bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of deformation of PTFE at high pressure
Authors: Davis L. A. , Pampillo C. A.
Published: February 2004

The dependence of the deformation behavior of PTFE on hydrostatic pressure is characterized by determination of the activation volume for plastic flow, V*, which is defined as V*=kT(∂ lnε̇/∂ lnσ)T,P(∂ lnσ/∂P)T,ε̇. At a given strain the first partial derivative in this equation, a measure of the strain-rate dependence of the flow stress, is observed to increase with pressure, but at a slower rate than the second partial derivative, a measure of the pressure dependence of the flow stress, decreases with pressure. Hence V* decreases from a value on the order of 300 Å3 at 0.7 kbar to about 160 Å3 at 3.5 kbar and 120 Å3 at 7.59 kbar. The decrease in V* occurs discontinuously near 2.4 kbar and we believe this to be due to a change in the rate-limiting mechanism for deformation. This transition has a marked similarity to that previously observed by the authors in polyethylene; it appears possible that the same deformation mechanisms are operative in both materials.
Biaxial stress relaxation in glassy polymers: polymethylmethacrylate
Authors: Sternstein S. S. , Ho T. C.
Published: February 2004

Biaxial stress relaxation studies were performed on glassy polymethylmethacrylate in combined torsion-tension strain fields using a specially designed apparatus with exceptionally high stiffness and low cross talk between the torsional and tensile load measuring transducers. It was found that at low strain levels uniaxial tension relaxation is slower than pure torsion relaxation; tensile-component relaxation rates are unaffected by the level of torsional strain; torsional-component relaxation rates decrease as tensile strain is increased; uniaxial tension relaxation rates approach the pure torsion rates at higher strains (∼2%). A phenomenological treatment is presented which shows that relaxation rates can be coupled to the strain fields in which they are observed and yet be consistent with the concepts of linear viscoelasticity and the Boltzmann superposition integral. It is concluded that the mean normal strain, and not the octahedral shear strain, is the principal factor that governs both the effect of strain field on relaxation kinetics and the onset of nonlinear viscoelastic behavior. A mechanistic interpretation based on long-term relaxation processes in glassy polymers is offered to explain the effects of mean normal strain on relaxation kinetics.
Influence of solute pairs on solute diffusion in a substitutional fcc alloy
Authors: Stark J. P.
Published: February 2004

In a moderately concentrated fcc alloy, the correlation factor for solute jumps becomes increasingly approximate as the probability of solute atom pairs increases. To compensate for this difficulty, a model of solute diffusion is presented which incorporates the number of solute pairs and their contribution to the diffusion coefficient by dissociation.
Acoustoelectric domains in GaAs: on and off axis
Authors: Moore A. R. , Davenport J. W.
Published: February 2004

Acoustoelectric domains in GaAs have been observed directly and photographed by stroboscopic illumination in the fundametal absorption band edge. Domains are 1 mm in width and often have internal structure with peaks of intensity several times average. The anisotropic propagation characteristics of the TA (acoustoelectrically active) quasishear mode have been calculated. Off-axis domains obey the geometrical requirements of the small-signal theory of Klein, provided the anisotropic character is taken into account.
Transient electromagnetic fields of a finite circular loop in the presence of a conducting half-space
Authors: Wait James R. , Hill David A.
Published: February 2004

A previous solution for a pulse-excited dipole is extended to allow for the finite size of the buried source loop. Numerical results for the above surface fields are presented. We also consider the situation when the finite source loop is located on the surface and the observer is buried. It is suggested that the waveform of the received pulse signals can be used for direction-finding and source location.
Modeling of a pulsed CO/N2 molecular laser system
Authors: Abraham George , Fisher Edward R.
Published: February 2004

A detailed numerical model has been developed for characterizing the important energy-transfer processes operative in the CO/N2 dc discharge laser system. The model is based upon a rate-equation formulation which includes 30 levels of both CO and N2 and treats multiquantum electron-molecule excitation processes, single-quantum vibration-vibration exchange and vibration-translation energy-transfer processes, and both harmonic and overtone spontaneous emission terms. In this paper the time evolution of the CO vibrational distribution with and without N2 is calculated, and the associated small-signal gain is predicted and compared to the measurements of Jeffers and Wiswall. Good agreement is obtained between the predicted and measured delay times to maximum gain in a pulsed CO laser system for reasonable assumptions on the important system parameters. The variation in these predicted gains and time delays is explored for various values of the electron density, the translational-rotational temperature, and the effect of added N2 as a contribution toward improved experiment design in furthering the understanding of the phenomenology in the pulsed CO/N2 laser system.
Photovoltaic properties of ZnS crystals and a comparative study with luminescence
Authors: Scarmozzino R.
Published: February 2004

In this paper we first analyze the problem of obtaining reproducible photovoltage measurements in ZnS crystals grown from the vapor phase in H2S atmosphere. We show that the photovoltaic spectrum of such crystals can be as follows: (a) the crystal may exhibit two peaks at about 335 and 341 nm; (b) the crystal may exhibit only the peak at about 335 nm; (c) the crystal may exhibit only the peak at 341 nm. We find that only crystals of type (a) and (c) exhibit storage effects, i.e., the photovoltaic spectrum obtained with increasing wavelength is different from the spectrum obtained with decreasing wavelength. To investigate the photovoltage build up, we perform simultaneously fluorescence and photovoltage measurements, and we show that a close peak-to-peak correspondence exists only when an excitation of an impurity level localized near the valence band or an excitation between a localized impurity level and the conduction band is involved. This analysis is supported also from the behavior of these spectra when laser light is added. We show that among the various models proposed to explain photovoltage in ZnS crystals, the one which postulates negative internal fields in the hexagonal region and positive internal fields in the cubic region appears to be the most suitable.
Hot-electron concept for Poole-Frenkel conduction in amorphous dielectric solids
Authors: Antula J.
Published: February 2004

The general calculation of Poole-Frenkel conduction for amorphous solids must take into account the existence of Coulombic centers and a range of shallow trap centers. The hot-electron concept leads to the proper distribution of electrons between these traps and the conduction band in the presence of the applied electric field and at finite temperatures. Including the effect of hot electrons we achieve a better agreement between the theory and experimental data obtained with amorphous Al2O3, Ge, and SiO films.
Laser interferometer for measuring high velocities of any reflecting surface
Authors: Barker L. M. , Hollenbach R. E.
Published: February 2004

A laser velocity interferometer instrumentation system has been developed which can measure the velocity history of either spectrally or diffusely reflecting surfaces. The system provides two interferometer fringe signals in quadrature to improve resolution and to distinguish between acceleration and deceleration. Accuracies of 2% or better are attainable for peak surface velocities of 0.2 mm/μsec or more. The system has been applied to the measurement of free surface motion in plate-impact experiments, and to the measurement of the velocity history of a projectile during its acceleration down a long gun barrel.
Cutting thin metal sheets with the cw CO2 laser
Authors: Gonsalves J. N. , Duley W. W.
Published: February 2004

A quantitative analysis of cw CO2 laser power required to cut thin stainless-steel sheets at varying speeds is reported. The results are interpreted theoretically in terms of a point-source model. Generalized curves have been plotted which allow predictions to be made for other metals.
Closed-form solutions for the photocount statistics of superposed coherent and chaotic radiation
Authors: Laxpati Sharad R. , Lachs Gerard
Published: February 2004

In recent years there has been considerable utilization of photocount statistics for studying theoretical and experimental properties of a quantized electromagnetic field. The electromagnetic field, which has been of greatest interest in these areas, is a superposition of coherent and chaotic radiation. In this paper closed-form recurrence equations are derived for the photocount distribution and the factorial moments for this case. The photocount distribution is then obtained by using a well-known solution for p(0, T), and the factorial moments are generated by using the fact that the zeroth factorial moment is unity.
Comment on ``The coefficient of friction of high polymers as a function of pressure''
Authors: Towle Laird C.
Published: February 2004

Bowers and Zisman have postulated a simple expression relating the friction coefficient of thin solid lubricant films to the shear strength of the film material and the contact pressure involved. They have attempted to demonstrate the validity of this expression by comparing shear strength and friction measurements made using two types of experimental configurations. It is argued here that the measurements compared are intrinsically equivalent and will yield equivalent results even when the friction mechanism is such that the postulated equation is not valid. Hence, the comparisons made do not in any way test the validity of the postulated equation.
Preferential diffusion of oxygen along grain boundaries in polycrystalline MgO
Authors: Hashimoto Hidehisa , Hama Masaaki , Shirasaki Shin-ichi
Published: February 2004

Self-diffusion coefficient of oxygen in polycrystalline MgO can be represented by D=4.5×10−5exp(−60200/RT)cm2/sec for 80–115 mesh particles and by D=1.3×10−5exp(−60200/RT)cm2/sec for 170–200 mesh particles. These two activation energies are exactly the same, but the magnitude of the diffusion coefficients varied from one sample to another. When D was recalculated by taking a as the grain radius instead of particle radius, all the data points fall on a single solid line expressed by D=4.5×10−7exp(−60200/RT) cm2/sec. It is important to note that this line approximately meets the Arrhenius plot for oxygen diffusion in single-crystal MgO. Therefore, we conclude that the diffusion of oxygen along the grain boundaries in polycrystalline MgO is considerably faster than diffusion through the bulk.
Stability of dislocation loops near a free surface
Authors: Narayan J. , Washburn J.
Published: February 2004

The effect of surface forces on the stability of edge dislocation loops, b=(1/2) [101], in MgO thin foils has been studied using transmission electron microscopy. The circular loops lying within a critical distance from the surfaces slip out without appreciable rotation. The critical distance in {100} foils, where the glide cylinders are at 45° to the foil surfaces, was found to increase with increasing loop size.
Kinetics and thermodynamics of thin-film deposition by molecular beam methods. I. Adsorption and clustering of cadmium on germanium single crystals
Authors: Voorhoeve R. J. H. , Carides J. N. , Wagner R. S.
Published: February 2004

The use of mass-spectrometric molecular beam techniques allowed a detailed study to be made of the kinetics and thermodynamics of thin-film deposition. Thermal accommodation, adsorption, nucleation, growth, and evaporation were measured for a single system. The deposits were characterized by their coverage-dependent steady-state evaporation rate, which is directly related to the thermodynamic potential of the evaporant in the film. The methods used and results obtained are exemplified by the present study of all stages of the ultrahigh-vacuum (UHV) deposition of cadmium on the (100), (110), (111), (211), and (331) faces of germanium. In this paper, the initial stages of adsorption and clustering are described. The thermal accommodation coefficient was found to be between 0.8 and 1.0. On (111) substrates, adsorption of one monolayer of immobile cadmium atoms precedes nucleation of bulk cadmium. On the other substrates, 40% to 70% of a monolayer is adsorbed prior to nucleation. The extent of this adsorption is predictable from the structure of the germanium surfaces. Adsorption energies range from 25 to 32 kcal/g atom, compared with a heat of sublimation of 26.7 kcal/g atom. The kinetics of the desorption of cadmium during deposition is in agreement with an evaporation mechanism in which desorption of mobile single cadmium adatoms is the rate-determining step. The desorption energy of mobile adatoms is approximately 12 kcal/g atom in the nucleation stage. It is shown that the stability of the cadmium deposit increases only slowly after nucleation. Electrically active dopants in the germanium increase the extent of cadmium adsorption which precedes nucleation.
Axial channeling in ThO2
Authors: Clinard F. W. , Sanders W. M.
Published: February 2004

Axial channeling in single-crystal ThO2 was investigated with 6.5-MeV3He++ ions. The thorium sublattice was studied by evaluation of pulse-height distributions from backscattered 3He ions, and the oxygen sublattice by evaluation of proton pulse-height distributions from 16O(3He, p)18 F reactions. Critical channeling angles (ψ1/2) and minimum yields (χmin) were determined for the 〈110〉 and 〈111〉 directions. Values for ψ1/2 were generally consistent with those reported for the isomorphic compound UO2, whereas χmin values were considerably smaller than those reported for UO2. These results are compared with those predicted by current channeling theories, and are discussed in terms of the relative crystal perfection of ThO2 and UO2.
Martensitic pretransformation phenomena in the Au-47.5 at.% Cd and the Fe-29.7 at.% Ni alloys
Authors: Livingston H. , Mukherjee K.
Published: February 2004

Premartensitic transformation characteristics have been investigated in the Au-47.5 at.% Cd and the Fe-29.7 at.% Ni alloys by measuring electrical resistivity and magnetoresistance. Preliminary electron diffraction studies have also been made for the Au–Cd alloy. An anomalous magnetoresistance peak was observed for both of these alloys prior to the martensitic transformation. In the Au–Cd alloy this peak was about 2–3°C above the Ms, and for the Fe–Ni alloy it was about 5–6°C above the Ms. Furthermore, when the Ms was lowered by isothermal stabilization, this peak moved in conjunction with the new Ms temperature. This indicates that the observed peak is truly associated with the premartensitic instability of the parent phase. The electron diffraction pattern of the parent phase of the Au–Cd alloy shows extensive 〈110〉 and 〈112〉 streaking in the temperature range where anomalous magnetoresistance was observed. These experimental results could tentatively be interpreted in terms of anisotropic scattering centers resulting from localized strain inhomogeneities. Presumably these inhomogeneities are associated with the atomic shuffling prior to the actual phase transformation and could be identified with the so-called ``strain embryos''.
CO2 laser-induced gas breakdown in hydrogen
Authors: Offenberger A. A. , Burnett N. H.
Published: February 2004

A single-mode CO2 laser pulse of approximately 10 MW peak power has been used to induce breakdown at pressures from 50 to 700 Torr in hydrogen. Measurements of the reflected and transmitted laser intensity were obtained and the properties of the resulting spark were studied by means of image converter camera and spectroscopic techniques. At pressures in excess of 100 Torr the spark was observed to grow preferentially towards the focusing lens, while at lower pressures a symmetric expansion was observed. The observed motion was consistent with the existence of a breakdown wave during the rising portion of the laser pulse followed by a laser-supported detonation. At pressures greater than 100 Torr, significant reflection (> 2%) was observed during the detonation phase.
Anode current density in high-current pulsed arcs
Authors: Shih K. T.
Published: February 2004

A method has been developed using a split anode to measure the anode current density distribution in high-current pulsed arcs. Rogowski coils were used to detect the current to each half of the split anode as a function of arc position relative to the splitting plane. Transformation equations were derived to obtain local values of current density from the measured lateral distributions. The data were taken using a copper anode in air at one atmosphere with arc current from 750 to 2250 A. The peak anode current densities were found to be between 3.4×105 and 5.5×105 A/cm2.
Drift mobilities in amorphous charge-transfer complexes of trinitrofluorenone and poly-n-vinylcarbazole
Authors: Gill W. D.
Published: February 2004

Hole and electron drift mobilities have been measured in thin films of charge-transfer complexes of 2,4,7-trinitro-9- fluorenone (TNF) with poly-n-vinylcarbazole (PVK). The film compositions ranged from pure PVK to mixtures of TNF : PVK in a 1.1 : 1 molar ratio with respect to the monomer unit. Measurements have also been made on amorphous films of pure TNF. The drift mobilities are extremely low (< 10−6 cm2/V sec) and are strongly field and temperature dependent. The field dependence is due to the measured activation energies decreasing as the square root of the applied field from zero-field values of about 0.7 eV for both carriers. The field dependence of the mobilities is similar to that observed for conductivity modified by the Poole-Frenkel mechanism; however, several objections make this model unacceptable for this case. At this time, no satisfactory explanation of the observed field dependence can be given. As the TNF concentration is increased, the hole mobility decreases rapidly, while the electron mobility increases. The results suggest that charge carriers are highly localized with transport taking place by a thermally assisted intermolecular hopping process as for the case of small ppolaron motion. Hole transport is apparently due to hopping via uncomplexed carbazole states, while electron transport is due to hopping between TNF sites which may be complexed or uncomplexed. Estimates of the charge-carrier localization obtained from the exponential dependence of mobility on the site separation give characteristic distances of 1.1 × 10−8 cm for holes and 1.8 × 10−8 cm for electrons.
Energy spectra transmitted through iron slabs of bremsstrahlung produced in iron and gold targets by 0.5–1.44-MeV electrons
Authors: Nakamura Takashi , Takemura Morio , Hirayama Hideo , Hyodo Tomonori
Published: February 2004

The bremsstrahlung spectra transmitted through iron slabs were measured as a function of incident electron energy and iron-slab thickness. In this experiment, the gold and the iron targets were bombarded by 0.5–1.44-MeV electron beams from the Van de Graaff accelerator. Bremsstrahlung produced in the target and transmitted through the iron slab, which emerged at the forward direction of the incident electron beam, was detected with a NaI(Tl) scintillator. The experimental results were in good agreement with those of the approximate numerical calculation of the forward photon spectra. From the slopes of attenuation curves of total photon number and intensity, the effective attenuation coefficients and the effective energies were obtained as a function of the incident electron energy.
Complex ion formation in Xe–Hg mixtures
Authors: Tombers Reid B. , Chanin L. M.
Published: February 2004

Ion sampling studies have been performed in dc discharges containing Xe–Hg mixtures. Ions observed include Xe+, Hg+, Xe2+, XeHg+, Hg2+, Xe2Hg+, XeHg2+, and Hg3+. Apparently Xe2Hg+, XeHg2+, and Hg3+ have not been mass identified previously.
Short-Range Order in Cu–Mn Alloys: Spurious Contribution of MnO2 to the Diffraction Pattern
Authors: Sato H. , Taketoshi K. , McCune R. C.
Published: February 2004

A weak diffraction line, sometimes observed in x-ray diffraction just at the location corresponding to the center of a diffuse neutron scattering peak located between the {100} and the {110} positions in Cu-rich Cu–Mn alloys, has been identified as that due to γ-MnO2 which has a rutile structure. When the degree of oxidation is minor, the oxide grows epitaxially on the surface of Cu–Mn crystals. The crystallographic relation of the epitaxy was found to be (110)Cu–Mn ∥ (121)MnO2 and [111]Cu–Mn ∥ [111]MnO2. Neutron diffraction experiments on a well-annealed polycrystalline alloy of 25-at. % Mn show a number of diffuse peaks which are consistent with the short-range ordering of the (M=1)-type long-period superlattice structure (DO22). However, only a part of the diffuse peak near the {100} reflection is due to the short-range ordering of atoms. In view of the small difference in the scattering amplitude between Cu and Mn, the diffuse peak due to the short-range ordering in Cu–Mn alloys would thus hardly be detectable in both x-ray and electron-diffraction patterns.
Radial Distribution Function of an Amorphous Mn–P–C Alloy
Authors: Sinha Ashok K. , Duwez Pol
Published: February 2004

An amorphous manganese base alloy having the composition Mn0.75P0.15C0.10 was synthesized by rapid quenching from the liquid state. Its structure was studied using x-ray diffraction. The interference function a(K) of this alloy is characterized by a shoulder on the high-angle side of the second peak, a feature which has been previously observed in several other amorphous alloys but not in amorphous Ni–Pt–P. Both the atomic distribution function W(r) as well as the radial distribution function (RDF) [=4πr2ρ(r)] contain a split double peak beyond the first maximum. The radius of the first near-neighbor shell is 2.63 Å, and its coordination number is approximately 12. The ratio of second to first near-neighbor average interatomic distance is 1.7. A structural model based upon ``dense random packing'' of Mn atoms with the metalloids P and C filling up some of the interstices may be appropriate for this alloy.
Effect of Na on CO2–N2 Gasdynamic Laser Gain
Authors: Anderson John D.
Published: February 2004

Recent theoretical and experimental results have shown that Na is extremely efficient in the T-V deactivation of vibrationally excited N2. By incorporating the best available kinetic rate information for this deactivation into an established analysis for gain in typical CO2–N2–H2O gasdynamic laser expansions, the effect of small amounts of Na on such expansions is studied. The results show that Na in amounts as small as 0.002 mole fraction can have serious effects on CO2–N2 gasdynamic laser gain.
Study of the Mössbauer Effect, Magnetization, and Crystal Structures of the Pseudobinary Compounds ThCo5−5xFe5x and ThNi5−5xFe5x
Authors: van Diepen A. M. , Buschow K. H. J. , van Wieringen J. S.
Published: February 2004

The compounds ThCo5−5xFe5x and ThNi5−5xFe5x form two series of complete solid solutions. All compounds investigated show the hexagonal CaCu5 structure. The lattice constants, the Curie temperatures, and the saturation moments at 4.2 K have been determined as a function of x. The ThM5 compounds possess two nonequivalent crystallographic sites for the M atoms (M = Fe, Co, Ni). By means of the Mössbauer effect it is shown that the physical nature of atoms occupying these sites differs appreciably. It is also shown that replacement of Co or Ni by Fe in ThCo5 or ThNi5 proceeds with a strong preference for one of these two sites. The crystalline anisotropy of the compounds ThCo5−5xFe5x was studied as a function of x. It could be shown that the anisotropy in ThCo5 is not particularly due to one of the two Co sites. With decreasing values for x, starting from ThFe5, the Fe moment increases down to x = 0.6. This is explained in terms of a rigid-band model.
Illuminating System for High-Resolution Transmission Microscopy Using a Field-Emission Source and Prefield of the Condenser-Objective
Authors: Hibino Michio , Siegel Benjamin M.
Published: February 2004

The characteristics of an illuminating system consisting of a field-emission source, a condenser lens, and the prefield of a condenser-objective were studied by computer experiments to determine its applicability for high-resolution transmission microscopy. The effects of demagnification and spherical aberration by the prefield on the illumination were calculated. The high brightness of the field emission source gives this system illumination characteristics that are different from those attainable with a thermionic gun system and provides illumination suitable for high-resolution phase-contrast transmission microscopy. The adjustment required to produce the desired illuminated areas and angular divergences at the specimen can be achieved by focusing the condenser lens. Typically areas of 500–1000 Å diam can be illuminated with angular divergences of less than 1 × 10−3 rad without requiring critical axial positioning of the specimen. Defocusing the condenser makes it possible to illuminate areas large enough for survey of the specimen.
Characteristic Energy-Loss Spectra of Titanium, Vanadium, and Chromium
Authors: Simmons Gary W. , Scheibner E. J.
Published: February 2004

Electron energy losses in titanium, vanadium, and chromium have been measured on evaporated-film specimens in ultrahigh vacuum. Measurements were made with a retarding-field analyzer, and the surface purity was monitored by Auger spectroscopy. The energy-loss spectra for clean surfaces of these metals showed similarities in line shape and in their behavior toward oxygen adsorption. In the energy range 0–30 eV, the loss spectra were composed of four peaks which we have interpreted as due to a surface-plasma loss, bulk-plasma loss, combination surface-bulk loss, and a second harmonic volume loss. The energy values (in eV) for these four peaks, in the order listed above, were measured as follows: Ti(5.0, 11.5, 17.0, 24.6), V(5.1, 10.5, 16.5, 24.0), and Cr(5.0, 9.5, 15.5, 23.5). Changes in the surface-loss intensity were observed for oxygen coverages on the order of 0.04 monolayer. The measured energies for the bulk-plasma excitation were found not to be in agreement with calculated values according to the classical theory for collective oscillations in solids. The present results are compared with characteristic energy-loss data reported in the literature.
Relationship between Sonic Velocity and Entropy in Molten Salts
Authors: Cantor Stanley
Published: February 2004

Sonic velocity in molten salts can be estimated from absolute molar entropy by means of an equation developed from the Debye theory of specific heats. When tested on 29 molten halide compounds, for which the required data are available, the equation reliably predicts sonic velocity and its negative temperature dependence. When applied to molten alumina, the equation predicts the magnitude of the sonic velocity, but does not yield the correct temperature dependence. For more complex molten salt compounds (such as nitrates and sulfates), a substantial reduction in the molar entropy is necessary for the predicted sonic velocity to agree with the experimental. When entropy contributions, associated with interatomic vibrations and free rotation of the complex ion, are subtracted from the total molar entropy, the equation yields excellent results for these complex molten salt compounds. The nature of the subtracted entropy terms implies that ``gaslike'' degrees of freedom, if present in the liquid, have very little effect on sonic volocities in salt melts containing complex ion species.
Fourier Analysis of Interdiffusion Penetration Curves
Authors: Gupta P. K.
Published: February 2004

Fourier analysis is suggested as superior to the conventional techniques of executing Matano analysis. Several additional advantages of the Fourier technique are brought out. The application of this technique is discussed.
Role of Ionization Inhomogeneities in the S-Type Characteristic of Moderately Heavily Doped n-GaAs
Authors: Southgate P. D.
Published: February 2004

The ionization occurring in n-GaAs with n0 ∼ 1017 cm−3 at fields high enough to produce Gunn domains is discussed. To produce ionization of the strength observed, high local fields such as can be generated by doping inhomogeneities are required, as well as the presence of Gunn domains. A previous theoretical explanation of the S-type current-voltage characteristic which does not involve inhomogeneities is shown to be inconsistent with the experimental data in this doping region.
Simulation of Superposed Coherent and Chaotic Radiation of Arbitrary Spectral Shape
Authors: Ruggieri Neil F. , Cummings Derald O. , Lachs Gerard
Published: February 2004

A simulation technique is described and utilized to generate superposed coherent and chaotic (thermal) radiation of arbitrary spectral shape. The statistical properties of a simulated radiation field with a Lorentzian spectral density is investigated with a photoelectron counting experiment. The experimental photocount distribution and normalized mth-order factorial moments are compared to theory and verify that the simulated radiation field, an appropriately modulated laser beam, has the expected statistical properties. The concept described indicates that one may, in principle, generate a thermal source of comparable intensity to that of a laser, arbitrary spectral shape, and bandwidth.
A Study of the Initial Photocurrent Due to Pulsed Light Absorbed in Finite Thickness
Authors: Seki H.
Published: February 2004

It is often assumed that light is absorbed in an infinitesimally thin region at the surface in analyzing the photocurrent in pulsed-light measurements. However, the incident light is generally absorbed within a finite depth from the surface. The effect of such finite light penetration on the initial photocurrent for a trap-free material is examined here assuming an initial exponential distribution of carriers in space and simple bulk recombination processes. It is shown that the initial photocurrent consists of three parts: a constant current due to carriers which get photoinjected into the sample, a current due to carriers of opposite polarity which are collected at the illuminated surface, and a current due to carriers which recombine. The latter two currents decay rapidly to zero resulting in a total current decay. Cases which approximate monomolecular recombination and bimolecular recombination are treated in detail. The results indicate that experimental observation of this initial current decay will yield information regarding free-carrier generation efficiency, recombination processes, and the mobility of the second carrier.
HF Chemical Laser Studies: Use of MoF6 to Increase Reaction Rates in H2–F2 Mixtures
Authors: Hess LaVerne D.
Published: February 2004

Addition of small amounts of MoF6 to the H2–F2 chain reaction system initiated by flash photolysis results in considerable enhancement of HF laser output power and energy with a reduction in pulse duration. Power and energy outputs up to 12 kW and 3.3 mJ/cm3, respectively, have been obtained from dilute mixtures at 600 Torr (H2:F2:MoF6:He=1:1:0.25:40) in a small scale apparatus (20 cm3). Chemical efficiencies of stoichiometric H2–F2 mixtures were increased from 0.2 to 0.8% by this technique. Computer calculations of reaction times, rates, and concentrations are in good qualitative agreement with the observed enhancement effect of MoF6 on the HF chain reaction chemical laser.
A Method for the Determination of High-Field Conduction Laws in Insulating Films in the Presence of Charge Trapping
Authors: Walden R. H.
Published: February 2004

The investigation of high-field electronic conduction in metal-insulator-metal (MIM) or metal-insulator-semiconductor (MIS) structures utilizing dc methods is frequently complicated by the fact that the observed currents decay with time. In cases where this time dependence is caused by charge trapping in the insulating film, the most direct study of conduction involves a determination of the initial current, i.e., that which flows before charging becomes significant. Direct observation of this current is sometimes difficult because the onset of trapping can occur within either a very short time or a very short distance. In films characterized by trapping, the initial current can be determined by monitoring the time dependence of the charging process itself. This method requires the use of an MIS structure with a nondegenerate semiconductor, usually serving as a cathode. The state of charge of the insulator is determined by measuring the MIS flat-band voltage. The calculation, which assumes that the trapping of electrons is essentially permanent and that the current is determined by the magnitude of the electric field near the cathode, shows that over a significant interval of time the flat-band voltage has a logarithmic dependence, i.e., VFB∝ln(1+t/t0), where the quantity t0 is a characteristic time which is inversely proportional to the initial current. Hence, a measurement of t0 determines the conduction properties at a given field and temperature.
Effect of Phase and Amplitude Errors in Conventional and Weak-Signal-Enhancement Holography
Authors: Keating P. N. , Gupta R. R. , Mueller R. K.
Published: February 2004

The effects of measurement errors on the quality of the images reconstructed from discretely sampled holograms (a) conventionally and (b) by the recently reported weak-signal-enhancement technique (WSET) are examined. Analytical results are obtained for far-field holograms in which (i) phase errors and (ii) amplitude gain errors are present. It is shown that, although weak images are fairly rapidly submerged in phase-error noise for conventional reconstruction (unless the number of sampling points is high), the enhanced weak images are relatively insentive to phase errors. The effect of amplitude errors are fairly similar in the two cases, although twice as serious in the WSET method because of the processing involved. Similar results obtained by computer for the near-field zone are shown.
Levitated Toroidal Multipole Design Study and Optimization
Authors: Steben John D.
Published: February 2004

Designing a useful plasma toroidal multipole requires optimization of many parameters. The selection and design of the Wisconsin levitated octupole involved study of over 200 multipole configurations with a computer program based on the stream function ψ=rAθ. Plasma bridge thickness was maximized subject to having equal MHD-stable flux inside and outside of the separatrices. To achieve sufficient outside flux in a quadrupole with reasonable stored energy and hoop weight requires hoops with a long and (radially) thin cross section. The field properties are then poor because of E lim →×B lim → drift into hoops. Octupoles do not have this problem, since (much lighter) hoops of circular cross section were essentially optimum. Sextupoles had disadvantages similar to quadrupoles. Octupole hoop levitation by the fields was achieved with two wall projections and no major sacrifice in outer flux. Perfect critical-point degeneracy was traded for improved horizontal injection geometry, but flux between separatrices was held to 1% of plasma flux. These criteria were satisfied independently of effective skin depth (up to 1.5 rms resistive skin depths at 10 Hz) of field penetration. Construction of the octupole has been completed, and initial experiments have largely confirmed the design qualities sought.
Electrical and Magnetic Properties of Amorphous Pd–Si Alloys Containing Fe and Cr
Authors: Hasegawa Ryusuke
Published: February 2004

Results of the measurements of the electrical resistivity, magnetization, and magneto-resistivity of amorphous FexCr2−xPd78Si20 alloys (0≤x≤2) are presented. Both the electrical and magnetic properties are affected considerably by small amounts of Fe (∼0.5 at.%). A large internal field due to the interactions between the magnetic atoms and a reduction of about 60% of the s-d exchange integral seem to explain the suppression of the Kondo effect in the Cr–Pd–Si alloys containing small amounts of Fe. The present results also show that the scattering of the data for the resistivity minimum temperature and for the magnetoresistivity previously found in the amorphous Cr–Pd–Si alloys can be attributed to the Fe impurities present in Pd.
Magnetostrictive Excitation of Sound in Magnetic Materials
Authors: Gorodetsky G. , Lüthi B. , Moran T. J. , Mullen M. E.
Published: February 2004

Experimental results for magnetostrictive generation of sound waves in various magnetic materials are given. Enhancement effects for this generation are studied near the spin reorientation transition in ErFeO3, near ferromagnetic resonance in Fe3O4, and near the magnetic phase transition in Tb. Second-harmonic sound generation in Fe3O4 and Tb is reported. All these results can be explained semiquantitatively using magnetic symmetry arguments.
Magnetically Soft Eutectic Composites
Authors: Batt J. A. , Thompson E. R.
Published: February 2004

Unidirectional solidification of pseudoeutectic alloys from the (Fe, Co, Ni)–NbC system resulted in the formation of a (Fe, Co, Ni) solid solution matrix reinforced by aligned NbC fibers. Room-temperature magnetic hysteresis loop and high-temperature saturation magnetization measurements were performed on controlled eutectic samples whose matrix compositions approximated those of well-known magnetic alloys. The most significant of these materials appears to be the (Fe, 50 wt% Co)–NbC eutectic which should combine useful high-temperature strength in the direction of the fibrous carbide with superior soft magnetic properties.
Liquid-Crystal Diffraction Grating
Authors: Carroll T. O.
Published: February 2004

Application of an electric field to a thin layer of nematic liquid-crystal causes the formation of a lattice of cylindrical lenses within the liquid-crystal material. An expression for the far-field diffraction pattern of light transmitted through this lattice is derived. The observed diffraction pattern agrees with that predicted by the theory.
Change in the Intrinsic Optical Absorption of Germanium and Silicon upon Irradiation
Authors: Primak William , Buck Warren
Published: February 2004

Optical constants calculated from ellipsometry data at 0.546 and 0.644 μ for germanium and for Ne+−140-keV-bombarded germanium indicated a 0.4-eV displacement of the optical-absorption edge to longer wavelength. Optical examination of silicon with a photomultiplier tube gave evidence of a radiation-induced increase of optical absorption in the tail of the absorption edge.
Area Influences and Floating Potentials in Langmuir Probe Measurements
Authors: Szuszczewicz Edward P.
Published: February 2004

An analysis has been conducted on the influence of a relatively small reference electrode in a Langmuir probe measurement of plasma density and temperature. The analysis employs the collisionless theory of Laframboise for spherical and cylindrical probes and in a completely general way includes a broad range of electron densities and temperatures as well as all possible values of ion mass and multiplicity of ionization. It is shown that a ratio α of reference-electrode area to probe area of 104 will guarantee no distortion of the measurement as a result of a shifting reference-electrode potential. It is further shown that the constraint on α can be relaxed by approximately two orders of magnitude when the charge-normalized ion mass mi/Z2 is decreased from 200 to 1 amu and the ratio of reference-electrode radius to Debye length, Rr/λD, is decreased from 100 to 0. An additional result of the analysis is the dependence of a probe's floating potential on its geometry and radius as well as on the properties of the plasma. A discussion of the latter result reveals in a striking manner the significant differences between the ion-current responses of spherical and cylindrical probes.
Note on Determining Electrical Ground Constants from the Mutual Impedance of Small Coplanar Loops
Authors: Wait J. R. , Spies K. P.
Published: February 2004

Curves are presented for inverting measured mutual impedance to yield the conductivity and permittivity of an equivalent half space. The displacement currents are allowed for, and the loop separation distance is unrestricted.
Investigation of the Early Phases of Plasma Production by Laser Irradiation of Plane Solid Targets
Authors: Stumpfel C. R. , Robitaille J. L. , Kunze H. -J.
Published: February 2004

The time development of line radiation emitted from a plasma produced by focusing a Q-switched ruby laser onto a solid magnesium target has been investigated in the vacuum-ultraviolet wavelength region using a 2-m grazing incidence monochromator. The electron temperature was obtained using the foil-absorption method. The time of appearance of MgIX and MgX lines at the target was measured as a function of the laser power. For the lowest laser power at which both ionic lines appeared, MgIX radiated before MgX. The appearance time of each line decreased as laser power was increased until at the higher powers they appeared at about the same time-2 nsec after the beginning of the laser pulse. The ionization processes occurring in front of the target are discussed using a simple model for the plasma. From the time of appearance of the lines, conclusions on the electron temperature in the ``heating zone'' can be drawn as well as on an over-all heating rate.
X-Ray Debye Temperatures of Zinc Sulfide and Zinc Telluride
Authors: Blattner R. J. , Walford L. K. , Baldwin T. O.
Published: February 2004

The x-ray Debye temperatures ΘM of zinc sulfide and zinc telluride have been determined to be 277 ± 7°K and 180 ± 6°K, respectively, by measurement of the temperature variation of the integrated intensities of Bragg reflections from powder specimens (method 1) in the temperature range 93–298°K. Only at the low end of the temperature range was Θm found to vary with temperature and Θm (93°K) appeared to be about 10% larger than the average values. The room-temperature (298°K) Debye temperature for ZnTe was determined to be 175 ± 8°K from integrated intensities of selected Bragg peaks (method 2). Measured absolute structure amplitudes were used to calculate the root-mean-square vibrational amplitudes of the individual ions in ZnTe, which were found to be 0.094 ± 0.025 Å and 0.135 ± 0.030 Å for the Zn and Te ions, respectively. These results are discussed in relation to previous work on other materials.
Techniques for the Study of Breakdown between Large-Area Electrodes in Vacuum
Authors: Farrall G. A. , Owens Michael
Published: February 2004

From experiments dealing with electrical breakdown phenomena in vacuum, it is clear that at voltages below that level actually required to produce breakdown, there occurs a low-level electron emission from highly localized regions of the cathode surface. This paper illustrates a technique for measuring the dependence of current upon voltage from one such region, utilizing variations in brightness of a phosphor screen. The technique avoids the possible confusion of a total current measurement which can result from the presence of simultaneously emitting areas or which can result from emission from regions of the electrode structure whose contribution to total current is unsuspected. This paper further demonstrates a method for the detailed location of particular emitting areas on the electrode surface. The procedure involves as a first step, the determination of the approximate location of the emitting region of interest using a phosphor screen. Following this, the electrode under study is used as a cathode opposite a lead anode without breakdown. This serves to evaporate lead metal from the anode surface areas lying directly opposite the cathode emitters. It is believed that charged vapor from the anode moves toward the cathode under the influence of the applied field and is deposited in the immediate region of the emitter. Subsequently, this lead can be detected in the scanning electron microscope using solid-state x-ray analysis. This serves to identify the emission region.
Steady Shock Waves in Composite Materials
Authors: Holmes B. S. , Tsou F. K.
Published: February 2004

The shock wave generated by a planar impact of a flyer plate and propagated along the direction of the fibers of a composite was studied. The sample composite used in the experiments was made of unidirectional aluminum fibers cast in an Epoxy matrix. Both the shock-wave velocity and the free surface velocity were measured by means of an optical technique. The shock front in the composite was found to be steady. The results of the measured Hugoniot also give a satisfactory comparison with those obtained from an analysis proposed earlier. The observation of a steady shock in the present work is significant in treating problems involving composite materials.
Dynamically Determined High-Pressure Compressibilities of Three Epoxy Resin Systems
Authors: Munson D. E. , May R. P.
Published: February 2004

Three Epon 828 epoxy systems which had significant variation in glass transition temperatures were tested dynamically in plate impact experiments to obtain their pressure-volume response. The choice of hardener determines the transition temperature of the system through the degree of crosslinking and structural changes. For this study, the hardeners used were metaphenylenediamine, Z and D. The dynamic ``equilibrium'' compression curves for the three systems are identical within experimental uncertainty and are adequately represented by the Z system shock-velocity-particle-velocity results of U=2.64+1.66u(mm/μsec); ρ0=1.194 g/cm3. The dynamic results may be reduced to isothermal conditions through the use of the Gruneisen equation and appropriate thermodynamic quantities. These dynamic isotherms are compared to static compressibilities obtained by other investigations using piston apparatus. While the static results show marked variation of compressibility with processing conditions, this was not confirmed by the dynamic results. Possible reasons for this discrepancy are advanced.
The Elastic Stiffness Moduli of Diamond
Authors: McSkimin H. J. , Andreatch P. , Glynn P.
Published: February 2004

The elastic stiffness moduli of a 22-carat Type II diamond have been measured at 25.0°C by the ultrasonic technique described by H. J. McSkimin. Basic wave velocities were obtained over a frequency range of 20–500 MHz in order to minimize errors due to diffraction and coupling effects. Moduli (in units of 1012 dyn/cm2) are as follows: c11=10.79±0.05, c12=1.24±0.05, c44=5.78±0.02. Comparison with literature values is made.
High-Temperature Creep of Lithium Fluoride
Authors: Rao C. V. S. H. Narayan , Ruoff A. L.
Published: February 2004

The creep behavior of single-crystal lithium fluoride was investigated over the temperature range 650–750°C. The behavior was similar to that observed in the case of pure metals. The strain rate was found to be proportional to the (stress)n with n taking values of 5.11 for T=650°C and 700°C and 3.74 for T=750°C. The activation energy for creep was 2.09 eV, the value expected for the diffusion of the fluorine ion. The results suggest that creep at high temperatures is due to diffusion-controlled dislocation motion.