Physics Commons^™

Scattering Amplitudes In Flat Space And Anti-De Sitter Space, Savan Kharel

Doctoral Dissertations

We calculate gauge theory one-loop amplitudes with the aid of the complex shift used in the Britto- Cachazo-Feng-Witten (BCFW) recursion relations of tree amplitudes. We apply the shift to the integrand and show that the contribution from the limit of infinite shift vanishes after integrating over the loop momentum, with a judicious choice of basis for polarization vectors. This enables us to write the one-loop amplitude in terms of on-shell tree and lower-point one-loop amplitudes. Some of the tree amplitudes are forward amplitudes. We show that their potential singularities do not contribute and the BCFW recursion relations can be applied …

Elucidating Fundamental Mechanisms In Focused Electron- And Ion-Beam Induced Synthesis, Carlos M. Gonzalez

Doctoral Dissertations

A focused electron beam deposition process (FEBID) coupled with in-situ infrared pulsed laser assist (LA-EBID) has been implemented for higher purity tungsten nanowires using W(CO)₆ [tungsten hexacarbonyl] as parent precursor gas. Nanowires made of Co from Co₂(CO)₈ [dicobalt octacarbonyl] and Pt from MeCpPtIVMe₃ [trimethyl methylcyclopentadienyl platinum] have also been realized by using inert focused ion beams of helium and helium and neon, respectively. In all cases, higher electrical conductivities, higher purities and larger grain sizes have been obtained when compared with preceding traditional additive edit techniques. These new approaches will make possible successful nanoscale direct-write …

Neutron Scattering Studies Of Phosphate Proton Conductors, Amal Bajes Al-Wahish

Doctoral Dissertations

Proton ceramic fuel cells operating in the intermediate temperature range of 300-500 °C offer potentially revolutionary advantages over existing fuel cells because expensive noble metal catalysts would not be needed, and in situ reforming of liquid bio-fuels such as ethanol or methanol would be possible.The chief obstacle facing intermediate fuel cells is the lack of a suitable electrolyte in the operating temperature range. A good electrolyte is thermally and chemically stable, inexpensive, environmentally friendly, and has a proton conductivity on the order of 10^-2 S cm^-1 [Siemens per centimeter] at 400 °C. Acceptor-doped lanthanum orthophosphate is an …

Nonlocal Polarization Interferometry And Entanglement Detection, Brian P. Williams

Doctoral Dissertations

At present, quantum entanglement is a resource, distributed to enable a variety of quantum information applications such as quantum key distribution, superdense coding, and teleportation. Necessarily, the distribution and characterization of entanglement is fundamental to its application. This dissertation details three research efforts to enable nonlocal entanglement detection, distribution, and characterization. Foremost of these efforts, we present the theory and demonstration of a nonlocal polarization interferometer capable of detecting entanglement and identifying Bell states statistically. This is possible due to the interferometer’s unique correlation dependence on the anti-diagonal elements of the density matrix, which have distinct bounds for separable states …

Hi-Fidelity Simulation Of The Self-Assembly And Dynamics Of Colloids And Polymeric Solutions With Long Range Interactions, Mahdy Malekzadeh Moghani

Doctoral Dissertations

Modeling the equilibrium properties and dynamic response of the colloidal and polymeric solutions provides valuable insight into numerous biological and industrial processes and facilitates development of novel technologies. To this end, the centerpiece of this research is to incorporate the long range electrostatic or hydrodynamic interactions via computationally efficient algorithms and to investigate the effect of these interactions on the self-assembly of colloidal particles and dynamic properties of polymeric solutions. Specifically, self-assembly of a new class of materials, namely bipolar Janus nano-particles, is investigated via molecular dynamic simulation in order to establish the relationship between individual particle characteristics, such as …

Laser-Induced Breakdown Spectroscopy For Analysis Of High Density Methane-Oxygen Mixtures, Matthew Dackman

Masters Theses

The applicability of laser-induced breakdown spectroscopy (LIBS) toward greater than atmospheric density combustion diagnostics is examined. Specifically, this involves ascertaining the feasibility of measuring chemical equivalence ratios directly from atomic emission spectra at high density. The need for such measurement arises from the desire to quantify real time, localized combustion performance in weakly mixed flows. Insufficiently mixed flows generally result in unwanted byproducts, possess the propensity for overall combustion instability, and are increasingly likely to experience localized flame extinction.

We simulate methane/oxygen combustion in ambient pressures ranging 1 to 4 atmospheres, demonstrating these results to be analogous to what would …

Design And Model Of The Frame For Hagrid (Hybrid Array Of Gamma Ray Detectors), Santiago Munoz

Masters Theses

Transfer reactions in inverse kinematics have provided critical information in the study of exotic nuclei. However, transfer reactions with charged particles suffer from poor resolution. The measurement of gamma-rays offers several advantages: they provide not only good resolution in measurements but also other information about the nuclei like lifetimes of unstable states. The combination of these two methods would be the ideal situation to gather information about nuclear structure.

HAGRiD, which stands for The Hybrid Array of Gamma Ray Detectors, is a LaBr3(Ce) [lanthanum bromide crystal with a cerium activator] scintillation array to measure gamma rays from transfer reactions and …

Evidence For Divisome Localization Mechanisms Independent Of The Min System And Slma In Escherichia Coli, Matthew W. Bailey, Paola Bisicchia, Boyd T. Warren, David J. Sherratt, Jaan Mannik

Physics and Astronomy Publications and Other Works

Cell division in Escherichia coli starts with assembly of FtsZ protofilaments into a ring-like structure, the Z-ring. Positioning of the Z-ring at midcell is thought to be coordinated by two regulatory systems, nucleoid occlusion and the Min system. In E. coli, nucleoid occlusion is mediated by the SlmA proteins. Here, we address the question of whether there are additional positioning systems that are capable of localizing the E. coli divisome with respect to the cell center. Using quantitative fluorescence imaging we show that slow growing cells lacking functional Min and SlmA nucleoid occlusion systems continue to divide preferentially at …

Growth, Structure, Electronic And Transport Properties Of Yttrium Disilicide Nanowires, Saban Mustafa Hus

Doctoral Dissertations

The electronic properties of low-dimensional materials deviate significantly from their bulk counterparts. Especially in quasi one-dimensional (1D) materials, a small number of structural defects can lead to strong electron localization. Electrons may also display unusual collective behavior in 1D. As integrated circuits continue to shrink in size, there is an increasing need for understanding and possibly manipulating electronic transport in quasi 1D materials. Here, we focus on electrical transport in self-assembled YSi₂ [yttrium disilicide] nanowires on Si(001). Being just a few atoms wide, these nanowires are one of the closest experimental realizations of a 1D conductor. YSi₂ nanowires …

Composition Dependence Of The Flory-Huggins Interaction Parameter In Polymer Blends: Structural And Thermodynamic Calculations, Travis H. Russell

Doctoral Dissertations

Flory-Huggins Theory has been the basis for understanding polymer solvent and blended polymer thermodynamics for much of the last 60 years. Within this theory, a parameter (χ) [chi] was included to quantify the enthalpic energy of dispersion between distinct components. Thin film self-assembly of polymer melts and block copolymers depends critically on this parameter, and in application, χ has generally been assumed to be independent of the concentrations of the individual components of the system. However, Small-Angle Neutron Scattering data on isotopic polymer blends, such as polyethylene and deuterated polyethylene, have shown a roughly parabolic concentration dependency for …

Structural Dynamics And Charge Transport In Room Temperature Ionic Liquids, Philip James Griffin

Doctoral Dissertations

Room temperature ionic liquids are an important class of materials due to their chemical tunability and numerous advantageous physicochemical properties. As a result, ionic liquids are currently being investigated for use in a wide array of chemical and electrochemical applications. Despite their great potential, however, the relationship between the chemical structure and physicochemical properties of ionic liquids is not well understood.

To this end, this dissertation presents experimental studies of the reorientational structural dynamics and charge transport properties of a variety of room temperature ionic liquids using quasielastic light scattering spectroscopy and broadband dielectric spectroscopy.

Studies of a series of …

Study Of Ferroelectric Oxides And Field Effect In Complex Oxides Heterostructures, Lu Jiang

Doctoral Dissertations

With the rapid development of technology, the need for novel materials and state-of-theart devices is growing fast. Complex oxides which have strongly correlated electrons are favorable candidates for materials industry, due to their rich phase diagrams and multiple functions. Especially, ferroelectric oxides is very promising materials in the industry for storage, due to their bistable polarization states triggered by external electrical field. This thesis is centered on ferroelectric oxides, analyzing their lattice structures and investigating the interface of ferroelectrics and other complex oxides to examine the potential of the heteostructures in the application in electronic devices.

The most notable feature …

Atomic And Molecular Laser-Induced Breakdown Spectroscopy Above A Titanium Target, Alexander Charles Woods

Doctoral Dissertations

The goal of this research is to use optical emission spectroscopy to investigate the processes occurring subsequent to laser ablation of a titanium sample. Laser-induced breakdown spectroscopy provides a procedure for atomic and molecular identification for particular constituents of a laser-induced plasma. Atomic spectral line shapes provide a diagnostic tool for characterizing laser induced plasma, particularly within the first hundreds of nanoseconds. Molecular recombination and/or excitation of selected molecules can lead to simultaneous detection of atomic and molecular species via spectral analysis. Nonlinear fitting of synthetic molecular spectra, calculated via diatomic quantum theory, provides tools for identification, temperature measurement, and …

Theoretical Studies Of The Growth And Functionality Of Layered Materials, Wei Chen

Doctoral Dissertations

In this thesis, we present several projects on the growth and functionality of layered materials, using density functional theory (DFT) method and phenomenological modeling approach. Beyond the understanding of growth mechanisms and exploration of properties, we propose novel avenues to realize controllable growth processes and layered materials with desirable properties. The contents have three major parts:

(1) Graphene growth on Cu(111) and Ni(111) substrates. We first demonstrate that the inherent multi-orientational degeneracy of the graphene islands on Cu(111) in the early stages of nucleation could result in the prevalence of grain boundaries (GBs). Next, we propose a possible solution to …

A Study Of The Structure Of Light Tin Isotopes Via Single-Neutron Knockout Reactions, Andrew Franklin Ayres

Doctoral Dissertations

The region around 100 Sn [100Sn] is important because of the close proximity to the N=Z=50 magic numbers, the rp process, and the proton drip-line. Alpha decay measurements show a reversal in the spin-parity assignments of the ground and first excited states in 101 Sn [101Sn] compared to 105 Te [105Te]. However, the lightest odd- mass tin isotope with a firm spin-parity assignment is 109 Sn [109Sn]. The d 5/2 [d5/2] and g 7/2 [g7/2] single-particle states above N=50 are near degenerate, evidenced by the excitation energy of the first excited state in 101 Sn at only 172 keV. The …

Probing The Size Dependent Chemical Properties Of Metals In Reduced Dimension, Xiangshi Yin

Doctoral Dissertations

Heterogeneously catalyzed reactions typically start with adsorption and dissociation of reactant molecules on the surface of a solid catalyst. In many instances, this is followed by surface diffusion of the adsorbed species, chemical reaction, and removal of the product molecule. According to the Sabatier principle, optimal catalytic performance requires that the bonding between the adsorbate molecule and the surface should neither be too strong nor too weak. This bonding strength is directly related to the catalyst’s surface electronic structure and hence, electronic structure modification would seem a promising approach for tuning catalytic activity.

There have been many studies along this …

Quantum Tuning Of Plasmons In Ultrathin Metal Films, Ao Teng

Doctoral Dissertations

The surface plasmon is a coherent charge density oscillation localized at a metal surface. It can couple with light and the resulting plasmon-polariton hybrid mode is confined to volumes that are much smaller than the classical diffraction limit of light. Nano-plasmonics is a rapidly evolving field where light manipulation at the nanoscale may lead to novel applications. However, as the size of plasmonic devices approaches the quantum-size regime, the macroscopic picture of plasmon may no longer be valid. To elucidate the influence of the discretization of the single particle spectrum on the collective plasmon response, we performed a systematic study …

Thick Target Yield Of Th-229 Via Low Energy Proton Bombardment Of Th-232, Justin Reed Griswold

Masters Theses

Actinium-225 is one of the more effective radioisotopes used in alpha radioimmunotherapy. Due to its ten-day half-life, it is more efficient to create its precursor, ²²⁹Th [Thorium-229] (t_1/2[half-life] = 7932 ± 55 years). In this work, ²²⁹Th was produced via 40 MeV [Mega electron Volts] proton bombardment of a thick ²³²Th [Thorium-232] target. The irradiation took place at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL). The target, consisting of 23 stacked natural thorium foils (137 mg/cm² [milligrams per square centimeter] each), was irradiated with 50 nA [nanoamps] of …

Radiation-Induced Radicals In Polyurea-Crosslinked Silica Aerogel, Benjamin Michael Walters

Masters Theses

Free radicals are atoms or molecules with an odd number of electrons in an outer shell. Since electrons typically occur in pairs, this leaves one electron that is unpaired. In seek of another electron to pair with, free radicals react with and steal electrons from neighboring molecules, which then become free radicals themselves. This can start a chain reaction, cascading into large scale damage.

Ionizing radiation can tear through molecules, just as bullets can tear through things that we see. If free radicals can be detected, and seen to increase in a material upon radiation exposure, this can indicate molecular …

Aluminum Monoxide Emission Measurements Following Laser-Induced Breakdown For Plasma Characterization, David Michael Surmick

Masters Theses

In this work, spectroscopic emissions from laser ablated aluminum samples are used to characterize the time dependent decay of laser-induced plasma. The plasma is created by tightly focusing nanosecond pulsed laser radiation. Time resolved measurements of the plasma are made with a gated, intensified linear diode array coupled to an optical multichannel analyzer and/or an intensified charged coupled device. Time resolution is achieved by synchronizing the laser with the measurement rate of the array detector.

Computed diatomic molecular aluminum monoxide emissions were used to infer the temperature of the plasma as a function of time. This was completed by comparing …

The Isotope Effect On Proton Conduction And Glass Transition In Phosphoric Acid, Maximilian Ferdinand Heres

Masters Theses

Hydrogen fuel cells combine hydrogen and oxygen to create water and electricity. Polymer electrolyte membranes (PEM) make up barriers within the fuel cell allowing only protons to pass through, while keeping other components separate. Many PEM contain phosphoric acid (PA) as a building block due to its excellent proton conducting properties. Improved ionic conductivity in PEM can lead to the development of better, more efficient fuel cells.

While ionic conductivity in PA at high temperatures is extensively characterized, the low temperature dynamics are not so well explored. Below the glass transition, molecular motion is frozen and proton motion is forced …

Structure Analysis Of Sn Bilayer Films On Si (111), Weisong Tu

Masters Theses

Chemical doping is a well-established method for controlling the electronic properties of bulk semiconductors and, e.g, complex oxide materials. In this process, dopant atoms are located at substitutional lattice locations, from where they introduce free charge carriers to the host material. These carriers greatly improve the electrical conductivity of the host material and can even induce an insulator-metal transition at high doping levels. Dopants, however, also introduce scattering centers that are detrimental to conductivity, especially in low-dimensional systems such as nanowires and ultrathin films. These problems can be overcome by using a modulation doping approach in which the dopant atoms …

Cross Sections Spring/Summer 2014, Department Of Physics And Astronomy

Cross Sections

No abstract provided.

Synthesis And Characterization Of Magnetic Nanowires Prepared By Chemical Vapor Deposition, Siwei Tang

Doctoral Dissertations

Various metal silicide and germanide magnetic nanowires were synthesized using a home-built CVD [chemical vapor deposition] system. The morphology, composition, and magnetic properties of the nanowires were studied and correlated with growth parameters such as temperature, pressure, time, and source-substrate distance.

One of the compositions targeted for synthesis was MnSi [manganese silicide]. In bulk, this material orders helimagnetically at T_c [curie temperature] = 30K, with a helical pitch of about 20 nm. After extensive study, we learned that the thickness of the silicon dioxide layer on the substrate is a critical parameter for the growth of MnSi nanowires. An …

Understanding The Plasmonic Properties Of Metallic Nanostructures With Correlated Photon- And Electron-Driven Excitations, Vighter Ozezinimize Iberi

Doctoral Dissertations

The collective oscillation of the conduction band electrons in metal nanostructures, known as plasmons, can be used to manipulate light on length scales that are smaller than the diffraction limit of visible light. In this dissertation, a correlated approach is used to probe localized surface plasmon resonances (LSPRs) in metallic nanostructures, and their application to surface-enhanced spectroscopy. This correlated approach involves the measurement of LSPRs with dark-field optical microscopy (resonance-Rayleigh scattering), and electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Structural parameters of the exact same nanostructures obtained from the STEM are subsequently used in performing fully …

Neutron Polarimetry With Polarized 3he For The Npdgamma Experiment, Matthew Martin Musgrave

Doctoral Dissertations

Cold neutrons enable the study of the fundamental interactions of matter in low-energy, low-background experiments that complement the efforts of high-energy particle accelerators. Neutrons possess an intrinsic spin, and the polarization of a beam of neutrons defines the degree to which their spins are oriented in a given direction. The NPDGamma experiment uses a polarized beam of cold neutrons to make a high precision measurement, on the order of one part in 100 million, of the parity-violating asymmetry in the angular distribution of emitted gamma-rays from the capture of polarized neutrons on protons. This asymmetry is a result of the …

Neutron Scattering Studies Of Cuprates And Iron Pnictides, Mengshu Liu

Doctoral Dissertations

Presented within are neutron scattering studies of several different high temperature superconducting materials: BaFe_1.9Ni_0.1As₂ [Barium Iron Nickel Arsenic], BaFe_1.85Ni_0.15As₂ [Barium Iron Nickel Arsenic], Ba_0.67K_0.33Fe₂As₂ [Barium Potassium Iron Arsenic], and Pr_0.88LaCe_0.12CuO_4-y [Praseodymium Lanthanum Cerium Copper Oxide]. The main focus is on the magnetic excitations within the systems.

For BaFe_1.9Ni_0.1As₂ [Barium Iron Nickel Arsenic], we measured the intensity of its magnetic excitations and compared the results with excitations in antiferromagnetic non-superconducting BaFe₂As_{2 …}

Studies Of Charge Collection In Diamond-Based Particle Detectors At The Lhc, Jared Smith

EURēCA: Exhibition of Undergraduate Research and Creative Achievement

See file

Cross Sections Fall 2013/Winter 2014, Department Of Physics And Astronomy

Cross Sections

No abstract provided.