Certain aspects of the present invention are directed to a liquid valve assembly that can be disposed in a wellbore through a fluid-producing formation. The liquid valve assembly can include a housing and a liquid valve. The housing can define an inner chamber and an opening adapted to allow fluid to flow between the inner chamber and a passageway. The liquid valve can be disposed in the inner chamber. The liquid valve can include a yield stress fluid. The yield stress fluid can prevent fluid from flowing between the inner chamber and the passageway.

Wells systems for extracting fluids such as an oil or gas from a subterranean formation can include devices for controlling the rate of fluid flow from a well. Such devices can include valves, such as a flapper valve, for selectively allowing and preventing the flow of fluid. However, debris in the tubing of a well system can obstruct a valve, thereby preventing proper operation of the valve.
It is desirable for a valve to continue regulating the flow of fluid despite the presence of debris in a well system.


Displaying calendars may be provided. In response to a first input initiated by a user, a first calendar may be displayed comprising a user's calendar. Next, a second calendar may be overlaid over the first calendar. The second calendar may be displayed transparently with respect to the first calendar. Then, a third calendar may be displayed beside the first calendar. The second or third calendar may each comprise an event calendar, a project calendar, or a calendar of another user not associated with the first calendar. In addition, a second user initiated input may be received selecting an entry on the second calendar. In response to the received second user initiated input, the second calendar may be redisplayed not transparently with respect to the first calendar. Moreover, in response to the received second user initiated input, the first calendar may be redisplayed transparently with respect to the redisplayed second calendar.

Many people use a calendar application program to keep their personal or business calendar. In some situations, a calendar application user may wish to compare, for example, the user's personal calendar to another calendar. For example, the user may wish to compare the user's personal calendar to a sports calendar showing all the scheduled games associated with a particular sports team. In order to make this comparison, the user may print the sports calendar and then compare the printed sports calendar to the user's own personal calendar. The conventional comparison strategy, however, does not provide a user friendly calendar comparison nor does it provide a convenient way to add events from one calendar to another calendar.


A chemical or corrosive environment sensing system, comprising a giant magnetoresistive effect device having at least one environmentally exposed film, and a device, for sensing changes in the GMR effect device resulting from environmental exposure of the at least one environmentally exposed film. The film may be reversibly or irreversibly altered by the exposure, and is preferably nano-textured to alter a reaction rate and surface area. The sensor may be enzyme linked, that is, respond to an enzyme reaction product rather than the substrate directly. The GMR property altered and/or sensed may be, for example, a lower or upper switching field, an electrical resistance, and the GMR value. The device may be used as a sensor or as part of a control system.

Corrosion causes substantial damage to devices, vehicles and infrastructure. In many cases, protective coatings are available to prevent corrosive environments from oxidizing exposed metals. However, in other cases, such coatings are unavailable or difficult to apply. This is particularly true with portable consumer electronic devices, such as cell phones, which have significant circuitry exposed to the environment, with modest voltages imposed over short distances. If the circuits in these device become immersed, especially in salt water, but even in tap water or rain, corrosion can occur which degrades performance or makes the device effectively unusable. In some cases, the faults that result are intermittent or difficult to diagnose.
Metals and alloys are commonly used as construction materials, in building, bridge, ship, oil, automotive, electric and microelectronic industries. Among others, magnetic metals, such as iron, nickel, cobalt and their alloys, are extensively used in transformers, permanent magnets and magnetic recording media. Corrosion of these media is an important problem affecting daily lives with economical consequences. There are needs for continuous improvement in the methods of corrosive detection and corrosion monitoring.
Corrosion in the atmosphere depends on air moisture and airborne impurities. To reduce the corrosion rate it is critical that corrosive species and dirt are not allowed to accumulate on the surface and thus create a wet poultice. Otherwise, this creates a situation similar to a crevice with possibility for decreased pH and high concentration of corrosive species like chlorides in a marine atmosphere, where corrosion can proceed uninterrupted. The atmosphere environment normally is classified into three categories; rural, industrial and marine. The corrosivity can vary a lot within each class depending on climate, level of pollution, distance to the sea, etc. In addition some atmospheres may be combinations of marine and industrial. In the oil and gas industry corrosion processes involve mainly water and H2S. The corrosivity of fresh waters depends on the hardness and pH of the water, chloride and heavy metal concentration in addition to temperature, flow rate and O2 concentration. In sea waters the main factor is the high content of chlorides. In aqueous environments microbiological organisms play an important role in corrosion. Soil corrosion, which is ascribed to low pH, stray currents, reactive chemicals, low resistivity and bacterial action, may be considered to encompass all corrosion taking place on buried structures.
Traditionally, corrosion in materials as in oil pipeline, offshore structures and vessels is monitored by various techniques such as ultrasonic thickness gauges, Eddy current imaging, X-ray tomography, and electrochemical spectroscopy techniques, designed to analyze interior microstructure and subsurface features. These techniques are less sensitive and some are quite expensive and inconvenient due to sophisticated equipment involved. There are also techniques based on in situ monitoring such as piezoelectric oscillator to measure changes in materials properties. Since the typical sensor sizes are about several micrometers, by distributing these sensors throughout a corroding surface one will be able to examine, with micrometer resolution, if the corrosion occurs locally (at micron scales) or in an uniform fashion.
Out of all the problems associated with corrosion, three aspects of corrosion detection in structures are important: (1) first, one should be able to sensitively detect the extent of corrosion taking place in a given structure at a given location and time, (2) second, one should be able to assess the total damage that has occurred and (3) third, one should assess remnant useful performance left in the structural component of the structure of interest.
The relative constancy of normal corrosion rates of different materials shows that most of the parameters for time of wetness and enhanced corrosion conditions are well defined if the composition of the corroding liquid and the involved metal is fixed. To attain more accurate data of atmospheric corrosion conditions parameters such as relativity humidity, pH and composition of condensing media and temperature need to be monitored. The development of atmospheric corrosion monitors was started a few decades ago in US and in Sweden and are usually called "time of wetness sensors" (TOWS)[1]. These designs are based on galvanic current measurement and they simply determine the periods of time during exposure of the sensors when condensation of moisture occurs on the sensors (>87% RH or relative humidity level) and leads to passage of current in a circuit, the condensate being used as a part of the circuit. In most recently manufactured corrosion sensing units, using bi-metallic thin film micro-sensors performs the monitoring of corrosion in an aggressive environment. The sensor output is essentially a polarized corrosion current of the active component in the couple (working electrode) and does only a qualitative measurement. Now such type of sensors is being employed as atmospheric corrosion sensors (ACS). It is also possible to do quantitative potentiometic measurement and corrosion rate determination by electrochemical linear polarization technique as a function of time and environmental conditions. Generally one potential close to the corrosion potential of the metal is chosen by the others and from the current passing through at this offset potential the corrosion current is determined by employing the Stern-Geary equation[1]. However, in all these methods no consideration was given to the corrosion product buildup and the corrosion potential variation as a function of time and the corrosion process itself. As a result the inferences obtained and the data generated could not be construed as very accurate.
ASTM G 31 7 is an immersion test procedure that typically requires extended exposure periods, up to years, to evaluate the resistance of materials, which are employed in the implant device industry, to corrosion. As such, accelerating the testing by inducing changes on the material and monitoring the results has been an industry-accepted method. The development of accelerated electrochemical tests to study corrosion began in earnest during the late 1960's and into the 1980's in the CPI. The original test standard, ASTM G 5, 8 was expanded from a stepped potentiostatic test to a potentiodynamic test as electronics developed, and subsequently to a cyclic experiment to examine susceptibility to localized pitting and crevice corrosion [ASTM G 61 9]. Galvanic studies between mixed metals in contact with each other were evaluated using the established ASTM G 71 10. See, Richard A. Corbett, "Laboratory Corrosion Testing of Medical Implants", Corrosion Testing Laboratories, www.corrosionlab.com/papers/medical-implant/medical-implant-testing.htm.
Corrosion sensors are typically electrochemical, and rely on changes in conductivity, resistivity, or redox potential to determine or predict corrosion. See, G. D. Davis, C. M. Dacres, and M. B. Shook, "Development of an electrochemistry-based corrosion sensor to monitor corrosion of boiler tubes, pipes, and painted structures", DACCO SCI, INC. (www.daccosci.com/SPIE98.htm), expressly incorporated herein by reference.
Corrosion monitoring is the practice of measuring the corrosivity of process stream conditions by the use of "probes" which are inserted into the process stream or environment to be measured and which are continuously exposed to the conditions. Corrosion monitoring "probes" can be mechanical, electrical, or electrochemical devices. These "probes" serve as a proxy for other elements of the system which are presumed to corrode in a corresponding manner to the probes. In some cases, the probe may be an actual element of interest, and indeed, all potentially corroding elements may be sensors. See, www.corrosionsource.com/technicallibrary/condoctors/Modules/MonitorBasics/Types.htm. The nature of the sensors depends on the various individual techniques used for monitoring but often a corrosion sensor can be viewed as an instrumented coupon. In older systems, electronic sensor leads were usually employed for these purposes and to relay the sensor signals to a signal-processing unit. Advances in microelectronics are facilitating sensor signal conditioning and processing by microchips, which can essentially be considered to be integral to the sensor units. Some corrosion measurement techniques can be used on-line, constantly exposed to the process stream, while others provide off-line measurement, such as that determined in a laboratory analysis. Some techniques give a direct measure of metal loss or corrosion rate, while others are used to infer that a corrosive environment may exist. Real-time corrosion measurements refer to highly sensitive measurements, with a signal response taking place essentially instantaneously as the corrosion occurs. Numerous real-time corrosion monitoring programs in diverse branches of industry have revealed that the severity of corrosion damage is rarely uniform with time. Complementary data from other relevant sources, such as process parameter logging and inspection reports can be acquired together with the data from corrosion sensors, for use as input to the management information system.
Known techniques include:
A. Direct techniques
1) Corrosion Coupons (intrusive) (samples are monitored for weight loss due to corrosive loss of material).
2) Electrical Resistance (ER) (intrusive) (measures the change in electrical resistance of a metallic element immersed in a product media relative to a reference element sealed within the probe body).
3) Inductive Resistance Probes (intrusive) (Mass changes in a sensor element are detected by measuring changes in the inductive resistance of a coil, located inside the element).
4) Linear Polarization Resistance (LPR) (intrusive) (a small voltage, or polarization potential, is applied to an electrode in solution and the current needed to maintain a specific voltage shift (typically 10 mV) is directly related to the corrosion on the surface of the electrode in the solution. By measuring the current, a corrosion rate can be derived.)5) Zero Resistance Asymmetry (ZRA) (intrusive) (In ZRA, also known as galvanic monitoring, two electrodes of dissimilar metals are exposed to the process fluid. When immersed in solution, a natural voltage (potential) difference exits between the electrodes. The current generated due to this potential difference relates to the rate of corrosion which is occurring on the more active of the electrode couple.)6) Electrochemical Impedance Spectroscopy (EIS) (intrusive) (an alternating potential perturbation is applied to one sensor element in a three-element probe, with a resultant current response, to measure the impedance.)7) Harmonic Analysis (intrusive) (Higher order harmonic analysis of EIS method)8) Electrochemical Noise (EN) (intrusive) (EN corrosion monitoring tracks extremely small current and voltage fluctuations among three electrodes, made of material as similar as possible to the waste tank material, placed in the waste solution. Current is measured between two electrically coupled electrodes (a working electrode and a counter electrode), while the third electrode is connected between the working electrode and a pseudo-reference electrode to measure the voltage. The magnitude and polarity of the signals, as well as the relationship of the timed signal traces to each other, provide indicators of type and significance of the corrosion processes occurring in the tank. Particular types of corrosion have unique and potential "signatures" that indicate when pitting or stress corrosion cracking is occurring.)9) Potentiodynamic Polarization (intrusive) (measurement of current through a sample with a change in applied voltage potential. An initial static potential is measured, and a scan made from an initial potential of 100 mV below the one-hour potential, in the positive (active to noble) direction at a rate of e.g., 0.16 mV per second, and then reversed when the current has reached two decades greater than that of the breakdown potential [Vb] (defined as a rapid increase of current per increment of applied potential). The reverse scan is stopped when the current becomes less than the current in the forward scan (defined as the protection potential, Vp) or the potential reaches the initial potential. The data is plotted on an x-y semi logarithmic diagram with the current density on the x-axis [logarithmic] in mA/cm2 and the potential versus a SCE on the linear y-axis. Appropriate references in their final form and finish are used as controls.)10) Thin Layer Activation (TLA) and Gamma Radiography (intrusive or non-intrusive) (In this technique developed from the field of nuclear science, a small section of material is exposed to a high energy beam of charged particles, to produce a radioactive surface layer. For example, a proton beam may be used to produce the radioactive isotope Co-56 within a steel surface. This isotope decays to Fe-56, with the emission of gamma radiation. The concentration of radioactive species is sufficiently low, that metallurgical properties of the monitored component are essentially unchanged. The radioactive effects utilized are at very low levels and should not be compared to those of conventional radiography. The change in gamma radiation emitted from the surface layer is measured with a separate detector to study the rate of material removed from the surface. The radioactive surfaces can be produced directly on components (non-intrusive) or on separate sensors).11) Electrical Field Signature Method (EFSM) (non-intrusive) (The technique measures corrosion damage over several meters of an actual structure, clearly distinguishing it from other smaller sensor systems. An induced current is fed into the monitored section of interest and the resulting voltage distribution is measured to detect corrosion damage. An array of pins is attached strategically over the structure for measuring purposes. Increased pin spacing implies lower resolution for localized corrosion. Typical applications involve pin attachment to the external surface of a pipeline, to monitor corrosion damage to the inside of the pipe walls.)12) Acoustic Emission (AE) (non-intrusive) (measurement of acoustic sound waves emitted during the growth of microscopic defects, such as stress corrosion cracks. The sensors act as microphones, positioned on structures, which detect sound waves generated from mechanical stresses generated during pressure or temperature changes.)B. Indirect techniques1) Corrosion Potential (non-intrusive) (The corrosion potential of the element to be monitored is measured relative to a reference electrode, which is characterized by a stable half-cell potential.)2) Hydrogen Monitoring (non-intrusive) (The generation of atomic hydrogen, as part of the cathodic half-cell reaction in acidic environments. Hydrogen monitoring probes are based on either of the following three principles: pressure increase, electrochemical current resulting from the oxidation of hydrogen under an applied potential, and current flow in an external circuit, based on a fuel cell principle.)3) Chemical Analyses (e.g., pH, conductivity, dissolved oxygen, metallic and other ion concentrations, water alkalinity, concentration of suspended solids, inhibitor concentrations and scaling indices)4) Corrosion sensors are typically electrochemical, and rely on changes in conductivity, resistivity, or redox potential to determine or predict corrosion. See, G. D. Davis, C. M. Dacres, and M. B. Shook, "Development of an electrochemistry-based corrosion sensor to monitor corrosion of boiler tubes, pipes, and painted structures", DACCO SCI, INC. (www.daccosci.com/SPIE98.htm), expressly incorporated herein by reference.5) Certain "magnetic" corrosion sensors are known, for example a mechanical breakage sensor whose output is magnetically coupled through a vessel wall. See, Dennis G. Douglas, Christopher M. Smith, Phillip C. Ohl, Carey M. Haas (Vista Engineering Technologies, LLC), "CORROSION MONITORING OF PLUTONIUM OXIDE AND SNF", WM'03—Topic No. 2.4, Technical Progress . . . Long Term Storage of SNF, www.vistaengr.com/library/CorrosionMonitoringofPlutoniumOxideandSNF.pdf.6) In addition, a number of sensors detect a current or magnetic field induced by a current with a superconducting quantum interference device (SQUID). See, e.g., Hitoshi Yashiro, Masahito Yoshizawa, Naoaki Kumagai, and Johann H. Hinken, "Effect of Spatial Distribution of Electronic and Ionic Currents on the Magnetic Field Induced by Galvanic Corrosion", J. Electrochem. Soc., Volume 149, Issue 3, pp. B65-B69 (March 2002); Eimutis Juzeliunas, Meilute Samuleviciene, Aloyzas Sudavicius, and Johann H. Hinken, "A SQUID Study of Magnetic Fields Resulting from In Situ Corrosion Reactions", Electrochem. Solid-State Lett., Volume 3, Issue 1, pp. 24-27 (January 2000); Weiss, Rick, "Taking corrosion's magnetic pulse. (research on monitoring magnetic fields associated with corrosion)", Science News; Feb. 27, 1988.
Recent progresses in magnetic field sensing, and magnetic materials research lend new technologies in monitoring corrosion. One idea consists of detecting changes in magnetic properties due to corrosion of specially designed magnetic materials. Because the corrosion products of magnetic materials are generally nonmagnetic or with distinctly different measuring the changes in these properties by corrosion can be a sensitive tool.
The Giant Magneto Resistance (GMR) effect was discovered in 1988 and it is the phenomenon where the resistance of certain materials drops dramatically as a magnetic field is applied. It is described as Giant since the effect is much larger than in regular metals. It has generated strong interests in research community, as there are perspectives both in exploring new physics and technological applications as in magnetic recording and sensors. The effect is seen in spin-valve structures, where two magnetic layers are closely separated by a thin non-magnetic spacer of a few nanometer thickness. It is analogous to a light polarization experiment, where aligned polarizers allow light to pass through, but crossed polarizers do not. A magnetic layer allows electrons in only one spin state to pass through easily. If the second magnetic layer is aligned then that spin channel can easily pass through the structure, and the resistance is low. If the second magnetic layer is misaligned then neither spin channel can get through the structure easily and the electrical resistance is high. The GMR effect effectively measures the difference in the angle between the two magnetic orientations in the magnetic layers, with small angles (parallel) giving low resistance, and large angles (antiparallel) giving higher resistance. This angle depends on the applied magnetic field, and thus the change in the magnetoresistance can be used to measure magnetic fields. In GMR spin-valve materials ΔR/R values of more than 65% at the ambient temperature have been reported. Since the sensitivity of a sensor is proportional to ΔR/R, the advantages of these GMR materials for field sensing is obvious.
U.S. Pat. No. 6,599,401, Wang, et al. (having a common inventor with the present application), expressly incorporated herein by reference, provides an in-plane anisotropic tri-layered magnetic sandwich structure which demonstrates a large magnetoresistance effect. Fe/Co/Cu/Co magnetoresistive structures deposited on Si (100) substrates were found to demonstrate uniaxial magnetic anisotropy. Samples magnetized along an easy anisotropy axis showed extremely sharp magnetization, and corresponding magnetoresistance, switching at low fields and maximum giant magnetoresistance of 9.5% at 5K (5.5% at room temperature) for the samples with 5 nm of Fe, 5 nm of Co, 2.5 nm of Cu and 2 nm of Co.
A GMR effect sensor is proposed in Wang et al., U.S. Pat. No. 6,462,541, expressly incorporated herein by reference. Wang et al., suggest a uniform sense condition magnetic field sensor using differential magnetoresistance. A ferromagnetic thin-film based sensing arrangement having a plurality of magnetic field sensors on a substrate, each having an intermediate layer of a nonmagnetic material with two major surfaces on opposite sides thereof, with one of a pair of permeable films each formed of a magnetoresistive, anisotropic ferromagnetic material correspondingly positioned thereon, with first and second oriented sensors therein respectively having a selected and a reversing magnetization orientation structure provided with one of the pair of permeable films thereof, for orienting its magnetization in a selected direction absent an externally applied magnetic field in at least partly opposing directions. The magnetizations of those films rotates over a smaller angle in a selected externally applied magnetic field present thereat than does the magnetization orientation of the other permeable film in the pair. The first and second oriented sensors are electrically connected between a pair of terminating regions suited for electrical connection across a source of electrical energization. Alternatively, these magnetizations of the films can be oriented in the same direction but with the other film member of the pair provided adjacent a coupling layer that antiferromagnetically couples thereto a further ferromagnetic layer on an opposite side thereof of a lesser thickness for one sensor, and a greater thickness for the other. The intermediate layer material can be either a conductive material or a dielectric material. Such a sensing arrangement can be formed by providing a succession of material layers on a substrate having therein the intermediate layer and the pair of permeable films, with the one of the pair of permeable films being adjacent a succession of magnetization orientation layers having at least one coupling layer for antiferromagnetically coupling ferromagnetic layers on opposite sides thereof. Removal of some of the succession to provide an unequal number of coupling layers between locations for the two kinds of sensors, or unequal thicknesses of corresponding ferromagnetic layers corresponding to the coupling layer, is followed by providing a pinning layer at both kinds of locations. Removal of the succession at other locations results in providing the two kinds of sensors.
U.S. Pat. No. 6,600,637 (Wang et al.), expressly incorporated herein by reference, relates to a magnetoresistive sensor for a magnetic storage system having an edge barrier to prevent spin valve corrosion. During fabrication of a transducing head, Wang et al. report that the MR sensor is subjected to many processing steps. Current contacts and biasing layers are commonly deposited adjacent to the MR sensor after the MR sensor is shaped, but before the second half gap is deposited. The formation of the contacts and biasing layers, as well as the patterning of the MR sensor itself, subjects the MR sensor to a harsh environment that may result in corrosion of the MR sensor. This is particularly true of a multi-layered sensor such as a spin valve sensor.
Multi-layered sensors generally are formed of multiple materials, several of which very easily corrode. Since an MR sensor relies on the existence of each of its layers to operate properly, corrosion of any of its layers will result in the sensor having a reduced amplitude, a distorted signal output, decreased stability, and/or increased noise. They do not suggest that this corrosion may be intentionally exploited, nor that conditions other than those of manufacture may have an effect on the sensor.
Spin valves are a type of solid state magnetic field sensors. See, www.stoner.leeds.ac.uk/research/spinv.htm. A spin valve is, in general, a sample consisting essentially of a GMR trilayer. One layer is magnetically soft—meaning its magnetization is very sensitive to small fields. The other is made magnetically 'hard' by various schemes—meaning it is insensitive to fields of moderate strength. As the soft 'free' layer changes its magnetic state, due to applied fields, the resistance of the whole structure will vary. The central part of the sample consists of two magnetic layers (e.g., permalloy with a thin covering of Co), separated by a Cu spacer layer. One magnetic layer is pinned or exchange biased by an antiferromagnetic material, e.g., FeMn and IrMn.
Spin valves are dedicated GMR systems, in which the electrical resistance is high or low, depending on the direction rather than the strength of the magnetic field. Contrary to water valves they are not fully open or closed, the change in resistance is typical in the range of 5% to 10%. A spin valve is typically made of only two ferromagnetic layers spaced by a layer of nonmagnetic metal. Contrary to a GMR multilayer, the two ferromagnetic layers are magnetically coupled. As a further difference the magnetization of one of the ferromagnetic layers is spatially fixed ("pinned") by an antiferromagnetic bottom layer. Thus it is called the "pinned layer", the other is called the "free layer", because it should easily follow the external magnetic field.
The resistance in the plane of a ferromagnetic thin-film is isotropic with respect to the GMR effect rather than depending on the direction of a sensing current therethrough as for the anisotropic magnetoresistive effect. The GMR effect has a magnetization dependent component of resistance that varies as the cosine of the angle between magnetizations in the two ferromagnetic thin-films on either side of an intermediate layer. In the GMR effect, the electrical resistance through the "sandwich" or superlattice is lower if the magnetizations in the two separated ferromagnetic thin-films are parallel than it is if these magnetizations are antiparallel, i.e. directed in opposing directions. Further, the anisotropic magnetoresistive effect, also present in GMR structures in very thin-films, is considerably reduced from the bulk values therefor in thicker films due to surface scattering, whereas very thin-films are a fundamental requirement to obtain a significant GMR effect. The GMR effect can be increased by adding further alternate intermediate and ferromagnetic thin-film layers to extend the "sandwich" or superlattice structure. The GMR effect is sometimes called the "spin valve effect" in view of the explanation that a larger fraction of conduction electrons are allowed to move more freely from one ferromagnetic thin-film layer to another if the magnetizations in these layers are parallel than if they are antiparallel with the result that the magnetization states of the layers act as sort of a valve.
In magnetic multilayers, these magnetization configurations often come about because of magnetic exchange coupling between the ferromagnetic thin-films separated by the intermediate layers, these intermediate layers typically formed from a nonferromagnetic transition metal. The effect of the exchange coupling between the ferromagnetic thin-film layers is determined to a substantial degree by a function of the thickness of the intermediate layer, which oscillates as a function of the separation thickness between ferromagnetic coupling and antiferromagnetic coupling. In spin valves, such exchange coupling is not as obvious, although Wang reported exchange coupling does affect the soft magnetic layer switching with applied magnetic field in pseudo spin valves.
The ferromagnetic thin-film layers may be formed with alternating high and low coercivity materials so that the magnetization of the low coercivity material layers can be reversed without reversing the magnetizations of the others. An alternative arrangement is to provide "soft" ferromagnetic thin-films and couple antiferromagnetically every other one of them with an adjacent magnetically hard layer (forming a anti-ferromagnetic thin-film double layer) so that the anti-ferromagnetic double layer will be relatively unaffected by externally applied magnetic fields even though the magnetizations of the other ferromagnetic thin-film layers will be subject to being controlled by such an external field. A multilayer structure may be provided that is etched into strips such that demagnetizing effects and currents can be used to orient the magnetizations antiparallel, and so that externally applied magnetic fields can orient the magnetizations parallel. Thus, parallel and antiparallel magnetizations can be established in the ferromagnetic thin-films of the structure as desired in a particular use. Such a structure must be fabricated so that any ferromagnetic or antiferromagnetic coupling between separated ferromagnetic films is not too strong so as to prevent such establishments of film magnetizations using practical interconnection arrangements.
A magnetic field sensor suited for fabrication with dimensions of a few microns or less can be fabricated that provides a suitable response to the presence of very small external magnetic fields and low power dissipation by substituting an electrical insulator for a conductor in the nonmagnetic layer. This sensor can be fabricated using ferromagnetic thin-film materials of similar or different kinds in each of the outer magnetic films provided in a "sandwich" structure on either side of an intermediate nonmagnetic layer which ferromagnetic films may be composite films, but this insulating intermediate nonmagnetic layer permits electrical current to effectively pass therethrough based primarily on a quantum electrodynamic effect "tunneling" current.
This "tunneling" current has a magnitude dependence on the angle between the magnetization vectors in each of the ferromagnetic layers on either side of the intermediate layer due to the transmission barrier provided by this intermediate layer depending on the degree of matching of the spin polarizations of the electrons tunneling therethrough with the spin polarizations of the conduction electrons in the ferromagnetic layers, the latter being set by the layer magnetization directions to provide a "magnetic valve effect". Such an effect results in an effective resistance, or conductance, characterizing this intermediate layer with respect to the "tunneling" current therethrough. The maximum fractional change in effective resistance is a function of the magnetic polarization of the conduction electrons given by (ΔR/R)=2P1 P2/(1+P1P2), where P1 and P2 are the conduction electron spin polarizations of the two ferromagnetic layers. These polarizations appear dependent on the ratio of spin up to spin down electrons in the 3D shell of the transition elements used in the ferromagnetic thin-films, i.e. the spin polarization P of the conduction electrons. The fraction f of 3D electrons which are spin up have typical values of 0.75 for iron, 0.64 for cobalt and 0.56 for nickel. Conduction electrons in metals are normally S shell electrons which theoretically would be equally divided between spin up and spin down electrons. However, because of band splitting the conduction electrons in the magnetic layers are assumed to have a fraction of spin up electrons like that of the electrons in the 3D shell. The spin polarization is then determined from P=2f−1.
In addition, shape anisotropy is often used in such a sensor to provide different coercivities in the two ferromagnetic layers, and by forming one of the ferromagnetic layers to be thicker than the other. Such devices may be provided on a surface of a monolithic integrated circuit to thereby allow providing convenient electrical connections between each such sensor device and the operating circuitry therefor.
A "sandwich" structure for such a sensor, based on having an intermediate thin layer of a nonmagnetic, dielectric or otherwise, separating material with two major surfaces on each of which a anisotropic ferromagnetic thin-film is positioned, exhibits the "magnetic valve effect" if the materials for the ferromagnetic thin-films and the intermediate layers are properly selected and have sufficiently small thicknesses. The resulting "magnetic valve effect" can yield a response which can be several times in magnitude greater than that due to the "giant magnetoresistive effect" in a similar sized sensor structure.
The current-voltage characteristics of such "sandwich" structure sensors will exhibit a relatively linear change in the quantum electrodynamic effect "tunneling" current therethrough from one ferromagnetic layer through the barrier to the other with respect to the voltage provided across the sensor, i.e. across the barrier layer between these ferromagnetic layers, for relatively lower value voltages, but the current magnitude increases more than linearly for higher values of voltage across the sensor. As the voltage across the sensor increases, the fractional change in the "tunneling" current through the sensor, for the ferromagnetic layers having magnetizations changing from parallel to one another to antiparallel, decreases to being only half as great with several hundred millivolts across the sensor as occurs in the situation with a hundred or less millivolts across the sensor so that this fractional change with sensor voltage will range from a few percent to 20% or more. The fractional change in the resistance of the sensor for the ferromagnetic layers having magnetizations changing from parallel to one another to antiparallel increases to about one and one-half the room temperature values when the sensor is cooled to 77° K, but the "tunneling" current through the sensor increases by only about 10% to 20% indicating that the effective resistivity of the sensor is relatively insensitive to temperature (around 500 to 1000 ppm/° C.).
The effective resistivity of such a sensor is set by the amount of "tunneling" current through the cell permitted by barrier layer for the voltage across the sensor. The high sensitivity of the "tunneling" current to the thickness of the barrier layer leads to a wide range of sensor resistivities which have been observed to be from 60.0Ω-μm2 to 10,000 MΩ-μm2. On the other hand, the barrier layer appears to permit relatively weak magnetic coupling between the ferromagnetic layers thereacross with the coupling fields typically being only a few Oe.
The barrier material for such sensing devices has typically been aluminum oxide, Al2O3 and other such oxides, but other dielectric materials have been used. A typical construction therefore has had two long rectangular ferromagnetic thin-film strips with the barrier layer therebetween such that the long axis of the bottom strip, supported directly on an electrically insulating substrate, at some angle with respect to that of the upper strip supported thereon through the barrier layer. This arrangement leaves the crossover area where these ferromagnetic strips overlap having the shape of a parallelogram defining the portion of the barrier layer through which there is effective current tunneling between the strips.
These devices are fabricated by depositing upon the insulating substrate a narrow stripe of the bottom ferromagnetic film typically using a separate, removable mask. A layer of dielectric material is then formed over this bottom film, and then a second narrow stripe ferromagnetic film is deposited through a mask such that the long direction axis of the second stripe is, typically, perpendicular to that of the first. The region of tunneling between the two stripes is then typically shaped as square or rectangle where the two stripes overlap. The shape of the interposed dielectric barrier is inconsequential so long as it is sufficiently large to completely separate the two ferromagnetic thin-film metal stripes. The ferromagnetic layers in these structures are typically simple single films of Fe, Co, NiFe or other common ferromagnetic alloys.
Generally, fabricating a very small overlap area in such sensors using masking techniques is difficult to accomplish because of deposition material spatial distribution variances which can lead to electrical short circuits between the strips. As a result, overlap area, or tunnel junction, dimensions are often of many millimeters in length and relatively thick barrier layers are needed.
The operating current for such sensors is typically supplied through a pair of current leads with one such lead connected to an end of the upper strip and the other lead connected to an end of the lower strip. The effective electrical resistance of the sensor is determined from measuring the voltage across the tunnel junction at two voltage leads each connected to one of the remaining two ends of these strips. Then, by providing a current of a known fixed value through the current leads and measuring the corresponding tunnel junction voltage on the voltage leads, the effective resistance can be simply calculated by dividing the measured voltage value by the chosen fixed current value.
Because, as indicated above, the conduction of current across the barrier of such a sensor is due to a quantum electrodynamic tunneling effect, the conduction turns out to be highly dependent on the thickness of the barrier. An increase of 2 Å in the barrier thickness can lead to an increase the junction resistance by a factor of 10. The measured resistances of tunnel junctions fabricated from the same starting material are inversely proportional to the areas of those junctions. Typical tunneling resistivities (ρT, calculated by multiplying the resistance by the tunnel junction area) range from 10−2 to 10−3 MΩ-μm2. These resistivities correspond to Al2O3 thickness of about 12 to 30 Å, respectively. Due to the sharp dependence of tunnel resistivity on the barrier thickness, ρT can easily vary across a single wafer by a factor of two.
As indicated above, the measured resistance of the tunnel junction in such a sensor is a function of the relative orientation of the magnetizations of the two ferromagnetic thin-film metal strips. The portion of the tunnel junction resistance that is subject to change as a result of that junction experiencing changes in external magnetic fields to which it is exposed is termed junction magnetoresistance (often written JMR, and defined as ΔR/Rmin but is equivalently ΔR/Rmin for voltage measurements with a fixed current with either being expressed as a percentage). The sensors described above demonstrated that the JMR therefore can be quite large at room temperature (>25%).
However, such sensors cannot be conveniently incorporated into integrated circuits because the sputter-mask mode of fabrication is not compatible with modern semiconductor fabrication. In addition, the magnetic response of these sensors is not optimized for applications. In particular, they exhibit considerable hysteresis, nonlinearity and other nonideal aspects in their JMR response, including small signal output and low areal density, as have the tunnel junction field sensor structures of subsequent designs.
A better magnetic field sensor can be made using modem semiconductor fabrication techniques having a junction structure in a sensor cell based on a nonmagnetic intermediate separating material with two major surfaces on one of which is a base anisotropic ferromagnetic thin-film which is also on a base electrode, and on the other of which there is at least one of a plurality of separate anisotropic ferromagnetic thin-films but of differing effective coercivities. The nonmagnetic intermediate separating material can be either a conductive material leading to a GMR device or an insulator leading to a spin dependent tunneling device. Similar structures have a separate film in each that can be interconnected to one another with the interconnections extending at least in part substantially parallel to the widths of the separated films. The base electrode and the separated films can have lengths with gradually narrowing widths toward each end which narrow to zero at the ends. The intermediate material supported on a base electrode can be common to all the separated films thereon.
Often more than one such magnetic field sensor is used in a sensing configuration to provide a larger output signal and, in many instances, to provide some sensor noise cancellation. These goals are many times pursued through use of a bridge circuit in which such GMR effect structures or spin dependent tunneling structures are provided as circuit resistors connected in two parallel branches between two power supply nodes with each such branch having two such resistors in series with one another. A single polarity voltage source is typically connected between the two power supply nodes with in many instances the negative side of the source being grounded. A signal sensing differential amplifier with a pair of inputs is typically electrically connected between the two bridge circuit output nodes, i.e. the internal nodes of each of the two branches which for each is the node between the two resistors connected in series therein.
To have such a bridge circuit operate properly, adjacent ones of the magnetoresistors in the circuit must vary in resistance differently under an applied magnetic field if a signal output is to result. If they each have the same resistance variation, there will be a zero value signal developed between the bridge circuit output nodes, i.e. between the sensing amplifier inputs. Since an externally applied magnetic field to be sensed will be approximately the same for each of the closely spaced resistors in the bridge circuit, design measures are necessary to assure the needed resistive differences nevertheless occur between the adjacent circuit structures or resistors. One such measure previously used has been to place two of these magnetoresistors on opposite sides of the bridge circuit each connected to different power supply terminals under a magnetic shield leaving only the other two such resistors exposed to the effects of externally applied magnetic fields. Such an arrangement, however, results in a smaller output signal for an applied eternal field than would otherwise be possibly available since two resistors are not being used to sense that field. Furthermore, provision of such shields adds risk to the fabrication process since they must be relatively large structures formed after most other steps are completed. Thus, there is a desire to obtain the needed resistive differences between the adjacent circuit structures or magnetoresistors while obtaining the full possible output signal without having to fabricate shielding structures.

System and method for the fabrication, characterization and use of magnetic corrosion and chemical sensors


An adaptable graphical user interface is provided. The interface may include a setup region to display a group of available solvers to a user and to display parameters for at least one of the group of solvers to the user. The interface may include an options region to display a first group of active options to a user without requiring a user input for the first group of active options, where the first group of active options is determined based on a selected one of the group of solvers. The options region may further display a second group of active options to the user when another one of the solvers is selected by the user, where the second group of active options differs from the first group of active options.

Users in disciplines, such as mathematics, science, engineering, finance, statistics, medicine, etc., may wish to optimize an objective or model to determine a minimum or a maximum of an objective or model. Some of these users may wish to optimize using computers to take advantage of processing capabilities provided by modern computers. Performing computer based optimizations can become problematic for some users because complicated optimization solvers may be required, constraints may need to be specified, tolerances for the optimization may need to be determined or selected, etc. In addition, certain optimization problems may benefit when certain types of optimization solvers are used. For example, a first optimization solver may provide a first result that is less satisfactory than a second result that is provided when a second optimization solver is used.
Certain users may further have difficulty performing computer-based optimizations because these users may not be highly skilled in performing optimizations, selecting optimization solvers appropriate for a particular optimization problem, determining constraints for optimization problems, determining optimization tolerances, etc. In addition, these users may have difficulty interacting with the computer environment because these users may not be skilled programmers or may not be skilled at representing mathematical expressions or functions in forms that can be interpreted by computers (e.g., representing an optimization algorithm or optimization problem in a textual form that is compatible with the computer). The shortcomings of available computer-based optimization applications may discourage some users from using computers to solve optimization problems.


A CT apparatus for scanning compact structures associated with a larger body uses radiation source producing a reduced field-of-view to simplify construction and reduce exposure of the larger body. Truncation artifacts in the reconstructed image caused by volume elements in the larger body imaged by the radiation beam only for projections at some angles, are reduced by acquiring two projections at two different energies and combining those projections to compensate for the attenuation of the radiation by the volume elements of the larger body.

In a computed tomography system ("CT system"), an x-ray source is collimated to form a fan beam with a defined fan beam angle and fan beam width. The fan beam is oriented to lie within the x-y plane of a Cartesian coordinate system, termed the "imaging plane", and to be transmitted through an imaged object to an x-ray detector array oriented within the imaging plane.
The detector array is comprised of detector elements which each measure the intensity of transmitted radiation along a ray projected from the x-ray source to that particular detector element. The detector elements can be organized along an arc each to intercept x-rays from the x-ray source along a different ray of the fan beam.
The intensity of the transmitted radiation received by each detector element in the detector array is dependent on the attenuation of the x-ray beam along a ray by the imaged object. Each detector element .alpha. produces an intensity signal I.sub..alpha. dependent on the intensity of transmitted radiation striking that detector element .alpha..
The x-ray source and detector array may be rotated on a gantry within the imaging plane so that the fan beam intercepts the imaged object at different angles. At each angle, a projection is acquired comprised of the intensity signals from each of the detector elements .alpha.. The projections at each of these different angles together form a tomographic projection set.
The acquired tomographic projection set is typically stored in numerical form for computer processing to "reconstruct" a slice image according reconstruction algorithms known in the art. The reconstructed slice images may be displayed on a conventional CRT tube or may be converted to a film record by means of a computer controlled camera.
The volume subtended by the fan beam, as intercepted by the detector elements during rotation of the gantry, defines the field-of-view of the CT system.
The amount of data required to reconstruct a CT image is a function of the CT system's field-of-view, the larger the field-of-view, the more data that must be collected and processed by the CT system and thus the longer the time required before an image can be reconstructed. The acquisition of additional data in each projection also increases the cost and number of the components of the CT system.
Therefore, for imaging compact structures within the body, it would be desirable to limit the field-of-view to an angle commensurate with the cross-sectional area of that compact structure. Such a reduction in field-of-view, accompanied by a reduction in the size of the fan beam, would reduce the total dose of x-rays received by the patient. In a CT machine constructed for only imaging compact structures, a reduced field-of-view would reduce the cost of the machine and provide increased image reconstruction speed as a result of the reduced amount of data required to be processed. Also, as is known in the art, smaller field of view images may be reconstructed faithfully using fewer projection angles, thereby further reducing the reconstruction times. The reduced cost of such a machine would result primarily from the reduced number of detectors and associated data handling circuitry required, and from the less powerful image reconstruction processor required to handle the amount of reduced data. Cost savings from a resulting simplified mechanical construction might also be achieved.
Unfortunately, for a CT system to accurately reconstruct images of a compact structure within an attenuating body, it is ordinarily necessary that the entire body containing the compact structure be within the CT system's field-of-view. Even when the only structure of interest is centrally located and its attenuation properties are very different than those of the rest of the section, such as the spine within an abdominal section, conventional CT methods require that substantially the entire object be within the field of view. If the body containing the compact structure extends beyond the field-of-view of the CT system, then projections at some gantry angles will include attenuation effects by volume elements of the body not present in projections at other gantry angles. For the present discussion, these volume elements present in only some projections are termed "external volumes".
In the reconstruction process, the attenuation caused by external volumes is erroneously assigned to other volume elements in the reconstructed image. This erroneous assignment produces artifacts, manifested as shading or cupping, and sometimes as streaks, in the reconstructed tomographic image and are termed "truncation artifacts".
Selective material imaging by use of x-ray transmission measurements at multiple energies is known. However, when used in a CT mode, prior methods acquired data for the entire object.

Reduced field-of-view system for imaging compact embedded structures


Various examples and schemes pertaining to uplink (UL) transmission timing for non-terrestrial networking (NTN) are described. An apparatus receives, from a network, downlink control information (DCI) indicating an NTN offset for a scheduling delay. Accordingly, the apparatus performs one or more UL transmissions to a satellite with the scheduling delay which accounts for the NTN offset.

Unless otherwise indicated herein, approaches described in this section are not prior art to the claims listed below and are not admitted as prior art by inclusion in this section.
In terms of addressing the issues of coverage and difficult use-cases associated with land-based communication and networking infrastructure, satellites can be a viable means to the solution. The 3rd-Generation Partnership Project (3GPP) specification for 5th Generation (5G) mobile communications considers non-terrestrial networks, including satellite segments, a recognized part of 5G connectivity infrastructure. However, there remain challenges to be addressed to ensure that satellite systems are integrated as an intrinsic part of the 5G ecosystem. For instance, the round-trip time (RTT) for a satellite is approximately 28 ms for a low-earth-orbit (LEO) satellite at 600 km above sea level and can be up to 544 ms for a geostationary (GEO) satellite at 35,786 km above sea level. Accordingly, timing advance needs to compensate for satellite RTT before a user equipment (UE) can transmit on an UL channel. Additionally, scheduling delay due to large satellite RTT also needs to be minimized to avoid negative impact on data rates.

Uplink transmission timing for non-terrestrial networks


A connector for connecting high-power RF coaxial joints uses a screw-thread locking ring to draw a body and a bushing of the joint together. The connector also includes an O-ring seal.

High-voltage, high-power RF signals, as employed for example in the field of broadcasting for communication and entertainment, are often coupled from transmitters, which are typically located at ground level or otherwise made readily accessible for maintenance, for distances up to thousands of feet to reach the antennas from which the signals radiate.
This coupling process usually takes place using rigid coaxial lines (coax) made from concentric pieces of tubing, spaced with insulators, carefully dimensioned and finished, assembled, sealed, and often pressurized, typically with aggressively dried air or with nitrogen gas that has been purged of water vapor, oxygen, and other contaminants to the greatest extent possible. Individual sections of coax, which may be from an inch or less up to a foot in diameter depending on the level of power carried, are typically joined end to end to each other and/or to other equipment using specialized connectors or couplings.
Where space is not at a premium, it is often possible to use the standard fittings that were developed and adopted by the Electronics Industry Association (EIA) as EIA-225 some decades ago. These fittings are generally standardized and interchangeable. However, for some applications, space can be critical, and for such circumstances the known fittings can be undesirably bulky. For example, some prior art devices employ radially projecting flanges joined by longitudinal bolts. The radial projection dimension can be significant, due to clearance for bolt heads and tool heads that drive the bolts. In the prior art, there is no suitable reduced-dimension substitute among EIA-225 standard RF power fittings.
Accordingly, there is a need in the art for an RF power coaxial coupling outer fitting that provides the capability for reduced size, reduced element spacing, and/or increased packing density when compared to conventional designs, while retaining RF performance that is essentially identical to conventional designs and mechanical strength that achieves a level of performance suitable for useful applications.

Method and apparatus for RF coaxial connections


The system includes a first unit adapted to communicate with a second unit. The second unit grants conditional access to a function or service in accordance with an authentication operation. Both units are capable of running software for generating passwords by means of encryption of several dynamic variables as for example a time dependent variable and/or a variable representing the number of formulated authentication requests. The encryption may be performed using a dynamic key. In order to synchronize the values of the variables generated in concert but independently in the units, only some of the least significant digits of the variables are transferred from the card-like unit to the other unit, with the transfer being performed by adding the digits to the password. This synchronization information is combined with corresponding variables in the second unit and used to calculate therein a value which has to match with the password calculated in the second unit in order to gain access to the function or service. In a "virtual token" implementation, the first unit can be a smart card, which stores the dynamic key and the variable representing the number of formulated authentication requests and executes an encryption algorithm, a smart card reader and a personal computer. Either the smart card reader or the personal computer can generate the time dependent variable. In a "software token" implementation, the functions of the first unit are performed by a computer such as a personal computer, thus eliminating the need for a smart card or a smart card reader.

1. Field of the Invention
The present invention relates to an electronic system for authentication of individuals and/or messages, in particular for controlling access to a function, enabling a user conditionally to obtain a service or some other provision to be delivered by a specialized service unit associated with the system in question.
More particularly, the invention relates to a system for control of access to, or authentication of messages handled in, a computer or, more generally, a computerized network, use of which is reserved for persons having been duly legitimately entitled. Such networks may serve, for example, to provide all kinds of services entailing a transaction, usually with a monetary consideration, such as television shopping, pay television, home banking, interactive televised games, or also confidential faxes etc.
2. Description of the Related Art
The known systems of this kind generally include at least one electronic device or token, preferably portable (referred to as a "card" for convenience in the remainder of the present description) and at least one central electronic verification device (referred to as a "server" in the remainder of the description) which is intended conditionally to deliver authorizations for access to the function or service.
Such authorization is delivered only in the event of agreement or matching between a password produced in the card and a password produced in the server. These passwords are obtained by encrypting a variable with the aid of an encryption algorithm, which operations take place simultaneously in the card and in the server.
Usually, the encryption process employs a time parameter, often involving the use of clocks both in the cards and in the servers. In the ideal case, these clocks should be synchronized with one another; synchronization is difficult to achieve in practice, especially if, for obvious cost reasons, it is sought to install in the cards clocks which do not have very high accuracy.
A system exhibiting the general characteristics stated above is described in U.S. Pat. No. 4,800,590. In this system, each card includes a processor intended iteratively to calculate a password with the aid of an encryption algorithm. This latter periodically encrypts a parameter (referred to as the "seed") which is itself dependent on the parameter used for the previous calculation.
In such a system, the clocks of the card and of the server must in principle be synchronous so as to avoid unjustified denials of access (which are not from fraudulent or erroneous requests on the part of the user of the card).
However, whereas the clock of the server may be highly accurate, the same is not the case for the cards. Indeed, since a modest cost in respect of the cards is a paramount design constraint, it is not possible to incorporate in the cards expensive high-quality clocks which would be free of drift. A high level of synchronization between the clocks of the cards and of the server cannot therefore be envisioned in practice.
In U.S. Pat. No. 4,885,778, passwords are also periodically calculated during given successive time spans. A time dependent validity range is established in the server with a length much greater than the time span. When an access request is formulated, the server computes as many passwords as there are time spans contained in the time dependent validity range. If a password of the card matches with one of the passwords thus calculated in the server, access is granted. This system also requires a significant amount of calculating work in the server.
U.S. Pat. No. 5,361,062 discloses an authentication system which involves transferring to the server, at the moment at which an access request is input, a part of the time value available in the card on the basis of its clock. The example given in the patent is the minutes value of the clock at the moment of access. When the password is transferred, this value will be used in the server which examines whether the seconds value of its clock is less than or greater than 30 seconds. If this value is less, the server takes the chosen minutes value. In the contrary case, the minutes value in the server is increased by one unit. This process can operate correctly only if the clock of the card is either synchronous with the clock of the server with a predefined tolerance or lags behind the latter. If, on the other hand, the clock of the card leads that of the server, the latter will be unable to find the password calculated in the card during the access request in progress, since the server will not perform iterations until reaching that of the current minute of its own clock. In this case, no access request, even formulated legitimately, will be able to succeed. However, in incorporating low-quality clocks into the cards, which, as described above, is necessary for cost reasons, it is not possible to determine during manufacture in which direction the clock of a card will drift with respect to the clock of the server, particularly since the drift may be caused by wholly unpredictable phenomena such as temperature variations to which the card may be subjected.
Another drawback of the system according to U.S. Pat. No. 5,361,062 is that the elemental time unit clocking the password calculation iterations cannot be chosen to be very small, since the smaller the time unit, the greater the calculational burden both for the server and for the cards. Therefore, in practice, this time unit has been fixed at between 1 and 10 minutes. This implies that each password generated in the card remains valid throughout the duration of such a time unit. This impairs the security of the system, in particular when it includes several servers. A hacker can in fact obtain a password by intercepting it on the link between the card and the server and could then enter it into another server and obtain authorization of access, since he has the right password.
EP Patent Application No. 0 324 954 discloses an access control system which involves transmission to the server by the user of a synchronization data item which pertains to the number of access requests made previously. More precisely, if after calculating the password in the card and in the server there is non-agreement, the server displays a data item relating to the access requests which it has made in respect of this card. This data item must be entered into the card by the user in order to ensure that the same number of access requests is recorded in the card and in the server. This prior system has the drawback of involving the user in the synchronization procedure and of disclosing to any hacker the number of access requests made, although this value serves in the calculation of the password. It would therefore be preferable to keep it secret.

System and method for user authentication having clock synchronization


In the tilt correction method, information about inclination of an object lens relative to an information recording medium is acquired. A direct current signal Sdc for correcting the inclination is produced based on the information. An alternating current signal Sac having a prescribed signal characteristic is superposed onto the direct current signal Sdc to produce a driving signal Sout. The driving signal Sout is supplied to a driving mechanism to correct the inclination of the object lens against friction.

1. Field of the Invention
The present invention generally relates to tilt correction for an object lens relative to an information recording medium in an optical disk recorder/player, and more particularly, to a method and apparatus for correcting tilt relative to an information recording medium through superposition of signals.
2. Description of Related Art
With an optical disk apparatus (i.e., an optical disk recorder/player), a laser beam is guided onto the recording side of an information recording medium, such as an optical disk, to record information. The recorded information is reproduced based on the light reflected from the recording side. In general, the optical disk apparatus is provided with an optical pickup device, which emits a laser beam to form a light spot on the recording side of the information recording medium, as well as receiving light reflected from the recording side.
Generally, an optical pickup device has an optical system including an object lens, which guides a laser beam emitted from a light source onto the recording side of the optical recording medium and guides return light flux reflected from the recording side to a prescribed light-receiving position. The optical pickup device also has a light receiving element arranged at the light-receiving position to receive the return light flux. The light receiving element outputs not only information reproduced from the data recorded in the recording side of the medium, but also signals containing servo information required for positioning of the object lens and the optical pickup device itself.
In recent years and continuing, the recording density in information recording media is increasing in response to demand for increased recording capacities of information recording media. In order to increase the recording density, the diameter of the light spot formed on the recording plane has to be decreased. To achieve this, use of an object lens with a large numerical aperture is becoming popular. However, as the numerical aperture increases, influence of wavefront aberration due to offset of the optical axis of the object lens from a line perpendicular to the recording plane also increases. The offset of the optical axis of the object lens is referred to as "tilt", which is likely to cause deformation of the light spot, as well as degradation of signals output from the light receiving element and containing reproduced information and servo information.
There are two types of tilt correction, namely, a method for inclining the information recording medium relative to a fixed object lens, and a method for inclining the object lens relative to the information recording medium. The recent trend is employing the latter method due to demand for reducing the size of the tilt correction mechanism and for increasing the tilt correction speed. To adjust the inclination of the object lens, a tilt control mechanism is known, which is designed to bring the guide shaft attached to a fixed part of the optical pickup device into an opening formed in the movable part having the object lens and to rotate the movable part of the optical pickup device about the guide shaft against a frictional force between the movable part and the guide shaft.
For example, JPA 2000-260042 discloses a control apparatus for driving a carriage of the optical pickup device against a force of static friction.
However, driving the movable part of the optical pickup device against the frictional force, as in the above-described tilt correction technique using a tilt control mechanism, has a problem in that smooth motion of the movable part is hindered by the frictional force and the movable part cannot follow up the driving signal used to correct the inclination of the object lens. Consequently, the correction accuracy is likely to be degraded.

Method and apparatus for tilt correction and tilt driving signal generating circuit


A system and method that enables testing of circuitry using an externally generated signature. An external tester is arranged external to a device under test (DUT). Such external tester is operable to input test data to the DUT, receive output data from the DUT, and generate a signature for at least a portion of such received output data. The external tester compares the generated signature with an expected signature to determine whether the DUT is functioning as expected. If the generated signature fails to match an expected signature, then error data can be written to an error map log. Preferably, further interaction with the DUT is not required after detecting that a generated signature fails to match an expected signature in order to perform such error evaluation. Thus, error evaluation can be performed concurrently with testing of the DUT. Mask data may be stored in a compressed form, and decompressed and used for masking certain non-deterministic output bits in generating the signature.

During typical semiconductor manufacturing processes, a plurality of integrated circuits are formed as individual dice on a semiconductor wafer. Each semiconductor wafer generally has hundreds to thousands of individual dice formed thereon. Once the dice are formed on a semiconductor wafer, the dice are then tested to determine which dice are functional and which dice are not functional. In most testing procedures, each die is probed using probe equipment while the dice are still on the wafer. This step is also known as "wafer sort."
The purpose of the wafer-level probe test is to determine, as early as possible in the manufacturing process, whether each individual die is defective or not. The earlier a defective die is detected, the less time and expense that is wasted on further processing of defective dice. That is, if it is determined that a detected defect cannot be repaired, the time and expense of completing a chip assembly will not be expended. After the wafer-level testing, the functional dice are then packaged, and generally the packaged part is tested again to ensure that no defects were introduced during packaging. Various techniques have been developed for performing wafer-level testing, such as those described further below, and as is known in the art similar techniques may also be used for testing a packaged device.
In typical semiconductor testing, the device under test (DUT) (which may be referred to as "circuitry under test" (CUT) and is intended to encompass a device under test on a wafer as well as a packaged device) receives a set of input stimuli from automatic test equipment (ATE) arranged external to the DUT, after which the ATE observes the DUT outputs. In general, the correct expected outputs of the DUT are stored in the ATE memory, and the ATE compares all of the output bits received from the DUT against the stored expected bit values to determine whether the DUT is functioning properly (e.g., whether the DUT is generating the expected output values responsive to the input values). Thus, a DUT (e.g., a device on a wafer or a packaged device) may be communicatively coupled to an external ATE, and such ATE may input test stimuli thereto and receive and analyze responses therefrom. As described further below, circuitry may be included on the DUT, which may, for example, generate a signature corresponding to the DUT's response to the input stimuli, and such signature may be output to the ATE. While much of the testing techniques described herein are described as testing a DUT that is on a wafer (i.e., wafer-level testing), it should be recognized that similar techniques may typically also be used for testing a packaged device.
In the case of wafer-level testing, a probe may be brought into contact with one or more bonding pads of a die in order to communicate signals (e.g., a test pattern) to the die and to receive the signals output by the die responsive to the input signals. The probe is typically communicatively coupled to an external ATE that is operable to generate the signals to be input to a die and to evaluate the signals output by the die in order to determine whether the die is functioning properly. Dice on a wafer may be tested serially (e.g., by contacting each die with the probe in series) or in parallel.
Traditional testing techniques of the existing art require an undesirably large amount of memory on the ATE utilized for the testing, which undesirably increases the cost of the ATE and the resulting product. For instance, sufficient data storage that is communicatively coupled to the ATE is generally required for storage of at least the following information for a testing technique: 1) input vector data, 2) output vector data, and 3) mask vector data. In general, the input vector data stored at the ATE comprises the data that is used as stimuli for inputs to the DUT (e.g., test pattern data), and the output vector data comprises the expected output data of the DUT given the input vector data, which is used for comparison with the actual output data of the DUT responsive to the input vector data to determine whether the DUT is functioning properly. Generally, the mask vector data comprises data designating which of the bits of the expected output data actually need to be compared to the received outputs of the DUT, e.g., the mask vector data maps the expected output data to the actual output data received from the DUT, as in certain configurations all of the output bits of the DUT may not be compared with expected output data (e.g., certain non-deterministic bits, or "don't care/unknown bits", may exist, the value of which is not relevant to the correct functioning of the DUT).
Such input vector data, output vector data, and mask vector data for a testing technique may consume an undesirably large amount of data storage space on the ATE. Further, as the comprehensiveness of a testing technique is increased and/or as the complexity of the device to be tested increases, the amount of data storage space consumed on the ATE for this vector data is likely also increased. For example, traditional testing techniques of the existing art commonly use approximately 400 to 800 bits per gate of the DUT being tested. Of course, depending on the complexity of the DUT and/or the comprehensiveness of the testing technique implemented (e.g., the number of flip-flops on the DUT being tested and/or the number of input test patterns utilized), the size of the input vector data, output vector data, and/or mask vector data may vary from testing technique to testing technique (but, in current ATE architectures, for each output bit a mask bit is required such that mask vector memory is equal to the output vector memory). Embodiments of the present invention breaks this barrier, thus enabling reduction in the amount of data storage required on an ATE for a test.
In general, it is desirable to minimize the amount of data storage required on the ATE for implementing a testing technique. Several solutions have been proposed in the existing art for reducing the ATE's data storage requirements for implementing a testing technique, and more particularly, for reducing the ATE's storage requirements for storing the output vector data for a testing technique. The most pervasive techniques for minimizing the amount of data storage required on an ATE for storing output vector data are vector set truncation techniques and on-chip signature analysis techniques, which are described further below.
One popular technique for minimizing the amount of data storage required on an ATE for storing output vector data is truncation. In general, truncation involves dropping a portion of the test, i.e., a portion of the output data, mask data, and/or input data (i.e., not using this test portion in determining whether the DUT is functioning properly). As a result, the amount of data stored on the ATE may be reduced. However, truncation of vector sets (e.g., input, output, and mask vector sets), for example, also results in a reduction of test coverage, and as a consequence, may result in reduction of product quality (i.e., truncation reduces the comprehensiveness of the testing of a DUT, which may result in an improperly functioning DUT passing the test). This reduction in product quality is often not acceptable. Sometimes this technique is used in combination with vector set reordering based on the likelihood of a vector actually detecting a defect for each vector, after which the tail of the vector data is truncated. This way, the impact on test coverage can be minimized. However, in most cases there is still a significant impact on the test coverage.
One of the most attractive output compression schemes is based on signature analysis. Signature analysis is a well-known technique for compressing a sequence of logic values output from a circuit under test into a relatively small number of bits of data (signature) that, when compared to stored data (e.g., an expected signature), will indicate the presence or absence of faults in the circuit. In general, a signature of a group of output bits compresses such group of output bits and uniquely identifies such group of output bits such that it may be determined whether the group of output bits are as expected. It should be noted that there is generally a slight possibility of obtaining a correct signature for incorrect output bits (aliasing). While a signature may be used to discern whether the group of output bits is as expected, if the signature is not as expected it generally cannot be discerned from the signature which one(s) of the group of output bits had unexpected values. Thus, diagnosis of errors or error debug is generally limited (e.g., unavailable) when on-chip signature generation is used. In general, error diagnosis refers to a process for identifying an error in a DUT, such as determining the situation(s) under which the DUT has an error and/or determining the bit(s) that are incorrect as a result of the error. Error debug generally refers to a process for determining the cause of an error.
Various techniques for generating a signature for output data are well known in the art. For example, one technique comprises feeding the complete output vector data through a linear feedback shift register with different exclusive OR (XOR) feedback loops, which results in a very short signature in the shift register that depends on all output vector data. When the feedback loops, i.e. the polynomials, of the shift register are selected carefully, no significant aliasing will occur. On-chip techniques for generating a signature of the chip's output data during testing have been proposed in the existing art using circuitry called a SISR (Single Input Signature Register) or (in the case of multiple XORed inputs) a MISR (Multiple Input Signature Register). Such SISR and MISR circuitry for generating signatures on-chip are well-known in the art, and therefore are not described in greater detail herein. Examples of test schemes that use signature analysis (e.g., via a MISR) are described in the following patents: 1) U.S. Pat. No. 6,442,722 entitled "METHOD AND APPARATUS FOR TESTING CIRCUITS WITH MULTIPLE CLOCKS", issued to Nadeau-Dostie et al.; 2) U.S. Pat. No. 6,393,594 entitled "METHOD AND SYSTEM FOR PERFORMING PSEUDO-RANDOM TESTING OF AN INTEGRATED CIRCUIT", issued to Anderson et al.; 3) U.S. Pat. No. 6,374,370 entitled "METHOD AND SYSTEM FOR FLEXIBLE CONTROL OF BIST REGISTERS BASED UPON ON-CHIP EVENTS", issued to Bockhaus et al.; 4) U.S. Pat. No. 6,363,506 entitled "METHOD FOR SELF-TESTING INTEGRATED CIRCUITS", issued to Karri et al.; 5) U.S. Pat. No. 6,327,685 entitled "LOGIC BUILT-IN SELF TEST", issued to Koprowski et al.; 6) U.S. Pat. No. 6,240,537 entitled "SIGNATURE COMPRESSION CIRCUIT AND METHOD", issued to Sim; 7) U.S. Pat. No. 6,158,033 entitled "MULTIPLE INPUT SIGNATURE TESTING & DIAGNOSIS FOR EMBEDDED BLOCKS IN INTEGRATED CIRCUITS", issued to Wagner et al.; 8) 5,978,946 entitled "METHODS AND APPARATUS FOR SYSTEM TESTING OF PROCESSORS AND COMPUTERS USING SIGNATURE ANALYSIS", issued to Needham; 9) U.S. Pat. No. 5,960,008 entitled "TEST CIRCUIT", issued to Osawa et al.; and 10) U.S. Pat. No. 5,938,784 entitled "LINEAR FEEDBACK SHIFT REGISTER, MULTIPLE INPUT SIGNATURE REGISTER, AND BUILT-IN SELF TEST CIRCUIT USING SUCH REGISTERS", issued to Kim, the disclosures of which are hereby incorporated herein by reference. A further example of a test scheme that uses signature analysis (e.g., via a MISR) is described in U.S. Published patent application No. 20,020,073,374 entitled "METHOD, SYSTEM AND PROGRAM PRODUCT FOR TESTING AND/OR DIAGNOSING CIRCUITS USING EMBEDDED TEST CONTROLLER ACCESS DATA", the disclosure of which is hereby incorporated herein by reference.
It should be recognized that because a signature is a compressed identification of the output bits, the amount of storage space required on an ATE for storing the output vector data (expected signatures) may be reduced well below that required for storing all of the actual expected output bits. Further, because a signature may identify an entire set of output bits (within the bounds of aliasing) desired to be analyzed (e.g., the entire output vector), test coverage is not reduced, as in the case of truncation.
However, on-chip signature analysis techniques of the existing art have several disadvantages. First, such techniques include circuitry on-chip for generating a signature of the chip's output data during testing. Such signature generation circuitry consumes area on the chip, thus increasing the overall size of the chip (or decreasing the amount of circuitry that may otherwise be included in the chip) and potentially hindering the chip's performance (e.g., because of the increased distance that signals may be required to travel given the increased size of the chip). Also, implementing the signature generation circuitry on-chip may require design modifications to be made to the circuitry under test in order to enable such signature generation circuitry to be implemented therewith. Further, the signature generation circuitry is typically utilized only during testing of the circuitry. That is, the signature generation circuitry is typically not utilized during normal operation of the circuitry in the target application. Thus, implementing the signature generation circuitry on-chip is disadvantageous in that it consumes area on the chip (thus increasing the overall size of the chip) and is useful only during-testing of the chip. Further, as mentioned above, on-chip signature generation is generally disadvantageous because it does not allow for error diagnosis (i.e., a determination as to which one(s) of a group of output bits that have incorrect outputs cannot be made from the signature of such output bits) or error debug. Further still, on-chip signature generation circuitry may itself have defects.
Additionally, since the signature depends on all output vector data, it also depends on the output vector data bits that have a non-deterministic behavior. This non-deterministic behavior can, for example, occur when a partial scan approach is used, e.g., only a subset of flip-flops on a DUT is scanned. In certain designs, some flip-flops cannot be scanned due to design constraints. Other sources of non-deterministic (unknown) output states include having multiple clock domains and tri-state buses. As a consequence, the values of these non-deterministic bits cannot be controlled without additional design modifications. However, these design modifications result in area overhead and potential performance degradation. The presence of unknown/non-deterministic output signals can corrupt the signature, making the signature and the test almost always useless. The design modifications impact on area, flow, and design performance can be a substantial disadvantage, and not acceptable for some designs.
In addition, in the on-chip signature generation techniques that do not provide on-chip masking capability, the user sometimes desires to perform only a part of the test or suppress certain non-deterministic outputs from the circuitry under test, e.g., during the debugging phase or when certain expected outputs turn out to be simulated incorrectly. In that case, depending on the number of masked outputs, signature analysis techniques of the existing art cannot be used. That is, because the signature generation techniques of the existing art comprise on-chip circuitry that is fixed for generating a signature for a certain set of output values, none of such output values can be masked out during the testing process. One could provide on-chip masking capability, however, in general extra channels/bandwidth are required to supply the masking data.
Moreover, it is very computationally intensive, and sometimes impossible, to reverse the signature analysis process. In other words, by using signature analysis techniques of the existing art, it is possible to determine a discrepancy between the actual output vector data and the expected output vector data. However, it is typically not possible to determine which received bits of the output vector data are wrong. This seriously limits the error diagnosis/debugging capability of signature-based testing methodologies of the existing art and typically requires a bypass mode for performing error diagnosis/debugging, which adds more circuitry and more inputs/outputs.
Proposals have been made for a tester that generates a signature off-chip. For example, "Low-Cost Testing of High-Density Logic Components", IEEE Design & Test of Computers, 0740–7475 (April, 1990) proposes a tester that includes signature generation logic that receives output from a DUT and generates a signature for such received output. However, such proposed tester has several shortcomings. For instance, the proposed tester does not allow for concurrent testing and error diagnosis/debugging. Further, the proposed tester does not allow for masking out of unknown states (e.g., masking of non-deterministic output bits) in generating a signature. We are aware of no commercially available ATEs that implement the technique proposed by the "Low-Cost Testing of High-Density Logic Components" article. Further, if an ATE were implemented in accordance with such proposal, it would not allow for masking of unknown states, and if such masking were implemented it would require a substantial amount of mask data stored at the ATE (as no compression of the mask data is proposed).
Because of the above-described disadvantages, the use of signature analysis techniques to reduce the ATE memory requirements is not wide spread.

System and method for testing circuitry using an externally generated signature