bluuebunny/crossref_metadata_2025 huggingface dataset:
Description of interdigital transducers
Authors: Emtage P. R.
Published: February 2004

Interdigital transducers can be represented as a linear array of elements that emit and reflect surface waves. This phenomenological description enables one to calculate the properties of these transducers accurately, provided that weak reflections between short-circuited finger pairs are taken into account. The theory is simple and is expressed in terms of known parameters.
Order-disorder transformation in gold-modified β-brass
Authors: Bowe R. C. , Muldawer L.
Published: February 2004

Tc, the critical temperature for disordering, was measured in the β-AuxCu52−xZn48 system as a function of Au concentration. Tc was found to initially decrease with increasing Au concentration, attaining a minimum at approximately x = 10, and then increase with further increases in Au concentration. Results are interpreted in terms of the lattice expansion and the change in the number of Au–Zn, Cu–Zn, and Cu–Au bonds that result when Cu is replaced by Au. It is proposed that the effect of lattice expansion tends to decrease Tc, while the effect of the increase in the number of Au–Zn bonds tends to increase Tc. The Tc predicted on the basis of these proposed mechanisms is in fair agreement with the experimental results.
Analysis of triple dislocations in ordered phases of the type Ni8X
Authors: van der Wekken C. J. , Larson J. M. , Taggart R. , Polonis D. H.
Published: February 2004

Superdislocations comprising a group of three (1/2)a 〈110〉 dislocations lying in a close-packed plane have been observed in ordered face-centered-tetragonal Ni8Ta and Ni8Nb alloys. The antiphase boundary (APB) energies of the areas between the dislocations have been evaluated for Ni8Ta in terms of the first- and higher-order nearest-neighbor atom pairs associated with the introduction of the dislocations in the ordered material. Values for the pair interaction have been calculated by employing a polar model for the ordering and a long-range oscillatory atomic pair interaction energy. The results indicate that higher than first nearest-neighbor interactions account for approximately 40% of the total ordering energy. The critical temperature of Ni8Ta has been estimated on the basis of Cowley's ordering theory and the calculated values of the pair interaction energies. The theoretical value for the critical temperature is within 12% of the value that was determined by experiment.
Steady-state high-density magnetized arc column
Authors: Jassby D. L.
Published: February 2004

A steady-state fully ionized plasma column of density 1016 cm−3 and temperature 1.6 eV has been achieved in a simple magnetically confined argon arc of 9- to 15-cm length and 1.2- cm-diameter current channel. The plasma potential fluctuation level, eV/kT, is 0.1%, or less when the initial gas pressure is above 4 Torr, or when the arc current and magnetic field are below critical values.
Measurement of electron distribution function in a cesium plasma
Authors: Chen Che Jen , Wu James , Wu Frank
Published: February 2004

A conventional plane Langmuir probe with dc superimposed on a small sinusoidal signal is used to measure the electron-energy distribution in a cesium discharge tube. The current-voltage characteristics and its second-derivative characteristics are obtained for various discharge conditions. The electron-energy distribution at different gas-particle densities and electric fields in the positive column are calculated. The deviation from a Maxwellian distribution is observed for a low gas density and high electric field plasma. The calculation of the distribution function is also carried out by solving numerically the Boltzmann equation with electric field, including the effects of the elastic and inelastic collisions.
Plasma and gaseous diagnostics with a tuned GaAs laser diode
Authors: Ku R. T. , Verdeyen J. T. , Cherrington B. E. , Goldstein L.
Published: February 2004

This paper demonstrates that the classical gaseous diagnostic techniques of resonant absorption, anomalous dispersion interferometry, and resonant scattering can be performed with considerable ease utilizing a tunable GaAs diode laser. Absorption measurements of Cs133 in the ground state have been performed by matching the GaAs laser emission to the 8521 Å transition (62S1/2→62P3/2). The measured number density of Cs in the ground state is in general agreement with the value obtained from the known vapor pressure of cesium. The same type of measurements have also been made for the 1s2 and 1s4 resonant states in an argon plasma by tuning the laser to the 8408 Å and 8424 Å lines, respectively. In addition, interferometry studies using the swept GaAs laser are also reported here for the first time. These studies have been carried out simultaneously with the absorption measurement for the same 1s2 and 1s4 states in the argon discharge. The number densities of argon atoms in these states as obtained by both methods are in reasonable agreement.
High electric field effects in n-silicon
Authors: Dalal Vikram L. , Lampert Murray A.
Published: February 2004

The velocity-field curve and the electron avalanche coefficient α(E) have been experimentally determined in bulk n-Si, at T=300°K, for fields up to 1×105 V/cm. Because of velocity saturation it has been necessary to take into account space-charge-induced nonuniformities in field and carrier density. The velocity-field curve is in good agreement with the time-of-flight results of Norris and Gibbons. The avalanche coefficient α(E) agrees with the experimental results of Lee et al. in p-n junctions, but disagrees with the results of Ogawa. From a comparison of the experiments with the theory of Baraff, the values of the electron phonon mean-free-path parameter λ and the ionization energy parameter Ei have been found to be within the ranges 60<λ<80 Å and Eg<Ei< 1.5Eg.
Contact potentials and barrier heights in gold-silicon and aluminum-silicon contacts
Authors: Ahmad K.
Published: February 2004

We have measured the contact potential difference (cpd) between evaporated films of gold, aluminum, and real silicon surfaces using the intersection method. The gold/silicon cpd for the most consistent set of results was 0.2 eV to within ±0.1 eV. The aluminum/silicon cpd was 0.7 eV to within ±0.2 eV. The accuracy was limited mainly by work-function drift due to surface contamination during measurement. The working pressure was 2×10−5 Torr. The intersection method essentially measures the integrated energy distribution of an electron beam in the cutoff region. It was observed that the integrated energy distribution of the collected electrons depended strongly on the collector surface probably due to surface (patch) fields. The barrier heights of the gold-silicon contacts were measured using the differential capacitance method. In the majority of cases there was no correlation between barrier heights and cpd suggesting that the barrier height is determined primarily by surface states.
Superconductivity in the Nb-rich Nb–Al alloys
Authors: Kammerdiner L. , Luo H. L.
Published: February 2004

Nb-rich Nb–Al alloys were prepared by both sputtering and quenching from the liquid state. Lattice constants and superconducting transition temperatures were measured and compared for as-quenched and as-sputtered samples and also for the same samples after annealing. For the samples with between 75 and 80 at.% Nb, annealing produced nearly single-phased β-W alloys with the highest transition temperatures of 18.6 °K for quenched samples and 16.6 °K for sputtered samples.
Power spectrum of Barkhausen noise in simple materials
Authors: Baldwin John A. , Pickles Gregory M.
Published: February 2004

The term ``Barkhausen noise'' employed herein does not have its customary meaning. In the present work, the flux in the sample is caused to vary linearly with time. Consequently Barkhausen noise appears as noise in the magnetomotive force (mmf) required to accomplish this. It is this mmf noise that is analyzed here. The general expression for the power spectral density, G(f), predicted by the spring model of hysteresis, is derived. This is then specialized to the case of an exponential distribution function. The method used to compare experiment with theory is outlined. The raw data consist of 2048 values of mmf voltage digitally sampled over a period of 37.12 sec. Smoothed power spectra were obtained by processing the time data with a digital inverse filter. Comparison of theory with experiment involves the determination of two parameters: S′Z, which is adjustable for best fit and N, which is not adjustable. The quality of the agreement between theory and experiment is measured in two ways: (i) comparison of experimental and theoretical spectra after choosing the parameter S′Z for best fit; (ii) comparison of parameter values so determined with values determined by other means. It is found that (within the experimental uncertainty due to the finite size of data set) the agreement between the predictions of the spring model and experimental spectra is quite good. This confirms the results of previous work on the autocorrelation function of Barkhausen noise. It is concluded that the spring model not only accurately describes the average shapes of hysteresis loops of simple materials, but also accurately describes statistical fluctuations from the average. These fluctuations are due to fluctuations in the number and strengths of the defects with which a wall interacts.
Some stochastic processes yielding a f−ν type of spectral density
Authors: Tunaley J. K. E.
Published: February 2004

Using a specific definition of spectral density for nonstationary stochastic processes, a randomization procedure is used to analyze three types of process likely to be important in physical applications. Thus the symmetric random walk, Ornstein-Uhlenbeck, and shot-noise models are generalized and are shown to lead to spectral densities of the form f−ν at low frequencies. Since most systems of interest will contain many contributing sources to the fluctuation, limit probability distributions are employed. It appears that randomized shot noise is probably the relevant process in the behavior of semiconductor current noise.
Efficient optically pumped InP and InxGa1−xAs lasers
Authors: Rossi J. A. , Chinn S. R.
Published: February 2004

Optically pumped InP and InxGa1−xAs are operated as pulsed room-temperature lasers with output power densities ≥ 105 W/cm2 and total power-conversion efficiencies of up to 4%.
Electrical breakdown in ferroelectric sodium nitrite crystals
Authors: Fok J. , Hanscomb J. R.
Published: February 2004

The electric strength of sodium nitrite crystals is measured in the temperature range 125–205°C embracing the Curie ferroelectric transition temperature. Single constant-amplitude voltage pulses are used to initiate breakdown. Experimental values of breakdown strength are obtained for time delays to breakdown of 10 and 100 msec. Measurements of high-field electric conductivity are used to determine theoretical impulse thermal breakdown strengths for comparison with experiment. The breakdown mechanism appears to be of thermal origin at temperatures exceeding the Curie point. It is suggested that at lower temperatures, breakdown is mechanical in origin arising from electrostrictive effects.
Pressure due to variations in the energy of a magnetic domain wall
Authors: Baldwin John A.
Published: February 2004

It is shown theoretically and experimentally that the model which says that there is a pressure on a domain wall which is proportional to the space rate of change of wall energy is incorrect.
Densities of complexed and uncomplexed molecules in amorphous films of trinitrofluorenone and poly-n-vinylcarbazole
Authors: Weiser G.
Published: February 2004

Absorption and electroabsorption measurements in the range of the charge-transfer absorption band were performed on amorphous films of TNF : PVK mixtures with different monomer ratio. Assuming localized excitation of the charge-transfer complex, the densities of charge-transfer complexes and of uncomplexed TNF and PVK monomers are determined from the optical data combined with the results of mass density measurements. The absorption and the electroabsorption response show a saturation above a ratio 0.6 : 1 of TNF : PVK resulting from a decreasing degree of complexing in these films with increasing portion of TNF. At a 1 : 1 monomer ratio of TNF : PVK only about 40% of the TNF molecules are complexed with PVK. This number rises with decreasing amount of TNF to about 72% in a 0.1 : 1 TNF : PVK film.
Reaction mechanisms of the CS2–O2 chemical laser
Authors: Sadie F. G. , Büger P. A. , Malan O. G.
Published: February 2004

CO cw laser action in the fundamental and first overtone was observed when reacting molecular oxygen with CS2, passing the latter through an electrical discharge. The overtone spectrum was resolved and compared with that resulting from reacting CS2 with oxygen passing through the electrical discharge. Also laser action was observed when replacing O2 by N2O, passing the latter through the electrical discharge as source of oxygen atoms.
Faraday induction and flux flow voltages in type-II superconductors
Authors: Khanna S. M. , LeBlanc M. A. R.
Published: February 2004

The integrated voltages S ∝ ∫ V(t) dt observed across an open single-layer superconducting coil, when a magnetic flux Δφ trapped in the body of the coil winding is expelled, are not uniquely described by the classical Faraday induction relation ∫ V(t) dt ∝ Δφ but depend dramatically on the procedure used for thermally destroying the superconducting state. The observed signals are larger (smaller) than Ss when the trapped flux is eliminated by heating the sample from the inside (outside), where Ss is the result encountered upon quenching of the trapped flux by slow heating of the sample equally and simultaneously from the inside and outside. Normalizing the measured signals to Ss, we find that limiting values of 3.15 and −1.05 are attained depending on whether the heating pulse which causes the trapped flux to be expelled is applied to the inner or the outer surface, respectively. Noting the contribution to the measurements arising from the collapse of the flux returning through the space embraced by the sample coil, we account for all our observations on the basis that (i) the migration of flux filaments across the wall of the sample produces no effect externally detected by the voltmeter and (ii) the collapse of a vortex at the inner surface of the sample coil induces a signal proportional to φ0, the flux enclosed by the vortex, whereas a vortex collapsing at the outer surface induces no signal. These measurements indicate that the observed voltages due to flux flow in a superconductor are produced by the change of magnetic flux embraced by the measuring circuit excluding the volume of the superconducting element.
Zero temperature sensitivity of bubble diameter
Authors: Dimyan Magid Y. , Torre Edward Della
Published: February 2004

The condition for zero temperature sensitivity of bubble diameter in some uniaxial magnetic materials is obtained in terms of the material parameters. The ratio of the fractional changes in wall energy density and saturation magnetization which gives zero temperature sensitivity of bubble diameter is plotted as a function of plate thickness and bubble diameter. The resulting curves can be used in designing bubble devices having fixed bubble sizes.
Propagation Characteristics of Surface Elastic Waves on Ba (Ti0.95Zr0.05)O3 Ceramic Plates
Authors: Toda K.
Published: February 2004

Propagation characteristics of surface waves on Ba(Ti0.95Zr0.05)O3 ceramics have been studied under various conditions. The Ba(Ti0.95Zr0.05)O3 ceramic has two second-phase transition temperatures, around 0 and 54 °C, and has a Curie temperature of 96 °C. The attenuation constant for surface wave propagation has a peak value in the vicinity of the phase transition temperature. The logarithmic decrement is nearly independent of frequency over the range 0.8–1.8 MHz. Also, the attenuation is nearly constant for the range of input voltage below 40 V, but increases rapidly beyond 40 V. It is concluded that for the input voltage with small amplitude, the attenuation due to the dielectric loss is predominant, but the attenuation due to the hysteresis mechanism increases for an input voltage above 40 V. Furthermore, it is found that at the second-phase transition temperature, the conversion efficiency of the transducer attains the peak value, while the propagation velocity takes a minimum value.
Variation of Concentration with Depth of Absorbed Oxygen in Niobium during Oxidation
Authors: Bellina J. J. , Lederich R. J. , O'Neal J. E.
Published: February 2004

The dissolution of oxygen in niobium is governed by Fick's second law applied with the appropriate boundary conditions. Two different boundary conditions have been proposed to describe the physical situation: (i) That the surface concentration of oxygen atoms is constant; and (ii) that the flux of oxygen into the metal is directly proportional to the difference between the actual concentration on the surface at any time and the concentration which would be in equilibrium with the partial pressure of the oxygen. The absorption of oxygen in (001) niobium at temperatures of 450–650 °C and pressures of 3×10−6−3×10−4 Torr O2 has been measured using ellipsometry. The results indicate that for the pressure and temperature ranges investigated the latter boundary condition is the appropriate one.
Spectroscopic Measurements of Parameters in a Low-Density Alkali-Metal Plasma
Authors: Fabry M. , Cussenot J. R.
Published: February 2004

The different parameters (temperature and density) of an alkaline plasma can be obtained by spectroscopic study provided that the plasma is of sufficiently high density. However if the electron density is lower than 1013 cm−3, the usual methods can no longer be directly applied. The aim of this study is to consider methods which hold good for low densities and to deduce the parameters and properties of a hot-cathode-discharge cesium plasma. The optical study of the cesium emission spectrum is limited to high excited levels for which partial local thermodynamic equilibrium is achieved and enables us to determine the gas temperature. We conclude that the population of high excited levels (greater than 10S, 9P, and 7F) of the cesium atoms is determined by collision processes among heavy particles. Electron density is measured from stark profiles of lines corresponding to the fundamental series 5D-nF with 14≤n≤17. This method allows density determination between 1012 and 1013 cm−3, i.e., for a region where spectroscopic density measurements are not usually possible.
Electromagnetic Wave Scattering from an Active Corrugated Structure
Authors: Lee S. W. , Fong T. T.
Published: February 2004

This paper studies the scattering of a plane wave by an active corrugated structure in which each slot region is connected to a microwave solid-state amplifier. Consequently, not only are we able to control the phase of the reflected wave but also its power gain. An exact solution to this problem has been obtained by the residue calculus method under the assumption that only the TEM wave propagates and is amplified in the slot region. Numerical results are presented for illustrating the scattering properties as a function of the slot dimension and the amplifier gain. An approximate but much simplified analytical expression for the reflection coefficient is derived and it should be found useful in other scattering problems (such as the design of a reflector antenna) by the ray-tracing method. A related problem of surface wave propagation on the active corrugated structure and its potential application as a high-power amplifier are also discussed.
Holographic Weak-Signal Enhancement Technique
Authors: Mueller R. K. , Gupta R. R. , Keating P. N.
Published: February 2004

A holographic weak-signal enhancement technique (WSET) is described which enhances the image of the source of a weak signal of interest in the presence of an unwanted strong signal with very little a priori knowledge of the latter. The technique is most suitable for imaging applications in fields such as seismic or oceanographic holography, where the desired weak-scattered signal is often overwhelmed by a strong reflected signal from interfaces between different media. The feasibility of the WSET has been shown by simulating a two-solid-layer acoustic problem on a digital computer. Well-defined enhanced images have been obtained for target scattering which is so much weaker than a strong reflected signal that the target images were lost in noise using conventional holographic reconstruction.
Y2O3 : Yb : Er-New Red-Emitting Infrared-Excited Phosphor
Authors: Wittke J.P. , Ladany I. , Yocom P.N.
Published: February 2004

Y2O3 : Yb : Er and Gd2O3 : Yb : Er are efficient phosphors that emit red light when excited by the absorption of ir radiation. A number of processes are important in suppressing the green emission normally seen in erbium-ytterbium double-doped phosphors, and in emphasizing the often weak red emission. These processes are discussed in detail. An over-all electrical-to-light power conversion efficiency of (3–5) × 10−4 was observed, from which an internal ir-to-visible conversion efficiency of 30–55% was inferred. It is concluded that, regardless of coupling efficiency, GaAs : Si ir generation efficiencies and inherently broad incoherent infrared diode emission spectra will limit over-all efficiencies in diode-excited phosphors to about 1%.
Mechanism of Imaging Molecules in the Field Ion Microscope
Authors: Burton J. J. , Machlin E. S.
Published: February 2004

It is proposed that the mechanism of imaging of molecules involves electron tunnelling from the image-gas ground state to the lowest unoccupied level of the intervening molecule and Zener breakdown through the molecule to the Fermi level of the metal-tip substrate. This mechanism is shown to be in quantitative agreement with the observed imaging fields and to account for the other experimental observations.
Cathodoluminescence Measurements on a Silicon Carbide Light-Emitting Diode
Authors: Potter Ralph M.
Published: February 2004

From cathodoluminescence measurements on a diffused SiC diode with the p layer removed, it has been possible to measure separately the variation of quantum efficiency of radiative recombination in the phosphor layer as a function of injected current density and of temperature. This has allowed a better understanding of the behavior of a diffused SiC diode excited by current flow as well as estimates of some important parameters.
Additional Excitation Transfer between Excited Helium Atoms and Neon in He–Ne Laser Discharges
Authors: Willett C. S. , Young R. T.
Published: February 2004

Measurements are given of the ratio of the excitation due to helium to the excitation due to electrons for a number of neon states in a He–Ne laser discharge. The ratio was obtained from spectral intensity measurements on dc discharges in pure neon at a pD of 2.2 Torr mm and in a helium-neon 5:1 mixture at a pD of 4 Torr mm, with a discharge tube diameter of 10 mm, at a current density of 0.23 A cm−2, where the electron temperature is deliberately chosen to be the same in both discharges. In Paschen notation, the ratios are 4d5−6; 5d4, 5d4′, 4d3, 4d1″, 4d1′, 4s3−7; 5d4, 5d4′, 5d3, 5d1′−8; 4s5−9, 4s4−51; 4s2−29; 5s3−3.5; and 5s2−12. It is shown that a selective-excitation reaction involving He 21P1 atoms is responsible for the excitation of neon atoms to the Ne-5s2 state. The reaction is spin conserved and has a cross section of about 10−16 cm2.
Low-Temperature Specific Heat of RbCl, RbBr, and RbI
Authors: Rollefson R. J. , Peressini P. P.
Published: February 2004

The specific heats of RbCl, RbBr, and RbI have been measured between 0.1° and 13°K. The Debye temperatures calculated from the specific heats have low temperature limits of 168.5±2.5 for RbCl, 134±2 for RbBr, and 106.5±1.5 for RbI. These are in satisfactory agreement with values of θD calculated from elastic-constant measurements.
Speed of Sound in Liquid Sodium from 1000 to 1500°C
Authors: Chasanov M. G. , Leibowitz L. , Fischer D. F. , Blomquist R. A.
Published: February 2004

Measurements have been made of the speed of sound in liquid sodium from 736 to 1489°C. This extends the temperature range of previously reported measurements by nearly 500°C. The data obtained at 1000°C and below are in good agreement with the work of other investigators; there are no previous data above 1001°C. A quadratic equation derived from the experimental data is presented.
Photothermoelectric Analysis of Chemically Deposited Cadmium Sulfide Layers
Authors: Wu Chen-ho , Feigelson Robert S. , Bube Richard H.
Published: February 2004

Carrier mobilities in the few thousandths cm2/V sec can be reliably inferred from thermoelectric power measurements, considerably smaller than can be determined by standard Hall measurements. Techniques of photothermoelectric analysis are applied to chemically deposited layers of CdS and CdS–CdSe, as prepared, and after photosensitization by impurity diffusion. Photoconductivity in the unsensitized films is due wholly to an increase in mobility; in the sensitized films, both carrier density and mobility increase with photoexcitation. The high-light mobility is increased by a factor of 102 by impurity sensitization.
Coupled-Wave Analysis of Holographic Storage in LiNbO3
Authors: Staebler D. L. , Amodei J. J.
Published: February 2004

This paper considers two effects for directly studying thick-phase holograms: (a) coupling between the two laser beams used to record a hologram and (b) interference between a readout beam and the diffracted beam within the hologram. Both effects were observed in experiments using single crystals of undoped LiNbO3. The results demonstrate that the holograms arise from electric field patterns caused by either diffusion or drift of photogenerated free electrons.
Light- and Electric-Field-Dependent Oscillation of Space-Charge-Limited Current in Bi12 GeO20
Authors: Lenzo P. V.
Published: February 2004

Low-frequency oscillations which are light and electric-field dependent have been observed in a positive resistance I-V characteristic in Bi12GeO20. The photocurrent-voltage characteristic has been interpreted in terms of space-charge-limited injection current theory and indicates that oscillation begins in the shallow-trapping regime and ceases in the trap-free insulator regime. Values for some of the material parameters involved have been calculated for the specific photoinjection conditions used.
Specific Heat of EuSe between 0.5 and 16°K
Authors: White H. W. , McCollum D. C.
Published: February 2004

Specific-heat measurements have been made on six polycrystalline samples of EuSe from 0.5 to 16°K. A sharp peak was found at 4.55±0.02°K. The purest samples had additional small peaks at 1.7 and 2.8°K. Below 1°K the magnetic specific heat could be described by CM=1.44T2 J/mole°K.
Response of the Electrical Resistance of Molybdenum Oxide Single Crystals to Hydrogen in Air
Authors: Buckman William G.
Published: February 2004

The electrical resistance of MoO3 single crystals activated with platinum was measured in air and in air containing 1% molar hydrogen concentration over the temperature region of 500–700 °K. The electrical resistance of the single crystal in air at 653 °K was about 108 Ω and decreased by a factor of 30 when exposed to the hydrogen atmosphere. These results strongly suggest that MoO3 may be used to monitor hydrogen concentrations where possible hazardous concentrations may occur.
Theory of Polymer Crystallization without Chain Folding
Authors: Calvert P. D. , Uhlmann D. R.
Published: February 2004

A theoretical treatment of nucleation-controlled polymer crystal growth is developed. A distinction is made between the end-surface energy of the crystal lamella and that of the nucleus for growth. The growth rate is related to the nucleation frequency using a thick-crystal treatment, and the lamellar thickness is viewed as limited by diffusion of the crystallizing chain in the liquid. Exponential growth kinetics are predicted by the model, and when compared with available experimental data on polyethylene, a reasonable value for the end-surface energy of the nucleus is obtained. The lamellae formed at a given under-cooling are expected to be distributed over a range of thicknesses, with a most probable value of about twice the minimum thickness stable at the undercooling.
Anisotropic Elasticity of a Prismatic Dislocation Loop in a Hexagonal Crystal
Authors: Ohr S. M.
Published: February 2004

Elasticity solutions for the stress and displacement fields around a finite circular prismatic dislocation loop in the basal plane of a hexagonal crystal have been obtained by taking into account crystal anisotropy. Following the method proposed by Elliott for the problems of axial symmetry in hexagonal crystals, the Hankel transforms of two stress functions were determined from the boundary conditions appropriate for a circular prismatic loop. From these stress functions, the components of stress and displacement have been derived in terms of a series of definite integrals which could in turn be expressed in terms of elliptic integrals. The expressions of anisotropic elasticity approach those of isotropic theory derived by Kroupa when the conditions of elastic isotropy are imposed on the elastic constants. Numerical calculations have been carried out specifically for the case of graphite. The over-all effect of crystal anisotropy is to reduce the magnitude of the stresses and the displacements around the loop, except for the component of displacement normal to the loop plane which is increased by about a factor of 2.
Low-Temperature Solid-State Phase Transformations in 2H Silicon Carbide
Authors: Powell J. Anthony , Will Herbert A.
Published: February 2004

Single crystals of 2H SiC were observed to undergo phase transformations at temperatures as low as 400°C. Some 2H crystals transformed to a structure with one-dimensional disorder along the crystal c axis. Others transformed to a faulted cubic/6H structure. The transformation is time and temperature dependent, and is greatly enhanced by dislocations. Our observations indicate that the transformation takes place by means of a slip process perpendicular to the c axis. Cubic SiC crystals were observed to undergo a solid-state transformation above 1400°C.
Impedance Characteristics of the Finite-Length Annular Induction MHD Generator
Authors: McCutcheon Martin J. , Russo Andrew W.
Published: February 2004

An analysis of the annular induction MHD (magnetohydrodynamic) generator is carried out for a model employing a finite-length winding and a constant-velocity fluid flowing in the annulus. An expression for the phase impedance is derived which accounts for entrance and exit of the fluid into the winding region. Impedance characteristics are presented which allow comparison with the infinite-length case in terms of dimensionless parameters.
Transverse Magnetoresistivity Anisotropy Measurements and the Geometrical Size Effect in Nickel Thin Films
Authors: Chen T. T. , Marsocci V. A.
Published: February 2004

The transverse magnetoresistivity anisotropy in both polycrystalline and single-crystal nickel films have been measured at room, liquid-nitrogen, and liquid-helium temperatures. A correction for the demagnetization field effect has been performed on the measured data. The size effects in nickel thin films have been estimated from the corrected results. It is found that these size effects depend on the electronic structure of the material and cannot be explained by the present theories of the electron conduction phenomena in thin films.
Electron Temperature and Hg(63P) Atom Density Decay in a Mercury—Rare-Gas Afterglow
Authors: Polman J. , Drop P. C.
Published: February 2004

The electron temperature decay in the afterglow of Hg–Ne and Hg–Ar low-pressure gas discharges has been investigated, both experimentally and theoretically. The temperature decay is not only determined by elastic losses but also by collisions of the first and second kind with excited Hg atoms. Collisions of the second kind have a heating effect on the electron gas and our results show that the energy relaxation time may increase by a factor of 10 by this process. Reasonable agreement has been obtained between the experimental data and the results of calculations which take the above processes into account. The electron temperature has been determined by means of 1.5-GHz noise measurements, the Hg (63P) densities by means of optical line absorption.
Oxygen-Processed Field Emission Source
Authors: Veneklasen Lee H. , Siegel Benjamin M.
Published: February 2004

An oxygen-enhanced thermal-field shaping method has been developed for obtaining high angular confinement of the electron emission from a 〈100〉−oriented tungsten tip. A source is obtained from which the beam is confined to a half-angle of ∼ 0.15 rad. This strongly-for-ward-direction beam gives a source that can be used to obtain beams with currents as high as 5×10−8 A within an acceptance angle of 5×10−3 rad with a total emission curve of only 10 μ A. The processed tip is operated at 900°C to give a source with long-term stability and reliability in a moderate ultrahigh vacuum of ∼ 10−9 Torr. Energy spread and flicker noise are slightly greater than for a ``clean'' tip operating at room temperature, but remain favorable for many applications. An interpretation of the shaping of the tip based on field-induced thermal migration is given.
Small-Angle X-Ray Scattering Study of Phase Separation in Glasses
Authors: Patel I. S. , Schmidt Paul W. , Ohlberg Stanley M.
Published: February 2004

Two heat-treated glasses, a calcium glass (76.1% SiO2, 11.0% CaO, and 12.9% Na2O by weight) and a strontium glass (69.8% SiO2, 18.4% SrO, and 11.8% Na2O by weight), have been investigated by small-angle x-ray scattering. The samples were studied with a Kratky camera and also with a four-slit collimation system of the type developed by Beeman et al. The use of two independent collimation systems provided a check for systematic errors. In addition, the results verify the reliability of the collimation correction methods routinely employed in correction of collimation effects in small-angle x-ray scattering data. The measured radii of gyration correspond to spherical droplets with diameters of about 500 Å in good agreement with the diameters obtained from electron micrographs. By comparison of the scattering from the glass samples with the scattering from calibrated silica suspensions, the difference in the electron densities of the droplet phase and the matrix was computed for each glass. The results indicate that the droplet phase is a high-density form of silica with density 2.32 g/cm3, as compared with the normal value of 2.20 g/cm3 for vitreous silica. A defective cristobalite structure with density 2.32 g/cm3 is proposed for the droplet phase.
Effects of Electron-Hole Pair Production on High-Field Transport of Electrons in the (000) Valley of n-InSb
Authors: Chou S. C.
Published: February 2004

A velocity-randomizing collision integral is constructed to describe electron-hole pair production by energetic electrons in the (000) valley of InSb. The Boltzmann equation is solved numerically by a variational-iterative method, and the electron-hole pair generation rates at high fields are obtained for a set of values of an over-all constant factor appearing in the collision integral. One of the cases solved is that in which this factor is chosen so as to give a pair-production scattering probability close to that calculated from the electron wave functions in InSb. Also studied is the hypothetical case in which the pair-production probability is significantly greater than the electron-phonon scattering probability at energies less than the threshold for electron transfer to the L1 minima. It is shown that in this case a single-valley negative differential mobility (NDM) can result at fields in which no significant transfer of electrons to the L1 minima occurs, but this hypothetical situation probably does not occur in InSb. The generation rates calculated in each of the cases solved are not inconsistent with experiments. Only polar optical-type phonon scattering is considered, and the calculations are for a lattice temperature of 77°K. The Kane band structure is used, and the band overlap integral is included in the electron-phonon scattering matrix elements.
M Signal in Magnetic Thin-Film Measurements
Authors: Wichner R. , Vindelov K. E.
Published: February 2004

An improvement in the hysteresigraph method for measuring magnetic thin-film properties is presented. Problems associated with the integrator and phase compensator are eliminated and the sensitivity of film evaluation is improved by analyzing the Ṁ signal obtained by the conventional technique. In demonstrating this technique, films of varying quality are compared and, whereas the Ṁ signal shows distinct differences between films, the M-H loops appear similar.
Simple Technique for Estimating Acoustic Diffraction Beam Spreading for Acoustic Modes Propagating along Arbitrary Directions in Crystals
Authors: Liu John M. , Green Robert E.
Published: February 2004

A simple technique to estimate the angular beam width of acoustic modes propagating along arbitrary directions in crystals is proposed. This technique is based on considerations of the relationship between the energy flux vectors and the geometry of the inverse speed surfaces of the acoustic modes. Experiments on sodium chloride and quartz single crystals and fused quartz, utilizing optical beam probing techniques, confirm the usefulness of the present method.
Electron Energy Distribution Function of Pure Helium in Cyclotron Resonance
Authors: Un C. K. , Lutz B. C.
Published: February 2004

The Boltzmann equation has been solved for the energy distribution function of electrons of pure helium bounded in a circular cylindrical medium under the influence of a high-frequency electric field and an externally applied dc magnetic field with the directions perpendicular to one another. The behavior of the electron energy distribution function at and near cyclotron resonance has been examined.
Hole Currents in Thermally Grown SiO2
Authors: Verwey J. F.
Published: February 2004

Results are reported on the current of holes injected into thermally grown SiO2 from a planar avalanching p-n junction. The current seems to be limited by a bulk process, viz., field-assisted thermal emission from traps in the SiO2 (Poole-Frenkel conduction). This mechanism accounts for the exponential dependence of the current on the field in the oxide. From the decay of the current as a function of time, a value of 6 ± 2 cm−1 was found for N0S, the concentration of hole-trapping centers in the SiO2 times the capture cross section.
Space-Charge-Perturbed Xerographic Discharge of Photoreceptors
Authors: Mort J. , Chen I. , Emerald R. L. , Sharp J. H.
Published: February 2004

The effect of space-charge perturbation due to either trapped or free charge on the xerographic discharge of photoreceptors has been studied. In the case of trapped charge, the xerographic gain vs field curves can be analyzed to yield estimates for the carrier range and this is illustrated by measurements on amorphous selenium. The achievement of space-charge-limited xerographic discharges in Se : poly(N-vinyl carbazole) layered structures will also be described. In this case it is shown that measurements of parameters which in the past have been viewed only from an applications viewpoint, e.g., contrast potential, can be useful in probing charge transport in appropriate solids.
Stimulated-Emission Cross Section of Nd3+ at 1.06 μ in POCl3, YAG, CaWO4, ED-2 Glass and LG55 Glass
Authors: Birnbaum Milton , Gelbwachs Jerry A.
Published: February 2004

Stimulated-emission cross sections of Nd3+ at 1.06 μ in POCl3, yttrium aluminum garnet (YAG), calcium tungstate (CaWO4), and two laser glasses (ED-2 and LG55) were measured by studying the laser threshold gain and inverted population. The technique of end pumping with pulsed xenon ion lasers was used with an identical laser cavity for all the Nd-doped samples. A direct comparison of the cross sections in the different hosts was obtained.
E×B Mass-Separator Design
Authors: Seliger R. L.
Published: February 2004

The equations of motion are developed and solved for ion trajectories inside an E×B type mass separator. Curves are presented which illustrate the focusing of the undeflected ion beam, the trajectories along which ions of different mass species disperse inside the separator channel, and the exit slopes of mass species leaving the separator, as functions of a separator strength parameter. For strong separators, beam focusing is significant and is shown to be nonaxisymmetric when the electric and magnetic fields are uniform and orthogonal. A method of correcting the astigmatism by tilting the magnetic pole pieces is presented.
Room-Temperature Electrical Properties of Ten I-III-VI2 Semiconductors
Authors: Tell B. , Shay J. L. , Kasper H. M.
Published: February 2004

The room-temperature electrical properties of ten I-III-VI2 (I=Cu, Ag; III=Al, Ga, In; VI=S, Se) compounds are presented. The resistivities of eight of these compounds are rapidly changed by annealing under maximum and minimum chalcogen pressures. The Cu compounds can readily be made p type, a feature lacking in the analogous II-VI compounds. However, the Cu compounds with energy gaps of 1.7 eV or above have not been made n type.
Composition of Electrotransport Reversal in Certain Liquid Alloys
Authors: Blough J. L. , Olson D. L. , Rigney D. A.
Published: February 2004

A simple method is presented for determining the composition of electrotransport reversal in certain liquid alloy systems. The method involves fewer measurements and is more accurate than procedures used previously. Implications for applications to purification are discussed.
Magnetic Domains of Thin Permalloy Film under Plastic Deformations
Authors: Ito Noboru
Published: February 2004

Observations of Bitter patterns on thin Permalloy films under plastic deformations clarified mechanical properties and polycrystalline structure of the films to some extent. Specimens used were 81 Ni Permalloy films with thickness of 1 μm electrodeposited onto copper wires with diameter of 0.5 mm. The plastic deformations were made with a pin tip or a razor edge. Domain walls usually appeared around the dislocations only after dislocations and were not straight but zigzag. This explains the ease with which dislocations developed around crystal grain boundaries. The domain walls which were annealed showed that a dislocation energy decreased rapidly by a distance from the deformed spot.
Magnetostatic Propagation in a Dielectric Layered Structure
Authors: Bongianni W. L.
Published: February 2004

The presence of a conductive plane near a thin magnetic film perturbs the propagation of a surface magnetostatic wave. This paper treats the case of a dielectric layered structure, and an expression for the characteristic dispersion is derived. The dispersion is unique with respect to magnetostatic propagation in that it is nonreciprocal and nonmonotonic. A dielectric layered structure consisting of an epitaxial YIG film separated from a conductive plane by a thin dielectric layer is considered theoretically. Experimental results for this structure are given for dispersion and insertion loss.
Elastic Behaviors of Twist Disclination Loops near a Free Surface
Authors: Chou Tsu-Wei , Lu Tien-Lin
Published: February 2004

For a twist disclination loop situated in an infinite homogeneous elastic medium or in a nonhomogeneous medium where the loop plane is parallel to the interface, its elastic field involves only shear stresses. However, when the plane of the loop is in some arbitrary orientation with respect to the interface of a two-phase system, there is a dilatational field associated with the loop. Consequently, it is likely to interact not only with screw dislocations but also with edge dislocations, point defects, and wedge disclinations. To demonstrate this point, we examined the interaction between a free surface and a disclination loop. Equilibrium orientations of disclination loops have been obtained. Interaction energies of loops and image forces acting on them also have been determined. They are affected by the Poisson's ratios of the elastic media. Some comparison between the behaviors of dislocation and disclination loops are discussed.
New Method for the Measurement of Electron Yield from Ion Bombardment
Authors: Stein J. D. , White F. A.
Published: February 2004

A new technique is described for measuring directly the statistical distribution of electrons produced by single positive ions striking a surface. This method complements present techniques and permits the determination of the electron emission coefficient γ due to ion impact on semiconductors or insulators. Previous measurements of this type have been difficult or impossible owing to charge buildup on the target. In this new experimental approach, a beam of mass- and energy-resolved positive ions is focused on the surface being studied. Electrons ejected by individual ions are then accelerated through from 10 to 30 keV and focused into a silicon surface barrier detector. The magnitude of the detector output pulse produced corresponds to the number of electrons striking the detector simultaneously thus giving the electron yield. Preliminary results for the secondary electron yield coefficient γ are reported for aluminum oxide and titanium oxide surfaces bombarded by cesium, barium, lithium, and strontium ions having incident kinetic energies in the range of 10–40 keV.
Calculation of an Enclosed Cylindrically Symmetric Green's Function and Its Comparison to Field Measurements
Authors: Porter G. D. , Weiss P. B.
Published: February 2004

An analytic representation for the field from an arbitrary current distribution (either expandable in a Fourier series or for a current distribution that varies as sin2kz over one period) with cylindrical symmetry and enclosed within conducting inner and outer walls is derived. The Green's function applicable to the dc field from a single loop lying between two perfectly conducting cylinders is first calculated. The inversion from measured magnetic field to current distribution, which can be obtained in principle from the Green's function, is done in detail only for the previously mentioned current distributions. For most experimental parameters, the Green's function is so sharply peaked, one can assume a periodic current distribution for long current layers (length-to-diameter ratio > 2). The predicted magnetic field amplitude and field shapes were experimentally verified on the Astron machine.
Magnetic Suspension and Propulsion Systems for High-Speed Transportation
Authors: Richards P. L. , Tinkham M.
Published: February 2004

High-speed transportation vehicles (trains) carrying superconducting magnets can be levitated by repulsion from diamagnetic currents induced in a conducting track. Various approximate methods are presented for calculating the lift and drag forces for such magnetic suspensions. Fourier analysis of periodic train magnet fields is used to analyze ``image-force'' and ``hybrid null-flux'' systems which involve homogeneous conducting sheet tracks. A lumped circuit analysis is used to discuss the ``null-flux'' principle and related systems with structured tracks. The stability and efficiency of linear induction and linear synchronous motor propulsion systems are studied using related methods.