Digital Commons Network^™

Lidar Observations Of Oscillations In The Middle Atmosphere, Karen L. M. Nelson

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The three major types of oscillations in the atmosphere are gravity waves, planetary waves, and tides. Identifying planetary waves and tides in nighttime-only lid are data is a challenge. The Lomb-Scargle method offers a possible solution to this problem, although aliasing is still a problem when tides are present in the data. The method has been applied to mesospheric Rayle high-scalier lidar temperature data taken at the Utah State University Atmospheric Lidar Observatory (ALO). This analysis is greatly enhanced by the length and completeness of the data set available through ALO, especially with regard to the identification of planetary waves. …

Investigation And Calculation Of Dose Coefficients For Radionuclides Produced In A Spallation Neutron Source Using The Ensdf And Nubase Nuclear Databases, Yayun Song

UNLV Theses, Dissertations, Professional Papers, and Capstones

Dose coefficients are useful for risk assessment during the design and siting of accelerator-driven nuclear facilities including the Spallation Neutron Source. There are seventy-two radionuclides with half-lives equal to or greater than one minute that will be produced by the spallation of a mercury target for which no published dose coefficients exist. Out of these seventy-two, twenty-four currently have conflicting published nuclear data in the Evaluated Nuclear Structure Data Files (ENSDF) and the NUBASE data files. In this research these twenty-four radionuclides have been studied. Because of missing ENSDF records, internal and external dose coefficients were determined for only six …

Self-Energy Correction To The Two-Photon Decay Width In Hydrogenlike Atoms, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

We investigate the guage invariance of the leading logarithmic radiative correction to the two-photon decay width in hydrogenlike atoms, was investigated. The effective treatment of the correction using a Lamb-shift led to the equivalent results in both the length and velocity gages. The relevant radiative corrections were found to be related to the energies that entered into the propagator denominators, to the Hamiltonian, to the wave functions, and to the energy conservation condition, that holds between two photons. The results show that the dominant radiative correction to the 2S two-photon decay width is about -2.020 536(α/π)(Zα)² 1n[(Zα)^-2] …

Calculation Of The Radiation Trapping Force For Laser Tweezers By Use Of Generalized Lorenz-Mie Theory. Ii. On-Axis Trapping Force, James A. Lock

Physics Faculty Publications

The efficiency of trapping an on-axis spherical particle by use of laser tweezers for a particle size from the Rayleigh limit to the ray optics limit is calculated from generalized Lorenz-Mie light-scattering theory and the localized version of a Gaussian beam that has been truncated and focused by a high-numericalaperture lens and that possesses spherical aberration as a result of its transmission through the wall of the sample cell. The results are compared with both the experimental trapping efficiency and the theoretical efficiency obtained from use of the localized version of a freely propagating focused Gaussian beam. The predicted trapping …

12C/13C Ratio In Planetary Nebulae From The Iue Archives, R. H. Rubin, Gary J. Ferland, E. E. Chollet, R. Horstmeyer

Physics and Astronomy Faculty Publications

We investigated the abundance ratio of ¹²C/¹³C in planetary nebulae by examining emission lines arising from C III 2s2p³P^o_2,1,0 → 2s²¹S₀. Spectra were retrieved from the International Ultraviolet Explorer archives, and multiple spectra of the same object were co-added to achieve improved signal-to-noise ratio. The ¹³C hyperfine structure line at 1909.6 Å was detected in NGC 2440. The ¹²C/¹³C ratio was found to be ~4.4+/-1.2. In all other objects, we provide an upper limit for the flux of the 1910 Å line. For 23 …

Decoherence In Josephson-Junction Qubits Due To Critical Current Fluctuations, Britton Plourde, D. J. Van Harlingen

Physics - All Scholarship

We compute the decoherence caused by 1/f fluctuations at low frequency f in the critical current I_0 of Josephson junctions incorporated into flux, phase, charge and hybrid flux-charge superconducting quantum bits (qubits). The dephasing time \tau_{\phi} scales as I_0/ \Omega \Lambda S_{I_0}^{1/2}(1 Hz),where \Omega / 2\pi is the energy level splitting frequency, S_{I_0}(1 Hz) is the spectral density of the critical current noise at 1 Hz, and \Lambda \equiv |I_0 d \Omega / \Omega d I_0| is a parameter computed for given parameters for each type of qubit that specifies the sensitivity of the level splitting to critical current fluctuations. …

The Elimination Of The Influence Of Ambient Environmental Effects On The Structure Of `Inert' Polymers, Luis G. Rosa, P.A. Jacobson, Raymond Lemoine, Peter A. Dowben

Peter Dowben Publications

The construction and use of a vacuum chamber suitable for conventional X-ray diffraction has revealed the influence of the ambient environment, including moisture, on the bulk structure of very thin polymer films. It is concluded that studies of thin film organic systems, even those thought not to be perturbed by ambient water vapor and other contaminants, may benefit from undertaking some studies in such small sample vacuum chambers.

High-Latitude Propagation Studies Using A Meridional Chain Of Lf/Mf/Hf Receivers, J Labelle

Dartmouth Scholarship

For over a decade, Dartmouth College has oper- ated programmable radio receivers at multiple high-latitude sites covering the frequency range 100–5000 kHz with about a 1-s resolution. Besides detecting radio emissions of auro- ral origin, these receivers record characteristics of the iono- spheric propagation of natural and man-made signals, docu- menting well-known effects, such as the diurnal variation in the propagation characteristics of short and long waves, and also revealing more subtle effects. For example, at auroral zone sites in equinoctial conditions, the amplitudes of dis- tant transmissions on MF/HF frequencies are often enhanced by a few dB just before …

Relative Timing Of Substorm Onset Phenomena, L. Kepko, M. G. Kivelson, R. L. Mcpherron, Harlan E. Spence

Physics & Astronomy

[1] In this paper we examine the temporal ordering of midtail flow bursts, Pi2 pulsations, and auroral arc brightening at substorm onset. We present three substorm events for which the Geotail spacecraft was situated at local midnight, near the inner edge of the plasmasheet. We show that high-speed, convective Earthward directed plasma flows observed by Geotail occurred 1–3 min before auroral onset as observed by the Polar Visible Imaging System and Ultraviolet Imager auroral imagers on board the Polar spacecraft. We also show that the onsets of both nightside Pi2 pulsations and magnetic bay variations were simultaneous with auroral onset. …

Extended Beg Model Of Monhalogenated Methanes Physisorbed On Ionic Crystals, T. E. Burns, John R. Dennison, Jason Kite

All Physics Faculty Publications

The 2D dielectric phases and phase transitions of adsorbed dipolar molecules are modeled using a dilute spin-one Ising model. This model is studied in the Blume–Emery–Griffiths formalism, using a mean-field approximation, where the interaction parameters are uniquely determined from the system interaction energies using an averaging procedure. The model is applied to four monhalogenated methane species physisorbed on MgO(1 0 0) and NaCl(1 0 0) surfaces using previous experimental and theoretical studies to estimate the interaction energy parameters. We find that temperature- and coverage-dependent antiferroelectric to ferroelectric, coverage-dependent ferroelectric up to ferroelectric down, reentrant ferroelectric to ferrielectric, and order-disorder dipole …

Closed Strings In Ramond-Ramond Backgrounds, Vatche Sahakian

All HMC Faculty Publications and Research

We write the IIB Green-Schwarz action in certain general classes of curved backgrounds threaded with Ramond-Ramond fluxes. The fixing of the kappa symmetry in the light-cone gauge and the use of supergravity Bianchi identities simplify the task. We find an expression that truncates to quartic order in the spacetime spinors and relays interesting information about the vacuum structure of the worldsheet theory. The results are particularly useful in exploring integrable string dynamics in the context of the holographic duality.

Double Excitations Within Time-Dependent Density Functional Theory Linear Response, Neepa T. Maitra, Fan Zhang, Robert J. Cave, Kieron Burke

All HMC Faculty Publications and Research

Within the adiabatic approximation, time-dependent density functional theory yields only single excitations. Near states of double excitation character, the exact exchange–correlation kernel has a strong dependence on frequency. We derive the exact frequency-dependent kernel when a double excitation mixes with a single excitation, well separated from the other excitations, in the limit that the electron–electron interaction is weak. Building on this, we construct a nonempirical approximation for the general case, and illustrate our results on a simple model.

Studies Of Atomic And Molecular Dynamics Using Photoelectron Spectroscopy, Sophie E. Canton

Dissertations

Photoexcitation and photoionization studies of free atoms and molecules in the gas phase provide a unique view into various aspects of radiation-matter interactions that are used as basic building blocks in many branches of physics, such as Solid State, Plasma Physics, Photochemistry or Astrophysics. With the advent of third generation synchrotron light sources delivering high photon flux (>10¹⁵ photons/s) with unprecedented resolving power over a broad energy range, it has become possible to investigate in great detail not only the internal structure of the targets, but also the dynamics of the process. Born in the 1960s,photoelectron spectroscopy specifically …

Scaling Laws For Single And Multiple Electron Loss From Projectiles In Collisions With A Many-Electron Target, Antonio C. Santos, Robert D. Dubois

Physics Faculty Research & Creative Works

Using measured cross sections, empirical scaling laws are extracted for projectile stripping induced by collisions with a many-electron target. by scaling both the cross sections and the impact velocities, it is shown that a single universal curve can be used to fit data for single and multiple electron loss from negative ions, neutral particles, and singly or multiply charged positive ions. The scaling applies to projectiles ranging from hydrogen to uranium and collision energies ranging from below keV∕u to hundreds of MeV∕u . At high energies, existing data are consistent with a v−1 impact velocity dependence for scaled velocities less …

Quasiparticle Line Shape Of Sr2ruo4 And Its Relation To Anisotropic Transport, S.-C. Wang, H.-B. Yang, A. K. P. Sekharan, H. Ding, J. R. Engelbrecht, X. Dai, Z. Whang, A. Kaminski, T. Valla, T. Kidd, A. V. Fedorov, P. D. Johnson

Faculty Work

The bulk-representative low-energy spectrum of Sr₂RuO₄ can be directly measured by angle-resolved photoemission. We find that the quasiparticle spectral line shape of Sr₂RuO₄ is sensitive to both temperature and momentum. Along the (0, 0)-(π, 0) direction, both gamma and ß bands develop a sharp quasiparticle peak near k_F at low temperatures, but as the temperature increases the spectra quickly lose coherent weight and become broad backgrounds above ~130 K, which is the metal-nonmetal crossover temperature, T_M, in the c-axis resistivity. However, spectra along the (0, 0)-(π, π) direction evolve smoothly …

Anisotropy Of Exchange Stiffness And Its Effect On The Properties Of Magnets, K. D. Belashchenko

Kirill Belashchenko Publications

Using the spin-spiral formulation of the tight-binding linear muffin-tin orbital method, the principal components of the exchange stiffness tensor are calculated for typical hard magnets including tetragonal CoPt-type and hexagonal YCo₅ alloys. The exchange stiffness is strongly anisotropic in all studied alloys. This anisotropy makes the domain wall surface tension anisotropic. Competition between this anisotropic surface tension and magnetostatic energy controls the formation and dynamics of nanoscale domain structures in hard magnets. Anisotropic domain wall bending is described in detail from the general point of view and with application to cellular Sm–Co magnets. It is shown that the repulsive …

Spin Structure Functions Of The Deuteron Measured With Clas In And Above The Resonance Region, Kahanawita G. Vipuli G. Dharmawardane

Physics Theses & Dissertations

Spin structure functions of the nucleon in the region of large x and small to moderate Q² continue to be of high current interest. The first moment of the spin structure function g₁, Γ₁, goes through a rapid transition from the photon point (Q² = 0), where it is constrained by the Gerasimov-Drell-Hearn sum rule, to the deep inelastic limit where it is sensitive to the nucleon spin fraction carried by quarks. The interesting behavior in the transition region is dominated by baryon resonance excitations. We concluded an experiment to measure these observables …

Electron Scattering From A High Momentum Neutron In Deuterium, Alexei V. Klimenko

Physics Theses & Dissertations

The deuterium nucleus is a system of two nucleons (proton and neutron) bound together. The configuration of the system is described by a quantum-mechanical wave function and the state of the nucleons at a given time is not known a priori. However, by detecting a backward going proton of moderate momentum in coincidence with a reaction taking place on the neutron in deuterium, the initial state of that neutron can be inferred if we assume that the proton was a spectator to the reaction. This method, known as spectator tagging, was used to study the electron scattering from high-momentum neutrons …

Heliospheric Plasma Sheets, N. U. Crooker, Chia-Lin L. Huang, S. M. Lamassa, D. E. Larson, S. W. Kahler, Harlan E. Spence

Physics & Astronomy

[1] As a high-beta feature on scales of hours or less, the heliospheric plasma sheet (HPS) encasing the heliospheric current sheet shows a high degree of variability. A study of 52 sector boundaries identified in electron pitch angle spectrograms in Wind data from 1995 reveals that only half concur with both high-beta plasma and current sheets, as required for an HPS. The remaining half lack either a plasma sheet or current sheet or both. A complementary study of 37 high-beta events reveals that only 5 contain sector boundaries while nearly all (34) contain local magnetic field reversals, however brief. We …

Optimized Search For Single-Top-Quark Production At The Fermilab Tevatron, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We use a neural-network technique to search for standard model single-top-quark production in the 106 pb^-1 dataset accumulated by the Collider Detector at Fermilab detector during the 1992–1995 collider run ("run I"). Using a sample of 64 W+1, 2, 3 jets events, we set a 95% confidence level upper limit of 24 pb on the W-gluon and W* combined single-top cross section.

Perturbative Analysis Of The Triply Differential Cross Section And Circular Dichroism In Photo-Double-Ionization Of He, Andrei Y. Istomin, N. L. Manakov, Anthony F. Starace

Department of Physics and Astronomy: Faculty Publications

We extend application of our lowest-order perturbative approach (in electron-electron correlation) for analysis of photo-double-ionization (PDI) of He [A.Y. Istomin et al., J. Phys. B 35, L543 (2002)] to excess energies up to 450 eV and to analysis of circular dichroism. We find that account of electron correlation in the final state to first order provides predictions for the triply differential cross section and circular dichroism that are in reasonable agreement with absolute data for excess energies up to 80 eV. For an excess energy of 450 eV, account of electron correlation in both initial and final states is necessary …

Identified Particle Distributions In Pp And Au+Au Collisions At √Snn=200 Gev, Star Collaboration, T.D. Gutierrez

Physics

Transverse mass and rapidity distributions for charged pions, charged kaons, protons, and antiprotons are reported for √s_NN=200  GeV pp and Au+Au collisions at Relativistic Heary Ion Collider (RHIC). Chemical and kinetic equilibrium model fits to our data reveal strong radial flow and long duration from chemical to kinetic freeze-out in central Au+Au collisions. The chemical freeze-out temperature appears to be independent of initial conditions at RHIC energies.

Bose-Einstein Correlations In One And Two Dimensions In Deep Inelastic Scattering, S. Chekanov, M. Derrick, D. Krakauer, J. H. Loizides, S. Magill, S. Miglioranzi, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, A. Montanari, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli

Faculty Publications

Bose-Einstein correlations in one and two dimensions have been studied in deep inelastic ep scattering events measured with the ZEUS detector at HERA using an integrated luminosity of 121 pb-1. The correlations are independent of the virtuality of the exchanged photon, Q2, in the range 0.1 < Q2 < 8000 GeV2. There is no significant difference between the correlations in the current and target regions of the Breit frame for Q2 > 100 GeV2. The two-dimensional shape of the particle-production source was investigated, and a significant difference between the transverse and the longitudinal dimensions of the source is observed. This difference also shows no Q2 dependence. The results demonstrate that Bose-Einstein interference, and hence the size of the particle-production source, is insensitive to the hard subprocess. …

New Enhanced Tunneling In Nuclear Processes, Boris Ivlev, Vladimir Gudkov

Faculty Publications

The small sub-barrier tunneling probability of nuclear processes can be dramatically enhanced by collision with incident charged particles. Semiclassical methods of theory of complex trajectories have been applied to nuclear tunneling, and conditions for the effects have been obtained. We demonstrate the enhancement of αparticle decay by incident proton with energy of about 0.25 MeV. We show that the general features of this process are common for other sub-barrier nuclear processes and can be applied to nuclear fission.

Deviation Of Time-Resolved Luminescence Dynamics In Mwir Semiconductor Materials From Carrier Recombination Theory Predictions, Peter M. Johnson

Theses and Dissertations

Time resolved luminescence spectroscopy was used to characterize luminescence decay curves for a bulk InAs sample and an InAsSb type-I quantum-well sample over the first 3ns following excitation. The luminescence decay curves were then converted to carrier densities and used to find recombination coefficients that provided the least-squared-error solution of the rate equation describing carrier recombination. Recombination coefficients describing Shockley Read-Hall (A_SRH) radiative (B_rad) and Auger (C_Aug) recombination were determined at two different temperatures and four excitation powers, then analyzed for consistency and physical significance. For all of the resulting least …

Effective Field Theory Approach To String Gas Cosmology, Scott Watson, Thorsten Battefeld

Physics - All Scholarship

We derive the 4D low energy effective field theory for a closed string gas on a time dependent FRW background. We examine the solutions and find that although the Brandenberger-Vafa mechanism at late times no longer leads to radion stabilization, the radion rolls slowly enough that the scenario is still of interest. In particular, we find a simple example of the string inspired dark matter recently proposed by Gubser and Peebles.

Optical Characterization And Modeling Of Compositionally Matched Indium Arsenide-Antimonide Bulk And Multiple Quantum Well Semiconductors, Scott C. Phillips

Theses and Dissertations

Indium arsenide-antimonide (InAsSb) semiconductors have been determined to emit in the 3-5 micrometer range, the window of interest for countermeasures against infrared electro-optical threats. This experiment set out to cross the bulk to quantum well characterization barrier by optically characterizing two sets of compositionally matched type I quantum well and bulk well material samples. Absorption measurements determined the band gap energy of the bulk samples and the first allowed subband transition for the quantum wells. By collecting absorption spectra at different temperatures, the trend of the energy transitions was described by fitting a Varshni equation to them. The expected result …

The Second Law Mystique, Alexey V. Nikulov, D. P. Sheehan

Physics and Biophysics: Faculty Scholarship

No abstract provided.

Afci Quarterly Input – Unlv January Through March, 2004, Harry Reid Center For Environmental Studies. Nuclear Science And Technology Division

Transmutation Research Program Reports (TRP)

Quarterly report highlighting research projects and objectives of the Transmutation Research Program at the Nuclear Science & Technology Division, Harry Reid Research Center.

The University of Nevada, Las Vegas supports the AFCI through research and development of technologies for economic and environmentally sound refinement of spent nuclear fuel. The UNLV program has four components: infrastructure, international collaboration, student-based research, and management and program support.

Student Explorations Of Quantum Effects In Leds And Luninescent Devices, Lawrence Escalada, N. Sanjay Rebekki, Dean A. Zollman

Faculty Work

We developed activity-based instructional units to introduce basic quantum principles to students with limited physics and mathematics backgrounds. To emphasize the practical applications of contemporary physics, we introduced concepts using the contexts of light-emitting devices such as light-emitting diodes (LEDs), fluorescent lamps, and glow-in-the-dark toys. As our standard of living becomes more dependent on the latest developments in science and technology, our students' literacy must be at a level that enables them to make educated decisions on science- and technology-related issues and their everyday applications. Students need to have at least a basic understanding of 20th-century physics and its applications …