Search Results

Genetic and Environmental Factors that Mediate Survival of Prolonged Oxygen Deprivation in the Nematode Caenorhabditis Elegans

Description: Ischemic events of even a very short duration are not tolerated Ill in humans. The human cost of ischemia, when looked at as combined cardiovascular disease, dwarfs all other causes of death in the United States. Annually, CVD kills as many people in the US as does cancer, chronic lower respiratory disease, accidents, and diabetes mellitus combined. In 2005 (the latest year for which final statistics are available), CVD was responsible for 864,480 deaths or 35.3 percent of total deaths for the year. In my study, I have used the nematode Caenorhabditis elegans to determine genetic and environmental modulators of oxygen deprivation a key component of ischemia. I have found that animals with mutations in insulin like signaling pathways, neuronal function, electron transport chain components, germline function, and animals that are preconditioned by being raised on a diet of E. coli HT115 bacteria at 25°C have an enhanced ability to survive long-term (>72 hours) anoxia (<.005 kPa O2) at 20°C. The enhanced anoxia survival phenotype partially correlates with increased levels of carbohydrate stores in the nematodes. Suppression of this enhanced anoxia survival phenotype is possible by altering expression of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase, the FOXO transcription factor DAF-16, and 5’-AMP kinase.
Date: August 2010
Creator: LaRue, Bobby Lee, Jr.
Partner: UNT Libraries

Electronic Sound Analysis with Hardware System and Remote Internet Display

Description: Currently, standards from government agencies such as the National Institute for Occupation Safety and Health exist to aid in safeguarding individuals’ capacity for hearing, but only in factory settings in which large machines often produce loud levels of sound. Neglecting the fact that these preventative measures are only in place in the most limited of settings, no system currently exists to observe and report sound exposure levels in a manner timely or easily recognizable enough to adequately serve its purpose of hearing conservation. Musicians may also incur significant levels of risk for hearing loss in their day-to-day rehearsals and concerts, from high school marching bands to university wind bands. As a result, music school accrediting organizations such as the National Association of Schools of Music and even the European Union have begun taking steps meant to determine the risks associated with music. To meet these goals and improve upon current technologies, a system has been developed that electronically records sound levels utilizing modern hardware, increases the speed of reporting by transmitting data over computer networks and the Internet, and displays measures calculated from these data in a web browser for a highly viewable, user-friendly interface.
Date: August 2010
Creator: McCord, Cameron Forrest
Partner: UNT Libraries

Investigations into the origins of polyatomic ions in inductively coupled plasma-mass spectrometry

Description: An inductively coupled plasma-mass spectrometer (ICP-MS) is an elemental analytical instrument capable of determining nearly all elements in the periodic table at limits of detection in the parts per quadrillion and with a linear analytical range over 8-10 orders of magnitude. Three concentric quartz tubes make up the plasma torch. Argon gas is spiraled through the outer tube and generates the plasma powered by a looped load coil operating at 27.1 or 40.6 MHz. The argon flow of the middle channel is used to keep the plasma above the innermost tube through which solid or aqueous sample is carried in a third argon stream. A sample is progressively desolvated, atomized and ionized. The torch is operated at atmospheric pressure. To reach the reduced pressures of mass spectrometers, ions are extracted through a series of two, approximately one millimeter wide, circular apertures set in water cooled metal cones. The space between the cones is evacuated to approximately one torr. The space behind the second cone is pumped down to, or near to, the pressure needed for the mass spectrometer (MS). The first cone, called the sampler, is placed directly in the plasma plume and its position is adjusted to the point where atomic ions are most abundant. The hot plasma gas expands through the sampler orifice and in this expansion is placed the second cone, called the skimmer. After the skimmer traditional MS designs are employed, i.e. quadrupoles, magnetic sectors, time-of-flight. ICP-MS is the leading trace element analysis technique. One of its weaknesses are polyatomic ions. This dissertation has added to the fundamental understanding of some of these polyatomic ions, their origins and behavior. Although mainly continuing the work of others, certain novel approaches have been introduced here. Chapter 2 includes the first reported efforts to include high temperature corrections to …
Date: January 1, 2010
Creator: McIntyre, Sally M.
Partner: UNT Libraries Government Documents Department

A search for the Standard Model Higgs boson in the process ZH → ℓ<sup>+</sup>ℓ<sup>-</sup>b$\bar{b}$ in 4.1 fb<sup>-1</sup> of CDF II data

Description: The standard model of particle physics provides a detailed description of a universe in which all matter is composed of a small number of fundamental particles, which interact through the exchange of force - carrying gauge bosons (the photon, W <sup>±</sup>, Z and gluons). The organization of the matter and energy in this universe is determined by the effects of three forces; the strong, weak, and electromagnetic. The weak and electromagnetic forces are the low energy manifestations of a single electro-weak force, while the strong force binds quarks into protons and neutrons. The standard model does not include gravity, as the effect of this force on fundamental particles is negligible. Four decades of experimental tests, spanning energies from a few electron-volts (eV) up to nearly two TeV, confirm that the universe described by the standard model is a reasonable approximation of our world. For example, experiments have confirmed the existence of the top quark, the W<sup>±</sup> and the Z bosons, as predicted by the standard model. The latest experimental averages for the masses of the top quark, W<sup>±</sup> and Z are respectively 173.1 ± 0.6(stat.) ± 1.1(syst.), 80.399 ± 0.023 and 91.1876 ± 0.0021 GeV/c<sup>2</sup>. The SM is a gauge field theory of zero mass particles. However, the SM is able to accommodate particles with non-zero mass through the introduction of a theoretical Higgs field which permeates all of space. Fermions gain mass through interactions with this field, while the longitudinal components of the massive W<sup>±</sup> and Z are the physical manifestations of the field itself. Introduction of the Higgs field, directly leads to the predicted existence of an additional particle, the Higgs boson. The Higgs boson is the only particle of the standard model that has not been observed, and is the only unconfirmed prediction of the theory. The …
Date: May 1, 2010
Creator: Shalhout, Shalhout Zaki
Partner: UNT Libraries Government Documents Department

A genetic algorithm approach in interface and surface structure optimization

Description: The thesis is divided into two parts. In the first part a global optimization method is developed for the interface and surface structures optimization. Two prototype systems are chosen to be studied. One is Si[001] symmetric tilted grain boundaries and the other is Ag/Au induced Si(111) surface. It is found that Genetic Algorithm is very efficient in finding lowest energy structures in both cases. Not only existing structures in the experiments can be reproduced, but also many new structures can be predicted using Genetic Algorithm. Thus it is shown that Genetic Algorithm is a extremely powerful tool for the material structures predictions. The second part of the thesis is devoted to the explanation of an experimental observation of thermal radiation from three-dimensional tungsten photonic crystal structures. The experimental results seems astounding and confusing, yet the theoretical models in the paper revealed the physics insight behind the phenomena and can well reproduced the experimental results.
Date: January 1, 2010
Creator: Zhang, Jian
Partner: UNT Libraries Government Documents Department

Measurement of Cross Section of Quark Pair Production Top With the d0 Experiment at the Tevatron and Determination the Top Quark Mass Using This Measure

Description: The top quark has been discovered by CDF and D0 experiments in 1995 at the proton-antiproton collider Tevatron. The amount of data recorded by both experiments makes it possible to accurately study the properties of this quark: its mass is now known to better than 1% accuracy. This thesis describes the measurement of the top pair cross section in the electron muon channel with 4, 3 fb<sup> -1</sup> recorded data between 2006 and 2009 by the D0 experiment. Since the final state included a muon, improvements of some aspects of its identification have been performed : a study of the contamination of the cosmic muons and a study of the quality of the muon tracks. The cross section measurement is in good agreement with the theoretical calculations and the other experimental measurements. This measurement has been used to extract a value for the top quark mass. This method allows for the extraction of a better defined top mass than direct measurements as it depends less on Monte Carlo simulations. The uncertainty on this extracted mass, dominated by the experimental one, is however larger than for direct measurements. In order to decrease this uncertainty, the ratio of the Z boson and the top pair production cross sections has been studied to look for some possible theoretical correlations. At the Tevatron, the two cross sections are not theoretically correlated: no decrease of the uncertainty on the extracted top mass is therefore possible.
Date: June 1, 2010
Creator: Chevalier-Thery, Solene
Partner: UNT Libraries Government Documents Department

Resonance searches with the $t\overline{t}$ Invariant Mass Distribution measured with the D\O\, Experiment at $\sqrt{s}=1.96\,\textrm{TeV}

Description: Understanding the universe, its birth and its future is one of the biggest motivations in physics. In order to understand the cosmos, the fundamental particles forming the universe, the components our matter is built of need to be known and understood. Over time physicists have built a theory which describes the physics of the known fundamental particles very well: the Standard Model (SM) of particle physics. The SM describes the particles, their interactions and phenomena with high precision. So far no proven deviations from the SM have been found, though recently evidence for possible physics beyond the SM has been observed. The SM is not describing the mass of the elementary particles however and even with the addition of the Higgs mechanism giving mass to the particles, we have no full theory for all four fundamental forces. We know the model needs to be extended or replaced by another one, as gravitation is not included in the SM. Having a theory which describes all fundamental particles found so far and all but one fundamental interaction is a great success. However, all this describes about 4% of the universe we live in. 23% is dark matter and 73% is dark energy. Dark matter is believed to interact only through gravity and maybe the weak force, which makes it hardly observable. Dark energy is even more elusive. Among other theories the cosmologic constant and scalar fields are discussed to describe it. One should also note that other models exist which for example modify the Newtonian law of gravity. The Higgs mechanism has become the most popular model for mass generation. Alternative theories like Super Symmetry (SUSY), large Extra Dimensions, Technicolor, String Theory, to name just a few, have spread to describe the necessary mass generation or new particles. As proof for new …
Date: June 1, 2010
Creator: Schliephake, Thorsten Dirk & U., /Wuppertal
Partner: UNT Libraries Government Documents Department

Leptonic Decays of the Charged B Meson

Description: The authors present a search for the decay B{sup +} {yields} {ell}{sup +}{nu}{sub {ell}} ({ell} = {tau}, {mu}, or e) in (458.9 {+-} 5.1) x 10{sup 6} {Upsilon}(4S) decays recorded with the BABAR detector at the SLAC PEP-II B-Factory. A sample of events with one reconstructed exclusive semi-leptonic B decay (B{sup -} {yields} D{sup 0}{ell}{sup -}{bar {nu}}X) is selected, and in the recoil a search for B{sup +} {yields} {ell}{sup +}{nu}{sub {ell}} signal is performed. The {tau} is identified in the following channels: {tau}{sup +} {yields} e{sup +}{nu}{sub e}{bar {nu}}{sub {tau}}, {tau}{sup +} {yields} {mu}{sup +}{nu}{sub {mu}}{bar {nu}}{sub {tau}}, {tau}{sup +} {yields} {pi}{sup +}{bar {nu}}{sub {tau}}, and {tau}{sup +} {yields} {pi}{sup +}{pi}{sup 0}{bar {nu}}{sub {tau}}. The analysis strategy and the statistical procedure is set up for branching fraction extraction or upper limit determination. They determine from the dataset a preliminary measurement of {Beta}(B{sup +} {yields} {tau}{sup +}{nu}{sub {tau}}) = (1.8 {+-} 0.8 {+-} 0.1) x 10{sup -4}, which excludes zero at 2.4{sigma}, and f{sub B} = 255 {+-} 58 MeV. Combination with the hadronically tagged measurement yields {Beta}(B{sup +} {yields} {tau}{sup +}{nu}{sub {tau}}) = (1.8 {+-} 0.6) x 10{sup -4}. They also set preliminary limits on the branching fractions at {Beta}(B{sup +} {yields} e{sup +}{nu}{sub e}) &lt; 7.7 x 10{sup -6} (90% C.L.), {Beta}(B{sup +} {yields} {mu}{sup +}{nu}{sub {mu}}) &lt; 11 x 10{sup -6} (90% C.L.), and {Beta}(B{sup +} {yields} {tau}{sup +}{nu}{sub {tau}}) &lt; 3.2 x 10{sup -4} (90% C.L.).
Date: June 11, 2010
Creator: Corwin, Luke A.; U., /Ohio State & ,
Partner: UNT Libraries Government Documents Department

Measurement of the inclusive forward-backward t$\bar{t}$ production asymmetry and its rapidity dependence dA<sub>fb</sub>/d(Δy)

Description: Early measurements of a large forward-background asymmetry at the CDF and D0 experiments at Fermilab have generated much recent interest, but were hampered by large uncertainties. We present here a new measurement of the parton level forward-backward asymmetry of pair-produced top quarks, using a high-statistics sample with much improved precision. We study the rapidity, y<sub>top</sub>, of the top quark production angle with respect to the incoming parton momentum in both the lab and t$\bar{t}$ rest frames. We find the parton-level forward-backward asymmetries to be A<sub>fb</sub><sup>p$\bar{t}$</sup> = 0.150 ± 0.050<sup>stat</sup> ± 0.024<sup>syst</sup> A<sub>fb</sub><sup>t$\bar{t}$</sup> = 0.158 ± 0.072{sup stat} ± 0.024<sup>syst</sup>. These results should be compared with the small p$\bar{p}$ frame charge asymmetry expected in QCD at NLO, A<sub>fb</sub> = 0.050 ± 0.015. Additionally, we introduce a measurement of the A<sub>fb</sub> rapidity dependence dA<sub>fb</sub>/d(Δy). We find this to be A<sub>fb</sub><sup>p$\bar{t}$</sup>(|Δy| &lt; 1.0) = 0.026 ± 0.104<sup>stat</sup> ± 0.012 <sup>syst</sup> A<sub>fb</sub><sup>p$\bar{t}$</sup>(|Δy| &gt; 1.0) = 0.611 ± 0.210<sup>stat</sup> ± 0.246<sup>syst</sup> which we compare with model predictions 0.039 ± 0.006 and 0.123 ± 0.018 for the inner and outer rapidities, respectively.
Date: January 1, 2010
Creator: Strycker, Glenn Loyd
Partner: UNT Libraries Government Documents Department

Finding the Higgs boson of the standard model in the channel ZH → e<sup>+</sup>e<sup>-</sup>b$\bar{b}$ with the D0 detector at the Tevatron; Recherche du boson de Higgs du nideke standard dans le canal ZH → e<sup>+</sup>e<sup>-</sup>b$\bar{b}$ Avec le Detecteur DØ Aupres du Tevatron

Description: The organization of this thesis consists of three main ideas: the first presents the theoretical framework and experimental, as well as objects used in the analysis and the second relates to the various work tasks of service that I performed on the calorimeter, and the third is the search for the Higgs boson in the channel ZH → e<sup>+</sup>e<sup>-</sup>b$\bar{b}$. Thus, this thesis has the following structure: Chapter 1 is an introduction to the standard model of particle physics and the Higgs mechanism; Chapter 2 is an overview of the complex and the acceleration of the Tevatron at Fermilab DØ detector; Chapter 3 is an introduction to physical objects used in this thesis; Chapter 4 presents the study made on correcting the energy measured in the calorimeter; Chapter 5 describes the study of certification of electrons in the calorimeter; Chapter 6 describes the study of certification of electrons in the intercryostat region of calorimeter; Chapter 7 Detailed analysis on the search for Higgs production in the channel ZH → e<sup>+</sup>e<sup>-</sup>b$\bar{b}$; and Chapter 8 presents the final results of the calculations of upper limits to the production cross section of the Higgs boson on a range of low masses.
Date: June 11, 2010
Creator: Calpas, Betty Constante
Partner: UNT Libraries Government Documents Department

Determination of saccharides and ethanol from biomass conversion using Raman spectroscopy: Effects of pretreatment and enzyme composition

Description: This dissertation focuses on the development of facile and rapid quantitative Raman spectroscopy measurements for the determination of conversion products in producing bioethanol from corn stover. Raman spectroscopy was chosen to determine glucose, xylose and ethanol in complex hydrolysis and fermentation matrices. Chapter 1 describes the motives and main goals of this work, and includes an introduction to biomass, commonly used pretreatment methods, hydrolysis and fermentation reactions. The principles of Raman spectroscopy, its advantages and applications related to biomass analysis are also illustrated. Chapter 2 and 3 comprise two published or submitted manuscripts, and the thesis concludes with an appendix. In Chapter 2, a Raman spectroscopic protocol is described to study the efficiency of enzymatic hydrolysis of cellulose by measuring the main product in hydrolysate, glucose. Two commonly utilized pretreatment methods were investigated in order to understand their effect on glucose measurements by Raman spectroscopy. Second, a similar method was set up to determine the concentration of ethanol in fermentation broth. Both of these measurements are challenged by the presence of complex matrices. In Chapter 3, a quantitative comparison of pretreatment protocols and the effect of enzyme composition are studied using systematic methods. A multipeak fitting algorithm was developed to analyze spectra of hydrolysate containing two analytes: glucose and xylose. Chapter 4 concludes with a future perspective of this research area. An appendix describes a convenient, rapid spectrophotometric method developed to measure cadmium in water. This method requires relatively low cost instrumentation and can be used in microgravity, such as space shuttles or the International Space Station. This work was performed under the supervision of Professor Marc Porter while at Iowa State University. Research related to producing biofuel from bio-renewable resources, especially bioethanol from biomass, has grown significantly in the past decade due to the high demand and rising costs …
Date: January 1, 2010
Creator: Shih, Chien-Ju
Partner: UNT Libraries Government Documents Department

Search for MSSM Higgs Bosons in Tau Final States with the D0 Detector

Description: The cross-section times branching ratio of the Higgs boson decaying to τ<sup>+</sup>τ<sup>-</sup> final state in the Standard Model (SM) is too small to play any role in the SM Higgs boson searches. This, however, is different in the Minimal Supersymmetric Standard Model (MSSM), which predicts two Higgs doublets leading to five Higgs bosons: a pair of charged Higgs boson (H<sup>±</sup>); two neutral CP-even Higgs bosons (h,H) and a CP-odd Higgs boson (A). A search for the production of neutral Higgs bosons decaying into τ<sup>+</sup>τ<sup>-</sup> final states in p{bar p} collisions at a centre-of-mass energy of √s = 1.96 TeV is presented in this thesis. One of the two τ leptons is required to decay into a muon while the other decays hadronically. The integrated luminosity is L = 1.0-5.36 fb <sup>-1</sup>, collected by the D0 experiment at the Fermilab Tevatron Collider from 2002 to 2009 in the Run II.
Date: January 1, 2010
Creator: Yang, Wan-Ching
Partner: UNT Libraries Government Documents Department

Testing CPT conservation using the NuMI neutrino beam with the MINOS experiment

Description: The MINOS experiment was designed to measure neutrino oscillation parameters with muon neutrinos. It achieves this by measuring the neutrino energy spectrum and flavor composition of the man-made NuMI neutrino beam 1km after the beam is formed and again after 735 km. By comparing the two spectra it is possible to measure the oscillation parameters. The NuMI beam is made up of 7.0%$\bar{v}$<sub>μ</sub>, which can be separated from the v<sub>μ</sub> because the MINOS detectors are magnetized. This makes it possible to study $\bar{v}$<sub>μ</sub> oscillations separately from those of muon neutrinos, and thereby test CPT invariance in the neutrino sector by determining the $\bar{v}$<sub>μ</sub> oscillation parameters and comparing them with those for v<sub>μ</sub>, although any unknown physics of the antineutrino would appear as a difference in oscillation parameters. Such a test has not been performed with beam $\bar{v}$<sub>μ</sub> before. It is also possible to produce an almost pure $\bar{v}$<sub>μ</sub> beam by reversing the current through the magnetic focusing horns of the NuMI beamline, thereby focusing negatively, instead of positively charged particles. This thesis describes the analysis of the 7% $\bar{v}$<sub>μ</sub> component of the forward horn current NuMI beam. The $\bar{v}$<sub>μ</sub> of a data sample of 3.2 x 10{sup 20} protons on target analysis found 42 events, compared to a CPT conserving prediction of 58.3<sub>-7.6</sub><sup>+7.6</sup>(stat.)<sub>-3.6</sub><sup>+3.6</sup>(syst.) events. This corresponds to a 1.9 σ deficit, and a best fit value of Δ$\bar{m}$<sub>32</sub><sup>2</sup> = 18 x 10<sup>-3</sup> eV<sup>2</sup> and sin<sup>2</sup> 2$\bar{θ}$<sub>23</sub> = 0.55. This thesis focuses particularly on the selection of $\bar{v}$<sub>μ</sub> events, and investigates possible improvements of the selection algorithm. From this a different selector was chosen, which corroborated the findings of the original selector. The thesis also investigates how the systematic errors affect the precision of Δ$\bar{m}$<sub>32</sub><sup>2</sup> and sin<sup>2</sup> 2$\bar{θ}$<sub>23</sub>. Furthermore, it describes a study to determine the gains of the PMTs via …
Date: March 1, 2010
Creator: Auty, David John
Partner: UNT Libraries Government Documents Department

Watching Electrons Transfer from Metals to Insulators using Two Photon Photoemission

Description: Ultrafast angle-resolved two photon photoemission was used to study the dynamics and interfacial band structure of ultrathin films adsorbed onto Ag(111). Studies focused on the image potential state (IPS) in each system as a probe for measuring changes in electronic behavior in differing environments. The energetics and dynamics of the IPS at the toluene/Ag(111) interface are strongly dependent upon coverage. For a single monolayer, the first IPS is bound by 0.81 eV below the vacuum level and has a lifetime of 50 femtoseconds (fs). Further adsorption of toluene creates islands of toluene with an exposed wetting layer underneath. The IPS is then split into two peaks, one corresponding to the islands and one corresponding to the monolayer. The wetting layer IPS shows the same dynamics as the monolayer, while the lifetime of the islands increases exponentially with increasing thickness. Furthermore, the island IPS transitions from delocalized to localized within 500 fs, and electrons with larger parallel momenta decay much faster. Attempts were made using a stochastic model to extract the rates of localization and intraband cooling at differing momenta. In sexithiophene (6T) and dihexyl-sexithiophene (DH6T), the IPS was used as a probe to see if the nuclear motion of spectating side chains can interfere with molecular conduction. The energy and band mass of the IPS was measured for 6T and two geometries of DH6T on Ag(111). Electrons injected into the thicker coverages of DH6T grew exponentially heavier until they were completely localized by 230 fs, while those injected into 6T remained nearly free electron like. Based off of lifetime arguments and the density of defects, the most likely cause for the mass enhancement of the IPS in this system is small polaron formation caused by coupling of the electron to vibrations of the alkyl substituents. The energetic relaxation of the …
Date: May 1, 2010
Creator: Johns, James E.
Partner: UNT Libraries Government Documents Department

Search for the Standard Model Higgs Boson in the $WH \to \ell \nu b\bar{b}$ Channel in 1.96-TeV Proton-Antiproton Collisions

Description: We have searched for the Standard Model Higgs boson in the WH → lvbb channel in 1.96 TeV pp collisions at CDF. This search is based on the data collected by March 2009, corresponding to an integrated luminosity of 4.3 fb<sup>-1</sup>. The W H channel is one of the most promising channels for the Higgs boson search at Tevatron in the low Higgs boson mass region.
Date: February 1, 2010
Creator: Nagai, Yoshikazu
Partner: UNT Libraries Government Documents Department

A search for $ZH\rightarrow \mu\mu b \bar{b}$ production at the Tevatron

Description: The Standard Model describes with a very good accuracy all interactions of the, so far, known elementary particles. However the Higgs mechanism, which gives rise to the observed mass of these particles, has not yet been confirmed. The Higgs particle has not yet been observed, and the observation or exclusion is an important test of the Standard Model. The Standard Model does not predict the mass of the Higgs particle, however it does impose some limits on the range in which this mass can lie. In direct searches a Higgs with a mass smaller than 114.4 GeV and within 162 GeV and 166 GeV has been excluded at 95% CL at the LEP and the Tevatron colliders. The analysis presented in this thesis is aimed to search for the ZH → μμb$\bar{b}$ events in 3.1 fb<sup>-1</sup> of data collected with the DØ detector in p$\bar{p}$ collisions at √s = 1.96 TeV.
Date: April 20, 2010
Creator: Ancu, Lucian-Stefan
Partner: UNT Libraries Government Documents Department

Rhodium Catalysts in the Oxidation of CO by O<sub>2</sub> and NO: Shape, Composition, and Hot Electron Generation

Description: It is well known that the activity, selectivity, and deactivation behavior of heterogeneous catalysts are strongly affected by a wide variety of parameters, including but not limited to nanoparticle size, shape, composition, support, pretreatment conditions, oxidation state, and electronic state. Enormous effort has been expended in an attempt to understand the role of these factors on catalytic behavior, but much still remains to be discovered. In this work, we have focused on deepening the present understanding of the role of nanoparticle shape, nanoparticle composition, and hot electrons on heterogeneous catalysis in the oxidation of carbon monoxide by molecular oxygen and nitric oxide. These reactions were chosen because they are important for environmental applications, such as in the catalytic converter, and because there is a wide range of experimental and theoretical insight from previous single crystal work as well as experimental data on nanoparticles obtained using new state-of-the-art techniques that aid greatly in the interpretation of results on complex nanoparticle systems. In particular, the studies presented in this work involve three types of samples: ~ 6.5 nm Rh nanoparticles of different shapes, ~ 15 nm Rh<sub>1-x</sub>Pd<sub>x</sub> core-shell bimetallic polyhedra nanoparticles, and Rh ultra-thin film (~ 5 nm) catalytic nanodiodes. The colloidal nanoparticle samples were synthesized using a co-reduction of metal salts in alcohol and supported on silicon wafers using the Langmuir-Blodgett technique. This synthetic strategy enables tremendous control of nanoparticle size, shape, and composition. Nanoparticle shape was controlled through the use of different organic polymer capping layers. Bimetallic core-shell nanoparticles were synthesized by careful choice of metal salt precursors. Rh/TiO<sub>x</sub> and Rh/GaN catalytic nanodiodes were fabricated using a variety of thin film device fabrication techniques, including reactive DC magnetron sputtering, electron beam evaporation, and rapid thermal annealing. The combination of these techniques enabled control of catalytic nanodiode morphology, geometry, and electrical …
Date: March 8, 2010
Creator: Renzas, James R.
Partner: UNT Libraries Government Documents Department

Search for the production of the standard model z boson in association with W<sup>±</sup> boson in proton anti-p collisions at 1.96 TeV center of mass energy

Description: The search for the production of the Standard Model Z boson in association with a W boson is motivated and discussed. This is performed using 4.3 fb<sup>-1</sup> of Tevatron Run II data collected with the CDF detector in √s = 1.96 TeV proton anti-proton collisions. This is a signature-based analysis where the W boson decays semileptonically into a high-P<sub>T</sub> electron or muon plus a neutrino, and where the Z boson decays into two b quark jets (b-jets). We increase the signal-to-background ratio by identifying the b-quarks in the jets with a new neural network-based algorithm. Another neural network then uses kinematic information to distinguish WZ to further increase the signal-to-background ratio. Since our sensitivity is still not enough to achieve an observation, we set a 95% Confidence Level upper limit on the product of the WZ production cross section and its branching fraction to the decay products specified above, and express it as a ratio to the theoretical Standard Model prediction. The resulting limit is 3.9 x SM (3.9 x SM expected).
Date: January 1, 2010
Creator: Keung, Justin Kien
Partner: UNT Libraries Government Documents Department

Yb-based heavy fermion compounds and field tuned quantum chemistry

Description: The motivation of this dissertation was to advance the study of Yb-based heavy fermion (HF) compounds especially ones related to quantum phase transitions. One of the topics of this work was the investigation of the interaction between the Kondo and crystalline electric field (CEF) energy scales in Yb-based HF systems by means of thermoelectric power (TEP) measurements. In these systems, the Kondo interaction and CEF excitations generally give rise to large anomalies such as maxima in ρ(T) and as minima in S(T). The TEP data were use to determine the evolution of Kondo and CEF energy scales upon varying transition metals for YbT<sub>2</sub>Zn<sub>20</sub> (T = Fe, Ru, Os, Ir, Rh, and Co) compounds and applying magnetic fields for YbAgGe and YbPtBi. For YbT<sub>2</sub>Zn<sub>20</sub> and YbPtBi, the Kondo and CEF energy scales could not be well separated in S(T), presumably because of small CEF level splittings. A similar effect was observed for the magnetic contribution to the resistivity. For YbAgGe, S(T) has been successfully applied to determine the Kondo and CEF energy scales due to the clear separation between the ground state and thermally excited CEF states. The Kondo temperature, T<sub>K</sub>, inferred from the local maximum in S(T), remains finite as magnetic field increases up to 140 kOe. In this dissertation we have examined the heavy quasi-particle behavior, found near the field tuned AFM quantum critical point (QCP), with YbAgGe and YbPtBi. Although the observed nFL behaviors in the vicinity of the QCP are different between YbAgGe and YbPtBi, the constructed H-T phase diagram including the two crossovers are similar. For both YbAgGe and YbPtBi, the details of the quantum criticality turn out to be complicated. We expect that YbPtBi will provide an additional example of field tuned quantum criticality, but clearly there are further experimental investigations left and more ideas …
Date: January 1, 2010
Creator: Mun, Eundeok
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

A Study of Muon Ionization Cooling at MICE

Description: A Neutrino Factory based on a high-energy muon storage-ring is proposed to study neutrino oscillation with high precision. An emittance reduction of muon beam by ionization cooling, which has never been demonstrated in practice, is one of the critical issues for Neutrino Factory. The international Muon Ionisation Cooling Experiment (MICE) is the first experiment to verify an effect of the ionization cooling with muons. MICE will measure a change in transverse emittance of approximately 10% with a precision of ±0.1%. In order to meet the requirements, muon trackers based on 350 μm diameter scintillating fibers have been proposed. The construction of such trackers is a very challenging task and some innovative techniques are needed to realize, since there have been no trackers made with such a small diameter of scintillating fibers in the world. Upstream and downstream SciFi trackers have been successfully constructed with the international collaboration of UK, US and Japan by 2008. Both of the trackers have been tested with cosmic-rays at the RAL by 2009, at which high tracking efficiencies more than 90% are measured for both trackers. It is also confirmed that by collecting the misalignments found in both of the trackers, the requirements for the emittance measurement is met.
Date: February 1, 2010
Creator: Sakamoto, Hideyuki
Partner: UNT Libraries Government Documents Department

Neutron scattering study of charge-ordering in R1/3Sr2/3FeO3 (R=La, Pr, Nd, Sm, and Y)

Description: The complicated physical phenomena in complex transition-metal oxides (TMO), such as high T<sub>c</sub> superconductivity, colossal magnetoresistivity, metal-insulator transitions, etc., have long been the focus of intense inquiry and debate in condensed matter science, since they are related to strong electronic correlations and cannot be explained within the 'standard model' of solid state physics. These novel functionalities of the correlated electron systems have a wide range of potential for applications in industry, such as information storage, energy transportation, and so on. The charge-ordering (CO) transition is very common in TMO and there is a specific CO transition temperature, TCO. Above TCO, the charge is not ordered, which means that the electrons in a compound are itinerant and the positions of the electrons are not fixed. Below TCO, the charge is ordered, which means that the electrons are localized and the positions of the electrons are settled. Hence, the electrical conductivity of a material is changed at TCO and this transition is classified as metal-insulator transition. Usually the CO with commensurate hole doping in TMO is thought to play an important role in various cases, including the superconducting cuprates, where the spin/charge stripe formation competes with superconducting states, colossal magnetoresistive manganites, where CO competes with ferromagnetic metallic state stabilized by an external magnetic field, layered nickelates, where CO takes the form of the small polaron lattices, and layered manganites, where CO could be bothered by the correlated dynamics of spins and charges. Therefore understanding the causes and implications of CO phenomena is significantly important.
Date: January 1, 2010
Creator: Ma, Jie
Partner: UNT Libraries Government Documents Department

A search for sterile neutrinos at the MINOS experiment

Description: MINOS is a long baseline neutrino oscillation experiment based at the Fermi National Accelerator Laboratory in Illinois, USA. The experiment was designed to study neutrino oscillation phenomena. The {nu}{sub {mu}} beam produced by the NuMI beam facility at FNAL is used along with two functionally identical detectors. The Near Detector at FNAL and a Far Detector 735 km away in the Soudan Underground Laboratory in northern Minnesota. Comparison of the observed spectra of neutrinos at the two detectors provides the evidence for neutrino oscillations. This thesis presents work on the postulated phenomena of sterile neutrinos. Oscillations between active and sterile neutrinos will lead to a deficit in the expected rate of measured Neutral Current interactions at the Far Detector. A technique for selecting Neutral Current events utilizing an Artificial Neural Network is presented with resulting overall efficiency of 91.1% and purity of 66.0%. A method of predicting the expected Charged and Neutral Current energy spectra at the Far Detector given the data recorded at the Near Detector is presented. A model to search for oscillations between sterile and active neutrinos is developed. Sources of systematic uncertainty that can effect the results of the analysis are discussed. The analysis developed is applied to a Standard Model 3 flavour oscillation model as a cross check under the scenarios with and without {nu}{sub e} appearance. The oscillation parameters measured by this model are {Delta}m{sub 32}{sup 2} = (2.39{sub -0.15}{sup +0.23}) x 10{sup -3} eV{sup 2} and {theta}{sub 23} = 0.727{sub -0.11}{sup +0.22} for the no {nu}{sub e} appearance result. An analysis of the resulting prediction reveals no evidence for active neutrino disappearance. The analysis is then performed using the 4 flavour neutrino oscillation model developed. Again this is done under the 2 scenarios of {nu}{sub e} appearance and no {nu}{sub e} appearance. The …
Date: August 1, 2010
Creator: Pittam, Robert Neil & U., /Oxford
Partner: UNT Libraries Government Documents Department

Sterile neutrino oscillations in MINOS and hadron production in pC collisions

Description: MINOS is a long baseline neutrino oscillation experiment, starting with a muon-neutrino beam, for the precise measurement of the atmospheric neutrino oscillation parameters |{Delta}m{sup 2}| and {theta}{sub 23}. The Near Detector measures the neutrino flux and spectra before oscillations. The beam propagates for 735 km to the Far Detector, which measures the depleted spectrum after oscillations. The depletion can be interpreted as {nu}{sub {mu}} {yields} {nu}{sub {tau}} oscillations. Subdominant {nu}{sub {mu}} {yields} {nu}{sub e} oscillations may be allowed if the mixing angle {theta}{sub 13} {ne} 0. The two detectors are functionally identical in order to cancel systematic errors when using the Near Detector data to constrain the Far Detector prediction. A crucial part of the analysis is the relative calibration between the two detectors, which is known at the 2% level. A calibration procedure to remove the time and temperature dependence of the detector response using through-going cosmic muons is presented here. Although the two-detector approach reduces the systematic uncertainties related to the neutrino flux, a cross check on the neutrino parent meson ratios is performed in this thesis. The cross sections of mesons produced in proton-carbon interactions from the NA49 experiment have been measured and the results have been compared to the MINOS expectations. A neutrino oscillation analysis allowing mixing to a sterile neutrino is performed, under the assumption that the additional mass splitting is {Omicron}(1 eV{sup 2}). The analysis uses the energy spectrum of the neutral current interaction products, as neutral current interactions are sensitive to sterile neutrino mixing but not to the active flavour neutrino mixing. The neutrino oscillation parameters have been found to be: |{Delta}m{sup 2}| = 2.43{sub -0.18}{sup +0.21} x 10{sup -3} eV{sup 2}, {theta}{sub 23} = 40.27{sup o}{sub -5.17}{sup +14.64}, {theta}{sub 24} = 0.00{sup o}{sup +5.99} and {theta}{sub 34} = 0.00{sup o}{sup +24.57} under …
Date: July 1, 2010
Creator: Tinti, Gemma Maria & U., /Oxford
Partner: UNT Libraries Government Documents Department
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