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Articles 11521 - 11550 of 14643

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Observation Of The Strange Sea In The Proton Via Inclusive Φ-Meson Production In Neutral Current Deep Inelastic Scattering At Hera, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan, D. Bartsch, I. Brock Feb 2003

Observation Of The Strange Sea In The Proton Via Inclusive Φ-Meson Production In Neutral Current Deep Inelastic Scattering At Hera, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan, D. Bartsch, I. Brock

Faculty Publications

Inclusive φ(1020)-meson production in neutral current deep inelastic e+p scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 45 pb-1. The φ mesons were studied in the range 10 < Q2 < 100 GeV2, where Q2 is the virtuality of the exchanged photon, and in restricted kinematic regions in the transverse momentum, pT, pseudorapidity, η, and the scaled momentum in the Breit frame, xp. Monte Carlo models with the strangeness-suppression factor as determined by analyses of e+e- annihilation events overestimate the cross sections. A smaller value of the strangeness-suppression factor reduces the predicted cross sections, but fails to reproduce the shapes of the measured differential cross sections. High-momentum φ mesons in the current region of the Breit frame give the first direct evidence for the strange sea in the proton at low x. © 2002 Published by Elsevier Science B.V.

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Index-Matched Boundary Techniques For The Elimination Of Acoustical Resonances, Jack H. Parker, Bradley D. Duncan Feb 2003

Index-Matched Boundary Techniques For The Elimination Of Acoustical Resonances, Jack H. Parker, Bradley D. Duncan

Electro-Optics and Photonics Faculty Publications

We extend the principle of optical index of refraction to apply the concept of acoustical index for transverse acoustical wave propagation in strings. The relationship between acoustical index and mass density of the acoustic material is developed. With this theoretical link established, classic index-matching techniques are explored at acoustical boundaries. Proper selection of boundary interface segments leads to the elimination of resonant vibrationalmodes that occur in rigidly supported strings, while maintaining the nonresonant vibration response.

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A Multi-Diagnostic Investigation Of Mesospheric Bore Phenomenon, S. M. Smith, Michael J. Taylor, G. R. Swenson, C. Y. She, W. Hocking, J. Baumgardner, M. Mendillo Feb 2003

A Multi-Diagnostic Investigation Of Mesospheric Bore Phenomenon, S. M. Smith, Michael J. Taylor, G. R. Swenson, C. Y. She, W. Hocking, J. Baumgardner, M. Mendillo

All Physics Faculty Publications

Imaging measurements of a bright wave event in the nighttime mesosphere were made on 14 November 1999 at two sites separated by over 500 km in the southwestern United States. The event was characterized by a sharp onset of a series of extensive wavefronts that propagated across the entire sky. The waves were easily visible to the naked eye, and the entire event was observed for at least 5 1 2 hours. The event was observed using three wide-angle imaging systems located at the Boston University field station at McDonald Observatory (MDO), Fort Davis, Texas, and the Starfire Optical Range …

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Chemical Abundances In Broad Emission Line Regions: The "Nitrogen-Loud'' Quasi-Stellar Object Q0353-383, J. A. Baldwin, F. Hamann, K. T. Korista, Gary J. Ferland, M. Dietrich, C. Warner Feb 2003

Chemical Abundances In Broad Emission Line Regions: The "Nitrogen-Loud'' Quasi-Stellar Object Q0353-383, J. A. Baldwin, F. Hamann, K. T. Korista, Gary J. Ferland, M. Dietrich, C. Warner

Physics and Astronomy Faculty Publications

The intensity of the strong N V λ1240 line relative to C IV λ1549 or to He II λ1640 has been proposed as an indicator of the metallicity of quasi-stellar object (QSO) broad emission line regions, allowing abundance measurements in a large number of QSOs out to the highest redshifts. Previously, it had been shown that the (normally) much weaker lines N III] λ1750 and N IV] λ1486 could be used in the same way. The redshift 1.96 QSO 0353-383 has long been known to have N III] and N IV] lines that are far stronger relative to Lyα or …

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Temperature Dependence Of Droplet Nucleation In A Yukawa Fluid, Jinsong Li, Gerald Wilemski Feb 2003

Temperature Dependence Of Droplet Nucleation In A Yukawa Fluid, Jinsong Li, Gerald Wilemski

Physics Faculty Research & Creative Works

We have studied the temperature dependence of gas-to-liquid nucleation in Yukawa fluids with gradient theory and density functional theory. Each of these nonclassical theories exhibits a weaker (i.e., better) temperature dependence than classical nucleation theory. At fixed temperature, the reversible work to form a critical nucleus found from gradient theory approaches the value given by density functional theory as the supersaturation increases. At high temperatures, the two theories remain quite close over a wide range of vapor densities. As the temperature is reduced, the difference between the two theories increases with decreasing vapor density. Compared to the classical theory we …

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Zeus Next-To-Leading-Order Qcd Analysis Of Data On Deep Inelastic Scattering, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, J. Repond, R. Yoshida, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, H. Labes, D. Lelas, B. Löhr, R. Mankel, M. Martínez, I. A. Melzer-Pellmann, M. Moritz, D. Notz, M. C. Petrucci, A. Polini Jan 2003

Zeus Next-To-Leading-Order Qcd Analysis Of Data On Deep Inelastic Scattering, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, J. Repond, R. Yoshida, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, H. Labes, D. Lelas, B. Löhr, R. Mankel, M. Martínez, I. A. Melzer-Pellmann, M. Moritz, D. Notz, M. C. Petrucci, A. Polini

Faculty Publications

Next-to-leading-order QCD analyses of the ZEUS data on deep inelastic scattering together with fixed-target data have been performed, from which the gluon and quark densities of the proton and the value of the strong coupling constant (Formula presented) were extracted. The study includes a full treatment of the experimental systematic uncertainties including point-to-point correlations. The resulting uncertainties in the parton density functions are presented. A combined fit for (Formula presented) and the gluon and quark densities yields a value for (Formula presented) in agreement with the world average. The parton density functions derived from ZEUS data alone indicate the importance …

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Lattice Supersymmetry And Topological Field Theory, Simon Catterall Jan 2003

Lattice Supersymmetry And Topological Field Theory, Simon Catterall

Physics - All Scholarship

It is known that certain theories with extended supersymmetry can be discretized in such a way as to preserve an exact fermionic symmetry. In the simplest model of this kind, we show that this residual supersymmetric invariance is actually a BRST symmetry associated with gauge fixing an underlying local shift symmetry. Furthermore, the starting lattice action is then seen to be entirely a gauge fixing term. The corresponding continuum theory is known to be a topological field theory. We look, in detail, at one example - supersymmetric quantum mechanics which possesses two such BRST symmetries. In this case, we show …

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Analysis Of The Shadow-Sausage Effect Caustic, James A. Lock, Charles L. Adler, Diana Ekelman, Jonathan Mulholland, Brian Keating Jan 2003

Analysis Of The Shadow-Sausage Effect Caustic, James A. Lock, Charles L. Adler, Diana Ekelman, Jonathan Mulholland, Brian Keating

Physics Faculty Publications

We analyze the optical caustic produced by light refracted at the curved meniscus surrounding a cylindrical rod standing partially out of a liquid-filled container. When the rod is tilted from the vertical or when light is diagonally incident, the caustic is a four-cusped astroid with two of its cusps obscured by the rod's shadow. If a portion of the flat end of the rod is raised above the water level, the caustic evolves into a pattern of five interlocking cusps. The five cusps result from symmetry breaking of a three-cusped surface perturbation caustic. (C) 2003 Optical Society of America.

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Simulating Coronas In Color, Stanley D. Gedzelman, James A. Lock Jan 2003

Simulating Coronas In Color, Stanley D. Gedzelman, James A. Lock

Physics Faculty Publications

Coronas are simulated in color by use of the Mie scattering theory of light by small droplets through clouds of finite optical thickness embedded in a Rayleigh scattering atmosphere. The primary factors that affect color, visibility, and number of rings of coronas are droplet size, width of the size distribution, and cloud optical thickness. The color sequence of coronas and iridescence varies when the droplet radius is smaller than similar to6-mum. As radius increases to approximately 3.5 mum, new color bands appear at the center of the corona and fade as they move outward. As the radius continues to increase …

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Experimental Observation Of Total-Internal-Reflection Rainbows, Charles L. Adler, James A. Lock, Jonathon Mulholland, Brian Keating, Diana Ekelman Jan 2003

Experimental Observation Of Total-Internal-Reflection Rainbows, Charles L. Adler, James A. Lock, Jonathon Mulholland, Brian Keating, Diana Ekelman

Physics Faculty Publications

A new class of rainbows is created when a droplet is illuminated from the inside by a point light source. The position of the rainbow depends on both the index of refraction of the droplet and the position of the light source, and the rainbow vanishes when the point source is too close to the center of the droplet. Here we experimentally measure the position of the transmission and one-internal-reflection total-internal-reflection rainbows, and the standard (primary) rainbow, as a function of light-source position. (C) 2003 Optical Society of America.

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Electronic Structure Of Eras(100), Takashi Komesu, Hae-Kyung Jeong, Jaewu Choi, C.N. Borca, Peter A. Dowben, A.G. Petukhov, B.D. Schultz, C.J. Palmstrom Jan 2003

Electronic Structure Of Eras(100), Takashi Komesu, Hae-Kyung Jeong, Jaewu Choi, C.N. Borca, Peter A. Dowben, A.G. Petukhov, B.D. Schultz, C.J. Palmstrom

Peter Dowben Publications

The experimental band structure of the rare-earth pnictide erbium arsenide (ErAs), grown epitaxially on GaAs(100), has been mapped out using photoelectron spectroscopy and inverse photoemission spectroscopy. The electronic structure is dominated by bulk bands qualitatively consistent with the calculated band structure. A number of additional nondispersing 4 f multiplet levels can be identified in the valence-band structure as well as at least one surface resonance band. From symmetry selection rules, photoemission provides strong evidence that the Δ5 (or e) symmetry bands are a consequence of hybridization between Er and As, while the Δ 1 (or a1) symmetry …

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Tt̅ Production Cross Section In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration Jan 2003

Tt̅ Production Cross Section In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

Results are presented on a measurement of the tt̅ pair production cross section in pp̅ collisions at √s = 1.8 TeV from nine independent decay channels. The data were collected by the DØ experiment during the 1992–1996 run of the Fermilab Tevatron Collider. A total of 80 candidate events is observed with an expected background of 38.8±3.3 events. For a top quark mass of 172.1 GeV/c2, the measured cross section is 5.69 ±1.21(stat) ±1.04(syst) pb.

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High-Field Magnetic Resonant Properties Of Β’–(Et)2sf5cf2so3, Gary L. Gard, Rolf Walter Winter, J. A. Schlueter, Brian H. Ward, E. Jobiliong, A. P. Reyes, P. Kuhns, J. Krzystek, J. S. Brooks, S. A. Zvyagin, B. Rutel Jan 2003

High-Field Magnetic Resonant Properties Of Β’–(Et)2sf5cf2so3, Gary L. Gard, Rolf Walter Winter, J. A. Schlueter, Brian H. Ward, E. Jobiliong, A. P. Reyes, P. Kuhns, J. Krzystek, J. S. Brooks, S. A. Zvyagin, B. Rutel

Chemistry Faculty Publications and Presentations

The charge transfer salt β′-(ET)₂SF₅CF₂SO₃, which has previously been considered a spin-Peierls material with a TSP;33 K, is examined using high-resolution high-field sub-millimeter/millimeter wave electron spin resonance (ESR), and nuclear magnetic resonance (NMR) techniques. A peak in the nuclear spin-lattice relaxation behavior in fields of 8 T, accompanied by a broadening and paramagnetic shift of the resonance line, indicates a phase transition at Tc~20 K. A pronounced change in the high-field ESR excitation spectra at ~24 T, observed at Tc~20 K, may indicate the onset of antiferromagnetic (AFM) correlations of the low temperature phase in β′-(ET)₂SF₅CF₂SO₃. Peculiarities of the low-temperature …

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The Mass Of Quasar Broad Emission Line Regions, J. A. Baldwin, Gary J. Ferland, K. T. Korista, F. Hamann, M. Dietrich Jan 2003

The Mass Of Quasar Broad Emission Line Regions, J. A. Baldwin, Gary J. Ferland, K. T. Korista, F. Hamann, M. Dietrich

Physics and Astronomy Faculty Publications

We show that the mass of ionized gas in the broad-line regions (BLRs) of luminous quasars is at least several hundred M☉, and probably of the order of 103-104 Msolar. BLR mass estimates in several existing textbooks suggest lower values but pertain to much less luminous Seyfert galaxies or include only a small fraction of the ionized/emitting volume of the BLR. The previous estimates also fail to include the large amounts of BLR gas that emit at low efficiency (in a given line) but that must be present based on reverberation and other …

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Study Of The Azimuthal Asymmetry Of Jets In Neutral Current Deep Inelastic Scattering At Hera, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan, D. Bartsch, I. Brock Jan 2003

Study Of The Azimuthal Asymmetry Of Jets In Neutral Current Deep Inelastic Scattering At Hera, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan, D. Bartsch, I. Brock

Faculty Publications

The azimuthal distribution of jets produced in the Breit frame in high-Q2 deep inelastic e+p scattering has been studied with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb-1. The measured azimuthal distribution shows a structure that is well described by next-to-leading-order QCD predictions over the Q2 range considered, Q2 > 125 GeV2. © 2002 Elsevier Science B.V. All rights reserved.

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Electrical And Spectroscopic Studies Of The Effects Of Dc Electric Fields On Pre-Mixed Propane-Air Flames, S D. Marcum, G D. Gillen, B N. Ganguly Jan 2003

Electrical And Spectroscopic Studies Of The Effects Of Dc Electric Fields On Pre-Mixed Propane-Air Flames, S D. Marcum, G D. Gillen, B N. Ganguly

Physics

The effects of DC electric fields on temperature distributions within pre-mixed propane-air flames have been measured by the technique of thin filament pyrometry (TFP). We have focussed on the dramatic electric-field-induced modifications of the shape and size of the inner cone and the concomitant changes in the temperature profiles of fuel-rich mixtures with equivalence ratios of 1-1.35. Temperature profile measurements show large decreases in the reaction zone volume that is dependent upon the applied voltage polarity, indicating that electron impact excitation is not responsible for the observed effects. Additionally, the observed flame temperature profile modifications are not strongly dependent on …

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Hole Drift-Mobility Measurements In Contemporary Amorphous Silicon, S. Dinca, Eric A. Schiff, V. Vlahos, C. R. Wronski, Q. Yuan Jan 2003

Hole Drift-Mobility Measurements In Contemporary Amorphous Silicon, S. Dinca, Eric A. Schiff, V. Vlahos, C. R. Wronski, Q. Yuan

Physics - All Scholarship

We present hole drift-mobility measurements on hydrogenated amorphous silicon from several laboratories. These temperature-dependent measurements show significant variations of the hole mobility for the differing samples. Under standard conditions (displacement/field ratio of 2×10-9 cm2/V), hole mobilities reach values as large as 0.01 cm2/Vs at room-temperature; these values are improved about tenfold over drift-mobilities of materials made a decade or so ago. The improvement is due partly to narrowing of the exponential bandtail of the valence band, but there is presently little other insight into how deposition procedures affect the hole drift-mobility.

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Magnetic Properties Of Al, V, Mn, And Ru Impurities In Fe–Co Alloys, B. V. Reddy, S. C. Deevi, S. N. Khanna Jan 2003

Magnetic Properties Of Al, V, Mn, And Ru Impurities In Fe–Co Alloys, B. V. Reddy, S. C. Deevi, S. N. Khanna

Physics Publications

Theoretical studies on the magnetic properties of impurities in Fe–Co alloys have been carried out using a molecular-orbital approach within a gradient corrected density functional formalism. The defected alloy is modeled by a large cluster and the calculations on the ordered alloy are used to show that a cluster containing 67 atoms can provide quantitative information on the local magnetic moment. It is found that although bulk Al, V, and Ru are nonmagnetic, all the impurities carry finite moments. While Al and V impurities couple antiferromagnetically, Ru impurities couple ferromagnetically to the host sites. It is shown that the observed …

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The Speed And Orientation Of The Parsec-Scale Jet In 3c 279, B. Glenn Piner, Stephen C. Unwind, Ann E. Wehrle, Alma C. Zook, C. Megan Urry, Diane M. Gilmore Jan 2003

The Speed And Orientation Of The Parsec-Scale Jet In 3c 279, B. Glenn Piner, Stephen C. Unwind, Ann E. Wehrle, Alma C. Zook, C. Megan Urry, Diane M. Gilmore

Physics

A high degree of relativistic beaming is inferred for the jets of blazars on the basis of several lines of evidence, but the intrinsic speed and angle of the jet to the line of sight for individual sources are difficult to measure. We have calculated inverse Compton Doppler factors for 3C 279 using the collection of VLBI data (including high-resolution space VLBI data at low frequencies) recently published by us (as Wehrle et al. and Piner et al.) and the collection of multiwavelength spectra recently published by Hartman et al. From the Doppler factor and superluminal apparent speed, we then …

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A Direct Simulation Monte Carlo Method For The Uehling-Uhlenbeck-Boltzmann Equation, Alejandro Garcia, W. Wagner Jan 2003

A Direct Simulation Monte Carlo Method For The Uehling-Uhlenbeck-Boltzmann Equation, Alejandro Garcia, W. Wagner

Faculty Publications

In this paper we describe a direct simulation Monte Carlo algorithm for the Uehling-Uhlenbeck-Boltzmann equation in terms of Markov processes. This provides a unifying framework for both the classical Boltzmann case as well as the Fermi-Dirac and Bose-Einstein cases. We establish the foundation of the algorithm by demonstrating its link to the kinetic equation. By numerical experiments we study its sensitivity to the number of simulation particles and to the discretization of the velocity space, when approximating the steady-state distribution.

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The Helically Reduced Wave Equation As A Symmetric Positive System, Charles G. Torre Jan 2003

The Helically Reduced Wave Equation As A Symmetric Positive System, Charles G. Torre

All Physics Faculty Publications

Motivated by the partial differential equations of mixed type that arise in the reduction of the Einstein equations by a helical Killing vector field, we consider a boundary value problem for the helically-reduced wave equation with an arbitrary source in 2+1 dimensional Minkowski spacetime. The reduced equation is a second-order partial differential equation which is elliptic inside a disk and hyperbolic outside the disk. We show that the reduced equation can be cast into symmetric-positive form. Using results from the theory of symmetric-positive differential equations, we show that this form of the helically-reduced wave equation admits unique, strong solutions for …

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Commentary: The Parameter-Free Track Structure Model Of Scholz And Kraft For Heavy-Ion Cross Sections, Robert Katz Jan 2003

Commentary: The Parameter-Free Track Structure Model Of Scholz And Kraft For Heavy-Ion Cross Sections, Robert Katz

Robert Katz Publications

The "parameter-free", "local effects" theory of Scholz and Kraft is an extension to mammalian cells of the theory of RBE for dry enzymes and viruses of Butts and Katz. Its claim for parameter freedom has been challenged elsewhere. Here we examine its conceptual base and find errors in its use of the physical concept of cross section and its neglect of the radiobiological relationship between target size and radio-sensitivity in evaluating the radiation damage to "point targets".

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Digital Image Processing, Russell C. Hardie, Majeed M. Hayat Jan 2003

Digital Image Processing, Russell C. Hardie, Majeed M. Hayat

Electrical and Computer Engineering Faculty Publications

In recent years, digital images and digital image processing have become part of everyday life. This growth has been primarily fueled by advances in digital computers and the advent and growth of the Internet. Furthermore, commercially available digital cameras, scanners, and other equipment for acquiring, storing, and displaying digital imagery have become very inexpensive and increasingly powerful. An excellent treatment of digital images and digital image processing can be found in Ref. [1]. A digital image is simply a two-dimensional array of finite-precision numerical values called picture elements (or pixels). Thus a digital image is a spatially discrete (or discrete-space) …

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Breakdown Of The Slowly Varying Amplitude Approximation: Generation Of Backward Traveling Second Harmonic Light, J. Z. Sanborn '01, C. Hellings '02, Thomas D. Donnelly Jan 2003

Breakdown Of The Slowly Varying Amplitude Approximation: Generation Of Backward Traveling Second Harmonic Light, J. Z. Sanborn '01, C. Hellings '02, Thomas D. Donnelly

All HMC Faculty Publications and Research

By numerically solving the nonlinear field equations, we simulate second-harmonic generation by laser pulses within a nonlinear medium without making the usual slowly-varying-amplitude approximation, an approximation which may fail when laser pulses of moderate intensity or ultrashort duration are used to drive a nonlinear process. Under these conditions we show that a backward-traveling, second-harmonic wave is created, and that the magnitude of this wave is indicative of the breakdown of the slowly-varying-amplitude approximation. Conditions necessary for experimental detection of this wave are discussed.

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Spectral Functions Of The Falicov-Kimball Model With Electronic Ferroelectricity, Wei-Guo Yin, Wai-Ning Mei, Chun-Gang Duan, Hai-Qing Lin, John R. Hardy Jan 2003

Spectral Functions Of The Falicov-Kimball Model With Electronic Ferroelectricity, Wei-Guo Yin, Wai-Ning Mei, Chun-Gang Duan, Hai-Qing Lin, John R. Hardy

John R. Hardy Papers

We calculate the angular resolved photoemission spectrum of the Falicov-Kimball model with electronic ferroelectricity where d- and f-electrons have different hoppings. In mix-valence regimes, the presence of strong scattering processes between d – f excitons and a hole, created by emission of an electron, leads to the formation of pseudospin polarons and novel electronic structures with bandwidth scaling with that of d – f excitons. Especially, in the two-dimensional case, we find that flat regions exist near the bottom of the quasiparticle band in a wide range of the d- and f-level energy difference.

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Cosmological Effects Of The First Stars: Evolving Spectra Of Population Iii, Jason Tumlinson, J Shull, Aparna Venkatesan Jan 2003

Cosmological Effects Of The First Stars: Evolving Spectra Of Population Iii, Jason Tumlinson, J Shull, Aparna Venkatesan

Physics and Astronomy

The first stars hold intrinsic interest for their uniqueness and for their potentially important contributions to galaxy formation, chemical enrichment, and feedback on the intergalactic medium (IGM). Although the sources of cosmological reionization are unknown at present, the declining population of large bright quasars at redshifts z > 3 implies that stars are the leading candidates for the sources that reionized the hydrogen in the IGM by z ~ 6. The metal-free composition of the first stars restricts the stellar energy source to proton-proton burning rather than the more efficient CNO cycle. Consequently, they are hotter, smaller, and have harder spectra …

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Lisa, Binary Stars, And The Mass Of The Graviton, Curt Cutler, William A. Hiscock, Shane L. Larson Jan 2003

Lisa, Binary Stars, And The Mass Of The Graviton, Curt Cutler, William A. Hiscock, Shane L. Larson

All Physics Faculty Publications

We extend and improve earlier estimates of the ability of the proposed LISA (Laser Interferometer Space Antenna) gravitational wave detector to place upper bounds on the graviton mass mg by comparing the arrival times of gravitational and electromagnetic signals from binary star systems. We show that the best possible limit on mg obtainable this way is ∼50 times better than the current limit set by solar system measurements. Among currently known, well-understood binaries, 4U1820-30 is the best for this purpose; LISA observations of 4U1820-30 should yield a limit ≈3-4 times better than the present solar system bound. AM …

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Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraftcharging, A. R. Fredrickson, John R. Dennison Jan 2003

Measurement Of Conductivity And Charge Storage In Insulators Related To Spacecraftcharging, A. R. Fredrickson, John R. Dennison

All Physics Faculty Publications

Novel methods have been developed to measure conductivity and charge storage in thin film insulating spacecraft materials subjected to space radiations. For a variety of such samples, conductivity values differ by up to 104 from values based on ASTM standards. Conductivity and charge storage properties are found to be functions of prior radiation history. A highly-charged insulator emits electrons for hours (Malter Effect) after the irradiation beam is turned off. Visible light can be used to induce emission from previously charged samples with shallow traps.

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Molecular Dynamics Simulation Of The Order- Disorder Phase Transition In Solid Nano2, Wei-Guo Yin, Chun-Gang Duan, Wai-Ning Mei, Jianjun Liu, Robert W. Smith, John R. Hardy Jan 2003

Molecular Dynamics Simulation Of The Order- Disorder Phase Transition In Solid Nano2, Wei-Guo Yin, Chun-Gang Duan, Wai-Ning Mei, Jianjun Liu, Robert W. Smith, John R. Hardy

Physics Faculty Publications

We present molecular dynamics simulations of solid NaNO2 using pair potentials with the rigid-ion model. The crystal potential surface is calculated by using an a priori method which integrates the ab initio calculations with the Gordon-Kim electron gas theory. This approach is carefully examined by using different population analysis methods and comparing the intermolecular interactions resulting from this approach with those from the ab initio Hartree-Fock calculations. Our numerics show that the ferroelectric-paraelectric phase transition in solid NaNO2 is triggered by rotation of the nitrite ions around the crystallographical c axis, in agreement with recent x-ray experiments @Gohda et al., …

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Lisa Data Analysis: Doppler Demodulation, Neil J. Cornish, Shane L. Larson Jan 2003

Lisa Data Analysis: Doppler Demodulation, Neil J. Cornish, Shane L. Larson

All Physics Faculty Publications

The orbital motion of the Laser Interferometer Space Antenna (LISA) produces amplitude, phaseand frequency modulation of a gravitational wave signal. The modulations have the effect of spreading a monochromatic gravitational wave signal across a range of frequencies. The modulations encode useful information about the source location and orientation, but they also have the deleteriousaffect of spreading a signal across a wide bandwidth, thereby reducing the strength of the signalrelative to the instrument noise. We describe a simple method for removing the dominant, Doppler,component of the signal modulation. The demodulation reassembles the power from a monochromatic source into a narrow spike, …

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