bluuebunny/crossref_metadata_2025 huggingface dataset:
Operation of a Levitated Superconducting Ring in a Plasma Physics Experimental Device
Authors: File J. , Martin G. D. , Mills R. G. , Wakefield K. E.
Published: February 2004

An isolated, isochoric Dewar and superconducting ring, operable up to 130 000 ampere turns, has been installed in the Princeton Spherator, and plasma physics experiments have been performed with the ring levitated and stabilized by means of a system similar to that discussed previously. The evolution of this device has progressed through three stages. Initially the poloidal field coil was a conventional copper conductor ring within a vacuum jacket supported within the reaction chamber from top and bottom by four thin bars. In its second stage of development, the conventional coil was replaced by a superconducting coil and Dewar, supported by thin wire-like hangars. The present mode eliminates the need for mechanical supports of any sort.
Superconducting Quadrupole Doublet for the Los Alamos Meson Physics Facility
Authors: Rogers J. D. , Hassenzahl W. V. , Laquer H. L. , Novak J. K. , Stokes R. W.
Published: February 2004

A superconducting quadrupole doublet for beam focusing has been operated with a 30-kG field at the center of the 30-cm-long straight section of the magnets and a 3-kG/cm field gradient. The magnets used twisted multifilament Nb–Ti superconductor imbedded in a Cu matrix of 0.050-in. diameter and operate at currents up to 500 A. Each magnet is equipped with a persistent mode superconducting switch. The room-temperature beam aperture of the magnet-Dewar system is 15 cm. The focal length of the magnet pair is about 1 m for 500-MeV pions. The magnets are mounted in a Dewar with thermally compensated supports to minimize motion upon cooling and a soft iron shield reduces external fields to less than 60 G.
Experimental Superconducting Transformer for Current Set Up
Authors: Voelker Ferd , Acker Robert C.
Published: February 2004

For certain applications one would like to use relatively few turns of a high current conductor to make superconducting magnets. High current conductors introduce the problem of large heat leaks, and also the problem of a high current power supply. These problems would be simplified if one could make a suitable current step-up transformer. A design equation for such a transformer is presented. An experimental test was performed on a transformer made of superconducting solenoids which we had on hand. It had a primary current of 79.2 A, and supplied 670 A to a small load solenoid. The transformer was operated in two modes. In the first, the primary current was held constant for 24 h. The magnetic field in the load solenoid was monitored and the rate of decay in field could be measured. In the second mode, the primary current was regulated to maintain constant field in the load solenoid. The time constant of the secondary circuit was 1.4×106 sec. Such a system could be operated for a number of weeks without recycling.
Constant Voltage Controller and Transition Monitor for Superconducting Magnets
Authors: Lester Donald H.
Published: February 2004

Superconducting magnets with long charge times require a power supply that will hold a constant voltage across a magnet during the charge, hold, and discharge periods. Conventional supplies regulate poorly during hold and lose control completely during discharge of the magnet. A simple circuit has been designed to connect between a magnet and the remote sense input of a conventional power supply which permits control and regulation at all times. During the testing of multisection superconducting magnets, it is desirable to know the order and approximate time interval in which each section undergoes a transition to the normal conducting state. A circuit has been designed which detects and displays this information.
Surface Residual Resistance of High-Q-Superconducting Resonators
Authors: Halbritter J.
Published: February 2004

The temperature-independent residual surface resistance Rres of high-Q-superconducting resonators is up till now not well understood. Experiments in lead-plated copper cavities and massive niobium cavities (ν≃GHz) have shown Rres ∝ω1.8±0.2, which excludes normal conducting regions as a cause for the rf losses. An explanation is presented which can describe the observed dependencies on frequency and on surface treatment: The losses are caused by the generation of phonons in fissured surfaces by locally excited rf fields. These losses are temperature independent, give Rres∝ω2 and can also explain the observed mode dependence in lead-plated copper cavities.
Analysis of Critical Power Loss in a Superconductor
Authors: Rabinowitz Mario
Published: February 2004

A critical power dissipation resulting from an oscillating magnetic field, Hp cosωt, can produce a magnetic breakdown field, Hp′ < Hc, the critical field of the superconductor. The analysis shows, for example, why the breakdown field of a superconducting microwave cavity can be well below Hc in some cases, and indicates what the functional dependence of the cavity Q may be for values of Hp near Hp′. The effective resistivity of a single isolated oscillating fluxoid, as well as that of a stationary normal region, is also derived for both type I and type II superconductors.
Plane Waves in Layered Media
Authors: Spielvogel Lester Q.
Published: February 2004

This paper describes how to couple equations describing pressure and shear waves of elastic materials with equations describing pressure waves in fluids. The media treated are homogeneous and occupy doubly infinite slabs of finite thickness. As a result, the transmission and reflection coefficients for a baffle composed of a finite number of slabs of elastic and fluid materials are obtained. These concepts are useful in the determination of transmission and reflection of sonar baffles, ocean bottom, etc. Limits can be taken, letting the thickness of a fluid layer go to zero, to see the effects of lubricated boundaries in baffles, etc.
Magnetic Recordings of the Heart's Electrical Activity with a Cryogenic Magnetometer
Authors: Rosen A. , Inouye G. T. , Morse A. L. , Judge D. L.
Published: February 2004

The greatest difficulty in measuring magnetic field generated by the heart's electrical activity is in eliminating noise from other sources. The common mode portion of the noise was rejected by using a magnetometer with a pair of differentially connected superconducting flux transformers. The high sensitivity associated with the two Josephson junction quantum interference device permitted highly resolved magnetiocardiograms of quality comparable to the normal electrocardiogram, without the use of shielded enclosures or signal averaging.
Strengthening Alumina by Quenching in Various Media
Authors: Kirchner H. P. , Walker R. E. , Platts D. R.
Published: February 2004

In well-made polycrystalline alumina ceramics subjected to external forces, fracture originates at surface flaws. In this investigation, compressive surface layers were formed by quenching both glazed and unglazed alumina rods in various quenching media. Improvements in flexural strength, tensile strength, thermal shock resistance, and impact resistance were observed. The strength increases with increasing compressive surface force as indicated by rod tests. Therefore, in quenched alumina compressive surface layers prevent surface flaws from acting to cause failure.
Ultrasonic Study of Elasticity-Porosity Relationship in Polycrystalline Alumina
Authors: Nagarajan A.
Published: February 2004

Ultrasonic pulse echo measurements on alumina bodies of porosities ranging from 1 to 40% show linear relationships between both the shear and longitudinal velocities and the total porosity. A quadratic relationship is deduced for the dependence of Young's and shear moduli on porosity. The values extrapolated to zero porosity agree reasonably well with results of other works. Poisson's ratio is constant within the limits of the experimental errors. The attenuation of the echoes increases substantially with increasing porosity. When the experimental results are compared with various theoretical models, it is clear that the ``dilute-suspension'' models are incapable of fitting the observations. Among the ``elastic-bound'' models, a cylindrical pore model seems to fit the data much better than a spherical model.
A Dense Modification of BaO and Its Crystal Structure
Authors: Liu Lin-gun
Published: February 2004

BaO displays a reversible phase transformation in the pressure range between approximately 110 and 180 kbar at room temperature. The high-pressure modification is the first high-pressure polymorph of an alkaline-earth oxide to be observed directly. The x-ray diffraction pattern of the high-pressure from at about 180 kbar can be satisfactorily indexed as tetragonal with a = 4.397 ± 0.007 Å and c = 3.196 ± 0.005 Å. Although there are intensity discrepancies, the high-pressure polymorph of BaO appears to have the structure of phosphonium iodide PH4I (SG P4/nmm), which is a distorted CsCl-type structure, and contains 2 molecule per unit cell. A transformation to this structure results in a volume decrease about 11–14% at the phase transformation. This study has also been carried out up to pressures of about 290 kbar, no further phase change was observed and the axial ratio c/a appears independent of pressure within experimental error.
Theory of Dislocation Cells. IV. Hybrid Cells
Authors: Moore J. T. , Kuhlmann-Wilsdorf D.
Published: February 2004

Extending the investigations of Papers I–III, infinitely tall ``hybrid cells'', i.e., dislocation cells derivable from mixtures of different orders of multipoles, are considered. A symbolism is developed aiding in the analysis of such cells. It is shown that at different distances the stress fields of hybrid cells are dominated, in turn, by the multipoles composing them. For example, a cell that may be regarded as an assembly of dipoles, tripoles, and hexapoles exhibits a stress field that has dipole nature at the farthest distances, has tripole nature in an intermediate range, and has hexapole nature at the closest distance just beyond the true short-range stress field of the cell walls. The latter is the same as that of the corresponding infinitely extended boundaries, as was shown in Paper III.
Coordinate Paths for Depinning and Repinning of Dislocations
Authors: Bauer Charles L.
Published: February 2004

The energy of a dislocation segment, anchored firmly at each end and bound by two (breakable) pinning points, is determined by computer as a function of pinning-point distribution and applied stress. Under appropriate conditions, multiple energy minima occur for various dislocation configurations characterizing the pinned, depinned, and half-pinned states, indicating a variety of energetically feasible coordinate paths for depinning and repinning of dislocations. Implications of these results are discussed and compared with those obtained from approximate analytic solutions.
Pyroelectric Voltage Response to Step Signals of Infrared Radiation in Triglycine Sulphate and Strontium-Barium Niobate
Authors: Simhony M. , Shaulov A.
Published: February 2004

Theoretical and experimental analysis of voltage transients obtained in triglycine sulphate and strontium-barium niobate in response to step radiation signals yields information important for pyroelectric ir detection. The response transients are shown to be symmetrical with respect to the electronic and thermal time constants τe and τT of the samples. When τe and τT differ appreciably, the rise of the response and its decay are exponentials whose time constants are, respectively, the smaller and the larger one from among τT and τe. The peak voltage values are proportional to the load resistance RL when τe≪τT; they become independent of RL and proportional to τT when τe≫τT. The initial slope of the response in a given sample is found to be independent of RL for a given radiation flux. The pyroelectric coefficient of a material, divided by the product of its permittivity, density, and specific heat is shown to be a figure of merit for use in pyroelectric ir detection
Effect of Hydrostatic Pressure on Self-Diffusion in Single Crystals of Indium
Authors: Ott Aadu , Nordén-Ott Aslaug
Published: February 2004

The pressure effect on the self-diffusion rate in single crystals of indium metal has been measured parallel and perpendicular to the tetragonal axis using a radioactive tracer deposition and sectioning method. The experiments were performed at three different temperatures 118, 132, and 148 °C, and at hydrostatic pressures varying from 1.2 to 9.6 kbar. The diffusion rate was observed to decrease with increasing pressure and the activation volume for the diffusion process was determined to be 8.1 ± 0.4 cm3/mole with no detectable dependence on temperature or crystallographic orientation. Comparison with theoretical relations suggests the vacancy mechanism for diffusion.
Calculation of Obstruction Effects on Rarefied Particle Streaming through Short Tubes
Authors: Choong Philip T. , Mason Edward A.
Published: February 2004

A numerical technique has been developed to study the behavior of the flow conductance through a cylindrical channel for various types of rarefied particles. The present method has the characteristics of being accurate and more efficient than the conventional Monte Carlo. In comparison with Clausing and DeMarcus's approaches of solving integral equations, the method is superior by being both versatile and flexible. The channel obstruction effects are characterized by a dimensionless parameter K which is computed in TUBNOF code. Some of the effects investigated are the specular reflection, adsorption, and absorption. The finite molecular mean free path effect on the rarefied particle flow is also considered. The technique can be very useful in studies involving sublimation, molecular beams, cold gas jets, and radiation streaming.
Field-Enhanced Photoelectron Emission from Metal-Oxide-Semiconductor Structures
Authors: Foss Norman A.
Published: February 2004

Field-enhanced photoelectron emission from metal-oxide-semiconductor (MOS) structures has been investigated. The device is a Si–SiO2–Al:Cs:O structure which incorporates a low work-function surface in conjunction with an internal-gain mechanism to give an increased infrared response. The avalanche gain increases the response by providing the diode stage with a high photoelectron yield in the infrared. This gives a photoelectron quantum efficiency of 0.1% at 1.1-μ wavelength for structures with 1-cm×0.3-cm active areas.
Creep of Dispersions of Ultrafine Amorphous Silica in Ice
Authors: Nayar H. S. , Lenel F. V. , Ansell G. S.
Published: February 2004

A technique was developed to produce ice containing a fine uniform dispersion of amorphous silica particles. Rates of creep in tension of dispersions with ½- and 1-volume % silica in ice were measured in the temperature range of −22 to −2°C and in the stress range of 4.64–17.8 bar and compared with those of pure ice. The silica dispersion strongly decreases creep in ice, resulting in steady-state creep rates in a 1-volume % dispersion 10–30 times slower than in pure ice. The activation energy for steady-state creep in dispersion-strengthened ice calculated from the temperature dependence of the creep rate is stress dependent with an average value of 97 kcal/mole, 6–7 times that for self-diffusion in pure ice. The steady-state creep rate increases exponentially with stress. This behavior differs from that of metallic coarse-grained dispersion-strengthened materials, in which the creep rate is proportional to a power of the stress and the activation energy is stress independent and equal to that for the self-diffusivity of the matrix metal. It is suggested that this unexpected behavior is due to particle-matrix decohesion in the ice-silica system, which interferes with the normal blockage of dislocation motion by second-phase particles during creep.
Properties of He–Ne–Zn Laser
Authors: Collins G. J.
Published: February 2004

A He–Ne–Zn gas mixture is demonstrated to be capable of providing tricolor laser oscillation in either the red (6328 Å-Ne I), yellow (5894 Å-Zn II), or blue (4924 Å-Zn II) spectral regions with a total output power of nearly 10 mW. An observed quenching of the blue (4924 Å-Zn II) laser transition in He–Ne–Zn mixtures when the neon partial pressure exceeds 0.10 Torr is shown to be the result of a thermal-energy charge-exchange reaction involving ground-state neon atomic ions and Zn I ground-state atoms. The total velocity averaged cross section for this reaction is measured, and the relatively large value obtained (10−15 cm2) accounts for the strong sensitivity of the 4924-Å laser output to increasing neon partial pressure.
Electron Temperature and Density in Positive Column He–Cd+ Lasers
Authors: Goto Toshio , Kawahara Atsushi , Collins G. J. , Hattori Shuzo
Published: February 2004

Electron temperature and density necessary for quantitative study of saturation mechanism of laser power have been measured over the range of the typical He–Cd+ laser discharge conditions with the double-probe method. It is shown that the electron temperature decreases very rapidly with increasing cadmium pressure and the electron density has a broad minimum at cadmium pressures around 10−3 Torr where the 4416-Å laser output power shows a sharp peak.
Characteristics of the HCN Laser Radiation at High-Excitation Currents
Authors: Turner R. , Poehler T. O.
Published: February 2004

The HCN gas laser using short (1 μsec) high-current (15 kA) pulsed excitation emits its 337-μm radiation in pulses approximately 50 μsec long and 90 μsec apart that last for almost 500 μsec; the output is similar, in many respects, to the spiking observed in solid-state lasers. The pulsed nature of the output is due to radial acoustic oscillations, produced in the gas by the high current, which modulate the electron density in the cavity. The output depends critically on the distribution of gas in the cavity and is a maximum when the density on the axis is a minimum. The mechanism by which the density change influences the output has not been definitely established. It appears, however, that the gradient in the index of refraction which is produced by the oscillations and is in the correct direction to defocus the cavity at the time of minimum output is the most likely source of the pulses.
Ultraviolet-Induced Transient and Stable Color Centers in Self-Q-Switching Laser Glass
Authors: Landry R. J. , Snitzer E. , Bartram R. H.
Published: February 2004

The optical absorption spectrum of ultraviolet- (uv-) induced room-temperature stable color centers and the uv spectrum for their generation in a laser self-Q-switching glass were obtained. The optical absorption spectrum is similar to that for x-ray-irradiated silicate glasses of simpler composition. The uv generation spectrum was found to consist of a narrow Gaussian line of width 2250 cm−1 with peak at 45 800 cm−1. The optical absorption spectrum of the uv-induced transient color centers was also obtained and appears to consist of the superposition of a broad asymmetric absorption band peaked near 740 nm and a Gaussian-shaped annihilation band peaked near 674 nm. The lifetime of the 740-nm band was found to be about 200 msec and that of the 674-nm band about 400 msec. The 740-nm transient absorption band is identified with the E1,2− band which Mackey, Smith, and Halperin attribute to a trapped electron polaron. The line shape of this transient absorption is interpreted in terms of a large-polaron strong-coupling model from which various properties are inferred. The transient annihilation band at 674 nm is identified with the temporary bleaching of a room-temperature stable trapped-hole center. A model is suggested for the production of both stable and transient color centers.
Mode Perturbations and Filamentary Coupling in GaAs Lasers
Authors: Wieder Harold
Published: February 2004

Three distinct types of mode perturbations are revealed in the temporal output of GaAs lasers: (a) mode hopping between longitudinal modes; (b) random noise associated with the sharing of power among modes; and (c) a sudden spatial redistribution of power brought on by the excitation of a different set of transverse modes. Filaments are shown to couple to one another at all power levels for narrow junction lasers, probably by means of diffraction effects.
Polarization of Light in Suspensions of Small Ferrite Particles in a Magnetic Field
Authors: Goldberg P. , Hansford Jane , van Heerden P. J.
Published: February 2004

Suspensions of small ferrite particles show polarization of light when placed in a magnetic field. Some observations and their interpretations are given.
Mechanism of Curie-Point Writing in Thin Films of Manganese Bismuth
Authors: G. Enrique Bernal
Published: February 2004

This paper presents the first detailed calculation of the demagnetizing field using the measured temperature dependence of the magnetization of manganese bismuth films and assuming realistic time-dependent temperature distributions. It yields calculated demagnetizing fields that are in good agreement with the measured values of field required to erase written spots in manganese bismuth in either of its two phases. Based on the agreement between measured erasure field and calculated demagnetizing field, we conclude that the demagnetizing field model of Curie-point writing is justifiable. The results can be used to explain the previously reported partial erasure characteristics of this material.
Temperature Dependence of the Bulk Modulus of Alkali Halides
Authors: Madan M. P.
Published: February 2004

There is very little data on the behavior of the bulk modulus of crystals over a wide temperature range. Recently, Anderson revived interest in a fundamental constant of a solid called δ, which was first introduced by Grüneisen. This parameter is similar in many respects to the well-known Grüneisen parameter γ and was used by Anderson to explain the temperature dependence of the bulk modulus of oxide compounds. In the present paper, general expressions for δ have been derived in a simple manner correlating the thermodynamical and the interatomic potential approaches. The parameter δ has also been related to the Grüneisen parameter using the Slater and Dugdale-MacDonald equations. The relative appropriateness of different expressions for δ has been discussed. The computed values of δ for NaCl- and CsCl-type alkali halides based on the Born-Mayer and the modified Born-Mayer potential forms have been reported and are found to be consistent and in essential agreement with other determinations. These values have been used to calculate the adiabatic bulk modulus as a function of temperature for KCl and NaCl. A good agreement is found with the experimental data over most of the temperature range in the neighborhood of and above the room temperature. This general accord with the predictions of theory clearly indicates that in the temperature range where the experimental data is inadequate, it is possible to predict the temperature dependence of the bulk modulus of nonoxide compounds also, using Anderson's equation and the relationships for δ developed in the present paper.
Method for Measuring the Incident-Beam Energy in Scanning Electron Microscopy Using Electron Channelling Patterns
Authors: Schulson E. M.
Published: February 2004

Based on recently developed electron channelling pattern techniques, a method is presented for determining directly the incident-beam energy in scanning electron microscopy. A ``standard'' crystal is oriented to give a high-resolution pair of electron channelling lines (hkl) and (h̄k̄l̄) from a known set of Bragg planes, and from the width of the pair, the Bragg angle is determined using a simple conversion procedure. The De Broglie wavelength of the incident electrons, and hence their energy, can then be calculated. The method is demonstrated experimentally and shown to be accurate to about ±1.5%. This accuracy is possible provided a goniometer tilt stage is available with a tilt accuracy of about ±1% (for example, ±0.02° in 2° tilts), and the effect of scan distortions on the final image is negligible. It is pointed out that the accuracy of lattice parameter measurements using the electron channelling pattern technique could be limited by the accuracy of the incident wavelength. An appendix is given discussing the curvature of channelling lines and the effect of curvature on pair-width measurements.
Adatom Capture and Growth Rates of Nuclei
Authors: Sigsbee R. A.
Published: February 2004

A comprehensive treatment for the growth of cap- and disk-shaped nuclei on surfaces is developed. The results are important for a description of high-vacuum thin-film deposition, chemical-vapor deposition, electrodeposition, oxidation, and dropwise-condensation heat-transfer processes. The curvature effects of small nuclei on the adatom concentration field are included and shown to be negligible for nuclei appreciably larger than the critical size. The extent of the nucleation-exclusion zone surrounding a growing nucleus is shown to be strongly size dependent and initially much smaller than the adatom-capture zone. This obtains until the nucleus radius approaches the mean adatom-diffusion distance. Growth is considered to begin at the instant a nucleus exceeds the critical size. Analytical solutions and numerical integration have yielded results which are suitable for the evaluation of nuclei growth rates and growth times under most experimental conditions. This treatment also enables an evaluation of the adatom mean surface-diffusion distance and desorption energy to be made independent of the nucleation-rate model (classical or atomistic) chosen. Growth rates and times are shown to be essentially independent of the critical nucleus size for supersaturations greater than 100 and sizes greater than several times the critical. Growth on a substrate saturated with nuclei is also treated.
Kinetics of Gas-Bubble Swelling in Silver
Authors: Patil H. R. , Huntington H. B.
Published: February 2004

A nondestructive method has been used to monitor continuously the volume changes in thin-walled tubes of oxygen-bearing silver which were heated in an argon ambient containing a few percent hydrogen. A large direct current was used to heat the samples while their ends were water cooled. Above ∼ 550°C rapid specimen elongation and swelling were immediately apparent but slowed up progressively with time. The microstructure consisted of an extensive network of void-infested grain boundaries with fissures and occasional cracks. The rate and extent of the dimensional changes depended sensitively on the duration of preanneal, the ambient hydrogen partial pressure, and the impurity content of the material. In addition to the initial elongation and swelling, a subsequent dimensional change manifesting itself in a predominantly radial contraction was observed at temperatures above ∼ 800°C. These results are discussed in terms of the formation and the growth by agglomeration of steam bubbles swept together by the moving substructure boundaries. The possibility of dissociation of water at high temperature and the consequent bubble collapse is considered probably responsible for the observed radial shrinkage.
Adsorption and Growth of Cadmium on Polycrystalline Tungsten
Authors: Wagner R. S. , Voorhoeve R. J. H.
Published: February 2004

The multilayer adsorption and growth of cadmium on clean polycrystalline tungsten ribbons (with strong preferred orientation) has been investigated with a molecular-beam and mass-spectrometric technique. The adsorption and desorption kinetics have been studied as a function of temperature, supersaturation, and coverage. Five distinct adsorption states have been found between 100 and 600°C. Growth of bulk cadmium occurs only after multilayer adsorption is complete. No measurable supersaturation or critical nucleation event is observed for the growth of cadmium. However, even at high supersaturation and heavy coverage, the condensation coefficient is still smaller than unity. The kinetic and structural data are explained by the evolution of faceted, crystallographic, and epitaxial cadmium islands on the cadmium multilayer adsorbate.
Effect of a Slit on the Measured Plasma Ion-Energy Distribution
Authors: Stallings Charles H. , Kuswa Glenn W.
Published: February 2004

Measured ion-energy distributions were found to vary with the width of the slit separating the body of a streaming plasma from the analyzing system. Slit widths from 0.1–75 Debye lengths were investigated. The flux of ions detected on centerline and at a given energy varied linearly with (W-i) for W sufficiently large. W is the width of the slit and i is a positive number independent of W but depending on the plasma parameters. Using this linearity the ion-energy distribution in the plasma could be extracted from two measurements of the distribution at different slit widths. An analysis of the effect predicted the variation of ion flux with slit width as a function of plasma parameters. This analysis gave a method for determining Debye length and electron temperature as well as the correct ion-energy distribution from measurements of the ion flux.
Penetration of a Dense Plasma by an rf Electric Field
Authors: Lépéchinsky D. , Tataronis J. A.
Published: February 2004

It is shown that the parallel-plate plasma capacitor can be used effectively to excite, in the absence of an external magnetic field, an electric field that is uniformly distributed across a plasma slab for frequencies well below the plasma frequency. The structure is analyzed in detail using the complete set of Maxwell's equations.
Thermal Conversion of Interstitials in Electron-Irradiated Copper
Authors: Simpson H. M. , Sosin A. , Seiffert S. L.
Published: February 2004

A study by internal friction measurements has been made on high-purity copper of the effects of 1-MeV electron irradiation on the rate of addition of point defects to dislocations in the temperature range 78–400°K. A distinct minimum in the point-defect pinning rate is observed at about 160°K. It is also observed that a peak in the decrement as a function of irradiation time occurs, having a peak-position time dependence which reflects the rate at which point defects arrive at dislocations. The above observations are discussed and taken as directed experimental evidence in support of the thermal-conversion model. The maximum in internal friction and the minimum in the pinning rate are accounted for in a model of damping due to the dragging of point defects by dislocations.
Photoionization of Electrons at Sulfur Centers in Silicon
Authors: Rosier L. L. , Sah C. T.
Published: February 2004

The photoionization of electrons from sulfur centers in silicon has been measured by the photocapacitance transient technique. The photoionization cross section of electrons was found to be much greater than that of holes. In the photon energy range of 0.70–1.00 eV, the photoionization cross section of electrons from neutral sulfur centers is approximately 2×10−16 cm2, and the photoionization cross section of electrons from singly ionized sulfur centers fits a Lucovsky delta-function potential model better than a scaled hydrogenic model. For photon energies above the threshold, there was no observable field dependences or temperature dependences; however, near the threshold, a large field and temperature dependence was observed. As the field was increased from 2.1×104 to 1.1×105 V/cm, the threshold was lowered by approximately 0.01 eV. This reduction in threshold is much lower than predicted by a Poole-Frenkel barrier lowering model. For photon energies below the threshold, there was evidence of a photothermal process.
Temperature Changes in Thin Films during Growth by Physical Vapor Deposition. I. Theoretical
Authors: Thornburg D. D. , Wayman C. M.
Published: February 2004

A theory has been developed to determine the temperature of a thin film during its growth by physical vapor deposition in vacuo from a resistance-heated source. Three sources of heat which contribute to the film temperature are radiation losses from the source, kinetic equilibration of the condensing vapor stream, and condensation of the evaporant. By assuming planar substrate geometry, the heat equation was solved for the case in which the bottom of the substrate was held at constant temperature and the top surface was subjected to the heat flux described above. Solutions of the heat equation were obtained with the aid of an analog computer constructed during the course of the investigation. By proposing a model for substrate surface coverage as a function of time during growth, it is shown that when a metal film is deposited on substrates of high emissivity, a plot of film temperature vs time displays a maximum which can be related to deposition rate.
Thermoelectric Currents in γ-Irradiated Lucite
Authors: Murphy P. H. , Hoecker F. E.
Published: February 2004

Thermoelectric currents have been observed in thin lucite disks after exposure to γ radiation. If an electric potential difference is also impressed upon the sample during the heating cycle, the currents are enhanced or depressed depending on the magnitude and polarity of the applied voltage. The measured charge is a linear function of the applied electric field strength and the field strength necessary to completely suppress the currents appears to be more closely related to the radiation dose than to the temperature gradient in the sample during heating.
Cholesteric Films as Optical Filters
Authors: Adams James , Haas Werner , Dailey John
Published: February 2004

A new class of large-area optical filters based on the special reflection properties of cholesteric liquid crystals is described. Several filtering functions are provided by various combinations of liquid-crystal films, polarizers, and retardation plates.
Propagation of Slip across a Twist Boundary by Means of Grain-Boundary Twist-Disclination Loops
Authors: Das E. S. P. , Marcinkowski M. J.
Published: February 2004

A new mechanism is proposed by which the motion of an edge dislocation across a twist boundary can be accomplished without recourse to dislocation climb. This mechanism involves the creation of a twist-disclination loop in the plane of the grain boundary and with an angle of rotation equal to the angle of misorientation. This will bring the two grains to crystallographic match within this loop and allows the edge dislocation to slip from one grain to the other through this disclination loop. An order-of-magnitude calculation for the diameter of the loop (≈ 70 Å at θ=5°) shows that these loops can be observed within the electron microscope.
Pulse Shape of a Mode-Locked Frequency-Doubled Nd:YAG Laser
Authors: Rice R. R.
Published: February 2004

The pulse shape of a mode-locked frequency-doubled Nd:YAG laser using a single Ba2NaNb5O15 crystal for both SHG and phase modulation has been compared at 1.06 and 0.53 μm. The two pulse shapes are identical within the limits of measurement. The phase-state switches normally observed in a mode-locked Nd:YAG laser are absent under the proper operating conditions.
Extensional, Flexural, and Width-Shear Vibrations of Thin Rectangular Crystal Plates
Authors: Lee P. C. Y.
Published: February 2004

An approximate one-dimensional theory is derived for thin crystal plates or bars with narrow rectangular cross section, and for cases in which the stiffness matrix of the crystal cij referring to the plate axes exhibits monoclinic symmetry. A set of five equations of motion is separated into two groups: the extensional, width-length flexural, and width-shear motion; and the transverse shear and width-twist motion. Closed form solutions of coupled extensional, flexural, and width-shear vibration are obtained for thin rectangular plates with free edges. Calculated resonant frequencies as a function of length-to-width ratio of the plate are compared with detailed measurements by Spears on +5° X-cut quartz plates. For the use in design, explicit algebraic formulas for predicting extensional and flexural frequencies are obtained in terms of elastic stiffnesses, density, and width-to-length ratio of the plates.
Viscous Effects on Hypervelocity Impact
Authors: Whitesides J. L. , Yuan S. W.
Published: February 2004

Based on assumption that the density of the material behind the shock front varies as a power function of the radial position, the equations of motion of a viscous, compressible fluid are solved analytically for the flow field in a spherical target which is impacted at hypervelocity by a spherical projectile. Good comparisons are obtained between the present solutions for velocity distribution and normal stress and various available experimental data as well as with another theoretical solution. The influence of viscosity of the material, which is assumed to be constant, on the velocity distribution and normal stress behind the shock is found to be significant after the initial hydrodynamic stage of the impact process.
Dynamic Deformation Twinning in Shock-Loaded Iron
Authors: Johnson J. N. , Rohde R. W.
Published: February 2004

Deformation twinning has been observed in shock-loaded samples of heat-treated Ferrovac E iron at peak stresses from 3 to 16 kbar. In this range, the volume fraction of twins increases monotonically from zero to approximately 4%. In instrumented transmitted-wave measurements stress relaxation was observed behind the elastic precursor for propagation distances of 12 mm or greater, but not at smaller distances. An analytical description of dynamic deformation twinning which adequately describes experimental observations on shock-wave propagation in Ferrovac E iron is proposed. This analysis is based on models for the growth of twin platelets combined with the equation γ=kα relating the plastic strain γ to the twinning shear k and the volume fraction of twins α. Dynamic deformation twinning in impact-loaded solids appears to be fairly well established both from experimental and analytical points of view and certainly must be considered as a possible physical mechanism in the description of plastic flow at high strain rates.
Criteria of Craze Initiation in Glassy Polymers
Authors: Wang Tsuey T. , Matsuo M. , Kwei T. K.
Published: February 2004

The craze-initiation criteria for craze-prone glassy polymers are examined with a model test method. In this method a prismatic sample of polystyrene with an embedded steel ball is subjected to a simple tension until crazing takes place around the interface. Stress analysis showed that various published craze-initiation criteria will predict the appearance of the first crazes at different locations on the interface in such samples. Thus by comparing the experimental and analytical results it is possible to determine from the actual craze-initiation locations which of the existing theories is likely to explain the craze initiation. The study revealed that the principal strain criterion gave the best prediction while the dilation criterion yielded the least likely result. The polystyrene samples with an embedded rubber ball were also tested and the data compared with the analytical results. In this case all criteria predict correctly that crazing will first occur at the equator of the rubber ball, indicating that the simple tension test of rubber ball samples is not suitable for determining the dominant craze-initiation mechanism. Comparison of the crazing behavior in the rubber ball sample and the steel ball sample revealed that the crazes which developed around the rubber ball were more stable than those developed around the steel ball. The above observation may explain why harder inclusions are not as effective as rubber inclusions in toughening the glassy polymers. The incipient craze angles were examined and found to be in agreement with the general observation that the crazes form in the direction normal to the major principal stress.
Propagation of Electromagnetic Waves in a Simplified Nonlinear Gas
Authors: Fante Ronald L.
Published: February 2004

Solutions are obtained for the electromagnetic field propagating in a gas in which the electron density and electric field strength are interdependent. The solutions are specialized to study the reflection and transmission of electromagnetic waves by a nonlinear gaseous slab. For a given slab thickness we find that no matter how large we make the incident power, the transmitted power cannot exceed the finite limiting value, which can be calculated from our theory.
Mass Spectrometer Analysis Studies of Cesium Discharges
Authors: Bergman R. S. , Chanin L. M.
Published: February 2004

Ion sampling measurements have been made on cesium plasmas for normalized pressures from 10−4 to 1 Torr using dc as well as rf excitation. For dc discharges, sampling was undertaken through both the anode and the cathode. The major cesium ions observed were Cs+, Cs2+, and Cs3+. Measurements were made of the ion current ratios, I(Cs2+)/I(Cs+) and I(Cs3+)/I(Cs2+) as a function of normalized pressure. Comparison of the observed dependencies with those predicted using steady-state kinetics provides estimates of the rate coefficients of the following reactions: Cs**+Cs→ lim K2Cs2++e,K2τ≃2×10−15 cm3,Cs++2Cs→ lim βCs2++Cs,β≃1.5×10−29 cm6/sec,Cs2++2Cs→ lim γCs3++Cs,γ≃3×10−29 cm6/sec, andCs3++e→ lim α33Cs+hν3,α3≃2×10−8 cm3/sec.
Mass Spectrometric Study of Neon Afterglow Plasmas
Authors: Bhattacharya A. K.
Published: February 2004

Mass-identified measurements of the time dependence of the density of atomic neon ions in decaying plasmas are reported. The conversion of Ne+ into Ne2+ occurs by the three-body reaction Ne++2Ne→Ne2++Ne at a rate given by the rate constant K=7.7×10−32 cm6 sec−1 in good agreement with the value reported by Smith and Cromey. The measured value of mobility of Ne+ ions in neon μ0 (Ne+) = 4.0 cm2 V−1 sec−1 at a temperature of 300°K is in agreement with the values obtained by other techniques.
High-Resolution Studies of Magnetic Domains in MnBi Films
Authors: Unger W. K. , Wolfgang E.
Published: February 2004

Magnetic domains existing during the magnetization reversal in oriented low-temperature phase MnBi films have been observed at room temperature by decorating the domains with iron particles obtained and brought onto the film investigated by evaporating iron in an argon atmosphere onto the film. By making a carbon replica of the film surface, the domains can be observed electron microscopically. The resolution obtained is 0.05 μm. The domain width in a 100-nm-thick MnBi film without applied field is approximately 0.35 μm. It increases with decreasing film thickness. Before the films reach saturation, bubble domains with diameters smaller than 0.5 μm are observed. Along minor hysteresis loops, filament domain configurations are observed. The width of the filament domains decreases with increasing strength of a field applied perpendicular to the film plane. The width is approximately 0.1 μm in a 90-nm-thick MnBi film with an applied field of 344 kA/m. The wall-energy density in MnBi film is estimated to be 2×10−3 W sec/m2.
Upper-Hybrid Resonance Absorption, Emission, and Heating of an Afterglow Plasma Column
Authors: Stenzel R. L. , Gould R. W.
Published: February 2004

Microwave absorption and emission and electron temperatures of a nonuniform axially magnetized afterglow plasma column in a waveguide geometry have been investigated experimentally. Frequency ω and magnetic field ωc are chosen to satisfy the upper-hybrid resonance condition ω2=ωc2+ωp2(r), where ωp(r) is the local electron plasma frequency. Nearly perfect absorption is observed in the range of upper-hybrid frequencies, while at other frequencies the absorption coefficient is essentially zero. The sharp absorption onset at the maximum upper-hybrid frequency yields an accurate measure for the peak electron density. Density decay and profile in the plasma column are observed—the latter using a new technique. In the range of high absorption the noise emission approaches the blackbody limit. The electron temperature is measured with a radiometer and a reference noise source in a new technique yielding both spatial and time dependence without perturbing the plasma. The time resolution is obtained by a sampling technique. The spatial resolution results from the fact that upper-hybrid resonance absorption and emission are confined to a narrow resonant layer. This property is also used to heat the electrons locally and observe the thermalization process.
Large Impulses of Self-Magnetic Origin
Authors: Malliaris A. C. , Garrison R. L. , John R. R.
Published: February 2004

Two electrodes are considered in an axisymmetric configuration: a central cathode rod and a ringlike coaxial anode, with a relatively small axial displacement. This assembly is mounted on an insulated plenum, fed by a gas pulse. In coincidence, an electrical power pulse (currents up to 50 000 A, powers up to 10 MW) is delivered to the electrodes with a duration of 1 to 2 msec. It is demonstrated that, under well-defined conditions, the resulting impulse has a predominantly self-magnetic origin. Individual impulses are experimentally determined by means of angular momentum measurements of an inertial platform, free of any parasitic impulses. The experimental results are shown to be in good agreement with analytical predictions. It is found that the self-magnetic impulse is directly proportional to the time integral of the square of the current. The proportionality coefficient is shown to depend only on the anode-to-cathode ratio of radii. This coefficient is also shown to be insensitive to other details of the configuration and, especially, independent of both the kind and flow rate of the gas feed.
New Experiments with Three-Pulse Echoes
Authors: Smith R. R. , Harp R. S.
Published: February 2004

We report experiments on three-pulse echoes in rare-gas magnetoplasmas. The results are consistent with a periodic perturbation in frequency space of the electron density. If this perturbation is due to a diffusion in physical space of ``hot'' electron bands, then it is not a simple diffusion governed by electron-neutral collisions. We observe absorption and emission which are periodically modulated after the application of two short S-band pulses. The clear connection between our measurements of echo amplitudes and of emission and absorption spectra shows that these experiments will be useful tests of future three-pulse echo theories.
Optical Properties of Some Silicone Diffusion-Pump Oils in the Vacuum Ultraviolet—Using an Open-Dish Technique
Authors: Kerr G. D. , Williams M. W. , Birkhoff R. D. , Painter L. R.
Published: February 2004

The optical properties of Dow Corning-704 and -705 diffusion-pump oils have been measured from 4→24.8 eV using an open-dish technique. These are the first liquids for which optical constants have been obtained above 11.8 eV. In the region above 10.6 eV, the real part of the dielectric constant is structureless. A collective oscillation involving π and σ electrons is seen in the region between 21→25 eV. Sum rule calculations indicate approximately 130 as the effective number of electrons per molecule participating in absorption processes up to 25 eV.
Surface Energy for Brittle Fracture in Metals from Phonon Frequencies
Authors: Caglioti G. , Rizzi G. , Bilello J. C.
Published: February 2004

A new method is presented for calculating the surface energy for brittle fracture in a solid. Use is made of the knowledge of some features of the crystal dynamics as well as of the Debye, melting, and boiling temperatures of the material. Predicted values for the surface energy of a number of metals are compared with those based on the elastic theory and with the experimental ones. In particular, easy cleavage of zinc and, in contrast with recent predictions of elastic theory, the preferred plane of fracture in tungsten and beryllium are made plausible.