bluuebunny/crossref_metadata_2025 huggingface dataset:
Incoherent Scattering of Gamma Rays in Uranium
Authors: Parthasaradhi K.
Published: January 2005

The effect of electron binding on the incoherent scattering of gamma rays in uranium in the energy region 320–1332 keV is studied using the total cross sections of Colgate [Phys. Rev. 87, 593 (1952)] and Wyard [Phys. Rev. 87, 165 (1952)]; total photoelectric cross sections of Rakavy and Ron [Phys. Letters 19, 207 (1965)]; and coherent-scattering cross sections based on Thomas—Fermi calculations [W. Brown, Boeing Co. Report D2–125137–1 (Dec. 1966)]. Combining these data, it is concluded that the effect of electron binding on the incoherent-scattering cross section for uranium in the region 320–662 keV exceeds that predicted by the Thomas—Fermi model.
Gas Incorporation into Sputtered Films
Authors: Winters Harold F. , Kay Eric
Published: January 2005

The concentration of argon in sputtered nickel films has been obtained as a function of the film-growth temperature, the discharge pressure, and of the energy (bias voltage) with which the argon ions bombard the growing film. The concentrations vary from about 10−1 argon atoms/Ni atom to 10−4 argon atoms/Ni atom, depending upon the conditions during film growth. The incorporation of both argon and nitrogen into nickel films is interpreted on the basis of results previously obtained from sorption studies in a more-idealized system on a pre-existing nickel surface.
X-Ray Diffraction Measurement of Strain in Multiphase Systems
Authors: Cucka P.
Published: January 2005

It is shown that failure to take into account the nonuniformity of stress in particles near a surface may lead to gross errors when stress measurements are made by x-ray diffraction on crystallites of one phase dispersed in a matrix of another phase. In particular, the measured strains may depend on the wavelength of the radiation used, and on the particle size of the dispersed phase even though the actual strains in particles not too close to the surface are not dependent on particle size. The measured strains may differ by a factor of two or three from the strains in particles below the x-ray penetration depth. Experimental evidence on a vitreous china (quartz—glass) system is presented, showing that the observed variation of strain with wavelength and particle size is of about the magnitude predicted by calculation on a simple model system.
Coma-Dominated Aberration in Magnetically Deflected Electron Beams
Authors: Wang C. C. T.
Published: January 2005

The aberration of coma, occurring in a magnetically deflected electron beam, has been studied. Shapes of the deflected spot and equal-density contours within it have been calculated for the cases where the density distribution across the beam before deflection is assumed to be either uniform or Gaussian. When coma is close to its minimum, the shape of the spot assumes a fan shape.
Enhanced Diffusion during Plastic Deformation by Mechanical Diffusion
Authors: Ruoff Arthur L.
Published: January 2005

It is shown that a tracer plate will diffuse into a specimen which is being plastically deformed by a process called mechanical diffusion. The magnitude of the penetration via mechanical diffusion is about equal to the offset of the individual glide packets; this offset, in turn, is caused by the nonhomogeneous character of the deformation. It is shown that several examples of enhanced diffusion previously attributed to either vacancy supersaturation or pipe diffusion may in large part be accounted for by mechanical diffusion. In general, mechanical-diffusion effects are probably considerably larger than enhanced-diffusion effects due to these other processes.
Ferromagnetic Resonance of 3He-Irradiated Thin Metal Films
Authors: Bailey G. C. , Schindler A. I. , Meijer P. H. E.
Published: January 2005

Ferromagnetic resonance measurements at 9.5 Gc/sec were made on a number of films of pure iron, pure nickel, and alloys of iron and nickel (Permalloy) before and after 2-MeV 3He-particle irradiation. The 3He particle flux was about 3×1017/cm2 and, during irradiation, the film temperature did not exceed 81°C, as determined by thin-film thermocouples. The resonance field as a function of angle in the film plane, H0(θ), and the half-width, ΔH, were measured at room temperature. In general, H0 decreased (by about 2, 35, and 15 Oe for the iron, Permalloy, and nickel films, respectively) as a result of the irradiation, except for the composition range between 26% and 37% Ni where H0 increased. Also, the half-width generally decreased with irradiation and the half-width change was smallest for compositions around 76% Ni. The changes in H0 were different for films of a given set evaporated onto various substrates (soft glass, fused quartz, single-crystal quartz). Irradiating films in a saturating magnetic field, in the remanent state, and in the demagnetized state gave Hk's which were larger, the larger the magnetic induction of the film during irradiation. Irradiating a film (or reirradiating a previously irradiated film) in a magnetic field also rotated the easy axis of the film into the direction of the field applied during irradiation. The rotation of the easy axis was observed over the entire composition range from pure iron to pure nickel. The variation with composition of the values of Hk after irradiation agrees qualitatively with the values obtained by others using static techniques.
Extraction of Dense Ion Beams from Plasmas
Authors: Kramer N. B. , King H. J.
Published: January 2005

An ion optical system suitable for extracting dense ion beams from gas discharges is described. A study of the beam forming characteristics of the system was performed by using an automatic trajectory tracer with space-charge simulation. Experimental measurements show that the extraction system operates satisfactorily over a wide range of current densities; total mercury-ion beam currents in excess of 1 A have been achieved. An empirical method of estimating perveance as a function of geometry, based on electrolytic tank measurements, is in agreement with experimental results.
Analytical Solutions for Representing Fiber Textures as Axial Pole Figures
Authors: Williams R. O.
Published: January 2005

An axial or inverse pole figure represents the density of a fiber axis over the crystallographic triangle for the crystal system. This function can be represented by a series over this triangle and the coefficients are defined by a least-squares solution. In a second method, the values of the density at a collection of points over the triangle can be calculated without using a series. Both these methods are easier to set up, have much greater flexibility in the data selection and weighting, and give impoved results over those obtained by using Legendre polynomials. Expressions for calculating the standard deviation for all three cases are given.
Dislocation Dynamics and Precursor Attenuation
Authors: Kelly James M. , Gillis Peter P.
Published: January 2005

The low-pressure plane-wave test in metals provides more sensitive measurements of the effects of strain rate on plastic behavior than rod-wave tests. Since strain-rate effects are due to the motion of dislocations in these materials, such tests should lead to an increased understanding of dislocation dynamics. Two current theories of dislocation mechanics are studied in the context of plane-wave propagation: the Gilman relation in which the dislocation velocity is proportional to the negative exponential of the reciprocal of the resolved shear stress, and the activation-energy model in which dislocation velocity is proportional to the exponential of the shear stress. These theories are applied to the problem of attenuation of the elastic precursor wave and the results compared with published experimental data. It is shown that both fit the presently available data and cannot be resolved by low-pressure plastic-wave tests. The analytical results, however, suggest the appropriate value of impact pressure above which the two theories predict different results for tests of thin specimens.
Electromagnetic Modes of Anisotropic Dielectric Waveguides at p-n Junctions
Authors: Nelson D. F. , McKenna J.
Published: January 2005

The field distributions and propagation constants of the lowest-order modes of anisotropic dielectric waveguide models, which are relevant to electro-optic diode modulators, are derived. Smoothly varying dielectric constant models yield results that are essentially identical to discontinuous-dielectric-constant models. The relative intensities of the two modes representing the two polarizations are shown to vary greatly with position. Models where the dielectric constant is asymmetric about the junction plane yield similar results for the propagation constants provided the asymmetry is small. The field distributions, however, can be markedly affected by even small asymmetries. For larger asymmetries no discrete modes can propagate for parameter values typical of GaP electro-optic diode modulators. Absorption differences inside and outside of the waveguide are shown to play a minor role in determining the mode characteristics, at least for GaP diodes. The variation with voltage of the various mode parameters depends on whether the dielectric discontinuities which produce the mode confinement are fixed or move with the junction boundaries. The crystalline orientation dependence is explored by considering individually the junction field in the [111], [100], and [110] directions with the light beam traveling in specific perpendicular directions. The wavefronts of the two lowest-order modes do not coincide when anisotropic absorption or arbitrarily oriented strains are present; the phase difference between the modes will then depend upon the lateral position of measurement.
Chain Folding in Polyethylene and Cyclic Paraffins
Authors: Newman B. A. , Kay H. F.
Published: January 2005

With a view to a study of fold configurations, the crystal and molecular structure of a large cyclic paraffin (CH2)34 was determined by x-ray diffraction. Three-dimensional data were collected and the structure refined using a structure-factor least-squares computer program. The standard deviations in the final carbon atom coordinates were 0.02 Å. The configuration of the molecule was that of a ``collapsed'' ring, with two parallel linear chains linked by two terminal carbon atoms at either end. The chains packed together to give a triclinic subcell with dimensions a=4.246  Åα=60∘30′b=5.470  Åβ=74∘08′c=2.564  Åγ=96∘47′.Restraints imposed by the fold configuration gave rise to a departure from optimum packing of the chains at some distance from the fold. A rough estimate of the surface free energy of polymer faces containing similar folds was made.
Molecular Mechanics of Point Defects in Polyethylene
Authors: McMahon P. E. , McCullough R. L. , Schlegel A. A.
Published: January 2005

Certain properties of crystalline polymers can be associated with the presence of local defects, e.g., deviations of short segments of the chain from the predominant conformation allied with the crystal structure. General methods are developed by which such chain defects may be simulated by computer techniques. The application of these methods to the polyethylene system gives detailed information concerning: stable defect structures, low-energy conversion paths between stable structures (molecular motions), interactions in defect assemblies, and intermolecular interactions between chains and crystalline environments.

Such an investigation of all fold structures containing seven (or less) dihedral angles indicates the existence of a small number of stable but immobile structures. The intramolecular energy of these structures is somewhat high and they do not pack efficiently. Expansion of fold structures to include eight and nine dihedral angles and slight relaxation of orientation constraints provides lower-energy structures which are mobile, more efficient packing, and a low-energy path for conversion between diagonal and b-axis folds.

In addition, stable structures and motions of other local defects (i.e., kinks and jogs) are identified, rigid segment rotation is found to be questionable, and certain mechanical properties are interpreted in terms of the over-all results.
Estimation of Nucleation Parameters from Continuous Cooling Droplet Experiments
Authors: Price Fraser P. , Gornick Fred
Published: January 2005

A theoretical and computational investigation has been made of the effect of temperature and of various energetic parameters upon the course of homogeneous nucleation in suspensions of droplets undergoing cooling at a constant rate. The applicable theory involves integrals, unsolvable in closed form, that were evaluated numerically. For a given size distribution of droplets, the plots of number-fraction crystallized vs time have virtually identical shapes regardless of the cooling rate. The curves can be superposed by translation along the time axis. This superposability obtains regardless of the breadth of the size distribution. Thus, the superposability assumption tacitly invoked by early investigators in this field is justified. Furthermore, it was found that the integrations performed numerically gave, in the range of experimental interest, results within 3% of the analytical solution obtained by Burns and Turnbull by series expansion of the integrand.

The pre-exponential term in the expression for the nucleation rate is calculable for specific values of droplet size and cooling rate and is extremely sensitive to the magnitude of the energetically determined constant term appearing in the exponent. For the specific case of suspensions of polyethylene droplets a change of 10% in the constant term, necessitates a change of three orders of magnitude in the exponential.

Finally, values of the interfacial energy product, σ2σe, of 1.59×104 and 1.50×104 erg3·cm−6 were calculated for polyethylene from the droplet cooling data of two independent groups of investigators.
Low-Temperature Internal-Friction Study of Diluent Effect in Some Polymethacrylates
Authors: Shen Mitchel C. , Strong Jack D.
Published: January 2005

A transverse resonance acoustic spectrometer was used to investigate the effect of diluents on the dynamic mechanical properties of poly-2-hydroxypropyl methacrylate (PHPMA) and poly-2-hydroxyethyl methacrylate (PHEMA) down to −196°C. Samples were prepared by polymerizing the monomer-diluent mixtures through ultraviolet radiation. In the dry sample of PHPMA, below the glass transition temperature, there is an internal friction peak at −90°C (gamma peak). With the introduction of 0.5 vol % water, the gamma peak broadens into a shoulder, with the concomitant appearance of a new ``diluent peak'' at −25°C. Addition of higher water content causes the internal friction curve to exhibit only one single peak, the position of which shifts to lower temperatures while the strengths of the loss peaks increase with increasing diluent concentration. Similar observations were made for other hydrogen-bonding diluents, i.e., deuterium oxide, methanol, and glycerol. For nonhydrogen-bonding diluents, chloroform and cyclohexane, the gamma peak was retained while a shoulder appears around −20°C. Isoproponal, on the other hand, produces an internal friction curve that appears to be ``borderline'' between the above two cases. For PHEMA, which has a gamma peak at −100°C in the absence of diluents, the addition of 0.5 vol % water produced an internal friction curve that possesses a doublet near −60°C. Again, at higher water concentration one observes only a single peak. When cyclohexane was used as the diluent, the doublet character persists up to 5% diluent concentration. These observations were examined in the light of the molecular motion hypothesis. A dual mechanism is suggested that attributes the new diluent peak to the composite of displaced beta and gamma processes. It is postulated that beta transition is lowered due to the plasticizing action of the diluents, while the gamma transition is elevated on account of the hindering effect of the immobilized diluent molecules. At sufficiently high diluent concentration, these two peaks merge into the single observed peak.
Properties of Ethylene-Methacrylic Acid Copolymers and their Sodium Salts: Mechanical Relaxations
Authors: MacKnight W. J. , McKenna L. W. , Read B. E.
Published: January 2005

A study has been made of the mechanical-relaxation behavior of an ethylene-methacrylic acid copolymer containing 4.1 mole % acid units and its partially ionized sodium salts. Degrees of ionization, estimated from infrared analysis, ranged from 0% to 78%. The weight-percent crystallinity of the samples, determined by differential-scanning calorimetry, varied from about 15 for the acid copolymer to about 7 for the 78% ionized copolymer. Four relaxation regions have been observed. They are labelled α, β′, β and γ, and each has been assigned to motions within the amorphous phase of the polymer. In plots of the logarithmic decrement against temperature (at 1 cps), the α peak for the annealed acid copolymer occurs at 50°C and shifts to higher temperatures with increasing degree of ionization. This trend is consistent with the increase in melt flow viscosity with increasing ionization and, on this basis, the α process is attributed to the long-range diffusional motions of chain segments. The β′ peak occurs at 23°C for the annealed acid copolymer and decreases in magnitude with increasing ionization. Hence the β′ mechanism is attributed to the micro-Brownian motions of chain segments involving the breaking and reforming of intermolecular hydrogen bonds between dimerized carboxylic-acid groups. The latter assignment is supported by infrared studies of hydrogen bonding as a function of temperature. The β peak is absent for the acid copolymer but appears at −10°C for the ionized polymers and increases in height with increasing ionization. Thus, the β process is attributed to motions of branched chain segments including the ionic (carboxylate) side groups. The onset of the γ peak is observed at −120°C and is associated with the local motions of linear methylene sequences. The observation that the β peak is located at a temperature very close to the β peak (−20°C) for ordinary branched polyethylene, must cast considerable doubt on the widely held view that the ionic side groups are associated to form strong interchain links. Alternative hypotheses are suggested to explain the increase in ultimate tensile strength and melt flow viscosity with increasing ionization.
Elastic Properties of Anisotropic Heterogeneous Materials
Authors: Von Schmeling H. H. Kausch-Blecken
Published: January 2005

In this paper the macroscopic elastic properties of heterogeneous bodies are studied in terms of the elastic properties of freely orienting microscopic units. Special attention is given to the differences in predicted macroscopic behavior which result from simplifying assumptions regarding stress or strain within a heterogeneous body. By comparison with experimental data, the possibilities and limitations of the concept of freely orienting microscopic elastic units are shown.
Electro-optic Effect in Transparent Niobate Glass—Ceramic Systems
Authors: Borrelli N. F.
Published: January 2005

A transverse quadratic electro-optic effect has been observed in a wide range of niobate transparent glass—ceramic systems. The electro-optic constant has been determined as a function of composition, temperature, and wavelength. A semiquantitative measurement of the frequency response has also been made. It has been found that the electro-optic constant correlates reasonably well with the square of the static dielectric constant. Remanent polarization has been induced under the influence of a dc field. The resulting linear electro-optic effect has been measured in both transverse and longitudinal modes.
Current Oscillations in Piezoelectric Semiconductors
Authors: Haydl W. H. , Harker K. , Quate C. F.
Published: January 2005

The current oscillations which are observed in piezoelectric semiconductors, such as cadmium sulfide, are often accompanied by a high field domain which moves through the sample at the velocity of sound. These domains may be a result of the negative differential conductivity which is produced in the material by a large component of acoustoelectric field. This field opposes the applied field when the drift velocity exceeds the velocity of sound. We determine from the linear theory a threshold condition for the onset of the negative differential conductivity and show that this model is in agreement with the experimental observations reported here on CdS and elsewhere on GaAs.
Cesium-Ion Bombardment of Aluminum Oxide in a Controlled Oxygen Environment
Authors: Hasseltine E. H. , Hurlbut F. C. , Olson N. Thomas , Smith Harold P.
Published: January 2005

Sputtering of aluminum oxide (sapphire) by 2.5 to 10 keV cesium ions has been investigated using neutron activation analysis. The sputtering yield (aluminum atoms/ion) was measured as a function of ion energy, target temperature, and R, the ratio of background oxygen molecular flux arriving at the target surface to the sputtered aluminum and oxygen flux leaving the surface. Positive-charge accumulation on the dielectric surface was neutralized by electron flooding of the ion-beam area while the ion current was measured by a periodic beam deflection technique. In all measurements the ion beam was normal to the target surface and the (001) crystallographic plane. The yield increased monotonically from 0.40 (aluminum atoms/ion) at 2.5 keV to 0.52 at 10 keV and was unaffected for R<0.1. The yield decreased slightly as R was increased, and for R>10 it approached the saturation value of monocrystalline aluminum. The yield exhibited a temperature dependence decreasing from 0.55 at 77°K to 0.48 at 475°K. The results were reproducible to within 5%.
Energy Transfer between Eu2+ and Ho3+ Ions in CaF2
Authors: Ewanizky T. F.
Published: January 2005

CaF2:Ho3+ has been reported as a visible laser at 5512 Å. Operation is at a relatively high threshold power due, principally, to weak and narrow absorption lines.

Preliminary experiments, using Eu2+ as a sensitizer, have indicated that an order of magnitude increase in Ho3+, 5512-Å emission intensity may readily be achieved through transfer of energy from Eu2+ to Ho3+ ions. Dopant concentrations, for each constituent, were nominally <1 mole%.
Superconductivity in the Technetium—Vanadium Alloy System
Authors: Koch C. C. , Kernohan R. H. , Sekula S. T.
Published: January 2005

The superconducting properties of Tc-V alloys with compositions ranging from 0 to 100 at.% V have been investigated in fields up to 15 kOe by measurements of the bulk magnetization determined ballistically. A phase diagram of the Tc-V system has been determined by several metallurgical techniques. The sequence of crystal structures at 1500°C with increasing vanadium content is hcp→bcc→CsCl→bcc. The technetiumrich bcc phase when quickly cooled to room temperature exhibits superlattice x-ray diffraction lines of the CsCl structure. The superconducting transition temperature of the technetium-rich hcp alloys increases with vanadium concentration from 7.73°K to a maximum for the system of 11.3°K at the limit of vanadium solubility (∼6.5 at.% V). This transition temperature remains constant for the two-phase alloys. The transition temperature decreases progressively with increasing vanadium content in the CsCl structure, and at compositions in the 50 to 80 at.% V interval no evidence of superconductivity is observed for temperatures as low as 1.4°K. Alloys containing the hcp phase show reversible behavior in the tails of their magnetization curves, while those with the CsCl structure exhibit a high degree of hysteresis in the tails. Estimates of the upper-critical field at 0°K, HC2(0), using the experimental data and theoretical calculations yield values of HC2(0) to approximately 45 kOe for the samples with high-transition temperatures. Results of heat treatment at 1100°C on the superconducting parameters of alloys near the 30 at.% V composition are presented.
Conduction Bands in GaSb-InSb Alloys
Authors: Kudman I. , Seidel T. E.
Published: January 2005

The Hall coefficients of selected n-type GaSb-InSb alloys have been measured in the range 300° to 800°K. The temperature dependence of the Hall coefficient showed the presence of two bands, and data were analyzed using a two-band model. The energy separation of the two conduction-band minima was found to increase, with increasing InSb concentration, from 0.034 to 0.52 eV in the composition range investigated. The temperature dependence of this separation was found to be positive for GaSb and negative for the alloys ranging between +1.8 to −2.0×10−4 eV/°K.
Radiative Recombination in Melt-Grown n-Type, Ge-Doped GaAs
Authors: Kressel Henry
Published: January 2005

Photoluminescence measurements were made of closely compensated, n-type GaAs grown by the horizontal Bridgman method. The ratio of Ge donors to Ge acceptors is estimated to be ∼1.25. At 77°K (n≅3× 1017 cm−3) emission bands are observed at 1.51, 1.49, and 1.22 eV. The second band is nearly comparable in intensity to the first in these materials and is ascribed to a recombination process involving a shallow Ge acceptor level. These data suggest that this level is located 0.02–0.03 eV above the valence band. The band at 1.22 eV is considerably more intense than the other bands. Evidence is presented suggesting that this band is due to a shallow donor to deep acceptor radiative transition. The shallow donor is probably Ge. The deep acceptor level is approximately 0.2 eV above the valence band and may involve a lattice defect particularly prominent in melt-grown GaAs. The low-energy emission band has been correlated with an absorption peak. On the basis of the absorption data, the deep acceptor concentration is roughly estimated to be of the order of 1016 cm−3.
Dynamics of Laser-Induced Breakdown in Gases
Authors: Young M. , Hercher M.
Published: January 2005

The breakdown of gases under the influence of a laser beam is analyzed. Classical diffusion theory is taken as a model, with electrons accelerated by inverse bremsstrahlung until they have sufficient energy to ionize neutral gas atoms. Both diffusion and recombination are included as losses.

For the rare gases in the range below atmospheric pressure it is found that the relation between the laser pulse duration and the plasma growth time is the primary factor which determines the breakdown threshold. The losses play roles of varying importance depending on gas, pressure, and geometry. The initial electrons are generally assumed to have come from multiphoton ionization of impurities, although multiphoton ionization of the gas itself becomes a factor at sufficiently low pressures (high photon fluxes).

A number of experimental results is presented. These are used to justify some of the theoretical assumptions and to corroborate the results of the theory. The agreement is good.
Reflection and Transmission of Electromagnetic Waves by a Dielectric Half-Space Moving Perpendicular to the Plane of Incidence
Authors: Shiozawa T. , Hazama K. , Kumagai N.
Published: January 2005

The present paper describes reflection and transmission of a plane electromagnetic wave by a dielectric half-space which is moving uniformly perpendicular to the plane of incidence. It is found that for the incident E plane wave both the reflected and transmitted waves are no longer an E plane wave but a linear combination of E and H plane waves. In addition, it is shown that for the incident E wave the E-wave components of the reflected and transmitted waves carry a positive power, but the power flow with regard to the H-wave component of the transmitted wave is always negative while the power carried by the H-wave component of the reflected wave is always positive.
Fatigue-Fracture Growth in Linearly Viscoelastic Material
Authors: Williams M. L.
Published: January 2005

Based upon the thermodynamic formulation for linearly viscoelastic fracture developed earlier, an extension has been made to fatigue fracture resulting from repeated (oscillatory) load applications. The theoretical analysis of internal spherical-flaw growth, due to a uniformly distributed radial oscillatory input of displacement, predicts a growth-rest cycle whose characteristics depend upon the mechanical properties of the medium. The results for this idealized problem are compared to experimental data for crack growth in a precracked sheet specimen subjected to oscillatory displacement input, and a qualitative similarity is observed. It is therefore believed that the analytical model is representative, and its study can reveal the main features of macroscopic flaw growth.
Some Electrical and Optical Effects of Dislocations in Semiconductors
Authors: Meyer M. , Miles M. H. , Ninomiya T.
Published: January 2005

Optical measurements on silicon and germanium together with Hall measurements on germanium were performed on crystals containing predominantly edge or screw dislocation arrays. An apparent extended absorption tail in deformed germanium and silicon was found to depend markedly upon the direction of light propagation relative to the active slip planes. Photographs of the transmitted radiation through deformed silicon showed that the apparent extended absorption tail was due to strong anisotropic scattering from active slip planes. Hall measurements on sections from plastically deformed germainium are interpreted to give evidence of dislocation acceptors located in the lower half of the band gap.
Computer Solutions of Laser Rate Equations for PTM Q-Switching and Comparison with PRM Results
Authors: Weidler Roy C. , Burkhalter James H. , Vuylsteke Arthur A.
Published: January 2005

A technique for solving the three-level Q-switched laser rate equations for both pulse reflection mode and pulse transmission mode switches is presented. Results are compared for both energy and peak power.
Investigation of a Shock-Induced Phase Transition in Antimony
Authors: Warnes R. H.
Published: January 2005

A solid-to-solid phase transition has been induced in antimony by an explosive-produced shock wave of about 130 kbar. Details of the transition were determined by measurement of the free—surface motion with electrical pin contactors. The first plastic wave pressure varied from 108 kbar for the thinnest samples to 91 kbar for the thickest samples. This variation is felt to be due to the sluggishness of the transition, the material requiring about 0.6 μsec to relax into its higher-density phase. The transition pressure was found to be 88 kbar. Hugoniot data are presented in conjunction with existing higher-pressure dynamic data.
The Field of a Switching Thin Magnetic Film in the Presence of a Finite-Permeability Keeper and a Semi-infinite Ground Conductor
Authors: Paton A.
Published: January 2005

A thin uniformly magnetized disk lies between a semi-infinite conductor and a half-space filled with magnetic material of finite permeability (keeper). Maxwell's equations are solved and an expression given for the magnetic field at the center of the disk when the magnetization is an arbitrary function of time. Numerical results are given for the case of a step rise in magnetization for varying permeability of the keeper and varying distance between the keeper and the disk.
Investigation of the Carbon K and Metal Emission Bands and Bonding for Stoichiometric and Nonstoichiometric Carbides
Authors: Holliday J. E.
Published: January 2005

The carbon K and metal LII,III emission bands from stoichiometric and nonstoichiometric transition metal carbides were measured with a high resolving power grating spectrometer. It was possible to relate the intensity distribution of the C K band to bonding. Groups IV and V transition metal carbides, which are strongly bonded carbides, have narrow C K bands. For the weakly bonded carbides, group VI and higher, the C K bands are broad and have an intensity distribution close to that of the C K band from graphite. The intensity distribution of the carbide and graphite C K bands was compared to Coulson and Taylor's π, σ subbands. The metal LII,III bands from the first series transition metal carbides showed a change in band characteristics relative to the LII,III band from the metal at group VI carbides. From shifts in wavelength of the metal emission in the carbide it is found that the vanadium and titanium atom is more negative in the carbide than in the metal.
Elastic Constants of KF from 300° to 4.2°K
Authors: Marshall B. J. , Miller R. E.
Published: January 2005

Measurements of the elastic constants from 300°−4.2°K have been made on single crystals of potassium fluoride. The values of the elastic constants at 4.2°K are c11 = 7.585±0.8%, c44 = 1.293±0.8%, and c12 = 1.473%±3% in units of 1011 dyn/cm2. The Debye temperature (θ0) at 0°K as calculated from the elastic constants is 327°K. The lattice energy at 0°K is calculated to be 194 kcal/mole.
Correction for Nonlinearity in X-Ray-Counting Systems of Electron-Probe Microanalyzers
Authors: Sawatzky A. , Jones S.
Published: January 2005

A method has been developed for determining the dead time of electron-probe detector circuits, which used the relative intensities of two diffraction lines corresponding to the same characteristic x-ray for a pure metal and one of its alloys. It is particularly adapted to single-detector probes with specimen and detector in a common vacuum chamber, and where most other techniques cannot be used. Dead times of 1.3×10−6 sec and 12×10−6 sec were obtained for CuKα radiation in two Philips gas-flow proportional counters using this method. These results were in excellent agreement with those obtained by using the multiple-foil technique.
Stress-Assisted Diffusion to Dislocations and its Role in Strain Aging
Authors: Meisel L. V.
Published: January 2005

The kinetics of Cottrell atmosphere formation around dislocations is studied numerically. The spirit of the calculation presented here follows closely that presented by Bullough and Newman, although our conclusions about strain aging are different. We have calculated solute distributions for a number of times using the standard dislocation-solute atom interaction potentials, − A/r and − A cos(θ)/r, for screw and edge dislocations, respectively. It is shown that for suitably strong dislocation-solute binding and appropriate dislocation densities, a Harper-type strain aging can be predicted on the basis of stress-assisted-diffusion theory without ascribing any special properties to the dislocation core regions. The place of the Harper law and the Bullough and Newman calculations in the over-all picture of strain aging is discussed.
Simple Theory for K-Ionization by Relativistic Electrons
Authors: Kolbenstvedt H.
Published: January 2005

The total cross section for ionization of K-electrons by electrons has been derived using the method of virtual photons combined with the photoelectric cross section for distant collisions and the Mo/ller cross section for close collisions. Good agreement with experiments is obtained for the elements silver (Z = 47) and tin (Z = 50) when the electron energy is much higher than the ionization energy.
Depolarization of Ferroelectrics at High Strain Rates
Authors: Linde Ronald K.
Published: January 2005

Poled specimens of barium titanate (BT) and lead zirconate titanate (PZT) ceramics have been successfully recovered after shock loading antiparallel to the polarization vector (short-circuit configuration) in the 3- to 23-kbar range. It has been shown that permanent depoling as a result of phase transitions or of domain switching can occur within the microsecond time scale of a shock experiment. Results of dynamic charge release measurements made during shock transit in PZT 52/48 tend to corroborate the findings of other investigators. Techniques for recovery of shock-loaded specimens are discussed.
Wave Propagation in a Waveguide Partially Filled with Plasma in an Infinite Axial Magnetic Field
Authors: Bevc Vladislav
Published: January 2005

Electromagnetic-wave propagation for axisymmetric and dipolar modes in a circularly cylindrical waveguide containing a plasma column in an infinite axial magnetic field is studied. The plasma column is assumed to be cold, collisionless, and of uniform density, with a diameter one-half the diameter of the waveguide. Numerical solutions of the dispersion equation for typical cases at various values of the plasma density are presented. The electric field and power-flow density distribution are examined quantitatively for representative modes with reference to the existence of surface waves. It is shown that for an infinite magnetic field the high-frequency field distribution within the plasma can be a modified Bessel function of the first kind only for the superluminous phase velocities and only at plasma frequencies that exceed the lowest vacuum waveguide cutoff frequency. For slow waves of very short wavelength, ω/c≪2π/λg, the electromagnetic field and the power-flow density distribution are found to be confined to the plasma column with practically no field existing in the vacuum between the plasma and the waveguide wall.
Noise Calculations in Continuous-Parameter Systems
Authors: Blue James L.
Published: January 2005

Noise in a Markoffian, stationary, quasilinear system may be computed by an elegant and very general procedure developed by Lax. When this procedure is applied to problems described by continuous Markoff variables, and when analytic solutions are not possible, the amount of numerical calculation required for solution may become excessively large. The present paper recasts Lax's procedure into a form which is suitable for computer evaluation, provided that the system meets two additional requirements: (1) the fluctuations in only a small number of linear combinations of the variables are of interest; (2) the diffusion matrix, or noise source term, is diagonal.

The calculation of avalanche noise in an avalanche transit-time diode is presented as an illustration.
Neutron Irradiation Effects in Superconducting Niobium
Authors: Kernohan R. H. , Sekula S. T.
Published: January 2005

The superconducting magnetization behavior and transition temperatures of single crystals of Nb were investigated prior to and after a series of fast-neutron irradiations (E>1 MeV) in the Oak Ridge Research Reactor at a temperature of approximately 40°C. The experimental results indicate that the point defects and defect aggregates which are created lead to increases in the upper critical field Hc2 and small changes in the superconducting transition temperature. In addition, the increase in nonequilibrium behavior of the magnetization with integrated fast-neutron flux establishes that defects are present with the ability to pin magnetic flux. For fast-neutron doses of approximately 2×1019 neutrons/cm2, the magnetization approaches in behavior that of a completely irreversible type-II superconductor. Successive reductions in cross-sectional area of this sample by chemical etching and subsequent measurements of the magnetization indicate only a small size dependence of the hysteresis, indicating essentially complete flux pinning in a macroscopic sheath approximately 0.1 mm thick. The flux-pinning defects are considered to be dislocation loops as evidenced by other work, and the present experimental results are discussed in terms of these loops.
Paraxial Charged-Particle Motion in Arbitrarily Varying, Azimuthally Symmetric Electric and Magnetic Fields
Authors: Gordon E. I. , Miller R. C.
Published: January 2005

The paraxial motion, described in terms of the guiding center and gyroradius, of noninteracting charged particles in arbitrarily varying, azimuthally symmetric electric and magnetic fields is considered. In particular, the case where the magnetic field passes through zero is treated exactly. It is shown that a complete interchange of the guiding center and radius vector coordinates can be obtained for a nonimpulsive field reversal. The formalism has use in electron optics as well as transverse wave-beam interactions.
Computer Simulation of Field-Ion Images of Hexagonal Structures and Superlattices
Authors: Ranganathan S. , Lyon H. B. , Thomas G.
Published: January 2005

The simulation of field-ion images by computation of the position of atoms which lie within an outer shell of given thickness on a spherical crystal has been extended to spherical crystals of a variety of structures. These include the hexagonal lattice, the hexagonal close-packed structure and a few of the common superlattices. The consequences of the invisibility of one atomic species in ordered alloys has been investigated. The results show that computations are in fact necessary for a detailed interpretation of the field-ion image.
Linear Shock-Velocity-Particle-Velocity Relationship
Authors: Ruoff Arthur L.
Published: January 2005

An equation of state, based on a bulk modulus variation with pressure of the form BS=B0S+B0S′P+B0S″P2/2,where B0S, B0S′, and B0S″ are constants, is developed in this analysis. The resultant equation of state is combined with the Rankine-Hugoniot conservation relations to obtain a Maclaurin series expansion for the shock velocity vs the particle velocityus=c+sup+s′up2+⋯.The coefficients c, s, and s′ are given in terms of the unshocked density and quantities available from ultrasonic elastic constant measurements at high pressures. Using new experimental data for sodium, it is shown that s′ is nearly zero. For ionic crystals such as KBr a theoretical expression is given for B0S″ (in terms of B0S′). In the case of KBr, the value of s′ is also very close to zero. The smallness of s′ depends on the cancellation of a number of terms brought about by the fact that B0S″ is negative. CsI and xenon are also discussed.
Current Pause in Exploding-Wire Discharges
Authors: Vlastós Antonios E.
Published: January 2005

Experiments with exploding wires made of constantan, copper, and lithium in atmospheric air have shown that the dwell time of an exploding wire for the examined lengths (3.2, 6.5, 9.7, and 13 cm), diameters (0.005 cm for constantan and copper, and 0.025 cm for lithium), and applied voltages (1 to 20 kV) is a function of the average electric-field strength along the wire. The function relating dwell time to field strength is not single-valued, but from a certain critical value there are two dwell times corresponding to each field strength. There is evidence that this duality of the dwell times is due to a change in the type of explosion at the critical gradient. Both types of observed dwell times depend in a simple way on the average field strength.
LEED Study of the Growth of Aluminum Films on the Ta(110) Surface
Authors: Jackson A. G. , Hooker M. P. , Haas T. W.
Published: January 2005

Growth of aluminum films on clean Ta(110) surfaces has been investigated by LEED techniques. Five phases of aluminum have been found, which are: (1) disordered Al(111), formed by depositing at T<600°C; (2) Al(111)c(2×2) formed by heating film, deposited at T<300°C, to 700°C; (3) Al(100)c(2×2), formed by heating film, deposited 300<T<600°C, to 700°C; (4) Epitaxial Al(111), formed by depositing film with substrate T in range 600<T<670°C; (5) Diffuse phase, formed by heating any of the preceding to 800°C. Two orientations of each structure have been observed; this results from the close match between primitive unit meshes of aluminum (111), (100) and Ta(110). A mechanism for the growth of Al(111) and Al(100) is suggested. Comparisons with some published LEED data on epitaxy are made.
Properties of Magnetic Materials with a Nonuniform Saturation Magnetization. II. Longitudinal Susceptibility
Authors: Schlömann Ernst
Published: January 2005

A theory of the longitudinal susceptibility (response to an rf field applied parallel to the dc field) of magnetic materials with a nonuniform saturation magnetization is described. According to this theory the imaginary part of the longitudinal susceptibility, χ″, considered as a function of dc magnetic field, should show a maximum when the internal magnetic field is approximately equal to (ω/γ)-π〈M0〉, where ω is the frequency, γ the gyromagnetic ratio, and 〈M0〉 the average saturation magnetization. The height of the absorption peak is calculated to be proportional to the degree of inhomogeneity (mean square deviation of the local saturation magnetization from its average) and approximately inversely proportional to the square of the frequency. The width of the absorption peak is approximately 2π〈M0〉. If the nonuniformity of the saturation magnetization is due to the presence of pores or nonmagnetic inclusions, the absorption at low dc fields (near remanence) is found to be proportional to the total cross-sectional area of the inclusions (rather than their volume). Thus many small inclusions have a stronger effect than few large ones of the same total volume. The real part of the susceptibility is negative on the low-field side, positive on the highfield side of the absorption peak. In most of the calculations, the effect of the inhomogeneity-induced scattering of spin waves has been neglected. This scattering is shown to be substantially equivalent to an additional damping of the spin waves, which is strongly frequency and field dependent.
Resonance-Rectification Effects in Warm Magnetoplasmas
Authors: Crawford F. W. , Harp R. S. , Mantei T. D.
Published: January 2005

This paper extends the study of resonance rectification phenomena in plasmas to the case where a static magnetic field is present. Parallel wire-probe geometry has been chosen so that the rf electric field is primarily perpendicular to the magnetic field. Under these conditions, experiments show that there are two distinct series of resonance peaks, one occurring between successive cyclotron harmonics, the other precisely at the cyclotron harmonics. Cold-plasma theory is inadequate to account for the existence of these resonances. An explanation is proposed, based on the form of the warm-plasma permittivity component perpendicular to the magnetic field, which explains satisfactorily all of the experimental observations.
First Pressure Derivatives of Polycrystalline Elastic Moduli: Their Relation to Single-Crystal Acoustic Data and Thermodynamic Relations
Authors: Chung D. H.
Published: January 2005

This paper demonstrates that, for a given crystalline solid, the first pressure derivatives of polycrystalline elastic moduli can be predicted either from the corresponding derivatives of anisotropic single-crystal elastic constants or from their single-crystal third-order elastic constants. Theoretical relations for the isotropic polycrystalline acoustic data in terms of their single-crystal acoustic data are presented here for cubic, hexagonal, trigonal, and tetragonal crystals; these have been successfully applied for four cubic solids (Al, Cu, α-Fe, and MgO) and one hexagonal metal (Mg). It is shown for these solids that the calculated isotropic acoustic data agree essentially with experimental acoustic data determined on their polycrystalline specimens, thus establishing the validity of the theoretical relations. It is concluded that the acoustic data measured on fully dense polycrystalline specimens may be as useful as the single-crystal acoustic data in the study of the equation of state of solids, for example. And further, when anisotropic single-crystal acoustic data are available, these can be converted into isotropic polycrystalline acoustic data so that in their applications, the use of the acoustic data becomes more practical.
Temperature Effects on Several Fluorescence Pair Lines in Ruby
Authors: Birang Behzad , Di Bartolo Baldassare , Powell Richard C.
Published: January 2005

The widths and positions of several lines in the fluorescence spectrum of ruby with 0.94 at.% Cr3+ belonging to the second (N1) and the fourth (N2) nearest neighbor pair systems have been measured between 20° and 270°K. The linewidths are explained in terms of microscopic strains, Raman scattering of phonons, and direct phonon processes. The lineshifts with temperature are due to the absorption and emission of virtual phonons, and are approximately the same for all the lines investigated. A Debye model of phonons was used with different effective Debye temperatures for linewidth and lineshift processes.