bluuebunny/crossref_metadata_2025 huggingface dataset:
Platinum-cobalt films for digital magneto-optic recording
Authors: Treves D. , Jacobs J. T. , Sawatzky E.
Published: February 2003

Platinum-cobalt thin films were prepared by rf sputtering with substrate biasing to contol composition. Contrary to what was expected from equilibrium bulk properties, films deposited at room temperature have the fcc structure, in-plane magnetization, and low coercivity. At deposition temperatures above about 500 °C the coercivity increases and x-ray analysis indicates some tetragonal phase. Annealing at 600 °C causes rapid conversion to the tetragonal phase. In the annealed state the films have a large component of magnetization normal to the film plane with typical remanence-to-saturation ratios of 0.8 and coercivities of 8 kOe perpendicular to the film plane. The saturation Faraday rotation of annealed films is about 5×105 deg/cm in the visible and near ir. Curie temperatures are in the range 270–430 °C for compositions with 35–44 at.% cobalt. Dynamic read-write experiments show that this material is an attractive candidate for digital magneto-optic recording. Problems due to the high Curie-point and high room-temperature coercivity are avoided by operating in a minor hysteresis loop mode.
Asymptotic expression for K-shell ionization cross section with electrons
Authors: Kolbenstvedt H.
Published: February 2003

The total cross section for K-shell ionization with electrons as given is a function of the K-shell screening parameter ϑ for target elements with Z≳13 and incident electron energies much higher than the K-shell binding energy. For an incident electron energy of 300 MeV, the cross section varies with the atomic number approximately as Z−2.55 compared to the experimental result Z−2.69.
Improved convective flow longitudinal discharge CO laser
Authors: Cohn D. B. , Griffin W. S. , Mendoza P. J.
Published: February 2003

Specific extraction efficiencies of 300 W g−1 sec−1 have been obtained with flow-stabilized electrodes in a longitudinal electric discharge CO laser, representing a 50% enhancement over previous results.
Electronic Raman scattering from Al, Ga, In, and Tl atoms
Authors: Vriens L. , Adriaansz M.
Published: February 2003

An experimental and theoretical study is made of Stokes and anti-Stokes Raman scattering from Al, Ga, In, and Tl atoms. Relative phases of 2P01/2,3/2→2D3/2 dipole matrix elements are obtained from the polarization properties of the scattered radiation. For Ga these phases are different from those obtained for Al, In, and Tl, and they are in contrast to what is expected on the basis of single configuration approximations. The experimentally determined phases are used to calculate the Raman cross sections.
Lift, drag, and guidance forces on alternating polarity magnets, using loop guideways
Authors: Lindenbaum S. D. , Lee M. S.
Published: February 2003

Exact solutions of track current, lift force, and drag force, together with their velocity dependence, have been computed for a vehicle carrying a finite number of fixed current alternating polarity superconducting magnets, suspended at various heights over structured track guideways of the single- and double-loop (’’null’’) types. Results for the double-loop case are compared with those of a previously reported approximate analysis. The analytical method is then applied to a study of a low-drag guidance loop guideway which is integrable with lift loop guideways utilizing a common set of vehicle magnets. Solutions are obtained for guidance track restoring forces, lateral destabilization forces, and lift force degradation as functions of lateral displacement from symmetry. The dependence of lift, drag, and lift-to-drag on track loop parameters is studied and the linear dependence of lift-to-drag on loop time constant confirmed. The contribution to the forces
Transmission of electromagnetic waves through stratified ferrite
Authors: Mueller R. S.
Published: February 2003

An analysis is made of the characterstics of ferrite films for normally incident electromagnetic plane waves. Four characteristic matrices are found which can be used to determine the transmission behavior. Two of the matrices correspond to circular polarization (longitudinal magnetization), while the others correpsond to perpendicular and parallel linear polarization (transverse magnetization). Formulas are presented for the reflection and transmission coefficients and Faraday rotation in lossy multilayer ferrite films. The reflectivity and Faraday rotation are evaluated for specific examples.
Observation and analysis of magnetic domain wall oscillations in Ga:YIG films
Authors: de Leeuw F. H. , Robertson J. M.
Published: February 2003

We report the observation of damped oscillations of a single straight magnetic domain wall stabilized by an externally applied field gradient in a Ga-YIG film (Y2.9La0.1Fe3.8Ga1.2O12). The measurements are performed at various field gradients, in-plane fields, and wall drive fields. We analyzed the results using the Landau-Lifshitz-Slonczewski (LLS) theory and obtained the wall width parameter Δ≡ (A/Ku)1/2 = (0.89±0.15) ×10−5 cm and the corresponding wall mass m0≡ (2πγ2Δ)−1= (5.2±0.9) ×10−11 g cm−2, where A is the exchange constant, Ku is the uniaxial anisotropy constant, and γ is the gyromagnetic ratio of the material; the Gilbert damping constant α=0.005±0.001; and the reduced Landau-Lifshitz damping constant λ/γ2= (1.3±0.3) ×10−9 Oe2 s. The wall mass according to Döring as calculated from γ, A, and Ku is m0=[2πγ2(A/Ku)1/2]−1= (8.1±0.6) ×10−11 g cm−2 and is higher than the experimental value. The observed oscillations allowed an independent determination of the magnetization of the material (4.2±0.8 G) in agreement with a direct measurement (4.8±0.5 G). In an applied in-plane field of 262 Oe the peak velocity was 530 m s−1. This value is lower by a factor of 1.6 compared to the peak velocity predicted from the LLS theory. From an observed asymmetry in the dependence of the wall oscillation frequency on the applied in-plane field we deduced that at the domain wall an effective in-plane field of 23±6 Oe is present, which is in the direction of the stray field at the film-air interface. A model of a film having two layers is proposed to explain this field. At a low in-plane field we observed a wall oscillation with a low frequency, depending on the drive field amplitude. It is not excluded that this slow oscillation is due to a wall containing Bloch lines.
Quantitative analysis of complex targets by proton-induced x rays
Authors: Reuter W. , Lurio A. , Cardone F. , Ziegler J. F.
Published: February 2003

We have explored the potential of proton-induced x-ray spectroscopy as a quantitative analytical technique to determine the composition of a homogeneous complex target. Direct production of x ray by protons in the low MeV range was considered using the binary encounter approximation and published data on the atomic number dependance of the stopping power. Also included is a correction scheme for secondary excitation processes if radiation is generated in the target capable of fluorescence excitation. The formalism of the correction scheme is closely related to the one commonly employed in electron microprobe spectroscopy. Our data indicate that the accuracy achievable in IIXS is of the order of ±5%, if one considers the two important corrections: (1) the difference in the stopping power properties of the composite target compared to the pure element target; (2) secondary excitation processes if required.
Optical absorption in Ge and Si after proton bombardment at 10 K
Authors: Stein H. J.
Published: February 2003

The first observation of annealing centered at ? 30 K for near-edge absorption in proton-bombarded Ge is reported, and direct production of the 2.4-μm band in Ge and of the 1.7-μm divacancy band in Si is shown to occur for 400-keV proton bombardment at 10 K. Annealing between 10 and 70 K has no effect within experimental uncertainties upon the 2.4-μm band in Ge or upon the proton-induced-defect absorption in Si.
Acoustic-surface-wave dispersion in periodically metallized structures
Authors: Haydl William H.
Published: February 2003

Periodically varying acoustic properties in the bulk and along the surface of a transmission medium for acoustic surface waves result in velocity dispersion with frequency. This change in the center frequency of interdigital acoustic-surface-wave filters, caused by a change in the periodic metallization pattern of the interdigital transducers, has been measured on ST quartz and YZ lithium niobate for single - and double-electrode transducers.
Broadly tunable lasers using color centers
Authors: Mollenauer L. F. , Olson D. H.
Published: February 2003

The potential of certain color centers to make efficient broadly tunable cw lasers for the infrared is discussed. We show how the range 0.9 ≲λ≲3.3 μm can be covered by using FA(II), FB(II) and F+2 centers. The pertinent physics of these centers is reviewed and appropriate laser cavity configurations are discussed. The construction and performance of an advanced FA(II) laser is reported. Finally, the possible use of color centers in distributed feedback devices is discussed.
Photoconductivity in AgInSe2
Authors: Tell B. , Hammonds E. M. , Bridenbaugh P. M. , Kasper H. M.
Published: February 2003

Photoconductivity spectra for AgInSe2 samples have been obtained which correlate reasonably well with the known band structure. Carrier lifetimes of greater than 1 msec for excitation near 1 μ have been obtained. Infrared quenching of the photoconductivity yields a center with a binding energy of 0.5 eV.
Electrical properties of nitrogen-doped GaP
Authors: Stringfellow G. B. , Hall Jr. H. T. , Burmeister R. A.
Published: February 2003

The electrical properties, namely, electron concentration and mobility, have been investigated in the temperature range from 53 to 400 K for undoped and nitrogen-doped VPE GaP. The undoped GaP has a background doping level of ND∼1017 cm−3 and NA∼1016 cm−3. The donor ionization energies vary from 49 to 74 meV and are proportional to NA1/3. These data identify the background donor to be Si. The mobility of the nondoped material is approximately 150 cm2/V s at 300 K and is dependent on ND+NA at 77 K, varying between 377 and 1263 cm2/V s. NH3 is added to the system to incorporate nitrogen into the GaP. This is found to decrease ND to ∼2×1016 cm−3 and increase the donor ionization energy. This is attributed to reaction of the volatile Si species acting as dopant with NH3 to form Si3N4, thus reducing the Si concentration in the solid. The electron mobility at 77 K is also reduced by the addition of N to the solid. This is attributed to neutral impurity scattering by the nitrogen.
Laser diagnostics using light intensity measurements for continuously emitting active media
Authors: Blanaru D. L.
Published: February 2003

The intensity of light extracted from an optical cavity is a sensitive function of the peak absorption coefficient, k0, and can be used in order to survey the evolution of k0 when the parameters of the active medium are changed during the process of laser development. This provides a means for identifying the spectral lines which may be suitable for lasing transitions and an indication of how to optimize k0 when it is still below the laser threshold. The theoretical dependence of the measured intensity on k0 is derived for continuously emitting media, arbitrary optically stable cavity configurations, and symmetric or asymmetric line profiles. The calculations show that the light intensity at an axial point is produced by those light sources which are confined in certain emission volumes within the active medium determined by the diaphragming conditions of the measuring system. Two basic measurement modes were identified according to whether the emission volumes are controlled (a) by the mirror apertures or (b) by an adjustable external diaphragm. The latter measuring mode is independent of all cavity geometrical parameters, and the experimental test which confirmed this conclusion indicates that the absolute error in the measurement of k0d, where d is the active medium length, is 0.015 for small absorptions and for cavity losses lower than 12% per round trip.
Oscillations in MOS tunneling
Authors: Lewicki G. , Maserjian J.
Published: February 2003

Oscillatory deviations from classical Fowler-Nordheim tunneling were measured in MOS capacitor structures with dry oxides ranging in thickness from 30 to 75 Å. The silicon was p type, the metallization chrome-gold, and the direction of tunneling that corresponding to electrons being injected from the metal into the SiO2 conduction band. The observed variation of oscillation phases and amplitudes with oxide thickness suggests the following conclusions. The Si-SiO2 interface is independent of oxide thickness only for thicknesses greater than 65 Å. At lower thicknesses, the barrier height at the interface decreases slowly with oxide thickness at a rate on the order of 10 mV/Å. At higher thicknesses, the barrier height is 4.08 eV. The interface is abrupt to within a few angstroms. The energy dispersion relationship within the SiO2 conduction band is parabolic, at least up to 3 eV above the band edge, with an effective-mass–to–free-electron-mass ratio of unity. The mean free path within the SiO2 conduction band is on the order of 13 Å.
Measurements of SO2 absorption coefficients using a tunable dye laser
Authors: Thompson Jr. R. T. , Hoell Jr. J. M. , Wade W. R.
Published: February 2003

High-resolution measurements of SO2 absorption coefficients in the uv are presented in the wavelength interval between 2962 and 3011 Å using a frequency-doubled dye laser as the radiation source. These measurements have application to pollution monitoring of SO2 using the differential absorption scattering (DAS) technique. The spectral resolution of the measurements was 0.2 Å (determined by the linewidth of the dye laser) and the generated spectra exhibited considerable rotational structure on the (000) ″ to (060) ′, (070) ′, and (080) ′ electronic-vibrational transitions. The latter transitions correspond to center wavelengths of 3001.8, 2981.0, and 2962 Å, respectively. The laser measurements were obtained with a signal-processing technique which eliminated calibration procedures associated with conventional optical-absorption measurements. Using this technique, the statistical uncertainty associated with measured absorption coefficients has been reduced to less than ±2% with a wavelength uncertainty of the laser source of ±0.1 Å.
Nonlinear stability of spin-flip excitations
Authors: Arunasalam V.
Published: February 2003

A rather complete discussion of the nonlinear electrodynamic behavior of a negative-temperature spin system is presented. The method presented here is based on a coupled set of master equations, one describing the time evolution of the photon (i.e., the spin-flip excitation) distribution function and the other describing the time evolution of the particle distribution function. It is found that the initially unstable (i.e., growing) sping-flip excitations grow to such a large amplitude that their nonlinear reaction on the particle distribution function becomes important. It is then shown that the initially totally inverted two-level spin system evolves rapidly (through this nonlinear photon-particle coupling) towards a quasilinear steady state where the populations of the spin-up and the spin-down states are equal to each other. Explicit expressions for the time taken to reach this quasilinear steady state and the energy in the spin-flip excitations at this state are also presented.
Spectroscopic measurements on a high-pressure Na-Xe discharge and comparison with a nonequilibrium calculation
Authors: Waszink J. H.
Published: February 2003

The spectral intensity distribution has been measured of the optically thick 32P0-32S and 32D-32P0 Na lines, emitted from a high-pressure Na-Xe discharge (axis temperature 4200 K, Na pressure 270 Torr, Xe pressure 170 Torr). The results are compared with those of a nonequilibrium calculation. The axis temperature and the Na pressure have been derived from a fit of the calculated to the measured spectrum of the 32P0-32S lines. The resulting data yield a calculated spectrum of the 32D-32P0 lines which is in agreement with experiment, within the limits of error. The 42S, 32D, and higher levels are not taken into account in the model. As a result, the calculated electric field is too low by about 25%.
Ferroelastic behavior of NdxLa1−xP5O14 crystals
Authors: Budin J. P. , Milatos-Roufos A. , Duc Chinh Nguyen , Le Roux G.
Published: February 2003

Ferroelastic behavior has been observed in NdxLa1−xP5O14 single crystals. In this paper experimental emphasis is on the x=0.75 composition. In these crystals, which belong to the monoclinic space group P21/c-C52h at room temperature, twinning is present and it gives rise to surface deformations. These have been studied by an optical method. The domains have also been studied by observation between crossed polarizers and by x-ray diffraction techniques. The ferroelastic nature of the twinning is demonstrated by the ability to alter the domain pattern by a small shear stress of suitable orientation. The domain structure vanishes at 141±2 °C. Above this temperature the crystals are most likely orthorhombic with space group Pncm-D72h (conventional setting Pmna). The characteristic ferroelastic parameter, the spontaneous strain, is a pure shear in the (010) plane, amounting to 4×10−3 at 20 °C. The temperature dependence of this strain indicates a second-order transition, in agreement with differential thermal analysis results. Besides the NdxLal−x ultraphosphates in the range x=0 to x=1, many other crystals such as the rare earth (La through Tb) and Bi ultraphosphates can be expected to behave in a similar manner.
Ionic motion in β-PbF2
Authors: Schoonman J. , Ebert L. B. , Hsieh C-H. , Huggins R. A.
Published: February 2003

A nuclear magnetic resonance and ionic conductivity study has been made of ionic motion in polycrystalline MnF2-doped β-PbF2. Narrowing of the 19F steady-state resonance line begins near room temperature and above about 400 K the line is fully narrowed. Analysis of the temperature dependence of the NMR linewidth gave an activation enthalpy for F− ion motion of 0.59–0.63 eV, the conductivity measurements gave 0.68 eV. These values are in good agreement with reported conduction activation enthalpies for single crystals over the temperature range involved, but are slightly greater than the value previously reported as obtained from conductivity data on pressed pellets.
Ferroelectric field-effect memory device using Bi4Ti3O12 film
Authors: Sugibuchi K. , Kurogi Y. , Endo N.
Published: February 2003

A ferroelectric field-effect transistor has been investigated using a thin film of bismuth titanate (Bi4Ti3O12) deposited on a Si substrate by rf sputtering. Achievement of the ferroelectric polycrystalline Bi4Ti3O12 films without any cracks necessitates postdeposition heat treatment in air at temperatures ?550 °C for 30 min. The film, heat treated at 650 °C, has a remanent polarization of 4.0 μC/cm2 and a coercive field of about 250 kV/cm at 1 kHz. A FET having a gate structure of Bi4Ti3O12-SiO2-Si was fabricated, where the SiO2 served to prevent charge injection from Si into the ferroelectric film. (This process would degrade the retention of memorized states.) The FET can be switched by voltages of as low as 15 V applied to the gate. The on and off states are very stable at room temperature.
Tracer mobility by a divacancy mechanism in an fcc lattice
Authors: Stark J. P.
Published: February 2003

The mobility and the diffusivity of a solute tracer are calculated by using the matrix defect walk equation of Manning and Stark for the case in which the defect moving the tracer is a divancancy that may dissociate. Calculations show that the ratio of mobility to diffusivity is insensitive to the dissociation of the divacancy. Thus, the effective heat of transport for thermomigration is the sum of contributions from tracer motion by single vacancies and by bound divacancies. A closed form for the heat of transport of a tracer by bound divacancies is determined. Tabulations are given for the instance of a mixed diffusion mechanism by single vacancies and divacancies.
Elastic and piezoelectric properties of lead potassium niobate
Authors: Yamada Tomoaki
Published: February 2003

All the elastic and piezoelectric constants of ferroelectric lead potassium niobate were measured by the use of the thickness vibrations of plates. Calculating the electromechanical coupling factors of rotated cuts, it was shown that the y-cut plate has the largest coupling factor of 0.73 for the shear mode and the z-cut plate has the largest coupling factor of 0.59 for the extensional mode. If the piezoelectricity arises from the effect of each oxygen octahedron, the metal ions seem to displace parallel to one of the 4mm axes of the oxygen octahedron within the tetragonal c plane.
Decay instabilities near the hybrid resonances in a plasma with two species of ions
Authors: Chan V. S. , Seshadri S. R.
Published: February 2003

The decay instabilities near the hybrid resonances in a homogeneous plasma with two species of ions and permeated by a uniform magnetostatic field are investigated for the case in which an ordinary mode is the pump wave. The extraordinary mode consists of four branches, namely, a high-frequency branch, an intermediate-frequency branch having a resonance at the upper hybrid resonant frequency, and two low-frequency branches having resonances at the first lower hybrid resonant frequency and the Buchsbaum two-ion hybrid resonant frequency, respectively. The ordinary mode can couple only with the intermediate frequency branch and the two low-frequency branches of the extraordinary mode in the presence of the pump. These couplings result in decay instabilities if the interacting waves propagate in opposite directions. Numerical results are presented to illustrate the characteristics of the parametrically excited instabilities near the first lower hybrid resonant frequency and the Buchsbaum two-ion hybrid resonant frequency. The dependences of the maximum growth rates of these instabilities on the strength of the magnetostatic
Thermalization of a spark discharge
Authors: Hill R. D.
Published: February 2003

A thermalization process that depends on both localized and channelized Ohmic heating of a plasma in a spark discharge is proposed. A satisfactory quantitative description of a spark current pulse observed in a recent experiment by Barreto, Reynolds, and Jurenka is given in terms of the proposed process.
Solid-phase epitaxial growth of Si through palladium silicide layers
Authors: Canali C. , Campisano S. U. , Lau S. S. , Liau Z. L. , Mayer J. W.
Published: February 2003

Epitaxial growth of 4000- to 9000-Å-thick Si layers has been obtained by solid-phase transport through Pd silicide layers. The structures were formed by evaporating Si on Pd deposited on 〈100〉 Si substrates. The transport and growth of Si were stuided by SEM and MeV 4He+ backscattering and channeling effect measurements. The structures were initially heated to 280 °C to form Pd2Si and subsequently heated to temperatures between 500 and 600 °C to obtain transport of Si. At 500 °C the transport rate of Si through the silicide layer is about 15 Å/min. Pd inclusions are found in the grown Si layer. The amount of Pd can be reduced by use of slow hearing between 280 °C and the transport temperature. Channeling measurements showed that the Si layers are well ordered and epitaxial with the underlying 〈100〉 substrate.
An averaging method for the shear modulus and Debye temperatures of cubic solids
Authors: Verma J. K. D. , Aggarwal M. D.
Published: February 2003

A new empirical method of averaging the shear modulus is proposed. The elastic Debye temperatures ϑ calculated for a number of cubic elements and semiconducting compounds have been found to be in excellent agreement with the corresponding computationally exact ϑ. The computed shear modulus is also in good agreement with the observed polycrystalline data.
Neutron-diffraction section topography: Observing crystal slices before cutting them
Authors: Schlenker M. , Baruchel J. , Perrier de la Bâthie R. , Wilson S. A.
Published: February 2003

The possibility of visualizing crystal defects within single crystals several centimeters thick by neutron-diffraction section topography is demonstrated. The technique consists in photographically recording the Bragg-diffracted beam produced by the crystal from a narrow incident neutron beam; in effect it amounts to investigating a slice of the specimen without cutting it. Subgrain boundaries and inclusions were visualized inside an as-grown cylindrical crystal of Fe-3% Si, 2 cm in diameter. The slice corresponding to the investigated region was subsequently cut out and studied by x-ray diffraction topography, yielding positive identification of the subgrain structure observed on the neutron topographs before cutting. By using a Polaroid camera with a sensitive neutron scintillator, the gross features of the subgrain structure can be obtained in minutes. The orientation of the virtual slice is predetermined at will; by making several section topographs the complete subgrain structure of the crystal can be investigated nondestructively.
High-frequency dielectric measurements on electro-optic single crystals
Authors: Teague J. R. , Rice R. R. , Gerson R.
Published: February 2003

A slotted line was used to measure the high-frequency dielectric constant and loss tangent of several electro-optic crystals useful for wide-band laser modulator applications. Dielectric measurements were made at 0.1, 0.3, 1.0, and 2.0 GHz.
Electromagnetic surface-wave interactions with a semi-infinite single stream of plasma
Authors: Yasumoto K.
Published: February 2003

The characteristics of an electromagnetic surface wave interacting with a semi-infinite single stream of a cold collisionless plasma are investigated by taking the plasma as a moving deformable polarized medium. The surface-wave dispersion equation shows the coupling of four waves, which are, approximately, the fast and slow space-charge waves in the plasma stream and the two waves in the free space whose phases progress in the same and opposite directions to the plasma stream. Compared to the analysis which has regarded the plasma stream as an equivalently stationary anisotropic plasma, the surface waves show drastically different characteristics. It is shown that there are no instabilities of the surface waves for any drift velocity of the plasma.
Threshold for the thermoplastic frost instability
Authors: Matthies D. L. , Johnson W. C. , Lampert M. A.
Published: February 2003

A quantitative theory is presented for the voltage threshold of the frost instability in thermoplastic films. This theory was experimentally tested, using polystyrene films, under a wide variety of conditions, including a large range of film thicknesses, as wide a range of temperatures as was permitted by the material, and two complementary modes, namely, a heat-and-charge mode and a charge-and-heat mode. Satisfactory agreement between theory and experiment was obtained.
Ionic polarization and electronic conduction in carbon-black-filled polyvinylchloride
Authors: Reboul Jean-Pierre
Published: February 2003

Extended space-charge distributions, near contacts, have been detected by voltage distribution measurements on samples of carbon-black-filled PVC, under applied dc voltage. The resulting variable screening would be responsible for the large discrepancies from Ohm’s law observed in such materials. An ionic contribution to the space-charge distribution near the contacts is suggested by anomalous current variations under rapid changes of temperature; such current variations would be connected with the ion transit times and a method for determining the mobility of the ions is deduced. However, the ionic contribution to current transport is not predominant. This is shown by the current response to voltage pulses which suggests, rather, an electronic current in the body of the material and local ionization near the contacts.
Experimental and theoretical electron-beam-sustained CO2 laser output at ∼200 and ∼300 °K
Authors: Douglas-Hamilton D. H. , Feinberg R. M. , Lowder R. S.
Published: February 2003

A six-temperature kinetic model of the He : He2Co2 : N2 : CO laser system is developed, in which five temperatures describe the vibrational excitation of the three CO2 modes, N2, and CO, while the sixth refers to the kinetic temperature. Theoretical predictions of gain and laser output are compared with experiments performed on an electron-beam sustainer laser used at atmospheric pressure. Gain and laser measurements have been made with initial gas temperature near 200 and 300 °K. A stable discharge can be produced in this type of laser in gas mixtures containing no He, and successful electric laser operation has been demonstrated using H2 as CO2ν2 deactivant. Various gas mixtures have been investigated experimentally and theoretically; specific output J≳100 J/liter atm was obtained both in He : N2 : CO2 : H2 3 : 2 : 1 : 0 and 0 : 3 : 1 : 0.08, with efficiencies near 30%. While the gain measured appears to peak later and decay later than predicted, in all laser output measurements there is good agreement between theoretical prediction and experiment.
Positron annihilation in AgBr microcrystals
Authors: Kelly T. M. , Quick N. R.
Published: February 2003

Positron decay rates have been measured in pure silver bromide microcrystals subjected to various surface treatments before and after exposure. Two distinct decay rates are observed in most samples. The results show no difference between the positron decay spectra in microcrystals exposed to uv light relative to unexposed samples, indicating that the chemical transitions induced on the surfaces of silver halide grains by the photographic process are in too low concentration to be detectable by the positron-lifetime technique.
Operating characteristics of thin-film rf-biased SQUID’s
Authors: Falco C. M. , Parker W. H.
Published: February 2003

Operating characteristics of rf-biased thin-film SQUID’s of diameter as large as 1 cm are reported. Observation on these SQUID’s have experimentally verified several of their conventionally assumed properties such as the dependence of the quantum interference signal on critical current of the weak link, total inductance of the SQUID, inductive coupling between drive coil and the SQUID, and random magnetic flux noise. A simple technique of lowering the inductance, and hence increasing the signal, of large-diameter SQUID’s is reported.
Scanning for ferroelectricity in polycrystalline materials
Authors: Litt M. , Hsu Che-hsiung , Basu P. , Aharoni S. M.
Published: February 2003

The dielectric behavior of polycrystalline pellets of 2-alkyl benzimidazoles are reported in this paper. The experimental technique consists of measuring the dielectric constant of a polycrystalline pellet as a function of temperature. Dielectric anomalies were found for which the position of the dielectric and loss-tangent peaks were independent of frequency, which showed a solid/solid first-order transition. When the sample dropped through the transition temperature, reversible charge storage showed poling of the sample, and therefore implies possible ferroelectric behavior. The experimental procedure was validated on thiourea, a known ferroelectric. 2-ethyl benzimidazole showed the same phenomena at a transition temperature of about −90 °C and is probably a new ferroelectric material.
Multiple reflections of electrons and the possibility of intense positive-ion flow in high ν/γ diodes
Authors: Prono D. S. , Creedon J. M. , Smith I. , Bergstrom N.
Published: February 2003

Variations of the nature and pressure of the background gas used for neutralizing the charge of a relativistic electron beam have been observed to alter the current waveform of the propagating beam, the time delay before propagation begins, and the voltage and current waveforms of the diode which accelerates the beam. This interaction between the beam region and the diode occurs during the delay phase before beam propagation begins and can be explained by (1) the reflection of electrons back into the diode from a virtual cathode which exists in the beam region during the delay phase and (2) the flow of a significant positive-ion current in the diode during this same period. A theory describing positive-ion flow in the presence of multiply reflected electrons is developed and compared to experimental observations.
Accuracy of the Leontovich boundary condition for continuous and discontinuous surface impedances
Authors: Alexopoulos Nicolaos G. , Tadler George A.
Published: February 2003

The accuracy of the Leontovich boundary condition is estimated for discontinuous impedance surfaces. This is accomplished by comparing the exact solution of a given canonical problem with the Leontovich boundary condition solution. The case of a circularly symmetric cylindrical cross section is considered. The cylindrical cross section can be composed of electrically similar or dissimilar materials so that a continuous or discontinuous surface impedance can be simulated. The index of refraction is chosen as an arbitrary parameter so that a wide range of surface impedances is included. In addition, the radius of the cylinder with respect to wavelength (i.e., ka) is varied to investigate the effect of curvature on the accuracy. Both magnetic line sources and H polarized plane waves are used to illuminate the surface. The error curves which are obtained represent the worst error situation for the chosen problem. One of the significant conclusions from this investigation is the observation that the error is largest at resonance.
Augmentation of heat transport in laminar flow of polystyrene suspensions. II. Analysis of the data
Authors: Ahuja Avtar Singh
Published: February 2003

It has been experimentally demonstrated in the preceding paper, I, that heat transport is augmented in the laminar flow of suspensions of 100- and 50-μ polystyrene spheres. The augmentation has been seen to be as much as 200% and depends on the shear rate and several other parameters. Here the experimental data are analyzed by proposing a model based on the particle rotations and the entrained fluid, and by presenting similarity arguments. It is shown that the augmentation in heat transport resides in the inertia of the entrained fluid rotating with the particle which is manifest in two parameters, namely, Reynolds (ωa2/νf) and Peclet (ωa2/αf) numbers, where ω is the angular velocity of the particle, a is the radius of the sphere, and νf and αf, respectively, are the kinematic viscosity and the thermal diffusivity of the suspending fluid. The other parameters on which the augmentation in heat transport depends are the particle volume fraction, tube-radius–to–particle-radius ratio, tube-length–to–particle-diameter ratio, and the doublet collision frequency ratio which is the cube of the ratio of the particle radius to 50 μ (taking a sphere of diameter 100 μ as a reference particle). Based on the experimental data, a relationship between the augmentation in the thermal conductivity of the flowing suspensions and the various parameters is proposed.
Comparison of the low-temperature crystallization of glasses in the ternary systems H2O-NaCl-dimethyl sulfoxide and H2O-NaCl-glycerol
Authors: Cocks F. H. , Hildebrandt W. H. , Shepard M. L.
Published: February 2003

Differential thermal analysis studies have resulted in quantitative evaluation of the transformation kinetics of unstable glassy phases formed during cooling of solutions from equivalent isoplethal sections in the H2O–NaCl–dimethyl-sulfoxide (DMSO) and H2O-NaCl-glycerol ternary systems. These ternary systems are of particular importance in the field of cryobiology, where knowledge of glassy phases may be especially crucial for long-term storage of biological materials at cryogenic temperatures. Activation energies for devitrification of glasses in both systems have been determined to be approximately 13 kcal/mole. The glasses were found to have approximately equal long-term stabilities. The DMSO-containing glasses appear to be more complex than glycerol-containing glasses because of the occurrence of a relatively high-temperature ternary eutectic reaction. The study of these systems appears to be a unique area for the cooperation of physical and biological scientists.
Control of binary gas mixtures by a pneumatic method
Authors: Nishi R. Y. , Kuehn L. A. , Stubbs R. A.
Published: February 2003

This paper describes a pneumatic method for the regulation and measurement of the composition of a binary gas mixture. It consists of a series combination of a nonlinear viscous pneumatic resistor (e.g., an elongated capillary tube) and a linear pneumatic resistor (e.g., a porous membrane) connected between a binary gas source and a gas sink with a measuring or regulating element responsive to pressure at the junction between the two resistors. Junction pressure varies as a function of the mean molecular weight of the gas passing through the junction and thus if two gases of dissimilar molecular weights are mixed, a reading of junction pressure can be used to determine the relative amounts of the two gases in the mixture, or the pressure can be used directly in an apparatus for regulating the composition of the mixture.
A multiply-pulsed double-pass laser schlieren system for recording the movement of shocks and particle tracers within a shock tube
Authors: Dewey J. M. , Walker D. K.
Published: February 2003

A system has been developed for the photographic study of the flows produced by nonplanar shocks generated in a shock tube. An array of particle tracers is injected into the flow being examined and the movement of the tracers, as well as the shock fronts, is recorded using a double-pass schlieren system. A repetitively pulsed ruby laser, synchronized with a high-speed 16-mm framing camera, is used as a light source. Analysis of the photographic record yields the time and space variation of the physical properties of the observed flow field.
Relative signs of forbidden nonlinear optical coefficients
Authors: Crane G. R.
Published: February 2003

Interference methods of determining signs of nonlinear optical coefficients have been extended to cover orthogonal second-harmonic waves. The method uses an external polarizer to induce interference between orthogonal waves. The method may also be used to determine the absolute orientation of some crystals. The sign of the Kleinman forbidden coefficient d14 for α-quartz is found to be the same as that of the allowed coefficient d11.
The coupling of light-emitting diodes to optical fibers using sphere lenses
Authors: Abram R. A. , Allen R. W. , Goodfellow R. C.
Published: February 2003

The use of a truncated sphere of high-refractive-index material is proposed as a lens designed to improve the coupling efficiency between a light-emitting-diode source and an optical fiber. A method of calculating the coupling efficiency for such lens systems is described. Numerical results for the variation of efficiency with lens parameters are presented and discussed for coupling to a fiber bundle with a numerical aperture of 0.14. Improvements of two orders of magnitude in the coupling efficiency over that attainable with the close coupling geometry are predicted.
Fast acousto-optic lens Q switch
Authors: Scott M. L. , Jernigan J. , Hutcheson L. , Gould D.
Published: February 2003

A fast acousto-optic Q switch has been demonstrated which relies on a linear FM pulse of acoustic energy to act as a moving lens. While one corrdinate of the focus of the lens is fixed by the rate of frequency sweep, the other coordinate is ’’swept’’ in time by the frequency variation of the pulse. The on time of the switch is proportional to the reciprocal of the pulse bandwidth. Experiments have been conducted which verify the characteristics of this technique. A TeO2 Bragg cell was used in a successful attempt to Q switch a Nd/YAG laser with the acousto-optic lens approach.
Analysis of the laser velocity interferometer
Authors: Goosman D. R.
Published: February 2003

A rigorous description is presented for the interference of two light beams which have undergone different time delays after reflection from a moving mirror. Conditions relating the optical delay and the motion of the mirror are given that must be satisfied for the usual velocity-interferometer relations to be valid.
The oxidation of Cs—uv photoemission studies
Authors: Gregory Paul E. , Chye Patrick , Sunami Hideo , Spicer W. E.
Published: February 2003

The oxidation of cesium has been studied using ultraviolet photoemission spectroscopy. Upon exposure of a fresh cesium film to oxygen, a very narrow peak appears in the energy distribution curves (EDC’s) about 2.6 eV below the Fermi level Ef and grows with increasing exposure. This peak is associated with oxygen ions dissolved in the cesium metal below the surface. After 3×10−5 Torr sec of exposure, additional structure begins to appear. This is associated with the precipitation of cesium oxides. The structure associated with the oxides changes with increasing oxygen exposure indicating the appearance of different oxides. The oxide penetrates appreciably to the surface only after strong oxide buildup has taken place beneath the surface. A sharp minimum of 0.7 eV is found in the work function over a relatively small range of oxygen exposure.
Multiple ligand substitutions in nonlinear optical materials
Authors: Bergman J. G. , Crane G. R.
Published: February 2003

By replacement of three of the tetrahedrally distributed oxygens in MoO4= (Td) by sulfurs to obtain MoOS3= (C3v), we have substantially increased both the optical anisotropy (tenfold increase) as well as the dipolar related nonlinear coefficients (fifty-fold increase). The oxysulfide ion was studied in the form K2MoOS3⋅KCl. The nonlinear optical coefficients, relative to d11 of quartz, are (d33=±16.5, d31=∓3.8; d32=∓3.1).
Low-loss optical waveguides in single layers of Ga1−xAlxAs
Authors: Jensen S. M. , Barnoski M. K. , Hunsperger R. G. , Kamath G. S.
Published: February 2003

Waveguiding has been experimentally observed in single layers of Ga1−xAlxAs grown on GaAs substrates, with absorption coefficients of α=0.17 cm−1 at 1.15-μm wavelength and α=1.5 cm−1 at 0.93 μm. By exploiting a gradient and a peak in the Al concentration, profile waveguiding can be obtained, in contrast with the case of a layer with a uniform Al concentration which would not support guided modes because of the higher index of refraction in the GaAs substrate.
Detection of surface nitrogen in high-T
c Nb3Ge films by Auger analysis
Authors: Shen L. Y. L.
Published: February 2003

Auger electron spectroscopy was applied to Nb3Ge films that possessed Tc’s above 20 K. The surface composition was determined from the Auger spectra. A considerable amount of nitrogen was detected on the surface. This amount, which varied by a factor of 3 across the surface, was 100 times higher than the nitrogen concentration in the film. The discrepancy is tentatively assigned to the effect of argon-ion sputter cleaning prior to the Auger measurements.
X-ray powder diffraction at low temperature applied to the determination of magnetoelastic properties in terbium iron garnet
Authors: Sayetat F.
Published: February 2003

An x-ray powder diffraction apparatus has been built to perform experiments between 2.6 and 350 K. The experimental procedure and the data analysis allow the measurement of small lattice distortions and very small parameter variations with a good accuracy. Relative variations of the crystal parameters of terbium iron garnet, with an accuracy up to 10−5, have been observed at low temperature. A very small lattice distortion has been determined: TbIG becomes rhombohedral below 100 K; at 4.2 K the rhombohedral angle of the distorted cell is αR=89°52′30″, while the cell side is slightly contracted. A noncollinear spin arrangement, an anomalous thermal expansion (Δa=28×10−4 at 4.2 K), and a rhombohedral distortion (β=90°−αR=7′30″ at 4.2 K) appear simultaneously at about 45 K. These phenomena are to be connected with a very large magnetostriction (λIII=2400×10−6 at 4.2 K).
Interference phenomenon in optical transition radiation and its application to particle beam diagnostics and multiple-scattering measurements
Authors: Wartski L. , Roland S. , Lasalle J. , Bolore M. , Filippi G.
Published: February 2003

The optical transition radiation emitted by electron-irradiated aluminum, silver, gold-coated plates, and self-supported aluminum and Mylar films has been investigated experimentally. The investigation was made with an electron beam incident at 45 °, having a mean intensity of 1 μA, and an energy which was varied from 35 up to 72 MeV (68.5<γ<140.9). The study of the angular distribution and degree of polarization has shown that the high-directivity radiation is emitted around the direction of specular reflection and that the contribution of the optical bremsstrahlung is negligible. When two parallel foils are used, the resulting angular distribution exhibits an oscillating behavior arising from the interference of the fields emitted at both interfaces. This interference phenomenon is strongly related to the so-called formation zone in a vacuum, introduced by Garibyan. The intensity of light integrated in a small aperture at the center of the interference pattern presents a strong γ dependence (of the form γ8) which was exploited in the optimization of the phase adjustment of the electron bunches in the accelerating sections of the machine. In such a device using the interference phenomena in transition radiation, the possibility of measurements of the beam energy with a precision of about 1% has also been shown. On the basis of the visibility of fringes, the angular spread of the electron beam and the mean-square scattering angle in a given material were also estimated.
A third-order adiabat for solids at high pressure
Authors: Huang Y. K.
Published: February 2003

This paper seeks to establish a new isentrope in the form of a generalized Murnaghan equation, by fitting its parameters with compressibility constants which are accurate to the third order. Such an isentrope corresponds also closely to the generalized shock adiabat of an earlier investigation by the author. Inasmuch as few third-order compression data and equations are available in the literature, this work is meant to provide one using reliable data and results from shock compression of solids.
Silicon-doped gallium arsenide antimonide electroluminescent diodes emitting to 1.06 μm
Authors: Brierley S. K. , Fonstad C. G.
Published: February 2003

We report efficient room-temperature emission to 1.06 μm from silicon-doped gallium arsenide antimonide electroluminescent diodes fabricated in GaAs1−xSbx layers grown on GaAs substrates in a single-step LPE growth from melts containing from 0.1 to 1.1 at.% Si. The spectral half-width of the emission is 42.5 nm at 0.96 μm and 79 nm at 1.06 μm.
Note on the elastic properties of zircon
Authors: Sirdeshmukh D. B. , Subhadra K. G.
Published: February 2003

VRH moduli, compressibility, Debye temperature, and Grüneisen constant of zircon are evaluated from three sets of elastic constants available in literature. The values of the compressibility, Young’s modulus, Debye temperature, and Grüneisen constant derived from the three sets are subjected to a critical examination. It is concluded that the elastic constants of zircon reported by Ryzhova et al. and by Ozkan et al. are physically realistic as against the values reported by Bhimsenachar and Venkataratnam.
Real-time visualization of standing acoustic waves
Authors: Bridoux E. , Rouvaen J. M. , Bruneel C. , Torguet R.
Published: February 2003

Acoustic standing waves have been visualized using a real-time acousto-optic technique. Some experimental results are given in this communication.
Homogeneity of solution-grown AlxGa1−xP alloys
Authors: Sonomura H. , Nanmori T. , Miyauchi T. , Tsunasawa E. , Yamanaka K.
Published: February 2003

Homogeneity of the AlxGa1−xP alloy, with x=0.54, which is synthesized from Ga-rich Al-Ga-P solution is studied. The crystals obtained from the same solution have nearly the same composition factor. Electron-beam microprobe x-ray microanalysis indicates that Al distribution in an individual crystal is also almost constant.