bluuebunny/crossref_metadata_2025 huggingface dataset:
Dislocation Damping due to Kink Motion
Authors: Suzuki Tetsuro , Elbaum Charles
Published: April 2005

The ultrasonic attenuation and velocity change that result from the damping due to motion of dislocation kinks have been calculated on the following assumptions: (1) the frequency of thermal creation of kinks is smaller than the frequency of the applied stress; (2) the frequency of thermal motion of the kinks is larger than the frequency of the applied stress.

The characteristics of the attenuation calculated from the above assumptions differ from those of the string model for dislocation damping as follows. First, the resonance frequency depends on kink spacings and on the distance between pinning points on the dislocation. Second, for strain amplitude in excess of a critical value given in terms of kink spacings and the distance between pinning points, the attenuation decreases with increasing strain amplitude.
Analytical Formulation of Incremental Electrical Conductivity in Semiconductors arising from an Accumulation Space-Charge Layer
Authors: Lee Vin-Jang , Mason Donald R.
Published: April 2005

Analytic expressions are derived which relate the incremental electrical conductivity in an accumulation layer on a semiconductor to the concentration of surface ions. The theory is checked both by comparing the predicted results with published graphs which were obtained by numerical integrations, and by evaluating three separate sets of experimental data on different semiconducting materials. The data of Weller and Voltz for the effect of oxygen adsorbed on Cr2O3 do not fit the assumptions of the theory, since their particles are too small. The data of Smith for oxygen adsorbed on CuO, and the data of Molinari et al. for hydrogen on ZnO indicate that the observed trends are all in the proper direction and of the proper magnitude to support this work, but they are not of sufficient precision to support these derivations conclusively. Although a definitive quantitative experimental check remains to be done, the reasonableness of the derivation has been established.
InSb Diodes under Controlled Surface Conditions
Authors: Maffitt K. N. , Mueller R. K.
Published: April 2005

The surface of anodized InSb cooled in the dark can be changed from n type over a conductance minimum to p type by controlled illumination. The characteristics of alloyed diodes on n- and p-type base material were studied at 78°K under controlled surface conditions. Under optimal surface conditions the voltage-current characteristic follows the relation predicted by Sah et al. for space-charge generation currents. An effective minority carrier lifetime of 2.4×10−9 for n-type and 2.8×10−9 for p-type InSb is required to fit the data. An anomalous capacitance is observed only if an inversion layer exists at the surface.
Disordering of Defects in Single Crystals of Zinc Sulfide
Authors: Chadderton L. T. , Fitzgerald A. G. , Yoffe A. D.
Published: April 2005

Stacking faults are observed in zinc sulfide (wurtzite) single crystals on basal planes (0001) and on prismatic planes (112̄0) and (12̄10) to the growth surface.

The degradation of these stacking faults in different environments is described. The loop contrast observed to form at stacking faults on prismatic planes when exposed to high electron beam intensities in the electron microscope is explained by a thermally activated mass-transport mechanism. Migration of vacancies or atoms occurs depending on whether the stacking fault is extrinsic or intrinsic, respectively. Subjecting crystals to high pressures (about 60 kbar) results in an increase in the number of basal plane stacking faults. This is equivalent to a gradual phase change occurring over several atomic planes. Thermal etch figures observed by transmission electron microscopy in crystals annealed at 700° and 900°C are identified as a crystallographic polarity effect.
Alternating Current Resistance of Nonideal Superconductors
Authors: Zar Jacob L.
Published: April 2005

A direct electrical measurement is made of the resistance of nonideal superconductors at power and audio frequencies, at 4.2°K and in zero applied field. The resistance of short samples of several Nb-Zr and Mo-Re alloys is found to be independent of the composition and of impressed current. The resistivity is found to depend on f0.5 above 1000 cps and on f1.7 for frequencies f below 500 cps. The resistance is also independent of wire diameter for some sizes near 0.25 mm. Three explanations are considered to account for resistance at low frequencies. Relaxation time effects are ruled out by the observed frequency dependence at high frequencies. Inductive coupling between the magnetic fields of the normal and the superconducting currents leads to a resistance effect six orders of magnitude lower than the observed ones, and an f2.0 dependence. Trapping of flux within the superconductor leads to an upper bound for the resistance that agrees with the experimental results in being independent of the wire diameter and the current, and giving the approximately correct resistance values, although an f1.0 dependence. The measurements suggest that the ac resistance may result from eddy currents induced in normal regions near the surface of heavily cold-worked superconductors.
Pulse Propagation in a Laser Amplifier
Authors: Wittke James P. , Warter Peter J.
Published: April 2005

Pulse propagation in maser-type traveling-wave amplifiers with a homogeneously broadened transition is treated by a formalism analogous to the Bloch equations. Phenomenological dephasing (T2) and recovery (T1) times are defined, and a linear (nonsaturable) loss mechanism is included. In the numerical calculations, only the case of negligible excitation during the time it takes a pulse to pass is considered. When pulses are allowed to grow until the amplifier is ``saturated,'' steady-state pulses having a unique shape and intensity independent of the initial pulse are found. The parameters of these steady-state pulses depend only on the ratio of the linear loss and gain coefficients. Steady-state pulses have a peak intensity that decreases monotonically from infinity to zero as the linear loss coefficient varies from zero to the gain coefficient, while the pulse width correspondingly varies from zero to infinity, and the pulse energy varies from a finite value to zero. Steady-state pulses propogate at a velocity less than that of the small signal velocity in the medium.
Sputtering of Polycrystalline Copper and Silver by 30–170 keV Argon Ions
Authors: Ramer C. E. , Narasimham Musti A. , Reynolds H. K. , Allred J. C.
Published: April 2005

Polycrystalline copper and silver have been sputtered by 30–170 keV singly ionized argon at various beam angles, and total yields (atoms/ion) have been measured as a function of energy and incident angle. Angular distributions of sputtered material about the target normal indicate a distribution approximately proportional to the cosine of the angle of emission, but with more material collected in the normal direction than for a strict cosine distribution. No significant variation of angular distribution with ion energy or with sputtering beam angle was observed. The yield appears to be independent of pressure, collector temperature, current, and current density. Erratic results were obtained when the target was not water cooled, and when the glass collector plates were not initially coated with a thin layer (∼50 Å) of evaporated metal.
Theory of Current Collection of Moving Cylindrical Probes
Authors: Kanal Madhoo
Published: April 2005

The theory of current collection of a moving cylindrical probe is investigated. Volt-ampere relations are derived for two distinct cases: (i) The general-ion current for accelerating collector potential and its special cases, including general-ion current to the stationary probe, orbital-motion-limited current to the moving and the stationary probes, and sheath-area-limited current to the moving and the stationary probes; (ii) the general-electron current for the retarding collector potential and its special cases, including general-electron current to the stationary probe and random-electron current to the moving and the stationary probes. Orientation of the cylinder with respect to the drift velocity vector is taken into account. Volt-ampere characteristics are included for illustrating the functional behavior of the current relations.
Vacuum Insulation of High Voltages Utilizing Dielectric Coated Electrodes
Authors: Jedynak L.
Published: April 2005

An experimental research program has demonstrated that the high-voltage performance of a vacuum gap can be improved by the simple expedient of coating the cathode surface with a suitable thin insulating film. Steady voltages ranging to 340 kV were obtained with 5-mm gaps composed of 15-cm-diam Rogowski electrodes. Simultaneously the average gap currents were suppressed to the 10−8 to 10−10 A range. Further, it was shown that an insulating film on the anode can be severely detrimental to gap performance. Experiments were performed, at voltages up to 380 kV, involving 12 different film materials. Film thicknesses ranged from 0.2 to 135 μ and film resistivities ranged from 1011 to 1019 Ω-cm. The dielectric constants were between 1.7 and 3.5, except for one at 90. Based upon the experimental results and their interpretation, a tentative set of specifications can be given for a good cathode film: (1) resistivity of at least 1011 Ω-cm; (2) dielectric constant in the range 1.5 to 4; (3) dielectric strength of at least 106 V/cm; (4) film thickness between 10 and 25 μ; (5) mechanically hard and smooth with high abrasion resistance and high adhesion strength; (6) no gas bubbles within the film. If bubbles are unavoidable they must be substantially smaller than the film thickness; (7) low vapor pressure; (8) the cathode substrate should be of a highly polished metal suitable for quality deposition of the desired film material.
Characteristics of a Continuous High-Power GaAs Junction Laser
Authors: Engeler W. E. , Garfinkel M.
Published: April 2005

The construction details and output characteristics of a high-power GaAs junction laser are described. With the diode cooled to 20°K, continuous coherent optical power outputs up to 3.1 W have been obtained. This output was achieved with power efficiency of 46%. The coherent spectral output at several power levels well above threshold is shown. High resolution measurements of the spectral output place an upper limit of 310 Mc/sec upon the laser linewidth.
Cataphoretic Purification of Neon
Authors: Miller H. Craig
Published: April 2005

The effectiveness of cataphoretic purification of neon was investigated in conjunction with work on breakdown potentials in neon below the Paschen minimum. The extreme sensitivity, resulting from the Penning effect, of the breakdown potential in neon to the presence of traces of argon was used as an indicator of the degree of purity of the neon. Under the conditions of this experiment the limit of sensitivity for argon was about 1:107. With a discharge current of 125 mA in a helically wound Pyrex tube 1.6-cm o.d. and 2 m long, original concentrations of argon in neon of 50 ppm and 2%±1% were decreased to ≤0.1 and ≤1 ppm, respectively.
Bismuth Substitution in Yttrium Iron Aluminum Garnets
Authors: Geller S. , Williams H. J. , Sherwood R. C. , Espinosa G. P.
Published: April 2005

Magnetic, crystallographic, and preparative data are reported on the system {Y2.75Bi0.25} Fe5−xAlxO12 for values of x to 1.50. For large x there appear to be differences in 0°K magnetic moment between this system and the straight yttrium analog, which imply that the replacement of Y3+ by the larger Bi3+ ions favors occupation of the tetrahedral sites by the smaller Al3+ ions. The replacement of Y3+ by Bi3+ ions leads to the reduction of the preparation temperature of aluminum substituted iron garnets by about 350°C.
Adsorption and Migration of Sr on W
Authors: Barnaby B. E. , Madey T. E. , Petrauskas A. A. , Coomes E. A.
Published: April 2005

A study of the migration of Sr on W by a field electron emission technique revealed two modes. In the first mode, for θ≥1, migration proceeds with a sharp boundary while in the second mode, θ<1, no boundary is observed. The activation energy for the first mode was found to be 0.79±0.06 eV/atom, and the activation energy for the second mode was found to be 1.44±0.08 eV/atom.
Primary Pyroelectric Effect in the PZT 95/5 Ceramic
Authors: Wentz J. L. , Kennedy L. Z.
Published: April 2005

An expression of the thermodynamic potential is examined in terms of the primary and secondary pyroelectric coefficients of a poled ferroelectric ceramic. Anisotropic expansion and zero electric field conditions are assumed. The pyroelectric coefficient is applied to the composition, Pb(Zr0.95Ti0.05)O3 (PZT 95/5) with 1 wt. % of Nb2O5, for which a complete set of elastic, piezoelectric, thermoelastic, and pyroelectric coefficients were determined. A value of −26.8×10−9C/cm2-°C was found for the total pyroelectric coefficient of which +3.77×10−9 was contributed towards the piezoelectric or secondary effect; therefore, −30.6×10−9C/cm2-°C is reported for the primary pyroelectric coefficient for this material over the temperature range 25°–50°C.
Photolytic and Reduction Coloring of CaWO4:Nd
Authors: Cronemeyer D. C. , Beaubien M. W.
Published: April 2005

Intense flash-tube irradiation produces a brownish color in CaWO4:Nd, principally by absorption of wavelengths shorter than 300 mμ. Initially, the photolytic optical absorption has a peak near 3.0 eV for E∥c, and at 3.0 eV for E⊥c. At 300°K, there is a fast partial decay of the optical absorption within a few hours followed by a slow subsequent decay which stabilizes within a few days. On approach to equilibrium, the initial 3.0-eV E∥c peak decomposes to two peaks at 2.5 and 3.0 eV. The absorption for E⊥c diminishes with time, but the peak remains near 3.0 eV. The absorption coefficient for E∥c in this photolytic case is always about twice that for E⊥c. The photolytic coloring is removed by heating at 300°C for a few hours. It is unaffected by compensation of Nd with Na. Reduction of lightly doped CaWO4:Nd induces an optical absorption which peaks at 2.5 eV for both E∥c and E⊥c. For heavily doped CaWO4:Nd:Na, absorption peaks at 2.2 eV for E⊥c and 2.2 and 2.9 eV for E∥c are produced. Thus, reduction and photolytic coloring have fairly similar spectra. The removal of reduction coloring requires 800°C heating in an oxidizing atmosphere, however. Pure CaWO4 does not color in the bulk by either reduction or photolytic processes. The observations seem to point to an oxygen vacancy model with possible trapping of two electrons (perhaps an oxygen vacancy in conjunction with two W5+ ions).
Preparation of Single-Crystal Films of PbS
Authors: Schoolar R. B. , Zemel J. N.
Published: April 2005

Thin single-crystal films of lead sulfide have been prepared by vapor deposition on heated rocksalt substrates in the 0.2–8.0-μ range. Electrical and optical measurements have established that the properties of the films compared favorably with the bulk material and are suitable for a large number of experimental investigations. The index of refraction for PbS is in good agreement with previously obtained bulk values. The various electrical properties of the films, particularly the Hall mobility, are in very good agreement with those of bulk material.
Effect of Chemisorbed Oxygen on Photovoltaic and Photoconductive Processes in Rutile
Authors: Keezer R.
Published: April 2005

Adsorbed oxygen increases both the response and the response time for the photovoltaic effect in rutile.

The model for the effect of chemisorbed oxygen on the photoconductivity has been modified to take into consideration the effect of oxygen pressure. The conductance of rutile, measured as a function of oxygen pressure, agrees with the modified model.

The increase in photovoltaic response and response time with exposure to oxygen has been explained in terms of the barrier layer formed by chemisorbed oxygen.
Photovoltaic Effects in Rutile
Authors: Keezer R. , Mudar J. , Brown D. E.
Published: April 2005

The ultraviolet photovoltaic response of barrier-layer cells formed from single-crystal rutile has been investigated. Typical samples have response maxima at 3200 Å, a D* of 109 cm cps1/2/W, and time constants of 100 μsec. Variations in time constant over several orders of magnitude have been observed, dependent largely on preparative technique. The effect of surface treatment on cell characteristics is discussed.
Temperature Autostabilizing Nonlinear Dielectric Element (TANDEL). I. Construction of TGS—Element and Its Properties
Authors: Glanc A. , Málek Z. , Mastner J. , Novák M. , Štrajblová J.
Published: April 2005

The operation is described of a novel dielectric element which can stabilize its own temperature within narrow limits in the highly nonlinear region close to the Curie temperature. The device employs a triglycine sulphate (TGS) single crystal, and its operation is based on heating due to dielectric loss that is a strong function of temperature near the Curie point. The element operating in this autostabilizing state exhibits extremely high dielectric nonlinearities up to the high-frequency region, the nonlinearities being only little dependent on the changes of ambient temperature, which was experimentally proved in the range from −35° to +45°C. The element has various applications; e.g., frequency multiplier, mixer, frequency modulator, pulse position modulator, dielectric amplifier, electrometer, electromechanical transducer, transducer sensitive to heat transfer, etc.
Carrier Transport Across Electroluminescent p-n Junctions in GaAs
Authors: Pankove J. I.
Published: April 2005

The relationship between the voltage across GaAs p-n junctions and the emission spectrum from carrier recombination in differently doped specimen has been carefully examined. The data are interpreted in terms of radiative recombination via levels 30 meV above the valence band edge. Furthermore, depending on the gradient of impurities in the p-n junction, the transport mechanism is tunneling, injection, or a combination of both.
Growth of GaP Crystals and p-n Junctions by a Traveling Solvent Method
Authors: Weinstein Martin , Mlavsky A. I.
Published: April 2005

A traveling solvent method has been used to grow GaP crystals from Ga solution. Growth rates of approximately 0.5 mm/h have been achieved at an average temperature as low as 850°C, from Ga zones 0.025 mm thick. Polycrystalline growth, 10 mm in diameter and 2 mm thick, has been achieved as a direct continuation of the crystal orientations in polycrystalline seeds. p-n junction structures have been grown by doping from a 2% Ge-Ga solvent zone. Some electrical characteristics of small diodes cut from polycrystalline crystals are described.
Piezoelectricity in Salicylidene Aniline Crystals
Authors: Aharoni A. , Sapoznikov D.
Published: April 2005

The resonance frequencies of various single crystals of salicylidene aniline were measured for different modes of vibration, and the velocities of sound waves in these materials were deduced. Values are given for the electric equivalent circuit parameters and elastic constants in such crystals.
Growth of Copper Crystals of Low Dislocation Density
Authors: Young F. W. , Savage J. R.
Published: April 2005

A study was made of the perfection and the factors controlling perfection of copper crystals grown by a Bridgman technique. Crystals grown from 99.999+% and from (OFHC) copper were acid sawed and polished, and dislocation densities determined by etch pit techniques. The orientation of the growth direction of unseeded crystals of both purities was random. There was a correlation between perfection and growth direction for the 99.999+% copper crystals in that the more perfect crystals had growth direction far from the [111] zone. Dislocation densities as low as 103/cm2, with no subboundaries, were obtained in some of the purer as-grown crystals. The OFHC crystals were much less perfect and contained many subboundaries. After annealing slices of the purer crystals at 1075°C, dislocation densities as low as 102/cm2 were obtained. The vacancy condensation mechanism for dislocation generation apparently was not significant in accounting for the residual dislocation density in these crystals.
Relation Between E′ Centers and Hydroxyl Bonds in Silica
Authors: Weeks R. A. , Lell E.
Published: April 2005

The relation between the concentration of intrinsic paramagnetic states (the E′ centers) of silica (silica glass) produced by irradiation and the concentration of OH− ions in the silica was investigated by introducing OH− ions into silica, initially free of these ions, in a controlled manner. Optical absorption and electron spin resonance measurements were used to establish the relation. The results of the investigation showed that in synthetic silicas the concentration of E′ centers varied linearly with the concentration of hydroxyl units, the sum of the concentrations of hydroxyl units and E′ centers being constant. A ``vacancy'' model for the silica structure is proposed. In terms of this model the estimated saturation concentration of E′ centers is of the same order as the concentration of ``vacancies,'' ∼1020 cm−3. The saturation concentration of hydroxyl units is also ∼1020 cm−3. Silica made by fusing natural quartz crystals differs from the synthetic silica with respect to the optical bands and the electron spin resonance spectra produced by irradiation. The effects of introducing hydroxyl units into natural quartz silica initially free of hydroxyl units is also different. These differences between natural quartz silica and synthetic silica are related to the models which have been suggested for the E′ centers. The models which are suggested are in agreement with the results of other experiments.
Residual Pressure Effects in Polycrystalline Aluminum
Authors: Miles M. H. , Gibbs P.
Published: April 2005

Internal friction measurements following application of hydrostatic pressure were used to study residual pressure effects in polycrystalline aluminum. Application of 4-kbar pressure was observed to increase irreversibly the amplitude-dependent damping of 99.99% and 99.996% Alcoa aluminum at a strain amplitude of approximately 3×10−5 by amounts up to 60 and 35 times the initial values, respectively. With successive pressure-anneal cycles an abrupt disappearance of the residual pressure effect was sometimes observed. The effect was studied as a function of grain size by annealing cold-worked aluminum at different temperatures. Measurements before and after application of 6-kbar pressure to zone-refined polycrystalline aluminum showed no changes in damping that could be ascribed to the effect of pressure. Polycrystalline alloys prepared by doping zone-refined aluminum to 99.99% purity by addition of copper, iron, or silicon showed no residual pressure effect. Vacuum-melted polycrystalline 99.996% aluminum showed no residual pressure effect. Zone-refined aluminum melted in air or under a hydrogen atmosphere showed residual pressure effects. The residual pressure effect observed in refined aluminum is attributed to quenched-in hydrogen present in the lattice. The pressure-sensitive defects are considered to be hydrogen-filled cavities.
Gamma-Ray Response of Simple Slit-Collimated Detectors
Authors: Lillegraven Arne L.
Published: April 2005

Formulas have been developed for the direct gamma-radiation (photopeak) response of a simple slit-collimated crystal detector as a function of position and gamma-ray energy of point sources that are embedded in isotropic absorbing matrices. Apart from optical considerations, the effects of edge penetration, crystal absorption, source matrix absorption, and for higher energies, penetration of the collimator wall have been taken into account. A comparison between measured and calculated response curves has been made.
Microwave Absorption and Density Variation in Moving Striations
Authors: Paik S. F. , Shapiro J. N. , Gilbert K. D.
Published: April 2005

Properties of a moving striation in the positive column of a dc glow discharge are investigated using a pulsed microwave technique. The electron density and the power absorption in various portions of the striation are determined from the time-resolved resonant curves of a microwave cavity containing the discharge, and the variation of the electron temperature is inferred from the absorption measurement. The results of the measurement show a large degree of variation of both the temperature and the density within one cycle of the striation. The variation of the light intensity measured with a photomultiplier tube is observed to be in phase with the temperature. These results are consistent with the Langmuir probe data and results of other microwave measurements previously reported.
Excitation of Characteristic X Rays by Protons, Electrons, and Primary X Rays
Authors: Birks L. S. , Seebold R. E. , Batt A. P. , Grosso J. S.
Published: April 2005

Protons, electrons, and primary x rays were used to excite characteristic x radiation from individual specimens of Ti, Cr, Fe, Cu, Ge, Zr, and Au. X-ray yield expressed as (photons /sr)/ quantum increased with quantum energy in a similar manner for protons in the range about 1 MeV and electrons in the range about 50 keV. For primary x-ray excitation, the yield decreased with increasing quantum energy, a relationship opposite to that for proton or electron excitation. It appears that the relative values of photo-electric absorption and scattering must be quite different for x rays and electrons to account for their opposite relationship of yield vs energy.
Spectral Output of Semiconductor Lasers
Authors: Statz H. , Tang C. L. , Lavine J. M.
Published: April 2005

This paper investigates problems associated with multimode oscillations in semiconductor lasers. In particular, even in semiconductors there can exist a spatially nonuniform distribution of excess electrons and holes because a given mode de-excites electrons most strongly at antinodes and not at all at nodes of the electric vector. This nonuniform distribution encourages the oscillation of other modes which have a different distribution of the electric field vector and which, in particular, have finite electric fields at nodes of the first oscillating mode. Diffusion of electrons and holes tends to wipe out nonuniform carrier distributions. For low temperatures, this diffusion is relatively slow, and for current densities only moderately above the threshold, several modes may oscillate simultaneously. At higher temperatures the suppression of additional modes is much more effective. Because of the complexity of the calculations, the present work had to be restricted to Fabry-Perot type modes and relatively low power levels. Comparisons are made between theory and experiments.
Direct Measurement of Xenon Flashtube Opacity
Authors: Emmett J. L. , Schawlow A. L. , Weinberg E. H.
Published: April 2005

The optical transmission of a xenon flashtube has been measured at wavelengths from 2500 to 10 000 Å and at currents up to 5000 A/cm2. It is found that the absorption increases with current and with wavelength. Above about 5000 Å and a current of 4000 A/cm2, a discharge tube 1 cm thick is nearly opaque. At shorter wavelengths or lower currents, the discharge is fairly transparent.
Errors in the Evaluation of Moments of a Paramagnetic Resonance Line
Authors: Judeikis Henry S.
Published: April 2005

The systematic errors inherent in the numerical evaluation of the various moments of an experimental paramagnetic resonance line are discussed as a function of the choice of the shapes and the arbitrary cutoff of wing contributions. Lorentzian and Gaussian first derivative shapes are used as models. Expressions for the zeroth, second, and fourth moments of these shapes are derived in generalized coordinates with an arbitrary cutoff. The generalized coordinates, which contain parameters related to easily measured experimental quantities, permit application of the results to any line of the Lorentzian or Gaussian shape.
Thermal and Fast Neutron Detection by Fission-Track Production in Mica
Authors: Prevo P. R. , Dahl R. E. , Yoshikawa H. H.
Published: April 2005

The recently developed method of etching fission fragment tracks in mica appears to be applicable to the measurement of neutron exposures in irradiation tests. The sensitivity of the method depends on the concentration of fissile elements. The naturally occurring uranium which is present in trace quantity can be used to measure thermal neutron exposures of 1016 to 1021 neutrons/cm2. Deposition of fissionable material on the mica would increase the sensitivity to permit measurement of 106 to 1011 neutrons/cm2. Density counts are reproducible to approximately 5% by using simple laboratory techniques.
Effect of Irradiation on Magnetic Properties of Fe-Ni Alloys
Authors: Schindler A. I. , Kernohan R. H. , Weertman J.
Published: April 2005

Hysteresis loop measurements were conducted on several commercial iron-nickel alloys during neutron irradiations at 90°K and at temperatures up to 175°C, in both zero and saturating magnetic fields. Isochronal annealing tests were also performed on the alloys after irradiation. The low-temperature irradiation results indicated that magnetic properties are affected not by the point defects themselves but by their motion and eventual disposition. The radiation-induced changes appeared similar in many ways to those observed in these alloys upon magnetic annealing.

Experiments on the alloys at temperatures from 70° to 175°C in a saturating magnetic field showed that the activation energy of the radiation-induced process was 0.3 eV. In all cases the radiation-induced changes were annealed out at temperatures below the usual ordering temperature for Ni3Fe. This recovery process appeared to be dependent upon the state of the magnetization of the sample.
Method for Hall Mobility and Resistivity Measurements on Thin Layers
Authors: Lange Julius
Published: April 2005

A method for measuring Hall mobility and resistivity in thin layers of semiconducting materials uses four contacts near the center of a sample that is large in comparison to the contact spacing. The measured value of the Hall coefficient is independent of the relative positions of the contacts. For resistivity measurements the contacts have to lie on a circle; the error due to a 10% deviation from this condition is 3%. If the contact spacing is110 of the smallest sample dimension the Hall coefficient is accurate to 2.5% and the resistivity measurement to 5.5%.

Where it is not possible to make the sample large in comparison to the contact spacing, a circular sample and a square array of contacts is proposed. Arrangements which do not fit either case but closely approach both can be treated by first using the infinite sheet method and then correcting for the finite size of the sample by the circular sheet method.

These methods may be useful where it is not convenient to form either Hall bridges or contacts to the edge of the sample, as in the van der Pauw method. Measurements on epitaxially grown layers might be carried out by this method.
Determination of Capture Cross Sections by Optical Quenching of Photoconductivity
Authors: Bube Richard H. , Cardon Felix
Published: April 2005

The electron capture cross section of sensitizing centers for photoconductivity has been measured as a function of temperature between 77° and 350°K in CdS, Cd(SSe), CdSe, GaAs, and InP crystals. The value of the cross section is obtained from the measurement of the minimum number of quenching photons per second required to initiate optical quenching, at a temperature below that at which thermal quenching occurs. Forty-one determinations of cross-section on nine different crystalline samples yield values between 10−20 and 10−22 cm2 with only slight temperature dependence. A consideration of the various models to account for such small capture cross sections without appreciable temperature dependence suggests that the cross section is associated with radiative capture by a neutral center.
Electrostrictively Generated and Modulated Fracture in Barium Titanate Ceramics
Authors: Goodman G.
Published: April 2005

A unique fracture of electrostrictive origin has been observed in ceramic barium titanate subjected to damped high-voltage oscillations. Such a nonexplosive method of producing impulse loading with an internal variable time marker makes this an attractive material in which to study fracture propagation.
Entropy Factors for Thermally Activated Unpinning of Dislocations
Authors: Granato A. V. , Lücke K. , Schlipf J. , Teutonico L. J.
Published: April 2005

The entropy factor and effective jump frequency for the thermally activated unpinning of dislocations are computed by use of the statistical mechanics treatment of absolute rate theory. Three problems are considered in detail: The first is a model problem of three mass points, the second a dislocation line of length 2l pinned by an impurity at its center, and third a dislocation line pinned uniformly over its length. The unique feature about the theoretical treatment of the diffusion of dislocations in crystals, as contrasted with the diffusion of point defects, is that good quantitative approximations for the frequencies of the system in both the ground state and the activated state can be obtained from the vibrating string model. The approximations of this model are good for the lowest frequencies, which turn out to be the important ones for the processes considered. The entropy factor is very large for long loop lengths. For a typical case of a binding energy of110 eV, the frequency factor for a dislocation pinned at its center is the order of 5×1010 cps, independent of the loop length or of the attack frequency. For a continuously pinned dislocation, the effective frequency is greater than the Debye frequency.
Anharmonicity Due to Glide Motion of Dislocations
Authors: Suzuki Tetsuro , Hikata Akira , Elbaum Charles
Published: April 2005

The generation, due to glide motion of dislocations, of the second harmonic of an ultrasonic stress or strain wave propagating in a crystal is studied by using the string model of dislocations in the presence of a static bias stress. The calculated results agree semiquantitatively with the experiment by Hikata, Chick, and Elbaum. The dependence of the amplitude of the second harmonic on bias stress, when this stress is sufficient to cause dislocation unpinning, can be accounted for by the dislocation damping effect that is associated with the anomalous velocity change due to unpinning.
Fracture of Polymer Melts at High Shear Stress
Authors: Bartos̆ Otakar
Published: April 2005

An analysis of the flow of polymer melts as well as of melt fracture at high shear rates has been carried out. On the basis of the flow properties of polyethylene, polypropylene, polystyrene, polymethylmetacrylate melts, and silicone rubbers measured over a wide range of shear rates from 10−3 up to 103 sec−1, the following conclusions have been drawn: Under low rates of shear the behavior of polymer melts is of Newtonian nature, whereas at high rates the character of flow depends on the value of the dimensionless criterion κ=τ/ηNγ̇=κ3τ·R/ηN·V, where τ is shear stress γ̇ is shear rate, ηN is Newtonian viscosity, R is characteristic dimension, and V is mean velocity of flow. The fracture of polymer melts occurs above a critical constant value of the number κ: κcrit=0.025. Available flow data, analysed by the method of reduced variables, show that most previously suggested criteria are essentially equivalent. This treatment eliminates their restricted validity and technological applicability and brings the description of fracture close to molecular theories of non-Newtonian flow.
Dependence of Current Degradation in Superconducting Solenoids on Flux Pinning Energy and Temperature
Authors: Meyerhoff R. W. , Heise B. H.
Published: April 2005

The cause of the current degradation of superconducting solenoids, a subject of continuing interest, is elucidated further in this work. Two types of measurement are reported here: (1) Flux pinning energies and straight wire critical currents of 0.25-mm (10-mil) Nb–Zr wire are measured as a function of magnetic field. (2) Solenoid critical currents are reported as a function of temperature for the same material. These measurements indicate that high pinning energy causes flux jumping which causes solenoid degradation. They further indicate that pinning energy can be weakened by increasing the temperature; therefore, flux jumping and coil degradation can be suppressed by increasing the temperature
Influence of Controlled Additions of Oxygen on the Superconductivity of Niobium
Authors: Tedmon C. S. , Rose R. M. , Wulff J.
Published: April 2005

The critical current density vs applied transverse magnetic field was measured, for a superconducting niobium single crystal of controlled oxygen content, at successively higher levels of concentration; the oxygen content was increased in increments ranging from 2 to 50 ppm, under conditions of constant substructure, from an initial level of approximately 5 ppm to a final level of 360 ppm. The over-all critical current density increased considerably on the addition of oxygen, and assuming γ to be independent of oxygen concentration, the upper critical field increases in accordance with the predictions of the GLAG theory for type II superconductivity. The critical current density above the upper critical field, which has been ascribed to nucleation effects at defects or surfaces, was also very sensitive to the oxygen content.
Radio-Frequency Breakdown in a dc Parabolic Potential Field
Authors: Karras Thomas W. , Lindman Erick
Published: April 2005

Electrons that are confined in a Penning discharge geometry by electric and magnetic fields are observed to gain energy from a superimposed rf field. By shaping the electrodes in the form of hyperboloids of revolution the prebreakdown motion can be accurately described by the Mathieu equation. Resonances are predicted when the frequency of the electron in the electrostatic well is a multiple of half the rf frequency. In the pressure range investigated (air at 10−2 to 10−5 Torr), values as low as 40-V dc and 3-V rf were observed at the first resonance under conditions where the Penning mechanism alone required over 400-V dc. Between resonances the Mathieu equation predicts runaway energy gain at considerably higher values of the rf voltage, but breakdown is observed at values much lower than the prediction. The explanation is found in energy gain through collisions with gas atoms. The collision resets the phase of the motion and allows the electron to continually gain energy from the rf field. Breakdown curves are calculated for the regions between resonances and are found to agree with experiment.
Current Transients in Insulators
Authors: Lindmayer Joseph
Published: April 2005

Electronic currents in insulators are strongly controlled by trap sites and therefore trapping can account for long-term charge and discharge currents. Some general calculations are carried out for the discharge of disorderly insulators; in most cases the discharge current decreases inversely with time. Measurements are demonstrated for SiO2 and SiO.
Dislocation Mechanisms in the Growth of Palladium Whisker Crystals
Authors: Webb W. W.
Published: April 2005

A case of metal whisker crystal growth has been identified in which axial screw dislocations are demonstrated to perform their expected role. Palladium metal whisker crystals grow at ∼0.02 cm/sec by decomposition of palladium chloride to palladium plus chlorine gas on the tips of whisker crystals while lateral growth is retarded by a thin film of liquid palladium chloride. Dislocations provide growth steps on the whisker tips, and dislocation climb systematically changes the effective growth direction in suitable cases to form helical crystals. Growth occurs in irrational crystallographic directions so that straight crystals have irrational axes and the helices always have <111> axes formed as the growth direction gyrates around it. Cinéphotomicrographic techniques facilitated the growth studies; x-ray diffraction techniques revealed the axial dislocations in situ subsequent to termination of growth (in contrast to most other cases of metal whisker growth).
Analysis of Enhanced Diffusivity in Nickel
Authors: Wazzan Ahmed R. , Dorn John E.
Published: April 2005

The coefficient of self-diffusion in annealed and prestrained nickel single crystals, Du, determined in the temperature range 948° to 1023°K by radioactive counting of the surface is Du=1.9 exp(−66 800/RT) cm2sec−1.

The coefficient of self-diffusion in annealed and prestrained fine-grained nickel crystals, Du′, in the same temperature range is independent of the degree of prestrain: Du′=1.1×10−7 exp(−32 300/RT) cm2sec−1.

The coefficient of self-diffusion in nickel single crystals undergoing plastic deformation, Dd, was determined for strain rates ranging from 0.01 to 0.1035 h−1 in the same temperature range. Dd appears to vary with strain but eventually reaches an asymtotic value D̄d. At a constant temperature, D̄d/Du is almost linearly dependent on the strain rate ε: D̄d/Du=1+Kε̇, where K is 162, 225, and 470, (h−1) for temperatures 1023°, 973°, and 948°K, respectively.
Dislocations in Molybdenite
Authors: Hörl Erwin M.
Published: April 2005

The formation of the different types of dislocations in molybdenite is discussed. An interpretation based on the occurrence of growth faults in natural crystals is advanced which explains the existence of dissociated and undissociated dislocations. In addition, features of dislocation ribbons and dislocation networks as well as the kinds of interactions observed between dislocations are analyzed.
Effects of Growth Parameters on Dislocations in CaF2
Authors: Abrahams M. S. , Herkart P. G.
Published: April 2005

The relationship between dislocation morphology and variations of growth parameters has been studied in CaF2 ingots grown by the Czochralski technique. The growth parameters investigated were growth rate, seed orientation, crystal size, temperature gradient, use of an afterheater, and doping. The effects of mechanical damage at room temperature and of annealing the crystals are also presented. Normal handling has no effect on the production of new dislocations but severe stress concentrations cause marked slip on {100}. Three main sources of dislocations in a growing ingot have been found: (1) propagation of dislocations present in the seed, (2) thermal stresses, and (3) precipitates of CaO. Methods are discussed for minimizing the production of dislocations in a growing ingot.
An Investigation of Interstitial Sites in the bcc Lattice
Authors: Beshers D. N.
Published: April 2005

The evidence for Snoek's model of interstitial position and diffusion in bcc metals is reviewed in the light of recent calculations. Other models are equally tenable in many instances, on the available evidence, if the internal friction relaxation strength associated with the tetrahedral sites is appreciable. To investigate the matter further, a systematic comparison of the models involving octahedral and tetrahedral sites is carried out using an elementary method for estimating strain energies about stable sites and about saddle points for diffusion. These estimates indicate that the tetrahedral sites are the more favored positions in many instances and that diffusion paths involving the tetrahedral sites may be important even when the octahedral sites are more favored. Next, a model of an interstitial in a tetrahedral site is developed for use in continuum mechanics, using the same forces as were hypothesized for the strain-energy calculation. It is deduced from this model that the relaxation strength associated with a tetrahedral site depends sensitively on an unknown angle, but that some values within a reasonable range for this angle do lead to significant relaxation strengths. It is also deduced that an impurity in a tetrahedral site interacts with strain gradients, as well as strains. A comparison of predicted patterns with measured relaxation strengths does not bear out Snoek's model but instead supports the hypothesis that in most systems based on the group VA metals the interstitial impurities occupy the tetrahedral sites.
Potential-Well Description of Electromagnetic Levitation
Authors: Hatch Albert J.
Published: April 2005

Levitational forces exerted by spatially nonuniform ac magnetic fields on nonmagnetic conducting spheres are derived as the negative gradient of a potential function. Surfaces representing this potential for a small rigid diamagnetic sphere are used to visualize the levitational properties of several typical fields established by circular coils. Topological characteristics of these surfaces indicate that dipole fields have very shallow potential wells only for vertical and near-vertical positions of the coil axis, and are only marginally levitational. Helmholtz and mirror fields have similar shallow potential wells. Quadrupole fields, however, have deeper potential wells in the vicinity of the central nodal point for all positions of the coil axis, and are strongly levitational. Higher-order multipole fields can have potential wells similar to those in quadrupole fields. The description is also applicable to the levitation of nonmagnetic superconducting bodies in nonuniform ac magnetic fields.
Electron Removal During the Early Oxygen Afterglow
Authors: Mentzoni Michael H.
Published: April 2005

Microwave diagnosis showed that the early afterglow of an oxygen plasma was controlled by ambipolar diffusion and by recombination (αr), depending upon pressure (from 0.15–4.0 mm Hg), at elevated gas temperatures (up to 900°K). At Tgas=300°K attachment also seemed to be important for higher pressures (p>0.65 mm Hg). For low plasma excitation energy the measurements yielded αr=2.1×10−7 cm3 sec−1 at Tgas=300°K, dropping gradually to 1.4×10−7 cm3 sec−1 at 894°K. The plasma excitation energy had a marked effect on the apparent recombination and attachment rates which tend to indicate that vibrationally excited ions and molecules do affect these rates as has been suggested previously.
Experimental Separation of Collective and Individual Phenomena in Plasmas-Anomalous Resistance
Authors: Thomassen K. I.
Published: April 2005

An experimental method for separating collective effects from collision dominated phenomena in plasmas consists of probing the plasma at a frequency between the collision and plasma frequencies that govern the rates of the individual and collective processes. This method is applied to the measurement of anomalous resistance by utilizing a re-entrant cavity to expose a quiescent plasma to the strong electric fields at this intermediate frequency, thus provoking anomalous resistance. The resistive loading of the cavity is then observed as a function of power level or field strength, giving evidence of an anomalous resistance above power levels which initiate the two-stream instability.