Physics Commons^™

The Thermoelectric Properties Investigation Of X0.05Mo3Sb7-YTeY (X=Mn, Fe, Ni, Co; Y=1.5, 1.6, 1.7), Tim Holgate

All Theses

With ever increasing energy costs, dwindling resources, and terms with the prefix 'green' filling headlines, the need for environmentally friendly energy sources has never been greater. Since the mid-20th century researchers have been pursuing greater efficiency in thermoelectric materials. Thermoelectric materials achieve energy conversion via the Seebeck effect (heat to electric power) and the Peltier effect (electricity to cooling power). Presented herein are the measured electrical and thermal transport properties and phenomenal analysis of the Ir₃Ge₇-type system: X_0.05Mo₃Sb_7-yTe_y (X=Mn, Fe, Ni, Co; y=1.5, 1.6, 1.7) where 'X' are interstitially …

Simulation And Analysis Of Cadmium Sulfide Nanoparticles, Chad Everett Junkermeier

Theses and Dissertations

I used ab initio molecular dynamics calculations to model cadmium sulfide nanoparticles. The nanoparticles were originaly spherical, bulk-like zinc-blende structures. Constant temperature molecular dynamics calculations reveals that CdS nanoparticles that are about 2 nm in diameter and have unpassivated surfaces are in an amorphous structure with short range order. The nearest neighbor distance on the surface of the nanoparticles being near the wurtzite nearest neighbor distance. I wrote the program xyzSTATS and used its results in justifying the amorphous nanoparticles claim. I also estimated the band gap of the CdS nanoparticles with unpassivated dangling bonds.

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 …

Intergranular Phases In Cyclically Annealed Yba2cu3o7-X And Their Implications For Critical Current Densities, Andrew Peter Clarke

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

We report changes in the intergranular material and grain morphology of YBa₂Cu₃O_7-x during cyclic anneals between 780 and 980 ºC in oxygen at atmospheric pressure. Two endothermic reactions were detected: (a) the eutectic reaction of YBa₂Cu₃O_7-x with CuO and BaCuO₂ at 900 ºC (enthalpy ∆H_a) and (b) the peritectic reaction of YBa₂Cu₃O_7-x with CuO at 950 ºC (∆H_b). During the first anneal, only reaction (b) is detected, and although it should only occur if there is an excess of CuO, …

Modeling The Electrodynamics Of The Low-Latitude Ionosphere, Christian Stephen Wohlwend

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The electrodynamics of the Earth's low-latitude ionosphere is dependent on the ionospheric conductivity and the thermospheric neutral density, temperature, and winds present. This two-part study focused on the gravity wave seeding mechanism of equatorial plasma depletions in the ionosphere and the associated equatorial spread F, as well as the differences between a two-dimensional flux tube integrated electrodynamics model and a three-dimensional model for the same time period. The gravity wave seeding study was based on a parameterization of a gravity wave perturbation using a background empirical thermosphere and a physics-based ionosphere for the case of 12 UT on 26 September …

The Adaptability Of Langmuir Probes To The Pico-Satellite Regime, Andrew Jay Auman

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The purpose of this thesis is to investigate whether it is feasible to use Langmuir probes on pico-satellites flying in low Earth orbit over mid- to low-latitude geographic regions. Following chapters on the expected ionospheric conditions and an overview of Langmuir probe theory, a chapter addressing the difficulties involved with pico-satellite Langmuir probes is presented. Also, the necessary satellite-to-probe surface area requirements in order to achieve confidence in pico-satellite Langmuir probe data, for the orbital regions of interest to this thesis, are stated.

Extending F10.7'S Time Resolution To Capture Solar Flare Phenomena, Ariel O. Acebal

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Solar ultraviolet (UV) radiation ionizes the neutral components in the atmosphere, which is partly responsible for the formation of the ionosphere, and contributes to heating of the atmosphere. Solar flares change the solar spectrum at times by several orders of magnitude. These changes modify the Earth's upper atmosphere, causing problems to communication systems and space operations, such as increased satellite drag. Unfortunately, solar UV measurements are limited since they can only be observed with space-based sensors. In order to work around this limitation, the solar radio emissions at a wavelength of 10.7 cm have been used as a proxy for …

The Origin Of The 511 Kev Positron Annihilation Emission Morphology, Bethany Johns

All Theses

The 511 keV positron annhilation emission from the Galactic bulge has yet to solely be attributed to any astrophysical source of positrons. The 511 keV line, characteristic of electron-positron annihilation, was discovered in 1970 by Johnson and Haymes [1973] almost 40 years ago. Most recently the INTERnational Gamma-Ray Astrophysical Laboratory (INTEGRAL) [Knodlseder 1997] has measured the annihilation rates of both components of the Galaxy. The bulge and disk annihilation rates are (1.5 ± 0.1) x 10^43 e+ s^-1 and(0.3 ± 0.2) x 10^43 e+ s^-1, respectively. The ratio of the bulge rate to that of the disk ranges from 3-9. …

Calculations Of K-Shell Fluorescence Yields And Photoabsorption Cross Sections For Carbon Ions At The K-Edge, Muhammet Fatih Hasoglu

Dissertations

The advent of new space missions providing high-precision observations has engendered the need for reliable and precise K-shell atomic data in order to interpret these X-ray spectra. In response to this need, we focused on the calculation of K-shell fluorescence yields for 2 nd -row ions. A secondary project was undertaken in order to treat theoretically the K-shell X-ray absorption processes in carbon ions. These calculated fluorescence yields of 2nd -row ions and theX-ray photoabsorption cross sections of carbon are astrophysically important in determining (1) charge-changing probabilities, such as Auger vs. radiative decay, and (2) chemical abundances of the interstellar …

Calculations Of Diffusion In Fcc Binary Alloys Using On-The-Fly Kinetic Monte Carlo, Erdi Bleda

All Dissertations

With the recent advancements in computer technologies and the improvements in simulation algorithms, along with the theories, has allowed scientists to carry out diffusion calculations more efficiently, especially for the cases where either the diffusion itself takes longer, or there is no available isotope to carry out the diffusion experiments such as tracer diffusion.
In this work, we present a systematic approach to diffusion in intermetallic alloys such as weakly clustered Cu — Ni and weakly ordered Au — Ag. We use Accelerated Molecular Dynamics (AMD) combined with the Embedded Atom Method (EAM) to find the necessary saddlepoint energies. With …

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 …

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 …

Do R_{Aa} And R_{Cp} Quantify Nuclear Medium Effects?, Robert Adrian Zaballa

Physics and Astronomy Dissertations

With the use of an incoherent binary nucleon-nucleon collision model of heavy ion collisions for simulating particle production, it is demonstrated that the nuclear modification factors, R_{AA} and R_{CP}, are less than unity for hard scattering in the absence of any nuclear modification effects. The nuclear modification factor R_{dAu} is also shown to approach or exceed unity only if p_T broadening is taken into account. With a simple phenomenological parameter, the mean nucleon energy loss fraction, this model yields particle distributions that are comparable to those of experiment. The nuclear geometry is described by the Glauber model, and particle production …

The Separated Fringe Packet Survey: Updating Multiplicity Of Solar-Type Stars Within 22 Parsecs, Christopher Donald Farrington

Physics and Astronomy Dissertations

Over the past half century, multiplicity studies have provided a foundation for the theories of stellar formation and evolution through understanding how likely it is that stars form alone or with companions. If spectroscopic orbits are combined with techniques that can determine visual orbits, we can access the most fundamental parameter of stellar evolution, stellar mass. This dissertation is composed of two main sections. The first involves the investigation of the seminal multiplicity study of Duquennoy & Mayor (1991b) which has been the ``gold standard" for solar-type stars for nearly 20 years. Improvements in technology in the intervening years have …

Theory Of Electronic And Optical Properties Of Nanostructures, Prabath Hewageegana

Physics and Astronomy Dissertations

"There is plenty of room at the bottom." This bold and prophetic statement from Nobel laureate Richard Feynman back in 1950s at Cal Tech launched the Nano Age and predicted, quite accurately, the explosion in nanoscience and nanotechnology. Now this is a fast developing area in both science and technology. Many think this would bring the greatest technological revolution in the history of mankind. To understand electronic and optical properties of nanostructures, the following problems have been studied. In particular, intensity of mid-infrared light transmitted through a metallic diffraction grating has been theoretically studied. It has been shown that for …

Short-Wave Infrared Diffuse Reflectance Of Textile Materials, Terence Haran

Physics and Astronomy Theses

This thesis analyzes the reflectance behavior of textiles in the short-wave infrared (SWIR) band (1 – 2 microns) in order to identify/design potential diagnostic tools that allow the remote detection of human presence in a scene. Analyzing the spectral response of fabrics in the SWIR band has gained significant interest in the remote sensing community since it provides a potential path to discriminate camouflaged clothing from backgrounds that appear similar to the object of interest in the visible band. Existing research, originating primarily from the textiles community, has thoroughly documented the behavior of clothing fabrics in the visible band. Other …

Closed-Loop Adaptive Optics Control In Strong Atmospheric Turbulence, Todd M. Venema

Theses and Dissertations

A self-referencing interferometer based closed-loop adaptive optics controller is developed which is designed to operate effectively under strong turbulence conditions. The aberrated optical field is modeled stochastically and then estimates of the state of the system are developed using a steady-state, fixed-gain Kalman filter. The phase of the optical field is considered the state of the system which is wrapped in a limited range of (-π, π]. This phase is unwrapped through the use of a least-squares reconstructor which has been modified to work effectively in the presence of branch points associated with strong turbulence. The conjugate of the optical …

Electronic State Distributions Of Y Ba2Cu3O7-X Laser Ablated Plumes, Patrick D. Kee

Theses and Dissertations

The application of spectral and imagery diagnostics to YBa₂Cu₃O₇ (YBCO) laser-ablated plumes was systematically studied to determine their effectiveness for process control. Emission signatures were collected for plumes created by ablating bulk YBCO with a pulsed laser source. A KrF (λ=248 nm) laser source operating at 4-10 J/cm² at a 4-10 Hz pulse repetition frequency was used to ablate a bulk YBCO target at O₂ background pressures ranging from 50 to 400 mTorr. Emission spectra were collected over the 500 to 860 nm bandpass at distances from the target ranging from 31.4 to …

A Study Of The Irradiance-And-Temperature-Dependence Of Mid-Wave-Infrared (Mwir)Absorption In Indium Antimonide (Insb), John M. Callahan

Theses and Dissertations

This work entails further investigation of the absorption of photons in indium antimonide (InSb). Previously work at the Air Force Institute of Technology (AFIT) attributed laser blooming effects in InSb focal plane arrays (FPA’s) to the Burstein-Moss effect. The contributing effect is from a decrease in the absorption of the InSb material, such that the transmitted optical energy scatters off the integrated circuitry beneath the InSb thin film back into the optical system. To evaluate this, irradiance-dependent laser-absorption experiments were performed on thinned, InSb wafers prior to their FPA fabrication. The samples were illuminated with a focused CO2 laser at …

Flexible Electronics : Materials And Sensor Fabrication, Katherine J. Duncan

Dissertations

This dissertation demonstrates how to fabricate piezoelectric/pyroelectric thin films by using different printing techniques. These techniques could replace vacuum techniques for manufacturing piezoelectric/pyroelectric sensors. Ink-jet, screen and stencil printing techniques were developed to print these devices.

This work outlines attempts to develop a solution processable conductive ink for ink-jet printing. It then details the printing of commercial conductive ink on flexible substrates employing the three printing methods. Raman spectroscopy and Fourier transform infrared spectroscopy, are both used to investigate the structure of the P(VDF-TrFE) films. Optical microscopy is used to investigate the thickness and uniformity of the deposited films. The …

Testing Direct Simulation Monte Carlo Methods Against The Fluid Equations In The Inductively Coupled Plasma Mass Spectrometer, William R. Somers

Theses and Dissertations

A Direct Simulation Monte Carlo fluid dynamics code named FENIX has been employed to study gas flow-through properties of the inductively coupled plasma mass spectrometer (ICP-MS). Simulation data have been tested against the Navier-Stokes and heat equations in order to see if FENIX functions properly. The Navier-Stokes and heat equations have been constructed from simulation data and are compared term by term. This comparison shows that FENIX is able to correctly reproduce fluid dynamics throughout the ICP-MS simulation, with an exception immediately behind the ICP-MS sampler cone, where the continuum criterion for the Navier-Stokes equation is not met. Testing the …

Implementation Of Optical Spectra Calculations In Fireball: A Local-Orbital Density Functional Theory Approach, Ivan Grigoryevich Okhrimenko

Theses and Dissertations

We have expanded the capabilities of the ab initio tight-binding molecular dynamics package FIREBALL to include calculations of optical properties. Basic zero order approximation is based on transitions between Kohn-Sham states. Corrections for electron-electron interactions are based on time dependant density functional theory (TDDFT). Consistent with the FIREBALL approach, we use precalculated integrals and approximations to make the program faster.

Lead Chalcogenide Nano-Composites: Synthesis, Thermal And Electrical Transport Properties, Bo Zhang

All Dissertations

This dissertation focused on the investigation of the thermoelectric properties of PbTe nanocomposites, presenting a series of experimental investigation and qualitative theoretical analysis regarding utilizing the nanostructures to enhance the thermoelectrical properties. Three innovative synthesis techniques, which are related to fabricating nanocomposites, were developed. These three techniques are the size-selective growth of PbTe nanoparticles by a convection CVD technique, the nanolayer coating technique by hydrothermal method, and the alkali-metal-nano-surface-treatment. In the future, these techniques can be applied to many other thermoelectric material systems.

We proposed to use the grain boundary engineering technique route in the thermoelectric nanocomposite field and successfully …

3-D Calculation Of Atom-Surface Collisions With Direct Scattering, Trapping And Desorption, Guoqing Fan

All Dissertations

In this work a scattering theory is developed to simulate the gas-surface scattering procedure in three dimensions, using an iterative algorithm and classical mechanics for the collision process, that describes both direct scattering and trapping-desorption of an incident beam of atomic particles. The initially trapped fraction of particles can be followed as they continue to make further collisions with the surface until they are all eventually promoted back into the positive energy continuum and leave the surface region.

With two different models, the discrete model and the smooth-surface model of the differential reflection coefficient, a series of calculation are made …

The Effects Of Nanoparticle Inclusions Upon The Microstructure And Thermoelectric Transport Properties Of Bismuth Telluride-Based Composites, Nick Gothard

All Dissertations

Research into materials that have high efficiencies of thermoelectric heat-energy conversion has been at a plateau since the middle of the last century. During this time, efficiencies have been engineered high enough for several interesting niche applications but not high enough for widespread adaptation into traditional power generation or refrigeration technologies. The past decade has seen considerable advancement as a number of theoretical works have suggested that lower dimensional structures could hold the key for enhanced efficiency, and several experiments have provided the proof of principle needed to inspire just such a research direction. The benefit of low dimensional structures …

Stimulated Brillouin Scattering Phase Conjugation In Fiber Optic Waveguides, Steven M. Massey

Theses and Dissertations

The objective of this research effort was to demonstrate the path to continuous wave, coherent beam combination through stimulated Brillouin scattering phase conjugation in optical fiber. This work experimentally determined the fiber parameters necessary for phase conjugation in step-index optical fiber. Continuous wave phase conjugation using stimulated Brillouin scattering in step-index fibers was achieved for the first time with a fidelity of 0.8 and a threshold power of 16 W in a 15-m fiber with 0.13 NA. A fidelity of 0.8 was also achieved using 40 m of fiber with 0.06-NA and a threshold power of 15 W. The fidelity …

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 …