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Constraints On The Minimal Supergravity Model From Non-Standard Vacua, Howard Baer, Michal Brhlik, Diego Castano

Chemistry and Physics Faculty Articles

We evaluate regions of parameter space in the minimal supergravity model where "unbounded from below" (UFB) or charge or color-breaking minima (CCB) occur. Our analysis includes the most important terms from the one-loop effective potential. We note a peculiar discontinuity of results depending on how renormalization group improvement is performed: One case leads to a UFB potential throughout the model parameter space, while the other typically agrees quite well with similar calculations performed using only the tree level potential. We compare our results with constraints from cosmology and naturalness and find a preferred region of parameter space which implies m …

Building A Competition Buzzer Set, John R. Dennison, Richard Davis

All Physics Faculty Publications

No abstract provided.

Investigation Of Ba, Bao, Sr And Sro Pulsed Laser-Induced Vapor Plumes In N2, O2, Microwave Discharged O2, And Vacuum At Low Laser Fluence, David L. Byers

Theses and Dissertations

Ba, BaO, Sr and SrO were ablated by 248 nm laser pulses at fluences ranging from 270 mJ-/cm² to 575 mJ-/cm² in vacuum and in 25 mtorr atmospheres of N2, O2 and microwave-discharged O₂. The spectral emissions of these plumes were compared for indications of ionization due to Ba or Sr collisions with each gas. The addition of a background gas increased the ion and neutral signature across the spectrum. SrO band emission was observed at 16,600-16,900/cm and possible BaO band emissions were observed in the 18,250-18,400/cm, 19,000-19700/cm and 19,800-20,000/cm regions. A screened plate ion probe …

Deconvolution From Wavefront Sensing Using Optimal Wavefront Estimators, Scott R. Maethner

Theses and Dissertations

A cost effective method to improve the space surveillance mission performance of United States Air Force (USAF) ground-based telescopes is investigated and improved. A minimum variance wavefront estimation technique is used to improve Deconvolution from Wavefront Sensing (DWFS), a method to mitigate the effects of atmospheric turbulence on imaging systems that does not require expensive adaptive optics. Both least-squares and minimum variance wavefront phase estimation techniques are investigated, using both Gaussian and Zernike polynomial elementary functions. Imaging simulations and established performance metrics are used to evaluate these wavefront estimation techniques for a one-meter optical telescope. Performance metrics include the average …

Estimation Of Satellite Orientation From Space Surveillance Imagery Measured With An Adaptive Optics Telescope, Gregory E. Wood

Theses and Dissertations

The use of the matched filter to automatically estimate the pose of a Low Earth Orbiting satellite from imagery taken with an adaptive optics telescope is explored. This work represents the first effort to solve the satellite pose estimation problem while considering the broad range of atmospheric turbulence levels and target visual magnitudes that are encountered in ground based space surveillance operations. Several Algorithms are examined in an effort to determine the performance bounds on the matched filter for this application. Results are given over an extremely wide range of seeing conditions. These results are weighted based on historical data …

Electrical Characterization Of Intrinsic And Induced Deep Level Defects In Hexagonal Sic, James D. Scofield

Theses and Dissertations

Deep level defects in hexagonal SiC were studied using digital deep level transient spectroscopy (DLTS) methods over the temperature range of 100 to 800 deg K. New centers were found in bulk and epitaxial 6H-SiC with ionization energies between 0.38 to 1.3 eV, and levels from 0.2 to 0.856 eV were identified in 4H-SiC epitaxy. Direct correlation between inequivalent lattice sites was identified for energetic pairs associated with both vanadium and ion implanted Mg impurities. Nonradioative carrier capture mechanisms were studied and deep level trapping was found to proceed via lattice relaxation multi-phonon emission, indicating efficient electronic lattice coupling in …

Theoretical Modeling Of Linear Absorption Coefficients In Si/Si1-Xgex Multiple Quantum Well Photodetectors, Kevin D. Greene

Theses and Dissertations

Si/Si_1-xGe_x MQW Infrared Photodetectors offer the promise of normal incidence photodetection tunable over the range of 3-12 micrometers wavelength range at temperatures above 40 K. This system is attractive because the Si_1-xGe_x offers greater compatibility with existing Si based signal processing circuitry. Band structures, momentum matrix elements and linear absorption coefficients are computed using a Luftinger-Kohn k/p analysis for Si/Si_1-xGe_x quantum wells grown in the 110 direction. The absorption coefficient as a function of energy and wavelength is calculated by two methods: a delta function fit to intersubband transitions, and a …

Demonstrating Optical Aberration Correction With A Mems Micro-Mirror Device, Shaun R. Hick

Theses and Dissertations

This research conducted the first demonstrated use of a micro-electro-mechanical structure (MEMS) mirror array to correct a static optical aberration. A well-developed technique in adaptive optics imaging systems uses a deformable mirror to reflect the incident wave front to the imaging stage of the system. By matching the surface of the deformable mirror to the shape of the wave front phase distortion, the reflected wave front will be less aberrated before it is imaged. Typical adaptive optics systems use piezo-electric actuated deformable mirrors. This research used an electrostatically actuated, segmented mirror array, constructed by standard MEMS fabrication techniques, to investigate …

Stars Classified As Constant In The General Catalogue Of Variable Stars, Ii, Edward G. Schmidt

Edward Schmidt Publications

Photometric observations have been made of 36 stars classified as CST or CST: in the General Catalogue of Variable Stars. Six of these stars are found to vary and three others were deemed possible variables. Of the certain variables, two (MR Her and TY Sge) are red pulsators, one (V1585 Cyg) is a rapid irregular variable, one is apparently a short period Cepheid-strip star (V432 Oph), one is an eclipsing binary (AQ Boo), and one is of uncertain type (V351 Cyg). The stars we have observed as MR Her and TY Sge are the same ones which were identified on …

L-Shell Resonant Electron Transfer And Excitation In Cu18-19+ + H2 Collisions, Jeffrey A. Wroblewski

Masters Theses

Measurements of L-shell resonant electron transfer and excitation (RTE) were conducted for 45-72 MeV Cu^18-19+ (Na-like and Ne-like, respectively) ions colliding with H₂ using the Western Michigan University EN tandem Van de Graaff accelerator. The RTE process involves an electron-electron interaction between the projectile and the target where electron capture occurs simultaneously with projectile excitation. In previous measurements involving RTE with subsequent L x-ray relaxation for Nb^q+ (q=28-31) ions, the magnitudes of the RTE cross sections were found to be nearly a factor of two smaller than theory. In the analogous electron-ion process of dielectronic recombination, measurements …

Angle-Resolved X-Ray Circular And Magnetic Circular Dichroisms: Definitions And Applications, Sy Y. Tong, X. Q. Guo, James G. Tobin, George Daniel Waddill

Physics Faculty Research & Creative Works

We introduce definitions of angle-resolved x-ray circular dichroism (ARXCD) and magnetic x-ray circular dichroism (ARMXCD). As defined, the much larger effect of circular dichroism (ARXCD) is separated from the smaller magnetic (ARMXCD) effect. In all materials, ARXCD is zero along mirror planes while nonzero elsewhere. ARMXCD is nonzero only in magnetic materials. The measurement and analysis of ARMXCD allow element specific surface magnetism and surface structure as well as their inter-relationship to be studied as functions of the outgoing electron's direction.

Far-Field Scattering Of A Non-Gaussian Off-Axis Axisymmetric Laser Beam By A Spherical Particle, James A. Lock, Joseph T. Hodges

Physics Faculty Publications

Experimental laser beam profiles often deviate somewhat from the ideal Gaussian shape of the axisymmetric TEM(00) laser mode. To take these deviations into account when calculating light scattering of an off-axis beam by a spherical particle, we use our phase-modeling method to approximate the beam-shape coefficients in the partial wave expansion of an experimental laser beam. We then use these beam-shape coefficients to compute the near-forward direction scattering of the off-axis beam by the particle. Our results are compared with laboratory data, and we give a physical interpretation of the various features observed in the angular scattering patterns. (C) 1996 …

Photoionization Of Atoms, Anthony F. Starace

Anthony F. Starace Publications

This chapter outlines the theory of atomic photoionization, and the dynamics of the photon-atom collision process. Those kinds of electron correlation that are most important in photoionization are emphasized, although many qualitative features can be understood within a central field model. The particle-hole type of electron correlations are discussed, as they are by far the most important for describing the single photoionization of atoms near ionization thresholds. Detailed reviews of atomic photoionization are presented in Refs. [I] and 121. Current activities and interests are well-described in two recent books [3,4]

Potentials With Two Shifted Sets Of Equally Spaced Eigenvalues And Their Calogero Spectrum, Asim Gangopadhyaya, Uday P. Sukhatme

Physics: Faculty Publications and Other Works

Motivated by the concept of shape invariance in supersymmetric quantum mechanics, we obtain potentials whose spectrum consists of two shifted sets of equally spaced energy levels. These potentials are similar to the Calogero-Sutherland model except the singular term αx−2 always falls in the transition region -1/4 < a < 3/4 and there is a δ-function singularity at x=0.

Asymptotic Conservation Laws In Field Theory, Ian M. Anderson, Charles G. Torre

All Physics Faculty Publications

A new, general, field theoretic approach to the derivation of asymptotic conservation laws is presented. In this approach asymptotic conservation laws are constructed directly from the field equations according to a universal prescription which does not rely upon the existence of Noether identities or any Lagrangian or Hamiltonian formalisms. The resulting general expressions of the conservation laws enjoy important invariance properties and synthesize all known asymptotic conservation laws, such as the Arnowitt-Deser-Misner energy in general relativity.

Laboratory Synthesis Of Molecular Hydrogen On Surfaces Of Astrophysical Interest, Gianfranco Vidali, V Pirronello, Chi Liu, Liyong Shen

Physics - All Scholarship

We report on the first results of experiments to measure the recombination rate of hydrogen on surfaces of astrophysical interest. Our measurements give lower values for the recombination efficiency (sticking probability S x probability of recombination upon H-H encounter \gamma) than model-based estimates. We propose that our results can be reconciled with average estimates of the recombination rate (1/2 n(H) n(g) v(H)A S \gamma) from astronomical observations, if the actual surface of an average grain is rougher, and its area bigger, than the one considered in models.

Electron Energy Distributions From Multiple Ionization In 20–120-Kev H+ + Ar Collisions, Yang-Soo Chung, M. Eugene Rudd

M. Eugene Rudd Publications

Energy-analyzed secondary electrons from H⁺ + Ar collisions at eight proton energies from 20 to 120 keV were detected in coincidence with recoil ions of charge states 1–3. The charge states were distinguished by time-of-flight measurements and the electron energies were analyzed by a newly designed electrostatic analyzer of the low-pass high-pass filter type which has a large (~1.45π steradian) solid angle acceptance. For each of nine electron energies from 10 to 160 eV, the ionizing events associated with each residual ion charge state were counted. The electron energy dependence of the charge-state ratios and the average charge determined …

Music And Mathematics, Roxanne Kitts

Humanistic Mathematics Network Journal

No abstract provided.

Spectral Content And Dispersion Of Hyper-Rayleigh Scattering, S. F. Hubbard, Rolfe G. Petschek, Kenneth D. Singer

Faculty Scholarship

We have used a high-intensity tunable picosecond infrared laser source to measure the spectral content of light scattered near the second harmonic for two well-known organic dyes, p-Nitroaniline and Disperse Red 1, at a number of wavelengths in the near infrared. We found that in Disperse red 1 a broad two-photon fluorescence competes with the sharp hyper-Rayleigh peak. Further, dephasing of the virtual excited state leads to elimination of hyper-Rayleigh scattering in favor of fluorescence if the harmonic is in the linear absorption tail. We determined the dispersion of the magnitude of the first hyperpolarizability for both dyes, using a …

A 2-D Numerical Simulation And Analysis Of A Simple Band Model For The Priz Spatial Light Modulator, Gary D. Barmore

Theses and Dissertations

This dissertation discusses the development of and analyzes the first complete, 2-D numerical simulation of the PRIZ. The simulation is based upon a simple band model of the PRIZ: a single donor, a single trap, and free electron carriers. Modeled mechanisms include photogeneration, energy level transitions, injection, drift currents, diffusion currents, photorefraction and diffraction. The model goes beyond the previous charge and field dynamics of 1-D numerical models to include optical effects, and it eliminates the oversimplifications and assumptions used in earlier mathematical models with closed solutions. Sensitivity analyses and selected simulations provide a better understanding of the dynamic imaging …

Surface Phenomena On The Tin-Dioxide Polycrystalline Layers, Andrei A. Fluerasu

Theses

Polycrystalline tin-dioxide is widely used in the detection of reducing gases (such as H₂, CO, CH₄, C₂H₅OH,...) in air by measuring its conductivity changes. The advantage of gas sensors based on such sensing devices is low cost and high sensitivity. In contrast to their widespread applications and to their successful empirical research and development work, the present understanding of the chemical sensing mechanisms is still immature.

In this thesis, for gas sensors based on thick and porous tin-dioxide layers, a study of the response function upon variation of the partial pressure of …

Radial Dose Distributions In The Delta-Ray Theory Of Track Structure, Francis A. Cucinotta, Robert Katz, John W. Wilson, Rajendra R. Dubey

Department of Physics and Astronomy: Faculty Publications

The radial dose distribution from delta rays, fundamental to the delta ray theory of track structure, is recalculated. We now include the model of Rudd for the secondary electron spectrum in proton collisions. We include the effects of electron transmission through matter and the angular dependence of secondary electron emission. Empirical formulas for electron range versus electron energy are intercompared in a wide variety of materials in order to extend the track structure theory to arbitrary media. Radial dose calculations for carbon, water, silicon, and gold are discussed. As in the past, effective charge is used to scale to heavier …

Effect Of Beam Attenuation On Photorefractive Grating Erasure, Martin M Liphardt, Arosha Goonesekera, Stephen Ducharme, James M. Takacs, Lei Zhang

Stephen Ducharme Publications

We investigate the influence of attenuation on the speed of erasure of photorefractive gratings by solving the coupled-wave equations in the undepleted pump approximation and by taking into account the attenuation and Gaussian intensity profile of all the beams. The extrinsic grating decay rate is significantly lower than the intrinsic photorefractive decay rate in samples with overall attenuation as low as 10%. The Gaussian beam profiles of the readout and the erasing beams result in a further reduction of the extrinsic decay rate. The results of these calculations are used to determine the spectrum of intrinsic decay rates in a …

Breakdown Of Landau-Ginzburg-Wilson Theory For Certain Quantum Phase Transitions, Thomas Vojta, Dietrich Belitz, Rajesh S. Narayanan, Theodore R. Kirkpatrick

Physics Faculty Research & Creative Works

The quantum ferromagnetic transition of itinerant electrons is considered. It is shown that the Landau-Ginzburg-Wilson theory described by Hertz and others breaks down due to a singular coupling between fluctuations of the conserved order parameter. This coupling induces an effective long-range interaction between the spins of the form 1/r^2d-1. It leads to unusual scaling behavior at the quantum critical point in 1 < d ≤ 3 dimensions, which is determined exactly.

The Current Energy Situation: Summary Points, David W. Hafemeister, A. Brecher, A. Fainberg, R. Howes, R. Socolow, D. Bodansky, P. Craig, B. Hammer, S. Smith, E. Stechel

Physics

Energy problems are now being largely ignored, despite their continuing importance. The near-disappearance of energy from the U.S. public agenda is apparent in the scant attention given to energy topics by the media and by public figures. Some suggestions for governmental action were stimulated by the rise in gasoline prices in the Spring of 1996, but the matter was treated as a short-term anomaly -- not as a harbinger of more severe difficulties to come. This lack of long term concern is perhaps natural, because fuel supplies are generally ample and prices are still relatively low, with the real cost …

Observation Of Events With An Energetic Forward Neutron In Deep Inelastic Scattering At Hera, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. R. Okrasinski, J. Repond, R. Stanek, R. L. Talaga, H. Zhang, Margarita C. K. Mattingly, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, R. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, I. Gialas, R. Giusti, G. Iacobucci, G. Laurenti, G. Levi, A. Margotti, T. Massam

Faculty Publications

In deep inelastic neutral current scattering of positrons and protons at the center of mass energy of 300 GeV, we observe, with the ZEUS detector, events with a high energy neutron produced at very small scattering angles with respect to the proton direction. The events constitute a fixed fraction of the deep inelastic, neutral current event sample independent of Bjorken x and Q2 in the range 3 · 10-4 < xBJ < 6 · 10-3 and 10 < Q2 < 100 GeV2.

Dijet Angular Distributions In Direct And Resolved Photoproduction At Hera, M. Derrick, D. Krakauer, S. Magill, D. Mikunas, B. Musgrave, J. R. Okrasinski, J. Repond, R. Stanek, R. L. Talaga, H. Zhang, Margarita C. K. Mattingly, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, R. Bruni, G. Cara Romeo, G. Castellini, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, I. Gialas, R. Giusti, G. Iacobucci, G. Laurenti, G. Levi, A. Margotti, T. Massam

Faculty Publications

Jet photoproduction, where the two highest transverse energy (ETjet) jets have ETjet above 6 GeV and a jet-jet invariant mass above 23 GeV, has been studied with the ZEUS detector at the HERA ep collider. Resolved and direct photoproduction samples have been separated. The cross section as a function of the angle between the jet-jet axis and the beam direction in the dijet rest frame has been measured for the two samples. The measured angular distributions differ markedly from each other. They agree with the predictions of QCD calculations, where the different angular distributions reflect the different spins of the …

Physical Conditions In Low-Ionization Regions Of The Orion Nebula, J. A. Baldwin, A. Crotts, R. J. Dufour, Gary J. Ferland, S. Heathcote, J. J. Hester, K. T. Korista, P. G. Martin, C. R. O'Dell, R. H. Rubin, A. G. G. M. Tielens, D. A. Verner, D. K. Walter, Z. Wen

Physics and Astronomy Faculty Publications

We reexamine the spectroscopic underpinnings of recent suggestions that [O I] and [Fe II] lines from the Orion H II region are produced in gas where the iron-carrying grains have been destroyed and the electron density is surprisingly high. Our new observations show that previous detections of [O I] 5577 were dominated by telluric emission. Our limits are consistent with a moderate density (≈ 10⁴ cm^-3) photoionized gas. We show that a previously proposed model of the Orion H II region reproduces the observed [O I] and [Fe II] spectrum. These lines are fully consistent with formation …

Fundamental Aspects Of Atomic Photoionization With High-Brightness Light Sources, Anthony F. Starace, Steven T. Manson

Anthony F. Starace Publications

The construction of numerous new synchrotron light sources worldwide is providing the means to study atomic and molecular photoionization processes at a level of detail that is unparalleled in even the recent past. Correspondingly, in theory, the availability of supercomputers and, perhaps more important, relatively inexpensive computer workstations, has permitted theoretical calculations to tackle more complex processes than ever before. In short, these technical developments are creating an unprecedented amount of data to be analyzed and understood.

In this volume, many of the experimental and theoretical advances of recent years will be described. We take the point of view in …

Ground-State Roughness Of The Disordered Substrate And Flux Line In D=2, Alan Middleton, Chen Zeng, Y. Shapir

Physics - All Scholarship

We apply optimization algorithms to the problem of finding ground states for crystalline surfaces and flux lines arrays in presence of disorder. The algorithms provide ground states in polynomial time, which provides for a more precise study of the interface widths than from Monte Carlo simulations at finite temperature. Using $d=2$ systems up to size $420^2$, with a minimum of $2 \times 10^3$ realizations at each size, we find very strong evidence for a $\ln^2(L)$ super-rough state at low temperatures.