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Articles 31441 - 31470 of 36571

Full-Text Articles in Physical Sciences and Mathematics

The Time Evolution Of Unstable Monopoles, Moataz Emam Jan 1997

The Time Evolution Of Unstable Monopoles, Moataz Emam

Moataz Emam

No abstract provided.

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Atomic And Electronic Structures Of Neutral And Charged Boron And Boron-Rich Clusters, J. Niu, B. K. Rao, P. Jena Jan 1997

Atomic And Electronic Structures Of Neutral And Charged Boron And Boron-Rich Clusters, J. Niu, B. K. Rao, P. Jena

Physics Publications

Ab initio molecular orbital theory based on both density functional formalism and quantum chemical methods has been used to calculate the equilibrium geometries, binding energies, ionization potentials, fragmentation patterns, and electronic structures of neutral and charged boron clusters containing up to six atoms. Calculations have also been performed on restricted geometries for BnX (n=1,5,12; X=Be, B, C) and B20 clusters to see if clusters can be designed so as to increase their stability. Energetics of doubly chargedB++n clusters have also been studied to find the critical size for Coulomb explosion. The results are compared with existing experimental and theoretical data.

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Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras Jan 1997

Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras

Faculty Publications

No abstract provided.

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Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy Jan 1997

Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy

Faculty Publications

The direct simulation Monte Carlo (DSMC) method is used to solve the three-dimensional nano-scale gas film lubrication problem between a gas bearing slider and a rotating disk, and this solution is compared to the numerical solution of the compressible Reynolds equations with the slip flow correction based on the linearized Boltzmann equation as presented by Fukui and Kaneko [molecular gas film lubrication (MGL) method] [ASME J. Tribol. 110, 253 (1988)]. In the DSMC method, hundreds of thousands of simulated particles are used and their three velocity components and three spatial coordinates are calculated and recorded by using a hard-sphere collision …

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Real Time 3-D Video Moire Inspection System With Enhanced Depth Resolution, Donald W.W. Dawson, Chris L. Hart, Bernard R. Gilbert, Gary L. Wallace, Joel H. Blatt Jan 1997

Real Time 3-D Video Moire Inspection System With Enhanced Depth Resolution, Donald W.W. Dawson, Chris L. Hart, Bernard R. Gilbert, Gary L. Wallace, Joel H. Blatt

Aerospace, Physics, and Space Science Faculty Publications

A variable resolution video machine vision systems has been built which generates twice the number of depth contours for a given grating spacing as a conventional moiré system. This variable resolution system uses a Mach-Zender interferometer to project interference fringes onto a reference surface and onto a target surface. Video images of the two structurally illuminated surfaces are mixed in a video mixer with the resulting output being moiré contours which are the intersections of the two surfaces. If the reference surface is a flat plate, we get equal depth contours of the target surface, and if the reference surface …

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Constraints On The Production Of Ultra–High-Energy Cosmic Rays By Isolated Neutron Stars, Aparna Venkatesan, M Coleman Miller, Angela V. Olinto Jan 1997

Constraints On The Production Of Ultra–High-Energy Cosmic Rays By Isolated Neutron Stars, Aparna Venkatesan, M Coleman Miller, Angela V. Olinto

Physics and Astronomy

The energetics, spectrum, and composition of cosmic rays with energies below ~1015 eV are fairly well explained by models involving supernova shocks. In contrast, no widely accepted theory exists for the origin of ultra-high-energy cosmic rays (UHECRs), which have energies above 1015 eV. Instead of proposing a specific model, here we place strong constraints on any model of UHECRs involving isolated neutron stars (no companions). We consider the total power requirements and show that the only viable power source associated with isolated neutron stars is rotation. Mechanisms based on accretion from the interstellar medium fall short of the …

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Depth Measurement Of Doped Semiconductors Using The Hall Technique, G. C. Desalvo, David C. Look, Christopher A. Bozada, J. L. Ebel Jan 1997

Depth Measurement Of Doped Semiconductors Using The Hall Technique, G. C. Desalvo, David C. Look, Christopher A. Bozada, J. L. Ebel

Physics Faculty Publications

No abstract provided.

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Identification Of Electron-Irradiation Defects In Semi-Insulating Gaas By Normalized Thermally Stimulated Current Measurements, David C. Look, Z-Q. Fang, Joseph W. Hemsky, P. Kengkan Jan 1997

Identification Of Electron-Irradiation Defects In Semi-Insulating Gaas By Normalized Thermally Stimulated Current Measurements, David C. Look, Z-Q. Fang, Joseph W. Hemsky, P. Kengkan

Physics Faculty Publications

No abstract provided.

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Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy Jan 1997

Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy

Alejandro Garcia

The direct simulation Monte Carlo (DSMC) method is used to solve the three-dimensional nano-scale gas film lubrication problem between a gas bearing slider and a rotating disk, and this solution is compared to the numerical solution of the compressible Reynolds equations with the slip flow correction based on the linearized Boltzmann equation as presented by Fukui and Kaneko [molecular gas film lubrication (MGL) method] [ASME J. Tribol. 110, 253 (1988)]. In the DSMC method, hundreds of thousands of simulated particles are used and their three velocity components and three spatial coordinates are calculated and recorded by using a hard-sphere collision …

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Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras Jan 1997

Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras

Alejandro Garcia

No abstract provided.

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Maximum Individual & Vicinity-Average Dose For A Geologic Repository Containing Radioactive Waste, Thomas H. Pigford Jan 1997

Maximum Individual & Vicinity-Average Dose For A Geologic Repository Containing Radioactive Waste, Thomas H. Pigford

RISK: Health, Safety & Environment (1990-2002)

Explains the basis for his strong dissent to an NAS report on Yucca Mountain.

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Academy Recommendations On The Proposed Yucca Mountain Waste Repository: Overview And Criticisms, Kristin S. Shrader-Frechette Jan 1997

Academy Recommendations On The Proposed Yucca Mountain Waste Repository: Overview And Criticisms, Kristin S. Shrader-Frechette

RISK: Health, Safety & Environment (1990-2002)

Offers alternative criticism of the NAS report.

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Momentum Spectra For Single And Double Electron Ionization Of He In Relativistic Collisions, C. J. Wood, Ronald E. Olson, W. Schmitt, R. Moshammer, J. Ullrich Jan 1997

Momentum Spectra For Single And Double Electron Ionization Of He In Relativistic Collisions, C. J. Wood, Ronald E. Olson, W. Schmitt, R. Moshammer, J. Ullrich

Physics Faculty Research & Creative Works

The complete momentum spectra for single and double ionization of He by [Formula Presented] [Formula Presented] [Formula Presented] have been investigated using a classical trajectory Monte Carlo method corrected for the relativistic projectile. The [Formula Presented] electron-electron interaction has been included in the post-collision region for double ionization to incorporate the effects of both the nuclear-electron and electron-electron ionizing interactions, and to access the effects of electron correlation in the electron spectra. Experimental measurements were able to determine the longitudinal momentum spectra for single ionization; these observations are in accordance with the theoretical predictions for the three-body momentum balance between …

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Complete Momentum Balance For Single Ionization Of Helium By Fast Ion Impact: Experiment, R. Moshammer, J. Ullrich, H. Kollmus, W. Schmitt, M. Unverzagt, H. Schmidt-Böcking, C. J. Wood, Ronald E. Olson Jan 1997

Complete Momentum Balance For Single Ionization Of Helium By Fast Ion Impact: Experiment, R. Moshammer, J. Ullrich, H. Kollmus, W. Schmitt, M. Unverzagt, H. Schmidt-Böcking, C. J. Wood, Ronald E. Olson

Physics Faculty Research & Creative Works

The collision dynamics of He single ionization by [Formula Presented] impact was explored using the reaction microscope of the Gesellschaft für Schwerionenforschung, a high-resolution integrated multielectron recoil-ion momentum spectrometer. The complete three-particle final-state momentum distribution (nine Cartesian components [Formula Presented]) was imaged with a resolution of [Formula Presented] by measuring the three momentum components of the emitted electron and the recoiling target ion in coincidence. The projectile energy loss has been determined on a level of [Formula Presented] and projectile scattering angles as small as [Formula Presented] became accessible. The experimental data which are compared with results of classical trajectory …

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Observation Of Upper Tropospheric Sulfur Dioxide- And Acetone-Pollution: Potential Implications For Hydroxyl Radical And Aerosol Formation, F. Arnold, J. Schneider, K. Gollinger, H. Schlager, P. Schulte, Donald E. Hagen, Philip D. Whitefield, Peter F. J. Van Velthoven Jan 1997

Observation Of Upper Tropospheric Sulfur Dioxide- And Acetone-Pollution: Potential Implications For Hydroxyl Radical And Aerosol Formation, F. Arnold, J. Schneider, K. Gollinger, H. Schlager, P. Schulte, Donald E. Hagen, Philip D. Whitefield, Peter F. J. Van Velthoven

Physics Faculty Research & Creative Works

Aircraft-based measurements of sulfur dioxide, acetone, carbon dioxide, and condensation nuclei (CN) were made over the north-eastern Atlantic at upper tropospheric altitudes, around 9000 m. On October 14, 1993, strong SO 2- and acetone-pollution (both up to 3 ppbv) were observed, which were accompanied by a CO 2-enhancement of up to 6 ppmv, and large CN-concentrations of up to about 1500 cm -3 (for radii ≥ 6 nm). CN, excess CO 2, and to a lesser degree also acetone, were positively correlated with SO 2. Air mass trajectory analyses indicate, that most of the air masses …

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A System For Collecting Milligram Quantities Of Cloud Condensation Nuclei, Darryl J. Alofs, Donald E. Hagen, Steven D. Medley, Daniel R. White, John L. Schmitt, Allen L. Williams Jan 1997

A System For Collecting Milligram Quantities Of Cloud Condensation Nuclei, Darryl J. Alofs, Donald E. Hagen, Steven D. Medley, Daniel R. White, John L. Schmitt, Allen L. Williams

Mechanical and Aerospace Engineering Faculty Research & Creative Works

An Experimental System to Collect Cloud Condensation Nuclei (CCN) Onto Filters in Amounts Sufficient for Chemical Analysis is Described. This Experimental Apparatus is Designed to Process Ambient Air at a Rate of More Than 1 M3/min. Two Identical Systems Have Been Built. One is Installed in a Laboratory at Rolla, MO. the Other is Installed on an 11 M Long Trailer. the System Isolates Three Size Classes of CCN, Having Mass Median Diameters of 0.27, 0.12, and 0.075 Μm, Respectively, and Mass Collection Rates of 11.5, 1.28, and 0.13 Mg/day, Respectively. the above Sizes and Collection Rates Are Obtained from …

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Ionization Of Helium In The Attosecond Equivalent Light Pulse Of 1 Gev/Nucleon U⁹²⁺ Projectiles, R. Moshammer, W. Schmitt, J. Ullrich, H. Kollmus, A. Cassimi, R. Dörner, O. Jagutzki, R. Mann, Ronald E. Olson, H. T. Prinz, H. Schmidt-Böcking, L. Spielberger Jan 1997

Ionization Of Helium In The Attosecond Equivalent Light Pulse Of 1 Gev/Nucleon U⁹²⁺ Projectiles, R. Moshammer, W. Schmitt, J. Ullrich, H. Kollmus, A. Cassimi, R. Dörner, O. Jagutzki, R. Mann, Ronald E. Olson, H. T. Prinz, H. Schmidt-Böcking, L. Spielberger

Physics Faculty Research & Creative Works

Single and double ionization of helium by 1 GeV/nucleon U92+ impact was explored in a kinematically complete experiment. The relativistic ion generates a subattosecond (10−18s) superintense (I > 1019W/cm2) electromagnetic pulse, which is interpreted as a field of equivalent photons (Weizsäcker-Williams method). Cross sections, the emission characteristics of ions and electrons as well as momentum balances, are quantitatively discussed in terms of photoionization of the atom in this broadband, ultrashort virtual photon field. © 1997 The American Physical Society.

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Preferential Bonding Orientations Of Ferrocene On Surfaces, C. Waldfried, D. Welipitiya, C. W. Hutchings, H. S. V. De Silva, Gordon A. Gallup, Peter A. Dowben, W. W. Pai, Jiandi Zhang, J. F. Wendelken, N. M. Boag Jan 1997

Preferential Bonding Orientations Of Ferrocene On Surfaces, C. Waldfried, D. Welipitiya, C. W. Hutchings, H. S. V. De Silva, Gordon A. Gallup, Peter A. Dowben, W. W. Pai, Jiandi Zhang, J. F. Wendelken, N. M. Boag

Peter Dowben Publications

We have measured the molecular orientation and bonding of adsorbed ferrocene on Ag(100) and Cu(100) using angle-resolved photoemission spectroscopy (ARPES). The results for molecular adsorption on Ag(100) are complemented by high-resolution electron energy loss spectroscopy (HREELS) measurments and ab initio calculations for the ferrocene vibrational modes. The measurements indicate that ferrocene adsorbs on Ag(100) with the molecular axis perpendicular to the surface. In contrast, as indicated using ARPES and scanning tunneling microscopy, ferrocene adsorbed on the Cu(100) surface is oriented with the molecular axis parallel with the surface. Model calculations allow us to assign all of the observed vibrational modes …

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Inner-Shell Excitation Spectroscopy Of Closo-Carboranes, Adam P. Hitchcock, Stephen G. Urquhart, Alex T. Wen, A. L. David Kilcoyne, Tolek Tyliszczak, Eckart Rühl, Nobuhiro Kosugi, John D. Bozek, James T. Spencer, David N. Mcilroy, Peter A. Dowben Jan 1997

Inner-Shell Excitation Spectroscopy Of Closo-Carboranes, Adam P. Hitchcock, Stephen G. Urquhart, Alex T. Wen, A. L. David Kilcoyne, Tolek Tyliszczak, Eckart Rühl, Nobuhiro Kosugi, John D. Bozek, James T. Spencer, David N. Mcilroy, Peter A. Dowben

Peter Dowben Publications

Oscillator strength spectra in the region of B 1s and C 1s excitation of three isomeric carborane cage compounds [closo-1,2-orthocarborane, closo-1,7-metacarborane, closo-1,12-paracarborane (C2B10H12)] have been derived from inner-shell electron energy loss spectra (ISEELS) recorded under electric dipole-scattering conditions. Total ion yield spectra recorded at high resolution with synchrotron radiation are also reported. The spectral features are assigned on the basis of comparisons with spectral predictions derived from the results of ab initio and semiempirical (extended Hückel) molecular orbital calculations. The isomeric and core level variations in the discrete core excitations …

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The Interaction Of A Point Vortex With A Wall-Bounded Vortex Layer, Oliver V. Atassi, Andrew J. Bernoff, Seth Lichter Jan 1997

The Interaction Of A Point Vortex With A Wall-Bounded Vortex Layer, Oliver V. Atassi, Andrew J. Bernoff, Seth Lichter

All HMC Faculty Publications and Research

The interaction of a point vortex with a layer of constant vorticity, bounded below by a wall and above by an irrotational flow, is investigated as a model of vortex–boundary layer interaction. This model calculates both the evolution of the interface which separates the vortex layer from the irrotational flow and the trajectory of the vortex. In order to determine the conditions which lead to sustained unsteady interaction, three cases are investigated where the mutual interaction between the vortex and interface is initially assumed to be weak. (i) When a weak point vortex lies outside the layer, the vortex moves …

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Prediction Of Firing Pin Shape And 3d Matching Of Shells And Firing Pins Based On Firing Pin Impressions In Primers, Donald W. Dawson, Chris Hart, Bernard S. Gilbert Iii, Rafael A. Andrade, Joel H. Blatt Jan 1997

Prediction Of Firing Pin Shape And 3d Matching Of Shells And Firing Pins Based On Firing Pin Impressions In Primers, Donald W. Dawson, Chris Hart, Bernard S. Gilbert Iii, Rafael A. Andrade, Joel H. Blatt

Aerospace, Physics, and Space Science Faculty Publications

A variable resolution video machine vision system has been built which will determine the 3-D shape of a firing pin from the dent it has made in the primer of a shell. The system can also compare primer dents in different shells and determine if a 3-D match exists. A real time optical 3-D shape recognition feature allows the operator to align the shells, determine if there is a match, and quantify the quality of the 3-D match. The system uses a laser interferometer to project variable spatial frequency structural illumination on the shells which are viewed by video cameras. …

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Projectile Charge-State Dependence On Final-State Momentum Distributions For Single Ionization Of Helium, C. J. Wood, C. R. Feeler, Ronald E. Olson Jan 1997

Projectile Charge-State Dependence On Final-State Momentum Distributions For Single Ionization Of Helium, C. J. Wood, C. R. Feeler, Ronald E. Olson

Physics Faculty Research & Creative Works

Single-ionization cross sections and final-state momentum distributions have been calculated for the single-ionization collision reactions H[Formula Presented], [Formula Presented], He[Formula Presented], C[Formula Presented], and C[Formula Presented] + He at 100 keV/u. The classical trajectory Monte Carlo method has been used with a Wigner distribution to improve both the He electron classical radial and momentum distributions. Final-state ionized electron momenta are projected into a collision plane defined by the initial projectile momentum and the final transverse component of the He[Formula Presented] recoil momentum, with the results displayed differentially in various components of electron and recoil momenta. Positively charged projectile impact shows …

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Comment On “Electronic Structure Of Insulating Salts Of The-(Bedt-Ttf Family Studied By Low-Temperature Specific-Heat Measurements”, Nathanael Fortune, Yu V. Sushko Jan 1997

Comment On “Electronic Structure Of Insulating Salts Of The-(Bedt-Ttf Family Studied By Low-Temperature Specific-Heat Measurements”, Nathanael Fortune, Yu V. Sushko

Physics: Faculty Publications

Recently reported specific-heat measurements by Nakazawa and Kanoda between 20 and 50 K show no evidence for an expected antiferromagnetic ordering transition in the quasi-two-dimensional (2D) molecular conductor (Formula presented)-(BEDT-TTF)(Formula presented)Cu[N(CN)(Formula presented)]Cl [Y. Nakazawa and K. Kanoda, Phys. Rev. B 53, R8875 (1996)]. Although the absence of an observable transition was taken as evidence for 2D short-range ordering at elevated temperatures, even a small increase in pressure from the application of the grease used to mount the sample would shift this magnetic transition below 20 K. In their paper, Nakazawa and Kanoda erroneously assume that pressure-induced effects can be ruled …

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Lithium Bonding Interaction In H2Cy⋯Lif (Y=O,S) Complexes: A Theoretical Probe, Salai Cheettu Ammal, P. Venuvanalingam, S. Pal Jan 1997

Lithium Bonding Interaction In H2Cy⋯Lif (Y=O,S) Complexes: A Theoretical Probe, Salai Cheettu Ammal, P. Venuvanalingam, S. Pal

Faculty Publications

Ab initio calculations at 6-31++G(d,p) level have been done on H2CY⋯LiF (Y=O,S) complexes choosing ten possible orientations in each complex. The effect of correlation on complex binding energies has been studied via single point MP2 (full) calculations done on 6-31++G(d,p) geometry. Binding energies have been corrected for basis set superposition error. Frequency calculations confirm that H2CO⋯LiF and H2CS⋯LiF complexes have three and two stable forms, respectively. The most stable form in each complex has been found to have a strong lithium bonding interaction and a secondary hydrogen bondinginteraction. NBO analysis has revealed that in this form oxygen donates nσ lone …

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Semiclassical Picture Of Collision-Induced Λ-Doublet Transitions In Diatomic Molecules, Laurie J. Kovalenko, J. B. Delos Jan 1997

Semiclassical Picture Of Collision-Induced Λ-Doublet Transitions In Diatomic Molecules, Laurie J. Kovalenko, J. B. Delos

Arts & Sciences Articles

We investigate collision-induced Λ-doublet transitions in a system similar to NO+Ar, based on a semiclassical model in which nuclear motion is treated classically and electronic motion quantum mechanically. We present a picture of this process by monitoring〈Λ〉, the expectation value of the projection of electronic orbital-angular momentum onto the molecular NO axis, over the duration of the collision. In a typical collision, the interaction with Ar would cause the electronic orbital-angular momentum to precess about the rotating NO–Ar vector. However, since this angular momentum is locked tightly to the diatomic axis, it is restricted to oscillation along this axis. This …

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General Remarks On Spectral Entropy Vs. Statistical Entropy, John D. Ramshaw Jan 1997

General Remarks On Spectral Entropy Vs. Statistical Entropy, John D. Ramshaw

Physics Faculty Publications and Presentations

Crepeau and Herzel [1] (CH) have recently compared the spectral entropy of Powell and Percival [2] with the standard statistical (Boltzmann-Gibbs-Shannon) entropy in three simple physical systems. Here we compare and contrast these two entropies in a more general way by considering their values for an arbitrary stationary process X(t).

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Optical Imaging Of Carrier Dynamics In Silicon With Subwavelength Resolution, Andres H. La Rosa, B. I. Yakobson, H. D. Hallen Jan 1997

Optical Imaging Of Carrier Dynamics In Silicon With Subwavelength Resolution, Andres H. La Rosa, B. I. Yakobson, H. D. Hallen

Physics Faculty Publications and Presentations

Characteristic rate variations of carrier processes are imaged using near-field scanning optical microscopy. We couple both a visible pump and an infrared probe light through a subwavelength aperture to investigate the interband recombination and intraband diffusion of excess carriers in oxidized silicon. Typical values of the locally measured life time constants agree well with those obtained by conventional space-averaged techniques. Moreover, the images locate defects, reveal variations, and can map the regions in which a recombination process is active.

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Effect Of Diurnal Convection On Trapped Thermal Plasma In The Outer Plasmasphere, Mark Anthony Reynolds, G. Ganguli, J.A. Fedder, D.J. Melendez-Alvira Jan 1997

Effect Of Diurnal Convection On Trapped Thermal Plasma In The Outer Plasmasphere, Mark Anthony Reynolds, G. Ganguli, J.A. Fedder, D.J. Melendez-Alvira

Publications

A kinetic, multi‐species model of the plasmasphere is constructed that includes the effect of convection and corotation electric fields on trapped particles in drifting flux tubes. The resulting morphology of the outer plasmasphere is significantly different from the morphology obtained using the assumption of diffusive equilibrium. The difference is due primarily to the contraction and expansion of the region of velocity space accessible to the trapped particles, and has implications for the interpretation of remote sensing experiments.

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Handbook Of Liquid Crystal Research, Peter J. Collings, J. S. Patel Jan 1997

Handbook Of Liquid Crystal Research, Peter J. Collings, J. S. Patel

Physics & Astronomy Faculty Works

No abstract provided.

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Point And Line Disclinations In Models Of The Blue Phases, Peter J. Collings Jan 1997

Point And Line Disclinations In Models Of The Blue Phases, Peter J. Collings

Physics & Astronomy Faculty Works

The model of the liquid crystalline blue phases proposed by Alfred Saupe in 1969 is examined in light of the recent, successful theoretical models for these phases. Such an analysis demonstrates that Saupe's model captures all of the important features of the recent models, differing only in the density of line disclinations. The fact that Saupe proposed this model over ten years before the more recent work and without the benefit of a significant amout of new experimental evidence is testimony for his keen physical insight. Such models continue to be useful as researchers direct their attention to the less …

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