Digital Commons Network^™

Approximate Thermodynamic State Relations In Partially Ionized Gas Mixtures, John D. Ramshaw

Physics Faculty Publications and Presentations

Thermodynamic state relations for mixtures of partially ionized nonideal gases are often approximated by artificially partitioning the mixture into compartments or subvolumes occupied by the pure partially ionized constituent gases, and requiring these subvolumes to be in temperature and pressure equilibrium. This intuitively reasonable procedure is easily shown to reproduce the correct thermal and caloric state equations for a mixture of neutral nonionized ideal gases. The purpose of this paper is to point out that (a) this procedure leads to incorrect state equations for a mixture of partially ionized ideal gases, whereas (b) the alternative procedure of requiring that the …

Geometry And Electronic Structure Of Vn(Bz)M Complexes, Anil K. Kandalam, B. K. Rao, Puru Jena, Michigan Technological University

Physics & Engineering Faculty Publications

No abstract provided.

Using Time-Resolved Photoluminescence To Measure The Excitation And Temperature Dependence Of Carrier Relaxation In Mid-Wave Infrared Semiconductors, Kevin Cumblidge

Theses and Dissertations

Research in the field of mid-wave infrared (MWIR) semiconductor photonic devices has led to applications in a variety of disciplines including atmospheric monitoring, optical communications, non-invasive glucose testing for diabetics, and infrared (IR) countermeasures. One of the limiting factors for improving the modulation rates of MWIR devices is the carrier relaxation time. This is the time required for energetic carriers to cool to the edge of their respective bands in a bulk semiconductor material, or to the bottom of a well through inter- and intra-sub-band scattering in a quantum well (QW) structure. From these lower energy states, they can then …

Search For Narrow Tt̅ Resonances In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

A search for narrow resonances that decay into tt̅ pairs has been performed using 130 pb^-1 of data in the lepton + jets channel collected by the DØ detector in pp̅ collisions at √s = 1.8 TeV. There is no significant deviation observed from the standard-model predictions at a top-quark mass of 175 GeV/c². We therefore present upper limits at the 95% confidence level on the product of the production cross section and branching fraction to tt̅ for narrow resonances as a function of the resonance mass M_x. These limits are used to …

Comparison Of Hyperspherical Versus Common-Reaction-Coordinate Close-Coupling Methods For Ion-Atom Collisions At Low Energies, Anh-Thu Le, C. D. Lin, L. F. Errea, L. Mendez, A. Riera, B. Pons

Physics Faculty Research & Creative Works

We present detailed comparisons between the two quantal approaches--hyperspherical close-coupling and common-reaction-coordinate close-coupling methods--on an exemplary case of He²⁺ + H(1s) collisions at center-of-mass energy from 20eV up to 1.6keV. It is shown that the partial-wave charge-transfer cross sections from the two approaches agree very well at low energy below 200eV down to 30eV. This good agreement is a strong indication of the validity of both methods. The small difference at very low energies and the convergence with respect to the number of channels in both approaches at higher energies are also discussed.

Microscopic Investigation Of Phonon Modes In Sige Alloy Nanocrystals, Shang-Fen Ren, Wei Cheng, Peter Y. Yu

Faculty publications – Physics

Phonon modes in spherical silicon germanium alloy (SiGe) nanocrystals containing up to 1147 atoms (3.6 nm) have been investigated as a function of the Si concentration. Microscopic details of phonon modes, including phonon frequencies and vibrational amplitudes, phonon density-of-states are calculated directly from the dynamic matrices. In particular, the dependence of phonon frequency on the configuration (such as a different ratio of Si to Ge atoms), and location (surface or interior) of clusters of atoms in SiGe alloy nanocrystals have been investigated. Low frequency surface phonons that are related to the spheroidal and torsional modes of a continuum sphere are …

Classroom Demonstrations: Learning Tools Or Entertainment?, Catherine Hirshfeld Crouch, A. P. Fagen, J. P. Callan, E. Mazur

Physics & Astronomy Faculty Works

We compared student learning from different modes of presenting classroom demonstrations to determine how much students learn from traditionally presented demonstrations, and whether learning can be enhanced by simply changing the mode of presentation to increase student engagement. We find that students who passively observe demonstrations understand the underlying concepts no better than students who do not see the demonstration at all, in agreement with previous studies. Learning is enhanced, however, by increasing student engagement; students who predict the demonstration outcome before seeing it, however, display significantly greater understanding.

Thickness Dependence Of Magneto-Transport In Cu-Co Granular Thin Films, Jian Qing Wang, Ngocnga Dao, Ham H. Kim, Scott L. Whittenburg

Chemistry and Biochemistry Faculty Publications

This work explores the thickness dependence of magneto-transport properties in granular thin films with different thickness. These results are compared with silver-based film series studied earlier. It was observed that the thickness dependence of the GMReffect was sensitive to the surface chemistry of the films. The extraordinary Hall effect (EHE) in these films was measured and found to be different from the Ag-based system. In the Cu-based system, the EHE is a weak function of film thickness over the range studied. When the variation of the spontaneous magnetization is taken into account the effective EHE has a universal thickness dependence

Nearest-Neighbor-Atom Core-Hole Transfer In Isolated Molecules, Renaud Guillemin, Oliver Hemmers, D. Rolles, S. W. Yu, A. Wolska, I. Tran, A. C. Hudson, J. Baker, Dennis W. Lindle

Environmental Studies Faculty Publications

A new phenomenon sensitive only to next-door-neighbor atoms in isolated molecules is demonstrated using angle-resolved photoemission of site-selective core electrons. Evidence for this interatomic core-to-core electron interaction is observable only by measuring nondipolar angular distributions of photoelectrons. In essence, the phenomenon acts as a very fine atomic-scale sensor of nearest-neighbor elemental identity.

Afci Quarterly Input – Unlv April Through June, 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.

Inelastic X-Ray Scattering Studies In Lithium And Metal Ammonia Solutions, Ayman Hasan Said

Dissertations

In this work, inelastic x-ray scattering was used to measure the ionic collective excitations of a metal-ammonia system and the atomic form factor of lithium in a single crystal. For lithium and sodium ammonia systems, the measurements were carried out for different metal concentrations (lithium-ammonia with 2 0 , 16, and 13 mole percent metal [MPM] at T'=240K and sodium-ammonia with 18, 14, and 10 MPM at T=222K). These data were analyzed to determine the acoustic collective excitation dispersion relation and the linewidth. Deviations from the Bohm-Staver model for electron-ion coupling are discussed for the low electronic densities. For the …

Resonant And Non-Resonant Inelastic X-Ray Scattering Of Copper Phthalocyanine, Michelle Deleene Tuel-Benckendorf

Masters Theses

With the ever-changing demands of technology and the desire to use new materials to replace the old, researchers have the job to not only find alternative materials, but also understand their properties. There continues to be extensive research in the properties of organic semiconductors, for use in many microelectronic applications. There is very little known about the excitation properties of these materials. For my research, I have chosen to study the electronic excitations of copper phthalocyanine (CuPc), one specific organic semiconductor. To do this, we used resonant and non-resonant inelastic x-ray scattering to measure the evolution of excitations as a …

New Limits On The Drift Of Fundamental Constants From Laboratory Measurements, Marc P. Fischer, Nikolai N. Kolachevsky, Marcus Zimmermann, Ronald Holzwarth, Th H. Udem, Theodor Wolfgang Hansch, Michel Abgrall, Jan Grunert, Ivan Maksimovic, Sebastien Bize, Harold Marion, Franck Pereira M Dos Santos, Pierre Lemonde, Giorgio Santarelli, Ph Laurent, Andre Clairon, Christophe Salomon, Martin K. Haas, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

We have remeasured the absolute 1S-2S transition frequency ν_H in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of (-29 ± 57) Hz for the drift of ν_H with respect to the ground state hyperfine splitting ν_Cs in ¹³³Cs. Combining this result with the recently published optical transition frequency in ¹⁹⁹Hg⁺ against ν_Cs and a microwave ⁸⁷Rb and ¹³³Cs clock comparison, we deduce separate limits on α˙ / α = (-0.9 &plusm; 2.9) x 10^-15 yr^-1 and the fractional time …

Electron Self-Energy For Higher Excited S Levels, Ulrich D. Jentschura, Peter J. Mohr

Physics Faculty Research & Creative Works

A nonperturbative numerical evaluation of the one-photon electron self-energy for the 3S and 4S states with charge numbers Z=1 to 5 is described. The numerical results are in agreement with known terms in the expansion of the self-energy in powers of Zα.

Close-Coupling And Distorted-Wave Calculations For Electron-Impact Excitation Of The (5p⁵6p) States Of Xenon, K. Bartschat, Anand Dasgupta, Don H. Madison

Physics Faculty Research & Creative Works

We report on a series of calculations for electron-impact excitation of the (5p56p) states in xenon from the ground state (5p6)1S0 . As in previous calculations for other noble-gas targets, we find strong evidence of channel coupling for all incident energies considered (between threshold and 200 eV ). Although qualitative agreement with the experimental results of Fons and Lin [Phys. Rev. A 58, 4603 (1998)] is achieved, severe quantitative discrepancies of sometimes more than a factor of 2 remain.

Search For New Particles In The Two-Jet Decay Channel With The Dø Detector, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We present the results of a search for the production of new particles decaying into two jets in p̅p collisions at √s =1.8 TeV, using the DØ 1992–1995 data set corresponding to 109 pb^-1. We exclude at the 95% confidence level the production of excited quarks (q^*) with masses below 775 GeV/c², the most restrictive limit to date. We also exclude standard-model-like W′ (Z′) bosons with masses between 300 and 800 GeV/c² (400 and 640 GeV/c²). A W8 boson with mass ,786 GeV/ …

Multidomain And Incoherent Effects In Magnetic Nanodots, Ralph Skomski, Arti Kashyap, Kory D. Sorge, David J. Sellmyer

David Sellmyer Publications

The magnetic ground state and the magnetization reversal of aspherical nanoparticles are investigated by model calculations and micromagnetic simulations. Essential deviations from Kittel's domain theory occur for very flat and very elongated particles, for particles whose size is comparable to the domain-wall width, and when the particle shape is strongly nonellipsoidal. For example, the single-domain state of square rod is much less stable than that of comparable elongated ellipsoids, because most of the surface charge of long ellipsoids is located on the sides. Another specific feature of flat particles is suppression of the curling mode.

Magnetism Of L10 Compounds With The Composition Mt (M = Rh, Pd, Pt, Ir And T = Mn, Fe, Co, Ni), Arti Kashyap, Ralph Skomski, Ashok K. Solanki, Yinfan Xu, David J. Sellmyer

David Sellmyer Publications

The electronic band structure of ordered equiatomic compounds of 3d transition elements (Mn, Fe, Co, Ni) with nonmagnetic 4d and 5d elements (Rh, Pd, Pt, Ir) are investigated by linear muffin-tin orbital calculations. The systematic study considers 3d and 4d/5d spin moments and interatomic exchange interactions, with emphasis on the comparison between ferromagnetic and antiferromagnetic order. Total and site-resolved exchange interactions are calculated from first principles, and the obtained exchange constants are used to estimate ordering temperatures on a mean-field level.

Kapitza-Dirac Diffraction Without Standing Waves: Diffraction Without A Grating?, Olga Smirnova, Daniel L. Freimund, Herman Batelaan, Misha Ivanov

Department of Physics and Astronomy: Faculty Publications

We discuss electron diffraction from two counterpropagating light waves with two different frequencies.We show that, even though these waves do not form a standing wave, electron diffraction similar to the conventional Kapitza-Dirac effect, i.e., scattering on a standing wave, is still possible. The nonlinear response of the electron to the laser fields creates a stationary diffraction grating from which the same electron scatters.

Characterization Of Ultrathin Gate Dielectrics And Multilayer Charge Injection Barriers, Edwin M. Dons

Dissertations

Since the invention of the first integrated circuit, the semiconductor industry has distinguished itself by a phenomenally rapid pace of improvements in device performance. This trend of ever smaller and faster devices is a result of the ability to exponentially reduce feature sizes of integrated circuits, a trend commonly known as "scaling". A reduction of overall feature sizes requires a simultaneous reduction in the thickness of the gate dielectric, SiO₂, of a MOSFET. Gate oxides in the ultrathin regime (<35 A) feature a large direct tunneling leakage current. The presence of this leakage current requires a reevaluation of standard characterization techniques as well as a reevaluation of the continued usefulness of SiO₂ as the gate dielectric of choice for future applications. On the other hand, a thorough understanding of …

Understanding The Origin Of The Recovery Of Superconductivity In Halogenated Ybco Single Crystal : Atomic Structure Study, Lamine Mohamed Kollakoye Dieng

Dissertations

The recovery of superconductivity in underdoped YBa₂Cu₃O_6+y (YBCO) by exposure to bromine, iodine, chlorine and fluorine is a long-standing problem which has not been clearly resolved. The key question concerns the role of these halogens in the lattice. In order to shed light to this problem, we have performed multiple-edge x-ray absorption fine structure (XAFS) measurements about the Y K, Ba L₃, I L₃, Cu K and Br K-edges at room temperature on brominated (non-brominated) and iodinated (non-iodinated) YBCO single crystals. Our XAFS results at the Br K (brominated) and I …

Simulations Of Dynamically Triangulated Gravity -- An Algorithm For Arbitrary Dimension, Simon Catterall

Physics - All Scholarship

Recent models for discrete euclidean quantum gravity incorporate a sum over simplicial triangulations. We describe an algorithm for simulating such models in general dimensions. As illustration we show results from simulations in four dimensions

Gold Adatoms And Dimers On Relaxed Graphite Surfaces, Guan Ming Wang, Joseph J. Belbruno, Steven D. Kenny, Roger Smith

Dartmouth Scholarship

The interaction of deposited gold adatoms and dimers with multilayer relaxed graphite surfaces is investigated through a density functional approach with numerical orbitals and a relativistic core pseudopotential. The energy landscape for a gold adatom along [110] agrees with scanning tunneling microscopy observations including the preferred β binding site for adatoms and the mobility difference between silver and gold adatoms. Deposited particles are shown to induce surface deformation and polarization. Static relaxation and dynamic simulations indicate that the energetically preferred binding orientation for a gold dimer is normal rather than parallel to the graphite surface. The dimer response to a …

Lattice Sigma Models With Exact Supersymmetry, Simon Catterall, Sofiane Ghadab

Physics - All Scholarship

We show how to construct lattice sigma models in one, two and four dimensions which exhibit an exact fermionic symmetry. These models are discretized and {\it twisted} versions of conventional supersymmetric sigma models with N=2 supersymmetry. The fermionic symmetry corresponds to a scalar BRST charge built from the original supercharges. The lattice theories possess local actions and in many cases admit a Wilson term to suppress doubles. In the two and four dimensional theories we show that these lattice theories are invariant under additional discrete symmetries. We argue that the presence of these exact symmetries ensures that no fine tuning …

Multistrange Baryon Production In Au-Au Collisions At √ SNn = 130 Gev, Star Collaboration, T.D. Gutierrez

Physics

The transverse mass spectra and midrapidity yields for Ξs and Ωs are presented. For the 10% most central collisions, the ¯Ξ¯+/h− ratio increases from the Super Proton Synchrotron to the Relativistic Heavy Ion Collider energies while the Ξ−/h⁻stays approximately constant. A hydrodynamically inspired model fit to the Ξ spectra, which assumes a thermalized source, seems to indicate that these multistrange particles experience a significant transverse flow effect, but are emitted when the system is hotter and the flow is smaller than values obtained from a combined fit to π, K, p, and Λs.

Moduli Stabilization With The String Higgs Effect, Scott Watson

Physics - All Scholarship

We review the notion of the Higgs effect in the context of string theory. We find that by including this effect in time dependent backgrounds, one is led to a natural mechanism for stabilizing moduli at points of enhanced gauge symmetry. We consider this mechanism for the case of the radion (size of the extra dimensions) and find that as decompactification of the large spatial dimensions takes place the radion will remain stabilized at the self dual radius. We discuss how this mechanism can be incorporated into models of string cosmology and brane inflation to resolve some outstanding problems. We …

Search For Qcd-Instanton Induced Events In Eeep Inelastic Ep Scattering At Hera, 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

A search for QCD-instanton-induced events in deep inelastic ep scattering has been performed with the ZEUS detector at the HERA collider, using data corresponding to an integrated luminosity of 38 pb-1. A kinematic range defined by cuts on the photon virtuality, Q2 > 120 GeV 2, and on the Bjorken scaling variable, x > 10-3, has been investigated. The QCD-instanton induced events were modelled by the Monte Carlo generator QCDINS. A background-independent, conservative 95% confidence level upper limit for the instanton cross section of 26 pb is obtained, to be compared with the theoretically expected value of 8.9pb.

Spectral Characteristics Of Water Megamaser Galaxies. Ii. Eso103-G035, Txs 2226-184, And Ic1481, N. Bennert, H. Schulz, C. Henkel

Physics

Long-slit optical emission-line spectra of the H₂O megamaser galaxies ESO 103-G035, TXS 2226-184, and IC 1481 are evaluated in order to look for characteristics typical for water-megamaser galaxies. We present rotation curves, line ratios, electron densities, temperatures, and H luminosities. The successful line-profile decompositions rest on d-Lorentzians with an additional parameter d to adjust the wings, rather than Gaussians or Lorentzians as basic functions. No significant velocity gradient is found along the major axis in the innermost 2 kpc of TXS 2226-184. IC 1481 reveals a spectrum suggestive of a vigorous starburst in the …

Mesospheric Temperature Climatology Above Utah State University, Joshua P. Herron

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A Rayleigh-scatter lidar has been in operation at Utah State University (41. 7° N, 111.8 ° W) starting in September 1993 until the present (October 2003). The return profiles from the atmosphere have been analyzed to provide temperature measurements of the middle atmosphere from 45 to 90 km. Various methods of averaging were used to construct a temperature climatology of the region based on these observations. The data analysis algorithm has been critically analyzed to find possible sources of error, and has been compared to an independently derived technique. The resulting temperatures have been compared to other mid-latitude lidars with …

Computational Scattering Models For Elastic And Electromagnetic Waves In Particulate Media, Timothy Edwin Doyle

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Numerical models were developed to simulate the propagation of elastic and electromagnetic waves in an arbitrary, dense dispersion of spherical particles. The scattering interactions were modeled with vector multipole fields using pure-orbital vector spherical harmonics, and solved using the full vector form of the boundary conditions. Multiple scattering was simulated by translating the scattered wave fields from one particle to another with the use of translational addition theorems, summing the multiple-scattering contributions, and recalculating the scattering in an iterative fashion to a convergent solution. The addition theorems were rederived in this work using an integral method, and were shown to …