Physical Sciences and Mathematics Commons^™

The Ising Model On A Dynamically Triangulated Disk With A Boundary Magnetic Field, Simon Catterall, Scott V. Mcguire, Mark Bowick, Simeon Warner

Physics - All Scholarship

We use Monte Carlo simulations to study a dynamically triangulated disk with Ising spins on the vertices and a boundary magnetic field. For the case of zero magnetic field we show that the model possesses three phases. For one of these the boundary length grows linearly with disk area, while the other two phases are characterized by a boundary whose size is on the order of the cut-off. A line of continuous magnetic transitions separates the two small boundary phases. We determine the critical exponents of the continuous magnetic phase transition and relate them to predictions from continuum 2-d quantum …

Time Dependent Density Functional Theory Of Dynamical Response In 3d And 4d Metals, James M. Sullivan

Doctoral Dissertations

Two different but complementary quantum mechanical many-body problems are investigated. These problems include both static and dynamic aspects of the electronelectron interaction in real materials. In Chapter One, we take up the cases of Ag and Ni with a microscopic evaluation of the dielectric function and loss function using the formalism of time dependent density functional theory and all-electron techniques. We address the striking line shapes that have been recently observed via inelastic scattering experiments. The present work reveals three relevant energy scales for excitations in the selected systems. These scales are argued to be generic to a large number …

Simulation Of Inviscid Multi-Species Plasma Flow, Alexandre Martin, Marcelo Reggio, Jean-Yves Trépanier

Alexandre Martin

A multi-species solver for plasma at thermodynamical equilibrium is developed. A numerical scheme, based on Roe's, is implemented with some modification regarding the average quantities. A perfect gas treatment is carried out for validations, and a quasi-real gas treatment is also presented. The latter takes into account the changes in the composition of the gas caused by fluctuations in temperature and density.

Overview Of Acousto-Optic Bistability, Chaos, And Logical Applications, Monish Ranjan Chatterjee, Erol Sonmez

Electrical and Computer Engineering Faculty Publications

An overview is presented of the key results in the field of acousto-optic bistability in the past two decades. It is shown that the basic acousto-optic bistable device may be described as a nonlinear dynamical system which satisfies a quadratic map. Thereafter, details are presented of several analytical methods, computer modeling approaches, including the SPICE circuit modeling technique, and experiments that have been used to understand the phenomenon.

Extensions to logical and digital applications are also discussed.

Numerical Modeling Of Magnetohydrodynamic Activity In The Swarthmore Spheromak Experiment, Vyacheslav S. Lukin , '00, G. Qin, W. H. Matthaeus, Michael R. Brown

Physics & Astronomy Faculty Works

Results from a three-dimensional axisymmetric resistive magnetohydrodynamic (MHD) simulation are compared to experimental data from the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)]. The MHD simulation is run under conditions and with dimensionless parameters similar to the experiment (Lundquist number S=1000, plasma beta beta =0.1). The simulation is shown to reproduce global equilibrium magnetic field profiles of the spheromaks as well as much of the detailed reconnection dynamics measured when two spheromaks are merged. It is concluded that SSX merger dynamics may be characterized as MHD reconnection, with the likelihood that extensions are needed to …

A Surface Insulator-To-Conductor Phase Transition In Colossal Magnetoresistive Manganese Perovskites Thin Films, C.N. Borca, Bo Xu, Takashi Komesu, Hae-Kyung Jeong, Sy-Hwang Liou, Peter A. Dowben

Peter Dowben Publications

We have observed a distinct surface phase transition for an important class of colossal magnetoresistive materials, La_0.65D_0.35MnO₃ (with D = Sr, Pb) occurring in a surface layer compositionally different from the bulk. The surface phase transition occurs around 240 K compared to 350 K for the bulk and is fundamentally different. In the bulk, a ferromagnetic metal to paramagnetic ‘bad metal’ occurs, while the lower-temperature surface transition is from an n-type (in case of La_0.65Sr_0.35MnO₃) or a p-type (in case of La_0.65Pb_0.35MnO_{3 …}

A Landau-Ginzburg Description Of Sb Overlayers, Ralph Skomski, T. Komesu, H.-K. Jeong, C.N. Borca, Peter A. Dowben, D. Ristoiu, J.P. Nozieres

Peter Dowben Publications

The spin polarization of Sb overlayers on the semi-Heusler alloy NiMnSb is investigated in terms of the Landau-Ginzburg approach. The half-metallic semi-Heusler alloy NiMnSb acts as a ferromagnetic perturbation and induces a spin polarization in the semimetallic Sb overlayer. Using a Gaussian approximation, the propagation of the spin perturbation in the overlayer is calculated. The results are compared with spin-polarized inverse photoemission spectroscopy (SPIPES) results and with recent spin-dependent envelope-function approximation (SDEFA) predictions. The Landau-Ginzburg parameters are both band-structure and temperature dependent, and it is argued that thermal spin excitations lead to an injection depth decreasing as 1//T law at …

Climatology Of Upper Thermospheric Daytime Neutral Winds From Satellite Observations, John T. Emmert

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

We studied the global climatology of mid- and low-latitude F region daytime neutral winds using extensive measurements by the Wind Imaging Interferometer (WINDII) instrument on board the Upper Atmosphere Research Satellite (UARS). Quiet-time winds are mostly poleward and westward during the day, and are generally 5-20 m/s smaller in the longitudinal sector closest to the magnetic pole, compared to longitudinally averaged winds. The pre-noon zonal winds are less westward with increasing solar flux, while the post-noon meridional winds are less poleward. Our quiet-time results are in good agreement with the NCAR Thermosphere-Ionosphere- Electrodynamics General Circulation Model (TIEGCM).

We computed residual …

On D0 Brane Polarization By Tidal Forces, Vatche Sahakian

All HMC Faculty Publications and Research

Gravitational tidal forces may induce polarization of D0-branes, in analogy to the same effects arising in the context of constant background gauge fields. Such phenomena can teach us about the correspondence between smooth curved spacetime and its underlying non-commutative structure. However, unlike polarization by gauge fields, the gravitational counterpart involves concerns regarding the classical stability of the corresponding polarized states. In this work, we study this issue with respect to the solutions presented in hepth0010237 and find that they are classically unstable. The instability however appears with intricate features with all but a few decay channels being lifted. Through a …

In-Situ Spectroscopic Studies Of Electronic Processes In Buckminsterfullerene Thin Films, Gordon Chambers

Doctoral

This study attempts to develop an understanding of the electronic processes active within the solid state of C60. The emphasis throughout the work has been upon the generation and spectroscopic identification of any species, which could potentially contribute to electronic conduction in thin films of C60. The relative importance of these inter-and intramolecular processes in terms of their contribution to the electronic transport is discussed through the comparison of the properties of the molecule with the properties of the bulk solid

Initially the low intensity optical properties of the C60 molecule in solution and in solid were assessed. Vibrational spectroscopy …

Search For The Supersymmetric Partner Of The Top Quark In Pp̅ Collisions At √S=1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report on a search for the supersymmetric partner of the top quark (top squark) produced in tt̅ events using 110 pb^-1 of pp̅ collisions at √s =1.8 TeV recorded with the Collider Detector at Fermilab. In the case of a light top squark, the decay of the top quark into a top squark plus the lightest supersymmetric particle (LSP) could have a significant branching ratio. The observed events are consistent with standard model tt̅ production and decay. Hence, we set limits on the branching ratio of the top quark decaying into a top squark plus LSP, excluding branching …

Anionic Photofragmentation Of Co: A Selective Probe Of Core-Level Resonances, Wayne C. Stolte, D. L. Hansen, Maria Novella Piancastelli, I. Dominguez-Lopez, A. Rizvi, Oliver Hemmers, H. Wang, Alfred S. Schlachter, M. S. Lubell, Dennis W. Lindle

Environmental Studies Faculty Publications

Anion-yield spectroscopy using x rays is shown to be a selective probe of molecular core-level processes, providing unique experimental verification of shape resonances. For CO, partial anion and cation yields are presented for photon energies near the C K edge. The O^- yield exhibits features above threshold related only to doubly excited states, in contrast to cation yields which also exhibit pronounced structure due to the well-known σ^* shape resonance. Because the shape resonance is completely suppressed for O^-, anion spectroscopy thus constitutes a highly selective probe, yielding information unobtainable with absorption or electron spectroscopy.

Large Amplitude Perturbations In Mesospheric Oh Meinel And 87-Km Na Lidar Temperatures Around The Autumnal Equinox, Michael J. Taylor, W. R. Pendleton Jr., H. L. Liu, C. Y. She, Larry Gardner, R. G. Roble, V. Vasoli

All Physics Faculty Publications

Two high‐precision CEDAR instruments, an OH Mesospheric Temperature Mapper (MTM) and a Na Temperature Lidar, have been used to investigate seasonal variability in the mid‐latitude temperature at ∼87 km altitude over the western USA. Here we report the observation of a large perturbation in mesospheric temperature that occurs shortly after the autumnal equinox in close association with the penetration of planetary‐wave energy from the troposphere into the mesosphere. This perturbation has been observed on three occasions and exhibits a departure of up to ∼25–30 K from the nominal seasonal trend during a disturbed period of ∼2 weeks. Such behavior represents …

Mesospheric Planetary Waves Atnorthern Hemisphere Fall Equinox, H. L. Liu, R. G. Roble, Michael J. Taylor, W. R. Pendleton Jr.

All Physics Faculty Publications

Northern hemisphere planetary waves are strong in the winter and weak in the summer, and they go through a fast transition around equinox. This transition is studied here using NCAR Thermosphere‐Ionosphere‐Mesosphere‐Electrodynamics general circulation model (TIME‐GCM) simulations with 1997 National Centers for Environmental Prediction (NCEP) analysis. The planetary wave variability during the transition and its effect on the temperature and winds in the mesosphere are examined. The simulated planetary wave structure agrees with climatological studies, and the fast transition of the planetary waves is captured by the model. The wave variability produces large temperature changes in the upper atmosphere above local …

Experimental Investigation Of Snapover: The Sudden Increase Of Plasma Current Drawn To A Positively Biased Conductor When Surrounded By A Dielectric, Clint D. Thomson

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Snapover is particularly relevant to Earth-orbiting spacecraft powered by high-voltage solar arrays. During snapover, the current collected by a positively biased conductor that is immersed in a plasma suddenly increases when two conditions are met: i) there is an immediately adjacent insulator; ii) the conductor exceeds a positive threshold voltage with respect to the plasma. The enhanced current develops as a consequence of the insulator, either through secondary electron (SE) emission or by material ionization. Experiments were performed to examine snapover onset potential and current collection dependence on conductor and insulator materials, conductor size and shape, sample history, biasing rate, …

A Laboratory-Based Nonlinear Dynamics Course For Science And Engineering Students, Nilgun Sungar, John P. Sharpe, Matthew J. Moelter, Neil Fleishon, Kent Morrison, Jean Mcdill, Rod Schoonover

Physics

We describe the implementation of a new laboratory-based interdisciplinary undergraduate course on nonlinear dynamical systems. Geometrical methods and data visualization techniques are especially emphasized. A novel feature of the course is a required laboratory where the students analyze the behavior of a number of dynamical systems. Most of the laboratory experiments can be economically implemented using equipment available in many introductory physics microcomputer-based laboratories.

Production Of Χ C1 And Χ C2 In Pp̅ Collisions At √S= 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We have measured the ratio of prompt production rates of the charmonium states χ _c1 and χ _c2 in 110 pb^-1 of pp̅ collisions at √s= 1.8 TeV. The photon from their decay into J/ψγ is reconstructed through conversion into e⁺e^- pairs. The energy resolution this technique provides makes the resolution of the two states possible. We find the ratio of production cross sections (σ _{χ c2}/ σ _{χ c1}=0.96 ± 0.27(stat) ± 0.11(syst) for events with p_T(J/ψ)> 4.0 GeV/c, |η(J/ψ)|, 0.6, and p_{T …}

Asymmetric Nanoscale Switching In Ferroelectric Thin Films By Scanning Force Microscopy, Alexei Gruverman, A. Kholkin, A. I. Kingon, H. Tokumoto

Alexei Gruverman Publications

Scanning force microscopy (SFM) has been used to perform nanoscale studies of the switching behavior of Pb(Zr, Ti)O₃ thin films via the direct observation of their domain structures. The study revealed a significant asymmetry of a switching pattern which is a function of the voltage polarity and original domain structure of individual grains. The phenomenon of asymmetric switching is attributed (1) to the presence of an internal built-in electric field at the bottom interface and (2) to the mechanical stress exerted by the SFM tip. The former effect results in incomplete 180° switching, while the latter effect leads to …

Design And Analysis For Melt Casting Metallic Fuel Pins Incorporating Volatile Actinides, Yitung Chen, Darrell Pepper, Randy Clarksean

Fuels Campaign (TRP)

UNLV investigators will evaluate and select a process for the melt casting of metallic fuel pins that contain volatile actinides. This work will be performed with the guidance of Argonne National Laboratory (ANL) engineers to insure that their knowledge and experience benefits the project. The research to be conducted during year one will center on selecting, evaluating, and modeling potential alternatives to the traditional injection casting process used at ANL. Processing conditions will be analyzed, basic models utilized, and detailed heat and mass transfer models will be developed to analyze the most promising processes. The goal of the first year …

The Vacuum Excitation And Squeezing Properties Of Two Quantum Oscillators With Delta-Kicked Interactions, J Y. Ji, David Peak

All Physics Faculty Publications

The vacuum excitation and squeezing of two harmonic oscillators with delta-kicked interactions for four types of elementary coupling are studied. The exact quantum motion for the Heisenberg operators and the explicit form of squeezing operators are found. The variances are calculated to study the squeezing properties for position, momentum and generalized quadrature operators.

Velocity Field Distributions Due To Ideal Line Vortices, Thomas D. Levi, David C. Montgomery

Dartmouth Scholarship

We evaluate numerically the velocity field distributions produced by a bounded, two-dimensional fluid model consisting of a collection of parallel ideal line vortices. We sample at many spatial points inside a rigid circular boundary. We focus on “nearest-neighbor” contributions that result from vortices that fall (randomly) very close to the spatial points where the velocity is being sampled. We confirm that these events lead to a non-Gaussian high-velocity “tail” on an otherwise Gaussian distribution function for the Eulerian velocity field. We also investigate the behavior of distributions that do not have equilibrium mean-field probability distributions that are uniform inside the …

Quasi-Model-Independent Search For New High PT Physics At D0, B. Abbott, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We apply a quasi-model-independent strategy (“Sleuth”) to search for new high p_T physics in ≈100 pb^-1 of pp̅ collisions at √s = 1.8 TeV collected by the D0 experiment during 1992–1996 at the Fermilab Tevatron. We systematically analyze many exclusive final states and demonstrate sensitivity to a variety of models predicting new phenomena at the electroweak scale. No evidence of new high p_T physics is observed.

Formation Of Rydberg Atoms In An Expanding Ultracold Neutral Plasma, Scott D. Bergeson, T. C. Killian, M. J. Lim, S. Kulin, R. Dumke, S. L. Rolston

Faculty Publications

We study the formation of Rydberg atoms in expanding plasmas at temperatures of 1–1000 K and densities from 10^5–10^10 cm^-3. Up to 20% of the initially free charges recombine in about 100 us, and the binding energy of the Rydberg atoms approximately equals the increase in the kinetic energy of the remaining free electrons. Three-body recombination is expected to dominate in this regime, yet most of our results are inconsistent with this mechanism.

What Determines The Emission Peak Energy Of The Blue Luminescence In Highly Mg-Doped P-Gan?, John S. Colton, P. Y. Yu

Faculty Publications

We report a study of the 2.8 eV blue luminescence (BL) in heaviliy Mg-doped p-GaN via resonant excitation with a tunable blue dye laser. The dependence of the BL on the excitation photon energy (Eex) is unlike that of the yellow luminescence found in n-type GaN. An Urbach-type band tail, with Urbach parameter of 33 meV is observed in the vicinity of the BL energy. We propose that the peak energy of the BL marks the transition from localized states to delocalized states within this band tail.

Affinity For Scalar Fields To Dissipate, Arjun Berera, Rudnei O. Ramos

Dartmouth Scholarship

The zero-temperature effective equation of motion is derived for a scalar field interacting with other fields. For a broad range of cases, involving interaction with as few as one or two fields, dissipative regimes are found for the scalar field system. The zero-temperature limit constitutes a baseline effect that will be prevalent in any general statistical state. Thus, the results found here provide strong evidence that dissipation is the norm not the exception for an interacting scalar field system. For application to inflationary cosmology, this provides convincing evidence that warm inflation could be a natural dynamics once proper treatment of …

Large-Scale Synchrony In Weakly Interacting Automata, Eric J. Friedman, Adam S. Landsberg

WM Keck Science Faculty Papers

We study the behavior of two spatially distributed (sandpile) models which are weakly linked with one another. Using a Monte Carlo implementation of the renormalization-group and algebraic methods, we describe how large-scale correlations emerge between the two systems, leading to synchronized behavior.

Double-Electron Removal From H2 By Slow, Highly Charged Xe²³⁺ Ions, Ronald E. Olson, C. R. Feeler

Physics Faculty Research & Creative Works

A five-body classical trajectory Monte Carlo model has been used to study double-electron removal from H2 by collisions with highly charged ions. The final-state correlations between ionized protons and projectile are calculated for Xe²³⁺ impact on H2 at collisions energies ranging from 2.6 eVu^-1 to 2.6 keVu^-1. In the center-of-mass frame of the recoiling protons, as the projectile energy decreases the proton energy distribution broadens considerably and also shifts to lower energies relative to that for an isolated molecule Franck-Condon transition. At low collision energies the protons are found to be scattered to the forward direction …

First Measurement Of The Ratio B (T →Wb)/ B (T → Wq) And Associated Limit On The Cabibbo-Kobayashi-Maskawa Element |VTb|, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present the first measurement of the ratio of branching fractions R≡ B(t→ Wb)/B(t →Wq) from pp̅ collisions at √s =1.8 TeV. The data set corresponds to 109 pb^-1 of data recorded by the Collider Detector at Fermilab during the 1992–95 Tevatron run. We measure R=_-0.24^+0.31(stat + syst) or R >0.61 (0.56) at 90% (95)% C.L., in agreement with the standard model predictions. This measurement yields a limit on the Cabibbo-Kobayashi-Maskawa quark mixing matrix element |V_tb| under the assumption of three generations …

Search For Dilepton Signatures From Minimal Low-Energy Supergravity In Pp̅ Collisions At √S = 1.8 Tev, B. Abbott, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We report on a search for supersymmetry using the DØ detector. The 1994–1996 data sample of √s =1.8 TeV pp̅ collisions was analyzed for events containing two leptons (e or μ), two or more jets, and missing transverse energy. Assuming the minimal supergravity model, with A₀=0 and μ < 0, various thresholds were employed to optimize the search. No events were found beyond expectation from the background. We set a lower limit at the 95% C.L. of 255 GeV/c² for equal mass squarks and gluinos for tan β =2, and present exclusion contours in the (m₀ , m_1/2) plane for tan β =2–6.

Deep Centers In A Free-Standing Gan Layer, Z-Q. Fang, David C. Look, P. Visconti, D. F. Wang, C. Z. Lu, F. Yun, H. Morkoç, Seong-Ju S. Park, K. Y. Lee

Physics Faculty Publications

Schottky barrier diodes, on both Ga and N faces of a ∼300-μm-thick free-standing GaN layer, grown by hydride vapor phase epitaxy (HVPE) on Al₂O₃ followed by laser separation, were studied by capacitance–voltage and deep level transient spectroscopy (DLTS) measurements. From a 1/C² vs V analysis, the barrier heights of Ni/Au Schottky contacts were determined to be different for the two polar faces: 1.27 eV for the Ga face, and 0.75 eV for the N face. In addition to the four common DLTS traps observed previously in other epitaxial GaN including HVPE-grown GaN a new trap …