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Physics Faculty Publications

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Articles 1831 - 1860 of 2178

Full-Text Articles in Physical Sciences and Mathematics

Known Source Detection Predictions For Higher Order Correlators, Lisa A. Pflug, George E. Ioup, Juliette W. Ioup May 1998

Known Source Detection Predictions For Higher Order Correlators, Lisa A. Pflug, George E. Ioup, Juliette W. Ioup

Physics Faculty Publications

The problem addressed in this paper is whether higher order correlation detectors can perform better in white noise than the cross correlation detector for the detection of a known transient source signal, if additional receiver information is included in the higher order correlations. While the cross correlation is the optimal linear detector for white noise, additional receiver information in the higher order correlations makes them nonlinear. In this paper, formulas that predict the performance of higher order correlation detectors of energy signals are derived for a known source signal. Given the first through fourth order signal moments and the noise …

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Valence Intersubband Lasers With Inverted Light-Hole Effective Mass, Greg Sun, Y. Lu, Jacob B. Khurgin Mar 1998

Valence Intersubband Lasers With Inverted Light-Hole Effective Mass, Greg Sun, Y. Lu, Jacob B. Khurgin

Physics Faculty Publications

We propose a novel intersubband laser based on transition between the ground-state heavy-hole subband (HH1) and light-hole subband (LH1) in a k-space region where the light-hole effective mass is inverted. The laser structure can be electrically pumped with a simple quantum cascade scheme. Our calculation shows that with only a small fraction of the carrier population in the upper subband (LH1), it is possible to achieve population inversion between the two subbands locally in K space where the light-hole effective mass is inverted. Optical gain in excess of 150/cm can be achieved with a pumping current density on the …

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Amplification Of High-Order Rainbows Of A Cylinder With An Elliptical Cross Section, James A. Lock, Charles L. Adler, Bradley R. Stone, Patrick D. Zajak Mar 1998

Amplification Of High-Order Rainbows Of A Cylinder With An Elliptical Cross Section, James A. Lock, Charles L. Adler, Bradley R. Stone, Patrick D. Zajak

Physics Faculty Publications

The intensity of high-order rainbows for normally incident light and certain rotation angles of a cylinder with an elliptical cross section is greatly amplified with respect to the intensity for a circular cross-sectional cylinder. The amplification is due to a number of the internal reflections occurring past the critical angle for total internal reflection, and the effect is especially strong for odd-order rainbows, beginning with the third order. Experimentally, the fourth-and the fifth-order rainbows of a nearly elliptical cross-sectional glass rod were observed and analyzed. (C) 1998 Optical Society of America.

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Rainbow Scattering By A Cylinder With A Nearly Elliptical Cross Section, Charles L. Adler, James A. Lock, Bradley R. Stone Mar 1998

Rainbow Scattering By A Cylinder With A Nearly Elliptical Cross Section, Charles L. Adler, James A. Lock, Bradley R. Stone

Physics Faculty Publications

We both theoretically and experimentally examine the behavior of the first-and the second-order rainbows produced by a normally illuminated glass rod, which has a nearly elliptical cross section, as it is rotated about its major axis. We decompose the measured rainbow angle, taken as a function of the rod's rotation angle, into a Fourier series and find that the rod's refractive index, average ellipticity, and deviation from ellipticity are encoded primarily in the m = 0, 2, 3 Fourier coefficients, respectively. We determine these parameters for our glass rod and, where possible, compare them with independent measurements. We find that …

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Ray Theory Analysis Of The Shadow Blister Effect, James A. Lock Mar 1998

Ray Theory Analysis Of The Shadow Blister Effect, James A. Lock

Physics Faculty Publications

When an extended light source such as the Sun illuminates two objects so that their shadows lie close to each other, the shadow of one of the objects occasionally appears to bulge out toward the shadow of the other. This effect is caused by the overlap of the penumbras of the shadows and is analyzed here with ray theory. A laboratory demonstration of this phenomenon is performed and compared with theoretical predictions. (C) 1998 Optical Society of America.

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In Situ Measurement Of Radiation Induced Conductivity In Oxide Insulators During Neutron Irradiation, D. P. White, L. L. Snead, S. J. Zinkle, W. S. Earthley Feb 1998

In Situ Measurement Of Radiation Induced Conductivity In Oxide Insulators During Neutron Irradiation, D. P. White, L. L. Snead, S. J. Zinkle, W. S. Earthley

Physics Faculty Publications

No abstract provided.

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Electron-Irradiation-Induced Deep Level In N-Type Gan, Z-Q. Fang, Joseph W. Hemsky, David C. Look, M. P. Mack Jan 1998

Electron-Irradiation-Induced Deep Level In N-Type Gan, Z-Q. Fang, Joseph W. Hemsky, David C. Look, M. P. Mack

Physics Faculty Publications

Deep-level transient spectroscopy measurements of n-type GaN epitaxial layers irradiated with 1-MeV electrons reveal an irradiation-induced electron trap at EC−0.18 eV. The production rate is approximately 0.2 cm−1, lower than the rate of 1 cm−1 found for the N vacancy by Hall-effect studies. The defect trap cannot be firmly identified at this time. ©1998 American Institute of Physics.

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Suppression Of Switchable Polarization In Kdp By Ionizing Radiation, Timothy D. Usher Jan 1998

Suppression Of Switchable Polarization In Kdp By Ionizing Radiation, Timothy D. Usher

Physics Faculty Publications

Switching curves were obtained from KH2PO4 single crystals exposed to x-ray radiation for various time intervals, up to 8 h. The applied electric field was varied between 370 and 740 V/cm, as well. The temperature was held constant at 99 K. The switching curves were fit to a three-parameter nucleation and growth model based on the original works by Johnson and Mehl, and independently by Avrami. The two dynamic parameters, characteristic time tc, and effective domain wall dimensionality n, produced values consistent with unirradiated studies, however, they did not show any clear dependancy on …

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Effect Of High-Temperature Annealing On Electrical And Optical Properties Of Undoped Semi-Insulating Gaas, Z-Q. Fang, D. C. Reynolds, David C. Look, N. G. Paraskevopoulos, T. E. Anderson, R. L. Jones Jan 1998

Effect Of High-Temperature Annealing On Electrical And Optical Properties Of Undoped Semi-Insulating Gaas, Z-Q. Fang, D. C. Reynolds, David C. Look, N. G. Paraskevopoulos, T. E. Anderson, R. L. Jones

Physics Faculty Publications

A comprehensive characterization, including room temperature Hall effect, near infrared absorption, temperature dependent dark current and photocurrent (using 1.13 eV light), normalized thermally stimulated current (NTSC), photoluminescence at 4.2 K in both near band edge and deep level regions, and selective pair photoluminescence (SPL) at 2 K, has been carried out on undoped semi-insulating GaAs samples, cut from four wafers which were grown by the low pressure liquid encapsulated Czochralski technique and annealed by three different schedules: a 1100 °C anneal with either fast or slow cooling, or a 1000 °C standard anneal. The 1100 °C anneal clearly introduces higher …

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Solar Cycle Variability Of Hot Oxygen Atoms At Mars, Jhoon Kim, Andrew F. Nagy, Jane L. Fox, Thomas E. Cravens Jan 1998

Solar Cycle Variability Of Hot Oxygen Atoms At Mars, Jhoon Kim, Andrew F. Nagy, Jane L. Fox, Thomas E. Cravens

Physics Faculty Publications

The population of hot oxygen atoms in the Martian exosphere is reexamined using newly calculated hot O production rates for both low and high solar cycle conditions. The hot oxygen production rates are assumed to result from the dissociative recombination of O2+ ions. These calculations take into account the calculated vibrational distribution of O2+ and the new measured branching ratios. Furthermore, these calculations also consider the variation of the dissociative recombination cross section with the relative speed of the participating ions and electrons, the rotational energy of the O2+ ions, and the spread of …

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Factorization For High-Energy Scattering, Ian Balitsky Jan 1998

Factorization For High-Energy Scattering, Ian Balitsky

Physics Faculty Publications

I demonstrate that the amplitude for the high-energy scattering can be factorized into a product of two independent functional integrals over “fast” and “slow” fields which interact by means of Wilson-line operators—gauge factors ordered along the straight lines.

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Factorization And Effective Action For High-Energy Scattering In Qcd, Ian Balitsky Jan 1998

Factorization And Effective Action For High-Energy Scattering In Qcd, Ian Balitsky

Physics Faculty Publications

The author demonstrates that the amplitude of the high-energy scattering can be factorized in a convolution of the contributions due to fast and slow fields. The fast and slow fields interact by means of Wilson-line operators -- infinite gauge factors ordered along the straight line. The resulting factorization formula gives a starting point for a new approach to the effective action for high-energy scattering.

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Novel Electronic And Magnetic Properties Of Ultrathin Chromium Oxide Films Grown On Pt(111), P S. Robbert, H Geisler, C A. Ventrice Jr, J Van Ek, S Chaturvedi, J A. Rodriguez, M Kuhn, U Diebold Jan 1998

Novel Electronic And Magnetic Properties Of Ultrathin Chromium Oxide Films Grown On Pt(111), P S. Robbert, H Geisler, C A. Ventrice Jr, J Van Ek, S Chaturvedi, J A. Rodriguez, M Kuhn, U Diebold

Physics Faculty Publications

The growth of epitaxial metal–oxide films on lattice-mismatched metal substrates often results in the formation of unique overlayer structures. In particular, epitaxial chromium oxide films grown on Pt(111) exhibit a p(2×2) symmetry through the first two monolayers of growth which is followed by a (√3×√3)R30° phase that is attributed to the growth of a Cr2O3(0001) overlayer. Ultraviolet photoelectron spectroscopy measurements have been performed on the CrOx/Pt(111) system. The electronic structures of CrO2, Cr2O3, and Cr3O4 were calculated using the linear muffin-tin orbital method in …

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Structure And Dynamics Of Few-Nucleon Systems, J. Carlson, R. Schiavilla Jan 1998

Structure And Dynamics Of Few-Nucleon Systems, J. Carlson, R. Schiavilla

Physics Faculty Publications

Few-nucleon physics is a field rich with high-quality experimental data and possibilities for accurate calculations of strongly correlated quantum systems. In this article the authors discuss the traditional model of the nucleus as a system of interacting nucleons and outline many recent experimental results and theoretical developments in the field of few-nucleon physics. The authors describe nuclear structure and spectra, clustering and correlations, elastic and inelastic electromagnetic form factors, low-energy electroweak reactions, and nuclear scattering and response in the quasi-elastic regime. Through a review of the rich body of experimental data and a variety of theoretical developments, a coherent description …

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Three-Dimensional Camera Calibration Technique For Stereo Imaging Velocimetry Experiments, Mark D. Bethea, James A. Lock, Frank Merat, Paul Crouser Dec 1997

Three-Dimensional Camera Calibration Technique For Stereo Imaging Velocimetry Experiments, Mark D. Bethea, James A. Lock, Frank Merat, Paul Crouser

Physics Faculty Publications

A three-dimensional camera calibration technique is developed by combining two, 2-D camera calibrations for an orthogonal stereo viewing geometry. The left camera view (YZ view) and the right camera view (XZ view) are calibrated separately and then combined to produce an XYZ (3-D) calibration routine, Our technique employs three parallel calibration planes. One is placed along the main diagonal of the cubic experimental chamber, and the other two planes are placed known distances in front of it and behind it within the chamber. Both cameras view the calibration points on the planes simultaneously. Given the coordinates of a number of …

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Spin Splitting Of Donor-Bound Excitons In Zno Due To Combined Stress And Spin Exchange, D. C. Reynolds, David C. Look, B. Jogai, T. C. Collins Dec 1997

Spin Splitting Of Donor-Bound Excitons In Zno Due To Combined Stress And Spin Exchange, D. C. Reynolds, David C. Look, B. Jogai, T. C. Collins

Physics Faculty Publications

No abstract provided.

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Upper Limits To The Outflow Of Ions At Mars: Implications For Atmospheric Evolution, Jane L. Fox Nov 1997

Upper Limits To The Outflow Of Ions At Mars: Implications For Atmospheric Evolution, Jane L. Fox

Physics Faculty Publications

Escape of ions is potentially important for the evolution of volatiles on Mars, but the mechanisms and rates of ion escape processes are not fully understood. Instruments on the Russian Phobos 2 orbiter have, however, measured fluxes of heavy ions apparently of ionospheric origin in the optical shadow of Mars. These ions are assumed to arise from escape processes induced by the interaction of the solar wind with the ionosphere. We determine here upper limits to the ion loss rates by imposing upward flux boundary conditions on models of the low and high solar activity Mars ionosphere. The maximum fluxes …

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Spectrum Of Hot O At The Exobases Of The Terrestrial Planets, Jane L. Fox, Aleksander B. Hać Nov 1997

Spectrum Of Hot O At The Exobases Of The Terrestrial Planets, Jane L. Fox, Aleksander B. Hać

Physics Faculty Publications

The distribution of energetic O produced in dissociative recombination of O2+ at the exobases of the terrestrial planets is important in determining the structure of the outer hot O coronas and for the escape flux of O from Mars. Using recently measured values for the branching ratios of the energetically allowed channels in O2+ dissociative recombination, along with models of the vibrational distribution of O2+, we compute the velocity distribution of hot O atoms produced at the exobases of Mars, Venus, and Earth. We take into account the effects of the ion and …

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Role Of Multiple Scattering In Cross-Correlated Light Scattering With A Single Laser Beam, James A. Lock Oct 1997

Role Of Multiple Scattering In Cross-Correlated Light Scattering With A Single Laser Beam, James A. Lock

Physics Faculty Publications

Previous systems for measuring cross-correlated light scattering by small particles suspended in a liquid with multiple-scattering suppression have illuminated the particles with two laser beams. It is shown that multiple-scattering suppression should also occur in cross correlation for a system that employs a single laser beam and two closely spaced detectors with wide fields of view. The single-scattering, double-scattering, and single-double-scattering cross-term contributions to the intensity cross-correlation function are calculated. It is found that the two cross terms, when added together, are unimportant for both autocorrelation and cross correlation. The amplitude of the double-scattering term can be greatly diminished by …

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Hybrid Reflection-Transmission Surface Light-Scattering Instrument With Reduced Sensitivity To Surface Sloshing, William V. Meyer, James A. Lock, H. Michael Cheung, Thomas W. Taylor, Padetha Tin, J. Adin Mann Oct 1997

Hybrid Reflection-Transmission Surface Light-Scattering Instrument With Reduced Sensitivity To Surface Sloshing, William V. Meyer, James A. Lock, H. Michael Cheung, Thomas W. Taylor, Padetha Tin, J. Adin Mann

Physics Faculty Publications

A hybrid reflection-transmission surface light-scattering instrumental design is presented, examined theoretically, and tested experimentally. The purpose of the design is to reduce the sensitivity of the instrument to vibration in general and surface sloshing in particular while sacrificing Little performance. Traditional optical arrangements and two new optical configurations with varying trade-offs between slosh resistance and instrumental simplicity and accuracy are examined by use of Fourier optics methods. The most promising design was constructed and tested with acetone, ethanol, and water as subject fluids. The test involved backcalculation of the wave number of the capillary wave examined with the known physical …

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Multiple-Scattering Suppression By Cross Correlation, William V. Meyer, David S. Cannell, Anthony E. Smart, Thomas W. Taylor, Padetha Tin Oct 1997

Multiple-Scattering Suppression By Cross Correlation, William V. Meyer, David S. Cannell, Anthony E. Smart, Thomas W. Taylor, Padetha Tin

Physics Faculty Publications

We describe a new method for characterizing particles in turbid media by cross correlating the scattered intensity fluctuations at two nearby points in the far field. The cross-correlation function selectively emphasizes single scattering over multiple scattering. The usual dynamic light-scattering capability of inferring particle size from decay rate is thus extended to samples that are so turbid as to be visually opaque. The method relies on single-scattering speckle being physically larger than multiple-scattering speckle. With a suitable optical geometry to select nearby points in the far field or equivalently slightly different scattering wave vectors (of the same magnitude), the multiple-scattering …

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Fiber-Optics Surface-Light-Scattering Spectrometer, Padetha Tin, J. Adin Mann, William V. Meyer, Thomas W. Taylor Oct 1997

Fiber-Optics Surface-Light-Scattering Spectrometer, Padetha Tin, J. Adin Mann, William V. Meyer, Thomas W. Taylor

Physics Faculty Publications

We have developed a fiber-optics surface-light-scattering spectrometer completely designed with optical fiber components. To the best of our knowledge, this is the first demonstration of a noninvasive measurement of the surface tension and the viscosity of simple liquid-vapor interfaces with a fiber-optics-based sensor system. With this approach we obtain a compact size, a significant increase in the signal-to-noise ratio, and the ability to select from a continuum of wave vectors. (C) 1997 Optical Society of America.

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Study Of The Effects Of Initial-Bred Nuclei On Zeolite Naa Crystallization By Quasi-Elastic Light Scattering Spectroscopy And Electron Microscopy, Leszek Gora, Kiril A. Streletzky, Robert W. Thompson, George D.J. Phillies Sep 1997

Study Of The Effects Of Initial-Bred Nuclei On Zeolite Naa Crystallization By Quasi-Elastic Light Scattering Spectroscopy And Electron Microscopy, Leszek Gora, Kiril A. Streletzky, Robert W. Thompson, George D.J. Phillies

Physics Faculty Publications

Synthesis studies have been conducted at 25, 60, and 80 °C with a clear solution batch composition that produces zeolite NaA. Aluminosilicate precursor material was added to promote the synthesis and to evaluate the effects of adding initial-bred nuclei that were created by a precursor “seed” reaction. It is shown that the initial-bred nuclei promoted the crystallization rate, that the crystalline mass produced was increased when using the initial-bred nuclei, and that the nucleation of a second population was not inhibited by the addition of initial-bred nuclei as seeds.

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High Quality Interfaces In Gaas-Alas Quantum Wells Determined From High Resolution Photoluminescence, D. C. Reynolds, David C. Look, B. Jogai, R. Kaspi, K. R. Evans, M. Estes Sep 1997

High Quality Interfaces In Gaas-Alas Quantum Wells Determined From High Resolution Photoluminescence, D. C. Reynolds, David C. Look, B. Jogai, R. Kaspi, K. R. Evans, M. Estes

Physics Faculty Publications

No abstract provided.

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Defect Donor And Acceptor In Gan, David C. Look, D. C. Reynolds, Joseph W. Hemsky, J. R. Sizelove, R. L. Jones, Richard J. Molnar Sep 1997

Defect Donor And Acceptor In Gan, David C. Look, D. C. Reynolds, Joseph W. Hemsky, J. R. Sizelove, R. L. Jones, Richard J. Molnar

Physics Faculty Publications

No abstract provided.

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Hydrocarbon Ions In The Ionosphere Of Titan, Jane L. Fox, Roger V. Yelle Sep 1997

Hydrocarbon Ions In The Ionosphere Of Titan, Jane L. Fox, Roger V. Yelle

Physics Faculty Publications

We have constructed a new model of the ionosphere of Titan that includes 67 species and 626 reactions. Although N2+ is the major ion produced over most of the ionosphere, the ionization flows to ions whose parent neutrals have lower ionization potentials and to ions formed from species with large proton affinities. In contrast to other models, which have predicted that HCNH+ should be the major ion, our calculations suggest that the major ions at and below the ion peak are hydrocarbon ions, and H, C, and N-containing ions. Our predicted peak electron density for a solar …

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Monte Carlo Study Of The Square-Lattice Annealed Ising Model On Percolating Clusters, P. D. Scholten, Miron Kaufman Jul 1997

Monte Carlo Study Of The Square-Lattice Annealed Ising Model On Percolating Clusters, P. D. Scholten, Miron Kaufman

Physics Faculty Publications

Simulations of an Ising q-state Pods model which is equivalent to the Ising model on annealed percolation clusters are used to determine the phase diagram of the model in two dimensions. Three topologically different phase diagrams are obtained: (i) for q=2, there are two critical Ising lines meeting at T=0 at the four-state Potts critical point; (ii) for 24, the Ising:critical line intersects a Line of first-order transitions at a critical end point.

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Core Scattering Of Stark Wave Packets, M. L. Naudeau, C. I. Sukenik, P. H. Bucksbaum Jul 1997

Core Scattering Of Stark Wave Packets, M. L. Naudeau, C. I. Sukenik, P. H. Bucksbaum

Physics Faculty Publications

We investigate the wave packet dynamics of electrons bound in the nonseparable potential of cesium in a static electric field using time-domain Ramsey interferometry. Specially shaped wave packets with low radial dispersion enable us to view the interaction between the wave packet and the atomic core. Experiments in cesium, together with quantum defect calculations of cesium and hydrogen, demonstrate changes in the motion and shape of these wave packets due to core scattering.

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Anharmonic Potentials In Supercooled Liquids: The Soft-Potential Model, Ulrich Zürcher, T. Keyes Jun 1997

Anharmonic Potentials In Supercooled Liquids: The Soft-Potential Model, Ulrich Zürcher, T. Keyes

Physics Faculty Publications

Instantaneous normal modes (INM) are the harmonic approximation to liquid dynamics. This is an extension of the phonon description of lattice dynamics, in which case Bloch's theorem shows that all modes are extended. Long-range order is destroyed in liquids and glasses, and the INM spectrum has contributions from both extended and localized modes. We use the soft-potential mode to describe localized modes. This model is a high-temperature extension of the standard two-level-system model for glasses. The equilibrium position of any atom in the liquid has only temporary character, and relaxation processes in the liquid are associated with particles hopping over …

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High-Order Interior Caustics Produced In Scattering Of A Diagonally Incident Plane Wave By A Circular Cylinder, Charles L. Adler, James A. Lock, Bradley R. Stone, Claudio J. Garcia Jun 1997

High-Order Interior Caustics Produced In Scattering Of A Diagonally Incident Plane Wave By A Circular Cylinder, Charles L. Adler, James A. Lock, Bradley R. Stone, Claudio J. Garcia

Physics Faculty Publications

We examine scattering of a family of initially parallel diagonally incident rays by a dielectric circular cylinder and show that the interior and exterior caustics that occur are qualitatively identical to those produced at normal incidence. We find, however, that (1) varying the plane-wave tilt angle has the same effect on the caustics as varying the refractive index of the cylinder at normal incidence and (2) high-order interior caustics are visible because of larger internal-reflection Fresnel coefficients at diagonal incidence than at normal incidence. We also observe noncaustic ray trajectories produced by the sharp peaking of internal-reflection Fresnel coefficients at …

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