bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring the dynamic moduli of glassy polymers: analysis of the Rheovibron
Authors: Massa Dennis J.
Published: February 2004

A mechanical model for the Rheovibron DDV-II, an instrument for measuring the dynamic tensile moduli of polymers, has been proposed and analyzed to derive expressions for the moduli which take into account system compliance, sample yielding within the tensile grips, and system inertia. These effects require a correction to the raw data of 20–30% for glassy polymer samples in the tensile geometry, and the correction factor varies substantially with temperature, frequency, sample width and thickness, and among different polymers. In addition to the standard tensile grips, a new sample holder was introduced which adapts the Rheovibron to the flexural geometry. Experiments were carried out on samples of poly(methyl methacrylate) (PMMA) in tension and in flexure, on rigid aluminum samples, on a PMMA tensile sample with variable system inertia, and on a tensile specimen of bisphenol-A polycarbonate at various temperatures, the model describing the behavior of the system quantitatively. It is concluded that for accurate determination of the dynamic moduli in tension, the temperature, frequency, and sample dependence of the correction factors must be taken into account.
Pressure dependence of the thermal conductivity, thermal diffusivity, and specific heat of polyethylene
Authors: Andersson P. , Bäckström G.
Published: February 2004

The pressure dependence of the specific heat of high-density polyethylene was determined from simultaneous measurements of thermal conductivity and diffusivity in a cylindrical geometry at 300 K and in the pressure range 0–25 kbar. The thermal conductivity and the diffusivity both increase strongly with pressure, the values at 25 kbar being higher by factors of 2.75 and 2.77, respectively, than those at atmospheric pressure. The specific heat decreases, most strongly so at low pressures, and its value at 25 kbar is 0.80 times that at atmospheric pressure. The thermal conductivity of low-density polyethylene was determined as a function of pressure. Its value at 25 kbar was found to be 2.19 times that at atmospheric pressure. The difference in conductivity response to pressure between the two varieties is given a simple theoretical interpretation.
``Sunspot'' technique for the visual detection of stimulated emission or absorption from excited states
Authors: Wieder Irwin
Published: February 2004

A new method is introduced whereby induced optical transitions from fluorescing excited states can be detected visually. An experiment is described in which the technique is used to detect stimulated emission from an excited state of a fluorescent dye. Applications of the method to the detection of hidden excited states in molecules, to the measurement of the intensity of focused tunable laser pulses, and to the study of sharp line spectra are suggested.
Xerographic discharge characteristics of photoreceptors with bulk generation. I. Flash exposure
Authors: Kao Cheng C. , Chen Inan
Published: February 2004

A theory for the photoinduced discharge characteristics of xerographic photoreceptors with bulk carrier generation is developed. In the case of flash exposure, analytic solutions for the surface potential as a function of time after exposure are obtained for two special cases: (i) small-signal case and (ii) uniform initial charge distribution at any signal level. The more general case, i.e., the initial charge distribution is an exponential function, is solved by a numerical iterative method. The accuracy of this method is tested by comparison with the analytic solutions for the special cases. The effect of bulk generation of carriers is to speed up the discharge especially at the early stage, by partially lifting the space-charge limitation. The optimum conditions, however, depend on the field dependence ω of the mobilities, the ratio β of the electron to the hole mobilities, and the optical density of the photoreceptor αL. The surface potential after exposure as a function of these parameters is computed numerically for the most common values of 0≤ω≤2, 0.1≤β≤1, and αL≥1, and the results are discussed.
Light coupling from a stripe-geometry GaAs diode laser into an optical fiber with spherical end
Authors: Kato Daisuke
Published: February 2004

The acceptance angle of a fiber is increased remarkably by forming the fiber end spherically. It was demonstrated with light coupling into a fused-silica-core glass fiber from a mesa-stripe-geometry GaAs diode laser. The coupling efficiency increased in this way is observed to be 5.2 times as high as that of a previous method. The proper design of a fiber in this manner will lead to a light coupling efficiency higher than 90%.
Unified theory of high-frequency noise in Schottky barriers
Authors: Viola Thomas J. , Mattauch Robert J.
Published: February 2004

A unified noise-temperature equation is presented which describes the high-frequency noise (>1/f noise) characteristic of Schottky barrier diodes from above room temperature to cryogenic temperatures. The unified noise equation takes into consideration the dominant transport mechanism of the barrier and is applicable to any metal-semiconductor system. Noise-temperature measurements on fabricated Schottky barrier diodes at 18, 77, and 300 °K confirm the validity of the noise theory presented.
Tunnelling in junctions with CdS barriers
Authors: Josefowicz J. , Smith H. J. T.
Published: February 2004

Junctions having an Al–CdS–Al configuration exhibited both a temperature-dependent zero-bias anomaly and a double energy gap when dynamic resistance measurements were made. The zero-bias anomaly and the double energy gap can be explained by assuming that Cd particles are embedded in the CdS synthetic tunneling barrier. The first energy gap corresponds with that of Al. The second is assumed to arise as a result of tunneling through Cd particles embedded in the CdS. Employing a double tunneling process, one corresponding to direct tunneling through CdS and the other involving Cd particles embedded in the CdS, quantitative agreement with experimental results was achieved.
Longitudinal and transverse critical currents of chemically deposited Nb3Sn in the temperature range 14.5–17.5°K
Authors: Cody G. D. , Cullen G. W.
Published: February 2004

Measurements are reported on the longitudinal and tranvserse critical currents of chemically deposited Nb3Sn at temperatures close to Tc. Significant and systematic deviations are observed between these measurements and a simple flux pinning model of volume currents. The analysis suggests that surface supercurrents, which depend on the fundamental superconducting properties of the material, dominate the superconductivity properties reported here.
Elastic properties of rare-earth-iron compounds
Authors: Clark A. E. , Belson H. S. , Strakna R. E.
Published: February 2004

Ultrasonic velocities have been measured and used to determine the elastic moduli of the highly magnetostrictive compounds: TbFe2, TbFe3, and ErFe2. A huge ΔE effect of 90% has been calculated for TbFe2 from our static stress-strain data.
Diffusion-controlled exchange of a finite cylinder with a finite amount of well-mixed gas
Authors: Jones W. M.
Published: February 2004

A substance is considered to diffuse into a finite cylinder through its entire surface from a finite amount of well-mixed gas which is at concentration equilibrium with the surface. Equations are derived for the time dependence of the amount of substance in the cylinder and its concentration at a point. The results are developed mainly in terms of isotopic self-diffusion (as in the diffusion-controlled exchange of isotopic oxygen with an oxide), but may also be applied to the diffusion of an inert substance or to a heat conduction situation.
Preparation of replicated germanium films and their applications to sensors
Authors: Onuma Yoshiharu , Sakai Yoshio
Published: February 2004

Germanium thin films were formed on flexible organic substrates by using a replica method, in order to obtain a sensitive transducer for stress and thermal energy. The average values of measured gauge factor were in the range from 45 to 65. The Seebeck coefficient was up to 560 μV/deg for p-type films. With regard to flexibility of the films, stiffness is more than three orders of magnitude smaller than that of a glass substrate. According to dynamic tests, the element attached to a beam could respond to mechanical vibrations up to a frequency of 20 kHz. From the study of the thermal properties using infrared and laser beams, a response time of about 100 msec or less and a responsiveness of about 40μV/μW were obtained.
Charge depletion mechanism operative in space-charge flows
Authors: Biblarz Oscar , Bohley Carl M.
Published: February 2004

Charge depletion is considered for negatively charged particles flowing with a dielectric medium (air). The problem is representative of those encountered in electrogasdynamic devices. A mechanism is proposed wherein electrons are depleted from the particles by the formation of O2−. These ions, being some 100 times more mobile than the particles, are essentially lost from the flow because of their high slip. Axisymmetric jets mixing with ambient air are investigated, and a computer program is used to solve the combined Poisson/Laplace equations. Results ranging from no-charge depletion to total depletion are presented.
Low-work-function metal-coated reed contacts: New method of increasing life of sealed reed contacts
Authors: Utsumi Takao
Published: February 2004

A new method for significantly increasing the life of sealed reed contacts by coating with low-work-function metal and a theory for this method are described. Some preliminary results demonstrate the soundness of the concept of this approach.
Erosion and ionization in the cathode spot regions of vacuum arcs
Authors: Kimblin C. W.
Published: February 2004

The net erosion rate at the cathode spots of 100-A vacuum arcs has been determined experimentally for Cd, Zn, Ag, Cu, Cr, Fe, Ti, C, Mo, and W electrodes. Ion currents to the metal walls surrounding each of these cathode materials have also been investigated. For each material, the dependence of the wall ion current on the electrode spacing and anode geometry is consistent with an arc model which assumes predominant vapor ionization in the cathode regions, with subsequent isotropic free flight motion from these regions. Comparison of the net erosion rate with the wall ion current indicates that, for high-vapor-pressure materials such as Cd and Zn, ≈ 15% of the vapor leaves the cathode regions ionized. For low-vapor-pressure materials such as C, Mo, and W, this fractional ionization is almost 100%. The ion current magnitudes observed at long electrode spacings are similar for each material, and lie in the range 7–10% of the arc current. Ion currents of this magnitude are also predicted for Mg, Al, and Ni using experimental data by Plyutto, Ryzhkov, and Kapin. Since these 13 materials span a wide range of thermal characteristics (from Cd: bp 1038 °K to the refractory materials C, Mo, and W: bp 5973 °K), it is concluded that ion currents of this magnitude can be expected from cathode materials in general. It is also shown that the erosion rate for nonrefractory electrodes can be reasonably estimated using Ecker's theoretical values for cathode spot current densities and temperatures. Furthermore, this comparison between experiment and theory indicates that the total probability for vapor ionization in the cathode region exceeds 50%.
Absorption processes associated with anti-Stokes fluorescence in rhodamine B solutions
Authors: Jain R. K. , Hu C. , Gustafson T. K. , Elliot S. S. , Chang M. S.
Published: February 2004

The absorption coefficient of several rhodamine B solutions excited at 632.8 nm has been measured for temperatures ranging from 200 to 385 °K. The weak monomer absorption coefficient (∼ 10−5 times the peak coefficient) at this anti-Stokes excitation wavelength facilitates a study of the other components of absorption in the dye solution, yielding valuable information on solvent effects and factors affecting the quantum efficiency of fluorescence, such as dimer absorption, impurity content, etc. Whereas at high temperatures (above 30 °C), linear singlet-singlet monomer absorption is observed to dominate, dimer formation is evident at temperatures below 30 °C, and the impurity absorption appears negligible in either case. From a least-squares fit of the experimental data with the theoretical dependence of the total (monomer and dimer) absorption upon temperature, the association energy for the dimer is found to be 5.0 kcal/mole. It also seems possible that at temperatures above 50 °C, for solutions with low impurity absorption, quantum efficiencies high enough for radiative cooling of the solution may be attained.
Interface stress of AlxGa1−xAs–GaAs layer structures
Authors: Reinhart F. K. , Logan R. A.
Published: February 2004

It is shown that stresses caused at the interface of a AlxGa1−xAs–GaAs heteroboundary are due to the different thermal expansion coefficients of the two layers involved. These interface stresses are elastic and depend on the crystallographic orientation of the heteroboundary plane. Based on these experimental observations, a planar stress model for double heterostructure (DH) devices is developed which results in stress levels in the order of 108 dyn/cm2 for typical low-threshold DH laser structures. It is demonstrated that this type of stress is responsible for the occasional preference of TM modes over the TE modes in DH lasers.
Phase matching by periodic variation of nonlinear coefficients
Authors: Yacoby Y. , Aggarwal R. L. , Lax B.
Published: February 2004

A scheme for phase matching in the parametric generation of far infrared is analyzed. It makes use of the periodic variation of the nonlinear coefficients. It is shown that a device can be constructed which is tunable over a wide range of generated frequencies.
Low-energy ion bombardment of silicon dioxide films on silicon. II. Inert ambient annealing of degradation in MOS devices
Authors: McCaughan Daniel V. , Murphy V. T.
Published: February 2004

It is shown that the degradation of the C-V properties of the SiO2/Si interface caused by low-energy ion bombardment may be completely removed by annealing to temperatures of 900 °C or higher. The low-energy ion bombardment, however, also causes damage to the dielectric strength of the SiO2. This damage only partially anneals out, even at the highest annealing temperatures. Annealing to temperatures between 400 °C and 600 °C apparently removes all C-V damage, as measured at room temperature, but bias-temperature instabilities, which require the higher temperature for their removal, remain. Annealing of any oxide to temperatures in the range 700–850 °C is not recommended, as it may introduce instabilities independent of ion bombardment. The same annealing procedure is required for 50, 500, and 1400 eV ion bombardment, leading to the conclusion that, in terms of ion bombardment damage, low-voltage sputtering gives no advantage over high-voltage sputtering. The dielectric breakdown damage is also independent of the ion energy in the range of 50–1500 V used in this study. We conclude that since all dielectric breakdown damage is not annealable, a method of prevention of oxide charge buildup during backsputtering is essential if this technique is to be used on insulating substrates. Appropriate choice of rf backsputtering voltage as a function of the insulator film thickness can significantly reduce or eliminate the bulk dielectric degradation.
Rapid recording of infrared spectra from pulsed chemical lasers
Authors: Greiner N. R. , Arnold G. P. , Wenzel R. G.
Published: February 2004

A method is described for rapidly recording permanent ir spectrograms of the output of a pulsed chemical laser. The method also lends itself to the simultaneous observation of the time behavior of several spectral lines. Spectra from an HF laser under different operating conditions are reported to demonstrate the utility of the method.
Superconducting paddle wheels, screws, and other propulsion units for high-speed ground transportation
Authors: Davis L. C. , Borcherts R. H.
Published: February 2004

High-speed ground vehicles magnetically suspended above a continuous aluminum guideway by superconducting coils can have a clearance of 0.1–0.3 m. To take full advantage of the large clearance, a propulsion system with a comparable clearance is needed. Two such systems based upon physically moving static magnetic fields produced by superconducting coils are proposed. With the use of a prime mover such as a gas turbine or a diesel engine, these systems avoid power collection problems and should result in a lower-weight propulsion unit. A numerical analysis of each has been made to determine the thrust, the lift force, and the efficiency as a function of various parameters. The mechanical efficiency of the paddle wheel appears to have a maximum of ∼60% at 483 km/h (300 mph), while that of the superconducting screw is (1-slip) for an infinitely long machine. End effects will degrade the efficiency somewhat for a screw of finite length.
Explicit solution for the photocount statistics with application to atmospheric turbulence
Authors: Lachs Gerard , Laxpati Sharad R.
Published: February 2004

The detection statistics of a light beam with randomly fluctuating intensity are of considerable interest. This paper derives an explicit form for the photocount statistics of a laser beam in the presence of an interfering background radiation. The result can be readily utilized to obtain the over-all photocount statistics by appropriate averaging over the random laser-beam intensity. The technique is quite suited to experimentally determined probability density. The analysis developed in this paper is applied to the propagation of light through turbulent media. Numerical results are obtained for the over-all photocount statistics for the two often considered probability distributions in this case: lognormal and Rice-Nakagami. The photocount distribution for the lognormally fluctuating medium is then utilized to obtain the probability of error and information rate for a laser binary communication system.
Precipitation of boron atoms implanted in silicon as detected by channeling analysis
Authors: Akasaka Youichi , Horie Kazuo
Published: February 2004

The precipitation of boron atoms in a silicon crystal which had been heavily implanted with boron ions at room temperature and then postannealed at high temperatures was studied by channeling analysis of the α-particles induced by the 11B(p,α)8 Be nuclear reaction. It was found that boron atoms which exceed the solubility limit precipitate on 〈110〉 strings in the region of the highest boron concentration (around the boron ion range) with a lattice distance somewhat different from that of the host crystal after annealing at 900 °C.
Dependence of xerographic discharge characteristics on carrier mobilities
Authors: Chen I. , Emerald R. L. , Mort J.
Published: February 2004

The effects of variations in carrier mobility and its field dependence on the xerographic discharge characteristics of a photoreceptor have been explored theoretically. Particular emphasis has been placed on the dependence of optimum exposure to reach optimum contrast potential and the latter values on mobility. The discharge characteristics are divided into three categories: (i) flash exposure where the exposure time is much shorter than the carrier transit time, (ii) emission-limited discharge which is realized by higher mobility photoreceptors, and (iii) space-charged-perturbed or space-charge-limited discharge which is seen in low-mobility photoreceptors. It is shown that in the latter case the optimum contrast potential is dependent on the time of observation (synonomous with development time).
Fresnel region fields produced by circular loops and annular slots antennas
Authors: Gonzalez Guillermo , Huerta Manuel A.
Published: February 2004

Exact closed-form expressions for the Fresnel region electric and magnetic fields of circular loop and annular slot antennas are given in terms of the functions en(σ,γ)=(1/2π) ∫ 02π cos(nΦ) sin[σ(1–2γ cosΦ)1/2] dΦand fn(σ,γ)=(1/2π) ∫ 02π cos(nΦ) cos[σ(1–2γ cosΦ)1/2] dΦ,where - ∞ < σ < ∞ and 0 ≤ γ ≤ 1/2. For a circular loope antenna with a constant current distribution the Fresnel region fields are obtained in terms of the functions qn (σ,γ)=fn (σ,γ)+ien(σ,γ), with n =0,1, and 2, and for a cosine current distribution the Fresnel region fields are obtained in terms of the functions qn(σ,γ), with n =0,1,2,3, and 4. The magnetic field of an annular slot antenna excited by a constant voltage is expressed exactly in terms of an infinite series involving the functions qn (σ,γ). The Fresnel region magnetic field of the annular slot antenna is simply given in terms of q1(σ,γ). The functions qn(σ,γ) permitted a simple evaluation of the electric and magnetic field strength in the Fresnel region. The functions qn(σ,γ) for n =0,1,2,3, and 4 are tabulated for values of σ=0.5, 1, 2, 5, 10, 25, and 50 and values of γ from 0.01 to 0.5.
Langmuir probe measurement of electron temperature in high-pressure plasmas
Authors: Clements R. M. , Smy P. R.
Published: February 2004

The effect upon measurements of electron temperature in high-pressure plasmas of the cooling of the plasma electrons by the inherently cold layer of gas surrounding the probe has been investigated. Theoretical considerations indicate that while cooling effects can be substantial, accurate electron temperature measurements can be obtained if the probe is sufficiently small or is moved through the plasma at sufficient velocity. These conclusions are at variance with the calculations of some other workers but are in good agreement with experimental results reported in this paper.
The nature of surface fission tracks in UO2
Authors: Ronchi C.
Published: February 2004

Fission fragment tracks produced on prepared surfaces of uranium dioxide were observed by replica electron microscopy. Several statistical analyses and measurements were performed on the observed tracks to be compared with theoretical studies of a fission fragment passing through a stopping medium. A temperature distribution around the fragment is evaluated by applying the thermal diffusion model to the particle energy losses. Since the temperatures attained at the surface could not explain any track formation, a shock wave is shown to be a possible cause by considering processes due to thermal pressures engendered by the very hot core surrounding the fragment path.
Determination of elastic constants in isotropic silicate glasses by Brillouin scattering
Authors: Huang Y. Y. , Hunt J. L. , Stevens J. R.
Published: February 2004

The hypersonic elastic constants and the ratio of the elasto-optic coefficients for two lead silicate optical-grade glasses and for a zinc silicate optical-grade glass have been obtained by observing the Brillouin scattering of 6328-Å laser light over the temperature range 24–107 °C. Brillouin scattering at 90° from both the transverse and longitudinal acoustic modes has been observed. The values of the hypersonic Young's modulus and shear modulus agree with low-frequency values and show a slight temperature dependence. Poisson's ratio and the ratio of the elasto-optic coefficients are found to be independent of temperature over the temperature range used. There is no evidence of dispersion from audio to hypersonic frequencies.
Simple electrode configuration for uv initiated high-power TEA laser discharges
Authors: Burnett N. H. , Offenberger A. A.
Published: February 2004

A simple Rogowski electrode configuration with capacitively coupled arcs on the sides of the discharge is described. With this configuration the authors have succeeded in dumping up to 500 J/1 into a gas mixture with as little as 41% He. The resulting small-signal gain characteristics and discharge current waveform are described. A 3-m oscillator has yielded output power > 1 GW and output energy of 125 J.
Experimental studies of laser-supported absorption waves with 5-ms pulses of 10.6-μ radiation
Authors: Stegman R. L. , Schriempf J. T. , Hettche L. R.
Published: February 2004

The response of materials to ≈5-ms pulses of 10.6-μ laser radiation at peak power densities of 1 to 2 MW/cm2 has been observed with simultaneous determination of (i) both front and back surface temperature rises, (ii) pressure delivered to the specimen as a function of time, (iii) total impulse delivered to the specimen, and (iv) absorption wave effects via high-speed framing camera coverage. The materials studied are 2024 aluminum alloy, 304 stainless steel, graphite, a Fiberglas-epoxy composite, alumina, MgO, and Pyroceram. It was found that Fiberglas-epoxy and graphite exhibit continuous coupling of the laser energy during the entire pulse, whereas the metals showed strong initial coupling which gradually diminished to near zero and then recoupled at the end of the pulse. The ceramics exhibited repetitive decoupling and recoupling during the entire pulse. The photographic evidence indicates the formation of laser-supported plasmatrons in the case of the metals and laser-supported combustion waves with the ceramic materials.
Transmission electron microscope investigation of the growth of copper precipitate colonies in silicon
Authors: Nes E. , Washburn J.
Published: February 2004

The growth of copper precipitate colonies in high-purity dislocation-free silicon single crystals has been examined by transmission electron microscopy. The colonies, being coplanar arrangements of copper-silicide particles on either {110} or {100) planes, nucleate and grow during rapid cooling from higher temperatures. The kinetics of the colony growth process has been analyzed in terms of a model based on repeated nucleation on a climbing dislocation. The possibility of having the growing copper-silicide particles dragged by the dislocations has been discussed, and a mechanism based on a particle dragging/dislocation climb effect has been suggested in order to explain the development of dendritic dislocation dipole branches.
Reflectance measurements of highly reflecting flat surfaces
Authors: Bauer W.
Published: February 2004

We have developed a compensation method for measuring the reflectivity of flat highly reflecting dielectric mirror coatings with the help of a laser beam. Using two coupled cavities it is possible to determine the reflectance of a spot with the diameter of the laser beam with an accuracy of about ± 3 × 10−5. The method also allows the measurement of the relative distribution of reflectance over the surface of a single mirror. Here the accuracy is equal to the sensitivity of the method, which is ± 2 × 10−5.
Nonlinear optical properties of the cuprous halides
Authors: Miller Robert C. , Nordland W. A. , Abrahams S. C. , Bernstein J. L. , Schwab C.
Published: February 2004

The absolute signs and magnitudes of the second-order nonlinear optical coefficients, d14, of CuCl, CuBr, and CuI have been determined with laser fundamentals at 1.32, 1.06, and 0.95 μm. All three d14's are real, negative, and show no dispersion over the measured spectral range. Except for CuI, the magnitudes of d14 are in agreement with data at 1.06 μm reported earlier by Chemla et al. The negative signs and magnitudes of d14 most likely require important Cu 3d electron contributions for their explanation.
Monte Carlo calculation of the electron drift velocity in GaAs with a superlattice
Authors: Andersen D. Lange , Aas Einar J.
Published: February 2004

Monte Carlo calculations of the drift velocity and mean energy vs electric field in n-type GaAs with a superlattice are reported. The model allows for phonon scattering, and a simple sinusoidal band shape in the direction of the superlattice is assumed. Negative differential mobility and energy saturation appear, and their variation with lattice temperature and miniband width is discussed. The threshold field decreases and the absolute value of the differential mobility increases with decreasing lattice temperature, while the miniband width has minor influence on these parameters. Schockley streaming is observed at low lattice temperature.
Further studies of bismuth-implanted cadmium sulfide
Authors: Eldridge G. , Chernow F. , Ruse G.
Published: February 2004

Cadmium sulfide implanted with bismuth at room temperature has been investigated. The sputtering efficiency was measured and related to the saturated bismuth concentration in the implanted layer. Etching experiments were performed to determine the role of the high surface concentration of the implanted bismuth and the visibly discolored damage region that results from the implantation. Diodes were fabricated and their forward-biased characteristic studied. It was found that the p-type behavior of the implanted layer was not confined to the visibly damaged surface layer. A critical minimum dose was necessary to observe p-type behavior.
Helium migration in alkali borate glasses
Authors: Shelby J. E.
Published: February 2004

Helium permeation, diffusion, and solubility have been measured for lithium, sodium, potassium, rubidium, and cesium borate glasses. The compositional dependence of each of these properties is related to the compositional dependence of the molar volume. Initial additions of alkali oxides (with the possible exception of lithium) to vitreous B2O3 serve to compact the glass network and reduce helium mobility and solubility. However, at higher alkali oxide concentrations, the network is expanded and helium diffusion actually increases with increasing alkali oxide concentration. These results are contrary to any previously reported for glasses, as inert gas mobility has always been reported to decrease with increasing alkali oxide content. However, the molar volume considerations used here can be applied to previous studies with equal success.
Scattering of sound by a viscoelastic cylindrical shell
Authors: Hageman D. H. , Glass V. L.
Published: February 2004

The pressure in the scattered wave resulting from irradiation of an infinitely long, circularly cylindrical, thin isotropic viscoelastic shell by a plane monochromatic sound wave is calculated. The shell is assumed to be freely suspended in an ideal fluid and to enclose a second ideal fluid. The motion of the shell is described by means of Lagrange's equations, altered so as to account for viscoelasticity. The result for the scattered wave has the form of that for the elastic case except that an expression involving elastic constants is replaced by an impedance function involving viscoelastic parameters. Some properties of this impedance function are drawn from electrical circuit theory and used in discussing the usefulness of the viscoelastic parameters relative to modifying the scattered wave.
Adhesion of gold particles to silicon and gold substrates in ultrahigh vacuum
Authors: Böhme G. , Hohn P. , Krupp H. , Rabenhorst H. , Schnabel W. , Walter G.
Published: February 2004

By use of an ultracentrifuge, the force of adhesion between small gold spheres (2–8 μ in diameter) and the following types of substrates has been measured: (111) cleavage planes of silicon single crystals with or without a chemisorbed oxygen monolayer and, alternatively, cleavage planes covered with oxide layers 40 and 130 Å thick. Further, instead of the silicon, gold substrates prepared in three different ways were used. The experiments were carried out at room temperature under ultrahigh vacuum (uhv) conditions. The experimentally determined forces are compared with the results of the theory of van der Waals interaction between extended solid bodies.
Theory of a steady-state nonisothermal positive column in a magnetic field
Authors: Ilić Dragan B.
Published: February 2004

The steady state of a nonisothermal cylindrical discharge in a longitudinal magnetic field is described by three moment equations in the plasma approximation for electrons and ions. Volume generation of electron-ion pairs by single-stage ionization, the presence of axial current, and collisions with neutrals are considered. The theory yields radial profiles of the charged particle velocities, density, potential, electron and ion temperatures, and demonstrates similarity laws for the positive column. The results are compared with two-moment theories and with experimental data on helium, argon, and mercury vapor found in the literature for a wide range of pressures.
Nonlinearity in the piezoresistance coefficient of impact-loaded manganin
Authors: Lee L. M.
Published: February 2004

The piezoresistance response of shock-loaded manganin wire embedded in C-7 epoxy insulation was experimentally determined over the stress range from 4 to 94 kbar. Manganin stress gauges of this configuration have been used extensively in previous shock wave studies. Interpretation of shock profiles below 50 kbar has been hampered, however, because the relationship between change in resistance and shock stress was not well established. The results of this work show the manganin piezoresistance coefficient to be nonlinear in the low-stress region, varying from 0.00246 Ω/Ω kbar at 9 kbar to 0.00291 Ω/Ω kbar at 40 kbar. Good agreement was observed between the shock and hydrostatic coefficients up to 9 kbar; the piezoresistance data above 40 kbar agreed with previously published high-stress results. The nonlinear increase in the manganin piezoresistance is attributed to defects generated in the wire by plastic deformation accompanying the shock loading. The stress-particle velocity response of the C-7 epoxy used in the stress gauge was also characterized, with Hugoniot and release adiabat data being generated. The epoxy Hugoniot data were significantly different from previously reported data for stresses below 20 kbar.
Absorption of CO2 laser radiation by carbonyl fluoride
Authors: Doughty J. R. , Jack J. L. , O'Pray J. E.
Published: February 2004

The absorption characteristics of COF2 both internal and external to the optical resonator of a CO2 laser were investigated over pressure ranges 1–26 Torr. Injection of small amounts of COF2 into the flow of an operating transfer chemical laser resulted in significant reductions in laser power. The absorption coefficient for COF2 was obtained from experiments using a CO2 laser with a line selection capability. For pure COF2 in the pressure range 1–10 Torr, the strongest absorption was on the P(24) line yielding an absorption coefficient of — 0.005 cm−1 Torr−1. When the COF2 was diluted with N2, the absorption was found to decrease as the operating laser line moves away from the COF2 absorption band centered at 965 cm−1 (10.36 μm).
Electroluminescence saturation and I — V measurements of Zn-diffused GaP diodes
Authors: Luther L. C. , Harrison D. A. , Derick L.
Published: February 2004

In this study of Zn-diffused red-emitting diodes, measurements of emission spectra, I - V characteristics, electroluminescence (EL) saturation, electron diffusion lengths, and photocapacitance have been compiled. Two factors which contribute to the observed low EL efficiency of diffused diodes have been identified. One is the presence of deep level centers, as indicated by large space-charge recombination currents. The other is a relatively small product of the Zn–O pair concentration and the electron diffusion length, which determines the EL level at Zn–O pair saturation. Results from photocapacitance measurements indicate that for diffused diodes, the oxygen, and hence the pair concentration, is smaller by a factor of 2–3 than that found in double liquid-phase epitaxy (LPE) diodes. The effects of an optimized annealing procedure (750°C for 8 h, followed by 525°C for 16 h) were also identified. The 750°C anneal primarily reduces the deep state concentration, whereas the 525°C annealing results in increased Zn–O pair concentrations.
cw degradation at 300°K of GaAs double-heterostructure junction lasers. II. Electronic gain
Authors: Hakki Basil W. , Paoli Thomas L.
Published: February 2004

The rapid degradation at 300°K in the cw regenerative output of stripe-geometry GaAs double-heterostructure junction lasers is shown to be a result of the formation of a local optical absorber in the laser cavity. Gain measurements performed on diodes before and after degradation show that the optical loss within the cavity increases during degradation. By observing the (predominantly) spontaneous emission from the active region directly through the n-GaAs substrate, it is confirmed that the increased loss is localized in a region where little or no spontaneous emission takes place at lasing energies. In such diodes, the internal radiative efficiency of the undegraded portion of the optical cavity shows a relatively small decrease compared to the external differential quantum efficiency. When the local absorber extends over a sufficient length of the cavity the electronic gain in the undegraded section is insufficient to overcome the loss and the device ceases to act as a regenerative optical oscillator. Net gain measurements on DH laser devices in which the active region is lightly (≈ 1017) n-doped indicate that the optical gain increases linearly with current prior to degradation. At lasing threshold the medium exhibits net gain over a wavelength range of 100 Å. After degradation the gain dependence on current can become superlinear due to the saturation of the optical absorber. Estimates on the attenuation constant in the local absorber at low currents give a value of ≈ 60 cm−1 at 8800 Å. For pulsed currents close to lasing threshold the attenuation constant increases to nearly 160 cm−1 at 8760 Å.
Characteristics of tunable Pb1−xSnx Te junction lasers in the 8–12-μm region
Authors: Antcliffe G. A. , Parker S. G.
Published: February 2004

The characteristics of tunable Pb1−xSnx Te (0.08⪝×⩽ lim ∼0.20) junction lasers are described. The lasers operate cw at liquid-helium temperatures and for the above alloy compositions, the wavelength is in the 8–12-μm region of the infrared. The devices are prepared by antimony diffusion into large p-type vapor-grown single crystals. Active region width, gain, and loss parameters are derived from measurements of the current density at the lasing threshold, efficiency, and cavity length dependence of the threshold current. Impurity diffused lasers favor oscillation in high-order TE modes and some evidence of filamentary lasing was obtained from the device parameters together with a study of far-field patterns. Results are presented which confirm the model of current tunability of these devices and provide data on refractive index and temperature dependence of the forbidden energy gap in these alloys. Finally, spectroscopic data are presented to show the present limitations and potential of the diode laser for rapid (≪50 μsec) high-resolution gas spectroscopy.
Absorption and noise in x-ray phosphors
Authors: Swank Robert K.
Published: February 2004

When the signal in an x-ray image system is formed by integrating the scintillation pulses rather than by counting them, the signal-to-noise ratio is reduced by a factor which depends on the shape of the pulse-height distribution. The signal-to-noise ratio cannot be related directly to either quantum absorption or energy absorption, and a new quantity called noise-equivalent absorption is defined which bears a simple relationship to the signal-to-noise ratio. Quantum, energy, and noise-equivalent absorption are calculated as a function of thickness and x-ray energy for CsI, Gd2O2S, LaOBr, Zn0.6Cd0.4S, and CaWO4.
Magnetic filtration
Authors: Watson J. H. P.
Published: February 2004

It has been shown that magnetic filters can be constructed that will extract micron-sized paramagnetic particles from a fluid passing through the filter. The purpose of this paper is to examine the filtering process, to calculate the performance of filters, and finally to consider application of magnetic filtering to the rapid treatment of sewage.
Electron density in a locally ionized plasma afterglow
Authors: Martin Benny E. , Ventrice Carl A.
Published: February 2004

An expression is derived for the electron density distribution in a weakly ionized plasma afterglow. The case for which the ionization is symmetrically localized about the center of the chamber is considered. It is shown that localization causes the existence of higher-order modes of decay to be present in the afterglow.
Red-light-emitting Alx Ga1−x As heterojunction laser diodes
Authors: Kressel H. , Hawrylo F. Z.
Published: February 2004

The properties of cooled Alx Ga1−x As heterojunction laser diodes operating at wavelengths below 7000 Å are described. At 77 K, the shortest wavelength at which pulsed laser operation is obtained is 6280 Å, while convenient cw operation has been obtained to 6570 Å. Pulsed laser diode operation to 6770 Å was obtained up to 223 K.
Time-harmonic induced current on a thin cylinder above a finitely conducting half-space
Authors: Bombardt John N.
Published: February 2004

A thin cylinder above a finitely conducting half-space is illuminated by a monochromatic plane wave. The electric vector of the incident plane wave is parallel to the axis of the cylinder and the Poynting vector of this incident plane wave intersects the surface of the finitely conducting half-space at an oblique angle. An imperfect image is used to derive the total current on the thin cylinder and the electric field at the surface of the half-space. The total induced current on the thin cylinder is shown to reduce to the appropriate limiting form when the height or the half-space conductivity becomes infinite.
Origin of ``energetic'' ions from laser-produced plasmas
Authors: Ehler Wayne , Linlor William I.
Published: February 2004

A fast-ion current peak, measured with an ion collector placed in the path of an expanding laser-produced plasma, was identified as carbon, nitrogen, and oxygen contaminants which originated from a tungsten target surface.
Epitaxial growth of high-vacuum evaporated EuS on mica
Authors: Reichelt K. , Viehweg J.
Published: February 2004

The deposition of epitaxial EuS films on mica is reported. The structure and orientation of the films on the mica surface are determined by transmission Laue photographs.
Acoustic densitometer with results for polyethylene oxide
Authors: Corsaro R. D. , Jarzynski J. , Davis C. M.
Published: February 2004

An acoustic densitometer has been developed for the precision measurement of PVT data over a wide range of temperatures and pressures. With this device, changes in the density of a solid or liquid are measured with a precision better than 3 parts in 105. Further, a density change of as much as 15% may be accommodated with no loss in the sensitivity or accuracy of the measurement. Finally, the electronic system used is straightforward, for which components are readily available. The system was tested on the polymer, polyethylene oxide, over a temperature range 10–50 °C and at pressures up to 1 kbar. Volume derivatives were obtained from the data and used to evaluate the Broadhurst-Mopsik model for linear polymers. The agreement is good for temperatures up to and including 30 °C. In the temperature interval 40–50 °C, changes in the degree of crystallinity of the sample are suggested by the data.
Systematic study of the electrical characteristics of the ``Trichel'' current pulses from negative needle-to-plane coronas
Authors: Lama W. L. , Gallo C. F.
Published: February 2004

When a negative dc voltage is applied to a needle in an electronegative gas such as atmospheric air, highly regular corona current pulses (Trichel pulses) are observed under some conditions. Systematic variation of the macroscopic experimental parameters has yielded the functional dependence of the pulse frequency, charge per pulse, and time-averaged corona current on the applied voltage, needle-tip radius, and needle-to-plane spacing. In combination with a theoretical analysis of the motion of the charge clouds, these results yield new insight into the physical mechanism of this gas-discharge phenomenon. For example, above threshold voltage, it appears that several negative-ion-charge clouds are simultaneously in transit across the gap.
Electronic conductivity in the presence of acoustoelectric domains
Authors: Macomber G. , Neudorfer M. , Yee S.
Published: February 2004

A nonlinear theory is developed for electronic conduction in the presence of acoustic energy in piezoelectric semiconductors. The theory is valid for the cases of large acoustic energy and large electric field. The resulting expression is of closed form. The conductivities of acoustoelectric domains are measured. The experimental results are consistent with the theory if the domains are assumed to be composed of more than one acoustic frequency.
Resonant cavities with mirrors made from graded-index rods
Authors: Vanderleeden J. C.
Published: February 2004

We study the stability conditions for resonant cavities with spherical mirrors made from graded-index (GRIN) rods. The spherical mirror is made by putting a high-reflective (HR) coating on one of the flat ends of a GRIN rod segment. It is shown that one or two GRIN mirrors can be used to make all the usual resonator configurations. In particular, two GRIN mirrors attached to a solid-state dielectric laser rod can be substituted for curved mirrors ground on the rod ends; the ends need only be reasonably flat. We present the following experimental verification: (i) The cw operation of a resonant cavity consisting of a flat/flat Nd : YAG rod with a GRIN mirror attached to one end, and (ii) the construction and operation of an array of GRIN mirrors which defines several independent simultaneously oscillating resonators within a single flat/flat Nd : YAG rod. We suggest the possibility of building a compact array of many closely packed miniature resonators by cementing a large number of GRIN mirrors to the top of a 5-mm-thick Nd : YAG disk, the bottom of which is HR coated. The disk can be diode pumped through the circumference and/or the bottom.
Light scattering by pores in polycrystalline materials: Transmission properties of alumina
Authors: Peelen J. G. J. , Metselaar R.
Published: February 2004

The in-line transmission of polycrystalline high-density ceramics is discussed in terms of light scattering by pores. The Mie theory for light scattering is applied to calculate scattering coefficients using generalized parameters. Results are shown for scattering by spherical pores with uniform size and with a lognormal size distribution. Specific examples are given of the calculated transmission of alumina in the wavelength region 0.4–5 μm. Experimentally determined transmission curves of normally sintered and of hot-pressed alumina are compared with calculated curves. The porosity, the position of the maximum, and the width of the lognormal distribution are treated as variables in the calculation. Good agreement with the experimental data is obtained.
Phosphorus concentration profiles in p-doped silicon dioxide measured using Auger spectroscopy
Authors: Chang C. C. , Adams A. C. , Quintana G. , Sheng T. T.
Published: February 2004

The depth distribution of phosphorus in silicon dioxide formed by reacting phosphine and silane with oxygen at 480°C, has been measured with Auger spectroscopy using (i) ramp-etched silicon dioxide films and (ii) in situ ion milling. Quantitative Auger analysis showed the phosphorus concentration to be 0.5 at.% throughout most of the oxide. However, when grown directly on silicon, a phosphorusrich oxide, [sine wave] 30 Å thick and containing > 3 at.% phosphorus, was first deposited, followed by a phosphorus-depleted region, [sine wave] 150 Å thick; both regions formed within the first minute of deposition and probably resulted from a rapid initial reaction of phosphine with the silicon surface. Neither region is formed when the doped oxide is deposited on silicon dioxide, and undoped oxides < 200 Å thick were successfully used to eliminate the phosphorus-rich layer. There was negligible diffusion (≲100  Å ) of phosphorus from a doped oxide containing 0.5 at.% phosphorus into steam oxide after heating for 30 min at 1000°C.
Optical analysis of vibration modes of elastic bars
Authors: Lowenthal S. , Lapierre J. , Phalippou D.
Published: February 2004

A simple method for measuring phase velocities of vibration modes in a bar is described. Experimental results for aluminum are compared with values computed from theoretical curves of the phase velocity versus frequency thickness product.