bluuebunny/crossref_metadata_2025 huggingface dataset:
Bandfilling in liquid phase epitaxial InP-In1−xGaxP1−zAsz-InP quantum-well heterostructure lasers
Authors: Rezek E. A. , Vojak B. A. , Holonyak N.
Published: February 2003

The bandfilling and gain behavior of thin (Lz∼400 Å) In1−xGaxP1−zAsz (x∼0.13, z∼0.29) layers imbedded in InP p-n junctions, or on one side of the active region of regular quaternary double heterojunctions (x∼0.09, z∼0.20), are described. Bandfilling and spontaneous emission are observed from the quaternary quantum-well band edge to the band edge of the InP confining layers (ΔEg∼245 meV, 77 K). Laser operation on confined-particle transitions can be observed in the range 0<hν−Eg(InGaPAs) ≲ (2/3) ΔEg. The reduced gain of a quantum-well heterostructure is demonstrated by comparison with the behavior of conventional quaternary double heterojunctions (active layer ≳0.1 μm) grown from the same set of LPE melts. To operate as lasers quantum-well heterostructures are shown to require greater diode lengths and higher excitation currents, consistent with large bandfilling (in a thin layer) leading to a large spectral spread in the recombination radiation. These effects are demonstrated also on quaternary double heterojunctions of standard active-layer thickness (≳0.1 μm) but modified with the inclusion of a quantum well on one side of the active region.
Intensified CCD readout system for ultrafast streak cameras
Authors: Cheng J. C. , Tripp G. R. , Coleman L. W.
Published: February 2003

The ultrafast streak camera is presently the only comprehensive temporal diagnostic tool available for laser-fusion studies. An internally emplaced CCD readout system has been designed to minimize the data reducing complexity, cost, and time delay associated with the present phosphor/intensifier/film readout technique. Experimental results using the front-illuminated Fairchild 202 CCD and the back-illuminated RCA SID 52501 CCD for direct imaging of the streak-camera photoelectrons are presented. The important sensor requirements which optimize the performance of the CCD in the streak-camera application have been defined.
The asymmetric deformation of GaAs single crystals
Authors: Booyens H. , Vermaak J. S. , Proto G. R.
Published: February 2003

The deformation of Si-doped GaAs single crystals with a carrier concentration of 1018 cm−3 was investigated by determining the stress/strain relationships for α and β bending at 500 °C. Marked differences were found between the α and β deformation curves. Using Gilman and Johnston’s model for dislocation multiplication and combining it with a linear relationship between the dislocation velocity and applied stress, a theoretical model was developed to explain the above-mentioned differences in terms of dislocation mobilities μ, dislocation multiplication factors C, activation stresses τa, and the initial densities of dislocation sources ρ0. Applying a numerical curve fitting procedure to the experimental curves, these parameters were found to have the following values for α and β bending, respectively: μα=8.5×10−12 and μβ=3.8×10−12 cm3 dyn−1 sec−1; Cα=89 and Cβ=130 cm−1; τaα=2.11×108 and τaβ=2.7×108 dyn cm−2; ρ0α=9×105 and ρ0β=4.5×102 cm−2.
Emission and gain studies of the Tl-Hg excimer
Authors: Chilukuri Santaram , Nayfeh Munir H.
Published: February 2003

The pressure and temperature dependence of the Tl-Hg excimer emission in the visible from an rf excited discharge has been studied. The gain of the system in the blue band at 4585 Å is probed with an Ar-ion laser. With gain sensitivity limited to 1/2% due to beam steering and defocusing effects, the system has no gain.
The effect of heating upon the optical properties of gaseous sulfur hexafluoride
Authors: Thomason William H. , Elbers Don C. , Macomber James D.
Published: February 2003

A gas cell containing SF6 was irradiated with pulses of infrared radiation from a CO2 laser. The time dependence of the transmittance of this cell is explained theoretically by means of a combination of saturation and heating. Heating effects are important even at SF6 pressures below 130 Pa. Intermolecular transfer of vibrational energy must play a major role in delocalizing the heating at pressures below 110 Pa. The transmittance of SF6 gas irradiated by a chopped CO2 laser beam depends upon the width and spacing of slots in the chopper wheel and upon the rotational frequency of the wheel.
A subpicosecond dye laser directly pumped by a mode-locked argon laser
Authors: Ferguson A. I. , Eckstein J. N. , Hänsch T. W.
Published: February 2003

We report on a mode-locked cw dye laser which reliably produces light pulses as short as 850 fsec. Short-pulse operation depends critically on the stability and spectral purity of a frequency synthesizer which generates the radio-frequency signal for the acousto-optic mode locker of the argon pump laser. The regular axial mode spectrum of the dye laser extends over 500 GHz and can provide an accurate calibration scale for the spectroscopic measurement of large frequency intervals. The high stability of the locked modes has been demonstrated by observing Doppler-free multiple-pulse two-photon spectra of the sodium 3S-5S transition linewidths as narrow as 4MHz.
RDF analysis for the degree of interchain ordering in amorphous solid polyethylene
Authors: Yoda Osamu , Kuriyama Isamu , Odajima Akira
Published: February 2003

The differential radial distribution function (DRDF) of solid polyethylene amorphized by γ irradiation has been derived from the measurements of x-ray diffuse scatterings. The first halo in the intensity distribution has been found to play the most important role on the degree of interchain ordering. The existence of interchain ordering which reaches as far as ∼20 Å has been proved in the amorphized polyethylene. The degree of ordering differs in accordance with the dose and atmosphere of irradiation and the heat treatment.
Search for the electronic phase transition in NiTi
Authors: Lee R. N. , Withers Richard
Published: February 2003

Soft x-ray appearance potential spectroscopy was used to search for evidence of the electronic phase change in NiTi which has been proposed by Mitchell, Wang, and Cullen. No such evidence was found. Any temperature-dependent changes in the filling of the d band or in the s-band–to–d-band ratio are at least an order of magnitude less than predicted by the proposed model. Electron transfer between Ni and Ti atoms accompanies changes in stoichiometry but is not characteristic of the NiTi II–to–NiTi III phase transition.
Magnetoferroelectricity in Cr2BeO4
Authors: Newnham R. E. , Kramer J. J. , Schulze W. A. , Cross L. E.
Published: February 2003

Chromium chrysoberyl undergoes a phase transformation from a paramagnetic state to a complex antiferromagnetic state at 28 K. The spiral spin structure of the antiferromagnetic state violates all the crystallographic symmetry elements, making Cr2BeO4 potentially ferroelectric. Chynoweth experiments conducted at low temperatures reveal a weak pyroelectric effect which disappears above 28 K. Cr2BeO4 ceramics can be poled electrically between 24 and 28 K, giving rise to remnant polarizations four to six orders of magnitude smaller than normal ferroelectrics. The pyroelectric coefficient and the remnant polarization reverse in sign with the poling field, but no anomalies in the electric permittivity or electric conductivity occur at the Nèel point.
Ferroelectric properties of poly(vinylidene fluoride-tetrafluoroethylene)
Authors: Hicks J. C. , Jones T. E. , Logan J. C.
Published: February 2003

Ferroelectric hysteresis of a copolymer of vinylidene fluoride with tetrafluoroethylene and of uniaxially stretched polyvinylidene fluoride has been observed at 60 Hz at room temperature. The measured remanent polarization of the copolymer was in good agreement with a calculated value using a frozen dipole model and measured piezoelectric coefficients. The dielectric constant for the copolymer has been measured at 1000 Hz as a function of temperature. Also, a set of copolymer films of varying thickness were poled above the melt temperature and their piezoelectric stress coefficients g31 were measured as a function of the poling field. These measurements indicate that the copolymer, when poled above the melt temperature, exhibits bulk polarization. These results suggest that this copolymer is ferroelectric and that poling aligns the dipoles in the β crystal phase of the material.
Measurements of excited-state absorption in Ce3+ : YAG
Authors: Miniscalco W. J. , Pellegrino J. M. , Yen W. M.
Published: February 2003

We have investigated Ce3+ : Y3Al5O12 (YAG) as a model system for a 5d-4f solid-state tunable laser. This system has been chosen since YAG has been extensively studied as a laser host and good quality crystals are readily available. Despite providing apparently adequate conditions to achieve stimulated emission, we were unable to detect laser action in Ce3+ : YAG. We find, however, strong excited-state absorption in this material at the wavelengths of its fluorescence and we report on this excited-state absorption (ESA) here. This self-absorption may explain the failure of all attempts to obtain stimulated emission in this material and has serious implications for any attempt to develop a 5d4fn−1-4fn laser.
Displacement currents in frog skeletal muscle: Contribution of the potassium conductance channels
Authors: Strandberg M. W. P.
Published: February 2003

The electric dipole moment displacement currents which are to be expected from the change with time of the electric dipole moment of the potassium conductance channels in squid axon membrane with change in transmembrane potential are compared with the displacement currents observed in frog skeletal muscle cell membrane. The parameters needed to describe the muscle displacement currents—the resting potential, the dipole moment magnitudes, and the channel surface densities—are remarkably similar to those needed to describe the observed voltage-dependent potassium ion conductance in the squid membrane. The smaller relaxation rates in muscle membrane can be accounted for by increasing by 5% the potential hindering conformation relaxation of the conductance system. It is also concluded that tetraethylammonium and tetracine modify the system permeability rather than the dipole moments of the configurations of the potassium conductance system.
Comparison of predicted signals from the delayed fission neutron and prompt fission neutron uranium logging methods
Authors: Renken James H.
Published: February 2003

A mathematical formalism is developed whereby the expected signal from a delayed fission neutron uranium logging experiment can be calculated efficiently. An assumption that the logging geometry can be approximated by one-dimensional spherical geometry is made in order to facilitate the calculation of neutron-transport results that are needed to evaluate the formalism. Sample results from these calculations are used to form a comparison of the magnitudes of prompt and delayed fission neutron logging signals, respectively, for various observation times and amounts of water in the logging borehole.
Surface-acoustic-wave characteristics on fresnoite (Ba2Si2TiO8) single crystal
Authors: Yamauchi Hisao
Published: February 2003

Characteristics of surface acoustic waves (SAW) on fresnoite (Ba2Si2TiO8) single crystals are calculated using published and recently measured data. It is found that Ba2Si2TiO8 is located between LiNbO3 and LiTaO3 in the SAW characteristics. No sets of temperature-compensated propagation planes and directions are found among major singly rotated cuts in Ba2Si2TiO8.
Some experimental aspects of dc reactive sputtering
Authors: Hecq M. , Hecq A. , Liemans M.
Published: February 2003

Reactive sputtering of targets of certain noble (Au, Pt) and oxidizable metals (Co, Sn) are studied by glow discharge mass spectrometry (GDMS) and by x-ray diffraction. It is concluded that (1) oxidation of the target occurs for Sn and Co, (2) a plasma reaction occurs for every metal, especially Au, and (3) a chemical decomposition of AuO and an oxidation to higher states occurs on the substrate for Pt, Co, and Sn.
Accurate calibration of gold film standards by neutron activation and gravimetry
Authors: Lindstrom Richard M. , Harrison Sally H. , Harris Joe M.
Published: February 2003

A set of evaporated gold films on silicon substrates has been prepared for use as standards in the measurement of film thickness by Rutherford backscattering. The mass of gold in the films was determined independently by gravimetry and by instrumental neutron activation. The area was measured with an optical comparator; film uniformity was assayed by backscattering. Systematic errors in the single-element comparator method of activation analysis have been assessed and either eliminated or compensated, with the result that the single-sample agreement in mass between the two methods was 0.3% and the mean relative bias was below the random errors, also 0.3%.
Gallium arsenide antimonide: The possibility of lattice-matched LPE growth on InP substrates
Authors: Fonstad Clifton G. , Quillec Maurice , Garone Stephen
Published: February 2003

The possibility of using liquid phase epitaxy (LPE) to grow GaAsxSb1−x on InP substrates has been investigated. Theoretical phase-diagram calculations for the GaAsSb system show the solidus compositions in the x?0.5 region, where lattice matching to InP occurs, to be strongly dependent on temperature and in some cases multivalued, making it extremely difficult to achieve the degree of temperature control required for deposition of uniform LPE layers. When growths were attempted two-phase deposits were consistently found, an observation which supports the above conclusions. Appreciable rapid dissolution of the InP substrates was also observed. It is concluded that successful LPE growth of GaAsSb lattice-matched to InP is unlikely by conventional variable-temperature LPE techniques.
Computer Fourier-transform techniques for precise spectrum measurements of oscillatory data with application to the de Haas–van Alphen effect
Authors: Kamm George N.
Published: February 2003

Methods are developed for the high-accuracy analysis of oscillatory data using the discrete fast Fourier transform. A wide dynamic range and linearity of response together with good separation of individual lines in a spectrum are achieved by using digital filtering to reduce the sidelobes to less than −120 dB relative to the central peak. Periodic errors associated with the discrete nature of the transform are reduced by interpolation fitting. To make use of the high accuracy inherent in the digital data, a least-squares method is developed which fits line shapes accurately matched to the digital filter to the Fourier-transform spectrum. Frequencies are measured to an accuracy (computational) of better than 0.00001% and amplitudes to better than 0.001%. Although more generally applicable to problems requiring highly precise spectral analysis, the techniques are here directed to the analysis of de Haas–van Alphen oscillations where many frequencies are present and amplitudes are a strong function of magnetic field. An interpretation is made of the ’’amplitude’’ from which it is possible to calculate frequencies (i.e., Fermi surface areas), Dingle temperatures (i.e., electron scattering times), and effective masses with an accuracy (computational) of 0.00005% or better. This accuracy is realized for a discrete record having only a modest number of data points.
Aggregation of defects and thermal-electric breakdown in MgO
Authors: Narayan J. , Weeks R. A. , Sonder E.
Published: February 2003

Transmission electron microscopy has been used to study defects in as-grown MgO single crystals and in crystals which had undergone high-temperature electrical conduction for long periods of time. Besides dislocation loops of (a/2〈110〉) Burgers vectors and precipitates, a new type of defect, dislocation loops of α〈100〉 Burgers vectors lying in {100} planes, has been observed in electric-field-treated specimens. The nature of both (a/2) 〈110〉 and a〈100〉 loops was determined to be vacancy type. The relation of this microstructure to the observed increase in electrical conductivity, which ultimately results in thermal-electric breakdown of the samples, is discussed.
Evidence for chemical annealing effects in indium oxide tunnel-junction barriers
Authors: Hebard A. F. , Arthur J. R. , Allara D. L.
Published: February 2003

Thermally grown native oxides of indium have the reputation of being rather poor-quality tunneling barriers when indium is used as the base electrode. We have developed a simple technique in which a freshly evaporated indium film is allowed to oxidize in the presence of acetic-acid vapor prior to the deposition of the lead counterelectrode. These easily reproduced tunnel junctions are of extremely high quality with Josephson critical current densities as high as 5000 A/cm2. Auger, electron energy loss, and ellipsometry studies reveal that there is a thinner and more uniform oxide coverage on the acid-oxidized films when compared to air-oxidized films. The absence of a pronounced Auger carbon peak on the tunnel junction samples, together with infrared evidence for acetate ion formation on indium samples exposed to significantly higher partial pressures of acetic-acid vapor, suggest that there is an absorption/desorption process in which a submonolayer amount of ionized acetic acid serves as a structural relaxation catalyst at oxide sites which are at higher energy than would occur in a uniform lattice.
Size and behavior of antiferromagnetic domains in Cr directly observed with x-ray and neutron topography
Authors: Ando M. , Hosoya S.
Published: February 2003

By the use of x-ray and neutron topography, spin-density-wave (SDW) domains in pure chromium (IOCHROME), both in the virgin state and after field cooling, have been found to be of the order of a few mm in length and of several mm3 in volume. The change in configuration of the domains before and after field cooling is reasonable. This was found in a nearly perfect well-characterized sample. In a strain-annealed sample, the domain size was below the resolution.
Generation of a plasma wave and second harmonic in a magnetoplasma
Authors: Thakur A. K. S. , Sharma R. P.
Published: February 2003

This paper presents an investigation of the generation of a plasma wave and a second-harmonic electromagnetic wave in a collilsionless hot magnetoplasma by a Gaussian EM beam (pump wave) propagating perpendicular to a static magnetic field in the ordinary mode. Because of the Gaussian intensity distribution of the EM wave, the ponderomotive force becomes finite and the electrons become redistributed; the electron density gradient (so created) and the intensity gradient of the EM wave lead to the generation of a plasma wave at the pump-wave frequency. The intensity of the magnetic field significantly affects the plasma-wave generation. When the pump-wave frequency is equal to the upper-hybrid frequency, resonant excitation of the plasma wave occurs. The plasma wave interacting with the pump wave leads to the generation of a second-harmonic electromagnetic wave. Moreover, as the pump wave propagates in the plasma, its self-focusing occurs; consequently, the plasma-wave and the second-harmonic generation become drastically affected.
Electron scattering cross sections for momentum transfer and inelastic excitation in carbon monoxide
Authors: Land James E.
Published: February 2003

Cross sections for momentum transfer and for rotational, vibrational, and electronic excitation were obtained from an analysis of experimental data for electron drift velocity, characteristic energy, and ionization coefficient. Recently measured data in the range 1×10−16?E/N?4×10−15 V cm2 were included in the analysis.
The effects of optical absorption in Ba2NaNb5O15 on internal frequency-doubled operation of Nd : YAG
Authors: Rice R. R. , Teague J. R. , Jackson J. E.
Published: February 2003

Absorption loss in barium sodium niobate (BSN) crystals at both the 1.064-μm fundamental and 0.532-μm SH wavelengths perturbs the SHG phase-matching condition, thereby coupling the circulating and SH power with the nonlinear loss. Discrete transitions in circulating power, hysteresis in the intracavity SHG temperature phase-matching signature, and bistable operation are the direct result of this absorption loss. Extensive analytical and experimental results were obtained and are reported.
Low-frequency instabilities in the high-pressure regime of Penning discharges
Authors: Guharay S. K. , SenGupta S. N. , Gupta M. R.
Published: February 2003

A general dispersion relation for the rotationally symmetric (m=0) and asymmetric (m≠0) low-frequency waves has been delineated, utilizing a dimensional treatment as done by Hoh, for a high-pressure (p∼10−2 Torr) Penning discharge having gradients (radial) of ion density, plasma potential, and electron temperature. The present analysis is found to be very helpful for investigating the role of the temperature gradient in exciting various modes; here, a positive temperature gradient has been found to have a destabilizing influence in general. The theoretical predictions of the growth condition and the frequency of the instability have been found to agree well with the present experimental observation of an m=0 mode. Further, an experiment on the suppression of this instability has been carried out for understanding the excitation mechanism.
Pulse charging of nanofarad capacitors from the shock depoling of PZT 56/44 and PZT 95/5 ferroelectric ceramics
Authors: Mock Willis , Holt William H.
Published: February 2003

Gas-gun impact techniques have been used to pulse charge nanofarad capacitors from the shock depoling of PZT 56/44 and PZT 95/5 ferroelectric ceramics. The PZT materials were depoled in the normal mode. Pulse powers of hundreds of kilowatts were produced in a few microseconds. The PZT 56/44 material was impacted in the stress range from 4.4 to 11.8 GPa. A maximum load voltage of 55 kV was produced at 7.9 GPa, resulting in a charge release of about 78%. Shock-induced electrical breakdown in the PZT material occurred at 11.8 GPa. The PZT 95/5 material was impacted at 1.4 and 2.9 GPa stress levels. A maximum load voltage of 81 kV was produced at the higher stress, resulting in a charge release of about 74% before electrical breakdown occurred in the PZT material.
The stress-strain curves for cemented tungsten carbide and sintered diamond compact
Authors: Dunn K. J. , Bundy F. P.
Published: February 2003

The stress-strain curves for 3% cobalt cemented tungsten carbide and sintered diamond compact are determined up to a plastic strain of 8 and 0.2%, respectively, by measuring the permanent deflection at the center of the circular flat face of anvils used in ultrahigh-pressure experiments. The yield strength based on 0.2% offset for 3% cobalt cemented tungsten carbide is 50±5 kbar, and that for sintered diamond compact ranges from 200 to more than 500 kbar, depending on the sintering quality.
Observation of acoustic harmonics generated by long-range motion of dislocations
Authors: Jon M. C. , Mason W. P. , Beshers D. N.
Published: February 2003

We report, for the first time, observations of the acoustic harmonics generated by steady-state vibration at amplitudes so large that long-range dislocation motion occurs. Most of the measurements have been made on the second and third harmonics A2 and A3. At low amplitudes the experimental results of Hikata and Elbaum et al. are confirmed, but there is some discrepancy with theory for A3. At amplitudes such that dislocation sources operate, the harmonic spectrum departs strongly from the Hikata-Elbaum predictions. The harmonic amplitudes do not always increase monotonically with strain; A2 occasionally shows a maximum, A3 sometimes, and A5 even more frequently, in a pattern sensitive to mechanical history. The spectrum depends on grain size and prestress, varying jointly with the modulus defect and internal friction as these indicators of dislocation motion vary. The results on strain dependence are in accord with a simplified model of dislocation breakaway and Frank-Read source operation proposed previously to account for the internal friction and modulus defect.
On the uniformity of amorphous metal ribbon formed by a cylindrical jet impinging on a flat moving substrate
Authors: Anthony T. R. , Cline H. E.
Published: February 2003

The process of making amorphous ribbon by impinging a liquid jet on a substrate to form a steady-state puddle from which the ribbon is drawn out by the moving substrate is examined. It is shown that lateral variations in the thickness of the ribbon across its width at any particular ribbon section are directly related to the puddle shape at an instant of time. Longitudinal dimensional variations in the thickness or width of the ribbon along its length indicate an unstable puddle whose shape varied with time. These longitudinal dimensional variations can be minimized by using nozzle geometries, jet velocities, and puddle sizes that induce uniformity and steadiness in the fluid flow. Various means to achieve such uniformity are suggested.
The operation of the semiconductor-insulator-semiconductor (SIS) solar cell: Theory
Authors: Shewchun J. , Dubow J. , Myszkowski A. , Singh R.
Published: February 2003

Recently 12% efficient indium tin oxide (ITO) on silicon solar cells have been reported. Experiments indicate the presence of a thin interfacial insulating layer. Thus, these devices appear to belong to a class of semiconductor-insulator-semiconductor (SIS) solar cells where one of the semiconductors is a degenerate wide-band-gap oxide. We have developed a theory in terms of minority-carrier tunnel current transport through the interfacial layer where one semiconductor is in a nonequilibrium mode. The wide-band-gap semiconductor serves to block band-to-band majority-carrier current and thus, in principle, give better device performance than with an MIS solar cell. The effects of interfacial layer thickness, substrate doping level, surface states and interface charge, temperature on the performance of SIS solar cells have been calculated. These indicate that real-world ITO on silicon cells should be able to achieve 20% efficiency under AMl illumination. Other combinations of semiconductors would yield even better performance.
Excitation of currents on a buried insulated cable
Authors: Wait James R.
Published: February 2003

Earlier results for guided electromagnetic waves on buried cables are recast in terms of internal and external impedances. Then it is possible to deduce the excited cable current in terms of the applied axial electric field. Explicit numerical data are presented for low frequencies when the outer cable diameter is small compared with the electrical skin depth of the surrounding earth. Of particular importance is the remarkable fact that the deduced attenuation rate and phase velocity of the dominant transmission mode depends only slightly on the burial depth of the cable.
Fabrication of a superconducting niobium cavity by the diffusion-bonding method
Authors: Isagawa S.
Published: February 2003

The diffusion-bonding method has been applied to the fabrication of a C-band (6.5-GHz) superconducting Nb cavity of TM010 mode. The cavity consists of two parts which are machined from a reactor-grade solid billet of Nb. The two parts are electropolished and joined in an ultrahigh-vacuum induction furnace by applying mechanical pressure of about 1.7 kg/mm2. For the bonding, it takes about 10 h at 1900 °C in 10−7–10−8 Torr. A tension test shows that the tensile strength of the joint is more than 24.4 kg/mm2. The cavity, which is vacuum annealed in the same furnace and lightly electropolished, shows an unloaded Q as high as 1.1×109 at 1.3 K in the rf field region of 0–7 G. The maximum surface field as high as 321 Oe and 22.7 MV/m is obtained. These results are compared with those obtained for cavities fabricated by the electron-beam welding method.
Dynamic stress effects in technical superconductors and the ’’training’’ problem of superconducting magnets
Authors: Pasztor G. , Schmidt C.
Published: February 2003

The behavior of NbTi superconductors under dynamic mechanical stress was investigated. A training effect was found in short-sample tests when the conductor was strained in a magnetic field and with a transport current applied. Possible mechanisms are discussed which were proposed to explain training in short samples and in magnets. A stress-induced microplastic as well as an incomplete pseudoelastic behavior of NbTi was detected by monitoring acoustic emission. The experiments support the hypothesis that microplastic or shape memory effects in NbTi involving dislocation processes are responsible for training. The minimum energy needed to induce a normal transition in short-sample tests is calculated with a computer program, which gives the exact solution of the heat equation. A prestrain treatment of the conductor at room temperature is shown to be a simple method of reducing training of short samples and of magnets. This is a direct proof that the same mechanisms are involved in both cases.
The electron capture cross section and energy level of the gold acceptor center in silicon
Authors: Brotherton S. D. , Bicknell J.
Published: February 2003

The electron capture cross section of the gold acceptor center has been measured by a direct technique which measures the electron-trapping rate. The value was found to be 9±2×10−17 cm2 over the temperature range 77–280 K. Using this value together with thermal emission data, the energy level of the center was calculated from the detailed balance equation. Assuming a degeneracy factor of 4, the calculated temperature variation of the energy level (as measured from the conduction band) was found to be very similar to the temperature variation of band gap itself, indicating that the acceptor level may be fixed to the valence band edge with a separation of 0.632±0.004 eV.
Magnetoelastic surface waves on the (110) plane of highly magnetostrictive cubic crystals
Authors: Ganguly A. K. , Davis K. L. , Webb D. C.
Published: February 2003

Dispersion characterisitcs of magnetoelastic surface waves in highly magnetostrictive cubic crystals are calculated for different bias fields applied along the direction of propagation. Effects of anisotropy are taken into account. The surface waves are found to be leaky or nonleaky depending on the direction of propagation. Velocity of surface waves is calculated both before and after saturation of the magnetic moment. Although most of the velocity change with bias field occurs while the magnetization vector rotates from the easy direction to the field direction, the velocity changes by a few percent even after the moment saturates. Theoretical results are in good agreement with experiment.
Ultrasonic, dilatometric, and dielectric study of uniaxial-stress effects in a barium-calcium titanate ceramic
Authors: Fritz I. J.
Published: February 2003

The effect of uniaxial stress up to 400 MPa (4 kbar) on a number of mechanical and dielectric properties of Ba0.92Ca0.08TiO3 ceramic has been studied. The various results have been interpreted in terms of domain reorientation processes (90° switching) which occur in response to the applied stress. The measurements made include the following: (1) logitudinal sound velocity normal to the stress direction at 23 °C, (2) mechanical strain parallel and normal to the stress direction at 23 °C, (3) dielectric constant ε3 parallel to the stress direction at 23 °C, (4) ε3 as a function of temperature in the range 23–160 °C at various stress levels, and (5) electrical hysteresis loops at 23 °C with poling field parallel to the stress direction. The samples used in experiments (1) – (4) were unpoled. Experiments (1), (2), (3), and (5) indicate anomalous behavior in the 0–200-MPa range which can be explained qualitatively in terms of domain reorientation effects, and this interpretation has been confirmed by annealing experiments which rerandomize the domains. Experiment (4) shows that the Curie temperature Tc increases with increasing stress. This is to be contrasted to the decrease of Tc as a function of hydrostatic pressure and can again be explained as due to domain reorientation effects. For experiments (1) – (3), a quantitative calculation has been made of the magnitude of the anomalies to be expected for complete reorientation by utilizing a modified Voigt averaging scheme, and the results are in good agreement with the measured values.
The Clausius-Mossotti problem for cubic arrays of spheres
Authors: Doyle William T.
Published: February 2003

The numerical solution of the Clausius-Mossotti problem for the permittivity of a suspension of perfectly conducting spheres in a cubic array is presented for sc, fcc, and bcc lattices. The results apply to electrical permittivity, magnetic permeability, electrical and thermal conductivity, and particle diffusivity. The calculations are compared with the Clausius-Mossotti relation. Rayleigh’s equation is corrected and compared with the numerical results. A simple interpolation formula for the permittivity of a medium of perfectly conducting spheres in a simple cubic lattice is found to give an excellent approximation at all volume ratios.
CO vibrational distributions in the presence of oxygen
Authors: Fisher Edward R. , Lightman Allan J.
Published: February 2003

Direct measurements of the vibrational distribution to v?30 obtained from the first overtone emission from CO in a liquid-N2-cooled laser plasma have been made in the presence of varying amounts of O2. These observed distributions show enhanced vibrational populations for small additions and show upper-level depopulation for larger additions. Both observations support a recent plasma-kinetic model of the effect of O2 in low-pressure CO laser plasmas.
High-current-pulsed linear ion accelerators
Authors: Humphries S.
Published: February 2003

Possible methods are described for constructing ion linear accelerators in the 100-MeV range which have pulsed current outputs 105 times higher than currently available. A drift-tube design with insulating magnetic fields between the tubes is presented. The fields not only prevent electron flow, but also are essential for beam neutralization by low-energy electrons and transverse beam focusing. Preliminary discussions are given on accelerator design and construction, transverse focusing and beam neutralization, and control of the beam in longitudinal phase space.
A low-energy high-fluence reflection-refraction x-ray spectrometer
Authors: Burginyon G. A. , Stoering J. P. , Hill R. W. , Singman L. V.
Published: February 2003

A high-fluence reflection-refraction x-ray spectrometer allows spectral diagnosis of intense bursts of x radiation from about 0.5 to 8 keV. Grazing-incidence x rays, reflected first by a vitreous carbon mirror, are rereflected off the flat polished face of a plastic scintillator that is viewed by a photomultiplier tube. By making the scintillator-mirror reflection angle greater than the carbon-mirror angle, one efficiently refracts an energy band out of the incident spectrum into the scintillator. Reflection by the carbon mirror determines the high-energy edge of the bin, whereas refraction into (or reflection from) the subsequent scintillator determines the lower edge. The current from the photomultiplier is a direct time-dependent measure of the contents of the band. The sharpness of the band edges (about 0.1 keV) determines the narrowest measurable energy band and hence best possible energy resolution. The response to light of the scintillator-photomultiplier limits the sensitivity. Measurements with continuum and monoenergetic sources are compared to theory.
A study of two-stage ion-beam optics
Authors: Kim Jinchoon , Whealton J. H. , Schilling Gerd
Published: February 2003

Ion-beam optics of a two-stage electrostatic accelerator (i.e., the extraction-accel-decel column) is studied by three approaches: (i) a linear optics analytic solution based on the paraxial equations which account for lens effects and beam space charge, (ii) a nonlinear optics solution based on the Poisson-Vlasov equations and including the two-dimensional source-plasma sheath, and (iii) a 60-kV single-beamlet experimental study. Principal results are that in certain operating modes, the minimum beam divergence in a two-stage source is significantly less than in the conventional single-stage source and that the optics of the two-stage source is less sensitive to variation in extraction perveance about the divergence minimum. This is because the optimum extraction perveance in such modes of operation is relatively high, causing the crucial residual aberration fields near the first electrode to be smaller.
Effect of spatial sampling on an acoustical image reconstruction
Authors: Bruneel C. , Bridoux E. , Delannoy B. , Nongaillard B. , Rouvaen J. M. , Torguet R.
Published: February 2003

It is often difficult and unpractical, in the acoustic imaging area, to insert a focusing lens between the observed object and the ultrasonic receiver. Furthermore, the focal length must, in the B scan mode, be varied very fast in order to keep the line sources lying at different depths well focused. A spatial-sampling scheme may be used for circumventing these problems by taking off the possibly complex processing unit from the element contacting the observed object, without additional complexity or degradation in the flexibility and usefulness of the apparatus. The sampling is done using a receiving transducer array to convert the acoustic signals into electrical ones, which may be amplified before being applied to another reemitting transducer array: an acoustical field identical to the original one is so reconstructed. The sampling operation will, however, alter the image quality by introducing parasitic images. The dependence of the perturbations upon the system parameters is studied in this paper and criteria are derived for limiting them.
Optimization of a transmission acoustic microscope
Authors: Bridoux E. , Nongaillard B. , Rouvaen J.M. , Bruneel C. , Thomin G. , Torguet R.
Published: February 2003

The acoustic field focused by a spherical solid-water interface has been computed and the results have been used to optimize the geometry of a transmission acoustic microscope. An experimental study has been performed, which enables the sampling of the focused acoustic field, as may be realized by using the Fourier-transform-operation concept for an ideal lens.
CO vibrational distributions to high levels in low-pressure CO/He mixtures
Authors: Lightman Allan J. , Fisher Edward R.
Published: February 2003

Experimental measurement of the first- and second-overtone spontaneous-emissions spectrum in a low-pressure CO/He plasma has enabled determination of the vibrational distribution up to v=30. The variation in the CO distribution as a function of CO and He partial pressure and plasma current has been correlated by a detailed model of the steady-state energy-transfer dynamics. The agreement between calculated and measured distributions has generated a consistent set of rate coefficients for CO/He mixtures for a temperature around 150 K.
Power density in direct nuclear-pumped 3He lasers
Authors: Wilson J. W. , DeYoung R. J.
Published: February 2003

The interaction of neutron beams with 3He gas is of interest for nuclear pumped lasers. The effects of spectral dependence of the neutron beam, neutron attenuation in the gas-filled laser tube, and transport of the charged-particle 3He(n,p)3H reaction products are treated in detail. An expression for the energy density as a function of position within the tube, tube radius, operating pressure, and neutron fluence is given. The maximum energy density within the optical cavity is achieved when the tube radius a (cm) is given by a=3.26/P where P (atm) is the operating pressure. The variation of radius by 50% above and below optimum will change the energy density at most by 10%, although performance degrades quickly for radii outside this range. If the optimum tube radius is used for each operating pressure, then the power density on the centerline (kW/cm3) is given as ξCL=9.3×10−18Pf0 in a thermal neutron environment of f0 (n/cm2 sec).
Neutron scattering studies of itinerant electron magnetism
Authors: Ishikawa Y.
Published: February 2003

The paper summarizes the results of neutron scattering from a weak itinerant ferromagnet MnSi (the itinerant electron system) and Invar alloys: Fe65Ni35 and Fe3Pt (the quasi-localized spin system). Well defined spin wave excitations as well as the excitations in the Stoner continuum could be detected at 5 K for MnSi in the induced ferromagnetic state. The spin dynamics in this weak itinerant ferromagnet were found to be compatible with a simple theory of an itinerant ferromagnet within RPA. The Stoner boundary is located at about 2.5 meV and the magnetic properties of MnSi are mainly determined by the Stoner excitations. In the case of Invar alloys, spin wave excitations could be detected up to 80 meV. The itinerant character of the magnetic properties is suggested not to be due directly to the Stoner excitations but to interactions between the spin waves and the Stoner modes in some higher order mechanisms.
Microstructure and magnetic properties of Fe-Cr-Co-V alloys
Authors: Belli Y. , Okada M. , Thomas G. , Homma M. , Kaneko H.
Published: February 2003

The relationship between the microstructure and magnetic properties of heat treated Fe–23 wt%Cr–15 wt% Co–5 wt%V has been studied by transmission electron microscopy and Lorentz microscopy. Three different heat treatments were adopted for the present investigations, viz., (1) isothermal aging, (2) thermomagnetic treatment (TMT) + step-aging, (3) continuous cooling. It has been found that the magnetic properties of the alloy are very sensitive to the temperature of the TMT. Step-aging gave the best magnetic properties, producing an elongated ferromagnetic phase, 300 Å in diameter and 1200 Å in length. Lorentz microscopy revealed domain walls and these lie within the Cr-rich phase and pinned by the Fe-rich phase in the isothermally aged alloy at 650 °C. Magnetic domains of optimally step-aged alloys, 0.5 μm in width, are elongated along the direction of the applied magnetic field. The results suggest that the magnetic anistropy is introduced parallel to the direction of the applied magnetic field during TMT and step-aging treatments.
Effect of B2O3 concentration on magnetic defects and properties of garnet films grown in PbO-B2O3 solvents
Authors: Yamaguchi K. , Kono N. , Asama K. , Inoue H. , Mori T.
Published: February 2003

For the purpose of eliminating magnetic defects on garnet films, various molar concentrations of R=B2O3/(PbO+B2O3) have been extensively studied. It was found that the density of magnetic defects was reduced remarkably in films grown in B2O3 rich solvent. Experiments were carried out on YSmLuCaGeIG films within the 4πMs range of 200 to 300 gauss, and defects were evaluated using an interference contrast microscope having a magnification of 1000×. Observed defects were broadly classified into four types of pitting: circular, triangular, hexagonal and elliptical. For the film thickness range of 2.5 to 4.0 μm grown in a solution, where R=6.0 mol%, the average pit densities of circular, triangular and hexagonal pits were 8.0, 6.4 and 2.1 cm−2, respectively. Each of these pit densities were reduced to 0.7, 0.2 and 0.0 for R=11.4 mol%. The effect of R on growth conditions was also investigated to obtain films suitable for 3 μm diameter bubbles with 4πMs=280 gauss and l=0.33 μm. The appropriate growth temperature TG and growth rate νg were 913 °C and 1.2 μm/min, respectively, for the solution where R=6.0 mol%, while TG and νg for R=11.4 mol% shifted to 866 °C and 0.28 μm/min, respectively.
Magnetostatic wave interdigital transducers
Authors: Adam J. D. , Patterson R. W. , O’Keeffe T. W.
Published: February 2003

The design and operation of a novel type of magnetostatic wave transducer is described. The transducer is formed from an interdigital arrangement of narrow, open circuited microstrip fingers, each half an electromagnetic wavelength long. Experimental results in the frequency range 9–9.4 GHz are presented for 2, 4 and 10 finger transducers which are in good agreement with the sin(Nx/2)/sin(x/2) response predicted by simple theory.
Magnetic properties of amorphous FeC thin films
Authors: Kazama N. , Heiman Neil , White R. L.
Published: February 2003

Thin films of amorphous FexC1−x (0.75⩽x⩽0.50) were prepared by sputter deposition. Room temperature values for 4πMs ranged from 13000 gauss (x=0.75) to 6500 gauss (x=0.50). Thus the room temperature magnetization is much higher than that for amorphous alloys of Fe with other group IV elements. The increased magnetization appears to be due to a higher Curie temperature as well as a larger atomic moment. It is well known that bulk amorphous samples of rapidly quenched alloys of transition metals with group III, IV and V elements can be prepared with low Hc; however, little is known of the properties of these alloys when prepared with thin films. We show that amorphous films of FeC can be prepared as Hc≈0.10 Oe without the need for post deposition annealing by proper selection of deposition parameters, in particular the argon gas pressure. The anisotropy energy is also dependent upon deposition gas presssure, going to zero for the same pressure that produces low Hc. Magnetostriction measurements have been made, and the films have large positive magnetostriction (Λ≈+1.5×10−5) which decreases with C content.
Photoelectronic processes in high-resistivity stannic oxide
Authors: De Murcia M. , Bonnafe J. , Manifacier J. C. , Fillard J. P.
Published: February 2003

Using Bube’s formulation of the sensitization process in photoconductors a particular exchange mechanism is proposed that associates a shallow trap (excited state) and a recombination level (fundamental state). Expressions are deduced describing the photocurrent behavior as a function of temperature and illumination on both sides of the continuous thermal quenching zone; explicit formulations are also deduced for the upper and lower break points in the lux-ampere characteristics. Such a phenomenological model is applied to photoconduction data on stannic oxide high-resistivity samples. Optical quenching and pulsed photoconductivity are also emphasized in order to propose a consistent scheme for the localized levels in the forbidden energy band. It is shown from this work that localized transitions occur between three possible recombination states and a common excited state working with the conduction band as a shallow trap; associated lifetimes are measured.
Magneto-transport properties of noble metals containing rare-earth impurities
Authors: Levy P. M. , Fert A.
Published: February 2003

Magneto-transport measurements of noble metals containing rare-earth impurities probe different aspects of the 4f-conduction electron interaction. The anisotropy of the magnetoresistance is primarily due to the quadrupolar term, the extraordinary Hall effect (skew scattering) is at least partially due to the orbital exchange term (l⋅L) and the negative isotropic magnetoresistance is due to the spin exchange term (s⋅S). The advantage of magneto-transport experiments over others, e.g., EPR g-shift and linewidth, is that they single out different terms in the 4f-conduction electron interaction. Estimates of the anisotropic terms based on conduction electrons in plane wave states give values too small to explain the experimental data. We have taken into account the admixture of 5d screening electrons into the conduction band and obtain a 4f-conduction electron interaction which has large anisotropic terms in addition to the conventional spin interaction. When we assume that the 5d electrons are in t2g states we find that our estimate of the anisotropy of the magnetoresistance and of the skew scattering effect are in fair agreement with the experimental data. However, our estimate of the negative isotropic magnetoresistance is too large.