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Surface Core-Level Phonon Broadening Of Li(110), D. Mark Riffe, G. K. Wertheim Jan 2000

Surface Core-Level Phonon Broadening Of Li(110), D. Mark Riffe, G. K. Wertheim

All Physics Faculty Publications

High-resolution core-level photoemission data from the 1s level of Li(110) have been obtained between 77 and 280 K. Analysis of the data reveals a significant difference in the zero-temperature phonon broadening between the bulk and surface atoms but only a small difference in the effective surface and bulk Debye temperatures. This latter result is in good agreement with an embedded-atom-method calculation of the bulk and surface Debye temperatures of Li. Implications of these results to surface core-level phonon broadening and surface lattice dynamics of the heavier alkali metals are discussed.

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Inhibition Of The Aminopeptidase From Aeromonas Proteolytica By L-Leucinethiol: Kinetic And Spectroscopic Characterization Of A Slow, Tight-Binding Inhibitor–Enzyme Complex, David L. Bienvenue, Brian Bennett, Richard C. Holz Jan 2000

Inhibition Of The Aminopeptidase From Aeromonas Proteolytica By L-Leucinethiol: Kinetic And Spectroscopic Characterization Of A Slow, Tight-Binding Inhibitor–Enzyme Complex, David L. Bienvenue, Brian Bennett, Richard C. Holz

Physics Faculty Research and Publications

The peptide inhibitor l-leucinethiol (LeuSH) was found to be a potent, slow-binding inhibitor of the aminopeptidase from Aeromonas proteolytica (AAP). The overall potency (KI*) of LeuSH was 7 nM while the corresponding alcohol l-leucinol (LeuOH) was a simple competitive inhibitor of much lower potency (KI=17 μM). These data suggest that the free thiol is likely involved in the formation of the E·I and E·I* complexes, presumably providing a metal ligand. In order to probe the nature of the interaction of LeuSH and LeuOH with the dinuclear active site of AAP, we have …

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Measurement Of Inclusive Prompt Photon Photoproduction At Hera, J. Breitweg, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Stanek, R. Yoshida, Margarita C. K. Mattingly, G. Abbiendi, F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, N. Coppola, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Laurenti Jan 2000

Measurement Of Inclusive Prompt Photon Photoproduction At Hera, J. Breitweg, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Stanek, R. Yoshida, Margarita C. K. Mattingly, G. Abbiendi, F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, N. Coppola, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Laurenti

Faculty Publications

© 2000 Published by Elsevier Science B.V. All rights reserved. First inclusive measurements of isolated prompt photons in photoproduction at the HERA ep collider have been made with the ZEUS detector, using an integrated luminosity of 38.4 pb-1. Cross sections are given as a function of the pseudorapidity and the transverse energy (ηγ, Eγ . of the photon, for E>5 GeV in the γ p centre-of-mass energy range T T 134-285 GeV. Comparisons are made with predictions from Monte Carlo models having leading-logarithm parton showers, and with next-To-leading-order QCD calculations, using currently available parameterisations of the photon structure. For …

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Measurement Of The Helicity Of W Bosons In Top Quark Decays, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Jan 2000

Measurement Of The Helicity Of W Bosons In Top Quark Decays, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We use the transverse momentum spectrum of leptons in the decay chain t → bW with W → lν to measure the helicity of the W bosons in the top quark rest frame. Our measurement uses a tt̅ sample isolated in 106 ± 4 pb-1 of data collected in pp̅ collisions at √s = 1.8 TeV with the CDF detector at the Fermilab Tevatron. Assuming a standard V-A weak decay, we find that the fraction of W’s with zero helicity in the top rest frame is F0 = 0.91 ± 0.37(stat)± 0.13(syst), consistent with the standard model …

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Observation Of Diffractive B-Quark Production At The Fermilab Tevatron, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Jan 2000

Observation Of Diffractive B-Quark Production At The Fermilab Tevatron, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report a measurement of the fraction of b quarks produced diffractively in p̅p collisions at √s =1.8 TeV. Diffraction is identified by the absence of particles in a forward pseudorapidity region. From events with an electron of transverse momentum 9.5< pTe /c within the pseudorapidity region |η| < 1.1, the ratio of diffractive to total b-quark production rates is found to be Rbb= [0.62 ± 0.19(stat) ± 0.16(syst)]%. This result is comparable in magnitude to corresponding ratios for W and dijet production but significantly lower than expectations based on factorization.

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W Production And The Search For Events With An Isolated High-Energy Lepton And Missing Transverse Momentum At Hera, J. Breitweg, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Stanek, R. Yoshida, Margarita C. K. Mattingly, G. Abbiendi, F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, N. Coppola, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Laurenti Jan 2000

W Production And The Search For Events With An Isolated High-Energy Lepton And Missing Transverse Momentum At Hera, J. Breitweg, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Stanek, R. Yoshida, Margarita C. K. Mattingly, G. Abbiendi, F. Anselmo, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, N. Coppola, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Laurenti

Faculty Publications

© 2000 Published by Elsevier Science B.V. All rights reserved. A search for the leptonic decays of W bosons produced in the reaction e+ p → e+ W± X at a centre-of-mass energy of 300GeV has been performed with the ZEUS detector at HERA using an integrated luminosity of 47.7 pb-1. Three events consistent with W → eν decay are found, giving a cross section estimate of 0.9+10-07±0.2 pb, in good agreement with the Standard Model prediction. The corresponding 95% C.L. upper limit on the cross section is 3.3 pb. A search for the decay W → μν has a …

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Nanoscopic Switching Behavior Of Epitaxial Srbi2Ta2O9 Films Deposited By Pulsed Laser Deposition, Alexei Gruverman, A. Pignolet, K. M. Satyalakshmi, M. Alexe, N. D. Zakharov, D. Hesse Jan 2000

Nanoscopic Switching Behavior Of Epitaxial Srbi2Ta2O9 Films Deposited By Pulsed Laser Deposition, Alexei Gruverman, A. Pignolet, K. M. Satyalakshmi, M. Alexe, N. D. Zakharov, D. Hesse

Alexei Gruverman Publications

We report results on scanning force microscopy (SFM) studies of epitaxial SrBi2Ta2O9 films which, in conjunction with complementary x-ray diffraction, scanning and transmission electron microscopy data, allow us to establish direct correlation between the crystallographic structure at the submicrometer range and the nano- and macroscopic switching behavior of the films. SFM topographic analysis of the films revealed a high degree of inhomogeneity at the submicrometer level: a number of rectangular and spherical grains protruding out of the flat surface. It has been found that the ferroelectric behavior of the films is primarily due to the …

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Intrinsic Ferroelectric Coercive Field, Stephen Ducharme, V.M. Fridkin, A.V. Bune, S.P. Palto, L.M. Blinov, N.N. Petukhova, S.G. Yudin Jan 2000

Intrinsic Ferroelectric Coercive Field, Stephen Ducharme, V.M. Fridkin, A.V. Bune, S.P. Palto, L.M. Blinov, N.N. Petukhova, S.G. Yudin

Stephen Ducharme Publications

The Landau-Ginzburg theory of ferroelectricity predicts the intrinsic coercive field for polarization reversal, but the observed extrinsic coercive field is always much smaller as a result of nucleation, dynamic processes not covered by the static theory. We have realized the intrinsic coercive field for the first time, in two-dimensional Langmuir-Blodgett polymer films as thin as 1 nm. The measured coercive field is in good agreement with the theoretical intrinsic value, exhibits the expected dependence on temperature, and does not depend on thickness below 15 nm.

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Theoretical Calculations Of Magnetic Order And Anisotropy Energies In Molecular Magnets, M. R. Pederson, D. V. Porezag, J. Kortus, S. N. Khanna Jan 2000

Theoretical Calculations Of Magnetic Order And Anisotropy Energies In Molecular Magnets, M. R. Pederson, D. V. Porezag, J. Kortus, S. N. Khanna

Physics Publications

We present theoretical electronic structure calculations on the nature of electronic states and the magnetic coupling in the Mn12O12 free cluster and the Mn12O12(RCOO)16(H2O)4 molecular magnetic crystal. The calculations have been performed with the all-electron full-potential NRLMOL code. We find that the free Mn12O12cluster relaxes to an antiferromagneticcluster with no net moment. However, when coordinated by sixteen HCOO ligands and four H2O groups, as it is in the molecular crystal, we find that the ferrimagnetic ordering and geometrical and magnetic structure observed in the experiments is restored. Local Mn moments for the free and ligandated molecular magnets are presented and …

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The Optical Depth To Reionization As A Probe Of Cosmological And Astrophysical Parameters, Aparna Venkatesan Jan 2000

The Optical Depth To Reionization As A Probe Of Cosmological And Astrophysical Parameters, Aparna Venkatesan

Physics and Astronomy

Current data of high-redshift absorption-line systems imply that hydrogen reionization occurred before redshifts of about 5. Previous works on reionization by the first stars or quasars have shown that such scenarios are described by a large number of cosmological and astrophysical parameters. Here we adopt a semianalytic model of stellar reionization in order to quantify how the optical depth to reionization depends on such parameters, and combine this with constraints from the cosmic microwave background (CMB). We find this approach to be particularly useful in alleviating the well-known degeneracy in CMB parameter extraction between the optical depth to reionization and …

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Modeling The Evolution Of Meso-Scale Ionospheric Irregularities At High Latitudes, Jan Josef Sojka, L. Zhu, M. David, Robert W. Schunk Jan 2000

Modeling The Evolution Of Meso-Scale Ionospheric Irregularities At High Latitudes, Jan Josef Sojka, L. Zhu, M. David, Robert W. Schunk

All Physics Faculty Publications

The modeling of ionospheric plasma density irregularities (ΔN/N) is a necessary first step towards forecasting ionospheric scintillation effects. This modeling challenge is difficult not only because the linear‐nonlinear saturation levels of instabilities are not completely understood but also because ΔN/N often evolves on time scales which are long compared to the characteristic time constants of the instability drivers. In this study, the linear 1‐D gradient drift instability (GDI) is used in a high latitude simulation of ΔN/N evolution. For the first time snapshots (maps) of ΔN/N are presented demonstrating that it is possible to use …

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Measurements Of Electronic Properties Of Conducting Spacecraft Materials With Application To The Modeling Of Spacecraft Charging, W. Y. Chang, John R. Dennison, Parker Judd Jan 2000

Measurements Of Electronic Properties Of Conducting Spacecraft Materials With Application To The Modeling Of Spacecraft Charging, W. Y. Chang, John R. Dennison, Parker Judd

All Physics Faculty Publications

This paper describes the results of the first stage of this project, measurements of the electronic properties of conducting spacecraft materials. We begin with a description of the required measurements and specifics of the experimental methods used. A complete list of the conducting materials studied, justification of their selection for study, and a summary of the important results of the measurements is presented. This is followed by detailed measurements and analysis for one representative conductor, namely polycrystalline Au. We end with a description of incorporation of these measurements into the NASCAP database.

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Measurement Of Silicon Surface Recombination Velocity Using Ultrafast Pump-Probe Reflectivityin The Near Infrared, A. J. Sabbah, D. Mark Riffe Jan 2000

Measurement Of Silicon Surface Recombination Velocity Using Ultrafast Pump-Probe Reflectivityin The Near Infrared, A. J. Sabbah, D. Mark Riffe

All Physics Faculty Publications

We demonstrate that ultrafast pump–probe reflectivity measurements from bulk Si samples using a Ti:sapphire femtosecond oscillator (λ=800 nm) can be used to measure the Si surface recombination velocity. The technique is sensitive to recombination velocities greater than ∼104 cm s−1

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Extended Conformal Symmetry, James Thomas Wheeler Jan 2000

Extended Conformal Symmetry, James Thomas Wheeler

All Physics Faculty Publications

We show that the grading of fields by conformal weight, when built into the initial group symmetry, provides a discrete, non-central conformal extension of any group containing dilatations. We find a faithful vector representation of the extended conformal group and show that it has a scale-invariant scalar product and satisfies a closed commutator algebra. The commutator algebra contains the infinite Heisenberg and Virasoro algebras. In contrast to the classical treatment of scale invariance, covariant derivatives and gauge transformations automatically incorporate the correct conformal weights when the extended symmetry is gauged.

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Inception Of Snapover And Gas Induced Glow Discharges, J. T. Galofaro, B. V. Vayner, D. C. Ferguson, W. A. Degroot, C. D. Thomson, John R. Dennison, R. E. Davies Jan 2000

Inception Of Snapover And Gas Induced Glow Discharges, J. T. Galofaro, B. V. Vayner, D. C. Ferguson, W. A. Degroot, C. D. Thomson, John R. Dennison, R. E. Davies

All Physics Faculty Publications

Ground based experiments of the snapover phenomenon were conducted in the large vertical simulation chamber at the Glenn Research Center (GRC) Plasma Interaction Facility (PIF). Two Penning sources provided both argon and xenon plasmas for the experiments. The sources were used to simulate a variety of ionospheric densities pertaining to a spacecraft in a Low Earth Orbital (LEO) environment. Secondary electron emission is believed responsible for dielectric surface charging, and all subsequent snapover phenomena observed. Voltage sweeps of conductor potentials versus collected current were recorded in order to examine the specific charging history of each sample. The average time constant …

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Towards Testing The Maldacena Conjecture With Sdlcq, Uwe Trittmann Jan 2000

Towards Testing The Maldacena Conjecture With Sdlcq, Uwe Trittmann

Physics Faculty Scholarship

We consider the Maldacena conjecture applied to the near horizon geometry of a D1-brane in the supergravity approximation and present numerical results of a test of the conjecture against the boundary field theory calculation using supersymmetric discrete light-cone quantization (SDLCQ). We present numerical results with approximately 1000 times as many states as we previously considered. These results support the Maldacena conjecture and are within 10–15% of the predicted numerical results in some regions. Our results are still not sufficient to demonstrate convergence, and, therefore, cannot be considered to a numerical proof of the conjecture. We present a method for …

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Characterization Of Poly-Si Thin Films Deposited By Magnetron Sputtering Onto Ni Prelayers, Elena A. Guliants, Wayne A. Anderson Jan 2000

Characterization Of Poly-Si Thin Films Deposited By Magnetron Sputtering Onto Ni Prelayers, Elena A. Guliants, Wayne A. Anderson

Electrical and Computer Engineering Faculty Publications

A method of producing a polycrystalline silicon thin film on a foreign substrate without subsequent annealing has been developed. Thermally evaporated 5–100 nm thick Nifilms served as prelayers for magnetron sputtered Si thin films. A continuous film was obtained as a result of metal induced growth of polysilicon during low temperature (below 600 °C) deposition. The film uniformity is promising for large area device applications. The influence of the Ni prelayer thickness on the grain size of thus obtained films was investigated. Atomic force microscopy and cross-sectional scanning electron microscopy studies revealed features in the 150–600 nm size range while …

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Measurements Of Electronic Properties Of Conducting Spacecraft Materials With Application To The Modeling Of Spacecraft Charging, W. Y. Chang, Jr Dennison, Parker Judd Jan 2000

Measurements Of Electronic Properties Of Conducting Spacecraft Materials With Application To The Modeling Of Spacecraft Charging, W. Y. Chang, Jr Dennison, Parker Judd

Conference Proceedings

Many spacecraft system anomalies and component failures are known to result from spacecraft charging which is due to the bombardments of spacecraft by energetic electrons, ions, and photons in natural space surrounding [Hastings and Garrett, 1996; Bedingfield et al., 1996; Leach et al., 1995]. To assist spacecraft designers in accommodating and mitigating the harmful charging effects on spacecraft, NASA has developed an extensive set of engineering tools to predict the extent of charging in various spacecraft environments (for example, NASCAP/LEO, NASCAP/GEO, and POLAR) [Mandell et al., 1993]. However, current NASCAP databases lack electronic properties …

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Alkalization Of Aluminum Clusters, B. K. Rao, P. Jena Jan 2000

Alkalization Of Aluminum Clusters, B. K. Rao, P. Jena

Physics Publications

Equilibrium geometries, binding energies, ionization potentials, and electron affinities of neutral and charged Aln clusters (n⩽8) decorated with alkali atoms such as Li and K have been calculated using molecular orbital theory based on density functional formalism and generalized gradient approximation. While the electron affinities and the ionization potentials depend on size, no clear signatures of shell closings are found in this size range. Similar studies on Al5Xm  (X=Li, K, 1⩽m⩽4) also fail to provide any indication consistent with shell closings. On the other hand, the ionization potentials and electron affinities of aluminum clusters decrease with the addition of alkali …

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Classical Subharmonic Resonances In Microwave Ionization Of Lithium Rydberg Atoms, Michael W. Noel, W. M. Griffith, T. F. Gallagher Jan 2000

Classical Subharmonic Resonances In Microwave Ionization Of Lithium Rydberg Atoms, Michael W. Noel, W. M. Griffith, T. F. Gallagher

Physics Faculty Research and Scholarship

We have studied the ionization of lithium Rydberg atoms by pulsed microwave fields in the regime in which the microwave frequency is equal to or a subharmonic of the classical Kepler frequency of the two-body Coulomb problem. We have observed a series of resonances where the atom is relatively stable against ionization. The resonances are similar to those seen previously in hydrogen, but with significant quantitative differences. We also present measurements of the distribution of states that remain bound after the microwave interaction for initial states near one of the classical subharmonic resonances.

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Superlattices, Polymorphs, And Solid State Nmr Spin-Lattice Relaxation Measurements Of 2,6-Di-T-Butylnaphthalene, Arnold L. Rheingold, Joshua S. Figueroa, Cecil Dybowski, Peter A. Beckmann Jan 2000

Superlattices, Polymorphs, And Solid State Nmr Spin-Lattice Relaxation Measurements Of 2,6-Di-T-Butylnaphthalene, Arnold L. Rheingold, Joshua S. Figueroa, Cecil Dybowski, Peter A. Beckmann

Physics Faculty Research and Scholarship

Two polymorphs of 2,6-di-tert-butylnaphthalene, which differ by a factor of twelve in the number of crystallographically independent tert-butyl group environments, have been characterized by a synergistic combination of low-frequency 1H NMR spin–lattice relaxation rate measurements and conventional crystallographic structure determinations.

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Magnetic Coupling In Neutral And Charged Cr-2, Mn-2, And Crmn Dimers, N. Desmarais, F. A. Reuse, S. N. Khanna Jan 2000

Magnetic Coupling In Neutral And Charged Cr-2, Mn-2, And Crmn Dimers, N. Desmarais, F. A. Reuse, S. N. Khanna

Physics Publications

Theoreticalab initio studies of neutral, cationic and anionic Cr2, Mn2, and CrMn dimers have been carried out to explore the progression of magnetic coupling with the number of electrons. It is shown that while Cr2 and Cr−2 have antiferromagnetically coupled atomic spins, Cr+2 has a ferromagneticground state closely followed by an antiferromagnetic state. On the other hand, all Mn2 dimers are ferromagnetic, irrespective of the charge. The neutral CrMn is ferrimagnetic while the charged CrMn are antiferromagnetic. In all cases, the charged dimers are found to be more stable than the neutral ones. The results are compared with available …

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On The Bosonic Spectrum Of Qcd (1+1) With Su(N) Currents, Uwe Trittmann Jan 2000

On The Bosonic Spectrum Of Qcd (1+1) With Su(N) Currents, Uwe Trittmann

Physics Faculty Scholarship

In this note we calculate the spectrum of two-dimensional QCD. We formulate the theory with SU(Nc) currents rather than with fermionic operators. We construct the Hamiltonian matrix in DLCQ formulation as a function of the harmonic resolution K and the numbers of flavors N f and colors N c.The resulting numerical eigenvalue spectrum is free from trivial multi-particle states which obscured previous results. The well-known ’t Hooft and large N f spectra are reproduced. In the case of adjoint fermions we present some new results.

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A Comprehensive Study Of Dielectric-Conductor Junctions In Low Density Plasmas, B. V. Vayner, J. T. Galofaro, D. C. Ferguson, W. A. De Groot, C. D. Thomson, John R. Dennison, R. E. Davies Jan 2000

A Comprehensive Study Of Dielectric-Conductor Junctions In Low Density Plasmas, B. V. Vayner, J. T. Galofaro, D. C. Ferguson, W. A. De Groot, C. D. Thomson, John R. Dennison, R. E. Davies

All Physics Faculty Publications

In this paper, results are presented of an experimental and theoretical study of snapover, glow discharge, and arc phenomena for different materials immersed in argon or xenon plasmas. The effect of snapover is investigated for several metal-dielectric junctions: copper-teflon, copper-Kapton, copper-glass, aluminum-teflon, aluminum-Kapton, steel-teflon, anodized aluminum with pinholes, and copper-ceramics. I-V curves are measured, and snapover inception voltages, essential parameters (increase in current and collection area due to secondary electrons), and glow discharge inception thresholds are determined. Optical spectra are obtained for glow discharges in both argon and xenon plasmas. These spectra provide information regarding atomic species entrapped in the …

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Experimental And Theoretical Study Of The Photoelectron Spectra Of Mnox-(X=1-3) Clusters, Gennady L. Gutsev, B. K. Rao, P. Jena, Xi Li, Lai-Sheng Wang Jan 2000

Experimental And Theoretical Study Of The Photoelectron Spectra Of Mnox-(X=1-3) Clusters, Gennady L. Gutsev, B. K. Rao, P. Jena, Xi Li, Lai-Sheng Wang

Physics Publications

We report a combined experimental and theoretical investigation of MnO−x and MnOx(x=1–3) clusters. Theoretically, geometrical configurations of various isomers of the clusters were optimized and vertical detachment energies for the anions were evaluated. The ground state of MnO− was predicted to be 5Σ+, followed by an excited state (7Σ+) 0.14 eV higher in energy. The ground state of MnO−2 is 5B2, with a 3B1 isomer 0.15 eV higher. MnO−3 is predicted to be a singlet D3h cluster. Vibrationally resolved photoelectron spectra of MnO−x were measured at several photon energies and under various experimental conditions, and were interpreted based on the …

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Quantum-Well Resistivity For Perpendicular Transport In Magnetic Layered Systems, Evgeny Y. Tsymbal, David G. Pettifor Jan 2000

Quantum-Well Resistivity For Perpendicular Transport In Magnetic Layered Systems, Evgeny Y. Tsymbal, David G. Pettifor

Evgeny Tsymbal Publications

We show that quantum-well states enhance the current-perpendicular-to-planes resistivity of a metal film compared to the resistivity in the bulk at film thicknesses comparable with the mean free path due to the reduced number of conducting channels within the potential-well structure. This makes the mean free path an important parameter, which must be taken into account for the accurate treatment of results on currentperpendicular- to-plane giant magnetoresistance, rather than ignored by applying the two-current series-resistor model.

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Investigation Of The First Snapover Of Positively Biased Conductors In A Plasma, C. D. Thomson, John R. Dennison, R. E. Davies, D. C. Ferguson, J. T. Galafaro, B. V. Vayner Jan 2000

Investigation Of The First Snapover Of Positively Biased Conductors In A Plasma, C. D. Thomson, John R. Dennison, R. E. Davies, D. C. Ferguson, J. T. Galafaro, B. V. Vayner

All Physics Faculty Publications

We describe a systematic experimental investigation of the phenomenon termed "snapover." In snapover, the current collected by a positively biased conductor, surrounded by a dielectric and immersed in a plasma, increases dramatically when the conductor potential is raised above some threshold value. The phenomenon is particularly relevant to the case of high-voltage solar arrays in Earth orbit. Our experiments examined the importance of conducting material, insulating material, size and shape of the conductor, sample history, biasing rate, and condition of the dielectric surface (contamination and smoothness) to the onset potential and current jump. In addition to a primary snapover occurring …

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Using Binary Star Observations To Bound The Mass Of The Graviton, Shane L. Larson, William A. Hiscock Jan 2000

Using Binary Star Observations To Bound The Mass Of The Graviton, Shane L. Larson, William A. Hiscock

All Physics Faculty Publications

Interacting white dwarf binary star systems, including helium cataclysmic variable (HeCV) systems, are expected to be strong sources of gravitational radiation, and should be detectable by proposed space-based laser interferometer gravitational wave observatories such as LISA. Several HeCV star systems are presently known and can be studied optically, which will allow electromagnetic and gravitational wave observations to be correlated. Comparisons of the phases of a gravitational wave signal and the orbital light curve from an interacting binary white dwarf star system can be used to bound the mass of the graviton. Observations of typical HeCV systems by LISA could potentially …

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Directional Correlation In Direct And Sequential Double Ionization Of Model Atoms, Stanley L. Haan, N. Hoekema, S. Poniatowski, W. C. Liu Jan 2000

Directional Correlation In Direct And Sequential Double Ionization Of Model Atoms, Stanley L. Haan, N. Hoekema, S. Poniatowski, W. C. Liu

University Faculty Publications and Creative Works

We discuss directional dependence in the time development of spatial wavefunctions, which includes jet formation, for two-electron model atoms exposed to intense laser fields. Two competing scenarios for double ionization are evident: (1) both electrons emerge simultaneously from the core region and on the same side of the nucleus, and (2) the electrons detach on opposite sides but not simultaneously. The importance of the electron-electron repulsion contribution to the competing processes is investigated for various laser intensities.

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Actions For Biconformal Matter, Andre Wehner, James Thomas Wheeler Jan 2000

Actions For Biconformal Matter, Andre Wehner, James Thomas Wheeler

All Physics Faculty Publications

We extend 2n-dim biconformal gauge theory by including Lorentz-scalar matter fields of arbitrary conformal weight. For a massless scalar field of conformal weight zero in a torsion-free biconformal geometry, the solution is determined by the Einstein equation on an n-dim submanifold, with the stress-energy tensor of the scalar field as source. The matter field satisfies the n-dim Klein-Gordon equation.

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