Physics

The Decision To Reactivate A First-Generation Soviet Nuclear Power Plant: Conceptual And Decision-Analytic Frameworks, John M. Gleason

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

Explores a variety of factors that led to reopening the Armenian Metsamor facility notwithstanding general agreement that this is unwarranted technologically.

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Recurrent Geomagnetic Storms And Relativistic Electron Enhancements In The Outer Magnetosphere: Istp Coordinated Measurements, D. N. Baker, X. Li, N. Turner, J. H. Allen, L. F. Bargatze, J. B. Blake, R. B. Sheldon, Harlan E. Spence, R. D. Belian, G. D. Reeves, S. G. Kanekal, B. Klecker

Physics & Astronomy

New, coordinated measurements from the International Solar-Terrestrial Physics (ISTP) constellation of spacecraft are presented to show the causes and effects of recurrent geomagnetic activity during recent solar minimum conditions. It is found using WIND and POLAR data that even for modest geomagnetic storms, relativistic electron fluxes are strongly and rapidly enhanced within the outer radiation zone of the Earth's magnetosphere. Solar wind data are utilized to identify the drivers of magnetospheric acceleration processes. Yohkoh solar soft X-ray data are also used to identify the solar coronal holes that produce the high-speed solar wind streams which, in turn, cause the recurrent …

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Quantum Coherence In Small Antiferromagnets, S. E. Barnes, R. Ballou, B. Barbara, J. Strelen

Physics Articles and Papers

An antiferromagnetic particle with an excess spin j⃗ has 2 degrees of freedom. The one associated with j⃗ is ferromagnetic, while the antiferromagnetic behavior involves Néel vector n⃗. It is shown that the spin-parity effect described by Loss et al. has to do with the ferromagnetic degree of freedom and does not imply the localization of n⃗ for small enough particles for half-integer spin. It is also shown that the tunnel splitting associated with n⃗ is insensitive to applied fields.

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Electron-Impact Total Ionization Cross Sections Of Silicon And Germanium Hydrides, M. A. Ali, Y.-K. Kim, W. Hwang, N. M. Weinberger, M. Eugene Rudd

M. Eugene Rudd Publications

Electron-impact total ionization cross sections of some silicon and germanium compounds have been calculated by applying a new theoretical model that has been found to be reliable for a wide range of molecules. The new theory, the binary-encounter-Bethe (BEB) model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical molecular orbital data—binding energies, average kinetic energies, and occupation numbers—which are readily available from molecular structure codes. Total ionization cross sections of SiH, SiH₂, SiH₃, SiH₄, Si₂H₆, Si(CH₃)₄, GeH, GeH_{2 …}

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Radial Dose Model Of Ssb, Dsb, Deletions And Comparisons To Montecarlo Track Structure Simulations, Francis A. Cucinotta, H. Nikjoo, J. W. Wilson, Robert Katz, D. T. Goodhead

Robert Katz Publications

The initial lesions formed in DNA by ionizing radiation include base damage, single strand breaks (SSB), double strand breaks (DSB), DNA cross links, and deletions. Deletions occur through energy deposition and perhaps more importantly through recombination repair of DSB's. Several mechanisms for the formation of DSB's and deletions related to energy deposition can be considered. Track simulation codes have indicated the importance of clusters of ionizations in small volumes similar to the size of a nucleosome. These clusters have been related to several types of damage to DNA, including DSB and deletions resulting from multiple DSB's formed by single electron …

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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

Faculty Publications

No abstract provided.

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An Instantaneous Normal Mode Description Of Relaxation In Supercooled Liquids, T. Keyes, G. V. Vijayadamodar, Ulrich Zurcher

Physics Faculty Publications

Relaxation in supercooled liquids is formulated from the instantaneous normal modes (INM) point of view. The frequency and temperature dependence of the unstable, imaginary frequency lobe of the INM density of states, ⟨ρu(ω,T)⟩ (for simplicity we write ω instead of iω), is investigated and characterized over a broad temperature range, 10⩾T⩾0.42, in the unit density Lennard-Jones liquid. INM theories of diffusion invoke Im-ω modes descriptive of barrier crossing, but not all imaginary frequency modes fall into this category. There exists a cutoff frequency ωc such that modes with ω<ωc correspond to “shoulder potentials,” whereas the potential profiles include barrier-crossing double wells for ω>ωc. Given that only modes with ω>ωc contribute to diffusion, …

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Spinors, Jets, And The Einstein Equations, Charles G. Torre

All Physics Faculty Publications

Many important features of a field theory, e.g., conserved currents, symplectic structures, energy-momentum tensors, etc., arise as tensors locally constructed from the fields and their derivatives. Such tensors are naturally defined as geometric objects on the jet space of solutions to the field equations. Modern results from the calculus on jet bundles can be combined with a powerful spinor parametrization of the jet space of Einstein metrics to unravel basic features of the Einstein equations. These techniques have been applied to computation of generalized symmetries and “characteristic cohomology” of the Einstein equations, and lead to results such as a proof …

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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

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

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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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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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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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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Astrophysical Bounds On Global Strings, Shane L. Larson, William A. Hiscock

All Physics Faculty Publications

Global topological defects produce nonzero stress energy throughout spacetime, and as a result can have observable gravitational influence on surrounding matter. Gravitational effects of global strings are used to place bounds on their cosmic abundance. The minimum separation between global strings is estimated by considering the defects' contribution to the cosmological energy density. More rigorous constraints on the abundance of global strings are constructed by examining the tidal forces such defects will have on observable astrophysical systems. The small number of observed tidally disrupted systems indicates there can be very few of these objects in the observable Universe.

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Comparison Of The Projector Augmented-Wave, Pseudopotential, And Linearized Augmented-Plane-Wave Formalisms For Density-Functional Calculations Of Solids, N. A. W. Holzwarth, G. E. Matthews, Rodney Dunning, A. R. Tackett, Y. Zeng

Chemistry & Physics Faculty Publications

The projector augmented-wave (PAW) method was developed by Blöchl as a method to accurately and efficiently calculate the electronic structure of materials within the framework of density-functional theory. It contains the numerical advantages of pseudopotential calculations while retaining the physics of all-electron calculations, including the correct nodal behavior of the valence-electron wave functions and the ability to include upper core states in addition to valence states in the self-consistent iterations. It uses many of the same ideas developed by Vanderbilt in his "soft pseudopotential'' formalism and in earlier work by Blöchl in his "generalized separable potentials,'' and has been successfully …

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A Child's Flashlight And Rc Circuit Concepts, Matthew J. Moelter, Rand S. Worland

No abstract provided.

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Structure And Magnetism Of Multiphase Sm0.080co0.645fe0.276 Powders, V. G. Harris, M. Liou, B. N. Das, V. M. Browning, J. E. Snyder, M. Rubinstein, S. H. Lawrence, R. Littleton Iii, D. P. Pappas

Physics Publications

A Sm-poor mixture of Fe-substituted Sm₂Co₁₇, having the nominal stoichiometry of Sm_0.080Co_0.645Fe_0.276, was ball-milled to explore the possibility of enhancing its remanence through direct microstructural refinement. With milling, the Sm₂(Co_0.7Fe_0.3)₁₇ compound disassociates to a body-centered-cubic supersaturated SmCoFe solid solution and a residual SmCoFe amorphous phase. Correspondingly, the coercive field values first increase, peaking at 0.83 kOe after 180 min of milling, then decrease with continued milling to

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Ionospheric Response To An Auroral Substorm, Robert W. Schunk, L. Zhu, Jan Josef Sojka, M. D. Bowline

All Physics Faculty Publications

The response of the ionosphere to a representative auroral substorm was simulated. The response was found to be significant at all altitudes in a large spatial region near midnight magnetic local time. In this midnight region, there were T_e and T_i hot spots, substantial O⁺ → NO⁺ composition changes, non‐Maxwellian velocity distributions, transient ion upwellings, a large‐scale lowering of the F‐layer, ionization peaks that occur in the E‐region, and sharp horizontal gradients. Also, during the expansion phase, the E‐region densities increase due to auroral precipitation, while the plasma densities above 300 km decrease due to the …

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Model Study Of Ground Magnetic Signatures Of Traveling Convection Vortices, Lie Zhu, P. Gifford, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

We conducted a model study of ground magnetic signatures of traveling convection vortices (TCVs) that included both the ionospheric conductivity enhancement associated with the TCVs and the ground induction effect. We found that the localized conductivity enhancement can cause a significant distortion of the TCV current system and lead to a distortion of the ground magnetic disturbance patterns. The patterns of all three magnetic components are asymmetric, mainly in the E-W direction, and the patterns of the Z component show the strongest asymmetry (20–30%). We also found that the effect of induction currents on ground magnetic signatures of the TCVs …

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Plateau Tank Apparatus For The Study Of Liquid Bridges, Andrew Resnick, J. Iwan D. Alexander

Physics Faculty Publications

An apparatus has been constructed and used to study the equilibrium and dynamical behavior of liquid bridges under reduced effective gravity. Liquid bridges are created and manipulated using six independent computer controlled stepper motors which drive linear motion tables. The bridges are visualized with a high magnification coherent Fourier optical system and in an orthogonal view using incoherent white light. By calibrating a density hydrometer and measuring the interfacial energy between the bridge and bath, reliable Bond numbers as low as 10−4 can be created and held stable for extended periods of time. Dimensional control of the liquid bridges approaches …

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Electron-Impact Ionization Cross Sections Of Atmospheric Molecules, Y.-K. Kim, W. Hwang, N. M. Weinberger, M. A. Ali, M. Eugene Rudd

M. Eugene Rudd Publications

A theoretical model for electron-impact total ionization cross sections, which has been found to be reliable for a wide range of molecules, is applied to molecules of interest to atmospheric science. The new theory, the binary-encounter-Bethe (BEB) model, combines the binary encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical data for the ground state of the target molecule, which are readily available from molecular structure codes. Total ionization cross sections of 11 molecules, CS, CS₂, COS, CH₄, H₂S, NH₃, NO₂, N₂O, O_{3 …}

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An Embedded Ring Approach To The Vibrational Dynamics Of Amorphous Materials, John R. Dennison, T. E. Doyle

All Physics Faculty Publications

A theoretical approach has been developed to model the vibrational modes of amorphous, two-dimensional materials. The method considers that the vibrational density of states is composed primarily of states originating from embedded ring structures of medium-range order. The materials are modeled as continuous random networks comprised of a statistical distribution of symmetric, planar rings with four to eight members. The rings are treated as local structural units embedded in the material, similar to molecules within a solid. The ring potentials are approximated with a valence force model (bond-stretching and bond-angle-bending force constants) modified by a third harmonic, effective force constant …

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

Physics & Astronomy Faculty Works

No abstract provided.

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Phase Structures And Transitions In Thermotropic Liquid Crystals, Peter J. Collings

Physics & Astronomy Faculty Works

No abstract provided.

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Semiclassical Effects In Black Hole Interiors, William A. Hiscock, Shane L. Larson, Paul R. Anderson

All Physics Faculty Publications

First-order semiclassical perturbations to the Schwarzschild black hole geometry are studied within the black hole interior. The source of the perturbations is taken to be the vacuum stress-energy of quantized scalar, spinor, and vector fields, evaluated using analytic approximations developed by Page and others (for massless fields) and the DeWitt-Schwinger approximation (for massive fields). Viewing the interior as an anisotropic collapsing cosmology, we find that minimally or conformally coupled scalar fields, and spinor fields, decrease the anisotropy as the singularity is approached, while vector fields increase the anisotropy. In addition, we find that for massless fields of all spins, the …

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The Global Ionosphere-Polar Wind System During Changing Magnetic Activity, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

A time-dependent, three-dimensional, multi-ion model of the global ionosphere-polar wind system was used to study the system's response to an idealized geomagnetic storm for different seasonal and solar cycle conditions. The model covered the altitude range from 90 to 9000 km for latitudes greater than 50° magnetic in the northern hemisphere. The geomagnetic storm contained a 1-hour growth phase, a 1-hour main phase, and a 4-hour decay phase. Four storm simulations were conducted, corresponding to winter and summer solstices at both solar maximum and minimum. The simulations indicated the following: (1) O⁺ upflows typically occur in the cusp and …

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Driving A Physical Ionospheric Model With A Magnetospheric Mhd Model, Jan Josef Sojka, Robert W. Schunk, M. D. Bowline, J. Chen, S. Slinker, J. Fedder

All Physics Faculty Publications

This is the first study in which a physical ionospheric model (time-dependent ionospheric model (TDIM)) has been driven through a substorm using self-consistent magnetospheric convection electric field and auroral electron precipitation inputs. Both of these were generated from a simulation of a real substorm event using the MHD model [Fedder et al., 1995b]. Interplanetary magnetic field (IMF) data were available for 1.5 hours until the substorm breakup. Hence the substorm growth and expansion dynamics is captured in a 1.5-hour time period. As a reference against which to compare this TDIM substorm simulation, a typical climatological TDIM simulation was …

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Why Quantum Mechanics Is Complex, James Thomas Wheeler

All Physics Faculty Publications

The zero-signature Killing metric of a new, real-valued, 8-dimensional gauging of the conformal group accounts for the complex character of quantum mechanics. The new gauge theory gives manifolds which generalize curved, relativistic phase space. The difference in signature between the usual momentum space metric and the Killing metric of the new geometry gives rise to an imaginary proportionality constant connecting the momentumlike variables of the two spaces. Path integral quantization becomes an average over dilation factors, with the integral of the Weyl vector taking the role of the action. Minimal U(1) electromagnetic coupling is predicted.

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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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Full-Text Articles in Physics

The Decision To Reactivate A First-Generation Soviet Nuclear Power Plant: Conceptual And Decision-Analytic Frameworks, John M. Gleason

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

Recurrent Geomagnetic Storms And Relativistic Electron Enhancements In The Outer Magnetosphere: Istp Coordinated Measurements, D. N. Baker, X. Li, N. Turner, J. H. Allen, L. F. Bargatze, J. B. Blake, R. B. Sheldon, Harlan E. Spence, R. D. Belian, G. D. Reeves, S. G. Kanekal, B. Klecker

Physics & Astronomy

Quantum Coherence In Small Antiferromagnets, S. E. Barnes, R. Ballou, B. Barbara, J. Strelen

Physics Articles and Papers

Electron-Impact Total Ionization Cross Sections Of Silicon And Germanium Hydrides, M. A. Ali, Y.-K. Kim, W. Hwang, N. M. Weinberger, M. Eugene Rudd

M. Eugene Rudd Publications

Radial Dose Model Of Ssb, Dsb, Deletions And Comparisons To Montecarlo Track Structure Simulations, Francis A. Cucinotta, H. Nikjoo, J. W. Wilson, Robert Katz, D. T. Goodhead

Robert Katz Publications

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

Physics Publications

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

Faculty Publications

An Instantaneous Normal Mode Description Of Relaxation In Supercooled Liquids, T. Keyes, G. V. Vijayadamodar, Ulrich Zurcher

Physics Faculty Publications

Spinors, Jets, And The Einstein Equations, Charles G. Torre

All Physics Faculty Publications

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

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

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

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

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

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

Physics & Astronomy Faculty Works

Astrophysical Bounds On Global Strings, Shane L. Larson, William A. Hiscock

All Physics Faculty Publications

Comparison Of The Projector Augmented-Wave, Pseudopotential, And Linearized Augmented-Plane-Wave Formalisms For Density-Functional Calculations Of Solids, N. A. W. Holzwarth, G. E. Matthews, Rodney Dunning, A. R. Tackett, Y. Zeng

Chemistry & Physics Faculty Publications

A Child's Flashlight And Rc Circuit Concepts, Matthew J. Moelter, Rand S. Worland

Physics

Structure And Magnetism Of Multiphase Sm0.080co0.645fe0.276 Powders, V. G. Harris, M. Liou, B. N. Das, V. M. Browning, J. E. Snyder, M. Rubinstein, S. H. Lawrence, R. Littleton Iii, D. P. Pappas

Physics Publications

Ionospheric Response To An Auroral Substorm, Robert W. Schunk, L. Zhu, Jan Josef Sojka, M. D. Bowline

All Physics Faculty Publications

Model Study Of Ground Magnetic Signatures Of Traveling Convection Vortices, Lie Zhu, P. Gifford, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

Plateau Tank Apparatus For The Study Of Liquid Bridges, Andrew Resnick, J. Iwan D. Alexander

Physics Faculty Publications

Electron-Impact Ionization Cross Sections Of Atmospheric Molecules, Y.-K. Kim, W. Hwang, N. M. Weinberger, M. A. Ali, M. Eugene Rudd

M. Eugene Rudd Publications

An Embedded Ring Approach To The Vibrational Dynamics Of Amorphous Materials, John R. Dennison, T. E. Doyle

All Physics Faculty Publications

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

Physics & Astronomy Faculty Works

Phase Structures And Transitions In Thermotropic Liquid Crystals, Peter J. Collings

Physics & Astronomy Faculty Works

Semiclassical Effects In Black Hole Interiors, William A. Hiscock, Shane L. Larson, Paul R. Anderson

All Physics Faculty Publications

The Global Ionosphere-Polar Wind System During Changing Magnetic Activity, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

Driving A Physical Ionospheric Model With A Magnetospheric Mhd Model, Jan Josef Sojka, Robert W. Schunk, M. D. Bowline, J. Chen, S. Slinker, J. Fedder

All Physics Faculty Publications

Why Quantum Mechanics Is Complex, James Thomas Wheeler

All Physics Faculty Publications

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