bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and properties of reduced LaCoO3
Authors: Sis L. B. , Wirtz G. P. , Sorenson S. C.
Published: February 2004

Changes occurring in the chemical state, and the crystallographic and electronic structure of LaCoO3 in a reducing atmosphere were determined. These determinations involved the use of thermogravimetric and calorimetric techniques, x-ray diffraction, and magnetic property measurements. It was shown that the reduction process proceeded through the formation of a series of oxygen-deficient structures. In the 0–3.25 wt% weight-loss region, corresponding to the general formula LaCo1−xO3−y, where 0.0<x≤0.08 and 0.0<y≤0.5, the structure is monoclinic. In this structure, the cobalt ion exists as either high-spin Co2+ or low-spin CoIII. At a weight loss of approximately 3.25 wt% the structure reverted to the original rhombohedral symmetry with a loss of lanthanum and cobalt. The chemical formula was again LaCoO3. Samples reduced to greater than 3.25 wt% possessed a different crystal structure than was previously observed.
Magnetic investigations on Tb0.25Fe0.75−xAlx and Tb0.105Fe0.895−xAlx
Authors: Oesterreicher H. , Pitts R.
Published: February 2004

Magnetization and susceptibility measurements on pseudobinary alloys Tb0.25Fe0.75−xAlx and Tb0.105Fe0.895−xAlx are reported for temperatures from 1.6 K to about room temperature. The magnetization behavior in the ordered regime indicates that the coupling scheme between the rare-earth and the transition-metal moments stays an antiferromagnetic one on Al substitution for the latter. An unusual magnetization behavior is observed at the lowest temperatures (1.6–10 K). Here strong S-type saturation develops partly with spontaneous increases of magnetization at critical fields of the order of 20 kOe. This is a result of highly energetic domain walls connected with high anisotropy and disorder on crystallographic sites. Coercive forces up to about 14 kOe are observed in the pseudobinary region at 4.2 K.
Effects of polishing anthracene single crystals on the triplet exciton lifetime
Authors: Weston William , Mey William , Pope Martin
Published: February 2004

Polishing anthracene single crystals creates defects which reduce the triplet lifetime not only at the surface but also throughout the bulk. By annealing the crystal, the triplet lifetime can be essentially restored to its initial value.
Reversed Carr-Purcell train for measurement of NMR relaxation times by approach to driven equilibrium
Authors: Headley L.C. , Wallace W.E. , Waldstein P.
Published: February 2004

An experimentally simple nuclear magnetic resonance pulse technique is described for measurement of longitudinal and transverse relaxation times. The sequence consists of a Carr-Purcell train with π and π/2 pulses interchanged. The technique offers time savings over traditional methods in cases where relaxation times are long. Experiment times may be halved in some cases. Results obtained with this technique compare well with results obtained using traditional techniques.
Evanescent field coupling of thin-film laser and passive waveguide
Authors: Watts R. K.
Published: February 2004

Evanescent field coupling is proposed as a practical way of coupling the output of a thin-film laser to an optical waveguide. Relevant parameters are estimated for the case of a GaAlAs LOC laser coupled to a guide.
Thermomechanical constitution of spalling elastic bodies
Authors: Davison Lee , Stevens A. L.
Published: February 2004

In this article we develop a theory of spallation of a brittle thermoelastic body, and of the interaction between propagating waves and accumulated damage. This theory is applied to the prediction of the effect of spall damage on the elastic stiffness and thermal conductivity of the material.
Flow via dislocations in ideal glasses
Authors: Gilman J. J.
Published: February 2004

Dislocation lines with variable Burgers vectors can exist in glasses and there is now experimental evidence for this, especially in metallic glasses. The kinematics and dynamics of their motion is discussed. It is suggested that dilatance at the core of a moving dislocation determines the viscous drag that acts on it in an ideal glass; and, this is discussed in terms of free-volume theory. Defect debris in the wake of a moving dislocation is also considered. The advantages of using dislocation theory for describing the flow of glasses are outlined.
Propagation of pressure waves in bubble-filled liquids
Authors: Dresner Lawrence
Published: February 2004

A number of simple problems soluble in closed form are considered in which pressure waves propagate in a bubble-filled liquid. It is assumed that the bubbles collapse under negligible pressure, following which the compacted liquid behaves perfectly elastically. The late stages of the motion in the problems considered approach a particular self-similar motion of a certain kind of locking medium.
Ellipsometric observations of an electron-bombarded stainless steel surface
Authors: Fane R. W. , Neal W. E. J. , Latham R. V.
Published: February 2004

It has been established, by electrical and electron-optical studies, that the oxide surface layer is responsible for the particularly stable properties of stainless steel when used for high-voltage electrodes. The growth of this surface oxide has been studied ellipsometrically. After cleaning the surface by electron bombardment the growth of the layer was monitored in the pressure range 10−8 Torr-atmospheric pressure, and the temperature range 300–1300°K. The equilibrium thickness at room temperature and at atmospheric pressure is [inverted lazy s]30 Å. A temperature in excess of 1000°C is required to remove the film at 10−8 Torr.
Laser optical double resonance and efficient infrared quantum counter upconversion in LaCl3 : Pr3+ and LaF3 : Pr3+
Authors: Wright J. C. , Zalucha D. J. , Lauer H. V. , Cox D. E. , Fong F. K.
Published: February 2004

In this paper, we report the first laser-excited optical double-resonance experiments in rare-earth-doped crystals. Infrared upconversion in LaCl3 : Pr3+ and LaF3 : Pr3+ has been achieved by means of a tunable cw dye laser pump. The quantum efficiency of the upconversion process at 2.03 μ in LaCl3 : Pr3+ is 1.2×10−3, which is an improvement of 4×105 over the highest efficiency found previously with incoherent sources. It is shown that an efficiency of 1 can be easily obtained with higher fluxes and improved crystal quality. Direct excitation of the output fluorescence from the 3P0 level is observed in both LaCl3 : Pr3+ and LaF3 : Pr3+ when the dye laser frequency is resonant with the states of the lower-lying 1D2 manifold in the absence of the infrared input. Detailed assignments of the observed double-resonance transitions have been made from wavelength and polarization measurements.
Excitation mechanism of the far-infrared sulfur dioxide molecular laser
Authors: Hassler J. C. , Hubner G. , Coleman P. D.
Published: February 2004

The published experimental data for the far-infrared SO2 molecular laser is correlated with the results of some new experiments. A satisfactory assignment of all of the lasing lines is presented. An excitation mechanism involving excitation to the first excited singlet electronic state, followed by crossing to the highly vibrationally excited levels of the ground electronic state, and then by selective vibrational relaxation, is shown to be consistent with the experimental data.
High-resolution study of anomalous dispersion in the ruby R lines
Authors: Izatt Jerald R. , Bean Brent L. , Daw Harold A.
Published: February 2004

The real and imaginary parts of the complex index of refraction in the R-line region of ruby have been measured near liquid-nitrogen temperature with sufficient resolution that the R-line doublet structure was well resolved. A modification of the usual Babinet compensator technique was used for the refractive-index measurements, which were found to correlate with the absorption measurements as predicted by the Kramers-Kronig relations. An attempt at direct quantitative verification of the dispersion relations for an optically pumped sample is also described.
Electrical transport and defect levels in ZnTe crystals
Authors: Larsen T. L. , Stevenson D. A.
Published: February 2004

Two acceptor levels at 0.06 and 0.12–0.14 eV were observed in nominally pure ZnTe crystals using electrical transport measurements. Results on as-grown and annealed crystal show that these two levels are associated with different defect centers. It is suggested that neither level represents the first or second state of ionization of the native defect which dominates the electrical properties of pure ZnTe crystals at high temperatures. The deeper level appears to be associated with an impurity, possibly Cu. The identity of the shallow-level center is unknown; however, this center may be a complex center involving the native defect. Analysis of the temperature dependence of the hole mobility confirms that optical phonon scattering is dominant near room temperature in nominally pure ZnTe; however, ionized impurity scattering may become dominant at low temperatures.
rf impedance of superconducting weak links
Authors: Auracher F. , Van Duzer T.
Published: February 2004

The rf impedance of a superconducting weak link with negligible capacitance is calculated for a variety of operating conditions. It is shown that the impedance is always real between harmonic steps of the I-V characteristic. The real part of the impedance is negative under certain conditions of bias for small rf signals, thus indicating the region of self-oscillation of the weak link.
Theory of thermal expansion in Invar alloys
Authors: Carr W. J. , Colling D. A.
Published: February 2004

A quantitative theory for the magnetostriction due to exchange interactions in metals has been developed, based on the ideas of Zener. The theory is in good agreement with the measured values for pure nickel and iron, and it explains the anomalous thermal expansion in the iron-nickel Invar alloys, as well as more complex alloys containing manganese and/or cobalt.
Comments on ``Grain boundary contrast in field-ion microscope images''. II
Authors: Page T. F. , Howell P. R. , Ralph B.
Published: February 2004

A recent paper by French and Bishop has discussed the field-ion contrast from a particular grain boundary configuration as a function of increasing angular misorientation, the images being constructed by computer simulation. Although their boundary configuration was pure tilt about [110], the resulting surface contrast displays apparent tilt and twist character because of the oblique surface section of the emitter tip chosen to contain the boundary trace. The present paper aims to distinguish the contrast events occurring in such images as a function of this apparent tilt and twist character and to quantify the expected contrast in terms of the ``ring-matching'' contrast theory proposed by the present authors.
Dielectric relaxation of ZnF2: LiF
Authors: Roth Thomas A.
Published: February 2004

The thermally activated release of the dielectric polarization of ZnF2: LiF crystals measured by the ionic thermoconductivity method is examined in terms of vacancy and interstitialcy models. The previously proposed vacancy model is reviewed and an interstitialcy model is introduced. (Li+–VF) and (Li+–Lii+) dipolar defects are proposed and the change in dipole orientation causing the current discharge is examined in relation to possible anion vacancy and interstitial cation movements. The relaxation process has been found to be very anisotropic and is characterized by the relaxation time, τ(T)=1.70×10−13 exp (0.32/kT). It is proposed that the dipolar relaxation is due to the (Li+–Lii+) ion pair and that the rotation of the dipolar efect is accomplished by interstitial lithium-ion movements parallel to the c axis of the crystal.
Flow near an accelerated plate in the presence of a magnetic field
Authors: Mishra Shankar Prasad , Mohapatra Priti
Published: February 2004

Hydromagnetic flow of an incompressible viscous liquid due to the time — varying motion of an infinite flat plate is discussed in this paper. The magnetic field present is fixed relative to the plate. It is observed that as the magnetic field strength increases, the velocity at a point increases while the skin friction at the plate decreases at any instant.
Mechanism for lamellar branching in isotactic polypropylene
Authors: Padden F. J. , Keith H. D.
Published: February 2004

Selected-area electron diffraction and x-ray diffraction have been used to study microstructure of spherulites in thin films of isotactic polypropylene crystallized from the melt. Our purpose has been to seek an explanation for a branching habit, unique to this polymer, in which parent and daughter lamellar crystals make an acute dihedral angle of ∼81°. We find that branching of this kind is invariably associated with the presence of a triclinic crystalline phase (γ form) and is sensitive to temperature changes during growth. We follow Khoury's suggestion that epitaxial overgrowth is responsible, but with the important difference that branching is initiated by deposition of blocks of γ-phase material onto (010) lateral surfaces of lathlike lamellar crystals of α phase; we propose that the a and c crystallographic axes in the γ-phase blocks are laid down along the −c and −a axes, respectively, of crystals of α phase. On the basis of this mechanism, hinging upon the presence of the γ phase, variations in the sign of optical birefringence in polypropylene spherulites crystallized over a range of temperatures can be accounted for. We propose that the same mechanism is responsible for similar branching in polypropylene crystallized from solution.
Electroluminescence from controlled splits in CdS, CdSe, and GaAs0.2P0.8
Authors: Khokhar R. U. , Haneman D.
Published: February 2004

The emission of visible (band-gap) radiation from current passed through controlled partial splits in n-type ∼5-Ω cm CdS has been studied in some detail. Some results are also reported for CdSe and GaAs0.2P0.8. Recombination occurs at the back-to-back surface barriers that occur in these materials at unhealed portions of the split. These barriers are effective at closed splits produced both in ultrahigh vacuum and in air for CdS and GaAs0.2P0.8 but only in high vacuum for CdSe. The radiation is emitted in a thin region at that side of the split which is biased in the forward direction. This is explained by a hole-tunnelling mechanism. Pulsed operation at room temperature and continuous operation (several seconds) at liquid-nitrogen temperatures gives light generation efficiencies in CdS of a few percent, at current levels in the region of 10 A cm−2. Such efficiencies have hitherto been unobtainable. Operation at about 50 A cm−2 results in failure which is shown to be due to breakdown of the surface barriers at isolated spots in the contact zone. A thin collodion layer between the surfaces greatly reduces this tendency.
Absolute instability of electromagnetic waves within large subcritically doped gallium arsenide samples
Authors: Baynham A. C.
Published: February 2004

When an electromagnetic wave enters a medium having an effective negative resistance it may be expected to grow spatially. The present paper describes experimental work in which an electromagnetic wave propagates within a medium which is biased into a region of negative differential conductivity. Microwave emission is observed when round-trip gain exists within the cavity formed by the specimen boundaries, and the factors which determine the form of the emission spectrum are studied. Finally, conclusions regarding the detailed mechanisms underlying the operation of this device are drawn.
Minimum current and related topics in Josephson tunnel junction devices
Authors: Zappe H. H.
Published: February 2004

Solutions of the equation of motion of Josephson junction devices are approximated by analytical relations in the pronounced nonlinear range of small voltages. The minimum current at which the junction switches back into the net zero voltage state is established for devices with resistive and inductive elements, including the nonlinear tunnel resistance of the junction. The stability of the voltage state is estimated. Conditions for which junctions fail to enter the zero-voltage state are discussed.
On the relation between thermally stimulated conductivity and thermoluminescence maxima
Authors: Chen R. , Fleming R. J.
Published: February 2004

The temperatures of thermoluminescence (TL) peaks and their corresponding thermally stimulated conductivity (TSC) counterparts are investigated for the case of temperature-dependent recombination probabilities and mobilities. The conditions under which the TL peaks will occur at higher temperatures than the TSC peaks, i.e., the normal order is inverted, are derived.
Excitation spectra for 1.06 μ luminescence in Nd3+-doped LaF3
Authors: Chang T. S. , Jackel J.
Published: February 2004

The 4°K excitation spectrum of the 4F3/2-4I11/2 luminescence of Nd3+ in LaF3 was measured in the region of the six A absorption lines.
X-ray diffraction topographs of silicon crystals with superposed oxide film. I. Theory and computational procedures
Authors: Kato N. , Patel J. R.
Published: February 2004

The principal aim of this paper is to develop the theoretical and computational procedures used in the following paper. The Eikonal theory of crystal diffraction is summarized, and the computational procedures for obtaining the ray trajectory and the phase change along the ray in distorted crystals are described. Specifically, the x-ray diffraction theory is applied to the analysis of dynamical diffraction effects observed by x-ray topography at the edge of a thin oxide film superposed on a silicon host crystal. The critical importance of symmetry properties of topographs in evaluating the computational procedures is emphasized. The present computational procedures are quite general and can be used with appropriate modifications for a quantitative understanding of diffraction effects, due to any general distortion in crystals observed in topographs of the section type.
Growth of boron-doped diamond seed crystals by vapor deposition
Authors: Poferl David J. , Gardner Nelson C. , Angus John C.
Published: February 2004

p-type semiconducting diamond was grown by vapor deposition from a 0.83% diborane in methane gas mixture at 1050°C and 0.2 Torr on 0 to 1-μ nominal size natural type-I diamond powder. Total mass increases of about 9% were achieved which correspond to average linear growth rates of less than 10−3 μ/day. Evidence showing the growth was boron-doped diamond included chemical etching, x-ray and electron diffraction, density measurements, Seebeck and resistivity measurements, chemical analysis, optical measurements, induced electron emission spectroscopy, and scanning electron microscopy. The crystalline quality of the new diamond has not been established; it may be highly defective. A distinct change in color of the diamond seed crystals from an off-white or gray for virgin crystals to light blue after growth was observed. The results are further confirmation that diamond may be grown at low pressures where it is thermodynamically metastable with respect to graphite. It is also further evidence that boron is the element responsible for blue p-type diamonds.
Finite pulse-time and heat-loss effects in pulse thermal diffusivity measurements
Authors: Heckman R. C.
Published: February 2004

The heat transfer problem associated with pulse thermal diffusivity measurements is analyzed for the cases of (i) triangular pulses whose widths are comparable with the transit time of temperature fronts across a sample (finite pulse width effects), (ii) heat losses from sample faces, and (iii) the simultaneous occurrence of heat losses and finite pulse-width effects. Methods for the analysis of experimental results which are affected by these conditions are discussed. Tabular and graphical data which facilitate the analysis are given.
Compression of Ag and phase transformation of NaCl
Authors: Liu Lin-gun , Bassett William A.
Published: February 2004

The isothermal compression of silver up to 309 kbar has been measured at 23±3°C by high-pressure x-ray diffraction employing a diamond-anvil cell. The B1 phase of NaCl mixed with the silver was used both as a pressure transmitting medium and as an internal pressure calibrant. The data fitted to two forms of the Birch equation yield K0=1180±50 kbar, K0′=3.8±0.5, and K0=1105±95 kbar, K0′=4.6±0.8. When the pressure exceeded 300 kbar, the NaCl underwent a phase transformation to the B2 phase. Increasing the load did not result in the complete disappearance of the B1 phase up to a pressure of 311 and 334 kbar based on the extrapolation of the Ag and Re compression data, respectively. The average volume change measured for the B1-B2 transformation is −0.83±0.11 cm3/mole, which is 17% smaller than the value reported by Bassett et al. This smaller volume change improves the agreement of NaCl with the linear relationship between volume change and entropy change proposed by Bassett et al. for the B1-B2 transformation in the alkali halides.
Theory of interdigital couplers on nonpiezoelectric substrates
Authors: Kino G. S. , Wagers R. S.
Published: February 2004

This paper is concerned with the theory of excitation of surface acoustic waves on a nonpiezoelectric material, by using an interdigital electrode structure overlaid with a piezoelectric film. The impedance and capacity of such transducers have been worked out. The results are given in terms of Δv/v, the perturbation in acoustic wave velocity when a perfect conductor is placed in the position of the transducer. A computer program which calculates surface wave propagation on a layered medium consisting of a film on a substrate, with arbitrary elastic and piezoelectric properties for both media, has been used to determine Δv/v, and hence the coupling coefficients and radiation resistance of the interdigital transducer. As a function of piezoelectric film thickness, two peaks in coupling are observed. The results for the interdigital couplers are in quantitative agreement with experiments employing single-crystal materials. Data for experiments using sputtered piezoelectric films also give qualitative agreement with the theory. If high-quality crystalline layers are used, the theory suggests that interdigital couplers on nonpiezoelectric delay lines with properties comparable to or better than the present piezoelectric delay lines may be achievable.
Evaluation of some transport integrals. IV. Nonparabolic bands
Authors: Wood Van E.
Published: February 2004

Formulas are presented for the practical evaluation of transport and related integrals for conduction in a single nonparabolic band of the simplest type: k ∝(ε+ε2/εg)1/2. It is shown that when Maxwell-Boltzmann statistics apply, these integrals may be evaluated in terms of modified Bessel functions plus a single additional function. For the Fermi-Dirac region, approximation formulas for small εg are given, complementing those for large εg found in the literature. It is shown how further approximations may be found using the Laplace transform technique. As an example, the Faraday rotation due to free carriers is considered. It is pointed out that nondegeneracy of the carriers does not mean that effects of nonparabolicity are negligible.
Hall-mobility measurements at elevated temperatures and pressures
Authors: Even Uzi , Levine Menahem , Magen Jacob , Jortner Joshua
Published: February 2004

We describe a system for the measurement of the Hall mobility in expanded liquid metals and in dense metallic vapors at elevated temperatures (30–1600 °C) and pressures (1–2000 atm). Performances of the experimental setup are presented for mercury up to its critical point.
Similarity solution for instabilities in double-phase flow through porous media
Authors: Verma A. P. , Mishra S. K.
Published: February 2004

This paper analytically discusses the phenomenon of instabilities (fingering) which arise frequently in displacement processes through porous media. The underlying assumptions of the investigation are that the two flowing phases are immiscible liquids with a large viscosity difference, the porous medium is homogeneous, and the instabilities are described by their statistical behavior. A mathematical solution of the nonlinear differential system governing fingering has been obtained by using the group-transformation technique of similarity analysis. Finally, an analytical expression for the average cross sectional area occupied by fingers has been derived, and the possibility of finger stabilization is shown under certain specific conditions.
Preparation and properties of nonstoichiometric MnAlGe thin films
Authors: Lee Kenneth , Sawatzky Erich , Suits J. C.
Published: February 2004

Films of MnAlGe which are nonstoichiometric have been prepared by rf sputtering. Structural, magnetic, and optical properties of these films have been determined. The Curie temperature of films with excess aluminum has been found to be as low as 190°C. The crystallographic orientation of these films may be adjusted by proper choice of substrate temperature.
Theory of domain-wall motion in magnetic films and platelets
Authors: Slonczewski J. C.
Published: February 2004

We calculate dynamical properties of plane and cylindrical magnetic domain walls in a uniaxial film or platelet whose plane is perpendicular to the easy axis. First, we calculate the internal structure of a freely moving wall to determine the nonlinear velocity-momentum relation. Using a Bloch-line approximation to the kinetic wall energy, we find that stray magnetic fields emanating from surface poles destabilize the structure at a critical velocity Vp, above which uniform motion is not possible. For a plane wall, we have Vp=24γA/hK1/2, where γ is the gyromagnetic ratio, A is the exchange stiffness, h is the film thickness, and K is the anisotropy. This velocity is usually much less than the critical velocity for bulk wall motion derived by Walker. Combination of the velocity-momentum relation with the conservation of momentum provides a simple method of calculating the time-dependent velocity in the presence of a small drive field and small viscous damping. For very small drive, the terminal velocity equals that given by the conventional linear-mobility theory. However, for small drives exceeding a critical value corresponding to Vp, a periodic cycle of Bloch-line generation, motion, and annihilation takes place at a frequency approaching the Larmor frequency corresponding to the driving field. This is accompanied by a synchronous nonsinusoidal oscillation of the wall, with a mean forward velocity tending to an asymptote V0. Our relation V0=7.1γA/hK1/2 agrees within a factor of 3 with the onset of nonlinear behavior observed by means of bubble collapse in certain low-loss garnet specimens. Partial support is also given by data for hexaferrite platelets. For radial motion of cylinders with finite diameter D, numerically computed values of V0 are larger but never exceed this expression by more than 17%. The critical velocity Vp also varies little for D/h>2, but varies rapidly and attains large values for small D/h.
Pressure dependence of the Curie temperature of intermetallic compounds of iron and rare-earth elements, Th, and Zr
Authors: Brouha M. , Buschow K.H.J.
Published: February 2004

The pressure dependence of the Curie temperature (Tc) of several intermetallic compounds of iron has been determined by means of the temperature dependence of the electrical resistivity at various pressures. Pressures up to 40 kbar were applied. The value of dTc/dp was observed to be negative in the compounds R2Fe17 (R=Pr,Nd,Er, and Th), Y6Fe23, Er6Fe23, ErFe3, Th2Fe7, ThFe3, CeFe2, and ZrFe2. The Curie temperature of the compound ThFe5 is pressure independent within experimental error. In the compounds RFe2 (R=Gd,Ho,Er, and Y), the value of dTc/dp was found to be positive. The experimental data are discussed in terms of Friedel's semilocalized model and the collective electron model.
Anisotropy of the magnetogyric ratio in hexagonal ferrites
Authors: Silber L. M.
Published: February 2004

Observations of ferromagnetic resonance at room temperature in several hexagonal ferrites have shown that the results can not be adequately described by a scalar magnetogyric ratio. Measurements were made on two compounds of the Y phase, with easy planes of magnetization, and compounds of the M, W, and X phases, which have easy axes of magnetization. In all materials the magnetogyric ratio may be described by a tensor having two components, g∥ and g⊥, measured parallel and perpendicular, respectively, to the hexagonal axis. g∥ is found to be constant for a given material, while g⊥ is magnetic field dependent, approaching g∥ at high fields. g-factor anisotrpies as large as 7% were observed. Possible origins of these effects and applications to microwave devices are discussed.
Photo-Compton currents in unbounded media
Authors: MacCallum Crawford J. , Dellin Theodore A.
Published: February 2004

A flux of photons passing through a condensed medium drives with it a flux of recoil electrons, continually generated by Compton and photoelectric processes and continually brought to rest by the stopping power of the medium. We formulate an analytical description of the magnitude and angular distribution of this electron flux in unbounded media. Numerical results for net, forward, and back-directed current densities are presented for a large set of elements and compounds and for photon energies from 10 keV to 20 MeV.
A study on zone refining: solid-phase impurity diffusion and the influence of separating the impure end
Authors: Fischer D.
Published: February 2004

Crystal quality during zone refining is usually poor. Owing to the great density of high-diffusivity paths, solid-state diffusion should not be neglected. Its influence on the concentration profile is described by experiment and theory. Since the concentration gradient and curvature become very large at the end of the bar (k<1), diffusion rates are especially high in this region. A successive separation of this enriched region may lead to a considerable improvement of zone refining. Theoretical and experimental results obtained with this method will be described.
Work hardening in ordered and disordered alloys
Authors: Sadananda K. , Marcinkowski M. J.
Published: February 2004

A work-hardening model for ordered and disordered single-crystalline alloys, where only one slip system is operative, is presented. The model is based on the experimental observation that most of the dislocations on parallel slip planes are locked as dipoles and this dipole formation is believed to be the principal source of work hardening. A detailed analysis of the behavior of passing dislocations is made as a function of frictional stress and vertical separation. Qualitative arguments for the observed strengthening in ordered and disordered alloys are presented based on the above analysis. The pronounced work hardening observed in ordered alloys is related to increased dipole strength as well as to reduced cross slip occasioned by atomic ordering.
Temperature dependence of the single-crystal elastic constants of Co-rich Co–Fe alloys
Authors: Wazzan A. R. , Bristoti A. , Robinson L. B. , Ahmedieh A.
Published: February 2004

The single-crystal elastic moduli, C11, C12, and C44 of three fcc cobalt-iron alloys (Co–6 at.% Fe, Co–8 at.% Fe, Co–10 at.% Fe) were measured in the range 0–315°C. In addition C11 for the Co–6 at.% Fe alloy, and C′=(1/2)(C11+C12+2C44) for the three alloys are measured over the temperature range 0–1250°C. Plots of the elastic moduli vs temperature exhibit a change in slope and deviation from linearity in the neighborhood of the Curie temperature. The temperature variation of the shear anisotropy in the fcc phase Afcc (≡2C44/C11−C12) differs among the three alloys. Afcc exhibits a highly positive temperature dependence in the Co–10 at.% Fe alloy and a slight negative dependence in the Co–6 at.% Fe and Co–8 at.% Fe alloys. Previous statements in the literature that the hcp⇄fcc transformation in cobalt is preceded by a highly negative temperature dependence of the shear anisotropy ratio A (≡C44/C66) in the hcp phase between 523°K and the transition at about 743°K is not borne out by the present results. Rather it appears that the hcp⇄fcc transformation involves a change from A>1 in the hcp phase to A<1 in the fcc phase.
Electromagnetic instability in a counterstreaming plasma
Authors: Seshadri S. R.
Published: February 2004

An electromagnetic wave propagating obliquely to a counterstreaming plasma is shown to be unstable for all directions of the stream. The stream direction normal to the wave vector is a singular case for which the growth rate increases from zero as the wave number is increased and asymptotically approaches a maximum value for very large wave numbers. For all other directions unstable waves exist for wave numbers below a critical value and the growth rate increases from zero as the wave number is increased, reaches a maximum value, and then decreases to zero at the critical wave number. The maximum growth rate is found to be the same for all stream directions other than very close to the normal to the wave vector. The dependence of the growth rate on the stream direction with respect to the wave vector and the validity of the quasistatic approximation in predicting the nature of this instability are also examined.
Cyclotron harmonic waves in a reflex discharge
Authors: Brand G. F. , Cohen D. D.
Published: February 2004

The propagation of cyclotron harmonic waves in a cold-cathode reflex discharge has been studied over a broad range of experimental parameters. Electron temperatures obtained from the waves and spectroscopic temperatures are in agreement but are an order of magnitude lower than double Langmuir probe temperatures. A non-Maxwellian electron velocity distribution for the plasma is suggested which can explain these results.
Measurement of refractive index of water under high dynamic pressures
Authors: Yadav H. S. , Murty D. S. , Verma S. N. , Sinha K. H. C. , Gupta B. M. , Chand Dal
Published: February 2004

The refractive index of water under conditions of dynamic loading up to a pressure of about 10 kbar has been measured by a geometrical refraction method with the high-speed Kerr-Cell camera system. Geometry of light transmission through the spherical front of shocked water has been worked out by applying Snell's law and the simple assumption of the zero-density gradient in the disturbed water and an attempt has been made to calculate the shock pressure underwater therefrom. The results obtained here are found comparable within 0.4% with those determined by Zeldovich employing the method of reflectivity.
Spectroscopic observations of subsonic and sonic vapor flow inside an open-ended heat pipe
Authors: Vidal C. R.
Published: February 2004

Spectroscopic measurements of the vapor flow velocities inside a heat-pipe oven have been performed as a function of pressure, heater power, and radial position inside the pipe. For this purpose the relative intensity of the collision-induced satellite lines in laser-induced resonance fluorescence spectra of the 7Li2 molecule has been employed. A one-dimensional flow model is presented which determines the vapor parameters as a function of position along the pipe. It predicts the onset of the sonic flow which has been verified experimentally. A criterion is derived from which the parameters of the vapor can be obtained from the ideal gas relation, neglecting velocity-dependent terms.
Confirmation of the effect of field-dependent scattering centers on electron mobility in gallium arsenide
Authors: Jervis T. R.
Published: February 2004

In an earlier paper, measurements of the electron mobility in GaAs as a function of electric field using a magnetoresistance technique were presented which revealed variations in the mobility due in part to field-dependent scattering centers. These centers were hypothesized to be multiply ionized acceptor impurities which by their large Coulomb cross section adversely affected the electron mobility in the material. Further studies using photoconductivity techniques at liquid-nitrogen temperatures to obtain the necessary sensitivity have shown that in the above case, acceptors, probably copper, exist in the material, and can be assumed to be the source of the observed field-dependent effect. The relatively high purity of these materials, as evidenced by their good performance as microwave sources, indicates that the concentration of the impurity is of the order of 1012/cm3.
Ion-expansion energy spectra correlated to laser plasma parameters
Authors: Olsen J. N. , Kuswa G. W. , Jones E. D.
Published: February 2004

The analysis of LiH and LiD nanosecond — created laser plasmas reveals correlations between the various parameters of each plasma event. Relationships are found involving the energy spectra of the ion species, the target reflectivity, neutron production, hard and soft x-ray emission, the electron temperature, and the input laser energy. Ion — expansion spectra of nonthermal origin are observed under the condition of high target reflectivity. High target reflectance is correlated to neutron and hard x-ray production as well as an apparent decrease in electron thermal content for laser energies of 18–70 J. The ion — expansion spectra are obtained with mass and charge separation by the parallel electric and magnetic fields of a Thomson parabola ion analyzer. A novel feature of this device is the conversion of the analyzed ion beam to a visible image via an electron multiplier array, providing complete information on a single — shot basis. The Nd+3 glass laser used in these experiments delivers up to 70 J to the target in 2.5 nsec (FWHM) pulses from a four-amplifier system. Isolation and protection of the smaller amplifiers from amplified target feedback is accomplished by insertion of a pulsed Faraday rotator between the second and third amplifiers.
Glass ceramic-a new laser host material
Authors: Müller G. , Neuroth N.
Published: February 2004

This paper reports on fluorescence and induced emission of Nd2O3-doped glass ceramics.
Laser mode locking using saturable absorbers
Authors: Garside B. K. , Lim T. K.
Published: February 2004

A theoretical model for mode locking induced by saturable absorbers is presented, employing an unidirectional ring laser cavity. Both the gain and loss media are assumed to be homogeneously broadened two-level systems, on-resonance with the radiation field. The loss of the cavity is treated as discrete and is supposed to occur at an equivalent mirror. Laser coupled equations are then derived, employing the density matrix formalism together with Maxwell's equations, using the rotating wave and slowly varying envelope approximations. Time-invariant solutions of the coupled equations are deduced exactly and mode-locking regions are predicted by a perturbation method. It is found that a suitable absorber can produce mode locking if the laser parameters are appropriately chosen. Generation of the steady-state pulses (SSP) by the finite-difference method shows that relatively short intense pulses can be obtained from a mode-locked laser. In addition, the theoretical model is extended to account for the possibility that the absorbing medium may be less easily saturated than the gain medium and/or the phase coherence times of the two media are very different. It is pointed out that our model can be a good approximation to a real laser system under certain circumstances. It can also be used as a guide in the search for a suitable absorber for particular laser systems.
Evaluation of the directivity of gravitational wave radiators
Authors: Seki Hideo , Obata Tsunehiro , Chiba Jiro
Published: February 2004

A method of evaluation of the directivity of gravitational wave (GW) radiators is given in the form of general equations applicable to most cases such as Weber's apparatus and the travelling wave (TW)-type radiator (the latter proposed by one of the authors). Although it is not generally accepted now, Einstein's weak-field theory is used for evaluating both near and distant fields. In a numerical example, using our general formula, the TW-type radiator is considered and it is found that a half-power angle width of ±5.3° is feasible using a crystal 30 cm in length. Intensity comparison is also made between the resonance vibrator and TW-type radiators. Under reasonable assumptions, the radiated power of the latter is about 1023 times larger than the former—that means 1040 times higher intensity than the spinning rod first considered by Einstein as a GW source
Approximations involving the transport equation for ions in drift tubes
Authors: Vorburger T. V. , Woo S. B. , Whealton J. H.
Published: February 2004

Questions have been raised on the validity of the transport equation for ions in drift tubes at high E/N, the ratio of the electric field to the gas number density. We investigate the approximations surrounding the derivation of the transport equation from the Boltzmann equation. The nature of these approximations, the range of their validity, and the magnitude of error introduced by them are discussed. A model for ion-molecule reactions is included in the collision integral of the Boltzmann equation.
Transport processes of photoinduced carriers in Bi12SiO20
Authors: Hou S. L. , Lauer R. B. , Aldrich R. E.
Published: February 2004

The optical absorption edge of undoped, lightly Al-doped, and heavily Al-doped Bi12SiO20 single crystals is found to be exponential and follows Urbach's rule with σ0=0.71 at room temperature. The band edge is at 3.25 eV and is broadened by excitons and perhaps by impurities or defects. At 80 °K, the band edge is found to be shifted to 3.40 eV. The broad shoulder in the optical absorption and the secondary peak in the photocurrent excitation spectrum are attributed to the presence of a silicon vacancy complex. The longitudinal photocarrier response due to pulsed uv excitation leads to a value of the electron drift mobility of μd=0.029±0.003 cm2/V sec and a value for the range of electrons (μτ)e=8.5×10−7 cm2/V. The response times of electrons and holes (or the relaxation times) are determined to be 6.5×10−3 and 4.3 ×10−3 sec, respectively. Electrons dominate the photocurrent in undoped and lightly Al-doped crystals, while holes dominate the photocurrent in the heavily Al-doped crystals. Thermally stimulated current between 80 and 360 °K shows three major electron traps with energetic depths of 0.34, 0.54, and 0.65 eV in undoped crystals, and major hole traps at 0.26, 0.31, and 0.43 eV in the heavily Al-doped crystals. A band diagram for the undoped single crystals is proposed to explain the photocurrent kinetics and the temperature dependences of the photoluminescence emission bands at 1.95 and 1.30 eV and the temperature dependence of the photocurrent.
Nonavalanche injection of hot carriers into SiO2
Authors: Verwey J. F.
Published: February 2004

Carriers can be injected into the SiO2 from a junction reverse biased below avalanche and lying in the silicon near the Si–SiO2 interface. This effect was studied for electron injection in n-channel MOS transistors. The electrons originated from a forward-biased (supply) junction lying below the source, drain, and channel region. The electrons were heated in the space-charge layers of source and drain reverse biased below avalanche breakdown and in the space-charge layer below the channel induced by the combined effect of a positive gate voltage and the reverse bias on source and drain. Injection into the oxide occurs mainly from the latter region. The current through the oxide and the charge trapped in the oxide were measured as a function of several parameters. These measurements yield the threshold values of the reverse source (drain) voltage, VTR, and of the gate voltage, VGT, necessary for injection. From the dependence of VTR on the concentration of dopant in the channel region, the value of the mean free path λ of hot electrons between inelastic phonon collisions in the silicon is estimated as 125 Å. The method presented may be a powerful tool for studying these collisions in other semiconductor materials. The injection of holes into the SiO2 was possible by virtue of the same nonavalanche mechanism. Some results are given of measurements in a slice with p-channel MOS transistors.
Liquid-phase sintering of SmCo5
Authors: Jorgensen P. J. , Bartlett R. W.
Published: February 2004

The initial sintering kinetics of stoichiometric SmCo5 powder containing a samarium-rich sintering addition (60 wt% Sm plus 40 wt% Co) have been investigated as a function of amount of liquid phase, time, temperature, and particle size. The shrinkage as a function of time exhibits the classical three stages of liquid-phase sintering, i.e., rearrangement, solution precipitation, and solid phase. The rate-controlling step during the solution-precipitation stage corresponds to a phase-boundary (solid/liquid) reaction leading to dissolution. Evidence for this conclusion is partially based on the logarithm-shrinkage—logarithm-time slopes being equal to 1/2 instead of 1/3. A 1/3 slope is predicted by the liquid-diffusion-controlled sintering model while the phase-boundary sintering model predicts a slope of 1/2. An activation energy of 52.8 kcal/mole was obtained for the temperature dependence, and this also suggests a phase-boundary reaction rather than rate control by diffusion in the liquid phase. The rate of sintering follows an r−1 particle-size dependence instead of an r−4/3 dependence, again suggesting that the solution-precipitation stage of sintering of SmCo5 is controlled by a phase-boundary reaction leading to dissolution.
On the application of cluster growth rates to heterogeneous nucleation theory
Authors: Hruska S. J. , Pocker D. J.
Published: February 2004

Recent applications of steady-state growth rates to heterogeneous nucleation rates are considered and rejected. The time-dependent solution of the differential equation governing adsorbed monomer behavior shows that the capture probability approach of Halpern is equivalent to a steady-state solution.
Conductivity of a system of metallic particles dispersed in an insulating medium
Authors: Springett B. E.
Published: February 2004

The variation of the conductivity of metal-particle—insulator systems with the volume percent of metal is explained in terms of an ``effective medium'' theory.
Measurement of electron-ion recombination rate of a dense high-temperature cesium plasma
Authors: Chen Che Jen , Wu James M. , Wu Frank T. , Shaw David T.
Published: February 2004

The result of the measurement of the electron-ion recombination rate of cesium plasma in a discharge tube is presented. The electron temperature has been extended to 5000 °K and the electron density to 1015 cm−3. The comparison of the experimental data with the calculated values (Ref. 7) is considered to be satisfactory
Pulsed microwave breakdown in gases with a low degree of preionization
Authors: Dawson E. F. , Lederman S.
Published: February 2004

This paper presents the results of experiments on microwave breakdown at an open-end waveguide antenna in air, argon, nitrogen, carbon dioxide, and methane at pressures of 0.3 and 30 Torr. The antenna was operated at 9.375 GHz under pulsed conditions at varying pulse rates. Very low degrees of preionization were obtained by adjusting to very slow pulse rates. The power needed to maintain the discharge was measured and from that the electric field strength was calculated. This is presented as a function of pressure for each gas at pulse rates ranging from 10 to 500 pulses/sec. At low pulse rates, significantly higher power levels are needed to maintain the discharge. An interesting feature is the double minima observed at low pulse rates in the data for breakdown field strength as a function of pressure for carbon dioxide and methane. The data were also used to calculate ionization frequency as a function of effective electric field for all five gases. Where possible, these data are compared with data reported by other investigators.