bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical solutions of planar and spherical magnetohydrodynamic blast waves
Authors: Rimer Norton , Jen Norman C.
Published: February 2004

The effect of a uniform magnetic field on the expansion of an isothermal high-pressure sphere of plasma (fireball) into a fully ionized atmosphere is investigated. The ideal magnetohydrodynamic (MHD) equations in Lagrangian coordinates are integrated numerically using the von Neumann-Richtmyer method of artificial viscosity. Numerical solutions are obtained to the unsteady two-dimensional spherical blast wave model and to the simpler planar one-dimensional model. For large magnetic fields, both a fast and a slow MHD shock wave propagate ahead of the fireball which is deformed into an elliptic shape with major axis in the direction of the uniform magnetic field.
Corona discharge photography
Authors: Boyers David G. , Tiller William A.
Published: February 2004

Using short (∼ 100 μsec) pulses of rf (1 MHZ) applied to parallel electrodes in air at small electrode spacings (∼ 250 μ) and at an applied field of ∼ 106 V/cm, discharges from both biological and metallic electrodes occurred from a network of points in the electrode surface. These discharges were recorded photographically. Multiple pulses lead to a superposition effect such that a uniform corona exposure appeared on the film. Some effects of electrode material, spacing, and orientation are presented. The results are found to be completely explicable in terms of the ``streamer'' phenomenon of corona discharge. In fact, the wide variety of color effects observed in ``Kirlian'' photography can be accounted for by this mechanism.
Some physical properties of two amorphous metallic alloys
Authors: Berry B. S. , Pritchet W. C.
Published: February 2004

Room-temperature values of the thermal-expansion coefficient, thermal diffusivity, thermal conductivity, density, Young's modulus E, and the temperature coefficient (1/E) dE/dT are presented for two splat-cooled amorphous alloys of composition (in atomic percent) Pd82Si18 and Fe75P15C10. Values of E were obtained from the flexural resonant frequencies of cantilever mounted reeds; the thermal properties were derived from internal friction measurements giving the height and location of the thermoelastic ``transverse thermal current'' peak. Compared to crystalline alloys, the amorphous samples are poorer thermal conductors but exhibit a comparable expansion behavior. In view of the small density difference between the amorphous and crystalline states, the most striking difference observed was the lower elastic modulus of the amorphous alloys. The present results supplement a growing body of evidence that materials in the amorphous condition may have a Young's or shear modulus which is typically 20–40% less than the value in the crystalline state.
Dynamic technique for measuring thermal conductivity in cylindrical geometry
Authors: Erdman Carl A. , Schilmoeller Neil H.
Published: February 2004

A dynamic technique for measuring thermal conductivity in cylindrical geometry is presented. A radially centered heater wire is used. The temperature difference between two different radial positions in the cylindrical specimen is monitored during heating. Measurements are made under vacuum and within a thermal shield to minimize heat losses. Bulk-specimen temperature rise is restricted to 1/2 °K. For a specified time interval, which is a function of specimen dimensions and thermal properties, the measured temperature difference is constant to within a fraction of 1% and is inversely proportional to the thermal conductivity of the specimen. The thermal diffusivity and heat capacity are not specifically needed to determine the thermal conductivity. Mathematical development of the theory of the technique is presented along with the results of measurements on single-crystal silicon and aluminum specimens.
Quantized fluctuations in the Josephson oscillations of a shunted superconducting point contact
Authors: Sandell R. D. , Wikswo J. P. , Pickler J. M. , Deaver B. S.
Published: February 2004

By detecting the oscillation of a tuned circuit resonant at frequency v0 coupled to a shunted superconducting point contact we have observed oscillations not only at the Josephson voltage V=φ0v0, where φ0 is the flux quantum, but also at voltages Vn=gn(T)φ0v0, where gn(T) is a continuous monotonic function of temperature. For most temperatures gn(T)=N(T)/n, where N and n are integers, however there are ranges of temperature over which g1(T) varies rapidly through nonintegral values and the voltages Vn are not harmonically related. The level of oscillation of the tuned circuit was used to measure the power spectrum of the voltage waveform at the point contact and the linewidths were found to be oscillatory functions of temperature with minima when V1=Nφ0v0 and maxima when V1=(N+1/2)φ0v0. The Josephson oscillation of the shunted point contact consists of pulses of N flux quanta (Nφ0) crossing the point contact at a repetition frequency v0. The temperature dependencies are interpreted in terms of fluctuations in N. The relationship between these results and some temperature dependent features observed on the I-V curves of point contacts and some implications for noise thermometry are discussed.
Escape of misfit dislocations from the interface in (111) silver-gold bicrystals
Authors: Snyman H. C. , Boswell F. W.
Published: February 2004

The behavior of misfit dislocations in (111) silver-gold bicrystals has been studied by transmission electron microscopy and it was found that severe heating in the electron beam results in complete elimination of dislocations from the interface. The possible mechanisms involved are discussed.
Crystallization of Te100−xTlx alloys (15≤x≤50) obtained by rapid cooling from the liquid state
Authors: Anseau M. R.
Published: February 2004

The crystallization of foils of Te100−xTlx prepared by rapid cooling from the liquid state has been studied. In most cases the early stages of the amorphous-crystalline transformation lead to a metastable cubic phase with a metallic character.
Comment on ``Determination of dislocation velocities and densities''
Authors: van den Beukel A. , Wijler A. , van Westrum J. Schade
Published: February 2004

Some recent attempts to use the properties of propagating deformation bands in order to obtain information on dislocation parameters are critically discussed.
Equivalent diffusion effect due to the dielectric relaxation effect
Authors: Kodama Toshikazu , Hasuo Shinya , Ohmi Tadahiro
Published: February 2004

The transport of a sheet of excess carriers in a conducting material having two types of mobile carriers is described in a small-signal approximation. It is shown that the carriers exhibit an equivalent diffusion in the drift direction due to the dielectric relaxation effect even in the absence of thermal diffusion, and that the total effective diffusion coefficient is given by the sum of the thermal diffusion coefficient and the two-carrier diffusion coefficient.
Scattering by water waves generated by a moving pressure point
Authors: Ott R. H. , Hufford G. A. , Howard A. Q.
Published: February 2004

An analysis for scattering of scalar waves in air by a wake on the surface of water is developed. The wake on the water surface is generated as a concentrated pressure point travels over the free water surface. The wake has characteristics resembling a diffraction grating. The grating produces maximum constructive interference (resonance) in the backscattered wave under certain conditions. At resonance the scalar wavelength, water wavelength, and angle of incidence satisfy a simple geometrical condition.
Time and frequency behavior of sound waves thermally induced by modulated laser pulses
Authors: Eichler H. , Stahl H.
Published: February 2004

A temporally and spatially periodic light intensity distribution generates thermally in an absorbing sample a corresponding density variation which can be considered a standing sound wave. This thermal excitation of ultrasonic waves by modulated laser light has been investigated theoretically and experimentally. The sound waves were excited by two light beams of equal intensity derived from a mode-locked ruby laser. The amplitude, velocity, and damping of the sound waves were examined by Debye Sears diffraction of argon laser pulses.
Measurement of resistivity change by a mutual inductance method
Authors: Hamdani A. J.
Published: February 2004

The resistivity of a nonferromagnetic conductor can be deduced from the change in mutual inductance between two coils when the sample is inserted. A method is described for measuring mutual inductance over a range of frequencies and this can be used to detect change in resistivities of the order of ± 10−13 Ω cm.
Decay of electrical conductance and temperature of arc plasmas
Authors: Lowke J. J. , Voshall R. E. , Ludwig H. C.
Published: February 2004

Calculations assuming thermal equilibrium have been made of properties of cylindrical arc plasmas which decay after the removal of the electric field. Account is taken of energy losses due to thermal conduction and radiation, self-absorption effects being included where possible in the treatment of radiation. The maximum possible influence of radial convection is calculated by assuming that convective flow maintains a uniform pressure in space and time. Comparisons are made of the calculated decay of electrical conductance with experimental measurements, where available, for A, N2, SF6, H2, and air; curves are given showing the contributions of thermal conduction, convection, and radiation to the decay. The theoretical results underestimate the rapid decays of electrical conductance that have been observed for plasma temperatures of less than 10 000 °K in air, and less than 7000 °K in SF6, but good agreement between theory and experiment is obtained for argon. Information from rate coefficients supports the view that the rate of atomic recombination to form molecules is insufficient to maintain thermal equilibrium and as a result there is an enhanced rate of cooling. Theoretical transient temperature profiles in air are also compared with published experimental profiles.
X-ray emission in laser-produced plasmas
Authors: Colombant D. , Tonon G. F.
Published: February 2004

Numerical results are presented for the characteristics of heavy-ion laser-produced plasmas. A conversion ratio defined as x-ray power/absorbed power is then computed. Collisional-radiative equilibrium is assumed for the ionization model. In the case of low radiation emission, a relation between laser flux and plasma temperature is derived. The one-dimensional geometrical model is then corrected in the expansion by assuming that the emission occurs, in fact, over a length L only. Results are given and compared with experimental ones. The influence of the laser wavelength is also discussed and conclusions on the possible applications of these laser-produced plasmas are drawn.
Simultaneously pinched electron beams
Authors: McClenny William A. , Bennett Willard H.
Published: February 2004

Treated is the steady state of a beam interacting with the plasma which it produces in a low-density gas and in which magnetic self-focusing must be considered. Self-focusing is assumed to exist when the second time derivative of the moment of inertia of the beam electrons is negative and when that of the ions is neglected. Predictions are related to experiments with 10–15-keV beam electron energies, beam currents of several hundred milliamps, and system pressures of 10−4 Torr. Simultaneous pinching is observed with approximately equal radial forces on the beam electrons due to overneutralization and due to magnetic self-focusing.
Circular twist disclination in viscoelastic materials
Authors: Kuo H. H. , Mura T.
Published: February 2004

A general formulation of the displacements induced by plastic distortion, β*ji, with small intertia forces in viscoelastic materials is derived. The elastic fields of a twist disclination in viscoelastic materials are then obtained from this formulation. Finally, the fading property of the strength of the disclination is determined for the disclination in the standard linear viscoelastic materials, and the variations of the elastic fields of the disclination are discussed.
Photovoltaic effect due to two-photon process in p-n junction devices in the presence of a built-in field
Authors: Deb S. , Mukherjee M. K. , Basu A. K.
Published: February 2004

Results of analysis of photovoltaic effect in a p-n junction arising out of the two-photon process in the presence of a constant built-in field are presented. The short-circuit current, the open-circuit voltage, and efficiency of typical GaAs cells exposed to 1.17-eV photon flux from a laser are computed. It is shown that marked improvement in the short-circuit current and efficiency with considerable saving in material are possible with a field of the order 100 v/cm. The effect of reflection at the back face are also discussed and the possible improvement in performance with a reflecting coating of the face estimated.
Refractive index of n-type gallium arsenide
Authors: Zoroofchi J. , Butler J. K.
Published: February 2004

The index of refraction for n-type GaAs is calculated as a function of photon energy by a method which accounts for the contribution of the fundamental absorption edge to the index of refraction. The absorption coefficient for n-type GaAs near the band-gap energy is determined from experimental data; free-carrier absorption is not included in the calculations; however, its contribution to the index of refraction is estimated to have a negligible effect compared to that due to the fundamental edge. Some applications to single- and double-heterojunction (AlGa)As–GaAs laser structures are discussed. The results indicate that occasionally the most important factor contributing to radiation confinement to the optical cavity in laser structures is the index-of-refraction change due to the differences in doping of various regions. Index calculations are made by using absorption data on GaAs at 77 and 300°K. The difference in the index of refraction of a material with different doping can be pronounced. For example, an index change of 1.3% occurs due to differences in the absorption edge of crystals with dopings n = 2 × 1016 cm−3 and n = 6.5 × 1018 cm−3 at an energy of 1.48 eV and T = 77°K. However, the same crystals had a 0.89% index differential at E = 1.37 eV and T = 300°K. These calculations agree extremely well with the index-of-refraction differentials determined from radiation pattern characteristics of laser devices.
Noise in the superconducting quantum flux detector
Authors: Kurkijärvi Juhani
Published: February 2004

An expression is derived for noise in the tank circuit of a superconducting quantum flux detector run at a radiofrequency. This noise is limited by the sensing element of the device, the superconducting ring with a weak link, and is therefore intimately related to the thermal fluctuations in the ring. Not considering external noise, the superconducting ring and the tank circuit together with the preamplifier should exhaust the important sources of noise in the flux detector.
Thermal hysteresis of magnetization curve in MnBi films below room temperature
Authors: Egashira K. , Yoshii S.
Published: February 2004

Magnetization curves of MnBi thin films have been measured in the temperature range between room temperature and 77°K. Films were prepared on glass substrates with a protection layer of SiO2 by vacuum deposition. There occurs a large thermal hysteresis of the magnetization curves, which has not been known of bulk specimens. The magnetic domain configuration at 77°K and the dependence of magnetic anisotropy energy on temperature were also studied. The thermal hysteresis is due to some relaxation mechanism. It is suggested that a thermomagnetic writing other than the Curie-point writing will be possible, if the thermal hysteretic property is made use of.
Magnetization reversal process in chemically precipitated and ordinary prepared BaFe12O19
Authors: Haneda Koichi , Kojima Hiroshi
Published: February 2004

BaFe12O19 particles were prepared by chemical precipitation and ordinary powder metallurgy methods. These particles were oriented in paraffin wax and the angular variation of coercive force was measured. By using the modified equation of Buessem et al., its variation was analyzed. It was found that reverse-domain nucleation greatly influences the intrinsic coercive force of BaFe12O19 particles; even stress-free chemically precipitated single-domain particles were influenced. Annealing the ball milled powder raised the coercive force drastically. This is due to the reduction of defect-nucleation centers. It should be noted that by the chemical precipitation method a coercive force of 6000 Oe was obtained, which is one of the highest reported up to this time for isotropic BaFe12O19.
Comparison of theory with simulations of 1/f noise
Authors: Alberding N. , Tunaley J. K. E.
Published: February 2004

Estimates of the spectral densities of a model thought to be appropriate to 1/f current noise are found using a Monte Carlo method. The results are compared with theory. It is concluded that the model should be useful in the explanation of the occurrence of this type of noise in many materials.
Relative Raman cross section of O3 for four Ar+ laser frequencies
Authors: Schwiesow R. L. , Abshire N. L.
Published: February 2004

We have measured the relative Raman scattering cross sections of O3 (referred to N2) and the depolarization ratios at four argon-ion laser pump frequencies to be, respectively, 2.3 and 0.05 at 20 981 cm−1, 2.5 and 0.03 at 20 487 cm−1, 2.8 and 0.04 at 20 135 cm−1, and 2.2 and 0.10 at 19 430 cm−1. The estimated uncertainty in cross section is ±12% and in depolarization, ±0.01, although the cross sections at different frequencies are thought to intercompare to ±5% or less. An improved sample preparation technique was used. We found no dependence of cross section on pressure and only weak evidence for any resonance dependence on pump frequency.
Comment on ``Appearance potential spectroscopy''
Authors: Park Robert L. , Houston J. E.
Published: February 2004

Contrary to assertions by Tracy that soft x-ray appearance potential spectroscopy cannot be applied to semiconductors and insulators, we have encountered no obstacles in obtaining good spectra from both classes of materials. In addition to previously published spectra of boron and transition-metal oxides, we present 1s and 2p spectra of clean silicon.
Determination of electron density and electron collision frequency in a plasma by an rf nonimmersive probe
Authors: Basu J. , Maiti J. N.
Published: February 2004

This paper presents a method for determining the electron density and electron collision frequency in a cylindrical plasma column by placing an rf coil coaxially around the plasma and measuring the coil impedance. Simplified expressions relating the impedance to plasma parameters are found to be valid under certain suitable conditions. The plasma of a hot-cathode low-pressure dc discharge in argon has been studied by an rf coil probe. The dependence of electron collision frequency on electron velocity has been taken into account. The values of the electron density and average collision frequency, as obtained from the rf probe under different discharge conditions, are in fairly good agreement with those given by a cylindrical Langmuir probe.
Complex rigidity of dispersions of spherical shell structures with material compressibility
Authors: Takano Yo , Sakanishi Akio
Published: February 2004

The effective modulus of rigidity μ* of dilutely dispersed systems of spherical shell structures, consisting of the shell region and the inside region, is calculated for the finite thickness of the shell, taking account of material compressibility.
Fundamental aspects of electron beam lithography. II. Low-voltage exposure of negative resists
Authors: Thompson L. F. , Feit E. D. , Melliar-Smith C. M. , Heidenreich R. D.
Published: February 2004

A study has been made of the use of low-voltage exposure of negative resists for electron lithography. Three resists have been investigatd; an esterified terpolymer, epoxidized polybutadiene, and polyglycidyl methacrylate. The optimum exposure conditions have been determined for each material, and the use of a low accelerating voltage (5 kV) found to be advantageous. The application of this technique for the pattern delineation of silicon dioxide and tungsten is described.
Generation of reproducible giant pulses with an optically regenerative Q switch
Authors: Baues Peter , von Hundelshausen Ulrich , Möckel Peter
Published: February 2004

In a new concept for an optically regenerative Q switch which is described, the oscillation of the laser with the cavity closed is sensed by a fast photodiode whose output signal opens the electro-optical Q switch. The threshold of the laser as a function of the modulator voltage is theoretically investigated; the empirical results obtained with a YAG:Nd3+ laser agree well with theory. The advantages offered by the optically regenerative Q switch are the easy controllability of the peak power of the giant pulses by way of the modulator voltage and the excellent reproducibility of the giant pulses. The experiments revealed the variations between pulses to be less than 3%. Thus the optically regenerative Q switch is practical for all giant-pulse lasers whose emission is required to be highly stable.
Impulse reaction resulting from the in-air irradiation of aluminum by a pulsed CO2 laser
Authors: Hettche L. R. , Schriempf J. T. , Stegman R. L.
Published: February 2004

The impulse reaction resulting from the in-air irradiation of aluminum by a high-intensity pulsed CO2 laser is experimentally examined in this study. Power densities of the order of 107−108 W/cm2 are obtained for focused beam energies between 100 and 700 J and pulse durations of between 15 and 50 μ sec. The targets are mounted in a sensitive pendulum in order to measure the total recoil impulse. The time history of the impulse during irradiation is determined by an interferometric technique. In addition, thermocouples are used to monitor the rear surface temperature of the thin (0.05 cm) targets. The thermal and mechanical response of the target is dominated by the effects of a high-intensity leading edge of the laser pulse. The precursor spike generates an opaque plasma at the target surface which effectively shields the target from the incident energy. Impulse and pressure transmitted to the target are related, therefore, to reaction of the expanding plasma against the target surface. Impulse coupling coefficients (I/E) between 5 and 7.8 dyn sec/J are measured for this mechanism of impulse production. The major contribution to the total impulse is associated with the plasma pressure during the initial stages of the plasma-surface interaction. The peak pressures generated during this time are found to depend on the second power of the initial beam intensity. It follows that the corresponding impulse coupling coefficients should increase linearly with beam intensity. However, a net increase in I/E is not realized at higher beam energies because of absorption losses (air breakdown) along the beam path.
Chromium-ytterbium energy transfer in silicate glass
Authors: Sharp E. J. , Miller J. E. , Weber M. J.
Published: February 2004

Energy transfer has been observed between trivalent chromium and ytterbium ions in a silicate glass. Optical absorption and emission spectra of Cr3+ and Yb3+ are presented and show that the chromium emission, which occurs as a broad-band fluorescence in the near-infrared, overlaps the ytterbium absorption. Hence Cr3+ ions can be used to sensitize YB3+ fluorescence. Cr3+-to-Yb3+ energy transfer was established from the Yb3+ fluorescence excitation spectrum and the decrease in the Cr3+ fluorescence intensity and lifetime. A decrease in the Yb3+ lifetime with increasing Cr3+ content was also observed indicating relaxation of Yb3+ by back transfer to the faster relaxing Cr3+ ions. Measurements of the Yb3+ and Cr3+ fluorescence lifetimes as a function of temperature and chromium content are reported.
Electron-beam-induced reversible transformations from glass to crystalline, liquid, and vapor phase in Se thin films
Authors: Herd S. R. , Chaudhari P.
Published: February 2004

A triple sandwich of C–Se–C was employed to study the transformation behavior of amorphous selenium by electron microscopy. The electron beam was used as energy source in all experiments. Reversible transformations from crystalline to amorphous Se was observed in well-defined localized areas. By application of a rapid heat pulse, void formation occurred in amorphous Se. Slow heating caused erasure of the voids by viscous flow. Crystalline Se held at low temperatures (< 50°C) was found to become amorphous by gradual breakdown of crystalline order under electron irradiation.
Superconducting single-junction interferometers with small critical currents
Authors: Hansma Paul K.
Published: February 2004

A simple theory of the superconducting single-junction interferometer (ac Squid) becomes possible if the critical current of the single junction is small relative to Φ0/LR, where Φ0=h/2e is one flux quantum and LR is the inductance of the interferometer loop. This theory predicts a magnetic flux sensitivity which has the same dependence on interferometer parameters as the existing theories for higher critical currents. In contrast to those theories, however, the present theory predicts that the maximum flux sensitivity will be achieved off resonance. Theoretical predictions for comparison with experiment are displayed as a function of the normalized difference between the operating frequency ω and the resonant frequency ω0.
Luminescence of Be- and Mg-doped GaN
Authors: Ilegems M. , Dingle R.
Published: February 2004

The luminescence of vapor-grown GaN doped with Be or Mg shows deep emission bands in the yellow-green (Be) or blue-violet (Mg) wavelength regions in addition to the near-gap features previously recognized in Zn- and Cd-doped GaN. The crystals are of high resistivity at high Be or Mg doping levels.
Passive Q switching of a CO laser by nitric oxide
Authors: Bonczyk P. A.
Published: February 2004

A CO laser which operates on the ν = 9 → 8 P(13) transition at 5.307 μ is passively Q switched by using magnetically tuned nitric oxide as the switching agent.
Measurement of the thermal diffusivity of mercury
Authors: Ang C. S. , Chan S. L. , Tan H. S.
Published: February 2004

The thermal diffusivity of mercury has been measured from 120 to 370 K, using the heat pulse method. The results are analyzed by computed solutions of the three-layer thermal diffusivity problem, and compared with recommended values published by the Thermophysical Properties Research Center. Agreement is obtained to within 5% in the liquid phase and 10% in the solid phase.
Tunneling in SiC electroluminescent diodes
Authors: Barnes C. E.
Published: February 2004

Experimental results are presented to support the contention that the light output of SiC electroluminescent diodes can be dominated by radiative tunneling over a wide temperature range. A spectral peak shift to higher photon energy with increasing junction voltage has been observed, as well as a temperature-independent slope of the light intensity-voltage curves. Both of these properties are characteristic of radiative tunneling. In addition, the value of the temperature-independent slope agrees with that calculated from a simple tunneling model using data from capacitance measurements. An energy-band scheme is proposed which leads to the tentative conclusion that the radiative recombination process is donor-acceptor pair recombination of tunneling carriers in the depletion layer.
Scattering of Rayleigh waves by surface defects
Authors: Steg R. G. , Klemens P. G.
Published: February 2004

The scattering of Rayleigh waves by defects is discussed by means of first-order perturbation theory. The defect is treated as a point defect of excess mass, either at the surface or some fixed distance below it. Scattering is into other Rayleigh waves or into bulk waves. Expressions are given for the scattering probability and for the relative scattering into these two groups of modes. For a point defect at the surface, scattering varies as the fifth power of frequency, and scattering into other Rayleigh waves is the dominant process. For point defects distributed through the volume of the solid, scattering varies as the fourth power of frequency. Expressions are also given for a line of defects normal to the surface and of finite length. For an infinite line, scattering varies as the cube of the frequency. Horizontal line defects and vertical sheets of defects have been treated in the doctoral dissertation of one of the authors (R.G.S.). These results are summarized.
Total oxygen content of gallium phosphide grown by the Czochralski technique using liquid encapsulation
Authors: Kim C. K.
Published: February 2004

The total oxygen content of a number of doped and undoped GaP crystals grown by the liquid encapsulated Czochralski technique has been determined using 10-MeV He3 beams. The level of oxygen ranges from 2 × 107 to 5 × 1017 atoms/cm3 for the undoped ingots. Oxygen concentrations at the tail ends of the crystals were approximately twice those at the seed ends of the same crystals. A slight increase in oxygen concentration was also found toward the center region of a circular slice of the crystal. Ga2O3-doped crystals contained up to five times more oxygen ([inverted lazy s]2×1018) than undoped crystals. The systematic increase of the total oxygen solubility as a function of the concentration of Ga2O3 added for the growth was also investigated. These results were then compared with total oxygen incorporated in crystals grown by vapor-phase epitaxy.
Phenomenological approach to the design of highly tunable pressure-broadened gas lasers
Authors: Degnan John J.
Published: February 2004

Recently published measurements of the gain in continuous-wave CO2 waveguide lasers have indicated that the small-signal gain decreases exponentially with pressure in the range beyond about 70 Torr. In the present paper, the observed dependence of the gain on pressure has been incorporated into the general theory of homogeneously broadened gas lasers to form a phenomenological model of the waveguide laser. The model is then used to generate a series of curves intended to aid in the selection of gas mixture, operating pressure, discharge length, and mirror reflectivities when tunability is the primary design goal. The operating parameters are chosen on the basis of the desired laser characteristics (bandwidth and output power) and a small number of molecular parameters. Although the discussion emphasizes CO2 waveguide systems, the design curves are applicable to all homogeneously broadened gas lasers. It is found that, although there exists a critical pressure beyond which the laser should not be operated for reasons of efficiency, the tunability can be increased indefinitely by incorporating a longer discharge and an appropriate tunable internal etalon.
Oxidation-induced stacking faults in silicon. I. Nucleation phenomenon
Authors: Ravi K. V. , Varker C. J.
Published: February 2004

Mechanisms for the nucleation of oxidation-induced stacking faults in silicon have been examined. Fault nucleation is found to occur at sites of mechanical damage and at impurity inhomogeneities in the silicon. In either case, nucleation occurs by the coalescence of excess interstitials into Frank loops surrounded by dislocations of the type (a/3)(111). Nucleation in damage-free crystals occurs along a banded or striated distribution. This is identical to the distribution of shallow noncrystallographic etch pits in the unoxidized wafer which have been linked to vacancy-oxygen complexes. The common distribution pattern indicates that the impurity inhomogeneities are nucleation sites for fault formation. Models for the nucleation phenomenon are proposed based upon local excess oxygen diffusion into regions of excess vacancy concentration in the crystals.
Oxidation-induced stacking faults in silicon. II. Electrical effects in P N diodes
Authors: Varker C. J. , Ravi K. V.
Published: February 2004

The electrical characteristics of boron-diffused P+N diodes containing electrically active stacking faults (EASF) are investigated. The method combines an analysis of the I-V characteristics of the diodes with information derived from a scanning-electron-beam technique, the electron-beam-induced current (EBIC) mode. Stacking faults (SF) measuring 1–2 μm in length nucleate and develop in the near-surface region of the silicon slice during the initial oxidation process. Subsequent to the boron diffusion, the SF are heavily decorated with impurity precipitates. Excess reverse currents are measured at room temperature over a broad range of voltage from the very-low-voltage region where VR < kT/q to the high-voltage preavalanche region where VR≫kT/q. Two distinct regions are observed in the I-V characteristics of all diodes containing EASF's. These regions are separated by an effective threshold voltage VTHE, which is characteristic of the EASF's in the particular diode. For typical diodes with a junction depth Xj=0.4 μm, experimentally determined values for VTHE are in the range 0.1–10.0 V. When the applied reverse voltage VR < VTHE the diode exhibits the two regions characteristic of silicon diodes at room temperature; a low-field Ohmic conductance region when VR < k T/q and a space-charge-generation region when VR > k T/q, which is similiar to a modified form of SNS theory. In this region, the excess generation currents are found to correlate with the threshold voltage of the EASF's. When VR > VTHE a voltage power-law dependence is observed where IRαVn, n≈4.75±0.25. This carrier-generation effect results from the interaction between the strain field and/or the impurity atmosphere surrounding the EASF and the depletion field of the P N junction. The composite defect introduces a local high-density zone of g-r centers which reduce the effective lifetime of minority charge carriers in the region of the SF. The localized g-r zones are typically 20 μm2 in cross-sectional area with an effective lifetime of 4 – 400 ps. They are distributed nonuniformly, and are the direct source of excess IR currents measured at room temperature.
Microcycle spectral estimates of 1/f noise in semiconductors
Authors: Caloyannides M. A.
Published: February 2004

Many physical occurrences are characterized by extremely low spectral variations, the measurement and estimation of which has been invariably difficult. An estimate of the density of the power spectrum of very-low-frequency semiconductor 1/f noise is experimentally obtained from 10−6.3 to 1.0 cps with a greater accuracy than that achieved in previous similar attempts; it is concluded that the spectrum is 1/fα with α approximately 1.3 over most of the frequency range, but appearing to have a value of about 1.0 in the lowest decade. A peculiar form of stationarity seems to distinguish 1/f noise from other noise in semiconductors. Ten independent noise sources were time multiplexed and their spectral estimates were subsequently averaged. If the sources have similar spectra, this reduces the necessary data-taking time by a factor of 10 for a given accuracy. An estimator is derived for optimal spectral estimation based on a number of statistically independent noise sources. Other related topics considered are nonequidistant sampling, and a plausible mathematical model of such flicker noise. Finally, the variance of the spectral estimate obtained through the Blackman/Tukey algorithm is analyzed in great detail; the variance is shown to diverge for α≥1.0 in an assumed power spectrum of k/|f|α, unless the assumed spectrum is ``truncated''.
A mathematical technique for use in a small-signal field analysis of double-stream interactions in finite semiconductors
Authors: Goodrich Lewis C. , Durney Carl H. , Grow Richard W.
Published: February 2004

This paper describes a double-stream analysis that can be used to investigate interactions in any finite multiple-charged drifting particle stream immersed in a finite longitudinal dc magnetic field that is parallel to the drift velocity. The advantages of the analysis are that collisions and longitudinal thermal velocity effects are included along with transverse waves (fast and slow) and space-charge waves with the only approximations being small-signal linearization and negligible transverse thermal velocity. In addition, the finiteness of the charged-particle streams and the boundary conditions are taken into account. The results of the analysis are field expressions which can be used to obtain a determinantal equation in ω by satisfying the appropriate boundary conditions.
Evaluation of the crystallographic optical anisotropy in MnBi
Authors: Treves D. , Lee Kenneth , Suits J. C.
Published: February 2004

A technique for evaluating the optical anisotropy of fine-grain polycrystalline thin films is developed. This method is applied to MnBi with the low-temperature NiAs structure. It is estimated that the optical anisotropy is less than half the magneto-optic effect.
Magnetoelastic Rayleigh waves propagating along a tangential bias field on a YIG substrate
Authors: Parekh J. P. , Bertoni H. L.
Published: February 2004

The propagation characteristics of magnetoelastic (ME) Rayleigh waves on a YIG substrate are treated for the parallel bias configuration, wherein the bias field is tangential to the substrate and parallel to the direction of propagation. The YIG surface is considered to be mechanically free and either adjoined to vacuum (unmetallized configuration) or electrically shorted by a thin perfectly conducting metallic film (metallized configuration). The ME Rayleigh waves are found to be bound surface waves outside of a spectrum of frequencies given approximately by the magnetostatic bulk-wave spectrum, and of the leaky type within it. By varying the frequency (or equivalently the bias field) over the leaky-wave spectrum, the direction of energy leakage into the substrate may be controlled over an angle of 180° from the direction of surface-wave propagation.
Ambipolar transport noise in a semiconductor in the presence of a magnetic field
Authors: Maldonado C. D.
Published: February 2004

The noise spectrum due to fluctuations in the electron-hole pair particle density in a semiconductor in the presence of a magnetic field is presented in this paper. This spectrum was obtained via the Green's function for the macroscopic differential equation which governs the behavior of the conditional average for fluctuations in the electron-hole pair particle density when ambipolar transport and generation-recombination are the important noise processes. The macroscopic differential equation is a generalization of van Roosbroeck's small-signal continuity equation to include the presence of a magnetic field. The resultant spectrum was evaluated numerically and a family of curves corresponding to different values of magnetic field strength generated. This was done for specified values of τ/τa and τ/τd, where τ is the mean volume lifetime of electron-hole pairs, τa is the characteristic ambipolar drift time, and τd is the characteristic ambipolar diffusion time. In the extreme situations when ambipolar drift is important and diffusion is negligible and vice versa, the obtained numerical results are consistent with those obtained previously by the author. For the case treated in this paper when both ambipolar drift and diffusion are equally important, the ``universal 3/2 power law'' still prevails in the high-frequency portion of the spectrum, thus indicating the dominance of ambipolar diffusion in that region of the spectrum.
Model for the phenomenon of photodoping of some amorphous semiconductors with silver
Authors: Salik J.
Published: February 2004

A model for the photodoping of some amorphous semiconductors with silver is given. This model attributes the phenomenon to the position of the metal Fermi energy relative to the semiconductor conduction- and valence-band energies.
Validity of the Ehrenfest relation for a system with more than one order parameter
Authors: DiMarzio Edmund A.
Published: February 2004

The relation ΔCpΔκ = TV(Δα)2 is shown to be obeyed under the same assumptions that Davies and Jones used to derive the weaker condition ΔCpΔκ ≥ TV(Δα)2. This means that if a material is found experimentally not to obey the above equality, then it is not describable by an order-parameter theory. A prescription is given which allows one to determine within the context of order-parameter theory whether the glass transition of a given material is basically thermodynamic or kinetic in origin.
Morphological, rheo-optical, and dynamic mechanical studies of a semicrystalline block copolymer
Authors: Shen M. , Mehra U. , Niinomi M. , Koberstein J. T. , Cooper S. L.
Published: February 2004

The morphology, rheo-optical behavior, and mechanical relaxation properties were investigated for a series of three segmented copolyesters containing blocks of crystalline poly(tetramethylene terephthalate) and amorphous poly(tetramethylene ether). Transmission and replica electron micrographs show that if cast from a hot solution of 1,1,2-trichloroethane on a heated surface, all the samples show distinct spherulitic structures. Annealing appears to increase the lamellar thickness. On the other hand, casting from a solution of 1,1,2,2-tetrachloroethane produced a film that showed no evidence of the presence of spherulites, although microphase separation persists and crystallites appear to be randomly oriented in the amorphous matrix. Small-angle light-scattering experiments for trichloroethane-cast samples confirmed the existence of spherulites. Dynamic mechanical data of these copolyesters show three principal relaxation peaks. These are the melting peak of the poly(tetramethylene terephthalate) block, the primary glass transition peak of the poly(tetramethylene ether) block, and the local mode relaxations of both blocks at low temperatures. Annealing and casting from different solvents did not affect the relaxation behavior of these copolyesters.
Internal friction study of polycrystalline n -paraffins
Authors: Crissman J. M.
Published: February 2004

Recent measurements have shown that mechanical relaxation peaks commonly observed in n -paraffins are absent in single crystals of n -eicosane (C20H42). This work has now been extended to include polycrystalline samples of several highly pure long-chain hydrocarbons. Internal friction data obtained for a variety of n -paraffins, pure or otherwise, have revealed no low-temperature γ relaxation. Moreover, the α relaxation peak is suppressed completely by purification. In attempts to induce an α or γ loss peak, several dilute mixtures of other n -paraffins in pure C20H42 have been examined. Only the addition of odd-numbered shorter chains induced loss peaks. On the other hand, the presence of a branched impurity, in this case the C20H42 isomers 2-methylnonadecane and 10-methylnonadecane, did induce loss peaks, one of which correlates very well to the α process found in as-received C20H42. It is proposed here that isomer impurities are an important factor in the mechanics of many of the loss processes in long-chain hydrocarbons observed both mechanically and dielectrically.
Finite-amplitude elastic-plastic wave propagation in laminated composites
Authors: Hegemier G. A.
Published: February 2004

An approximate nonlinear theory is developed to describe finite-amplitude wave propagation parallel to the alternating layers of a laminated composite with elastic-plastic constituents. Model construction is based upon an asymptotic method in which dominant signal wavelengths are assumed large compared to typical composite microdimensions. The final equations evolve as a one-dimensional binary mixture theory.
Lagrangian analysis for multiple stress or velocity gages in attenuating waves
Authors: Seaman Lynn
Published: February 2004

Numerical techniques are presented for extending and implementing the Lagrangian analysis originated by Fowles, Williams, and Cowperthwaite. The analysis derives internal energy, specific volume, and stress and particle velocity histories from either stress or particle velocity records from a series of gages embedded in material undergoing uniaxial strain flow. The material may have an arbitrarily complex constitutive relation. The accuracy of the analysis for attenuating waves is studied by handling analytically derived stress and velocity histories. Waves with attenuation of 40–75% can be treated, depending upon the accuracy desired. The analysis is applied to waves measured in graphite, sandstone, asbestos phenolic composite, and porous alumina.
Coupling of surface and volume acoustic waves by a photoconductive grating
Authors: Auld B. A. , Farnow S. A.
Published: February 2004

The scattering of Rayleigh surface waves into longitudinal volume waves has been carried out utilizing optical patterns imaged on photoconductive cadmium sulfide films. A 100-MHz interdigital transducer was used to launch surface waves along the top face of a lithium niobate delay line. Imaging of an optical grating pattern onto a CdS film overlay produces photoconductive variations which interact with the fields associated with the surface wave. The optical pattern, a series of bars, will cause constructive interference of volume waves scattered normal to the surface when the grating periodicity is one wavelength of the surface wave. A theoretical calculation of this scattering efficiency is made and is found to be in excellent agreement with the experimental results. This device offers significant advantages over similar devices in that the scattering grating may be changed or translated quite readily.
Hall effect in the ``composite sphere'' material
Authors: Mathew Moni G. , Mendelson Kenneth S.
Published: February 2004

A number of recent papers have discussed the Hall effect in a material consisting of high-conductivity grains surrounded by thin low-conductivity layers. These discussions were based on a model in which the grains are identical parallel cubes and the layers are of uniform thickness. The effective Hall constant of this model is approximately equal to the Hall constant of the grains. To test the effect of grain geometry on the effective Hall constant, the present paper discusses the Hall effect in the ``composite sphere'' material in which the grains are spheres of various sizes and the intergranular layers are formed from spherical shells. In this model also the effective Hall constant is approximately equal to the Hall constant of the grains, suggesting that, in general, the effective Hall constant is not strongly dependent on the grain geometry.
Light scattering from Ne, Ar, and Xe arcs
Authors: Vriens L. , Adriaansz M.
Published: February 2004

A procedure is described whereby nonresonant polarized and depolarized Rayleigh, electronic Raman, and Thomson scattering are used as a diagnostic tool for high-pressure nonhomogeneous plasmas. The method is applied to 0.1–3 atm Ne, Ar, and Xe arcs, with currents not exceeding 3 A. Polarized Rayleigh scattering is dominant in these cases. Radial gas temperature and density distributions, an axis electron density, and upper limits of excited state and electron densities are obtained. The temperature range covered extends from about 350 K (near the wall) up to 4500 K (at the axis of a 2-A 3-atm Ne arc). A comparison with spectroscopically obtained temperatures is shown to yield interesting information on the deviations from local thermodynamic equilibrium.
P,v,E,T equation of state for 1,3,5-triamino-2,4,6-trinitrobenzene
Authors: Pastine D. John , Bernecker Richard R.
Published: February 2004

A theoretical P,v,E,T equation of state has been derived for the secondary explosive TATB. From this it has been found that the pressures generated within TATB and similar secondary explosives, when they are compressed, should be relatively insensitive to temperature changes at constant volume. For TATB this means that the shock Hugoniot of the nonporous material should remain close to the room-temperature isotherm up to pressures of about 200 kbar.