bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiative transfer theory for passive microwave remote sensing of a two-layer random medium with cylindrical structures
Authors: Chuang S. L. , Kong J. A. , Tsang L.
Published: February 2003

In passive microwave remote sensing of earth terrain, the application of the radiative transfer theory to the model of random medium has been used in the interpretation of various experimental data. For vegetation fields with cylindrical structures, we model the vegetation layer as a two-layer random medium with a small correlation length lρ in the horizontal direction, and a large correlation length lz in the vertical direction. The closed form solutions for the brightness temperatures are obtained as lz approaches infinity. Using this model, the kernels in the scattering terms of the radiative transfer equations give rise to delta functions, indicating that forward scattering is dominant over all the other directions. For the case that lz is only a few wavelengths long, we find the first-order solution with an iterative method. The results are compared with that obtained using the Gaussian quadrature method to solve the radiative transfer equations numerically. We also apply this model to match experimental data collected from corn fields.
Measurement of tracer elements in inertial fusion target fuel
Authors: Weinstein B. W. , Weir J. T.
Published: February 2003

For some inertial confinement fusion experiments, a tracer impurity element is added to the deuterium-tritium fuel gas as an aid in diagnosing the implosion conditions. We have developed a general, nondestructive technique for measuring the initial tracer density in an individual fusion target. We take advantage of the fact that beta emission from the tritium excites the tracer characteristic x-ray lines. Using an energy dispersive x-ray detector, we measure the intensity ratio of a tracer x-ray line to the bremsstrahlung background. The ratio is proportional to the tracer density and the inner radius of the target and is independent of other parameters. We have measured argon tracer densities as low as 0.01 atm with an accuracy of ±15%.
Capacitance of a finite-length conducting cylindrical tube
Authors: Butler Chalmers M.
Published: February 2003

Two simple formulas are presented for the capacitance of a finite-length, conducting right-circular cylindrical tube which resides in a homogeneous medium of permittivity ε. The formulas may be used to determine capacitance for all ratios (radius/length). The range of (radius/length) over which each formula applies is established by comparisons with capacitance calculated from numerical solutions of an integral equation.
Operating point of long magnetically insulated vacuum transmission lines
Authors: Wang Ming Y. , Di Capua Marco S.
Published: February 2003

This theoretical investigation addresses the propagation of a power pulse in a long magnetically insulated vacuum transmission line (MITL). Relativistic Brillouin flow, with an arbitrary choice of the potential Vm at the flow boundary, explains the relationships among anode voltage, anode current, and cathode current that have been observed experimentally. The results of this investigation suggest that minimum energy considerations may be used to establish the value of Vm and hence determine the operating point of the MITL. This operating point compares very favorably with experimental data and with results from numerical simulations.
Theoretical gain optimization studies in CO2-N2 lasers. III. Inclusion of line shape effects
Authors: Shanmugasundaram V. , Reddy N. M.
Published: February 2003

The influence of Lorentz and Doppler line-broadening mechanisms on the small-signal optical gain of lasers and, in particular, gasdynamic lasers, is discussed. A relationship between the critical parameter reflecting the line-broadening mechanisms and some of the important parameters arising out of the gain optimization studies in CO2-N2 gasdynamic lasers is established. Using this relationship, methods by which the deleterious effect of the Doppler mechanisms on small-signal gain can be suppressed are suggested.
The effect of rf power on reactively sputtered zinc oxide
Authors: Aita C. R. , Lad R. J. , Tisone T. C.
Published: February 2003

Zinc oxide is a piezoelectric material which, in thin-film form, is finding wide application in surface acoustic wave devices. In order to obtain good electromechanical coupling, the polycrystalline film must simulate single-crystal properties. In this study, we report the effect of rf power on the crystallographic orientation and grain structure of reactively sputtered ZnO. Films were deposited at forward power levels ranging from 300 to 640 W on both uncoated and Al-coated Si substrates by sputtering a ZnO target using a 75% Ar/25% O2 gas mixture. The results of this study show that both film microstructure and crystallography are dependent upon the rf power level, with an increase in the amount of structural disorder occurring with increasing power. The magnitude of this effect is dependent upon the substrate. The results are discussed in terms of the average deposition rate, the relative number of Zn to ZnO ions in the plasma, monitored by glow discharge mass spectrometry, and bombardment of the growing film by secondary electrons emitted from the target.
Mode locking a diode laser
Authors: Johnson L. F.
Published: February 2003

A criterion for mode locking a semiconductor diode laser is proposed. The criterion is based on reducing the difference frequency associated with unequally spaced, longitudinal modes to a value smaller than the mode width narrowed by stimulated emission. An integrated GaAs-GaAlAs structure that satisfies this condition is described. In addition to providing a more compact structure than the external mirror geometries previously used to generate mode-locked pulses, the integrated composite resonator avoids the critical alignment problems and subcavity reflection limitations of an external resonator system.
Transient spectra in transverse-mode stabilized GaAlAs double-heterostructure lasers
Authors: Hanamitsu K. , Ishikawa H. , Nishi H. , Takusagawa M.
Published: February 2003

We investigated the dynamic characteristics related to the transient spectra of two types of transverse-mode stabilized GaAlAs double-heterostructure lasers: internally-striped-planar (ISP) and channeled-substrate-planar (CSP) lasers. These lasers exhibited a linear light-current relation, stable transverse-mode oscillation, and dynamic response with suppressed relaxation oscillations. Several differences in their spectral behavior have been observed. The dc spectrum of the CSP laser shows a single longitudinal mode, whereas the dc spectrum of the ISP laser shows multilongitudinal modes. In the ISP laser, the transient spectrum under fast pulse modulation is nearly identical to its dc spectrum. The CSP laser shows a transient spectrum that is broader than that in cw operation. The experimental results may be explained from the differences of their device structure and waveguiding mechanisms.
Inelastic scattering of ultrasound
Authors: Morris J. R.
Published: February 2003

The scattering formalism of Gubernatis, Domany, and Krumhansl is extended to accommodate a description of inelastic scattering of elastic vibration waves. A viscoelastic scattering target is embedded in an elastic host medium. Owing to the absorptive nature of the target, besides the longitudinal and transverse scattering channels, there is also an absorption channel. By postulating the general form of viscoelastic constitutive relations, a simple prescription is arrived at for the modification of the elastic scattering formalism.
Evidence for mixed clusters formed during sulfur hexafluoride expansions in an argon carrier gas
Authors: Kim Sang Soo , Stein Gilbert D.
Published: February 2003

Nucleation of sulfur hexafluoride in an argon carrier gas has been studied in very small supersonic adiabatic nozzle expansions. Light scattering is used to detect the onset of condensation, and high-energy electron diffraction is used to ascertain cluster structure for a range of operating conditions where mixed clusters and/or binary nucleation can occur. For the limited range in SF6 mole fraction, χ0=0.01 to 0.03, both the thermodynamic and cluster diffraction data indicate that the SF6 nucleates homogeneously with Ar accruing onto the condensed SF6 after the Ar supersaturates.
Compound formation between amorphous silicon and chromium
Authors: Yacobi B.G. , Szadkowski A.J. , Zukotynski S. , Corbett J.M.
Published: February 2003

The reaction between evaporated amorphous silicon films and chromium layers was studied using transmission electron microscopy and both transmission electron diffraction and reflection electron diffraction. When a-Si and Cr films were deposited in the same pumpdown, the formation of CrSi2 was observed at temperatures as low as 400 °C. No reaction was observed when a-Si was deposited on electrodeposited Cr.
Removal of the high-resistivity layer at the n on n+ liquid phase epitaxial GaAs layer-substrate interface by controlled i
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i
t
u etch-back
Authors: Seabaugh Alan C. , Mattauch Robert J.
Published: February 2003

A high-resistivity layer often forms at the gallium arsenide layer-substrate interface following preepitaxial growth heat treatment and subsequent layer growth. An in situ etch-back technique was developed for use on the substrate which resulted in the removal of the high-resistivity interfacial layer. This simple technique yielded reproducible etch-back versus time control and thus controllable removal of the high-resistivity layer.
Validity of the resistively shunted Josephson junction model for small-area superconductor-normal-superconductor junctions in a magnetic field
Authors: Barnes S. E.
Published: February 2003

A theoretical study of small superconductor-normal-superconductor Josephson junctions shows that while low-critical-current junctions do obey the resistively shunted junction model (RSJM), large-current-density junctions do not and are thereby much less sensitive to strong magnetic fields than the RSJM equivalent.
High-performance amorphous-silicon field-effect transistors
Authors: Matsumura Masakiyo , Nara Yasuo
Published: February 2003

p-channel and n-channel amorphous-silicon field-effect transistors with thermally grown SiO2 as a gate insulator have been investigated. On-off current ratios of 4×106 and 105 were obtained for n- and p-channel modes, respectively, and the electron and hole mobilities were about 0.1 and 2×10−3 cm2/V/s, respectively.
Estimation of uncertainty in isotherms deduced from Hugoniots resulting from shockwave generated defects
Authors: Ruoff Arthur L.
Published: February 2003

The problem of how defect concentrations produced in a shock experiment affect the isothermal equation of state is considered. From the few experimental results available that bear directly on this question, it appears the effect could be substantial, i.e., the pressure in material free of defects may be 10–25% lower at a given volume than the isothermal pressure deduced from Hugoniot data on the assumption that defects are negligible in the shocked material. This correction caused by the presence of defects is called the defect pressure.
Admittance spectroscopy of deep levels in Hg1−xCdxTe
Authors: Polla D. L. , Jones C. E.
Published: February 2003

We report the application of diode admittance spectroscopy in characterizing traps in Hg1−xCdxTe. Measurements performed on n+-p junction photodiodes have identified a hole trap located 0.16 eV above the valence band in x=0.305 liquid-phase-epitaxy-grown material and a single hole trap located 0.046 eV above the valence band in x=0.219 bulk-grown material. Measurements of trap density and majority-carrier capture cross section have also been carried out, with results suggesting hole capture at a neutral trapping center. Trap energies determined by the admittance spectroscopy technique were found to be in good agreement with lifetime-versus-temperature data analyzed in terms of a single Shockley-Read recombination center.
The plasma resonance in the response and in the rf impedance of a capacitively shunted Josephson junction in the presence of thermal noise
Authors: Poorter T. , Tolner H.
Published: February 2003

The rf impedance and the wide-band response to radiation of a resistively shunted junction (RSJ) model Josephson junction have been measured in the presence of thermal noise, using a phase-locked-loop analog of the RSJ model. In the conditions for which analytical calculations are valid there is good agreement between the theory and the analog. When the RSJ model is shunted with a capacitance, a plasma type resonance can occur in the rf impedance when the junction is biased in the supercurrent (in-lock). When thermal noise is present, this plasma resonance can also occur when a nonzero average voltage is generated across the junction. We found that in this case a resonance also occurs in the wide-band response to radiation. This resonance takes place at a frequency that can be identified as the attempt frequency, with which the junction attempts to escape the phase locked condition in which it exists for a fraction of the time even though the average voltage across the junction is nonzero. The average lifetimes of the junction in lock τin (?=0) and out of lock τout (?=?out) were also measured in the presence of thermal noise. τin is in good agreement with existing theory and τout is derived from the measurements.
Magnetic and thermal anomalies of Invar alloys
Authors: Matsui M. , Adachi K. , Chikazumi S.
Published: February 2003

The anomalous volume contraction ωa(T) of Fe-Ni and Fe-Pt Invar alloys were analyzed in terms of the Grüneisen equation using the experimental data of thermal expansion coefficient. It was found that ωa(T) increases with increasing Fe composition or temperature and remains nonzero even above the Curie point ϑ f for both the Invar alloys. The susceptibility of Fe-Ni alloys and the magnetization of Fe-Pd alloys were measured. The magnetic anomalies of Invar alloys are summarized. A calculation by molecular field theory in terms of a high and low spin state transition model can well explain the anomalous isothermal magnetization curve and the anomalous volume contraction as well as instability of ferromagnetism, where the center of the low spin state has higher energy than the high spin state at high temperatures and the distribution of low spin state energy and the exchange field of the high spin state were considered. From the x-ray diffraction experiments at low temperatures, an anomalous random static displacement (?2s)1/2 was obtained after subtracting the mean-square displacement of the lattice vibration of Fe-Ni Invar. Such a displacement may come from the mixed state of high and low spins.
Large aperture stark modulated retroreflector at 10.8 μm
Authors: Klein M. B. , Sipman R. H.
Published: February 2003

We describe the analysis, design, and construction of a large aperture, wide-field-of-view modulator at 10.8 μm using the Stark effect in ammonia (NH3). The modulator configuration incorporates a longitudinal electric field produced between closely spaced, large-diameter germanium windows. The windows are antireflection coated for high transmission, and their relatively low resistivity allows their direct use as (transparent) Stark electrodes. Enhanced modulation depth and improved electrical breakdown performance are obtained by using multiple interaction regions. The modulator is mounted at the entrance aperture of a corner cube reflector, thus allowing two passes of the signal beam in a configuration which is retroreflecting and polarization insensitive. This completed device has an aperture of 5.5 cm, a field of view of 38°, and a measured modulation depth of 25% at 1.4 MHz.
On the theory of the prism waveguide coupler in the strong coupling regime
Authors: Sarid Dror , Kermisch Dorian , Revelli Joseph
Published: February 2003

It is shown that under practical assumptions both ray and wave theories of the prism waveguide coupler can be applied to the whole range of the coupling strength parameter 0⩽h⩽1, and yield identical results. A numerical example is given, which shows the range of validity of the weak coupling approximation.
Jet formation experiments and computations with a Lagrange code
Authors: van Thiel M. , Levatin JoAnne
Published: February 2003

A jet formation routine has been generated that can be used with (Lagrange) explosive cone-collapse calculations. It calculates the velocities of jet and slug elements, as well as their mass, formation point, and time. The equations and method of operation are presented here. Experimental jet velocities agree with the model to 10%. Jet deformation calculations required yield strengths up to 24 kbar to yield agreement with experiments on copper jets.
Release wave calibration of manganin gauges
Authors: Yaziv D. , Rosenberg Z. , Partom Y.
Published: February 2003

A calibration curve for the response of commercial Manganin gauges upon unloading in plane dynamic experiments is presented. The data obtained from 18 plane impact experiments cover shock stresses in the 1.5–15 GPa range and involves various materials. The calibration curve was drawn through normalized data points. The normalization is based on the assumption that the ratio between resistances of the gauge at the shock and unloading states depends on the ratio of the respective stresses.
Use of a radioactive tracer to determine the fraction of fusion target debris collected
Authors: Campbell E. M. , Hicks H. G. , Mead W. C. , Coleman L. M. , Hatcher C. W. , Dellis J. H. , Boyle M. J. , Larsen J. T. , Lane S. M.
Published: February 2003

In order to obtain the pusher attenuation length (ρΔR) of inertial confinement fusion targets by neutron activation, it is necessary to know what fraction of the target debris is counted. One method of measuring this quantity experimentally is by means of a radioactive tracer. We demonstrate the usefulness of this technique by experiments utilizing a 24Na tracer.
Collective acceleration of electrons using an autoacceleration process
Authors: Lockner Thomas R. , Friedman Moshe
Published: February 2003

A means of collectively accelerating an intense electron beam is demonstrated. A long pulse (800 ns) electron beam is propagated through cavity structures which redistributed the energy in the beam such that most of the beam energy is transferred to a short segment (6 ns) in the tail of the beam. Electrons are accelerated in a two cavity system from 200 keV to energies of 2.4–3.0 MeV at a beam current of ∼8 kA. The extension of this principle to larger number of cavities appears feasible.
The photoacoustic effect at first-order phase transition
Authors: Korpiun P. , Tilgner R.
Published: February 2003

Thermal properties are essentially involved in the acoustic response of a liquid or solid sample to the absorption of chopped light. Recently, the first experimental observation of the photoacoustic effect at first-order phase transitions has been published. In the present work we calculate the temperature variation in the gas at the surface of a sample and determine its amplitude and phase angle. Therefore we solve the differential equation of conduction of heat for a medium exhibiting a temperature gradient superposed by a temperature oscillation due to absorption of light with sinusoidal varying intensity. In the medium there exist two regions of different thermodynamic phases separated by an interface at transition temperature. The latent heat for phase transition is taken into account via a boundary condition for the heat flow at the interface. We have assumed the optical-absorption coefficient to be much larger than the thermal-diffusion coefficient realized in strongly absorbing materials. The application of our calculation to measured data is discussed with respect to the technique used to detect the acoustic signal. With the model, we present here, the experimental results can be described fairly well.
Hard-x-ray spectrum from a single-electron-temperature laser plasma model
Authors: Colombant D.G. , Manheimer W.M.
Published: February 2003

Comparisons between hard-x-ray experimental spectra and those obtained from a planar one-dimensional one-temperature fluid laser-produced plasma model show good agreement over several orders of magnitude in x-ray intensity and for Nd-laser irradiances varying between 2×1014 and 8×1015 W/cm2. The key to this agreement is the careful modeling of electron-energy flux limitation by return-current-driven ion-acoustic turbulence. The hard-x-ray temperature agrees with a (Iλ2)1/3 scaling law.
Multichannel discharges in low-pressure rare-gas–mercury mixtures caused by anode oscillation
Authors: Watanabe Yoshio , Yamane Mikiya
Published: February 2003

Stable formation of a multichannel arc is observed in low-pressure rare-gas–mercury discharges in a concentric tube where a hot cathode is located in the inner tube and two to six anodes are arranged symmetrically in the space between the inner tube and the outer bulb. The discharge current for each discharge channel is found to be deeply modulated at high frequencies by the anode oscillations which take place in a regular, complex sequence depending on the anode configuration. In a discharge tube with two anodes, anode oscillation occurs alternately, causing discharge transfers between the anodes. With three anodes, the discharge transfers take place in a manner similar to a ring counter, as anode oscillations occur in turn in geometrical order. In the four and five anode configurations, oscillations occur sequentially in time, but not sequentially in the anode configuration. In the case of six anodes, stable formation of a multichannel arc is not observed.
Spherical shock development near laser-heated microshell targets
Authors: Leonard Thomas A. , Hammerling Peter
Published: February 2003

Spherical expansion of the luminous front around a laser-heated microshell target in 20 Torr of helium is compared with theory in the mass-dependent region. Microshell targets from 74- to 7970-ng initial mass irradiated with up to 0.13 TW (Terawatt) of 1.06-μm light were studied. Effects of the initial mass and changing γ on the front history are discussed. It is concluded that extraction of expansion energy from the front motion is not easily accomplished in this close-in region.
Cutoff frequencies of intermediate frequency waves in a bounded magnetoplasma
Authors: Basu J. , Das S. K.
Published: February 2003

The paper presents a study of the cutoff frequencies of a class of electromagnetic waves, designated here as intermediate frequency waves, which can propagate in a plasma column enclosed in a conducting cylinder and embedded in a static axial magnetic field. These waves reduce to lower hybrid waves or magnetohydrodynamic TE waves under suitable conditions. The cutoff frequencies of the intermediate frequency modes have been investigated, covering all possible values of ωpe,ωce, and a, where ωpe is the plasma frequency, ωce is the electron cyclotron frequency, and a is the plasma radius. The study includes all the possible types of modes, namely, circularly symmetric I0m modes and asymmetric Inm modes with n ? 1, each Inm mode being split into two, called I+nm and I−nm modes, corresponding to two different polarizations of the field components. The cutoff frequency ωc 0 of any Inm mode with n ? 0 is found to be confined to the frequency domain 0 to ωnm, where ωnm is the cutoff frequency of the TEnm mode in an empty waveguide. The zero frequency is approached if ωpe or a tends to infinity or ωce tends to zero, the other parameters remaining constant in each case. The frequency ωc 0 tends to ωnm if ωce is sufficiently large for any given set of ωpe and a. The study of intermediate frequency modes reveals that these modes can broadly be divided into the following two categories: (1) I−n1 modes with n ? 1, and (2) modes other than I−n1 modes. The nature of variation of ωco ith ωpe for fixed values of ωce and a for I−n1 modes is, in general, quite different from that for the other modes. Furthermore, ωc 0 tends to ωci as a tends to zero with ωpe and ωce held fixed in the case of I−n1 modes, while for other modes ωc 0 tends to ωlh under the same condition, where ωci is the ion cyclotron frequency and ωlh is the lower hybrid frequency. Any Inm mode with n ? 0 is found to reduce to the magnetohydrodynamic TEnm mode at or near the cutoff under the condition: ωpi≫ωnm, where ωpi is the ion plasma frequency. Finally, it is shown how the charge density in a bounded magnetoplasma can easily be determined in most experimental situations by using the cutoff frequency characteristic of the dominant I−11 mode.
Study of buried silicon nitride layers synthesized by ion implantation
Authors: Bourguet P. , Dupart J. M. , Le Tiran E. , Auvray P. , Guivarc’h A. , Salvi M. , Pelous G. , Henoc P.
Published: February 2003

The formation of buried layers of silicon nitride by nitrogen-ion implantation in single-crystal silicon is studied. He+ backscattering, x-ray diffraction, scanning and transmission electron microscopies, and infrared absorption measurements were used for the physico-chemical characterization; sheet resistivity determination, spreading-resistance profile, and current-voltage characteristics for the electrical characterization. It is shown that, for 180-keV nitrogen ions, a fluence about 1018 N/cm2 must be implanted in order to obtain a continuous layer of silicon nitride and that annealing must be performed at 1200 °C to make it homogeneous and electrically insulating. The Si3N4 layer obtained crystallizes in the α phase and presents properties nearly similar to those of deposited layers. It is demonstrated that the conditions of implantation (energy, substrate temperature, beam intensity) play a fundamental role in the structure of the superficial silicon layer: the substrate must not be amorphized up to the surface during the implantation to obtain, after annealing, a monocrystalline surface layer suitable, for instance, for further epitaxy.
An application of the Boltzmann transport equation to ion range and damage distributions in multilayered targets
Authors: Christel L. A. , Gibbons J. F. , Mylroie S.
Published: February 2003

A method for the direct calculation of primary ion and recoil range distributions, as well as energy deposition profiles in multilayered targets, is presented. The technique is based on stepwise numerical integration of the Boltzmann transport equation. Range distributions for arsenic, phosphorus, and boron and damage density distributions resulting from antimony and boron implants in silicon are found to compare favorably with other calculations and experimental results. Oxygen recoil fluxes from SiO2 into Si also agree well with experiment. Silicon and nitrogen recoil range distributions resulting from a 400-keV selenium implantation through 1000 Å of Si3N4 on GaAs are calculated and are shown to have a significant effect on doping profiles determined from electrical measurements.
The ’’inhibition effect’’ of a trichloroethane oxidation to suppress the stacking-fault nucleation in silicon
Authors: Claeys C. L. , Declerck G. J. , Van Overstraeten R. J.
Published: February 2003

A high-temperature treatment in a chlorine containing oxidizing ambient can be used to achieve a shrinkage or a complete annihilation of the oxidation-induced stacking faults (OSF’s). This paper discusses in more detail the efficiency of a trichloroethane (C33) oxidation to inhibit the OSF nucleation during a prolonged oxidation or a reoxidation in dry and wet oxygen, respectively. Preferential-etching studies demonstrate that one has to be very careful in interpreting the results available in the literature. Dependent on the parameters (temperature, time, and gas atmosphere) of both the first and the second oxidation, the OSF’s are annihilated either throughout the entire volume of the wafer or only in a near-surface region. The influence of different oxidation cycles on the leakage current of p+n diodes is analyzed.
Charging effects in the secondary ion mass spectrometric analysis of targets containing low-conductivity regions
Authors: Reuter W. , Yu M. L. , Frisch M. A. , Small M. B.
Published: February 2003

Common ion sputtering techniques for depth profiles can cause buildup of charge in low-conductivity regions such as p-n junctions in semiconductors, leading to erroneous results. We analyzed Ga0.1Al0.9As liquid phase epitaxial (LPE) layers on GaAs with secondary ion mass spectrometry (SIMS) and observed that the profiles of 69Ga+ and 27Al+ in the low-conductivity region of these Zn-diffused LPE layers were a function of the sample bias. We noticed that this artifact was due to the shift and broadening of the secondary ion energy distributions caused by positive charging of the specimen surface. We also found that this could be effectively remedied by integrating the secondary ion yields over a wide energy range. The use of an electron flood gun reduced this charging effect, but complete charge compensation was not achieved even at electron current densities far exceeding the ion current density. This can be explained by the fact that the electron-induced secondary electron coefficient of GaAlAs is larger than unity.
Fluorescence of guest molecules in a scattering state of a liquid crystal
Authors: Hochbaum A. , Yu L. J. , Labes M. M.
Published: February 2003

Fluorescence emission of guest molecules in cholesteric liquid crystal hosts was modulated by an electric-field-induced cholesteric-nematic transition. The contrast ratio between the two states can be greater than 15, and is affected primarily by the scattering properties of the phase and the order parameter of the guest. Data are presented on the dependence of the contrast ratio on the cell parameters and the structure of both guest and host. A simple model is presented accounting for the observed behavior.
Plane electromagnetic waves in moving media and reflections from moving interfaces
Authors: Kunz Kaiser S.
Published: February 2003

A general discussion is given of the properties of electromagnetic plane waves in moving isotropic and anisotropic media. This includes working out the general constitutive relations and the dispersion relation for the isotropic case. Treatment of the moving interface involves determining not only the Doppler shifts but also generalization to a moving interface of the law of reflection, Snell’s law, formula for the critical angle, Brewster’s angle, and the reflection and transmission coefficients. The latter involve generalization of the Slater impedances associated with the incident, reflected, and transmitted waves. The maximum angle of incidence in the frame moving with the interface is shown to be that which represents a flow of energy parallel to the interface.
Laser action of pulse-pumped Nd3+ : Gd3Ga5O12 at 1.054 μm
Authors: Honda T. , Kuwano T. , Masumoto T. , Shiroki K.
Published: February 2003

Laser action at 1.054 μm was obtained in a neodymium-doped Gd3Ga5O12 crystal pumped by a Xe flashlamp. The output power of laser oscillation at 1.054 μm have been measured comparable to that of Nd3+ : YAG laser at 1.052 μm.
Nonlinear interactions in degenerate surface acoustic wave elastic convolvers
Authors: Ganguly A. K. , Davis K. L.
Published: February 2003

The degenerate surface acoustic wave elastic convolver is analyzed by solving the nonlinear piezoelectric equations of motion subject to appropriate boundary conditions. The nonlinear equations are treated by a perturbation theory by assuming that the nonlinear stress and nonlinear electric displacement are small compared to the respective linear quantities. We obtain expressions for the open-circuit voltage (V0) and short-circuit current (I0) in terms of power (P(i)) in the incident waves and linear and nonlinear constants of the material. We also calculate the figure of merit M=Vrms0(P(1)P(2)/W2)−1/2 (W is the width of the incident acoustic beam) and the internal impedance Z0=V0/I0. We obtain numerical values of M and V0 from an estimate of the nonlinear constants available in the existing literature and compare them with experiments.
Comparison of ultrasonic velocity changes caused by dissolution of hydrogen, deuterium, and tritium in bcc vanadium and niobium
Authors: Fisher E. S. , Remark J. F.
Published: February 2003

The effects of dilute additions of deuterium (D) and tritium (T) on the elastic moduli of single crystals of Nb and V were measured at room temperature. The coefficients ΔC44/C44 and ΔC′/C′, per at.% isotope, are evaluated and compared with published data for H additions and previous measurements of D additions. The agreement among data from different laboratories is well within experimental error. The ΔC′ effects in Nb are isotope dependent and closely related to the square root of the inverse mass. In the case of V, the ΔC′ effect is the same for T and H but smaller for D, suggesting a possible change from tetrahedral to octahedral site occupancy with increasing isotope mass.
Heat transfer model for cw laser material processing
Authors: Mazumder J. , Steen W. M.
Published: February 2003

(Received 19 September 1979; accepted for publication 12 October 1979)

A three-dimensional heat transfer model for laser material processing with a moving Gaussian heat source is developed using finite difference numerical techniques. In order to develop the model, the process is physically defined as follows: A laser beam, having a defined power distribution, strikes the surface of an opaque substrate of infinite length but finite width and depth moving with a uniform velocity in the positive x direction (along the length). The incident radiation is partly reflected and partly absorbed according to the value of the reflectivity. The reflectivity is considered to be zero at any surface point where the temperature exceeds the boiling point. This is because a ’’keyhole’’ is considered to have formed which will act as a black body. Some of the absorbed energy is lost by reradiation and convection from both the upper and lower surfaces while the rest is conducted into the substrate. That part of the incident radiant power which falls on a keyhole is considered to pass into the keyhole losing some power by absorption and reflection from the plasma within the keyhole as described by a Beer Lambert absorption coefficient. Matrix points within the keyhole are considered as part of the solid conduction network, but operating at fictitiously high temperatures. The convective heat transfer coefficient is enhanced to allow for a concentric gas jet on the upper surface as used for shielding in welding and surface treatment, but not cutting. The system is considered to be in a quasi-steady-state condition in that the thermal profile is considered steady relative to the position of the laser beam. The advantages of this method of calculation over others are discussed together with comparisons between the model predictions and experiments in laser welding, laser arc augmented welding, laser surface treatment, and laser glazing. The system is assumed to be in a quasi-steady-state condition after the keyhole initiation period which for most practical purposes may be considered instantaneous.
The random walk of a drilling laser beam
Authors: Anthony T. R.
Published: February 2003

Holes were drilled through 330-μ-thick single-crystal sapphire wafers with a pulsed laser beam. The hole exit positions on one face of the wafer were found to have undergone a random-walk displacement relative to the entrance hole positions on the opposing face of the wafer. This random displacement increased with the number of laser pulses required to drill through the wafer. A model in which the bottom of the drill hole experiences small random displacements during each laser pulse was used to describe the experimental observations. The model indicates that the average random displacement caused by each laser pulse is only a few percent of the hole diameter. Laser-drill-hole wandering can be minimized by using as few laser pulses as necessary to drill through the sapphire wafers while at the same time avoiding the cracking and spalling of the wafer that occur with a hole drilled through the wafer with a single pulse.
Retention and re-emission of 0.125– 1-keV deuterium in stainless steel
Authors: Thomas E.W.
Published: February 2003

Retention and re-emission of 125– 1000–eV D+ ions in stainless steel has been measured at 90, 300, and 500 °K. Saturation of retained fluence in a 90 °K target occurs when there is approximately one retained atom for every metal atom within the range of this projectile. Implantation at 300 and 500 °K shows saturation at densities three to five times smaller than the low-temperature implant. Backscattering coefficients are determined to range from 0.5 at 125 eV to 0.3 at 1 keV; these are consistent with computer simulations. Thermally induced re-emission of deuterium retained after bombarding a room temperature target has a diffusive character with an activation energy of 14.7 kcal/mole.
Thermionic emission from single-crystal LaB6 tips with [100], [110], [111], and [210] orientations
Authors: Oshima C. , Aono M. , Tanaka T. , Kawai S. , Shimizu R. , Hagiwara H.
Published: February 2003

Thermionic emission patterns from the single-crystal LaB6 [100], [110], [111], and [210] tips have been observed under the Schottky condition. The observed emission patterns are interpreted on the basis of a model involving an anisotropic work function of LaB6; the regions around the [111] crystal orientation have a high-work function, while those around the [210] crystal orientation have a low work function. This model also explains qualitatively the order of the total emission currents from those tips. The observed patterns predominantly consist of the emission from the conical face rather than the top of the tips under this experimental condition. Changes in the emission pattern and cathode surface in operation at 10−4 Torr are also discussed.
Relation of the ’’solid Hugoniot’’ to the ’’fluid Hugoniot’’ for aluminum and coppera)
Authors: Morris C. E. , Fritz J. N.
Published: February 2003

Strength effects confuse equation-of-state data obtained by shock waves. In order to take these effects properly into account in the high-pressure regime, reduction from uniaxial-strain experimental shock loci to a mean-stress curve and from the mean-stress curve to the ’’fluid Hugoniot’’ curve are derived. Applications to aluminum and copper are given.
Reply to ’’Comment on ’charge transfer in metal/polymer contacts and the validity of contact charge spectroscopy’ ’’
Authors: Cottrell G. A. , Lowell J. , Rose-Innes A. C.
Published: February 2003

A reply to the points raised in the previous communication confirming our contention that the true final charge transferred to a given area on an insulator after contact to a series of metals depends only on the last metal to contact that area.
On the adequacy of one-dimensional treatments of the photoacoustic effect
Authors: Quimby R. S. , Yen W. M.
Published: February 2003

It is demonstrated both theoretically and experimentally that the one-dimensional theories of the photoacoustic effect in solids are still applicable when the heat flow is three dimensional, provided that the thermal diffusion length in the gas is much less than the radius of the sample chamber.
Calculation of solid-phase reaction rates induced by a scanning cw laser
Authors: Gold R. B. , Gibbons J. F.
Published: February 2003

An analytical model is presented for solid-phase reactions induced by a scanning cw laser. The results are applicable for both rate-limited reactions, such as the regrowth of implanted amorphous Si, and diffusion-limited reactions, such as the formation of metal silicides. The effect of the laser is interpreted in terms of a furnace anneal at an ’’effective temperature,’’ Teff, for an ’’effective time,’’ teff. Teff is shown to be equal to the maximum laser-induced surface temperature, while teff equals the laser dwell time multiplied by a ’’dwell-time reduction factor’’ which is a rational function of several material and annealing parameters and is typically on the order of

(1)/(3) . A comparison of theory and experiment is made for the specific case of the formation of Pd2Si.
A new way to calculate scattering of acoustic and elastic waves. I. Theory illustrated for scalar waves
Authors: Visscher William M.
Published: February 2003

Matrix theories of elastic and acoustic wave scattering are reviewed and unified, and a new one is devised and discussed. Called MOOT (method of optimal truncation), it has tangible and aesthetic advantages over other methods, particularly its convergence properties and its conceptual straightforwardness. The exposition is, for simplicity, in terms of scalar waves; the following paper contains detailed applications to scattering of elastic waves. A family of matrix equations, which includes the present method and others, is derived in a simple way from the boundary conditions. Integral equations and their solution by matrix methods are discussed, MOOT is developed and compared with other matrix methods, symmetry principles are developed and their enforcement discussed, and certain computational methods, details, and limitations are expounded. Briefly, we proceed by expanding the scattered wave in a truncated series of eigenfunctions of the unperturbed wave equation, and determine the expansion coefficients (scattered amplitudes) by requiring that the mean square of the deviance (discontinuity in value or normal derivative in the scalar case) from the boundary conditions at the surface of the scatterer be minimized. This results in matrix equations for the scattered amplitudes which may, in many cases, be easily solved. The method is useful for computing scattering of acoustic, elastic, or electromagnetic waves from defects which are internally piecewise homogeneous, so that conditions on the wave function derivatives and values at the boundaries characterize the scatterers. Although the method is applicable to general shapes, the computations are accelerated if the scatterers are axially symmetric. The matrix equations are superficially similar to others derived and used in the past, which were not based on an optimization principle. Differences are exhibited and their significance is discussed.
A new way to calculate scattering of acoustic and elastic waves. II. Application to elastic waves scattered from voids and fixed rigid obstacles
Authors: Visscher William M.
Published: February 2003

The method expounded in the preceding paper is applied to the calculation of the scattering of elastic waves from axially symmetric voids and rigid obstacles. The eigenfunctions and surface tractions are presented in detail. Results are exhibited for direct and mode-converted cross sections for a variety of scatterer shapes, including oblate and prolate spheroids with aspect ratios up to 7, pillboxes, and cones for ka varying from 0.1 to 10. Accuracy, computer time, and convergence properties are discussed.
Acceptor energy level for Zn in Ga1−xAlxAs
Authors: Masu Kazuya , Konagai Makoto , Takahashi Kiyoshi
Published: February 2003

Electrical properties and the acceptor energy level in Zn-doped p-Ga1−xAlxAs (0<x<0.85) prepared by liquid-phase epitaxy have been investigated. During the LPE growth of Zn-doped p-Ga1−xAlxAs layer, Zn diffuses from Zn-doped Ga-Al-As melt into the undoped n-GaAs substrate to form the p-GaAs region. The modified van der Pauw method proposed by Petritz was used to measure the electrical properties of p- (GaAl)As and p-GaAs. The resistivity and the hole concentration of Zn-doped p-Ga1−xAlxAs were found to be strongly affected by the acceptor energy level for Zn. The acceptor energy level in Zn-doped p-Ga1−xAlxAs was found to increase from 15 meV for x=0 to 90 meV for x=0.85. The increase of the acceptor energy level with increasing x has been theoretically explained by the modified hydrogenic model proposed by Baldereschi and Lipari.
Flux pinning by crystalline precipitates in an amorphous superconducting matrix
Authors: Clemens B. M. , Johnson W. L. , Bennett J.
Published: February 2003

The introduction of a small volume fraction of σ-phase MoRu particles into an otherwise amorphous superconducting matrix of composition (Mo0.6Ru0.4)80Si10B10 is observed to result in substantial flux-pinning interactions and an increase of the sample Tc. The critical current density in the presence of an externally applied field is increased by two to three orders of magnitude as compared to that of the amorphous matrix alone. The proximity effect explains the observed increase of Tc which results from the σ-phase precipitate particles having a Tc higher than that of the amorphous matrix.
Correlation of mechanical and electrical losses in ferroelectric ceramics
Authors: Gerthsen P. , Härdtl K. H. , Schmidt N. A.
Published: February 2003

The correlation between electrical and mechanical losses in ferroelectric ceramics has been investigated theoretically and experimentally. The theoretical derivation is based on the assumption that both loss types are induced by 90° domain walls moving under the influence of electrical or mechanical fields. A proportionality between both loss types is found. The factor of proportionality includes material constants such as spontaneous polarization and striction, permittivity, and elastic compliance, but is independent of the specific energy dissipation mechanism of a moving domain wall. In a compositional series of differently doped PLZT ceramics with a broad range of losses the theoretically derived relations have been checked experimentally. Good agreement between the experimental and theoretical results was found.
Subsurface flaw detection in metals by photoacoustic microscopya
Authors: Thomas R. L. , Pouch J. J. , Wong Y. H. , Favro L. D. , Kuo P. K. , Rosencwaig Allan
Published: February 2003

The scanning photoacoustic microscope (SPAM) is used in both the conventional and phase-contrast modes to detect a well-characterized subsurface flaw in Al. The physical mechanism is that of thermal diffusion, with a subsurface probe depth and flaw resolution length of approximately one thermal-diffusion length. Comparison of the dependences of the photoacoustic signal upon chopping frequency from the different regions of the sample confirm that the differential signal from the flaw corresponds to a transition from thermally thick to thermally thin boundary conditions. Experimental results are in good agreement with calculations based upon a three-dimensional thermal-diffusion model.
Microstructure of TiC precipitates in Ti-implanted α-Fe
Authors: Follstaedt D. M.
Published: February 2003

We demonstrate that Ti implanted into α-Fe (with ∼60 appm C impurity) getters C (along with a lesser amount of N) upon postimplantation annealing and precipitates as TiC. The microstructure of the TiC precipitates is examined with TEM for annealing temperatures up to 860 °C. The precipitate size evolution is discussed in terms of growth, ripening, and dissolution processes. The precipitate size increases with anneal temperature for 1 h anneals. At 700 °C no change in precipitate size is observed for anneal times up to 16 h. At 800 °C, an increase in size is observed for increasing anneal times between 1–64 h, while at 860 °C this increase is thought to occur prior to 1 h and the precipitates are observed to decrease with increasing anneal times between 1 and 4 h. At 800–860 °C, the precipitates have a disk-like shape, and their orientation in the α-Fe matrix can be used to identify two types of interfacial area with different degrees of coherency. The implications of the observed microstructure for studies of trapping of embrittling impurities in α-Fe and for modifying the surface mechanical properties are discussed.
Snoek peak figures of impure iron in various strain amplitude ranges
Authors: Otabe Soji
Published: February 2003

The Snoek peak figures and peak heights on impure iron were investigated in various ranges of strain amplitude. The Snoek peak heights Δ−Δb decreases as strain amplitude increases, and the amount of decrease is related to the amount of plastic strain damping. There is failure of superposition at high amplitude and at Snoek peak site, probably due to microstrain.