bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarity Effects and Charge Liberation in Lead Zirconate Titanate Ceramics under High Dynamic Stress
Authors: Cutchen J. Thomas
Published: April 2005

A polarity effect has been observed in dynamically stressed ferroelectric lead zirconate titanate ceramics Pb0.99Nb0.02(Zr0.65Ti0.35)0.98O3, which depends on the motion of the stress wave relative to the direction of remanent polarization. From the observations it is concluded that p-type mobile charge carriers are being liberated at the stress front, which in turn are acted upon by local internal fields. This action causes dielectric degradation when the stress wave travels opposite to the direction of remanent polarization. The charge liberation is attributed to a combination of ionization and failure mechanisms. Graham has reported a similar effect in alpha quartz, in which electrons are liberated.
Age Approximation to X-Ray Transport
Authors: Hogan William S.
Published: April 2005

The well-known age approximation of neutron transport theory has been applied to the photon transport problem. By treating photoelectric absorption analogously to resonance absorption in the neutron problem and using a first collision source term, calculations done for air compare favorably with Monte Carlo calculations for photon energies up to 100 keV, and to values of density times distance of about 30 g/cm2.
Quantitative Nonlinear Optical Sum-Frequency Experiments using Incoherent Light
Authors: McMahon D. H.
Published: April 2005

Nonlinear optical sum-frequency signals can be produced using pencils of incoherent light. The principal difficulty in making quantitative calculations of sum-frequency power stems from the relatively low f-number lens systems which must be used to focus light into the nonlinear crystal. For pencils of light with angular diameters between 0.05 and 0.5 rad, the most important factor which must be taken into account is the change in phase-matching angle which occurs when the two interacting rays are not parallel. A graphical method which takes this factor into account is used to calculate the magnitude of nonlinear sum signal produced and its dependence upon crystal orientation. These calculations agree well with experimental measurements and show that the technique can be successfully applied to predict the results of a wide variety of sum-frequency generation experiments utilizing incoherent light pencils.
High-Temperature Specific Heat of Germanium
Authors: Smith Richard C.
Published: April 2005

The specific heat of a germanium whisker has been measured by an ac heating method and found to increase smoothly from 0.325 J/g°K at 350°C to 0.345 J/g°K at 650°C. This result agrees closely with Greiner's values and disagrees with those of Gerlich, Abeles, and Miller. Apparent sources of the discrepancy are discussed.
Diffusion Analysis of the Observed Time Lag of the Thermal Coefficient of Resistivity of Germanium
Authors: Smith Richard C. , Holland Lawrence Rozier
Published: April 2005

A time lag in the thermal coefficient of resistivity of a germanium whisker is reported, and a probable explanation in terms of the diffusion of point defects (probably vacancies) is given. The necessary diffusion constant ranges from 3×10−4 cm2/sec to 12×10−4 cm2/sec in the temperature range 400° to 620°C with a probable error of ±20%. These values are above the highest reported in previous quenching experiments, among which there is large disagreement.
Plane Shock Initiation of an RDX Plastic-Bonded Explosive
Authors: Lindstrom I. E.
Published: April 2005

The plane-wave shock initiation of a plastic-bonded RDX explosive, initial density 1.60 g/cc, has been investigated by measurement of shock buildup to detonation using the explosive wedge technique. Impedance-match techniques were employed to determine the pressure and particle velocity associated with the shock in the explosive. Using a graphical representation in which the shock distance and time coordinates are referred to the beginning of detonation, a similarity between overlapping portions of buildup curves from different experiments, having different initial shock pressures, has been observed. While closer study of the data of this paper did not support the assumption of identical buildup curves, certain implications of such behavior, which have relevance to various models of initiation, are subject to experimental evaluation.
Radiation Hardening in Strained NaCl Single Crystals
Authors: López F. Agulló
Published: April 2005

The effect of room-temperature γ-ray radiation on the stress—strain behavior of prestrained NaCl single crystals has been investigated. After irradiation, a large increase in macroscopic flow stress and an initial ``soft'' region have been observed. Experimental data on the increase in flow stress vs γ dose are reported for different levels of prestraining. Finally, possible hardening mechanisms are explored in the light of experimental behavior.
High-Pressure Space-Charge-Limited Diode
Authors: Sherman Christopher
Published: April 2005

Solutions are obtained for the potential distributions in space-charge-limited diodes operating at pressures for which the mean free path is much smaller than other lengths characteristic of the problem.
Continuum Theory of Electrostatic Probes
Authors: Su C. H. , Kiel R. E.
Published: April 2005

Electrostatic probes of general ellipsoidal configurations are analyzed from a continuum viewpoint for the conditions of a quiescent slightly ionized plasma. Approximate analytic current—voltage characteristics are obtained for arbitrary ellipsoidal shapes. The cylindrical probe and circular disk probe are discussed in detail as two special cases.
High Electron Mobility of Cubic SiC
Authors: Patrick Lyle
Published: April 2005

The high mobility of electrons in cubic SiC is shown to be due to selection rules which severely restrict intervalley scattering. Only longitudinal acoustic (LA) phonons are permitted, and these have such a high energy (79.4 meV) that they are unimportant at room temperature. On the other hand, electron mobility in the common SiC polytypes, 6H and 15R, is limited by intervalley scattering.
Determination of the Gas Temperature in the Afterglow of Pulsed Discharges by Microwave Probing of Standing Acoustic Waves
Authors: Born Gunthard K. , Buser Rudolf G.
Published: April 2005

The time-varying gas temperature of afterglow plasmas is determined from the frequencies of standing acoustic waves which are produced during the breakdown of low-pressure gases (0.1–20 Torr). The sound field is probed with free-space microwave (9 and 70 Gc/sec) interferometers in transmission and reflection. Capacitor discharges are found to heat the gas significantly. The temperature does not decay to room temperature within the observed afterglow periods.
Coalescence Energy of Two Moving Dislocations of Like Sign
Authors: Weertman J.
Published: April 2005

A direct determination is made of the energy that must be supplied to cause coalescence of two dislocations of like sign moving with the same velocity on the same slip plane. This energy is always positive and is equal to twice the self-energy of a single moving dislocation even though the forces between the dislocations may be attractive.
Cesium—Antimony Films in Equilibrium with Cesium Vapor
Authors: Caulfield H. J. , Chapman R. A.
Published: April 2005

Photoemissive yield, thermionic emission, contact potential difference with clean tungsten, and electrical resistance measurements were made on cesium—antimony films in equilibrium with cesium vapor. A search was made for those combinations of cesium—antimony temperatures TCs-Sb and cesium reservoir temperatures TCs which mark discontinuous changes in the properties of these films. The loci of those TCs-Sb-TCs points mark the boundaries of distinct Cs-Sb ``states.'' Three clearly separable states, the familiar photo-sensitive state and its two neighboring states, were studied in detail. The first state occurred for TCs-Sb only slightly greater than the cesium reservoir temperature TCs. The state is characterized by a low maximum photoemissive yield (0.04 electrons/photon), moderate work function (1.65 eV), and high resistivity proportional to exp[−0.4 (eV)/kTCs-Sb]. The material in this state is p-type Cs3Sb with adsorbed cesium metal. The second state arises after a rapid transition from the first state as TCS-Sb is increased further. This state is characterized by a high maximum photoemissive yield (up to 0.23 electrons/photon), moderate work function (1.60 eV), and resistivity proportional to exp[−1.0 (eV)/kTCS-Sb]. This material is Cs3Sb without appreciable adsorbed cesium. From prior measurements of cesium partial pressure we obtain a cesium—antimony temperature T0 at which the film is Cs3Sb at its cesium deficiency limit. The third state occurs abruptly as TCs-Sb exceeds T0. The state for TCs-Sb > T0 is a less cesium-rich phase (probably Cs2Sb). This state is characterized by a low maximum photoemissive yield (0.04 electrons/photon), low work function (1.35 eV), and a higher resistance than the previous state.
Effects of Electron Bombardment on Single-Crystal CdSe at 77°K
Authors: Kulp B. A.
Published: April 2005

A threshold for electron radiation damage in CdSe is observed at 250 keV. A fluorescence emission band is produced with a peak intensity at 1.25 μ. Only a slight amount of annealing takes place up to 125°C. Above 150°C the fluorescence band at 1.25 μ increases in intensity due to heat treatment alone. The fluorescence can be removed by annealing at 500°C in excess selenium or cadmium.
Some Characteristics of Laser-Induced Air Sparks
Authors: Young M. , Hercher M. , Wu Chung-Yiu
Published: April 2005

Some of the optical properties of laser-produced air sparks have been measured. The sparks have been photographed to determine their structure. The angular distribution of incident laser light scattered by the plasma has been found to have a strong peak in the forward direction. The spark spectrum has been recorded and used to determine the total energy in the sparks. Application as an intense light source is considered.
Moiré Patterns with Display-Type Low-Energy Electron Diffraction Apparatus
Authors: McCurry R. E.
Published: April 2005

This paper describes an investigation of the origin of moiré patterns which occur in display-type lowenergy electron diffraction apparatus. With both planar and spherical geometry, ``real'' multiple source moiré patterns have been observed. With planar geometry, quantitative comparison of experiment and theory for the average moiré fringe spacing and pattern location are shown to be in good agreement. Spherical geometry patterns can be understood qualitatively on the same basis.
Evidence for Radiative Recombination between Deep Donor-Acceptor Pairs in GaP at Room Temperature
Authors: Gershenzon M. , Trumbore F. A. , Mikulyak R. M. , Kowalchik M.
Published: April 2005

Radiative donor-acceptor pair recombination between the deep-donor oxygen and a shallow acceptor (zinc or cadmium) in p-type crystals remains a dominant radiative recombination process in GaP at room temperature as it is at low temperatures. This mechanism is deduced from the spectral shift when one shallow acceptor is replaced by another, and from the dependence of photoluminescence intensities upon the simultaneous presence of both oxygen and the acceptor (zinc or cadmium). The minority carrier electron captured by the ionized donor is not readily released back to the conduction band thermally because the donor is quite deep. The thermal population of holes on the shallow acceptors is quite large even at room temperature, so that the trapped electrons can recombine with these holes. No radiative transitions between free holes and the trapped electrons are observed, implying that the capture cross section of a neutral oxygen donor for a free hole is <10−19 cm2. Since the widths of the pair bands involving oxygen are greater than the difference in binding energies between zinc and cadmium, the two bands overlap in crystals containing oxygen and both acceptors. The sum band exhibits no structure but its position depends on the zinc-to-cadmium ratio.
Electrical Conductivity in Evaporated Silicon Oxide Films
Authors: Johansen I. T.
Published: April 2005

Evaporated silicon oxide films can be made with reproducible electrical conductivity when the evaporation rate, the oxygen pressure, the substrate temperature during the evaporation, and the subsequent heat treatment are controlled.

In the high electric field region the conductivity follows a Schottky emission law and it is shown to be bulk limited. The conductivity is also shown to be a function of the degree of oxidation, and a variation in conductivity of a factor of 109 has been accomplished by varying the composition from SiO to SiOx, where x is between 1.5 and 2. At an electric field of 250 V/μ the variation is from 10−7 (Ω·cm)−1 to 10−16 (Ω·cm)−1.

A model for the conduction mechanism is proposed, where the rate-limiting process is assumed to be Schottky emission from small silicon islands into a silica structure in which the silicon islands are imbedded.
Magnetization of Synthetic Filamentary Superconductors. A. The Dependence of Flux Jumping on Temperature and Magnetic Field Sweep Rate
Authors: Watson J. H. P.
Published: April 2005

Synthetic high-field superconductors have been prepared by impregnating porous glasses of various pore size with indium, using pressures up to 70 000 psi. The magnetic field Hfi at which the first flux jump occurred in the initial magnetization of the sample was measured as a function of temperature T and magnetic field sweep rate dH/dt. Values of dH/dt between 24 and 375 Oe/sec were used. For a given value of dH/dt, Hfi increased initially as T was lowered, reached a maximum, and finally fell with T. For a given T, Hfi was reduced as dH/dt increased.

For large values of dH/dt, Hfi was almost independent of T and dH/dt. Hfi was reproducible to 50 Oe from cycle to cycle except for T <1.5°K, where the behavior became more erratic. After the sample was warmed to room temperature, Hfi was reduced. The samples showed hysteresis in the magnetization. Flux jumping occurred around the hysteresis loop; the values of field at which flux jumps occurred were reproducible from cycle to cycle. The field interval Δ between flux jumps had a temperature dependence similar to Hfi; Δ is slightly reduced for large values of the applied magnetic field. The size of the flux jumps were also reduced for large values of magnetic field. For small values of T, the flux jumping behavior became erratic. Measurements of the critical field and transition temperature have been made using a low-frequency mutual-inductance technique. The critical field, that is the magnetic field for the normal-superconducting transition, for a sample with a 65-Å pore diameter was 25 770 Oe at 2.67°K. At a reduced temperature of 0.6°K, samples with pore diameters of 65, 117, and 250 Å have critical fields of 156, 102, and 39 times the critical field of bulk indium (176 Oe). The transition temperatures for the samples were 4.24°, 4.04°, and 3.61°K, respectively, compared with 3.408°K for bulk indium. The over-all behavior of these samples was similar to inhomogeneous type II superconductors.
Defects in Synthetic Quartz
Authors: Spencer W. J. , Haruta K.
Published: April 2005

The defects in hydrothermally grown synthetic quartz have been studied by x-ray diffraction topography. Linear defects which are apparently associated with the growth of the crystal are the predominant defects in z-growth material. These defects which originate at inclusions or other defect sites on the seed surface are believed to be areas of high impurity content. If there are dislocations associated with the defects, their effect on the diffracted x-ray intensity is affected by a surrounding cloud of impurity atoms. Defect densities range from 10 to 104 lines per square cm and the crystals with high densities of defects exhibit high acoustic loss at 5 Mc/sec and 300°K. The defects observed in synthetic quartz by etch, γ-ray coloration, and polarized light are compared to those observed by x-ray diffraction topography.
Calculations of the Conductivity of a Medium Containing Cylindrical Inclusions by the Method of Orthogonalized Particular Solutions
Authors: Rabinowitz Philip
Published: April 2005

Calculations of the conductivity of an infinite medium containing a square array of perfectly conducting cylindrical inclusions were carried out using the method of orthogonalized particular solutions. The results agree with those reported by Keller and Sachs using the method of finite differences.
Proposed Method for Microgram Surface Density Measurements by Observation of Proton-Produced X Rays
Authors: Khan J. M. , Potter D. L. , Worley R. D.
Published: April 2005

X-ray production by proton bombardment may be used to determine the surface density of thin films. It is desirable that the energy loss of the protons in the film be small and that the self-absorption of the produced x-ray be negligible. To illustrate the method, thin surface films of aluminum are discussed. The aluminum x-ray yield (x rays/proton) as a function of surface density is presented for the range 0 to 115 μg/cm2 and at an incident proton energy of 100 keV. Under the conditions of a 10-μA proton current incident on a thick target, a typical detection system would record 10 000 counts/sec with a counter signal-to-noise ratio of 104. At a signal-to-noise ratio as low as unity, the calculated surface density is 0.005 μg/cm2 or approximately 1014 atoms/cm2. Details of the calculation are presented, along with a table of eleven elements to which the method is currently applicable.
Grain Boundary Migration and Other Processes in the Formation of Ice Sheets on Water
Authors: Knight Charles A.
Published: April 2005

Direct observations of the growth of ice on, and perpendicular to, a water-air interface are described, in an experiment reproducing the conditions of formation of natural lake ice. The final, preferred crystal orientation is affected by the initial orientations and by selective wedging cut of grains of certain orientations, but often the most important factor is grain boundary migration. Boundary migration is driven in part by interfacial energy and probably in part by stress. The origin of the stress is not known. Preferred intergrain orientations are found.
Dielectric Thin Films through rf Sputtering
Authors: Davidse P. D. , Maissel L. I.
Published: April 2005

Insulators cannot be sputtered with standard dc glow discharge techniques, because the accelerating potential cannot be directly applied and because the positive charge which accumulates on the surface during ion bombardment cannot be neutralized. Direct sputtering of insulators can be achieved by applying a high-frequency potential to a metal electrode behind the dielectric target. This technique was used to deposit thin insulating films. With a properly optimized electrode configuration and a superimposed magnetic field, deposition rates up to 2000 Å/min were obtained. Electrode potentials between 700 and 5500 V peak-to-peak were used. In all experiments described herein, the frequency was 13.56 Mc/sec and the pressure was 5×10−3 Torr. It was found that the introduction of oxygen into the argon sputtering atmosphere greatly reduced the deposition rate. Most experiments were carried out with borosilicate glass (Corning Pyrex 7740) and fused quartz. Without any special measures, films with a low pinhole density were obtained.
Diocotron Instability in Plasmas and Gas Discharges
Authors: Knauer W.
Published: April 2005

The wave interaction underlying the diocotron effect is re-examined and a physical model of the instability presented. A wave analysis is then given for circular, wall-enclosed charge layers with finite length in the axial direction. Circular layers are of particular interest, since they apply to various plasma, discharge, and electron device geometries. Their instability behavior is found to be similar in many respects to the behavior of linear charge sheets, described in earlier work by R. W. Gould. In contrast to linear sheets, however, circular layers are unstable only when their thickness is sufficiently small. This effect is associated with the inability of charge perturbations to have a wavelength which exceeds the layer circumference. Data are presented for the magnitude of growth in various configurations and for the critical layer width at which growth terminates.
Influence of Mode Number and Mode Degeneracy on the Output of a Ruby Laser
Authors: Wieder Harold
Published: April 2005

The conjugate-concentric ruby resonator is a system in which a ruby lens images each of the external mirrors on the other. By merely perturbing the geometry of the resonator, it is possible to obtain three distinct types of output: quasicontinuous, regular spiking, and random spiking. From the results of various experiments which have been performed on the system, it was concluded that two parameters are sufficient to determine which of these outputs will be obtained from a multimode resonator. Regular spiking is favored over random spiking if the mode number exceeds some critical value; quasicontinuous behavior is favored over regular spiking if, in addition, the modes exhibit degeneracy. The experimental results are compared with some existing theories.
Nonlinear Limiting of the Double-Stream Instability
Authors: Mihran Theodore G.
Published: April 2005

The double-stream instability in finite-diameter beams has been investigated by numerical experiments on a digital computer using the disk electron model. The nonlinear level is found to be a quadratic function of the linear-theory double-stream parameters ωδ/ωq. Computed electron trajectories show electron trapping to be the cause of rf current saturation. A simple analytic trapping theory is given which predicts observed peak nonlinear current levels to within a factor of three.

This investigation suggests that current conversion efficiencies approaching 50% can be achieved by operating near the upper edge of the gain band. On the other hand, nonlinear behavior occurs at perturbation levels of the order of 1% for weak instabilities near the lower edge of the gain band. The time to reach the nonlinear level is surprisingly short in most cases, ranging from 2 to 30 plasma wavelengths, depending on gain and excitation level.
Terminal Properties of Alfvén Waveguides
Authors: Kliman G. B. , Rink R. E.
Published: April 2005

In this paper attention is focused on the terminal properties of Alfvén waveguides. The electrical input impedance at the terminals of a set of coaxial excitor electrodes is derived. This result is then used to investigate the behavior of a lossy Alfvén wave resonator and the conditions under which the waveguide may be matched by a lumped, active load. Matching with a lossy reactive sheet is also discussed. The discussion is limited to the case of axisymmetric, transverse magnetic field modes since these are of the greatest experimental interest.
Holographic Interferometry
Authors: Heflinger L. O. , Wuerker R. F. , Brooks R. E.
Published: April 2005

A new method of interferometry, based upon holographic photography, is described. The interferometer uses a common optical path in which beam separation is achieved by two exposures separated in time. Its significant advantages are (1) accurate alignment and precision optical elements are not required, (2) differential interferometry, used to measure small changes in either optical path or position of complex subjects, is easily performed, (3) a complete three-dimensional record of the interference phenomena is obtained, permitting post-exposure focusing and examination from various directions, and (4) the technique is well-suited to the recording of transient as well as stationary phenomena. Experimental examples of its use with aerodynamic phenomena are given.
Experimental and Theoretical Ruby Laser Amplifier Dynamics
Authors: Avizonis Petras V. , Grotbeck Ronald L.
Published: April 2005

Experimental measurements of the energy contributed by one or more ruby amplifier rods driven by a ``Q-switched'' (pulse length of 10−7 sec) ruby oscillator are correlated to theoretical equations describing amplifier action. The equations describe amplification in all energy gain regimes, i.e., exponential, nonlinear, and saturated. The necessary requirements for the use of these equations are the prior knowledge of energy stored in the R1 level just before lasing, the energy input from an oscillator, and a ``nonsaturable loss coefficient'' (loss term) for the particular laser rod. Agreement between theory and experiment is demonstrated in all amplifier gain regimes. Energies of over 50 J in single submicrosecond pulses have been observed. No pulse narrowing has been noticed, but appreciable ruby damage occurs at these energy and power levels.
Technique for Producing High-Sensitivity Rubidium-Cesium-Antimony Photocathodes
Authors: Morrison Carl W.
Published: April 2005

A technique for producing relatively high luminous sensitivity, translucent, rubidium-cesium-antimony (Rb-Cs-Sb) photocathodes is described. Equipment and materials used to obtain the results are also described. It is indicated from spectral response data that the Rb-Cs-Sb photocathode has increased blue response and extended red response over that of the standard Cs-Sb-O (S-11) photocathode. Absolute spectral response curves for the rubidium-antimonide (Rb-Sb), the initial photocathode surface obtained before the addition of cesium, along with curves for the final Rb-Cs-Sb cathode are reported. It is suggested that the Rb-Cs-Sb photocathode has a stoichiometric formula similar to the other bi-alkali photocathodes of Rb2CsSb, although this remains to be verified experimentally. Absolute response curves are also given for the Rb-Cs-Sb photocathode as compared to other standard photocathodes.
Effect of Internal Reflection on Optical Faraday Rotation
Authors: Piller Herbert
Published: April 2005

Recent Faraday rotation measurements in n-type GaAs give an effective mass which is smaller than predicted by theory using accepted band parameters. These discrepancies can be interpreted by considering the multiple internal reflection effects in the measured rotation. The calculation was made for two cases: (1) when interference effects are directly observable (that is, λ and d are well defined and the optical path length of the internal reflected beam is shorter than coherence length), and (2) when an average value over a region of phase angle Δ≫»2π is measured. In the first case the rotation changes and oscillates as a function of wavelength and magnetic field. In the second case the rotation θ = VHd is given by the measured rotation γ minus a term which depends on the absorption, reflection, and the rotation in the sample.
Giant Laser Pulse Formation using Ultrasonic Q-Spoiling
Authors: Suprynowicz V. A.
Published: April 2005

This paper presents the results of an experimental study of the formation of ultrasonically gated giant laser pulses. The results include photographs of the ruby under such conditions, the influence of ruby temperature, the effect of acoustical amplitude, and the influence of the gating medium. Some of the experimental results appear to indicate that cavitation plays a role in such gating processes, and the possibility that reflection from cavitation-induced shock waves is the responsible gating mechanism is discussed.
Interaction of Metallic Powders with a Shock Wave through an Oxidizing Atmosphere
Authors: Tyte D. C.
Published: April 2005

The time-resolved light output of a shock wave through an oxidizing gas containing powdered aluminum, magnesium, and lead has been studied. The shape of the light pulse has been found to be dependent on the position of introduction and on the nature of the powdered solid. The results indicate that the shock-wave particle interaction is best explained by a combustion model rather than by the more normal ablation mechanisms.
Schottky Emission and Conduction in Some Organic Insulating Materials
Authors: Lengyel G.
Published: April 2005

Voltage-current curves of such organic insulators as polyethylene-terephthalate and polyvinylformal display the familiar Richardson-Schottky characteristics for fields between 20 and 200 kV/cm and temperatures from 25° to 100°C. Assuming the Schottky emission mechanism being the limiting factor in establishing the steady-state current, comparison between measured values and the Richardson-Schottky equation yields data on the work function of these materials. 0.88 eV was found for polyethylene-terephthalate and 1.24 eV for polyvinylformal. The calculations indicate an increase of the electric field at the injecting electrode over the value which would apply to an ideal, nonconducting insulator. This increase may be caused by space-charge effects.
Plastic Behavior of Titanium Carbide
Authors: Hollox G. E. , Smallman R. E.
Published: April 2005

Single crystals of titanium carbide with cube orientations have been deformed in compression in the temperature range 900°–1250°C. Earlier evidence presented by Williams that the primary slip system is {111} 〈11̄0〉 has been confirmed by contrast analysis using the electron microscope and this is maintained in material which deviates from the stoichiometric composition. Dislocation structures typical of a fcc metal with high stacking fault energy have been observed in transmission electron micrographs. The mechanical properties are discussed in terms of a high lattice-friction stress arising from the strong directional bonding between carbon and titanium atoms.
Environmental Factors in the Luminescence and Photoconductivity of Zinc Oxide
Authors: Oster Gerald , Yamamoto Masahide
Published: April 2005

Oxygen quenches the room-temperature fluorescence of powder zinc oxide but enhances the low-temperature phosphorescence and thermoluminescence. The low-temperature ultraviolet emission (edge emission) is quenched by oxygen. Water in the presence of oxygen is particularly effective and this is ascribed to the production of hydrogen peroxide.

Parallel effects are observed for the photoconductivity but water is less effective due apparently to enhanced contact conductivity.

Flash desorption of oxygen shows a parallel behavior of room-temperature luminescence and photoconductivity.
Likelihood Detection with a Multiple-Markov Process
Authors: Potter D. S. , Leedham C. D.
Published: April 2005

The problem of signal detection in the presence of noise has received considerable attention in the literature. The problem is approached historically by minimization of a signal-to-noise ratio. This formulation utilizes the properties of the process under consideration in terms of the frequency content as expressed by the correlation function and/or the power spectral density. The integral equations that evolve have, as their solution, the impulse response or the Fourier transform of the optimum processing device. With this approach, the statistics of the process do not enter the mechanism of solution explicity.

An alternative approach to the problem is to consider the statistics expressed in terms of the distribution function, explicitly. In general, a process with a frequency distribution that is other than white will yield a likelihood ratio in a form that is complicated algebraically. The linear prediction possible with processes that exhibit mth-order Markovian properties allows a solution, however, and this solution embodies both the statistical and the correlation properties explicitly. For the special case of Gaussian statistics, the equivalence with other techniques is demonstrated.
Propagation of a Glow Discharge into the Annular Gap between the Discharge Tube Wall and the Cathode
Authors: Veron Harry , Wainfan Nathan
Published: April 2005

Time-resolved spectroscopic measurements and electrostatic probe measurements were used to study that part of a high-voltage pulsed glow discharge in hydrogen that propagated into the annular gap between the cathode and the Pyrex discharge tube wall. The spectroscopic and probe measurements revealed that a luminous front and a potential wave started to propagate into the annular gap at the same time as the electric field in the cathode fall region at the face of the cathode reached its maximum value. The dependence of the propagation velocity on the discharge parameters is presented and the importance of the secondary emission at the wall of the discharge tube is established as a factor in the propagation of the discharge.
Strong Plane Shock Produced by Hypervelocity Impact and Late-Stage Equivalence
Authors: Chou Pei Chi , Allison F. E.
Published: April 2005

The attenuation of a strong plane shock produced in aluminum by the impact of a thin striker has been studied using the method of characteristics and a realistic equation of state. An approximate analytical solution, which is based on the assumption that the characteristics are straight lines along which the sum of the sound speed and particle velocity is a constant, is shown to be in good agreement with results obtained from the method of characteristics. For pressures up to 750 kbar, the analytical solution yields results that are in good agreement with experimental observations obtained using annealed 1100F aluminum. The theoretical calculations and experimental data show that plane shocks produced by impacts involving aluminum are equivalent at late times provided that u0αd is constant where d is the thickness of the striker, u0 the impact velocity, and α a constant in the neighborhood of 1.3.
Tunability of the Raman Laser
Authors: Puthoff H. E. , Pantell R. H. , Huth B. G.
Published: April 2005

A discussion of the stimulated Raman effect, with special emphasis on the possibility of constructing a tunable Raman laser in which tuning over tens of angstroms can be expected, is presented. The requirement which must be satisfied to obtain a broad tuning range is that the vibrational transition involved in the Raman scattering be simultaneously infrared active, i.e., infrared absorbing. The tuning characteristic of the 704-cm−1 line in methylene chloride is examined in detail to illustrate the considerations presented.
Microstructure of Epitaxial Ge Films Deposited on (111) CaF2 Substrates
Authors: Sloope Billy W. , Tiller Calvin O.
Published: April 2005

A more comprehensive experimental investigation of the microstructure of single-crystal Ge films deposited on polished (111) CaF2 substrates in a vacuum of 10−9 to 4×10−7 Torr has been made as a function of deposition rate, substrate temperature during deposition, and film thickness. Comparisons have also been made using cleaved substrates and a vacuum of 10−5 Torr. Transmission electron microscopy of thin films has shown that the density and complexity of defects increased with deposition rate and decreasing substrate temperature. The initial defect density was 109-1011 per cm2 for cleaved or polished substrates and for deposition in both vacuum systems. Little change occurred up to thicknesses of 2000–4000 Å. Electron microscopy of surface replicas for thicker films indicated that the density of faults intersecting the surface decreased by three orders of magnitude over the 5100- to 171 000-Å thickness range. The results for thin films, consistent with the growth mechanism associated with nucleation theory, indicated that for this unlike substrate-film combination the principal source of defects was the intergrowth of neighboring nuclei in other than perfect register and the decrease in density with thickness a result of interactions of defects as they are propagated with film growth.
Width of the Spontaneous Emission Region in Degenerate GaAs p-n Junctions
Authors: Casey H. C. , Archer R. J. , Kaiser R. H. , Sarace J. C.
Published: April 2005

The spontaneous emission of GaAs mesa diodes fabricated from 2×1018 cm−3 n-type material was observed at 77°K as a function of applied voltage in a direction normal to the plane of the junction. The emission observed from the p side represents the spectral shape as generated at the junction. When observed from the n side the spectra whose peaks shift with forward bias (due to band filling) have a periodically occurring enhancement and attenuation. These periodic features in the spectra are caused by interference of the spontaneous emission reflected from the gold contact that partially covers the diffused surface. Analysis of reflection from the Au-GaAs interface indicates that the adjacent minima or maxima in the spectra should have the observed average separation in energy of 150/xj meV, where xj is the junction depth in microns. In addition, this analysis relates the maximum enhancement or attenuation in the spectra to the active region width and demonstrates that the band-filling radiative recombination width is 600 Å or less. When the applied voltage exceeds 1.5 V and recombination of thermally injected carriers dominates, the emission peak (hvp≃1.47 eV) no longer shifts with voltage, and interference is not observed. This absence of interference in the stationary peak indicates that the active region width has become greater than 10 000 Å.
Analog of the Procopiu Effect in Type II Superconducting Wires Carrying an Alternating Current
Authors: LeBlanc M. A. R.
Published: April 2005

The longitudinal magnetization of a ferromagnetic wire which carries an alternating current in the presence of a stationary longitudinal magnetic field varies at twice the frequency of the applied current. This effect discovered by Procopiu has recently been studied by Skórski and Duracz. An analogous effect is observed when the ferromagnetic wire is replaced by a wire of a nonideal type II superconductor and the current alternates below the critical value Ic. In the superconducting case, the longitudinal magnetization of the wire may oscillate from strongly paramagnetic to strongly diamagnetic as the conduction current is varied. The frequency of oscillation of the magnetization is twice that of the applied current as in the ferromagnetic case. With the current varying as I=Ic cos ωt the longitudinal magnetization can be described by Mz≈A+B cos (2ωt), where A and B are temperature- and field-dependent parameters. This phenomenon in the superconducting state is shown to arise from helical patterns of induced and conduction current flow in the presence of a longitudinal field.
Propagation of Persistent Current Decay in Nb-Zr Wires
Authors: Walker M. S. , Hulm J. K.
Published: April 2005

Nb+25% Zr wires of several sizes and critical current densities were placed in a longitudinal magnetic field at 4.2°K, and persistent eddy currents were induced in them by changing the magnetic field strength. In the absence of any transport current it was found that a decay of these stored currents started at one point in the wire would propagate along the wire length. Decay was generally initiated by small pulses of heat, but would also start spontaneously under certain conditions. The velocity of propagation ranged from 105 to 106 cm/sec depending upon the wire and field strength during the experiment. Analysis of the flux change within the wire suggests an electromagnetically controlled propagation mechanism.
Electrical Resistivity of Chromium-Rich Chromium-Iron Alloys between 4° and 320°K
Authors: Arajs Sigurds , Dunmyre George R.
Published: April 2005

Electrical resistivity, with and without transverse magnetic fields, of iron-chromium alloys containing 0.9, 2.3, 3.3, 4.9, 6.5, 9.5, and 11.2 at. % iron have been studied between 4° and 320°K. Additions of iron to chromium decrease the Néel temperature from that of pure chromium. Below the Néel point, observable as a minimum in the ρ vs T curve, the electrical resistivity increase becomes larger with higher iron content. This anomaly cannot be explained by the energy gaps alone due to the antiferromagnetic ordering. Additions of iron to chromium drastically reduce its transverse positive magnetoresistivity to negative values. Magnetoresistivity data support the model that iron atoms enter the chromium matrix as localized magnetic moments.
Magnetic Form Factor of Chromium
Authors: Moon R. M. , Koehler W. C. , Trego A. L.
Published: April 2005

Neutron-diffraction measurements of the magnetic Bragg peaks from single crystals of chromium with small additions of manganese have been used to determine the magnetic form factor of chromium. The addition of manganese simplifies the experimental problem by stabilizing the simple antiferromagnetic structure. A single magnetic peak is observed at reciprocal lattice positions, rather than a group of six satellite peaks as in pure chromium. Also, manganese increases the Néel point so that the measurements were performed at room temperature. The results are in good agreement with free-atom Hartree-Fock calculations for the chromium 3d electrons. A definite indication of nonspherical symmetry was obtained by comparing the (221) and (300) reflections. These reflections come at the same scattering angle, yet the (221) intensity is larger by about a factor of six. This indicates a t2g population of 79%, compared to 60% for a spherical spin distribution. The results are independent of manganese concentration over a range from 1.7 to 4.1 at. %.
Spin-Wave Dispersion in KMnF3
Authors: Pickart S. J. , Collins M. F. , Windsor C. G.
Published: April 2005

The spin-wave dispersion curve of antiferromagnetic KMnF3 at 4.2°K has been measured by means of neutron inelastic scattering. With incident neutron energies of 105° and 165°K, propagation was observed out to the zone boundary in the pseudocubic (110) plane. Least-squares fitting of the spin-wave energies to an expression involving the nearest and next-nearest-neighbor exchange interactions J1 and J2 and an anisotropy field HA yielded the results J1/k=3.80°±0.04°K, J2/k=0.11°±0.02°K and HA=3.1±0.4 kOe.
Temperature Variation of the Spin-Wave Dispersion Relation
Authors: Weber R. , Tannenwald P. E.
Published: April 2005

The spin-wave dispersion relation, including the quartic term, has been measured at 61.8 Gc/sec between 4° and 300°K by spin-wave resonance in Permalloy films. Both the quadratic and the quatric terms vary as T52 up to 80°K and approximately as T32 up to room temperature. This is the same behavior previously reported for the quadratic term using a different Permalloy film at 10 Gc/sec. The long-range exchange interaction 〈ρ2〉=ΣJ(r)r4/ ΣJ(r)r2, where J(r) is the exchange integral between spins a distance r apart, has been obtained as a function of temperature from the ratio of the coefficient of the quatric term to the coefficient of the quadratic term.
Microwave Generation in Pulsed Ferrites
Authors: Shaw H. J. , Elliott B. J. , Harker K. J. , Karp A.
Published: April 2005

A pulsed magnetic field applied to a magnetically saturated ferrite sample is capable of initiating a coherent precession and of translating upward both the frequency and energy associated with this precession. A coupled circuit resonance can then extract energy from the system at a desired frequency. For large precession amplitude the rise of the pulsed magnetic field up to the bias field level must be nonadiabatic; the precession buildup is described by computer calculations. To avoid destructive effects of spin-wave buildup, the total risetime of the pulsed magnetic field must be less than a threshold value which depends on the precession angle; this threshold is determined from computer calculations of transient spin-wave growth. Operation within this time allows the precession angle to appreciably exceed the usual steady-state precession threshold set by spin-wave instabilities.

In experiments performed with YIG spheres mounted in an integral circuit element containing a tunable X-band slot resonator and a pulsed field coil, providing pulsed magnetic fields rising beyond 3 kG in approximately 1 nsec, energy in the range of hundreds of W·nsec has been generated over the X-band frequency range, with pulse widths of the order of 1 nsec. The output pulses have good interpulse phase coherence and are studied in detail using a sampling oscilloscope to observe the instantaneous rf waveforms.
Temperature Stabilization of Unsaturated Microwave Ferrite Devices
Authors: Stern E. , Ince W. J.
Published: April 2005

A technique utilizing a composite magnetic series circuit is described wherein the flux density of unsaturated microwave ferrite is maintained constant in spite of large changes in microwave ferrite saturation magnetization, coercive force, and hysteresis loop shape. The composite circuit consists of a driver, a flux limiter, and a microwave ferrite. The driver supplies the necessary mmf to maintain constant flux level in the circuit throughout the temperature range. The flux limiter, a particularly stable ferrite material, establishes the constant flux level. The driver and flux limiter may lie outside the microwave region and may in consequence possess indifferent microwave properties.

A simple design procedure is described for determining the driver and flux limiter dimensions. Special attention is given to the effects of air gaps and leakage fluxes which tend to reduce the effectiveness of the technique.

A remanence phase shifter is described which suffers a 16% loss of phase shift as a result of an 80°C rise of temperature. By the application of composite circuit techniques, the temperature sensitivity was reduced to less than 2½% over the same temperature range.
Constant-Phase Electrically Controllable rf Attenuator using Permalloy Films at Resonance
Authors: Ngo D. T.
Published: April 2005

A constant-phase, electrically controllable attenuator using Permalloy films has been investigated both analytically and experimentally. The well known behavior of the permeability as a function of bias field near resonance is utilized. The permeability of a Permalloy film can be expressed as μ=μ1−jμ2. In a film-loaded strip line, the attenuation constant is strongly affected by μ2 while the phase constant depends on the magnitude and sign of μ1. Controllable attenuation with net zero phase change can be realized with the following arrangement: Two film strips, identical in properties and geometry are used in a strip line and both are biased at H0, the resonance bias field, resulting in a maximum attenuation and zero phase shift. Super-imposed is a control field of opposite polarity on the two film strips. If the control field is set at ΔH, then the net bias field is H0−ΔH on one film strip and H0+ΔH on the other, yielding a permeability, −|μ1|−j|μ2| on one and +|μ1|−j|μ2| on the other. As a result, the phase change due to the reactive permeability components cancel each other out and only the attenuation due to the loss component remains.

Such an attenuator has been built and tested successfully over a frequency range from 1 to 3 Gc/sec.
Control of the Electromagnetic Properties of the Polycrystalline Garnet Y3Fe3.75Al1.25O12
Authors: Cohen H. M. , Chegwidden R. A.
Published: April 2005

The relationship of the composition to the dielectric loss tanδ and dielectric constant ε′ of the polycrystalline garnet Y3Al1.25FexO12 has been quantitatively determined. Single-phase dense garnet which has a tanδ<0.0002 can be prepared for values of x between 3.73 and 3.78. A high yield process, based on these data, to synthesize polycrystalline garnet with dielectric loss <0.0002 (X-band) and dielectric constant controlled within 1% is discussed briefly. The room-temperature saturation moment of garnets in the system Y3Fe5−xAlxO12 can be changed by a short heat treatment. The effect of the heat treatment of the 25°C 4πMs increases as the aluminum content of the garnet increases. Heat treatment can change the 4πMs of Y3Fe3.75Al1.25O12 by as much as 40%. In the heat-treatment range 1000° to 1250°C the data obtained by quenching small samples of Y3Fe3.75Al1.25O12 after a half-hour equilibration at temperature are thermodynamically reversible and reflect changes in the Al3+ and Fe3+ ion distribution between tetrahedral and octahedral sites. Heat treatment from 1250° to 1500°C causes tanδ at 25°C to increase continuously from 0.0001 to 0.001. The lattice defects formed by heat treatment above 1250°C decrease the activation energy required to cause a change in the aluminum and iron ion distribution between tetrahedral and octahedral sites.