bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model of Temperature Rise Induced by Adiabatic Strain-Cycling in Crystalline Materials: Application of the Dispersion Relations
Authors: Schipper J. F.
Published: February 2004

A relation is derived between the adiabatic and the isothermal stiffness tensor coefficients cijkl, using the Maxwell relations relating change-of-stress at constant strain and change-of-entropy at constant temperature. The concept of frequency-dependent phase shift between applied stress and strain reponse is introduced, and a quantitative prediction of time-dependent temperature rise is obtained in terms of (1) phase shift, (2) material coefficients of change-of-stress with temperature, (3) stiffness-tensor and stress-tensor coefficients, (4) temperature dependence of material's specific heat capacity. The temporal rise in temperature is found to be bounded above if cijkl decreases linearly with temperature and with a sufficiently high slope. A simple kinetic model is considered which accounts for heat transfer within the material and radiation at the boundary, and a quantitative bound on temperature is again obtained. The Kramers-Krönig dispersion relations are utilized to obtain an expression for stress-strain phase shift, which is shown to be positive and to lie in [0, π/2] for a general class of stiffness tensors. This answers a troublesome question concerning some possible ambiguities in the ad hoc introduction of the phase shift.
Striation Phenomenon in Electrical Prebreakdown
Authors: Palmer J. D. , Qassemzadeh H.
Published: February 2004

Measurements are made of the fast striations immediately after ionization begins in an electrical discharge. First the basic phenomena leading to the existence of the so-called wave of stratification, produced by the external perturbation of an unstriated positive column, is given. It is explained that the analysis of the latter problem based on these phenomena leads to formulations that predict the presence of slow as well as fast striations. The result of this formulation for the fast striations is given. The formulation is modified to obtain results more suitable for the experimental technique used. For the measurement a microwave signal is impinged on the discharge tube that is ionized by a high-voltage pulse. The signal is reflected from the dense layers of ionized gas that are successively formed along the discharge tube and is shifted according to Doppler effect. The shifted signal is mixed with the incident microwave signal in a mixer and the difference frequency is observed on a spectrum analyzer. The klystron oscillator operates on continuous wave (cw) mode and the signal is frequency modulated by the velocity variations of the wave of stratification so that the system can be considered as a special superheterodyne microwave receiver. The results are of the same order of magnitude as those predicted by an analysis made for the case when an unstriated positive column is externally perturbed in order to artificially produce striations. On the basis of this result and other investigations made under prebreakdown and glow conditions, it can be concluded that (a) there may be inter-relationships among the parameters of striations occurring immediately after ionization is initiated, during the entire period of prebreakdown, and in the positive column, and (b) the phenomena leading to striations start with beginning of ionization and grow with its growth. As an outcome of such conclusions further work is recommended for the investigation of the origin and temporal evolution striations in all phases of an electrical discharge.
Transient Interference Studies of Passively Q-Switched Ruby-Laser Emission
Authors: Flamholz A. , Wolga G. J.
Published: February 2004

An experiment has been performed to examine the time variation of the position and visibility of a transient interference pattern from a single-mode, passively Q-switched ruby laser. A blue shift in the emission frequency as a function of time is observed. The power-dependent rate of frequency shift is 3.4 MHz/nsec·MW. This frequency shift is consistent with the results from previous experiments with a normally spiking ruby laser. A model is proposed which correlates the change in optical length of the ruby to changes in population inversion during emission. Predictions based on the model are in agreement with experimental results and with previous work.
Multiple Sensitization Effects in CaF2:Yb+Nd
Authors: Ewanizky T. F. , Grosse D. W. , Caplan P. J.
Published: February 2004

Transfer of energy between three different ions has been observed in CaF2 doped with Yb and Nd. In CaF2, Nd occurs in only the trivalent state, while Yb forms both divalent and trivalent luminescent centers. Evidence for both Yb2+→Nd3+ and Nd3+→Yb3+ energy transfer is presented. Measurement and analysis of Yb2+ fluorescence decay times in crystals containing 0.1 mole % Yb and 1.0 mole % Nd, gave a figure of 0.62 for nonradiative transfer efficiency at 77°K. Sensitization of Yb3+ by Nd3+ produces strong ir emission, principally at 0.9752μ. An approximate estimate of sensitized increase of Yb3+ emission achieved approaches two orders of magnitude.
Evolution of Water from Alkali Halide Single Crystals
Authors: Green A. K. , Bauer E.
Published: February 2004

The evolution of water upon heating in vacuum of NaCl and KCl single crystals which were exposed to controlled humidities for definite time intervals has been studied. Three types of water evolution are observed: (I) a constantly increasing rate of H2O with increasing temperature attributed to bulk H2O impurity; (II) desorption peaks which are believed to be connected with a NaOH-hydrate (KOH-hydrate) formation; and (III) bursts which are characteristic of crystals exposed to a saturated-solution vapor pressure.
The Stress to Move a Dislocation through a Solid Containing a Pileup of Dislocations
Authors: Smith E.
Published: February 2004

Previous theoretical analyses have shown that an isolated dislocation moving through a solid, subject to a uniform applied shear stress and containing an array of dislocation pileups, is always subject to a positive shear stress. This result has been obtained by assuming that the dislocations within the pileups are smeared into continuous distributions and are unaffected by the stress field of the mobile dislocation. The present paper demonstrates that if this second assumption is relaxed, the conclusion is no longer strictly correct, since regions of negative shear stress exist near the pileup tips.
Proton-Radiation-Induced Blistering of Aluminum
Authors: Milacek Leonard H. , Daniels Raymond D. , Cooley James A.
Published: February 2004

High-purity aluminum exhibited surface pitting and blistering when irradiated with protons in the 10–200 KeV energy range. Pitting occurred during irradiation and is the predominant surface damage at lower proton energies. Blistering occurred at ambient temperature for samples irradiated at energies of 70 KeV or lower. Samples irradiated at energies of 100 KeV or higher exhibited a small amount of spontaneous blistering, but annealing above 200°C was necessary to produce large concentrations of blisters. Pitting and blistering phenomena were studied using optical and electron microscopy. Attention was given to the influence of surface preparation, material purity, microstructure, and cold work on the occurrence and appearance of blistering. These observations were correlated with radiation parameters to delineate the processes responsible for blistering.
Stress State Required for Pyramidal Dislocation Movement in Zinc
Authors: Blish R. C. , Vreeland T.
Published: February 2004

A tension or compression stress in such a direction that basal slip is minimized can produce second-order pyramidal slip bands in zinc single crystals. The stress required to initiate pyramidal dislocation motion is not sensitive to temperature. However, dislocation velocity at a given stress is sensitive to temperature and the very small dislocation velocity at low temperatures has lead to an erroneous estimate of a ``starting stress'' for pyramidal dislocations. Dislocation velocity at a constant temperature was found to be a function of the magnitude, but not the sense of the resolved shear stress.
Analytical Solutions to Eddy-Current Probe-Coil Problems
Authors: Dodd C. V. , Deeds W. E.
Published: February 2004

Solutions have been obtained for axially symmetric eddy-current problems in two configurations of wide applicability. In both cases, the eddy currents are assumed to be produced by a circular coil of rectangular cross section, driven by a constant amplitude alternating current. One solution is for a coil above a semi-infinite conducting slab with a plane surface, covered with a uniform layer of another conductor. This solution includes the special cases of a coil above a single infinite plane conductor or above a sheet of finite thickness, as well as the case of one metal clad on another. The other solution is for a coil surrounding an infinitely long circular conducting rod with a uniformly thick coating of another conductor. This includes the special cases of a coil around a conducting tube or rod, as well as one metal clad on a rod of another metal. The solutions are in the form of integrals of first-order Bessel functions giving the vector potential, from which the other electromagnetic quantities of interest can be obtained. The coil impedance has been calculated for the case of a coil above a two-conductor plane. The agreement between the calculated and experimental values is excellent.
Determination of the Electromechanical Coupling Coefficient of Thin-Film Cadmium Sulphide
Authors: Bahr A. J. , Court Ian N.
Published: February 2004

The use of transducer input admittance data for deriving the value of the electromechanical coupling coefficient of thin piezoelectric films is described. The results of admittance measurements made in the uhf frequency range have shown that partially oriented cadmium sulphide (CdS) films may have laterally clamped thickness longitudinal-mode coupling coefficients as large as 0.15±0.01. Within the experimental accuracy this is the same as the bulk value. The admittance measurements have also shown the presence of a series resistance in the transducer. It is shown that this resistance is sufficiently large to account for most of the loss of a tuned and matched transducer.
The Influence of Stoichiometric Defects and Foreign Atom Additions on Steady-State Creep in Lead Sulfide Single Crystals
Authors: Seltzer Martin S.
Published: February 2004

The effects of stoichiometric defects and foreign atom additions on steady-state creep of lead sulfide single crystals have been investigated in the temperature range 650°–700°C. Creep rates for undoped PbS increase with decreasing PS21/2 in the region where p-type sulfur excess crystals are obtained and then decrease with decreasing PS2−1/2 in the region where n-type, lead excess crystals are produced. Under the lowest sulfur pressures employed, creep rates are independent of composition. The maximum creep rate for a given temperature occurs at the sulfur pressure corresponding to stoichiometric PbS. Creep rates for PbS with ½ mole % Bi2S3 increase with decreasing PS21/4, and are independent of sulfur pressure for values below 10−4 atm, whereas creep rates for crystals doped with ½ or 1/20 mole % Ag2S decrease with decreasing PS2−1/4 and are independent of sulfur pressure below 10−3 atm. It is suggested that several different atomic defects control diffusion-limited creep in PbS, the predominant defect depending on compound composition and dopant concentration.
Anisotropy in the Electrical Resistivity of Vanadium Dioxide Single Crystals
Authors: Everhart C. R. , MacChesney J. B.
Published: February 2004

Electrical resistivity of vanadium dioxide single crystals undoped and iron-doped was determined as a function of temperature around the transition temperature in the a monoclinic and a perpendicular directions. Results of this experiment indicated a greater resistivity in the a perpendicular direction than in the a parallel direction for both the doped and the undoped crystals. The appearance of anisotropy is in agreement with Goodenough's explanation for the mechanism of electrical conductivity in this phase.
Bremsstrahlung Produced in Thick Aluminum and Iron Targets by 0.5 to 2.8 MeV Electrons
Authors: Dance W. E. , Rester D. H. , Farmer B. J. , Johnson J. H. , Baggerly L. L.
Published: February 2004

The bremsstrahlung produced by electrons with incident energies of 0.5, 1.0, 20., and 2.8 MeV bombarding aluminum and iron targets of sufficient thickness to stop the electrons, has been measured. Spectral distributions of external bremsstrahlung intensity per unit solid angle, at representative emission angles ranging from 0 to 150 deg are presented graphically. Spectral distributions of radiation energy integrated over all angles and integrated over only the forward hemisphere are presented. Plots of total intensity as a function of angle show the degree of peaking in the forward direction with increasing electron energy. Total external radiation energy is found to vary as the square of the bombarding electron energy T0 over this energy range. The external efficiency for bremsstrahlung production is found to be 4.8×10−3 T0 for Al and 9.2×10−3 T0 for Fe, where T0 is in MeV.
Introduction Rates of Electrically Active Defects in n- and p-Type Silicon by Electron and Neutron Irradiation
Authors: Stein H. J. , Gereth R.
Published: February 2004

Carrier-removal rates produced in n- and p-type silicon by 1.7 MeV electron and reactor neutron irradiations were measured at 270°K on samples with resistivities between 0.1 and 50 Ω·cm. The measurements were performed under well-defined conditions on test samples selected from float-zone, quartz-crucible, Dash, and Lopex silicon crystals, and from epitaxial silicon slices. Most of the carrier-removal rates were determined from the initial 10% decrease in conductivity. Carrier-removal rates also were determined in heavily irradiated samples of float-zone and crucible-grown silicon. The electron-produced carrier-removed rate is strongly crystal growth dependent in n-type silicon, and the smallest removal rate is observed in quartz-crucible-grown material. The hole removal rate in p-type silicon under electron irradiation exhibits only weak crystal-growth dependence which becomes more pronounced during subsequent isochronal annealing. After 370°K annealing of both n- and p-type 10 Ω·cm materials, the smallest carrier-removal rate is observed in p-type Lopex silicon. Carrier-removal rates decrease with increasing electron fluence in both n- and p-type silicon. Neutron-produced carrier removal at 270°K is only weakly dependent upon crystal-growth method and conductivity type. Crystal-growth and conductivity-type dependence become significant, however, during subsequent isochronal annealing. After annealing to 370°K, the carrier removal remaining in n-type silicon is smallest for the crucible grown material, and the hole removal remaining in p-type silicon is smallest for the Lopex material. Carrier-removal rates increase with increasing carrier concentration and decrease with increasing neutron fluence in both n- and p-type silicon.
Growth of Diamond Seed Crystals by Vapor Deposition
Authors: Angus John C. , Will Herbert A. , Stanko Wayne S.
Published: February 2004

Carbon was deposited on virgin, natural diamond powder from methane gas at 1050°C and 0.3 Torr. The deposits were identified as new diamond by chemical analysis, chemical etching, density measurements, x-ray and electron diffraction, microwave absorption, electron spin resonance, and visual observations. The crystalline quality of the new diamond layers has not been established; it cound range from polycrystalline material with a large number of defects to true epitaxial layers.
Use of the Faraday Effect to Determine Electron Concentrations and Concentration Profiles in n-GaAs
Authors: Alfano R. R. , Baird D. H.
Published: February 2004

The use of the Faraday rotation for determining the electron concentration and the electron concentration profile in n-GaAs with n=1015 to 1018 cm−3 has been investigated. It is shown that correction can be made for the errors in the measurement introduced by multiple reflections and that accurate subtraction of the interband contribution to the total rotation will yield a well-defined value of the free-carrier contribution.
A Simple Liquid-Immersed Dielectric Motor
Authors: Secker P. E. , Scialom I. N.
Published: February 2004

Measurements have been made on a simple motor consisting of a cylindrical dielectric rotor supported between two plane electrodes and immersed in a semi-insulating liquid. The experimental speed-voltage characteristics are in good general agreement with a theory in which it is postulated that free charge attaches to the rotor surface, as a result of bipolar conduction in the liquid. Following rotor motion, the axes of the electric field and the charge maxima are no longer coincident and there is a net driving torque. The no load operating speed is determined by the balance of this driving torque and the torque due to viscous drag.
The Effect of Electrode Temperature on Vacuum Electrical Breakdown between Plane-Parallel Copper Electrodes
Authors: Davies D. Kenneth , Biondi Manfred A.
Published: February 2004

Combined measurements of current-voltage, prebreakdown characteristics, and breakdown voltage have been made for plane-parallel, copper electrodes in ultrahigh vacuum as a function of both cathode initial temperature and anode initial temperature. These measurements have been carried out for an electrode separation of 0.1 cm over the temperature range from 313° to 913°K. From the experimental data the temperatures of the hottest point of the cathode surface, (TC)s, and of the anode surface, (TA)s, at breakdown have been determined as a function of electrode initial temperature. Over the whole range of the investigation it is found that (TA)s is greater than (TC)s. Moreover, the calculated values of (TA)s at breakdown are essentially independent of anode initial temperature and have a mean value of (1100±150)°K. In contrast, the values of (TC)s at breakdown increase with increasing values of cathode initial temperature. The results suggest that a thermal instability of a point on the anode surface leads to breakdown. A model for the breakdown mechanism is presented in terms of electron avalanche amplification of current in copper vapor. The vapor is generated by the detachment of an anode macroparticle and its subsequent evaporation during its transit to the cathode. The prebreakdown current plays an important role in the breakdown mechanism since it causes the initial thermal instability at the anode surface and, in addition, provides the necessary source of bombardment for evaporating the macroparticle.
Electromagnetic Scattering by a Moving Small Particle
Authors: Shiozawa T.
Published: February 2004

The problem of scattering of a plane electromagnetic wave by a small particle which is moving uniformly in vacuum is investigated. On the basis of the covariance of Maxwell's equations and the principle of phase invariance, the scattered field and the scattering cross section are obtained for a small particle with spherical symmetry which is composed of an arbitrary isotropic material. Then the general scattering formula is applied to the following four cases: (a) a dielectric or permeable particle, (b) a perfectly conducting particle, (c) a charged particle, and (d) a plasma particle. It is found that the scattered radiation is concentrated, in general, in the direction of motion. In addition, it is shown that the scattering cross section increases monotonically with the increase of the velocity when a particle is moving toward the incident wave, while it decreases monotonically when it is moving away from the incident wave.
Surface Effects on Metal-Silicon Contacts
Authors: Yu A. Y. C. , Snow E. H.
Published: February 2004

Surface effects on metal-silicon contacts have been studied in detail using gate-controlled Schottky-barrier diode structures. The ``excess'' forward and reverse currents at small and moderate bases, respectively, and low breakdown voltages usually associated with metal-silicon contacts are clearly shown to be due to high fields near the corner region when the surface is accumulated. These currents can be eliminated and breakdown voltage increased by depleting or inverting the surface. By studying the diode characteristics when the surface is inverted, it is shown that the generation current in the depletion region often constitutes a significant part of the total reverse current and cannot in general be neglected.
Electrical Resistivity and Shear Modulus of Copper during Cyclic Stressing
Authors: Dawson H. I.
Published: February 2004

Available data on the production of electrical resistivity due to point defects in high-purity copper during fatigue and unidirectional deformation are analyzed. Per unit of deformation energy, fewer point defects are produced during fatigue than during unidirectional deformation, except perhaps during the first few cycles of cyclic stressing. A qualitative relation that appears to exist between changes in electrical resistivity and shear modulus during cyclic stressing is discussed.
Third-Order Elastic Constants of Single-Crystal and Polycrystalline Columbium
Authors: Graham L. J. , Nadler H. , Chang Roger
Published: February 2004

The second-order and third-order elastic constants for both single-crystal and polycrystalline columbium were determined at 298°K using an ultrasonic phase comparison method. It is shown that any dislocation contribution to the measurements is negligible with respect to other uncertainties. The third-order elastic constants (Brugger convention) in units of 1012 dyn/cm2 are c111=−25.64±0.25;c144=−3.43±0.10;ν1=−4.8±1.2;c112=−11.40±0.25;c166=−1.677±0.05;ν2=−3.70±0.2;c123=−4.67±0.25;c456=+1.366±0.05;ν3=+0.75±0.05.The Grüneisen parameter calculated from these values is 1.511±0.026 for the single crystal, and 1.546±0.092 for the polycrystal, in good agreement with the value 1.52 calculated from bulk-property measurements. The polycrystalline third-order elastic constants are in very good agreement with those calculated from the single-crystal values by the method of Chang.
Crystal Growth and Electro-optic Effect of Some Double Sulfates with the Langbeinite Structure
Authors: Emmenegger Franzpeter , Nitsche Rudolf , Miller Arthur
Published: February 2004

Single crystals of several isomorphs of the mineral langbeinite, K2Mg2(SO4)3, space group T4, were prepared from aqueous solutions and from the melt. The electro-optic powers, n03r41 of (NH4)2Mn2(SO4)3, K2Mn2(SO4)3, Rb2Mn2(SO4)3, Tl2Mn2(SO4)3 and K2Ni2(SO4)3 were found respectively to be 0.7, 8.6, 7.7, 12.4, and 4.9×10−10 cm/V. Refractive indices and dielectric constants were also measured. By analysis of the observed data it was found possible to partially resolve the over-all electro-optic effect into single ion contributions.
Shear-Stress Field of a Simple Dislocation Cell
Authors: Duncan T. R. , Kuhlmann-Wilsdorf Doris
Published: February 2004

The shear-stress distribution due to a particular example of the simplest, two-dimensional dislocation array, representing a cell of material misoriented with respect to its surroundings, was calculated numerically. The results are found to be virtually independent of the size of the cell, provided its shape and the magnitude of its angular misorientation are kept constant. For cells of same size and shape the stresses are proportional to the magnitude of the angular misorientation, i.e., inversely proportional to the dislocation spacing. In the example studied, the long-range stresses are always less intense than the extrema of the short-range stresses, meaning that the subboundaries, but not the cell interior, could serve as obstacles against glide dislocation motion. The direction of the long-range stresses is such as to attract from the surroundings dislocations which would reduce the relative misorientation of the cells, so as to clear the cell interior of dislocations.
Charged-Particle Motion in Large-Amplitude Electromagnetic Fields
Authors: Jory H. R. , Trivelpiece A. W.
Published: February 2004

The relativistic motion of a charged particle in large amplitude, inhomogeneous electromagnetic fields is studied for several situations. This study involved the numerical integration of the equations of motion including the relativistic mass correction and the nonlinear rf v×B force term. The cases studied include particle motion in linearly and circularly polarized, homogeneous plane waves with a homogeneous steady magnetic field parallel to the direction of propagation; particle motion in linearly and circularly polarized TE-11 modes in waveguides of circular cross section immersed in a uniform steady axial magnetic field; and particle motion in cavity resonators of circular cross section (TE-111 mode) immersed in a nonuniform steady axial magnetic field. This study is concerned with the maximum energy gains possible in the above situations with field amplitudes appropriate to high-power microwave experiments. To verify the features of the particle motion as predicted in the numerical study, and to investigate effects which could not be easily included in the analysis, such as space charge from the electron beams, beam-induced cavity fields, and ionization of residual gas in a cavity resonator, certain experiments were performed. These involved the injection of 1–100-mA electron beams at 100–1000 V on the axis of circular cross-section cavity resonators (10 GHz and 1.0 GHz) immersed in a steady axial magnetic field. With pulsed operation, an energy increase of 460 keV was obtained for a drive power of 46 kW at an over-all efficiency of acceleration of approximately 10%. Higher-efficiency pulsed operation and continuous operation at lower power levels were also investigated experimentally.
Linewidth and Relaxation Processes for the Main Resonance in the Spin-Wave Spectra of Ni–Fe Alloy Films
Authors: Patton Carl E.
Published: February 2004

Measurements of the position and linewidth of the main resonance in the spin-wave spectra of 80% Ni-20% Fe evaporated films 150 to 3200 Å thick at frequencies from 0.8 to 4.0 GHz, at room temperature and with the static magnetic field perpendicular to the film plane have been performed. The center field for resonance was independent of thickness and consistent with the Kittel resonance condition for the uniform precession. The linewidth was about 30 Oe (measured as the field separation of inflection points on the absorption curve), independent of film thickness and frequency. The linewidth data have been compared to previous data for resonance with the static field parallel to the film plane and interpreted in terms of relaxation processes for the uniform precession. In general, frequency-swept linewidths, not field-swept linewidths, are proportional to the relaxation rate and are the quantities which should be compared. The frequency-swept linewidth for perpendicular resonance is equal to that obtained for parallel resonance in films thinner than 500 Å. This result indicates that two-magnon scattering between the uniform precession mode and spin-wave states for which the exchange energy term is large (wavenumber k appreciably different from zero) does not contribute to the perpendicular resonance linewidth and is the origin of the linewidth increase with thickness for parallel resonance. It appears that scattering to states with k≈0 and exchange conductivity broadening are the most reasonable sources for the residual 30 Oe linewidth.
Observation of Resistive Instabilities in a Toroidal Plasma
Authors: Stuart K. , Levi E.
Published: February 2004

An experiment is described in which resistive instabilities have been observed. Diagnostics of a hydrogen toroidal plasma indicate that a current-carrying plasma sheet breaks up into separate filaments. Experimental data for three distinct filament configurations agree well with the theoretical predictions.
Electrical Conductance of Thin Ultrahigh-Vacuum-Evaporated Films of Tungsten on Glass
Authors: Dobson P. J. , Hopkins B. J.
Published: February 2004

Electrical conductance measurements have been made on thin tungsten films deposited onto Pyrex glass substrates cooled to 90°K under ultrahigh-vacuum conditions. The variation of the conductance with temperature indicated that the films were discontinuous for average thicknesses less than about 30 Å. This structure was confirmed by electron micrographs of the films after removal from the vacuum system. Irreversible changes in the conductance were found to take place when the low-temperature-deposited films were annealed at 300°K. The direction of the changes depended on the average film thicknesses. Theories of conduction based on an activated tunneling process are inadequate to explain these changes, but a model based on internal thermoinic emission provides a qualitative explanation. It is suggested that the conduction current contains contributions from a space-charge-limited current through the substrate as well as that arising from the thermionic emission process. The experimentally observed voltage dependence of the conductance appears to confirm this suggestion. Irreversible changes in the conductance could also be brought about both by exposure of the ultrahigh-vacuum-deposited films to a gas pressure of 10−8 Torr and by the application of high voltages at 300°K.
Restrike Mechanisms of Exploding Wire Discharges
Authors: Vlastós Antonios E.
Published: February 2004

The development of the early stages of restrike channels initiated by electrically exploded thin wires was studied, using high-speed Kerr-cell and rotating-mirror streak photographic techniques. The experiments were performed mainly with constantan and copper wires (length: 13.8 cm, diameter: 0.005 cm). Complementary measurements were also made on five lengths between 1.6 and 13.8 cm at voltages up to 23 kV. The results show that at low voltages the restrike is always initiated at the exterior of the exploded wire. At higher voltages, above a critical voltage, the restrike is initiated either at the exterior or in the interior of the exploded wire. The majority of the restrikes are initiated in the interior. Restrikes initiated at the exterior of the exploded wire always have much shorter dwell times than those initiated in the interior and a good dwell-time reproducibility. During the dwell-time which precedes these restrikes, luminous dots appear at the surface of the wire. The dots are distributed helicoidally along the whole wire length. The presence of these dots may indicate an intense local ionization on the wire surface due to the emission of thermal electrons from the wire material. The ionization increases to the point at which a thin helicoidal channel is built up near the surface and along the whole length of the exploded wire. The restrike starts and develops in this channel until it loses its form through instability. For restrikes initiated in the interior of the exploded wire, no local ionization was observed at the surface of the wire during the dwell time. This may have been due to the rapid vaporization of the wire material. During the dwell time the exploded wire shows a diffuse low luminosity, which increases when ionization by impact is initiated in the interior of the wire. The luminosity of the wire remains diffuse until the ionized medium contracts and the restrike starts in a very narrow channel near the axis of the wire. The channel expands with a very high velocity towards the inner shell of the exploded wire. The initial phase of the channel shows an helicoidal form. The channel tends to be straight when its diameter increases. The type of restrike which follows the wire explosion seems to be dictated by the vaporization rate of the wire material.
A Diagonal Sum Rule Concerning Demagnetization Tensors in Composite Bodies
Authors: Iwata Takao
Published: February 2004

Demagnetization tensors are introduced for the description of demagnetizing fields inside a system which is composed of parts with different intensity of magnetization. It is shown that the diagonal sum of the tensor is constant and given by a combination of magnetizations and volume fractions of component parts. This rule is conveniently used for the calculation of the magnetostatic energy of samples of some complicated geometry. The inner demagnetization factor of internally isotropic bodies is also discussed on the basis of the rule.
Intensities of 2288 Å and 3261 Å Radiation from Low-Pressure Cadmium Rare-Gas Discharges
Authors: Springer R. H. , Barnes B. T.
Published: February 2004

The uv power radiated, at 3261 Å and 2288 Å, and the input power to the positive column of Cd-1.6-Torr Ar and Cd-5-Torr Ne discharges are presented for both ac and dc currents. The maximum 3261-Å radiation output occurs at a Cd pressure in the range from 5 to 10 mTorr, the same pressure range as found for Hg in the Hg rare-gas low-pressure discharge. The Cd discharge is compared with the well-known Hg-3-Torr Ar discharge, using a simplified model for the discharge. It is believed that the Cd-1.6-Torr Ar data presented here are near the optimum uv production efficiency for the Cd rare-gas discharge.
Precipitates Formed by High-Concentration Phosphorus Diffusion in Silicon
Authors: Jaccodine R. J.
Published: February 2004

In high-concentration phosphorus diffusion (∼1020 atoms/cc) observations have been made of small (<200 Å) precipitate particles and dislocation loops in the region immediately adjacent to the surface. These particles occur in the high-concentration flattened portion of the concentration vs depth profile curves. Their presence is an assigned cause for the discrepancy between total and electrically active phosphorus. Electron microscopic techniques were used to identify the defects as ``interstitial.'' Contrast effects similar to those expected of a spherically symmetrical coherent precipitate were observed. Strains in the precipitates were found in the range ε=0.001→0.004 and seemed unaffected by low-temperature heat treatments (at 650°C).
Effect of ac Impedance on dc Voltage-Current Characteristics of Superconductor Weak-Link Junctions
Authors: McCumber D. E.
Published: February 2004

Because the Josephson pair current in a weak-link superconductor junction is a nonlinear parametric function of junction voltage, the ac impedance seen by the junction influences both the response time to changes in bias and the dc voltage-current characteristics. The first effect is obvious; the second, considered here, has not been generally recognized. Both are relevant to device design. Two special cases which illustrate the basic principles involved are worked out in detail; they correspond, respectively, to ac capacitive and inductive loading. The results partly explain differences in the dc voltage-current characteristics of plane-parallel and point-contact junctions.
Quartz-Crystal Microbalance Technique for the Preparation of Alkali-Antimonide Photocathodes
Authors: Florio John V.
Published: February 2004

A quartz-crystal microbalance technique has been developed which measures the chemical composition of an alkali-antimonide film during photocathode formation at the normal photocathode processing temperatures. It is possible to measure continuously and simultaneously the chemical composition, photoelectric emission, resistance, and optical transmission of the alkali-antimonide during photocathode formation. A thermal ionization source, which acts as a relative partial pressure indicator, yields additional data on the kinetics of the reaction mechanisms. Results are reported for the Cs–Sb and the K–Sb systems. The data indicate the importance of the experimental parameters (antimony film thickness, temperature, and alkali-metal. vapor pressure) upon the reaction rates. Correlation of electro-optical properties with composition depends on a knowledge of these parameters.
The Scattering of Laser Light by Ruby Crystals
Authors: Powell Richard C.
Published: February 2004

The use of a laser as a light source for studying light scattering from solids is discussed and results are presented of an investigation of the scattering of laser light by ruby crystals. Both single particle and bulk scattering were studied as a function of crystal growth direction, annealing, boule morphology, polarization, chromium concentration, γ irradiation, and temperature. Randomly distributed scatterers, decorated small-angle grain boundaries, and gross scattering regions were all observed by laser ultramicroscopy. The intensity of the scattered light was monitored vs scattering angle and crystal orientation. It appears from the results of these bulk-scattering measurements that the scattering can be attributed to regions in the crystals which lie in specific planes and are oriented in specific directions. There is some indication that the individual scattering units may consist of impurity precipitates.
Evidence for the Small Polaron as the Charge Carrier in Glasses Containing Transition Metal Oxides
Authors: Schmid A. P.
Published: February 2004

Low-temperature conductivity measurements on glasses containing transition-metal oxides TiO2 and V2O5 reveal a sharp break in the slope of the dependence of log conductivity upon reciprocal temperature. At low temperatures, the slope corresponds to a low-activation-energy process (0–0.2 eV) while at high temperatures the slope of the conductivity is that appropriate to a much higher activation energy (0.4–1 eV). Typical data obtained on some samples of V2O5–P2O5 glass are shown. Arguments for the small polaron as the charge carrier in such glasses are presented as well as a brief nonmathematical review of the theory of conduction by small polarons. A comparison with the previous Theory of Bridging and Nonbridging Oxygen Ratios is given. Finally, some difficulties with the suggested small polaron model are pointed out and some speculations which may avoid or explain these difficulties are made.
Effect of Inductive and Capacitive Walls on the Diocotron Instability
Authors: Fisher Shalom , Neil V. Kelvin , Briggs Richard J.
Published: February 2004

The influence of inductive and capacitive walls on the diocotron effect in a cylindrical charge layer of arbitrary thickness and infinite length is analyzed by means of a hydromagnetic model. The density in the layer is such that ωp2/ωc2≪1 holds, where ωp is the plasma frequency and ωc the cyclotron frequency. A dispersion relation is derived which relates the oscillation frequency and wavenumber to the wall impedances and the geometric parameters of the system. Stability criteria are also derived.
Temperature Dependence of the Field-Effect Conductance in Thin Polycrystalline CdS Films
Authors: Neugebauer C. A.
Published: February 2004

The field-effect conductance and the capacitance-voltage characteristics of thin-film, polycrystalline CdS–SiO2–Al field-effect structures were measured as a function of temperature in the range from 100° to −50°C, and mechanical stress because of differential thermal expansion. It was concluded that (1) the channel mobility varies exponentially with temperature with an activation energy of the order of 0.06 eV, which corresponds to the height of the intercrystalline barriers at the grain boundaries, (2) the channel mobility increases with the induced charge-carrier density, (3) the flat-band voltage varies linearly with temperature at a rate of the order of 0.01 V/deg, which corresponds to an interface state density of the order of 1013 cm−2 eV−1 in the bandgap in the vicinity of the conduction band, (4) the flat-bond voltage increases with compressive stress at a rate as high as several hundred volts per percent strain and (5) contact barriers between the source and drain electrodes and the surface channel become significant at temperatures below −25°C.
A Cesium MHD Arc Jet
Authors: Blackstock A. W. , Fradkin D. B. , Roehling D. J. , Stratton T. F.
Published: February 2004

A cesium-fueled magnetohydrodynamic arc jet was operated between 4 and 12 kW at magnetic field strengths up to 1000 G. Electrostatic probe, spectroscopic, and microwave measurements were made on the exhaust beam. Beam momentum was determined from the deflection of a downstream sieve. The magnitude and position of Hall currents were determined using magnetic-loop pickup coils. The over-all arc voltage is a linear function of applied axial magnetic-field strength. The thrust is a linear function of the product of the arc current and applied axial magnetic-field strength, and is of a magnitude too great to be produced by the measured Hall currents. A partial theory is developed that describes the functional dependence of the arc voltage and thrust. Data are presented that show mass entrainment was present and that when the arc is operated with mass entrainment the exhaust velocity is predicted by the Alfvén ``critical velocity.''
A Mechanism to Account for Observed Morphological Changes in Discontinuous Gold Films following Deposition
Authors: Phillips W. B. , Desloge E. A. , Skofronick J. G.
Published: February 2004

Experimental results on the behavior of discontinuous metal films on amorphous substrates of carbon and silicon monoxide are extended and reviewed. These results are discussed in terms of possible mechanisms to account for the experimental behavior. The mechanism of island motion with subsequent coalescence is selected, for it agrees best with the observed results. This mechanism is used as a basis for a calculation in which the behavior of the islands is treated by statistical methods. Solutions predict the time and temperature dependence for the mean radius and dispersion of the island distribution. Comparison to experiment is favorable and yields a quantity which corresponds to the binding energy of gold islands to carbon or to silicon monoxide substrates. For the gold-carbon case, the binding energy is 1.29±0.04 eV, while the gold-silicon monoxide case yields 1.52±0.23 eV.
Dynamic Observations of the Course of a Shock-Induced Polymorphic Phase Transition in Antimony
Authors: Breed B. R. , Venable Douglas
Published: February 2004

Flash radiographs have been taken which clearly illustrate the formation of both the first and second plastic waves in shocked Sb. The first plastic wave, whose initial pressure and speed are 115 kbar and 3.25 mm/μsec, respectively, is formed in a time much less than 0.2 μsec, the time exposure of the radiograph. However, the second wave builds up gradually to a steady state where the pressure and speed are 135 kbar and 2.9 mm/μsec. At an initial specimen temperature of about 25°C, the time required to complete the phase transformation behind the first plastic wave is determined to be 2–3 μsec.
A Low-Frequency Drift Instability in a Semiconductor Electron-Hole Plasma
Authors: Gueret P.
Published: February 2004

A theory is presented which describes a wave instability occurring in a semiconductor electron-hole plasma when this plasma drifts at an angle to the direction of propagation of the wave. This instability is of the collision-dominated type and is therefore typical of semiconductors. The coupling mechanism by which energy is fed into the growing oscillation is shown to be the Lorentz force between the drifting carriers and the wave magnetic field. The theory is applied to p-type InSb at 77°K and it is found that the growth time of the instability is comparable to the period of the oscillation (0.2 μsec typically), so that the instability is relatively weak. A suggestion is made to relate the present theory to some experimental observations of electron-hole plasma instabilities in p-InSb.
Electron-Mirror Microscopy Study of BaTiO3 Surface Layers
Authors: English F. L.
Published: February 2004

Electron-mirror photomicrographs of the domain structure and topography of the surface of BaTiO3 single crystals are compared to those obtained by optical-transmission microscopy. The results differentiate the domain structure of the bulk crystal from the domain structure of the surface layer and, in addition, indicate a maximum thickness of 0.7 μ for the surface layer.
Recoil of Fission Products. II. In Heterogeneous Carbon Structures
Authors: Evans R. B. , Rutherford J. L. , Perez R. B.
Published: February 2004

A previously reported investigation of the recoil behavior of ``light'' and ``heavy'' fission fragments in a uniform pyrocarbon structure has been extended to include five additional structures with porosities ranging from 5 to 23 vol%. As before, fragments were induced to penetrate target structures as nearly monoenergetic beams with random r-space directions. Data were collected and arranged to produce plots of fractional activities remaining at various grinding levels along the z coordinate normal to thin (neutron-activated) 235U source planes. Such plots are integrated forms of the z-space probability-density functions (called distribution functions); these, in turn, are specified by associated r-space functions. An important facet of these studies was the development of integrated z-space equations that would exhibit good agreement with data for porous structures. Selection of realistic r-space functions was therefore mandatory. Application of the proper integrated equations permitted evaluation of several sets of range values that were nearly identical and independent of the structures involved. A compact expression for all results in revised form is log10(R′)i=0.478 log10(E0)i−0.465,where R′ (mg/cm2) is the range of any ith fragment with an initial fission energy E0 (MeV). Although the range values for homogeneous and heterogeneous materials are the same, applicable distribution functions varied in form because of variations in pore-size characteristics from one structure to the next. In some cases, the pore sizes were equal to or greater than the range. This resulted in large straggling effects and asymmetric r-space distributions; furthermore, the R′ in the above expression corresponds to the most probable distance of r-space travel. Range results for only two of the six structures investigated are correlated on the basis of a normal (or Gaussian) r-space distribution, where the average and most probable range are synonymous. Results for all other structures are correlated by using general forms of the Maxwell distribution. In these cases, the average distance traveled is always greater than R′ (to an extent depending on the skewness of the distribution function selected for data correlation).
Anisotropy of Magnetization and Magnetostriction of Single Crystals of Tb, Dy, Er, and Gd in Pulsed Fields up to 150 kOe
Authors: Belov K. P. , Levitin R. Z. , Ponomarjov B. K.
Published: February 2004

The uniaxial anisotropy and magnetostriction along the hard direction of single crystals of Gd, Tb, Dy, and Er have been measured in pulsed fields up to 150 kOe. The magnetic anisotropy and magnetostriction are very large for Tb, Dy, and Er; with effective anisotropy fields considerably greater than 150 kOe. In Gd the magnetic anisotropy and magnetostriction are two orders of magnitude smaller.
Predicting the Critical Supersaturation for Homogeneous Nucleation of Vapor Condensation
Authors: Abraham Farid F.
Published: February 2004

We propose a phenomenological theory for determining the critical supersaturation for homogeneous nucleation of a given vapor. The method is illustrated by predicting the critical supersaturations of water, ethanol, methanol, and hexane as a function of temperature. These predictions are shown to be in good quantitative agreement with experiment.