bluuebunny/crossref_metadata_2025 huggingface dataset:
The high-frequency permeability of composite magnets
Authors: Finnegan R. D. , Savage R. O. , Tauber A.
Published: February 2003

The real part of the complex initial permeability (K′m), as obtained from impedance measurements between 0.5 and 100 MHz, was found to range between 1 and 10 for composite magnetic materials for concentrations 25–50 vol%. Composites were prepared from Q1-ferrite, RD3-ferrite, and carbonyl iron in a matrix of silicone rubber. To zero order a good fit of K′m to a 1/p3 (p=porosity) dependence was found to extend to 100 MHz.
Insulating Pb oxide layers formed in a dc oxygen glow discharge
Authors: Singer I. L.
Published: February 2003

Pb oxide insulating layers on Pb films have been produced using a dc oxygen glow discharge. Resistances from 105 to 108 Ω and capacitances of 15 nF are measured on 1-mm2 Pb/Pb oxide/Sn diodes. The insulating properties of these Pb oxide layers are discussed in terms of the dielectric properties of bulk PbO.
Comment on ’’Evidence of a precipitatelike zone in as-grown GaAs and its influence on optical absorptivity’’
Authors: Swaminathan V. , Narayanan G. H. , Copley S. M.
Published: February 2003

Evidence is presented that diffuse streaks in electron diffraction patterns from GaAs single crystals are due to the thermal diffuse scattering of electrons by phonons. Conclusions by Vander Sande and Peters regarding the crystallographic orientation and shape of zones in GaAs based on the observation of such streaks are not justified.
On precipitatelike zones in as-grown GaAs
Authors: Vander Sande J. B. , Peters E. T.
Published: February 2003

The presence of precipitatelike zones in as-grown GaAs is reviewed in light of recent criticisms. It is concluded that there is sufficient evidence to support the existence of precipitatelike zones in GaAs and, therefore, the role of these precipitates in determining optical absorptivity coefficients must be considered.
Augmentation of heat transport in laminar flow of polystyrene suspensions. I. Experiments and results
Authors: Ahuja Avtar Singh
Published: February 2003

The effective thermal conductivity of suspensions of 50− and 100-μ-diam polystyrene spheres in aqueous sodium chloride or glycerine, flowing in laminar motion, has been shown to be a function of the state of the motion (unlike single-phase fluids) and has been seen to be as much as 3 times the thermal conductivity of stationary suspensions. Detailed experiments have indicated its dependence upon the particle concentration, particle size, shear rate, kinematic viscosity, and thermal diffusivity of the suspending liquid, and tube diameter and length. The Graetz solution corresponding to uniform wall temperature was used to determine the value of thermal conductivity in an apparatus calibrated with tap water. The over-all accuracy of the results is within 10%.
Alternating field loss in a multifilament superconducting wire for weak ac fields superposed on a constant bias
Authors: Carr W. J. , Walker M. S. , Murphy J. H.
Published: February 2003

Expressions are given for the alternating field loss in a twisted filamentary superconductor as a function of frequency and magnetic field, for the case of small ac applied fields which do not completely penetrate the filaments. The ac field is superimposed on a fixed bias field. In this limit the effective diamagnetism of the filament leads to a permeability less than unity for the composite. Expressions are presented for both the hysteresis and the eddy current loss.
Electromagnetic fields and torque for a rotating gyroscope with a superconducting shield
Authors: Ebner C. , Sung C. C.
Published: February 2003

In a proposed experiment, a measurement is to be made of the angular precession of a rotating superconducting gyroscope for the purpose of testing different general relativity theories. For various reasons having to do with the design of the experiment, the superconducting shield surrounding the gyroscope is not spherically symmetric and so produces a torque. There are two distinct features of the shield which lead to a torque on the gyroscope. First, its shape is a sphere intersected by a plane; if the angular momentum of the gyroscope is not parallel to the rotational symmetry axis of the shield, there is a torque which we calculate. Second, there are small holes in the spherical portion of the shield; the earth’s field can penetrate through these holes and give an additional torque. This is also calculated here. In the actual experiment these torques must be accurately known or made very small in order to obtain meaningful results. Our calculation is sufficiently general for application over a wide range of experimental design parameters.
A metal-film high-frequency ultrasonic transducer
Authors: Chimenti D. E. , Maxfield B. W.
Published: February 2003

It is shown that moderately pure metal films deposited on an insulating substrate can act as an efficient transducer for ultrasound in the 100–1000-MHz range. Electromechanical conversion takes place in the skin depth of the film by direct action of the electric field on the ions. Displacements comparable to those achievable using bonded-quartz resonant-plate transducers can be obtained between 100 and 1000 MHz. The main advantages of this method of generating ultrasound are its large inherent bandwidth and the absence of troublesome mechanical bonds at high frequencies.
Low-temperature heat capacity of CrH0.97
Authors: Viswanathan R. , Khan H. R. , Knoedler A. , Raub Ch. J.
Published: February 2003

Reported here are the low-temperature (1.7–10 K) heat-capacity data of a CrH0.97 sample prepared by an electrochemical method. The electronic heat-capacity coefficient γ and the Debye temperature ϑD are found to be 4.5 mJ/g mole K2 and 360 K, respectively. These results are compared with the available literature data.
Surface effects on the angular distributions of samarium vapor effusing from cylindrical orifices
Authors: Grimley R. T. , Wagner L. C. , Castle P. M.
Published: February 2003

A mass-spectrometric investigation has been made of the angular distributions of atomic samarium vapor effusing from cylindrical orifices of varying geometries and materials. Neither the theoretical angular distribution curves obtained from the Clausing theory nor any of the existing modifications of this theory coincided with the experimental distributions. The substantial effect of orifice material on the angular distribution curves suggests the possibility of bulk diffusion in the orifice walls as a contributory factor.
Coherence length of a Q-switched Nd:YAG laser
Authors: Barnes N. P. , Crabbe I. A.
Published: February 2003

The coherence length of a Q-switched Nd:YAG laser was measured as a function of the ratio of input energy to threshold input energy. The coherence length was determined by photographing, with the aid of an image converter, the fringes produced by a Michelson interferometer. It was found that both the coherence length and the visibility at zero pathlength difference decreased as the ratio of input energy to threshold input energy was increased. The longest coherence length measured was 16.8 mm at a ratio of input energy to threshold input energy of 1.33.
Griffith fracture equation—An experimental test
Authors: Doremus R. H. , Pavelchek E. K.
Published: February 2003

The Griffith fracture equation was not followed when the strengths of rods of soda-lime glass tested immediately after abrading and then after abrading and ageing for 24 h in water were compared. The aged samples were stronger than samples not aged, but the cracks in both were of nealry the same length. Two possible explanations of this discrepancy are explored.
Compressibility of selenium glass to 5 GPa
Authors: Singh A. K. , Kennedy G. C.
Published: February 2003

The compressibility of selenium glass has been measured to 5.0 GPa by a piston-cylinder apparatus. The discontinuity in the pressure derivative of the compressibility reported by Bridgman is not observed is this study; the compression behavior is found to be normal up to 5.0 GPa. The variation of the bulk modulus B (p) can be described by the relation B (p) =B0+B0′p+(1/2) B0′′p2+(1/6) B0′′′p3 with B0=8.73±0.4 GPa, B0′=7.07±0.7, B0′′=−1.15±0.7 (GPa)−1, and B0′′′=0.219±0.2 (GPa)−2.
Extraction of the speed distribution function from a time-of-flight signal
Authors: Young Wen S.
Published: February 2003

The molecular-beam speed distribution functions obtained in free-jet expansions using existing time-of-flight (TOF) techniques are subject to distortions caused by the gate function of the beam chopper, A (t), and the dynamic function of the detector and its electronics, gd(t). Mathematically, the TOF signal is represented by a doubly convoluted Volterra integral equation involving the three functions cited above. In this paper, the Volterra integral equation is inverted twice, using the Laplace-transform method, for known functions of gd(t) and A (t). The time-domain distribution function F (t) is decoupled from the functions gd(t) and A (t). Hence, the distortion-corrected speed distribution function is obtained. An example using the CO2 TOF signal demonstrates the numerical inverting technique.
Traveling-wave amplification by interaction with a current in a semiconductor
Authors: Thiennot J.
Published: February 2003

The electrons of a semiconductor may interact with a quasielectrostatic wave guided by an external structure and produce amplification if their velocity is large enough. The mechanism of interaction is described by a perturbation theory, the results of which are always valid near the threshold of amplification. The interaction occurs through the charges which are induced on the surface of the semiconductor by the electric field of the wave. The gain is proportional to an ’’effective resistance’’ of the semiconductor and to the excess of the drift velocity of surface electrons over a threshold velocity which is a characteristic of the line and is affected by space harmonics. Surface states may have a very important effect on the interaction. An experiment is presented, which is in agreement with the theory. Quasimagnetostatic surface waves may also be amplified. The interaction occurs through the current due to Lorentz’s force in the bulk of the semiconductor. The gain is proportional to the inverse of the effective resistance.
Intraband radiative transitions and plasma–electromagnetic-wave coupling in periodic semiconductor structure
Authors: Gover A. , Yariv A.
Published: February 2003

Intraband radiative transitions can occur in a semiconductor with an artificial periodic structure (superlattice). The ’’lattice momentum’’ of the periodic structure makes possible the conservation of momentum during the electronic transition. When the electrons in the band are drifting in an electric field, an intraband population inversion may occur, providing optical wave amplification. Under conditions where the Landau damping of the semiconductor carrier’s plasma wave is low, phase-matched coupling may occur between the plasma wave and a Floquet component of the electromagnetic wave and result in a high rate of power transfer from one of the waves to the other. These effects are discussed and analyzed quantum mechanically and suggestions are made with regard to possible device applications (amplifier, modulator) in the infrared regime.
Rotational temperature determinations in molecular gas lasers
Authors: Weaver L. A. , Taylor L. H. , Denes L. J.
Published: February 2003

The small-signal gain expressions for vibrational-rotational transitions are examined in detail to determine possible methods of extracting the rotational temperature from experimental gain measurements in molecular gas lasers. Approximate values of Tr can be deduced from the rotational quantum numbers for which the P- and R-branch gains are maximum. Quite accurate values of Tr and the population inversion density (nv′−nv″) can be determined by fitting data to suitably linearized gain relationships, or by performing least-squares fits of the P- and R-branch experimental data to the full gain expressions. Experimental gain measurements for 15 P-branch and 12 R-branch transitions in the 10.4-μm CO2 band have been performed for pulsed uv-preionized laser discharges in CO2 : N2 : He=1 : 2 : 3 mixtures at 600 Torr. These data are subjected to the several gain analyses described herein, yielding a rotational temperature of 401±10 °K and an inversion density of (3.77±0.07) ×1017 cm−3 for conditions of maximum gain. These techniques provide accurate values of the gas temperature in molecular gas lasers with excellent temporal and spatial resolution, and should be useful in extending the conversion efficiency and arcing limits of high-energy electrically excited lasers.
Photoluminescence in high-resistivity CdTe : In
Authors: Barnes C. E. , Zanio K.
Published: February 2003

Photoluminescence measurements have been performed at 4.2 K between 1.2 and 1.6 eV on compensated high-resistivity CdTe containing from 1015 to 1018 cm−3 indium. A series of phonon-coupled emission bands with a no-phonon peak at 1.454 eV is dominant in most samples and grows in intensity with increasing In concentration. On the basis of the compensation model, the 1.454-eV emission is attributed to radiative recombination at an [cadmium vacancy-In] acceptor complex. Comparison of the experimental results with this model suggests that the chemical equilibria governing formation of the acceptor complex are frozen in at approximately 500 K as the sample is cooled from the growth temperature. The existence of significant changes at 500 K in the mobility of defects related to the acceptor complex is confirmed by the observation of a prominent growth in the 1.454-eV emission at an annealing temperature of 500 K in A+-implanted n-type CdTe. Exciton emission in the CdTe : In samples is dominated by a narrow bound exciton band at 1.584 eV which is assigned to recombination at a center associated with In. Edge emission is relatively weak in all samples with the peak positions varying from 1.538 to 1.546 eV.
Enhanced interband recombination in Pb1−xSnxTe
Authors: Cammack D. A. , Nurmikko A. V. , Pratt G. W. , Lowney J. R.
Published: February 2003

Photoconductive measurements have been performed on Pb1−xSnxTe in the small-energy-gap region. Experimentally observed shortening of the photoconductive lifetime is inferred to occur as a result of strong coupling of photoexcited carriers to some elementary excitations (phonon and phonon-plasmon modes) in the material. Applications to fast infrared detectors are discussed.
Four-photon parametric amplification in semiconductors
Authors: Jain M. , Gersten J. , Tzoar N.
Published: February 2003

A theoretical study of four-photon parametric amplification in narrow-band-gap semiconductors is made. It is shown that phase matching is achievable in a linear geometry if a magnetic field is employed. Furthermore, a substantial cyclotron resonance enhancement occurs in the presence of a magnetic field. We calculate the growth rates and threshold fields associated with the parametric amplification and conclude that an efficient laser may be designed based on this process.
Surface-potential decay in insulators with field-dependent mobility and injection efficiency
Authors: Sonnonstine T. J. , Perlman M. M.
Published: February 2003

Surface-potential decay characteristics of corona-charged insulators are analyzed theoretically. The effects of field-dependent drift mobility and injection efficiency, as well as time-dependent injection, are included. The theoretical results are compared with existing surface-potential decay data on polyethylene. At the highest initial surface potentials all the surface charge is injected into the insulator on a time scale which is small compared to that of the measurement, and the injected charge drifts under its own self-field to the collecting electrode by means of a field-dependent transport process without significant range limitation. At the lowest initial surface potentials little or no charge is injected, and the surface potential is constant in time. For intermediate initial surface potentials the injection process is time and field dependent, with the time dependence being stronger than an injection process associated with a surface charge density that decreases exponentially in time, but weaker than that for instantaneous complete injection.
Ion implantation during film growth and its effect on the superconducting properties of niobium
Authors: Heim G. , Kay Eric
Published: February 2003

Low-energy (?500 eV) Kr+ ion bombardment during film growth and its consequences on superconducting properties of Nb are studied in a triode glow discharge sputtering configuration. Tc is depressed from the bulk value at a rate of −0.19 °C/at.% dissolved in the lattice. The residual resistivity shows an increase of 3.4 μΩ cm/at.% Kr. It is shown that radiation damage due to ion bombardment dominates the superconducting properties up to 0.2 at.% dissolved, whereas above this Kr concentration, up to ∼2 at.% Kr, the noble-gas content dominates the transport properties. All films show a dilated lattice which is mainly caused by energetic bombardment during film growth rather than subsequent trapping of the Kr gas.
Electrical resistivities of normal-superconducting two-phase mixtures
Authors: Callaghan Timothy J. , Toth Louis E.
Published: February 2003

Electrical resistivities of multiphased wires in which one phase is a continuous normal conductor and the other is a discontinuous superconducting phase have been studied as a function of mechanical reduction (Re) and current density J. Even for J values of 103 A/cm2 the electrical resistivity decreases somewhat faster than 1/Re3, a dependence that can be predicted from a number of metallurgical microstructure models. For J values of 10 A/cm2 or less, most of the current is carried by superconducting or superconductinglike paths. Metallurgical studies rule out the possibility of continuous Nb paths and, therefore, the proximity effect is the most likely cause for the reduced resistivity even though the average interparticle spacing is large.
Conductivity, permeability, and dielectric constant in a multifilament superconductor
Authors: Carr W.J.
Published: February 2003

Results are given for the permeability, conductivity, and dielectric constant of a multifilament superconductor, treated as an anisotropic state of matter. The calculations are made for the limiting cases of strong and weak ac magnetic fields compared with the field required for complete penetration of the filaments. General expressions are given for the ac power loss.
Dislocation damping and defect dragging in aluminum: The slow modulus effect
Authors: Seiffert S. L. , Sosin A.
Published: February 2003

Dislocation damping and Young’s modulus changes were measured on aluminum irradiated at low temperature by 1-MeV electrons. These measurements, taken at fixed temperatures, demonstrate good agreement with the prediction of the defect dragging model proposed by Simpson and Sosin and provide quantitative support of the model. Good agreement with the theoretical results is also obtained following interrupted electron-beam bombardments which take into account the temperature-dependent background damping. The very slow change in modulus reported earlier was studied further and it is shown that this slow change can be fully understood simply within the framework of the defect dragging model.
X-ray emission from laser-produced magnesium plasmas
Authors: Lee T. N. , Nagel D. J.
Published: February 2003

Characteristics of x-ray emission produced by focusing a 0.5-GW laser to about 1012 W/cm2 on magnesium metal targets were measured. Approximately 0.01% of the incident laser energy of 10 J was emitted in a 11-nsec (FWHM) pulse of x rays with photon energy in the range 1.3–1.8 keV.
Effects of voltage polarity, electric current, external resistance, number of sparkings, supply frequency, and addition of hydrogen and air on electrical breakdown in vacuum
Authors: Hackam Reuben
Published: February 2003

The breakdown potential of a vacuum gap is measured using parallel planar electrodes made of sterling silver as a function of gap separations, number of sparkings, external resistance, and variation of hydrogen and air pressures using dc and ac (50 Hz) applied voltages. It is found that the dc and ac vacuum breakdown voltages become equal after full conditioning by repeated sparkings of both electrodes either with ac or with both polarities of the dc applied voltage. The vacuum breakdown voltage is found to be independent of supply frequency up to 250 Hz. The vacuum breakdown voltage decreases with decreasing the external circuit resistance in series with the gap in the range below 103 Ω. This decrease in the breakdown potential is attributed to the very short discharge time of the stray capacitive energy of the connecting leads into the gap compared to the time necessary for the current growth leading to breakdown. The minimum energy necessary to decondition (degrade) a vacuum gap is measured and the degree of deconditioning is determined as a function of energy discharged into the gap. The dc dielectric strength of the vacuum gap always recovers to its original value after a few sparkings.
Interaction of the cathode spot with low pressures of ambient gas
Authors: Emtage P. R.
Published: February 2003

This paper presents a calculation of the interaction of the cathode spot in an electric arc with a low pressure of ambient gas. It is assumed throughout that the basic structure of the spot is unaffected by the gas, the relatively large vacuum spot being a loose collection of smaller fundamental spots. Most of the interaction comes from the smaller current (∼8% of the total) of highly energetic positive ions emitted by the spot; these ions exclude the gas from the neighorhood of the spot which, therefore, never sees the surrounding gas. The equations of the motion yield the pressure dependence of the force on the cathode, the total rate of cathode erosion, and the outward flux of the ions; these agree reasonably well with the experiment, but no force that seems able to separate the components of the vacuum spot has been found (the force that holds them together in vacuum is equally unknown).
A simple equation of state for metals
Authors: Midha Y. R. , Nanda V. S.
Published: February 2003

An equation of state for metals is obtained by assuming that the electronic free energy varies very slowly with volume. In this derivation, the static contribution of the lattice to the free energy is based upon the LJD potential while the lattice vibrations are considered in the harmonic approximation. The theoretical results are compared with experiment for copper with respect to thermal expansion, and good agreement in the temperature range 20–600 K is obtained. For the isothermal variation of volume with pressure, the theory is found to be in agreement with experiment up to 25 000 kg/cm2.
Acousto-helicon coupling in semiconductors with strain-dependent dielectric constants
Authors: Sharma Satish K.
Published: February 2003

It is shown that the strain dependence of the dielectric constant gives rise to strong acousto-helicon coupling in the presence of a dc electric field E0. The phenomenological approach (valid for ql<1, where q is the wave vector of the acoustic wave and l is the mean free path of the electrons) has been used to derive the acousto-helicon dispersion equation for <001≳−oriented transverse acoustic wave propagation in a cubic system parallel to the applied electrostatic and magnetostatic fields. The coupling is found to be proportional to ε40 E20 (ε0 is the dielectric constant in the absence of any strain) for ε0≫1. The solution of the dispersion equation shows that a convective-type instability exists, provided the drift velocity of the electrons exceeds the sound velocity (i.e., v0≳vs). A comparison with the piezoelectric coupling in ordinary piezoelectric semiconductors shows that the ratio of the growth rates αsRe/αpRe=103 for typical parameters of interest. αsRe and αpRe are the growth rates for strain-dependent dielectric constant coupling and piezoelectric coupling, respectively. The present coupling should be observable in semiconductors with an anomalously high dielectric constant, of the order of 2000 (e.g., barium titanate, rutile, etc.) in moderate electric fields.
Elastic moduli of precompressed pyrophyllite used in ultrahigh-pressure research
Authors: Sachse Wolfgang , Ruoff Arthur L.
Published: February 2003

The propagation of ultrasonic pulses in pyrophyllite specimens was studied to investigate the effect of specimen precompression on the measured elastic moduli. Measurements were made at room pressure and, for the precompressed specimens, to pressures of 3 kbar. We find pyrophyllite to be elastically anisotropic, apparently the result of the fabric present in our material. The room-pressure adiabatic bulk modulus as measured on specimens made of isostatically compacted powdered pyrophyllite was determined to be 96.1 kbar. We found the wave speeds of ultrasonic pulses in pyrophyllite to decrease with increasing specimen precompression. A limiting value of precompression was found, above which no further decrease in wave speed is observed. For the shear-wave speeds this occurs at 10 kbar, while for the longitudinal wave at 25 kbar. In the limit, the shear waves propagate 20% slower than in the unprecompressed samples; for the longitudinal wave the difference is 30%. The change in bulk modulus resulting from increasing pressure shows a behavior which can be approximated by a bilinear curve with decreasing slope, the discontinuity occurring between 1.6 and 1.8 kbar. In the second portion of the curve, the bulk modulus derivative is determined to be 22.1. We believe that this value indicates the presence of voids which are closing under pressure. A regression analysis of the data shows that a P1/2 equation appears to give the best fit. The resulting empirical law for the bulk modulus derivative at pressure P becomes: dB/dP=[CL0(0.251P−0.147)−1/2 −CS0(2.76P−2.56)−1/2]×10−1, where P is in kbar and in the present measurements CL0, the longitudinal modulus, is 204 kbar and CS0, the average shear modulus, is 113 kbar.
Acoustic diffraction and the electrostrictive transducer
Authors: Alig R. Casanova
Published: February 2003

Permanent photoinduced periodic space-charge gratings in LiNbO3 are used to modulate the optical refractive index and diffract light. Since this periodic space-charge distribution is the source of a periodic electric field, these gratings ought to modulate the elastic constants and diffract bulk acoustic waves. In addition, these gratings ought to modulate the piezoelectric constant via the electrostrictive effect and behave as distributed transducers for bulk acoustic waves. These phenomena should be observable for frequencies near 10 GHz with grating amplitudes reported in the literature. Some applications of these phenomena are discussed.
Some characteristics of Co2-laser-induced multiple spark breakdown at pressures up to 11 atm
Authors: Morrison R. W. , Swail C.
Published: February 2003

A study has been made of the visible breakdown plasma produced by focusing single TEA CO2 laser pulses 200 nsec wide with salt lenses of 16- and 22-cm focal lengths in argon, helium, neon-helium, and nitrogen at pressures up to 11 atm. Pulse energies ranged from 0.9 to 11 J, with a maximum intensity at the 1-mm focal diameter of 6.6×109 W/cm2. At this incident intensity, well above the breakdown threshold, the main breakdown plasma in argon occurred well upstream of the focus and its multiple structure extended over 5–9 cm. In the focal region only a few isolated sparks were seen. At incident powers closer to threshold, the breakdown occurred closer to, or at, the focus, and migrated upstream toward the laser as the pressure was increased. The spatial structure of the breakdown plasma as seen by time-integrated photography, and the temporal development, monitored by photon drag observations of the transmitted power pulse, were studied with various gases, pressures, and incident pulse energies. A description of the breakdown process is offered which accounts for many of its features, especially the absence of breakdown in the focal region.
A theory and a model experiment on the focusing effect of a Gaussian beam in an inhomogeneous medium
Authors: Kozaki S. , Mushiake Y.
Published: February 2003

For the purpose of radio and optical propagation, it is useful to study the behavior of a beam wave in an inhomogeneous medium. A fundamental problem when the two-dimensional Gaussian beam is obliquely incident on the inhomogeneous medium whose permittivity decreases linearly in one direction is theoretically analyzed. The characteristics of the amplitude and phase front for the beam are made clear quantitatively for the first time. With increasing propagation distance, the amplitude of the incident beam becomes increasingly stronger and a very narrow beam is also obtained (focusing effect). These theoretical results are also applicable for the cases where aλ≪1 (collimated beam), bλ≪1 (slowlying varying medium), and cos2φ−bz is not close to zero. In order to corroborate the validity of the theory, a model experiment was performed in the millimeter-wave region. Thus the predicted strong increase of the field intensity was observed by measuring the beam along the ray path, so that the focusing effect was qualitatively corroborated.
Low-temperature elastic properties of four austenitic stainless steels
Authors: Ledbetter H. M. , Weston W. F. , Naimon E. R.
Published: February 2003

The elastic properties of four austenitic stainless steels—AISI 304, AISI 310, AISI 316, and A286—are reported over the temperature range 300–4 K. These properties include longitudinal modulus, shear modulus, Young’s modulus, bulk modulus (reciprocal compressibility), Poisson’s ratio, and elastic Debye temperature. Elastic constants were determined from measurements of longitudinal and transverse sound-wave velocities using an ultrasonic (10 MHz) pulse-superposition method. Measurements were made in the absence of a magnetic field; these alloys undergo paramagnetic-to-antiferromagnetic transitions at low temperatures. For all four alloys, the shear modulus behaves regularly with respect to temperature. The other elastic constants, all of which have a dilatational component, decrease anomalously at temperatures below 80 K. The largest anomaly, about 3%, is in the bulk mudulus of the 304 alloy; this modulus is lower at 0 K than at 300 K. Results are interpreted on the basis of the Döring effect, which results from a large volume magnetostriction in the magnetic phase. This may be the first report of a Döring effect in antiferromagnetic materials.
Electroreflectance measurements of melt-doped and ion-implanted GaAs
Authors: Anderson Wayne J. , Douglass III Charles A. , Park Y. S.
Published: February 2003

Electroreflectance (ER) is used to detect shallow impurity levels in GaAs doped with Si, Te, Zn, and Cd impurities. The ER of Si-doped GaAs as a function of doping concentration shows that the impurity band merges with the conduction band when the concentration is ∼5×1016 cm3. Ion-implanted samples of GaAs are monitored with electroreflectance to detect annealing stages and impurity substitution. The Te, S, Zn, and Cd ion-implanted impurities are detected and compared to the melt-doped samples. Several advantages of using electroreflectance rather than other detection methods are discussed.
Single-crystal elastic constants of Zr2Ni
Authors: Eshelman F. R. , Smith J. F.
Published: February 2003

The ultrasonic pulse-echo-overlap technique has been used to determine the six independent elastic constants of tetragonal Zr2Ni over the temperature range 4.2–300 K. The temperature dependence of the shear constants, particularly C66, are atypical and indicate a significant degree of mode softening at low temperatures. The results correlate with the recent calculation of Sinha and Harmon in that Zr2Ni satisfies their conditions for the development of charge density waves with attendant mode softening and support the view that mode softening and superconductivity are correlated.
Critical current changes in Nb3Sn irradiated with fast neutrons at 6 K
Authors: Brown B. S. , Blewitt T. H. , Wozniak D. G. , Suenaga M.
Published: February 2003

Multifilament copper-clad wires of Nb3Sn have been irradiated at 6 K to a dose of 1.8×1018 n/cm2 (E≳0.1 MeV). The critical current (Jc) was measured as a function of dose and applied magnetic field to 33 kOe. After 1.2×1018 n/cm2, an increase of 33% in Jc occurred at 33 kOe from an initial value of 1.5×106 A/cm2 at 4.5 K. The increase was smaller at lower applied fields, and Jc actually decreased for H<8 kOe. For all fields, the increase in Jc eventually saturated and then decreased as the dose increased, with the saturation dose increasing with increasing applied field. The critical temperature (Tc) changed by <1 K at the highest dose. Approximately 25% of the change in Jc recovered after a 295 K anneal. The Jc changes are explained as an increase in flux pinning from radiation-induced defect cascades that leads to an increase in Jc greater than the decrease in Jc which results from a decrease in Tc of 1 K and from the increase in Hc2 produced by the increase in normal resistivity. A model is proposed that allows the prediction of the dose dependence of various terms in the pinning-force density and explains the field and dose dependence of the Jc changes. Measurements of the superconducting–to–normal-state thermal transition indicate that the decrease in thermal conductivity of the Cu cladding is important when considering the degradation of the thermal transition current that occurs at high doses.
Revised dynamical theory of thermoplastic deformation
Authors: Killat U.
Published: February 2003

A method of quantifying the influence of the surface charge on the deformation of thermoplastics has been proposed. The results obtained from our analysis are compared with measurements of the spatial frequency distribution of thermoplastic frost deformation. The agreement between theory and experiment is found to be satisfactory in view of the approximations made in analysis.
Temperature dependence of current flows in nondegenerate MIS tunnel diodes
Authors: Shewchun J. , Green M. A.
Published: February 2003

Current flows in the nondegenerate metal-insulator-semiconductor (MIS) tunnel diode are temperature sensitive. This temperature sensitivity can be an aid in interpreting the properties of these devices. It allows information regarding the energy distribution of particles tunneling between the metal and the semiconductor to be obtained as well as providing another technique for estimating metal-semiconductor barrier height. Experimental support is given for the existence of minority- and majority-carrier diodes as well as for devices where the current flow is dominated by tunneling between the metal and surface-state levels.
Computations of cylindrical antenna characteristics in a uniaxial medium by the matrix method
Authors: Cheng Karl C.H. , Chen Hollis C.
Published: February 2003

A closed−form dyadic Green’s function appropriate to radiation of sources in a uniaxially anisotropic medium is derived. The current distribution, the input admittance, and impedance of a cylindrical antenna immersed in such a medium are then calculated by the matrix method. From the current distribution, the far−field power gain patterns of the antenna are also obtained.
Transient electromagnetic response of a permeable nonuniformly conducting sphere
Authors: Verma Saurabh K. , Joshi Madhu S.
Published: February 2003

Quasistatic response of a nonuniformly conducting and magnetically permeable sphere to a step pulse is obtained. the effect of conductivity distribution pattern and permeability of the sphere on the transient response is examined in detail. The results show that the introduction of conductivity inhomogeneity has considerable effect on the observed secondary fields and that the magnetic permeability contrast further
Electromagnetic scattering from an elliptic cylinder loaded by continuous and discontinuous surface impedances
Authors: Alexopoulos Nicolaos G. , Tadler George A.
Published: February 2003

The electromagnetic scattering from elliptic cylinders with a surface which consists of sections of dissimilar electrical material is considered. The problem is solved by applying Galerkin’s method in conjunction with the Leontovich impedance boundary condition. The method applies to elliptic cylinders of arbitrary lossy or active materials and corrugated or rough surface cylinders. The accuracy of the Leontovich impedance boundary condition is discussed in terms of the radius−of−curvature−to−wavelength ratio and in terms of the index of refraction. In addition, the scattering cross section is computed for various cases of impedance loading or cylinder material
Linear force and dislocation multipoles in anisotropic elasticity
Authors: Hartley C. S.
Published: February 2003

The displacement field of a linear singularity in an anisotropic medium is developed by superimposing the displacement of a distribution of simple singularities. The result can be expressed in terms of the moments of the distribution. This approach provides a means of comparing atomic displacements obtained by computer simulations of dislocations with analytical results to obtain numerical values for the moments of the effective distribution. Distributions of linear force dipoles can also be used to construct models of solute segregation to dislocations.
Anomalous diffusion in nonmetals (origin and effects of internal electric fields)
Authors: DeFord J. W. , Johnson O. W.
Published: February 2003

When electrically active impurities or defects diffuse in a material with a band gap ≳ 10kT, the changing concentration of these ions may result in internal electric fields which will significantly alter the diffusion process, and result in gross misinterpretation of diffusion experiments. Equations are derived which describe the diffusion of interstitial impurities in such a system, and which take proper account of compensating immobile impurities. A technique for numerical solution of these equations is described and the results of calculations for the case of H+ in TiO2 are presented. These calculations predict a large enhancement of the over−all diffusion rate and a very distinctive concentration profile. The latter is of critical importance in identifying this effect, since our calculations show that a measurement of total impurity content vs time will appear to agree fairly well with Fick’s law; however, the apparent diffusion coefficient obtained in this way can be in error by a factor of 100 or more. Experimental results for the H+−TiO2 system are presented, which agree quantitatively with our calculations.
Diffusion of H and D in TiO2: Suppression of internal fields by isotope exchange
Authors: Johnson O. W. , Paek S.−H. , DeFord J. W.
Published: February 2003

Measurements of H and D diffusion in TiO2, using the isotope exchange technique described in the preceding paper, are reported. Use of this technique resulted in diffusion which was accurately described by Fick’s law with a constant diffusion coefficient, as predicted theoretically, in sharp contrast to single ion diffusion, where dramatic departures from classical diffusion theory were observed. The measured diffusion coefficients for H were 1.8×10−3 exp(−0.59eV/kT) and 3.8×10−1 exp(−1.28eV/kT) and 3.8×10−1 exp(−1.28eV/kT) cm2/sec for diffusion ∥ and ⊥ to the c axis, respectively. Ionic conductivity measurements are reported, which agree well with the bulk diffusion measurements, and permitted us to extend the temperature range of the measurements for c−axis diffusion from 125 to 750 °C, corresponding to a range of more than four orders of magnitude in D. The measured diffusion parameters were found to be essentially independent of sample purity, although it was observed that significant concentrations of lattice defects sharply inhibited H diffusion.
Electron−irradiation−induced damage recovery effects in lightly doped n− and p−type α−tin
Authors: Myhra S. , Gardiner R. B.
Published: February 2003

The recovery of the electrical resistivity and thermoelectric power in a number of n− and p−type α−tin samples, irradiated at low temperature, is considered. Three distinct first−order stages in the temperature range 20−50 K are observed. A fractional defect recovery has been deduced such that relative percentages of IA : IB : IC=90 : 4 : 6 anneal in the three stages. Activation energy scaling factors were found to be 69, 94, and 122 meV, respectively, for the three stages. Carrier mobilities as functions of carrier and defect concentration were calculated and found to be in good agreement with previously published values. Estimates for these quantities were also deduced when the samples were near to their intrinsic states (ne∼nh). A close−pair−defect charge carrier trapping model provides a consistent explanation for all damage and recovery data.
Nonlinear surface−wave propagation over plasmas and conductors
Authors: Bhat B. , Tripathi V. K.
Published: February 2003

An investigation of nonlinear surface−wave propagation over plasmas and conductors has been carried out when the nonlinearity in the complex dielectric constant arises on account of ponderomotive force and energy−dependent collisions. Analytical expressions have been obtained for the decay rate and phase velocity of the evanescent wave in the limit of perturbation approximation. The nonlinearity is found to reduce the rate of decay of an evanescent wave in a conductor and also in the case of a dense plasma. A study of the phenomenon of total internal reflection reveals that the critical angle increases due to nonlinearity and the evanescent wave decays slower.
Ohmic contact and impurity conduction in P−doped CdTe
Authors: Gu Jyongsil , Kitahara Toshiyuki , Kawakami Kouichi , Sakaguchi Tadao
Published: February 2003

Good Ohmic contacts to P−doped and undoped p−type CdTe have been obtained by evaporating Au or Pt on the surfaces in high vacuum (p<1×10−6 Torr) and firing these in a H2 atmosphere. This contact has been used on the crystals having carrier concentrations between 3×1014 and 3×1017 cm−3 and stayed nearly Ohmic down to 4 °K. Consequently, temperature dependences of Hall coefficients and resistivities have been measured and an impurity conduction has been found in the P−doped CdTe.
Influence of surface energy anisotropy on morphological changes occurring by surface diffusion
Authors: Brailsford A. D. , Gjostein N. A.
Published: February 2003

The influence of surface energy anisotropy on morphological changes occurring by surface diffusion, on simply shaped bodies, is investigated. A preliminary analysis of the equilibrium shape of a two-dimensional body for arbitrary anisotropy is given, the primary aim being to determine the range of validity of the perturbation scheme used in the subsequent time-dependent analysis. It is shown that such a scheme is valid for the entire range of shapes later considered if γ (ϑ)+d2γ (ϑ)/dϑ2≳0, where γ (ϑ) is the specific surface free energy of a surface whose normal is oriented at an angle ϑ to the reference crystallographic axes. Under this condition the complete relaxation, from an assumed initial circle to the final equilibrium shape, is derived, providing the surface diffusivity is isotropic. When γ (ϑ)+d2γ/dϑ2 is negative, the perturbation scheme furnishes proof of an initial unstable growth away from the circle, although it cannot be used to derive the complete relaxation behavior. Nevertheless, thereby a proof is provided of the existence of such an instability, which was derived earlier by Mullins for only a semi-infinite body, in a finite body (in two dimensions). For completeness, a brief discussion is given of the influence of small surface energy anisotropy in three dimensions for surface-diffusion-controlled shape changes from an initial sphere. Application of these results to the kinetics of particle shaping during the early stages of thin-film growth is also presented.
Acoustic characterization of two unreacted explosives
Authors: Sutherland Herbert J. , Kennedy James E.
Published: February 2003

Acoustic wave experiments were conducted on two unreacted heterogeneous explosives, PBX-9404 (HMX-based) and X-0219 (TATB-based), to study low-amplitude wave dispersion. Viscoelastic dispersion was found to be common to both explosives and is a direct result of the viscoelastic nature of the materials. This mechanism was studied using a direct transmission ultrasonic technique to measure acoustic phase velocity and acoustic attenuation as a function of temperature at a constant frequency (−10 to 40 °C at 1.0 and 0.5 MHz). Geometric dispersion was found to be important in the PBX-9404, but was not significant in the X-0219. This mechanism was studied by using an ultrasonic water-bath technique to measure the phase velocity as a function of frequency at constant temperature (0.5–4.0 MHz at 20 °C).
Characteristics of a plasma generated by combustion in a spark ignition engine
Authors: Rado W. G.
Published: February 2003

Plasma probe measurements at dc and bulk absorption measurements at microwave frequencies have been made on a plasma generated by the combustion in a spark ignition engine. From these measurements, estimates of the charge concentration and characteristics of the space-charge region formed around the plasma probe under the condition of positive-ion collection have been deduced. The degree of ionization is estimated to be as high as 1 : 104 in the burned gases, depending on engine load. The charge species are concluded to consist primarily of electrons and positively charged ions. In addition, the applicability of various plasma probe theories predicting I-V relationships has been investigated. The available data strongly indicate that the probe theory including the effect of flow of the ionized gases is the applicable one.
Capacitance of Kelvin guard-ring capacitors with modified edge geometry
Authors: Heerens W. Chr. , Vermeulen F. C.
Published: February 2003

An exact solution has been obtained for the capacitance of Kelvin guard-ring capacitors with strongly limited radial dimensions compared with the distances between the electrodes. This is done by solving the three-dimensional Laplace equation by means of separation of variables. From the achieved equations, formulas expressing the influences of several systematic errors are derived. Calculated capacitances, using these equations, are in full agreement with corresponding measured capacitances. This enables us to construct stable highly sensitive standard displacement transducers. Also small capacitors with low capacitance supplied with trim facilities can be easily constructed with this knowledge.
Fields of short radio-frequency probes in a magnetized plasma
Authors: Singh Nagendra
Published: February 2003

The diagnostics of a magnetized plasma can be done by measuring the spacings of the interference structure in the angular distribution of the field of a properly excited probe in the plasma. In this paper the effect of probe dimensions on the interference structure is investigated. The sheath around the probe is found to have profound effects on the angular distribution of both the phase and the amplitude of the filed of the probe. This investigation reveals that only thin electric dipole of half-length less than 30 Debye lengths or so is useful for the plasma diagnostics.