Physical Sciences and Mathematics Commons^™

Excited Heavy Baryons In The Bound State Picture, Joseph Schechter, Anand Subbaraman

Physics - All Scholarship

The orbitally excited heavy quark baryons are studied in the Callan Klebanov bound state model with heavy spin symmetry. First, a compact description of the large N_c, infinite heavy quark mass bound state wavefunctions and the collective quantization is given. In order to study the kinematical corrections due to finite masses we motivate an approximate Schrodinger-like equation for the bound state. The effective potential in this equation is compared with the quadratic approximation (spherical harmonic oscillator) to it. This oscillator approximation is seen to be not very accurate. It is noted that the present experimental information cannot be even qualitatively …

Low-Frequency Line Shapes In Guided Acoustic-Wave Brillouin Scattering, Benjamin I. Greene, Peter N. Saeta

All HMC Faculty Publications and Research

Guided acoustic‐wave Brillouin scattering (GAWBS) measurements were performed on 20‐cm lengths of optical fibers with particular attention focused on the lowest lying resonance. In 125‐μm‐diam silica fibers, this resonance was observed to occur at ~22 MHz and have a line shape which varied erratically from sample to sample. Significant line shape fluctuations were evident even between sequential samples from the same fiber spool. We speculate that the observed effects are attributable to 0.01-0.1 μm distributed geometric deviations from a perfect cylinder.

Boundary Conditions For The Diffusion Equation In Radiative Transfer, Richard C. Haskell, Lars O. Svaasand, Tsong-Tseh Tsay, Ti-Chen Feng, Matthew S. Mcadams, Bruce J. Tromberg

All HMC Faculty Publications and Research

Using the method of images, we examine the three boundary conditions commonly applied to the surface of a semi-infinite turbid medium. We find that the image-charge configurations of the partial-current and extrapolated-boundary conditions have the same dipole and quadrupole moments and that the two corresponding solutions to the diffusion equation are approximately equal. In the application of diffusion theory to frequency-domain photon-migration (FDPM) data, these two approaches yield values for the scattering and absorption coefficients that are equal to within 3%. Moreover, the two boundary conditions can be combined to yield a remarkably simple, accurate, and computationally fast method for …

Nondestructive Mapping Of Carrier Concentration And Dislocation Density In N(+)-Type Gaas, David C. Look, D. C. Walters, M. G. Mier, J. R. Sizelove

Physics Faculty Publications

Transmission mappings (500 μm×500 μm resolution) at wavelengths of 0.9–1.5 μm on 3 in., n⁺‐GaAs wafers (n≂1–2×10¹⁸ cm^-3) correlate well with carrier concentration n, measured by the Hall effect, and dislocation density, as confirmed by KOH etch‐pit patterns. The absorption for λ≳1.0 μm (below band edge) varies directly with n via free‐carrier interconduction‐band transitions, while the absorption for λ≲0.95 μm (near band edge) varies inversely with n because of band‐filling effects. Both phenomena are highly useful for n⁺‐GaAs wafer characterization.

Diamagnetic Shifts Of Excitons Associated With Symmetrical And Antisymmetric Wave Functions In Coupled Inxga1-Xas-Gaas Quantum Wells, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz

Physics Faculty Publications

Magneto‐optical data obtained from photoluminescence and photoluminescence excitation measurements performed in the presence of applied magnetic fields were used to determine the diamagnetic shifts of free excitons. The samples studied were coupled In_xGa_1−xAs–GaAs quantum wells. In all cases the excitons associated with antisymmetric wave functions were found to have larger diamagnetic shifts than the excitons associated with symmetric wave functions. This suggests that the excitons associated with antisymmetric wave functions have a smaller binding energy than excitons associated with symmetric wave functions. These properties are consistent with the fact that excitons associated with antisymmetric wave …

Magnetoluminescence Studies In Gaas-Alxga1-Xas Single Heterojunctions - Observation Of Parity-Forbidden Landau-Level Transitions, D. C. Reynolds, David C. Look, B. Jogai, C. E. Stutz, R. Jones, K. K. Bajaj

Physics Faculty Publications

We have observed a number of allowed and parity-forbidden Landau-level transitions in a modulation-doped GaAs-Al_xGa_1-xAs single heterojunction structure using photoluminescence-excitation spectroscopy at 2 K. The GaAs layer in this structure is 5000 Å thick. From the allowed Landau-level transitions we determine the reduced mass of the electron-hole pair to be 0.07m_e. Using a heavy-hole mass of 0.45m_e, we determine the average value of the electron effective mass to be 0.084m_e. From the parity-forbidden transitions where the hole Landau level is the same but the electron Landau levels are different, we …

Quantum Electromagnetic Wormholes And Geometrical Description Of The Electric Charge, Marco Cavaglia

Physics Faculty Research & Creative Works

I present and discuss a class of solutions of the Wheeler-DeWitt equation describing wormholes generated by coupling of gravity to the electromagnetic field for Kantowski-Sachs and Bianchi type-I spacetimes. Since the electronic charge can be viewed as electric lines of force trapped in a finite region of spacetime, these solutions can be interpreted as the quantum corresponding to the Einstein-Rosen-Misner-Wheeler electromagnetic geon.

Simulation Of Active Control Of Asymmetric Flows Around Slender Pointed Forebodies, Hazem Sharaf El-Din

Mechanical & Aerospace Engineering Theses & Dissertations

At high angles of attack, the flowfield over slender forebodies becomes asymmetric with substantial side force, which may exceed the available control capability. The unsteady compressible Navier-Stokes equations are used to investigate the effectiveness of different active control methods to alleviate and possibly eliminate the flow asymmetry and the subsequent side force. Although the research work focuses on active control methods, a passive control method has been investigated. The implicit, Roe flux-difference splitting, finite volume scheme is used for the numerical computations. Both locally-conical and three-dimensional solutions of the Navier-Stokes equations are obtained.

The asymmetric flow over five-degree semi-apex angle …

Dosimetry Of High-Energy Heavy-Ion Beams Using Energy-Dependent Green's Functions, Sang Yull Chun

Physics Theses & Dissertations

A theoretical description of the transport of high-charge and high-energy (HZE) ion bombardment of biological tissue is developed. The energy-dependent Green’s functions and particle fluxes are obtained for two boundary distributions - the monoenergetic and the Gaussian. Approximate energy-dependent Green’s functions for the collision terms are obtained for computational simplicity. As an application of the energy-dependent Green’s function method, dosimetric quantities, such as dose, dose-equivalent, and average quality factor, for 600A MeV⁵⁶Fe , 517A MeV ⁴⁰Ar, and 625A MeV ²⁰Ne ion beams incident on a water target are obtained and compared with the values obtained from …

The Current Voltage Characteristics Of Electron Beam Controlled Thin Film Diamond Switches, Christopher Anthony Molina

Electrical & Computer Engineering Theses & Dissertations

The dark current of natural diamond thin films and the induced current due to electron-beam irradiation was measured up to a range of 7000Ncm'. The contact material was aluminum, annealed and unannealed. Switching experiments were performed with electron energies ranging from 70keV to 172keV. The switching results obtained are strongly dependent on the biasing polarity, incident electron energy, and whether the contact is blocking or Ohmic in nature. A simple model which takes traps into consideration allows us to explain the various switching responses. The range of electrons which define, in part, the switch mode was measured for one sample …

Novel Methods For The Fabrication Of Ferromagnetic Nickel And Nickel Boride Thin Films, D. Zych, A. Patwa, S.S. Kher, N.M. Boag, Peter A. Dowben

Peter Dowben Publications

Metal-rich nickel boride thin films fabricated from boron-containing precursor compounds by a cluster deposition process are shown to be ferromagnetic. The metal-rich films fabricated by this approach exhibit hysteresis curves similar to those obtained for pure nickel foils. These films are a mixture of pure nickel and the Ni₃B nickel boride phases. It is postulated that the hysteresis curves with smaller remnant magnetizations obtained from these films are a consequence of Ni₃B inclusions within the films. Other novel organometallic source compounds for nickel chemical-vapor deposition are briefly reviewed. Journal of Applied Physics is copyrighted by The …

Time-Resolved Electron Temperature Measurement In A Highly-Excited Gold Target Usingfemtosecond Thermionic Emission, W. Y. Wang, D. Mark Riffe, Y. S. Lee, M. C. Downer

All Physics Faculty Publications

We report direct measurement of hot-electron temperatures and relaxation dynamics for peak electron temperatures between 3400 and 11 000 K utilizing two-pulse-correlation femtosecond (fs) thermionic emission. The fast relaxation times (<1.5 ps) are described by extending RT characterizations of the thermal conductivity, electron-phonon coupling, and electronic specific heat to these high electron temperatures.

Neutron-Diffraction And Mössbauer Effect Study Of The Tb₂Fe₁₇₋ₓalₓ Solid Solutions, Gaya Kanishka Marasinghe, Sanjay R. Mishra, Oran Allan Pringle, Gary J. Long, Zhong Bo Hu, William B. Yelon, Fernande Grandjean, D. P. Middleton, K. H. J. Buschow

Physics Faculty Research & Creative Works

The magnetic properties of a series of Tb₂Fe_17-xAl_x solid solutions, with nominal x compositions of 0, 2, 3, 4, 5, 6, 7, and 8, have been studied by neutron diffraction and Mössbauer spectroscopy. Neutron-diffraction data indicate that the compounds all crystallize with the Th₂Zn₁₇ structure and that the aluminum atoms are excluded from the 9d site and show a distinct preference for the 6c site only for an aluminum content greater than 6. The unit-cell volume increases by approximately 1% per aluminum atom substituted in the formula unit. The magnetic moment per …

Differential Double Excitation Cross Sections In Proton-Helium Collisions Studied By Energy-Loss Spectroscopy, W. T. Htwe, Tibor Vajnai, M. Barnhart, A. D. Gaus, Michael Schulz

Physics Faculty Research & Creative Works

We have measured ion energy-loss spectra for 150 keV proton-helium collisions as a function of the projectile scattering angle. From the data we obtained double excitation cross sections differential in the proton scattering angle as well as the ratios of both double excitation and single ionization to single excitation. In these ratios pronounced peak structures are observed at about 0.7 mrad. Two alternative interpretations of these peak structures are offered: They may be due to binary collisions between the projectile and the target electrons, or they could be a manifestation of an interference between different transition amplitudes leading to the …

Clean Ultrahigh Vacuum System With Single-Structure Diffusion Pumps, Timothy J. Gay, M.C. Fritts, J.E. Furst, M.A. Khakoo, E.R. Mell, M.T. Seiger, M.W.K.P. Wijayaratna

Timothy J. Gay Publications

A practical example of the use of single-structure diffusion pumping groups in an experiment requiring hydrocarbon-free, ultrahigh vacuum is presented. With the use of proper vacuum procedures and careful foreline design and operation, but with no exotic hardware or liquid nitrogen, we have demonstrated that such a pump could provide vacuum that was "clean," i.e., which had no residual pump-oil contamination to a partial pressure below 10^-8 mbar. Their use is thus compatible, at least in peripheral vacuum chambers, with standard "UHV-surface science" processes. We discuss our vacuum system in detail, and present a review of the literature on …

Clean Ultrahigh Vacuum System With Single-Structure Diffusion Pumps, Timothy J. Gay, M.C. Fritts, J.E. Furst, M.A. Khakoo, E.R. Mell, M.T. Seiger, M.W.K.P. Wijayaratna

Timothy J. Gay Publications

A practical example of the use of single-structure diffusion pumping groups in an experiment requiring hydrocarbon-free, ultrahigh vacuum is presented. With the use of proper vacuum procedures and careful foreline design and operation, but with no exotic hardware or liquid nitrogen, we have demonstrated that such a pump could provide vacuum that was "clean," i.e., which had no residual pump-oil contamination to a partial pressure below 10-8 mbar. Their use is thus compatible, at least in peripheral vacuum chambers, with standard "UHV-surface science" processes. We discuss our vacuum system in detail, and present a review of the literature on the …

Superelastic And Inelastic He2++He State-Selective Electron Capture, V. D. Irby, Timothy J. Gay, J. T. Park, S. W. Bross, A. D. Gaus

Timothy J. Gay Publications

Experimental studies have been made of superelastic and inelastic collision processes involved in the state-selective single-electron capture reaction ³He²⁺+He(1 ¹S)→ ⁺He+(n)+He+(n’), where n and n’ are the final principal quantum-number states of the collision products. Total cross sections have been measured at projectile energies of 15, 30, and 45 keV/u, by examining the energy loss-gain of the fast ³He⁺ product ions, for the superelastic n=n’=1 channel, and for the sum of the inelastic n=2, n’=1 and n=1, n’=2 states. Measurements …

Radiative Recombination At The Alxga1-Xas-Gaas Heterostructure Interface By 2-Dimensional Excitons, D. C. Reynolds, David C. Look, B. Jogai, Phil W. Yu, K. Evans, C. E. Stutz, L. Radomsky

Physics Faculty Publications

Radiative recombination from the Al_xGa_1-xAs-GaAs heterostructure interface was investigated using photoluminescence and photoluminescence-excitation spectroscopy in modulation-doped and undoped samples. This emission is identified as H-band A, resulting from an indirect excitonlike transition in real space. The exciton is made up of a two-dimensional electron in the interface notch and a valence-band hole in the neutral region, having a binding energy of 1.8 meV. The H-band A exciton is directly excited by a free exciton making a vertical transition in real space. H-band A may be a distortion of the vertical direct free exciton in real space …

Rigorous Justification Of The Localized Approximation To The Beam Shape Coefficients In Generalized Lorenz-Mie Theory .1. On-Axis Beams, James A. Lock, Gérard Gouesbet

Physics Faculty Publications

Generalized Lorenz-Mie theory describes electromagnetic scattering of an arbitrary light beam by a spherical particle. The computationally most expensive feature of the theory is the evaluation of the beam-shape coefficients, which give the decomposition of the incident light beam into partial waves. The so-called localized approximation to these coefficients for a focused Gaussian beam is an analytical function whose use greatly simplifies Gaussian-beam scattering calculations. A mathematical justification and physical interpretation of the localized approximation is presented for on-axis beams.

Experiment Using Infrared Spectroscopy To Study The Effect Of Soil Characteristics Upon The Rate Of Trichloroethylene Desorption, Benjamin T. Kindt

Theses and Dissertations

This research investigated the influence of soil characteristics on the desorption of trichloroethylene (TCE). TCE is one of the most common contaminants at Superfund sites. Unfortunately, extraction of TCE from contaminated soils has been hindered by its slow and poorly understood desorption from soil particles. The rate and progress of desorption of TCE from seven types of soil with varying particle diameters and elemental compositions was measured using optical absorption techniques. Fitting the data to the Langmuir Isotherm functional form predicted in the literature yielded parameters for the desorption rate and total amount desorption each soil type. These parameters were …

High Resolution Fourier Transform Spectroscopy Of The First Overtone Of The N-O Stretch In Nitrosyl Bromide, Todd E. Wiest

Theses and Dissertations

Infrared Fourier transform spectroscopy of the first overtone of the nitric oxide (NO) bond stretch in nitrosyl bromide (ONBr) has been performed at a resolution of 0.02cm^-1 to obtain the rotational parameters of the V₁ = 2 energy level. Roughly 1000 transitions have been observed for rotational levels up to J = 80 and K_a = 7. The calculation of the complete set of rotational energy levels of this asymmetric molecule requires the numerical diagonalization of four, tridiagonal matricies for each J. From a non-linear least squares fit of observed transitions with J ≤ 40 using an …

A Three Region Analysis Of A Bounded Plasma Using Particle In Cell And Fluid Techniques, Don F. Nichols

Theses and Dissertations

A detailed collisionless sheath theory and a three-region collisional model of a bounded plasma are presented, and the suitability of the collisional model for analysis of ignited mode thermionic converters is investigated. The sheath theory extends previous analyses to regimes in which the sheath potential and electron temperatures are comparable in magnitude. In all operating regimes typical of a ignited mode thermionic converter, the predicted sheaths extend several mean-free paths. The apparent collisionality of the sheaths prompted development of a collisional, three-region model of the converter plasma. By interfacing Particle-in-Cell regions for the sheaths and fluid regions for the bulk …

X-Ray Studies Of Bond-Orientational Order In Liquid-Crystalline Orthogonal Hexatic-B Phase, E. Gorecka, Li Chen, Oleg Lavrentovich, W. Pyzuk

Oleg Lavrentovich

X-ray scattering measurements have been carried out for free-standing, thick . monodomain films of the orthogonal hexatic-B phase. From Fourier analysis of X-scans, 6n-fold-symmetry order parameters were determined and proved to fulfill the scaling relation C6n = C6n+lambdan(n-1). The temperature behavior of C6 and lambda was found nonuniversal when comparing homologues, PIR5 and PIR7, differing in their range of the hexatic phase. The hexatic order parameter varies with the critical exponents 0.25, 0.20 (+/- 0.03), respectively. For comparison results for compound RFL6, of other homologue series, are presented.

Orientation Induced Scattering Asymmetry, Jee-Ching Wang, Ronald E. Olson

Chemical and Biochemical Engineering Faculty Research & Creative Works

Projectile angular scattering is investigated following electron capture by protons from circular Rydberg atoms oriented along a quantization axis perpendicular to the incident projectile direction. We find strong left-right scattering asymmetry as a function of the orientation angle at collision speeds comparable to the electron orbital speed. The capture cross section is dramatically enhanced due to velocity matching when the angular momenta of the proton and the electron are aligned. The scattering asymmetry exhibits characteristic impact parameter dependencies suitable for studying three-body dynamics influenced by both long and short range forces of comparable strength. © 1994 IOP Publishing Ltd.

Nanometer Scale Patterning And Oxidation Of Silicon Surfaces With An Ultrahigh Vacuum Scanning Tunneling Microscope, J. W. Lyding, G. C. Abeln, T. -C. Shen, C. Wang, J. R. Tucker

T. -C. Shen

Nanoscale patterning of the Si(100)‐2×1 monohydride surface has been achieved by using an ultrahigh vacuum (UHV) scanning tunneling microscope(STM) to selectively desorb the hydrogen passivation. Hydrogen passivation on silicon represents one of the simplest possible resist systems for nanolithography experiments. After preparing high quality H‐passivated surfaces in the UHV chamber, patterning is achieved by operating the STM in field emission. The field emitted electrons stimulate the desorption of molecular hydrogen, restoring clean Si(100)‐2×1 in the patterned area. This depassivation mechanism seems to be related to the electron kinetic energy for patterning at higher voltages and the electron current for low …

Light Front Qcd And The Constituent Quark Model, Kenneth G. Wilson, David G. Robertson

Physics Faculty Scholarship

A general strategy is described for deriving a constituent approximation to QCD, inspired by the constituent quark model and based on light-front quantization. Some technical aspects of the approach are discussed, including a mechanism for obtaining a confining potential and ways in which spontaneous chiral symmetry breaking can be manifested

Dissociative Attachment In Selected Monochloroalkanes, D. M. Pearl, Paul Burrow

Paul Burrow Publications

The total cross sections for the dissociative attachment (DA) process are reported for eight normal chloroalkanes C_nH_2n+1Cl for n=2–9, two secondary compounds 2-chloropropane and 2-chlorobutane, one tertiary compound t-butyl chloride, and three cyclic chloroalkanes c-C_nH_2n-1Cl for n=4–6, for electron energies below 4 eV. Using vertical attachment energies (VAEs) determined by electron transmission spectroscopy elsewhere and in this work, we show that the resonance widths vary linearly with VAE in this series of compounds and that the peak DA cross sections decline exponentially with increasing VAE. …

Light Cone Quantization Of Electrodynamics, David G. Robertson

Physics Faculty Scholarship

Light-cone quantization of (3+1)-dimensional electrodynamics is discussed, using discretization as an infrared regulator and paying careful attention to the interplay between gauge choice and boundary conditions. In the zero longitudinal momentum sector of the theory a general gauge fixing is performed and the corresponding relations that determine the constrained modes of the gauge field are obtained. The constraints are solved perturbatively and the structure of the theory is studied to lowest nontrivial order.

He²⁺-He Collisions: One-Electron Capture And Target-Ion Excitation, H. O. Folkerts, F. W. Bliek, L. Meng, Ronald E. Olson, R. Morgenstern, M. V. Von Hellermann, H. P. Summers, R. Hoekstra

Physics Faculty Research & Creative Works

By means of photon emission spectroscopy the authors have studied state selective one-electron capture and target-ion excitation in collisions of He2+ with He. The collision energy has been varied from 1 to 75 keV amu-1. Four-body classical trajectory Monte Carlo calculations have been performed in the energy range of 50-300 keV amu-1. In the energy range where experiment and theory overlap there is in general fair agreement, although the l-distributions within a principal quantum shell exhibit differences. At energies below 50 keV amu-1 the experiments confirm the results of atomic orbital calculations, presented in an accompanying paper by Fritsch (1994). …

Interface Motion In Random Media At Finite Temperature, Lee-Wen Chen, M. Cristina Marchetti

Physics - All Scholarship

We have studied numerically the dynamics of a driven elastic interface in a random medium, focusing on the thermal rounding of the depinning transition and on the behavior in the

T = 0 pinned phase. Thermal effects are quantitatively more important than expected from simple dimensional estimates. For sufficient low temperature the creep velocity at a driving force equal to the T = 0 depinning force exhibits a power-law dependence on T, in agreement with earlier theoretical and numerical predictions for CDW’s. We have also examined the dynamics in the T = 0 pinned phase resulting from slowly increasing the …