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A Search for Neutrino Induced Coherent NC($\pi^{0}$) Production in the MINOS Near Detector (open access)

A Search for Neutrino Induced Coherent NC($\pi^{0}$) Production in the MINOS Near Detector

The production of single, highly forward {pi}{sup 0} mesons by NC coherent neutrino-nucleus interactions ({nu}{sub {mu}} + N {yields} {nu}{sub {mu}} + N + {pi}{sup 0}) is a process which probes fundamental aspects of the weak interaction. This reaction may also pose as a limiting background for long baseline searches for {nu}{sub {mu}} {yields} {nu}{sub e} oscillations if the neutrino mixing angle {theta}{sub 13} is very small. The high-statistics sample of neutrino interactions recorded by the MINOS Near Detector provides an opportunity to measure the cross section of this coherent reaction on a relatively large-A nucleus at an average E{sub {nu}} = 4.9 GeV. A major challenge for this measurement is the isolation of forward-going electromagnetic (EM) showers produced by the relatively rare coherent NC({pi}{sup 0}) process amidst an abundant rate of incoherently produced EM showers. The backgrounds arise from single {pi}{sup 0} dominated NC events and also from quasi-elastic-like CC scattering of electron neutrinos. In this Thesis the theory of coherent interactions is summarized, and previous measurements of the coherent NC({pi}{sup 0}) cross section are reviewed. Then, methods for selecting a sample of coherent NC({pi}{sup 0}) like events, extracting the coherent NC({pi}{sup 0}) event rate from that sample, estimating …
Date: November 1, 2010
Creator: Cherdack, Daniel David & U., /Tufts
System: The UNT Digital Library
Increasing the efficiency of organic solar cells by photonic and electrostatic-field enhancements (open access)

Increasing the efficiency of organic solar cells by photonic and electrostatic-field enhancements

Organic photovoltaic (OPV) technology is an attractive solar-electric conversion paradigm due to the promise of low cost roll-to-roll production and amenability to flexible substrates. Power conversion efficiency (PCE) exceeding 7% has recently been achieved. OPV cells suffer from low charge carrier mobilities of polymers, leading to recombination losses, higher series resistances and lower fill-factors. Thus, it is imperative to develop fabrication methodologies that can enable efficient optical absorption in films thinner than optical absorption length. Active layers conformally deposited on light-trapping, microscale textured, grating-type surfaces is one possible approach to achieve this objective. In this study, 40% theoretical increase in photonic absorption over flat OPVs is shown for devices with textured geometry by the simulation results. For verifying this theoretical result and improving the efficiency of OPVs by light trapping, OPVs were fabricated on grating-type textured substrates possessing t pitch and -coat PV active-layer on these textured substrates led to over filling of the valleys and shunts at the crest, which severely affected the performance of the resultant PV devices. Thus, it is established that although the optical design is important for OPV performance but the potential of light trapping can only be effectively tapped if the textures are amenable …
Date: November 3, 2012
Creator: Nalwa, Kanwar
System: The UNT Digital Library
A small low energy cyclotron for radioisotope measurements (open access)

A small low energy cyclotron for radioisotope measurements

Direct detection of {sup 14}C by accelerator mass spectrometry has proved to be a much more sensitive method for radiocarbon dating than the decay counting method invented earlier by Libby. A small cyclotron (the cyclotrino'') was proposed for direct detection of radiocarbon in 1980. This combined the suppression of background through the use of negative ions, which had been used effectively in tandem accelerators, with the high intrinsic mass resolution of a cyclotron. Development of a small electrostatically-focused cyclotron for use as a mass spectrometer was previously reported but the sensitivity needed for detection of {sup 14}C at natural abundance was not achieved. The major contributions of this work are the integration of a high current external ion source with a small flat-field, electrostatically-focused cyclotron to comprise a system capable of measuring {sup 14}C at natural levels, and the analysis of ion motion in such a cyclotron, including a detailed analysis of phase bunching and its effect on mass resolution. A high current cesium sputter negative ion source generates a beam of carbon ions which is pre-separated with a Wien filter and is transported to the cyclotron via a series of electrostatic lenses. Beam is injected radially into the cyclotron …
Date: November 1, 1989
Creator: Bertsche, Kirk Joseph
System: The UNT Digital Library
A measurement of the 2 neutrino double beta decay rate of Te-130 in the CUORICINO experiment (open access)

A measurement of the 2 neutrino double beta decay rate of Te-130 in the CUORICINO experiment

CUORICINO was a cryogenic bolometer experiment designed to search for neutrinoless double beta decay and other rare processes, including double beta decay with two neutrinos (2{nu}{beta}{beta}). The experiment was located at Laboratori Nazionali del Gran Sasso and ran for a period of about 5 years, from 2003 to 2008. The detector consisted of an array of 62 TeO{sub 2} crystals arranged in a tower and operated at a temperature of #24;10 mK. Events depositing energy in the detectors, such as radioactive decays or impinging particles, produced thermal pulses in the crystals which were read out using sensitive thermistors. The experiment included 4 enriched crystals, 2 enriched with {sup 130}Te and 2 with {sup 128}Te, in order to aid in the measurement of the 2{nu}{beta}{beta} rate. The enriched crystals contained a total of #24;350 g {sup 130}Te. The 128-enriched (130-depleted) crystals were used as background monitors, so that the shared backgrounds could be subtracted from the energy spectrum of the 130- enriched crystals. Residual backgrounds in the subtracted spectrum were fit using spectra generated by Monte-Carlo simulations of natural radioactive contaminants located in and on the crystals. The 2{nu}{beta}{beta} half-life was measured to be T{sup 2{nu}}{sub 1/2} = [9.81{+-} #6;0.96(stat){+-} 0.49(syst)]#2;x10{sup …
Date: November 3, 2011
Creator: Kogler, Laura
System: The UNT Digital Library
THE INTERACTION OF THE Eco RI RESTRICTION ENZYME FROM E.coli WITH NUCLEOTIDES (open access)

THE INTERACTION OF THE Eco RI RESTRICTION ENZYME FROM E.coli WITH NUCLEOTIDES

The Eco R1 restriction enzyme can be shown to be inhibited by nucleotides which correspond to any part of its known site of phosphodiesterase activity. A series of di-, tetra-, and hexa-nucleotide fragments were synthesized and their effect on the activity of the enzyme upon superhelical Co1 E1 DNA studied. The inhibition caused by the individual mononucleotides were also studied. In general all the nucleotide fragments showed some form of interaction with the enzyme system. Tetranucleotides were stronger inhibitors than dinucleotides, which in turn were stronger inhibitors than the mononucleotides. Within each category of inhibitors, those containing the phosphodiester bond which is acted upon by the enzyme were the strongest inhibitors. Only those fragments which were consistent with the enzymes site of activity showed competitive inhibition kinetics. Nucleotides which do not fit within the site of phosphodiesterase activity show non-competitive inhibition kinetics.
Date: November 1, 1979
Creator: Hollis, Donald F.
System: The UNT Digital Library
Multicore Architecture-aware Scientific Applications (open access)

Multicore Architecture-aware Scientific Applications

Modern high performance systems are becoming increasingly complex and powerful due to advancements in processor and memory architecture. In order to keep up with this increasing complexity, applications have to be augmented with certain capabilities to fully exploit such systems. These may be at the application level, such as static or dynamic adaptations or at the system level, like having strategies in place to override some of the default operating system polices, the main objective being to improve computational performance of the application. The current work proposes two such capabilites with respect to multi-threaded scientific applications, in particular a large scale physics application computing ab-initio nuclear structure. The first involves using a middleware tool to invoke dynamic adaptations in the application, so as to be able to adjust to the changing computational resource availability at run-time. The second involves a strategy for effective placement of data in main memory, to optimize memory access latencies and bandwidth. These capabilties when included were found to have a significant impact on the application performance, resulting in average speedups of as much as two to four times.
Date: November 28, 2011
Creator: Srinivasa, Avinash
System: The UNT Digital Library
Imaging gene expression in real-time using aptamers (open access)

Imaging gene expression in real-time using aptamers

Signal transduction pathways are usually activated by external stimuli and are transient. The downstream changes such as transcription of the activated genes are also transient. Real-time detection of promoter activity is useful for understanding changes in gene expression, especially during cell differentiation and in development. A simple and reliable method for viewing gene expression in real time is not yet available. Reporter proteins such as fluorescent proteins and luciferase allow for non-invasive detection of the products of gene expression in living cells. However, current reporter systems do not provide for real-time imaging of promoter activity in living cells. This is because of the long time period after transcription required for fluorescent protein synthesis and maturation. We have developed an RNA reporter system for imaging in real-time to detect changes in promoter activity as they occur. The RNA reporter uses strings of RNA aptamers that constitute IMAGEtags (Intracellular MultiAptamer GEnetic tags), which can be expressed from a promoter of choice. The tobramycin, neomycin and PDC RNA aptamers have been utilized for this system and expressed in yeast from the GAL1 promoter. The IMAGEtag RNA kinetics were quantified by RT-qPCR. In yeast precultured in raffinose containing media the GAL1 promoter responded faster …
Date: November 2, 2012
Creator: Shin, Il Chung
System: The UNT Digital Library
Single crystal Processing and magnetic properties of gadolinium nickel (open access)

Single crystal Processing and magnetic properties of gadolinium nickel

GdNi is a rare earth intermetallic material that exhibits very interesting magnetic properties. Spontaneous magnetostriction occurs in GdNi at T{sub C}, on the order of 8000ppm strain along the c-axis and only until very recently the mechanism causing this giant magnetostriction was not understood. In order to learn more about the electronic and magnetic structure of GdNi, single crystals are required for anisotropic magnetic property measurements. Single crystal processing is quite challenging for GdNi though since the rare-earth transition-metal composition yields a very reactive intermetallic compound. Many crystal growth methods are pursued in this study including crucible free methods, precipitation growths, and specially developed Bridgman crucibles. A plasma-sprayed Gd{sub 2}O{sub 3} W-backed Bridgman crucible was found to be the best means of GdNi single crystal processing. With a source of high-quality single crystals, many magnetization measurements were collected to reveal the magnetic structure of GdNi. Heat capacity and the magnetocaloric effect are also measured on a single crystal sample. The result is a thorough report on high quality single crystal processing and the magnetic properties of GdNi.
Date: November 2, 2012
Creator: Shreve, Andrew John
System: The UNT Digital Library
Hot nuclear matter (open access)

Hot nuclear matter

The goal in this thesis is thus twofold: The first is to investigate the feasibility of using heavy ion collisions to create conditions in the laboratory which are ripe for the formation of a quark-gluon plasma. The second is to develop a technique for studying some of the many non-perturbative features of this novel phase of matter.
Date: November 1, 1992
Creator: Chapman, S.
System: The UNT Digital Library
Water-enhanced solubility of carboxylic acids in organic solvents and its applications to extraction processes (open access)

Water-enhanced solubility of carboxylic acids in organic solvents and its applications to extraction processes

The solubilities of carboxylic acids in certain organic solvents increase remarkably with an increasing amount of water in the organic phase. This phenomenon leads to a novel extract regeneration process in which the co-extracted water is selectively removed from an extract, and the carboxylic acid precipitates. This approach is potentially advantageous compared to other regeneration processes because it removes a minor component of the extract in order to achieve a large recovery of acid from the extract. Carboxylic acids of interest include adipic acid, fumaric acid, and succinic acid because of their low to moderate solubilities in organic solvents. Solvents were screened for an increase in acid solubility with increased water concentration in the organic phase. Most Lewis-base solvents were found to exhibit this increased solubility phenomena. Solvents that have a carbonyl functional group showed a very large increase in acid solubility. 71 refs., 52 figs., 38 tabs.
Date: November 1, 1991
Creator: Starr, J. N. & King, C. J.
System: The UNT Digital Library
Fast beam studies of free radical photodissociation (open access)

Fast beam studies of free radical photodissociation

The photodissociation of free radicals is studied in order to characterize the spectroscopy and dissociation dynamics of the dissociative electronic states in these species. To accomplish this, a novel method of radical production, based on the photodetachment of the corresponding negative ion, has been combined with a highly complementary form of photofragment translational spectroscopy. The optical spectroscopy of transitions to dissociative states is determined by monitoring the total photofragment yield as a function of dissociation photon energy. Branching ratios to various product channels, internal energy distributions of the fragments, bond dissociation energies, and the translational energy-dependent photofragment recoil angular distributions are then determined at selected excitation energies. A detailed picture of the dissociation dynamics can then be formulated, allowing insight concerning the interactions of potential energy surfaces involved in the dissociation. After an introduction to the concepts and techniques mentioned above, the experimental apparatus used in these experiments is described in detail. The basis and methods used in the treatment of data, especially in the dissociation dynamics experiments, are then put forward.
Date: November 1, 1993
Creator: Cyr, D. R.
System: The UNT Digital Library
Vibration-rotation-tunneling dynamics in small water clusters (open access)

Vibration-rotation-tunneling dynamics in small water clusters

The goal of this work is to characterize the intermolecular vibrations of small water clusters. Using tunable far infrared laser absorption spectroscopy, large amplitude vibration-rotation-tunneling (VRT) dynamics in vibrationally excited states of the water dimer and the water trimer are investigated. This study begins with the measurement of 12 VRT subbands, consisting of approximately 230 transitions, which are assigned to an 82.6 cm{sup {minus}1} intermolecular vibration of the water dimer-d{sub 4}. Each of the VRT subbands originate from K{sub a}{double_prime}=0 and terminate in either K{sub a}{prime}=0 or 1. These data provide a complete characterization of the tunneling dynamics in the vibrationally excited state as well as definitive symmetry labels for all VRT energy levels. Furthermore, an accurate value for the A{prime} rotational constant is found to agree well with its corresponding ground state value. All other excited state rotational constants are fitted, and discussed in terms of the corresponding ground state constants. In this vibration, the quantum tunneling motions are determined to exhibit large dependencies with both the K{sub a}{prime} quantum number and the vibrational coordinate, as is evidenced by the measured tunneling splittings. The generalized internal-axis-method treatment which has been developed to model the tunneling dynamics, is considered for …
Date: November 1, 1992
Creator: Pugliano, N.
System: The UNT Digital Library
Nuclear magnetic resonance studies of the regulation of the pentose phosphate pathway (open access)

Nuclear magnetic resonance studies of the regulation of the pentose phosphate pathway

The goal of this work is to investigate the potential for and limitations of in vivo nuclear magnetic resonance (NMR) spectroscopy for quantitation of glucose flux through the pentose phosphate pathway (shunt). Interest in the shunt is motivated by the possibility that its activity may be greatly increased in cancer and in the pathological states of cardiac and cerebral ischemia. The ability to dynamically monitor flux through the pentose shunt can give new knowledge about metabolism in pathological states. {sup 13}C NMR spectroscopy was used to monitor shunt activity by determination of the ratios of [{sup 13}C-4] to [{sup 13}C-5]-glutamate, [{sup 13}C-3] to [{sup 13}C-2]-alanine or [{sup 13}C-3] to [{sup 13}C-2]-lactate produced when [{sup 13}C-2]-glucose is infused. These methods provide measures of the effect of oxidative stresses on shunt activity in systems ranging from cell free enzyme-substrate preparations to cell suspensions and whole animals. In anaerobic cell free preparations, the fraction of glucose flux through the shunt was monitored with a time resolution of 3 minutes. This work predicts the potential for in vivo human studies of pentose phosphate pathway activity based on the mathematical simulation of the {sup 13}C fractional enrichments of C4 and C5-glutamate as a function of …
Date: November 1, 1991
Creator: Bolo, N. R.
System: The UNT Digital Library
Design, development and evaluation of a precision air bearing rotary table with large diameter through-hole (open access)

Design, development and evaluation of a precision air bearing rotary table with large diameter through-hole

A large diameter precision air bearing rotary table with a 16.0 inch diameter through-hole was designed, fabricated and tested in the course of this research. The rotary table will be used in conjunction with a specialized, computer controlled precision inspection machine being designed for the Department of Energy`s (DOE) Nuclear Weapons Complex (NWC). The design process included a complete engineering analysis to predict the final performance of the rotary table, and to ensure that the rotary table meets the required accuracy of 4.0 microinches of total radial (3.5 microinches average radial) and 4.0 microinches total axial (3.5 microinches average axial) errors. The engineering analysis included structural deformation, thermal sensitivity and dynamic analyses using finite element methods in some cases, as well as other analytic solutions. Comparisons are made between predicted and tested values, which are listed in the rotary table error budget. The rotary table performed as predicted with measured axial and radial stiffnesses of 1.1E06 lbf/inch and 2.9E06 lbf/inch, respectively, as well as average radial, axial and tilt errors of 2.5 microinches, 1.5 microinches, and less than 0.05 arcseconds, respectively.
Date: November 1, 1991
Creator: Accatino, M. R.
System: The UNT Digital Library
Search for the Standard Model Higgs Boson in associated production with w boson at the Tevatron (open access)

Search for the Standard Model Higgs Boson in associated production with w boson at the Tevatron

A search for the Standard Model Higgs boson in proton-antiproton collisions with center-of-mass energy 1.96 TeV at the Tevatron is presented in this dissertation. The process of interest is the associated production of W boson and Higgs boson, with the W boson decaying leptonically and the Higgs boson decaying into a pair of bottom quarks. The dataset in the analysis is accumulated by the D0 detector from April 2002 to April 2008 and corresponding to an integrated luminosity of 2.7 fb{sup -1}. The events are reconstructed and selected following the criteria of an isolated lepton, missing transverse energy and two jets. The D0 Neural Network b-jet identification algorithm is further used to discriminate b jets from light jets. A multivariate analysis combining Matrix Element and Neural Network methods is explored to improve the Higgs boson signal significance. No evidence of the Higgs boson is observed in this analysis. In consequence, an observed (expected) limit on the ratio of {sigma} (p{bar p} {yields} WH) x Br (H {yields} b{bar b}) to the Standard Model prediction is set to be 6.7 (6.4) at 95% C.L. for the Higgs boson with a mass of 115 GeV.
Date: November 1, 2009
Creator: Chun, Xu
System: The UNT Digital Library
NMR Studies of Liquid Crystals and Molecules Dissolved in Liquid Crystal Solvents (open access)

NMR Studies of Liquid Crystals and Molecules Dissolved in Liquid Crystal Solvents

This thesis describes several studies in which nuclear magnetic resonance (nmr) spectroscopy has been used to probe the structure, orientation and dynamics of liquid crystal mesogens and molecules dissolved in liquid crystalline phases. In addition, a modern high field nmr spectrometer is described which has been used to perform such nmr studies. Chapter 1 introduces the quantum mechanical formalisms used throughout this thesis and briefly reviews the fundamentals of nuclear spin physics and pulsed nmr spectroscopy. First the density operator is described and a specific form for the canonical ensemble is derived. Then Clebsch-Gordon coefficients, Wigner rotation matrices, and irreducible tensor operators are reviewed. An expression for the equilibrium (Curie) magnetization is obtained and the linear response of a spin system to a strong pulsed r.f. irradiation is described. Finally, the spin interaction Hamiltonians relevant to this work are reviewed together with their truncated forms. Chapter 2 is a deuterium magnetic resonance study of two 'nom' liquid crystals which possess several low temperature mesomorphic phases. Specifically, deuterium quadrupolar echo spectroscopy is used to determine the orientation of the liquid crystal molecules in smectic phases, the changes in molecular orientation and motion that occur at smectic-smectic phase transitions, and the order …
Date: November 1, 1982
Creator: Drobny, G. P.
System: The UNT Digital Library
Multiple-Quantum NMR in Solids (open access)

Multiple-Quantum NMR in Solids

Time domain multiple-quantum (MQ) nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for spectral simplification and for providing new information on molecular dynamics. In this thesis, applications of MQ NMR are presented and show distinctly the advantages of this method over the conventional single-quantum NMR. Chapter 1 introduces the spin Hamiltonians, the density matrix formalism and some basic concepts of MQ NMR spectroscopy. In chapter 2, {sup 14}N double-quantum coherence is observed with high sensitivity in isotropic solution, using only the magnetization of bound protons. Spin echoes are used to obtain the homogeneous double-quantum spectrum and to suppress a large H{sub 2}O solvent signal. Chapter 3 resolves the main difficulty in observing high MQ transitions in solids. Due to the profusion of spin transitions in a solid, individual lines are unresolved. Excitation and detection of high quantum transitions by normal schemes are thus difficult. To ensure that overlapping lines add constructively and thereby to enhance sensitivity, time-reversal pulse sequences are used to generate all lines in phase. Up to 22-quantum {sup 1}H absorption in solid adamantane is observed. A time dependence study shows an increase in spin correlations as the excitation time increased. In chapter 4, a statistical theory …
Date: November 1, 1982
Creator: Yen, Y-S.
System: The UNT Digital Library
Pulsed laser deposition of AlMgB14 thin films (open access)

Pulsed laser deposition of AlMgB14 thin films

Hard, wear-resistant coatings of thin film borides based on AlMgB{sub 14} have the potential to be applied industrially to improve the tool life of cutting tools and pump vanes and may account for several million dollars in savings as a result of reduced wear on these parts. Past work with this material has shown that it can have a hardness of up to 45GPa and be fabricated into thin films with a similar hardness using pulsed laser deposition. These films have already been shown to be promising for industrial applications. Cutting tools coated with AlMgB{sub 14} used to mill titanium alloys have been shown to substantially reduce the wear on the cutting tool and extend its cutting life. However, little research into the thin film fabrication process using pulsed laser deposition to make AlMgB{sub 14} has been conducted. In this work, research was conducted into methods to optimize the deposition parameters for the AlMgB{sub 14} films. Processing methods to eliminate large particles on the surface of the AlMgB{sub 14} films, produce films that were at least 1m thick, reduce the surface roughness of the films, and improve the adhesion of the thin films were investigated. Use of a femtosecond laser …
Date: November 18, 2008
Creator: Russell, Alan; Bastawros, Ashraf & Tan, Xiaoli
System: The UNT Digital Library
Error Detection, Factorization and Correction for Multi-View Scene Reconstruction from Aerial Imagery (open access)

Error Detection, Factorization and Correction for Multi-View Scene Reconstruction from Aerial Imagery

Scene reconstruction from video sequences has become a prominent computer vision research area in recent years, due to its large number of applications in fields such as security, robotics and virtual reality. Despite recent progress in this field, there are still a number of issues that manifest as incomplete, incorrect or computationally-expensive reconstructions. The engine behind achieving reconstruction is the matching of features between images, where common conditions such as occlusions, lighting changes and texture-less regions can all affect matching accuracy. Subsequent processes that rely on matching accuracy, such as camera parameter estimation, structure computation and non-linear parameter optimization, are also vulnerable to additional sources of error, such as degeneracies and mathematical instability. Detection and correction of errors, along with robustness in parameter solvers, are a must in order to achieve a very accurate final scene reconstruction. However, error detection is in general difficult due to the lack of ground-truth information about the given scene, such as the absolute position of scene points or GPS/IMU coordinates for the camera(s) viewing the scene. In this dissertation, methods are presented for the detection, factorization and correction of error sources present in all stages of a scene reconstruction pipeline from video, in the …
Date: November 10, 2011
Creator: Hess-Flores, M.
System: The UNT Digital Library
Development of high-spatial and high-mass resolution mass spectrometric imaging (MSI) and its application to the study of small metabolites and endogenous molecules of plants (open access)

Development of high-spatial and high-mass resolution mass spectrometric imaging (MSI) and its application to the study of small metabolites and endogenous molecules of plants

High-spatial and high-mass resolution laser desorption ionization (LDI) mass spectrometric (MS) imaging technology was developed for the attainment of MS images of higher quality containing more information on the relevant cellular and molecular biology in unprecedented depth. The distribution of plant metabolites is asymmetric throughout the cells and tissues, and therefore the increase in the spatial resolution was pursued to reveal the localization of plant metabolites at the cellular level by MS imaging. For achieving high-spatial resolution, the laser beam size was reduced by utilizing an optical fiber with small core diameter (25 μm) in a vacuum matrix-assisted laser desorption ionization-linear ion trap (vMALDI-LTQ) mass spectrometer. Matrix application was greatly improved using oscillating capillary nebulizer. As a result, single cell level spatial resolution of ~ 12 μm was achieved. MS imaging at this high spatial resolution was directly applied to a whole Arabidopsis flower and the substructures of an anther and single pollen grains at the stigma and anther were successfully visualized. MS imaging of high spatial resolution was also demonstrated to the secondary roots of Arabidopsis thaliana and a high degree of localization of detected metabolites was successfully unveiled. This was the first MS imaging on the root for …
Date: November 30, 2011
Creator: Jun, Ji Hyun
System: The UNT Digital Library
Fabrication of metal matrix composite by semi-solid powder processing (open access)

Fabrication of metal matrix composite by semi-solid powder processing

Various metal matrix composites (MMCs) are widely used in the automotive, aerospace and electrical industries due to their capability and flexibility in improving the mechanical, thermal and electrical properties of a component. However, current manufacturing technologies may suffer from insufficient process stability and reliability and inadequate economic efficiency and may not be able to satisfy the increasing demands placed on MMCs. Semi-solid powder processing (SPP), a technology that combines traditional powder metallurgy and semi-solid forming methods, has potential to produce MMCs with low cost and high efficiency. In this work, the analytical study and experimental investigation of SPP on the fabrication of MMCs were explored. An analytical model was developed to understand the deformation mechanism of the powder compact in the semi-solid state. The densification behavior of the Al6061 and SiC powder mixtures was investigated with different liquid fractions and SiC volume fractions. The limits of SPP were analyzed in terms of reinforcement phase loading and its impact on the composite microstructure. To explore adoption of new materials, carbon nanotube (CNT) was investigated as a reinforcing material in aluminum matrix using SPP. The process was successfully modeled for the mono-phase powder (Al6061) compaction and the density and density distribution were …
Date: November 28, 2012
Creator: Wu, Yufeng
System: The UNT Digital Library
Measurement of the Branching fraction ratio B ---> D K / B ---> D pi with the CDF II detector (open access)

Measurement of the Branching fraction ratio B ---> D K / B ---> D pi with the CDF II detector

In this thesis the author has described the first measurement performed at a hadron collider of the branching fraction of the Cabibbo-suppressed mode B{sup +} {yields} {bar D}{sup 0} K{sup +}. The analysis has been performed with 360 pb{sup -1} of data collected by the CDF II detector.
Date: November 1, 2006
Creator: Squillacioti, Paola & /INFN, Pisa /Siena U.
System: The UNT Digital Library
Lifetime difference in the Bs0 system from untagged Bs0 ---> J/psi phi decay at s**(1/2) = 1.96 TeV at D0 detector (open access)

Lifetime difference in the Bs0 system from untagged Bs0 ---> J/psi phi decay at s**(1/2) = 1.96 TeV at D0 detector

In this dissertation, they present a study of the untagged decay of B{sub s}{sup 0} {yields} J/{psi}{phi}, the final state of which is a superposition of the CP-even and CP-odd states. Within the framework of the standard model (SM), to a good approximation, the two CP eigenstates of the (B{sub s}{sup 0}, {bar B}{sub s}{sup 0}) system are equivalent to mass eigenstates. The data collected by the D0 detector between June 2002 to August 2004 (an integrated luminosity of approximately 450 pb{sup -1}) has been used for the analysis presented in this thesis. From a simultaneous fit to the B{sub s}{sup 0} candidate mass, lifetime, and the angular distribution of the decay products, they obtain the CP-odd fraction in the final state at production time to be 0.16 {+-} 0.10(stat) {+-} 0.02(syst). The average lifetime of the (B{sub s}{sup 0}, {bar B}{sub s}{sup 0}) system is measured to be 1.39{sub -0.16}{sup +0.13}(stat){sub -0.02}{sup +0.01}(syst) ps, with the relative width difference between the heavy and light mass eigenstates, {Delta}{Gamma}/{bar {Gamma}} = ({Gamma}{sup L}/{Gamma}{sup H})/{bar {Gamma}} = 0.24{sub -0.38}{sup +0.28}(stat){sub -0.04}{sup +0.03}(syst). With the additional constraint from the world average of the B{sub s}{sup 0} lifetime measurements using semileptonic decays, they find …
Date: November 1, 2006
Creator: Chandra, Avdhesh & Inst., /Tata
System: The UNT Digital Library
Search for r-parity violating supersymmetry in the multilepton final state (open access)

Search for r-parity violating supersymmetry in the multilepton final state

This thesis presents a search for physics beyond the standard model of elementary particles in events containing three or more charged leptons in the final state. The search is based on an R-parity violating supersymmetric model that assumes supersymmetric particles are pair produced at hadron colliders and the R-parity violating coupling is small enough so that these particles ''cascade'' decay into the lightest supersymmetric particle. The lightest supersymmetric particle may only decay into two charged leptons (electrons or muons) plus a neutrino through a lepton number violating interaction. Proton-antiproton collision events produced with {radical} s= 1.96 TeV are collected between March 2002 and August 2004 with an integrated luminosity of 346 pb{sup -1}. R-parity violating supersymmetry is sought for in two data samples, one with exactly three leptons and one with four or more leptons. The trilepton sample has a modest background primarily from Drell-Yan events where an additional lepton is a result of photon conversions or jet misidentification while the four or more lepton sample has an extremely low background. In the three lepton samples 6 events are observed while in the four or more lepton sample zero events are observed. These results are consistent with the standard model …
Date: November 1, 2006
Creator: Attal, Alon J.
System: The UNT Digital Library