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Ultrafast Control of Magnetism in Ferromagnetic Semiconductors via Photoexcited Transient Carriers

Description: The field of spintronics offers perspectives for seamless integration of coupled and inter-tunable electrical and magnetic properties in a single device. For integration of the spin degree of freedom with current electronic technology, new semiconductors are needed that show electrically-tunable magnetic properties at room temperature and above. Dilute magnetic semiconductors derived from III-V compounds, like GaMnAs and InMnAs, show coupled and tunable magnetic, transport, and optical properti… more
Date: December 12, 2008
Creator: Cotoros, Ingrid A.
Partner: UNT Libraries Government Documents Department
open access

First measurement of the b^0_s semileptonic branching ratio to an orbitally excited d _s** state

Description: In a data sample of approximately 1.3 fb{sup -1} collected with the D0 detector between 2002 and 2006, the orbitally excited charm state D{sub s1}{sup {+-}}(2536)has been observed with a measured mass of 2535.7 {+-} 0.6(stat) {+-} 0.5(syst) MeV/c{sup 2} via the decay mode B{sub s}{sup 0} {yields} D{sub s1}{sup -}(2536){mu}{sup +}{nu}X followed by D{sub s1}{sup {+-}}(2536) {yields} D*{sup {+-}}K{sub S}{sup 0}. By normalizing to the known branching ratio Br({bar b} {yields} D*{sup -} {mu}{sup +}{… more
Date: December 1, 2007
Creator: Rieger, Jason
Partner: UNT Libraries Government Documents Department
open access

Measurement of the cp asymmetry in semimuonic b decays produced in ppbar collision at s**(1/2) = 1.96 TeV

Description: The authors measure the asymmetry between positive and negative same-sign muon pairs originating from semileptonic decays of pairs of B hadrons. Low transverse momentum dimuon pairs are evaluated to determine B hadron content using a log likelihood fit to two-dimensional impact parameter significance templates. Corrections are made for asymmetries arising from the detector, trigger, and hadrons which are reconstructed as muons. Using 1.1 million muon pairs from data corresponding to an integrat… more
Date: December 1, 2007
Creator: Marino, Christopher Phillip
Partner: UNT Libraries Government Documents Department
open access

Nanostructured Solid Oxide Fuel Cell Electrodes

Description: The ability of Solid Oxide Fuel Cells (SOFC) to directly and efficiently convert the chemical energy in hydrocarbon fuels to electricity places the technology in a unique and exciting position to play a significant role in the clean energy revolution. In order to make SOFC technology cost competitive with existing technologies, the operating temperatures have been decreased to the range where costly ceramic components may be substituted with inexpensive metal components within the cell and stac… more
Date: December 15, 2007
Creator: Sholklapper, Tal Zvi
Partner: UNT Libraries Government Documents Department
open access

High Temperature Oxidation Behavior of gamma-Ni+gamma'-Ni3Al Alloys and Coatings Modified with Pt and Reactive Elements

Description: Materials for high-pressure turbine blades must be able to operate in the high-temperature gases (above 1000 C) emerging from the combustion chamber. Accordingly, the development of nickel-based superalloys has been constantly motivated by the need to have improved engine efficiency, reliability and service lifetime under the harsh conditions imposed by the turbine environment. However, the melting point of nickel (1455 C) provides a natural ceiling for the temperature capability of nickel-base… more
Date: December 1, 2007
Creator: Mu, Nan
Partner: UNT Libraries Government Documents Department
open access

Search for CP violation in B0s to Jpsi Phi

Description: The CDF experiment, which uses p{bar p} collisions at {radical}s = 1.9 TeV produced at the Fermilab Tevatron, is unique in its ability to observe all flavors of B hadrons and measure their properties. Among them, CP violation is of fundamental interest. In the B{sup +} and B{sup 0} systems, measurements of CP violation parameters performed essentially at B factories have borne out the predictions of CKM model. Little is known, experimentally, about CP violation in the B{sub s}{sup 0} system. Th… more
Date: December 1, 2008
Creator: Liu, Chunlei & U., /Pittsburgh
Partner: UNT Libraries Government Documents Department
open access

The Development and Optimization of Techniques for Monitoring Water Quality on-Board Spacecraft Using Colorimetric Solid-Phase Extraction (C-SPE)

Description: The main focus of this dissertation is the design, development, and ground and microgravity validation of methods for monitoring drinking water quality on-board NASA spacecraft using clorimetric-solid phase extraction (C-SPE). The Introduction will overview the need for in-flight water quality analysis and will detail some of the challenges associated with operations in the absence of gravity. The ability of C-SPE methods to meet these challenges will then be discussed, followed by a literature… more
Date: December 1, 2007
Creator: Hill, April
Partner: UNT Libraries Government Documents Department
open access

High-Throughput Analysis of Enzyme Activities

Description: High-throughput screening (HTS) techniques have been applied to many research fields nowadays. Robot microarray printing technique and automation microtiter handling technique allows HTS performing in both heterogeneous and homogeneous formats, with minimal sample required for each assay element. In this dissertation, new HTS techniques for enzyme activity analysis were developed. First, patterns of immobilized enzyme on nylon screen were detected by multiplexed capillary system. The imaging re… more
Date: December 1, 2007
Creator: Lu, Guoxin
Partner: UNT Libraries Government Documents Department
open access

Measurement of CP-Violating Asymmetries In Neutral B Meson Decays Into Three Kaons

Description: The Standard Model (SM) of particle physics successfully describes all of the observed interactions of the fundamental particles (with the exception of non-zero neutrino mass). Despite this enormous success, the SM is widely viewed as an incomplete theory. For example, the size of the asymmetry between matter and antimatter is not nearly large enough to account for the abundance of matter observed throughout the universe. It is thus believed that as-yet-unknown physical phenomena must exist tha… more
Date: December 1, 2008
Creator: Thompson, Joshua M.
Partner: UNT Libraries Government Documents Department
open access

Measurement of Cabibbo-Suppressed Tau Lepton Decays and the Determination of |Vus|

Description: This work presents simultaneous branching fraction measurements of the decay modes {tau}{sup -} {yields} K{sup -} n{pi}{sup 0}{nu}{sub {tau}} with n = 0,1,2,3 and {tau}{sup -} {yields} {pi}{sup -} n{pi}{sup 0}{nu}{sub {tau}} with n = 3,4. The analysis is based on a data sample of 427 x 10{sup 6} {tau}{sup +}{tau}{sup -} pairs recorded with the BABAR detector, which corresponds to an integrated luminosity of 464.4 fb{sup -1}. The measured values are {Beta}({tau}{sup -} {yields} K{sup -}{nu}{sub … more
Date: December 16, 2008
Creator: Schenk, Stefan
Partner: UNT Libraries Government Documents Department
open access

Developments and Applications of Electrophoresis and Small Molecule Laser Desorption Ionization Mass Spectrometry

Description: Ultra-sensitive native fluorescence detection of proteins with miniaturized one- and two-dimensional polyacrylamide gel electrophoresis was achieved with laser side-entry excitation, which provides both high excitation power and low background level. The detection limit for R-phycoerythrin protein spots in 1-D SDS-PAGE was as low as 15 fg, which corresponds to 40 thousand molecules only. The average detection limit of six standard native proteins was 5 pg per band and the dynamic range spanned … more
Date: December 1, 2007
Creator: Zhang, Hui
Partner: UNT Libraries Government Documents Department
open access

Studies on zinc nodules electrodeposited from acid electrolytes

Description: The development of morphology of electrodeposited zinc was investigated by studying the initial stages of deposition. Zinc was deposited galvanostatically from 1.0 M ZnCl/sub 2/ electrolyte (0.7 < pH < 4.6) on rotating disc electrodes at current densities from 5 to 130 ma/cm/sup 2/. Pine glassy carbon, Union Carbide pyrolytic graphite, Gould pyrolytic graphite, Exxon graphite loaded polymer, and platinum substrates were used. The number densities of nodules (diameter greater than 1 ..mu..m), ty… more
Date: December 1, 1984
Creator: Anderson, R. & Tobias, C.W.
Partner: UNT Libraries Government Documents Department
open access

Effect of nuclear spin on chemical reactions and internal molecular rotation

Description: Part I of this dissertation is a study of the magnetic isotope effect, and results are presented for the separation of /sup 13/C and /sup 12/C isotopes. Two models are included in the theoretical treatment of the effect. In the first model the spin states evolve quantum mechanically, and geminate recombination is calculated by numerically integrating the collision probability times the probability the radical pair is in a singlet state. In the second model the intersystem crossing is treated vi… more
Date: December 1, 1980
Creator: Sterna, L.L.
Partner: UNT Libraries Government Documents Department
open access

Diffusion of trichloroethylene through the threaded joints of PVC (polyvinylchloride) pipe

Description: The data engineers and scientists use to determine if the groundwater supply is contaminated are derived from analysis of samples taken largely from monitoring wells. For these data to be reliable several factors must be considered. One factor is the integrity of the monitoring well. In this project, emphasis has been placed on the potential impact on water quality caused by diffusion across the threaded joints of PVC pipe. In this study, the diffusion of trichloroethylene across several common… more
Date: December 1, 1990
Creator: Jerome, Karen M.
Partner: UNT Libraries Government Documents Department
open access

Further studies of the effects of oxidation on the surface properties of coal and coal pyrite

Description: The objective of this research was to investigate the oxidation behavior of coal and coal pyrite and to correlate the changes in the surface properties induced by oxidation, along with the intrinsic physical and chemical properties of these organic and inorganic materials, with the behavior in physical coal cleaning processes. This provide more fundamental knowledge for understanding the way in which different factors interact in a medium as heterogeneous as coal. Fourteen coal samples of diffe… more
Date: December 31, 1994
Creator: Herrera, Miguel Nicholas
Partner: UNT Libraries Government Documents Department
open access

Gas phase thermochemistry of organogermanium compounds

Description: A variety of silyl- and alkyl-germylene precursors have been synthesized and subsequently pyrolyzed in the gas phase. Arrhenius parameters were obtained employing a pulsed-stirred flow reactor for these unimolecular decompositions. These precursors are divided into two major categories by mechanism of germylene extrusion: {alpha}-elimination precursors and germylacetylenes. The extrusion of germylenes from germylacetylene precursors is of primary interest. A mechanism is proposed employing a ge… more
Date: December 7, 1993
Creator: Engel, J. P.
Partner: UNT Libraries Government Documents Department
open access

An analysis of monojet data in p{bar p} collisions at {radical}s = 1.8 TEV

Description: An analysis is presented of events with a single jet and significant missing transverse energy selected from 4.7 pb{sup {minus}1} of data collected at the Fermilab Tevatron with the CDF detector. The goal is to identify events of the type p{bar p} {yields} Z{sup 0} + jet; Z{sup 0} {yields} {nu}{bar {nu}}. Event selection and backgrounds are discussed. The number of observed monojet events is compared to the number of observed Z{sup 0} {yields} e{sup +}{sup {minus}} events in which the Z{sup 0} … more
Date: December 31, 1992
Creator: Markeloff, R.
Partner: UNT Libraries Government Documents Department
open access

Infrared diode laser studies of the products from the reaction CH{sub 2}({tilde X}{sup 3}B{sub 1}) + O{sub 2} and from the near-UV photolysis of CH{sub 3}NCS

Description: Absolute yields of CO, CO{sub 2}, and H{sub 2}CO formed in reaction of triplet methylene ({tilde X} {sup 3}B{sub 1} {triple_bond} CH{sub 2}) with O{sub 2} were determined using a flash kinetic spectrometer. CH{sub 2} radicals were generated by excimer laser photolysis of ketene and product formation was monitored by time-resolved infrared diode laser absorption. Reaction was carried out in a static gas cell at room temperature at 1--25 torr. Measured product yields were CO, 0.34 {plus_minus} 0.… more
Date: December 1, 1993
Creator: Alvarez, R. A.
Partner: UNT Libraries Government Documents Department
open access

A correlation between soil descriptions and {sup 226}Ra concentrations in Florida soils

Description: The soil radium content in Florida is highly variable. The range in radium concentrations, where the samples involved in this study are concerned, is from 0.1 pCi/g to 18.5 pCi/g. Low {sup 226}Ra concentrations (0.1 to 5 pCi/g) are evidenced in sands, moderate concentrations (5 to 11 pCi/g) are found in silt and gravel, and high {sup 226}Ra concentrations (>11 pCi/g) are found in soil horizons with shell, clay, and strata with phosphate. Strata containing phosphate yields a high concentration o… more
Date: December 31, 1992
Creator: Harrison, D. P.
Partner: UNT Libraries Government Documents Department
open access

Vibrational spectroscopy of water interfaces

Description: The second order nonlinear optical processes of second harmonic generation and sum frequency generation are powerful and versatile tools for studying all kinds of surfaces. They possess unusual surface sensitivity due to the symmetry properties of the second order nonlinear susceptibility. The technique of infrared-visible sum frequency generation (SFG) is particularly attractive because it offers a viable way to do vibrational spectroscopy on any surfaces accessible to light with submonolayer … more
Date: December 1, 1994
Creator: Du, Q.
Partner: UNT Libraries Government Documents Department
open access

Investigation of the phase equilibria and phase transformations associated with the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} superconductor

Description: The solid solution region and reaction kinetics of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} (2212) superconductor were examined as a function of temperature and oxygen partial pressure. Crystallization studies from the glassy and molten states were undertaken to determine the phase transformation and kinetics associated with the formation of 2212 and other competing phases. Crystallization of nominal 2212 glasses was found to proceed in two steps with the formation of Bi{sub 2}Sr{sub 2{minus}x… more
Date: December 9, 1993
Creator: Holesinger, T.
Partner: UNT Libraries Government Documents Department
open access

Optical field ionization of atoms and ions using ultrashort laser pulses

Description: This dissertation research is an investigation of the strong optical field ionization of atoms and ions by 120-fs, 614-run laser pulses and 130-fs, 800-nm laser pulses. The experiments have shown ionization that is enhanced above the predictions of sequential tunneling models for He{sup +2}, Ne{sup +2} and Ar{sup +2}. The ion yields for He{sup +l}, Ne{sup +l} and Ar{sup +l} agree well with the theoretical predictions of optical tunneling models. Investigation of the polarization dependence of t… more
Date: December 1, 1993
Creator: Fittinghoff, D. N.
Partner: UNT Libraries Government Documents Department
open access

The Effect of surface morphology on the friction of Electrogalvanized sheet steel in forming processes

Description: The effect in the drawbead simulator test were evaluated for a set of commercially coated steels and a set of laboratory coated steels with underlying surfaces produced by laser textured, shot blast, and electro-discharge textured rolls. In general, surfaces with higher roughness (R{sub a} parameter) measured lower friction in the DBS tests. The requisite roughness amplitude necessary for low friction was moderated somewhat by having a more closely spaced roughness as described by the median wa… more
Date: December 1, 1993
Creator: Skarpelos, P. N.
Partner: UNT Libraries Government Documents Department
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