bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion of Interstitial Solutes in the Group V Transition Metals
Authors: Powers R. W. , Doyle Margaret V. 
Published: April 2005

Mechanical relaxation measurements are used extensively to obtain information on the diffusion rate of interstitial solute atoms in body-centered cubic metals. Such studies have been stimulated by a model, developed by J. L. Snoek, which yielded a relationship between a relaxation time, an experimental parameter, and the diffusion coefficient of the solute atom. Although Snoek's model was confirmed very well for solid solutions of carbon or nitrogen in α-iron, a number of anomalies were observed when relaxation studies were extended to the group V transition metals.
An extensive experimental study has been made of the factors that influence relaxation times. The anomalous behavior of the group VA metals can be accommodated within the framework of Snoek's model by taking account of the specific nature of solid solutions based on these metals.
Diffusion data obtained by a variety of relaxation techniques are presented for oxygen, nitrogen, and carbon in vanadium, niobium (columbium), and tantalum. These data are in agreement with those obtained by the more conventional concentration gradient techniques in the few instances where such information is available. The pattern of activation energies suggest that lattice strain considerations alone are insufficient to explain the activation process involved in interstitial diffusion.
Elastic Moduli of Single-Crystal Gallium Arsenide
Authors: Bateman T. B. , McSkimin H. J. , Whelan J. M. 
Published: April 2005

Velocities of propagation of high-frequency ultrasonic waves and the adiabatic elastic moduli for single-crystal gallium arsenide are reported. Data at 25°C were obtained in the range of 20–180 mc/sec.
The elastic moduli based on a density of 5.307 g/cm3 in units of 1012 dynes/cm2 are c11 = 1.188±0.14%; c12 = 0.538±0.36%; c44 = 0.5940±0.14%.
Power Density of Optimally Focused Space-Charge-Limited Electron Beams
Authors: Schwarz Helmut 
Published: April 2005

Factors affecting the power density of optimally bundled electron beams used for the welding, cutting, and machining of solid material are described. The power density and spot size of these beams are expressed as a function of acceleration voltage, beam current, and electron optical characteristics of the system. Assuming that the spherical aberration of the beam-focusing lens system limits the spot size of the space-charge-limited beam, the power density under optimum conditions increases approximately with the fifth power of the acceleration voltage, and decreases with the 7/4 power of the beam current.
A criterion is also given which enables one to determine whether the electron beam at its impact on the workpiece is space-charge-limited or not. Some considerations are given to the neutralization of the electron space charge by ions originating from the background pressure of the vacuum system.
Mechanism for Dislocation Pinning in the Alkali Halides
Authors: Bauer Charles L. , Gordon Robert B. 
Published: April 2005

Changes in the elastic modulus and internal friction of plastically deformed rocksalt, caused by changes in the mean free length of oscillating dislocation segments, have been observed during x-irradiation at temperatures ranging from 10° to 300°K. The rates at which the modulus and damping changes occur during irradiation are found to be independent of temperature; but during irradiation at helium temperature, the magnitude of the effects are smaller. This decrease in magnitude has been shown to be due to the absence of thermal unpinning. Explanations of the pinning process based on the diffusion of point defects to dislocations appear to be ruled out by the rapidity of the low temperature modulus change.
The dislocation pinning produced by irradiation of NaCl, KCl, KBr, and KI at low temperatures is found to be reversible when the crystals are subjected to illumination in, or near, the visible. The wavelength of the illumination which produces the maximum unpinning increases as the lattice constant increases; the effect disappears when the crystals are warmed to room temperature. However, at all temperatures, bleaching a deformed and partially irradiated crystal with F light causes a further modulus increase. The pinning point produced by low temperature irradiation is identified as a dislocation jog in close association with an F center whose absorption band is displaced towards the red by the dislocation strain field. Ionization of the F center results in recombination of its vacancy with the jog; warmup allows the F center to diffuse beyond recombination range.
Optimized Method for Correcting Smearing Aberrations: Complex X-Ray Spectra
Authors: Porteus J. O. 
Published: April 2005

The problem considered is one of obtaining a true spectrum from an observed spectrum containing the effects of finite resolution and noise. The finite resolution gives rise to a smearing aberration which may be represented by the convolution or fold of the true spectrum with a smearing function. The noise introduces an uncertainty which deserves careful consideration if a meaningful correction for the smearing aberration is to be effected.
In this paper an optimized practical solution to this problem is developed for the case of complex x-ray spectra as measured with modern high-precision spectrometers. The solution is based on the conventional Fourier transform solution of the convolution integral and is evaluated by means of a high-speed digital computer. The noise term is handled by a modification of the Wiener smoothing theory in which the stationarity condition is relaxed to permit application to complex x-ray spectra. Introduction of the inherent line shape permits easy evaluation of the required autocorrelation properties of the spectrum. Special consideration is given to the complicating difficulty of long ``tails'' or ``wings'' on the smearing functions encountered in x-ray spectroscopy. The corrected Cl K emission and absorption spectra of crystalline potassium chloride are presented as examples of the correction. Although the present solution was developed for the specific purpose indicated, it may be applied immediately to perform smearing corrections or differentiation of any data adequately represented by the present model and assumption regarding the errors. One possible additional application is the differentiation of electron energy-loss spectra recorded by the retarding field method.
Debris Mechanism of Strain-Hardening
Authors: Gilman J. J. 
Published: April 2005

Strain-hardening caused by ``debris'' produced by multiple cross-glide is discussed. This form of strain-hardening is often linearly proportional to strain, because the debris concentration increases in proportion to strain. The rate of debris production should be sensitive to the applied stress, crystal structure, and crystal orientation as is observed.
The debris mechanism is the only one that explains the self-hardening of isolated half-loops. It also explains the negative temperature dependence of strain-hardening at low temperatures, unlike other theories.
The cross-gliding that leads to debris production is influenced by free surfaces which exert a cross-glide force on obliquely incident dislocations, and which cause extended dislocations to become contracted so they can more easily cross-glide.
Interaction of Parallel Dislocations in a Hexagonal Crystal
Authors: Chou Y. T. 
Published: April 2005

Based on the theory of anisotropic elasticity, the stress field of a single dislocation, the force between two parallel dislocations, and the stress field of various types of infinite dislocation walls and arrays are fully analyzed for a hexagonal crystal.
The attraction sector of an edge dislocation with respect to another edge dislocation of the same sign is no longer the half-quadrant as in the isotropic case. For graphite crystals the attraction sector is about 70° instead of 45°.
The force between two parallel screw dislocations is not central. A tangential component exists, being zero along x and y axes. The tangential force will retard the formation of screw dislocation arrays along any plane except those parallel or normal to the basal plane. Cross slip may be aided or opposed by this force, depending on the direction of applied stress.
The stress field of an infinite dislocation wall or array, either parallel or normal to the basal plane, has similar characteristics to those from isotropic treatment, although their magnitudes and geometries may differ considerably.
Numerical data of six important material constants are tabulated for many common hexagonal crystals.
A New Semiempirical Equation for Gas Flow through Capillaries
Authors: Creutz E. S. , Zumwalt L. R. 
Published: April 2005

A new equation for gas flow through capillaries in low and intermediate pressure ranges is derived without attempting to distinguish between Poiseuille flow with slip and Knudsen flow. It is assumed here simply that the total flow has two components, one characterized by an effective mean free path and the other by an effective viscosity, both of which depend on the ratio of the average pressure in the capillary to a characteristic pressure p1 and, in addition, on the mean hydraulic radius of the capillary and properties of the gas. At low pressure, the usual expression for Knudsen flow is obtained, but in a form which separates out a term, due to a viscous effect, that is related to the ``free-molecule viscosity.'' At high pressure, Poiseuille flow with slip is obtained, but the slip term is cast in a new form in terms of the characteristic pressure p1. Also, our equation has a minimum in the relationship between the permeability and the pressure, which is not given by most permeability formulas but which is observed experimentally under some conditions. At this minimum, diffusion flow and viscous flow are equal in magnitude. At pressures below that corresponding to minimum flow, the phenomenon becomes more ``diffusionlike'' and at higher pressures more ``viscouslike.''
Original data of Knudsen and Klose on the flow rates of various gases through capillaries are well fitted by this new equation at low pressure as well as in the ``transition region'' between Knudsen flow and Poiseuille flow. This fit is obtained by setting the adjustable constant α, which defines p1, equal to unity. Elementary theory of the slip-flow correction also indicates that α should be about unity. Results obtained with this equation are compared with those obtained with Knudsen's four-constant formula.
Avalanche Effects in Silicon p—n Junctions. I. Localized Photomultiplication Studies on Microplasmas
Authors: Haitz R. H. , Goetzberger A. , Scarlett R. M. , Shockley W. 
Published: April 2005

An improved experimental technique is described for the investigation of carrier multiplication in very small areas, particularly microplasmas. A light spot of a few microns diameter is positioned to cover a microplasma of comparable or smaller size and the multiplied photocurrent is measured as a function of reverse voltage.
When the size of the microplasma is much smaller than the light spot, then the multiplication as a function of voltage is dependent upon the characteristics of the microplasma in an upper voltage range just below the microplasma breakdown voltage. In a lower voltage range the microplasma has negligible effect on multiplication. By comparing for the upper and lower voltage ranges the behavior of the reciprocal of the multiplication factor as a function of voltage, it is possible to determine that the diameters of the area of the microplasma regions vary from less than one to more than 5 μ.
Multiplication factors as high as 106 were measured. At high multiplication (M&gt;100), a deviation from the theoretically expected linear dependence of 1/M vs V is observed. This deviation can be described by two effects: (1) the influence of the space charge of the multiplied carriers and (2) the pulsing mechanism of the microplasma. Because of this deviation, microplasma diameters of less than 1 μ cannot be accurately determined.
Another consequence of the pulsing effect is an apparent negative resistance in the V—I characteristic of a diode containing a microplasma. Dependence of the apparent negative resistance on load resistance, shunting capacity, and light intensity was investigated, and can be explained with the pulse model.
Faulting and Electroluminescence in Hexagonal ZnS Phosphors
Authors: Peters T. , Singer J. , Brophy V. A. , Birman J. L. 
Published: April 2005

Controlled experiments have been conducted to isolate the processing parameters which produce bright electroluminescence in hexagonal ZnS:Cu, Cl phosphors. Crystal structure, in particular, was studied as it is affected by the mechanical, thermal, and chemical treatments of this processing. The correlation between electroluminescent brightness and stacking disorder which has often been suggested has been more quantitatively established. It was possible only partially to separate the effects of the entry of activator (Cu) from those of faulting upon electroluminescence. It was found that these two phenomena are intimately related in their importance for high brightness.
The nature and extent of the disorder has been investigated by precision x-ray diffractometry of the powders and by single-crystal x-ray diagrams of individual granules from them. Each granule has been found to be heterogeneous to xrays so that the analysis of the powder patterns is not straightforward. Much, or most of the disorder is obscured in the background of powder patterns and shows itself clearly only on single-crystal diagrams. The latter have been analyzed according to Jagodzinski's model based on two independent fault parameters; the fits obtained with this model between calculated and observed x-ray scattering are impaired by heterogeneity. The analysis discloses that the disorder in the homogeneously scattering-faulted regions may be an order of magnitude larger than indicated by the line breadth of the parent phase, which indicate faulting frequencies seldom exceeding 3%. Coherence in both the transformed and residual parent phase is favored by faulting in the presence of activator during the processing which produces bright EL. This coherence is lacking, even when faulting is extensive, if the disorder occurs without activator; under such conditions EL is practically not observed.
Conclusions reached in the past about the effect of structure upon EL, and also upon birefringence in ZnS phorphors, should be re-examined for the validity of the x-ray diffraction work on which they may have been based, inasmuch as in the course of the present work it has been shown that high precision diffractometry and single granule diagrams are needed to obtain an adequate picture of the disorder. Film diffraction may be entirely misleading.
Work Function and Thermal Desorption in the System Thorium-on-Rhenium
Authors: Anderson J. , Danforth W. E. , Williams A. J. 
Published: April 2005

This investigation consists of two different but related parts.
1. The thermionic properties of rhenium and rhenium with an adsorbed layer of thorium atoms, were investigated. The Richardson constants for rhenium were found to be φ=4.85 eV, A=66 A per cm2-deg2. The work function decreases with increasing thorium coverage σ to a minimum of 3.15 eV at σ=4.2×1014 atoms per sq cm then rises to a constant value of 3.3 eV at σ=8×1014 atoms per sq cm. A comparison with the system tungsten—thorium shows that: (a) φmin occurs at the same surface density in both cases, (b) φconst is attained at the same surface density in both cases, and this density is that of the atoms in a (100) plane of thorium metal, and (c) the values of φconst are equal and different from that of bulk thorium by only 0.1 eV.
On the basis of these regularities a model is proposed to explain the variation of φ with σ.
2. The thermal desorption of the adsorbed atoms was studied at temperatures between 2203° and 2468°K. At low coverage the desorption rate per atom η0, was found to be constant with coverage, and to obey the relation η0=CT exp (-ε/kT) with C=4×1010 sec−1 deg−1 and ε=8.30 eV. The desorption rate increased for coverages between 0.05 and 0.5 monolayer and this increase agreed well with the predictions of a theory based on interactions among the adsorbed atoms.
Heat-Transfer Intensity from Induction Plasma Flames and Oxy-Hydrogen Flames
Authors: Reed Thomas B. 
Published: April 2005

The heat transfer of flames generated in the induction plasma torch was measured with a water-cooled copper split-surface probe moved with respect to the flame. The resultant data were inverted mathematically to give the radial distribution of heat-transfer intensity q.
The distribution of q was measured for plasma flames as a function of distance from the nozzle and gas composition, using argon and mixtures of argon with oxygen or helium. For comparison, q was also measured for two oxy-hydrogen flames. The peak q for the various flames ranged from 56 to 145 W/cm2, with total heat transfer ranging from 0.64 to 4.21 kW.
Electron-Beam Probing of a Penning Discharge
Authors: Dow D. G. 
Published: April 2005

An electron beam probe has been used to study the distribution of electric fields within the cold-cathode Penning discharge. Three basically different potential distributions have been observed, in addition to the high pressure mode, which could not be studied with this technique. At the lowest pressures, the potential is roughly parabolic. As the pressure increases, a region develops in the center of the discharge, in which there is no electric field, that is, the potential profile is flat. Upon further increase in pressure, this central portion enlarges until it fills the majority of the discharge. At a pressure in the vicinity of 10−4 mm Hg the mode abruptly changes to one in which there is very little electric field throughout the discharge, although there are reasons to suspect a narrow region of high electric field near the anode. At still higher pressures (about 10−3 mm Hg) there is another abrupt change into the high pressure mode which acts essentially like a magnetically confined glow discharge.
Due to instrumentation difficulties, and end effects of considerable magnitude, it was not possible to measure numerical values for the electric field and potential, but their qualitative behavior has been plotted over a range of pressure, voltage, and magnetic field which is characteristic of the device.
Studies of the Longitudinal Development of Electron—Photon Cascade Showers
Authors: Zerby C. D. , Moran H. S. 
Published: April 2005

Numerical results of the track lengths of photons and charged particles and the energy deposition as a function of depth out to 10 radiation lengths in copper are presented for the case of electron-initiated electron—photon cascade showers. The incident energy varied from 50 to 45 000 MeV in these cases.
Monte Carlo methods were used to calculate the longitudinal development of the showers in order to obtain the data that are presented. The Bethe—Heitler cross sections which include screening and the correct energy dependence were used from bremsstrahlung and pair production events. The Klein—Nishina formula was used for Compton scattering. Energy losses by ionization collisions were treated as a continuous energy degradation process.
Temperature Transients in Oxide-Coated Cathodes during Pulsed Operation
Authors: Campbell D. A. , Shepherd W. G. 
Published: April 2005

Experimental results presented demonstrate that transient changes in the thermionic emission of oxidecoated cathodes which occur during heavy pulse current drain depend upon the anode material and its past history. When an anode is used which has not been suitably processed a decay characterized by a 100-μsec time constant occurs similar to that described by Sproull, and by Matheson and Nergaard. When a Ti anode which has been suitably processed is used the emission decay no longer occurs and contrariwise an emission enhancement is observed. An experimental study of the emission enhancement leads to the postulate that the effect is a consequence of a temperature increase at the emitting surface.
A solution to the heat equation subject to boundary conditions appropriate to an oxide-coated cathode during pulsed current drain is obtained taking into account the Joule heating (J2ρ), emission cooling (Jχ), and radiation at the emitting surface. The analysis shows that for active cathodes significant temperature changes can develop at the surface of the oxide coating during single pulses of microseconds duration. The temperature changes inferred from experimental results presented are in agreement with the predictions of the theory. A numerical solution appropriate for conditions during temperature limited current drain has been obtained for the nonlinear heat equation which shows that a thermal instability can develop in active cathodes passing high current densities. It is proposed that this thermal instability can account for the phenomenon of cathode sparking.
Slow Waves in Ferrites and Their Interactions with Electron Streams
Authors: Spector J. , Trivelpiece A. W. 
Published: April 2005

The slow waves that propagate in longitudinally magnetized ferrite rods enclosed in cylindrical wave-guides are investigated theoretically. The backward, azimuthally symmetric volume waves that propagate in a lossy ferrite rod are studied with the quasistatic analysis and the lossy permeability tensor derived from the Bloch-Bloembergen phenomenological formulation. The attenuation constant is proportional to the linewidth, and for polycrystalline yttrium iron garnet (YIG) (ΔH ≈ 50 Oe), the loss is approximately 30 dB/cm. The interaction of these waves with an electron stream which passes longitudinally through a hole in the center of the ferrite rod is studied; for normal values of beam perveance (∼10−6 A/V3/2), backward-wave oscillations should occur only for rods having a linewidth less than several oersteds and a length greater than a few centimeters. When the ratio of rod radius to beam hole radius is 1.5, the interaction parameter C is reduced by about 25% of the value when this ratio approaches infinity.
Brillouin diagrams are shown for the azimuthally dependent volume and surface waves in a lossless ferrite. Also, the results of a dynamic analysis are shown demonstrating the relationship between the magnetostatic modes and the waveguide modes. The quasistatic analysis is shown to give a close approximation to the correct dispersion relation even in the limit of fast waves, provided the radius is sufficiently small.
Flicker Noise in Oxide Cathodes Arising from Diffusion and Drift of Ionized Donors
Authors: Van Vliet K. M. , Johnson R. R. 
Published: April 2005

A theory is presented which investigates the emission fluctuations arising from random arrival of barium at the surface of the grains followed by donor migration through the effective emitting part of the grains. The basic causes for the noise are diffusion of donor centers and electrolysis in the coating, processes which are known to be vital in cathode operation. The computed spectra are characterized by a diffusion relaxation time, a diffusion-conduction time constant, and a parameter involving the electric field in the coating surface layer. Three different types of spectra result from this.
Experimental data are reported, mainly on 2×2 diodes which support various aspects of the theory. The dependence of the turnover frequencies on temperature, activation, and current is in good agreement with the predicted results. The magnitude of the noise is close to Poissonian, contrary to previous claims. Recommendations for attaining low flicker noise are given.