Physics Commons^™

Structural And Magnetic Properties Of Manganites Pr1-XCa1+XMno4, Oxypnictides Cefeaso1-XFX, And Filled Skutterudite Pros4As12, Songxue Chi

Doctoral Dissertations

We present neutron scattering, with triple-axis and time-of-flight spectrometers, to study the structural and magnetic properties of the layered manganites Pr_1-xCa_1+xMnO₄ (PCMO), and to determine the crystalline electric field (CEF) levels in iron pnictides CeFeAsO_1-xF_x and filled skutterudite compound PrOs₄As₁₂.

For the single-layered manganites PCMO, four dopings (x=0.5, 0.45, 0.40 and 0.35) have been studied. At half-doping, the system first becomes charge- and orbital- ordered (CO/OO) near T_CO = 300 K and then develops CE-type antiferromagnetic (AF) order below T_N = 130 K. …

Explicit Methods In The Nuclear Burning Problem For Supernova Ia Models, Viktor Chupryna

Doctoral Dissertations

Most modern astrophysical problems such as supernova simulation require application of state-ofthe- art computational tools. Despite the fact that number of nuclei included in coupled simulations tends to be small, problems such as nuclear burning networks are often part of a large set of interconnected programs that require significant computing resources. Expansion of the nuclear reaction network to realistic sizes can easily make element and energy production the leading consumer of both time and memory in simulations. Therefore, in solving nuclear reaction networks coupled to (radiation) hydrodynamics in astrophysics simulations, the development of methods capable of improving on the traditional …

Collective Behavior Of Interacting Magnetic Nanoparticles, Noppi Widjaja

Doctoral Dissertations

In the past, Low Dimensional Materials by Design group at ORNL in collaboration with students from the University of Tennessee, have successfully tailored and studied magnetic nanostructures in 2D, 1D and 0D spatial confinement on Cu(111) substrates. They observed a striking collective ferromagnetic long-range order in Fe-nanodots on Cu(111) surface which can be stabilized through the indirect exchange interaction mediated by the substrate. This type of magnetic interaction was expected to have little effect on promoting a global ferromagnetic order in a randomly distributed dot assembly. It is for certain that we need a better understanding of the relative roles …

Emergent Phenomena In Spatially Confined Manganites, Thomas Z. Ward

Doctoral Dissertations

Rare earth manganites exhibit colossal magnetoresistance (CMR). There is evidence that alloyed single crystal materials in this class can display electronic inhomogeneity in which areas with vastly different electronic and magnetic properties can form and coexist in phase separated domains ranging in size from a few nanometers to micrometers. This phase separation (PS) is of particular interest, as it has been suggested that it is the central feature that leads to CMR in manganites, the Mott transition in VO₂ and may play a role in high-TC superconductivity in cuprates. However there is debate as to its precise role.

The …

Environmental Analysis And White Cell Applications Ftir Spectroscopy, Maria Gabriela Oliveros

Masters Theses

The research is concerned with atmospheric chemistry & physics, and analyzing the environment with respect to the quantity of molecules is in the air we breathe. Fourier Transform Infrared Spectroscopy is used to identify the IR active molecules in our atmosphere. FTIR Spectrometer determines the intensity loss for molecules that have absorbed IR light. The FTIR spectroscopy is performed using the light from the sun or a carbon rod light source in the lab. A Sun-tracking device was employed to direct the sunlight into the spectrometer. Open-path measurements were made using multiple mirror reflections of the carbon rod light source …

Experimental Determination Of Emissivity And Resistivity Of Yttria Stabilized Zirconia At High Temperatures, Howard Mosley Frederick

Masters Theses

The emissivity and resistivity of yttria stabilized zirconia (YsZ), Y₂O₃-ZrO₂, a ceramic material that has been specially fabricated for use as an electrically powered high temperature air heater are determined for temperatures above 2000 K. Published results of measurements of emissivity and resistivity of yttria, zirconia, and their alloys at temperatures above 2000 K are rare in the technical literature. A survey of literature describing the properties of YsZ, particularly literature concerning the ionic conduction process at high temperatures, is assembled to provide a theoretical basis for the formulation of a temperature and resistivity …

Direct Observation Of H2 Binding To A Metal Oxide Surface, J. Z. Larese, T. Arnold, L. Frazier, R. J. Hinde, A. J. Ramirez-Cuesta

Chemistry Publications and Other Works

Inelastic neutron scattering is used to probe the dynamical response of H₂ films adsorbed on MgO(100) as a function of film thickness. Concomitant diffraction measurements and a reduced-dimensionality quantum dynamical model provide insight into the molecule-surface interaction potential. At monolayer thickness, the rotational motion is strongly influenced by the surface, so that the molecules behave like quasiplanar rotors. These findings have a direct impact on understanding how molecular hydrogen binds to the surface of materials used in catalytic and storage applications.

Cross Sections Fall 2008, Department Of Physics And Astronomy

Cross Sections

No abstract provided.

A Measurement Of Open Charm Using Single Muons At Forward Angles For P+P Collisions At Center Of Mass Energy 200 Gev, Donald Eric Hornback

Doctoral Dissertations

This dissertation presents the measurement of single muons from the semi-leptonic decay of heavy quark mesons (charm and bottom) in √s=200 GeV p+p collisions at the Relativistic Heavy Ion Collider at Brookhaven National Lab. The data were recorded in 2005 by the PHENIX experiment. The PHENIX muon spectrometer measures particles at forward angles from approximately 15º to 33º relative to the beam line in both forward and backward directions.

A new analysis technique was developed to estimate and subtract backgrounds from light hadrons in a statistical fashion to reveal the yield of heavy flavor single muons. The yield of single …

Collision-Induced Dissociation Of Multiply-Charged Anions, Nasrin Mirsaleh Kohan

Doctoral Dissertations

Electrospray ionization has proven to be a powerful method for the study of multiply-charged-anions (MCA) in the gas-phase. Stability of the MCA toward ionic fragmentation and electron detachment has attracted wide interest. The stability of dianions is due to the “repulsive Coulomb barrier” to the addition or removed of an excess electron to a negative ion. The repulsive Coulomb barrier (RCB) is primarily the result of a long-range Coulomb repulsion and the short-range polarizibility attraction between an electron and a negative ion. The RCB can render unbound MCAs metastable or add stability to bound MCAs. In this dissertation, a collision-induced …

The Applications Of The Tracer Particle Method To Multi-Dimensional Supernova Simulations, Ching-Tsai Lee

Doctoral Dissertations

A new tracer particle implementation has been developed for the 2D supernova code ”CHIMERA”. 2D supernova simulations have been performed for a wide range of progenitors, between 10 and 25 solar mass. In the case of the Heger12 model, we have obtained a successful explosion. Analysis of the tracer particle data generated by supernova simulations reveals the aspherical geometry of the ejecta. Using the hydrodynamic trajectories provided by the tracer particles, we have performed the nucleosynthesis calculations in the post processing approximation, including the effects of neutrino captures, to understand the nucleosynthesis consequences of these models.

The Qse-Reduced Nuclear Reaction Network For Silicon Burning, Suzanne T. Parete-Koon

Doctoral Dissertations

Iron and neighboring nuclei are formed by silicon burning in massive stars before core collapse and during supernova outbursts. Complete and incomplete silicon burning is responsible for the production of a wide range of nuclei with atomic mass numbers from 28 to 70. Because of the large number of nuclei involved, accurate modeling of these nucleosynthetic stages is computationally expensive. For this reason, hydrodynamic models of supernovae often employ a limited set of nuclei to track the nuclear energy generation until nuclear statistical equilibrium is reached. These limited approximations do not include many of the reaction channels important for the …

Simulation Of Single Molecule Trapping In A Nanochannel, William Neil Robinson

Masters Theses

Trapping of single fluorescent molecules in solution is numerically simulated. Optical trapping provides insufficient force for trapping molecules much smaller than the optical wavelength. Instead, a means for trapping by sensing the molecule position and applying real-time feedback of flow to compensate diffusional displacement is used. The solution is contained in a nanochannel, reducing the problem to one spatial dimension. The position of the molecule is estimated from the fluorescence signals generated by two focused laser beams, which originate from a single laser source that is split and temporally alternated between the two focal spots. Photon collection is time gated, …

Fusion Reaction Cross-Section Measurements Near 100Sn, Elton Lewis Freeman

Masters Theses

This thesis describes the measurement of production rates of A=109 isobars produced with beams of ⁵⁴Fe ions accelerated to 207 MeV bombarding ⁵⁸Ni target. The reaction products have been electromagnetically separated according to their mass over charge ratio and implanted into a semiconductor detector. The spontaneous decay radiation from the implanted radioactive isobars has been measured in a detection system with known detection efficiency, enabling to determine absolute intensities of observed isotopes. Known branching ratios of alpha decays of ¹⁰⁹Xe, ¹⁰⁹Te, proton decay of ¹⁰⁹I and beta delayed gamma radiation of ¹⁰⁹Te and ^{109 …}

Nanomagnets: Magnetic Properties And Inelastic Neutron Scattering Studies, Jason T. Haraldsen

Doctoral Dissertations

In this thesis, small quantum spin systems, known as nano-magnets or molecular magnets, have been investigated. This is an area of great interest in the development of nanotechnology and quantum computers. Previous research on molecular magnets has concentrated on large, complex materials, which have many magnetic ions competing for superexchange pathways. Due to the large number of magnetic ions, the Hamiltonians resulted in very large Hilbert spaces, which makes it difficult for the magnetic interactions to be characterized and analyzed. Through the analysis of smaller and simpler magnetic clusters, insight can be gained from the interactions of the magnetic ions …

Imaging By Detection Of Infrared Photons Using Arrays Of Uncooled Micromechanical Detectors, Dragoslav Grbovic

Doctoral Dissertations

The objective of this dissertation was to investigate the possibility of uncooled infrared imaging using arrays of optically-probed micromechanical detectors. This approach offered simplified design, improved reliability and lower cost, while attaining the performance approaching that contemporary uncooled imagers. Micromechanical infrared detectors undergo deformation due to the bimetallic effect when they absorb infrared photons. The performance improvements were sought through changes in structural design such as modification and simplification of detector geometry as well as changes in the choice of materials. Detector arrays were designed, fabricated and subsequently integrated into the imaging system and relevant parameters, describing the sensitivity and …

Modeling The Ground State Baryon Octet Using A Generalization Of The Lagrange Triangle Solution, Matthew P. Duran

Masters Theses

The baryon octet is modeled using relativistic and nonrelativistic Hamiltonians with interquark confining potentials. Using the works of Crater, a nonrelativistic three-body Hamiltonian is obtained where the corresponding eigenvalue equation will be shown to be separable and can be treated as three two-body like systems. Next, using relativistic constraint dynamics, our eigenvalue equation is treated relativistically following the works of Sazdjian and Yang. Using the free-mass-shell Hamiltonian constraints, Yang gives us an effective energy and reduced mass of relative motion for two particle systems which we expand to a three body case. With the help of work done by Sazdjian, …

Optimization Of Cosmological Simulations With Artificial Intelligence, Jay Billings

Masters Theses

Galaxy collisions are an important part of the large-scale structure of the Universe and an important catalyst for intragalactic processes like star formation. Therefore, realistic models of these interactions are an important part of any theory that plans to accurately describe the evolutionary processes of the Universe and, given the size of the problem, efficient computation and data analysis are key. This dissertation presents a proof-of-concept that an artificial intelligence suite, nominally composed of a genetic algorithm and neural network, can optimize the search of the galaxy collision parameter space. Furthermore, this dissertation discusses the possibility that this method can …

Observation Of Analyte-Induced Deflections For Uncoated Microcantilevers Using The Focused Ion Beam Procedure, Jacques S. Stacco

Masters Theses

It has been found that structural modifications, involving the creation of submicron scale grooves on uncoated silicon nitride microcantilevers, allow microcantilevers to display analyte-induced deflections which have not been previously observed. The submicron grooves were created through the use of a focused ion beam procedure to mill deep and narrow grooves without the subsequent deposition of a chemically reactive coating. These modifications significantly increase (by approximately 400%) an uncoated microcantilever’s ability detect analytes such as water vapor, ethyl alcohol, acetone vapor, argon, and 1-mononitrotoluene. The intention of the experiment was to achieve greater microcantilever deflections by increasing an uncoated microcantilever’s …

Cross Sections Spring 2008, Department Of Physics And Astronomy

Cross Sections

No abstract provided.

A Six-Dimensional H2–H2 Potential Energy Surface For Bound State Spectroscopy, Robert Hinde

Chemistry Publications and Other Works

We present a six-dimensional potential energy surface for the (H₂)₂ dimer based on coupled-cluster electronic structure calculations employing large atom-centered Gaussian basis sets and a small set of midbond functions at the dimer’s center of mass. The surface is intended to describe accurately the bound and quasibound states of the dimers (H₂)₂, (D₂)₂, and H₂–D₂ that correlate with H₂ or D₂ monomers in the rovibrational levels (v, j) =(0,0), (0,2), (1,0), and (1,2). We employ a close-coupled approach to compute the …