Physics Commons^™

Non-Perturbative Renormalization Group Flows In Two-Dimensional Quantum Gravity, Simon Catterall, Ray L. Renken, John B. Kogut

Physics - All Scholarship

Recently a block spin renormalization group approach was proposed for the dynamical triangulation formulation of two-dimensional quantum gravity. We use this approach to examine non-perturbatively a particular class of higher derivative actions for pure gravity.

The Algorithmic Complexity Of Neural Spike Trains Increases During Focal Seizures, P. E. Rapp, I. D. Zimmerman, E. P. Vining, N. Cohn, Alfonso M. Albano, M. A. Jimenez Montano

Physics Faculty Research and Scholarship

The interspike interval spike trains of spontaneously active cortical neurons can display nonrandom internal structure. The degree of nonrandom structure can be quantified and was found to decrease during focal epileptic seizures. Greater statistical discrimination between the two physiological conditions (normal vs seizure) was obtained with,measurements of context-free grammar complexity than by measures of the distribution of the interspike intervals such as the mean interval, its standard deviation, skewness, or kurtosis. An examination of fixed epoch data sets showed that two factors contribute to the complexity: the firing rate and the internal structure of the spike train. However, calculations with …

Multiple Hadron Production By 14.5 Gev Electron And Positron Scattering From Nuclear Targets, P V. Degtyarenko, J Button-Shafer, L Elouadrhiri, R A. Miskimen, Gerald Alvin Peterson, K Wang

Gerald Alvin Peterson

Multiple proton and pion electroproduction from nuclei are studied. Final states including at least two protons produced by the interaction of 14.5 GeV electrons and positrons with light nuclei (mainly 12C and 16O) have been measured, and compared with analogous data from 40Ar. Scattered electrons and positrons were detected in the energy transfer range from 0.2 to 12.5 GeV, and four-momentum transfer squared range from 0.1 to 5.0 GeV2/c2. Phenomenological characteristics of the secondary hadron production cross sections such as temperature and velocity of the effective source of hadrons were found to be dependent on energy transfer to the nucleus …

Performance Of An Inertially Coupled, 3-Mode Gravitational-Wave Antenna Prototype, Linda E. Marchese, Mark F. Bocko, Guizhen Zhang, Munawar Karim

Physics Faculty/Staff Publications

A prototype three‐mode gravitational wave antenna which employs a two‐mode torsional transducer has been constructed and tested. For the torsional transducer the coupling from one stage to the next is via inertial forces, whereas in a conventional transducer the stage‐to‐stage coupling is proportional to the relative displacements via the springs. Experiments with our antenna‐torsional transducer prototype demonstrate a maximum antenna bandwidth of 260 Hz (29% of the antenna resonant frequency of 900 Hz) and a mechanical amplification factor of 40. A mathematical model for the three‐mode antenna has been developed and predictions of the system transfer functions and transient response …

Landau-Zener Treatment Of Intensity-Tuned Multiphoton Resonances Of Potassium, J. Greg Story, D. I. Duncan, Thomas F. Gallagher

Physics Faculty Research & Creative Works

When exposed to intense light of ~580 nm, the ground state of K shifts up in energy, passing through two photon resonances with Rydberg states, and finally crossing the two-photon ionization limit. We have used laser pulses of varying duration to study the nature of the population transfer from the ground state to the excited state due to the intensity-tuned resonances encountered during the rising edge of the pulse. A dynamic Floquet approach in which the resonances are treated as avoided crossings of the Floquet energy levels is used to model the population transfer and gives excellent agreement with the …

A Procedure For G-Matrix Calculation From A Momentum Space Potential, Zhaohui Gao Busche

Masters Theses

In this work a numerical procedure was found to calculate the G-matrix in momentum space with a momentum space potential. The integral equation for the G-matrix was solved by conversion to a matrix equation. Two numerical integral methods, three-point Simpson method and Gaussian integral method, were employed in this process to determine the more efficient method.

The resulting G-matrix in momentum space was Fourier transformed into coordinate space. This was compared with the results of the G-matrix calculated from coordinate space directly as well as the results from solving the Bethe-Goldstone equation. A 2% accuracy was achieved with both the …

Reply To D. E. Watt, A. S. Alkharam, M. B. Child And M. S. Salikin, “Dose As A Damage Specifier In Radiobiology For Radiation Protection." A Comment On "Dose" (Radiat. Res. 137, 410-413, 1994), Robert Katz

Robert Katz Publications

The authors are generous in observing that "the high degree of success achieved by (Katz's δ-ray theory of track structure) in fits to survival curves for heavy ions, and in analysis and prediction of other biological effects is almost legend." We remind them that the model is physical, and has little to do with biology in an explicit way, except that an oversimplified "bean bag" model of a eukaryotic cell is used, in which the bag represents the cell nucleus and the beans represent internal targets. No explicit biologically mechanistic structure or response is inferred. No reference is made to …

Asymmetric Adsorbate And Substrate Interactions In Physisorbed Systems: N2 On Graphite And Dipolar Molecules On Ionic Substrates, Teresa Ellen Burns

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Asymmetries in physisorbed systems give rise to interesting phases and phase transitions in two-dimensional (2D) monolayer and multilayer systems. The effects of asymmetric adsorbate and substrate interactions in monolayers of dipolar molecules on ionic substrates and N₂ on graphite are studied.

In the case of dipolar molecules on ionic substrates, 2D dielectric phase transitions using a modified Blume-Emery-Griffiths (BEG) model are determined theoretically. A dipole adsorbed vertically above a metal ion lattice site, and pointing up (down), is assigned a spin S=+1 (S=-1). An empty lattice site is assigned a spin S=0. Analytic solutions for both ferroelectrically and antiferroelectrically …

Use Of Infrared Spectrometry To Determine The Effect Of Temperature On The Description Rates Of Trichloroethylene From Plastic Clay 98b, Abdellatif Fares

Theses and Dissertations

This thesis investigated the influence of temperature on the desorption rated of trichloroethylene (TCE) from plastic clay. It was expected that an increase in temperature will cause an increase in both the desorption rates of TCE and in the desorbed quantity. Previous studies on other chemicals indicated a faster decrease in the remaining sorbed concentration with an increase in temperature. This research made use of the infrared optical absorption technique. IR spectroscopy was used to measure the concentration of the vapor TCE that desorbed from the soil. The soil was exposed to liquid TCE for 2 days then placed inside …

The Optical Emission And Absorption Properties Of Silicon-Germanium Superlattice Structures Grown On Non-Conventional Silicon Substrate Orientation, Theodore L. Kreifels

Theses and Dissertations

Optical emission and absorption properties of Si_1-x Ge_x/Si superlattices grown on (100), (110), and (111) Si substrates were investigated to determine the optimal growth conditions for these structures to be used as infrared detectors. Fully-strained Si_1-x Ge_x/Si superlattices were grown by molecular beam epitaxy MBE and examined using low-temperature photoluminescence PL to identify no-phonon and phonon-replica interband transitions across the alloy bandgap. Phonon-resolved emission was most intense for undoped quantum wells grown at 710°C for all three silicon orientations. Room temperature absorption measurements were conducted on (100) and (110) Si_1-x Ge_x/Si …

Effect Of Carrier Gas Pressure On Condensation In A Supersonic Nozzle, Barbara Ellen Wyslouzil, Gerald Wilemski, M. G. Beals, Michael B. Frish

Physics Faculty Research & Creative Works

Supersonic nozzle experiments were performed with a fixed water or ethanol vapor pressure and varying amounts of nitrogen to test the hypothesis that carrier gas pressure affects the onset of condensation. Such an effect might occur if nonisothermal nucleation were important under conditions of excess carrier gas in the atmospheric pressure range, as has been suggested by Ford and Clement [J. Phys. A 22, 4007 (1989)]. Although a small increase was observed in the condensation onset temperature as the stagnation pressure was reduced from 3 to 0.5 atm, these changes cannot be attributed to any nonisothermal effects. The pulsed nozzle …

Neutron-Diffraction Study Of Γ-Fe At High Pressure, Oran Allan Pringle, Rafael Calvo, R. E. Parra

Physics Faculty Research & Creative Works

Face-centered-cubic iron (γ-Fe) coherently precipitated in a single crystal of Cu has been studied by neutron diffraction at high pressures up to 0.9 GPa and in the temperature range from about 5 to 110 K. It undergoes antiferromagnetic ordering at 67±2 K at ambient pressure. The ordering temperature T_N monotonically decreases with increasing pressure following a relation T_N(K)=67-12.8p - 11.1p² - 6.17p³, where p is in units of GPa. The change of T_N in γ-Fe is discussed in terms of the volume change caused by pressurization or by alloying.

36th Rocky Mountain Conference On Analytical Chemistry

Rocky Mountain Conference on Magnetic Resonance

Program, abstracts, and information about the 36th annual meeting of the Rocky Mountain Conference on Analytical Chemistry, co-sponsored by the Colorado Section of the American Chemical Society and the Rocky Mountain Section of the Society for Applied Spectroscopy. Held in Denver, Colorado, July 31 - August 5, 1994.

Building Of A Thermoacoustic Refrigerator And Measuring The Basic Performance, Torsten Blumreiter

Dissertations and Theses

The application of thermoacoustic phenomena for cooling purposes has a comparatively short history. However, recent experiments have shown that thermoacoustic refrigeration can achieve practical significance for both every day cooling in households and cryocooling for scientific purposes due to its high reliability, environmental safety and functioning under extreme conditions.

We build a thermoacoustic refrigerator driven by a commercial loudspeaker. It was equipped with a vacuum pump and an entrance port for introducing different gases under different pressures as working fluids. It contained two thermocouples and a pressure transducer for quantitative measurements of the basic performance. The resonance frequency of the …

The Optical-Ultraviolet-Γ-Ray Spectrum Of 3c 279, Hagai Netzer, D. Kazanas, Beverley J. Wills, D. Wills, Han Mingsheng, M. S. Brotherton, J A. Baldwin, Gary J. Ferland, I. W. A. Browne

Physics and Astronomy Faculty Publications

We have obtained spectrosocpy of the violently variable quasar 3C 279, simultaneous with γ-ray observations, in 1992 April. Our combined optical (McDonald Observatory and Cerro Tololo InterAmerican Observatory (CTIO) and ultraviolet (HST) observations, made when the source was faint, show a very steep power-law continuum (F_ν∝ν^-1.95) and strong broad emission lines. This is the first time that the broad ultraviolet lines of this object have been measured, and we note several unusual properties of the spectrum. In particular, the profiles of C IV λ1549 and Mg II λ …

Rainbow Scattering By A Coated Sphere, James A. Lock, J. Michael Jamison, Chih-Yang Lin

Physics Faculty Publications

We examine the behavior of the first-order rainbow for a coated sphere by using both ray theory and Aden-Kerker wave theory as the radius of the core alpha12 and the thickness of the coating delta are varied. As the ratio delta/alpha12 increases from 10(-4) to 0.33, we find three classes of rainbow phenomena that cannot occur for a homogeneous-sphere rainbow. For delta/alpha12 less than or similar to 10(-3), the rainbow intensity is an oscillatory function of the coating thickness, for delta/alpha12 almost-equal-to 10(-2), the first-order rainbow breaks into a pair of twin rainbows, and for delta/alpha12 almost-equal-to 0.33, various rainbow-extinction …

Light And Color In The Open Air: Introduction By The Feature Editors, James A. Lock

Physics Faculty Publications

The natural environment is still rich in new observable phenomena despite centuries of scientific observation. Reflecting this fact, the papers in this feature issue of Applied Optics report the observation and analysis of both new and well-known naked-eye optical phenomena.

Correlated Light Scattering By A Dense Distribution Of Condensation Droplets On A Window Pane, James A. Lock, Chin-Lien Chiu

Physics Faculty Publications

An analytical model of the scattering structure factor for an assembly of noninteracting hard disks has recently appeared in the literature [Phys. Rev. A 42, 5978-5989 (1990)]. We employ this model to calculate correlated light scattering by monodispersions and binary mixtures of condensation droplets on a window pane. We find that an area fraction of f greater-than-or-equal-to 0.6 is required for producing the near-forward direction scattering suppression and that a moderately wide polydispersion of droplet sizes is capable of producing the experimentally observed bright ring of colored light.

Self-Organized Criticality In Non-Conserved Systems, Alan Middleton, Chao Tang

Physics - All Scholarship

The origin of self-organized criticality in a model without conservation law (Olami, Feder, and Christensen, Phys. Rev. Lett. {\bf 68}, 1244 (1992)) is studied. The homogeneous system with periodic boundary condition is found to be periodic and neutrally stable. A change to open boundaries results in the invasion of the interior by a ``self-organized'' region. The mechanism for the self-organization is closely related to the synchronization or phase-locking of the individual elements with each other. A simplified model of marginal oscillator locking on a directed lattice is used to explain many of the features in the non-conserved model: in particular, …

Twin-Boundary Pinning Of Superconducting Vortex Arrays, M. Cristina Marchetti, Valerii M. Vinokur

Physics - All Scholarship

We discuss the low-temperature dynamics of magnetic flux lines in high-temperature superconductors in the presence of a family of parallel twin planes that contain the $c$ axis. A current applied along the twin planes drives flux motion in the direction transverse to the planes and acts like an electric field applied to {\it one-dimensional} carriers in disordered semiconductors. As in flux arrays with columnar pins, there is a regime where the dynamics is dominated by superkink excitations that correspond to Mott variable range hopping (VRH) of carriers. In one dimension, however, rare events, such as large regions void of twin …

Compositional Short-Range Ordering In Metallic Alloys: Band-Filling, Charge-Transfer, And Size Effects From A First-Principles All-Electron Landau-Type Theory, J. B. Staunton, Duane D. Johnson, F. J. Pinski

Duane D. Johnson

Using a mean-field statistical description, we derive a general formalism to investigate atomic short-range order in alloys based on a density-functional description of the finite-temperature, grand potential of the random alloy. This ‘‘first-principles,’’ Landau-type approach attempts to treat several contributions (electronic structure, Fermi surface, electrostatics, magnetism, etc.) to the electronic energy on an equal footing. An important ingredient for the statistical averaging is the replacement of the molecular mean fields (Weiss fields) with Onsager cavity fields, which forces the diagonal part of the fluctuation-dissipation theorem to be obeyed. To show its general applicability and usefulness, we apply the theory to …

First-Principles All-Electron Theory Of Atomic Short-Range Ordering In Metallic Alloys: D022- Versus L12-Like Correlations, Duane D. Johnson, J. B. Staunton, F. J. Pinski

Duane D. Johnson

We use a ‘‘first-principles’’ concentration-wave approach based on a finite-temperature, electronic density-functional, mean-field, grand potential of the random alloy to investigate the high-temperature atomic short-range order (ASRO) in Ni75V25 and Pd75V25 solid solutions. Experimentally, these similar alloys both develop D022-type long-range order at low temperatures but different ASRO at high temperatures. Our calculations describe the measured ASRO well. We compare these results with those found for a hypothetical Co75Ti25 solid solution. Since this alloy orders directly from the melt into the L12 phase, it should exhibit strong L12-like ASRO, as we find in our calculations. We analyze the features in …

Deep Traps In Molecular-Beam-Epitaxial Gaas Grown At Low Temperatures, David C. Look, Z-Q. Fang, H. Yamamoto, J. R. Sizelove, M. G. Mier, C. E. Stutz

Physics Faculty Publications

Deep‐level transient spectroscopy has been performed on Si‐doped GaAs layers grown by molecular‐beam epitaxy at substrate temperatures of 400–450 °C. The λ effect is taken into account and overlapping peaks are analyzed numerically. An 0.65 eV electron trap of concentration 2×10¹⁶ cm⁻³ is believed to be related to the As_Ga‐associated 0.65 eV Hall‐effect center, and also to the trap EB4 found in electron‐irradiated GaAs.

Interfacing A Computer To A Scanning Tunneling Microscope, Markus Jarasch

Dissertations and Theses

A program was written in 'C' to control the functions of an already existing Scanning Tunneling Microscope (STM). A DAS-1601 data acquisition card (from Keithley Data Acquisition) was installed together with its drivers for 'C' on a computer with a 486-DX motherboard. The computer was interfaced to the electronics of the STM. Images taken of HOPG (highly oriented pyrolitic graphite) were of a reasonable quality and showed atomic resolution.

Electrophoretic Studies Of Ion Adsorption To Sarcoplasmic Reticulum And Phosphatidylcholine Membranes, Andreas Schilling

Dissertations and Theses

In this study, electrophoretic mobilities of native and two types of trypsin digested sarcoplasmic reticulum vesicles have been determined by microelectrophoresis using a Doppler Electrophoretic Light Scattering Analyzer to investigate the influence of hydrodynamic drag, caused by the Ca2⁺, Mg2⁺ -ATPase protruding from the surface of native sarcoplasmic reticulum vesicles. After the prolonged digestion (protein:trypsin ratio of 20 for 3 hours at 25°C), the ATPase was cleaved and removed from the sarcoplasmic reticulum membrane as shown with SDS gel electrophoresis and an ATPase activity assay. Ionic strength and pH dependence of mobility showed a nearly pH independent …

Interactions Of Ruthenium Red With Phospholipid Vesicles, Dirk Voelker

Dissertations and Theses

We have studied the electrostatic and other interactions of the inorganic, hexavalent dye Ruthenium Red (RR) with phospholipid vesicles composed of phosphatidylcholine (PC) and phosphatidylserine (PS) or phosphatidylinositol (Pl) in various mixtures and concentrations. Experiments were based on spectrophotometric absorption measurements which compared RR concentrations in the presence and in the absence of liposomes at different dye concentrations. Multilamellar liposomes were obtained by handshaken preparations. Five freeze-and-thaw cycles of the lipid-RR suspension produced an ion equilibrium distribution at the membrane-water interface. Results are given in terms of the Gouy-Chapman-Stem adsorption theory with the linear partition coefficient and a newly introduced …

Comparison Of Magnetic Properties Of Polysaccharide Iron Complex (P.I.C.) And Ferritin, M. E. Y. Mohie-Eldin, Richard B. Frankel, L. Gunther

Physics

The synthetic polysaccharide iron complex (PIC) molecule has been suggested as a ‘biomimic’, i.e. a counterpart, to the naturally occurring biological molecule ferritin with respect to its magnetic properties based on the identification of ferrihydrite as the major mineral in both. Magnetization measurements were used to investigate the magnetic properties of PIC in relation to those of ferritin, as well as to identify differences in such properties between naturally occurring ferritin, which we designate here as Ferritin I, and ferritin with an artificially high content of Fe²⁺ ions bound to its core, which is designated here as Ferritin II. …

Surface-Induced Ordering In Asymmetric Block Copolymers, Y. Liu, W. Zhao, X. Zheng, Alexander H. King, A. Sing, M. H. Rafailovich, J. Sokolov, K. H. Dai, E. J. Kramer, S. A. Schwarz, O. Gebizlioglu, S. K. Sinha

Alexander H. King

The surface-induced ordering in thin films of asymmetric deuterated polystyrene (dPS)- poly(viny1pyridine) (PVP) diblock and triblock copolymers of comparable polymerization index and PVP volume fraction - 0.25) was studied using transmission electron microscopy, atomic force microscopy, secondary ion massspectrometry, and neutron reflectivity. The morphology of both di- and triblock copolymer films was found to be cylindrical except for the layer adjacent to the silicon oxide surface, which due to the strong interaction of silica with PVP, was lamellar. The spacing between adjacent cylindrical layers was found to be consistent with mean field theory predictions. In the triblock copolymer films the …

Direct Relation Between Fresnel's Interface Reflection Coefficients For The Parallel And Perpendicular Polarizations: Erratum 2, R. M.A. Azzam

Electrical Engineering Faculty Publications

The record is set straight concerning two equations that determine the reflection phase shifts at a single interface from the intensity reflectances forp- and s-polarized light at one angle of incidence. These equations appeared previously in this journal [J. Opt. Soc. Am. 69, 1007 (1979); erratum, J. Opt. Soc. Am. 70, 261 (1980)].

Magneto-Hall Characterization Of Delta-Doped Pseudomorphic High-Electron-Mobility Transistor Structures, David C. Look, B. Jogai, C. E. Stutz, R. E. Sherriff, G. C. Desalvo, T. J. Rogers, J. M. Ballingall

Physics Faculty Publications

Conventional Hall‐effect determination of the two‐dimensional electron gas (2DEG) concentration n_2D in pseudomorphic high electron mobility transistor structures is invalid because of interference from the highly doped GaAs cap. Furthermore, the usual methods of dealing with this cap‐interference problem, namely, (1) etching off the cap totally, (2) etching the cap until the mobility reaches a maximum, or (3) growing a separate structure with a thin, depleted cap, in general, give n_2D values that are too low. However, we show here that magnetic‐field‐dependent Hall (M‐Hall) measurements can separately determine the carrier concentrations and mobilities in the cap and 2DEG …