bluuebunny/crossref_metadata_2025 huggingface dataset:
Power Radiated by Oscillating Magnetic and Oscillating Electric Dipoles in a Cold, Streaming Plasma
Authors: Bergeson John E.
Published: February 2004

The power radiated by oscillating magnetic and oscillating electric point dipoles is calculated for the case where the dipoles are immersed in a cold, streaming plasma. The power output of the dipoles in a streaming plasma is less than it is in a stationary plasma, although the correction term is of order β2, where β is the ratio of the plasma's streaming velocity to the velocity of light. The power output is calculated by a generalized Poynting vector method, using electromagnetic-field expressions derived from a set of linearized, covariant cold-plasma equations. The results of this paper are compared with the results of Daly, Lee, and Papas, and of McKenzie, who calculate the power output of the oscillating electric dipole from a ``dispersive medium'' point of view.
Transient Color Centers in Fused Quartz
Authors: Holzrichter J. F. , Emmett J. L.
Published: February 2004

Transient color centers, induced by pulses of uv light, have been observed in fused quartz. The absorption peaks appear to agree with the wavelengths of the weaker permanent coloration. The band at 3000 Å has a lifetime of 0.38 milliseconds; that at 5000 Å has a lifetime of about 12 sec.
Steady-State Gain of Stimulated Brillouin Scattering in Liquids
Authors: Barocchi F.
Published: February 2004

The S.B.S. steady-state gain is derived taking into account the energy-transfer relaxation properties of the liquids. Calculation of the gain for C6H6 and CCl4 are performed. Quantitative comparison between experimental and theoretical gain in n-hexane, ethyl-ether, and CS2 are also derived.
Dislocation Arrangements in Fluorapatite
Authors: McManus G. M. , Hopkins R. H. , Takei W. J.
Published: February 2004

Some observations on the microstructure of Czochralski-grown fluorapatite, Ca5F(PO4)3, single crystals are presented. From etching and x-ray topographic studies we have found that slip in this material is on (101̄0) planes, with one Burgers vector in the c direction, and another in the basal plane and probably along the [101̄0] direction.
New Method of Obtaining Volume, Grain-Boundary, and Surface Diffusion Coefficients from Sintering Data
Authors: Johnson D. Lynn
Published: February 2004

A sintering model is proposed by which all of the significant mechanisms of material transport may be identified, even though more than one mechanism may be operating simultaneously. For diffusion-controlled sintering it is possible to calculate both the volume and the grain-boundary diffusion coefficients from measurements of neck size, shrinkage, and shrinkage rate. Furthermore, the surface diffusion coefficient may be estimated through computer synthesis of the sintering curves. Preliminary results on iron and copper have yielded values of the diffusion coefficients which are in good agreement with those measured by other techniques.
Dispersion-Corrected Three-Wavelength Laser Heterodyne Measurement of Plasma Densities
Authors: Liu C. S. , Verdeyen J. T. , Cherrington B. E.
Published: February 2004

A three-wavelength laser heterodyne system for plasma diagnostics has been developed using the 0.6328, 1.15, and 3.39 μ transitions in He–Ne. In order to use the 3.39 μ transition, an experimental technique has been developed to measure the dispersion introduced by the lasering atoms under the same conditions that are used for plasma measurements. The dispersion-corrected 3.39 μ data, when combined with the data at 1.15 and 0.6328 μ, give excellent agreement in the measurement of temporally and spatially resolved electron densities and changes in neutral densities in the afterglow of a pulsed argon discharge. The electron-density measurements agree with integrated electron-density measurements made with a microwave cavity operating in the TM010 mode.
Elastic and Anelastic Behavior during the Martensitic Transformation in Indium-Thallium Alloys
Authors: de Morton M. E.
Published: February 2004

Measurement of internal friction at strain amplitudes <10−5 in In-rich In–Tl alloys has shown an amplitude-dependent peak associated with the fcc→fct martensitic transformation. The peak is thermally activated when the transformation occurs near the melting point Tm, but not at lower temperatures. It is suggested that the peaks originate from the stress-assisted motion of twin boundaries that are known to spontaneously coalesce immediately below the transformation temperature. The activation energy associated with the transformation peak near Tm is 10–13 kcal/mole higher than for the diffusion of Tl in In. A mechanism is proposed for this relaxation, invoking an interaction between twin boundaries and solute, whereby reordering of solute is effected in differently orientated tetragonal regions by twin-boundary motion. Shear modulus measurements indicated abrupt changes at the transformation temperature and positive temperature coefficients of modulus in the high-temperature fcc phase, implying structural instability and an ``entropy-elastic'' state. At 0.9 Tm, about 60% of the elasticity in a 19.5% Tl–In alloy arises from a change in vibrational entropy with extension. The results are consistent with the known crystallography of the transformation.
Structural and Optical Evaluation of Vacuum-Deposited GaP Films
Authors: Davey John E. , Pankey Titus
Published: February 2004

Optical absorption-edge shifts of up to 1.5 eV have been observed for GaP films deposited in textured polycrystalline states and in the amorphous state. The amorphous-crystalline transition occurs for a substrate temperature Ts of about 240°C. The films deposited at 240°C≤Ts≤270°C exhibiting the large optical absorption-edge shift are nontransparent, metallic-appearing, and exhibit a strong [110] texture. The amorphous films deposited at just below 240°C exhibit the same optical properties. With increasing Ts, the films exhibit decreasing optical absorption-edge shifts, becoming transparent-yellow for Ts≥425°C. However, a bulk optical behavior is achieved only by annealing the films at temperatures up to 600°C. The principal textures found by x-ray diffraction are [110] for 240°≤Ts≤270°C, and [111] for Ts>350°C. Reflection-electron-diffraction (RED) observations agree substantially with those obtained by x ray, but also indicate some mixed textures. A weak (101̄0) reflection is observed by both x rays and RED, indicating an incipient hcp phase; it is shown that this is not causally related to the optical-edge shift. X-ray lattice-constant measurements over the range of Ts from 250°–425°C indicate no observable systematic deviation from bulk values; these observations rule out any causal relationship between changes in lattice constant and the optical absorption-edge shift. Extinction bands or bounded-plasma resonance effects do not seem to be able to explain the experimental behavior; the shifts are most probably due to large concentrations of self-compensated natural defects. It is emphasized that these as-deposited and annealed GaP films cover the entire absorption spectrum (α vs E) of all III-V compounds (except InAs and InSb) plus Ge and Si.
Efficient Second-Harmonic Generation with Diffraction-Limited and High-Spectral-Radiance Nd-Glass Lasers
Authors: Hagen W. F. , Magnante P. C.
Published: February 2004

Efficient second-harmonic generation (SHG) at 5300 Å has been achieved with KDP and LiNbO3 crystals when Nd-glass lasers of high radiance and narrow bandwidth were used. With KDP and a diffraction-limited laser system having a 19 Å bandwidth, 15 J of radiant energy at 5300 Å were obtained with a 51% energy-conversion efficiency. Since the harmonic light pulse was narrower than the fundamental pulse, the peak-power-conversion efficiency was 70%. The peak power in the green was 1.0 GW. The ratio of harmonic-fundamental pulse duration increased as SHG increased into the saturation region as expected. For LiNbO3, the relatively large dependence of phase-matching angle on wavelength limits the maximum SHG efficiency to several percent when broad-band lasers are used. With LiNbO3, therefore, a laser system was used having mode selectors which limited the bandwidth to less than 0.5 Å while the beam divergence was 1.5 mrad. In this case 21% energy conversion and 33% peak-power conversion were obtained with a fundamental flux density of only 2 MW/cm2 inside the crystal. The values found for the elements of the nonlinear dielectric tensor, corrected for the random multimode nature of the laser, are d36(KDP) = (1.1±0.1)×10−9 esu and d31(LiNbO3) = (17±6)×10−9 esu. At low conversions a laser beam with fluctuations due to random multimoding is expected to give as much as twice the harmonic produced by a single-mode laser. At high conversions in the saturation region this ``doubling'' does not occur as verified by our measurements.
An Approximate Theory of Skin-Effect Acoustic Generation in Conductors
Authors: Southgate P. D.
Published: February 2004

Abeles has shown that a marked acoustoelectric coupling can occur due to the penetration of a high-frequency electric field into a conductor. Calculations are presented here of the coupling due to the spatial phase shift between the Coulomb force on the lattice ions and the reaction force of the electrons, and due to the localized electron reaction on the surface. The latter is largest for diffuse electron reflection, and is the most important coupling mechanism at frequencies above 30 GHz. Efficiencies are fairly low, being in the 10−2 to 10−3 range under ideal conditions; however, they remain of this magnitude up to the lattice vibration frequency. The model used is approximate: a classical free-electron model, idealized cases of fixed electron free paths with either uniaxial or isotropic electron motion being considered. For specular surface reflection of electrons, the exact model of Quinn is available for comparison, and it is shown that the results are very similar. Single and multilayered film structures are considered in addition to the semi-infinite conductor.
Magnetic Susceptibility of ε and η Phase Alloys in the Silver-Zinc System
Authors: Noguchi S. , Yoneyama T. , Massalski T. B.
Published: February 2004

Magnetic susceptibility measurements are reported in the range of the hcp ε and η phases of the Ag–Zn system. The observed trend suggests that a minimum occurs in the magnetic susceptibility of the conduction electrons within the phase field of the ε phase at an electron concentration of approximately 1.8 electrons per atom. In the η phase the magnetic susceptibility increases rapidly, but the trend is less steep than that extrapolated from the ε phase. The results show certain similar features with the measurements of the lattice spacings and of thermodynamic properties reported in the literature. The magnetic susceptibility of the ε phase alloys can be related to the possible interactions between the Fermi surface and the Brillouin zone, but the behavior of the susceptibility in the η phase appears to be also dependent on local interactions between zinc atoms.
Radiative Tunneling in GaAs Abrupt Asymmetrical Junctions
Authors: Casey H. C. , Silversmith Donald J.
Published: February 2004

A representative number of abrupt GaAs junctions, asymmetrically doped, have been studied to delineate quantitatively the properties of spectra (called shifting-peak spectra) whose peak energy approximately equals the applied voltage V, and shifts in position and intensity with V. The free-electron concentration n on the more lightly doped side was varied from 3×1017 cm−3 to 8×1018 cm−3, the voltage range was ∼1.0 to ∼1.5 V, and the temperature was varied from 12° to 255°K. Because the active region width is 600 Å or less, and the spectral shape agrees in all details with Morgan's theory of photon-assisted tunneling, these shifting-peak spectra have been identified as radiative tunneling. It is shown here that no adjustable parameters are needed to calculate the experimental spectral shape when only T, V, and n are specified. This means that for any given temperature, n alone represents the influence of the junction on the spectral shape, while the independent parameter in terms of excitation is the voltage and not the current, as usually stated. The agreement between the calculated and experimental spectra includes the logarithmic slope of the low energy tail, and the difference between V and the energy of the peak-emission intensity hvp: eV0=eV-hvp. This agreement emphasizes the necessity of including the parabolic junction potential as obtained from Poisson's equation when calculating the tunneling-hole and electron-wave functions. The usual simplifying assumption of a linear potential is inadequate. To clarify previous observations of one or two types of shifting-peak spectra, linear-graded and abrupt-asymmetrical junctions were made from adjacent wafers of the same crystal, and the resulting shifting-peak spectra were compared. Only band-to-band radiative tunneling was observed for the abrupt junction, but for the linear-graded junction two shifting-peak spectra were observed. In the low excitation region for linear-graded junctions, the shifting-peak spectra may be described by band-to-impurity radiative tunneling that results in a narrow active-region width, while at higher bias the emission becomes band-to-band radiative tunneling with a wider active region. These results demonstrate that shifting-peak spectra previously attributed to band filling may be described in terms of photon-assisted tunneling.
Ionic Analysis of Cataphoresis in He–Ne Mixtures
Authors: Gaur J. P. , Chanin L. M.
Published: February 2004

For studies of cataphoresis in He–Ne mixtures, an analytic expression is derived for the functional dependence of the neon atoms in the axial direction. The analysis, which involves the continuity equation, considers the production and loss mechanisms of the Ne+ ions. The present theory can be used to predict the degree of ionization of neon at a given pressure and current, when the appropriate rate coefficients are known. In addition, techniques for ion sampling from gaseous plasmas have been used in the present investigation. Measurements have been made in commercial helium-gas samples having a quoted neon concentration ≤0.001% and in samples containing 0.05% neon. Studies were conducted over a pressure and current range of 7–30 Torr and 8–80 mA, respectively. Depending on the experimental conditions, the following ions were observed: He2+, Ne+, Ne2+, and HeNe+. For the case of HeNe+, the present studies permit an estimate of the rate coefficient for the reaction Ne++2He→HeNe++He which is comparable to values obtained from afterglow studies. Measured values of the degree of ionization are in good agreement with values calculated using the present theory.
The Measurement of the Erosion Rate at the Electrodes of an Arc Rotated by a Transverse Magnetic Field
Authors: Harry J. E.
Published: February 2004

The measurement of the erosion at the electrodes of an arc rotated between water-cooled nonrefractory coaxial electrodes in an axial magnetic field has been made in air at atmospheric pressure. Values of erosion rate an order-of-magnitude less than those previously reported have been obtained. The effect of variation in axial magnetic flux density, arc velocity, rotational frequency, cooling-water flow-rate, and electrode wall thickness have been investigated. A steady-state model, taking into account the nonuniform thermal distribution in the electrode below the arc root, has been obtained in terms of the electrode dimensions normalized with respect to the diameter of the arc root. The minimum conditions for the surface of a cold-cathode electrode to be maintained below the melting point of the electrode material are deduced.
Interaction of Li and O with Radiation-Produced Defects in Si
Authors: Young R. C. , Westhead J. W. , Corelli J. C.
Published: February 2004

The interaction of Li atoms with O impurities and with defects produced in Si by 1.5 MeV and 47 MeV electrons was studied using infrared spectroscopy. Li was diffused in low oxygen-containing uncompensated Si with initial resistivity in the range 15–28 500 Ω·cm and in high oxygen-containing Si with initial resistivity of 15–200 Ω·cm. The Li concentration in the samples varied from about 1016 to ≲1019 Li atoms/cm3. New radiation-induced bands at 1.4 and 1.7 μ are observed. Divacancy production as measured by the 1.8 and 3.3 μ defect bands is markedly decreased in samples of high Li content with concomitant growth of the Li-associated 1.4 and 1.7 μ bands. Annealing of the 1.4 and 1.7 μ bands strongly depends upon the Li concentration. Recovery occurs at a temperature of 150°C for the 1.4 μ band, and at 350°C for the 1.7 μ band, for samples containing ∼6×1017 Li/cm3. In samples containing ∼2×1016Li/cm3, the bands at 1.4 and 1.7 μ disappear after annealing at 330° and 470°C, respectively. Sharp Li- and O-associated defect bands in the 700–1000 cm−1 range are produced only in high O-containing samples, and the presence of Li has a pronounced effect on the production and recovery of the A-center defect (830 cm−1 band). In samples of high Li content, the predominant absorption is due to free carriers and is found to be in agreement with predictions of theory. A search for defect absorption bands attributable to vibrational modes of the isolated interstitial Li+ ions yielded negative results.
Fowler-Nordheim Tunneling into Thermally Grown SiO2
Authors: Lenzlinger M. , Snow E. H.
Published: February 2004

Electronic conduction in thermally grown SiO2 has been shown to be limited by Fowler-Nordheim emission, i.e., tunneling of electrons from the vicinity of the electrode Fermi level through the forbidden energy gap into the conduction band of the oxide. Fowler-Nordheim characteristics have been observed over more than five decades of current for emission from Si, Al, and Mg. If previously measured values of the barrier heights are used, the slopes of the Fowler-Nordheim characteristics (log J/E2 vs 1/E) imply values of the relative effective mass in the forbidden band of about 0.4. These values take into account corrections for image-force barrier lowering and for temperature effects. The absolute values of the currents are lower by a factor of five to ten than the theoretically expected values, probably due to trapping effects. The temperature dependence of the current was found to follow the theoretical curve from 80°–420°K. However, an inconsistent relative effective mass of about 0.95 had to be assumed. These results are believed to provide the most complete examination of the Fowler-Nordheim-emission theory.
The Change in Work Function of the (100) Surface of Tungsten as O2, N2, CO2, and H2 are Adsorbed
Authors: Abey A. E.
Published: February 2004

The change in work function of the (100) surface of a tungsten single crystal was measured as a function of time as gas adsorbed on the surface. Using a simple model, the work function changes for monolayer coverage were found to be 0.94 eV, −0.7 eV, 0.21 eV, and 0.44 eV, for O2, N2, H2, and CO2, respectively. The initial bare surface sticking probabilities were found to be 0.24, 0.37, 0.63, and 0.29, respectively. The initial changes in work function per molecule were found to be 9.4×10−16 eV, −7×10−16 eV, 2.1×10−16 eV, and 1.75×10−15 eV, respectively.
Dielectric Breakdown of Polymer Films
Authors: Blok J. , LeGrand D. G.
Published: February 2004

Strong electric fields have been applied to dielectric polymer films to study field-induced mechanical stresses. For voltages near breakdown the mechanical forces are sufficient to cause localized deformation in some polymer films. Considerable field enhancement can occur at the deformation sites, leading to reduced nominal dielectric strength for the samples. Experimental evidence for electromechanical deformation is presented as a possible explanation for the poor agreement between the observed dielectric strength and that predicted theoretically.
Coherent Emission from Rare Earth Ions in Electro-optic Crystals
Authors: Johnson L. F. , Ballman A. A.
Published: February 2004

We report the observation of coherent emission from three rare-earth ions in electro-optic crystals. Oscillation is observed from Nd3+ ions in Bi4Ge3O12, LiNbO3, and Ba0.75Ca0.25Nb26O at room temperature, and from Tm3+ and Ho3+ ions in LiNbO3 at 77°K. Second-harmonic radiation is obtained from LiNbO3:Tm3+ and electric-field modulation of threshold is observed for certain crystals of LiNbO3:Nd3+. The latter effect is believed to arise from crystal strain. The propagation angle for phase-matched second-harmonic generation is calculated to lie at 43° to the c axis for both LiNbO3:Tm3+ and LiNbO3:Ho3+ at 77°K. Phasematched second-harmonic generation from LiNbO3:Nd3+ is not possible, since the maser line is an extraordinary wave. However, the polarization of the maser line in LiNbO3:Nd3+ is appropriate for phasematched parametric frequency conversion in the near infrared. Attempts to observe such radiation were not successful due to the limited power available in the fundamental.
Perturbation of Microwave Cavities by Lossy Dielectrics and Plasmas
Authors: Hall Richard B.
Published: February 2004

The frequency shift and Q change of a microwave cavity caused by lossy dielectrics or plasma spheres or cylinders is calculated. The necessity for this analysis is prompted by the use of microwave cavities to measure the expansion of nearly spherical plasmas created by focused high-power lasers. The conditions required for the perturbing volume to behave as if it were a perfect conductor are examined. It is found that much lower conductivities (or permittivities) are required when the perturbing volume is placed in a cavity region where electric energy is predominant.
The Heat Problem in Magneto-optic Readout
Authors: Michael W. A. , Treves D.
Published: February 2004

The transient temperature distribution produced by a surface heat source with Gaussian distribution in one dimension and of infinite extent in the other is calculated. The heated medium is a thin metallic film on a thick substrate. The transverse temperature gradient in the thin film is neglected and it is assumed that all the heat is generated in the thin film. The heat source is assumed to be a light beam. A stationary medium and one moving at constant velocity under the beam are considered. Numerical result of maximum temperature and heated area width are given for a glass and copper substrate.
Tunneling and Resistive Determinations of the Transition Temperature of Thin Lead Films
Authors: Feldmann W. L. , Rowell J. M.
Published: February 2004

The transition temperature Tc of a lead film has been determined from both the resistance along the film and from tunnel measurements of an aluminum-aluninum-oxide-lead junction. Tc by resistivity was 7.214°K and from tunneling 7.208°K. The agreement indicates that tunneling measurements may be used for accurate determinations of the transition temperature.
Determination of Surface Structures using LEED and Energy Analysis of Scattered Electrons
Authors: Weber R. E. , Johnson A. L.
Published: February 2004

It is shown that the energy analysis of scattered electrons (EASE) is a useful tool when used in conjunction with the conventional LEED surface studies. It is demonstrated that the sensitivity is such that 0.02 monolayers of Cs can be detected on a Si surface. The Auger peak for K on a Ge(111) surface has been calibrated quantitatively and this calibration has been used to determine the K coverage after the overlayer was partially desorbed by heat treatments. The coverage measurements were used along with the LEED patterns to determine the surface structure.
Magnetic Pinch Effect in the Thermal rf Induction Plasma
Authors: Chase J. D.
Published: February 2004

The pinch effect or excess magnetic pressure is calculated and measured for an rf induction plasma in argon. This excess magnetic pressure (Pm), which hitherto has been overlooked in all previous investigations concerning the induction plasma, explains the reported anomalous flow behavior of the plasma torch. Theory for calculating Pm is given using a model of the plasma as a solid conductor of constant electrical conductivity. From current density and magnetic field distribution within the plasma, the local Lorentz force is evaluated, and summation across the plasma radius gives the maximum Pm at the center of the peripheral discharge path. Published values for coupling efficiency and temperature profile are employed in conjunction with measured oscillator circuit parameters in order to make the calculation. The calculated Pm at the center of a 4.7 MHz, 2.5 kW argon induction plasma in a 30 mm tube is 64.5 dyn/cm2. At the center of the plasma, Pm was measured with a cooled probe and found to be 71.5±3 dyn/cm2. Although Pm/P≈10−4, the magnetic pressure has an appreciable effect on the fluid mechanics of the discharge. The pinch or compressive force acts inward around the circumference, but not at the ends of the cylindrical plasma. Consequently, a magnetically induced flow occurs out from both ends of the plasma.
Evaluation of Some Transport Integrals. III
Authors: Glasser M. L.
Published: February 2004

The integrals ∫ 0∞xl(x2n+a2n)−1ex(ex±1)−2dxare evaluated in closed form in terms of the trigamma function. The case n=2, l=4, and some related integrals are discussed.
Dynamic Fatigue of Soda-Lime-Silica Glass
Authors: Ritter J. E.
Published: February 2004

The effect of strain rate on the room-temperature strength of soda-lime-silica glass was determined. The strength of acid-etched glass rods increased continuously from 190 200 to 284 800 psi on increasing the strain rate from 9×10−4 to 15×10−2 in./in./min. No difference in strengths was observed on testing in laboratory atmosphere or with the specimens wetted with distilled water. For abraded glass rods the strength in laboratory atmosphere varied from 12 555 to 16 540 psi on varying the strain rate from 3×10−3 to 9×10−2 in./in./min. Tests conducted with the abraded samples wetted with distilled water caused approximately a 10% reduction in strength, but no appreciable change in the strain-rate sensitivity. The stress corrosion model proposed by R. J. Charles successfully predicts the room-temperature strain-rate sensitivity of the failure process for both acid-etched and abraded glass samples. Using relationships derived from this model, it was further shown that the stress concentration relationship proposed by Inglis is valid for acid-etched glass.
Electron Irradiation of Single Crystals of Aluminum
Authors: Longshore R. E. , Chaplin R. L.
Published: February 2004

Details are given about the preparation of suitable aluminum samples for studying the effects of electron irradiation of single crystals. The observed annealing spectra of stage I differ for samples irradiated along different crystallographic directions. Results show that when the atomic-recoil energy is slightly greater than the threshold energy, the IB substage is enhanced for irradiations parallel to the 〈100〉 but is suppressed for the 〈110〉. Evidently, the most favorable conditions for producing IB-type defects occur when the initial atomic displacements cause atoms to move in the 〈100〉. A qualitative discussion is given which explains the observed energy dependence of the single-crystal samples in terms of atomic displacements along 〈100〉 and 〈110〉 directions.
The Fracture of Surface Coatings on a Strained Substrate
Authors: Grosskreutz J. C. , McNeil M. B.
Published: February 2004

The fracture of brittle coatings on a strained substrate is examined from two points of view. In the first case, the substrate deforms continuously and regularly spaced fractures occur in the coating. The spacing d at any strain ε is given by In ε/ε0 = (4g/d) (1−d/d0), where d0, ε0 are any convenient set of data points, and g is a parameter having the units of length. In the second case, the substrate deforms by crystallographic slip and fracture of the oxide may or may not occur at the slip step. The criteria for fracture are that the interface adhesive stresses be too large for the coating to sustain the necessary peel stress. Quantitative relations are given in terms of the coating thickness, fracture strain, and the orientation of the slip step with respect to the surface. The results for both cases are compared with experiment and found to be in essential agreement.
Anisotropic Pinning and Guided Motion of Vortices in Type-II Superconductors
Authors: Niessen A. K. , Weijsenfeld C. H.
Published: February 2004

Guided motion of vortices in type-II superconductors is studied by measuring transverse voltages. The experiments were performed mainly on a Nb–Ta alloy for various magnetic fields, transport currents, and temperatures. The experiments show that in general, the onset of apparent resistance in the mixed state is coupled with fully guided motion of the vortices. With increasing magnetic field, the ratio of transverse and longitudinal voltages decreases. However, this ratio goes through a maximum in materials where the apparent resistivity goes through a minimum. A model is discussed with a guiding force becoming independent of current at higher current densities. The voltages calculated with this model are in agreement with those measured on a Nb–Ta alloy and on a Pb–In alloy. The model is also applied to the situation where a true Hall effect is measured. The conclusion is that pinning and guiding can reduce the Hall angle when the current density is small. The large Hall angles measured in the mixed state cannot be related to guided motion with the existing models of flux flow.
Dysprosium-Gadolinium Exchange Interactions in Gadolinium Metal
Authors: Nowik Israel
Published: February 2004

Recent experimental results on the temperature dependence of the hyperfine field acting on dysprosium impurity nuclei in gadolinium metal are used to check the validity of the molecular field model for such systems, and to reduce the Dy–Gd exchange coupling parameter. It is concluded that the molecular field model is able to explain successfully the experimental observations. The exchange field acting on dysprosium ions embedded in gadolinium metal, βHe(0°K) / k=110±5°K, is approximately equal to the field acting on the gadolinium ions (βHe(0°K) / k=98°K).
Electron Flow in Gas Diodes. I. Transition from Inertia-Limited Flow to Mobility-Limited Flow
Authors: Ingold J. H.
Published: February 2004

The transition from inertia-limited flow (vacuum) to mobility-limited flow (high pressure) in gas-filled diodes is studied theoretically by taking velocity moments of the Boltzmann equation for the electron-velocity distribution function. It is shown that the momentum-transfer equation can be integrated when νc(C), the frequency of elastic collisions between electrons and gas atoms, is independent of the electron speed c, and the hydrostatic-pressure term is neglected. The resulting current-voltage (J-V) curve, which is valid for all gas pressures, reduces to the proper vacuum law (J ∝ V3/2) at extremely low gas pressure and to the proper high-pressure law (J ∝ V2) at high gas pressure, while it is a mixture of the two laws for intermediate gas pressures. The importance of the ratio νc/νp, where νc is the average value of νc(C) and νp is the electron-plasma frequency, is emphasized. It is shown that the current is inertia limited for νc/νp<1, and is mobility limited for νc/νp>1. It is shown further that mobility-limited flow divides naturally into two cases, according to whether the electrons retain the energy imparted to them by the electric field or whether this energy is given up in elastic collisions with atoms. The former situation, called the low-pressure case, prevails when (m/M)1/2νc/νp<1, and the latter, called the high-pressure case, prevails when (m/M)1/2νc/νp>1, where m/M is the ratio of electron mass to atom mass.
Electron Flow in Gas Diodes. II. Mobility-Limited Flow for Collision Frequency Proportional to Electron Speed
Authors: Ingold J. H.
Published: February 2004

The voltage (V) dependence of the mobility-limited electron current density (J) in a gas-filled diode is calculated for low pressure [(m/M)1/2νc/νp]<1 <νc/νp as well as for high pressure [1<(m/M)1/2νc/νp], where m/M is the ratio of electron mass to atom mass, νc is the average frequency of elastic collisions between electrons and gas atoms, and νp is the electron-plasma frequency. It is assumed that νc(C) is proportional to the electron speed c, which corresponds to the case of an energy-independent mean free path. It is shown that J should be proportional to V3/2p−1d−3 for low pressure, and to V3/2p−1/2d−6/2 for high pressure, where p is the gas pressure and d is the (planar) diode spacing. Corresponding expressions for cylindrical geometry are derived and compared with experiment.
Nonlinear Photovoltaic Effect in Silver Bromide
Authors: Tan Y. T. , Trautweiler F.
Published: February 2004

The photovoltage of silver bromide single crystals has been measured at room temperature as a function of light intensity and wavelength. A two-part photoresponse was observed: a fast part with a risetime in the millisecond range, followed by a slower part with a response time of seconds. The fast response was nonlinear, the voltage varying approximately as the ⅔ power of the incident light intensity. A model based on a Dember-type effect was formulated to explain the results. Electrons are assumed to diffuse from the surface into the bulk, owing to their own concentration gradient, while holes are trapped near the surface to form interstitial silver ions which then move under the influence of the field of the electrons. The resulting differential equation was then solved with the aid of a computer. The slow response was ascribed to the effect of photodecomposition products on the initial photovoltage.
Line Integral Expressions of Interaction Energy of Dislocation Loops in Anisotropic Materials
Authors: Mura T.
Published: February 2004

The interaction energy of two dislocation loops in anisotropic materials is expressed by the Fourier transform of line integrals along the dislocation loops. The result can also be used for the expression of the self-energy of one dislocation loop. The Fourier integrals are performed for the cases when the elastic constants differ by a small amount from the isotropic elastic constants.
Single-Crystalline Elastic Constants of ZrCo2 and HfCo2 in the Temperature Range 4.2°–300°K
Authors: Shannette G. W. , Smith J. F.
Published: February 2004

The elastic constants of single crystals of the cubic Laves phases ZrCo2 and HfCo2 were determined by the pulse-echo technique over the temperature range 4.2°–300°K. Debye temperatures for the two materials were computed from extrapolations of the elastic constants to 0°K. The ratio of these Debye temperatures is such as to indicate that the primary difference between the two materials is a difference in vibrational amplitudes resulting from the mass difference between zirconium and hafnium. Further substantiation of a close similarity of interatomic force interactions in the two materials is obtained by comparison of appropriate combinations of lattice parameters and force constants.
High-Density Saturation Effects of the Dislocations in n-Type Germanium
Authors: Calzecchi F. , Gondi P. , Mantovani S.
Published: February 2004

The dislocation effects on electrical resistivity and Hall coefficient at the liquid-nitrogen temperature were examined in n-type germanium specimens whose dislocation density, distribution, and nature were determined by means of optical and electron microscopy. In particular, the high dislocation density regions were considered, where the space-charge cylinders and the low-mobility rings around the dislocations overlap. Three stages were revealed, the first connected with the bulk conductivity, the second with the conductivity in the low-mobility regions, the third with the prevalence of the minority hole conductivity. The interpretation of the experimental data led to the following determinations: the specific volumes of the space-charge cylinders and the low-mobility rings around the edge dislocations; the ratios between low mobility and bulk mobility of the electrons; the degree of the contamination specific of the deformations; the saturation hole concentrations and mobilities. Further, the availability of differentiated specimens with prevalence of either screw or edge dislocations made it possible to resolve the effects of the two types of dislocations.
Theory of the Thermal Breakaway of a Dislocation from a Row of Equally Spaced Pinning Points
Authors: Blair D. G. , Hutchison T. S. , Rogers D. H.
Published: February 2004

This paper gives a comprehensive description of the breakaway of a dislocation from a row of equally spaced pinning points, under the combined action of stress and temperature, within the model of Teutonico, Granato, and Lücke (TGL). The method is to obtain an algebraic solution, for a general pinning force, using, in turn, the continuous-pinning approximation of TGL and the ``independent-joint approximation''; the conditions of validity of these approximations are investigated in detail. For β«1, the pinning is effectively continuous; here, β=LcU0/Cr2, where Lc is the distance between pins, U0 is the maximum binding energy between a dislocation and a pin, C is the tension of the dislocation, and the pinning force has its maximum at a displacement of order r, the ``range.'' For β»1, the independent-joint approximation holds (except near the mechanical breakaway stress). Then major breakaway (breakaway from the whole row) is activated at a single pin down to the stress σs = (4CU0/b2Lc3)1/2, where b is the Burgers vector. As the stress drops further, a saddle configuration still exists for breaking the first pin, but the dislocation must surmount higher saddle points to break subsequent pins. Major breakaway is activated over an increasing number of pins as the stress decreases, and for σ«σs the pinning becomes ``quasicontinuous.'' A paradox encountered by TGL is thus resolved.
Theory of High Field Conduction in a Dielectric
Authors: O'Dwyer J. J.
Published: February 2004

A dimensionless solution is given for continuous current flow in a solid dielectric, which undergoes electron-induced collision ionization. A method is developed for finding the current-voltage characteristic of the dielectric from this solution, given the emission function of the cathode and a blocking anode. The results are used to infer the thickness dependence of dielectric breakdown strength based on the model considered.
Resonances (TEmn, TMlm) of a Cylindrical Cavity Containing a Nonuniform Plasma Column
Authors: Blevin H. A. , Reynolds J. A.
Published: February 2004

Solutions of the wave equation are obtained for TE0mn and TMlm0 modes in cylindrical cavities containing a coaxial, annular plasma column. The radial electron density distribution is assumed to be of the form ne=n0[1−γ1 (r/a)2−γ2(a/r)2], where n0, γ1, and γ2 are constants and a is the outer radius of the plasma. The results can be used to determine the effects of density gradients on measurements of electron densities and collision frequencies by the cavity method. Some illustrative examples are presented.
Microwave Transmission Through a Magnetoplasma Slab Near the Plasma Cutoffs
Authors: Tetenbaum S. J.
Published: February 2004

The extraordinary wave transmission through the afterglow of an rf-excited, electrodeless, helium discharge has been investigated experimentally. The discharge approximates a low collision frequency plasma slab of relatively uniform electron density in a uniform magnetic field. Measurements were performed at 18.0 and 9.15 GHz. A transmission minimum occurs very close to the higher frequency cutoff and a large decrease in transmission occurs close to the lower frequency cutoff. The plasma cutoff positions are approximately independent of energy in the electron energy range from thermal energy to a few electron volts and of pressure in the pressure range from 0.08 to 2.5 Torr. The position of the transmission minimum coincides with the position of the emission peak previously observed.
Distribution of Crystal Orientation and Work Function in Tungsten Ribbons
Authors: Haas George A. , Thomas Richard E.
Published: February 2004

Polycrystalline tungsten ribbons tend to recrystallize on extended outgassing to a preferred orientation near the 〈1̄10〉 zonal axis between the 〈001〉 to 〈112〉 directions, the most probable orientations being in the 〈115〉 to 〈113〉 directions. Work function measurements on nine different crystal planes between the 〈001〉 to 〈112〉 directions have been made and show variations from 4.34 to 4.72 eV. The area average value from 15 different ribbons is 4.46 eV but the variation between ribbons can be as high as 0.2 eV.
Epitaxial Deposition of Platinum on Iridium at Low Temperatures
Authors: Graham W. R. , Hutchinson F. , Nadakavukaren J. J. , Reed D. A. , Schwenterly S. W.
Published: February 2004

Platinum evaporated on a clean iridium surface at temperatures as low as 200°K produces epitaxial layers, as shown by field ion microscopy. If the iridium surface has been exposed to the atmosphere after forming, the temperature required for epitaxy rises to about 375°K (100°C). Even this temperature is well below that required for high mobility of the incoming atoms over the surface, as assumed in present theories of the formation of epitaxial layers.
Statistics of Transmission Secondary Emission from Thin Films of Alkali Halides
Authors: Llacer J. , Garwin E. L.
Published: February 2004

The statistical distribution of the number of emitted secondary electrons per primary incident on transmission alkali-halide dynodes has been studied. For high primary energies (1 MeV), a model based on the theory of dielectric energy loss and the secondary electron-phonon interaction is proposed to account for statistical distributions. Measurements of distributions from 500-Å-thick films of CsI, KCl, and LiF have been carried out both at high energies and for primary energies near 9 keV corresponding to the maximum of secondary yield. It is shown that with some simplifying approximations, the model proposed can be used to calculate the distributions observed with high-energy primaries. Qualitatively, it is also possible to use the ideas proposed to understand the experimental results at low energy. Although in the literature the statement is often made that secondary emission distributions can be expected to be Poissonian, it is shown in this paper that there is very little firm basis for such a statement, and it is only through a knowledge of the detailed phenomena controlling secondary emission that a particular distribution can be predicted.
Effect of Gravity on the Shape of Water Bells
Authors: Dumbleton J. H.
Published: February 2004

The solution of the equations representing the shape of an axially symmetric sheet of fluid is given. It is shown that under certain conditions gravity can greatly influence the shape of these sheets (or water bells as they are commonly known). The calculated shape is compared with a photograph of a water bell and it is shown that there is good agreement between the theory and experiment. The effect of gravity on the stability of a water bell is also considered.
Relationship between the Growth Rate of Laser-Induced Damage in Polyalkylmethacrylates and Their Glass Transition Temperature
Authors: Kusakawa Hideaki , Takahashi Kenzo , Ito Katsuyoshi
Published: February 2004

The interaction of laser light with the transparent organic high polymers with Q-switching dye was investigated. Several sorts of polyalkylmethacrylate plates, for which glass transition temperature was a function of composition of copolymers made of methylmethacrylate and n-butylmethacrylate, were prepared, and the relationship between the growth rate of the laser-induced damage and the thermal properties was examined. When the ambient temperature of these copolymer plates was 27°C, the growth rate of the damage becomes slower with the decrement of their glass transition temperature. The authors found that the difference (Tg-T) or the ratio (Tg/T) of glass transition temperature (Tg) and ambient temperature (T) of the organic high polymers exerts predominant influence on the growth rate of laser-induced damage.
Reflected Shock-Velocity-Particle-Velocity Relationship in Solids
Authors: Urtiew P. A.
Published: February 2004

The linearity of the reflected shock-velocity-particle-velocity (UR-up) relationship is probed for some materials that already have a linear fit through their initial shock-wave data. A pure hydrodynamic theory was used in this investigation with no elastic strength of the material taken into account. Based on the result of this analysis, it is concluded that, for all practical purposes, the UR-up) relationship is linear and can readily be used to calculate the reflected shock Hugoniot. Explicit forms of both first and second coefficients of the relationship are also given.
Temperature Dependence of the Excitation Transfer Rate Constants for He(23S1)+Ne→He+Ne(2s) and He(21S)+Ne→He+Ne(3s)
Authors: Jones C. R. , Niles F. E. , Robertson W. W.
Published: February 2004

A temperature dependence of the form K=K0 exp (−E/kT) has been observed for the rate constants for excitation transfer from the helium metastable atoms to neon. For He(23S)+Ne→He+Ne(2s), K0=3.3×10−11 cm3/sec and E=0.051 eV. For He(21S)+Ne→He+Ne(3s), K0=2.1×10−10 cm3/sec and E=0.041 eV.
Large-Aperture Glass Disk Laser System
Authors: Swain J. E. , Kidder R. E. , Pettipiece K. , Rainer F. , Baird E. D. , Loth B.
Published: February 2004

A study of a glass laser designed to operate at extremely high power and radiance for possible use in the production of strong shock waves and high-temperature plasmas is presented. The design makes use of titled face-pumped disks of neodymium-doped glass. The advantages and disadvantages of the four proposed ways to use such a laser are considered. To test the disk concept, a system of five 12.5-cm-diam, 1.25-cm-thick disks was constructed. Design considerations and the results of several measurements with the experimental system are presented. Measurements of the single-pass gain of the five disks showed a gain coefficient of 0.054/cm, which indicates an energy storage of 0.68 J/cm3, or 100 J per disk.
Operation of a Transverse Mode-Controlled Hydrogen Stokes Laser Oscillator
Authors: McClung F. J. , Close D. H.
Published: February 2004

A giant pulse ruby laser was used to optically pump a hydrogen gas laser oscillator, operating at the first Stokes-shifted Raman line at 0.975 μ. Transverse mode control of the high-Q, curved mirror resonator was provided by controlling the geometry of the pump beam; this allowed operation in the fundamental (TEM00) mode of the cavity. Operating characteristics, including threshold, beam divergence, and spatial and temporal behavior, are discussed.
Ternary Superconducting Alloys of the Titanium-Niobium-Vanadium System. Transition Temperature Variation
Authors: Bellin P. H. , Sadagopan V. , Gatos H. C.
Published: February 2004

The superconducting transition temperature (Tc) variation in the bcc region of the titanium-niobium-vanadium ternary system was studied. Cold-rolled alloys at 10% composition intervals were employed. The Tc values were found to vary smoothly with composition. The highest value in the ternary system was Tc=8.8°K for Ti0.6Nb0.3V0.1. The largest decrease in superconducting properties, relative to the Ti binaries, occurred at the first 10% addition of the third element. Additions of Nb to the Ti–V system and of V to the Ti–Nb system led to more sharply defined peaks in the Tc versus n relationship (n stands for the average number of valence electrons per atom) than found in the binaries. The Tc maximum occurred at n=4.5 for the ternaries with constant vanadium concentration and between n=4.4 and 4.5 for constant niobium concentration. The minimum of Tc in the Nb–V system was found to shift towards higher Nb concentrations with increasing content of Ti. The Tc values were taken to reflect the density of states at the Fermi surface N(0) and their variation was found to be consistent with the rigid d-band model.