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Articles 34411 - 34440 of 36546

Full-Text Articles in Physical Sciences and Mathematics

Absence Of Minimum Metallic Conductivity In Gd(3-X)Vxs4 At Very Low Temperature And Evidence For A Coulomb Gap, S. Washburn, Richard A. Webb, S. Von Molnar, F. Holtzberg Nov 1984

Absence Of Minimum Metallic Conductivity In Gd(3-X)Vxs4 At Very Low Temperature And Evidence For A Coulomb Gap, S. Washburn, Richard A. Webb, S. Von Molnar, F. Holtzberg

Faculty Publications

Gd(3-x)vxS4 provides a convenient analog of a compensated semiconductor in which, for x≃0.3, the mobility edge can be tuned smoothly through the Fermi energy by the application of a magnetic field. The results of a search for a minimum metallic conductivity demonstrate that, down to T=6 mK, the metal-insulator transition is smooth. In the insulating regime, the temperature dependence of the conductivity was more consistent with the theory of mutual interactions than with the theory of pure localization.

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String Induced Space Compactification, P. G. Freund, P. Oh, James Thomas Wheeler Nov 1984

String Induced Space Compactification, P. G. Freund, P. Oh, James Thomas Wheeler

All Physics Faculty Publications

Motivated by the possibility of a finite theory of gravity provided by superstrings in ten space-time dimensions, we analyze the problem of space compactification in the context of string dynamics. Such an analysis is hampered by conceptual and technical problems, stemming from the existence of the quantum string's own graviton mode on the one hand, and from Witten's observation of anomalies in a not specially chosen curves space-time on the other hand. Still, in the context of a classical local field presentation of string theory à la Nambu and Hosotani, supplemented by gravitational and Kalb-Ramond interactions, we are able to …

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Superspace Ward Identities In Supersymmetric Gauge Theories, Asim Gangopadhyaya, Darwin Chang Nov 1984

Superspace Ward Identities In Supersymmetric Gauge Theories, Asim Gangopadhyaya, Darwin Chang

Physics: Faculty Publications and Other Works

In superspace formulation of supersymmetric gauge theories, gauge invariance requires an infinite set of identities between the infinite set of renormalization constants. Using Ward identities in superspace, the same is derived. These identities at one loop level are also demonstrated.

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Central-Peak-Soft-Mode, Coupling In Ferroelectric Gd2(Moo4)3, J. Petzelt, F. Smutny, V. Katkanant, F. G. Ullman, John R. Hardy, A. A. Volkov, G. V. Kozlov, S. P. Lebedev Nov 1984

Central-Peak-Soft-Mode, Coupling In Ferroelectric Gd2(Moo4)3, J. Petzelt, F. Smutny, V. Katkanant, F. G. Ullman, John R. Hardy, A. A. Volkov, G. V. Kozlov, S. P. Lebedev

John R. Hardy Papers

Transmission measurements on Gd2(MoO4)3 in the ( 5-50)-cm-1 region were performed with use of tunable backward-wave oscillator sources (5-30 cm>-1) and a Fourier spectrometer (30-50 cm>-1). The resulting dielectric spectra show an additional low-frequency dispersion which was fitted with a standard central-peak model. Its characteristic relaxation frequency is ~20 cm>-1 and the coupling between the soft mode and central mode increases near the transition temperature. This model also accounts very well for the weak anomaly in the clamped permittivity Ec measured at 63 MHz. The same central mode …

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Cosmic Rays And The Emission-Line Regions Of Active Galactic Nuclei, Gary J. Ferland, R. F. Mushotzky Nov 1984

Cosmic Rays And The Emission-Line Regions Of Active Galactic Nuclei, Gary J. Ferland, R. F. Mushotzky

Physics and Astronomy Faculty Publications

We discuss the effects that the synchrotron emitting relativistic electrons, which are known to exist throughout many distance scales in active nuclei, could have on the emission-line regions that characterize these objects. Detailed models of both the inner, dense, broad-line region and the outer, lower density, narrow-line region are presented, together with the first models of the optically emitting gas often found within extended radio lobes. We show that, in all cases, if the relativistic gas that produces the synchrotron radio emission is mixed with the gas in the emission-line region, then significant changes in the emission-line spectrum will result. …

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The Spectral Momentum Density Of Amorphous Carbon From (E, 2e) Spectroscopy, A. L. Ritter, John R. Dennison, R. Jones Nov 1984

The Spectral Momentum Density Of Amorphous Carbon From (E, 2e) Spectroscopy, A. L. Ritter, John R. Dennison, R. Jones

All Physics Faculty Publications

The spectral momentum density of the valence band of an amorphous carbon film has been measured by (e, 2e) spectroscopy. Two "bands," energy as a function of momentum, are resolved. One extends from 23 eV below the Fermi energy to about 10 eV below EF. The other, ∼ 9 eV below EF, does not disperse significantly. Although the existence of diamond bonding in the film cannot be ruled out, the bands are more suggestive of the graphite band structure.

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Multiple Determination Of The Optical Constants Of Thin-Film Coating Materials, D. P. Arndt, R. M.A. Azzam, J. M. Bennett, J. P. Borgogno, C. K. Carniglia, W. E. Case, J. A. Dobrowolski, U. J. Gibson, T. Tuttle Hart, F. C. Ho, V. A. Hodgkin, W. P. Klapp, H. A. Macleod, E. Pelletier, M. K. Purvis, D. M. Quinn, D. H. Strome, R. Swenson, P. A. Temple, T. F. Thonn Oct 1984

Multiple Determination Of The Optical Constants Of Thin-Film Coating Materials, D. P. Arndt, R. M.A. Azzam, J. M. Bennett, J. P. Borgogno, C. K. Carniglia, W. E. Case, J. A. Dobrowolski, U. J. Gibson, T. Tuttle Hart, F. C. Ho, V. A. Hodgkin, W. P. Klapp, H. A. Macleod, E. Pelletier, M. K. Purvis, D. M. Quinn, D. H. Strome, R. Swenson, P. A. Temple, T. F. Thonn

Electrical Engineering Faculty Publications

The seven participating laboratories received films of two different thicknesses of Sc2O3 and Rh. All samples of each material were prepared in a single deposition run. Brief descriptions are given of the various methods used for determination of the optical constants of these coating materials. The measurement data are presented, and the results are compared. The mean of the variances of the Sc2O3refractive-index determinations in the 0.40–0.75-nm spectral region was 0.03. The corresponding variances for the refractive index and absorption coefficient of Rh were 0.35 and 0.26, respectively.

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The Luminosity Scale Of Cepheid Variable Stars: A Revision, Edward G. Schmidt Oct 1984

The Luminosity Scale Of Cepheid Variable Stars: A Revision, Edward G. Schmidt

Edward Schmidt Publications

The period-luminosity-color relation for classical Cepheids is discussed in terms of a recent re-determinations of the distance moduli of open clusters with Cepheid members. The distance moduli of eight clusters with well established Cepheid members were determined from Stromgren four-color and Hβ photometry of the B stars. Possible sources of systematic errors in these distance moduli are discussed. Zero points are derived from these data for the period-luminosity-color (PLC) relation on the UBV system and the period-luminosity relations for near-infrared magnitudes. The present relations yield absolute magnitudes which are fainter by 0.4-0.6 mag than those now commonly used. The source …

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Statement Of Dr. David Hafemeister Regarding The Need To Convert Domestic Research Reactors From Highly Enriched To Low-Enriched Uranium Fuels, David W. Hafemeister Oct 1984

Statement Of Dr. David Hafemeister Regarding The Need To Convert Domestic Research Reactors From Highly Enriched To Low-Enriched Uranium Fuels, David W. Hafemeister

Physics

No abstract provided.

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Surface-Wave-Induced Interference Effects In Angle-Resolved Photoemission, Peter A. Dowben, D. Heskett, E.W. Plummer, Y. Sakisaka, T.N. Rhodin, Cyrus Umrigar Oct 1984

Surface-Wave-Induced Interference Effects In Angle-Resolved Photoemission, Peter A. Dowben, D. Heskett, E.W. Plummer, Y. Sakisaka, T.N. Rhodin, Cyrus Umrigar

Peter Dowben Publications

New features are observed in normal-emission photoelectron spectra from Ni(100) in a narrow range of photon energies around 25 eV. These features are inconsistent with either direct transitions from the bulk or emission from occupied surface states or resonances. We suggest that they are a consequence of interference between the ordinary direct transition emitting an electron in the normal direction and the excitation from the same initial state into a final state that would normally be emitted from the surface at Γ― in the second surface Brillouin zone, but at this energy is trapped in a surface wave.

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Radiation Pressure And The Stability Of Broad-Line Region Clouds, Gary J. Ferland, Moshe Elitzur Oct 1984

Radiation Pressure And The Stability Of Broad-Line Region Clouds, Gary J. Ferland, Moshe Elitzur

Physics and Astronomy Faculty Publications

We discuss two constraints on the existence and stability of quasar emission-line gas. The case of a constant pressure photoionized cloud in pressure equilibrium with a surrounding hot gas is considered. We show that the radiation pressure of the internally generated line emission makes a significant contribution to the total pressure in standard broad-line region models, and that models with either a higher ionization parameter or lower gas density are dominated by radiation pressure and hence unstable. Further, clouds with ionization parameters lower than the standard value cannot be supported by any hot gas which is heated only by the …

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Some Comments On The Concepts Of Dose And Dose Equivalent, Robert Katz, Werner Hofmann Oct 1984

Some Comments On The Concepts Of Dose And Dose Equivalent, Robert Katz, Werner Hofmann

Robert Katz Publications

Although dose is the simplest and most widely used measurement of a radiation field, it does not always lead to an unambiguous estimate of response. This is reflected in the very wide range of relative biologic effectiveness (RBE) values for biological systems. The ambiguity arises from the focus on energy deposition as the source of biological effect, whether in macroscopic or microscopic volumes. The properties of the biological detector play a role equally important to the properties of the radiation field in their interaction. To predict even the most experimentally accessible biological response, cell killing, we must know the probability …

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Photoionization Of Atomic Chlorine Above The 1S Threshold, Siamak Shahabi , Anthony F. Starace, T.N. Chang Oct 1984

Photoionization Of Atomic Chlorine Above The 1S Threshold, Siamak Shahabi , Anthony F. Starace, T.N. Chang

Anthony F. Starace Publications

The total photoionization cross section of the 3p subshell of atomic chlorine is presented with use of the recently developed open-shell transition-matrix method of Starace and Shahabi. The role of electron correlations is studied by comparison with Hartree-Fock and close-coupling calculations. In contrast to 3p-subshell photoionization of argon, it is shown that, in chlorine, final-state interchannel interactions are very strong while virtual pair excitations have a weak effect on the shape of the cross section, serving mainly to reduce the discrepancy between length and velocity results. Our results are compared in detail with other theoretical results above …

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Magnetoresistance Of Small, Quasi-One-Dimensional, Normal-Metal Rings And Lines, C. P. Umbach, S. Washburn, R. B. Laibowitz, Richard A. Webb Oct 1984

Magnetoresistance Of Small, Quasi-One-Dimensional, Normal-Metal Rings And Lines, C. P. Umbach, S. Washburn, R. B. Laibowitz, Richard A. Webb

Faculty Publications

The magnetoresistance of sub-0.4-μm-diam Au and Au60Pd40 rings was measured in a perpendicular magnetic field at temperatures as low as 5 mK in search of simple, periodic resistance oscillations that would be evidence of flux quantization in normal-metal rings. However, instead of simple oscillations, a very complex structure developed in the magnetoresistance at low temperatures. Fourier analysis of all the data did not reveal convincing evidence for flux quantization in the rings. Complex structure similar to that observed in the rings was also found in the magnetoresistance of short, narrow, Au and Au60Pd …

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Rare-Earth—Gallium—Iron Glasses. Ii. Anomalous Magnetic Hysteresis In Alloys Based On Pr, Nd, And Sm , S.G. Cornelison, J.G. Zhao, David J. Sellmyer Sep 1984

Rare-Earth—Gallium—Iron Glasses. Ii. Anomalous Magnetic Hysteresis In Alloys Based On Pr, Nd, And Sm , S.G. Cornelison, J.G. Zhao, David J. Sellmyer

David Sellmyer Publications

Giant magnetic coercivity is reported in several metallic glasses of the form (R80G20)100-xFex where R represents Pr, Nd, or Sm, G represents Ga or Au, and 15≤x≤30. An unusual temperature variation of the coercive field is observed showing peaks at intermediate temperatures (≃90 K). In contrast to similar glasses based on heavy rare-earth metals, these glasses exhibit significant chemical short-range order and even phase separation as is shown by the Mössbauer effect and other measurements. The results are consistent with a recent theory which predicts that large coercivity can result from the presence …

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Magnetic Properties And Chemical Short-Range Order In Fe-Pd-Based Metallic Glasses , J.G. Zhao, David J. Sellmyer Sep 1984

Magnetic Properties And Chemical Short-Range Order In Fe-Pd-Based Metallic Glasses , J.G. Zhao, David J. Sellmyer

David Sellmyer Publications

High-field magnetization and ac susceptibility measurements are reported on a series of FexPd80-xSi10B10 rapidly quenched alloys for 0<~x<~80. X-ray diffraction data show that these alloys are amorphous up to at least x=40 and that the x=60 and 80 samples are partially crystalline. The ac susceptibility data can be interpreted in terms of ferromagnetic, spin-glass, and double transitions, and a qualitative magnetic phase diagram of the system is obtained. The concentration dependence of the saturation magnetization, as well as the magnetic phase diagram, exhibits sharp anomalies at about x=13. These data suggest the presence of chemical short-range order for x≳13. X-ray photoelectron and Mössbauer results are consistent with this model.

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Rare-Earth—Gallium—Iron Glasses. I. Magnetic Ordering And Hysteresis In Alloys Based On Gd, Tb, And Er , S.G. Cornelison, David J. Sellmyer Sep 1984

Rare-Earth—Gallium—Iron Glasses. I. Magnetic Ordering And Hysteresis In Alloys Based On Gd, Tb, And Er , S.G. Cornelison, David J. Sellmyer

David Sellmyer Publications

Results of magnetic measurements are presented on the new metallic glass systems (R80Ga20)100-xFex and (R80Ga20)90B10, where R denotes the heavy rare earths Gd, Tb, and Er, for x=10, 20, and 30, respectively. High-field magnetization (to 80 kOe) and ac and dc susceptibility measurements were made from 1.4 to 300 K. The Gd-Fe glasses are simple ferrimagnets with opposing Gd and Fe moments. The Gd-B glass exhibits two apparent transitions (paramagnetic—ferromagnetic—like, and ferromagnetic spin-glass) as the temperature is lowered. As Fe is added, the low-temperature transition …

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Trajectories Of An Atomic Electron In A Magnetic Field, John B. Delos, Stephen Knudson, D. W. Noid Sep 1984

Trajectories Of An Atomic Electron In A Magnetic Field, John B. Delos, Stephen Knudson, D. W. Noid

Arts & Sciences Articles

Classical trajectories of an atomic electron in a magnetic field are calculated for various values of the field strength B. Qualitative properties of these trajectories are examined. With use of a scaling law, it is shown that the equations of motion can be written in a form such that they depend upon only one parameter, which may be regarded as a reduced angular momentum (proportional to LzB13). For small values of this parameter there is an "elliptical regime" in which the trajectory may be regarded as a Kepler ellipse with orbital parameters that evolve slowly in time. For large values …

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Effects Of Magnetic And Electric Fields On Highly Excited Atoms, Charles W. Clark, K. T. Lu, Anthony F. Starace Aug 1984

Effects Of Magnetic And Electric Fields On Highly Excited Atoms, Charles W. Clark, K. T. Lu, Anthony F. Starace

Anthony F. Starace Publications

This review describes primarily recent theoretical developments on highly excited atoms in uniform external fields, and complements the experimental review of Gay in the present volume. The Zeeman and Stark effects on low-lying atomic states, on the other hand, constitute a mature field of study which has been reviewed previously by Garstang, Kollath and Standage, Bayfield, and Kleppner. Most theoretical work on highly excited states in laboratory strength fields has heretofore focused on the prototype system of atomic hydrogen, and accordingly hydrogen receives special emphasis in this article. For nonhydrogenic atoms we review theoretical work using the framework of quantum …

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Three-Reflection Halfwave And Quarterwave Retarders Using Dielectric-Coated Metallic Mirrors, T. F. Thonn, R. M.A. Azzam Aug 1984

Three-Reflection Halfwave And Quarterwave Retarders Using Dielectric-Coated Metallic Mirrors, T. F. Thonn, R. M.A. Azzam

Electrical Engineering Faculty Publications

A design procedure is described to determine the thicknesses of single-layer coatings of a given dielectric on a given metallic substrate so that a specified net phase retardance (and/or a net relative amplitude attenuation) between the p and s polarizations is achieved after three reflections from a symmetrical arrangement of three mirrors that maintain collinearity of the input and output beams. Examples are presented of halfwave and quarterwave retarders (HWR and QWR) that use a ZnS-Ag film-substrate system at the CO2-laser wavelength λ = 10.6 µm. The equal net reflectances for the p and s polarizations are computed …

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Comment On Aproaches To The Tricritical Point In Quasibinary Liquid Mixtures, Miron Kaufman, Robert B. Griffiths Aug 1984

Comment On Aproaches To The Tricritical Point In Quasibinary Liquid Mixtures, Miron Kaufman, Robert B. Griffiths

Miron Kaufman

No abstract provided.

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26th Rocky Mountain Conference Aug 1984

26th Rocky Mountain Conference

Rocky Mountain Conference on Magnetic Resonance

Program and abstracts from the 26th annual meeting of the Rocky Mountain Conference, co-sponsored by the Rocky Mountain Section of the Society for Applied Spectroscopy and the Rocky Mountain Chromatography Discussion Group. Held in Denver, Colorado, August 7-8, 1984.

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Structure, Morphology And Crystal Growth Of Bacterial Magnetite, Stephen Mann, Richard B. Frankel, Richard P. Blakemore Aug 1984

Structure, Morphology And Crystal Growth Of Bacterial Magnetite, Stephen Mann, Richard B. Frankel, Richard P. Blakemore

Physics

Recent high-resolution transmission electron microscopy (HRTEM) studies of the structure and morphology of bacterial magnetite (Fe3O4) crystals isolated from a magnetotactic coccus1 and from an unidentified bacterium extracted from sediment2 have shown the crystals to be well ordered single-domain particles with a morphology based on a hexagonal prism of {011} faces truncated by specific low index planes. We report here a HRTEM study of intact magnetite crystals (magnetosomes) in the microaerophilic bacterium Aquaspirillum magnetotacticum, grown in pure culture3,4. Our aim has been to investigate the structure, morphology and crystal growth of …

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Pseudodimensional Variation And Tricriticality Of Potts Models By Hierarchical Breaking Of Translational Invariance, Miron Kaufman, Mehran Kardar Aug 1984

Pseudodimensional Variation And Tricriticality Of Potts Models By Hierarchical Breaking Of Translational Invariance, Miron Kaufman, Mehran Kardar

Miron Kaufman

Potts models with equivalent- and nearest-neighbor interactions are solved exactly on Cayley trees. A parameter D is identified that plays a role similar to the spatial dimension on Bravais lattices. Breaking translational symmetry by the Cayley-tree hierarchy reduces D, leading to a changeover in the order of the phase transition via a novel tricritical point.

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Angular Differential And Total Cross Sections For The Excitation Of Atomic Hydrogen To Its N=2 Level By 25-150-Kev Hydrogen Molecular Ions, Jerry Peacher, Paul J. Martin, Denver G. Seely, Judith E. Aldag, Thomas J. Kvale, E. Redd, D. M. Blankenship, V. C. Sutcliffe, John T. Park Aug 1984

Angular Differential And Total Cross Sections For The Excitation Of Atomic Hydrogen To Its N=2 Level By 25-150-Kev Hydrogen Molecular Ions, Jerry Peacher, Paul J. Martin, Denver G. Seely, Judith E. Aldag, Thomas J. Kvale, E. Redd, D. M. Blankenship, V. C. Sutcliffe, John T. Park

Physics Faculty Research & Creative Works

Experimentally and theoretically determined differential and total cross sections are reported for excitation of atomic hydrogen to its n=2 level by 25-150-keV hydrogen molecular ions. The differential cross sections decrease 3-4 orders of magnitude over the measured center-of-mass scattering-angular range from 0 to 4.5 mrad. The results of a first Born approximation and two other theoretical calculations based upon the Glauber approximation are presented and compared with the experimental results. Both calculations based on the Glauber approximation agree fairly well with the experimental results. The Born approximation agrees moderately well with the experimental results at the very small scattering angles …

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Speed Of The Photorefractive Effect In A Batio3 Single Crystal, Stephen Ducharme, Jack Feinberg Aug 1984

Speed Of The Photorefractive Effect In A Batio3 Single Crystal, Stephen Ducharme, Jack Feinberg

Stephen Ducharme Publications

We present data on the speed of light-induced refractive index changes in a BaTiO3 single crystal. The light-induced erasure rate of a refractive index grating is shown to depend on optical intensity as I x where x<1. The exponent x depends weakly on temperature and increases from 0.62±0.02 to 0.71±0.02 when the temperature is varied between 12 and 40 °C. The sublinear dependence of rate on intensity implies that higher optical intensity is required to achieve high-speed operation of BaTiO3 devices than previously thought. The dark erasure rate has an anomolously strong temperature dependence; it increases by a factor of …

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Bags Vs. Strings: Hadrons In Type I And Type Ii Superconducting Vacua, V. Parameswaran Nair, C. Rosenzweig Aug 1984

Bags Vs. Strings: Hadrons In Type I And Type Ii Superconducting Vacua, V. Parameswaran Nair, C. Rosenzweig

Publications and Research

Two popular models for hadronic structure are bags and strings. Both involve analogies with superconductivity. We claim that the most appropriate analogies are type I superconductors for bags and type II superconductors for strings. The structures of hadrons is somewhat different for the two situations. In principle, and in practice in the real world, it is the similarities which are most important. These include linear confining potentials, linearly rising Regge trajectories and short distance Coulomb potentials. These are all generic properties of bound states in a superconductor and the main distinctions between bags and strings is under what circumstances these …

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Spin Systems On Hierarchical Lattices. Ii. Some Examples Of Soluble Models, Miron Kaufman, Robert B. Griffiths Jul 1984

Spin Systems On Hierarchical Lattices. Ii. Some Examples Of Soluble Models, Miron Kaufman, Robert B. Griffiths

Miron Kaufman

Several examples are given of soluble models of phase-transition phenomena utilizing classical discrete spin systems with nearest-neighbor interaction on hierarchical lattices. These include critical exponents which depend continuously on a parameter, the Potts model on a lattice with two different coupling constants, surface tension, and excess free energy of a line of defects. In each case we point out similarities and differences with a corresponding Bravais-lattice model.

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Duality And Potts Critical Amplitudes On A Class Of Hierarchical Lattices, Miron Kaufman Jul 1984

Duality And Potts Critical Amplitudes On A Class Of Hierarchical Lattices, Miron Kaufman

Miron Kaufman

By using the duality transformation on a class of hierarchical lattices, I show that the Potts critical amplitudes above and below the critical temperature are equal. Logarithmic modifications of the power-law singularity occur when the exponent 2—alpha is an even integer, but do not occur when 2—alpha equals an odd integer.

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Inverting The Ratio Of The Complex Parallel And Perpendicular Reflection Coefficients Of An Absorbing Substrate Using A Transparent Thin-Film Coating, R. M.A. Azzam Jul 1984

Inverting The Ratio Of The Complex Parallel And Perpendicular Reflection Coefficients Of An Absorbing Substrate Using A Transparent Thin-Film Coating, R. M.A. Azzam

Electrical Engineering Faculty Publications

An absorbing substrate can be coated with a transparent thin film of refractive index N1 (within a certain range) and thickness d such that the ratio of complex reflection coefficients for the p_and s polarizations of the film-covered substrate ρ = Rp/Rs is the inverse of that of the film-free substrate ρ¯ = R¯p/R¯s at an angle of incidence ø. A method to determine the relationship among ø, N1, and d that inverts ρ (i.e., makes ρ = 1/ρ¯) for a given substrate at a given wavelength is described and is …

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