bluuebunny/crossref_metadata_2025 huggingface dataset:
Shock profiles caused by different end conditions in one-dimensional quiescent lattices
Authors: Strenzwilk Denis F.
Published: February 2003

Shock propagation in a one-dimensional discrete lattice is generated by accelerating the end-most particle from zero to its final velocity in a finite rise time after which the end particle is maintained at that velocity. The wave profiles for various rise times are compared to the zero-time case in a quiescent lattice. For the anharmonic lattice the classical equations of motion of the atoms are solved numerically on the computer. A Morse-type potential is assumed. For a finite rise time the amplitude of the wave passing through the surface atoms is diminished when compared with he zero-time case. For the anharmonic lattice the head of the wave develops into a solitary wave train with an oscillatory tail, and for certain rise times and anharmonicity parameters an apparent envelope soliton forms behind the shock front. This envelope soliton travels much slower than the shock wave.
Planar and cylindrical jet streaming of water and of molten Fe40Ni40B20 alloy
Authors: Liebermann H. H.
Published: February 2003

The nature of liquid streaming instabilities is an important consideration in many processes. In chill-block melt spinning of glassy metallic alloys, for example, molten alloy is expelled from a pressurized crucible in order to form a jet which is impinged and chilled against a rapidly moving substrate surface, thereby continuously casting ribbon or tape. The geometry of wide glassy alloy ribbons made by using a melt ejection crucible with a slit-shaped orifice is partially controlled by the tendency for the planar melt jet to undergo capillary inversion. The current investigation describes experiments in which the inversion lengths of planar water and molten Fe40Ni40B20 alloy streams were studied. The results show agreement with values obtained by using a theoretical model based on an inviscid isothermal liquid. Also, measurement of cylindrical jet break-up length has been conducted for both water and for molten Fe40Ni40B20 alloy. Results in both instances show agreement with a theoretically derived expression applying to an inviscid isothermal liquid if an experimentally measured stream perturbation factor is determined for each liquid. Therefore, it is shown that modeling of both planar and cylindrical molten alloy jet behavior is possible by either theoretical calculation based on an inviscid isothermal liquid or by water streaming experiments if differences in liquid density, surface tension, and stream perturbation factor are considered.
Correlation of the glass transition and the pressure dependence of viscosity in liquids
Authors: Munro R. G. , Block S. , Piermarini G. J.
Published: February 2003

The determination of the glass-transition pressure by the ruby R1 line-broadening method is quantitatively confirmed to within 10% by an independent method. The procedure utilizes a model which describes the pressure dependence of the viscosity and contains the glass-transition pressure as a parameter. The two methods are compared for three liquids, n-butyl chloride, 4 : 1 methanol-ethanol, and isopropyl alcohol. Data from earlier works are used for 4 : 1 methanol-ethanol and isopropyl alcohol. The viscosity of n-butyl chloride at room temperature is measured as a function of pressure to 36 kbars in a diamond-anvil falling-sphere viscometer, and the glass-transition pressure is determined by a separate measurement using the ruby R1 line-broadening method.
A general characteristic equation for a diffusion-controlled gas discharge column of arbitrary shape with electron production and loss rates linear and quadratic in electron density
Authors: Rogoff Gerald L.
Published: February 2003

A simple yet general expression characterizes the electrical properties of a steady-state positive column of arbitrary cross-sectional shape with electron production and loss rates linear or quadratic in electron density in addition to electron loss by diffusion. This equation relates effective ionization and diffusion coefficients (or applied electric field), the total number of electrons per unit column length (or electron current), the area of the column cross section, and the cross-sectional shape, which is represented by a single dimensionless number. The derivation and some implications of this equation are described. For the limiting case of a linear production rate only (e.g., one-step electron-impact ionization), the effective ionization coefficient depends on the cross-sectional area but is independent of the number of electrons per unit length. However, in the limit of a quadratic production rate only (e.g., two-step electron-impact ionization), the dependence is reversed; the effective coefficient varies with the number of electrons per unit length but is independent of the size of the cross section.
Experimental study of CO2-laser-induced air breakdown over long distances
Authors: Caressa J-P. , Autric M. , Dufresne D. , Bournot Ph.
Published: February 2003

Results of an experimental study on air breakdown produced by radiation from a high-power CO2 laser are presented. From these measurements, the breakdown threshold over a flux range (1.5×108 <φ<7×108 W cm−2) is obtained as a function of the focal length varying from 1 to 55 m. The first of these experiments was carried out in the laboratory atmosphere (10<f/D<100), whereas the second part (f/D=135) was done outdoors under typical atmosphere conditions. The temporal evolution of the energy transmitted through the breakdown region for different laser parameters (5<Ei<220 J) was found.
Observation of small defects in silicon crystal by diffuse x-ray scattering
Authors: Yasuami Shigeru , Harada Jimpei , Wakamatsu Katsuei
Published: February 2003

Two kinds of diffuse x-ray scattering due to defects were observed from a very perfect silicon single crystal. One forms the shape of a cigar, elongated along the [111] direction, and the other is a disk, which is broad and perpendicular to the [111] direction. The cigar-shaped diffuse scattering is asymmetric around the 111 relp with respect to the Bragg peak. Fourier transforms reveal two types of defects; platelike defects [200 Å (φ) ×30 Å (t)] of vacancy type and needlelike defects (400 A (l)). The platelike defect dimensions are in fairly good agreement with those of B-swirl defects observed by de Kock et al. The platelike defects also have a close correlation with the crystal pulling direction. They are contained predominantly in the (111) planes for a crystal grown along the [111] direction.
The identification of key variables in the solid phase epitaxial growth of silicon
Authors: Ottaviani G. , Majni G.
Published: February 2003

Silicon solid-phase epitaxy utilizing Al as the transport medium was carried out using either 〈111〉 or 〈100〉 Si single-crystal substrates. By analyzing samples made by a different method we show that the presence of a barrier on the metal plays a fundamental role. The barrier inhibits the diffusion of the metal through the evaporated semiconductor. In the case of Al, the barrier is made by deposition of a thin oxide layer grown on top of the metal, by leaving the sample in vacuum for two days, or by heating the sample in vacuum before the Si deposition.
Hardening mechanisms of hard gold
Authors: Lo C. C. , Augis J. A. , Pinnel M. R.
Published: February 2003

Electrodeposited hard gold with 0.6 at.% cobalt has a hardness about four times that of annealed bulk gold and this high hardness cannot be reproduced by standard metallurgical methods. By measuring the hardness for gold and gold alloys subjected to various quenching, annealing, and deformation processes, all common hardening mechanisms such as solution hardening, precipitation hardening, strain hardening, and ’’voids’’ hardening were eliminated as possible major hardening contributors with the exception of the grain size effect. Pure gold with grain sizes ranging from 200 Å to 3 μm were prepared using sputtering deposition by varying the substrate temperature during deposition from 55 to 310 °C. Larger grain sizes from 5 to 200 μm were prepared by annealing cold-drawn gold wire at 300–750 °C. The hardness versus grain diameter followed the Hall-Petch relation up to a grain size of 0.1 μm. Beyond that, the hardness increased less rapidly. At the grain size of electrodeposited hard gold of 250–300 Å, the sputtered pure gold gave the same hardness value also. Therefore, the grain size effect accounts for the observed high hardness of electrodeposited hard gold, with other mechanisms accounting for only small alterations.
Freedericksz transition and anchoring effects of a nematic liquid crystal for general configurations
Authors: Motooka T. , Fukuhara A.
Published: February 2003

General formulas are derived for the Freedericksz transition of a nematic liquid crystal between parallel plates under a magnetic field. It is shown that the clear-cut Freedericksz transition exists when the magnetic field is perpendicular to the initial director direction. The critical field strength for arbitrary stiffness of anchoring is also given in an analytical form.
Characteristics of rib waveguides in AlGaAs
Authors: Shelton J. C. , Reinhart F. K. , Logan R. A.
Published: February 2003

We have studied the properties of isolated and coupled optical rib waveguides (RWG) as a function of rib height and width in GaAs layers on AlGaAs for TE-like and TM-like polarizations. We compare mode shape parameters for isolated RWG to the coupling constant, K, obtained from distributed couplers. The effective index model accurately describes the mode distributions and the coupling constant for single-mode RWG. The model also gives an accurate estimate for anodic oxide loaded strip waveguides. In this model, the relative lateral difference in the effective dielectric constant, Δx, is determined by the depth characteristics (the rib height, layer thicknesses, and compositions) and the free-space wavelength. The lateral confinement of guided modes and K are then determined by Δx, the effective dielectric constant, the waveguide width, the waveguide spacing, and the free-space wavelength. At λ?1.06 μm, ribs of height h?0.05 μm on GaAs waveguiding layers of thickness t?0.75 μm with underlying Al0.1Ga0.9As cladding provide Δx?1.7×10−3 for TE polarization and ?2×10−3 for TM polarization. In such layers K?1/mm for pairs of RWG with 3 μm width and 3 μm spacing. Model Δx results are given for typical layer compositions and typical layer and rib dimensions. Eigensolution results for K are given as a function of Δx for typical rib width and spacing dimensions. For more general application to RWG, to anodic loaded strip guides, and to metal gap guides, scaled K and linearized Δx results are given in dimensionless form. We also report experiments on lateral tapers to widen or narrow the waveguides for control of mode shapes, and on lateral ramps to control the location of the RWG. Tapers introduce negligible loss, but cause some mode conversion if multimoded guides are involved. Ramps introduce negligible loss if they are at sufficiently low angles.
A large-aperture electro-optic diffraction modulator
Authors: Bocker R. P. , Meana G. M. , Monahan M. A. , Mooradian G. C. , Richards W. E. , Taylor H. F.
Published: February 2003

Efficient modulation of a large-diameter light beam based on diffraction by an electro-optic phase grating has been demonstrated. The modulator consists of a y-cut lithium niobate crystal with interdigital electrodes on one surface. With a polarized HeNe laser beam incident normal to the surface, an extinction ratio of 100 : 1 was obtained for the zeroth-order transmitted beam at an applied voltage of 1650 V for single-pass transmission. This device has been used to modulate a retroreflected beam in an optical communications experiment, with good performance for aperture areas greater than 15 cm2 and incidence angles up to 30°.
Power flow and energy distribution of magnetostatic bulk waves—In dielectric-layered structure
Authors: Gupta S. S. , Srivastava N. C.
Published: February 2003

This paper presents a theoretical investigation of guided propagation of the magnetostatic bulk waves in a normally magnetized ferrite film separated from a perfect conductor by a dielectric layer. Starting from the generalized Poynting theorem for dispersive media, the expressions for time-averaged power flow and energy density have been obtained in the magnetostatic approximation. The velocity of time-averaged energy flow has been shown to be equal to the group velocity, which establishes the consistency of magnetostatic approximation from the energy point of view.
Explosive puncturing of metal plates by lasers
Authors: Steverding B. , Conrad R. W. , Dudel H. P.
Published: February 2003

Substantial energy savings in puncturing metal plates by laser radiation can be achieved by heating the metal by cw radiation to a temperature closely below the melting point and then applying a sharp radiation pulse to push the hot metal plug through the plate. An analysis of this process is presented, in which the non-Newtonian viscosity behavior of metals is considered. Scale-up effects and efficiency calculations are presented for laser-supported detonation waves and point explosions. Flow characteristics as well as penetration criteria are given for aluminum, copper, and steel which are in good agreement with experimental data.
Theoretical analysis of liquid immersion development in electrophotography
Authors: Crofoot R. B. , Cheng Y. C.
Published: February 2003

Liquid ink development depends upon the electrophoretic migration of charged toner particles towards a latent image, which is a pattern of surface charge on a dielectric. The electric field under which this occurs has two fundamental components—a driving field due to the latent image and an internal field which arises because of the space charge within the ink layer. A general analytic expression is obtained for the spatial frequency components of the electric field in terms of the frequency components of the charge distributions. The kinetics of the development process is then described by assuming two noninteracting species of charged particles within the ink and obtaining a solution for the motion of these particles. The problem is solved numerically for the case of a solid-area latent image and for a periodic image. The analysis is sufficiently general so that previous results in electrophoretic development emerge as special cases, which hold within certain limitations. Guidelines are provided with regard to the importance of the space-charge effect in a real liquid ink system.
The effect of added hydrogen on the rf discharge chemistry of CF4, CF3H, and C2F6
Authors: Truesdale E. A. , Smolinsky G.
Published: February 2003

The products of 50-W 0.5 Torr rf discharges of CF4, CF3H, C2F6, and mixtures of these gases with H2 were investigated as a function of mass-flow rate (5–80 STD cm3/min) or H2 concentration. In addition, the C2F6 discharge was studied as a function of pressure (0.2–0.8 Torr) and power (50–200 W). Products from the CF4 discharge included F, F2, and C2F6; from CF3H: HF, CF4, C2F4, C2F6, C2HF and C2H2 were produced; from C2F6: essentially CF4 and C2F4. The addition of H2 to CF4 or C2F6 gave the same products as those from CF3H. The product distribution was a function of H2 concentration. The extent of conversion of starting material was a monotonic function of the residence time in the discharge zone. A mechanistic rationalization follows: CF4e−?F +CF3e−?F+CF2e−?F+CF. The various radicals formed underwent abstraction and recombination reactions. Addition of hydrogen altered the above equilibria as well as the nature of the discharge.
X-ray spectra of beta NiAl
Authors: Pease Douglas M. , Azároff Leonid V.
Published: February 2003

The nickel L absorption spectra have been measured in equiatomic NiAl and found to agree well with the one-electron density of states calculated by Connolly and Johnson [J.W.D. Connolly and K.H. Johnson, in Electronic Density of States, edited by L.H., Bennett, Natl. Bur. Stand. Spec. Publ. No. 323 (U.S. GPO, Washington, D.C., 1971), pp. 19–25]. Comparisons with like spectra for nickel metal show an apparent shift of the main LIII edge in NiAl, but a more critical comparison of experimental and theoretical curves shows that the 2p core holes remain equidistant from the Fermi level. This is also confirmed for the 1s core holes by remeasured Ni K spectra. The common practice of locating the Fermi level at the initial inflection point in an absorption edge, therefore, is incorrect for these spectra. Good agreement is found between x-ray K, L, and M absorption spectra and inner-shell emission measurements in NiAl.
Experimental properties of injection lasers. VII. Narrow stripe lasers with rigid waveguide
Authors: Sommers H. S.
Published: February 2003

The properties of a type of (AlGa)As double-heterojunction laser with buried cavity are studied as a function of current and of delay after the start of a 10-μs square current pulse. It is found that the waveguide walls are rigid, for the mode shapes, mode dispersion, threshold, efficiency, and power-current characteristic are independent of current and delay. The spectra are also independent of delay except for a wavelength shift from the change of temperature. The modes are tightly confined with a half-width of 2 μm of the fundamental mode at the facet. The two lowest spatial modes dominate the emission, which is almost completely contained in one spectral doublet. The power in each member of the doublet (single-mode power) is linear in junction voltage from less than 100 μW to the full output of 3 mW, with slope giving a critical power P*≈10 mW as in wide lasers with rigid guides. The strong doublet is transferred to successively longer wavelength modes as the current or delay is increased. The transfer suggests that a narrow gain profile is being swept past the cavity modes by a rise in temperature.
Acoustic emission from gallium arsenide single crystals during deformation
Authors: Ogura M. , Adachi Y. , Ikoma T.
Published: February 2003

A preliminary study was performed to detect acoustic emission from GaAs single crystals which were deformed by compression and heating. Acoustic pulses and continuous waves are emitted from GaAs single crystals when the crystals are deformed by compression at elevated temperatures. Acoustic pulses are apparently correlated with the formation of cracks, while continuous waves are due to bursts of flat planar slip by a rigid dislocation. In the latter case, the slip is confined to planar {111} planes and hence many dislocations are simultaneously multiplied and propagate in a synchronized fashion.
Thermal conversion mechanism in semi-insulating GaAs
Authors: Ohno Hideo , Ushirokawa Akio , Katoda Takashi
Published: February 2003

Formation of both p- and n-type thermally converted surface layers in semi-insulating GaAs is explained in terms of outdiffusion of impurities. Carrier concentrations and impurity profiles calculated on the basis of this outdiffusion model are in close agreement with the experimental values which were obtained by Hall measurements on a variety of heat-treated samples. This excellent agreement is further backed by the mass-spectrometric data and gives strong evidence to the adequacy of the model.
Suppression of thermal conversion in Cr-doped semi-insulating GaAs
Authors: Kasahara J. , Arai M. , Watanabe N.
Published: February 2003

Thermal conversion in the vicinity of the surface of a Cr-doped semi-insulating GaAs wafer to n-type conductivity was effectively suppressed by annealing the wafer under arsenic vapor pressure. For the ion implantation of Si into qualified wafers, the arsine-controlled capless-anneal method provided a uniform and reproducible carrier concentration profile which was in good agreement with that predicted by the LSS theory. The doping efficiency of 100% was attained without anomaly due to thermal conversion.
Heat-treatment behavior of microdefects and residual impurities in CZ silicon crystals
Authors: Kishino Seigô , Kanamori Masaru , Yoshihiro Naotsugu , Tajima Michio , Iizuka Takashi
Published: February 2003

Thermal behavior of both microdefects and residual impurities in pulled silicon wafers has been studied, using x-ray diffraction and infrared absorption techniques. Several tens of wafers from different suppliers have been investigated after heat treatments at temperatures between 450 and 1250 °C. The results separate the wafers into two categories. In some wafers (category I), interstitial oxygen content is significantly decreased by heat treatments at temperatures between 650 and 800 °C. A high microdefect density is induced by heat treatment at a high temperature around 1050 °C. On the other hand, only slight oxygen reduction and defect introduction by heat treatments occur in other wafers (category II). Conversion from the category I to the category II wafers and vice versa are successfully performed by adding an appropriate preannealing. It is proposed that the wafer category depends on both the carbon content and thermal history of the crystal in addition to the oxygen content.
Lifetime determination of MOS diodes with very thin oxide by their photocurrent spectra
Authors: Hirose M. , Kono S. , Osaka Y.
Published: February 2003

A new method for measuring the minority-carrier lifetime in semiconductors is presented. The bulk lifetime in a wide range, 10−11–10−4 sec, can be determined from a simple analysis of photocurrent spectra of MOS tunnel diodes or of Schottky barrier diodes under deep depletion condition.
Extremely uniform electrodeposition of submicron Schottky contacts
Authors: McColl M. , Chase A. B. , Garber W. A.
Published: February 2003

A plating technique has been developed that yields extremely uniform metal deposits on semiconductor surfaces. This technique utlilizes high-field pulses which are extremely short in duration. The technique has produced theoretical Schottky barrier diode spreading resistances for contacts with dimensions ranging from 2.5 to 0.12 μm in diameter.
Molecular-field coefficients of Tm3Fe5O12
Authors: Dionne Gerald F. , Tumelty Paul F.
Published: February 2003

The molecular-field coefficients of Tm3Fe5O12 were determined by a trial and error procedure used previously in the determination of coefficients for other members of the rare-earth iron garnet family. Since an error was detected in the application of the original computer program, a corrected set of coefficients is also given for these compositions. Results of calculations of magnetization-temperature curves of ferrimagnetic garnet systems with mixtures of rare-earth ions are also reported.
Extinction efficiency of obliquely and randomly oriented infinite cylinders
Authors: Cohen Ariel , Alpert Pinhas
Published: February 2003

The extinction efficiency is calculated for a volume containing randomly oriented long circular cylinders. The results are compared with the extinction efficiency of spheres with the same refractive index and are shown to be almost identical. Special attention is given to a corrected definition of the extinction efficiency for obliquely oriented cylinders with respect to the incident radiation direction. The corrected definition presented here is justified by use of the physical concept of the extinction efficiency as used in the case of other scatterers such as spheres. Calculations are presented for a polarized incident light (normal to the incident plane) when discussing the definition of the extinction efficiency. For the randomly oriented particles the incident light is assumed to be unpolarized.
Internal losses in polyvinylidene fluoride (PVF2) ultrasonic transducers
Authors: Leung W. P. , Yung K. K.
Published: February 2003

The dielectric and acoustic losses in oriented PVF2 have been measured from 0.1 MHz to 100 MHz and from 1.5 MHz to 39 MHz, respectively, in the direction perpendicular to the stretching direction at room temperature. A broad absorption peak located at around 5 MHz is observed in each case. The locations of these absorption peaks are of great disadvantage for ultrasonic transducer fabrication. The longitudinal acoustic velocity in the direction perpendicular to the stretching direction is also measured from 1.5 MHz to 39 MHz at room temperature. It is found that the velocity increases monotonically in this frequency range. As a result, the resonance frequency of a PVF2 transducer will be affected proportionally.
Relations between melting point, glass transition temperature, and thermal expansion for inorganic crystals and glasses
Authors: Van Uitert L. G.
Published: February 2003

Thermal expansion coefficients correlate with a number of physical properties of crystals. Cubic ionic insulators that have two completely filled sets of lattice sites have a maximum value for the product of the coefficient and melting point. Expansion is diminished by the presence of various internal degrees of freedom, singly or in combination. These factors depend upon the array, band gap, bond length, and character and coupling between orbital sets. For screwlike chain structures and glasses αT 2m is a constant.
Adhesive bondline interrogation using Stoneley wave methods
Authors: Claus Richard O. , Kline Ronald A.
Published: February 2003

In this work, a new technique for analyzing interfacial conditions in completed adhesive bonds is discussed. This method is based on the sensitivity of Stoneley waves, which propagate along the boundary between dissimilar solid media, to changes in the material properties of the interface region. Stoneley wave attenuation measured after processing was found to increase as a function of increasing surface roughness in specimens of borosilicate crown glass bonded with an aerobic cement to a substrate of 7740 Pyrex mirror glass. Possible extensions of these results to high-strength structural adhesively bonded composites are discussed.
Trap-controlled transient photoconductivity in dielectrics
Authors: Fleming R. J.
Published: February 2003

Computer programs have been developed to solve numerically the equations governing transient photoconductivity in dielectrics in the presence of a continuous distribution of traps. The Schmidlin prescription for the trap distribution equivalent to the Scher and Montroll stochastic model of dispersive transport in the small signal limit has been confirmed. It is shown that, with increasing amounts of charge in transit, the pre-transit time slope of a double logarithmic current vs. time plot increases algebraically, with the post-transit slope being largely unaffected. Investigation of other trapping distributions suggest that transient photoconductivity data will need to be supplemented by thermally stimulated conductivity, thermoluminescence, and thermally stimulated depolarization data in any work aimed at a comprehensive documentation of trapping parameters in dielectrics.
The transient response of hot electrons in quasi-two-dimensional semiconductors
Authors: Moore J. Scott , Das P.
Published: February 2003

The behavior of hot electrons in quasi-two-dimensional semiconductors has been calculated, using a displaced Maxwellian distribution function applied to a 〈100〉 inversion layer in silicon. Under a high electric field, energy levels become grouped into subbands, so that motion of carriers perpendicular to the surface becomes quantized; thus, the energy, momentum, and population transfer relaxation times appropriate to the individual levels must be considered in the calculations, along with their relation to velocity overshoot. Previous work has been performed under the assumption that intervalley scattering is a local phenomenon, i.e., a function only of electron temperature of the initial valley. In this paper, this assumption is relaxed, and the intervalley coupling of electron temperature is taken into account. dc and transient response characteristics for both uncoupled and coupled models are performed, and the results are compared.
Charge injection in metal-ZnO-SiO2-Si structures
Authors: Pierret R. F. , Gunshor R. L. , Cornell M. E.
Published: February 2003

The charge injection phenomenon occurring in metal-ZnO-SiO2-Si (MZOS) structures is quantitatively analyzed yielding a detailed model of the injection process. Theoretical capacitance-voltage and charge-voltage relationships describing the operational behavior of the gated MZOS-C structure are first established to provide a firm foundation for the interpretation of experimental data. Key experimental results, arranged so as to retrace the logical sequence of conclusions leading to the adopted charge injection model, are next described and discussed. In negatively biased illumination-relaxed structures all of the injected charge is shown to be located in deep-level interfacial traps and a dipole-like layer or surface barrier is found to exist in the near vicinity of the ZnO-SiO2 interface. Finally, a discussion is presented detailing both the stationary and transient aspects of the charge injection model formulated in accordance with experimental observations.
Analysis of threshold curves for superconducting interferometers
Authors: Peterson R. L. , Hamilton C. A.
Published: February 2003

Threshold curves for multijunction superconducting interferometers have been calculated previously, showing general agreement with observed features, especially in symmetric cases. We here add some more details to the analysis, paying particular attention to the effects of asymmetries in coupling, inductance, or critical currents. Feed-loop inductance and flux quantization in the feed loop can be important. A changing lobe pattern over many periods, asymmetries within a period, shifting patterns between runs spanning a warm-up, and sudden changes in pattern because of noise in the environment are all quantitatively explainable on the basis of this model. By use of a single ’’calibration curve’’, the inductance for symmetric two- or three-junction interferometers can be obtained immediately.
Absence of anisotropy effects in the magnetization of ferrofluids
Authors: Krueger David A.
Published: February 2003

Existing magnetization measurements on magnetic colloids known as ferrofluids have been analyzed using the Langevin theory for spherical particles with no anisotropy energy. Deviations from simple Langevin theory are interpreted as being a reflection of a distribution of particle sizes. We consider the more general situation of ellipsoidal particles with a general anisotropy energy which depends only upon the relative orientation of the magnetic moment and the particle. By assuming that the orientation of the particle is in thermodynamic equilibrium, we show that the anisotropy has no effect on the magnetization of the colloid and that the Langevin theory obtains. Physically this result can be thought of as follows. The magnetic field tends to align the magnetic moment along that field. The anisotropy energy, Ea, then favors aligning the easy axis of the particle along that moment and this second alignment has no effect on the moment.
Index of refraction of shock-compressed fused silica and sapphire
Authors: Setchell Robert E.
Published: February 2003

Explicit relations between index of refraction and density are obtained for shock-compressed fused silica and sapphire. The relations are derived from the Doppler-frequency corrections to velocity-interferometry data obtained by Barker and Hollenbach in plate-impact experiments. The index-density relation for sapphire was found using an expression for the Doppler-frequency shift produced by a window material experiencing shock compression. For fused silica, a numerical calculation was required to compute frequency corrections for the combined ramp/shock waveforms produced in the experiments. In both cases the behavior of the refractive index over the density range of the data was found to be predicted quite accurately by adding a correction term to the Gladstone-Dale relation. A particular power-law dependence on density was found for this correction term in each case. The explicit index-density relations permit detailed calculations to be made for index-of-refraction effects from window materials in plate-impact experiments using velocity interferometry. As an example, refractive-index effects are calculated for a fused silica window experiencing a slowly rising compression wave generated in a glass-ceramic material. The present results also permit the polarizability behavior of these materials under shock compression to be examined.
Defect luminescence in cw laser-annealed silicon
Authors: Street R. A. , Johnson N. M. , Gibbons J. F.
Published: February 2003

Several new luminescence transitions are found in cw laser-annealed silicon. We report the spectra, temperature dependences, and thermal-annealing effects. At least two defects are shown to be present, and their possible identity is discussed.
Circular differential photoacoustic spectroscopy
Authors: Saxe Jeffrey D. , Faulkner Thomas R. , Richardson Frederick S.
Published: February 2003

A theoretical analysis of left/right circular-polarization modulated photoacoustic spectra is presented. The amplitude of the photoacoustic (PA) signal generated by exciting an absorbing sample alternately with left- and right-circularly polarized light is shown to be proportional to sample circular dichroism, Δα=αL−αR (where αL and αR are sample absorptivities for left and right circularly polarized light, respectively). Expressions appropriate for analyzing photoacoustically detected circular dichroism (referred to as PACD) are developed within the general framework of the Rosencwaig-Gersho model [J. Appl. Phys. 47, 64 (1976)] for the photoacoustic effect in solids and liquids. Extensive calculations based on these expressions are carried out for a number of parameter sets reflecting sample properties, sample cell/detector characteristics, and excitation properties. The results of these calculations indicate that PACD signal strengths for a wide variety of sample types should exceed detectability thresholds, and that PACD should be readily observable for many sample types whose circular dichroism cannot be measured using the conventional transmission techniques. Among this latter class of samples are optically opaque solids and highly scattering suspensions. The expressions for PACD signal strengths are shown to take on particularly simple forms for certain sets of sample properties and excitation modulation frequencies.
Phase-matched second-harmonic generation in vapor-grown GaP ribbon waveguides
Authors: Stone J. , Burrus C. A. , Standley R. D.
Published: February 2003

Phase-matched second-harmonic generation has been achieved in twinned as-grown ribbon ’’whiskers’’ of GaP about 50 μm wide and of submicrometer thicknesses. These naturally occurring slab waveguides were pumped with a Nd : YAG laser at a wavelength of 1.064 μm, and the second-harmonic output was observed as greenlight at 0.532 μm wavelength. Experiments concerning the second-harmonic generation are described, and the results are related to those expected from the crystallography of, and the modal dispersion in, the slab-waveguide ribbons.
CO2-laser-produced plasma-initiated neutral-gas recombination lasers
Authors: Silfvast W. T. , Szeto L. H. , Wood O. R.
Published: February 2003

Plasmas produced with focused 10.6-μm radiation from a high-pressure pulsed CO2 laser have been used to initiate a number of neutral-gas recombination lasers. The results have implications for the future development of high-efficiency lasers in the near infrared.
Operation characteristics of buried-stripe GaInAsP/InP DH lasers made by melt-back method
Authors: Kano H. , Sugiyama K.
Published: February 2003

A buried-stripe configuration of GaInAsP/InP dh laser was made by using a melt-back method combined with a chemical etching for obtaining a mesa-stripe geometry. The wavelength of laser emission was 1.3 μm at room temperature. The lowest threshold current of cw operation at room temperature was 30 mA with the 2-μm-wide buried-stripe laser. External differential quantum efficiency was 24% per facet, and the laser power increased up to 40 mW (dc current of 230 mA) without any significant kink. As the buried-stripe laser had good thermal characteristics, cw operation was realized at 100 °C in a laboratory atmosphere. When the buried-stripe laser was activated by a pulse current of 3 ns in width, no relaxation oscillation was observed in the pulse response of laser emission, which is considered to be preferable for high-speed modulation of the laser power.
Laser heating of a slab having temperature-dependent surface absorptance
Authors: Warren R. E. , Sparks M.
Published: February 2003

The exact solution obtained here for the temperature in a laser-heated slab with surface absorptance A=Ai+A1 T (0,t) proportional to temperature and with negligible radial heat flow, shows that the temperature is considerably greater in general than for A1=0. In the limit of long time, for negligible cooling, the surface temperature increases exponentially as TA{ exp[(I/Il)(t/τl)]−1} for I≲Il and as TA{2 exp[(I/Il)2(t/τl)]−1} for I≳Il, where TA=Ai/A1, Il=K/lA1, τl=Cl2/K, K is the thermal conductivity, C is the heat capacity per unit volume, and l is the slab thickness. The limiting temperature derived here for t≳τl/5 and that derived by Sparks and Loh for t≲τl/5 afford simple closed-form expressions for T (z,t) for all z and t. With cooling, the temperature increases without bound (thermal runaway) for I≳Ihl, where Ihl=Il[Hs+H/(1+H)] with Hs and H normalized heat-transfer coefficients at the front and rear surfaces of the slab. The intrinsic cw damage threshold, which is slightly less than Ihl, can be quite low—from 100 W/cm2 to 150 kW/cm2 for the examples considered. The ability to withstand a given irradiance in a small beam does not imply the ability to withstand the same irradiance in a large beam.
Enhanced arcing as a function of organic exposure and arc current for Pd and Pd/Ag electrodes
Authors: Gray Eoin W. , Pharney Julian R.
Published: February 2003

We report the existence of a region within which enhanced arcing (activation) exists for palladium and palladium/silver contacts, as a function of arc current and of exposure to organic vapors. The current range where activation exists is from ∼0.1 to ∼1.2 A, where the range of exposures (partial pressure times time) used for diethyl phthalate was from ∼10−3 to ∼10 Pa s. At very low organic exposure levels (depending upon the organic vapor and the electrode metal), arc-duration statistics show an exponential behavior. Under moderate to high organic exposure levels, arc-duration show a log-normal distribution similar to that obtained under clean conditions when the arc current exceeds the minimum arc-sustaining current. At sufficiently high currents arc-duration statistics become independent of organic exposure. The envelope of the activated curves is predicted by the activation theory of Gray, Uhrig, and Hohnstreiter.
Spectra of a glow discharge in flowing nitrogen
Authors: Keren H. , Kaufman Y. , Dothan F. , Avivi P.
Published: February 2003

The visible spectrum of the positive column of a glow discharge in flowing nitrogen was investigated. There is experimental evidence that the emission spectra depend on the flow velocity and that the changes in the intensity of the first positive and second positive bands of nitrogen are quite different. The results cannot be explained by one-step excitation of electronic levels from the ground state. On the other hand they are consistent with the assumption of stepwise excitation and of atomic recombination to electronically excited molecular levels.
Precessional rotation and other nonlinear effects due to standing waves and other two-wave resonant interactions in a magnetized plasma
Authors: Khan Manoranjan , Chakraborty B.
Published: February 2003

When two electromagnetic waves propagate along the fixed direction of an uniform and constant magnetic field in a homogeneous, cold, and collisionally damped plasma, the effects of their nonlinear interaction are large and so important in two special cases. One is the case in which the beat frequency equals the characteristic plasma frequency and moreover, one of the wave frequencies equals the gyration frequency of electrons (or ions). The other is the nonlinear evolution of the wave pattern formed by an appropriate superposition of the two waves in a manner which produces standing waves from them in the linear approximation. These two cases have been theoretically investigated in this paper. Moreover, the nonlinear evolution of the standing-wave patterns has been discussed with a view to initiate the exploration of the application side of this effect.
Free-electron lasers, boundary deformation, and the Robinson-Liouville theorem
Authors: Madey J. M. J. , Deacon D. A. G. , Smith T. I.
Published: February 2003

We consider the evolution of the electrons’ phase-space distribution as they move through the interaction region in a free-electron laser.
Optoacoustic measurements of diesel particulate emissions
Authors: Faxvog Fred R. , Roessler David M.
Published: February 2003

Infrared absorption by acetylene and diesel smoke particles was measured using a differential optoacoustic cell driven by a 3.4-W CO2 laser. Real-time particle mass concentration measurements are demonstrated. In addition we found the average particle extinction cross sections per unit mass of acetylene and diesel smoke were 0.94±0.1 m2/g and 0.83±0.2 m2/g, respectively, at the 10.6-μm wavelength.
Thin-film sputtering yields for Fe, Cr, and an Fe-Cr alloy measured by proton-induced x rays
Authors: Sartwell B. D.
Published: February 2003

Proton-induced x-ray emission (PIXE) was used to measure the sputtering yields of thin films bombarded by 1.0 keV Ar+ at normal incidence. The films consisted of vacuum-evaporated iron, chromium, and an Fe-Cr alloy. An integral approximation to the theoretical x-ray yield equation was developed that resulted in the determination of the thicknesses of the thin films. In general, this appoximation can be used to measure film thicknesses up to several hundred nanometers. The sputtering yields were determined by measuring the slope of the straight-line fit to the experimental data which was obtained as film thickness versus accumulated sputtering charge. The chromium sputtering yield, measured by PIXE for a chromium film evaporated onto an electropolished iron substrate, agreed within 5% of that obtained using an energy-dispersive x-ray analyzer attached to an SEM. The sputtering yields measured for iron and chromium films with initial thicknesses between 5×1017 and 9×1017 atoms/cm2 deposited onto a nickel substrate were S (Fe) =1.23 atoms/ion and S (Cr) =0.93 atoms/ion. The agreement with previously published data for S (Fe) is good; no published data on S (Cr) are known. Using recently derived values for the nuclear stopping power, the measured iron and chromium sputtering yields agree well with Sigmund’s theory. The total sputtering yield obtained for an Fe-35Cr alloy was 1.17 atoms/ion, and the elemental sputtering yields for the alloy were in the ratio of their concentrations. The advantages of using the PIXE technique over other techniques currently being used, particularly for compounds, are discussed.
Associated incorporation of boron, lead, and oxygen vacancies in garnets
Authors: Andlauer B. , Tolksdorf W.
Published: February 2003

Local vibrational modes observed in the IR spectrum of iron garnets and noniron garnets have been identified and arise from a complex formed by a boron-oxygen group [BO3]3−, a heavy metal ion M2+, and an oxygen vacancy. The energy of the local modes is affected by the electron population of the vacancy ranging from 0 to 2, and by the exact nature of the M2+ ion, being in most cases Pb2+. This is a first spectroscopic indication of the occurrence of oxygen vacancies in iron garnets. In iron-containing garnets, the whole complex can act as a charge compensator of additional lattice defects, owing to the associated M2+ ion and oxygen vacancy, the latter having different states of ionization. From the boron spectrum observed in a particular yttrium iron garnet (YIG) sample, one may infer at least in a qualitative way the underlying position of the Fermi level. Measurements at different temperatures reveal that the donor level of the singly ionized oxygen vacancy in YIG should lie about 0.15 eV below the level of a silicon donor residing nearby. Formation of the boron-oxygen complex near the M2+ ion seems to be facilitated since it tends to compensate the expansive lattice strain induced by the heavy metal ion.
Kinetics of growth of the oxidation stacking faults
Authors: Leroy Bernard
Published: February 2003

A model for the growth of oxidation stacking faults (OSF) has been developed with three main hypotheses: (1) The growth of the OSF is due to the diffusion of silicon self-interstitials from the Si-SiO2 interface to the partial dislocation. The diffusion coefficient of the interstitials can be determined from the data of silicon self-diffusion. (2) The concentration of interstitials at the Si-SiO2 interface, Cs, is determined by the equilibrium between the interstitials and the atoms of oxygen free to react with the silicon atoms, Cs =4.1×1018t−0.25 PO20.25 exp(−0.5/kT)  F, where Cs is in cm−3, t is the time in seconds, PO2 is the oxygen partial pressure in atmospheres, and kT is in eV. F value is 1 for wafers of (001) orientation, and 0.7 for the (111) wafers. (3) The concentration of the interstitials in equilibrium with the partial dislocation, C0, in cm−3, is C0=12×1025 exp(−3.02/kT), with kT in eV. The majority of the experimental data can be calculated from R =1640Ft0.75 PO20.25 exp(−2.5/kT) −3.6×1010t exp(−5.02/kT), where R is one-half of the OSF length in cm, t is in sec, PO2 is in atmospheres, and kT is in eV. The role of the vacancies in the OSF growth is also discussed, but the model favors a mechanism of silicon self-diffusion involving a silicon interstitial, and a double mechanism for boron diffusion.
Effect of morphology on the properties of alkaline earth silicate glasses
Authors: Shelby J. E.
Published: February 2003

The effect of morphology on the thermal expansion behavior, helium permeability, density, and refractive index of alkaline earth silicate glasses has been determined for the calcium, strontium, and barium silicate systems. These data have been used to determine the miscibility limits and the limits of connectivity of the high silica phase for each of these systems. The miscibility limits occur at approximately 46, 42, and 40 mol% CaO, SrO, and BaO, respectively. The limit for a connected high silica phase occurs at approximately 33, 25, and 22 mol% CaO, SrO, and BaO, respectively. This paper demonstrates the use of these techniques in the determination of the morphology of simple glass-forming systems.
Net lateral flow during a twist-cell cycle
Authors: Berreman Dwight W. , Sussman Alan
Published: February 2003

The flow pattern that is caused by the backflow effect when a twist cell is turned on is not exactly reversed when the cell is turned off. Computer simulation of flow far from the boundary of an element shows an average lateral flow distance of up to several percent of the cell thickness in each cycle. This flow would account for observed transport and deposition of particles of debris at one edge or corner of deteriorating cells. Such flow has also been observed directly by introducing dye markers into cells.