bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrostatic Self-Focusing of an Electron Beam in a Planar Diode
Authors: van Hulsteyn D. B.
Published: February 2004

An electron beam accelerated by a planar anode can be electrostatically self-focused if the ambient pressure of an ionizable gas within the diode is sufficiently high. A theoretical analysis is presented which uses an integral representation of Poisson's equation. A first-order solution for the potential allows the trajectories of the beam electrons emitted from the cathode under temperature-limited conditions to be determined. For a wide beam, it is found that the degree of constriction is given, approximately, by Δρ=−17d, where d is the cathode-anode separation.
Propagation of Finite-Amplitude Waves in Unidirectionally Reinforced Composites
Authors: Ben-Amoz M.
Published: February 2004

The behavior of unidirectionally reinforced composites under intense-impact conditions is considered. Based on asymptotic expansions of the basic equations it is shown that the composite behavior can be asymptotically described in terms of effective conservation equations and associated jump conditions. In particular, it is found that such equations differ from the ordinary balance equations by the presence of a compaction ratio which appears as a measure of compactibility of composite materials. An effective caloric equation of state is also derived from the expansions as the weighted geometric mean of the constituent equations of state.
Electromagnetic Field in Electrodeless Discharge
Authors: Henriksen B. B. , Keefer D. R. , Clarkson M. H.
Published: February 2004

A closed-form solution is given for the electromagnetic field in a cylindrical electrodeless discharge of infinite length in which the conductivity of the plasma is assumed to be complex and have a parabolic variation with plasma radius. The low-pressure ambipolar diffusion-controlled electrodeless discharge is closely approximated by this model. Solutions are presented for various values of the ratio of collision frequency to applied frequency and for various values of plasma conductivity. The variation in magnitude of the fields within the plasma is qualitatively similar to the well-known solutions based on Thomson's model, but the phase shift is considerably reduced.
Reciprocity of Electromagnetic Waves Scattered by Anisotropic Composite Obstacles
Authors: Okamoto Naomichi
Published: February 2004

It is shown that reciprocity holds for electromagnetic waves scattered by various anisotropic composite obstacles, including obstacles touched together, isolated obstacles, obstacles composed of stratified layers, and combinations of them. The individual obstacles can be of different media, provided that the medium of each obstacle is either anisotropic with tensor permeability and tensor permittivity which are continuous functions of position or perfectly conducting. The incident waves are considered uniform plane waves.
Calculation of Photon-Absorption Coefficient in Laser-Produced Hydrogen Plasmas
Authors: Tsai Hsian-Shi , Oktay Erol , Akcasu A. Ziya
Published: February 2004

The absorption coefficient for ruby-laser photons in laser-produced hydrogen plasmas is calculated for temperatures up to 5×105°K using second-order perturbation theory. The calculations include inverse bremsstrahlung in the field of ions and excited neutral atoms and photoionization. The results are compared to the existing data in literature, which cover the temperature range only below 10 000 °K.
Hollow Cathode Discharge with Thermionic Cathodes
Authors: Witting H. L.
Published: February 2004

The electrical and visual characteristics of a dc hollow cathode discharge with indirectly heated thermionic cathodes were obtained in argon at a few Torr. Two facing planar cathodes of variable separation form the hollow cathode geometry. A hollow cathode effect was observed in the ``ball-of-fire'' mode and in the ``low-voltage arc'' mode. The results are explained in terms of cumulative ionization processes, diffusion losses, and mutual interactions of the glow regions.
Conical Z-Pinch Gun
Authors: Mendel C. W.
Published: February 2004

A pulsed plasma gun is described which has several advantages over other commonly used guns. Among these are simplicity of operation, construction and analysis, and stability of operation. The output has a sharply peaked velocity distribution. The initial model, described herein, emits a burst of 5×1018 Ar ions moving at 9 cm/μsec. A snowplow analysis predicts operating characteristics generally in agreement with observations.
Dynamic Tensile Failure of Glycerol
Authors: Erlich David C. , Wooten David C. , Crewdson Richard C.
Published: February 2004

A tensile strain was induced in shock-loaded glycerol by the intersection of two rarefaction waves, one of which was caused by the partial reflection of a shock from an interface with octane, a material of lower shock impedance. The maximum tensile stress and the subsequent tensile stress relaxation due to void nucleation and growth were measured indirectly by a stress gauge placed in the octance. The dynamic tensile strength of the glycerol was measured to be ≈ 0.25 kbar for an initial tensile stress rate on the order of 107 kbar/sec. Calculations indicated that spherical voids in glycerol of between 0.01 and 10 μ in radius follow a viscous growth law under tensile strain, and computations using this growth law showed the influence of fractional void volume and strain rate upon the macroscopic stress history during cavitation. Several possible void nucleation mechanisms are discussed.
Shock-Wave Structure in Porous Solids
Authors: Davison Lee
Published: February 2004

In this paper several variations of a simple theory of dynamic compaction of porous solids are presented and discussed. This theory elaborates the conventional theory of shock propagation in such a way that the shock structures observed to propagate in these materials can be described. Steady-wave profiles are calculated for several compaction models, and the inference of constitutive equations from experimental data is discussed. It is shown that the theory can be made to reproduce steady-wave profiles observed in the usual plate-impact experiments exactly.
Shock Propagation Produced by Planar Impact in Linearly Elastic Anisotropic Media
Authors: Johnson J. N.
Published: February 2004

Plate-impact experiments and shock-wave propagation in isotropic materials have become a standard technique for the study of material properties at very high strain rates. Recent work has also included shock propagation in anisotropic materials for specific wave-propagation directions in which pure longitudinal motion can exist. In this work, the effect of anisotropic elasticity and its influence on plane-wave propagation for arbitrary loading directions in plate-impact experiments is studied. The analysis applies specifically to the propagation of elastic disturbances produced by planar impact in a series of anisotropic plates of dissimilar materials each of arbitrary crystallographic orientation. The boundary conditions that exist between adjacent materials as well as conditions at free surfaces are considered in detail. It is found that for general orientations of single-crystal Be and Ti (hexagonal symmetry), multiple-wave effects, and transverse particle motion resulting from the elastic anisotropy are small. However, for y-cut α quartz (trigonal symmetry) these effects are significant. Transverse velocity components have been found to be greater than 35% of the maximum longitudinal velocity component.
Bulk Diffusion of Carbon-14 through Polycrystalline Nickel Foil between 350 and 700°C
Authors: Massaro Thomas A. , Petersen Eugene E.
Published: February 2004

The bulk diffusion of C-14 through polycrystalline Ni foil was investigated in the temperature range of 350 to 700°C. A thin Ni foil was bombarded by a molecular beam of acetylene tagged with C-14. A masking device situated very close to the ribbon surface shielded part of the surface from this beam, producing a well-defined pattern of high and low concentration of absorbed acetylene on the top surface of the foil. After diffusion annealing, this pattern would appear on the underside of the ribbon. Autoradiographic techniques were used to obtain radiation intensities from both surfaces. The ratio of these intensities determined bulk diffusion coefficients after the method of Kryukov. Most previous data had been obtained at temperatures of 700°C or higher. There is acceptable agreement between these data and the higher-temperature experiments of the present work. However, the present results show an activation energy of approximately 20 kcal/mole from 350 to 700°C, while there is substantial evidence that above 700°C the activation energy for this process is of the order of 40 kcal/mole.
Influence of Lasing on the Electron Energy Distribution in CO2 Mixtures
Authors: Avivi P. , Dothan-Deutsch F. , Keren H.
Published: February 2004

Experimentally derived electron energy distribution functions in CO2–N2–He and CO2+He mixtures are presented. It is shown that lasing results in a significant depletion of electrons in the energy range 1.0–3.0 eV. This is accounted for by the decrease in the vibrational temperature under lasing conditions as compared to a nonlasing discharge of similar mixtures.
Hot Carriers in Si and Ge Radiation Detectors
Authors: Drummond W. E. , Moll J. L.
Published: February 2004

Characteristics of silicon and germanium radiation detectors are developed from an analysis of the energy-loss mechanisms for hot carriers. The carrier behavior is described in terms of phonon and ionization scattering rates. A calculation of the probability of ionization vs primary electron energy in silicon, using Kane's characterization of the scattering rates, indicates an effective ionization threshold several times the band-gap energy. Calculations of phonon losses and the carriers' residual kinetic energies are combined to give an average energy expended per created pair ε of 4.24 eV. Closer agreement with the experimental value of 3.67 eV is achieved by lowering the phonon to ionization scattering-rate ratio. Temperature effects, which enter through changes in the band gap, are calculated to be ∂ε/∂Eg=1.73. The analysis also predicts a Fano factor of 0.059 for silicon. Discussion of the germanium situation is based on the premise of hot-carrier behavior similar to that in silicon. Because germanium has a more complicated band structure, two sets of calculations are made using different effective band gaps. With ε=2.96 eV at 90 °K, very similar results are obtained in both cases and indicate ∂ε/∂Eg≈1.77 and F≈0.066.
Sign of the Hall Coefficient in a Relaxation-Case Semiconductor
Authors: Queisser H. J.
Published: February 2004

In a relaxation-case semiconductor the dielectric relaxation time exceeds carrier diffusion-length lifetime, and the neutrality condition no longer holds. It is shown that the sign of the Hall coefficient in a p-type relaxation-case material is positive, if the hole density exceeds the electron density times the square of the mobility ratio. This relation is identical to the one for conventional lifetime-case materials, but has here been derived without assuming neutrality. Practical Hall-effect measurements with relaxation-case samples may, however, be seriously altered by space-charge effects. We describe one case where a negative Hall coefficient always results regardless of the initial doping; this situation may be related to the ``Hall-effect/Seebeck-effect anomaly'' in amorphous films.
Space-Charge Scattering and Electron Transport in n GaAs
Authors: Hamerly R. G. , Heller M. W.
Published: February 2004

The effect of the space-charge scattering mechanism on the Seebeck coefficient of n GaAs was examined in the temperature range 4–300 K. The measured Seebeck coefficient was combined with the Hall coefficient and conductivity to determine the dominant electron scattering mechanism from 100 to 300 K. Impurity-band conduction dominated at lower temperatures. The measurements were performed on highly compensated samples with electron carrier concentrations in the range 1015−1018 cm−3. The measured transport properties are compared to theoretical predictions based on polar, ionized impurity, and space-charge scattering mechanisms. Satisfactory agreement with theory is obtained if the space-charge mechanism is included in the Seebeck coefficient as well as in mobility calculations. The experimental results indicate that the space-charge mechanism can dominate at room temperature and below for highly compensated n GaAs.
High-Field Microwave Permittivity of Electrons in Bulk GaAs
Authors: Glover G. H.
Published: February 2004

Measurements of the permittivity of bulk n-type GaAs have been obtained at a frequency of 35 GHz with microwave heating field strengths up to 16 kV/cm. The measurements are in good agreement with predictions of a simple two-valley model using an energy-independent thermal relaxation time τT=1.5×10−12 sec. The peak value of the large-signal permittivity is found to be considerably smaller than the small-signal high-field values reported in the past. This disparity is substantiated by calculations with the two-valley model. It is felt that the large-signal function measured here is considerably more relevant to LSA-mode circuit design, as well as to calculations of electron parametric operation, than small-signal values.
Calculation of Grain-Boundary Diffusion Parameters and Comparison with Experiment
Authors: Tiernan Robert J.
Published: February 2004

Calculations of Cp (the solute concentration at the grain-boundary edge) vs the reduced penetration η have been carried out for β values of 5.0, 1.0, 0.5, and 0.1, and η values from 2.0 to 7.0 in increments of 0.5. The small increments in η for the calculations were taken in order to better resolve the slopes of ``lnCp vs penetration'' curves for small η values. It is just this region of η values that is of interest in electron-probe analysis when the β's are small and the signal-to-noise ratio of the diffusing species is at low levels. Grain-boundary diffusion permeabilities-derivable from electron-probe analysis of thallium diffusion in nineteen bicrystals of potassium chloride-were determined both by comparison of the slopes of the isoconcentration contours at the grain-boundary edge, and, from the slopes of the grain-boundary penetration curves, using the results of the present numerical calculations. The agreement between the two methods was erratic. The values of η differed by as much as a factor of 4 in some cases and agreed to within 5% in others. This is attributed to the inability of the probe to resolve within 1 μ of the grain boundary, and to the poor signal-to-noise ratio of the electron-probe detector system for thallium.
Capacitance-Voltage Characteristics of Metal Barriers on p PbTe and p InAs: Effects of the Inversion Layer
Authors: Walpole J. N. , Nill K. W.
Published: February 2004

The dependence of the capacitance C on the voltage is derived for metal-semiconductor barriers in which there is a strong inversion layer at the metal-semiconductor interface, a case of interest in the study of surface effects and in applications for laser structures. Experimental results for evaporated lead and tin barriers on p PbTe at 77 °K and for evaporated gold barriers on p InAs at 77 and 4.2 °K are presented and compared to calculations performed with the inversion layer model. Both the theory and experiment show an essentially linear dependence of C−2 with voltage, as in the usual Schottky barrier, but a voltage intercept which is surprisingly dependent on band-structure parameters, bulk carrier concentration, and temperature. Reasonable quantitative agreement between the theory and experiment is obtained. In all cases the presence of a strong inversion layer can be clearly established. The analysis of the capacitance-voltage data, however, gives only a lower limit to the amount of inversion present.
Simultaneous Optical Parametric Oscillation and Second-Harmonic Generation
Authors: Ammann E. O. , Yarborough J. M. , Falk J.
Published: February 2004

The simultaneous occurrence of optical parametric oscillation and second-harmonic generation (SHG) of the oscillator signal or idler is studied. These processes, which occur in a single crystal, generate a new output which, depending upon whether the signal or idler is involved, can lie above or below the pump wavelength. This effect is of interest because (1) it provides a technique for generating a tunable output in the vicinity of the oscillator pump and (2) in normal oscillator operation, it is undesirable since it acts as a loss mechanism for the signal. We show that the simultaneous occurrence of oscillation and SHG is a phenomenon which can occur in a number of parametric oscillators. Techniques are given for predicting and studying this process for any nonlinear material. Methods of tuning the generated second harmonic (SH) are also considered. Experiments were performed on an oscillator/doubler consisting of a single lithium niobate crystal pumped by a repetitively Q-switched 1.06-μ laser. More than 20 mW of average SH power were obtained over the region 0.92 to 0.98 μ, with a maximum output of 95 mW occurring at 0.935 μ.
Plastic Deformation in Central Regions of Epitaxial Silicon Slices
Authors: Dyer L. D. , Huff H. R. , Boyd W. W.
Published: February 2004

Central yielding, as well as peripheral slip, was observed in curved epitaxial silicon slices produced in the laboratory. The central plastic deformation is the result of compressive stresses set up by the entrapment of a hot central region within a colder annular zone. A stress analysis was performed which explains the occurrence and relative intensities of slip in the two regions by reference to the distortion energy densities throughout the slice. A model of the centrally localized plastic deformation in {111} slices was presented in which the 〈110〉 slip vectors inclined to the {111} surface are activated and produce relief of the central compressive stresses by vertical movements of pyramidal sections of the crystal.
Invar Behavior in Antiferromagnetic Fe–Mn–(Ni) Alloys
Authors: Colling D. A. , Mathur M. P.
Published: February 2004

Occurrence of the Invar anomaly in thermal expansion characteristics of antiferromagnetic Fe–Mn–(Ni) alloys having constant Mn/Fe atomic ratios of ⅔ has been investigated. Linear spontaneous magnetostriction, Néel temperature, and inflection temperature were found to be well described by electron concentration; Ni substitution decreased all of these parameters. Such results are shown to be consistent with Zener's Invar theory based on competing exchange interactions.
Alternating Current Losses of Stabilized NbN
Authors: Deis D. W. , Gavaler J. R. , Jones C. K.
Published: February 2004

The ac losses of thin films of NbN have been measured on uncoated samples and samples coated with copper and aluminum. The reversibility of the superconducting to normal transition was studied under conditions of swept current at fixed field and swept field at fixed current. It is observed that stabilized NbN has ac losses significantly lower than those in the equivalent unstabilized material.
Domain-Wall Energy and Coercive Force of Cobalt Rare-Earth Permanent Magnet Materials
Authors: Westendorp F. F.
Published: February 2004

Domain structures in RCo5 compounds were observed with Kerr effect in fields up to 8000 Oe. The domain structures in SmCo5 are much coarser than in the other compounds. It is shown that this difference may be due to a higher wall energy in SmCo5. The idea is developed that this higher wall energy is responsible for the higher coercivities of SmCo5.
Magnetic Domain Structures in Thin Uniaxial Plates with Perpendicular Easy Axis
Authors: Cape J. A. , Lehman G. W.
Published: February 2004

We present a convenient formulation of the single-domain energy in the wall-energy model and minimize the total energy of a lattice of cylindrical domains and of a parallel-stripe array in an infinite plate. The latter structure is shown to have the lower energy for external transverse fields Hex<H1 while the lattice is favored for H1≤Hex<H2. The critical domain sizes and fields bounding these structures are calculated as functions of the plate thickness and the material parameters. The factors which affect the evolution of the domain structures in finite and nearly defect-free plates are discussed and the following conclusions drawn: Domain nucleation is favored by the presence of nonuniformities such as cracks or mounds. Stripes nucleated at cracks or boundaries expand and contract with one end tied to the nucleation point and there may be only as many stripes as nucleation centers. An energy barrier inhibits the separation of a domain from (or the joining to) a free edge boundary or another domain. Closed domains are repelled by boundaries and alternate between stripe- and bubble-domain configurations as the local field varies below and above the critical stripe-bubble instability value. The qualitative conclusions can be quantified to some extent in the wall-energy model and provide a satisfactory explanation of the domain structures observed in a high-mobility garnet film.
Domain-Wall Energies in Orthoferrites
Authors: Rosencwaig A.
Published: February 2004

Domain-wall energies and effective wall thicknesses are derived for the rare-earth orthoferrites. The geometric factors arising from the orthorhombic symmetry make the Bloch walls more energetic and thicker than the Néel walls.
Decay of Injected Electron-Hole Plasmas in p-Type InSb
Authors: Robbins William P. , Ancker-Johnson Betsy
Published: February 2004

The decay of high-density (4×1014−1012 cm−3) injected electron-hole plasmas in pure p-InSb (p0≈1014 cm−3) at 77 K is investigated in detail by means of a double-pulse technique that determines the decay of the plasma conductivity. The decay curves show two distinct modes: a high-density mode (>1013 cm−3) characterized by rapid decay and a low-density mode (<1013 cm−3) of relatively slow decay. The high-density mode is dominated by electrons and lasts for a period of time ranging from several hundred nanoseconds to only a few tens of nanoseconds depending on sample size. The effective time constants in the high-density mode decrease as the plasma density is reduced. This is true whether the reduction is accomplished by letting decay proceed in time or by starting decay at a lower initial density. This trend is observed independent of sample cross section and surface conditions, factors that do affect, however, the magnitude of the time constants. An electron trapping mechanism in the sample bulk accounts for this density-dependent effective plasma lifetime. The maximum high-density lifetime allowed by the trapping mechanism is T∞=0.9 μsec (accurate to within a factor of 2), but the observed time constants are generally smaller because of surface recombination. Since the measurements show no evidence of hyperbolic decay, a characteristic of radiative recombination, and since the theoretical radiative lifetime is much larger than the measured lifetimes, it is concluded that radiative recombination is not important in this decay process. When the low-density mode controls, the shape of the decay curves becomes independent of the initial plasma density. All curves in a family obtained from a sample of given size and surface condition have the same time constant. In the low-density mode the plasma is a one-component plasma composed of holes, the electrons having been bound in traps or returned to the valence band. In large cross-section samples (≥1×1 mm2), the holes decay with the well-known hole lifetime, 1–2 μsec. In both decay modes, surface recombination must be considered. This mechanism causes the measured time constants to be less than would be predicted on the basis of bulk recombination alone, and, in addition, it causes the measured lifetimes to decrease as the sample size is reduced or when the surface recombination velocity of small samples (<0.4×0.4 mm2) is increased. In the high-density mode the observed dependence of the initial time constant on the sample size is in agreement with an approximate theoretical treatment of surface recombination. This work, both theory and experiment, yields a value of the ambipolar diffusion length of 0.14 mm.
Microeddy Current Magnetic Damping in Nickel
Authors: Ganganna H. V. , Fiore N. F. , Cullity B. D.
Published: February 2004

The damping of 〈100〉 and 〈111〉 Ni single crystals has been obtained at 3 to 150 kHz by resonance-bar techniques. The measurements have been made in biasing fields to 200 Oe and at strains to 10−5. The experimental conditions have been adjusted so that the microeddy current loss Δi has been separated from other magnetic and nonmagnetic losses. In all cases, damping is larger for the 〈100〉 crystals, and the microeddy current loss is suppressed by application of a biasing field. In addition, the loss is independent of strain amplitude below 2×10−7 and passes through a maximum with frequency. This behavior is qualitatively explained by a theory which treats domain walls as damped driven harmonic oscillators, which generate microeddy currents as they vibrate in response to applied stress and dissipate energy through Ohmic losses. The quantitative explanation of the field, frequency, orientation, or strain dependence requires an explicit expression for eddy current power loss as a function of the number and arrangement of domains in the sample.
Determination of Kilovolt Electron Energy Dissipation vs Penetration Distance in Solid Materials
Authors: Everhart T. E. , Hoff P. H.
Published: February 2004

A universal curve of energy-dissipation range vs normalized electron energy is proposed, which includes the average atomic number Z of the material being bombarded in the energy normalization factor. Range-energy expressions of the form R=kEBα, derived from the Bohr-Bethe energy-loss relation, are valid over limited energy ranges, but the exponent α differs for materials of greatly different atomic numbers over the same energy range. For the aluminum-silicon dioxide-silicon system used here, RG = 4.0 EB(keV)1.75 μg/cm2 has been found accurate for 5 <EB <25 keV. Using this value of range, and taking the steady-state electron-beam-induced current through a thin insulating layer of SiO2 as a measure of the energy dissipation in that layer, an energy-dissipation (depth-dose) function has been determined which should be valid for 10 <Z <15. Using this normalized expression, λ(y) = 0.60 + 6.21y − 12.40y2 + 5.69y3 and the range RG, the energy dissipated at any depth may be determined, and hence the carrier-pair generation in semiconductors, light generation in phosphors, etc., may be predicted. An expression relating the depth-dose function to the applied voltage drop across the oxide provided an independent check on the experimental measurements and the assumptions used in reducing the data. The ratio of (mobility × lifetime) to the (mean electron excitation energy in the oxide) was found to be (μτ/EA) = (2.97 ± 0.06) × 10−13(cm/V)2 using the energy-dissipation formulation, and (μτ/EA) = (3.00 ± 0.05) × 10−13(cm/V)2 using the check expression, where the errors quoted are root-mean-square deviations computed for 12 or more points.
Photovoltaic Cells from Ceramic CdS Treated in a Solution Containing Bi Ions
Authors: Konstantinova E. , Kanev S.
Published: February 2004

The first results from experiments for obtaining photoelectric cells from CdS with minimized Cu impurities, based on a p-layer formation treatment in a solution containing Bi ions, are given. The basic characteristics of converters with time-stable parameters and efficiency 3−5% are investigated. The heterojunction is probably between CdS: Cu and one of the bismuth-sulfide modifications.
Self-Induced Sputtering during Electron-Beam Evaporation of Ta
Authors: Schuermeyer Fritz L. , Chase Wayne R. , King Emerson L.
Published: February 2004

A pronounced nonuniformity in films of Ta deposited by electron-beam evaporation is reported. This effect is explained by the fact that positive Ta ions are generated during evaporation and, due to reflected electrons, the substrate acquires a high negative potential which accelerates the Ta ions and causes sputtering.
Green Injection Luminescence from Forward-Biased Au–GaP Schottky Barriers
Authors: Card H. C. , Smith B. L.
Published: February 2004

Improvements in the minority-carrier injection efficiency of GaP Schottky diodes are achieved by the incorporation, into the device, of a thin insulating layer separating the metal and the semiconductor. This enables visible green luminescence to be obtained from the diodes in forward bias. Measurements of the optical and electrical characteristics of this device are reported.
Direct Measurement of Built-in Voltage in MOS Structures
Authors: Viswanathan C. R. , Ogura S.
Published: February 2004

It is shown that it is possible to measure directly, using a photoelectric technique, the built-in voltage in a MOS structure. The experimentally measured values, using this method, are compared with values obtained by another method, and the validity of this method is established.
Analysis of the Efficiency of Thin-Film Magnetic Recording Heads
Authors: Paton Andrew
Published: February 2004

Equations for the flux, magnetic field, and current distributions in a single-turn planar magnetic recording head are derived making the assumption that the magnetic material has constant permeability. These equations are solved in the frequency domain and an expression is given for the head efficiency in terms of the head dimensions, permeability, and frequency.
Pulsed Microwave Breakdown of Air from 1 to 1000 Torr
Authors: Tetenbaum S. J. , MacDonald A. D. , Bandel H. W.
Published: February 2004

Pulsed breakdown electric field strengths have been measured in two S-band cavities filled with dry air at a temperature of 4 °C in the approximate pressure range from 1 to 1000 Torr. The data were taken at a pulse repetition frequency of 20 Hz and for effective pulsewidths of 0.6, 0.2, and 0.1 μ sec. The results are in reasonable agreement with the predictions of Felsenthal based upon pulsed dc breakdown fields.
Technique for Measuring High-Temperature Thermal Conductivity of Solids by the Use of a Heat Pipe
Authors: Forman Ralph
Published: February 2004

A suggested technique for accurately measuring thermal conductivity of solids in the temperature range 800–1500 °C is presented. The procedure employs the sample to be tested in series combination with a high-temperature heat pipe and a heat-transfer device, which has a variable thermal conductance. By changing the thermal conductance of the heat-transfer unit and measuring the change in heat-pipe power input to maintain a constant heat-pipe temperature, one can accurately measure the heat flux through the sample in conjunction with the temperature drop across it. This steady-state technique has some inherent advantages over methods currently employed to measure thermal conductivity at elevated temperatures.
Impulse-Voltage Breakdown Characteristics of Large Gaps at Low Pressures
Authors: Nandagopal M. R. , Gopalakrishna H. V.
Published: February 2004

A study of the gap breakdown voltage characteristic at a low pressure of 7×10−5 Torr with a standard (1/50)-μsec impulse-voltage wave reveals an agreement with the criterion Vb=Cd0.5 suggested by Cranberg. Voltage-time-to-breakdown characteristics has also been determined. From these studies, it is concluded that impulse breakdown in vacuum is initiated by an electron current heating an anode spot and thereby liberating a clump which causes breakdown.
Relationship between Wavelength Tuning and Lasing Threshold in Electron-Beam Pumped GaAs Lasers
Authors: Kawasaki B. S. , Shewchun J. , Garside B. K.
Published: February 2004

The method of electron-beam pumping has been used to study the time and frequency variations of the laser light output from GaAs crystals. A study of the faster-than-bandgap tuning to longer wavelengths of this laser light has revealed a significant correlation between the saturation of the tuning rate and the lasing threshold of the crystal. This relation has been investigated as a function of beam current density and voltage. The implications of these observations are discussed with reference to previously proposed general models of the wavelength tuning behavior of the stimulated output from semiconductor lasers.
Quantitative X-Ray Emission Analysis of Thin Oxide Films on Tantalum
Authors: Sewell P. B. , Mitchell D. F.
Published: February 2004

A low-energy (1800-V) electron beam is used at normal incidence to excite the characteristic x-ray emission from oxygen in thin oxide films on smooth tantalum substrates. From films having known thickness increments, a calibration procedure is used to relate the oxygen Kα signal/background ratio to oxygen concentrations in the films. Films ranging from less than one monolayer to several hundred Å mean thickness can be measured. At the submonolayer level, oxygen concentrations of about 1×10−9 g cm−2 can be detected on a tantalum surface.
Isothermal Annealing of the 0.97-eV Luminescene in Electron-Irradiated Si
Authors: Wong E. H. , Streetman B. G.
Published: February 2004

Low-temperature photoluminescence in pulled Si irradiated with 3-MeV electrons exhibits a prominent zero-phonon line at 0. 97 eV which anneals between 200 and 275°C according to previous isochronal data. Isothermal annealing measurements are reported which reveal an activation energy of about 1. 34 eV for the annealing of this line.
Evidence of a Negative Resistance Characteristic in Circuits Consisting of Thin Mylar Films Connected in Series with High Resistances
Authors: Swaroop N. , Predecki Paul , Bharat R.
Published: February 2004

Evidence of a negative-resistance characteristic in a circuit consisting of a thin film of Mylar, in series with a high resistance, at high dc fields is reported. This characteristic is a result of a reversible electrical breakdown of Mylar films at a temperature-dependent high dc field, which precedes an irreversible thermal breakdown. Without an adequate series resistance these two types of breakdown occur essentially simultaneously and in this event the negative-resistance characteristic cannot be observed.
High-Resolution Electron Microscopy of Crystal Lattice of Titanium-Niobium Oxide
Authors: Iijima Sumio
Published: February 2004

The detailed structure within the two-dimensional projection of the unit cell of a Ti2Nb10O29 crystal, showing the arrangement of the metal atoms, has been revealed by careful use of a high-resolution electron microscope. The image shows good agreement with the model of the structure deduced from x-ray diffraction studies.
Sputter Deposition of EuO Thin Films
Authors: Coburn J. W. , Lee Kenneth
Published: February 2004

High-quality EuO films with properties similar to bulk EuO have been deposited by sputtering a polycrystalline EuO target in an ultrahigh-vacuum sputtering system. In addition, Eu-rich EuO films with enhanced ferromagnetic properties have been sputter deposited, but with considerable difficulty. The difficulty is caused by oxidizing impurities present in the vacuum system and is sufficiently severe as to indicate that multiple-source vaporization is a more suitable technique for fabricating Eu-rich EuO films with the enhanced ferromagnetic properties required for beam-addressable file applications.
Epitaxial Growth of Ice Crystals on the Muscovite Cleavage Plane and Their Relation to Partial Dislocations
Authors: Caslavsky J. L. , Vedam K.
Published: February 2004

The arrangement of oxygen atoms in hexagonal rings in crystals of ice and muscovite gives two possible alternatives of epitaxial connection between these two structures. Which one of these two alternatives is favored depends entirely on the location of potassium atoms in the cleavage plane of the muscovite structure. Since potassium atoms are displaced from the normal environment by the slip taking place along partial Burgers vectors, epitaxial growth of ice crystals on muscovite can be used for the determination of the slip directions and hence for the study of partial dislocations in muscovite crystals.
Self-Diffusion Measurement of Oxygen in UO2 by the Nuclear Reaction 18O(p, γ)19F
Authors: Hadari Z. , Kroupp M. , Wolfson Y.
Published: February 2004

The 18O(p, γ)19F nuclear reaction has been employed for measuring self-diffusion coefficients, in sintered U16O2 at temperatures between 925° and 1425°C. This method allows the determination of concentrations in a well-defined diffusion layer due to the resonant nature of the reaction.
Velocity Distribution Measurements in a Near-Free Molecule Orifice Flow
Authors: Lou Y. S.
Published: February 2004

Measurements have been made of the velocity distribution of the flow of cesium gas from an orifice in the near-free molecule regime. The apparatus design is based on the time-of-flight method using a single disk chopper and a surface ionization gauge. Measured velocity distributions are compared with the corresponding Maxwellian distribution adjusted to have the same peak amplitude. Although the two distributions agree closely at high Knudsen numbers (i.e., Kn>10), the comparison at smaller Knudsen numbers indicates that the measured distribution is deficient in low-speed molecules. This deficiency increases with decreasing Knudsen number and with decreasing angular position from the centerline of the orifice. The experimental results are compared with the predictions of existing analyses of near-free molecule flow through an orifice.
Shielding of Electromagnetic Waves by a Spherical Shell
Authors: Einaudi F.
Published: February 2004

An approximate expression is derived for the first n terms of exact series expansions for the electromagnetic fields inside a metallic spherical shell due to an impinging plane monochromatic wave. The formulas derived are valid if the ratio (n+1) (n+2) / 2Ri | k2 | ≪1, where k2 is the propagation constant in the metallic screen and Ri is the radius of the inner sphere. Contrary to some existing approximate formulas, the present ones describe the fields also at the resonance frequencies corresponding to the first n terms. They fail to represent the fields near or at the resonance frequencies corresponding to the (n+1) th term and higher ones.
Alternating Current Losses in Hollow Cylinders
Authors: Kim Y. B.
Published: February 2004

Electromagnetic responses of hollow cylinders under ac excitations are discussed with a particular reference to the end effect and the skin effect. When hollow cylinders are used for damping ripples, a specific shape factor, length-to-diameter ratio of 0.88, was found to be most effective. The electromagnetic characteristics revealed in the present analysis are shown to manifest themselves also in the superconducting states.
Metal-Oxide-Metal (M-O-M) Detector
Authors: Kwok S. P. , Haddad G. I. , Lobov G.
Published: February 2004

The properties of a metal-oxide-metal (M-O-M) tunneling detector are presented and the parameters influencing its operation are discussed. The theory of operation and experimental results for small as well as large signals are presented. The polarity reversal at large-signal levels is predicted theoretically and observed experimentally.
Exciton-Induced Photoemission from KCl Films
Authors: Pong W.
Published: February 2004

The photoelectric yield of evaporated KCl films was measured for photon energies from 7 to 14 eV. A gradual rise of photoelectron emission with time was observed under steady ultraviolet excitation of approximately 8 eV. In the presence of strong biasing radiation (visible light), the gradual rise of photomission did not appear. An attempt is made to explain the transient enhancement in terms of electron emission from new F centers formed by excitons.
Relationship between Photoelectric and Secondary Electron Emission, with Special Reference to the Ag–O–Cs (S-1) Photocathode
Authors: Sommer A. H.
Published: February 2004

On the basis of experimental evidence, it is suggested that the high secondary emission gain of Ag–O–Cs photocathodes is not associated with the photoemission of this material in the visible and near-infrared region of the spectrum. Addition of Ag enhances photoemission but reduces secondary emission whereas superficial oxidation reduces photoemission but increases secondary emission. It is concluded that the Cs2O contained in the cathode, although by itself not sensitive to visible light, is responsible for the high secondary emission as well as for the high uv photoemission.
Role of Cs in the (Cs)Na2KSb (S-20) Multialkali Photocathode
Authors: McCarroll W. H. , Paff R. J. , Sommer A. H.
Published: February 2004

Chemical analyses and qualitative observations during the processing of S-20 photocathodes indicate that the cesium produces a bulk as well as a surface effect. Quantitative confirmation for a bulk effect is provided by x-ray studies of Na2KSb and (Cs)Na2KSb. It was found that addition of Cs increases the lattice constant from 7.727±0.003 to 7.745±0.004 Å. It is suggested that the larger lattice constant leads to a greater excess of Sb in the lattice and thereby to enhanced p-type doping and band bending.
Photoinjection into SiO2: Electron Scattering in the Image Force Potential Well
Authors: Berglund C. N. , Powell R. J.
Published: February 2004

The voltage dependence of photoinjected currents in SiO2 films for electric fields less than about 106 V/cm exhibits anomalous behavior. It is shown that the physical mechanism responsible for this behavior is the scattering of photoinjected electrons in the SiO2 image force potential well between the emitter and the potential maximum. A previously published model attributing the effect to electron trapping in SiO2 is shown to be inconsistent with the experimental results. A theoretical model is presented and the voltage dependence of photocurrents is derived including the effects of scattering and barrier lowering. Experimental results from MIS structures using thermally grown SiO2 are found to be in excellent agreement with theoretical predictions when a 34 Å mean free path for scattering in SiO2 is used in the model.
Anode Phenomena in Metal-Vapor Arcs at High Currents
Authors: Rich J. A. , Prescott L. E. , Cobine J. D.
Published: February 2004

The present investigation is concerned with the conditions associated with the development of an anode spot for metal-vapor (vacuum) arcs. Chief among the aims of the investigation is the determination of the threshold current density for anode-spot formation for a variety of electrode materials spanning a wide range of thermal and electrical properties. Electrodes of Sn, Al, Ag, Cu, Mo, and W were chosen for study in a plane-parallel electrode geometry. Arcing was over one-half cycle of a 60-Hz current wave. The onset of anode-spot formation was determined from high-speed streak photographs of the discharge. An oscillographic record of the arc voltage was obtained simultaneously with the streak picture. From the data obtained particular interest attaches to the threshold current for anode-spot formation, the threshold current density derived from it, and the arc voltage-current characteristic. The threshold current densities (peak values) range from a low of 0.9×102 A/cm2 for tin to a high of 5.4×102 A/cm2 for tungsten, copper having the value 4.0×102 A/cm2. In general, high-current metal-vapor arcs have positive volt-ampere characteristics and exhibit an hysteresis effect. Rapid changes in arc voltage, noise voltage, and in the magnitude of the hysteresis effect are associated with the formation of an anode spot. The noise voltage and arc drop decrease as the spot develops. In addition a marked increase in luminosity appears in the plasma at the site of the spot. There is a strong correlation between the threshold current for anode-spot formation and the thermal characteristic Tm(kρc)1/2 of the electrode material.
Utility of the Green-Rivlin Theory in Polymer Mechanics
Authors: Yannas I. V. , Haskell V. C.
Published: February 2004

For the case of stress relaxation at constant strain, the Green-Rivlin theory for nonlinear materials with memory predicts that the stress is a power series in the strain where the coefficients, called kernels, characterize the material. This prediction of the theory has been tested using data obtained on the polycarbonate of bisphenol A in the timescale range 10–1000 sec and temperature range 23°–130°C. At each temperature level of this study, the two leading terms of the power series account for actual behavior within the standard deviation of the experimental data (3%) up to the level of tensile strain where instability (cold-drawing) occurs. The first (``linear'') kernel decreases monotonously with temperature as Tg is approached, but the second and higher kernels each vary with temperature in a complex manner. The utility of summarizing the nonlinear behavior of polymers by kernel functions is appraised and discussed in the light of recent findings on the range of validity of linear viscoelasticity theory. It is concluded that the second and higher kernels of the theory do not have any obvious physical significance. It is also suggested that the first and the second kernels might represent adequately by themselves the nonlinear viscoelastic behavior of glassy, amorphous polymers up to about 5% strain, whereas the third and higher kernels appear in addition to be necessary for semicrystalline polymers.
Influence of Particle Size on the Electrical Resistivity of Compacted Mixtures of Polymeric and Metallic Powders
Authors: Malliaris Angelos , Turner D. T.
Published: February 2004

Powder samples of high-density polyethylene and nickel of particle sizes Rp and Rm, respectively, were mixed and compacted at room temperature under a pressure of 1000 kg/cm2. Microscopic examination of polished sections of the compact, by reflected light, showed that the metallic particles did not penetrate the polymeric particles and that this resulted in a segregated distribution of metallic particles at high ratios of Rp/Rm. The electrical resistivity of the compacts had a value of 1016 Ω cm unless the composition of metal reached a critical value, beyond which the resistivity decreased markedly by as much as twenty orders-of-magnitude. This critical composition was found to decrease with an increase in the ratio Rp/Rm throughout the range studied of from 1 to 16. The general features of the dependence of electrical resistivity on composition of metal could be rationalized by reference to a model according to which small particles of nickel form a monolayer on the large particles of polymer in the mixture of powders. This arrangement was supposed to be but little changed during compaction and to result in a segregated distribution of metal which can be visualized as approximating to the accommodation of metallic particles on three mutually perpendicular sets of lattice planes. The critical composition for a sudden decrease in electrical resistivity was assumed to correspond to the first nonzero probability for infinitely long chains of contiguously occupied lattice sites.
Absorbing Centers in Laser Materials
Authors: Bennett Herbert S.
Published: February 2004

One of the severe problems encountered in high-power-solid-state laser systems is the thermal damage to laser rods and optical elements arising from metallic or dielectric inclusions; i.e., impurities with physical and optical properties which differ substantially from those of the host material. Such inclusions may absorb an appreciable amount of the incident radiation and thereby may produce major stresses within the host material. In this paper, the dependence of the maximum value of the tensile stress upon the size of the inclusion and upon the physical properties of the host is examined. The feasibility of using optical techniques to detect metallic and dielectric inclusions in laser materials before they cause damage also is studied. The computations suggest that the use of laser pulse widths of the order of microseconds or longer may be more promising for the detection of small incipient absorbing centers than the use of nanosecond pulse widths.