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Microstructure study of the rare-earth intermetallic compounds R5(SixGe1-x)4 and R5(SixGe1-x)3

Description: The unique combination of magnetic properties and structural transitions exhibited by many members of the R{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} family (R = rare earths, 0 ≤ x ≤ 1) presents numerous opportunities for these materials in advanced energy transformation applications. Past research has proven that the crystal structure and magnetic ordering of the R{sub 5(Si{sub x}Ge{sub 1-x}){sub 4} compounds can be altered by temperature, magnetic field, pressure and the Si/Ge ratio. Results of this thesis study on the crystal structure of the Er{sub 5}Si{sub 4} compound have for the first time shown that the application of mechanical forces (i.e. shear stress introduced during the mechanical grinding) can also result in a structural transition from Gd{sub 5}Si{sub 4}-type orthorhombic to Gd{sub 5}Si{sub 2}Ge{sub 2}-type monoclinic. This structural transition is reversible, moving in the opposite direction when the material is subjected to low-temperature annealing at 500 ˚C. Successful future utilization of the R{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} family in novel devices depends on a fundamental understanding of the structure-property interplay on the nanoscale level, which makes a complete understanding of the microstructure of this family especially important. Past scanning electron microscopy (SEM) observation has shown that nanometer-thin plates exist in every R{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} (“5:4”) phase studied, independent of initial parent crystal structure and composition. A comprehensive electron microscopy study including SEM, energy dispersive spectroscopy (EDS), selected area diffraction (SAD), and high resolution transmission electron microscopy (HRTEM) of a selected complex 5:4 compound based on Er rather than Gd, (Er{sub 0.9Lu{sub 0.1}){sub 5}Si{sub 4}, has produced data supporting the assumption that all the platelet-like features present in the R{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} family are hexagonal R{sub 5}(Si{sub x}Ge{sub 1-x}){sub 3} (“5:3”) phase and possess the same reported orientation relationship that exists for the Gd{sub 5}Ge{sub 4} and Gd{sub ...
Date: July 26, 2012
Creator: Cao, Qing
Partner: UNT Libraries Government Documents Department

Surfaces of Intermetallics: Quasicrystals and Beyond

Description: The goal of this work is to characterize surfaces of intermetallics, including quasicrystals. In this work, surface characterization is primarily focused on composition and structure using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) performed under ultrahigh vacuum (UHV) conditions.
Date: October 26, 2012
Creator: Yuen, Chad
Partner: UNT Libraries Government Documents Department

Measurement of the Hadronic Mass Spectrum in B to Xulnu Decaysand Determination of the b-Quark Mass at the BaBar Experiment

Description: I present preliminary results of the measurement of the hadronic mass spectrum and its first three spectral moments in inclusive charmless semileptonic B-meson decays. The truncated hadronic mass moments are used for the first determination of the b-quark mass and the nonperturbative parameters {mu}{sub {pi}}{sup 2} and {rho}{sub D}{sup 3} in this B-meson decay channel. The study is based on 383 x 10{sup 6} B{bar B} decays collected with the BABAR experiment at the PEP-II e{sup +}e{sup -} storage rings, located at the Stanford Linear Accelerator Center. The first, second central, and third central hadronic mass moment with a cut on the hadronic mass m{sub X}{sup 2} < 6.4GeV{sup 2} and the lepton momentum p* > 1 GeV are measured to be: M{sub 1} = (1.96 {+-} 0.34{sub stat} {+-} 0.53{sub syst}) GeV{sup 2}; U{sub 2} = (1.92 {+-} 0.59{sub stat} {+-} 0.87{sub syst}) GeV{sup 4}; and U{sub 3} = (1.79 {+-} 0.62{sub stat} {+-} 0.78{sub syst}) GeV{sup 6}; with correlation coefficients {rho}{sub 12} = 0.99, {rho}{sub 23} = 0.94, and {rho}{sub 13} = 0.88, respectively. Using Heavy Quark Effective Theory-based predictions in the kinetic scheme we extract: m{sub b} = (4.60 {+-} 0.13{sub stat} {+-} 0.19{sub syst} {+-} 0.10{sub theo} GeV); {mu}{sub {pi}}{sup 2} = (0.40 {+-} 0.14{sub stat} {+-} 0.20{sub syst} {+-} 0.04{sub theo}) GeV{sup 2}; {rho}{sub D}{sup 3} = (0.10 {+-} 0.02{sub stat} {+-} 0.02{sub syst} {+-} 0.07{sub theo}) GeV{sup 3}; at {mu} = 1 GeV, with correlation coefficients {rho}{sub m{sub b}{mu}{sub {pi}}{sup 2}} = -0.99, {rho}{sub {mu}{sub {pi}}{sup 2}{rho}{sub D}{sup 3}} = 0.57, and {rho}{sub m{sub b}{rho}{sub D}{sup 3}} = -0.59. The results are in good agreement with earlier determinations in inclusive charmed semileptonic and radiative penguin B-meson decays and have a similar accuracy. Through the comparison of this result to those obtained in other channels, ...
Date: June 26, 2008
Creator: Tackmann, Kerstin & /UC, Berkeley /SLAC
Partner: UNT Libraries Government Documents Department

First Observation of An Excited Charm Baryon Decaying to Omega Charm Baryon at the BaBar Experiment

Description: We have carried out a search for a charmed baryon {Omega}{sup *}{sub c} decaying to {Omega}{sup 0}{sub c} and a {gamma} where {Omega}{sub c} candidates are reconstructed using decay modes {Omega}{sup -}{pi}{sup +}(c1), {Omega}{sup -}{pi}{sup +}{pi}{sup 0}(c2), {Omega}{sup -}{pi}{sup +}{pi}{sup -}{pi}{sup +}(c3) and {Xi}{sup -}K{sup -}{pi}{sup +}{pi}{sup +}(c4). This search is performed by analyzing integrated luminosity of 230.7 fb{sup -1} data collected by the BABAR detector at the Stanford Linear Accelerator Center. In decay channel {Omega}{sup *}{sub c} {yields} {Omega}{sup 0}{sub c}({Omega}{sup -}{pi}{sup +}){gamma} (C1), we observe a signal yield of 39.2{sup +9.8}{sub -9.1}(stat){+-}6.0(syst) events with a significance of 4.2 standard deviations. In decay channels {Omega}{sup *}{sub c} {yields} {Omega}{sup 0}{sub c}({Omega}{sup -}{pi}{sup +}{pi}{sup 0}){gamma} (C2) and {Omega}{sup *}{sub c} {yields} {Omega}{sup 0}{sub c}({Xi}{sup -}K{sup -}{pi}{sup +}{pi}{sup +}){gamma} (C4), we observe signal yields of 55.2{sup 16.1}{sub -15.2} {+-} 5.6 and 20.2{sup +9.3}{sub -8.5} {+-} 3.1 with significances of 3.4 and 2.0 {sigma}, respectively. As for the {Omega}{sup *}{sub c} {yields} {Omega}{sup 0}{sub c}({Omega}{sup -}{pi}{sup +}{pi}{sup -}{pi}{sup +}){gamma} (C3) decay channel, we observe signal yields of -5.1{sup +5.3.8}{sub -4.7}{+-}1.0 without a positive significance. We assume the same production mechanism for the four decay channels of {Omega}{sup *}{sub c} studied. By combining these four channels, the fit results in a signal yield of 105.3{sup +21.2}{sub -20.5} {+-} 6.0 events with a significance of 5.2 {sigma}. We report the mass difference {Omega}{sup *}{sub c} - {Omega}{sup 0}{sub c}({delta}m) of the singly charmed baryon {Omega}{sup *}{sub c} to be 70.8{sup +1.0}{sub -1.0} {+-} 1.1 MeV. Finally, the ratios of production cross sections are calculated: {sigma}(e{sup +}e{sup -}{yields}C1)/{sigma}(e{sup +}e{sup -}{yields}c1) = 0.71{sup +0.19}{sub -0.18}{+-}0.11, {sigma}(e{sup +}e{sup -}{yields}C2)/{sigma}(e{sup +}e{sup -}{yields}c2) = 1.76{sup +0.71}{sub -0.69}{+-}0.19, {sigma}(e{sup +}e{sup -}{yields}C3)/{sigma}(e{sup +}e{sup -}{yields}c3) = -0.66{sup +0.74}{sub -0.66}{+-}0.13, {sigma}(e{sup +}e{sup -}{yields}C4)/{sigma}(e{sup +}e{sup -}{yields}c4) = 1.70{sup +1.0}{sub -1.0}{+-}0.27 and {sigma}(e{sup +}e{sup -}{yields}{Omega}{sup ...
Date: November 26, 2007
Creator: Bula, Rahmi & /SUNY, Albany
Partner: UNT Libraries Government Documents Department

Bioinspired synthesis of magnetic nanoparticles

Description: The synthesis of magnetic nanoparticles has long been an area of active research. Magnetic nanoparticles can be used in a wide variety of applications such as magnetic inks, magnetic memory devices, drug delivery, magnetic resonance imaging (MRI) contrast agents, and pathogen detection in foods. In applications such as MRI, particle uniformity is particularly crucial, as is the magnetic response of the particles. Uniform magnetic particles with good magnetic properties are therefore required. One particularly effective technique for synthesizing nanoparticles involves biomineralization, which is a naturally occurring process that can produce highly complex nanostructures. Also, the technique involves mild conditions (ambient temperature and close to neutral pH) that make this approach suitable for a wide variety of materials. The term 'bioinspired' is important because biomineralization research is inspired by the naturally occurring process, which occurs in certain microorganisms called 'magnetotactic bacteria'. Magnetotactic bacteria use biomineralization proteins to produce magnetite crystals having very good uniformity in size and morphology. The bacteria use these magnetic particles to navigate according to external magnetic fields. Because these bacteria synthesize high quality crystals, research has focused on imitating aspects of this biomineralization in vitro. In particular, a biomineralization iron-binding protein found in a certain species of magnetotactic bacteria, magnetospirillum magneticum, AMB-1, has been extracted and used for in vitro magnetite synthesis; Pluronic F127 gel was used to increase the viscosity of the reaction medium to better mimic the conditions in the bacteria. It was shown that the biomineralization protein mms6 was able to facilitate uniform magnetite synthesis. In addition, a similar biomineralization process using mms6 and a shorter version of this protein, C25, has been used to synthesize cobalt ferrite particles. The overall goal of this project is to understand the mechanism of magnetite particle synthesis in the presence of the biomineralization proteins, mms6 and C25. ...
Date: May 26, 2009
Creator: David, Anand
Partner: UNT Libraries Government Documents Department

Current developments in laser ablation-inductively coupled plasma-mass spectrometry for use in geology, forensics, and nuclear nonproliferation research

Description: This dissertation focused on new applications of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The diverse fields that were investigated show the versatility of the technique. In Chapter 2, LA-ICP-MS was used to investigate the rare earth element (REE) profiles of garnets from the Broken Hill Deposit in New South Wales, Australia. The normalized REE profiles helped to shed new light on the formation of deposits of sulfide ores. This information may be helpful in identifying the location of sulfide ore deposits in other locations. New sources of metals such as Pg, Zn, and Ag, produced from these ores, are needed to sustain our current technological society. The application of LA-ICP-MS presented in Chapter 3 is the forensics analysis of automotive putty and caulking. The elemental analysis of these materials was combined with the use of Principal Components Analysis (PCA). The PCA comparison was able to differentiate the automotive putty samples by manufacturer and lot number. The analysis of caulk was able to show a differentiation based on manufacturer, but no clear differentiation was shown by lot number. This differentiation may allow matching of evidence in the future. This will require many more analyses and the construction of a database made up of many different samples. The 4th chapter was a study of the capabilities of LA-ICP-MS for fast and precise analysis of particle ensembles for nuclear nonproliferation applications. Laser ablation has the ability to spatially resolve particle ensembles which may contain uranium or other actinides from other particles present in a sample. This is of importance in samples obtained from air on filter media. The particle ensembles of interest may be mixed in amongst dust and other particulates. A problem arises when ablating these particle ensembles directly from the filter media. Dust particles other than ones of interest ...
Date: August 26, 2008
Creator: Messerly, Joshua D.
Partner: UNT Libraries Government Documents Department

Search for lepton flavor violating decay τ<sup>-</sup> →ℓ<sup>-</sup>ℓ<sup>+</sup>ℓ<sup>-</sup>ℓ = e, μ at BaBar

Description: The Standard Model (SM) is one of the most tested and verified physical theories of all time, present experimental observations are consistent with SM expectations. On the other hand SM can not explain many physical observations: the cosmological observations possibly infer the presence of dark matter which is clearly beyond the SM expectations; the SM Higgs model, while explaining the generation of fermion masses, can not explain the hierarchy problem and a non natural fine tuning of SM is needed to cancel out quadratic divergences in the Higgs boson mass. New physics (NP) beyond SM should hence be investigated: rising the energy above NP processes thresholds, and detecting new particles or new effects not predicted by the standard model directly, is one of the possible approaches; another approach is to make precision measurements of well known processes or looking for rare processes which involve higher order contribution from NP processes, this approach need higher luminosities with respect to the previous approach but lower beam energies. Search for Lepton Flavor Violation (LFV) in charged lepton decays is promising: neutrino physics provides indeed a clear and unambiguous evidence of LFV in the neutral lepton sector via mixing processes, which have been observed for the first time by the Homestake collaboration. We expect LFV in the charged sector as well, both in {mu} and {tau} sector, but current experimental searches for LFV processes did not find any evidence for those processes, and more results are expected to come from new experiments in the coming years.
Date: May 26, 2010
Creator: Cervelli, Alberto
Partner: UNT Libraries Government Documents Department

Solidification/Stabilization of High Nitrate and Biodenitrified Heavy Metal Sludges with a Portland Cement/Flyash System

Description: Pond 207C at Rocky Flats Environmental Technology Site (RFETS) contains process wastewaters characterized by high levels of nitrates and other salts, heavy metal contamination, and low level alpha activity. The purpose of this research was to investigate the feasibility of treating a high-nitrate waste, contaminated with heavy metals, with a coupled dewateriug and S/S process, as well as to investigate the effects of biodenitrification pretreatment on the S/S process. Pond 207C residuals served as the target waste. A bench-scale treatability study was conducted to demonstrate an S/S process that would minimize final product volume without a significant decrease in contaminant stabilization or loss of desirable physical characteristics. The process formulation recommended as a result a previous S/S treatability study conducted on Pond 207C residuals was used as the baseline formulation for this research. Because the actual waste was unavailable due to difficulties associated with radioactive waste handling and storage, a surrogate waste, of known composition and representative of Pond 207C residuals, was used throughout this research. The contaminants of regulatory concern added to the surrogate were cadmium, chromium, nickel, and silver. Product volume reduction was achieved by dewatering the waste prior to S/S treatment. The surrogate was dewatered by evaporation at 60 to 80 C to total solids contents from 43% to 78% by weight, and treated with Portland cement and fly ash. Two cement to flyash ratios were tested, 2:1 and 1:2, by weight. Contaminant leachability testing was conducted with a 0.5 water to pozzolan (the cement/flyash mixture) ratio and both cement to flyash ratios. Each product was tested for unconfined compressive strength (UCS) and for contaminant leachability by the Toxicity Characteristics Leaching Procedure (TCLP). At the highest solids content achieved by dewatering, 78% solids by weight, the predicted final waste form volume f or Pond 207C residuals after ...
Date: July 26, 1995
Creator: Canonico, J.S.
Partner: UNT Libraries Government Documents Department

Self- and zinc diffusion in gallium antimonide

Description: The technological age has in large part been driven by the applications of semiconductors, and most notably by silicon. Our lives have been thoroughly changed by devices using the broad range of semiconductor technology developed over the past forty years. Much of the technological development has its foundation in research carried out on the different semiconductors whose properties can be exploited to make transistors, lasers, and many other devices. While the technological focus has largely been on silicon, many other semiconductor systems have applications in industry and offer formidable academic challenges. Diffusion studies belong to the most basic studies in semiconductors, important from both an application as well as research standpoint. Diffusion processes govern the junctions formed for device applications. As the device dimensions are decreased and the dopant concentrations increased, keeping pace with Moore's Law, a deeper understanding of diffusion is necessary to establish and maintain the sharp dopant profiles engineered for optimal device performance. From an academic viewpoint, diffusion in semiconductors allows for the study of point defects. Very few techniques exist which allow for the extraction of as much information of their properties. This study focuses on diffusion in the semiconductor gallium antimonide (GaSb). As will become clear, this compound semiconductor proves to be a powerful one for investigating both self- and foreign atom diffusion. While the results have direct applications for work on GaSb devices, the results should also be taken in the broader context of III-V semiconductors. Results here can be compared and contrasted to results in systems such as GaAs and even GaN, indicating trends within this common group of semiconductors. The results also have direct importance for ternary and quaternary semiconductor systems used in devices such as high speed InP/GaAsSb/InP double heterojunction bipolar transistors (DHBT) [Dvorak, (2001)]. Many of the findings which will ...
Date: March 26, 2002
Creator: Nicols, Samuel Piers
Partner: UNT Libraries Government Documents Department