bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between single-crystal and polycrystal electrical conductivity
Authors: Schulgasser Kalman
Published: February 2003

The problem of the prediction of the effective electrical conductivity of a polycrystal from the electrical conductivity of a single crystal is considered. It is shown that the familiar Voigt-Reuss bounds on the behavior of a polycrystal are the very best generally valid bounds that have thus far been proposed and that the various methods that are claimed to predict exact effective conductivity (or narrow bounds) all include implicit restrictions on the internal geometry of the polycrystal. This is accomplished by constructing a series of statistically homogeneous and isotropic polycrystal models for which the effective conductivity can be exactly calculated. It is hence to be expected that no universal relationship between single-crystal and polycrystal conductivity exists. Experimental evidence is adduced to support this conclusion. The results are also applicable to the analogous problems of thermal conductivity and electrical permittivity.
Electron transport parameters and excitation rates in N2
Authors: Newman L. A. , DeTemple T. A.
Published: February 2003

Using recently measured vibrational and electronic electron impact cross sections, a self-consistent set of cross sections was obtained by numerically solving the Boltzmann transport equation and requiring that calculated and measured transport quantities be in agreement. The resulting set of cross sections and the calculated drift velocity, characteristic energy, equivalent electron temperature, and excitation and ionization rates are presented.
Analysis of current growth measurements in attaching gases
Authors: Davies D. Kenneth
Published: February 2003

An alternative procedure is presented for the analysis of spatial current growth measurements in attaching gases. The analysis gives unambiguous values of the net ionization coefficient for low values of Nd even when detachment and charge transfer of the primary negative ion occur simultaneously with ionization and attachment, provided secondary ionization processes are negligible. Examples are given of the application of the analysis to data in CO2, in a mixture of CO2, N2, and He, and in O2.
Effect of electrode surface conditions on the self-breakdown strength and jitter of a high-pressure pulsed gas switch
Authors: Ramirez Juan J.
Published: February 2003

Measurements were made of the impulse breakdown strength versus pressure for a self-breaking near-uniform-field gas switch. Both roughened and polished electrodes were tested. The breakdown strength was found to be proportional to the pressure for the roughened electrodes; however, the polished electrodes displayed anomalously high but erratic voltage breakdown characteristics at pressures below 5.6 atm. This anomalous behavior was found to be independent of both the electrode material and insulating gas. Electrode roughness or damage appears to play an important role in this process. This damage was significantly reduced by removal of all absorbed machining oils. All efforts to reduce the voltage breakdown jitter, while maintaining the high breakdown strengths, failed. Open shutter photographs of the switch with polished electrodes showed multichannel switch operation which was not expected to occur. Multiple channeling was not observed with the roughened electrodes.
Mass analysis of plasma in a laser-initiated negative-ion source
Authors: Romesser Thomas E. , Tang John T.
Published: February 2003

The components of a laser-initiated alkali hydride plasma are investigated using a magnetic-deflection mass detector. Peaks corresponding to H−, electrons, and H+ are observed. A total H− charge of 5×10−6 C is obtained for 0.2 J of incident laser energy.
Interaction of a high-current relativistic electron beam with a dense plasma
Authors: VanDevender J. P. , Kilkenny J. D. , Dangor A. E.
Published: February 2003

Laser-scattering and line-emission measurements of a plasma heated by an intense electron beam are reported. The e-beam’s parameters are 350 kV and 36 kA for 100 ns, and the beam density is either 6×1011 or 5×1012 cm−3 for injection into a plasma and into a neutral gas, respectively. The plasma number density is varied from 5×1013 to 3×1015 cm−3, and the initial temperature is less than 10 eV. There is no external magnetic field. When there is a large net current in the beam-plasma system, as there is for injection into a neutral gas, the dominant energy transfer is from the beam to the ions through a radially outward plasma acceleration in the Hall electric field jp×B/npe. The laser-scattering data is consistent with large azimuthal and radial plasma currents which are presumed to be driven by the azimuthal asymmetry of the Hall electric field. When the beam is injected into a preformed plasma, the net current and the effects of the Hall field are sufficiently small to allow the electron heating mechanisms to be studied. The final electron energy density is consistent with heating via anomalous collisions arising from the ion-acoustic instability in addition to classical collisions. Furthermore, the expected energy transfer via the electron-electron two-stream instability is not observed.
Generation of charged drops of insulating liquids by electrostatic spraying
Authors: Kim Kyekyoon , Turnbull Robert J.
Published: February 2003

Development of a new method for the generation of microparticles of controlled size and charge is reported. The method, which is particularly suited for insulating liquids, is to generate stable fine jets through electrostatic spraying. Charge in the liquid is produced by placing a sharp electrode inside the liquid and raising it to a high potential. High electric fields then disrupt the liquid to form fine jets which later break up into small drops. A theoretical explanation of these phenomena is presented and compared with experimental results with a qualitatively good agreement. Among the possible applications of this work is generation of cryogenic droplets for refueling fusion reactors and for laser fusion targets.
1/fα noise in aqueous solutions of poly(ethylene oxide) in Couette flow
Authors: Klason Carl , Kubát Josef
Published: February 2003

Current-noise spectra have been determined for aqueous solutions of poly(ethylene oxide) subjected to different shear rates in a Couette-type measuring cell. Different electrode arrangements did not influence the results obtained. The current noise had a 1/fα-type frequency distribution, with the value of α depending on the shear rate, the molecular weight, and the concentration. At low shear rates, below 50 s−1, the current-noise intensity was immeasurably small. In general, the degree of pseudoplasticity of the solutions was reflected in the noise intensity and the value of the exponent α; non-Newtonian solutions give rise to a more intense noise. This tendency was expressed quantitatively in an inverse-type relation between α and n, the exponent of the pseudoplasticity in the Ostwald-deWaele power law of flow. The relation was slightly affected by the conditions of measurement. Newtonian solutions appeared to be associated with pure 1/f noise (α?1).
Permeation of helium and hydrogen from glass-microsphere laser targets
Authors: Tsugawa R. T. , Moen I. , Roberts P. E. , Souers P. C.
Published: February 2003

Isothermal outgassing curves of hollow glass microspheres filled with helium, hydrogen, or deuterium gas have been determined. Four million 40–45-μm soda-lime glass microspheres, similar to laser-fusion targets, were filled by gas permeation at 693–763 K and outgassed at 292–573 K. The permeabilities were calculated by an exponential theory, and they agree to an order of magnitude with the literature values. The outgassing curves are not pressure dependent. Two irregularities are apparent. First, the counting of target-quality individual D-T–filled microspheres shows a permeability spread of an order of magnitude from one microsphere to the next, which may be caused by variable chemical composition. Second, all the gases show deviations from exponential behavior in the form of tails at long times. Chemical reaction of the hydrogen with the glass, as well as incomplete filling and outgassing, may cause the hydrogen tails; the cause of the helium tails is not known.
On the index of refraction of shock-compressed liquid nitromethane
Authors: Hardesty D. R.
Published: February 2003

The index of refraction of shock-compressed liquid nitromethane has been determined from 7.5 to 9.5 GPa. These data were obtained under the condition of one-dimensional compression in the liquid in the course of powder gun projectile impact studies of the shock initiation of the liquid explosive. Diagnostic information obtained by means of streak camera photography and velocity interferometry was compared with previously obtained equation-of-state information in order to evaluate the refractive index of the shocked liquid prior to the onset of chemical decomposition. Our results suggest the validity of the Gladstone-Dale relationship for the prediction of the density dependence of the index of refraction of nitromethane at pressures in the range 5–10 GPa.
Ce3+→Nd3+ energy transfer in silicate glass
Authors: Jacobs Ralph R. , Layne Clyde B. , Weber Marvin J. , Rapp Charles F.
Published: February 2003

Radiative and nonradiative energy transfer from optically excited Ce3+ to Nd3+ has been studied in silicate laser glass. The quantum efficiency for nonradiative Ce3+→Nd3+ transfer was determined from the Ce3+ fluorescence decay rates. The Ce3+ fluorescence decayed exponentially with a rate proportional to the Nd3+ concentration. Physical processes to account for the observed energy transfer are discussed. In addition, the utility of Ce3+→Nd3+ energy transfer is considered for laser applications. In this context, the energy deposited in a Ce3+-Nd3+–codoped glass was calculated using a computer program containing a model of the xenon flashlamp spectrum as a function of current density. The results indicate that improvements in the optical pumping efficiency in typical Nd lasers are limited to <40%.
Calculations on output pulse shapes, gain pulse profiles, and gain limitation in the CO2 TEA laser
Authors: Davies A. R. , Smith Kenneth , Thomson R. M.
Published: February 2003

An eight-equation kinetics model for the CO2-N2-He-CO system has been developed to predict the output power pulse shapes from laser oscillators and the small-signal gain from laser amplifiers. The model takes into account CO2 dissociation into CO, variation in the ambient temperature, as well as the possibility that the lower laser vibrational level is not in equilibrium with the other vibrational levels of the CO2 symmetric stretch mode. Theoretical predictions are compared with experimental data and show good agreement. Calculations have been carried out to determine the factors underlying the limitation of gain at specific input energies.
Reply to ’’Comment on ’Griffith fracture equation—An experimental test’ ’’
Authors: Doremus R. H.
Published: February 2003

If surface energy is related to crack-tip radius, then the surface energy is not a material property and depends on sample history. If the surface energy is a material property, our results show that samples with cracks of the same length fail at different stresses contrary to the Griffith criterion.
Charge centroid and trapping model for MNOS structures
Authors: Lehovec Kurt , Crain D. W.
Published: February 2003

Charge centroid, trap density, and capture cross section for an MNOS structure are derived from measurements of the change in flat band voltage with varying pulse duration and temperature using the Arnett-Yun model. The temperature dependence of these parameters suggests that the Arnett-Yun model for the initial space-charge buildup is not entirely valid. The observations are in qualitative agreement with partially ionized traps whose occupancy by electrons decreases with increasing temperature and electric field.
Approximate calculation of the shear modulus and Debye temperatures of alkali halides
Authors: Verma J. K. D. , Aggarwal M. D.
Published: February 2003

The Verma-Aggarwal approximation for the shear modulus is employed to calculate elastic Debye temperatures of alkali halides and results are compared with those obtained by three other approximations and also with the exact values. It is found that this approximation yields values of Debye temperatures much closer to exact values than other approximations.
Volume dependence of phonon frequencies
Authors: Reynolds C. L. , Couchman P. R.
Published: February 2003

An explicit equation for the complete volume dependence of phonon frequency is derived from the compression dependence of the Grüneisen parameter.
Effect of adsorbed films on friction of Al2O3-metal systems
Authors: Pepper Stephen V.
Published: February 2003

The kinetic friction of polycrystalline Al2O3 sliding on Cu, Ni, and Fe in ultrahigh vacuum was studied as a function of the surface chemistry of the metal. Clean metal surfaces were exposed to O2, Cl2, C2H4, and C2H3Cl, and the change in friction due to the adsorbed species was observed. Auger electron spectroscopy assessed the elemental composition of the metal surface. It was found that the systems exposed to Cl2 exhibited low friction, interpreted as the van der Waals force between the Al2O3 and metal chloride. The generation of metal oxide by oxygen exposures resulted in an increase in friction, interpreted as due to strong interfacial bonds established by reaction of metal oxide with Al2O3 to form the complex oxide (spinel). The only effect of C2H4 was to increase the friction of the Fe system, but C2H3Cl exposures decreases friction in both Ni and Fe systems, indicating the dominance of the chlorine over the ethylene complex on the surface.
Laser focusing limitations from nonlinear beam instabilities
Authors: Holzrichter J. F. , Speck D. R.
Published: February 2003

Compression of fusion targets by irradiation with Nd : glass lasers requires precise focusing of large-aperture high-power laser beams. Nonlinear propagation instabilities cause growth of small-scale amplitude perturbations which reduce the focusing properties of such beams. We present temporal measurements of the focus of a high-power glass laser and we show that the integrated nonlinear phase retardation of the beam (or B value) can be used to determine the maximum focusable energy available from an unspatially filtered amplifier chain.
Measurement of nonlinear refractive-index coefficients using time-resolved interferometry: Application to optical materials for high-power neodymium lasers
Authors: Milam D. , Weber M. J.
Published: February 2003

An improved time-resolved interferometric method for measuring intensity-dependent changes in the refractive index of optical materials is described. An intense 125-ps pulse from a 1064-nm Nd : YAG laser-glass amplifier system is propagated throguh the sample which is placed in one arm of a modified Michelson interferometer. The nonlinear refractive-index coefficient is measured from the time-dependent fringe formed at the output of the interferometer. Values are reported for several low-index optical glasses (BK-7, FC-5, FK-51), fused silica, a silicate laser glass (ED-2), a Faraday rotator glass (FR-5), and a nonlinear crystal (KH2PO4). Possible sources of error in using this approach are discussed.
Selection and measurement of microsphere laser targets based on refraction
Authors: Reedy R. P.
Published: February 2003

The hollow glass or plastic microspheres used as laser targets range in diameter from a few micrometers to several hundred micrometers and can be selected from batches of commercially available microspheres. Preliminary selection of the very few that appear satisfactory for further testing can be accomplished by a practical nondestructive technique based on their refractive properties; when they are transilluminated and viewed through a microscope focused upon the surface upon which they rest, deviations from sphericity and uniform wall thickness appear as deviations from the ideal pattern of a perfectly symmetrical bright circular disk surrounded by a black ring of uniform thickness; wall defects appear as anomalies in this pattern. The method is shown to be soundly based on optical principles and theory. A model of the illumination distribution, including intensity profiles of model microspheres with specified characteristics, is compared with the rigorous measurements necessary for final selection of laser targets. The ratio between the inside diameter of the black ring and the outside diameter of the microsphere is a function of wall thickness, which can be calculated accurately on this basis. The same relationship also permits determination of the density of DT gas in a gas-filled sphere or the thickness of a layer of solid DT on the inner surface. Either microspheres or their photographs can be rapidly scanned and digitized by a computer-controlled microdensitometer; data points can be recorded for 1-μm intervals in the X and Y directions and can be displayed as density contours, density profiles, or isometric density profiles. Another convenient instrument for viewing microspheres as well as for rigorous measurements is a color-isodensity television system with a microscope attachment.
CO chain-reaction chemical laser. I. Experimental
Authors: Jeffers W. Q. , Ageno H. Y. , Wiswall C. E.
Published: February 2003

A chain-reaction CO chemical laser fueled by carbon monosulfide (CS) and molecular oxygen (O2) has been demonstrated. Initiation by the chain carriers (either O or S atoms) is necessary; the chain lenght λ* increases rapidly with the CS/CS2 fuel mole ratio, reaching a value λ*?10 at CS/CS2=1.57. Mass flow efficiencies up to 67 kJ/1b have been measured with a small-scale subsonic device, and laser operation has been observed up to 64-Torr cavity pressure. Gain measurements and subsonic mixing effects have been investigated. This work was made possible by developing a thermoelectric CS gas generator, which is also described.
Semi-insulating layers of GaAs by oxygen implantation
Authors: Favennec P. N.
Published: February 2003

High-energy oxygen ions (400 keV <E<3.6 MeV) are used to obtain a semi-insulating (SI) layer. Our objective is to determine the location of the above-mentionned SI layer in the substrate and its thickness, on one hand, and the influence of the carrier concentration and that of the doping impurity on the other. For low doses, we have shown that the measured compensation existing after an anneal at high temperature is only due to oxygen atoms and that an implanted oxygen impurity might be a deep double-electron trap. We can get a buried semi-insulating layer through a suitable choice of the incident energy and the oxygen dose. The surface layer crossed by incident ions is well insulated from the substrate by the SI layer and its quality would not be affected by ion crossing, the carrier concentration and mobility of this surface layer being nearly recovered after a suitable anneal (T?800 °C).
Hydrogen-sensitive palladium gate MOS capacitors
Authors: Steele Martin C. , Hile John W. , MacIver Bernard A.
Published: February 2003

The C-V characteristics of palladium gate MOS capacitors change significantly when exposed to an air ambient containing up to 4% hydrogen. From these experiments, it is concluded that these changes are due to the lowering of the palladium work function (by as much as 1 V) brought on by the formation of palladium hydride. Mobile charges in the oxide do not contribute to the observed C-V shifts brought about by exposure to hydrogen.
Lifetime-controlling recombination centers in platinum-diffused silicon
Authors: Miller M. D. , Schade H. , Nuese C. J.
Published: February 2003

The diffusion of Pt into Si from a silica film at temperatures between 800 and 1000 °C has been found to provide room-temperature minority-carrier lifetimes between 10 nsec and 1 μsec. Evaluation of the dependence of lifetime on ambient temperature and on majority-carrier doping concentration as well as the measurement of thermally stimulated currents indicate the presence of two recombination centers: an acceptor located 0.26 eV below the conduction band edge for n-type Si and a donor located 0.32 eV above the valence band edge for p-type Si. The concentration of electrically active Pt centers increases exponentially with increasing diffusion temperature, and is in the range 7×1013 to 7×1014 cm−3. Minority-carrier capture cross sections for the n- and p-type Si are about 1×10−14 and 6×10−15 cm2, respectively. A simple single-level Shockley-Read model incorporating these centers has been used to fit observed minority-carrier lifetime values over a wide range of temperature and to calculate the dependence of lifetime on majority-carrier doping concentration for n- and p-type Si.
Some optical properties of the AlxGa1−xAs alloys system
Authors: Monemar B. , Shih K. K. , Pettit G. D.
Published: February 2003

Optical transmission data covering the Γ15V–Γ1C absorption edge are presented, together with photoluminescence (PL) results, for AlxGa1−xAs crystals of high purity [n (293 K) <1017 cm−3] for 0<x<0.9. The results indicate that the fundamental absorption edge is domnnated by electron-hole interaction even in an an alloy. In the direct-gap region the bound-exciton ground-state peak is clearly resolved. In the indirect-gap region the relaxation of crystal momentum conservation in optical transitions for an alloy apparently has significant effects on the Γ15V–Γ1C absorption edge, and the discrete peak in absorption spectra disappears. From the variation of the absorption coefficient αth at the Γ15V–Γ1C edge with x, we can deduce the corresponding variation of the excitonic binding energy Eex, excitonic effective mass m*, and electron mass mc for the Γ1C minimum. Extrapolated values for these quantities in AlAs are Eex=5 meV, m*=0.060 m0, and mc=0.11 m0 for a value αth = 2.3×104 cm−1. Further, there is a shift of the Γ15V-Γ1C absorption edge towards lower energies only in the indirect-gap region. Thus the usually employed quadratic expression for the bowing of band gaps in alloys is inadequate for the Γ15V-Γ1C gap in AlxGa1−xAs. We observe no bowing of band gaps in alloys is inadequate for the Γ15V-Γ1C gap in AlxGa1−xAs. We observe no bowing at all (<0.01 eV) in the direct-gap region, in sharp disagreement with earlier experiments employing other methods. Our PL data for the indirect-gap region indicate no significant bowing in the Γ15VC gap either (<0.01 eV). The PL results for the direct-gap region establish significant deviations in near-ban-gap luminescence peak positions from the band gap established in absorption, in agreement with detailed balance predictions.
Influence of the current-phase relation on the critical-current-applied-magnetic-flux dependence in parallel-connected Josephson junctions
Authors: Tsang Won-Tien , Van Duzer T.
Published: February 2003

The form of the current-phase relations for the Josephson junctions is shown to have a significant influence on the relation Ic(ϑa) between critical current and applied flux for two junctions connected in parallel in a superconducting circuit. The observed one-flux-quantum periodicity and inversion symmetry of the Ic(ϑa) relation are shown to result from the fact that the current-phase, i-φ, relations of the junctions satisfy i (φ+2mπ) =i (φ) and i (−φ) =−i (φ), respectively. It is also shown that if the current-phase relations for the two junctions are different, an asymmetry appears in the Ic(ϑa).
Magnetic properties of Sm :  (Co,Cu) alloys. I. Electron microscopy
Authors: Melton K. N. , Perkins R. S.
Published: February 2003

The effect of aging on the microstructures of Sm-Co-Cu alloys is reported. It is shown that small precipitates are present within the SmCo5-type phase in as-cast material. On aging below 650 °C these precipitates are exceptionally stable, but at 800 °C they coarsen rapidly. These results are rationalized in terms of a coherent precipitate phase boundary. Macroscopic regions of the Sm2Co17-type phase contain twins and antiphase domain boundaries. The density of these defects is considerably altered by heat treatment. The observed structures are related to the magnetic properties of the alloys concerned, and in Part II a theory is developed to explain the coercivity mechanisms.
Magnetic properties of Sm(Co,Cu) alloys. II. Coercivity mechanism
Authors: Perkins R. S. , Bernasconi J. , Wiesmann H. J.
Published: February 2003

A theoretical interpretation of the hard-magnetic properties of Sm(Co,Cu)z compounds with 5<z<8.5 is presented. Based on the microstructures determined in Part I by electron microscopy for compositions z<6.0 and z≳6.0, two simplified models are considered. The first is a one-dimensional system consisting of microscopic precipitates of an Sm2Co17-like phase lying in a lattice-strained matrix of Sm(Co,Cu)5. The pinning-type coercivity and its angular and temperature dependences are considered. The second model evaluates the interaction between macroscopic Sm2Co17-like precipitates and an Sm(Co,Cu)6-type matrix typical of composition z≳6.0. The effect upon the demagnetization curves is illustrated. Despite their simple nature, both models allow order of magnitude agreement with experimental results. In addition a quantitative understanding of the influence of the various features involved is provided.
Magnetoelastic surface waves in a magnetic film–piezoelectric substrate configuration
Authors: Ganguly A. K. , Davis K. L. , Webb D. C. , Vittoria C.
Published: February 2003

This paper treats the propagation characteristics of magnetoelastic surface waves in a delay line consisting of a ferromagnetic film deposited on a piezoelectric substrate. Magnetoelastic coupling within the film and mechanical coupling between the film and substrate enables the acoustic velocity to be varied by changing the magnetic bias field. A theory to predict the dependence of the surface wave velocity upon applied dc magnetic field, material constants, and frequency is presented. The velocity change occurs predominantly in a bias field range where the static magnetization vectors are undergoing a rotation. The two orientations of the magnetic field in the sagittal plane considered exhibit significantly different characteristics. With the field parallel to the direction of propagation the velocity first decreases, attains a minimum, and then increases toward a saturation value as the external field is increased. With the field normal to the plane of the film, the velocity increases monotonically toward a saturation value with an increase in field. The calculated velocity changes are in good agreement with changes measured on a Ni-LiNbO3 delay line.
Heat-treatment behavior of the magnetic properties of epitaxial Sm0.4Y2.6Fe.3.8Ga1.2O12
Authors: Enoch R. D. , Jones M. E. , Murrell D. L. , Fiddyment P. J. , Waters D. G. P.
Published: February 2003

Magnetization, characteristic length, uniaxial anisotropy constant, and domain wall mobility of garnet films have been measured following heat treatments in the range 900–1300 °C. Changes in the properties of films heat treated in oxygen are caused mainly by the lowering of the uniaxial anisotropy constant. The activation energy for this process is 4.1±0.2 eV, which is substantially lower than a previously reported value. Heat treatment in nitrogen leads to a lowering both of the magnetization and of the uniaxial anisotropy constant. The lowering of the magnetization is caused by a redistribution of Fe3+ and Ga3+ ions among lattice sites during the cooling part of the heat-treatment cycle. Heat treatments in oxygen are slightly more effective in lowering the uniaxial anisotropy constant than heat treatments in nitrogen.
Analytic solutions for constant-tension coil shapes
Authors: Gralnick S. L. , Tenney F. H.
Published: February 2003

An analytical solution of the differential equation describing the shape of a flexible filamentary conductor (incapable of supporting bending stresses) in a toroidal magnetic field has been obtained—previously only numerical solutions were available. The solution derives from a series expansion of modified Bessel functions of integer order. The characteristics of toroidal field magnets for proposed tokamak devices are obtainable by term integration of the solution series. General expressions are given for the following coil characteristics: the conductor turn length, the solenoid inductance, the area enclosed by the coil, and the coil support dimensions. For several particular cases of interest these coil chararacteritics are obtained as closed-form analytical formulas. A new type of coil, called a compound-constant-tension coil, is proposed. It is formed by selecting and matching (point and slope) segments chosen from two or more members of the one parameter family of solution curves found for the shape equation. These coils may be supported by tension members at the intersections of the solution curves or by a compression ring support and provide a unique and highly attractive solution to the toroidal field coil centering force support problem of tokamak designs.
Determination of physical parameters and processes in hologram formation in ferroelectrics
Authors: Su S. F. , Gaylord T. K.
Published: February 2003

The material parameters and physical processes during hologram formation in ferroelectric crystals have previously been identified. Some methods (based largely on new diagnostic techniques) for evaluating these critical parameters and for quantifiying the physical processes are summarized here.
On the momentum of ferromagnetic domains
Authors: Thiele A. A.
Published: February 2003

In a previous paper it was shown that the precession of the spins in a ferromagnetic domain produces an ’’extra’’ force on the domain. In this communication it is shown that this extra force may be treated as arising from a change in momentum.
Gold decoration of precipitates in doped alkali-halide surfaces
Authors: Yacamán M. José , Bassett G. A.
Published: February 2003

Sodium-chloride crystals doped with Ca++, Fe++, and Cd++ exhibit precipitation phenomena of various phases. Gold decoration of cleaved crystal surfaces has been found to be highly sensitive to the formation of these phases. The study extended to other alkali halides and a wide range of other divalent impurity atoms.
Random walk of liquid droplets migrating in silicon
Authors: Anthony T. R. , Cline H. E.
Published: February 2003

The dislocation-induced randum walk of an aluminum-rich droplet migrating in a thermal gradient along the 〈100〉 axis in silicon is shown to lead to an appreciable mean square displacement of the droplet from is original 〈100〉 thermal trajectory over migration distances of about 1 cm. When ordered arrays of droplets are migrated to produce columnar diode arrays in silicon, this random walk causes disregistry in the arrays. The disregistry can be minimized by introducing a small off-〈100〉-axis thermal gradient superimposed on the major 〈100〉 thermal gradient. This off-axis component of the thermal gradient overwhelms dislocation intersection effects which cause random walk and leads to a uniform nonrandom displacement which preserves the registry in the columnar diode arrays.
Internal friction during ultrasonic deformation of alpha-brass
Authors: Jon M. C. , Mason W. P. , Beshers D. N.
Published: February 2003

A high-intensity ultrasonic apparatus was utilized to study the variation with strain amplitude ε of internal friction Q−1 and modulus defect ΔS/S in α-brass, as influenced by composition, grain size, and prestress. Q−1(ε) manifests three regions: I, where Q−1 is independent of ε; II, where Q−1 rises and then levels off; III, where Q−1 rises rapidly. Regions I and II are superficially similar to the Granato-Lücke regions, but different mechanisms seem to be acting; region II has not been recognized before in brass. The strain at the onset of region III, εu, is found to be proportional to the flow stress and to increase with decreasing grain size. Above εu, ΔS/S varies much faster than Q−1, both quantities increasing with increasing grain size, increasing with a small prestress, but decreasing when the prestress exceeds the yield stress. The slope m′≡d logQ−1P/d logε decreases with increasing ε, reaching values in the range 0–1 for ε≳2εu. Between εu and 2εu, m′ is sensitive to structure, increasing with zinc content and prestress, decreasing with grain size. It is concluded that the effects are due to the operation of the few Frank-Read sources most easily turned. Simple models based on this idea produce some agreement with experiment. It appears that when ε≳2εu, the loops thrown off by the source are only viscosity limited, as suggested by Frost and Ashby, reaching the grain boundaries in times of the order of 10−8 sec and piling up there in the manner described by Rosenfield and Kanninen.
Focusing of ions scattered by crystals
Authors: Mashkova E. S. , Molchanov V. A.
Published: February 2003

Angular and energy distributions of 30-keV energy argon ions scattered by (100) face of copper crystal were experimentally studied. It was found that the half-widths of the angular distributions vs azimuthal angle of target rotation exhibit dips at aligned orientations of the target relative to primary ions.
Solid-state growth of Si to produce planar surfaces
Authors: Boatright R. L. , McCaldin J. O.
Published: February 2003

Paralleling the sophisticated control of Si and GaAs growth from fluid media, we demonstrate control of Si growth using a solid growth medium. Faceted dissolution pits were first produced in a Si substrate using standard photolithographic techniques and Al metallization. Si was then evaporated onto the cold structure, depositing as amorphous material. Upon heating, the amorphous Si migrated through the solid Al and grew rapidly in the faceted pits, typically refilling them flush with the surrounding substrate. Evidence that the rapid growth occurs only while the amorphous Si is dissolving into the Al is presented.
Damping of elastic surface waves by density fluctuation on solid surfaces. II. Depth effects of density fluctuation
Authors: Nakayama Tsuneyoshi , Sakuma Tetsuro
Published: February 2003

We investigate theoretically the damping rate of elastic surface waves due to the density fluctuation on solid surfaces. In a previous work, we presented the formula for the damping rate due to density fluctuation localized on solid surfaces. We extend the previous work to allow the density fluctuation with finite depth from surface. The decay processes considered are from Rayleigh mode to Rayleigh mode and to total reflection mode. The finite depth effects of density fluctuation makes the damping rate quite different from that for the case of the density fluctuation localized on solid surfaces.
Hurter-Driffield exposure characteristics of oriented M centers in NaF
Authors: Casasent David , Caimi Frank
Published: February 2003

The dichroism of the M and MA color centers in NaF is used for data storage. Optical-density–vs–exposure (Hurter-Driffield) curves are obtained for eight NaF samples with different impurity content and doping. Lithium-doped NaF samples are found to exhibit a larger dichroism and a better sensitivity and fatigue resistance than other NaF samples.
Dynamic scattering in nematic liquid crystals under dc conditions. II. Monitoring of electrode processes and lifetime investigation
Authors: Barret S. , Gaspard F. , Herino R. , Mondon F.
Published: February 2003

The electrochemical properties of a pure liquid crystal are presented which lead to the conclusion that the nonreversible liquid crystal oxidation is the main cause of degradation in dc-driven devices. This phenomena is avoided by the use of electroactive dopants which fulfill the conditions established in Paper I. It is shown that very-long-term dynamic scattering is obtained which could afford the feasibility of dc-driven industrial devices.
Extraction and focusing of intense ion beams from a magnetically insulated diode
Authors: Humphries S. , Sudan R. N. , Wiley L.
Published: February 2003

A magnetically insulated diode has been used to produce cylindrically converging intense proton beams. By providing electron neutralization along field lines, the beams can be propagated across the magnetic field to within 1 cm of the axis. Proton currents up to 5 kA have been propagated to achieve current densities up to 70 A/cm2. Divergences less than 3° have been achieved with new plasma anode designs. Calculations are presented on the extrapolation of magnetic diodes to achieve power densities needed for ion-beam pellet-fusion breakeven.
A repulsive-field technique for obtaining the mobility-spectra of the ion species created in a corona discharge
Authors: Goldman A. , Haug R. , Latham R. V.
Published: February 2003

A repulsive-field technique has been developed for obtaining the mobility spectra of a distribution of ions present in a dynamic gas environment. It has been applied to an investigation of the negative-ion spectra of corona discharges in ambient air, oxygen, and related oxygen-nitrogen mixtures. Spectra are presented as a function of the inverse mobility (1/K); the present resolution of the technique - (1/K) is ∼ 0.1 V sec/cm2. Future applications of the technique are discussed.
Axial segregation of additives in mercury–metal-halide arcs
Authors: Fischer E.
Published: February 2003

In most arcs burning vertically in a gas mixture, axial segregation of the components is observed. This segregation can be explained by the combined action of radial diffusion and axial convection. The effect is very strong in arc plasmas which consist of large amounts of a chemically inert component together with a molecular additive of high thermal stability. For mercury arcs with admixtures of TlI, InI, NaI, and SnI2, axial concentration profiles have been calculated numerically from the theoretical model and are compared with experimental data derived from spectroscopic measurements.
Thickness and refractive-index changes associated with photodarkening in evaporated As2S3 films
Authors: Shimizu I. , Fritzsche H.
Published: February 2003

Employing a sensitive variable angle interference technique the changes in thickness Δl/l and in refractive index Δn/n accompanying the photo-induced shift of the optical absorption edge toward longer wavelengths were determined in evaporated As2S3 films. The irreversible heat or light-induced structural change was found to be associated with a decrease in thickness Δl/l=0.011±0.001 and an increase in refractive index Δn/n=0.045±0.005. Changes of l and n associated with the reversible photodarkening effect were found to be less than 0.2 and 0.5 percent, respectively.
Transport of photogenerated carriers in poly N-vinylcarbazole
Authors: Slowik John H.
Published: February 2003

Thermally stimulated current (TSC) data for PVK are interpreted according to a model which is independent of the distinction between hopping conduction and band transport. Although TSC structure shifts with both heating rate and applied field, the activation energy is found to shift with field only, as expected. Activation energy and transit time are found to agree with time-of-flight results in magnitude and less well in field dependence. In addition, TSC structure is found to contain information about the distribution of hopping transport parameters. Techniques for ascertaining that TSC response is due to photogenerated carrier transport are discussed. Comparison of TSC transport energy with dielectric spectroscopy supports the suggestion that molecular rotation may play a role in hopping transport.
Theory of thermally stimulated current in hopping systems
Authors: Chen Inan
Published: February 2003

Using the concept of thermally activated mobility, a theory is developed to calculate the thermally stimulated current (TSC) in hopping systems as a function of temperature. Unlike the existing theories which describe only the band transport systems, the present theory is applicable to both band and hopping transport systems. Various features of this ’’mobility-induced’’ TSC are illustrated with numerical examples and compared with experiments performed on polymer films (e.g., PVK). These features form the basis of a new method (reported in an earlier paper) for determination of the activation energy, and a technique for studying very low mobilities and/or very low field transport phenomena. It is also found that an observation of shift in TSC peak temperature with applied field does not necessarily imply a field-dependent activation energy.
An Auger analysis of the SiO2-Si interface
Authors: Johannessen J. S. , Spicer W. E. , Strausser Y. E.
Published: February 2003

Auger electron spectroscopy has been used in conjunction with argon ion sputtering in a study of the chemical structure of the interface region between thermally grown SiO2 and the Si substrate. The distorting effects of the electron and ion beams are dealt with in detail, and we show how the beam parameters can be chosen to minimize instrumental artifacts in the Auger spectra and the chemical depth profiles of the SiO2-Si interface. We discuss the SiO2-Si interface in terms of a morphology model which includes a natural interface roughness and inclusions of silicon in the oxide close to the interface. The width of the interface of a 1000-Å oxide grown at 1200 °C in dry O2 on Si (100) is approximately 35 Å.
Electrically initiated pulsed chemical DF-CO2 and DF lasers
Authors: Turner R. , Poehler T. O.
Published: February 2003

The time-resolved spectral output of pulsed DF and DF-CO2 chemical lasers initiated by fast electrical pulses has been investigated. Short-pulse electrical initiation of the D2+F2 mixture in the high-pressure DF-CO2 laser results in prompt laser emission from both DF and CO2 molecules in addition to the usual more energetic, but delayed, CO2 emission. Studies of the time correlation of the vibrational-rotational transitions observed in the DF and DF-CO2 systems provide evidence that the transfer of energy from DF (v?4) to CO2 involves transitions in which the rotational level change in DF is greater than one.
Bremsstrahlung-induced K-fluorescent radiation
Authors: Storm Ellery
Published: February 2003

Bremsstrahlung radiation has been used to excite nearly monoenergetic x rays in secondary targets which can be utilized to study the energy response of radiation detectors if the intensity and purity are known. A method is suggested of calculating the spectral intensity of the secondary-target radiation, including the K-fluorescent x rays, and the bremsstrahlung plus characteristic-line radiation scattered from the target. Both coherent and incoherent scatter are included in the calculation. To test the theory, bremsstrahlung radiation from an x-ray unit operating in the 100–300-kV potential range was used to excite K-fluoresecent radiation in secondary targets ranging in atomic number from 29 to 90. Both the primary and secondary spectra were measured with NaI and germanium detectors. The measured primary spectral intensities were used as input to the secondary spectral intensity calculation. Calculated secondary spectra were within 20% agreement with measurement. Optimization of the secondary-target intensity and purity is discussed as a function of target thickness, potential, and selective filtration.
Correction of distortions in spectral line profiles: Applications to electron spectroscopies
Authors: Madden H. H. , Houston J. E.
Published: February 2003

The problem of distortions in measured spectral line shapes is reviewed with special attention given to the distortions in electron spectroscopies that arise from electron-energy-loss processes in solids. Results of model calculations are presented in an evaluation of an iterative (van Cittert) method for solving the convolution equation governing the relation between the true spectrum, the measured spectrum, and the instrument response function. The measured spectrum is generated initially by convoluting the true function with a function A that represents the intensity distribution that the spectrometer system would give for a completely monoenergetic excitation originating within the sample. These calculations illustrate the effects of relative function widths and of noise on the rate and degree of convergence of the method. Techniques are developed which markedly reduce the buildup of random errors and of truncation errors during the iterations. The van Cittert deconvolution method and the techniques developed for handling errors are flexible and simple to use, requiring no assumptions as to the analytic form of the functions involved, and the method is found to converge rapidly for the kind of loss-related distortions encountered in electron spectroscopic data. Applications of the method to the results of four electron spectroscopies, i.e., x-ray continuum isochromats, Auger electron spectroscopy, core-level characteristic loss spectroscopy, and soft x-ray appearance potential spectroscopy, are discussed. The model calculations are germane to all fields of research in which solutions to the convolution integral are required.
Diagnostic forbidden lines of highly ionized elements for tokamak plasmas
Authors: Doschek G. A. , Feldman U.
Published: February 2003

The possibility of observing forbidden lines of highly ionized elements in tokamak plasmas is discussed. The forbidden lines are magnetic-dipole transitions between levels of the 2s22pk configuration of ions of the F I through B I isoelectronic sequences. Some of the forbidden lines of iron have already been found in spectra of solar flares obtained from Skylab. The 2s22p5 2P3/2-2s22p5 2P1/2 forbidden line of the F I sequence, and the 2s22p 2P1/2-2s22p 2P3/2 forbidden line of the B I sequence, are extrapolated from zinc through molybdenum. These lines fall in the wavelength region between 105 and 509 Å. The two allowed lines of the F I sequence, i.e., 2s22p5 2P3/2-2s2p6 2S1/2 and 2s22p5 2P1/2-2s2p6 2S1/2, are also extrapolated. The wavelengths of these lines fall between 38 and 87 Å. It is shown that the forbidden line of a given ion should be comparable in intensity to the allowed lines of the same ion due to transitions of the type 2s22pk-2s2pk+1 for electron densities characteristic of tokamak plasmas. The intensity ratio between the forbidden line and the allowed lines is sensitive to electron density between ≈1012 and ≈1016 cm−3. Calculations of the ratios of the forbidden to one of the allowed lines are given for Cr XVI, Fe XVIII, Fe XXII, and Ni XX. The effect of electron temperature on the ratios is also calculated. The widths of the forbidden lines allow the ion temperature of the plasma or nonthermal motions to be determined.
X-ray diffraction study of interdiffusion in bimetallic Ag/Cu thin films
Authors: Murakami M. , deFontaine D.
Published: February 2003

An x-ray diffraction technique recently developed by Houska and co-workers was applied to the problem of measuring interdiffusion at 600°C in 11.2 μ Ag/Cu bimetallic thin films prepared by vapor deposition on mica. The technique consists in matching experimental intensity bands to those calculated from assumed concentration profiles. The profiles which gave best fit in the Ag-rich layer were analyzed by means of a linear diffusion equation solved in a finite region with fixed interface. The value of 1.45×10−12 cm2/sec was obtained for the interdiffusion coefficient in the Ag-rich phase.
Thermal analysis of laser damage in thin-film photoconductors
Authors: Kruer M. , Esterowitz L. , Bartoli F. , Allen R.
Published: February 2003

A closed-form thermal model is presented which describes heat transfer in thin-film photoconductors under laser irradiation. Previously published thermal models for laser damage are not valid for thin-film detectors fabricated with thick protective layers. In these detectors it is necessary to take into account heat diffusion from the absorbing film into the protective layer as well as the substrate. The thermal model was validated by measuring the damage thresholds of PbS and PbSe photoconductors and comparing theoretical and experimental results. The model was then used to analyze the thermal response of thin-film detectors fabricated with different substrates and thermal coupling parameters. It is shown that considerable improvement in the performance of thin-film photoconductors under high thermal loading can be achieved.