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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 …

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 …

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 …

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 …

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 …

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 …

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 …

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.

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 …

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.

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 …

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 …

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 …

Homeotropic, Rub-Free Liquid-Crystal Light Shutter, Karl A. Crandall, Michael R. Fisch, Rolfe G. Petschek, Charles Rosenblatt

Faculty Scholarship

A liquid-crystal light shutter based upon homeotropic orientation has been fabricated, such that no rubbing is required. The device, which is dark in the voltage-off state and transmitting in the voltage-on state, exhibits contrast ratios in excess of 3000:1, with transmission efficiencies of 70% to 95%. Characterization results of one prototype are reported herein.

Layer-By-Layer Growth Of Hg On W(110), Jiandi Zhang, Dongqi Li, Peter A. Dowben

Peter Dowben Publications

Using photoelectron spectroscopy, the overlayer electronic structure was observed to he modulated by the Hg growth mode for Hg adsorbed on W(110) at 200 K. The Hg layer-by-layer growth was also characterized by variations in the ratio between the Hg 5d shallow core level and W 4f photoemission intensities. This layer-by-layer growth occurs in spite of surprisingly weak electronic interactions between the adatoms and the substrate.

Convection In Chemical Waves, D. A. Vasquez, J. M. Littley, J. W. Wilder, Boyd F. Edwards

All Physics Faculty Publications

We present a theory for the vertical propagation of chemical waves near the onset of convection. Fluid motion, coupled to a standard reaction-diffusion mechanism for chemical wave propagation, determines the speed and shape of the reaction front in a two-dimensional slab. Our model is compared with experiments in capillary tubes. For tilted and horizontal tubes, fluid motion is always present with a corresponding increase in front speed.

Inter-Relations Of Solvable Potentials, Asim Gangopadhyaya, Prasanta K. Panigrahi, Uday P. Sukhatne

Physics: Faculty Publications and Other Works

Solvable Natanzon potentials in nonrelativistic quantum mechanics are known to group into two disjoint classes depending on whether the Schrödinger equation can be reduced to a hypergeometric or a confluent hypergeometric equation. All the potentials within each class are connected via point canonical transformations. We establish a connection between the two classes with appropriate limiting procedures and redefinition of parameters, thereby inter-relating all known solvable potentials.

Subpicosecond Thomson Scattering Measurements Of Optically Ionized Helium Plasmas, T. E. Glover, Thomas D. Donnelly, E. A. Lipman, A. Sullivan, R. W. Falcone

All HMC Faculty Publications and Research

We present the first subpicosecond time-resolved temperature measurements of plasmas produced by high-intensity optical ionization. Thomson scattering is used to measure electron and ion temperatures of helium plasmas created by 125 fs, 800 nm laser pulses focused to an intensity of 2 × 10¹⁷ W/cm². We find that the electron temperature is accurately predicted by a tunneling ionization model. The measured ion temperature is consistent with direct heating by the laser pulse.

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 …

Critical Correlations And Susceptibilities In The Random-Field Spherical Model, Thomas Vojta, Michael Schreiber

Physics Faculty Research & Creative Works

We investigate the behavior of the correlation function and the susceptibility of the random-field spherical model at the critical point. In particular we calculate the critical exponents η and η- describing the divergences of the susceptibility and its disconnected part, respectively. In the case of short-range interactions we obtain η=η-=0. For power-law interactions Uij~rij-σ we find η=1/2η-=D+2-σ (for D<σ

Differential Transfer Ionization Cross Sections For 50175-Kev Proton-Helium Collisions, S. W. Bross, S. M. Bonham, A. D. Gaus, Jerry Peacher, Tibor Vajnai, Michael Schulz, Horst Schmidt-Bocking

Physics Faculty Research & Creative Works

We have measured coincidences between neutralized projectiles and He recoil ions for 50175-keV proton-helium collisions. From the data we obtained transfer ionization (TI) cross sections differential in the projectile scattering angle. Laboratory scattering angles range from 0 to 2.0 mrad. The experimental method allowed separation of the postcollision charge states of the target atoms. The ratio of the cross sections for TI to the sum of TI and single capture, F, is presented as a function of projectile scattering angle. Comparison is made to previous measurements of this ratio where data is available. The differential cross sections are compared to …

Mesostructure Of Photoluminescent Porous Silicon, David D. Allred, F. Ruiz, C. Vázquez-López, Jesus González-Hernández, G. Romero-Paredes, R. Peña-Sierra, G. Torres-Delgado

Faculty Publications

Scanning electron microscopy, atomic force microscopy, and Raman spectroscopy were used to characterize the microstructure of photoluminescent porous silicon (PS) layers formed by the anodic etching (HF:H2O:ethanol), at various current densities, of p-type (100) silicon wafers possessing resitivity in the range 1-2 Ω cm. Existing models for the origin of luminescence in PS are not supported by our observations. Cross-sectional as well as surface atomic force micrographs show the material to be clumpy rather than columnar; rodlike structures are not observed down to a scale of 40 nm. A three-dimensional model of the mesostructure of porous silicon is discussed. Room-temperature …

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)].

Layer-By-Layer Growth Of Hg On W(110), Jiandi Zhang, Dongqi Li, Peter A. Dowben

Peter Dowben Publications

Using photoelectron spectroscopy, the overlayer electronic structure was observed to he modulated by the Hg growth mode for Hg adsorbed on W(110) at 200 K. The Hg layer-by-layer growth was also characterized by variations in the ratio between the Hg 5d shallow core level and W 4f photoemission intensities. This layer-by-layer growth occurs in spite of surprisingly weak electronic interactions between the adatoms and the substrate.