in the vicinity of the solid surface. It was recently demonstrated experimentally and numerically that an array of electrodes and magnets distributed all around the body and energized at all times can suppress vortex shedding and delay flow separation [1]. We show here that more localized electrode and magnet arrays, activated only at times when they are needed, can achieve similar results and even suppress separation completely. In addition the drag is zero at all times. Our technique is based on closed loop control using reduced flow information. [1] T. Weier, G. Gerbeth, G. Mutschke, O. Lielausis, E. Platacis, ``Experiments on cylinder wake stabilization in an electrolyte solution by means of electromagnetic forces localized on the cylinder surface", Experimental Thermal and Fluid Science (1998).
Electron velocity distribution instability in magnetized plasma wakes and artificial electron mass
Hutchinson, Ian H.
The wake behind a large object (such as the moon) moving rapidly through a plasma (such as the solar wind) contains a region of depleted density, into which the plasma expands along the magnetic field, transverse to the ...
Normal Component of Induced Velocity for Entire Field of a Uniformly Loaded Lifting Rotor with Highly Swept Wake as Determined by Electromagnetic Analog
NASA Technical Reports Server (NTRS)
Castles, Walter, Jr.; Durham, Howard L., Jr.; Kevorkian, Jirair
Values of the normal component of induced velocity throughout the entire field of a uniformly loaded r(rotor at high high speed are presented in the form of charts and tables. Many points were found by an electromagnetic analog, details of which are given. Comparisons of computed and analog values for the induced velocity indicate that the latter are sufficiently accurate for engineering purposes.
Vortex shedding in compressor blade wakes
NASA Technical Reports Server (NTRS)
Epstein, A. H.; Gertz, J. B.; Owen, P. R.; Giles, M. B.
The wakes of highly loaded axial compressor blades were often considered to be turbulent, unstructured flows. Recent work has suggested that the blade wakes are in fact dominated by a vortex street-like structure. The work on the wake structure at MIT is reviewed, the results of a viscous numerical simulation are presented, the blade wake vortices are compared to those shed from a cylinder, and the implications of the wake structure on compressor performance are discussed. In particular, a two-dimensional, time accurate, viscous calculation shows both a periodic wake structure and time variations in the passage shock strength. The numerical calculations are compared to laser anemometer and high frequency response probe data. The effect of the wake structure on the entropy production and apparent adiabatic efficiency of the compressor rotor is discussed.
Wake effects in a Fayette 95-IIS wind turbine array
Simon, R.L.; Matson, D.F.; Fuchs, J.M.
A group of 35 wind turbines on the Castello Ranch in Altamont Pass, California, was investigated to quantify array wake effects (losses in energy production due to operation of upwind turbines) and the factors influencing them. Approximately 65 hours of field measurements were made in summer 1986, with turbine energy production and wind velocity data recorded for various scenarios of array operation. Customized software and hardware were developed and installed by Fayette to facilitate these measurements. The existence of wake effects was fairly well established. Relative energy-production losses averaged 6% at the second row, when the first row was operating, and 7 to 8% at the third row, when the first two were operating. Apparently, then, the impact of the first row on the third (at a 21-rotor-diameter distance) was minimal. Ambient wind speed did not appear to affect the relative wind speed pattern within the array due to wakes, but because of the shape of the performance curve, it did affect relative energy production losses (particularly for the low-RPM mode of machine operation). The influences of ambient atmospheric conditions, such as stability, turbulence, and shear on the array wakes, were also investigated by testing over a range of the conditions available during a typical 24-hour day at the test site. None of these variables showed any significant effect on the degree of wake-induced energy losses. While the results of this study apply only to this specific array and type of wind turbine, the methodology could be applied to study wake effects at other wind farms. 6 refs., 7 figs., 20 tabs.
Dynamics of wake structure in clapping propulsion
NASA Astrophysics Data System (ADS)
Kim, Daegyoum; Gharib, Morteza
Some animals such as insects and frogs use a pair of symmetric flaps for locomotion. In some cases, these flappers operate in close proximity or even touch each other. In order to understand the underlying physics of these kinds of motion, we have studied the wake structures induced by clapping and their associated thrust performance. A simple mechanical model with two acrylic plates was used to simulate the power stroke of the clapping motion and three-dimensional flow fields were obtained using defocusing digital particle image velocimetry. Our studies show that the process of vortex connection plays a critical role in forming a downstream closed vortex loop. Under some kinematic conditions, this vortex loop changes its shape dynamically, which is analogous to the process of an elliptical vortex ring switching its minor and major axis. As the length of the plate along the rotating shaft decreases to change an aspect ratio, the downstream motion of the vortex is retarded due to the outward motion of side edge vortices and less propulsive force is generated per the surface area of the plate. The impact of compliance and stroke angle of the plate on wake structures and thrust magnitudes are also presented.
An integrated Navier-Stokes - full potential - free wake method for rotor flows
NASA Astrophysics Data System (ADS)
Berkman, Mert Enis
The strong wake shed from rotary wings interacts with almost all components of the aircraft, and alters the flow field thus causing performance and noise problems. Understanding and modeling the behavior of this wake, and its effect on the aerodynamics and acoustics of helicopters have remained as challenges. This vortex wake and its effect should be accurately accounted for in any technique that aims to predict rotor flow field and performance. In this study, an advanced and efficient computational technique for predicting three-dimensional unsteady viscous flows over isolated helicopter rotors in hover and in forward flight is developed. In this hybrid technique, the advantages of various existing methods have been combined to accurately and efficiently study rotor flows with a single numerical method. The flow field is viewed in three parts: (i) an inner zone surrounding each blade where the wake and viscous effects are numerically captured, (ii) an outer zone away from the blades where wake is modeled, and (iii) a Lagrangean wake which induces wake effects in the outer zone. This technique was coded in a flow solver and compared with experimental data for hovering and advancing rotors including a two-bladed rotor, the UH-60A rotor and a tapered tip rotor. Detailed surface pressure, integrated thrust and torque, sectional thrust, and tip vortex position predictions compared favorably against experimental data. Results indicated that the hybrid solver provided accurate flow details and performance information typically in one-half to one-eighth cost of complete Navier-Stokes methods.
Base Flow Asymmetry Effects on the Absolute Stability of Non-uniform Density Wakes
NASA Astrophysics Data System (ADS)
Emerson, Benjamin; Noble, David; Lieuwen, Tim
This work investigates the hydrodynamic stability of bluff body wakes with non-uniform mean density. Such flows are common in bluff body combustors. The absolute/convective stability characteristics of the wake are important, because vortex shedding from the bluff body participates in such processes as mixing, flame blowoff, and combustion instability. Non-uniform density is a sensitive stability parameter for wake flows. Reduction of the wake density relative to the free stream density can stabilize the flow and suppress coherent vortex shedding. Practical bluff body combustors operate at a range of flame density ratios spanning this stability limit. Recent experimental bluff body combustor work by Tuttle et al. investigates wakes with asymmetry in the base flow density profiles. This motivates a hydrodynamic stability model for non-uniform density wakes that includes base flow asymmetry. The model developed in this study investigates the effects of asymmetric base flow velocity and density profiles. It begins with a parameterization of the base flow asymmetries. Results show that base flow asymmetry influences the absolute stability of the flow, and has a strong effect on the most amplified mode shape. The investigation concludes with a comparison to the vorticity equation. Here, we elucidate the physics of the model, and comment on the limitations of such a model.
Neurons containing orexin or melanin concentrating hormone reciprocally regulate wake and sleep
Konadhode, Roda Rani; Pelluru, Dheeraj; Shiromani, Priyattam J.
Neurons containing orexin (hypocretin), or melanin concentrating hormone (MCH) are intermingled with each other in the perifornical and lateral hypothalamus. Each is a separate and distinct neuronal population, but they project to similar target areas in the brain. Orexin has been implicated in regulating arousal since loss of orexin neurons is associated with the sleep disorder narcolepsy. Microinjections of orexin into the brain or optogenetic stimulation of orexin neurons increase waking. Orexin neurons are active in waking and quiescent in sleep, which is consistent with their role in promoting waking. On the other hand, the MCH neurons are quiet in waking but active in sleep, suggesting that they could initiate sleep. Recently, for the first time the MCH neurons were stimulated optogenetically and it increased sleep. Indeed, optogenetic activation of MCH neurons induced sleep in both mice and rats at a circadian time when they should be awake, indicating the powerful effect that MCH neurons have in suppressing the wake-promoting effect of not only orexin but also of all of the other arousal neurotransmitters. Gamma-Aminobutyric acid (GABA) is coexpressed with MCH in the MCH neurons, although MCH is also inhibitory. The inhibitory tone of the MCH neurons is opposite to the excitatory tone of the orexin neurons. We hypothesize that strength in activity of each determines wake vs. sleep. PMID:25620917
Numerical prediction of wakes in cascades and compressor rotors including the effects of mixing. II - Rotor passage flow and wakes including the effects of spanwise mixing
NASA Technical Reports Server (NTRS)
Lakshminarayana, B.; Suryavamshi, N.
The results of a numerical investigation to predict the flow field including wakes and mixing in axial-flow compressor rotors are presented. The wake behavior in a moderately loaded compressor rotor is studied numerically using a 3D incompressible Navier-Stokes solver with a high Reynolds number form of a turbulence model. The equations are solved using a time dependent implicit technique. The agreement between the measured data and the predictions is good; including the blade boundary-layer profiles, wake mean-velocity profiles, and decay. The ability of the pseudocompressibility scheme to predict the entire flow field including the near and far wake profiles and its decay characteristics, effect of loading, and the viscous losses of a 3D rotor flow field are demonstrated. The mixing in the downstream regions away from the hub and annulus walls is dominated by wake diffusion. In regions away from the walls the radial mixing is predominantly caused by the transport of mass, momentum, and energy by the radial component of velocity in the wake.
Compressor and fan wake characteristics
NASA Technical Reports Server (NTRS)
Lakshminarayana, B.
Approaches for developing an analytical model capable of determining the effects of rotor flow and blade parameters and turbulence properties (i.e. energy, velocity correlations, and length scale) on the rotor wake characteristics and its diffusion properties are discussed. The three-dimensional model will employ experimental measurements, instantaneous velocities, and turbulence properties at various stations downstream from a rotor. A triaxial probe and a rotating conventional probe, which is mounted on a traverse gear operated by two step motors, are to be used for these measurements. The final rotor wake model will be capable of predicting the discrete and broadband noise generated in a fan rotor and of evaluating the aerodynamic losses, efficiency and optimum spacing between a rotor and stator in turbomachinery.
Variation of weed-suppressing potential of Vietnamese rice cultivars against barnyardgrass (Echinochloa crus-galli) in laboratory, greenhouse and field screenings
Tran Dang Khanh; Luong Chi Cong; Ill Min Chung; Tran Dang Xuan; Shinkichi Tawata
A total of 73 different varietal groups and cultivars of Vietnamese rice (Oryza sativa L.) were evaluated for the allelopathic potential on barnyardgrass (Echinochloa crus-galli) in laboratory, greenhouse and field screenings. In a bioassay, Y1, U17, Nep Thom and Lua Huong, cultivars showed the highest weed-suppressing ability against the length of shoot and root of barnyardgrass. Y-1, Nhi Uu and
Field applications of three different classes of known host plant defence elicitors did not suppress infection of Geraldton waxflower by Botrytis cinerea
S.-Q. Dinh; D. C. Joyce; D. E. Irving; A. H. Wearing
Ethylene-mediated flower abscission caused by Botrytis infection afflicts cut Geraldton waxflower stems. Preharvest spray applications of three known host plant defence elicitors,\\u000a benzothiadiazole (BTH), methyl jasmonate (MeJA) or silicon (Si), were applied to Geraldton waxflower cvv. Mullering Brook\\u000a and My Sweet Sixteen. Their individual efficacy in postharvest suppression of Botrytis disease developmentwas assessed. Field applications of BTH or Si generally
Wake Instabilities Behind Bluff Bodies
Michel Provansal
\\u000a The observation by B�nard of a vortex street in the wake of a circular cylinder has been commonly associated with the stability\\u000a analysis of the double alternate street proposed by von K�rm�n. After a short historical review of these studies, we present\\u000a the main progress in understanding this instability during the last decade. New experiments and the control of two-dimensional
Oscillating airfoils and their wake
NASA Technical Reports Server (NTRS)
Send, W.
The unsteady phenomena in the wake of an oscillating wing or rotor blade are examined theoretically using the Prandtl approximation of the vortex-transport equation. A mathematical model is developed and applied to such problems as the effect of winglets on the performance of fixed wings and the possibly of employing similar designs in rotor blades. Model predictions for several profiles are compared with published and experimental measurements, and good agreement is found. Graphs and diagrams are provided.
Ventilation of an hydrofoil wake
NASA Astrophysics Data System (ADS)
Arndt, Roger; Lee, Seung Jae; Monson, Garrett
Ventilation physics plays a role in a variety of important engineering applications. For example, hydroturbine ventilation is used for control of vibration and cavitation erosion and more recently for improving the dissolved oxygen content of the flow through the turbine. The latter technology has been the focus of an ongoing study involving the ventilation of an hydrofoil wake to determine the velocity and size distribution of bubbles in a bubbly wake. This was carried out by utilizing particle shadow velocimetry (PSV). This technique is a non-scattering approach that relies on direct in-line volume illumination by a pulsed source such as a light-emitting diode (LED). The data are compared with previous studies of ventilated flow. The theoretical results of Hinze suggest that a scaling relationship is possible that can lead to developing appropriate design parameters for a ventilation system. Ventilation physics plays a role in a variety of important engineering applications. For example, hydroturbine ventilation is used for control of vibration and cavitation erosion and more recently for improving the dissolved oxygen content of the flow through the turbine. The latter technology has been the focus of an ongoing study involving the ventilation of an hydrofoil wake to determine the velocity and size distribution of bubbles in a bubbly wake. This was carried out by utilizing particle shadow velocimetry (PSV). This technique is a non-scattering approach that relies on direct in-line volume illumination by a pulsed source such as a light-emitting diode (LED). The data are compared with previous studies of ventilated flow. The theoretical results of Hinze suggest that a scaling relationship is possible that can lead to developing appropriate design parameters for a ventilation system. Sponsored by ONR and DOE.
Wind-Tunnel Simulation of the Wake of a Large Wind Turbine in a Stable Boundary Layer: Part 2, the Wake Flow
NASA Astrophysics Data System (ADS)
Hancock, Philip E.; Pascheke, Frauke
Measurements have been made in the wake of a model wind turbine in both a neutral and a stable atmospheric boundary layer, in the EnFlo stratified-flow wind tunnel, between 0.5 and 10 rotor diameters from the turbine, as part of an investigation of wakes in offshore winds. In the stable case the velocity deficit decreased more slowly than in the neutral case, partly because the boundary-layer turbulence levels are lower and the consequentially reduced level of mixing, an `indirect' effect of stratification. A correlation for velocity deficit showed the effect of stratification to be the same over the whole of the measured extent, following a polynomial form from about five diameters. After about this distance (for the present stratification) the vertical growth of the wake became almost completely suppressed, though with an increased lateral growth; the wake in effect became `squashed', with peaks of quantities occurring at a lower height, a `direct' effect of stratification. Generally, the Reynolds stresses were lower in magnitude, though the effect of stratification was larger in the streamwise fluctuation than on the vertical fluctuations. The vertical heat flux did not change much from the undisturbed level in the first part of the wake, but became much larger in the later part, from about five diameters onwards, and exceeded the surface level at a point above hub height.
Ship wake signatures in radar/optical images of the sea surface: observations and physical mechanisms
NASA Astrophysics Data System (ADS)
Ermakov, S.; Kapustin, I.; Lazareva, T.
Ship wakes can be clearly seen in satellite radar and optical images of the sea surface, and understanding of physical mechanisms responsible for the wake signatures is very important to develop methods of ship detection/identification. The wake surface signatures at small and intermediate stages are characterized by a smooth centerline area where surface waves are depressed due to the vessel turbulence and by a pair of rough bands at the sides of the centerline wake. At large wake ages two slick bands (a "railroad track" wake) appear instead of the rough bands, while the smooth centerline band is practically absent. In this paper results of field studies of the mean flow structure near the wake are presented. It is shown that two mean circulating currents ("rolls") rotating in the opposite directions are formed at two sides of the median vertical plane of the wake. Near the water surface the rolls result in diverging horizontal flows, decreasing near the wake edges. Wind waves propagating against the diverging currents are amplified due to a wave straining mechanism thus increasing the surface roughness. Film sampling was carried out when crossing the wakes and analysis of films collected within the "railroad" slick bands and outside the bands has revealed enhanced surface wave damping, obviously due to accumulation of surfactants in the slick bands; the surfactant compression is explained by the action of the diverging currents. The diverging currents as part of the rolls and the surfactant transport to the water surface are supposed to be associated with air bubbles generated by ship propellers.
Linear and nonlinear auditory response properties of interneurons in a high-order avian vocal motor nucleus during wakefulness
Raksin, Jonathan N.; Glaze, Christopher M.; Smith, Sarah
Motor-related forebrain areas in higher vertebrates also show responses to passively presented sensory stimuli. However, sensory tuning properties in these areas, especially during wakefulness, and their relation to perception, are poorly understood. In the avian song system, HVC (proper name) is a vocal-motor structure with auditory responses well defined under anesthesia but poorly characterized during wakefulness. We used a large set of stimuli including the bird's own song (BOS) and many conspecific songs (CON) to characterize auditory tuning properties in putative interneurons (HVCIN) during wakefulness. Our findings suggest that HVC contains a diversity of responses that vary in overall excitability to auditory stimuli, as well as bias in spike rate increases to BOS over CON. We used statistical tests to classify cells in order to further probe auditory responses, yielding one-third of neurons that were either unresponsive or suppressed and two-thirds with excitatory responses to one or more stimuli. A subset of excitatory neurons were tuned exclusively to BOS and showed very low linearity as measured by spectrotemporal receptive field analysis (STRF). The remaining excitatory neurons responded well to CON stimuli, although many cells still expressed a bias toward BOS. These findings suggest the concurrent presence of a nonlinear and a linear component to responses in HVC, even within the same neuron. These characteristics are consistent with perceptual deficits in distinguishing BOS from CON stimuli following lesions of HVC and other song nuclei and suggest mirror neuronlike qualities in which �self� (here BOS) is used as a referent to judge �other� (here CON). PMID:22205651
Wake vortex detection at Denver Stapleton Airport with a pulsed 2-micron coherent lidar
NASA Technical Reports Server (NTRS)
Hannon, Stephen M.; Thomson, J. Alex
This report describes the effort undertaken to relate aircraft wake history to the local environment. This involved the monitoring of the embedded windfield, monitoring of local meteorological parameters, a high-resolution velocity field analysis in vertical scan planes and measurement of the axial velocity signature. A flashlight pumped 2.09 micron solid state coherent laser radar system was used to detect and track wake vortices. Strong wake vortex signatures were measured for moderate to large aircraft at Denver's Stapleton airport and a large vortex database was compiled.
Statistical axisymmetry of the turbulent sphere wake
NASA Astrophysics Data System (ADS)
Grandemange, M.; Gohlke, M.; Cadot, O.
The turbulent sphere wake is studied experimentally at using an axisymmetric support that holds the body from upstream. This setup allows the axisymmetry of the mean wake and preserves the global mode activity at . The analysis of the PIV snapshots in a cross-flow plane indicates that this axisymmetry is due to an equal exploration of all the azimuths by the instantaneous wake. Using conditional averaging techniques, we extract the flow topology associated with one azimuthal direction; the obtained wake shows strong similarities with the unsteady planar symmetric flow reported in the laminar regime. In addition, the use of perturbations of the axisymmetry leads to modifications of the azimuthal statistics: The periodicity of the perturbation is recovered in the wake since one or several preferred orientations are identified. Hence, such statistics pave the way to multi-stable behaviors in three-dimensional wakes.
Evolution of Rotor Wake in Swirling Flow
NASA Technical Reports Server (NTRS)
El-Haldidi, Basman; Atassi, Hafiz; Envia, Edmane; Podboy, Gary
A theory is presented for modeling the evolution of rotor wakes as a function of axial distance in swirling mean flows. The theory, which extends an earlier work to include arbitrary radial distributions of mean swirl, indicates that swirl can significantly alter the wake structure of the rotor especially at large downstream distances (i.e., for moderate to large rotor-stator spacings). Using measured wakes of a representative scale model fan stage to define the mean swirl and initial wake perturbations, the theory is used to predict the subsequent evolution of the wakes. The results indicate the sensitivity of the wake evolution to the initial profile and the need to have complete and consistent initial definition of both velocity and pressure perturbations.
Effect of wind turbine wakes on cropland surface fluxes in the US Great Plains during a Nocturnal Low Level Jet
M. E. Rhodes; M. Aitken; J. K. Lundquist; E. S. Takle; J. H. Prueger
Installation of large scale wind farms is becoming a common operation in the Midwest, and wind farms frequently are situated among fields of agricultural crops. Each wind turbine is known to alter the behavior of the air mass downwind of the rotor; consequently, the rotor wakes alter the local microclimate. Quantification of the effects of wind turbine wakes on local
Evaluation of Fast-Time Wake Vortex Models using Wake Encounter Flight Test Data
NASA Technical Reports Server (NTRS)
Ahmad, Nashat N.; VanValkenburg, Randal L.; Bowles, Roland L.; Limon Duparcmeur, Fanny M.; Gloudesman, Thijs; van Lochem, Sander; Ras, Eelco
This paper describes a methodology for the integration and evaluation of fast-time wake models with flight data. The National Aeronautics and Space Administration conducted detailed flight tests in 1995 and 1997 under the Aircraft Vortex Spacing System Program to characterize wake vortex decay and wake encounter dynamics. In this study, data collected during Flight 705 were used to evaluate NASA's fast-time wake transport and decay models. Deterministic and Monte-Carlo simulations were conducted to define wake hazard bounds behind the wake generator. The methodology described in this paper can be used for further validation of fast-time wake models using en-route flight data, and for determining wake turbulence constraints in the design of air traffic management concepts.
Wake Detection Capacity of Actigraphy During Sleep
Paquet, Jean; Kawinska, Anna; Carrier, Julie
Study Objectives: To evaluate the ability of actigraphy compared to polysomnography (PSG) to detect wakefulness in subjects submitted to 3 sleep conditions with different amounts of wakefulness: a nocturnal sleep episode and 2 daytime recovery sleep episodes, one with placebo and one with caffeine. A second objective was to compare the ability of 4 different scoring algorithms (2 threshold algorithms and 2 regression analysis algorithms) to detect wake in the 3 sleep conditions. Design: Three nights of simultaneous actigraphy (Actiwatch-L, Mini-Mitter/Respironics) and PSG recordings in a within-subject design. Setting: Chronobiology laboratory. Participants: Fifteen healthy subjects aged between 20 and 60 years (7M, 8F). Interventions: 200 mg of caffeine and daytime recovery sleep. Results: An epoch-by-epoch comparison between actigraphy and PSG showed a significant decrease in actigraphy accuracy with increased wakefulness in sleep conditions due to the low sleep specificity of actigraphy (generally <50%). Actigraphy overestimated total sleep time and sleep efficiency more strongly in conditions involving more wakefulness. Compared to the 2 regression algorithms, the 2 threshold algorithms were less able to detect wake when the sleep episode involved more wakefulness, and they tended to alternate more between wake and sleep in the scoring of long periods of wakefulness resulting in an overestimation of the number of awakenings. Conclusion: The very low ability of actigraphy to detect wakefulness casts doubt on its validity to measure sleep quality in clinical populations with fragmented sleep or in situations where the sleep-wake cycle is challenged, such as jet lag and shift work. Citation: Paquet J; Kawinska A; Carrier J. Wake detection capacity of actigraphy during sleep. SLEEP 2007;30(10):1362-1369 PMID:17969470
Wake measurements around operating wind turbines
Baker, R.W.; Katen, P.C.; Walker, S.N.
Researchers at Oregon State University have conducted wind measurement programs to describe the wake behind large horizontal axis turbines at Goodnoe Hills, Washington, (MOD-2), and behind the FloWind vertical axis wind turbine near Ellenburg, Washington. Wake measurements were taken using portable kite anemometers as well as fixed place anemometers under several atmospheric stability conditions and turbine operating conditions. Centerline hub height (midrotor) measurements were taken downwind and crosswind from 3-9 diameters. These wake programs are discussed and the velocity deficits measured are compared to the estimated deficits calculated from wake models.
The 3-D wake measurements near a hovering rotor for determining profile and induced drag
NASA Technical Reports Server (NTRS)
Mcalister, K. W.; Schuler, C. A.; Branum, L.; Wu, J. C.
Primarily an experimental effort, this study focuses on the velocity and vorticity fields in the near wake of a hovering rotor. Drag terminology is reviewed, and the theory for separately determining the profile-and-induced-drag components from wake quantities is introduced. Instantaneous visualizations of the flow field are used to center the laser velocimeter (LV) measurements on the vortex core and to assess the extent of the positional mandering of the trailing vortex. Velocity profiles obtained at different rotor speeds and distances behind the rotor blade clearly indicate the position, size, and rate of movement of the wake sheet and the core of the trailing vortex. The results also show the distribution of vorticity along the wake sheet and within the trailing vortex.
Histaminergic Control of Sleep-Wake Cycles: Recent Therapeutic Advances for Sleep and Wake Disorders
A. J. Barbier; M. J. Bradbury
The role of histaminergic neurotransmission in the promotion of waking has been extensively studied in pre- clinical species. Appreciation for the role of histamine continues to expand with increasing understanding of the interac- tion of histamine within the broad network of neuromodulators that regulate sleep and wake. The effects of histamine on waking are transduced through the H1 and the
Comparison of Wake Model Simulations with Offshore Wind Turbine Wake Profiles Measured by Sodar
Pryor, Sara C.
Comparison of Wake Model Simulations with Offshore Wind Turbine Wake Profiles Measured by Sodar R of most of the commonly used models for predicting wind speed decrease (wake) downstream of a wind turbine between 1.7 and 7.4 rotor diameters downstream of the wind turbine. Evaluation of the models compares
Trapping, compression, and acceleration of an electron beam by the laser wake wave
A. G. Khachatryan
The scheme of laser wake-field acceleration in plasma is proposed and considered for the case where a relatively rare nonrelativistic\\u000a or weakly relativistic electron beam is initially situated ahead of the intense laser pulse. It is shown that an electron\\u000a beam is trapped in the region of the first accelerating wake maximum; then it is strongly compressed and accelerated to
Effects of Solar Wind Conditions on the Plasma Wake Within a Polar Crater: Preliminary Results
NASA Technical Reports Server (NTRS)
Zimmerman, M. I.; Farrell, W. M.; Stubbs, T. J.
As the solar wind sweeps horizontally past a shadowed lunar crater it simultaneously diffuses toward the surface through an ambipolar process, forming a plasma wake (e.g., Figure 1). Importantly, the resulting electric field structure diverts solar wind protons toward the cold crater floor where they may represent a source of surficial hydrogen. We present a handful of two-dimensional kinetic simulations exploring the range of wake structures and surface particle fluxes possible under various background plasma conditions.
Inertial Motions and Mixing in the Wake of Typhoon Fanapi
NASA Astrophysics Data System (ADS)
Rainville, L.; Lee, C. M.; St Laurent, L.; Jayne, S. R.
Typhoon Fanapi (September 2010) generated an intense cold wake and a large upper ocean inertial response as it transited the Western Pacific. Ship- and glider-based surveys captured the upper ocean evolution beginning only a few days after the Fanapi's passage, providing measurements used to quantify the spatial scale and decay time of the inertial response. The near-inertial internal wave field transitioned from well-defined, downward propagating wave packets in the first week, to a field composed of mostly low modes with smaller vertical shear and larger spatial coherence 10 days later. In addition, micro-temperature sensors integrated onto the Seagliders collected hundred of profiles of turbulent rates of dissipation in the upper ocean, allowing us to link the time series of mixing at the base of the cold wake to the inertial motions.
Collisionless Damping of Laser Wakes in Plasma Channels
Li, X.; Shvets, G.
Excitation of accelerating modes in transversely inhomogeneous plasma channels is considered as an initial value problem. Discrete eigenmodes are supported by plasma channels with sharp density gradients. These eigenmodes are collisionlessly damped as the gradients are smoothed. Using collisionless Landau damping as the analogy, the existence and damping of these "quasi-modes" is studied by constructing and analytically continuing the causal Green's function of wake excitation into the lower half of the complex frequency plane. Electromagnetic nature of the plasma wakes in the channel makes their excitation nonlocal. This results in the algebraic decay of the fields with time due to phase-mixing of plasma oscillations with spatially-varying fequencies. Characteristic decay rate is given by the mixing time, which corresponds to the dephasing of two plasma fluid elements separated by the collisionless skin depth. For wide channels the exact expressions for the field evolution are derived. Implications for electron acceleration in plasma channels are discussed.
Jay L. Hirshfield
Experimental results are reported for test beam acceleration and deflection in a two-channel, cm-scale, rectangular dielectric-lined wakefield accelerator structure energized by a 14-MeV drive beam. The dominant waveguide mode of the structure is at {approx}30 GHz, and the structure is configured to exhibit a high transformer ratio ({approx}12:1). Accelerated bunches in the narrow secondary channel of the structure are continuously energized via Cherenkov radiation that is emitted by a drive bunch moving in the wider primary channel. Observed energy gains and losses, transverse deflections, and changes in the test bunch charge distribution compare favorably with predictions of theory.
Pluto's plasma wake oriented away from the ecliptic plane
NASA Astrophysics Data System (ADS)
P�rez-de-Tejada, H.; Durand-Manterola, H.; Reyes-Ruiz, M.; Lundin, R.
Conditions similar to those observed in the solar wind interaction with Venus and Mars where there is a planetary atmosphere in the absence of a global intrinsic magnetic field may also be applicable to Pluto. With up to 24 ?bars inferred for the Pluto atmosphere it is possible that the feeble solar photon radiation flux that reaches by its orbit, equivalent to ?10-3 that at Earth, is sufficient to produce an ionization component that can be eroded by the solar wind. In view of the reduced solar wind density (?10-3 with respect to that at 1 AU) that should be available by Pluto its total kinetic energy will be significantly smaller than that at Earth. However, the parameter values that are implied for the interaction process between the solar wind and the local upper ionosphere are sufficient to produce a plasma wake that should extend downstream from Pluto. In view of its low gravity force the plasma wake should have a wider cross-section than that in the Venus and Mars plasma environment. Since Pluto rotates with the axis tilted ?30� away from the ecliptic plane the plasma wake will be influenced by a Magnus force that has a large component is the north-south solar polar direction. That force will be responsible for propelling the plasma wake with a component that can be directed away from that plane. It is estimated that transport of solar wind momentum to the upper Pluto's ionosphere implies rotation periods smaller than that of the solid body, and thus large values of the Magnus force that can increase the orientation of the plasma wake away from the ecliptic plane.
Pluto's Plasma Wake Oriented Away from the Ecliptic Plane
NASA Astrophysics Data System (ADS)
Perez De Tejada, H. A.; Durand-Manterola, H.; Lundin, R. N.; Reyes-Ruiz, M.
Conditions similar to those observed in the solar wind interaction with Venus and Mars with a planetary atmosphere and in the absence of an intrinsic magnetic field should also be applicable to Pluto. With up to 24 ?bars inferred for the Pluto atmosphere it is possible that the feeble solar photon radiation flux that reaches by its orbit, equivalent to ~10-3 of that at earth, is sufficient to produce an ionization component that can be eroded by the solar wind. In view of the reduced solar wind density (~ 10-3 with respect to that by 1 AU) that should be available by Pluto its kinetic energy will be significantly smaller than that by earth. However, the parameter values that are implied for the interaction process between the solar wind and the local upper ionosphere are sufficient to produce a plasma wake that should extend downstream from Pluto. In view of its low gravity force the plasma wake should have a wider cross-section than that in the Venus and Mars plasma environment. Since Pluto rotates with its rotational axis tilted close to its orbital plane the plasma wake will be influenced by a Magnus force that is nearly north-south oriented. That force will be responsible for propelling the plasma wake with a component that can be directed away from the ecliptic plane. It is estimated that transport of solar wind momentum to the upper Pluto's ionosphere implies rotation periods smaller than that of the solid body, and thus larger values of the Magnus force that can increase the orientation of the plasma wake away from the ecliptic plane.
The Effect of Wake Passing on Turbine Blade Film Cooling
NASA Technical Reports Server (NTRS)
Heidmann, James David
The effect of upstream blade row wake passing on the showerhead film cooling performance of a downstream turbine blade has been investigated through a combination of experimental and computational studies. The experiments were performed in a steady-flow annular turbine cascade facility equipped with an upstream rotating row of cylindrical rods to produce a periodic wake field similar to that found in an actual turbine. Spanwise, chordwise, and temporal resolution of the blade surface temperature were achieved through the use of an array of nickel thin-film surface gauges covering one unit cell of showerhead film hole pattern. Film effectiveness and Nusselt number values were determined for a test matrix of various injectants, injectant blowing ratios, and wake Strouhal numbers. Results indicated a demonstratable reduction in film effectiveness with increasing Strouhal number, as well as the expected increase in film effectiveness with blowing ratio. An equation was developed to correlate the span-average film effectiveness data. The primary effect of wake unsteadiness was found to be correlated well by a chordwise-constant decrement of 0.094-St. Measurable spanwise film effectiveness variations were found near the showerhead region, but meaningful unsteady variations and downstream spanwise variations were not found. Nusselt numbers were less sensitive to wake and injection changes. Computations were performed using a three-dimensional turbulent Navier-Stokes code which was modified to model wake passing and film cooling. Unsteady computations were found to agree well with steady computations provided the proper time-average blowing ratio and pressure/suction surface flow split are matched. The remaining differences were isolated to be due to the enhanced mixing in the unsteady solution caused by the wake sweeping normally on the pressure surface. Steady computations were found to be in excellent agreement with experimental Nusselt numbers, but to overpredict experimental film effectiveness values. This is likely due to the inability to match actual hole exit velocity profiles and the absence of a credible turbulence model for film cooling.
The effect of wake passing on turbine blade film cooling
NASA Astrophysics Data System (ADS)
Heidmann, James David
The effect of upstream blade row wake passing on the showerhead film cooling performance of a downstream turbine blade has been investigated through a combination of experimental and computational studies. The experiments were performed in a steady-flow annular turbine cascade facility equipped with an upstream rotating row of cylindrical rods to produce a periodic wake field similar to that found in an actual turbine. Spanwise, chordwise, and temporal resolution of the blade surface temperature were achieved through the use of an array of nickel thin-film surface gauges covering one unit cell of showerhead film hole pattern. Film effectiveness and Nusselt number values were determined for a test matrix of various injectants, injectant blowing ratios, and wake Strouhal numbers. Results indicated a demonstrable reduction in film effectiveness with increasing Strouhal number, as well as the expected increase in film effectiveness with blowing ratio. An equation was developed to correlate the span-average film effectiveness data. The primary effect of wake unsteadiness was found to be correlated well by a chordwise-constant decrement of 0.094*St. Measurable spanwise film effectiveness variations were found near the showerhead region, but meaningful unsteady variations and downstream spanwise variations were not found. Nusselt numbers were less sensitive to wake and injection changes. Computations were performed using a three-dimensional turbulent Navier-Stokes code which was modified to model wake passing and film cooling. Unsteady computations were found to agree well with steady computations provided the proper time-average blowing ratio and pressure/suction surface flow split are matched. The remaining differences were isolated to be due to the enhanced mixing in the unsteady solution caused by the wake sweeping normally on the pressure surface. Steady computations were found to be in excellent agreement with experimental Nusselt numbers, but to overpredict experimental film effectiveness values. This is likely due to the inability to match actual hole exit velocity profiles and the absence of a credible turbulence model for film cooling.
Application of Three-Component PIV to a Hovering Rotor Wake
NASA Technical Reports Server (NTRS)
Yamauchi, Gloria K.; Lourenco, Luiz; Heineck, James T.; Wadcock, Alan J.; Abrego, Anita I.; Aiken, Edwin W. (Technical Monitor)
The key to accurate predictions of rotorcraft aerodynamics, acoustics, and dynamics lies in the accurate representation of the rotor wake. The vortical wake computed by rotorcraft CFD analyses typically suffer from numerical dissipation before the first blade passage. With some a priori knowledge of the wake trajectory, grid points can be concentrated along the trajectory to minimize the dissipation. Comprehensive rotorcraft analyses based on lifting-line theory rely on classical vortex models and/or semi-empirical information about the tip vortex structure. Until the location, size, and strength of the trailed tip vortex can be measured over a range of wake ages, the analyses will continue to be adjusted on a trial and error basis in order to correctly predict blade airloads, acoustics, dynamics, and performance. Using the laser light sheet technique, tip vortex location can be acquired in a straightforward manner. Measuring wake velocities and vortex core size, however, has been difficult and tedious using point-measurement techniques such as laser velocimetry. Recently, the Particle Image Velocimetry (PIV) technique has proven to be an efficient method for acquiring velocity measurements over relatively large areas and volumes of a rotor wake. The work reported to date, however, has been restricted to 2-component velocity measurements of the rotor wake. Three-component velocity measurements of a hovering rotor wake were acquired at NASA Ames Research Center in May 1999. This experiment represents a major step toward understanding the detailed structure of a rotor wake. This paper will focus primarily on the experimental technique used in acquiring this data. The accuracy and limitations of the current technique will also be discussed. Representative velocity field measurements will be included.
Site Suitability Assessment with Dynamic Wake Meandering Model. A Certification Point of View.
NASA Astrophysics Data System (ADS)
Tomas Bayo, Ricard; Parro, Gema
Establishment of large wind farms requires enormous investments putting steadily greater emphasis on optimal topology design and control of these. This requires not only an optimization of the power output, but also the development of strategies to cope with the higher loading expected. The cornerstone of such strategies is a realistic characterization and modelling of the wake flow field inside the wind farm, beyond Frandsen's equivalent turbulence method. Whereas Frandsen model has been mostly considered in the industry so far, it has not proved completely satisfactory when facing current problems such as wake effects on turbines placed at short distances or consequences of half wake for turbine loading. The objective of the present work is to address these questions from a certification point of view within the framework of Risoe's Dynamic Wake Meandering (DWM) model. The DWM model is based on the combination of three parts: modeling of quasi-steady wake deficits, a stochastic model of the downwind wake meandering and an added or self-generated wake turbulence. The analysis carried out is two-fold: First, a comparative study of the wake effects generated in Frandsen model as well as in various realizations of the DWM model is performed. For this purpose wake-induced loads are calculated using two different aeroelastic codes: HAWC2 and Bladed. Second, the applicability of DWM for the assessment of wind turbines under site-specific conditions is discussed and the conclusions summarized in a Recommended Practice. Clear prescriptions are thereby provided for the use of DWMM for site suitability assessments, including the aforementioned extreme situations, along with the interpretation of the future version of the IEC 61400-1 standards.
Neurobiology of Sleep-Wake Control
Yong-Won Cho
The regulations of sleep-wake cycle is complicated and many neurochemicals are involved. It is the consequence of an active process requiring appropriate interactions ofbrainstem and the cerebral system. The homeostatic drive and circadian factors are major controls in this regulation. The reticular activation system is a wake promoting area and the neurons in pons and preoptic areas are involved in
Neuropeptidergic control of sleep and wakefulness.
Richter, Constance; Woods, Ian G; Schier, Alexander F
Sleep and wake are fundamental behavioral states whose molecular regulation remains mysterious. Brain states and body functions change dramatically between sleep and wake, are regulated by circadian and homeostatic processes, and depend on the nutritional and emotional condition of the animal. Sleep-wake transitions require the coordination of several brain regions and engage multiple neurochemical systems, including neuropeptides. Neuropeptides serve two main functions in sleep-wake regulation. First, they represent physiological states such as energy level or stress in response to environmental and internal stimuli. Second, neuropeptides excite or inhibit their target neurons to induce, stabilize, or switch between sleep-wake states. Thus, neuropeptides integrate physiological subsystems such as circadian time, previous neuron usage, energy homeostasis, and stress and growth status to generate appropriate sleep-wake behaviors. We review the roles of more than 20 neuropeptides in sleep and wake to lay the foundation for future studies uncovering the mechanisms that underlie the initiation, maintenance, and exit of sleep and wake states. PMID:25032501
C. Presser; J. C. Yang
\\u000a Water sprinkler sprays (with relatively large droplet sizes) in residential and commercial structures are probably the most\\u000a well-known application of sprays in fire suppression. In more recent years, water mists (characterized by reduced droplet\\u000a sizes, which may contain additives) have been considered as a replacement for Halon 1301, the most common fire suppressant\\u000a chemical aboard aircraft and ships, but banned
Study for prediction of rotor/wake/fuselage interference. Part 2: Program users guide
NASA Technical Reports Server (NTRS)
Clark, D. R.; Maskew, B.
A method was developed which permits the fully coupled calculation of fuselage and rotor airloads for typical helicopter configurations in forward flight. To do this, an iterative solution is carried out based on a conventional panel representation of the fuselage and a blade element representation of the rotor where fuselage and rotor singularity strengths are determined simultaneously at each step and the rotor wake is allowed to relax (deform) in response to changes in rotor wake loading and fuselage presence. On completion of the iteration, rotor loading and inflow, fuselage singularity strength (and, hence, pressure and velocity distributions) and rotor wake are all consistent. The results of a fully coupled calculation of the flow around representative helicopter configurations are presented. The effect of fuselage components on the rotor flow field and the overall wake structure is discussed as well as the aerodynamic interference between the different parts of the aircraft. Details of the computer program are given.
Are the wake angles of a duck and a ship really the same?
NASA Astrophysics Data System (ADS)
Rabaud, Marc; Moisy, Frederic
The wake of a disturbance moving at the water surface, like a ship or a duck, owes its shape to the dispersive property of surface gravity waves. According to Kelvin's theory, it is widely accepted, and sometimes observed, that the wake angle is independent of the disturbance velocity, and given by sin-1 (1 / 3) = 19 . 4 degrees. However, field observations often show much smaller angles for fast ships, down to 5 - 10 degrees. The angle of these narrow wakes is actually found to decrease as the inverse of the disturbance velocity, similarly to the Mach cone of a supersonic disturbance in a non-dispersive medium. We propose here a simple model for this transition from a Kelvin regime (at low Froude number) to a Mach regime (at large Froude number) -- where the Froude number is based on the disturbance length. This model is confirmed by numerical simulations, reproducing the variety of wake patterns observed for disturbances of various size and velocity.
The Effect of Upstream Vane Wakes on Annular Diffuser Flows
NASA Astrophysics Data System (ADS)
Cherry, Erica; Padilla, Angelina; Elkins, Christopher; Eaton, John
Experiments were performed to determine the sensitivity to inlet conditions of the flow in two annular diffusers. One of the diffusers was a conservative design typical of a diffuser directly upstream of the combustor in a jet engine. The other had the same length and inlet shape as the first diffuser but a larger area ratio and was meant to operate on the verge of separation. Each diffuser was connected to two different inlets, one containing a fully-developed channel flow, the other containing wakes from a row of airfoils. Three-component velocity measurements were taken on the flow in each inlet/diffuser combination using Magnetic Resonance Velocimetry. Results will be presented on the 3D velocity fields in the two diffusers and the effect of the airfoil wakes on separation and secondary flows.
NASA Astrophysics Data System (ADS)
Herczynski, Andrzej; Weidman, Patrick D.; Burde, Georgy I.
Similarity solutions for laminar two-fluid jets and wakes are derived in the boundary-layer approximation. Planar and axisymmetric fan jets as well as classical and momentumless planar wakes are considered. The interface between the immiscible fluids is stabilized by the action of gravity, with the heavier fluid, taken to be a liquid, placed beneath the lighter fluid. Velocity profiles for the jets and the classical wake depend intimately, but differently, on the parameter ?=?1?1/?2?2, where ?i and ?i are, respectively, the density and absolute viscosity of the fluid in the upper (i=1) and lower (i=2) fluid domains, while the momentumless wake profile depends on the parameter ?=?1?23/?2?13. Generally, all interfaces deflect from horizontal except the fan jet. However, while the interface for the classical planar two-fluid wake is never flat, the interfaces for the planar jet and the momentumless wake become flat in the particular case ?1=?2. Velocity profiles illustrating the strongly asymmetrical jet and wake profiles that arise in air-over-water, oil-over-water, and air-over-oil flows are presented.
Large HAWT wake measurement and analysis
NASA Technical Reports Server (NTRS)
Miller, A. H.; Wegley, H. L.; Buck, J. W.
From the theoretical fluid dynamics point of view, the wake region of a large horizontal-axis wind turbine has been defined and described, and numerical models of wake behavior have been developed. Wind tunnel studies of single turbine wakes and turbine array wakes have been used to verify the theory and further refine the numerical models. However, the effects of scaling, rotor solidity, and topography on wake behavior are questions that remain unanswered. In the wind tunnel studies, turbines were represented by anything from scaled models to tea strainers or wire mesh disks whose solidity was equivalent to that of a typical wind turbine. The scale factor compensation for the difference in Reynolds number between the scale model and an actual turbine is complex, and not typically accounted for. Though it is wise to study the simpler case of wakes in flat topography, which can be easily duplicated in the wind tunnel, current indications are that wind turbine farm development is actually occurring in somewhat more complex terrain. Empirical wake studies using large horizontal-axis wind turbines have not been thoroughly composited, and, therefore, the results have not been applied to the well-developed theory of wake structure. The measurement programs have made use of both in situ sensor systems, such as instrumented towers, and remote sensors, such as kites and tethered, balloonborne anemometers. We present a concise overview of the work that has been performed, including our own, which is based on the philosophy that the MOD-2 turbines are probably their own best detector of both the momentum deficit and the induced turbulence effect downwind. Only the momentum deficit aspects of the wake/machine interactions have been addressed. Both turbine power output deficits and wind energy deficits as measured by the onsite meteorological towers have been analyzed from a composite data set. The analysis has also evidenced certain topographic influences on the operation of spatially diverse wind turbines.
Review of CFD for wind-turbine wake aerodynamics
B. Sanderse; Pijl van der S. P; B. Koren
This article reviews the state of the art of the numerical calculation of wind-turbine wake aerodynamics. Different CFD techniques for modeling the rotor and the wake are discussed. Regarding rotor modeling, recent advances in the generalized actuator approach and the direct model are discussed, as far as it attributes to the wake description. For the wake, the focus is on
Multi-Point Velocity Correlations in the Wake of a Three-Dimensional Bluff Body
NASA Astrophysics Data System (ADS)
Shea, Patrick; Glauser, Mark
Three-dimensional bluff-bodies known as turrets are commonly used for housing optical systems on airborne platforms. These geometries generate highly turbulent wakes that decrease the performance of the optical systems and the aircraft. The current experimental study used dynamic suction in both open and closed-loop control configurations to actively control the wake turret. The experiments were carried out at a Reynolds number of 5 � 105, and the flow field was characterized using stereoscopic PIV measurements acquired in the wake of the turret. These data were processed using traditional single-point statistics which showed that the active control system was able to significantly alter the wake of the turret. Using multi-point correlations, turbulent characteristics such as the integral length scale can be calculated. For the turret wake, estimates of the integral length scales were found to be highly dependent upon the region of the flow that was evaluated, especially when comparing the shear layers to the center of the wake. With the application of the active control, the integral length scales were generally found to increase.
Analysis of long distance wakes behind a row of turbines - a parameter study
NASA Astrophysics Data System (ADS)
Eriksson, O.; Nilsson, K.; Breton, S.-P.; Ivanell, S.
Large Eddy Simulations (LES) of the long distance wake behind a row of 10 turbines are conducted to predict wake recovery. The Navier-Stokes solver EllipSys3D is used in combination with the actuator disc concept. Neutral atmospheric conditions are assumed in combination with synthetic turbulence using the Mann method. Both the wind shear profile and turbulence are introduced into the flow field using body forces. Previous simulations using the same simulation method to model the Horns Rev wind farm showed a higher wake recovery at long distances compared to measurements. The current study investigates further the sensitivity to parameters such as the grid resolution, Reynolds number, the turbulence characteristics as well as the impact of using different internal turbine spacings. The clearest impact on the recovery behind the farm could be seen from the turbulence intensity of the incoming flow. The impact of the wind shear on the turbulence intensity in the domain needs further studies. A lower turbulence level gives slower wake recovery as expected. A slower wake recovery can also be seen for a higher grid resolution. The Reynolds number, apart from when using a very low value, has a small impact on the result. The variation of the internal spacing is seen to have a relatively minor impact on the farm wake recovery.
Hippocampal corticosterone impairs memory consolidation during sleep but improves consolidation in the wake state
Kelemen, Eduard; Bahrendt, Marie; Born, Jan; Inostroza, Marion
We studied the interaction between glucocorticoid (GC) level and sleep/wake state during memory consolidation. Recent research has accumulated evidence that sleep supports memory consolidation in a unique physiological process, qualitatively distinct from consolidation occurring during wakefulness. This appears particularly true for memories that rely on the hippocampus, a region with abundant expression of GC receptors. Against this backdrop we hypothesized that GC effects on consolidation depend on the brain state, i.e., sleep and wakefulness. Following exploration of two objects in an open field, during 80 min retention periods rats received an intrahippocampal infusion of corticosterone (10 ng) or vehicle while asleep or awake. Then the memory was tested in the hippocampus-dependent object-place recognition paradigm. GCs impaired memory consolidation when administered during sleep but improved consolidation during the wake retention interval. Intrahippocampal infusion of GC or sleep/wake manipulations did not alter novel-object recognition performance that does not require the hippocampus. This work corroborates the notion of distinct consolidation processes occurring in sleep and wakefulnesss, and identifies GCs as a key player controlling distinct hippocampal memory consolidation processes in sleep and wake conditions. � 2014 Wiley Periodicals, Inc. PMID:24596244
Visualization of airflow in the wake of a ship superstructure
NASA Astrophysics Data System (ADS)
Brownell, C. J.; Stillman, W. P.; Golden, J. H.; Simpson, S. A.; Luznik, L.; Miklosovic, D. S.; White, G.; Burks, J. S.; Snyder, M. R.
Helicopter landings on naval surface ships, such as cruisers and destroyers, must take place in the presence of an air wake created by flow over the ship superstructure. Wake turbulence over the flight deck makes piloted landings dangerous and difficult, and poses significant problems for the use of unmanned rotorcraft. To address this problem, a comprehensive set of experimental and simulation data are being collected via concurrent field tests, wind tunnel measurements, and CFD simulations. These data will facilitate an understanding of the wake turbulence produced under a variety of weather conditions, and will allow assessment of the fidelity of lower order flowfield estimates. A U.S. Navy Auxiliary Patrol (YP) Craft is used as a representative ship platform. The YP is over 100 ft long, has a similar shape to a modern destroyer, and has been modified to include a flight deck and hangar-like superstructure. Presented here are preliminary CFD results along with results from a large-scale flow visualization experiment. Qualitative information gleaned from the flow visualization is being used in the experimental design of upcoming quantitative air velocity measurements.
Wake-up effects in Si-doped hafnium oxide ferroelectric thin films
Zhou, Dayu, E-mail: firstname.lastname@example.com [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China) [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Key Laboratory for Materials Modification by Laser, Ion and Electron Beams, Ministry of Education, Dalian University of Technology, Dalian 116024 (China); State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China); Xu, Jin [Department of Electronic Engineering, Dalian Neusoft University of Information, Dalian 116023 (China)] [Department of Electronic Engineering, Dalian Neusoft University of Information, Dalian 116023 (China); Li, Qing; Guan, Yan [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China)] [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Cao, Fei; Dong, Xianlin [Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China)] [Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); M�ller, Johannes [Fraunhofer IPMS-CNT, Koengisbruecker Strasse 180, 01109 Dresden (Germany)] [Fraunhofer IPMS-CNT, Koengisbruecker Strasse 180, 01109 Dresden (Germany); Schenk, Tony; Schr�der, Uwe [Namlab gGmbH/TU Dresden, Noethnitzer Strasse 64, 01187 Dresden (Germany)] [Namlab gGmbH/TU Dresden, Noethnitzer Strasse 64, 01187 Dresden (Germany)
Hafnium oxide based ferroelectric thin films have shown potential as a promising alternative material for non-volatile memory applications. This work reports the switching stability of a Si-doped HfO{sub 2} film under bipolar pulsed-field operation. High field cycling causes a �wake-up� in virgin �pinched� polarization hysteresis loops, demonstrated by an enhancement in remanent polarization and a shift of negative coercive voltage. The rate of wake-up is accelerated by either reducing the frequency or increasing the amplitude of the cycling field. We suggest de-pinning of domains due to reduction of the defect concentration at bottom electrode interface as origin of the wake-up.
Characterizing Wake Turbulence with Staring Lidar Measurements
NASA Astrophysics Data System (ADS)
Bastine, D.; W�chter, M.; Peinke, J.; Trabucchi, D.; K�hn, M.
Lidar measurements in the German offshore wind farm Alpha Ventus were performed to investigate the turbulence characteristics of wind turbine wakes. In particular, we compare measurements of the free flow in the surroundings of the wind turbines with measurements in the inner region of a wake flow behind one turbine. Our results indicate that wind turbines modulate the turbulent structures of the flow on a wide range of scales. For the data of the wake flow, the power spectrum as well as the multifractal intermittency coefficient reveal features of homogeneous isotropic turbulence. Thus, we conjecture that on scales of the rotor a new turbulent cascade is initiated, which determines the features of the turbulent wake flow quite independently from the more complex wind flow in the surroundings of the turbine.
Secure Wake-Up Scheme for WBANs
NASA Astrophysics Data System (ADS)
Liu, Jing-Wei; Ameen, Moshaddique Al; Kwak, Kyung-Sup
Network life time and hence device life time is one of the fundamental metrics in wireless body area networks (WBAN). To prolong it, especially those of implanted sensors, each node must conserve its energy as much as possible. While a variety of wake-up/sleep mechanisms have been proposed, the wake-up radio potentially serves as a vehicle to introduce vulnerabilities and attacks to WBAN, eventually resulting in its malfunctions. In this paper, we propose a novel secure wake-up scheme, in which a wake-up authentication code (WAC) is employed to ensure that a BAN Node (BN) is woken up by the correct BAN Network Controller (BNC) rather than unintended users or malicious attackers. The scheme is thus particularly implemented by a two-radio architecture. We show that our scheme provides higher security while consuming less energy than the existing schemes.
Review of Idealized Aircraft Wake Vortex Models
NASA Technical Reports Server (NTRS)
Ahmad, Nashat N.; Proctor, Fred H.; Duparcmeur, Fanny M. Limon; Jacob, Don
Properties of three aircraft wake vortex models, Lamb-Oseen, Burnham-Hallock, and Proctor are reviewed. These idealized models are often used to initialize the aircraft wake vortex pair in large eddy simulations and in wake encounter hazard models, as well as to define matched filters for processing lidar observations of aircraft wake vortices. Basic parameters for each vortex model, such as peak tangential velocity and circulation strength as a function of vortex core radius size, are examined. The models are also compared using different vortex characterizations, such as the vorticity magnitude. Results of Euler and large eddy simulations are presented. The application of vortex models in the postprocessing of lidar observations is discussed.
Analysis of vortex wake encounter upsets
NASA Technical Reports Server (NTRS)
Johnson, W. A.; Teper, G. L.
The problem of an airplane being upset by encountering the vortex wake of a large transport on takeoff or landing is currently receiving considerable attention. This report describes the technique and results of a study to assess the effectiveness of automatic control systems in alleviating vortex wake upsets. A six-degree-of-freedom nonlinear digital simulation was used for this purpose. The analysis included establishing the disturbance input due to penetrating a vortex wake from an arbitrary position and angle. Simulations were computed for both a general aviation airplane and a commercial jet transport. Dynamic responses were obtained for the penetrating aircraft with no augmentation, and with various command augmentation systems, as well as with human pilot control. The results of this preliminary study indicate that attitude command augmentation systems can provide significant alleviation of vortex wake upsets; and can do it better than a human pilot.
Sleep-wake abnormalities in narcolepsy.
Zorick, F; Roehrs, T; Wittig, R; Lamphere, J; Sicklesteel, J; Roth, T
To evaluate the degree to which sleep (REM vs. NREM) intrudes into wake and wake intrudes into sleep in narcolepsy, 103 patients with narcolepsy were compared to 105 patients with other diagnoses of disorders of excessive sleep (DOES). Narcoleptic patients had more frequent REM onsets on the multiple sleep latency test (MSLT) and nocturnal polysomnograms. But the MSLT latencies to REM versus NREM in narcoleptic patients did not differ. Nocturnal measures of REM pressure, percentage of REM, and REM latency excluding the REM onsets, did not differ among patient groups. With respect to the intrusion of wake into sleep, narcoleptic patients had more and longer awakenings compared with other DOES patients, but the distribution of wake into REM and NREM sleep did not differ among groups. These data suggest that narcolepsy is not exclusively a REM-related disorder, but involves an inability to sustain a specific neural state for periods comparable to those in normal subjects or other DOES patients. PMID:3704441
Three-Phased Wake Vortex Decay
NASA Technical Reports Server (NTRS)
Proctor, Fred H.; Ahmad, Nashat N.; Switzer, George S.; LimonDuparcmeur, Fanny M.
A detailed parametric study is conducted that examines vortex decay within turbulent and stratified atmospheres. The study uses a large eddy simulation model to simulate the out-of-ground effect behavior of wake vortices due to their interaction with atmospheric turbulence and thermal stratification. This paper presents results from a parametric investigation and suggests improvements for existing fast-time wake prediction models. This paper also describes a three-phased decay for wake vortices. The third phase is characterized by a relatively slow rate of circulation decay, and is associated with the ringvortex stage that occurs following vortex linking. The three-phased decay is most prevalent for wakes imbedded within environments having low-turbulence and near-neutral stratification.
A wake detector for wind farm control
NASA Astrophysics Data System (ADS)
Bottasso, C. L.; Cacciola, S.; Schreiber, J.
The paper describes an observer capable of detecting the impingement on a wind turbine rotor of the wake of an upstream machine. The observer estimates the local wind speed and turbulence intensity on the left and right parts of the rotor disk. The estimation is performed based on blade loads measured by strain gages or optical fibers, sensors which are becoming standard equipment on many modern machines. A lower wind speed and higher turbulence intensity on one part of the rotor, possibly in conjunction with other information, can then be used to infer the presence of a wake impinging on the disk. The wake state information is useful for wind plant control strategies, as for example wake deflection by active yawing. In addition, the local wind speed estimates may be used for a rough evaluation of the vertical wind shear.
NASA Wake Vortex Research for Aircraft Spacing
NASA Technical Reports Server (NTRS)
Perry, R. Brad; Hinton, David A.; Stuever, Robert A.
The National Aeronautics and Space Administration (NASA) is addressing airport capacity enhancements during instrument meteorological conditions through the Terminal Area Productivity (TAP) program. Within TAP, the Reduced Spacing Operations (RSO) subelement at the NASA Langley Research Center is developing an Aircraft Vortex Spacing System (AVOSS). AVOSS will integrate the output of several inter-related areas to produce weather dependent, dynamic wake vortex spacing criteria. These areas include current and predicted weather conditions, models of wake vortex transport and decay in these weather conditions, real-time feedback of wake vortex behavior from sensors, and operationally acceptable aircraft/wake interaction criteria. In today's ATC system, the AVOSS could inform ATC controllers when a fixed reduced separation becomes safe to apply to large and heavy aircraft categories. With appropriate integration into the Center/TRACON Automation System (CTAS), AVOSS dynamic spacing could be tailored to actual generator/follower aircraft pairs rather than a few broad aircraft categories.
Nanosecond pulsed electric fields act as a novel cellular stress that induces translational suppression accompanied by eIF2? phosphorylation and 4E-BP1 dephosphorylation.
Morotomi-Yano, Keiko; Oyadomari, Seiichi; Akiyama, Hidenori; Yano, Ken-ichi
Recent advances in electrical engineering enable the generation of ultrashort electric fields, namely nanosecond pulsed electric fields (nsPEFs). Contrary to conventional electric fields used for DNA electroporation, nsPEFs can directly reach intracellular components without membrane destruction. Although nsPEFs are now recognized as a unique tool in life sciences, the molecular mechanism of nsPEF action remains largely unclear. Here, we present evidence that nsPEFs act as a novel cellular stress. Exposure of HeLa S3 cells to nsPEFs quickly induced phosphorylation of eIF2?, activation of its upstream stress-responsive kinases, PERK and GCN2, and translational suppression. Experiments using PERK- and GCN2-knockout cells demonstrated dual contribution of PERK and GCN2 to nsPEF-induced eIF2? phosphorylation. Moreover, nsPEF exposure yielded the elevated GADD34 expression, which is known to downregulate the phosphorylated eIF2?. In addition, nsPEF exposure caused a rapid decrease in 4E-BP1 phosphorylation irrespective of the PERK/GCN2 status, suggesting participation of both eIF2? and 4E-BP1 in nsPEF-induced translational suppression. RT-PCR analysis of stress-inducible genes demonstrated that cellular responses to nsPEFs are distinct from those induced by previously known forms of cellular stress. These results provide new mechanistic insights into nsPEF action and implicate the therapeutic potential of nsPEFs for stress response-associated diseases. PMID:22652449
Coupling of a free wake vortex ring near-wake model with the Jensen and Larsen far-wake deficit models
NASA Astrophysics Data System (ADS)
van Heemst, J. W.; Baldacchino, D.; Mehta, D.; van Bussel, G. J. W.
This paper presents a simple physical model to improve the currently used far-wake deficit models in the wind industry. The main improvement is deemed on the determination of the wake deficit in the near-wake. A Vortex Ring Model (VRM) is used to calculate the induced velocities in the near-wake, which are then coupled to the Jensen far-wake model and the Larsen far-wake model based on the concept of Eddy Viscosity (EV). The inviscid near-wake VRM is based on the shedding of discrete tip vortex rings released from a uniformly loaded actuator disc. The model is validated against wind tunnel measurements from experiments with a two- bladed turbine and a circular metal mesh with a uniform porosity to represent an actuator disc. The VRM shows a good agreement with the experimental data with respect to the wake deficit evolution. The VRM is coupled with two well-known engineering type far-wake models: the Jensen and Larsen wake deficit models. The results of the coupling of the VRM and the more elaborated Larsen far-wake model are compared against a 3D Large Eddy Simulation (LES) CFD model. This comparison shows the effect of different near-wake models on the development of centreline velocities in the far-wake. The centreline velocity deficit predicted by the VRM-Larsen model more closely matches LES calculations in comparison with the reference Larsen model.
Wake-Vortex Hazards During Cruise
NASA Technical Reports Server (NTRS)
Rossow, Vernon J.; James, Kevin D.; Nixon, David (Technical Monitor)
Even though the hazard posed by lift-generated wakes of subsonic transport aircraft has been studied extensively for approach and departure at airports, only a small amount of effort has gone into the potential hazard at cruise altitude. This paper reports on a studio of the wake-vortex hazard during cruise because encounters may become more prevalent when free-flight becomes available and each aircraft, is free to choose its own route between destinations. In order to address the problem, the various fluid-dynamic stages that vortex wakes usually go through as they age will be described along with estimates of the potential hazard that each stage poses. It appears that a rolling-moment hazard can be just as severe at cruise as for approach at airports, but it only persists for several minutes. However, the hazard posed by the downwash in the wake due to the lift on the generator aircraft persists for tens of minutes in a long narrow region behind the generating aircraft. The hazard consists of severe vertical loads when an encountering aircraft crosses the wake. A technique for avoiding vortex wakes at cruise altitude will be described. To date the hazard posed by lift-generated vortex wakes and their persistence at cruise altitudes has been identified and subdivided into several tasks. Analyses of the loads to be encounter and are underway and should be completed shortly. A review of published literature on the subject has been nearly completed (see text) and photographs of vortex wakes at cruise altitudes have been taken and the various stages of decay have been identified. It remains to study and sort the photographs for those that best illustrate the various stages of decay after they are shed by subsonic transport aircraft at cruise altitudes. The present status of the analysis and the paper are described.
Experimental investigation of a stratified buoyant wake�
Kraft, Wayne Neal
, v?rms, in the wake of a cylinder with stable buoyancy (triangles), unstable buoyancy (squares), no buoyancy (circles), and a typical Rayleigh Taylor mixing layer for the same.... Decay of vertical velocity fluctuations, v?rms, in the very near wake of a cylinder with stable buoyancy, unstable buoyancy, and no buoyancy. .................36 12. Variation of the location of peak v?rms with mixing...
[Sleep-wake regulation by prostaglandin D2 and adenosine].
Nagata, Nanae; Urade, Yoshihiro
Prostaglandin (PG) D2 and adenosine are potent endogenous somnogens that accumulate in the brain during prolonged wakefulness. Lipocalin-type PGD synthase (L-PGDS) catalyzes the isomerization of PGH2, a common precursor of various prostanoids, to produce PGD2. L-PGDS is localized in the leptomeninges, choroid plexus, and oligodendrocytes of the central nervous system. PGD2 stimulates DP1 receptors localized in the basal forebrain and increases the local extracellular concentration of adenosine, a paracrine signaling molecule, to promote sleep. Adenosine activates adenosine A2A receptor-expressing neurons in the basal forebrain and ventrolateral preoptic area (VLPO) and inhibits adenosine A1 receptor-possessing arousal neurons. Sleep-promoting neurons in the VLPO send inhibitory signals to suppress the histaminergic neurons in the tuberomammillary nucleus (TMN); the histaminergic neurons contribute to arousal through histamine H1 receptors. GABAergic inhibition of TMN is involved in the induction of non-rapid eye movement (non-REM) sleep by PGD2 and adenosine A2A agonists. The neural network between the VLPO and TMN is considered to play a key role in regulation of vigilance states. Administering an L-PGD inhibitor (SeCl4), DP1 antagonist (ONO-4127Na), or adenosine A2A receptor antagonist (caffeine) suppresses both non-REM and REM sleep, indicating that the PGD2-adenosine system is crucial for maintaining physiological sleep. Selective gene-deletion strategies based on Cre/loxP technology and focal RNA interference have been used for silencing the expression of the A2A receptor by local infection with adeno-associated virus carrying Cre-recombinase or short hairpin RNA. The results of these studies have shown that the A2Asubreceptors in the shell region of the nucleus accumbens are responsible for the effect of caffeine on wakefulness. PMID:22647469
Force estimation and turbulence in the wake of a freely flying European Starling
NASA Astrophysics Data System (ADS)
Ben-Gida, Hadar; Kirchhefer, Adam; Kopp, Gregory; Gurka, Roi
Flapping wings are one of the most complex yet widespread propulsion method found in nature. Although aeronautical technology has advanced rapidly over the past 100 years, natural flyers, which have evolved over millions of years, still feature higher efficiency and represent one of nature's finest locomotion methods. One of the key questions is the role of the unsteady motion in the flow due to the wing flapping and its contribution to the forces acting on a bird during downstroke and upstroke. The wake of a freely flying European Starling is investigated as a case study of unsteady wing aerodynamics. Measurements of the near wake have been taken using long duration high-speed PIV in the wake behind a freely flying bird in a specially designed avian wind tunnel. The wake has been characterized by means of velocity and vorticity fields. The measured flow field is decomposed based on the wing position phases. Drag and lift have been estimated using the mean velocity deficit and the circulation at the wake region. In addition, kinematic analysis of the wing motion and the body has been performed using additional high-speed cameras that recorded the bird movement simultaneously with the PIV. Correlations between the wing kinematics and the flow field characteristics are presented as well as the time evolution of the velocity, vorticity and additional turbulence parameters.
Waking dreams and other metachoric experiences.
Green, C
This paper summarizes the development of the concept of metachoric experiences from 1961 onwards. The name of metachoric experience was given to one in which the whole of the environment was replaced by a hallucinatory one, although this may provide a precise replica of the physical world and appear to be completely continuous with normal experience. Prior to 1968 three types of metachoric experiences had been recognized; lucid dreams, out-of-the-body experiences (OBEs) and false awakenings, all of which showed interrelationships. The Institute's 1968 appeal for apparitional experiences led to a recognition that many of these were probably metachoric. This was suggested among other things by certain cases in which the lighting of the whole field of view changes, thus indicating that the experience was completely hallucinatory. The study of apparitions led also to the concept of waking dreams, i.e. completely hallucinatory experiences which may be initiated and terminated without any awareness of discontinuity on the part of the subject. These experiences seem to be capable of considerable apparent extension in time, thus providing a possible explanation of some reports of UFO sightings and of some of the more anomalous experiences of psychical research. In this connection the paper discusses the well-known Versailles experience of Miss Moberly and Miss Jourdain, and a published case of C.G. Jung. In conclusion some of the most obvious similarities and differences between the different types of metachoric experiences are discussed. PMID:2374788
Increase in the mitotic recombination frequency in Drosophila melanogaster by magnetic field exposure and its suppression by vitamin E supplement
Takao Koana; Mikie O Okada; Masateru Ikehata; Masayoshi Nakagawa
In order to estimate possible mutagenic and\\/or carcinogenic activity of electromagnetic fields, wing spot tests were performed in Drosophila melanogaster. A DNA repair defective mutation mei-41D5 was introduced into the conventional mwh\\/flr test system to enhance mutant spot frequency. Third instar larvae were exposed to a 5-Tesla static magnetic field for 24 h, and after molting, wings were examined under
Analysis of the Radar Reflectivity of Aircraft Vortex Wakes
NASA Technical Reports Server (NTRS)
Shariff, Karim; Wray, Alan; Yan, Jerry (Technical Monitor)
Radar has been proposed as a way to track wake vortices to reduce aircraft spacing and tests have revealed radar echoes from aircraft wakes in clear air. The results are always interpreted qualitatively using Tatarski's theory of weak scattering by isotropic atmospheric turbulence. The goal of the present work was to predict the value of the radar cross-section (RCS) using simpler models. This is accomplished in two steps. First, the refractive index is obtained. Since the structure of the aircraft wakes is different from atmospheric turbulence, three simple mechanisms specific to vortex wakes are considered: (1) Radial density gradient in a two-dimensional vortex, (2) three-dimensional fluctuations in the vortex cores, and (3) Adiabatic transport of the atmospheric fluid in a two-dimensional oval surrounding the pair of vortices. The index of refraction is obtained more precisely for the two-dimensional mechanisms than for the three-dimensional ones. In the second step, knowing the index of refraction, a scattering analysis is performed. Tatarski's weak scattering approximation is kept but the usual assumptions of a far-field and a uniform incident wave are dropped. Neither assumption is generally valid for a wake that is coherent across the radar beam. For analytical insight, a simpler approximation that invokes, in addition to weak scattering, the far-field and wide cylindrical beam assumptions, is also developed and compared with the more general analysis. The predicted RCS values for the oval surround the vortices (mechanism C) agree with the experiments of Bilson conducted over a wide range of frequencies. However, the predictions have a cut-off away from normal incidence which is not present in the measurements. Estimates suggest that this is due to turbulence in the baroclinic vorticity generated at the boundary of the oval. The reflectivity of a vortex itself (mechanism A) is comparable to that of the oval (mechanism C) but cuts-off at frequencies lower than those considered in all the experiments to date. The RCS of a vortex happens to peak at the frequency (about 49 MHz) where atmospheric radars (known as ST radars) operate and so the present prediction could be verified in the future. Finally , we suggest that hot engine exhaust could increase RCE by 40 db and reveal vortex circulation, provided its mixing with the surroundings is prevented in the laminarising flow of the vortices.
Evolution and breakdown of helical vortex wakes behind a wind turbine
NASA Astrophysics Data System (ADS)
Nemes, A.; Sherry, M.; Lo Jacono, D.; Blackburn, H. M.; Sheridan, J.
The wake behind a three-bladed Glauert model rotor in a water channel was investigated. Planar particle image velocimetry was used to measure the velocity fields on the wake centre-line, with snapshots phase-locked to blade position of the rotor. Phase- locked averages of the velocity and vorticity fields are shown, with tip vortex interaction and entanglement of the helical filaments elucidated. Proper orthogonal decomposition and topology-based vortex identification are used to filter the PIV images for coherent structures and locate vortex cores. Application of these methods to the instantaneous data reveals unsteady behaviour of the helical filaments that is statistically quantifiable.
Effect of velocity ratio on the streamwise vortex structures in the wake of a stack
NASA Astrophysics Data System (ADS)
Adaramola, M. S.; Sumner, D.; Bergstrom, D. J.
The time-averaged velocity and streamwise vorticity fields within the wake of a stack were investigated in a low-speed wind tunnel using a seven-hole pressure probe. The experiments were conducted at a Reynolds number, based on the stack external diameter, of ReD=2.3�104. The stack, of aspect ratio AR=9, was mounted normal to a ground plane and was partially immersed in a flat-plate turbulent boundary layer, where the ratio of the boundary layer thickness to the stack height was ?/H?0.5. The jet-to-cross-flow velocity ratio was varied from R=0 to 3, which covered the downwash, crosswind-dominated and jet-dominated flow regimes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip vortex pair located close to the free end of the stack, and the base vortex pair located close to the ground plane within the flat-plate boundary layer, were similar to those found in the wake of a finite circular cylinder, and were associated with the upwash and downwash flow fields within the stack wake, respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair had the same orientation as the base vortex pair and was associated with the jet rise. The peak vorticity and strength of the streamwise vortex structures were functions of the jet-to-cross-flow velocity ratio. For the tip vortex structures, their peak vorticity and strength reduced as the jet-to-cross-flow velocity ratio increased.
Efficacy and residues of phloxine B and uranine for the suppression of Mediterranean fruit fly in coffee fields.
Licudine, Jocelyn A; McQuate, Grant T; Cunningham, Roy T; Liquido, Nicanor J; Li, Qing X
The field efficacy of a bait containing phloxine B, uranine and Provesta 621 protein was tested against Mediterranean fruit fly (Ceratitis capitata; Medfly) by aerial and ground spraying in about 84 ha of coffee fields in Kauai, Hawaii, USA. Concurrently, soil and crop samples were collected from the aerially sprayed field and its unsprayed control field for residue studies. Efficacy of the sprays was assessed through trapping with both protein-baited and trimedlure-baited traps and through the infestation level of coffee cherries collected at least three-quarters ripe. The C capitata population was low at the start of the aerial and ground spray studies, but dramatically increased in the control fields. This increase coincided with initial ripening of coffee cherries. During times of peak population levels, C capitata populations were reduced by more than 91% in the ground-sprayed field and 99% in the aerial-sprayed field, relative to the populations in their respective control fields and based on protein-baited trap catches. Results of residue analyses indicated that uranine dissipated quickly compared with phloxine B on coffee and soil. Coffee samples collected at pre-spray periods had phloxine B residues of 7.2-25.5 ng g-1 on berries. Phloxine B concentrations were much higher on coffee leaves (163-1120 ng g-1). Lower concentrations of the dye were found from coffee samples collected during rainy days. Average phloxine B concentrations immediately after spraying were 56 and 2840 ng g-1 in coffee berries and leaves, respectively. Dissipation of phloxine B on berries was fast, with a half-life (t1/2) of 3 days. Dissipation of phloxine B on leaves was fitted to two linear phases: the initial (0-4 days) with a shorter t1/2 of 3 days and the later phase (4-28 days) with a longer t1/2 of 15 days. Average concentrations of phloxine B in the top soil ranged from 50 to 590 ng g-1 at pre-spray. Phloxine B initial concentration (770 ng g-1) reached a plateau immediately after the last spraying, but showed a steady decline over time with t1/2 of 16 days. Fast dissipation of the dyes in the field indicates that these chemicals may be environmentally compatible and therefore a promising alternative for fruit fly control. PMID:11838283
Thermoelectric effects in the field-suppressed superconducting state of quasi-one-dimensional Li0.9Mo6O17
NASA Astrophysics Data System (ADS)
Cohn, Joshua L.; Dos Santos, Carlos A. M.; Neumeier, John J.
We present resistivity, thermopower (S), and Nernst (?) measurements in the range 0 . 4 K <= T <= 20 K on single crystals of the quasi-one-dimensional (q1D) metal, Li0.9Mo6O17 (LiPB) along the q1D metallic chains. The low- T limits of S / T and ? / T , determined in the magnetic-field suppressed superconducting state (Tc = 2 K), indicate a very small Fermi temperature (TF ~ 30 K), contrary to expectations from prior work including photoemission. Possible insights from these results into the nature of the mysterious density-wave order, responsible for the upturn in resistivity below ~ 25 K will be discussed. Work supported by the U.S. Department of Energy Office of Basic Energy Sciences (DE-FG02-12ER46888, Univ. Miami), the National Science Foundation (DMR-0907036, Mont. St. Univ.), and in Lorena by the CNPq (308162/2013-7) and FAPESP (2009/54001-2).
Study and Suppression of the Microstructural Anisotropy Generated During the Consolidation of a Carbonyl Iron Powder by Field-Assisted Hot Pressing
NASA Astrophysics Data System (ADS)
Garc�a-Junceda, Andrea; Acebo, Laura; Torralba, Jos� Manuel
A spherical carbonyl iron powder was consolidated by the field-assisted hot pressing technique using graphite tools at two different temperatures, both above the austenitizing temperature. The microstructures obtained exhibited a compositional gradient in carbon along the consolidated material. Thus, the outer rim of the cylindrical samples was composed of cementite and pearlite that gradually turned to pearlite, leading to a fully ferritic microstructure at the core of the sample. The increase in the temperature has led to a higher introduction of carbon within the sample. The interposition of a thin tungsten foil between the graphite die/punches and the powders has significantly reduced the diffusion of the carbon through the iron matrix and has suppressed the microstructural anisotropy.
Study and Suppression of the Microstructural Anisotropy Generated During the Consolidation of a Carbonyl Iron Powder by Field-Assisted Hot Pressing
NASA Astrophysics Data System (ADS)
Garc�a-Junceda, Andrea; Acebo, Laura; Torralba, Jos� Manuel
A spherical carbonyl iron powder was consolidated by the field-assisted hot pressing technique using graphite tools at two different temperatures, both above the austenitizing temperature. The microstructures obtained exhibited a compositional gradient in carbon along the consolidated material. Thus, the outer rim of the cylindrical samples was composed of cementite and pearlite that gradually turned to pearlite, leading to a fully ferritic microstructure at the core of the sample. The increase in the temperature has led to a higher introduction of carbon within the sample. The interposition of a thin tungsten foil between the graphite die/punches and the powders has significantly reduced the diffusion of the carbon through the iron matrix and has suppressed the microstructural anisotropy.
Anderson lattice with explicit Kondo coupling revisited: metamagnetism and the field-induced suppression of the heavy fermion state.
Howczak, Olga; Spa?ek, Jozef
We apply the extended (statistically consistent, SCA) Gutzwiller-type approach to the periodic Anderson model (PAM) in an applied magnetic field and in the strong-correlation limit. The finite-U corrections are included systematically by transforming the PAM into the form with the Kondo-type interaction and the residual hybridization, both appearing at the same time and on equal footing. This effective Hamiltonian represents the essence of our Anderson-Kondo lattice model. We show that in ferromagnetic phases the low-energy single-particle states are strongly affected by the presence of the applied magnetic field. We also find that for large values of hybridization strength the system enters the so-called locked heavy fermion state introduced earlier. In this state the chemical potential lies in the majority-spin hybridization gap and, as a consequence, the system evolution is insensitive to further increase of the applied field. However, for a sufficiently strong magnetic field, the system transforms from the locked state to the fully spin-polarized phase. This is accompanied by a metamagnetic transition, as well as by a drastic reduction of the effective mass of the quasiparticles. In particular, we observe no effective mass enhancement in the fully polarized state. The findings are in overall agreement with experimental results for the Ce compounds in high magnetic fields. The mass enhancement for the spin-minority electrons may also diminish with the increasing field, unlike for the quasiparticle states in a single narrow band in the same limit of strong correlations. PMID:22510783
JULY 1998 1907K N I E V E L A N D J O H N S O N Pressure Transients within MCS Mesohighs and Wake Lows
Knievel, Jason Clark
JULY 1998 1907K N I E V E L A N D J O H N S O N Pressure Transients within MCS Mesohighs and Wake. First, these transients, with magnitudes of a few millibars, horizontal dimensions of order 100 km at least part of the total pressure field within mesohighs and wake lows. Transients did not apparently
User's guide for a flat wake rotor inflow/wake velocity prediction code, DOWN
NASA Technical Reports Server (NTRS)
Wilson, John C.
A computer code named DOWN was created to implement a flat wake theory for the calculation of rotor inflow and wake velocities. A brief description of the code methodology and instructions for its use are given. The code will be available from NASA's Computer Software Management and Information Center (COSMIC).
Recalibrating Wind Turbine Wake Model Parameters - Validating the Wake Model Performance for Large Offshore Wind Farms
Thomas S�rensen; Per Nielsen; Morten Lybech Th�gersen
Summary As part of the Danish PSO sponsored project 'The Necessary Distance between Large Wind Farms at Sea ' EMD International A\\/S has implemented a number of wake models in the WindPRO software. In this paper we report the preliminary results of a case study on Horns Rev offshore wind farm, where the actual observed wake losses are compared with
Dynamic wake prediction and visualization with uncertainty analysis
NASA Technical Reports Server (NTRS)
Holforty, Wendy L. (Inventor); Powell, J. David (Inventor)
A dynamic wake avoidance system utilizes aircraft and atmospheric parameters readily available in flight to model and predict airborne wake vortices in real time. A novel combination of algorithms allows for a relatively simple yet robust wake model to be constructed based on information extracted from a broadcast. The system predicts the location and movement of the wake based on the nominal wake model and correspondingly performs an uncertainty analysis on the wake model to determine a wake hazard zone (no fly zone), which comprises a plurality of wake planes, each moving independently from another. The system selectively adjusts dimensions of each wake plane to minimize spatial and temporal uncertainty, thereby ensuring that the actual wake is within the wake hazard zone. The predicted wake hazard zone is communicated in real time directly to a user via a realistic visual representation. In an example, the wake hazard zone is visualized on a 3-D flight deck display to enable a pilot to visualize or see a neighboring aircraft as well as its wake. The system substantially enhances the pilot's situational awareness and allows for a further safe decrease in spacing, which could alleviate airport and airspace congestion.
Technology Transfer Automated Retrieval System (TEKTRAN)
Field pennycress (FP; Thlaspi arvense L.) is a winter annual species of the Brassicaceae which is a native of Europe but has a wide distribution throughout temperate North America. FP tissues contain the glucosinolate sinigrin, and release a mixture of the biocides allyl thiocyanate and allyl isoth...
Wake dynamics and hydrodynamic forces on a perforated circular plate in cross-flow
NASA Astrophysics Data System (ADS)
Huera-Huarte, Francisco
The cross-flow past a perforated plate is known to become steady, if certain critical porosity or number of holes is imposed to the plate. This happens because the air bleed in the near wake, disrupts the vortex street formation behind the plate, and leads to suppression of the near wake shear layer interaction, forcing the instabilities to take place further away from the disk. This phenomenon is accompanied by a drag reduction. It is not clear however, what is the effect of the porosity distribution used in the plate, neither the effect of the angle of attack on the wake dynamics and the force coefficients. The experimental apparatus consists of an acrylic model in which different number and configuration of holes can be used. The disk hangs upside down from a 2-axis balance, in a way that it is being exposed to a uniform water current generated in a free surface channel. Angles of attack, porosity and its distribution on the disk, can be easily changed. Measurements of force coefficients for different angles of attack, and porosities have been taken. Digital Particle Image Velocimetry (DPIV) has been used to quantify the wake and to investigate the flow structures past the disk. Funding provided by the Spanish Ministry of Science through grant DPI2009-07104 is acknowledged.
Effect of External Turbulence on the Evolution of a Towed Wake in a Stratified Environment
NASA Astrophysics Data System (ADS)
Pal, Anikesh; Sarkar, Sutanu
Direct numerical simulation (DNS) is used to study the effect of external turbulence on the evolution of a towed turbulent wake in a stratified fluid. The simulations are carried out at a Reynolds number of 10,000, Froude number of 3 and Prandtl number of 1. The external turbulence is generated from a triply periodic rectangular domain in an auxiliary simulation performed to obtain turbulence with desired uext' /U0 , where uext' is the root mean square velocity of the external turbulence and U0 is the maximum defect velocity of the pure towed wake. This field of external turbulence is added to the initial field of the towed turbulent wake. Simulations are performed for uext' /U0 = 0 . 10 , 0 . 20 , and 0.30. The kinetic energy of the towed wake decays faster with progressively increasing values of uext' /U0 . This effect of external turbulence is found to be stronger in stratified flow relative to the neutral case. Although the horizontal spread of the stratified wake is enhanced owing to external turbulence there is little effect on the vertical spread.
Recent Developments on Airborne Forward Looking Interferometer for the Detection of Wake Vortices
NASA Technical Reports Server (NTRS)
Daniels, Taumi S.; Smith, William L.; Kirev, Stanislav
A goal of these studies was development of the measurement methods and algorithms necessary to detect wake vortex hazards in real time from either an aircraft or ground-based hyperspectral Fourier Transform Spectrometer (FTS). This paper provides an update on research to model FTS detection of wake vortices. The Terminal Area Simulation System (TASS) was used to generate wake vortex fields of 3-D winds, temperature, and absolute humidity. These fields were input to the Line by Line Radiative Transfer Model (LBLRTM), a hyperspectral radiance model in the infrared, employed for the FTS numerical modeling. An initial set of cases has been analyzed to identify a wake vortex IR signature and signature sensitivities to various state variables. Results from the numerical modeling case studies will be presented. Preliminary results indicated that an imaging IR instrument sensitive to six narrow bands within the 670 to 3150 per centimeter spectral region would be sufficient for wake vortex detection. Noise floor estimates for a recommended instrument are a current research topic.
Suppression of Effects of Parasitic MetalOxideSemiconductor Field-Effect Transistors on Si Single-Electron Transistors
Akira Fujiwara; Yasuo Takahashi; Hideo Namatsu; Kenji Kurihara; Katsumi Murase
Si single-electron transistors (SETs), which are fabricated in ultrathin Si of a silicon-on-insulator substrate by pattern-dependent oxidation, are accompanied by parasitic metal-oxide-semiconductor field-effect transistors (MOSFETs) on both sides of the SET. While the Si island of a SET is formed by design in a one-dimensional Si wire, the parasitic MOSFETs are inevitably formed in two-dimensional Si pad layers, between which
Technologies for suppressing charge-traps in novel p-channel Field-MOSFET with thick gate oxide
NASA Astrophysics Data System (ADS)
Miyoshi, Tomoyuki; Oshima, Takayuki; Noguchi, Junji
High voltage laterally diffused MOS (LDMOS) FETs are widely used in analog applications. A Field-MOSFET with a thick gate oxide is one of the best ways of achieving a simpler design and smaller circuit footprint for high-voltage analog circuits. This paper focuses on an approach to improving the reliability of p-channel Field-MOSFETs. By introducing a fluorine implantation process and terminating fluorine at the LOCOS bird�s beak, the gate oxide breakdown voltage could be raised to 350 V at a high-slew rate and the negative bias temperature instability (NBTI) shift could be kept to within 15% over a product�s lifetime. By controlling the amount of charge in the insulating layer through improving the interlayer dielectric (ILD) deposition processes, a higher BVDSS of 370 V and 10-year tolerability of 300 V were obtained with an assisted reduced surface electric field (RESURF) effect. These techniques can supply an efficient solution for ensuring reliable high-performance applications.
Waking effectiveness of visual alerting signals.
Bowman, S K; Jamieson, D G; Ogilvie, R D
People who are unable to hear acoustic alarm signals because they have a complete or partial hearing loss must rely on visual or tactile signals to warn them in the event of an emergency. However, consumers report that personal smoke detector devices which provide a visual alarm do not wake people reliably. We examined the ability of visual alerting devices to wake people from the deepest stages of sleep: slow wave sleep (SWS) and rapid-eye-movement sleep (REM). These results were related to the physical (optical) characteristics of devices currently on the market. In Experiment 1, a range of strobe intensities and locations were investigated. Experiment 2 confirmed the results of this pilot study on an independent set of subjects. On each trial, the strobe was allowed to run at a constant intensity until the subject awoke, or a maximum of 5 min had elapsed. Even though a diffuse light remained directly over the subject's face for each trial, subjects did not wake consistently. Under the favorable optical (smoke-free) conditions of the present study, the most intense of the devices presently offered for sale in Canada cannot be relied on to wake a sleeping person in the event of a fire. It remains unclear whether any visual alerting device can be expected to safely wake a sleeper in an emergency situation. PMID:7760267
Wake structure of a deformable Joukowski airfoil
NASA Astrophysics Data System (ADS)
Ysasi, Adam; Kanso, Eva; Newton, Paul K.
We examine the vortical wake structure shed from a deformable Joukowski airfoil in an unbounded volume of inviscid and incompressible fluid. The deformable airfoil is considered to model a flapping fish. The vortex shedding is accounted for using an unsteady point vortex model commonly referred to as the Brown-Michael model. The airfoil�s deformations and rotations are prescribed in terms of a Jacobi elliptic function which exhibits, depending on a dimensionless parameter m, a range of periodic behaviors from sinusoidal to a more impulsive type flapping. Depending on the parameter m and the Strouhal number, one can identify five distinct wake structures, ranging from arrays of isolated point vortices to vortex dipoles and tripoles shed into the wake with every half-cycle of the airfoil flapping motion. We describe these regimes in the context of other published works which categorize wake topologies, and speculate on the importance of these wake structures in terms of periodic swimming and transient maneuvers of fish.
Wake Vortex Tracking Using a 35 GHz Pulsed Doppler Radar
NASA Technical Reports Server (NTRS)
Neece, Robert T.; Britt, Charles L.; White, Joseph H.; Mudukutore, Ashok; Nguyen, Chi; Hooper, Bill
A 35 GHz, pulsed-Doppler radar system has been designed and assembled for wake vortex detection and tracking in low visibility conditions. Aircraft wake vortices continue to be an important factor in determining safe following distances or spacings for aircraft in the terminal area. Currently, under instrument meteorological conditions (IMC), aircraft adhere to conservative, fixed following-distance guidelines based primarily on aircraft weight classifications. When ambient conditions are such that vortices will either drift or dissipate, leaving the flight corridor clear, the prescribed spacings are unnecessarily long and result in decreased airport throughput. There is a potential for significant airport efficiency improvement, if a system can be employed to aid regulators and pilots in setting safe and efficient following distances based on airport conditions. The National Aeronautics and Space Administration (NASA), the Federal Aviation Agency, and Volpe National Transportation Systems Center have promoted and worked to develop systems that would increase airport capacity and provide for safe reductions in aircraft separation. The NASA Aircraft Vortex Spacing System (AVOSS), a wake vortex spacing system that can provide dynamic adjustment of spacings based on real-time airport weather conditions, has demonstrated that Lidar systems can be successfully used to detect and track vortices in clear air conditions. To fill the need for detection capability in low-visibility conditions, a 35 GHz, pulsed-Doppler radar system is being investigated for use as a complimentary, low-visibility sensor for wake vortices. The radar sensor provides spatial and temporal information similar to that provided by Lidar, but under weather conditions that a Lidar cannot penetrate. Currently, we are analyzing the radar design based upon the data and experience gained during the wake vortex Lidar deployment with AVOSS at Dallas/Fort Worth International Airport. As part of this study, two numerical models were utilized in system simulations. The results of this study improve our understanding of the method of detection, resolution requirements for range and azimuth, pulse compression, and performance prediction. Simulations applying pulse compression techniques show that detection is good in heavy fog to greater than 2000 m. Both compressed and uncompressed short pulses show the vortex structure. To explore operational challenges, siting and scanning strategies were also analyzed. Simulation results indicate that excellent wake vortex detection, tracking and classification is possible in drizzle (+15 dBZ) and heavy fog (- 13 dBZ) using short pulse techniques (<99ns) at ranges on the order of 900 m, with a modest power of 500 W output. At 1600 m, detection can be expected at reflectivities as low as -13 dBZ (heavy fog). The radar system, as designed and built, has the potential to support field studies of a wake vortex spacing system in low-visibility conditions ranging from heavy fog to rain, when sited within 2000m of the flight path.
Suppressing of slow magnetic relaxation in tetracoordinate Co(II) field-induced single-molecule magnet in hybrid material with ferromagnetic barium ferrite.
Nemec, Ivan; Herchel, Radovan; Tr�vn�?ek, Zden?k
The novel field-induced single-molecule magnet based on a tetracoordinate mononuclear heteroleptic Co(II) complex involving two heterocyclic benzimidazole (bzi) and two thiocyanido ligands, [Co(bzi)2(NSC)2], (CoL4), was prepared and thoroughly characterized. The analysis of AC susceptibility data resulted in the spin reversal energy barrier U?=?14.7?cm(-1), which is in good agreement with theoretical prediction, Utheor.?=?20.2?cm(-1), based on axial zero-field splitting parameter D?=?-10.1?cm(-1) fitted from DC magnetic data. Furthermore, mutual interactions between CoL4 and ferromagnetic barium ferrite BaFe12O19 (BaFeO) in hybrid materials resulted in suppressing of slow relaxation of magnetization in CoL4 for 1:2, 1:1 and 2:1 mass ratios of CoL4 and BaFeO despite the lack of strong magnetic interactions between two magnetic phases. PMID:26039085
Suppressing of slow magnetic relaxation in tetracoordinate Co(II) field-induced single-molecule magnet in hybrid material with ferromagnetic barium ferrite
Nemec, Ivan; Herchel, Radovan; Tr�vn�?ek, Zden?k
The novel field-induced single-molecule magnet based on a tetracoordinate mononuclear heteroleptic Co(II) complex involving two heterocyclic benzimidazole (bzi) and two thiocyanido ligands, [Co(bzi)2(NSC)2], (CoL4), was prepared and thoroughly characterized. The analysis of AC susceptibility data resulted in the spin reversal energy barrier U?=?14.7?cm?1, which is in good agreement with theoretical prediction, Utheor.?=?20.2?cm?1, based on axial zero-field splitting parameter D?=??10.1?cm?1 fitted from DC magnetic data. Furthermore, mutual interactions between CoL4 and ferromagnetic barium ferrite BaFe12O19 (BaFeO) in hybrid materials resulted in suppressing of slow relaxation of magnetization in CoL4 for 1:2, 1:1 and 2:1 mass ratios of CoL4 and BaFeO despite the lack of strong magnetic interactions between two magnetic phases. PMID:26039085
Wake interference for a heated oscillating cylinder
NASA Technical Reports Server (NTRS)
Mceligot, D. M.; Smith, S. B.; Verity, R. L.
Penney and Jefferson (1966) have studied heat transfer from an oscillating, horizontal wire. The present investigation has the objective to determine the governing parameters which indicate when interaction between an oscillating circular cylinder and its wake will reduce the apparent heat transfer coefficient in quasi-steady conditions, taking into account, if possible, also the determination of the approximate magnitude of the reduction. A definition is provided of a nondimensional vertical mass flux, representing the induced flow due to heating of the stagnant fluid. It is hypothesized that the flux is related to a natural convection parameter which describes the heating of the wake. For oscillation of a circular cylinder in air under the conditions studied, it is found that the application of a cross-flow correlation in a quasi-steady, transient analysis predicts heat transfer parameters in close agreement with experiment over a certain range, provided interaction with the heated wake is avoided.
Full-potential circular wake solution of a twisted rotor blade in hover
NASA Technical Reports Server (NTRS)
Aggarwal, Hans R.
A solution for transonic flow past a twisted rotor blade in hover is obtained using a modified version of the full-potential code ROT22 and a circular wake. The flow is also evaluated for a fixed-wing-type straight wake. The solutions for the straight wake and circular wake, and the circular wake and a two-dimensional wake are compared. The data reveal that the circular wake and the general two-dimensional wake solutions have similar characteristics.
Ground-based wake vortex monitoring, prediction, and ATC interface
NASA Technical Reports Server (NTRS)
Campbell, Steven D.; Evans, James E.
This talk will discuss three elements of a proposed Wake Vortex Advisory Service: monitoring, prediction and ATC interface. The monitoring element is needed to ensure safety by warning controllers of hazardous wake vortex conditions. Such conditions exist when wake vortices persist in the approach/departure flight paths due to advection or to atmospheric conditions which prevent their decay. The prediction element is needed to provide ATC supervisors with advance warning that wake vortex separation conditions are about to change (i.e., require increased or decreased wake vortex separation). The ATC interface element is needed to provide controllers with adaptive wake vortex separations. The use of these adaptive wake vortex separations would lead to increased airport capacity under most conditions, while maintaining safety under conditions of wake vortex hazard.
Three-Centimeter Doppler Radar Observations of Wingtip-Generated Wake Vortices in Clear Air
NASA Technical Reports Server (NTRS)
Marshall, Robert E.; Mudukutore, Ashok; Wissel, Vicki L. H.; Myers, Theodore
This report documents a high risk, high pay-off experiment with the objective of detecting, for the first time, the presence of aircraft wake vortices in clear air using X-band Doppler radar. Field experiments were conducted in January 1995 at the Wallops Flight Facility (WFF) to demonstrate the capability of the 9.33 GHz (I=3 cm) radar, which was assembled using an existing nine-meter parabolic antenna reflector at VVTT and the receiver/transmitter from the NASA Airborne Windshear Radar-Program. A C-130-aircraft, equipped with wingtip smoke generators, created visually marked wake vortices, which were recorded by video cameras. A C-band radar also observed the wake vortices during detection attempts with the X-band radar. Rawinsonde data was used to calculate vertical soundings of wake vortex decay time, cross aircraft bearing wind speed, and water vapor mixing ratio for aircraft passes over the radar measurement range. This experiment was a pathfinder in predicting, in real time, the location and persistence of C-130 vortices, and in setting the flight path of the aircraft to optimize X-band radar measurement of the wake vortex core in real time. This experiment was conducted in support of the NASA Aircraft Vortex Spacing System (AVOSS).
Ship wakes: Kelvin or Mach angle?
Rabaud, Marc
From the analysis of a set of airborne images of ship wakes, we show that the wake angles decrease as $U^{-1}$ at large velocities, in a way similar to the Mach cone for supersonic airplanes. This previously unnoticed Mach-like regime is in contradiction with the celebrated Kelvin prediction of a constant angle of $19.47\\degree$ independent of the ship's speed. We propose here a model, confirmed by numerical simulations, in which the finite size of the disturbance explains this transition between the Kelvin and Mach regimes at a Froude number $Fr = U/\\sqrt{gL} \\simeq 0.5$, where $L$ is the hull ship length.
Wake potential in a nonuniform self-gravitating dusty magnetoplasma in the presence of ion streaming
Salimullah, M.; Ehsan, Z.; Zubia, K.; Shah, H. A.; Murtaza, G. [Salam Chair in Physics and Department of Physics, Government College University, Lahore 54000 (Pakistan); Department of Physics, Government College University, Lahore 54000 (Pakistan); Salam Chair in Physics, Government College University, Lahore 54000 (Pakistan)
A detailed investigation of the electrostatic asymmetric shielding potential and consequent generation of the dynamical oscillatory wake potential has been examined analytically in an inhomogeneous self-gravitating dusty magnetoplasma in the presence of uniform ion streaming. It is found that the wake potential depends significantly on the test particle speed, ambient magnetic field, ion streaming velocity, and the plasma inhomogeneity. The periodic oscillatory potential might lead to an alternative approach to the Jeans instability for the formation of dust agglomeration leading to gravitational collapse of the self-gravitating systems.
Experimental Study of the Temporal Nature of an Actively Controlled Three Dimensional Turret Wake
NASA Astrophysics Data System (ADS)
Shea, Patrick; Glauser, Mark
Experimental measurements have been performed to characterize the actively controlled wake of a three-dimensional, non- conformal turret which is a bluff body commonly used for housing optical systems on airborne platforms. As a bluff body, turrets can generate strong turbulent flow fields that degrade the performance of the optical systems and the aircraft. Experiments were performed in a low-speed wind tunnel at Syracuse University using particle image velocimetry and dynamic pressure measurements with the objective of developing a better understanding of the spatial and temporal nature of the wake flow field. Active control was achieved using dynamic suction in the vicinity of the turret aperture and was found to have a significant impact on the structure of the wake as well as the temporal characteristics of the flow field. With a better understanding of the wake characteristics, closed-loop, active flow control systems will be developed to help reduce fluctuating loading and aero- optical distortions associated with the turbulent flow field.
Demo Abstract: A Sensornet-inspired Underwater Acoustic Modem for Wake-up and Data
Heidemann, John
Demo Abstract: A Sensornet-inspired Underwater Acoustic Modem for Wake-up and Data Affan A. Syed most radio frequencies. Acoustic modems are a viable alternative, but most commercial acoustic modems. While matched for some vertical applications that are fielded today, these modems are the antithesis
Radio-Triggered Wake-Up for Wireless Sensor Networks
Lin Gu; John A. Stankovic
Power management is an important technique to prolong the lifespan of sensor networks. Many power management protocols employ wake-up\\/sleep schedules, which are often complicated and inefficient. We present power management schemes that eliminate such wake-up periods unless the node indeed needs to wake up. This type of wake-up capability is enabled by a new radio-triggered hardware component inspired by the
Activation of 5-HT6 Receptors Modulates Sleep�Wake Activity and Hippocampal Theta Oscillation
The modulatory role of 5-HT neurons and a number of different 5-HT receptor subtypes has been well documented in the regulation of sleep�wake cycles and hippocampal activity. A high level of 5-HT6 receptor expression is present in the rat hippocampus. Further, hippocampal function has been shown to be modulated by both 5-HT6 agonists and antagonists. In the current study, the potential involvement of 5-HT6 receptors in the control of hippocampal theta rhythms and sleep�wake cycles has been investigated. Hippocampal activity was recorded by intracranial hippocampal electrodes both in anesthetized (n = 22) and in freely moving rats (n = 9). Theta rhythm was monitored in different sleep�wake states in freely moving rats and was elicited by stimulation of the brainstem reticular formation under anesthesia. Changes in theta frequency and power were analyzed before and after injection of the 5-HT6 antagonist (SAM-531) and the 5-HT6 agonist (EMD386088). In freely moving rats, EMD386088 suppressed sleep for several hours and significantly decreased theta peak frequency, while, in anesthetized rats, EMD386088 had no effect on theta power but significantly decreased theta frequency, which could be blocked by coadministration of SAM-531. SAM-531 alone did not change sleep�wake patterns and had no effect on theta parameters in both unanesthetized and anesthetized rats. Decreases in theta frequency induced by the 5-HT6 receptor agonist correspond to previously described electrophysiological patterns shared by all anxiolytic drugs, and it is in line with its behavioral anxiolytic profile. The 5-HT6 antagonist, however, failed to potentiate theta power, which is characteristic of many pro-cognitive substances, indicating that 5-HT6 receptors might not tonically modulate hippocampal oscillations and sleep�wake patterns. PMID:23336058
Investigating three-dimensional wake topology of a low aspect ratio dual step cylinder with 2D PIV measurements
NASA Astrophysics Data System (ADS)
Morton, Chris; Yarusevych, Serhiy
A dual step cylinder is composed of a large diameter cylinder (D) of small aspect ratio (L/D) attached to the mid-span of a small diameter cylinder (d). The present work investigates the flow past dual step cylinders for ReD = 2100, 0.2 <= L/D <= 3, and 1.33 <= D/d <= 2.67. Experiments are completed in a water flume facility employing Laser Doppler Velocimetry (LDV) and planar Particle Image Velocimetry (PIV), as well as hydrogen bubble flow visualization. Turbulent vortex shedding occurs in the wake of the dual step cylinder for all the cases investigated. However, wake topology and vortex dynamics are influenced significantly by the geometrical parameters of the model, namely, L/D and D/d. A novel method is introduced for reconstructing salient features of the three-dimensional wake topology using phase-averaged 2D PIV measurements. The results show that flow development in the small cylinder wake away from the large cylinder is similar to that expected for a uniform cylinder of the same diameter. However, complex three-dimensional vortex deformations and splitting occur downstream of the large diameter cylinder. Four distinct flow regimes are identified based on changes in large cylinder wake development: (i) vortex shedding at a frequency lower than that expected for a uniform cylinder, (ii) irregular shedding, (iii) vortex shedding at a frequency higher than that for a uniform cylinder, and (iv) suppression of large cylinder vortex shedding.
Vortex research facility improvements and preliminary density stratification effects on vortex wakes
NASA Technical Reports Server (NTRS)
Satran, D. R.; Holbrook, G. T.; Greene, G. C.; Neuhart, D.
Recent modernization of NASA's Vortex Research Facility is described. The facility has a 300-ft test section, scheduled for a 300-ft extension, with constant test speeds of the model up to 100 ft/sec. The data acquisition hardware and software improvements included the installation of a 24-channel PCM system onboard the research vehicle, and a large dedicated 16-bit minicomputer. Flow visualization of the vortex wake in the test section is by particle seeding, and a thin sheet of argon laser light perpendicular to the line of flight; detailed flow field measurements are made with a laser velocimeter optics system. The improved experimental capabilities of the facility were used in a study of atmospheric stratification effects on wake vortex decay, showing that the effects of temperature gradient must be taken into account to avoid misleading conclusions in wake vortex research.
Laser Doppler velocimeter system simulation for sensing aircraft wake vortices
NASA Technical Reports Server (NTRS)
Thomson, J. A. L.; Meng, J. C. S.
A hydrodynamic model of aircraft vortex wakes in an irregular wind shear field near the ground is developed and used as a basis for modeling the characteristics of a laser Doppler detection and vortex location system. The trailing vortex sheet and the wind shear are represented by discrete free vortices distributed over a two-dimensional grid. The time dependent hydrodynamic equations are solved by direct numerical integration in the Boussinesq approximation. The ground boundary is simulated by images, and fast Fourier Transform techniques are used to evaluate the vorticity stream function. The atmospheric turbulence was simulated by constructing specific realizations at time equal to zero, assuming that Kolmogoroff's law applies, and that the dissipation rate is constant throughout the flow field. The response of a simulated laser Doppler velocimeter is analyzed by simulating the signal return from the flow field as sensed by a simulation of the optical/electronic system.
Wake pattern and wave resistance for anisotropic moving disturbances
NASA Astrophysics Data System (ADS)
Benzaquen, Michael; Darmon, Alexandre; Rapha�l, Elie
We present a theoretical study of gravity waves generated by an anisotropic moving disturbance. We model the disturbance by an elliptical pressure field of given aspect ratio W. We study the wake pattern as a function of W and the longitudinal hull Froude number Fr = V/sqrt{gL}, where V is the velocity, g is the acceleration of gravity, and L is the size of the disturbance in the direction of motion. For large hull Froude numbers, we analytically show that the rescaled surface profiles for which sqrt{W}/Fr is kept constant coincide. In particular, the angle outside which the surface is essentially flat remains constant and equal to the Kelvin angle, and the angle corresponding to the maximum amplitude of the waves scales as sqrt{W}/Fr, thus showing that previous work on the wake's angle for isotropic objects can be extended to anisotropic objects of given aspect ratio. We then focus on the wave resistance and discuss its properties in the case of an elliptical Gaussian pressure field. We derive an analytical expression for the wave resistance in the limit of very elongated objects and show that the position of the speed corresponding to the maximum wave resistance scales as sqrt{gL}/sqrt{W}.
Underlying Brain Mechanisms that Regulate Sleep�Wakefulness Cycles
Irma Gvilia
Daily cycles of wakefulness and sleep are regulated by coordinated interactions between wakefulness- and sleep-regulating neural circuitry. Wakefulness is associated with neuronal activity in cholinergic neurons in the brainstem and basal forebrain, monoaminergic neurons in the brainstem and posterior hypothalamus, and hypocretin (orexin) neurons in the lateral hypothalamus that act in a coordinated manner to stimulate cortical activation on the
The neural circuit of orexin (hypocretin): maintaining sleep and wakefulness
Takeshi Sakurai
Sleep and wakefulness are regulated to occur at appropriate times that are in accordance with our internal and external environments. Avoiding danger and finding food, which are life-essential activities that are regulated by emotion, reward and energy balance, require vigilance and therefore, by definition, wakefulness. The orexin (hypocretin) system regulates sleep and wakefulness through interactions with systems that regulate emotion,
Sleep in the Unresponsive Wakefulness Syndrome and Minimally Conscious State
Delorme, Arnaud
Sleep in the Unresponsive Wakefulness Syndrome and Minimally Conscious State Victor Cologan,1 Laureys1,7 Abstract The goal of our study was to investigate different aspects of sleep, namely the sleep-wake cycle and sleep stages, in the vegetative state/unresponsive wakefulness syndrome (VS
A New Green's Function for the Wake Potential Calculation of the SLAC S-band Constant Gradient Accelerating Section
Novokhatski, A,; /SLAC
The behavior of the longitudinal wake fields excited by a very short bunch in the SLAC S-band constant gradient accelerating structures has been studied. Wake potential calculations were performed for a bunch length of 10 microns using the author's code to obtain a numerical solution of Maxwell's equations in the time domain. We have calculated six accelerating sections in the series (60-ft) to find the stationary solution. While analyzing the computational results we have found a new formula for the Green's function. Wake potentials, which are calculated using this Green's function are in amazingly good agreement with numerical results over a wide range of bunch lengths. The Green's function simplifies the wake potential calculations and can be easily incorporated into the tracking codes. This is very useful for beam dynamics studies of the linear accelerators of LCLS and FACET.
High-voltage interactions in plasma wakes: Simulation and flight measurements from the Charge Hazards and Wake Studies (CHAWS) experiment
V. A. Davis; M. J. Mandell; D. L. Cooke; C. L. Enloe
The Charge Hazards and Wake Studies (CHAWS) flight experiment flew on the Wake Shield Facility (WSF) aboard STS-60 and STS-69. The experiment studied high-voltage current collection within the spacecraft wake. The wake-side sensor was a 45-cm-long, biasable cylindrical probe mounted on the 3.66-m-diameter WSF. Operations were performed in free flight and at various attitudes while on the shuttle orbiter remote
Experimental Results on Rotor Wakes Narayanan Komerath
-Gray deconstruction of the hover wake structure into tip vortices and helical vortex sheets, done in the early 1960s through chaotic processes, even at high Reynolds number. Similarly, mysterious "jitter" phenomena have these advances, shown both experimentally and through analysis and computation, it has become possible
Linear instability of supersonic plane wakes
NASA Technical Reports Server (NTRS)
Papageorgiou, D. T.
In this paper we present a theoretical and numerical study of the growth of linear disturbances in the high-Reynolds-number and laminar compressible wake behind a flat plate which is aligned with a uniform stream. No ad hoc assumptions are made as to the nature of the undisturbed flow (in contrast to previous investigations) but instead the theory is developed rationally by use of proper wake-profiles which satisfy the steady equations of motion. The initial growth of near wake perturbation is governed by the compressible Rayleigh equation which is studied analytically for long- and short-waves. These solutions emphasize the asymptotic structures involved and provide a rational basis for a nonlinear development. The evolution of arbitrary wavelength perturbations is addressed numerically and spatial stability solutions are presented that account for the relative importance of the different physical mechanisms present, such as three-dimensionality, increasing Mach numbers enough (subsonic) Mach numbers, there exists a region of absolute instability very close to the trailing-edge with the majority of the wake being convectively unstable. At higher Mach numbers (but still not large-hypersonic) the absolute instability region seems to disappear and the maximum available growth-rates decrease considerably. Three-dimensional perturbations provide the highest spatial growth-rates.
Space shuttle molecular and wake vacuum measurements
NASA Technical Reports Server (NTRS)
Naumann, R. J.; Carignan, G. R.; Miller, E. R.
The wake environment of the space shuttle is analyzed to determine whether it is feasible to perform ultrahigh vacuum experiments in or near the payload bay with the shuttle oriented such that the payload bay faces the antivelocity direction. Several mechanisms were considered by which molecules could approach the payload bay from this direction and their relative contributions to the wake environment are estimated. These mechanisms include ambient atmospheric molecules that have velocities in excess of the orbital velocity which can overtake the shuttle, ambient atmospheric molecules that are backscattered by collisions with the shuttle induced atmosphere, and self scattering from the induced atmosphere. These estimates are compared with the measurements made with the collimated mass spectrometer which was part of the Induced Environment Contamination Monitor flown on several of the early shuttle flights. Although the collimated mass spectrometer was not designed for this purpose and the instrument background for the species for which the collimator is effective is above the expected levels, upper limits can be established for these species in the wake environment which are consistent with the analysis. There was considerably more helium and argon observed in the wake direction than was predicted, however. Possible origins of these gases are discussed.
Explicit Expressions of Impedances and Wake Functions
Ng, K.Y.; /Fermilab; Bane, K,; /SLAC
Sections 3.2.4 and 3.2.5 of the Handbook of Accelerator Physics and Engineering on Landau damping are combined and updated. The new addition includes impedances and wakes for multi-layer beam pipe, optical model, diffraction model, and cross-sectional transition.
Explicit expressions of impedances and wake functions
Ng, K.Y.; /Fermilab; Bane, K,; /SLAC
Sections 3.2.4 and 3.2.5 of the Handbook of Accelerator Physics and Engineering on Landau damping are combined and updated. The new addition includes impedances and wakes for multi-layer beam pipe, optical model, diffraction model, and cross-sectional transition.
Wake structure of a deformable Joukowski airfoil
Adam Ysasi; Eva Kanso; Paul K. Newton
We examine the vortical wake structure shed from a deformable Joukowski airfoil in an unbounded volume of inviscid and incompressible fluid. The deformable airfoil is considered to model a flapping fish. The vortex shedding is accounted for using an unsteady point vortex model commonly referred to as the Brown�Michael model. The airfoil�s deformations and rotations are prescribed in terms of
The reticular formation and behavioral wakefulness
This paper presents a brief review of literature addressing the role of the brain stem reticular formation (BSRF) in behavioral wakefulness. Papers by R. J. Ellingson (1956), N. Kleitman (1939), W. H. Funderburk and T. J. Case (1951) are cited, among others. The pharmacological data cited here indicate inactivity of the BSRF by itself is an insufficient condition for the
Wake County Public School System Design Guidelines.
ERIC Educational Resources Information Center
Wake County Public School System, Raleigh, NC.
The Wake County Public School System has published its guidelines for planning and design of functional, cost effective, and durable educational facilities that are attractive and enhance the students' educational experience. The guidelines present basic planning requirement and design criteria for the entire construction process, including: codes�
Radiative Forcing Over Ocean by Ship Wakes
NASA Technical Reports Server (NTRS)
Gatebe, Charles K.; Wilcox, E.; Poudyal, R.; Wang, J.
Changes in surface albedo represent one of the main forcing agents that can counteract, to some extent, the positive forcing from increasing greenhouse gas concentrations. Here, we report on enhanced ocean reflectance from ship wakes over the Pacific Ocean near the California coast, where we determined, based on airborne radiation measurements that ship wakes can increase reflected sunlight by more than 100%. We assessed the importance of this increase to climate forcing, where we estimated the global radiative forcing of ship wakes to be -0.00014 plus or minus 53% Watts per square meter assuming a global distribution of 32331 ships of size of greater than or equal to 100000 gross tonnage. The forcing is smaller than the forcing of aircraft contrails (-0.007 to +0.02 Watts per square meter), but considering that the global shipping fleet has rapidly grown in the last five decades and this trend is likely to continue because of the need of more inter-continental transportation as a result of economic globalization, we argue that the radiative forcing of wakes is expected to be increasingly important especially in harbors and coastal regions.
Experiments in Waking Hypnosis for Instructional Purposes
W. R. Wells
The author discusses the theory of hypnotism and the possibility of employing it for experimental purposes in the class-room. He distinguishes between sleeping and waking hypnosis, justifying his use of the latter term with a wealth of historical and contemporary evidence. He reports the success of class experiments in both types of hypnosis, particularly the latter which he describes minutely.
Lucid Dreaming, Waking Personality and Cognitive Development
Russell E. Gruber; John J. Steffen; Steven P. Vonderhaar
Findings are presented from a comparison of waking personality traits (16PF, Cattell, Eber, & Tatsuoka, 1970) characteristic of male and female groups totaling 247 frequent, and 201 infrequent lucid dreamers. Discriminant analyses produced significant findings and similar profiles, for both males and females. Overall, findings are considered suggestive of a strong link between lucid awareness and volition within dreams and
Helicopter rotor wake geometry and its influence in forward flight. Volume 2: Wake geometry charts
NASA Technical Reports Server (NTRS)
Egolf, T. A.; Landgrebe, A. J.
Isometric and projection view plots, inflow ratio nomographs, undistorted axial displacement nomographs, undistorted longitudinal and lateral coordinates, generalized axial distortion nomographs, blade/vortex passage charts, blade/vortex intersection angle nomographs, and fore and aft wake boundary charts are discussed. Example condition, in flow ratio, undistorted axial location, longitudinal and lateral coordinates, axial coordinates distortions, blade/tip vortex intersections, angle of intersection, and fore and aft wake boundaries are also discussed.
Suppression of unimolecular decay of laser desorbed peptide and protein ions by entrainment in rarefied supersonic gas jets under weak electric fields.
Hieke, Andreas
Unimolecular decay of sample ions imposes a limit on the usable laser fluence in matrix-assisted laser desorption/ionization (MALDI) ion sources. Traditionally, some modest degree of collisional sample ion cooling has been achieved by connecting MALDI ion sources directly to gas-filled radio frequency (RF) multipoles. It was also discovered in the early 1990s that gas-filled RF multipoles exhibit increased ion transmission efficiency due to collisional ion focusing effects. This unexpected experimental finding was later supported by elementary Monte Carlo simulations. Both experiments and simulations assumed a resting background gas with typical pressures of the order of 1 Pa. However, considerable additional improvements can be achieved if laser desorbed sample ions are introduced immediately after desorption, still within the ion source, in an axisymmetric rarefied supersonic gas jet with peak pressure of the order of 100 Pa and flow velocities >300 m/s, and under weak electric fields. We describe here the design principle and report performance data of an ion source coined "MALDI-2," which incorporates elements of both rarefied aerodynamics and particle optics. Such a design allows superb suppression of metastable fragmentation due to rapid collisional cooling in <10 ?s and nearly perfect injection efficiency into the attached RF ion guide, as numerous experiments have confirmed. PMID:25669372
Suppression of unimolecular decay of laser desorbed peptide and protein ions by entrainment in rarefied supersonic gas jets under weak electric fields
Hieke, Andreas, E-mail: firstname.lastname@example.com [Department of Structural Biology, School of Medicine, Stanford University, 299 Campus Drive West, Fairchild Building, 148, Stanford, California 94305-5126 (United States)] [Department of Structural Biology, School of Medicine, Stanford University, 299 Campus Drive West, Fairchild Building, 148, Stanford, California 94305-5126 (United States)
Unimolecular decay of sample ions imposes a limit on the usable laser fluence in matrix-assisted laser desorption/ionization (MALDI) ion sources. Traditionally, some modest degree of collisional sample ion cooling has been achieved by connecting MALDI ion sources directly to gas-filled radio frequency (RF) multipoles. It was also discovered in the early 1990s that gas-filled RF multipoles exhibit increased ion transmission efficiency due to collisional ion focusing effects. This unexpected experimental finding was later supported by elementary Monte Carlo simulations. Both experiments and simulations assumed a resting background gas with typical pressures of the order of 1 Pa. However, considerable additional improvements can be achieved if laser desorbed sample ions are introduced immediately after desorption, still within the ion source, in an axisymmetric rarefied supersonic gas jet with peak pressure of the order of 100 Pa and flow velocities >300 m/s, and under weak electric fields. We describe here the design principle and report performance data of an ion source coined �MALDI-2,� which incorporates elements of both rarefied aerodynamics and particle optics. Such a design allows superb suppression of metastable fragmentation due to rapid collisional cooling in <10 ?s and nearly perfect injection efficiency into the attached RF ion guide, as numerous experiments have confirmed.
An exploratory investigation of a wake disruption technique for studying wake reestablishment time
NASA Technical Reports Server (NTRS)
Clark, L. E.; Jones, R. A.
An exploratory investigation was made of a wake disruption technique for studying the hypersonic-wake reestablishment time in a blowdown wind tunnel. In this technique, a highly underexpanded jet issuing from the base of a 10 deg half-angle cone totally disrupts and displaces the conventional wake. The jet was rapidly shut off by an explosively actuated valve and the time for wake reestablishment was measured. The tests were conducted in the Mach 6 high Reynolds number tunnel at a stagnation temperature of 506 K and stagnation pressure of 2.86 MPa. The model base jet stagnation pressure was 3.55 MPa at room temperature. High-speed schlieren motion pictures indicated that disappearance of the disrupting jet and reestablishment of the wake-recompression shock were probably occurring simultaneously and that the time disruptive-jet-air shutoff to wake recompression shock reestablishment was probably between 200 and 450 microseconds (flow lengths from 1.8 to 4.2). The values of flow lengths are about one-thord to one-half the values measured in impulse facilities in a previous study. This shorter time is believed to be largely due to difference in flow conditions between the jet disruption technique and impulse facilities.
[Testing results of telemechanic system controlling train operators wakefulness].
Serikov, V V; Zakrevskaia, A A; Zakharchenko, D V; Alpaev, D V; At'kova, E O
Expert and instrumental assessment covered efficiency of telemechanic system controlling train operators wakefulness in simulation of real night travel, through special simulator complex "Locomotive operator cabin". The telemechanic system controlling train operators wakefulness, if exploited correctly, provides wakefulness of the train operators at the level sufficient for the effective work. That is supported by distribution of falling asleep cases in experiments with activated or deactivated telemechanic system controlling train operators wakefulness. The study proved efficiency of telemechanic system controlling train operators wakefulness. PMID:25826880
Vortex shedding in high-speed compressor blade wakes
NASA Technical Reports Server (NTRS)
Epstein, A. H.; Gertz, J. B.; Owen, P. R.; Giles, M. B.
The wakes of highly loaded compressor blades are generally considered to be turbulent flows. Recent work has suggested that the blade wakes are dominated by a vortex streetlike structure. The experimental evidence supporting the wake vortex structure is reviewed. This structure is shown to redistribute thermal energy within the flowfield. The effect of the wake structure on conventional aerodynamic measurements of compressor performance is noted. A two-dimensional, time-accurate, viscous numerical simulation of the flow exhibits both vortex shedding in the wake and a lower-frequency flow instability that modulates the shedding. The numerical results are shown to agree quite well with the measurement from transonic compressor rotors.
Wind-tunnel measurements in the wakes of structures
NASA Technical Reports Server (NTRS)
Woo, H. G. C.; Peterka, J. A.; Cermak, J. E.
Detailed measurements of longitudinal mean velocity, turbulence intensity, space correlations, and spectra made in the wake of two rectangular scaled models in simulated atmospheric boundary-layer winds are presented. The model buildings were 1:50 scale models of two trailers. Results of a flow visualization study of the wake geometry are analyzed with some singular point theorems. Two hypothetical flow patterns of the detailed wake geometry are proposed. Some preliminary studies of the vortex wake, effects of the model size, model aspect ratios, and boundary layer characteristics on the decay rate and extent of the wake are also presented and discussed.
ELF magnetic fluctuations detected by Kaguya in deepest lunar wake associated with type-II protons
NASA Astrophysics Data System (ADS)
Nakagawa, Tomoko; Nakashima, Tatsuya; Wada, Takuya; Tsunakawa, Hideo; Takahashi, Futoshi; Shibuya, Hidetoshi; Shimizu, Hisayoshi; Matsushima, Masaki; Saito, Yoshifumi
Magnetic fluctuations in the extremely low-frequency (ELF) range from 0.1 to 10 Hz were found by the Lunar Magnetometer (LMAG) of the magnetic field and plasma experiment (MAP) on board the spacecraft Kaguya in the deepest wake behind the moon, where the magnetic field is usually quiet. The fluctuations were compressional and non-monochromatic, showing no preferred polarization. They were often accompanied by "type-II entry" solar wind protons that were reflected by the dayside lunar surface or crustal magnetic field, gyrated around the solar wind magnetic field, then entered the deepest wake. The ELF waves persisted for 30 s to several minutes. The duration was often shorter than that of the type-II protons. Most of the waves were detected on the magnetic field lines disconnected from the lunar surface, along which the solar wind electrons were injected into the wake. Since a large cross-field velocity difference is expected between the type-II protons and the solar wind electrons injected along the magnetic field, some cross-field current-driven instability such as the lower hybrid two-stream instability is expected to be responsible for the generation of the waves.
Experimental investigation of an actively controlled three-dimensional turret wake
NASA Astrophysics Data System (ADS)
Shea, Patrick R.
Hemispherical turrets are bluff bodies commonly used to house optical systems on airborne platforms. These bluff bodies develop complex, three-dimensional flow fields that introduce high mean and fluctuating loads to the turret as well as the airframe support structure which reduce the performance of both the optical systems and the aircraft. An experimental investigation of the wake of a three-dimensional, non-conformal turret was performed in a low-speed wind tunnel at Syracuse University to develop a better understanding of the fundamental flow physics associated with the turret wake. The flow field was studied at a diameter based Reynolds number of 550,000 using stereoscopic particle image velocimetry and dynamic pressure measurements both with and without active flow control. Pressure measurements were simultaneously sampled with the PIV measurements and taken on the surrounding boundary layer plate and at several locations on the turret geometry. Active flow control of the turret wake was performed around the leading edge of the turret aperture using dynamic suction in steady open-loop, unsteady open-loop, and simple closed-loop configurations. Analysis of the uncontrolled wake provided insight into the complex three-dimensional wake when evaluated spatially using PIV measurements and temporally using spectral analysis of the pressure measurements. Steady open-loop suction was found to significantly alter the spatial and temporal nature of the turret wake despite the control being applied locally to the aperture region of the turret. Unsteady open-loop and simple closed-loop control were found to provide similar levels of control to the steady open-loop forcing with a 45% reduction in the control input as calculated using the jet momentum coefficient. The data set collected provides unique information regarding the development of the baseline three-dimensional wake and the wake with three different active flow control configurations. These data can be used to help guide future studies, both experimental and computational, of similar geometries and to provide insight for developing active control systems for complex, three-dimensional flows.
Wind turbine wake detection with a single Doppler wind lidar
NASA Astrophysics Data System (ADS)
Wang, H.; Barthelmie, R. J.
Using scanning lidar wind turbine wakes can be probed in three dimensions to produce a wealth of temporally and spatially irregular data that can be used to characterize the wakes. Unlike data from a meteorological mast or upward pointing lidar, the spatial coordinates of the measurements are not fixed and the location of the wake also varies in three dimensions. Therefore the challenge is to provide automated detection algorithms to identify wakes and quantify wake characteristics from this type of dataset. Here an algorithm is developed and evaluated on data from a large wind farm in the Midwest. A scanning coherent Doppler wind lidar was configured to measure wind speed in the wake of a continuously yawing wind turbine for two days during the experiment and wake profiles were retrieved with input of wind direction information from the nearby meteorological mast. Additional challenges to the analysis include incomplete coverage of the entire wake due to the limited scanning domain, and large wind shear that can contaminate the wake estimate because of the height variation along the line-of-sight. However, the algorithm developed in this paper is able to automatically capture wakes in lidar data from Plan Position Indicator (PPI) scans and the resultant wake statistics are consistent with previous experiment's results.
Manipulation of electromagnetic fields with plasmonic nanostructures: Nonlinear frequency mixing, optical manipulation, enhancement and suppression of photocurrent in a silicon photodiode, and surface-enhanced spectroscopy
NASA Astrophysics Data System (ADS)
Grady, Nathaniel K.
Metallic nanostructures are one of the most versatile tools available for manipulating light at the nanoscale. These nanostructures support surface plasmons, which are collective excitations of the conduction electrons that can exist as propagating waves at a metallic interface or as localized excitations of a nanoparticle or nanostructure. Plasmonic structures can efficiently couple energy from freely propagating electromagnetic waves to localized electromagnetic fields and vice-versa, essentially acting as an optical antenna. As a result, the intensity of the local fields around and inside the nanostructure are strongly enhanced compared to the incident radiation. In this thesis, this ability to manipulate electromagnetic fields on the nanoscale is employed to control a wide range of optical phenomena. These studies are performed using structures based on metallic nanoshells, which consist of a thin Au shell coating a silica nanosphere. To investigate the parameters controlling the plasmonic response of metallic nanoshells, two changes to the nanoshell composition are studied: (1) the Au shell is replaced with Cu which has interband transitions that strongly influence the plasmon resonance, and (2) the silica core is replaced by a semiconducting Cu 2O core which has a significantly higher dielectric constant and non-trivial absorbance. The focusing of electromagnetic energy into intense local fields by plasmonic nanostructures is then directly investigated by profiling the nanoshell near field using a Raman-based molecular ruler. Next, plasmons supported by Au nanoshells are used to control the fluorescence of near-infrared fluorophores placed at controlled distances from the nanoshell surface. In this context, the analogy of an optical antenna is very relevant: the enhanced field at the surface of the nanoshell increases the absorption of light by the fluorophore, or equivalently couples propagating electromagnetic waves into a localized receiver, while the large scattering cross section enhances the coupling of energy from a localized source, the fluorophore, to far-field radiation. Excellent agreement with models based on Mie theory is achieved for both Raman and fluorescence. Experimentally measured enhancements of the radiative decay rate for fluorophores on Au nanoshells and Au nanorods are also consistent with this model. Plasmonic nanostructures can also control the flow of light into larger structures. This is observed by measuring the nanoparticle-induced enhancement and suppression of photocurrent in a silicon photodiode is at the single particle level for silica nanospheres, Au nanospheres, and two types of Au nanoshell Finally, the simultaneous physical manipulation of an individual plasmonic nanostructure on the few-nanometer scale using light and detection of the local electromagnetic field during this ongoing process with the same incident beam is performed. For this experiment, a Au nanoshell is separated from a metallic surface by a few-nanometer thick polymer layer to form a nanoscale junction, or nanogap Illuminating this structure with ultrashort optical pulses, exciting the plasmon resonance, results in a continuous, monitorable collapse of the nanogap. An easily detectable four-wave mixing (FWM) signal is simultaneously generated by this illumination of the nanogap, providing a continuous, highly sensitive optical monitor of the nanogap spacing while it is being optically reduced. The dramatic increase in this signal upon contact provides a clear, unambiguous signal of the gap closing.
Numerical simulations of the near wake of a sphere moving in a steady, horizontal motion through a linearly stratified fluid at Re = 1000
NASA Astrophysics Data System (ADS)
Orr, Trevor S.; Domaradzki, J. Andrzej; Spedding, Geoffrey R.; Constantinescu, George S.
A numerical investigation of the near wake of a sphere moving horizontally through a linearly stratified fluid is presented. Simulations are first performed on a flow with Reynolds number Re = 200 for a range of internal Froude number, 0.1 ? Fr ? ?. The simulations capture buoyant characteristic behavior, the presence of vortex shedding at low Fr, and lee waves. Simulations at higher Reynolds number, Re = 1000, for 1 ? Fr ? ? provide a description and parametrization of the near wake, including the density field. At Re = 1000, the effects of utilizing two different averaging techniques in the unsteady near wake region are discussed. Perturbation quantities in the stratified near wake are anisotropic, and based on the oscillations of the centerline vertical perturbation velocity, the Fr at which the stratified near wake may be considered indistinguishable from the uniform density near wake is suggested to be O(100). Parametrization of the near wake is accomplished using the parameterized vertical wake height, downstream distance from the sphere, and Fr as parameters.
Cosmic string wakes and large-scale structure
NASA Technical Reports Server (NTRS)
Charlton, Jane C.
The formation of structure from infinite cosmic string wakes is modeled for a universe dominated by cold dark matter (CDM). Cross-sectional slices through the wake distribution tend to outline empty regions with diameters which are not inconsistent with the range of sizes of the voids in the CfA slice of the universe. The topology of the wake distribution is found to be spongy rather than cell-like. Correlations between CDM wakes do not extend much beyond a horizon length, so it is unlikely that CDM wakes are responsible for the correlations between clusters of galaxies. An estimate of the fraction of matter to accrete onto CDM wakes indicates that wakes could be more important in galaxy formation than previously anticipated.
A comparison of dispersion calculations in bluff body wakes using LES and unsteady RANS
Paschkewitz, J S
Accurate modeling of the dispersion behavior of sprays or particles is critical for a variety of problems including combustion, urban pollution or release events, and splash and spray transport around heavy vehicles. Bluff body wakes are particularly challenging since these flows are both highly separated and strongly unsteady. Attempting to model the dispersion of droplets or particles interacting with bluff body wakes is even more difficult since small differences in the flow field encountered by particles can lead to large differences in the dispersion behavior. Particles with finite inertia can exhibit additional complicating effects such as preferential concentration. In this preliminary study, we consider the dispersion of solid particles in the wake of a rectangular plane at a Reynolds number (Re) of 10000 and that of droplets in the wake of a simplified tractor-trailer geometry at Re = 2 x 10{sup 6} using both the Large Eddy Simulation (LES) and Unsteady Reynolds-Averaged Navier-Stokes (URANS) turbulence modeling approaches. The calculations were performed using identical meshes for both the LES and URANS models. Particle stresses are not backcoupled to the carrier fluid velocity solution. In the case of the rectangular plane wake, the LES calculation predicts a finer-scale and more persistent wake structure than the URANS one; the resulting particle dispersion is considerably ({approx} 40%) underpredicted for low inertia particles. For the case of the simplified tractor-trailer geometry, although the LES is underresolved, similar trends are observed with strong differences in the vertical and horizontal dispersion of the smallest particles. These results suggest that it may be necessary to use LES to accurately capture the dispersion behavior of small, low inertia particles or droplets, but that URANS may be sufficient for problems in which only large particles with substantial inertia are of primary concern.
Viscous effects on a vortex wake in ground effect
NASA Technical Reports Server (NTRS)
Zheng, Z.; Ash, Robert L.
Wake vortex trajectories and strengths are altered radically by interactions with the ground plane. Prediction of vortex strength and location is especially important in the vicinity of airports. Simple potential flow methods have been found to yield reasonable estimates of vortex descent rates in an otherwise quiescent ambient background, but those techniques cannot be adjusted for more realistic ambient conditions and they fail to provide satisfactory estimates of ground-coupled behavior. The authors have been involved in a systematic study concerned with including viscous effects in a wake-vortex system which is near the ground plane. The study has employed numerical solutions to the Navier-Stokes equations, as well as perturbation techniques to study ground coupling with a descending vortex pair. Results of a two-dimensional, unsteady numerical-theoretical study are presented in this paper. A time-based perturbation procedure has been developed which permits the use of analytical solutions to an inner and outer flow domain for the initial flow field. Predictions have been compared with previously reported laminar experimental results. In addition, the influence of stratification and turbulence on vortex behavior near the ground plane has been studied.
A CFD code comparison of wind turbine wakes
NASA Astrophysics Data System (ADS)
van der Laan, M. P.; Storey, R. C.; S�rensen, N. N.; Norris, S. E.; Cater, J. E.
A comparison is made between the EllipSys3D and SnS CFD codes. Both codes are used to perform Large-Eddy Simulations (LES) of single wind turbine wakes, using the actuator disk method. The comparison shows that both LES models predict similar velocity deficits and stream-wise Reynolds-stresses for four test cases. A grid resolution study, performed in EllipSys3D and SnS, shows that a minimal uniform cell spacing of 1/30 of the rotor diameter is necessary to resolve the wind turbine wake. In addition, the LES-predicted velocity deficits are also compared with Reynolds-Averaged Navier Stokes simulations using EllipSys3D for a test case that is based on field measurements. In these simulations, two eddy viscosity turbulence models are employed: the k-epsilon model and the k-epsilon-fp model. Where the k-epsilon model fails to predict the velocity deficit, the results of the k-epsilon-fP model show good agreement with both LES models and measurements.
ARTEMIS observations of lunar wake structure compared with hybrid �kinetic simulations and an analytic model
NASA Astrophysics Data System (ADS)
Gharaee, H.; Rankin, R.; Marchand, R.; Paral, J.
The ARTEMIS mission has made extensive measurements on the density and magnetic field structure of the lunar wake under different solar wind and magnetosphere conditions. Hybrid-kinetic simulations of the lunar wake have been found to be generally in good agreement with observations [Wiehle, S., et al., Planet. Space Sci., 2011], but are not readily available as they require access to large computers and human resources with expertise using this technology. It would be very useful to have an analytic model of the lunar wake, and one such model will be presented. It is based on an approach outlined by Hutchinson [Hutchinson, I., Physics Of Plasmas, 2008], and makes assumptions of cylindrical geometry, a strong and constant magnetic field, and fixed transverse velocity and temperature. Under these approximations the ion fluid equations (with massless electrons assumed) can be solved analytically by the method of characteristics. This paper demonstrates that the analytic model under these assumptions provides excellent agreement with observations and hybrid-kinetic simulations of the lunar wake. The approach outlined by Hutchinson is generalized to include an arbitrary angle between the interplanetary magnetic field and solar wind flow. This results in two angle-dependent characteristics for the fluid flow that can be solved for the density inside the wake region. The Density profiles for different orientations of magnetic field with respect to solar wind flow are in a good qualitative agreement with 2D Hybrid simulation results of the model developed by [Paral and Rankin, Nature Comms, 2012], and with ARTEMIS observations. Refrences, -Wiehle, S., et al. (2011), First Lunar wake passage of Artemis: Discrimination of wake effects and solar wind flactuations by 3D hybrid simulations, Planet. Space Sci., 59, 661-671, doi:10.1016/j.pss.2011.01.012. -Hutchinson, I. (2008),Oblique ion collection in the drift approximation:How magnetized Mach probes really work, Physics Of Plasmas, 15, 123503, doi:10.1063/1.3028314. - Paral and Rankin (2012),Dawn-dusk asymmetry in the Kelvin-Helmholtz instability at Mercurry, Nature Communications, 4, 1645, doi:10.1038/ncomms2676.
A Vortex Array Model of the Unsteady Wake of a Two-dimensional Pitching Airfoil
NASA Astrophysics Data System (ADS)
Naguib, Ahmed; Koochesfahani, Manoochehr
Motivated by recent interest in MAV aerodynamics, the present study is focused on obtaining a simplified, vortex-array model of the unsteady flow in the wake of an airfoil undergoing small-amplitude but high-reduced-frequency pitch oscillations. The model is used to predict the mean and unsteady velocity field in the wake of a NACA 0012 airfoil executing a sinusoidal as well as non-sinusoidal pitch oscillation. The model predictive accuracy is assessed by comparison to the LDV measurements of the streamwise velocity by Koochesfahani (AIAA J. 37, 1999) at a chord Reynolds number of 12,000 and a reduced frequency as high as 10. The results demonstrate the ability of the vortex-array model to successfully reproduce the experimentally measured mean and phase-averaged streamwise velocity profiles in the wake of the airfoil. Moreover, by using the model to reconstruct the complete velocity field in the wake, the mean streamwise force acting on the airfoil is computed for different frequencies, amplitudes and waveforms of the oscillation.
Separation of circadian and wake duration-dependent modulation of EEG activation during wakefulness
NASA Technical Reports Server (NTRS)
Cajochen, C.; Wyatt, J. K.; Czeisler, C. A.; Dijk, D. J.
The separate contribution of circadian rhythmicity and elapsed time awake on electroencephalographic (EEG) activity during wakefulness was assessed. Seven men lived in an environmental scheduling facility for 4 weeks and completed fourteen 42.85-h 'days', each consisting of an extended (28.57-h) wake episode and a 14.28-h sleep opportunity. The circadian rhythm of plasma melatonin desynchronized from the 42.85-h day. This allowed quantification of the separate contribution of circadian phase and elapsed time awake to variation in EEG power spectra (1-32 Hz). EEG activity during standardized behavioral conditions was markedly affected by both circadian phase and elapsed time awake in an EEG frequency- and derivation-specific manner. The nadir of the circadian rhythm in alpha (8-12 Hz) activity in both fronto-central and occipito-parietal derivations occurred during the biological night, close to the crest of the melatonin rhythm. The nadir of the circadian rhythm of theta (4.5-8 Hz) and beta (20-32 Hz) activity in the fronto-central derivation was located close to the onset of melatonin secretion, i.e. during the wake maintenance zone. As time awake progressed, delta frequency (1-4.5 Hz) and beta (20-32 Hz) activity rose monotonically in frontal derivations. The interaction between the circadian and wake-dependent increase in frontal delta was such that the intrusion of delta was minimal when sustained wakefulness coincided with the biological day, but pronounced during the biological night. Our data imply that the circadian pacemaker facilitates frontal EEG activation during the wake maintenance zone, by generating an arousal signal that prevents the intrusion of low-frequency EEG components, the propensity for which increases progressively during wakefulness.
CFD Simulations for the Effect of Unsteady Wakes on the Boundary Layer of a Highly Loaded Low-Pressure Turbine Airfoil (L1A)
NASA Technical Reports Server (NTRS)
Vinci, Samuel, J.
This report is the third part of a three-part final report of research performed under an NRA cooperative Agreement contract. The first part was published as NASA/CR-2012-217415. The second part was published as NASA/CR-2012-217416. The study of the very high lift low-pressure turbine airfoil L1A in the presence of unsteady wakes was performed computationally and compared against experimental results. The experiments were conducted in a low speed wind tunnel under high (4.9%) and then low (0.6%) freestream turbulence intensity for Reynolds number equal to 25,000 and 50,000. The experimental and computational data have shown that in cases without wakes, the boundary layer separated without reattachment. The CFD was done with LES and URANS utilizing the finite-volume code ANSYS Fluent (ANSYS, Inc.) under the same freestream turbulence and Reynolds number conditions as the experiment but only at a rod to blade spacing of 1. With wakes, separation was largely suppressed, particularly if the wake passing frequency was sufficiently high. This was validated in the 3D CFD efforts by comparing the experimental results for the pressure coefficients and velocity profiles, which were reasonable for all cases examined. The 2D CFD efforts failed to capture the three dimensionality effects of the wake and thus were less consistent with the experimental data. The effect of the freestream turbulence intensity levels also showed a little more consistency with the experimental data at higher intensities when compared with the low intensity cases. Additional cases with higher wake passing frequencies which were not run experimentally were simulated. The results showed that an initial 25% increase from the experimental wake passing greatly reduced the size of the separation bubble, nearly completely suppressing it.
Numerical simulation of near wake stratified flow at low Reynolds number
NASA Astrophysics Data System (ADS)
Frauni�, Philippe; Houcine, Hatem; Gharbi, Adel; Chashechkin, Yuli; Redondo, Jose Manuel
Numeric modeling of a flow past vertical and horizontal strips towed in a linearly stratified tank are preformed by comparison to laboratory experiments using Schlieren visualization, density marker and probe measurements of internal wave fields. Both parts of the wave fields including upstream transient and downstream stationary waves were resolved. Analysis is here focusing on observed near wake singular components. Acknowledgements : This research was supported by the Modtercom program of Region PACA
PKC in rat dorsal raphe nucleus plays a key role in sleep-wake regulation.
Li, Sheng-Jie; Cui, Su-Ying; Zhang, Xue-Qiong; Yu, Bin; Sheng, Zhao-Fu; Huang, Yuan-Li; Cao, Qing; Xu, Ya-Ping; Lin, Zhi-Ge; Yang, Guang; Cui, Xiang-Yu; Zhang, Yong-He
Studies suggest a tight relationship between protein kinase C (PKC) and circadian clock. However, the role of PKC in sleep-wake regulation remains unclear. The present study was conducted to investigate the role of PKC signaling in sleep-wake regulation in the rat. Our results showed that the phosphorylation level of PKC in dorsal raphe nucleus (DRN) was decreased after 6h sleep deprivation, while no alterations were found in ventrolateral preoptic nucleus (VLPO) or locus coeruleus (LC). Microinjection of a pan-PKC inhibitor, chelerythrine chloride (CHEL, 5 or 10nmol), into DRN of freely moving rats promoted non rapid eye movement sleep (NREMS) without influences on rapid eye movement sleep (REMS). Especially, CHEL application at 5nmol increased light sleep (LS) time while CHEL application at 10nmol increased slow wave sleep (SWS) time and percentage. On the other hand, microinjection of CaCl2 into DRN not only increased the phosphorylation level of PKC, but also reduced NREMS time, especially SWS time and percentage. While CHEL abolished the inhibitory effect of CaCl2 on NREMS and SWS. These data provide the first direct evidence that inhibition of intracellular PKC signaling in DRN could increase NREMS time including SWS time and percentage, while activation of PKC could suppress NREMS and reduce SWS time and percentage. These novel findings further our understanding of the basic cellular and molecular mechanisms of sleep-wake regulation. PMID:25970525
Wake patterns of the wings and tail of hovering hummingbirds
NASA Astrophysics Data System (ADS)
Altshuler, Douglas L.; Princevac, Marko; Pan, Hansheng; Lozano, Jesse
The flow fields of slowly flying bats and faster-flying birds differ in that bats produce two vortex loops during each stroke, one per wing, and birds produce a single vortex loop per stroke. In addition, the circulation at stroke transition approaches zero in bats but remains strong in birds. It is unknown if these difference derive from fundamental differences in wing morphology or are a consequence of flight speed. Here, we present an analysis of the horizontal flow field underneath hovering Anna�s hummingbirds ( Calypte anna) to describe the wake of a bird flying at zero forward velocity. We also consider how the hummingbird tail interacts with the wake generated by the wings. High-speed image recording and analysis from three orthogonal perspectives revealed that the wing tips reach peak velocities in the middle of each stroke and approach zero velocity at stroke transition. Hummingbirds use complex tail kinematic patterns ranging from in phase to antiphase cycling with respect to the wings, covering several phase shifted patterns. We employed particle image velocimetry to attain detailed horizontal flow measurements at three levels with respect to the tail: in the tail, at the tail tip, and just below the tail. The velocity patterns underneath the wings indicate that flow oscillates along the ventral-dorsal axis in response to the down- and up-strokes and that the sideways flows with respect to the bird are consistently from the lateral to medial. The region around the tail is dominated by axial flows in dorsal to ventral direction. We propose that these flows are generated by interaction between the wakes of the two wings at the end of the upstroke, and that the tail actively defects flows to generate moments that contribute to pitch stability. The flow fields images also revealed distinct vortex loops underneath each wing, which were generated during each stroke. From these data, we propose a model for the primary flow structures of hummingbirds that more strongly resembles the bat model. Thus, pairs of unconnected vortex loops may be shared features of different animals during hovering and slow forward flight.
Wake patterns of the wings and tail of hovering hummingbirds
NASA Astrophysics Data System (ADS)
Altshuler, Douglas L.; Princevac, Marko; Pan, Hansheng; Lozano, Jesse
The flow fields of slowly flying bats and fasterflying birds differ in that bats produce two vortex loops during each stroke, one per wing, and birds produce a single vortex loop per stroke. In addition, the circulation at stroke transition approaches zero in bats but remains strong in birds. It is unknown if these difference derive from fundamental differences in wing morphology or are a consequence of flight speed. Here, we present an analysis of the horizontal flow field underneath hovering Anna's hummingbirds (Calypte anna) to describe the wake of a bird flying at zero forward velocity. We also consider how the hummingbird tail interacts with the wake generated by the wings. High-speed image recording and analysis from three orthogonal perspectives revealed that the wing tips reach peak velocities in the middle of each stroke and approach zero velocity at stroke transition. Hummingbirds use complex tail kinematic patterns ranging from in phase to antiphase cycling with respect to the wings, covering several phase shifted patterns. We employed particle image velocimetry to attain detailed horizontal flow measurements at three levels with respect to the tail: in the tail, at the tail tip, and just below the tail. The velocity patterns underneath the wings indicate that flow oscillates along the ventral-dorsal axis in response to the down- and up-strokes and that the sideways flows with respect to the bird are consistently from the lateral to medial. The region around the tail is dominated by axial flows in dorsal to ventral direction. We propose that these flows are generated by interaction between the wakes of the two wings at the end of the upstroke, and that the tail actively defects flows to generate moments that contribute to pitch stability. The flow fields images also revealed distinct vortex loops underneath each wing, which were generated during each stroke. From these data, we propose a model for the primary flow structures of hummingbirds that more strongly resembles the bat model. Thus, pairs of unconnected vortex loops may be shared features of different animals during hovering and slow forward flight.
Introduction to wakefields and wake potentials
Wilson, P.B.
What are wakefields and wake potentials, and why are these concepts useful in the physics of linear accelerators and storage rings We approach this question by first reviewing the basic physical concepts which underlie the mathematical formalism. We then present a summary of the various techniques that have been developed to make detailed calculations of wake potentials. Finally, we give some applications to current problems of interest in accelerator physics. No attempt at completeness can be made in an introductory article of modest length. Rather, we try to give a broad overview and to list key references for more detailed study. It will also be apparent that the last chapter on this subject, with all the loose ends neatly tied up, has yet to be written. There are subtle points, there are controversial questions, and active calculations to resolve these questions are continuing at the time of this writing. 61 refs., 10 figs., 1 tab.
Ship wakes and their manifestations on the sea surface
NASA Astrophysics Data System (ADS)
Ermakov, Stanislav; Kapustin, Ivan; Kalimulin, Rashid
Spatial/temporal evolution of turbulence generated by surface ships and the effect of the wake on short wind waves has been studied on the Black Sea and on the Gorky Water Reservoir. Measurements of currents in ship wakes were conducted using an Acoustic Doppler Current Profiler deployed from a motor boat. It was obtained that the temporal/spatial evolution of the wake width could be described approximately by a 0.4-power dependence, and the wake depth remained nearly constant at its initial stage. This allowed one to consider the wake widening as a one-dimensional process. We have developed a simple one-dimensional model of ship wake evolution using a semi-empirical theory of turbulence, and the initial stage of the wake widening (when neglecting dissipation) was described by the equation of turbulent energy balance with the pulse initial condition. Mean circulating currents in the wake zone resulting in the wind wave intensification ("suloi" areas) at the boundaries of the wake were detected in experiment. The asymmetry of the "suloi" bands was observed when the wind was blowing nearly perpendicular to the wake axis. It was shown that the later stage of the wake evolution is characterized by the formation of slick bands at the edges of the wake. The slick bands is a result of the transport of surfactants to the water surface by air bubbles in the wake and their compression due to the mean circulating currents. The work was supported by RFBR (projects 12-05-31237, 11-05-00295), the Program RAN Radiophysics, and by the Russian Government (Grants No. 11.G34.31.0048 and 11.G34.31.0078).
Plasma lens and wake experiments in Japan
NASA Astrophysics Data System (ADS)
Ogata, Atsushi
Plasma lens and wake experiments performed and planned in Japan are reviewed. Overdense plasma lens experiments were conducted at the University of Tokyo on a 18 MeV linac. The change in energy distribution of linac beams caused by the plasma wakefield was measured at KEK on a 500 MeV linac. Laser wakefield acceleration experiments are planned at Osaka University using a 30TW Nd:glass laser.
Adenosine and sleep�wake regulation
Radhika Basheer; Robert E. Strecker; Mahesh M. Thakkar; Robert W. McCarley
This review addresses three principal questions about adenosine and sleep�wake regulation: (1) Is adenosine an endogenous sleep factor? (2) Are there specific brain regions\\/neuroanatomical targets and receptor subtypes through which adenosine mediates sleepiness? (3) What are the molecular mechanisms by which adenosine may mediate the long-term effects of sleep loss? Data suggest that adenosine is indeed an important endogenous, homeostatic
First comparison of LES of an offshore wind turbine wake with dual-Doppler lidar measurement in the offshore wind farm "alpha ventus"
NASA Astrophysics Data System (ADS)
Vollmer, L.; Trabucchi, D.; Witha, B.; van Dooren, M.; Trujillo, J. J.; Schneemann, J.; K�hn, M.
The planning of offshore wind farms is still tainted with high risks due to unknown power losses and a higher level of fatigue loads due to wake effects. Recently, Large Eddy Simulations (LES) are more and more used for simulating offshore wind turbine wakes as they resolve the atmospheric turbulence as well as the wake turbulence.However, for an application of LES wind fields to assess offshore wind farm flow a proper validation with measured data is necessary.Several methods have been investigated at the University of Oldenburg to compare LES wind fields and lidar measurements. In this study we apply one of these methods to validate wake simulations of a single wake of a 5MW wind turbine in the German offshore wind farm "alpha ventus" with processed dual-Doppler lidar measurements in the same wind farm.The simulations are performed with the LES model PALM, which has been enhanced by two different approaches of actuator models to simulate the wake of single wind turbines and the interaction of wakes in wind farms. Effects of tower and nacelle are regarded as well as simple turbine control mechanisms. The simulations are initialized with comparable atmospheric conditions as during the time of lidar operation by using measurements from the adjacent meteorological mast FINO 1.Plan Position Indicator (PPI) measurements have been performed with two long-range wind lidars installed at different opposing platforms at the border of the wind farm. A Cartesian grid was overlapped to the scanned region and a dual-Doppler algorithm was applied in order to estimate the horizontal stationary wind field on the grid nodes. To our knowledge, the presented study is one of the first validations of LES wake simulations with lidar measurements and first which validates offshore LES wake simulations with 2D lidar data.
Suppression of the metal-insulator transition by magnetic field in (Pr1-yYy)0.7Ca0.3CoO3 (y = 0.0625)
NASA Astrophysics Data System (ADS)
Naito, Tomoyuki; Fujishiro, Hiroyuki; Nishizaki, Terukazu; Kobayashi, Norio; Hejtm�nek, Ji?�; Kn�ek, Karel; Jir�k, Zden?k
The (Pr1-yYy)0.7Ca0.3CoO3 compound (y = 0.0625, TMI-SS=40 K), at the lower limit for occurrence of the first-order metal-insulator (MI) and simultaneous spin-state (SS) transitions, has been studied using electrical resistivity and magnetization measurements in magnetic fields up to 17 T. The isothermal experiments demonstrate that the low-temperature insulating phase can be destabilized by an applied field and the metallic phase returns well below the transition temperature TMI-SS. The reverse process with decreasing field occurs with a significant hysteresis. The temperature scans taken at fixed magnetic fields reveal a parabolic-like decrease in TMI-SS with increasing field strength and a complete suppression of the MI-SS transition in fields above 9 T.
Direct Simulation and Theoretical Study of Sub- and Supersonic Wakes
NASA Astrophysics Data System (ADS)
Hickey, Jean-Pierre
Wakes are constitutive components of engineering, aeronautical and geophysical flows. Despite their canonical nature, many fundamental questions surrounding wakes remain unanswered. The present work studies the nature of archetypal planar splitter-plate wakes in the sub- and supersonic regimes from a theoretical as well as a numerical perspective. A highly-parallelizable computational fluid dynamic solver was developed, from scratch, for the very-large scale direct numerical simulations of high-speed free shear flows. Wakes maintain a near indelible memory of their origins; thus, changes to the state of the flow on the generating body lead to multiple self-similar states in the far wake. To understand the source of the lack of universality, three distinct wake evolution scenarios are investigated in the incompressible limit: the Kelvin-Helmholtz transition, the bypass transition in an asymmetric wake and the initially turbulent wake. The multiplicity of self-similar states is the result of a plurality of far wake structural organizations, which maintains the memory of the flow. The structural organization is predicated on the presence or absence of near wake anti-symmetric perturbations (as a result of shedding, instability modes and/or trailing edge receptivity). The plurality of large-scale structural organization contrasts with the commonality observed in the mid-sized structures, which are dominated by inclined vortical rods, and not, as previously assumed, by horseshoe structures. The compressibility effects are a direct function of the maximal velocity defect in the wake and are therefore only important in the transitional region - the far wake having an essentially incompressible character. The compressibility simultaneously modifies the growth rate and wavelength of the primary instability mode with a concomitant effect on the emerging transitional structures. As a direct result, the spanwise rollers have an increasing ellipticity and cross-wake domain of influence with the increasing Mach number of the wake. Consequently, structural pairing - a key feature of wake transition - is inhibited at a critical Mach number, which greatly modifies the transitional dynamics. In idealized wakes, the increased stability caused by the compressibility effects leads to a vortex breakdown of secondary structures prior to the full transition of the principal mode. These findings open the door to novel mixing enhancement and flow control possibilities in the high-speed wake transition. Keywords: FLUID DYNAMICS, DIRECT NUMERICAL SIMULATIONS, FREE SHEAR FLOWS, TURBULENCE, NUMERICAL METHODS
Wake models are used to improve predictions of Annual Energy Production (AEP) of wind farms.
Daraio, Chiara
models take account of the effects of wakes on downstream wind turbines. �Wake models used in the wind and wind turbine wakes in large windfarms offshore, Wind Energy 12, pp. 431-444, 2009. [2] L.P. Chamorro�Wake models are used to improve predictions of Annual Energy Production (AEP) of wind farms. �Wake
Preliminary Velocity Measurements in the Wake of a Submarine Model
NASA Astrophysics Data System (ADS)
Jimenez, J. M.; Reynolds, R.; Smits, A. J.
Preliminary Particle Image Velocimetry (PIV) over a submarine shape has been conducted in a low speed wind tunnel at Princeton University. The model is a 1/67 replica of the USS Albacore, an experimental submarine designed to achieve maximum underwater performance, and based on "bodies of revolution." The model is tested with a sail, and different tail appendages. Velocity vector fields and flow visualizations in the wake region are presented for Reynolds numbers based on model length up to 10^5. The experiments establish the groundwork for future investigations of submarine models in the new High Reynolds Number Test Facility (http://www.princeton.edu/ gasdyn/HRTF.html). Supported by ONR Grants N00014-97-1-0325, N00014-97-1-0340 and N00014-97-1-0618.
Experimental study of rotor wake/body interactions in hover
NASA Technical Reports Server (NTRS)
Bagai, A.; Leishman, J. G.
Experiments were conducted to document the tip vortex geometries and interactional effects betwen a hovering rotor and a body representing a simplified helicopter fuselage. The wide-field shadowgraph technique was used to visualize the rotor tip vortices and to obtain quantitative information on the trajectories, with and without the presence of the body. It was found that the effects of the body caused significant changes to both the radial contraction and axial displacements of the tip vortices compared to the isolated case. Direct impingement of the tip vortices on the body surface was also observed, and found to cause large local wake deformations. The rotor performance was significantly affected by the body, producing a higher figure of merit relative to the isolated case.
Effects of energetic coherent motions on the power and wake of an axial-flow turbine
NASA Astrophysics Data System (ADS)
Chamorro, L. P.; Hill, C.; Neary, V. S.; Gunawan, B.; Arndt, R. E. A.; Sotiropoulos, F.
A laboratory experiment examined the effects of energetic coherent motions on the structure of the wake and power fluctuations generated by a model axial-flow hydrokinetic turbine. The model turbine was placed in an open-channel flow and operated under subcritical conditions. The incoming flow was locally perturbed with vertically oriented cylinders of various diameters. An array of three acoustic Doppler velocimeters aligned in the cross-stream direction and a torque transducer were used to collect high-resolution and synchronous measurements of the three-velocity components of the incoming and wake flow as well as the turbine power. A strong scale-to-scale interaction between the large-scale and broadband turbulence shed by the cylinders and the turbine power revealed how the turbulence structure modulates the turbine behavior. In particular, the response of the turbine to the distinctive von K�rm�n-type vortices shed from the cylinders highlighted this phenomenon. The mean and fluctuating characteristics of the turbine wake are shown to be very sensitive to the energetic motions present in the flow. Tip vortices were substantially dampened and the near-field mean wake recovery accelerated in the presence of energetic motions in the flow. Strong coherent motions are shown to be more effective than turbulence levels for triggering the break-up of the spiral structure of the tip-vortices.
Quantifying error of remote sensing observations of wind turbine wakes using computational fluid dynamics
NASA Astrophysics Data System (ADS)
Lundquist, J. K.; Churchfield, M.; Lee, S.; Clifton, A.
Wind-profiling lidars are now regularly used in wind energy for wind resource assessment, inflow characterization, and wake measurements. Lidar wind profilers exploit the Doppler shift of laser light backscattered from particulates carried by the wind to measure a line-of-sight (LOS) velocity. The Doppler Beam Swinging (DBS) technique, used by many commercial systems, considers measurements of this LOS velocity in multiple radial directions in order to estimate horizontal and vertical winds. The method relies on the assumption of homogeneous flow across the region sampled by the beams. Use of such a system in inhomogeneous flow, such as wind turbine wakes or complex terrain, will result in error which may or may not be significant. To quantify the error expected from such violation of the assumption of horizontal homogeneity, we simulate inhomogeneous flow in the atmospheric boundary layer, notably stably-stratified flow past a wind turbine using large-eddy simulation. This slightly stable case results in 15 degrees of wind direction change across the turbine rotor disk. The resulting flow-field is sampled in the same fashion that a lidar samples the atmosphere with the DBS approach, enabling quantification of the error in the DBS observations. The observations from the instruments located upwind have small error, which is further ameliorated with time-averaging. However, the downwind observations, particularly within the first two rotor diameters downwind from the wind turbine, suffer from errors due to the heterogeneity of the wind turbine wake. Errors in the stream-wise component of the flow are generally small, less than 0.5 m s-1. Errors in the cross-stream and vertical velocity components are much larger: cross-stream component errors are on the order of 1.0 m s-1, while errors in the vertical velocity exceed the actual values of the vertical velocity. DBS-based assessments of wake wind speed deficits based on the stream-wise velocity can be relied upon even within the near wake within 0.5 m s-1, but cross-stream and vertical velocity estimates in the near wake are compromised. Measurements of inhomogeneous flow such as wind turbine wakes are susceptible to these errors, and interpretations of field observations should account for this uncertainty.
Orexin neurons suppress narcolepsy via 2 distinct efferent pathways.
Hasegawa, Emi; Yanagisawa, Masashi; Sakurai, Takeshi; Mieda, Michihiro
The loss of orexin neurons in humans is associated with the sleep disorder narcolepsy, which is characterized by excessive daytime sleepiness and cataplexy. Mice lacking orexin peptides, orexin neurons, or orexin receptors recapitulate human narcolepsy phenotypes, further highlighting a critical role for orexin signaling in the maintenance of wakefulness. Despite the known role of orexin neurons in narcolepsy, the precise neural mechanisms downstream of these neurons remain unknown. We found that targeted restoration of orexin receptor expression in the dorsal raphe (DR) and in the locus coeruleus (LC) of mice lacking orexin receptors inhibited cataplexy-like episodes and pathological fragmentation of wakefulness (i.e., sleepiness), respectively. The suppression of cataplexy-like episodes correlated with the number of serotonergic neurons restored with orexin receptor expression in the DR, while the consolidation of fragmented wakefulness correlated with the number of noradrenergic neurons restored in the LC. Furthermore, pharmacogenetic activation of these neurons using designer receptor exclusively activated by designer drug (DREADD) technology ameliorated narcolepsy in mice lacking orexin neurons. These results suggest that DR serotonergic and LC noradrenergic neurons play differential roles in orexin neuron-dependent regulation of sleep/wakefulness and highlight a pharmacogenetic approach for the amelioration of narcolepsy. PMID:24382351
A mathematical model of the sleep\\/wake cycle
Michael J. Rempe; Janet Best; David Terman
We present a biologically-based mathematical model that accounts for several features of the human sleep\\/wake cycle. These\\u000a features include the timing of sleep and wakefulness under normal and sleep-deprived conditions, ultradian rhythms, more frequent\\u000a switching between sleep and wakefulness due to the loss of orexin and the circadian dependence of several sleep measures.\\u000a The model demonstrates how these features depend
Initialization and Simulation of Three-Dimensional Aircraft Wake Vortices
NASA Technical Reports Server (NTRS)
Ash, Robert L.; Zheng, Z. C.
This paper studies the effects of axial velocity profiles on vortex decay, in order to properly initialize and simulate three-dimensional wake vortex flow. Analytical relationships are obtained based on a single vortex model and computational simulations are performed for a rather practical vortex wake, which show that the single vortex analytical relations can still be applicable at certain streamwise sections of three-dimensional wake vortices.
Detection and Behavior of Pan Wakes in Saturn's A Ring
NASA Technical Reports Server (NTRS)
Horn, L. J.; Showalter, M. R.; Russell, C. T.
Six previously unseen Pan wakes are found interior and exterior to the Encke gap in Saturn's A ring, one in the Voyager 2 photopolarimeter (PPS) stellar occultation data and five in the Voyager 1 radio science (RSS) Earth occultation data. Pan orbits at the center of the Encke gap and maintains it...The detection of Pan wakes at longitudes greater than 360(deg) demonstrates that wakes persist for much longer than originally hypothesized and may interact with one another.
A General Free Wake Geometry Calculation For Wings and Rotors
Wayne Johnson
A general free wake geometry calculation for wings and rotors is presented. The method, which has been implemented in CAMRAD II, gives good performance and airloads correlation at advance ratios of 0.05 and above, with reasonable computation speed. The wake geometry distortion can be calculated for multiple wings, multiple rotors, and non-identical blades; for all wake structures, including multiple rolled-up
Using the coupled wake boundary layer model to evaluate the effect of turbulence intensity on wind farm performance
NASA Astrophysics Data System (ADS)
Stevens, Richard J. A. M.; Gayme, Dennice; Meneveau, Charles
We use the recently introduced coupled wake boundary layer (CWBL) model to predict the effect of turbulence intensity on the performance of a wind farm. The CWBL model combines a standard wake model with a �top-down� approach to get improved predictions for the power output compared to a stand-alone wake model. Here we compare the CWBL model results for different turbulence intensities with the Horns Rev field measurements by Hansen et al., Wind Energy 15, 183196 (2012). We show that the main trends as function of the turbulence intensity are captured very well by the model and discuss differences between the field measurements and model results based on comparisons with LES results from Wu and Port�-Agel, Renewable Energy 75, 945-955 (2015).
Flow visualization study of the MOD-2 wind turbine wake
Liu H.T.; Waite, J.W.; Hiester, T.R.; Tacheron, P.H.; Srnsky, R.A.
The specific objectives of the study reported were: to determine the geometry of the MOD-2 wind turbine wake in terms of wake height and width as a function of downstream distance under two conditions of atmospheric stability; to estimate the mean velocity deficit at several downstream stations in the turbine wake; and to investigate the behavior of the rotor-generated vortices, particularly their configuration and persistence. The background of the wake problem is briefly examined, including a discussion of the critical issues that the flow visualization study addresses. Experimental techniques and data analysis methods are described in detail. (LEW)
Solutions for the turbulent classical wake using Lie symmetry methods
NASA Astrophysics Data System (ADS)
Hutchinson, A. J.; Mason, D. P.; Mahomed, F. M.
We investigate the turbulent planar classical wake and derive the governing equations using the eddy viscosity closure model. The Lie point symmetry associated with the elementary conserved vector is used to generate the invariant solution. We first consider the case where the eddy viscosity depends only on the distance along the wake. We then relax this condition to include the dependence of the eddy viscosity on the perpendicular distance from the axis of the wake. The profiles of the mean velocity show that the role of the eddy viscosity is to increase the effective width of the wake and decrease the magnitude of the maximum mean velocity deficit.
The three-dimensional evolution of a plane wake
NASA Technical Reports Server (NTRS)
Maekawa, H.; Moser, R. D.; Mansour, N. N.
In the past three decades, linear stability analysis has led to a comprehensive understanding of the linear stages of transition in plane wakes. Our understanding of the nonlinear and turbulent stages is less developed. Nonlinear theory developed by Papageorgiou and Smith was used to study the long-wavelength regime in wakes. The nonlinear and turbulent stages were investigated experimentally, and few numerical studies examined the early nonlinear stages of forced wakes. The evolution of three dimensional disturbances in an incompressible wake is investigated using direct numerical simulations. The instantaneous three-dimaensional structures and corresponding statistics are presented.
Rotor wake characteristics of a transonic axial flow fan
NASA Technical Reports Server (NTRS)
Hathaway, M. D.; Gertz, J.; Epstein, A.; Strazisar, A. J.
State of the art turbomachinery flow analysis codes are not capable of predicting the viscous flow features within turbomachinery blade wakes. Until efficient 3D viscous flow analysis codes become a reality there is therefore a need for models which can describe the generation and transport of blade wakes and the mixing process within the wake. To address the need for experimental data to support the development of such models, high response pressure measurements and laser anemometer velocity measurements were obtained in the wake of a transonic axial flow fan rotor.
Rotor wake characteristics of a transonic axial flow fan
NASA Technical Reports Server (NTRS)
Hathaway, M. D.; Gertz, J.; Epstein, A.; Strazisar, A. J.
State of the art turbomachinery flow analysis codes are not capable of predicting the viscous flow features within turbomachinery blade wakes. Until efficient 3D viscous flow analysis codes become a reality there is therefore a need for models which can describe the generation and transport of blade wakes and the mixing process within the wake. To address the need for experimental data to support the development of such models, high response pressure measurements and laser anemometer velocity measurements have been obtained in the wake of a transonic axial flow fan rotor.
An experimental investigation on wind turbine aeromechanics and wake interferences among multiple wind turbines
NASA Astrophysics Data System (ADS)
Ozbay, Ahmet
A comprehensive experimental study was conducted to investigate wind turbine aeromechanics and wake interferences among multiple wind turbines sited in onshore and offshore wind farms. The experiments were carried out in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) Wind Tunnel available at Iowa State University. An array of scaled three-blade Horizontal Axial Wind Turbine (HAWT) models were placed in atmospheric boundary layer winds with different mean and turbulence characteristics to simulate the situations in onshore and offshore wind farms. The effects of the important design parameters for wind farm layout optimization, which include the mean and turbulence characteristics of the oncoming surface winds, the yaw angles of the turbines with respect to the oncoming surface winds, the array spacing and layout pattern, and the terrain topology of wind farms on the turbine performances (i.e., both power output and dynamic wind loadings) and the wake interferences among multiple wind turbines, were assessed in detail. The aeromechanic performance and near wake characteristics of a novel dual-rotor wind turbine (DRWT) design with co-rotating or counter-rotating configuration were also investigated, in comparison to a conventional single rotor wind turbine (SRWT). During the experiments, in addition to measuring dynamic wind loads (both forces and moments) and the power outputs of the scaled turbine models, a high-resolution Particle Image Velocity (PIV) system was used to conduct detailed flow field measurements (i.e., both free-run and phase-locked flow fields measurements) to reveal the transient behavior of the unsteady wake vortices and turbulent flow structures behind wind turbines and to quantify the characteristics of the wake interferences among the wind turbines sited in non-homogenous surface winds. A miniature cobra anemometer was also used to provide high-temporal-resolution data at points of interest to supplement the full field PIV measurement results. The detailed flow field measurements are correlated with the dynamic wind loads and power output measurements to elucidate underlying physics in order to gain further insight into the characteristics of the power generation performance, dynamic wind loads and wake interferences of the wind turbines for higher total power yield and better durability of the wind turbines sited in atmospheric boundary layer (ABL) winds.
Scanning laser-velocimeter surveys and analysis of multiple vortex wakes of an aircraft
NASA Technical Reports Server (NTRS)
Corsiglia, V. R.; Orloff, K. L.
A laser velocimeter capable of rapidly scanning a flow field while simultaneously sensing two components of the velocity was used to measure the vertical and streamwise velocity structure 1.5 spans downstream in the wake of a model typical of a large subsonic transport (Boeing 747). This flow field was modeled by a superposition of axisymmetric vortices with finite cores. This theoretical model was found to agree with the measured velocities everywhere except where two vortices were in close proximity. Vortex strengths derived from the span loading on the wing as predicted by vortex-lattice theory also agree with the present measurements. The axisymmetric vortex model used herein is a useful tool for analytically investigating the vortex wakes of aircraft.
Wake measurements for flow around a sphere in a viscoelastic fluid
NASA Astrophysics Data System (ADS)
Fabris, Drazen; Muller, Susan J.; Liepmann, Dorian
The flow field around a sphere falling at its terminal velocity in a column of viscoelastic non-shear-thinning fluid is experimentally measured with digital particle image velocimetry. The working fluid is an extensively characterized, monodisperse, polystyrene based Boger fluid. The sphere radius relative to the radius of the column of fluid is small (a/rc=0.083). The Weissenberg number (?Ut/a) ranges from 0.5 to 14 over which the sphere experiences a drag increase up to 8 times that of the Newtonian flow. The flow field is investigated in detail for We 0.5 to 2.5. A length and width scale is defined for the wake. Over this range of We the wake is found to grow linearly with We and become self-similar in a transverse cross-section of the axial component of the velocity. Streamlines along with extension and rotation rates along those streamlines are also determined.
Helicopter rotor wake geometry and its influence in forward flight. Volume 1: Generalized wake geometry and wake effect on rotor airloads and performance
NASA Technical Reports Server (NTRS)
Egolf, T. A.; Landgrebe, A. J.
An analytic investigation to generalize wake geometry of a helicopter rotor in steady level forward flight and to demonstrate the influence of wake deformation in the prediction of rotor airloads and performance is described. Volume 1 presents a first level generalized wake model based on theoretically predicted tip vortex geometries for a selected representative blade design. The tip vortex distortions are generalized in equation form as displacements from the classical undistorted tip vortex geometry in terms of vortex age, blade azimuth, rotor advance ratio, thrust coefficient, and number of blades. These equations were programmed to provide distorted wake coordinates at very low cost for use in rotor airflow and airloads prediction analyses. The sensitivity of predicted rotor airloads, performance, and blade bending moments to the modeling of the tip vortex distortion are demonstrated for low to moderately high advance ratios for a representative rotor and the H-34 rotor. Comparisons with H-34 rotor test data demonstrate the effects of the classical, predicted distorted, and the newly developed generalized wake models on airloads and blade bending moments. Use of distorted wake models results in the occurrence of numerous blade-vortex interactions on the forward and lateral sides of the rotor disk. The significance of these interactions is related to the number and degree of proximity to the blades of the tip vortices. The correlation obtained with the distorted wake models (generalized and predicted) is encouraging.
Effect of grain charging dynamics on the wake potential of a moving test charge in a dusty plasma
Shafiq, Muhammad; Raadu, Michael A. [Royal Institute of Technology, School of Electrical Engineering, Division of Space and Plasma Physics, SE-100 44 Stockholm (Sweden)
The response potential of a dusty (complex) plasma to a moving test charge strongly depends on its velocity. For a test charge moving with a velocity exceeding the dust-acoustic speed, a distinctive wake-field is produced trailing behind the test charge. Here the response to a fast moving test charge, when dispersion effects are small and the dust behaves as a cold plasma component, is considered. The effects of dynamical grain charging are included, and the cases with and without these effects are analyzed and compared. The plasma dielectric function is chosen assuming that all grains are of the same size and includes a response term for charging dynamics. The wake field potential is found either explicitly in terms of known functions or by using numerical methods for the integral expression. Maximum response is found on the wake cone with apex angle determined by the ratio between the dust acoustic velocity and the test charge velocity. The structure of the wake field stretches in the direction of the test charge velocity when this increases. The functional form of the field is given by separately changing the length scales parallel and perpendicular to the velocity. The potential on the axis gives an electric field close behind the test charge that can attract charges with the same sign. The grain charging dynamics leads to a spatial damping and a phase shift in the potential response.
Sleep�wake cycles in normal fetuses
Chitkasaem Suwanrath; Thitima Suntharasaj
Objective��To study the normal ranges of sleep�wake cycles in normal fetuses.\\u000a \\u000a \\u000a \\u000a Materials and methods��A total of 600 fetal heart rate (FHR) tracings were studied from uncomplicated singleton pregnancies at a gestational age\\u000a between 30 and 40�weeks with a 1-h recording. Two obstetricians interpreted all the FHR recordings independently.\\u000a \\u000a \\u000a \\u000a Results��The mean baseline FHR was 141.6 (7.6)�beats\\/min. The median relative percentage time
Geometrical Wake of a Smooth Flat Collimator
Stupakov, G.V.; /SLAC
A transverse geometrical wake generated by a beam passing through a smooth flat collimator with a gradually varying gap between the upper and lower walls is considered. Based on generalization of the approach recently developed for a smooth circular taper we reduce the electromagnetic problem of the impedance calculation to the solution of two much simpler static problems - a magnetostatic and an electrostatic ones. The solution shows that in the limit of not very large frequencies, the impedance increases with the ratio h/d where h is the width and d is the distance between the collimating jaws. Numerical results are presented for the NLC Post Linac collimator.
Wakes from arrays of buildings. [flight safety
NASA Technical Reports Server (NTRS)
Logan, E., Jr.; Lin, S. H.
Experiments were carried out in a small wind tunnel in which atmospheric flow around buildings was simulated. Arrays of one, two, three, and four model buildings were tested, and wake profiles of velocity and turbulence were measured. The data indicate the effect of the buildings on the wind environment encountered by aircraft during landing or takeoff operations. It was possible to use the results to locate the boundaries of the air regions affected by the obstacles and to recommend preferred arrangements of buildings to maximize light safety.
Wakes from arrays of buildings. [flight safety
NASA Technical Reports Server (NTRS)
Logan, E., Jr.; Lin, S. H.; Alexander, M. B.
Experiments were carried out in a small wind tunnel in which atmospheric flow around buildings was simulated. Arrays of one, two, three, and four model buildings were tested, and wake profiles of velocity and turbulence were measured. The data indicate the effect of the buildings on the wind environment encountered by aircraft during landing or takeoff operations. It was possible to use the results to locate the boundaries of the air regions affected by the obstacles and to recommend preferred arrangement of buildings to maximize light safety. Previously announced in STAR as N83-14430
Wake Forest University Physics Demonstration Videos
NSDL National Science Digital Library
Physics is plenty exciting on its own, but this clutch of physics demonstration videos offered up by Wake Forest University's Physics departments will probably have students running out to learn more about string theory and cosmology. Teachers will definitely appreciate this resource, as they can use these videos in the classroom or just recommend to their students. Visitors can view the videos in their entirety by subject headings, which include "Motion", "Heat", "Optics", and not surprisingly, "Newton". All told there are dozens of videos, including "Bed of Nails", "Cartesian Diver", and the surreal yet appropriately titled "Marshmallow Man". Overall, this resource is a delightful find.
Directivity and trends of noise generated by a propeller in a wake
P. J. W. Block; C. L. Gentry Jr.
An experimental study of the effects on far-field propeller noise of a pylon wake interaction was conducted with a scale model of a single-rotation propeller in a low-speed anechoic wind tunnel. A detailed mapping of the noise directivity was obtained at 10 test conditions covering a wide range of propeller power landings at several subsonic tip speeds. Two types of
Suppression of vortex shedding from bluff bodies with a fixed wavy separation line
NASA Astrophysics Data System (ADS)
Darekar, R. M.; Sherwin, S. J.
A numerical investigation has been performed of flow past rectangular cylinders with a three dimensional geometric perturbation on the front stagnation face which results in the suppression of the von K�rm�n shedding frequency. The perturbation is applied in the form of a sinusoidal spanwise waviness as experimentally studied by Bearman and Owen. The computations were performed using a spectral/hp element solver, Nektar at a Reynolds number of Re=100 and are in good agreement with experiments. After a transient time period where shedding is observed the near wake stabilises to a near time-independent state. Once vortex shedding is suppressed, the detached shear layer from the upper and lower fixed separations points is observed to have a spanwise form which has a maximum displacement at the valleys of the geometry and a minimum displacement at the peaks. The vortex suppression is associated with a drag reduction and corresponding increase in base pressure as compared with the straight cylinder of about 14% at Re=100. Furthermore, the computations clearly show two counter-rotating cells in the near wake. Using the coherent structure identification proposed by Jeong and Hussain, the vortical structure of the near wake has been extracted and a distorted vortex ring is observed in the near wake connecting the upper and lower shear layers. Current investigation are focused towards understanding the stabilising nature and formation of the vortical structures.
Investigation on 3D t wake flow structures of swimming bionic fish
NASA Astrophysics Data System (ADS)
Shen, G.-X.; Tan, G.-K.; Lai, G.-J.
A bionic experimental platform was designed for the purpose of investigating time accurate three-dimensional flow field, using digital particle image velocimetry (DSPIV). The wake behind the flapping trail of a robotic fish model was studied at high spatial resolution. The study was performed in a water channel. A robot fish model was designed and built. The model was fixed onto a rigid support framework using a cable-supporting method, with twelve stretched wires. The entire tail of the model can perform prescribed motions in two degrees of freedom, mainly in carangiform mode, by driving its afterbody and lunate caudal fin respectively. The DSPIV system was set up to operate in a translational manner, measuring velocity field in a series of parallel slices. Phase locked measurements were repeated for a number of runs, allowing reconstruction of phase average flow field. Vortex structures with phase history of the wake were obtained. The study reveals some new and complex three-dimensional flow structures in the wake of the fish, including "reverse hairpin vortex" and "reverse Karman S-H vortex rings", allowing insight into physics of this complex flow.
Relationship between vortex ring in tail fin wake and propulsive force
NASA Astrophysics Data System (ADS)
Imamura, Naoto; Matsuuchi, Kazuo
Our aim was to investigate the three-dimensional (3D) vortex ring in the wake of a tail fin and to clarify the propulsion mechanism of dolphins and fish. In this study, we replaced a tail fin in pitching motion with an oscillating wing having a drive unit. The flow fields around the wing were measured by stereoscopic particle image velocimetry. To visualize the 3D structure of the vortex in the wake, we determined the flow fields in equally spaced cross-sectional planes. We reconstructed the 3D velocity fields from the velocity data with three components in two dimensions. We visualized the 3D vortex structure from these velocity data and plotted an iso-vorticity surface. As a result, we found that the vortex ring was generated by the kick-down and kick-up motions of the wing and that the wake structure was comparable with that obtained numerically. Moreover, we calculated the propulsive forces from the temporal variations in circulation and in the area surrounded by the vortex ring.
Dexamethasone suppression test
DST; ACTH suppression test; Cortisol suppression test ... During this test, you will receive dexamethasone. This is a strong man-made (synthetic) glucocorticoid medication. Afterward, your blood is drawn ...
Multi-component wind measurements of wind turbine wakes performed with three LiDARs
NASA Astrophysics Data System (ADS)
Iungo, G. V.; Wu, Y.-T.; Port�-Agel, F.
Field measurements of the wake flow produced from the interaction between atmospheric boundary layer and a wind turbine are performed with three wind LiDARs. The tested wind turbine is a 2 MW Enercon E-70 located in Collonges, Switzerland. First, accuracy of mean values and frequency resolution of the wind measurements are surveyed as a function of the number of laser rays emitted for each measurement. Indeed, measurements performed with one single ray allow maximizing sampling frequency, thus characterizing wake turbulence. On the other hand, if the number of emitted rays is increased accuracy of mean wind is increased due to the longer sampling period. Subsequently, two-dimensional measurements with a single LiDAR are carried out over vertical sections of the wind turbine wake and mean wake flow is obtained by averaging 2D measurements consecutively performed. The high spatial resolution of the used LiDAR allows characterizing in details velocity defect present in the central part of the wake and its downstream recovery. Single LiDAR measurements are also performed by staring the laser beam at fixed directions for a sampling period of about ten minutes and maximizing the sampling frequency in order to characterize wake turbulence. From these tests wind fluctuation peaks are detected in the wind turbine wake at blade top-tip height for different downstream locations. The magnitude of these turbulence peaks is generally reduced by moving downstream. This increased turbulence level at blade top-tip height observed for a real wind turbine has been already detected from previous wind tunnel tests and Large Eddy simulations, thus confirming the presence of a source of dangerous fatigue loads for following wind turbines within a wind farm. Furthermore, the proper characterization of wind fluctuations through LiDAR measurements is proved by the detection of the inertial subrange from spectral analysis of these velocity signals. Finally, simultaneous measurements with two LiDARs are performed over the mean vertical symmetry plane of the wind turbine wake, while a third LiDAR measures the incoming wind over a vertical plane parallel to the mean wind direction and lying outside of the wake. One LiDAR is placed in proximity of the wind turbine location and measures pointing downstream, whereas a second LiDAR is located along the mean wind direction at a downstream distance of 6.5 diameters and measures pointing upstream. For these measurements axial and vertical velocity components are retrieved only for measurement points where the two laser beams result to be roughly orthogonal. Statistics of the two velocity components show in the near wake at hub height strong flow fluctuations with magnitudes about 30% of the mean value, and a gradual reduction for downstream distances larger than three rotor diameters.
Auditory Processing across the Sleep-Wake Cycle
Chiara M. Portas; Karsten Krakow; Phillip Allen; Oliver Josephs; Jorge L. Armony; Chris D. Frith
We combined fMRI and EEG recording to study the neurophysiological responses associated with auditory stimulation across the sleep-wake cycle. We found that presentation of auditory stimuli produces bilateral activation in auditory cortex, thalamus, and caudate during both wakefulness and nonrapid eye movement (NREM) sleep. However, the left parietal and, bilaterally, the prefrontal and cingulate cortices and the thalamus were less
Linear instability in the near wake of channels cascade
Abderrahim Achiq; Jaafar Khalid Naciri
The growth of linear disturbances in the high-Reynolds number laminar wake of a channels cascade is investigated. Disturbances in the near wake respond according to the Rayleigh equation which is solved numerically for a spatial stability problem. The unperturbed flow is studied using a double deck analysis. The results of This analysis allow for the basic flow profiles at different
Flight safety, aircraft vortex wake and airport operation capacity
Victor V. Vyshinsky
One of the major problems that challenge today's aeronautics is the problem of improving flight safety. A zone of increased hazard is the aerospace in the vicinity of an airport. Here, one of aircraft accidents' causes is wake turbulence generated by aircraft. The encountering of an aircraft on take-off or landing with the vortex wake of a preceding aircraft can
Turbulent Energy Balance and Spectra of the Axisymmetric Wake
Mahinder S. Uberoi; Peter Freymuth
Axisymmetric turbulent wake behind a sphere in an incompressible fluid has been experimentally investigated from 50 to 300 diam downstream from the sphere at Reynolds numbers from 4000 to 150 000. Mean and turbulent velocity measurements show that the region of self-preservation starts 50 sphere diam downstream, and the virtual origin of the wake is 12 sphere diam downstream. Detailed
On the investigation of cascade and turbomachinery rotor wake characteristics
NASA Technical Reports Server (NTRS)
Raj, R.; Lakshminarayana, B.
The objective of the investigation reported in this thesis is to study the characteristics of a turbomachinery rotor wake, both analytically and experimentally. The constitutive equations for the rotor wake are developed using generalized tensors and a non-inertial frame of reference. Analytical and experimental investigation is carried out in two phases; the first phase involved the study of a cascade wake in the absence of rotation and three dimensionality. In the second phase the wake of a rotor is studied. Simplified two- and three-dimensional models are developed for the prediction of the mean velocity profile of the cascade and the rotor wake, respectively, using the principle of self-similarity. The effect of various major parameters of the rotor and the flow geometry is studied on the development of a rotor wake. Laws governing the decay of the wake velocity defect in a cascade and rotor wake as a function of downstream distance from the trailing edge, pressure gradient and other parameters are derived.
Proceedings of the ARO Rotorcraft Wake Prediction Basic Research Workshop
Vortex Calculations To Wind Tunnel Measurements 5 S. P�eron, C. Benoit, G. Jeanfaivre ONERA High of the rotor wake continues to pose challenges in prediction and measurement. There have been advances Wake Structure Of A Horizontal-Axis Wind Turbine 7 A.G. Brand BHTI The Nature Of Vortex Ring State 8 S
Vacuum in the wake of space vehicles
NASA Technical Reports Server (NTRS)
Oran, W. A.; Naumann, R. J.
Vacuum conditions to be encountered in the wakes of high altitude unmanned space vehicles are calculated in order to demonstrate possibilities for conducting experiments using the high pumping speeds and very high vacuum (down to 10 to the -15th torr) attainable. The flux of ambient particles backscattered by emissions from spacecraft surfaces is modelled for an idealized Long Duration Exposure Facility spacecraft structure in an orbit of 550 km altitude. The total backscattered fluxes are found to be between 3 x 10 to the 4th and 3 x 10 to the 5th per sq cm sec for H and between 10 to the 6th and 10 to the 7th per sq cm sec for He and O, depending on the angle with respect to the wake axis. It is found that the direct ambient hydrogen flux is an order of magnitude greater than the backscattered flux, while the backscattered fluxes of He and O are greater than the direct fluxes. It is pointed out that care should be taken in designing space experiments to enable these theoretical conditions to be met.
The Structure of Cosmic String Wakes
Sornborger, A T; Fryxell, B; Olson, K
The clustering of baryons and cold dark matter induced by a single moving string is analyzed numerically making use of a new three-dimensional Eulerian cosmological hydro code$^{1)}$ which is based on the PPM method to track the baryons and the PIC method to evolve the dark matter particles. A long straight string moving with a speed comparable to $c$ induces a planar overdensity (a``wake"). Since the initial perturbation is a velocity kick towards the plane behind the string and there is no initial Newtonian gravitational line source, the baryons are trapped in the center of the wake, leading to an enhanced baryon to dark matter ratio. The cold coherent flow leads to very low post--shock temperatures of the baryonic fluid. In contrast, long strings with a lot of small-scale structure (which can be described by adding a Newtonian gravitational line source) move slowly and form filamentary objects. The large central pressure due to the gravitational potential causes the baryons to be expelled from the central ...
Particles in the wake of other particles
NASA Astrophysics Data System (ADS)
Block, Dietmar; Miloch, Wojciech Jacek
The charging of dust grains in the wake of another grains in sonic and supersonic collisionless plasma flows is studied by numerical simulations. The simulations are carried out with DiP3D, a three dimensional particle-in-cell code with both electrons and ions represented as numerical particles. We consider two grains aligned with the flow, as well as dust chains and multiple grain arrangements. It is found that the dust charge depends significantly on the flow speed, distance between the grains, and the grain arrangement. Special attention is paid to typical experimental situations like a particle below a layer of particles and small 3D clusters. The charging of dust grains in the wake of another grains in sonic and supersonic collisionless plasma flows is studied by numerical simulations. The simulations are carried out with DiP3D, a three dimensional particle-in-cell code with both electrons and ions represented as numerical particles. We consider two grains aligned with the flow, as well as dust chains and multiple grain arrangements. It is found that the dust charge depends significantly on the flow speed, distance between the grains, and the grain arrangement. Special attention is paid to typical experimental situations like a particle below a layer of particles and small 3D clusters. Funded by DFG in the framework of the SFB TR24 project A3.
The sleep-wake cycle and motor activity, but not temperature, are disrupted over the light-dark cycle in mice genetically depleted of serotonin.
Solarewicz, Julia Z; Angoa-Perez, Mariana; Kuhn, Donald M; Mateika, Jason H
We examined the role that serotonin has in the modulation of sleep and wakefulness across a 12-h:12-h light-dark cycle and determined whether temperature and motor activity are directly responsible for potential disruptions to arousal state. Telemetry transmitters were implanted in 24 wild-type mice (Tph2(+/+)) and 24 mice with a null mutation for tryptophan hydroxylase 2 (Tph2(-/-)). After surgery, electroencephalography, core body temperature, and motor activity were recorded for 24 h. Temperature for a given arousal state (quiet and active wake, non-rapid eye movement, and paradoxical sleep) was similar in the Tph2(+/+) and Tph2(-/-) mice across the light-dark cycle. The percentage of time spent in active wakefulness, along with motor activity, was decreased in the Tph2(+/+) compared with the Tph2(-/-) mice at the start and end of the dark cycle. This difference persisted into the light cycle. In contrast, the time spent in a given arousal state was similar at the remaining time points. Despite this similarity, periods of non-rapid-eye-movement sleep and wakefulness were less consolidated in the Tph2(+/+) compared with the Tph2(-/-) mice throughout the light-dark cycle. We conclude that the depletion of serotonin does not disrupt the diurnal variation in the sleep-wake cycle, motor activity, and temperature. However, serotonin may suppress photic and nonphotic inputs that manifest at light-dark transitions and serve to shorten the ultraradian duration of wakefulness and non-rapid-eye-movement sleep. Finally, alterations in the sleep-wake cycle following depletion of serotonin are unrelated to disruptions in the modulation of temperature. PMID:25394829
Computation and analysis of a cylinder wake flow
NASA Astrophysics Data System (ADS)
Townsend, J. C.; Rudy, D. H.; Sirovich, L.
The Karman vortex wake of a circular cylinder at low Reynolds number was computed by a time-accurate, two-dimensional compressible Navier-Stokes equation solver which uses the MacCormack predictor-corrector finite-difference scheme and a nonreflecting boundary condition on the outer flow boundary. The results from a large number of time steps were analyzed using Fast Fourier Transform techniques to identify the important frequency components for comparison with published experimental data. A strong low-frequency component was found below the vortex shedding frequency and not harmonically related to it. The experimentally discovered low-frequency fluctuations in the cylinder wake are considered possibly to be precursors to transition from laminar to turbulent flow conditions. The present finding of similar frequencies in a computed wake tends to confirm their existence as a real wake phenomenon. This computational work provides a complementary means to experimental investigations of wake phenomena.
Computation and analysis of a cylinder wake flow
NASA Technical Reports Server (NTRS)
Townsend, J. C.; Rudy, D. H.; Sirovich, L.
The Karman vortex wake of a circular cylinder at low Reynolds number was computed by a time-accurate, two-dimensional compressible Navier-Stokes equation solver which uses the MacCormack predictor-corrector finite-difference scheme and a nonreflecting boundary condition on the outer flow boundary. The results from a large number of time steps were analyzed using Fast Fourier Transform techniques to identify the important frequency components for comparison with published experimental data. A strong low-frequency component was found below the vortex shedding frequency and not harmonically related to it. The experimentally discovered low-frequency fluctuations in the cylinder wake are considered possibly to be precursors to transition from laminar to turbulent flow conditions. The present finding of similar frequencies in a computed wake tends to confirm their existence as a real wake phenomenon. This computational work provides a complementary means to experimental investigations of wake phenomena.
Contrail ice particles in aircraft wakes and their climatic importance
NASA Astrophysics Data System (ADS)
Schumann, Ulrich; Je�Berger, Philipp; Voigt, Christiane
Measurements of gaseous (NO, NOy, SO2, HONO) and ice particle concentrations in young contrails in primary and secondary wakes of aircraft of different sizes (B737, A319, A340, A380) are used to investigate ice particle formation behind aircraft. The gas concentrations are largest in the primary wake and decrease with increasing altitude in the secondary wake, as expected for passive trace gases and aircraft-dependent dilution. In contrast, the measured ice particle concentrations were found larger in the secondary wake than in the primary wake. The contrails contain more ice particles than expected for previous black carbon (soot) estimates. The ice concentrations may result from soot-induced ice nucleation for a soot number emission index of 1015 kg-1. For a doubled ice particle concentration in young contrails, a contrail cirrus model computes about 60% increases of global radiative forcing by contrail cirrus because of simultaneous increases in optical depth, age, and cover.
Exploration of Salt Wedge Dynamics in the Columbia River Estuary Using Optical Measurements of Internal Ship Wakes.
NASA Astrophysics Data System (ADS)
Holman, R. A.; Greydanus, S. J.
In May of 2013 and beyond, Argus optical measurements of the mouth of the Columbia River estuary and plume were collected as part of the RIVET II multi-investigator field experiment. One surprise was the strength of eddy and internal wave signatures observed in movies computed from one-minute averages of high-frequency snapshots (such that gravity waves were averaged out but slicks and variable surface roughness remained). In particular, passing ships left wakes that propagated away at speeds on the order of 0.5 m/s, much slower than gravity waves and presumably surface manifestations of internal waves associated with the time-varying salt-wedge. Thus, these internal ship wakes appear to act as probes of internal stratification dynamics. This paper will explore the time variations of these internal wakes and relate them to corresponding variations in the estuary salt wedge.
Study of wake meandering by means of fixed point lidar measurements: Spectral analysis of line-of-sight wind component
NASA Astrophysics Data System (ADS)
Trabucchi, Davide; Steinfeld, Gerald; Bastine, David; Trujillo, Juan-Jos�; Schneemann, J�rge; K�hn, Martin
The validation of dynamic wake meandering models by full field measurements is an important but challenging task. Recently a new approach has been proposed, where a long range lidar was employed to analyse the power spectral density of the line of sight wind component measured across the wake trajectory. The method is promising, but the number of useful time series within a measurement campaign depends to a large extent on a favourable geometrical setup of the lidar position and the wind direction. In the first part of the paper the approach is further investigated. To this avail, lidar simulations based on large eddy simulation results are analysed. In the second part, the approach is applied to real measurement data from a campaign with a long range lidar windscanner in the offshore wind farm "alpha ventus". Eventually results about the wake dynamics are discussed.
Fermionic suppression of dipolar relaxation.
Burdick, Nathaniel Q; Baumann, Kristian; Tang, Yijun; Lu, Mingwu; Lev, Benjamin L
We observe the suppression of inelastic dipolar scattering in ultracold Fermi gases of the highly magnetic atom dysprosium: the more energy that is released, the less frequently these exothermic reactions take place, and only quantum spin statistics can explain this counterintuitive effect. Inelastic dipolar scattering in nonzero magnetic fields leads to heating or to loss of the trapped population, both detrimental to experiments intended to study quantum many-body physics with strongly dipolar gases. Fermi statistics, however, is predicted to lead to a kinematic suppression of these harmful reactions. Indeed, we observe a 120-fold suppression of dipolar relaxation in fermionic versus bosonic Dy, as expected from theory describing universal inelastic dipolar scattering, though never before experimentally confirmed. Similarly, low inelastic cross sections are observed in spin mixtures, also with striking correspondence to predictions. The suppression of relaxation opens the possibility of employing fermionic dipolar species in studies of quantum many-body physics involving, e.g., synthetic gauge fields and pairing. PMID:25635544
Quantifying error of remote sensing observations of wind turbine wakes using computational fluid dynamics
NASA Astrophysics Data System (ADS)
Lundquist, J. K.; Churchfield, M. J.; Lee, S.; Clifton, A.
Wind-profiling lidars are now regularly used in boundary-layer meteorology and in applications such as wind energy and air quality. Lidar wind profilers exploit the Doppler shift of laser light backscattered from particulates carried by the wind to measure a line-of-sight (LOS) velocity. The Doppler Beam Swinging (DBS) technique, used by many commercial systems, considers measurements of this LOS velocity in multiple radial directions in order to estimate horizontal and vertical winds. The method relies on the assumption of homogeneous flow across the region sampled by the beams. Using such a system in inhomogeneous flow, such as wind turbine wakes or complex terrain, will result in errors. To quantify the errors expected from such violation of the assumption of horizontal homogeneity, we simulate inhomogeneous flow in the atmospheric boundary layer, notably stably-stratified flow past a wind turbine. This slightly stable case results in 15� of wind direction change across the turbine rotor disk. The resulting flow field is sampled in the same fashion that a lidar samples the atmosphere with the DBS approach, enabling quantification of the error in the DBS observations. The observations from the instruments located upwind have small errors, which are ameliorated with time averaging. However, the downwind observations, particularly within the first two rotor diameters downwind from the wind turbine, suffer from errors due to the heterogeneity of the wind turbine wake. Errors in the stream-wise component of the flow are generally small, less than 0.5 m s-1. Errors in the cross-stream and vertical velocity components are much larger: cross-stream component errors are on the order of 1.0 m s-1 and errors in the vertical velocity exceed the actual measurements of the vertical velocity. DBS-based assessments of wake wind speed deficits based on the stream-wise velocity can be relied on even within the near wake within 0.5 m s-1, but cross-stream and vertical velocity estimates in the near wake are compromised. Measurements of inhomogeneous flow such as wind turbine wakes are susceptible to these errors, and interpretations of field observations should account for this uncertainty.
Effect of wake structure on blade-vortex interaction phenomena: Acoustic prediction and validation
NASA Technical Reports Server (NTRS)
Gallman, Judith M.; Tung, Chee; Schultz, Klaus J.; Splettstoesser, Wolf; Buchholz, Heino
During the Higher Harmonic Control Aeroacoustic Rotor Test, extensive measurements of the rotor aerodynamics, the far-field acoustics, the wake geometry, and the blade motion for powered, descent, flight conditions were made. These measurements have been used to validate and improve the prediction of blade-vortex interaction (BVI) noise. The improvements made to the BVI modeling after the evaluation of the test data are discussed. The effects of these improvements on the acoustic-pressure predictions are shown. These improvements include restructuring the wake, modifying the core size, incorporating the measured blade motion into the calculations, and attempting to improve the dynamic blade response. A comparison of four different implementations of the Ffowcs Williams and Hawkings equation is presented. A common set of aerodynamic input has been used for this comparison.
Prediction of BVI noise patterns and correlation with wake interaction locations
NASA Astrophysics Data System (ADS)
Marcolini, Michael A.; Martin, Ruth M.; Lorber, Peter F.; Egolf, T. A.
High resolution fluctuating airloads data were acquired during a test of a contemporary design United Technologies model rotor in the Duits-Nederlandse Windtunnel (DNW). The airloads are used as input to the noise prediction program WOPWOP, in order to predict the blade-vortex interaction (BVI) noise field on a large plane below the rotor. Trends of predicted advancing and retreating side BVI noise levels and directionality as functions of flight condition are presented. The measured airloads have been analyzed to determine the BVI locations on the blade surface, and are used to interpret the predicted BVI noise radiation patterns. Predicted BVI locations are obtained using the free wake model in CAMRAD/JA, the UTRC Generalized Forward Flight Distorted Wake Model, and the UTRC FREEWAKE analysis. These predicted BVI locations are compared with those obtained from the measured pressure data.
First Results from ARTEMIS, a New Two-Spacecraft Lunar Mission: Counter-Streaming Plasma Populations in the Lunar Wake
NASA Technical Reports Server (NTRS)
Halekas, J. S.; Angelopoulos, V.; Sibeck, D. G.; Khurana, K. K.; Russell, C. T.; Delory, G. T.; Farrell, W. M.; McFadden, J. P.; Bonnell, J. W.; Larson, D.; Ergun, R. E.; Plaschke, F.; Glassmeier, K. H.
We present observations from the first passage through the lunar plasma wake by one of two spacecraft comprising ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun), a new lunar mission that re-tasks two of five probes from the THEMIS magnetospheric mission. On Feb 13, 2010, ARTEMIS probe P1 passed through the wake at 3.5 lunar radii downstream from the Moon, in a region between those explored by Wind and the Lunar Prospector, Kaguya, Chandrayaan, and Chang'E missions. ARTEMIS observed interpenetrating proton, alpha particle, and electron populations refilling the wake along magnetic field lines from both flanks. The characteristics of these distributions match expectations from self-similar models of plasma expansion into vacuum, with an asymmetric character likely driven by a combination of a tilted interplanetary magnetic field and an anisotropic incident solar wind electron population. On this flyby, ARTEMIS provided unprecedented measurements of the interpenetrating beams of both electrons and ions naturally produced by the filtration and acceleration effects of electric fields set up during the refilling process. ARTEMIS also measured electrostatic oscillations closely correlated with counter-streaming electron beams in the wake, as previously hypothesized but never before directly measured. These observations demonstrate the capability of the comprehensively instrumented ARTEMIS spacecraft and the potential for new lunar science from this unique two spacecraft constellation.
Sound Generation by Aircraft Wake Vortices
NASA Technical Reports Server (NTRS)
Hardin, Jay C.; Wang, Frank Y.
This report provides an extensive analysis of potential wake vortex noise sources that might be utilized to aid in their tracking. Several possible mechanisms of aircraft vortex sound generation are examined on the basis of discrete vortex dynamic models and characteristic acoustic signatures calculated by application of vortex sound theory. It is shown that the most robust mechanisms result in very low frequency infrasound. An instability of the vortex core structure is discussed and shown to be a possible mechanism for generating higher frequency sound bordering the audible frequency range. However, the frequencies produced are still low and cannot explain the reasonably high-pitched sound that has occasionally been observed experimentally. Since the robust mechanisms appear to generate only very low frequency sound, infrasonic tracking of the vortices may be warranted.
Increased salivary cortisol after waking in depression
Zubin Bhagwagar; Sepehr Hafizi; Philip J. Cowen
Rationale��Cortisol hypersecretion is regarded as important in the pathophysiology of major depression. However, recent studies in community-based\\u000a samples have been inconclusive.\\u000a \\u000a \\u000a \\u000a Objective��To determine whether acutely depressed, medication-free subjects show an exaggerated release of cortisol in saliva in relation\\u000a to awakening.\\u000a \\u000a \\u000a \\u000a Methods��We studied the pattern of waking salivary cortisol in 20 unmedicated acutely depressed subjects and 40 healthy controls.\\u000a \\u000a \\u000a \\u000a Results��In both
Vortex wake alleviation studies with a variable twist wing
NASA Technical Reports Server (NTRS)
Holbrook, G. T.; Dunham, D. M.; Greene, G. C.
Vortex wake alleviation studies were conducted in a wind tunnel and a water towing tank using a multisegmented wing model which provided controlled and measured variations in span load. Fourteen model configurations are tested at a Reynolds number of one million and a lift coefficient of 0.6 in the Langley 4- by 7-Meter Tunnel and the Hydronautics Ship Model Basin water tank at Hydronautics, Inc., Laurel, Md. Detailed measurements of span load and wake velocities at one semispan downstream correlate well with each other, with inviscid predictions of span load and wake roll up, and with peak trailing-wing rolling moments measured in the far wake. Average trailing-wing rolling moments are found to be an unreliable indicator of vortex wake intensity because vortex meander does not scale between test facilities and free-air conditions. A tapered-span-load configuration, which exhibits little or no drag penalty, is shown to offer significant downstream wake alleviation to a small trailing wing. The greater downstream wake alleviation achieved with the addition of spoilers to a flapped-wing configuration is shown to result directly from the high incremental drag and turbulence associated with the spoilers and not from the span load alteration they cause.
Signature of cosmic string wakes in the CMB polarization
Danos, Rebecca J.; Brandenberger, Robert H.; Holder, Gil [Department of Physics, McGill University, Montreal, QC, H3A 2T8 (Canada)
We calculate a signature of cosmic strings in the polarization of the cosmic microwave background. We find that ionization in the wakes behind moving strings gives rise to extra polarization in a set of rectangular patches in the sky whose length distribution is scale-invariant. The length of an individual patch is set by the comoving Hubble radius at the time the string is perturbing the cosmic microwave background. The polarization signal is largest for string wakes produced at the earliest post-recombination time, and for an alignment in which the photons cross the wake close to the time the wake is created. The maximal amplitude of the polarization relative to the temperature quadrupole is set by the overdensity of free electrons inside a wake which depends on the ionization fraction f inside the wake. For a cosmic string wake coming from an idealized string segment, the signal can be as high as 0.06 {mu}K in degree scale polarization for a string at high redshift (near recombination) and a string tension {mu} given by G{mu}=10{sup -7}.
Stratospheric aircraft exhaust plume and wake chemistry
NASA Technical Reports Server (NTRS)
Miake-Lye, R. C.; Martinez-Sanchez, M.; Brown, R. C.; Kolb, C. E.; Worsnop, D. R.; Zahniser, M. S.; Robinson, G. N.; Rodriguez, J. M.; Ko, M. K. W.; Shia, R-L.
Progress to date in an ongoing study to analyze and model emissions leaving a proposed High Speed Civil Transport (HSCT) from when the exhaust gases leave the engine until they are deposited at atmospheric scales in the stratosphere is documented. A kinetic condensation model was implemented to predict heterogeneous condensation in the plume regime behind an HSCT flying in the lower stratosphere. Simulations were performed to illustrate the parametric dependence of contrail droplet growth on the exhaust condensation nuclei number density and size distribution. Model results indicate that the condensation of water vapor is strongly dependent on the number density of activated CN. Incorporation of estimates for dilution factors into a Lagrangian box model of the far-wake regime with scale-dependent diffusion indicates negligible decrease in ozone and enhancement of water concentrations of 6-13 times background, which decrease rapidly over 1-3 days. Radiative calculations indicate a net differential cooling rate of the plume about 3K/day at the beginning of the wake regime, with a total subsidence ranging between 0.4 and 1 km. Results from the Lagrangian plume model were used to estimate the effect of repeated superposition of aircraft plumes on the concentrations of water and NO(y) along a flight corridor. Results of laboratory studies of heterogeneous chemistry are also described. Kinetics of HCl, N2O5 and ClONO2 uptake on liquid sulfuric acid were measured as a function of composition and temperature. Refined measurements of the thermodynamics of nitric acid hydrates indicate that metastable dihydrate may play a role in the nucleation of more stable trihydrates PSC's.
Measurements of Unsteady Wake Interference Between Tandem Cylinders
NASA Technical Reports Server (NTRS)
Jenkins, Luther N.; Neuhart, Dan H.; McGinley, Cahterine B.; Choudhari, Meelan M.; Khorrami, Mehdi R.
A multi-phase, experimental study in the Basic Aerodynamics Research Tunnel at the NASA Langley Research Center has provided new insight into the unsteady flow interaction around cylinders in tandem arrangement. Phase 1 of the study characterized the mean and unsteady near-field flow around two cylinders of equal diameter using 2-D Particle Image Velocimetry (PIV) and hot-wire anemometry. These measurements were performed at a Reynolds number of 1.66 x 10(exp 5), based on cylinder diameter, and spacing-to-diameter ratios, L/D, of 1.435 and 3.7. The current phase, Phase 2, augments this dataset by characterizing the surface flow on the same configurations using steady and unsteady pressure measurements and surface flow visualization. Transition strips were applied to the front cylinder during both phases to produce a turbulent boundary layer upstream of the flow separation. For these flow conditions and L/D ratios, surface pressures on both the front and rear cylinders show the effects of L/D on flow symmetry, pressure recovery, and the location of flow separation and attachment. Mean streamlines and instantaneous vorticity obtained from the PIV data are used to explain the flow structure in the gap and near-wake regions and its relationship to the unsteady surface pressures. The combination of off-body and surface measurements provides a comprehensive dataset to develop and validate computational techniques for predicting the unsteady flow field at higher Reynolds numbers.
Inviscid Interactions Between Wake Vortices and Shear Layers
NASA Technical Reports Server (NTRS)
Zheng, Z. C.; Baek, K.
Aircraft trailing vortices can be influenced significantly by atmospheric conditions such as crosswind, turbulence, and stratification. According to the NASA 1994 and 1995 field measurement program in Memphis, Tennessee, the descending aircraft wake vortices could stall or be deflected at the top of low-level temperature inversions that usually produce pronounced shear zones. Numerical simulations of vortex/shear interactions with ground effects have been performed by several groups. Burnham used a series of evenly spaced line vortices at a particular altitude to model the ground shear layer of the cross- wind. He found that the wind shear was swept up around the downwind vortex and caused the downwind vortex to move upward, and claimed that the effect was actually produced by the vertical gradient in the wind shear rather than by the wind shear directly, because uniformly distributed wind-shear vortices would have no effect on the trailing vortex vertical motion. Recently, Proctor et al. numerically tested the effects of narrow shear zones on the behavior of the vortex pair, motivated by the observation of the Memphis field data. The shear-layer sensitivity tests indicated that the downwind vortex was more sensitive and deflected to a higher altitude than its upwind counterpart. The downstream vortex contained vorticity of opposite sign to that of the shear. There was no detectable preference for the downwind vortex (or upwind vortex) to weaken (or strengthen) at a greater rate.
Wake of a beam passing through a diffraction radiation target
NASA Astrophysics Data System (ADS)
Xiang, Dao; Huang, Wen-Hui; Lin, Yu-Zheng; Park, Sung-Ju; Ko, In Soo
Diffraction radiation (DR) is one of the most promising candidates for electron beam diagnostics for International Linear Collider and x-ray free electron lasers due to its nonintercepting characteristic. One of the potential problems that may restrict its applications in real-time monitoring beam parameters is the wakefield generated by the presence of the DR target. In this paper, a comparative study of the wakefield and the backward DR (BDR) field is performed to clarify the relationship between them. The wakefield is studied with a particle-in-cell code MAGIC and the DR field is calculated based on virtual photon diffraction model. It is found that they have the same frequency spectrum and angular distribution, which indicates that the difference only exists in the subjective terminology. The longitudinal and transverse wake for a beam passing through a DR target is calculated for a general case when the beam�s velocity is smaller than that of light. The resulted emittance growth and energy spread growth due to the short range wakefield is estimated and found to be permissible. In real measurement where BDR propagates in the direction perpendicular to the trajectory, it may add a transverse kick to the beam as a requirement of momentum conservation. The kick is found to be large enough to degrade the performance of accelerator driven facilities and needs to be corrected.
Effects of sleep and wake on oligodendrocytes and their precursors.
Bellesi, Michele; Pfister-Genskow, Martha; Maret, Stephanie; Keles, Sunduz; Tononi, Giulio; Cirelli, Chiara
Previous studies of differential gene expression in sleep and wake pooled transcripts from all brain cells and showed that several genes expressed at higher levels during sleep are involved in the synthesis/maintenance of membranes in general and of myelin in particular, a surprising finding given the reported slow turnover of many myelin components. Other studies showed that oligodendrocyte precursor cells (OPCs) are responsible for the formation of new myelin in both the injured and the normal adult brain, and that glutamate released from neurons, via neuron-OPC synapses, can inhibit OPC proliferation and affect their differentiation into myelin-forming oligodendrocytes. Because glutamatergic transmission is higher in wake than in sleep, we asked whether sleep and wake can affect oligodendrocytes and OPCs. Using the translating ribosome affinity purification technology combined with microarray analysis in mice, we obtained a genome-wide profiling of oligodendrocytes after sleep, spontaneous wake, and forced wake (acute sleep deprivation). We found that hundreds of transcripts being translated in oligodendrocytes are differentially expressed in sleep and wake: genes involved in phospholipid synthesis and myelination or promoting OPC proliferation are transcribed preferentially during sleep, while genes implicated in apoptosis, cellular stress response, and OPC differentiation are enriched in wake. We then confirmed through BrdU and other experiments that OPC proliferation doubles during sleep and positively correlates with time spent in REM sleep, whereas OPC differentiation is higher during wake. Thus, OPC proliferation and differentiation are not perfectly matched at any given circadian time but preferentially occur during sleep and wake, respectively. PMID:24005282
Numerical modeling studies of wake vortex transport and evolution within the planetary boundary layer
NASA Technical Reports Server (NTRS)
Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael L.
The proposed research involves four tasks. The first of these is to simulate accurately the turbulent processes in the atmospheric boundary layer. TASS was originally developed to study meso-gamma scale phenomena, such as tornadic storms, microbursts and windshear effects in terminal areas. Simulation of wake vortex evolution, however, will rely on appropriate representation of the physical processes in the surface layer and mixed layer. This involves two parts. First, a specified heat flux boundary condition must be implemented at the surface. Using this boundary condition, simulation results will be compared to experimental data and to other model results for validation. At this point, any necessary changes to the model will be implemented. Next, a surface energy budget parameterization will be added to the model. This will enable calculation of the surface fluxes by accounting for the radiative heat transfer to and from the ground and heat loss to the soil rather than simple specification of the fluxes. The second task involves running TASS with prescribed wake vortices in the initial condition. The vortex models will be supplied by NASA Langley Research Center. Sensitivity tests will be performed on different meteorological environments in the atmospheric boundary layer, which include stable, neutral, and unstable stratifications, calm and severe wind conditions, and dry and wet conditions. Vortex strength may be varied as well. Relevant non-dimensional parameters will include the following: Richardson number or Froude number, Bowen ratio, and height to length scale ratios. The model output will be analyzed and visualized to better understand the transport, decay, and growth rates of the wake vortices. The third task involves running simulations using observed data. MIT Lincoln Labs is currently planning field experiments at the Memphis airport to measure both meteorological conditions and wake vortex characteristics. Once this data becomes available, it can be used to validate the model for vortex behavior under different atmospheric conditions. The fourth task will be to simulate the wake in a more realistic environment covering a wider area. This will involve grid nesting, since high resolution will be required in the wake region but a larger total domain will be used. During the first allocation year, most of the first task will be accomplished.
Aspects of the influence of an oscillating mini-flap upon the near wake of an airfoil NACA 4412
NASA Astrophysics Data System (ADS)
Delnero, J. S.; Mara��n Di Leo, J.; Colman, J.; Garc�a Sainz, M.; Mu�oz, F.; H�rouard, N.; Camocardi, M. E.
A NACA 4412 airfoil was tested, in a boundary layer wind tunnel, with the aim to study the effect of a Gurney mini-flap, as an active and passive flow control device submitted to a turbulent flow field. The main objective was the experimental determination of flow pattern characteristics downstream the airfoil in the near wake. The untwisted wing model used for the experiments had 80cm wingspan and 50cm chord, with airfoil NACA 4412. The mini-flap was located on the lower surface at a distance, from the trailing edge, of 8%c (c airfoil chord). The Reynolds number, based upon the wing chord and the mean free stream velocity was 326,000 and 489,000. The turbulence intensity was 1.8%. The model was located into the wind tunnel between two panels, in order to assure a close approximation to two-dimensional flow over the model. As an active control device a rotating mini-flaps, geared by an electromechanical system (which rotate to a 30�) was constructed. The wake pattern and pressure values near the trailing edge were measured. The results obtained, for this mechanism, show us that the oscillating mini-flap change the wake flow pattern, alleviating the near wake turbulence and enhancing the vortex pair near the trailing edge at the mini-flap level and below that level, magnifying the effect described first by Liebeck [1]. That effect grows with the oscillating frequency. Additionally, the wake alleviation probably affects also the far wake. All of these facts suggest us to continue with the experiments, trying to measure the pressure distribution around the airfoil in all the cases, obtaining the lift and drag characteristics.
Suppression of Beam-Ion Instability in Electron Rings with Multi-Bunch Train Beam Fillings
Wang, L.; Cai, Y.; Raubenheimer, T.O.; /SLAC; Fukuma, H.; /KEK, Tsukuba
The ion-caused beam instability in the future light sources and electron damping rings can be serious due to the high beam current and ultra-small emittance of picometer level. One simple and effective mitigation of the instability is a multi-bunch train beam filling pattern which can significantly reduce the ion density near the beam, and therefore reduce the instability growth rate up to two orders of magnitude. The suppression is more effective for high intensity beams with low emittance. The distribution and the field of trapped ions are benchmarked to validate the model used in the paper. The wake field of ion-cloud and the beam-ion instability is investigated both analytically and numerically. We derived a simple formula for the build-up of ion-cloud and instability growth rate with the multi-bunch-train filling pattern. The ion instabilities in ILC damping ring, SuperKEKB and SPEAR3 are used to compare with our analyses. The analyses in this paper agree well with simulations.
Characterization of High-Frequency Excitation of a Wake by Simulation
NASA Technical Reports Server (NTRS)
Cain, Alan B.; Rogers, Michael M.; Kibens, Valdis; Mansour, Nagi (Technical Monitor)
Insights into the effects of high-frequency forcing on free shear layer evolution are gained through analysis of several direct numerical simulations. High-frequency forcing of a fully turbulent plane wake results in only a weak transient effect. On the other hand, significant changes in the developed turbulent state may result when high-frequency forcing is applied to a transitional wake. The impacts of varying the characteristics of the high-frequency forcing are examined, particularly, the streamwise wavenumber band in which forcing is applied and the initial amplitude of the forcing. The high-frequency excitation is found to increase the dissipation rate of turbulent kinetic energy, to reduce the turbulent kinetic energy production rate, and to reduce the turbulent kinetic energy suppression increases with forcing amplitude once a threshold level has been reached. For a given initial forcing energy, the largest reduction in turbulent kinetic energy density was achieved by forcing wavenumbers that are about two to three times the neutral wavenumber determined from linear stability theory.
Rotor Wake Vortex Definition Using 3C-PIV Measurements: Corrected for Vortex Orientation
NASA Technical Reports Server (NTRS)
Burley, Casey L.; Brooks, Thomas F.; vanderWall, Berend; Richard, Hughues Richard; Raffel, Markus; Beaumier, Philippe; Delrieux, Yves; Lim, Joon W.; Yu, Yung H.; Tung, Chee
Three-component (3-C) particle image velocimetry (PIV) measurements, within the wake across a rotor disk plane, are used to determine wake vortex definitions important for BVI (Blade Vortex Interaction) and broadband noise prediction. This study is part of the HART II test program conducted using a 40 percent scale BO-105 helicopter main rotor in the German-Dutch Wind Tunnel (DNW). In this paper, measurements are presented of the wake vortex field over the advancing side of the rotor operating at a typical descent landing condition. The orientations of the vortex (tube) axes are found to have non-zero tilt angles with respect to the chosen PIV measurement cut planes, often on the order of 45 degrees. Methods for determining the orientation of the vortex axis and reorienting the measured PIV velocity maps (by rotation/projection) are presented. One method utilizes the vortex core axial velocity component, the other utilizes the swirl velocity components. Key vortex parameters such as vortex core size, strength, and core velocity distribution characteristics are determined from the reoriented PIV velocity maps. The results are compared with those determined from velocity maps that are not corrected for orientation. Knowledge of magnitudes and directions of the vortex axial and swirl velocity components as a function of streamwise location provide a basis for insight into the vortex evolution.
Unsteady Vortex Structures in the Wake of a Piezoelectric Flapping Wing
NASA Astrophysics Data System (ADS)
Clemons, Lucas; Igarashi, Hirofumi; Hu, Hui
An experimental study was conducted to characterize the behavior of Unsteady Vortex Structures in the Wake of a piezoelectric flapping wing with miniaturized size (about 10mm in chord length), large flapping amplitude (up to 2.0 times of chord length) and high flapping frequency (60Hz) to explore the potential application of piezofans as the compact, gearless flapping-wings for the development of novel piezoelectric-flapping-wing-based Nano-Air-Vehicles (NAVs). The experimental investigation was performed in a low-speed wind tunnel. A digital particle image velocimetry (PIV) system was used to achieve phased-locked flow field measurements to quantify the transient behavior of the unsteady vortex structures in wake of the piezoelectric flapping wing. The effects of important parameters such as incoming flow velocity (i.e., forward flight speed), the flapping amplitude, and the incline angle of the flapping wing in relation to the incoming flow direction (i.e. the angle of attack) on the wake vortex shedding processes were examined to elucidate underlying physics in order to explore/optimize design paradigms for the development of novel piezoelectric-flapping-wing-based NAVs.
The structure of the wake generated by a submarine model in yaw
NASA Astrophysics Data System (ADS)
Ashok, A.; Van Buren, T.; Smits, A. J.
The turbulent wake of a submarine model in yaw was investigated using stereoscopic particle image velocimetry at The model (DARPA SUBOFF idealized submarine geometry) is mounted in a low-speed wind tunnel using a support that mimics the sail, and it is yawed so that the body moves in the plane normal to the support. The measurements reveal the formation of a pair of streamwise vortices that are asymmetric in strength. The weaker vortex quickly diffuses, and in the absence of further diffusion, the stronger vortex maintains its strength even at the furthest downstream location. It is suggested that the flow fields obtained here using a semi-infinite sail as a support will be similar to those obtained using a finite length sail since its tip vortex would not interact significantly with the body vortices present in the wake, at least for a considerable distance downstream of the stern Hence, a submarine in yaw is expected to generate wakes which are inherently more persistent than one in pitch, and the strong asymmetries in yaw are expected to produce a net rolling moment on the body.
Exquisitely sensitive seal whisker-like sensors detect wakes at large distances
Beem, Heather R
Blindfolded harbor seals are able to use their uniquely shaped whiskers to track vortex wakes left by moving animals and objects that passed by up to 30 seconds earlier; this is an impressive feat as the flow features they detect may have velocity as low as 1 mm/s, and the seals have some capacity to identify the shape of the object as well. They do so while swimming forward at high speed, hence their whiskers are sensitive enough to detect small-scale changes in the external flow field, while rejecting self-generated flow noise. Here we identify and illustrate a novel flow mechanism that allows artificial whiskers with the identical unique geometry as those of the harbor seal to detect the features of minute flow fluctuations in wakes produced by objects far away. This is shown through the study of a model problem, consisting of a harbor seal whisker model interacting with the wake of an upstream circular cylinder. We show that whereas in open water the whisker geometry results in very low vibration, once it...
Free-wake computation of helicopter rotor flowfields in forward flight
NASA Technical Reports Server (NTRS)
Ramachandran, K.; Schlechtriem, S.; Caradonna, F. X.; Steinhoff, John
A new method has been developed for computing advancing rotor flows. This method uses the Vorticity Embedding technique, which has been developed and validated over the last several years for hovering rotor problems. In this work, the unsteady full potential equation is solved on an Eulerian grid with an embedded vortical velocity field. This vortical velocity accounts for the influence of the wake. Dynamic grid changes that are required to accommodate prescribed blade motion and deformation are included using a novel grid blending method. Free wake computations have been performed on a two-bladed AH-1G rotor at low advance ratios including blade motion. Computed results are compared with experimental data. The sudden variations in airloads due to blade-vortex interactions on the advancing and retreating sides are well captured. The sensitivity of the computed solution to various factors like core size, time step and grids has been investigated. Computed wake geometries and their influence on the aerodynamic loads at these advance ratios are also discussed.
Numerical and Experimental Methods for Wake Flow Analysis in Complex Terrain
NASA Astrophysics Data System (ADS)
Castellani, Francesco; Astolfi, Davide; Piccioni, Emanuele; Terzi, Ludovico
Assessment and interpretation of the quality of wind farms power output is a non-trivial task, which poses at least three main challenges: reliable comprehension of free wind flow, which is stretched to the limit on very complex terrains, realistic model of how wake interactions resemble on the wind flow, awareness of the consequences on turbine control systems, including alignment patterns to the wind and, consequently, power output. The present work deals with an onshore wind farm in southern Italy, which has been a test case of IEA- Task 31 Wakebench project: 17 turbines, with 2.3 MW of rated power each, are sited on a very complex terrain. A cluster of machines is investigated through numerical and experimental methods: CFD is employed for simulating wind fields and power extraction, as well as wakes, are estimated through the Actuator Disc model. SCADA data mining techniques are employed for comparison between models and actual performances. The simulations are performed both on the real terrain and on flat terrain, in order to disentangle the effects of complex flow and wake effects. Attention is devoted to comparison between actual alignment patterns of the cluster of turbines and predicted flow deviation.
Periodicity of the density wake past a vortex ring in a stratified liquid
NASA Astrophysics Data System (ADS)
Prokhorov, V.
Spatial coherent structure of the density wake past a vortex ring moving horizontally in viscid stratified liquid is experimentally revealed. It follows from analysis that repetition period of the structure is determined by rotation radial frequency (or mean vorticity) of the vortex core and toward speed of the vortex ring. The wake formation of the ring is considered in respect to vorticity shedding which produces velocity disturbances in ambient medium. In case of stratified liquid velocity fluctuations, in their turn, cause density field distortion. This process is superimposed by vortex core oscillations, and, in result, vorticity shedding will be not monotonous but modulated at some frequency. So, the density wake is periodically structured, and the spatial period is defined by intrinsic frequency of the core and forward speed of the ring. To support analysis, experiments were conducted in which vortex rings excited by spring-piston generator were observed with high-sensitive Schlieren instrument and computer-controlled camera. Experimental tank was filled with salt-stratified water of constant buoyancy period, vortex ring velocities range from 3 to 16 cm/s. Spatial period is derived from schlieren image using two independent methods, both 2D spectral analysis and geometry calculations of the vortex core. Spatial periods and vortex intrinsic frequencies calculated by both algorithms are in good agreement; they vary in power lows depending on vortex speed
Atmospheric Boundary Layer Sensors for Application in a Wake Vortex Advisory System
NASA Technical Reports Server (NTRS)
Zak, J. Allen; Rutishauser, David (Technical Monitor)
Remote sensing of the atmospheric boundary layer has advanced in recent years with the development of commercial off-the-shelf (COTS) radar, sodar, and lidar wind profiling technology. Radio acoustic sounding systems for vertical temperature profiles of high temporal scales (when compared to routine balloon soundings- (radiosondes) have also become increasingly available as COTS capabilities. Aircraft observations during landing and departures are another source of available boundary layer data. This report provides an updated assessment of available sensors, their performance specifications and rough order of magnitude costs for a potential future aircraft Wake Vortex Avoidance System (WakeVAS). Future capabilities are also discussed. Vertical profiles of wind, temperature, and turbulence are anticipated to be needed at airports in any dynamic wake avoidance system. Temporal and spatial resolution are dependent on the selection of approach and departure corridors to be protected. Recommendations are made for potential configurations of near-term sensor technologies and for testing some of the sensor systems in order to validate performance in field environments with adequate groundtruth.
The Plasma Wake Downstream of Lunar Topographic Obstacles: Preliminary Results from 2D Particle Simulations
NASA Technical Reports Server (NTRS)
Zimmerman, Michael I.; Farrell, W. M.; Snubbs, T. J.; Halekas, J. S.
Anticipating the plasma and electrical environments in permanently shadowed regions (PSRs) of the moon is critical in understanding local processes of space weathering, surface charging, surface chemistry, volatile production and trapping, exo-ion sputtering, and charged dust transport. In the present study, we have employed the open-source XOOPIC code [I] to investigate the effects of solar wind conditions and plasma-surface interactions on the electrical environment in PSRs through fully two-dimensional pattic1e-in-cell simulations. By direct analogy with current understanding of the global lunar wake (e.g., references) deep, near-terminator, shadowed craters are expected to produce plasma "mini-wakes" just leeward of the crater wall. The present results (e.g., Figure I) are in agreement with previous claims that hot electrons rush into the crater void ahead of the heavier ions, fanning a negative cloud of charge. Charge separation along the initial plasma-vacuum interface gives rise to an ambipolar electric field that subsequently accelerates ions into the void. However, the situation is complicated by the presence of the dynamic lunar surface, which develops an electric potential in response to local plasma currents (e.g., Figure Ia). In some regimes, wake structure is clearly affected by the presence of the charged crater floor as it seeks to achieve current balance (i.e. zero net current to the surface).
THEMIS Observations of Electron Phase-Space Holes, the Lunar Wake, and Turbulence
NASA Astrophysics Data System (ADS)
Tao, Jianbao
THEMIS is a recent multi-satellite mission launched in 2007 with five identical spacecraft orbiting in the equatorial plane of the Earth. Featuring a comprehensive package of particle and field instruments on each THEMIS spacecraft and multi-resolution data products, the THEMIS mission offers great opportunities to study space plasma dynamics in both large MHD scales and relatively small kinetic scales. This work focuses on kinetic aspects of space plasma dynamics using THEMIS observations, especially electric field observations, which are critical to study kinetic effects. Three specific topics, electron phase-space holes (EHs), kinetic instabilities in the lunar wake, and turbulent electric and magnetic fields in the Earth's magnetotail, are investigated in detail. EHs are good indicators of nonlinear activities in space plasmas and have attracted many interests in both observational and theoretical work. In a traditional theoretical picture, EHs are understood as purely electrostatic structures. However, THEMIS recently observed electromagnetic EHs, which cannot be fully described with traditional theory, in the plasma sheet boundary layer. This work seeks to understand the magnetic signals of the observed electromagnetic EHs. In addition to the interpretations of the observed magnetic signals, a statistical study of the properties of the observed electromagnetic EHs reveals that those electromagnetic EHs feature fast speeds, large sizes, and strong potentials, which intrigues interests in their generation mechanism and influences on the space plasma environment. The lunar wake, resulting from the interaction between the solar wind and the Moon, is an excellent example to study the expansion of plasmas into a more tenuous space. One of the THEMIS spacecraft, THB (known as ARTEMIS P1 after winter 2009) provided new observations of the lunar wake from a lunar-wake flyby in early 2010. Kinetic instabilities from that flyby are examined in this work. Wavelengths and phase velocities of the observed kinetic instabilities are derived from electric field instrument voltage measurements using interferometric techniques, providing unprecedented information of the properties of kinetic instabilities in the lunar wake. In addition, the mode of the observed kinetic instabilities is identified as the electron beam mode, confirming a global-scale dynamics, electron velocity filtration by the negative lunar-wake potential, as proposed in previous works. Turbulence, an efficient mechanism to dissipate kinetic energy into thermal energy, plays an important role in the global energy budget in the plasma sheet. Previous studies of turbulence in the plasma sheet generally focused on MHD scales and did not include electric field measurements. This work combines both electric and magnetic field measurements from THEMIS in the Earth's magnetotail with a frequency range that extends from MHD scales to kinetic scales. Statistical results of Poynting flux and spectral behavior of the turbulent electric and magnetic fields are presented. The Poynting flux results suggest that the turbulent electric and magnetic fields play an important role in the energy coupling between the ionosphere and the magnetosphere, whereas the spectral results may include information on universal relations between electric and magnetic fields for turbulence in plasmas.
Plume and wake dynamics, mixing, and chemistry behind an HSCT aircraft
NASA Technical Reports Server (NTRS)
Miake-Lye, R. C.; Martinez-Sanchez, M.; Brown, R. C.; Kolb, C. E.
The chemical evolution and mixing and vortical motion of a High Speed Civil Transport's engine exhausts must be analyzed in order to track the gas and its speciation as emissions are mixed to atmospheric scales. Attention is presently given to an analytic model of the wake dynamical processes which accounts for the roll-up of the trailing vorticity, its breakup due to the Crow instability, and the subsequent evolution and motion of the reconnected vorticity. The concentrated vorticity is noted to wrap up the buoyant exhaust and suppress its continued mixing and dilution. The species tracked encompass those which could be heterogeneously reactive on the surfaces of the condensed ice particles, and those capable of reacting with exhaust soot particle surfaces to form active contrail and/or cloud condensation nuclei.
Resonance effects in wake shedding from compressor blading
R. Parker
Sounds omitted from a single stage experimental compressor at a sequence of frequencies have been recorded and investigated. They are found to be due to a series of acoustic resonances excited by periodic wakes shed from the rotor blades.
Electromagnetic signature of human cortical dynamics during wakefulness and sleep
Paris-Sud XI, Universit� de
Electromagnetic signature of human cortical dynamics during wakefulness and sleep Signature.1.1 Electroencephalography (EEG) . . . . . . . . . . . . . . . . . . . . . 21 1.1.2 Magnetoencephalography (MEG Studies 45 4 Overview 47 4.1 Electromagnetic properties of the extracellular medium
NASA AVOSS Fast-Time Wake Prediction Models: User's Guide
NASA Technical Reports Server (NTRS)
Ahmad, Nash'at N.; VanValkenburg, Randal L.; Pruis, Matthew
The National Aeronautics and Space Administration (NASA) is developing and testing fast-time wake transport and decay models to safely enhance the capacity of the National Airspace System (NAS). The fast-time wake models are empirical algorithms used for real-time predictions of wake transport and decay based on aircraft parameters and ambient weather conditions. The aircraft dependent parameters include the initial vortex descent velocity and the vortex pair separation distance. The atmospheric initial conditions include vertical profiles of temperature or potential temperature, eddy dissipation rate, and crosswind. The current distribution includes the latest versions of the APA (3.4) and the TDP (2.1) models. This User's Guide provides detailed information on the model inputs, file formats, and the model output. An example of a model run and a brief description of the Memphis 1995 Wake Vortex Dataset is also provided.
32 CFR 707.10 - Wake illumination light.
Code of Federal Regulations, 2012 CFR
...NAVY NAVIGATION SPECIAL RULES WITH RESPECT TO ADDITIONAL STATION AND SIGNAL LIGHTS � 707.10 Wake illumination light. Naval vessels may display a white spot light located near the stern to illuminate the...
32 CFR 707.10 - Wake illumination light.
Code of Federal Regulations, 2011 CFR
...NAVY NAVIGATION SPECIAL RULES WITH RESPECT TO ADDITIONAL STATION AND SIGNAL LIGHTS � 707.10 Wake illumination light. Naval vessels may display a white spot light located near the stern to illuminate the...
32 CFR 707.10 - Wake illumination light.
Code of Federal Regulations, 2010 CFR
...NAVY NAVIGATION SPECIAL RULES WITH RESPECT TO ADDITIONAL STATION AND SIGNAL LIGHTS � 707.10 Wake illumination light. Naval vessels may display a white spot light located near the stern to illuminate the...
Ship wake and oil slick observed by multi-sensor
NASA Astrophysics Data System (ADS)
Wang, Bo; Chen, Haiyang
Ship wake and oil slick signatures imaged by both multispectral ETM (enhanced thematic mapper) onboard Landsat-7 (L7) and multi-polarization SAR (synthetic aperture radar) onboard Radarsat-2 (R2) were analyzed in this paper. Spectral analysis used all the available band data together, not as an image but as a set of spectral features. Multipolarization imagery offers scattering information of the ground surface. Ship wake signatures were readily detected by local Hough transmission. Oil slicks are expected to benefit from spectral reflectance deviation from the background water color or phase differences between polarization channels. The appearance of ship wake in an area surrounded by oil slicks was also considered, although we have not yet conclusion at this moment. Comparing to our former efforts with polarized radar data only, the combined view by multispectral and multi-polarization sensors indicated detailed radiation and scattering characteristics of ship wake and oil slick signatures.
Passive wake detection using seal whisker-inspired sensing
Beem, Heather Rachel
This thesis is motivated by a series of biological experiments that display the harbor seal's extraordinary ability to track the wake of an object several seconds after it has swum by. They do so despite having auditory ...
Brain spatial microstates of human spontaneous alpha activity in relaxed wakefulness, drowsiness period, and REM sleep.
Cantero, J L; Atienza, M; Salas, R M; G�mez, C M
Spontaneous alpha activity clearly present in relaxed wakefulness with closed eyes, drowsiness period at sleep onset, and REM sleep was studied with spatial segmentation methods in order to determine if the brain activation state would be modulating the alpha spatial microstates composition and duration. These methods of spatial segmentation show some advantages: i) they extract topographic descriptors independent of the chosen reference (reference-free methods), and ii) they achieve spatial data reduction that are more data-driven than dipole source analysis. The results obtained with this study revealed that alpha activity presented a different spatio-temporal pattern of brain electric fields in each arousal state used in this study. These differences were reflected in a) the mean duration of alpha microstates (longer in relaxed wakefulness than in drowsy period and REM sleep), b) the number of brain microstates contained in one second (drowsiness showed more different microstates than did relaxed wakefulness and REM state), and c) the number of different classes (more abundant in drowsiness than in the rest of brain states). If we assume that longer segments of stable brain activity imply a lesser amount of different information to process (as reflected by a higher stability of the brain generator), whereas shorter segments imply a higher number of brain microstates caused by more different steps of information processing, it is possible that the alpha activity appearing in the sleep onset period could be indexing the hypnagogic imagery self-generated by the sleeping brain, and a phasic event in the case of REM sleep. Probably, REM-alpha bursts are associated with a brain microstate change (such as sleep spindles), as demonstrated by its phasic intrusion in a desynchronized background of brain activity. On the other hand, alpha rhythm could be the "baseline" of brain activity when the sensory inputs are minimum and the state is relaxed wakefulness. PMID:10449257
Wind turbine wake characterization using long-range Doppler lidar
NASA Astrophysics Data System (ADS)
Aitken, M.; Lundquist, J. K.; Hestmark, K.; Banta, R. M.; Pichugina, Y.; Brewer, A.
Wind turbines extract energy from the freestream flow, resulting in a waked region behind the rotor which is characterized by reduced wind speed and increased turbulence. The velocity deficit in the wake diminishes with distance, as faster-moving air outside is gradually entrained. In a concentrated group of turbines, then, downwind machines experience very different inflow conditions compared to those in the front row. As utility-scale turbines rarely exist in isolation, detailed knowledge of the mean flow and turbulence structure inside wakes is needed to correctly model both power production and turbine loading at modern wind farms. To this end, the Turbine Wake and Inflow Characterization Study (TWICS) was conducted in the spring of 2011 to determine the reduction in wind speeds downstream from a multi-MW turbine located at the National Renewable Energy Laboratory's National Wind Technology Center (NWTC) near Boulder, Colorado. Full-scale measurements of wake dynamics are hardly practical or even possible with conventional sensors, such as cup anemometers mounted on meteorological (met) masts. Accordingly, the High Resolution Doppler Lidar (HRDL) developed by the National Oceanic and Atmospheric Administration's Earth System Research Laboratory was employed to investigate the formation and propagation of wakes under varying levels of ambient wind speed, shear, atmospheric stability, and turbulence. HRDL remotely senses line-of-sight wind velocities and has been used in several previous studies of boundary layer aerodynamics. With a fully steerable beam and a maximum range up to about 5 km, depending on atmospheric conditions, HRDL performed a comprehensive survey of the wind flow in front of and behind the turbine to study the shape, meandering, and attenuation of wakes. Due in large part to limited experimental data availability, wind farm wake modeling is still subject to an unacceptable amount of uncertainty, particularly in complex terrain. Here, analytical techniques are developed to distinguish wakes from the background variability, and moreover, wakes are then classified by width, height, length, and velocity deficit based on atmospheric stability and inflow conditions. By integrating these advanced observational capabilities with innovative approaches to atmospheric modeling, this work will help to improve simulation tools used to quantify power loss and fatigue loading due to wake effects, thereby aiding the optimization of wind farm layouts.
Aerosol particle evolution in an aircraft wake: Implications for the high-speed civil transport fleet impact on ozone
NASA Astrophysics Data System (ADS)
Danilin, M. Y.; Rodriguez, J. M.; Ko, M. K. W.; Weisenstein, D. K.; Brown, R. C.; Miake-Lye, R. C.; Anderson, M. R.
Previous calculations of the ozone impact from a fleet of high-speed civil transports (HSCTs) have been carried out by global two-dimensional (2-D) models [Bekki and PyIe, 1993; Pitari et al., 1993] which have not included explicit wake processing of sulfur species. This processing could be important for the global sulfate aerosol and ozone perturbations [Weisenstein et al., 1996]. For an HSCT scenario with emission indices of NOx and sulfur equal to 5 and 0.4, respectively, and a cruise speed of Mach 2.4 [Stolarski and Wesoky, 1993b], the Atmospheric and Environmental Research (AER) 2-D model gives 0.50-1.1% as the range of the annually averaged O3 column depletion at 40�-50�N. This range is determined by the extreme assumption that emitted SO2 is diluted into the global model grid box either as gas or as 10 nm sulfate particles. A hierarchy of models is used here to investigate the impact of processes in the wake on the calculated global ozone response to sulfur emissions by a proposed HSCT fleet. We follow the evolution of aircraft emissions from the nozzle plane using three numerical models: the Standard Plume Flowfield-II/Plume Nucleation and Condensation model (SPF-II/PNC), an AER far wake model incorporating microphysics of aerosol particles, and the AER global 2-D chemistry-transport model. Particle measurements in the wake of the Concorde [Fahey et al., 1995a] are used to place constraints on sulfur oxidation processes in the engine and the near field. To explain the Concorde measurements, we consider cases with different fractions of SO3 (2%, 20%, and 40%) in the sulfur emissions at the nozzle plane and also the possibility of other unknown heterogeneous or homogeneous oxidation processes for SO2 in the wake. Assuming similar characteristics for the proposed HSCT fleet, the global ozone response is then calculated by the 2-D model. Using the model-calculated wake processing of sulfur emissions under the above assumptions and constrained by the Concorde particle measurements, the range of annually averaged O3 column depletion at 40�-50�N is reduced from 0.5-1.1% to 0.75-1.0%. Our analysis shows that the global ozone response is more sensitive to the assumed partitioning of sulfur emissions between SO2 and SO3 at the nozzle plane than to the wake dilution rate. Outstanding uncertainties and recommendations for further wake-sampling experiments are also discussed.
Turbulent large-scale structure effects on wake meandering
NASA Astrophysics Data System (ADS)
Muller, Y.-A.; Masson, C.; Aubrun, S.
This work studies effects of large-scale turbulent structures on wake meandering using Large Eddy Simulations (LES) over an actuator disk. Other potential source of wake meandering such as the instablility mechanisms associated with tip vortices are not treated in this study. A crucial element of the efficient, pragmatic and successful simulations of large-scale turbulent structures in Atmospheric Boundary Layer (ABL) is the generation of the stochastic turbulent atmospheric flow. This is an essential capability since one source of wake meandering is these large - larger than the turbine diameter - turbulent structures. The unsteady wind turbine wake in ABL is simulated using a combination of LES and actuator disk approaches. In order to dedicate the large majority of the available computing power in the wake, the ABL ground region of the flow is not part of the computational domain. Instead, mixed Dirichlet/Neumann boundary conditions are applied at all the computational surfaces except at the outlet. Prescribed values for Dirichlet contribution of these boundary conditions are provided by a stochastic turbulent wind generator. This allows to simulate large-scale turbulent structures - larger than the computational domain - leading to an efficient simulation technique of wake meandering. Since the stochastic wind generator includes shear, the turbulence production is included in the analysis without the necessity of resolving the flow near the ground. The classical Smagorinsky sub-grid model is used. The resulting numerical methodology has been implemented in OpenFOAM. Comparisons with experimental measurements in porous-disk wakes have been undertaken, and the agreements are good. While temporal resolution in experimental measurements is high, the spatial resolution is often too low. LES numerical results provide a more complete spatial description of the flow. They tend to demonstrate that inflow low frequency content - or large- scale turbulent structures - is an important parameter when simulating wake meandering and plays a significant role.
Hypothalamic contribution to sleep�wake cycle development
Infant mammals cycle rapidly between sleep and wakefulness and only gradually does a more consolidated sleep pattern develop. The neural substrates responsible for this consolidation are unknown. To establish a reliable measure of sleep-wake cyclicity in infant rats, nuchal muscle tone was measured in 2-, 5-, and 8-day-old rats, as were motor behaviors associated with sleep (i.e. myoclonic twitching) and
The Comprehensive Cancer Center of Wake Forest University
The Wake Forest University (WFU) School of Medicine was founded in 1902 and North Carolina Baptist Hospital opened in 1923. It has grown into a large academic medical center with 900 faculty members, more than 100 buildings on 290 acres, and 900 licensed beds. The Comprehensive Cancer Center of Wake Forest University (CCCWFU) started in the early 1960�s and became an NCI-designated cancer center in 1972 and a comprehensive center in 1990.
Rotor wake\\/stator interaction noise-predictions versus data
D. A. Topol
A rotor wake\\/stator interaction noise prediction method is presented and evaluated with fan rig and full-scale engine data. The noise prediction method uses a two-dimensional (2D) semi-empirical wake model and an analytical stator response function and noise calculation. The stator response function is a 2D strip theory which is linked to a noise calculation formulated in a constant area annular
A remote sensing study of a surface ship wake
Rodney D. Peltzer; William D. Garrett; Peter M. Smith
The turbulent wake of the USNS Hayes, a twin hulled ship, was imaged simultaneously by a thermal infrared scanner, an X-band microwave radar and a 35 mm strip camera mounted in an NRL RP-3A aircraft. Thermal surface effects and centimeter-scale surface roughness characteristics were determined for both natural ship wakes and those treated with oleyl alcohol, an organic material which
Nonlinear two-dimensional potential plasma wake waves
Amatuni, A.Ts.
The conditions for potential description of the wake waves, generated by flat electron driving bunch in cold plasma, are derived. The nonlinear equation for potential, valid for small values of that, is obtained and exact solutions are found for two-dimensional nonlinear plasma wake-waves. In particular,at some boundary conditions, corresponding to blow-out regime, the solution in form of solitary wave is found.
Adaptive Sleep�Wake Discrimination for Wearable Devices
Walter Karlen; Dario Floreano
Sleep\\/wake classification systems that rely on phys- iological signals suffer from intersubject differences that make accurate classification with a single, subject-independent model difficult. To overcome the limitations of intersubject variability, we suggest a novel online adaptation technique that updates the sleep\\/wake classifier in real time. The objective of the present study was to evaluate the performance of a newly developed
Sleep�wake architecture in mouse models for Down syndrome
Damien Colas; Jacqueline London; Abdallah Gharib; Raymond Cespuglio; Nicole Sarda
Sleep�wake homeostasis is crucial for behavioral performances and memory both in the general population and in patients with learning disability, among whom were Down syndrome (DS) patients. We investigated, in mouse models of DS, cortical EEG and sleep�wake architecture under baseline conditions and after a 4-h sleep deprivation (SD). Young hemizygous mice (hSODwt\\/+) transgenic for the human CuZn superoxide dismutase
Activity-based sleep�wake identification in infants
Edward Sazonov; Nadezhda Sazonova; Stephanie Schuckers; Michael Neuman
Actigraphy offers one of the best-known alternatives to polysomnography for sleep�wake identification. The advantages of actigraphy include high accuracy, simplicity of use and low intrusiveness. These features allow the use of actigraphy for determining sleep�wake states in such highly sensitive groups as infants. This study utilizes a motion sensor (accelerometer) for a dual purpose: to determine an infant's position in
Sleep�wake changes and cognition in neurodegenerative disease
Sharon L. Naismith; Simon J. G. Lewis; Naomi L. Rogers
With the increasing aging population, neurodegenerative disorders will become more common in clinical practice. These disorders involve multiple pathophysiological mechanisms that differentially affect cognition, mood, and physical functions. Possibly due to the involvement of common underlying neurobiological circuits, sleep and\\/or circadian (sleep�wake) changes are also common in this disease group. Of significance, sleep�wake changes are often a prodromal feature and
SLAM: Sleep-Wake Aware Local Monitoring in Sensor Networks
Issa Khalil; Saurabh Bagchi; Ness B. Shroff
Sleep-wake protocols are critical in sensor networks to ensure long-lived operation. However, an open problem is how to develop efficient mechanisms that can be incorporated with sleep-wake protocols to ensure both longlived operation and a high degree of security. Our contribution in this paper is to address this problem by using local monitoring, a powerful technique for detecting and mitigating
SLAM: Sleep-Wake Aware Local Monitoring in Sensor Networks
Issa Khalil; Saurabh Bagchi; Ness B. Shroff
Sleep-wake protocols are critical in sensor networks to ensure long-lived operation. However, an open problem is how to develop efficient mechanisms that can be incorporated with sleep-wake protocols to ensure both long-lived operation and a high degree of security. Our contribution in this paper is to address this problem by using local monitoring, a powerful technique for detecting and mitigating
Effect of the number of blades on propeller wake evolution
Mario Felli; Giulio Guj; Roberto Camussi
The effect of the number of blades on wake evolution was investigated on three propellers having the same blade geometry but\\u000a different numbers of blades. The experiments concerned velocity measurements along nine transversal planes of the wake by\\u000a LDV phase-sampling techniques. The study was performed with all the propellers having the same tip vortex intensity. In addition,\\u000a high-speed visualizations were
Raman gain suppression with multimode lasers
Heinrichs, R.M.; Winkler, I.C.
We have found the gain of a Raman amplifier to be almost completely suppressed when the amplifier is pumped by a multilongitudinal mode laser and seeded with an initially uncorrelated Stokes beam that is nearly as intense as the pump. This effect is predicted by a plane-wave model of Raman amplification that accounts for multimode pump and Stokes fields. Our experiments have also demonstrated that the beam quality of the pump is maintained to the extent that the amplification is suppressed.
Wake Vortex Inverse Model User's Guide
NASA Technical Reports Server (NTRS)
Lai, David; Delisi, Donald
NorthWest Research Associates (NWRA) has developed an inverse model for inverting landing aircraft vortex data. The data used for the inversion are the time evolution of the lateral transport position and vertical position of both the port and starboard vortices. The inverse model performs iterative forward model runs using various estimates of vortex parameters, vertical crosswind profiles, and vortex circulation as a function of wake age. Forward model predictions of lateral transport and altitude are then compared with the observed data. Differences between the data and model predictions guide the choice of vortex parameter values, crosswind profile and circulation evolution in the next iteration. Iterations are performed until a user-defined criterion is satisfied. Currently, the inverse model is set to stop when the improvement in the rms deviation between the data and model predictions is less than 1 percent for two consecutive iterations. The forward model used in this inverse model is a modified version of the Shear-APA model. A detailed description of this forward model, the inverse model, and its validation are presented in a different report (Lai, Mellman, Robins, and Delisi, 2007). This document is a User's Guide for the Wake Vortex Inverse Model. Section 2 presents an overview of the inverse model program. Execution of the inverse model is described in Section 3. When executing the inverse model, a user is requested to provide the name of an input file which contains the inverse model parameters, the various datasets, and directories needed for the inversion. A detailed description of the list of parameters in the inversion input file is presented in Section 4. A user has an option to save the inversion results of each lidar track in a mat-file (a condensed data file in Matlab format). These saved mat-files can be used for post-inversion analysis. A description of the contents of the saved files is given in Section 5. An example of an inversion input file, with preferred parameters values, is given in Appendix A. An example of the plot generated at a normal completion of the inversion is shown in Appendix B.
Simulation of Wake Vortex Radiometric Detection via Jet Exhaust Proxy
NASA Technical Reports Server (NTRS)
Daniels, Taumi S.
This paper describes an analysis of the potential of an airborne hyperspectral imaging IR instrument to infer wake vortices via turbine jet exhaust as a proxy. The goal was to determine the requirements for an imaging spectrometer or radiometer to effectively detect the exhaust plume, and by inference, the location of the wake vortices. The effort examines the gas spectroscopy of the various major constituents of turbine jet exhaust and their contributions to the modeled detectable radiance. Initially, a theoretical analysis of wake vortex proxy detection by thermal radiation was realized in a series of simulations. The first stage used the SLAB plume model to simulate turbine jet exhaust plume characteristics, including exhaust gas transport dynamics and concentrations. The second stage used these plume characteristics as input to the Line By Line Radiative Transfer Model (LBLRTM) to simulate responses from both an imaging IR hyperspectral spectrometer or radiometer. These numerical simulations generated thermal imagery that was compared with previously reported wake vortex temperature data. This research is a continuation of an effort to specify the requirements for an imaging IR spectrometer or radiometer to make wake vortex measurements. Results of the two-stage simulation will be reported, including instrument specifications for wake vortex thermal detection. These results will be compared with previously reported results for IR imaging spectrometer performance.
The ultra-low Reynolds number airfoil wake
NASA Astrophysics Data System (ADS)
Alam, Md. Mahbub; Zhou, Y.; Yang, H. X.; Guo, H.; Mi, J.
Lift force and the near wake of an NACA 0012 airfoil were measured over the angle (?) of attack of 0�-90� and the chord Reynolds number ( Re c ), 5.3 � 103-5.1 � 104, with a view to understand thoroughly the near wake of the airfoil at low- to ultra-low Re c . While the lift force is measured using a load cell, the detailed flow structure is captured using laser-Doppler anemometry, particle image velocimetry, and laser-induced fluorescence flow visualization. It has been found that the stall of an airfoil, characterized by a drop in the lift force, occurs at Re c ? 1.05 � 104 but is absent at Re c = 5.3 � 103. The observation is connected to the presence of the separation bubble at high Re c but absence of the bubble at ultra-low Re c , as evidenced in our wake measurements. The near-wake characteristics are examined and discussed in detail, including the vortex formation length, wake width, spanwise vorticity, wake bubble size, wavelength of K-H vortices, Strouhal numbers, and their dependence on ? and Re c .
Are "Bondi-Hoyle Wakes" detectable in clusters of galaxies?
Irini Sakelliou
In clusters of galaxies, the reaction of the intracluster medium (ICM) to the motion of the co-existing galaxies in the cluster triggers the formation of unique features, which trace their position and motion. Galactic wakes, for example, are an apparent result of the ICM/galaxy interactions, and they constitute an important tool for deciphering the motion of the cluster galaxies. In this paper we investigate whether Bondi-Hoyle accretion can create galactic wakes by focusing the ICM behind moving galaxies. The solution of the equations that describe this physical problem provide us with observable quantities along the wake at any time of its lifetime. We also investigate which are the best environmental conditions for the detectability of such structures in the X-ray images of clusters of galaxies. We find that significant Bondi-Hoyle wakes can only be formed in low temperature clusters, and that they are more pronounced behind slow-moving, relatively massive galaxies. The scale length of these elongated structures is not very large: in the most favourable conditions a Bondi-Hoyle wake in a cluster at the redshift of z=0.05 is 12 arcsec long. However, the wake's X-ray emission is noticeably strong: the X-ray flux can reach ~30 times the flux of the surrounding medium. Such features will be easily detectable in Chandra's and XMM-Newton's X-ray images of nearby, relatively poor clusters of galaxies.
The 21 cm signature of cosmic string wakes
Brandenberger, Robert H.; Danos, Rebecca J.; Hern�ndez, Oscar F.; Holder, Gilbert P., E-mail: firstname.lastname@example.com, E-mail: firstname.lastname@example.com, E-mail: firstname.lastname@example.com, E-mail: email@example.com [Department of Physics, McGill University, Montr�al, QC, H3A 2T8 (Canada)
We discuss the signature of a cosmic string wake in 21cm redshift surveys. Since 21cm surveys probe higher redshifts than optical large-scale structure surveys, the signatures of cosmic strings are more manifest in 21cm maps than they are in optical galaxy surveys. We find that, provided the tension of the cosmic string exceeds a critical value (which depends on both the redshift when the string wake is created and the redshift of observation), a cosmic string wake will generate an emission signal with a brightness temperature which approaches a limiting value which at a redshift of z+1 = 30 is close to 400 mK in the limit of large string tension. The signal will have a specific signature in position space: the excess 21cm radiation will be confined to a wedge-shaped region whose tip corresponds to the position of the string, whose planar dimensions are set by the planar dimensions of the string wake, and whose thickness (in redshift direction) depends on the string tension. For wakes created at z{sub i}+1 = 10{sup 3}, then at a redshift of z+1 = 30 the critical value of the string tension ? is G? = 6 � 10{sup ?7}, and it decreases linearly with redshift (for wakes created at the time of equal matter and radiation, the critical value is a factor of two lower at the same redshift). For smaller tensions, cosmic strings lead to an observable absorption signal with the same wedge geometry.
Thermal bottomonium suppression
NASA Astrophysics Data System (ADS)
Strickland, Michael
I discuss recent calculations of the thermal suppression of bottomonium states in relativistic heavy ion collisions. I present results for the inclusive ?(1s) and ?(2s) suppression as a function of centrality. I compare with the most recent CMS preliminary data available at central rapidities and make predictions at forward rapidities which are within the acceptance of the ALICE dimuon spectrometer.
Wake fields effects for the eRHIC project
Fedotov A. V.; Belomestnykh, S.; Kayran, D.; Litvinenko, V.; Ptitsyn, V.
An Energy Recovery Linac (ERL) with a high peak electron bunch current is proposed for the Electron-Ion collider (eRHIC) project at the Brookhaven National Laboratory. The present design is based on the multi-pass electron beam transport in existing tunnel of the Relativistic Heavy Ion Collider (RHIC). As a result of a high peak current and a very long beam transport, consideration of various collective beam dynamics effects becomes important. Here we summarize effects of the coherent synchrotron radiation, resistive wall, accelerating cavities and wall roughness on the resulting energy spread and energy loss for several scenarios of the eRHIC project.
An Analysis of Closure Mechanisms in the Plasma Wake of the TSS-1R Satellite
NASA Technical Reports Server (NTRS)
Stone, N. H.; Wright, K. H.; Samir, U.; Winningham, J. D.
Collisionless Plasma Expansion (CPE), also known as "plasma expansion into a vacuum," in its most fundamental form, is the process by which a plasma expands into a void, or region highly depleted of particles. In CPE, the expansion is driven by the highly mobile electron constituent of the plasma as it moves across the density gradient and into the void region. A bi-polar electric field is set up between this rapidly expanding electron front and the massive ions, which have a low thermal speed and lag behind in the region of the plasma-void interface. These ions are quickly accelerated by the expansion electric field and can, theoretically, approach the thermal speed of the electrons. CPE is a fundamental and a very robust process in that it only requires that a sharp density gradient exist in a plasma. It has already been observed to exist in various plasmas ranging over five orders of magnitude in density. The range of phenomena in which CPE has been observed includes the closure of plasma wakes created in simulated space plasmas in the laboratory; it was found to be the process controlling the refilling of the wake created by the Space Shuttle in the ionospheric plasma; and recent in situ data, obtained by the WIND spacecraft as it passed through the wake of the earth's moon last year, have shown CPE to be involved in the closure of the Lunar wake. CPE is also expected to influence the morphology and physics of the solar wind interactions with Mercury and Mars, and has been suggested as a potential factor in such wide ranging phenomena as the acceleration of plasma away from the coma of comets and the energization of ions that underlies the upward expansion of the polar wind into the earth's magnetosphere. The Tethered Satellite System (TSS)-1R data provides an opportunity to test this process in situ under semi-controlled conditions. The available data shows the intensity, drift energy and angle of inclination to the wake of the converging ion streams at a down stream distance of one satellite radius (80 CM).
Modeling von Karman vortex shedding in cylinder wake to examine energetic coherent motions on hydrokinetic turbines
NASA Astrophysics Data System (ADS)
Neary, V. S.; Gunawan, B.; Chamorro, L. P.; Stekovic, S.; Hill, C.
Numerous investigators have examined vortex-shedding in the wake of cylinders. This is a classical flow problem that has many engineering applications, including pronounced flow disturbance, turbulence generation, and sediment scour in the wakes of in stream structures, e.g. bridge piers and towers for marine and hydrokinetic (MHK) turbines. It is also important to understand the contribution of large coherent motions on the unsteady loading and performance of hydrokinetic turbines. Unsteady vortex shedding is caused by flow separation and detachment within the near-wall region along the cylinder surface. Our aim is to examine the unsteady flow field and von Karman vortex shedding resulting from unsteady turbulent flow around an emergent cylinder mounted perpendicular to a fixed surface by conducting physical and numerical modeling experiments. The numerical simulation emulates an open-channel flow experiment at the St. Anthony Falls Laboratory at the University of Minnesota, where instantaneous velocity was measured using three synchronized acoustic Doppler velocimeters (ADVs). The open-channel flume is 80 m long, and 2.75 m wide. The flow depth is 1.15 m. The cylinder diameter is 0.116 m. The flow is turbulent, with a cylinder Reynolds number equal to 5.44E4. We use the commercial CFD software, STAR-CCM+, to generate the computational mesh that models the flow geometry around the cylinder, and to numerically solve the unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. The generated mesh is fine enough (> 2 million elements) to resolve the coherent structures of vortex shedding. The Frost high-performance cluster (an ORNL supercomputer) is used to run the simulation. The results show how a validated CFD model can be used to design the layout and spacing of synchronized ADV point measurements to characterize essential features of the Karman shedding in the cylinder wake. A similar approach can be used to design field ADV arrays for measuring more complex vortex shedding, e.g. the tip vortices, occurring in the wakes of MHK turbine rotors.; Numerical simulation of Karman shedding in the wake of cylinder (diameter 0.116 m, Reynolds number, 5.44E4).
Separated flow over bodies of revolution using an unsteady discrete-vorticity cross wake. Part 2: Computer program description
NASA Technical Reports Server (NTRS)
Marshall, F. J.; Deffenbaugh, F. D.
A method is developed to determine the flow field of a body of revolution in separated flow. The computer was used to integrate various solutions and solution properties of the sub-flow fields which made up the entire flow field without resorting to a finite difference solution to the complete Navier-Stokes equations. The technique entails the use of the unsteady cross flow analogy and a new solution to the two-dimensional unsteady separated flow problem based upon an unsteady, discrete-vorticity wake. Data for the forces and moments on aerodynamic bodies at low speeds and high angle of attack (outside the range of linear inviscid theories) such that the flow is substantially separated are produced which compare well with experimental data. In addition, three dimensional steady separated regions and wake vortex patterns are determined. The computer program developed to perform the numerical calculations is described.
Evaluating Sleepiness-Related Daytime Function by Querying Wakefulness Inability and Fatigue: Sleepiness-Wakefulness Inability and Fatigue Test (SWIFT)
Sangal, R. Bart
Study Objectives: Routine assessment of daytime function in Sleep Medicine has focused on �tendency to fall asleep� in soporific circumstances, to the exclusion of �wakefulness inability� or inability to maintain wakefulness, and fatigue/tiredness/lack of energy. The objective was to establish reliability and discriminant validity of a test for wakefulness inability and fatigue, and to test its superiority against the criterion standard for evaluation of sleepiness�the Epworth Sleepiness Scale (ESS). Methods: A 12-item self-administered instrument, the Sleepiness-Wakefulness Inability and Fatigue Test (SWIFT), was developed and administered, with ESS, to 256 adults ? 18 years of age (44 retook the tests a month later); consecutive patients with symptoms of sleep disorders including 286 with obstructive sleep apnea ([OSA], apnea-hypopnea index ? 5/h sleep on polysomnography [PSG]), 49 evaluated with PSG and multiple sleep latency test for narcolepsy and 137 OSA patients treated with continuous positive airway pressure (CPAP). Results: SWIFT had internal consistency 0.87 and retest intraclass coefficient 0.82. Factor analysis revealed 2 factors�general wakefulness inability and fatigue (GWIF) and driving wakefulness inability and fatigue (DWIF). Normal subjects differed from patients in ESS, SWIFT, GWIF, and DWIF. SWIFT and GWIF (but not DWIF) had higher area under ROC curve, Youden's index, and better positive and negative likelihood ratios than ESS. ESS, SWIFT, GWIF, and DWIF improved with CPAP. Improvements in SWIFT, GWIF, and DWIF (but not ESS) were significantly correlated with CPAP compliance. Conclusions: SWIFT is reliable and valid. SWIFT and its factor GWIF have a discriminant ability superior to that of the ESS. Citation: Sangal RB. Evaluating sleepiness-related daytime function by querying wakefulness inability and fatigue: Sleepiness-Wakefulness Inability and Fatigue Test (SWIFT). J Clin Sleep Med 2012;8(6):701-711. PMID:23243405
Lift and wakes of flying snakes
NASA Astrophysics Data System (ADS)
Krishnan, Anush; Socha, John J.; Vlachos, Pavlos P.; Barba, L. A.
Flying snakes use a unique method of aerial locomotion: they jump from tree branches, flatten their bodies, and undulate through the air to produce a glide. The shape of their body cross-section during the glide plays an important role in generating lift. This paper presents a computational investigation of the aerodynamics of the cross-sectional shape. Two-dimensional simulations of incompressible flow past the anatomically correct cross-section of the species Chrysopelea paradisi show that a significant enhancement in lift appears at a 35� angle of attack, above Reynolds numbers 2000. Previous experiments on physical models also obtained an increased lift, at the same angle of attack. The flow is inherently three-dimensional in physical experiments, due to fluid instabilities, and it is thus intriguing that the enhanced lift also appears in the two-dimensional simulations. The simulations point to the lift enhancement arising from the early separation of the boundary layer on the dorsal surface of the snake profile, without stall. The separated shear layer rolls up and interacts with secondary vorticity in the near-wake, inducing the primary vortex to remain closer to the body and thus cause enhanced suction, resulting in higher lift.
Wakeful rest alleviates interference-based forgetting.
Mercer, Tom
Retroactive interference (RI)--the disruptive influence of events occurring after the formation of a new memory--is one of the primary causes of forgetting. Placing individuals within an environment that postpones interference should, therefore, greatly reduce the likelihood of information being lost from memory. For example, a short period of wakeful rest should diminish interference-based forgetting. To test this hypothesis, participants took part in a foreign language learning activity and were shown English translations of 20 Icelandic words for immediate recall. Half of the participants were then given an 8-min rest before completing a similar or dissimilar interfering distractor task. The other half did not receive a rest until after the distractor task, at which point interference had already taken place. All participants were then asked to translate the Icelandic words for a second time. Results revealed that retention was significantly worse at the second recall test, but being allowed a brief rest before completing the distractor task helped reduce the amount of forgetting. Taking a short, passive break can shield new memories from RI and alleviate forgetting. PMID:24410154
NASA Astrophysics Data System (ADS)
Yang, W.; Meng, H.
The dynamics of vortex structures in the wake of surface-mounted trapezoidal tab at Re=600 based on tab height was studied in detail using time-series, 2D particle image velocimetry. From a total of over 20,000 PIV realizations acquired in x-y, x-z, and y-z planes, we successfully identified vortex structures using the methods proposed by Jeong and Hussain (JFM, vol 285, 1995) and proposed by Chong, Perry, and Cantwell (Phys. Fluids A2, 1990), and cross-checked them with conventional velocity subtraction. Similar to prior measurement at Re=2080, secondary vortices, reverse vortices, and tertiary vortices were observed frequently in the present study. Higher PIV spatial resolution and higher temporal resolution (relative to the flow periodicity) allow us to investigate these dynamical phenomena in much greater detail and confidence. Furthermore, y-z measurements demonstrate that hairpin vortex legs, taking the shape of streamwise vortices, pair with their neighbor counterparts while traveling downstream, and possibly merge with each other. Circulation distribution of the hairpin vortex heads along the x direction shows that it increases at the very near-tab region with the help of pressure induced counter-rotating vortex pairs, but gradually decreases very slowly with the increasing downstream distance, indicating that hairpin vortices are long-lived vortex structures.
Parkinson's disease and sleep/wake disturbances.
Suzuki, Keisuke; Miyamoto, Masayuki; Miyamoto, Tomoyuki; Hirata, Koichi
Sleep disturbances are a common non-motor feature in patients with Parkinson's disease (PD). Early diagnosis and appropriate management are imperative for enhancing patient quality of life. Sleep disturbances can be caused by multiple factors in addition to age-related changes in sleep, such as nocturnal motor symptoms (rigidity, resting tremor, akinesia, tardive dyskinesia, and the "wearing off" phenomenon), non-motor symptoms (pain, hallucination, and psychosis), nocturia, and medication. Disease-related pathology involving the brainstem and changes in the neurotransmitter systems (norepinephrine, serotonin, and acetylcholine) responsible for regulating sleep structure and the sleep/wake cycle play a role in emerging excessive daytime sleepiness and sleep disturbances. Additionally, screening for sleep apnea syndrome, rapid eye movement sleep behavior disorder, and restless legs syndrome is clinically important. Questionnaire-based assessment utilizing the PD Sleep Scale-2 is useful for screening PD-related nocturnal symptoms. In this review, we focus on the current understanding and management of sleep disturbances in PD. PMID:25687697
Effects of Aircraft Wake Dynamics on Measured and Simulated NO(x) and HO(x) Wake Chemistry. Appendix B
NASA Technical Reports Server (NTRS)
Lewellen, D. C.; Lewellen, W. S.
High-resolution numerical large-eddy simulations of the near wake of a B757 including simplified NOx and HOx chemistry were performed to explore the effects of dynamics on chemistry in wakes of ages from a few seconds to several minutes. Dilution plays an important basic role in the NOx-O3 chemistry in the wake, while a more interesting interaction between the chemistry and dynamics occurs for the HOx species. These simulation results are compared with published measurements of OH and HO2 within a B757 wake under cruise conditions in the upper troposphere taken during the Subsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS) mission in May 1996. The simulation provides a much finer grained representation of the chemistry and dynamics of the early wake than is possible from the 1 s data samples taken in situ. The comparison suggests that the previously reported discrepancy of up to a factor of 20 - 50 between the SUCCESS measurements of the [HO2]/[OH] ratio and that predicted by simplified theoretical computations is due to the combined effects of large mixing rates around the wake plume edges and averaging over volumes containing large species fluctuations. The results demonstrate the feasibility of using three-dimensional unsteady large-eddy simulations with coupled chemistry to study such phenomena.
Novel analysis of sleep patterns in rats separates periods of vigilance cycling from long-duration wake events
Steven M. Simasko; Sanjib Mukherjee
Rats are polyphasic sleepers. However, a formal definition of when one sleep episode ends and another begins has not been put forth. In the present study we examine the distribution of wake episode durations and based on this distribution conclude there are multiple components of wake. If the wake episode exceeds 300s the wake episode is assigned to long-duration wake
Wake-up radio architecture for home wireless networks Florin Hutu, Aissa Khoumeri, Guillaume Villemaud, Jean-Marie Gorce
Paris-Sud XI, Université de
Wake-up radio architecture for home wireless networks Florin Hutu, Aissa Khoumeri, Guillaume by simulation a wake-up radio receiver (WuRx), allowing to both addressing and wake-up a main radio, with best. The wake-up receiver is designed to be able to detect a wake-up signal which has a frequency signature
Collisional Simulations of Wakes at the Encke Gap
NASA Astrophysics Data System (ADS)
Lewis, M. C.; Stewart, G. R.
We simulate wake evolution in the Encke Gap forced by a nearby moon. The N-body calculations run on a single processor, include a few hundred thousand particles, and explicitly include collisions. The motivation for these simulations is to explain the morphology and the persistence of the wakes seen in the Voyager PPS data. Showalter et al. (1986, Icarus 66, 297) proposed that the oscillatory patterns observed in the radial profiles around this gap in the A Ring were due to the perturbations of a small moon. This small moon, Pan, was later located by Showalter (1991, Nature 351, 709). From the analytic work of Showalter et al. in 1986, which describes the evolution of the wake without self-gravity, the wakes should essentially disappear 20-30 degrees downstream from the moon. However, Showalter noted in 1991 that the wakes were still visible in the data 330 degrees downstream. More recent analysis has shown that the wakes persist well beyond re-encountering Pan and can be found superimposed over the more recent perturbations. To better understand how collisions affect the evolution of these wakes, we use the collisional model of Bridges et al. (1984, Nature 309, 333) for a velocity dependent coefficient of restitution. Our simulations differ from previous work in that we have tried to keep the parameters in the simulation as close as possible to those at the actual Encke Gap. We preserve the satellite to planet mass ratio and run the simulations for a full synodic period to determine damping rates for the wakes. We have run simulations with particles ranging from 133 meters in radius down to 6.7 meters in radius at an optical depth of 0.3. For lower optical depths we have used particles as small as 1 meter in radius. Our simulations show how cell size, particle size, and optical depth affect the results. Preliminary results are that with particle sizes of several meters and optical depths around 0.3, collisions can sustain the wakes further downstream than the collisionless theory would predict. Also, we find that the collisions produce a phase shift in the wake near the ring edge.
Simulating Virtual Terminal Area Weather Data Bases for Use in the Wake Vortex Avoidance System (Wake VAS) Prediction Algorithm
NASA Technical Reports Server (NTRS)
Kaplan, Michael L.; Lin, Yuh-Lang
During the research project, sounding datasets were generated for the region surrounding 9 major airports, including Dallas, TX, Boston, MA, New York, NY, Chicago, IL, St. Louis, MO, Atlanta, GA, Miami, FL, San Francico, CA, and Los Angeles, CA. The numerical simulation of winter and summer environments during which no instrument flight rule impact was occurring at these 9 terminals was performed using the most contemporary version of the Terminal Area PBL Prediction System (TAPPS) model nested from 36 km to 6 km to 1 km horizontal resolution and very detailed vertical resolution in the planetary boundary layer. The soundings from the 1 km model were archived at 30 minute time intervals for a 24 hour period and the vertical dependent variables as well as derived quantities, i.e., 3-dimensional wind components, temperatures, pressures, mixing ratios, turbulence kinetic energy and eddy dissipation rates were then interpolated to 5 m vertical resolution up to 1000 m elevation above ground level. After partial validation against field experiment datasets for Dallas as well as larger scale and much coarser resolution observations at the other 8 airports, these sounding datasets were sent to NASA for use in the Virtual Air Space and Modeling program. The application of these datasets being to determine representative airport weather environments to diagnose the response of simulated wake vortices to realistic atmospheric environments. These virtual datasets are based on large scale observed atmospheric initial conditions that are dynamically interpolated in space and time. The 1 km nested-grid simulated datasets providing a very coarse and highly smoothed representation of airport environment meteorological conditions. Details concerning the airport surface forcing are virtually absent from these simulated datasets although the observed background atmospheric processes have been compared to the simulated fields and the fields were found to accurately replicate the flows surrounding the airport where coarse verification data were available as well as where airport scale datasets were available.
Numerical investigation of the turbulent energy budget in the wake of freely oscillating elastically mounted cylinder at low reduced velocities
NASA Astrophysics Data System (ADS)
Sarkar, Abhishek; Schl�ter, J�rg
We present a numerical study of the turbulent kinetic energy budget in the wake of cylinders undergoing Vortex-Induced Vibration (VIV). We show three-dimensional Large Eddy Simulations (LES) of an elastically mounted circular cylinder in the synchronization regime at Reynolds number of Re=8000. The Immersed Boundary Method (IBM) is used to account for the presence of the cylinder. The flow field in the wake is decomposed using the triple decomposition splitting the flow variables in mean, coherent and stochastic components. The energy transfer between these scales of motions are then studied and the results of the free oscillation are compared to those of a forced oscillation. The turbulent kinetic energy budget shows that the maximum amplitude of VIV is defined by the ability of the mean flow to feed energy to the coherent structures in the wake. At amplitudes above this maximum amplitude, the energy of the coherent structures needs to be fed additionally by small scale, stochastic energy in form of backscatter to sustain its motion. Furthermore, we demonstrate that the maximum amplitude of the VIV is defined by the integral length scale of the turbulence in the wake.
A Parametric Study of Accelerations of an Airplane Due to a Wake Vortex System
NASA Technical Reports Server (NTRS)
Stewart, Eric C.
A study was conducted using strip theory to systematically investigate the effects of progressively more complete descriptions of the interaction of an airplane with a wake vortex system. The emphasis was in roll-dominant, parallel, vortex encounters. That is, the simulated airplane's longitudinal axis was nearly parallel to the rotation axis of the vortex system for most of the results presented. The study began with a drag-less rectangular wing in the flow field of a single vortex and progressed to a complete airplane with aerodynamic surfaces possessing taper, sweep, dihedral, and stalling and immersed in the flow field of a vortex pair in ground effect. The effects of the pitch, roll, and yaw attitudes of the airplane on the calculated accelerations were also investigated. The airplane had the nominal characteristics of a Boeing 757, and the vortex flow field had the nominal characteristics of the wake of a Boeing 767. The Bumham-Hallock model of a vortex flow field was used throughout the study. The data are presented mainly in terms of contours of equal acceleration in a two-dimensional area centered on the vortex pair and having dimensions of 300 feet by 300 feet.
Changnon, S A; Farhar, B C; Swanson, E R
An interdisciplinary assessment of hail suppression in the past, present, and future has shown it to be currently scientifically uncertain but a potentially beneficial future technology. An established suppression technology would be widely adopted in the Great Plains, providing benefits to agriculture and secondarily to the American consumer. Development of a reliable technology will require a sizable longterm federal commitment to atmospheric and social research. Subcritical funding would be a mistake. Orderly future usage of hail suppression, with its scientific complexities and regional character, will necessitate development of governmental regulations, evaluation procedures, interstate arrangements, and means for compensating those who lose from modification. PMID:17757286
Wind tunnel investigation on wind turbine wakes and wind farms
NASA Astrophysics Data System (ADS)
Iungo, G. V.; Co�ff�, J.; Port�-Agel, F.
The interaction between atmospheric boundary layer and wind farms leads to flow modifications, which need to be deeply characterized in order to relate them to wind farm performance. The wake flow produced from a wind farm is the result of a strong interaction between multiple turbine wakes, so that the wind farm configuration turns out to be one of the dominant features to enhance power production. For the present work a wind tunnel investigation was carried out with hot-wire anemometry and velocity measurements performed with multi-hole pressure probes. The tested wind farms consist of miniature three-bladed wind turbine models. Preliminarily, the wake flow generated from a single wind turbine is surveyed, which is characterized by a strong velocity defect lying in proximity of the wind turbine hub height. The wake gradually recovers by moving downstream; the characteristics of the incoming boundary layer and wind turbulence intensity can strongly affect the wake recovery, and thus performance of following wind turbines. An increased turbulence level is typically detected downstream of each wind turbine for heights comparable to the wind turbine blade top-tip. These wake flow fluctuations produce increased fatigue loads on the following wind turbines within a wind farm, which could represent a significant hazard for real wind turbines. Dynamics of vorticity structures present in wind turbine wakes are also investigated; particular attention is paid to the downstream evolution of the tip helicoidal vortices and to oscillations of the hub vortex. The effect of wind farm layout on power production is deeply investigated. Particular emphasis is placed on studying how the flow adjusts as it moves inside the wind farm and can affect the power production. Aligned and staggered wind farm configurations are analysed, also with varying separation distances in the streamwise and spanwise directions. The present experimental results are being used to test and guide the development of improved parameterizations of wind turbines in high-resolution numerical models, such as large-eddy simulations (LES).
Modeling of Radio Emission from Saturn's Rings Including Wakes
NASA Astrophysics Data System (ADS)
Molnar, L. A.; Dunn, D. E.; Cully, J. C.; Young, D. J.
We have extended the ``simrings" radiative transfer software package (Dunn, Molnar, and Fix 1999) to include idealized ring wakes. The package consists four principle, modular components: ``simprob," which computes Mie scattering functions for individual particles specified by size and composition; ``simrings," which uses a Monte Carlo simulation to compute the complete scattering function and thermal emission of a ring slab specified by particle size distribution and density (including the possibility of wake density enhancements); ``simplot," which uses these functions along with geometric information and a full description of the planet brightness to compute the ring brightness as a function of azimuth as viewed from Earth; and "simcoord", which combines this information for a series of rings to make a final model of the radio emission as viewed on the sky. We compare sample results from this package with those of a simple, analytic model that ignores multiple scattering. This allows us to show qualitatively under what conditions one might observe east-west asymmetry in the rings caused by multiple scattering off wakes (as we earlier suggested may be the case: Dunn, Molnar, and Fix 1996), and to quantitatively compare models with data maps. The principle advantage of our idealized wakes is the relative ease with which we can consider a wide range of parameter space. The utility of this depends on these wakes having net scattering properties resembling those of more realistic wakes. We compare our idealized wakes with the gravitational simulations of Daisaka and Ida (1999) and find that this is the case for directly transmitted flux as a function of azimuth and inclination. As complete scattering properties of realistic simulations become available, we can use them as alternative inputs to ``simplot," producing model radio maps for them. Finally, we compare preliminary runs of the ``simrings" package with radio data spanning a range of observing wavelengths and ring inclinations to demonstrate the sensitivity to various physical parameters of the rings. This work was funded by a grant from Research Corporation.
Feedback Control of the Wake of a Three-Dimensional Blunt Bluff Body
NASA Astrophysics Data System (ADS)
Flinois, Thibault; Morgans, Aimee
When cars or trucks drive on motorways, more than two thirds of their fuel consumption is due to aerodynamic drag, a significant part of which is caused by the large scale separation that takes place near their trailing edge. We tackle this problem using Large Eddy Simulations and use feedback control of synthetic jets to reduce the losses associated with large-scale structures in the wake. The geometry is a long surface mounted block, whose leading edge is not modelled for computational efficiency and the structure of the unforced flow field around this body is similar to the flow over a surface mounted block or hump. Considering this flow field as a control system, the base pressure force was used as the system output and the input is a slot jet actuator located near the trailing edge. Using open-loop forcing, a form drag reduction of about 7.5% was obtained. Open-loop system identification also allowed a transfer function that models the system's response to actuation to be found. Finally, a set of feedback controllers were applied to the plant and their performance was analysed. These controllers successfully reduce the fluctuations in the near wake, with only a small control effort. However, more significant mean drag reductions are expected at higher Reynolds numbers. When cars or trucks drive on motorways, more than two thirds of their fuel consumption is due to aerodynamic drag, a significant part of which is caused by the large scale separation that takes place near their trailing edge. We tackle this problem using Large Eddy Simulations and use feedback control of synthetic jets to reduce the losses associated with large-scale structures in the wake. The geometry is a long surface mounted block, whose leading edge is not modelled for computational efficiency and the structure of the unforced flow field around this body is similar to the flow over a surface mounted block or hump. Considering this flow field as a control system, the base pressure force was used as the system output and the input is a slot jet actuator located near the trailing edge. Using open-loop forcing, a form drag reduction of about 7.5% was obtained. Open-loop system identification also allowed a transfer function that models the system's response to actuation to be found. Finally, a set of feedback controllers were applied to the plant and their performance was analysed. These controllers successfully reduce the fluctuations in the near wake, with only a small control effort. However, more significant mean drag reductions are expected at higher Reynolds numbers. PhD Student, Imperial College London.
Wake Studies at the Flowind Vertical Axis Wind Turbine Generator Site.
Baker, Robert W.; Walker, Stel Nathan; Katen, Paul C.
In a continuing effort to study and characterize various types and sizes of wind turbine generator wakes a test program was conducted at the FloWind 170 kW vertical axis wind turbine (VAWT) near Ellensburg, Washington. Oregon State University (OSU) scientists measured the wake behind the 90 ft. tall Darrieus VAWT using fixed place and portable kite anemometers. Downwind velocity deficits were measured from 3-9 diameters along the wake centerline at rotor midpoint (55 ft.) and perpendicular to the wake. Wake turbulence characteristics were also measured. The measured velocity deficits were compared to wake model calculations.
Tracking and Characterization of Aircraft Wakes Using Acoustic and Lidar Measurements
NASA Technical Reports Server (NTRS)
Booth, Earl R., Jr.; Humphreys, William M., Jr.
Data from the 2003 Denver International Airport Wake Acoustics Test are further examined to discern spectral content of aircraft wake signatures, and to compare three dimensional wake tracking from acoustic data to wake tracking data obtained through use of continuous wave and pulsed lidar. Wake tracking data derived from acoustic array data agree well with both continuous wave and pulsed lidar in the horizontal plane, but less well with pulsed lidar in the vertical direction. Results from this study show that the spectral distribution of acoustic energy in a wake signature varies greatly with aircraft type.
Y. T. John Kwong
Largely due to the low diffusivity of dissolved oxygen in water, reactive tailings are often rendered harmless upon disposal underwater. However, both field observations and results of simulated weathering studies in the laboratory have shown that as long as a water cover remains oxygenated, sulfides exposed at the tailings\\/water interface are susceptible to oxidation. The two primary factors that determine
Progress Towards the Investigation of Technical Issues Relevant to the Design of an Aircraft Wake Vortex Advisory System (WakeVAS)
NASA Technical Reports Server (NTRS)
Rutishauser, David K.
Wake vortex separations applied to aircraft during instrument operations have been shown to potentially introduce inefficiencies in air traffic operations during certain weather conditions conducive to short duration wake hazards between pairs of landing aircraft. NASA Langley Research Center (LaRC) demonstrated an integration of technologies that provided real-time observations and predictions of aircraft wake behavior, from which reduced wake spacing from the current criteria was derived. In order to take this proof of concept to an operational prototype system, NASA has been working in cooperation with the FAA and other government and industry members to design operational concepts for a Wake Vortex Advisory System (WakeVAS). In addition to concept development, open research issues are being addressed and activities to quantify system requirements and specifications are currently underway. This paper describes the technological issues relevant to WakeVAS development and current NASA efforts to address these issues.
Exploration of Terminal Procedures Enabled by NASA Wake VAS Technologies
NASA Technical Reports Server (NTRS)
Lunsford, Clark R.; Smith, Arthur P., III; Cooper, Wayne W., Jr.; Mundra, Anand D.; Gross, Amy E.; Audenaerd, Laurence F.; Killian, Bruce E.
The National Aeronautics and Space Administration (NASA) tasked The MITRE Corporation's Center for Advanced Aviation System Development (CAASD) to investigate potential air traffic control (ATC) procedures that could benefit from technology used or developed in NASA's Wake Vortex Advisory System (WakeVAS). The task also required developing an estimate of the potential benefits of the candidate procedures. The main thrust of the investigation was to evaluate opportunities for improved capacity and efficiency in airport arrival and departure operations. Other procedures that would provide safety enhancements were also considered. The purpose of this investigation was to provide input to the WakeVAS program office regarding the most promising areas of development for the program. A two-fold perspective was desired: First, identification of benefits from possible procedures enabled by both incremental components and the mature state of WakeVAS technology; second identification of procedures that could be expected to evolve from the current Federal Aviation Administration (FAA) procedures. The evolution of procedures should provide meaningful increments of benefit and a low risk implementation of the WakeVAS technologies.
Analog Processing Assembly for the Wake Vortex Lidar Experiment
NASA Technical Reports Server (NTRS)
Stowe, Edwood G.
The Federal Aviation Administration (FAA) and NASA have initiated a joint study in the development of reliable means of tracking, detecting, measuring, and predicting trailing wake-vortices of commercial aircraft. Being sought is an accurate model of the wake-vortex hazard, sufficient to increase airport capacity by reducing minimum safe spacings between planes. Several means of measurement are being evaluated for application to wake-vortex detection and tracking, including Doppler RADAR (Radio Detection and Ranging) systems, 2-micron Doppler LIDAR (Light Detection And Ranging) systems, and SODAR (Sound Detection And Ranging) systems. Of specific interest there is the lidar system, which has demonstrated numerous valuable capabilities as a vortex sensor Aerosols entrained in the vortex flow make the wake velocity signature visible to the lidar, (the observable lidar signal is essentially a measurement of the line-of-sight velocity of the aerosols). Measurement of the occurrence of a wake vortex requires effective reception and monitoring of the beat signal which results from the frequency-offset between the transmitted pulse and the backscattered radiation. This paper discusses the mounting, analysis, troubleshooting, and possible use of an analog processing assembly designed for such an application.
The wake of a single vertical axis wind turbine
NASA Astrophysics Data System (ADS)
Barsky, Danielle A.; Leftwich, Megan C.
The purpose of this study is to measure the wake of a Windspire vertical axis wind turbine (VAWT). In recent years, research on VAWTs has increased due to various potential advantages over the more common horizontal axis wind turbines (HAWTs). Unlike very large HAWTs, moderately sized-and virtually silent-VAWTs can be placed in urban and suburban regions where land space is limited. To date, many VAWT studies have assumed that the turbine has the same aerodynamic structure as a spinning cylinder despite a significant increase in geometric complexity. This experiment attempts to understand the fundamental wake structure of a single VAWT (and compare it to the wake structure of a spinning cylinder). In this experiment, a scaled-down VAWT is placed inside a wind tunnel under a controlled laboratory setting. A motor rotates the scale model at a constant angular speed. Stereo particle image velocimetry (PIV) is used to visualize the wake of the turbine and image processing techniques are used to quantify the velocity and vorticity of the wake.
Improvement of a near wake model for trailing vorticity
NASA Astrophysics Data System (ADS)
Pirrung, G. R.; Hansen, M. H.; Madsen, H. A.
A near wake model, originally proposed by Beddoes, is further developed. The purpose of the model is to account for the radially dependent time constants of the fast aerodynamic response and to provide a tip loss correction. It is based on lifting line theory and models the downwash due to roughly the first 90 degrees of rotation. This restriction of the model to the near wake allows for using a computationally efficient indicial function algorithm. The aim of this study is to improve the accuracy of the downwash close to the root and tip of the blade and to decrease the sensitivity of the model to temporal discretization, both regarding numerical stability and quality of the results. The modified near wake model is coupled to an aerodynamics model, which consists of a blade element momentum model with dynamic inflow for the far wake and a 2D shed vorticity model that simulates the unsteady buildup of both lift and circulation in the attached flow region. The near wake model is validated against the test case of a finite wing with constant elliptical bound circulation. An unsteady simulation of the NREL 5 MW rotor shows the functionality of the coupled model.
Skin layer recovery of free-surface wakes: Relationship to surface renewal and dependence on heat flux and background turbulence
NASA Astrophysics Data System (ADS)
Zappa, C. J.; Jessup, A. T.; Yeh, Harry
The thermal signatures of free-surface wakes observed in the open ocean show that the recovery of the cool skin layer is related to the degree of surface mixing and to ambient environmental conditions. Wakes produced by two surface-piercing cables of O(10-2 m) in diameter are analyzed using infrared imagery. Under low-wind-speed conditions when the swell and surface current were aligned, the wakes exhibited distinctive patchlike features of O(1 m) in diameter that were generated by the passage of individual waves. The time t* required by the skin layer to recover from these disturbances is compared to the surface-renewal timescale ? used in heat and gas flux models. At low wind speeds, t* is comparable to ?, but at moderate wind speeds the agreement is poor. The spatial and temporal variations in the skin temperature of these wakes are related to a wave Reynolds number used to characterize the strength of the disturbance due to the waves. The recovery process is characterized in terms of the restoring internal energy flux Jr which is proportional to both the initial thickness and the thermal recovery rate of the skin layer and was found to be directly related to the strength of the surface disruption. Comparison of the wake results with laboratory and other field measurements of breaking waves implies that Jr is also a strong function of the net heat flux and background turbulence, which relate directly to the existing environmental conditions such as wind stress and sea state. Our results demonstrate that Jr may vary by several orders of magnitude, depending on the environmental conditions.
Development of a Wake Vortex Spacing System for Airport Capacity Enhancement and Delay Reduction
NASA Technical Reports Server (NTRS)
Hinton, David A.; OConnor, Cornelius J.
The Terminal Area Productivity project has developed the technologies required (weather measurement, wake prediction, and wake measurement) to determine the aircraft spacing needed to prevent wake vortex encounters in various weather conditions. The system performs weather measurements, predicts bounds on wake vortex behavior in those conditions, derives safe wake spacing criteria, and validates the wake predictions with wake vortex measurements. System performance to date indicates that the potential runway arrival rate increase with Aircraft VOrtex Spacing System (AVOSS), considering common path effects and ATC delivery variance, is 5% to 12% depending on the ratio of large and heavy aircraft. The concept demonstration system, using early generation algorithms and minimal optimization, is performing the wake predictions with adequate robustness such that only 4 hard exceedances have been observed in 1235 wake validation cases. This performance demonstrates the feasibility of predicting wake behavior bounds with multiple uncertainties present, including the unknown aircraft weight and speed, weather persistence between the wake prediction and the observations, and the location of the weather sensors several kilometers from the approach location. A concept for the use of the AVOSS system for parallel runway operations has been suggested, and an initial study at the JFK International Airport suggests that a simplified AVOSS system can be successfully operated using only a single lidar as both the weather sensor and the wake validation instrument. Such a selfcontained AVOSS would be suitable for wake separation close to the airport, as is required for parallel approach concepts such as SOIA.
Laboratory Evidence That Line-Tied Toroidal Magnetic Fields Can Suppress Loss-of-Equilibrium Flux Rope Eruptions in the Solar Corona
NASA Astrophysics Data System (ADS)
Myers, C. E.; Yamada, M.; Belova, E.; Ji, H.; Yoo, J.; Fox, W. R., II; Jara-Almonte, J.
Loss-of-equilibrium mechanisms such as the ideal torus instability [Kliem & T�r�k, Phys. Rev. Lett. 96, 255002 (2006)] are predicted to drive arched flux ropes in the solar corona to erupt. In recent line-tied flux rope experiments conducted in the Magnetic Reconnection Experiment (MRX), however, we find that quasi-statically driven flux ropes remain confined well beyond the predicted torus instability threshold. In order to understand this behavior, in situ measurements from a 300 channel 2D magnetic probe array are used to comprehensively analyze the force balance between the external (potential) and internal (plasma-generated) magnetic fields. We find that forces due to the line-tied toroidal magnetic field, which are not included in the basic torus instability theory, can play a major role in preventing eruptions. The dependence of these toroidal magnetic forces on various potential field and flux rope parameters will be discussed. This research is supported by DoE Contract Number DE-AC02-09CH11466 and by the NSF/DoE Center for Magnetic Self-Organization (CMSO).
Large Eddy Simulation of Aircraft Wake Vortices in a Homogeneous Atmospheric Turbulence: Vortex Decay and Descent
NASA Technical Reports Server (NTRS)
Han, Jongil; Lin, Yuh-Lang; Arya, S. Pal; Proctor, Fred H.
The effects of ambient turbulence on decay and descent of aircraft wake vortices are studied using a validated, three-dimensional: large-eddy simulation model. Numerical simulations are performed in order to isolate the effect of ambient turbulence on the wake vortex decay rate within a neutrally-stratified atmosphere. Simulations are conducted for a range of turbulence intensities, by injecting wake vortex pairs into an approximately homogeneous and isotropic turbulence field. The decay rate of the vortex circulation increases clearly with increasing ambient turbulence level, which is consistent with field observations. Based on the results from the numerical simulations, simple decay models are proposed as functions of dimensionless ambient turbulence intensity (eta) and dimensionless time (T) for the circulation averaged over a range of radial distances. With good agreement with the numerical results, a Gaussian type of vortex decay model is proposed for weak turbulence: while an exponential type of Tortex decay model can be applied for strong turbulence. A relationship for the vortex descent based on above vortex decay model is also proposed. Although the proposed models are based on simulations assuming neutral stratification, the model predictions are compared to Lidar vortex measurements observed during stable, neutral, and unstable atmospheric conditions. In the neutral and unstable atmosphere, the model predictions appear to be in reasonable agreement with the observational data, while in the stably-stratified atmosphere, they largely underestimate the observed circulation decay with consistent overestimation of the observed vortex descent. The underestimation of vortex decay during stably-stratified conditions suggests that stratification has an important influence on vortex decay when ambient levels of turbulence are weak.