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1 May 1971

Volume 42, Issue 6, pp. 2159-2578

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Single‐Crystal Folded‐Path Delay Lines Utilizing Ultrasonic Pure Shear Modes

K. Brugger and R. N. Thurston

J. Appl. Phys. 42, 2159 (1971); http://dx.doi.org/10.1063/1.1660519 (3 pages)

Online Publication Date: 17 December 2003

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We describe the principle of folded‐path single‐crystal delay lines for pure shear modes, utilizing the fact that in most crystal classes there exist special planes with the following properties: (1) A pure shear wave with polarization normal to such a plane can propagate along any direction in it. (2) Upon reflection of this wave on a boundary normal to the plane, no mode conversion occurs. Hence, in a crystal with two or more boundary surfaces normal to such a special plane, a pure shear wave can be reflected back and fourth between these boundaries without reflection loss. Moreover, with an entire plane of propagation directions available, the design can be optimized by selecting the path giving either the largest delay, or, if the attenuation for all propagation directions is known, giving the lowest loss per unit delay. Examples for the propagation and reflection of pure shear modes in cubic and rhombohedral crystals are presented.

Physical Properties of Lead Molybdate Relevant to Acousto‐Optic Device Applications

G. A. Coquin, D. A. Pinnow, and A. W. Warner

J. Appl. Phys. 42, 2162 (1971); http://dx.doi.org/10.1063/1.1660520 (7 pages) | Cited 36 times

Online Publication Date: 17 December 2003

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All of the elastic and photoelastic constants of crystalline lead molybdate (PbMoO4) and various optical and thermal properties of the material have been measured. This information has been used to evaluate the material for a number of practical acousto‐optic device applications. The high figure of merit found in earlier preliminary studies is only 10% smaller than the maximum figure of merit of the material. Thus the material is well suited for acousto‐optic modulator and deflector applications. However, the material is not particularly useful for tunable acousto‐optic filters because the relevant elasto‐optic coefficient is small. Acoustic and optical losses, and changes in sound velocity and index of refraction with temperature, can cause operating limitations in practical devices, and these are discussed.

Experimental Hydroacoustic Imaging System

G. C. Knollman, A. E. Brown, J. L. Weaver, and J. L. S. Bellin

J. Appl. Phys. 42, 2168 (1971); http://dx.doi.org/10.1063/1.1660521 (13 pages) | Cited 3 times

Online Publication Date: 17 December 2003

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An underwater acoustic imaging system is described which has been developed especially for close‐range, high‐resolution (on the order of millimeters) viewing in very turbid water. The system operates at nominal 2.5‐MHz frequency and has a range up to 10 m in water of suspended ocean sediment concentration as high as several thousand parts per million. Larger range capability is possible with lower sediment concentration. Real‐time kinescope displays are presented by the system of the acoustic field of view, which is that insonified by a high‐intensity sound transmitter of total beamwidth variable up to 30° in 10° increments. The sensitive (better than 10−10 W∕cm2) piezoelectric image converter is augmented by a mechanical scanning system to provide in effect a 10 000‐element pickup matrix. A Plexiglas lens moved by remote‐control drive is employed for focusing. System parameters and performance are discussed, and some typical hydroacoustic images are displayed.

Temperature Variation of Susceptibility of Some Amorphous Antiferromagnetic Oxides

A. W. Simpson and J. M. Lucas

J. Appl. Phys. 42, 2181 (1971); http://dx.doi.org/10.1063/1.1660522 (5 pages) | Cited 18 times

Online Publication Date: 17 December 2003

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The temperature dependence of the susceptibilities of amorphous magnetic oxides with various iron∕yttrium and iron∕gadolinium stoichiometries have been studied between 4.2° and 320°K. The reciprocal susceptibilities of the iron∕yttrium oxides exhibited an unusual downward curvature at low temperatures. These measurements are interpreted by means of a simple effective field model for amorphous antiferromagnetic materials recently proposed by one of the authors. Good agreement between the experimental results and the theory is obtained. The analysis enables certain broad conclusions to be drawn about the number and distribution of interacting pairs of magnetic atoms.

Temperature Gradient Induced Migration of Gas‐Filled Bubbles in KCl

R. E. Carter, J. H. Rosolowski, and J. S. Nadeau

J. Appl. Phys. 42, 2186 (1971); http://dx.doi.org/10.1063/1.1660523 (8 pages) | Cited 6 times

Online Publication Date: 17 December 2003

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The temperature gradient induced migration of gas bubbles has been studied in KCl. This material was selected because of its high vapor pressure and transparency. The experimental variables of temperature, temperature gradient, and diffusion coefficient of the vapor species were investigated and the observed velocities were shown to agree with those expected from the theoretically derived model. The ratio of the temperature difference across a bubble of low thermal conductivity to that across an equal length of the surrounding solid was determined from analogue experiments.

Morphology of Migrating Bubbles in KCl Crystals

J. S. Nadeau, R. E. Carter, and J. H. Rosolowski

J. Appl. Phys. 42, 2194 (1971); http://dx.doi.org/10.1063/1.1660524 (9 pages) | Cited 3 times

Online Publication Date: 17 December 2003

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Gas bubbles migrating under the influence of a temperature gradient in KCl gradually evolve stable shapes which have a low length (in the direction of migration) to width ratio and are bounded by cube planes (100). The shape is determined by evaporation‐condensation kinetics and not by the equilibrium surface energies. A significant part of the bubble volume is left behind in a trail of very fine bubbles resulting in as much as a fivefold increase in bubble surface area. Most of the observed phenomena can be correlated with the detailed temperature distribution around a migrating bubble.

Cell‐Wall Dislocation Damping in Single‐Crystal Cu

H. Akita and N. F. Fiore

J. Appl. Phys. 42, 2203 (1971); http://dx.doi.org/10.1063/1.1660525 (6 pages) | Cited 1 time

Online Publication Date: 17 December 2003

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The dislocation substructure of 〈111〉 Cu single crystals has been controlled by varying crystal growth rates from 1.57 to 109 cm∕h. Etch‐pitting and x‐ray studies reveal that the substructure consists of a random dislocation network, with density 1×106∕cm1 independent of growth rate, and dislocation cells whose size and intercell misorientation angle increase with decreasing growth rate. Longitudinal resonance bar and ultrasonic pulse‐echo damping measurements at frequencies from 25 kHz to 100 MHz show that the larger the cell size, the higher the damping over the entire frequency range. There is strong evidence that damping from cell‐wall dislocations overshadows that due to the random network. The results are interpreted in terms of a modification of the Granato‐Lücke damping theory, which treats cell walls as pseudomembranes vibrating under the action of the applied stress.

Dislocation Etch Pits in Silver

C. C. Chen and A. A. Hendrickson

J. Appl. Phys. 42, 2208 (1971); http://dx.doi.org/10.1063/1.1660526 (8 pages) | Cited 6 times

Online Publication Date: 17 December 2003

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A modification of the etchant used by Levinstein and Robinson is shown to be a reliable solution in producing etch pits at dislocations on the (111) surface of silver crystals and is used to investigate the dislocation structures in as‐grown, annealed, and deformed silver crystals. Single crystals of silver with dislocation densities on the order of 104 cm−2 with a few subboundaries were prepared by high‐temperature annealing. Two distinct sizes of dislocation etch pits are found in both as‐grown and deformed crystals. The two sizes of etch pits are concluded to be associated with positive and negative edge dislocations through detailed observations of etch‐pit rosettes produced by indentation. The modified Levinstein‐Robinson etchant for silver thus corresponds to the Livingston etchant for copper. Additional observations are made on polygonization, dislocation interactions, and etch‐pit morphology. Large etch pits not associated with individual dislocations are also described.

Low‐Frequency Dielectric Constants of the Alkaline Earth Fluorides by the Method of Substitution

Carl Andeen, John Fontanella, and Donald Schuele

J. Appl. Phys. 42, 2216 (1971); http://dx.doi.org/10.1063/1.1660527 (4 pages) | Cited 12 times

Online Publication Date: 17 December 2003

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The 1000‐Hz 300°K dielectric constants of the alkaline earth fluorides were measured to an accuracy of 0.01% by the method of substitution. Reproducibly different values for various crystals of the same type were obtained which varied beyond the experimental error. The ranges of results for various crystals of each type measured along with further separation by manufacturer are: CaF2, Harshaw, 6.7984–6.7988, Optovac, 6.8074–6.8432; SrF2, Harshaw, 6.4647–6.4664, Optovac, 6.4700–6.4703; and BaF2, Harshaw, 7.3590–7.3595, Optovac, 7.3606–7.3630. The spread for each type of crystal is thought to be attributable to random trace impurities.

Temperature Dependence of the Elastic, Piezoelectric, and Dielectric Constants of Lithium Tantalate and Lithium Niobate

R. T. Smith and F. S. Welsh

J. Appl. Phys. 42, 2219 (1971); http://dx.doi.org/10.1063/1.1660528 (12 pages) | Cited 139 times

Online Publication Date: 17 December 2003

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The elastic, piezoelectric, and dielectric constants, and their temperature dependence within the range 0°–110°C, have been determined for single crystals of lithium tantalate and lithium niobate. For each material, the constants were extracted from a combination of many ultrasonic phase‐velocity measurements, the measured resonant and antiresonant frequencies of a single length‐extensional bar resonator, and the measured low‐frequency capacitances of two thin flat‐plate specimens. For lithium tantalate, the normalized first temperature derivatives of the elastic constants range from −0.4 to −6.7×10−4∕°C, while the derivatives for the piezoelectric stress constants range from −1.3 to +1.5×10−4∕°C. In the case of lithium niobate, the elastic constant temperature derivatives are all on the order of −2×10−4∕°C, while the piezoelectric temperature derivatives are all positive in the range 0.8–8.9×10−4∕°C. The dielectric or permittivity temperature derivatives are positive for both materials.

Properties of Vacuum‐Insulated Single‐Crystal Tungsten Electrodes in High Electric Fields. Part I. Surface Structural Changes

T. J. Fabiniak, R. A. Dodd, and L. Jedynak

J. Appl. Phys. 42, 2231 (1971); http://dx.doi.org/10.1063/1.1660529 (10 pages) | Cited 3 times

Online Publication Date: 17 December 2003

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The surface structures of variously oriented single‐crystal tungsten electrodes in a vacuum of ∼2×10−5 Torr have been examined after the application of electric fields leading to breakdown. Electron microscope replica techniques were chiefly used. Various surface irregularities were found, including ``splash'' and ``burn'' areas where material was transferred from one electrode to the other, protrusions and depressions, and identical twin or triplet defects of undetermined origin. However, the most interesting defects were characterized as thermal‐electrical traces, and they clearly resulted from evaporation of atoms from slip steps. It is tentatively suggested that breakdown may be initiated by that electrode most likely to undergo plastic deformation, and that crystal orientation is important in this connection.

Properties of Vacuum‐Insulated Single‐Crystal Tungsten Electrodes in High Electric Fields. Part II. Nature of Prebreakdown Currents

T. J. Fabiniak, L. Jedynak, and R. A. Dodd

J. Appl. Phys. 42, 2240 (1971); http://dx.doi.org/10.1063/1.1660530 (7 pages) | Cited 1 time

Online Publication Date: 17 December 2003

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The nature of the emission currents associated with electropolished single‐crystal tungsten electrodes in vacuum insulation has been studied. Schottky‐Richardson curves indicate that the emission current is thermionic at voltages above 1.5 kV, this conclusion being supported by Fowler‐Nordheim curves which show no evidence for field emission. It is uncertain whether the emission currents below 1.5 kV are of the thermionic or field‐emission type. The origin of the thermionic currents can be associated with various surface structures on the electrodes, notably slip plane ledges and surface hole ledges, as discussed in Part I. Polycrystalline electrodes were not studied in detail, but appear to be associated with field emission.

Temperature Dependence of the Effective Diffusion Coefficient for Zinc in Gallium Arsenide

C. H. Ting and G. L. Pearson

J. Appl. Phys. 42, 2247 (1971); http://dx.doi.org/10.1063/1.1660531 (5 pages) | Cited 5 times

Online Publication Date: 17 December 2003

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The temperature dependence of the effective diffusion coefficient D of Zn in GaAs has been measured at fixed temperatures between 600° and 1000°C. The isoconcentration diffusion technique was used throughout this investigation. It was found that D is essentially temperature independent over the entire range. The relationship is revealed only when the total zinc concentration is held constant since D is strongly concentration dependent. At a fixed Zn concentration of 2×1019 cm−3 the measured value was 9.0×10−10 cm2sec−1 with a standard deviation of 1.15. This experimental result is interpreted in terms of the interstitial‐substitutional diffusion model.

Ultra‐Fast Diffusion of Copper in Praseodymium

M. P. Dariel

J. Appl. Phys. 42, 2251 (1971); http://dx.doi.org/10.1063/1.1660532 (4 pages) | Cited 6 times

Online Publication Date: 17 December 2003

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The serial sectioning method has been used to measure the solute diffusivities of copper in praseodymium. In the bcc phase the diffusivity of copper can be expressed by D=5.7×10−2 exp(−17 800∕RT) cm2∕sec, and in the double‐hcp phase by D=8.4×10−2 exp(−18 100∕RT) cm2∕sec. It is most likely that copper diffuses in praseodymium by means of the combined substitutional‐interstitial mechanism, similar to the other noble‐metal solutes. Comparison of the present results with the previously measured diffusivities of zinc indicates that the solute diffusivities increase with decreasing solute valence.

Emission of Radiation from a Modulated Electron Beam

D. Marcuse

J. Appl. Phys. 42, 2255 (1971); http://dx.doi.org/10.1063/1.1660533 (4 pages) | Cited 4 times

Online Publication Date: 17 December 2003

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Schwarz and Hora have observed emission of radiation from an electron beam that was modulated by laser light in passing through a thin film. The modulated beam radiated at the modulation frequency on entering a dielectric (nonfluorescent) target material. In this paper the mechanism of emission of radiation of a modulated electron beam is studied on the simplified model of a klystron cavity. It is found that one modulated electron alone is incapable of emitting a photon coherently at the modulation frequency. However, the expectation value of the field intensity does show the expected resonance behavior. If the wave functions of n electrons per unit length overlap they contribute coherently to the expectation value of the field intensity. It is thus the collective interaction of many electrons with overlapping wave functions that makes possible the coherent emission of light at the modulation frequency.

Transition Radiation from a Modulated Electron Beam

D. Marcuse

J. Appl. Phys. 42, 2259 (1971); http://dx.doi.org/10.1063/1.1660534 (5 pages) | Cited 4 times

Online Publication Date: 17 December 2003

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It appears most natural to try to explain the Schwarz‐Hora effect as transition radiation that is emitted when a modulated beam enters a target composed of either a good metallic conductor or a dielectric material. This study comes to the conclusion that the signal‐to‐noise ratio at the beam current reported by Schwarz and Hora is so small that transition radiation could not be observed. One is thus led to the conclusion that transition radiation cannot explain the light emission that Schwarz and Hora have observed.

Reflection and Refraction of Plane Waves from Plane Ferrite Surfaces

R. S. Mueller

J. Appl. Phys. 42, 2264 (1971); http://dx.doi.org/10.1063/1.1660535 (10 pages) | Cited 7 times

Online Publication Date: 17 December 2003

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Wave vector surfaces, phase velocity surfaces, and ray velocity surfaces have been evaluated for electromagnetic waves traveling through magnetized ferrite. These surfaces are shown to have unique shapes depending upon the precessional, magnetization, and excitation frequencies. Double refraction of the waves occur at the interface between different ferrites. A transcendental equation for determining the angle of transmission is presented and a discussion is made on the possibility of total reflection. Since the direction of propagation, boundary surface normal, and direction of magnetization each present a degree of freedom to the incident plane wave problem a general set of coordinates is introduced that takes into account their relative orientation. The two cases for which the static magnetization is parallel and perpendicular to the plane of incidence is solved in detail and expressions are given for the reflection and transmission coefficients. It is shown that for the parallel magnetic polarization case the reflected component of the electric vector can be eliminated if the incident wave strikes the boundary plane at a magnetically dependent Brewster angle.

Simple Model for Internal Photoemission

Vikram L. Dalal

J. Appl. Phys. 42, 2274 (1971); http://dx.doi.org/10.1063/1.1660536 (6 pages) | Cited 27 times

Online Publication Date: 17 December 2003

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We have studied the influence of film thickness and collision processes upon the internal photoemission process in metal‐semiconductor systems. A simple, one‐dimensional random walk model has been used. The analysis shows that significantly larger yields may be expected for film thicknesses of the order of or less than electron‐phonon mean free paths. The influence of energy dependent mean free paths has also been studied. The results are in qualitative agreement with the results of Fermi‐age theory, but are somewhat different quantitatively.

Analysis of Photoemissive Schottky Barrier Photodetectors

Vikram L. Dalal

J. Appl. Phys. 42, 2280 (1971); http://dx.doi.org/10.1063/1.1660537 (5 pages) | Cited 1 time

Online Publication Date: 17 December 2003

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The performance of Schottky barrier photodetectors employing internal photoemission process is studied. Background‐photon‐noise limited detectivities Dλ* have been calculated for typical operating conditions. The use of cooled optical filters has also been investigated. The analysis shows that the detectivities may be considerably less (by about an order of magnitude) than those realized for the more conventional quantum detectors employing photovoltaic or photoconductive effects.

Correlation of Electrical Breakdown and Centers of Strong Electron Emission on a Zone‐Refined Iron Cathode in Vacuum

G. A. Farrall

J. Appl. Phys. 42, 2284 (1971); http://dx.doi.org/10.1063/1.1660538 (10 pages) | Cited 8 times

Online Publication Date: 17 December 2003

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The present work is a study of the whiskerlike protuberances upon the surface of a ☒‐in‐diam zone‐refined electrode in vacuum. The experimental technique employs a phosphor screen parallel to the electrode surface. The electron emission from the surface protuberances are projected upon this screen. The experiment consisted of more than 40 trials, each trial involving the recording of an emission pattern, the determination of a Fowler‐Nordheim plot, and the application of 60‐cycle high voltage sufficiently large to produce occasional breakdown. Further, the electrode surface was photographed directly during each application of 60‐cycle voltage so that the locations of individual breakdown events could be recorded. In general, good correlation was found between the location of emitters as determined from the phosphor screen display and the locations of breakdowns.

Analysis of Nonequilibrium Plasmas in Close‐Spaced Thermionic Converters

D. T. Shaw and F. T. Wu

J. Appl. Phys. 42, 2294 (1971); http://dx.doi.org/10.1063/1.1660539 (8 pages) | Cited 1 time

Online Publication Date: 17 December 2003

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The effects of varying interelectrode spacings, current outputs, and cesium pressures on the spatial profiles of the electron temperature and density are determined for an ignited thermionic converter. A new method is introduced for the determination of the boundary conditions of the three transport equations which describe the electron and ion diffusion and the electron energy transport in the interelectrode plasma. Special emphasis is placed on the change of plasma properties as the interelectrode spacing varies from large values to very small values.

Minimal Energy Dissipation and Maximal Error for the Computational Process

Rolf Landauer and James W. F. Woo

J. Appl. Phys. 42, 2301 (1971); http://dx.doi.org/10.1063/1.1660540 (8 pages) | Cited 15 times

Online Publication Date: 17 December 2003

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In a preceding paper, the execution of elementary logic steps was analyzed for minimal energy requirements and for bounds on the unavoidable error probabilities. This was done with the aid of a hypothetical device involving the use of a particle held in a time‐modulated potential well, and coupled through springs to other such particles. The previous analysis was limited to the case of wells modulated very slowly compared to the relaxation time for particle redistribution. The present analysis extends these studies to the case of computations proceeding at arbitrary velocity. The same hypothetical device is invoked, with minor modifications for analytical tractability. Energy dissipation is found to be minimal for potential wells endowed with critical damping and the dissipation is roughly proportional to computing rate. The error rate also increases with computing velocity and is lowered by critical damping, but is less sensitive to these parameters, and is largely dependent on the magnitude of the interaction potentials between wells.

Improved Thermal Diffusivity Method Applied to TiB2, ZrB2, and HfB2 from 200°–1300°C

T. M. Branscomb and O. Hunter

J. Appl. Phys. 42, 2309 (1971); http://dx.doi.org/10.1063/1.1660541 (7 pages) | Cited 5 times

Online Publication Date: 17 December 2003

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The thermal diffusivities of dense polycrystalline TiB2, ZrB2, and HfB2 were measured by a laser flash method over the temperature range 200°–1300°C. An investigation of the effects of radial heat flow was performed and a special sample shape was used to comply with the assumption of one‐dimensional heat flow. The values of the diffusivities were found to be described by the empirical equations
math
Values of thermal conductivity computed from the diffusivity data were found to be described by
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Inferences from the Transfer Function of Maser Media

E. O. Schulz‐DuBois

J. Appl. Phys. 42, 2316 (1971); http://dx.doi.org/10.1063/1.1660542 (6 pages)

Online Publication Date: 17 December 2003

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The transfer function for transmission through a maser medium is derived. It is valid within the dynamic range of linear maser response and under the assumption of weak dispersion. All signal distortions due to propagation in a maser medium may be canceled by subsequent propagation in a complementary absorbing medium. The signal leaves the cascaded media undistorted with a delay corresponding to propagation at the vacuum velocity of light. This possibility of recovering the speed of light makes it difficult to talk of the propagation of information in a dispersive medium as taking place at a signal velocity below that of light. A potentially useful scheme is shown in which a severely distorting low‐noise maser amplifier is used. After further amplification the signal distortions are eliminated by transmission through a complementary absorbing medium. The mathematical form of the transfer functions also leads to a new integral formula involving Bessel functions.

Quantitative Control of Surface Pinning in a Low‐κ Type II Alloy

D. D. Morrison and R. M. Rose

J. Appl. Phys. 42, 2322 (1971); http://dx.doi.org/10.1063/1.1660543 (6 pages) | Cited 5 times

Online Publication Date: 17 December 2003

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Quantitative control of surface pinning in the case of In☒2% Bi foils was achieved by pressing diffraction gratings into the foil surfaces. The resulting grooves were effective pinners when they were 8.4ξ or wider and ineffective when 4ξ or narrower; the critical Lorentz force for flux flow was consistent with simple static calculations based on the groove geometry. No pinning occurred for flux flow along the grooves. Near Hc2, the strength of pinning decreased linearly with H, and was essentially constant at lower fields. The Jc(H) peak effect was found to depend on pinner spacing.
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