bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Instabilities and Flux Annihilation in Grossly Inhomogeneous Superconductors
Authors: Blaugher R. D. , Joiner W. C. H.
Published: April 2005

Magnetic instabilities in the form of reversed field flux annihilation pulses have been observed in a grossly inhomogeneous superconductor. The magnetic field values for which the instabilities are observed depend on the previous field history of the sample. In particular, the annihilation begins at lower values the higher the previous reversed field maximum, and the annihilation instabilities for a given field direction have as an upper limit the maximum field achieved in the opposite direction. The origin of this behavior, as well as the more common phenomenon of flux jumping, is discussed in terms of large-scale potential wells which trap large quantities of fluxoids. Magnetic instabilities are a result of a critical difference between the density of fluxoids within the well and the density of those outside.
Dislocation Climb and Determination of Stacking-Fault Energies in Al and Al-1% Mg
Authors: Kannan V. C. , Thomas G.
Published: April 2005

Quenching and annealing experiments on bulk specimens and hot-stage investigations of climb of loops in thin foils have been made on Al-1% Mg, and the results compared to those for pure aluminum. One percent Mg in solid solution has no effect on the type of loop produced after quenching nor on the precipitation of vacancies after subsequent aging. As in pure aluminum, quenching stresses determine whether Frank or perfect loops are formed in the alloy. Magnesium has little effect on the climb rate of loops, the activation energy being in the range 1.2–1.28 eV, which is similar to the values obtained by identical experiments on pure aluminum. It is concluded that the vacancy-magnesium-atom binding energy is extremely small.

The stacking-fault energies were estimated by comparing the rates of climb of large Frank and perfect loops in the same area of the foil so as to minimize the errors that arise if only the climb of Frank loops is measured. The stacking-fault energies were determined to be 190±10 erg/cm2 for Al-1% Mg and 210±10 erg/cm2 for pure Al.
Numerical Solution of Fick's Equation with Concentration-Dependent Diffusion Coefficients
Authors: Kass W. , O'Keeffe M.
Published: April 2005

A method is developed for obtaining numerical solutions to Fick's diffusion equation when the diffusion coefficient is of the form D=D0Cn, n being an arbitrary positive parameter. The method is applicable to two different types of boundary condition corresponding to frequently encountered physical situations. Some numerical results are presented.
Effect of Thermal and Ultraviolet Radiation on Thermionic Emission from Tungsten
Authors: Stickney R. E. , Sun P. B. , Shaw M. L.
Published: April 2005

When thermal or ultraviolet radiation is focused upon a thermionic cathode, the resulting elevation of the cathode temperature causes the thermionic emission current to increase. Hence a thermionic diode may be used to measure radiation intensity, and it provides a convenient technique for measuring the spectral emissivities of materials at high temperatures. Also thermionic diodes may provide new techniques for detecting molecular beams and for studying chemical reactions at surfaces.

Reported here are experimental data on the effect of thermal and ultraviolet radiation on the electron emission from a tungsten cathode. At high cathode temperatures, the increase in thermionic emission produced by ultraviolet radiation is much larger than the photoelectric emission. The results are described by a simple expression derived from the Richardson equation for thermionic emission.
Effect of Electrostatic Field Gradient in Semiconductors with Diffused Impurities
Authors: Jain G. C. , Al-Rifai R. M. S.
Published: April 2005

Previous works on the evaluation of the collection efficiency of diffused radiant energy converters have assumed a constant electrostatic field in the diffused region. In order to match the theoretical spectral response based on this assumption with the experimental results, extremely low values of minority carrier lifetime were further assumed. No physical explanation is available for these assumptions.

Using the basic diffusion theory, a theoretical investigation of the effects of impurity distribution in diffused semiconductors has been carried out for diffused impurity profiles produced by (1) diffusion from an infinitesimally thin layer of dopant and (2) diffusion from a constant podant source. It has been established that the electrostatic field gradient in the diffused semiconductor acts as an equivalent recombination effect with an equivalent minority carrier lifetime of the order of 10−10 sec. It has been shown that the effect of an electrostatic field gradient is much more predominant than the radiative and nonradiative recombinations.
Equilibrium of Linear Dislocation Arrays in Heterogeneous Materials
Authors: Chou Y. T.
Published: April 2005

The analysis of linear dislocation arrays, piled up in the soft phase of a two-phase material, is extended. The equilibrium positions of dislocations are determined by numerical analysis. A result of the computation is the confirmation of the linear approximation L/n = (A/σ) (α+βK), 0<K≤1. Here, L is the length of the array, n is the number of dislocations, σ is the applied stress, α and β are constants for a fixed n, and A is the usual material constant for the dislocation field. The heterogeneity parameter K is defined as a function of the elastic constants of the neighboring phases, ranging from 0 to 1 for the present study. It is shown that for large arrays of either screw dislocations against a welded boundary or edge dislocations against a slipping boundary, α and β are practically constants for all large n's and α =̇ 2 and β =̇ 1.1. For edge arrays against a welded boundary, only a simple case is examined, i.e., when Poisson's ratio for the two neighboring phases is identical. The linear relation is good in certain ranges. By using the above relation, an inverse square root expression for the applied stress and the length of the array (the Hall-Petch type) is derived for heterogeneous materials.
Propagation of Magnetostatic Spin Waves at Microwave Frequencies. II. Rods
Authors: Damon R. W. , Van De Vaart H.
Published: April 2005

The theoretical transit time is derived for propagation of magneto static spin waves in a rod magnetized either along the axis or transversely to the axis. The group velocity for these waves in an infinite cylinder is combined with the inhomogeneous internal field of a rod to compute the time delay of a wave packet. Experimental observations of microwave pulse delay time in rods of yttrium iron garnet are compared with these theoretical results.
Refractive Index of Calcium Oxide
Authors: Liu C. J. , Sieckmann E. F.
Published: April 2005

A method is described which has been successfully used to produce single crystals of calcium oxide of excellent optical quality from the melt. The absolute refractive index of two of these crystals was determined by the method of minimum deviation at room temperature (22°–26°C) for six wavelengths in the visible spectrum. The observed values for one of the crystals varied from 1.8328±5×10−5 at the wavelength 6562.82 Å to 1.8702±5×10−5 for the Hg line at 4358.35 Å. The corresponding values at these wavelengths for the other specimen were 1.8335±6×10−5 and 1.8708±6×10−5, respectively.
Distribution and Precipitation of Gold in Phosphorus-Diffused Silicon
Authors: Joshi M. L. , Dash S.
Published: April 2005

Distribution of gold in silicon wafers diffused with phosphorus was studied at different depths through electron-transmission microscopy and radio-tracer techniques. Phosphorus-gold precipitates were observed in the surface of the wafer in which gold was diffused from the other side. The distribution and precipitation of gold in the phosphorus-rich regions is shown to be consistent with the Reiss theory of solubility of impurities in doped semiconductors.
Correlation of Metal-Semiconductor Barrier Height and Metal Work Function; Effects of Surface States
Authors: Geppert D. V. , Cowley A. M. , Dore B. V.
Published: April 2005

The validity of the Schottky theory of metal-semiconductor contacts is examined. This is accomplished by deriving values of metallic work function for several metals on Si, CdS, GaAs, and GaP through the use of published values of barrier heights. Values of electron affinity for the four semiconductors are also derived. Close agreement is obtained between the work function values of a given metal on different semiconductors. The derived work function values also agree in most cases with values measured recently under conditions that correspond at least approximately to the conditions existing for evaporated-metal-semiconductor systems. The derived values of electron affinity do not agree, however, in general with the values measured by photoelectric means. It is shown that this disagreement can be accounted for on the basis of a high density of surface states near the valence band edge of the semiconductor. In the case of GaAs, it appears that these surface states move up to the Fermi level for the high work function metals and ``pin'' the barrier at about 0.85 to 0.90 eV.
Effect of Neutron-Induced Defects on the Current-Carrying Behavior of Vapor-Deposited Niobium Stannide
Authors: Cullen G. W. , Novak R. L.
Published: April 2005

The current-carrying capacity of vapor-deposited Nb3Sn can be increased by introduction of structural defects by neutron irradiation. The change in current density per unit of neutron flux is a function of the initial perfection of the material. The characteristics of low-α material (α≈J cH) are altered more than high-α material by irradiation. The current capacity of the material is eventually decreased by continued irradiation. The current behavior of material exhibiting an α less than 15 kG·A/cm2 can be described by a simple Lorentz force model. Material exhibiting an α higher than this is not adequately described by such a model. The electrical scattering cross section of a neutron-damaged area is calculated to be ∼4×10−12cm2.
Singularities in the Coherent Diffuse Scattering of X Rays
Authors: Ishibachi T. , Rudee M. L.
Published: April 2005

It is demonstrated that there is an error in von Laue's treatment of diffuse scattering of x rays from random alloys and that a correct formulation predicts that the diffuse intensity must vanish at reciprocal lattice points. Thus there is no reason to reconstruct the Cowley theory, as has been recently suggested. The physical origin of this effect and some of its consequences are discussed.
Fine-Grain Nickel Ferrite for Microwave Applications at High Peak-Power Levels
Authors: Paladino A. E. , Waugh J. S. , Green J. J. , Booth A. E.
Published: April 2005

Fine-grain ferrites were fabricated by hot-pressing ball-milled and flame-sprayed powders of Ni1−xCoxFe2O4 (where 0≤x≤0.04) and Ni0.973Mn0.027Fe2O4. Threshold fields for subsidiary absorption at Ku-band were significantly increased by decreasing the grain size to 5 μ or less. Between 5 and 10 μ, the critical field hcrit decreased gradually and above 10 μ was independent of grain size. The highest value observed was 192 Oe on a fine-grained nickel-cobalt ferrite vs ∼24 Oe for conventionally fired nickel ferrites. Dielectric losses were reduced to values below 5×10−4 at X-band, and low-field magnetic losses were approximately two to four times those of conventionally fired ferrites of the same composition. No systematic variation in threshold field or magnetic loss was observed with cobalt substitution in fine-grain samples, although threshold fields in general were found to be higher when cobalt was present. The threshold field increased linearly with cobalt substitution on large-grain samples. A Ku-band 90° ferrite phase shifter using a fine-grained, hot-pressed ferrite was capable of operating at power levels in excess of 750 kW/750 W, whereas the same device with a conventional ferrite exhibited nonlinearity below 20-kW peak power.
Growth of Sputtered vs Evaporated Metal Films
Authors: Chopra K. L.
Published: April 2005

The early growth stages of sputtered (S) vs evaporated (E) Ag/mica and Ag/NaCl films have been studied by transmission electron microscopy and electron diffraction. The observed maximum density of the islands at thicknesses less than 20 Å is slightly higher for S films, although the order of magnitude is the same (∼1011/cm2) for both the S and E films. Electrostatic charges carried by the S atoms and the point defects caused by the penetration of the energetic S atoms could account for the observed higher S-island density.

As the film thickness increases, the S-island density at 25°C decreases rapidly to reach a constant value before the film becomes continuous. The corresponding E-island density decreases slowly. The higher mobility, as indicated by the rate of change of the island density, and the observed epitaxial growth of the S films at a temperature considerably lower than that obtained for E films, are attributed to the higher kinetic energy of the S atoms. The E-island density decreases rapidly as the substrate temperature is increased. The decrease in S-island density is, however, accompanied by an increase in the surface area of the islands and formation of bridges between the islands, thereby resulting in coalescence at a smaller nominal thickness than is observed in E films. These observations are explained on the basis of the effects of higher electrostatic charges and kinetic energy of the S atoms.

The activation energies for the diffusion processes, calculated from the temperature dependence of the separation between the islands, are 0.1 and 0.15 eV for S and E films, respectively, at substrate temperature below 250°C. Above 250°C, the activation energies increase rapidly to 0.5 and 0.9 eV, respectively.
Observation of Dislocations in CaWO4 by Transmission Electron Microscopy
Authors: Arbel A. , Stokes R. J.
Published: April 2005

The distribution of dislocations in deformed calcium tungstate was studied by electron transmission microscopy. The photomicrographs confirmed earlier optical observations that (001) 〈100〉 is the slip system of this material between 500°–900°C. Screw dislocations, long edge-dislocation dipoles, quadrupoles, and tangles of dislocations were observed in foils prepared from specimens deformed at 500°C. Specimens deformed at 700°C showed similar features, except that many of the long dipoles had split into long strings of prismatic loops. At 900°C the loops were more isolated and sometimes grew to a diameter exceeding the thickness of the foil. Many single dislocations could also be seen with nearly pure edge or screw orientation. Two models are proposed for quadrupole formation and their relative stability considered. Strain hardening is thought to be due to the interaction of dislocations with multipoles and prismatic circular loops.
Conditions for the Generation of Slip by Diffusion of Phosphorus into Silicon
Authors: Czaja W.
Published: April 2005

On the basis of theoretical considerations it is shown that the critical surface-impurity concentration Nscrit for the generation of slip during diffusion, as well as the depth η0 to which dislocations will move, depend strongly on the impurity concentration profile. A weak dependence of Nscrit on crystal orientation has to be expected also. Nscrit has been calculated for phosphorus diffusing into silicon to be 4.11×1020 cm−3 with the reasonable assumption of a complementary error-function impurity profile. The experimental value is 2.0×1020 cm−3 <Nscrit <2.5×1020 cm−3. The theory has been used to explain details in slip patterns displayed on a {110} surface after etching the sample. Finally the markedly different appearance of slip patterns due to apparently small variations in diffusion parameters is demonstrated and discussed.
Electrical and Magnetic Properties of Compositions in the Tantalum-Carbon System
Authors: Steinitz Robert , Resnick Robert
Published: April 2005

Electrical and magnetic properties have been measured in the tantalum-carbon system from Ta2C to TaC1.0. A large variation of these properties has been found within the wide homogeneity range of TaC: the resistivity increases with carbon deficiency from 25 to about 150 μΩ. cm, and the magnetic susceptibility changes its sign, the material being paramagnetic at stoichiometry and diamagnetic at the low-carbon phase boundary. The temperature coefficient of the resistivity has also been found to be characteristic for each composition and to depend strongly on the Ta:C ratio.

A method for preparation of homogeneous samples of a predetermined carbon content has been developed. The experimental results are discussed in the light of previous theories.
Optical Properties of Epitaxial Films of CdxHg1−xTe
Authors: Ludeke Rudolf , Paul William
Published: April 2005

Epitaxial crystal films of alloys of CdTe and HgTe and BaF2 substrates have been produced by a flash-evaporation technique. The energies of several interband electronic transitions have been measured and found to vary linearly with composition. Arguments are presented that this method produces single-crystal alloy films of accurately predetermined composition.
Transient Resonant Response of a Spin System to a Pulsed Electromagnetic Field
Authors: Joseph R. I. , Silverman B. D.
Published: April 2005

It is shown that the transient response of an inhomogeneously broadened nuclear spin system to a pulsed electromagnetic field can be written as a series of Bessel functions modulated by time-varying coefficients. This series describes the initial buildup of the transverse magnetization and its oscillatory behavior thereafter. When the linewidth is large compared with the oscillation frequency (a), the first term of the series, which involves the zeroth-order Bessel function J0(at), is sufficient to describe the behavior of the system for all times. The leading term of the series differs, however, from the usual result (involving only the zeroth-order Bessel function) by the time-dependent modulating factor, which insures the correct behavior of the magnetization for times comparable with or much shorter than the inverse linewidth.
Photoconductivity in Tetragonal and Orthorhombic Lead Monoxide Layers
Authors: Schottmiller John C.
Published: April 2005

The photoconductive behavior of evaporated layers of lead monoxide in both the tetragonal and orthorhombic crystalline modifications has been investigated. Stoichiometry was controlled on a relative scale by controlling the oxygen pressure during sample preparation, yielding both n- and p-type material. Current—voltage characteristics, optical absorption, and variation of photocurrent with (1) wavelength, (2) applied field, and (3) light intensity are presented and discussed for the two forms. Energy band gaps of 2.0 eV for the tetragonal form and 2.6 eV for the orthorhombic form are indicated. A maximum resistivity of 3×1011Ω·cm with a μτ product of 4×10−7 cm2/V was measured for the tetragonal phase. The corresponding values for the orthorhombic phase were 1×1013Ω·cm and 1×10−9 cm2/V. Whereas in earlier pictures photosensitivity was explained as a contact phenomenon, the present data demand a model such as impurity sensitization or interparticle barrier modulation to explain the observed bulk photosensitivity.
Melting Temperatures of Copolymers
Authors: Colson J. P. , Eby R. K.
Published: April 2005

The melting temperatures (532° to 580°K) of copolymers of tetrafluoroethylene and hexafluoropropylene have been measured on a microscope hot stage. The copolymers had concentrations of perfluoromethyl groups between 0.0275 and 0.075 groups per carbon atom and lamella thicknesses which varied from 340 to 500 Å independently of comonomer concentration. An equation based on the concept of inclusion of the groups within the lamellar crystals as defects has been fitted to the data. The constants of fitting yield the equilibrium melting temperature, 616.6°±4.9°K, the surface energy, 4.5×10−13±1.6×10−13 erg/fold, and the perfluoromethyl defect energy, 0.047±0.003 eV/defect. Within the limits of error, these values are shown to be satisfactory by the possible comparisons with previously reported values or with values deduced from physical models. Neglecting the effect of lamella thickness yields a significantly poorer fit of the data.
Magnetic Interaction Experiments with Shock-Ionized Neon
Authors: Mullaney G. J. , Brown E. A.
Published: April 2005

A shock-tube study of the ionization process in neon and its coupling with an axially symmetric magnetic field is described. Shock Mach number was about 14 and the calculated electron densities were ∼1016 cm−3. The increase in plasma luminosity from the upstream to downstream side of the coil when the magnetic field (25-kG range) was present, stimulated an investigation of the light emission with and without the magnetic field. The emission data and pressure measurements were used to substantiate the model of a magnetically formed diffuser.
Effect of Mechanical Stress on p—n Junction Device Characteristics. II. Generation—Recombination Current
Authors: Wortman J. J. , Hauser J. R.
Published: April 2005

A theoretical model is developed for the effects of stress on generation—recombination currents in p—n junctions. The model is based on stress-induced changes in the energy band structure of the semiconductor and energy changes of the generation—recombination centers. Experimental data taken on silicon mesa diodes are presented which are in good agreement with the theory.
Evaporative Lifetimes of Copper, Chromium, Beryllium, Nickel, Iron, and Titanium on Tungsten and Oxygenated Tungsten
Authors: Shelton H. , Cho A. Y. H.
Published: April 2005

The evaporative lifetimes of Cu, Cr, Be, Ni, Fe, and Ti on W and O-covered W ribbon filaments at temperatures from 1250° to 1750°K have been measured as a function of coverage. The low-coverage lifetimes of these materials on clean polycrystalline tungsten at 1500°K are Cu, 0.01; Cr, 3.0; Be, 0.05; Ni, 1.0; and Fe, 0.7 sec. Less precise measurement of the lifetime of titanium showed it to be much longer than the lifetimes of the other metals studied and extremely coverage dependent.
Wave Propagation in Homogeneous Gyrotropic Compressible Drifting Plasma
Authors: Chawla B. R. , Rao S. S. , Unz H.
Published: April 2005

The three-dimensional electric field wave equation for propagation in homogeneous, gyrotropic, compressible, drifting plasma is derived. The static magnetic field and the drift velocity are both arbitrarily directed. The refractive index equation for oblique plane waves and other particular cases are obtained and shown to agree with previous results.
Optical Mixing with Different Relative Polarization of the Beams
Authors: Weber H. P. , Mathieu E. , Meyer K. P.
Published: April 2005

The phase-matching condition (Δk=0) for optical mixing of electromagnetic waves with parallel k vectors can be attained for various directions in a crystal, if all combinations of direction of polarization for the primary and the generated beams are considered. The phase-matching angles are calculated for the different possible combinations in KDP, ADP, and LiNbO3 at several usual laser wavelengths. The relative strength of interaction for the different combinations for optical mixing is given. Furthermore the sensitivity of the phase-matching condition upon the angle (θ) between the wave vectors (k) and the optical axis (dΔk/dθ or the ``mismatch gradient'') is calculated. The reciprocal mismatch gradient is an important quantity for calculating the conversion ratio in optical mixing of divergent beams. For some cases the numerical result for the relative strengths of interaction and the mismatch gradients lead to more conversion for divergent beams, if we consider combinations of the three interacting waves where two of them are extraordinary rays.
Analysis of a Room-Temperature cw Ruby Laser of 10-mm Resonator Length: The Ruby Laser as a Thermal Lens
Authors: Roess Dieter
Published: April 2005

A nominally plane-parallel ruby laser of 10-mm length was investigated in continuous operation in an ellipsoidal pumping system under water cooling. The laser emits pure transverse modes of low order. The zero-order mode can be described by Gaussian distributions; it corresponds approximately to the mode of a confocal resonator of 9-cm radius of curvature. The resonator curvature is induced by a thermal curvature of the ruby end faces and by a bulk thermal lens effect.

The axial-mode frequencies and the emission-center frequency shift to smaller values with increasing pump power as a consequence of the increasing ruby temperature in cw operation. The relaxation pulses of single axial modes do not overlap in this short laser, and the interaction of different axial modes can be observed in the emission of one mode. Consequences of the observed thermal curvature for the transverse mode selection of cw and pulsed crystal lasers are discussed.
Effect of Interstitial Gases on the Superconducting Critical Temperature of Columbium
Authors: Wiseman Carl D.
Published: April 2005

High-purity electron-beam-melted columbium was doped up to levels of 15 at.% with nitrogen, hydrogen, or oxygen, the precision lattice spacing measured, and the superconducting transition temperatures determined. The relationship between transition temperature and volume change developed for substitutional alloys is shown to be valid also for interstitial gaseous impurities. Beyond the effect each gas had upon lattice distortion, no critical temperature characteristics were observed which were dependent upon the specific element.
Shock Waves in Xenon Flashtubes and Tube Deterioration
Authors: Lang Kenneth R. , Barnes Frank S.
Published: April 2005

The xenon-filled arc discharge tube has found wide applications as an optical pumping source for ruby lasers. An experimental study of the shock waves in the flashtube at laser pumping energies and their effect on tube deterioration has been made. The plasma discharge was investigated by taking high-speed image converter and streak photographs of the discharge and by measuring the relative shock amplitude at the tube walls with a piezoelectric transducer. The velocity of the luminous boundary of the plasma discharge was proportional to the input energy in the range from 60 to 500 J and varied from 90 to 900 m/sec. The luminous boundary velocity remained constant for pressures from 100 to 1500 Torr. The relative shock amplitude measured by the electromechanical transducer was independent of the tube diameter up to 12 mm, increased linearly with the input energy, and increased with gas pressure. Shock data were correlated with efficiency measurements to determine optimum tube and operational parameters. The microscopic effects of the shock wave upon the tube wall indicated that prestressing in compression the exterior surfaces of the glass wall would yield a stronger flashtube capable of higher intensities.
Static Theory of Density and Potential Distribution in a Beam-Generated Plasma
Authors: Dunn D. A. , Self S. A.
Published: April 2005

An electron beam passing through a gas ionizes the gas, and the electrons and ions so produced collect in the vicinity of the beam to form a plasma with a number density that can be much greater than the density of the beam. A one-dimensional static theory for such a system, with a beam either partially or completely filling the space between two parallel planes, gives the plasma density and potential distribution in the space. The theory requires only minor modifications of the Langmuir-Tonks free-fall theory of the positive column. A plasma filling the space occupied by the beam is separated by a low potential sheath from a somewhat lower density plasma that extends to the walls where a second higher potential sheath is formed. A comparison between the results of this theory and some density measurements on beam-generated plasmas reported in the literature gives reasonable agreement.
Grain Boundary Conductivity of Zr0.84Ca0.16O1.84 Ceramics
Authors: Tien T. Y.
Published: April 2005

The effect of microstructure on the ionic conductivity of Zr0.84Ca0.16O1.84 ceramic specimens was evaluated. At low temperatures (<800°C), those specimens of smaller grain size exhibited a higher electrical conductivity. These data suggest high grain boundary conductivity owing to a higher diffusion rate for the oxygen ion along the grain boundary. Activation energy vs logarithm of average grain diameter data gave a linear plot; thus, an estimate of the activation energy for grain boundary conduction could be obtained by extrapolation. This value was found to be about 0.96 eV, whereas the activation energy for the bulk specimen lies in the range 1.24 to 1.30 eV. At temperatures of 1000°C or higher, the difference between grain boundary and bulk conductance is insignificant.
Phonon Radiation by Uniformly Moving Charged Particles in Piezoelectric Solids
Authors: Tsu Raphael
Published: April 2005

The rate of emission and the radiation pattern of coherent phonon radiation were obtained for a charged particle traveling along the symmetry axis of a piezoelectric crystal of hexagonal symmetry. The phonon power per unit frequency radiated by a charged particle is proportional to frequency. Macroscopic equations used in the derivation permit solution of a phonon radiation problem which otherwise would be quite complicated.
Multiple Probe Measurements in High-Frequency Plasma Lasers
Authors: Aisenberg Sol
Published: April 2005

A multiple probe technique is described for the accurate measurement of the retarding potential characteristics of probes in high-frequency electrodeless plasmas. Earlier multiple probe methods are discussed along with their advantages, assumptions, and limitations. The improved triple probe technique, developed for diagnostic measurements in plasma lasers, allows the complete probe characteristic to be traced rapidly. From the retarding potential characteristic for the electrons, the electron temperature and density can be determined for the low-energy electrons, together with the electron energy distribution function.
Slow Viscous Flow of Rarefied Gases through Short Tubes
Authors: Hanks Richard W. , Weissberg Harold L.
Published: April 2005

The semiempirical equation which was shown by Weissberg to be a very close approximation to the rigorous variational calculation of the pressure drop for creeping flow of incompressible viscous fluids through short tubes has been generalized to take into account the slip of a rarefied gas at the tube wall. The generalized equation is ω=ωs+βa/λ̄, where a is the tube radius, λ̄=(μ/P̄)(12πRT/M)12, and ω=F/[14πa2ΔP(8RT/πM)12]. Here, μ and M are the viscosity and molecular weight of the gas, ΔP is the pressure drop P1−P2, P̄ is the average pressure ½(P1+P2), R is the gas constant per mole, T is the absolute temperature, and F=P̄Q where Q is the volume flow. The coefficient β and the slip parameter ws depend only on L/a, the length to radius ratio of the tube: β=(π/8)/[(L/a)+(3π/8)], ωs=(β2/3π)[(128L/a)+(27π2/4)]. Excellent agreement is noted between values of w calculated from the equation given here and values obtained by Knudsen for long tubes and by Lund for short tubes.
Generation of Spin Waves in Nonuniform Magnetic Fields. I. Conversion of Electromagnetic Power into Spin-Wave Power and Vice Versa
Authors: Schlömann Ernst
Published: April 2005

The conversion of electromagnetic power into spin-wave power and vice versa is investigated from a theoretical point of view. The analysis applies to a rod of ferromagnetic material whose two ends are each in a resonant cavity that is connected to a waveguide. The dc magnetic field is assumed to be nonuniform in such a way that the effective wavelength of the spin waves becomes large in those regions of the sample that protrude into the cavities. The theoretical analysis of the excitation process leads to a differential equation which is of the same form as the well-known wave equation except that the wavenumber is a function of position. The conversion efficiency depends on the solution of this wave equation through a simple integral over the wavefunction which has the physical significance of a coupling length. A numerical estimate indicates that substantially complete conversion should be possible.
Generation of Spin Waves in Nonuniform dc Magnetic Fields. II. Calculation of the Coupling Length
Authors: Schlömann Ernst , Joseph R. I.
Published: April 2005

The coupling length is calculated by using two approaches: (a) For a simple model the wavefunction and the coupling length are determined rigorously; (b) More general, approximate results are obtained by means of the WKB method, which is valid if the dc magnetic field varies sufficiently slowly. It is shown that the coupling length is inversely proportional to the square root of the field gradient at the turning point.
Elastic Constants of a (73.8% Ni-26.2% Fe) Ferromagnetic Alloy
Authors: Einspruch Norman G. , Claiborne Lewis T.
Published: April 2005

The elastic constants of a (73.8% Ni-26.2% Fe) ferromagnetic alloy have been measured at 300°K with the following results: C11=23.04, C12=14.44, and C44=11.92 (in units of 1011 dyn cm−2). These results are compared with previously reported work on pure Ni and a (30% Ni-70% Fe) alloy.
Temperatures Generated by the Flow of Liquids in Pipes
Authors: Gruntfest I. J. , Young J. P. , Johnson N. L.
Published: April 2005

In the development of molecular theories of liquid and polymer structure, great importance is attached to stress and time dependences of the apparent viscosity of materials and their solutions. Some of these dependences can be accounted for by the heating of the fluid which is a consequence of the flow. In this report, solutions for the time and space distributions of the temperature in an incompressible fluid flowing steadily in a capillary with isothermal walls are presented. A comparison of the computed temperature changes with observed changes in apparent viscosity of some lubricating oils suggests that the temperature effect is significant. The possible usefulness of the solutions for understanding the origin of turbulence in flow and the heating of a cylindrical rod loaded in torsion is also discussed.
Normal Stress Effects in Second-Order Fluids
Authors: Coleman Bernard D. , Markovitz Hershel
Published: April 2005

In the general theory of the behavior of simple fluids with fading memory in slow deformations, the constitutive equation of those fluids called second-order fluids gives to the equation of Newtonian fluids a correction for viscoelastic effects that is complete to within terms of order greater than two in the time scale. The hydrodynamical behavior of incompressible second-order fluids is determined by three material constants: η0, β, γ, besides the density. We show here that not only the viscosity η0, but also the constant γ which governs certain normal stress effects, is determined by the shear-relaxation modulus of classical infinitesimal viscoelasticity. This result enables us to show that in a slow Couette flow the viscoelastic contribution to the difference in normal thrusts on the inner and outer cylindrical walls has a sign opposite to that of the inertial contribution. We also suggest several practicable methods for measuring β and γ.
Diffusion Mechanism for Tungsten Sintering Kinetics
Authors: Vasilos T. , Smith J. T.
Published: April 2005

The sintering kinetics of cold-pressed tungsten powders have been determined from 1300° to 1750°C. Diffusion coefficients calculated from the sintering kinetics are considerably larger than the diffusion coefficients determined for volume self-diffusion in tungsten. The activation energy for the sintering process is 110.7 kcal/mole, lower than the activation energy for volume self-diffusion. The larger diffusion coefficients and lower activation energy of the sintering process are indicative that the densification of tungsten powder in the temperature range 1300°–1750°C is probably a grain boundary diffusion controlled process.
Crystal Interfaces
Authors: Fletcher N. H.
Published: April 2005

An expression for the energy of an interface of general form between two crystals of arbitrary structures and relative orientations is derived in a form suitable for a variational calculation. This variational approach is applied to a one-dimensional interface between two two-dimensional crystals of differing lattice constants. In general there is a minimum in the interfacial energy when the lattice distances in the two crystals are in the ratio of small integers. Particular cases in which the surface potential is either sinusoidal or parabolic are discussed and detailed curves of interfacial energy as a function of lattice misfit are calculated.
Mechanism of Gold Diffusion into Silicon
Authors: Wilcox W. R. , LaChapelle T. J.
Published: April 2005

Gold was found to diffuse into silicon by a complex mechanism involving a vacancy-controlled interstitial-substitutional equilibrium. This led to very complex diffusion concentration profiles. In analyzing the problem, a new experimental value was found for the self-diffusion coefficient of silicon, 1.81×104 exp(−112±20 kcal/RT) cm2/sec, which compared very favorably with previous data on diffusion of bismuth, germanium, and tin in silicon. The interstitial gold-diffusion coefficient was found to be 2.4×10−4 exp(−8.9±2 kcal/RT), the substitutional gold-diffusion coefficient to be 2.75×10−3 exp(−47±10 kcal/RT), the equilibrium-interstitial gold solubility to be 5.95×1024 exp(−58±10 kcal/RT), and the equilibrium-substitutional gold solubility (Collin's data) below 1200°C to be 8.15×1022 exp(−40.6 kcal/RT).
Molecular Theory for the Tensile Strength of Gum Elastomers
Authors: Bueche F. , Halpin J. C.
Published: April 2005

The tensile strength and ultimate elongation properties of any given amorphous elastomer can be described by a characteristic failure curve. It is shown in this paper that the failure curve can be predicted from a knowledge of the creep curve of the elastomer together with the data from a Mooney-Rivlin plot. The theory relating the ultimate properties to the viscoelastic properties of the elastomer is based upon the idea of a propagating crack, the rate of propagation being limited by viscoelastic mechanisms. Data for the failure curves and creep response for EPR and SBR elastomers are presented and shown to support the theory. Literature data for butyl rubber are also shown to confirm the theory.
Relationship between Morphology and Deformation Mechanisms of Polyolefins
Authors: Sasaguri K. , Hoshino S. , Stein R. S.
Published: April 2005

The birefringence of polyolefins undergoes a change from an initial negative value at low elongation to a positive value at higher elongations. The extent of the negative contribution depends upon time after quenching the sample and upon temperature. The changes result from a change in the mode of crystal orientation. A model involving spherulite deformation and reorientation of crystals within the spherulite is proposed. Changes with time and temperature are ascribed to changes in a parameter γ describing the mobility of crystals within the spherulites. The model is also used to account for variation in the dynamic birefringence with straining frequency.
Evaluation of Small-Angle X-Ray Scattering of Polymers
Authors: Reinhold Chr. , Fischer E. W. , Peterlin A.
Published: April 2005

The influence of the particle factor and lattice factor on the positions of the small-angle reflections of polymer crystalline samples is investigated. Since a single-crystal cake or a polymer solid crystallized from melt supposedly consists of stacks of nearly parallel plate-like lamellae, one may describe the scattering behavior of polymer crystals based on a periodic step function with fluctuating periods (linear paracrystal). In this model the particle factor as well as the lattice factor may shift the scattering maxima out of the positions given by the Bragg equation. Good agreement with the observation that the first order leads to a larger spacing than the second one may be obtained by introduction of an unsymmetrical distribution function for the lamellar thickness.
Secondary Crystallization and Annealing of Polyethylene
Authors: Peterlin A.
Published: April 2005

Annealing of single crystals and of single-crystal cakes of polyethylene leads to an increase in density because the growth of crystal thickness with time reduces the area of the density deficient surface regions. When the same process is applied to the isothermal crystallization and to the annealing of bulk samples, one has to consider the long period distribution of the crystals due to their varying age and thermal history; then one is able to reproduce sufficiently well the experimental data. In particular, starting with inhomogeneous athermal nucleation and uniform three-dimensional growth (n = 3), one obtains a higher initial value of the Avrami exponent (n′ = 3.7), i.e., a faster density increase as a consequence of the relatively rapid decrease of the surface mass defect contribution to the density of the crystals in the first stage of their thickness growth. The extremely slow reduction of this contribution with growing age of the crystals also explains the long tail of secondary crystallization and annealing curves where the crystallinity, although slowly approaching, never reaches unity. The early drop of crystallinity below the calculated values and particularly the observed transition from primary to secondary crystallization, however, being much gentler than predicted by the theory, have to be explained by additional effects, i.e., mainly by impurity rejections during crystallization by negative pressure relaxation developing in areas completely blocked by growing spherulites and by tied molecules partly included in two different crystals so that the intervening loops from pure geometrical reasons are prevented from further crystallization.
Crystallization and Melting Behavior of Polyethylene Oxide Copolymers
Authors: Simon Frederick T. , Rutherford J. M.
Published: April 2005

The course of isothermal crystallization of a series of high molecular weight polyethylene oxide copolymers was studied with a microdensity balance. The comonomers, butylene and styrene oxides, ranged from 0.2 to 4 mole%; several examples of different polymerization conditions were also studied. The consequence of adding noncrystallizing components to a presumably linear polymer was observed in both melting point depression and the shape of the crystallization isotherm. From the melting points obtained on the experimental copolymers, the heat of fusion appeared to be lowered by the addition of noncrystallizable sequences. Inasmuch as the shape of the crystallization isotherm is changed when different amounts of comonomers are present in a random copolymer, an estimate can be made of the amount of noncrystallizing polymer acting like a block from the crystallization kinetics data and the melting point depression.
Glass Transition and Ionic Conductivity in Cellulose Acetate
Authors: Barker R. E. , Thomas Charles R.
Published: April 2005

For many polymers an effective glass transition Tg′ can be defined via a change in slope of logσ[Ω−1cm−1] vs T−1[°K−1]. Measurements for dry cellulose acetate (CA), previously doped by soaking (48 h) in 0.1M alkali-chloride solutions, indicate that Tg′ depends on ion and polymer properties. A model based on fluctuation theory and ``free volume'' concepts is developed. The main assumptions are: (1) ions partially fill void space reducing the available local free volume; and (2) reduction in local free volume about an ion can be accounted for in the statistical expression 〈(V−V0)2〉av=RTV0/B by subtracting an effective ion volume Vi from the total volume (per mole) V of a reference aggregation of particles of most probable volume V0. (B is the bulk modulus, R the gas constant.) With simplified distribution functions, we obtained the expressions Tg≈Bδ2/6RV0 and Tg′=Tg−2a(δ/m)m2Wi+am2Wi2, where a = B/6V0R, Wi is ionic volume (per mole) from x-ray measurements on crystals, m = Vi/Wi, and δ is a measure of free volume. For CA, the best fit is Tg′≈Tg−0.3Wi+0.14Wi2 corresponding to a fractional free volume fg≈δ/V0, which may be as much as 12%. Below Tg′, activation energies for conduction by alkali-chloride-doped CA were found to be given by Eb[kcal / mole]≈ 15+0.7Wi≈16.1+2.45(1024α), where α[cm3/ion] is the electronic polarizability of the ion. Above Tg′, the energy Ea was approximately 29 kcal/mole, independent of the ion. Alternative interpretations in terms of internal pressure and polarization effects are discussed.
Velocity Modulation of a Relativistic Electron Beam
Authors: DeBoer P. C. T.
Published: April 2005

Velocity modulation of a one-dimensional electron beam is treated relativistically, starting from the collisionless Boltzmann equation and using first-order perturbation theory. A general expression for the perturbation current density j1 is applied first to a mono-energetic unperturbed beam. Compared to the non-relativistic case, the magnitude of j1 is reduced by the factor (1−u2/c2)3/4, where u is the unperturbed beam velocity and c the velocity of light. The distance between the maxima of j1 is increased by the inverse of the same factor. Relativistic effects decrease the efficiency of modulation η, which is defined as the energy carried by the electric field generated by the perturbations, divided by the energy flux in the unperturbed beam. For an unperturbed beam with a rectangular velocity distribution of narrow width w and a fixed mean velocity um, the results are independent of w to first order. Expressions for j1 and η are also found for an unperturbed beam with a rectangular momentum distribution of arbitrary width. When this width is small and increasing as um is fixed, j1 increases in second order if the beam is highly relativistic or if its plasma frequency is larger than the frequency of modulation, while it decreases otherwise. Under either condition η decreases in second order.
First Townsend Ionization Coefficient Measurements in Deuterium
Authors: Rork G. D. , Chanin Lorne M.
Published: April 2005

The electron ionization coefficient α/p0 (cm×Torr)−1 has been measured over an E/p0 (volts/cm×Torr) range from 20 to 100 in deuterium subjected to various purification procedures. The results obtained lie slightly below those previously reported by Rose; however, the agreement is within the combined experimental error. Comparison is also made with the measurements of the ionization frequency νi/p (sec×Torr)−1 of Cottingham and Buchsbaum. The present results, at a given E/p0 value, lie above their data. The discrepancy between the ac and dc results is discussed.
Modulated Dipole Plasma Probes
Authors: Robinson L. C.
Published: April 2005

Plasma density profiles are determined by microwave reflection from a modulated dipole probe. The applications of this method to quiescent plasmas and in other plasma explorations are discussed.
Electromagnetic Waves in Parameter Space for Finite Magnetoplasmas
Authors: Granatstein V. L. , Schlesinger S. P.
Published: April 2005

High-frequency electromagnetic waves guided by an air-bounded, axially magnetized, plasma column of radius a are studied through the technique of parameter space mapping. The parameter space is 3-dimensional with coordinates ωp/ω, ωb/ω, and c/ωa. In this 3-space, cutoff and resonance loci form surfaces which enclose approximate domains of existence for various classes of waves.

Three wave classes, characterized by distinctive cutoff and resonance surfaces, are identified for a magnetized plasma column, and their relation to waves in a boundless plasma, and on a column of small radius (quasistatic waves) is investigated. Also, evidence is found for the continued existence of the surface wave class into the regime ωb>ωp.

Parameter space analysis leads to a determination of salient dispersion characteristics for all wave classes and all order of azimuthal variation by a method contributing to physical insight but which avoids exact but laborious numerical computation. Waves are found which change from forward to backward or vice versa with increasing wave number.