bluuebunny/crossref_metadata_2025 huggingface dataset:
Limiting Magnetic Fields for High-Field Superconductivity
Authors: Ralls K. M. , Rose R. M. , Wulff J.
Published: April 2005

In order to calculate the limiting magnetic field for superconductivity of a type II superconductor, the free-energy contributions of the Abrikosov mixed state and the electron spin paramagnetism are combined. The solutions which result are applied to the niobium—zirconium alloy system and compared with the available resistive critical field data, as a function of composition. The calculated curve is generally closer to the experimental curve than either the paramagnetic limit or Hc2 alone, and rather good agreement is obtained for niobium-rich alloys.
Modes in Spherical-Mirror Resonators
Authors: Specht Walter A.
Published: April 2005

This work is the examination of a cavity mode approach to the mode structure of a laser. Solutions of the vector wave equation for electromagnetic fields in and between perfectly conducting oblate spheroidal cavities are examined for the case of wavelengths much less than cavity dimensions. These solutions are the field modes in Fabry—Perot type resonators with equal-radius concave spherical mirrors, or with concave—convex spherical mirrors, when the parameters of the oblate spheroids are chosen so that the radii of curvature and spacing on the axis of rotation match those of the resonator mirrors. Expressions for the transverse and longitudinal mode structures are derived. The eigenvalue equations are written, and are solved for the case of the two lowest-order modes.
An Ionization Process in a Low-Energy Cesium Plasma
Authors: Witting Harald L. , Gyftopoulos Elias P.
Published: April 2005

The mechanisms of ion formation in cesium plasmas at relatively low electron temperatures (3500°K) and pressures of a few Torr are investigated. It is concluded that most of the ions are molecular and that they are formed by collisions between cesium atoms in the first excited state. The excited atoms are predominantly produced by inelastic electron collisions.

The excitation cross section is computed by means of the impact parameter method. It has a maximum value of 100×10−16 cm2 at 7 eV. The de-excitation cross section is computed and found to be approximately constant at 50×10−16 cm2. Radiation trapping and diffusion of excited atoms are also studied.

The ionization cross section is calculated by means of statistical thermodynamics from the measured recombination coefficient for the inverse of the ionizing process. It is found to be 1450×10−16 cm2. The plasma is uniform throughout its volume except in the immediate vicinity of the bounding electrodes.

The proposed mechanism results in performance characteristics for cesium thermionic converters, operating in the ``ignited mode,'' which are in qualitative and quantitative agreement with experimental data.
Vacuum Distillation of LiF
Authors: Singh A. J. , Ross R. G. , Thoma R. E.
Published: April 2005

Vacuum distillation methods were demonstrated to be effective for producing high-purity crystals of LiF. It was established from chemical analyses of condensate products that under the experimental conditions adopted, 995°C and 4 to 5×10−2 Torr, the order of vaporization for the fluorides, NaF, MnF2, LiF, MgF2, and CaF2, corresponds to the order of their decreasing vapor pressures. Under similar experimental conditions LiF containing no more than 200 ppm of oxygen could be produced from mixtures of LiF and Li2O.
Cathodoluminescence at p-n Junctions in GaAs
Authors: Wittry David B. , Kyser David F.
Published: April 2005

A decrease in the cathodoluminescence produced in GaAs by a scanning electron probe has been observed when the probe is close to a p-n junction. The decreased intensity is shown to result from the drift of excess carriers across the junction. Measurements of the short-circuit current of the diode confirm this interpretation and provide a means of estimating minority carrier diffusion lengths.
Method for the Determination of Electron Drift Velocity in Gases from the Characteristics of High-Pressure Gas Diodes
Authors: Meisel Lawrence V.
Published: April 2005

A method has been developed for determining electron drift velocities from measured current-voltage characteristics of gas-filled cylindrical diodes. Experimental data, taken in diodes filled with helium, nitrogen, and argon, are presented to illustrate the utility of the method.
Spectral Measurements with Aligned and Misaligned Two-Crystal Spectrometers. I. Theory of the Geometrical Window
Authors: Schnopper Herbert W.
Published: April 2005

It is shown in this paper that (1) the geometrical window of the instrument is a function of the alignment of the crystals, the beam, and the rotation axes as well as the vertical divergence, (2) even for the case of perfect spectrometer alignment, errors are introduced into the measurement of the spectral parameters because of the presence of a finite vertical divergence in the x-ray beam, and (3) improper beam and crystal alignment cause inaccuracies in the measurement of spectral parameters, e.g., wavelength position, linewidth, line shape, and asymmetry.

Calculations which predict the effects of vertical divergence and of beam and crystal misalignment on the geometrical window and also on the wavelength position, line shape, linewidth, and line asymmetry of the (1,+1) and (1,−1) curves are made for the case of CuKα radiation reflected from calcite crystals. In particular, it is shown that the error in the measurement of the Bragg angle, i.e., wavelength, is 61/2 times more sensitive to misalignment of the central ray of the x-ray beam than it is to total vertical divergence.
Spectral Measurements with Aligned and Misaligned Two-Crystal Spectrometers. II. Alignment
Authors: Schnopper Herbert W.
Published: April 2005

Conditions for and methods of aligning a two-crystal spectrometer are discussed. These include the alignment of rotation axes, crystals, and x-ray beam. The results of a new nondispersive crystal alignment procedure are compared in detail with theory for a typical case of CuKα radiation and calcite crystals. This method is contrasted with other procedures which lead only to pseudo-alignments.

It is shown that x-ray methods which are sensitive to vertical divergence do not lead to crystal alignment unless the beam is already perfectly aligned. It is concluded that the x-ray beam can be aligned only after the crystals have been aligned.
Dislocation Energy and Dislocation Networks in α-Iron
Authors: Chou Y. T.
Published: April 2005

A refined analysis of dislocation energy and dislocation networks in {110} planes of α-iron crystals is presented on the basis of anisotropic elasticity.

Contrary to the conclusions given by isotropic theory, the elastic energy per unit length of a screw segment, with Burgers vector a〈100〉, is greater than that of an edge segment with the same Burgers vector lying in a {110} plane. The latter in turn is greater than the sum of the energies of two screw segments with Burgers vector (a/2)〈111〉.

The shape of a stable net composed of a〈100〉 screw segments and (a/2)〈111〉 segments of mixed character in {110} planes is determined by the line tension method. Comparison between theory and experiment is discussed. It is shown that the anisotropic theory agrees well with the observations.
Plastic Deformation of Calcium Tungstate Single Crystals
Authors: Arbel A. , Stokes R. J.
Published: April 2005

Calcium tungstate deforms by slip on the (001) 〈100〉 system above 400°C. Simple shear over this plane is the only deformation mode observed under compression at temperatures up to 900°C and a strain rate of 10−3sec−1. The critical resolved shear stress is strongly temperature dependent. Crystals cannot be plastically deformed at room temperature, at 400°C they are still quite brittle but by 900°C they are soft (yield stress, 500 psi) and plastic. Slip traces at all temperatures are fine and straight but those produced at lower temperatures (600°–700°C) have a greater surface tilt and are more sharply defined than those produced above 800°C. This is due to fewer dislocation sources and restrictions on dislocation multiplication at lower temperatures.

The role of bonding and crystal structure in the selection of slip parameters is discussed. It is considered that the stacking of the oxygen ions is the dominant factor dictating the slip plane and slip direction. Slip cannot occur without some distortion of the covalently bonded WO42− radical, which probably accounts for the strong temperature dependence of the critical resolved shear stress. It is shown that relatively easy slip in a given [100] or [010] direction can only occur between every other pair of (001) planes. Thus, a jogged dislocation which is mobile on one plane will become immobile on the next (or any odd number) plane. This is considered to restrict dislocation multiplication at low temperatures.
Observations of Impurity Precipitates in Magnesium Oxide Single Crystals by Ultramicroscopy
Authors: Miles G. D.
Published: April 2005

Magnesium oxide crystals have been examined in an ultramicroscope and the arrangements of precipitate particles in the material are illustrated. Unusual dislocation configurations are revealed by decoration in certain crystals.

It has been suggested in the literature that most precipitate particles in magnesia are of zirconium oxide. The present observations of particle density indicate that it is unlikely that this is completely true at least for heat-treated samples, even if the particles are finer than has formerly been assumed.
Observations of Individual Dislocations and Oxygen Precipitates in Silicon with a Scanning Electron Beam Method
Authors: Czaja W. , Patel J. R.
Published: April 2005

Individual edge dislocations created by heat treating indentations on the n side of a shallow phosphorus-diffused silicon p-n junction have been detected by the scanning electron beam technique. The width of contrast produced by edge dislocations is close to 1 μ in agreement with expectation. The contrast mechanism is discussed and can be explained by enhanced recombination at dislocations with an edge component. Furthermore, it is shown that oxygen precipitates in silicon can be displayed as well as individual dislocations introduced by twisting the crystal.
Disappearance of Magnetocrystalline Anisotropy Effects on Spin Resonance of YIG
Authors: Czerlinsky E. , Gianino P. D.
Published: April 2005

The effect of the magnetocrystalline anisotropy on the resonance of the saturation magnetization vanishes in single-crystal spheres of YIG for a continuous multiplicity of crystalline directions which form a cone about each 〈100〉. Consequently, the resonance shift caused by the change of anisotropy with temperature is eliminated when the external magnetic field coincides with any direction lying on this cone. It is shown that deviations from the ideal alignment become inconsequential if they occur in predictable crystallographic planes tangent to this contour.
X-Ray Topography of Decorated Dislocations in Magnesium Oxide
Authors: Lang A. R. , Miles G. D.
Published: April 2005

Combined x-ray topographic and ultramicroscopic studies have shown a one-to-one correspondence between dislocation lines and chains of submicroscopic light-scattering bodies within a magnesium oxide crystal in the ``as-received'' state. Dislocations with any orientation and Burgers' vector were found to be decorated. The geometry and Burgers' vectors of various unusual dislocation configurations have been determined. These special configurations all arose from the extension of edge segments in the course of intense dislocation climb combined with a strong preference for a line orientation parallel to a cube direction. The relationship of such configurations to the general distribution of dislocations showed that the epoch of intense dislocation climb had occurred late in the evolution of the dislocation distribution. X-ray diffraction evidence on whether the climb was due to the absorption of interstitials or of vacancies is as yet inconclusive.
Matteucci Effects in the Case of Dynamical Torsion
Authors: Rothenstein B. F. , Policec A.
Published: April 2005

Experimental arrangements and procedures in the Matteucci-effects study of ferromagnetics for the case of dynamic torsion in alternating or in direct magnetic fields are described.
Problem of Mode Deformation in Optical Masers
Authors: Statz H. , Tang C. L.
Published: April 2005

Fox and Li first calculated mode shapes in Fabry-Perot-type oscillators assuming a passive homogeneous medium between the mirrors. In laser oscillators the gain is strongly depressed by saturation in regions where the amplitude of the mode is large, thus giving a nonuniform gain distribution in the cavity. In addition, nonuniformities in the excitation may lead to gain variations. Through numerical solutions it is found that even with nonuniform gain distribution in the transverse direction, the lower order optical modes as originally calculated represent the electromagnetic fields in the cavity rather accurately. The present work justifies earlier calculations of the number of oscillating off-axis modes in lasers.
Directional Characteristics in Optical Heterodyne Detection Processes
Authors: Corcoran Vincent J.
Published: April 2005

Because of the spatial variation of the electric fields and the finite size of the detector, the output current in a coherent optical detection process varies as a function of orientation. When two unfocused light beams impinge upon the detector, the output current is shown to be identical in form to the amplitude of the field generated at the origin of one of the sources by the other source when the detector is replaced by a reflector. If the effective aperture is increased by focusing the light beams with a single lens, then the directivity increases. However, if multiple apertures are used in order to maintain the images in the same position, the directivity is reduced. The detection of coangular beams, such as from the longitudinal modes of a laser, is relatively insensitive to angle of incidence.
Plasma Diagnosis by Means of Optical Scattering
Authors: Schwarz S. E.
Published: April 2005

When a pulse of intense light from a laser passes through a plasma, a very small fraction of the light is scattered out of the beam by free electrons. Measurements of the intensity and spectral distribution of the scattered light can be related to the electron density and velocity distribution in the plasma. This paper presents a general discussion of the use of optical scattering as a plasma diagnostic technique. Applicability to various experimental situations is discussed, and considerations of interest in the design of diagnostic apparatus are presented.

An apparatus has been constructed for the measurement of electron density in cold plasma. The apparatus is described in some detail. Typical results are given for densities as low as 1013 electrons/cm3.
Infrared Refractive Index and Absorption of InAs and CdTe
Authors: Lorimor O. G. , Spitzer W. G.
Published: April 2005

Transmission interference fringes from 2690 to 320 cm−1 for InAs and from 1330 to 320 cm−1 for CdTe have been analyzed with classical dispersion theory to obtain the room-temperature dielectric constants. For InAs the dielectric constant between the band edge and the reststrahl ε∞ and the static dielectric constant ε0 are: ε∞ = 11.8±0.1, ε0 = 14.55±0.3; and for CdTe: ε∞ = 7.05±0.05, ε0 = 10.60±0.15. These values agree favorably with previously reported values. The absorption of InAs has been measured from 2500 cm−1, near the fundamental absorption edge, to 260 cm−1. Eight absorption peaks were observed between 444 and 269 cm−1 which are attributed to multiphonon combinations with the following characteristic phonon frequencies: TO1 = 222 cm−1, TO2 = 214 cm−1, LO = 196 cm−1, and LA = 143 cm−1. The transmission of CdTe has been observed from 10 000 to 220 cm−1. From 10 000 to 450 cm−1 the transmission is essentially constant at ∼60%. Below 400 cm−1 only two previously reported transmission minima were observed.
Collision-Rate Theory and the Coagulation of Free-Molecule Aerosols
Authors: Brock J. R. , Hidy G. M.
Published: April 2005

Collision-rate theory is used to describe the collision and coagulation of aerosols moving in the free-molecule regime where the particle diameter σ(v) is small compared to the mean free path L(g) of the suspending gas. A general expression is obtained for the rate of collision between particles. This relation accounts for the directing influences of electrical charging of the particles, external fields of force, and nonuniform states in the suspending medium, including surfaces of discontinuity. It is shown that the results of the free-molecule theory for thermal coagulation do not agree with the classical theory which has been corrected for the effects of large values of the ratio L(g)/σ(ν). In addition, the free-molecule results indicate that the directing effects can substantially increase the coagulation rate, even for aerosol particles of small size.
Ultraviolet Ion Laser Transitions between 2300 and 4000 Å
Authors: Cheo P. K. , Cooper H. G.
Published: April 2005

Fifty-five ultraviolet laser transitions in the wavelength region 2300–4000 Å have been observed from the ions of N, O, Ne, Ar, Kr, and Xe. The electron transition is p → s for all identified lines, with the exception of two xenon transitions which are p → d. Threshold currents for laser action in a 4-mm-bore tube were in the ranges 10–100, 100–500, and >400 A, respectively, for singly, doubly, and triply ionized atoms. Current saturation and current quenching of laser action both were observed. Results with two tube bores show that the usual inverse relation between gain and tube diameter does not hold in ultraviolet ion lasers.
Reduction of Electromagnetic Backscatter from a Plasma-Clad Conducting Body
Authors: Murphy E. L.
Published: April 2005

The investigation of dipole resonance effects in electromagnetic scattering from cylindrical plasma columns is currently directed toward understanding the observed multiplicity of resonances and the effect of magnetic fields, finite temperature, glass envelopes, etc., on these resonances. When a conducting core is embedded in the column, the analysis of this paper shows that not only are the shapes and locations of the resonances modified, but in addition, the possibility then exists for a decrease in the backscatter cross section considerably below the value for the conducting core itself. Although such plasma-conducting core configurations may not be realizable in the laboratory, large decreases or ``dips'' in the electromagnetic backscatter from hypersonic projectiles have been observed, and there is the possibility that an ionized cloud surrounding the projectile is responsible for the dip, perhaps through the mechanism described here. In this paper, an analysis of this ``resonance-dip'' phenomenon is described in some detail for the problem of a cylindrical or spherical conducting core surrounded by a uniform concentric plasma layer.
Peierls Stress Dependence on Dislocation Width
Authors: Hobart R.
Published: April 2005

A numerical calculation of the Peierls stress and energy in the Frenkel—Kontorova dislocation model is reported. The calculated stresses are compared with the theoretical predictions of V. L. Indenbom that they decrease exponentially and I. M. Lifshitz that they decrease as the inverse fifth power with dislocation width. The results are in essential agreement with those of Indenbom. The Peierls stress and energy values obtained by Indenbom are, however, only about half those of the present calculation. This is, perhaps, due to the fact that Indenbom, like Peierls and Nabarro, uses a continuum approximation to determine the atom positions. The present method has particular advantages for calculating the small difference in energy between the unstable and stable dislocation configurations and for verifying that this difference is indeed the minimum barrier. When the elastic constants of polycrystalline copper are used, the present model predicts a Peierls stress to shear-modulus ratio of 6×10−5, which is about an order of magnitude less than the value obtained by Seeger in his interpretation of the Bordoni experiment on copper.
Magnetoresistance of Copper-Plated Bismuth Fibers
Authors: Del Castillo G. , Fast R. W.
Published: April 2005

The magnetoresistance of bismuth fibers has been used in our laboratory for measuring magnetic fields at low temperatures. Fibers 2.2 mm long and 25 μ in diameter are quite sensitive and have a very good spatial resolution. It was found that the magnetic field sensitivity of these fibers can be increased by electrolytic copper plating; there is, however, an optimum amount of copper deposited which gives maximum sensitivity. At 14 kG the sensitivity can be increased by about a factor of three from the no-plating case. Magnetic field sensitivities of 1.4 V/A-kG at 14 kG and 4.2°K have been obtained. It has been observed that the response of the copper-plated fibers is quite linear below 1 or 2 kG and above 4 or 5 kG. The low-field sensitivity is several times greater than the sensitivity at 14 kG.
Electron Irradiation of Al-1.7 at.% Cu in the Reverted Condition
Authors: Herman H. , Kauffman J. W. , Fine M. E.
Published: April 2005

Electron irradiation with doses of 1018 electrons/cm2 at 1.5 MeV of an Al-1.7 at.% Cu alloy in the reverted condition does not result in enhanced nucleation of Guinier-Preston zones. An incubation time is still observed on reaging at 30°C, after irradiation at the temperature of liquid nitrogen. The difference in nucleation after quenching from 500°C and after reversion at 200°C is thus apparently not due to the difference in vacancy concentration alone. Irradiation, however, does result in an increased degree of decomposition of the solid solution, and this demonstrates the important role played by vacancies in the formation of zones.
Shear-Wave Interference observed by Optical Birefringence Induced in a Viscoelastic Liquid
Authors: Schrag J. L. , Guess J. F. , Thurston G. B.
Published: April 2005

A theoretical and experimental study of the shear-wave field and the associated optical birefringence produced by interfering primary and reflected wavetrains propagating in a viscoelastic medium is presented. The shear-wave field is generated by two parallel planes, one oscillating sinusoidally in its own plane, the other held motionless at a fixed distance from the driving plane. The shear-wave propagation is characterized by a complex propagation constant, while the optical birefringence is related to the shear strain rate in the field by a complex mechano-optic constant. The shear-wave-induced birefringence is analyzed by a determination of the modification of the state of polarization of incident circularly polarized light upon passage through the medium. The limiting cases of small and large separation between generating surface and reflecting surface with respect to the shear wavelengths in the medium are useful for determination of the propagation constant and the mechano-optic constant, while intermediate values of separation of surfaces are useful for demonstrations of the character of the stationary wave patterns. Theoretical determinations of the velocity gradient distribution in the medium for various ratios of surface separation to shear wavelength are presented, together with experimental determinations for an aqueous suspension of milling yellow.
Refractive Index of SiO2 Films Grown on Silicon
Authors: Pliskin W. A. , Esch R. P.
Published: April 2005

By more precise variable angle monochromatic fringe observation (VAMFO), it has been found possible to improve the precision of thickness determinations of transparent thin films (800 Å to several microns) on reflective substrates to better than 0.1%, and to extend the determination of the refractive index to films as thin as 900 Å. The measured refractive indices (at 5459 Å) of silicon dioxide films grown in steam and/or dry oxygen (atmosphere pressure) at 980° to 1200°C varied from 1.4610 to 1.4624 for 3500- to 6800-Å films. These compare with the refractive indices (at 5461 Å) of 1.4614 for a thick (2.148 μ) steam-grown film (at 980°C) and 1.4619 for a thick (2.135 μ) oxygen-grown film (at 1200°C). The technique has also been used to measure the refractive indices of thin films (>900 Å) other than thermal SiO2.
Dielectric Properties of Cobalt Oxide, Nickel Oxide, and Their Mixed Crystals
Authors: Rao K. V. , Smakula A.
Published: April 2005

Dielectric constant κ′, loss κ″, and conductivity σ of single crystals of CoO, NiO, and mixed crystals of CoO–NiO as a function of frequency from 102 to 1010 cps and temperature from −193°C to 400°C have been determined. The dielectric constant κ′ is constant (12.9 at 25°C) in the whole frequency range in CoO. It decreases with frequency in NiO and mixed crystals CoO–NiO. In NiO κ′ reaches a constant value (11.9 at 25°C) at 105 cps, and in CoO·NiO (12.3 at 25°C) at 1010 cps. The dielectric constants extrapolated to 0°K are 10.9, 10.0, and 9.1 for CoO, CoO·NiO, and NiO, respectively. In all crystals the dielectric constant increases exponentially with temperature. Using modified Debye equations, two thermal activation energies for κ′ have been obtained: 0.042, 0.027, and 0.018 eV for temperatures below 40°C (frequency-independent region); 0.33, 0.20, and 0.16 eV for temperatures above 40°C, for CoO, NiO, and CoO·NiO (frequency-dependent region). The plot of log σ vs 1/T gives straight lines for CoO from 400° to 100°C, and NiO from 400° to 25°C with activation energies 0.73 and 0.66 eV. At lower temperatures the activation energies decrease continuously. The mixed crystals have two activation energies, one at high temperatures and the other at low temperatures. Variation of the activation energy with composition at high temperatures is less than that at low temperatures. The variation of activation energies in mixed crystals is correlated to lattice distortion and an increase of trivalent ion concentration.
Effect of Initial Velocity on One-Dimensional, Bipolar, Space-Charge Currents
Authors: Howes Walton L.
Published: April 2005

Oppositely directed flows of positive and negative charges constitute a bipolar current. A general case is analyzed in which the charges traverse the evacuated space between plane-parallel boundaries and all particles of a given charge species are monoenergetic. Moreover, it is assumed that the charges may possess nonvanishing initial kinetic energy. This represents an extension of analyses by Langmuir and Müller-Lübeck for vanishing initial kinetic energy.

Sample calculations of dimensionless current densities, electric and potential fields, and charge-density distributions are exhibited for cases where the electric field is assumed to vanish at one boundary but the species initial velocities may not. It is shown that resulting ion currents may be several times the Child's law limit if initial kinetic energies are of the order of the potential energy.
Changes in the Soft X-Ray L Emission Spectra with Oxidation of the First Series Transition Metals
Authors: Fischer David W.
Published: April 2005

Changes which occur in peak positions, band shapes, and intensities with oxidation are presented for the five main L emission lines from the first-series transition metals. It is shown that the L bands shift in wave-length when going from metal to oxide, the amount of shift depending on the metal target and its state of oxidation. The dependence of the LII/LIII intensity ratio on accelerating potential, valence state, and atomic number are also presented and discussed.

A flat-crystal vacuum spectrometer with electron excitation and a thin-window flow-proportional counter was used to obtain the data.
Production of Large Electric Fields in Dielectrics by Electron Injection
Authors: Lackner H. , Kohlberg I. , Nablo S. V.
Published: April 2005

Targets of Lucite and polystyrene were irradiated by a 1.5-MeV electron beam until breakdown occurred. Framing camera films of these events show a steadily decreasing thickness of the fluorescing region until breakdown, at which time the thickness returns to its original value. This is interpreted as a decrease in electron range with charge buildup, with electric field strengths in excess of 6.3 MV/cm inferred for one of the cases (Lucite) studied.
Inelastic Scattering of Fast Electrons by Crystals. I. Interband Excitations
Authors: Whelan M. J.
Published: April 2005

The inelastic scattering of fast electrons due to interband electron transitions in crystals of Li, Be, Ne, Al, and Cu is examined making use of single atom matrix elements given by Freeman. Values of the Fourier coefficients Vg and Vgi of the real and imaginary part of the potential are computed for 100-kV electrons. It is concluded that while interband transitions may account for an appreciable part of the average absorption due to Voi, Vgi is too small to account for the anomalous absorption effect observed in crystals. The result is in agreement with Yoshioka's conclusion based on the Fermi-Thomas model.
Extinction Contours in Whiskers
Authors: Jackson K. A. , Wagner R. S.
Published: April 2005

Extinction contours observed in silicon whiskers in the electron microscope have been studied. The details of the extinction contours depend, in general, on the orientation of the whisker and the geometry of the reflection. Several interesting diffraction effects have been observed. The intrinsic angular width of the electron beam can be determined from the extinction contours. In some cases, the extinction contours outline the cross section of the whisker, revealing directly the morphology of the whisker.
Design of Efficient Explosively Driven Electromechanical Energy Converters
Authors: Frankenthal Shimshon , Manley Oscar P. , Treve Yvain M.
Published: April 2005

The conversion efficiency of a lumped-parameter, explosively driven electromechanical energy converter is studied. Numerical results of the study, which show the relationship among the device parameters required for unit conversion efficiency, are presented.
Single-Crystal Growth of Thorium Dioxide from Lithium Ditungstate Solvent
Authors: Finch C. B. , Clark G. Wayne
Published: April 2005

Single crystals of ThO2 were grown from molten Li2O· 2WO3 solvent at 1225°–1300°C. Growth occurred primarily by solution transfer from ThO2 nutrient at 1250°–1350°C to seeds in regions 20°–75° cooler. The resulting crystals, optically transparent octahedra up to 3 mm on edge, contain <500 ppm W and <50 ppm Li as major impurities. The method was also used to prepare ThO2 crystals containing limited amounts of several lanthanide ions. Increased growth rates were obtained by adding 1 wt% B2O3 to the Li2O· 2WO3 solvent.
Intermediate Forms of Stacking-Fault Tetrahedra in fcc Metals
Authors: Mendelson S.
Published: April 2005

Equations for intermediate forms of stacking-fault tetrahedra in fcc metals are derived. The energies for truncated diverging and converging stacking-fault tetrahedra and multiple truncated tetrahedra are evaluated. The results show that intermediate forms of stacking-fault tetrahedra are stable for sizes in the range for which the Frank dislocation triangle is usually assumed to be the stable form. It is found that the multiple truncated form can start to collapse into an (a/2)[110] prismatic dislocation triangle in gold and aluminum for sizes greater than 900 and 100 Å, respectively.
Energy Distribution in a Glass: Nd3+ Laser Rod
Authors: Borrelli N. F. , Charters M. L.
Published: April 2005

The radial dependence of the absorbed energy distribution in a cylindrical rod of Nd3+-glass pumped with a xenon source has been determined. Using the exact Nd3+-glass absorption spectrum, both the total absorbed energy and the absorbed inversion energy are calculated to determine the magnitude of the energy dissipated by the host glass. In general, absorbed inversion energy and the dissipated energy are not uniform across the radius of the rod, although a value of 5×1020 ions/cm2 for the Nd3+ concentration, multiplied by the rod radius, gives a fairly uniform distribution.
Hysteresis Studies of Reactor-Irradiated Single-Crystal Barium Titanate
Authors: Glower D. D. , Hester D. L.
Published: April 2005

Nuclear reactor irradiation of single-crystal BaTiO3 causes an increase in the coercive field (Ec) and a decrease in the remanent polarization (Pr). The magnitude of these changes, for a particular level of irradiation, depends upon the polarization state of the crystal during irradiation; crystals in the polarized state during irradiation are more resistant to radiation damage than are virgin crystals. The radiation damage rate is only slightly dependent upon crystal thickness. The magnitude of the change in Pr depends significantly, for irradiation levels below 1018 nvt (E>0.1 MeV) fast neutron flux and the associated 1010 rad (H2O) gamma dose, upon the particular loop for which data are reported; the first loop after irradiation indicates a damage accumulation but this damage is annealed by an external field in approximately 70 consecutive loops. The coercive field is relatively insensitive to irradiation until the total accumulated exposure mentioned above, but Ec increases in an asymptotic manner at levels which are about a factor of two or three greater. The changes in Ec and Pr are interpreted in terms of a radiation damage model involving a buildup of a space charge (with associated strain) due to the trapping of ionized carriers in the domain walls of the crystals.
Infrared Dielectric Constant and Ultraviolet Optical Properties of Solids with Diamond, Zinc Blende, Wurtzite, and Rocksalt Structure
Authors: Cardona Manuel
Published: April 2005

The room-temperature optical constants of InP, CdTe, and ZnTe are calculated for photon energies up to 20 eV by the Kramers-Kronig analysis of the normal-incidence reflection spectra. Data at 77°K are also presented for ZnTe and CdTe. At these temperatures, asymmetries in some of the peaks in ε2, of the type attributed by Phillips to resonant exciton effects interacting with a continuous background, are seen. The position of the E2 peaks (due to transitions at X) is listed for materials of the diamond-zinc blende family, as observed in the spectrum of R (the reflection coefficient), ε1, ε2 (real and imaginary parts of the dielectric constant) n, k (real and imaginary parts of the refractive index), and the absorption coefficient α. We have also listed the various peaks corresponding to E2 peaks of zinc blende for materials with wurtzite structure. The infrared dielectric constant ε∞ is calculated for these materials from the position of E2 on the base of Penn's model for an isotropic free electron gas with an energy gap. Good agreement with the experimental values of ε∞ is obtained. The model is generalized to treat PbS, PbSe, PbTe, and SnTe. Good agreement between calculated and experimental values of ε∞ is also obtained for these materials.
Turbulent Free Convection in Czochralski Crystal Growth
Authors: Wilcox W. R. , Fullmer L. D.
Published: April 2005

Turbulent free convection of the melt during growth of calcium fluoride crystals by the Czochralski technique has been observed visually and by thermocouple measurement of the attendant temperature fluctuations. Such fluctuations, on the order of 30°C, were shown to cause growth rate fluctuations, and explain the origin of some of the striations previously observed in Czochralski-grown semiconductor crystals. Effects of operating variables on the turbulence were measured. The best method for reducing or eliminating the turbulence was shown to be reduction of the vertical temperature gradient by use of reflectors or after-heaters around the crystal.
Thermal Conductivity of High-Purity Iron at Low Temperatures
Authors: Arajs Sigurds , Oliver B. F. , Dunmyre G. R.
Published: April 2005

Thermal conductivity (λ) of a high-purity iron (99.998+% Fe) has been studied as a function of temperature (T) between 7° and 200°K. The λ vs T curve reaches a maximum of about 15 W-cm−1 °K−1 at 21°K. This value is considerably larger than that of 4.5 W-cm−1 °K−1 observed before by Kemp et al. in 1959. Our measurements are in qualitative agreement with the theoretical expectations for a high-purity iron. The problem, associated with accurate determination of the Lorenz number and the thermal resistivity due to electron-phonon scattering at low temperatures in iron, is briefly discussed.
Observations of Dislocations in Copper using Borrmann Transmission Topographs
Authors: Young F. W. , Sherrill F. A. , Wittels M. C.
Published: April 2005

Using the Borrmann diffracted beams for Ag Kα radiation, x-ray topographs have been made of copper crystal plates 1 × 1 × Z cm, Z ≦ 0.1, with (111) faces. Dislocation lines were generally recorded as lines of less intensity on the x-ray plate. Both annealed and neutron irradiated crystals were investigated. In the latter the dislocations were pinned and were not moved by the small stresses accidently imposed while making the topographs; and dislocation arrangements in the bulk crystal were determined. The Burgers vectors were deduced from {111} topographs, employing the condition that for no contrast g· b = 0. For edge dislocations, the additional condition g × n = 0 was necessary for no contrast, and it was demonstrated that this type of contrast was more pronounced for dislocations grouped in a slip trace. It was found that dislocations could be seen all the way through crystals for Z = 0.06 cm. A semiquantitative correlation has been established between etch pits formed at dislocation sites on the (111) surfaces and the dislocations revealed by the x-ray topography. It has been possible to obtain complete sets of topographs on only a few annealed crystals; for these, an analysis of the dislocations produced by accidental microstrains has been possible.
Field Effect of the Reflectivity in Germanium
Authors: Seraphin B. O. , Hess R. B. , Bottka N.
Published: April 2005

This paper reports on simultaneous measurements of the reflectivity at normal incidence between 0.7 and 4.6 eV and the field effect of the surface conductance over a wide range of different surface conditions in germanium samples. In the wavelength region of direct interband transitions, the reflectivity is a function of the surface potential. It is concluded that the electric fields in the surface potential barrier are strong enough to change the optical properties of the surface region by Franz—Keldysh effect. A theoretical estimate based on this assumption reproduces the experimental results qualitatively. Since the effect is observed in reflection rather than in transmission, the influence of an electric field on interband transitions can be studied well above the fundamental absorption edge. It is shown that they are affected by an electric field in a way similar to the transitions which produce the fundamental absorption edge. It is further concluded that the field-induced change in the absorption coefficient ``undercuts'' the field-free absorption curve in the top portion of the fundamental absorption edge as predicted by the theory of the Franz—Keldysh effect.
Current Distribution in a Thin-Film Superconducting Strip Transmission Line
Authors: Sass A. R. , Skurnick I. D.
Published: April 2005

In the long-wavelength limit, the current distribution in a thin-film superconducting strip transmission line can be described by an inhomogeneous Fredholm equation of the second kind. By considering a fluxoid conservation derivation of this equation, physical insight into the structure of the kernel follows naturally. An approximate analytic solution to the integral equation is derived for a specified range of geometrical parameters commonly encountered in practice. The solution is obtained by making use of the Liouville—Neumann method of successive iterations and approximating the resulting series by a series involving powers of a defined coupling factor. It is shown that the critical current of the thin-film superconducting strip transmission line, based on the calculations in the paper and a critical-current-density hypothesis, is underestimated by less than 10%.
Transition Probabilities for some Ar II Laser Lines
Authors: Statz H. , Horrigan F. A. , Koozekanani S. H. , Tang C. L. , Koster G. F.
Published: April 2005

In the Ar II system transition probabilities are being calculated between states arising from the 3p44p and 3p44s configurations and between states of the 3p44s and 3p5 configurations. We compare these calculations with previous theoretical and experimental work relating to the above-mentioned transitions as well as to laser data. It is found that the various observed laser transition thresholds between the considered configurations are in reasonable agreement with the calculations. It appears that the various upper maser states are being pumped nonuniformly. It is also found that laser action should persist to rather high current densities. We estimate that, in 2-mm-diam tubes, output powers of at least 10 W/cm3 of gas should be obtainable.
Thermal Diffusivity Measurements with Radial Sample Geometry
Authors: Carter R. L. , Maycock P. D. , Klein A. H. , Danielson G. C.
Published: April 2005

A method has been developed for taking thermal diffusivity data at elevated temperatures with a cylindrically symmetric sample consisting of a stack of disks. An axial heater is turned on and the temperatures at three radii in the midplane are recorded as functions of time. The temperature data from the inner and outer radii are used as empirical boundary conditions, and the temperature data from the middle radius are used to obtain the thermal diffusivity. A computer has been programmed to make the calculations by the method of finite differences. Thermal diffusivity measurements have been made from 26° to 895°C on Armco iron. The values found for the thermal diffusivity by this radial method agree well with the values found by Shanks et al. who used a longitudinal method with a finite rod. The radial method is particularly advantageous when samples in the form of disks, but not in the form of long rods, are available.
Chemical Inhomogeneities and Square B-H Loops
Authors: Goodenough John B.
Published: April 2005

It is shown that in ferrites exhibiting spontaneously square B-H loops, reverse-domain nucleation may occur either at a grain boundary or at a chemical inhomogeneity having a volume roughly 0.1 of a grain volume, a magnetization about 2% different from that of the parent matrix, and no static crystallographic discontinuity at the inhomogeneity-matrix interface. It is pointed out that such chemical inhomogeneities may occur in spinels having Jahn-Teller ions in concentrations that are too small to produce a cooperative, static distortion of the entire crystal from cubic symmetry. It is postulated that the formation of such inhomogeneities is responsible for the sharp knee in spontaneously square B-H loops found in many ferrites containing Mn3+ and Cu2+ ions, in particular the magnesium-manganese composition used in memory-core ferrites.
Work Function Measurements of Nickel, Molybdenum, and Tungsten in a Cesium-Hydrogen Atmosphere
Authors: Rump B. S. , Gehman B. L.
Published: April 2005

The addition of a second component to the cesium gas phase of a thermoionic generator could increase its efficiency by reducing the work functions of the electrodes.

The different possible additives were screened and hydrogen, since it appeared to be the most promising, was chosen for further study.

The work function reduction of cesium-covered nickel, molybdenum, and tungsten due to the presence of H2 in the gas phase ranges from 0 to 0.5 eV. An equilibrium condition can be established between the surface and the gas phase to make the low work function surface stable at elevated temperatures.
Crystal Growth and Electro-Optic Effect of Bismuth Germanate, Bi4 (GeO4)3
Authors: Nitsche Rudolf
Published: April 2005

Single crystals of bismuth germanate Bi4(GeO4)3 having the eulytine structure, space group Td6, were grown. They were crucible-free pulled from a pool of molten material produced in its own powder at 1040°C by a thermal imaging technique. The material has an index of refraction of 2.07 and transmits light between 0.4 and 6.0 μ. The electro-optic coefficient r41 was determined to be 1.03·10−10cm/V. Although materials with higher r41 values are known, Bi4(GeO4)3 may find applications because the growth of large crystals appears possible by classical pulling techniques. A large variety of chemical substitutions are possible in the eulytine structure and might lead to improvements in the magnitude of r41.
Validity of the Floating Double-Probe Method in a Magnetic Field
Authors: Sugawara M. , Hatta Y.
Published: April 2005

This paper is concerned with the experimental determination of the arrangement of the double-plane probes and of an upper limit of a magnetic field for valid double-probe measurement. One of the most reliable arrangements is that of two probes facing each other and situated parallel to the field. Also, the spacing of the probes must be significantly larger than 2λD. The upper limit of the magnetic field, below which the double-probe method remains reliable, is determined mainly by the diffusion-controlled collecting mechanism.
Demagnetizing Factors of Rods and Tubes Computed from Analog Measurements
Authors: Okoshi Takanori
Published: April 2005

A method of computing demagnetizing factors using a resistance network analog or an electrolytic tank has been devised, and the demagnetizing factors for spheres, rods, disks, and tubes have been computed for the case μ = ∞. When the size of the model on the analog is appropriate, the value obtained for a sphere is within 1% of the theoretical value of ⅓. Although the demagnetizing factor is not a precise concept for rods, disks, or tubes, in which the induced magnetization is not uniform, this term is often used for convenience. In this paper, the ``ballistic demagnetizing factor'' (defined in terms of the mean magnetization over the median cross section of the object) is considered. The values obtained for rods and disks are compared with those found in the literature, principally with Bozorth and Chapin's compiled values. Typical results are 0.37 (0.47), 0.223 (0.27), 0.117 (0.14), and 0.052 (0.056) for (L/d) = ½, 1, 2, and 4, respectively, where (L/d) denotes the length-to-diameter ratio and the values in the brackets are the previously used values. The axial nonuniformity of the magnetization in rods and tubes is also measured and discussed.
Harmonic Generation and Parametric Oscillations in a Plasma
Authors: Krenz J. H. , Kino G. S.
Published: April 2005

Nonlinear rf effects in plasmas are discussed in this paper. It is shown that the strong type of harmonic generation mechanism is due to the equation of motion for the plasma electrons being nonlinear, as is the relationship between current and velocity. A theory of plasma harmonic generators and parametric oscillators is given. Input reaction is taken into account and it is shown that a resonance at the output frequency tends to lead to high efficiency. Such a resonance is the electrostatic resonance of a plasma sphere. Experiments carried out with a small spherical rf discharge are described. A 25% conversion efficiency to the second harmonic of an S-band signal has been obtained. Measurements have been made up to the seventh harmonic. For maximum efficiency a plasma resonance at the harmonic of interest is required. By tuning the system to be resonant at half the input frequency, parametric oscillations were obtained at this frequency, thus proving that the nonlinearity must be of a reactive type. It is believed this is the first time that parametric oscillations have been observed in a plasma.