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Electroweak phase transitions (open access)

Electroweak phase transitions

An analytic treatment of the one Higgs doublet, electroweak phase transition is given. The phase transition is first order, occurs by the nucleation of thin walled bubbles and completes at a temperature where the order parameter, {l_angle}{phi}{r_angle}{sub T} is significantly smaller than it is when the origin becomes absolutely unstable. The rate of anomalous baryon number violation is an exponentially function of {l_angle}{phi}{r_angle}{sub T}. In very minimal extensions of the standard model it is quite easy to increase {l_angle}{phi}{r_angle}{sub T} so that anomalous baryon number violation is suppressed after completion of the phase transition. Hence baryogenesis at the electroweak phase transition is tenable in minimal of the standard model. In some cases additional phase transitions are possible. For a light Higgs boson, when the top quark mass is sufficiently large, the state where the Higgs field has a vacuum expectation value {l_angle}{phi}{r_angle} = 246 GeV is not the true minimum of the Higgs potential. When this is the case, and when the top quark mass exceeds some critical value, thermal fluctuations in the early universe would have rendered the state {l_angle}{phi}{r_angle} = 246 GeV unstable. The requirement that the state {l_angle}{phi}{r_angle} = 246 GeV is sufficiently long lived constrains the …
Date: September 16, 1991
Creator: Anderson, G. W.
System: The UNT Digital Library
Experimental determination of the loss coefficient in an annular diffuser (open access)

Experimental determination of the loss coefficient in an annular diffuser

None
Date: December 16, 1974
Creator: Angelelli, T.A.
System: The UNT Digital Library
Evaluating Radionuclide Air Emission Stack Sampling Systems (open access)

Evaluating Radionuclide Air Emission Stack Sampling Systems

The Pacific Northwest National Laboratory (PNNL) operates a number of research and development (R&D) facilities for the U.S. Department of Energy at the Hanford Site, Washington. These facilities are subject to Clean Air Act regulations that require sampling of radionuclide air emissions from some of these facilities. A revision to an American National Standards Institute (ANSI) standard on sampling radioactive air emissions has recently been incorporated into federal and state regulations and a re-evaluation of affected facilities is being performed to determine the impact. The revised standard requires a well-mixed sampling location that must be demonstrated through tests specified in the standard. It also carries a number of maintenance requirements, including inspections and cleaning of the sampling system. Evaluations were performed in 2000 – 2002 on two PNNL facilities to determine the operational and design impacts of the new requirements. The evaluation included inspection and cleaning maintenance activities plus testing to determine if the current sampling locations meet criteria in the revised standard. Results show a wide range of complexity in inspection and cleaning activities depending on accessibility of the system, ease of removal, and potential impact on building operations (need for outages). As expected, these High Efficiency Particulate Air …
Date: December 16, 2002
Creator: Ballinger, Marcel Y.
System: The UNT Digital Library
Monte Carlo Calculations on Intranuclear Cascades (open access)

Monte Carlo Calculations on Intranuclear Cascades

The basic assumption of the Serber model in the description of high- energy nuclear reactions is that the interactions of incident particles with complex nuclei can be described in terms of individual particle-particle collisions within the nucleus. Calculations were performed making use of the basic assumption of the Serber model, a more realistic nuclear model, recent cross-section data, and an exact statistical sampling technique. The sampling technique has not been used previously in calculations of this type. Calculations were performed for incident e (as Fe/sup 59 /sup +/, e (as Fe/sup 59 /sup -/, neutrons, and protons on nuclei from lithium to uranium. The energy range of the incident particles varied from about 50 to 350 Mev, i.e., the energy region in which pion production is not likely. Free-particle cross sections were used in determining the collisions within the nucleus, and statistical sampling techniques were used throughout, The problem was coded for the IBM-7090. Extensive comparisons with experiment were made and the results indicate that the calculation can be used to predict most of the cascade data for incident nucleons on complex nuclei, but only the gross features of the data are predictable for incident pions on nuclei. The effects …
Date: May 16, 1963
Creator: Bertini, H. W.
System: The UNT Digital Library
I. Excluded Volume Effects in Ising Cluster Distributions and Nuclear Multifragmentation II. Multiple-Chance Effects in Alpha-Particle Evaporation (open access)

I. Excluded Volume Effects in Ising Cluster Distributions and Nuclear Multifragmentation II. Multiple-Chance Effects in Alpha-Particle Evaporation

In Part 1, geometric clusters of the Ising model are studied as possible model clusters for nuclear multifragmentation. These clusters may not be considered as non-interacting (ideal gas) due to excluded volume effect which predominantly is the artifact of the cluster's finite size. Interaction significantly complicates the use of clusters in the analysis of thermodynamic systems. Stillinger's theory is used as a basis for the analysis, which within the RFL (Reiss, Frisch, Lebowitz) fluid-of-spheres approximation produces a prediction for cluster concentrations well obeyed by geometric clusters of the Ising model. If thermodynamic condition of phase coexistence is met, these concentrations can be incorporated into a differential equation procedure of moderate complexity to elucidate the liquid-vapor phase diagram of the system with cluster interaction included. The drawback of increased complexity is outweighted by the reward of greater accuracy of the phase diagram, as it is demonstrated by the Ising model. A novel nuclear-cluster analysis procedure is developed by modifying Fisher's model to contain cluster interaction and employing the differential equation procedure to obtain thermodynamic variables. With this procedure applied to geometric clusters, the guidelines are developed to look for excluded volume effect in nuclear multifragmentation. In part 2, an explanation is …
Date: May 16, 2005
Creator: Breus, Dimitry E.
System: The UNT Digital Library
Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy (open access)

Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy

One and two dimensional time-resolved vibrational spectroscopy has been used to investigate the elementary reactions of several prototypical organometallic complexes in room temperature solution. The electron transfer and ligand substitution reactions of photogenerated 17-electron organometallic radicals CpW(CO){sub 3} and CpFe(CO){sub 2} have been examined with one dimensional spectroscopy on the picosecond through microsecond time-scales, revealing the importance of caging effects and odd-electron intermediates in these reactions. Similarly, an investigation of the photophysics of the simple Fischer carbene complex Cr(CO){sub 5}[CMe(OMe)] showed that this class of molecule undergoes an unusual molecular rearrangement on the picosecond time-scale, briefly forming a metal-ketene complex. Although time-resolved spectroscopy has long been used for these types of photoinitiated reactions, the advent of two dimensional vibrational spectroscopy (2D-IR) opens the possibility to examine the ultrafast dynamics of molecules under thermal equilibrium conditions. Using this method, the picosecond fluxional rearrangements of the model metal carbonyl Fe(CO){sub 5} have been examined, revealing the mechanism, time-scale, and transition state of the fluxional reaction. The success of this experiment demonstrates that 2D-IR is a powerful technique to examine the thermally-driven, ultrafast rearrangements of organometallic molecules in solution.
Date: December 16, 2008
Creator: Cahoon, James Francis
System: The UNT Digital Library
Toward Femtosecond X-ray Spectroscopy at the Advanced Light Source (open access)

Toward Femtosecond X-ray Spectroscopy at the Advanced Light Source

The realization of tunable, ultrashort pulse x-ray sources promises to open new venues of science and to shed new light on long-standing problems in condensed matter physics and chemistry. Fundamentally new information can now be accessed. Used in a pump-probe spectroscopy, ultrashort x-ray pulses provide a means to monitor atomic rearrangement and changes in electronic structure in condensed-matter and chemical systems on the physically-limiting time-scales of atomic motion. This opens the way for the study of fast structural dynamics and the role they play in phase transitions, chemical reactions and the emergence of exotic properties in materials with strongly interacting degrees of freedom. The ultrashort pulse x-ray source developed at the Advanced Light Source at the Lawrence Berkeley Laboratory is based on electron slicing in storage rings, and generates {approx}100 femtosecond pulses of synchrotron radiation spanning wavelengths from the far-infrared to the hard x-ray region of the electromagnetic spectrum. The tunability of the source allows for the adaptation of a broad range of static x-ray spectroscopies to useful pump-probe measurements. Initial experiments are attempted on transition metal complexes that exhibit relatively large structural changes upon photo-excitation and which have excited-state evolution determined by strongly interacting structural, electronic and magnetic degrees …
Date: April 16, 2004
Creator: Chong, Henry Herng Wei
System: The UNT Digital Library
X-ray absorption spectroscopy on the calcium cofactor to the manganese cluster in photosynthetic oxygen evolution (open access)

X-ray absorption spectroscopy on the calcium cofactor to the manganese cluster in photosynthetic oxygen evolution

Along with Mn, calcium and chloride ions are necessary cofactors for oxygen evolution in Photosystem II (PS II). To further test and verify whether Ca is close to the Mn cluster, the authors substituted strontium for Ca and probed from the Sr point of view for any nearby Mn. The extended X-ray absorption fine structure (EXAFS) of Sr-reactivated PS II indicates major differences between the intact and NH{sub 2}OH-treated samples. In intact samples, the Fourier transform of the Sr EXAFS shows a Fourier peak that is missing in inactive samples. This peak II is best simulated by two Mn neighbors at a distance of 3.5 Angstrom, confirming the proximity of Ca (Sr) cofactor to the Mn cluster. In addition, polarized Sr EXAFS on oriented Sr-reactivated samples shows this peak II is dichroic: large magnitude at 10 degrees (angle between the PS II membrane normal and the x-ray electric field vector) and small at 80 degrees. Analysis of the dichroism yields the relative angle between the Sr-Mn vector and membrane normal (23 degrees {+-} 4 degrees), and the isotropic coordination number for these layered samples. X-ray absorption spectroscopy has also been employed to assess the degree of similarity between the manganese …
Date: December 16, 1999
Creator: Cinco, Roehl M.
System: The UNT Digital Library
Search for Rare Quark-Annihilation Decays, Charged B Mesons Decaying to Charged D(S) Mesons And Phi Mesons (open access)

Search for Rare Quark-Annihilation Decays, Charged B Mesons Decaying to Charged D(S) Mesons And Phi Mesons

The authors report on a search for the decay B{sup {+-}} {yields} D{sub s}{sup (*){+-}} {phi} using 212.2 fb{sup -1} of data collected with the BABAR detector at the PEP-II B Factory at the Stanford Linear Accelerator Center between 1999 and 2004. This sample of 234 x 10{sup 6} e{sup +}e{sup -} {yields} {Upsilon}(4S) {yields} B{bar B} events yields no significant signal. They report the Bayesian upper limits {Beta}(B{sup {+-}} {yields} D{sub s}{sup {+-}} {phi}) x {Beta}(D{sub s}{sup {+-}} {yields} {phi}{pi}{sup {+-}}) < 8.6 x 10{sup -8} and {Beta}(B{sup {+-}} {yields} D*{sub s}{sup {+-}}{phi}) x {Beta}(D{sub s}{sup {+-}} {yields} {phi}{pi}{sup {+-}}) < 5.4 x 10{sup -7} at the 90% C.L. Using the latest measurement of {Beta}(D{sub s}{sup {+-}} {yields} {phi}{pi}{sup {+-}}), they report: {Beta}(B{sup {+-}} {yields} D{sub s}{sup {+-}}{phi}) < 1.8 x 10{sup -6} and {Beta}(B{sup {+-}} {yields} D*{sub s}{sup {+-}}{phi}) < 1.1 x 10{sup -5} at the 90% C.L.
Date: January 16, 2008
Creator: Cunha, J.Adam M.
System: The UNT Digital Library
A Study of Factorization and a Measurement of CP Violation (open access)

A Study of Factorization and a Measurement of CP Violation

We report on a study of the decay {bar B}{sup 0} {yields} D*{sup +} {omega}{pi}{sup -} with the BABAR detector at the PEP-II B-factory at the Stanford Linear Accelerator Center. Based on a sample of 232 million B{sup 0}{bar B}{sup 0} decays collected between 1999 and 2004, we measure the branching fraction {Beta}({bar B}{sup 0} {yields} D*{sup +} {omega}{pi}{sup -}) = (2.88 {+-} 0.21(stat.) {+-} 0.31(syst.)) x 10{sup -3}. We study the invariant mass spectrum of the {omega}{pi}{sup -} system in this decay. This spectrum is in good agreement with expectations based on factorization and the measured spectrum in {tau}{sup -} {yields} {omega}{pi}{sup -} {nu}{sub {tau}}. We also measure the polarization of the D*{sup +} as a function of the {omega}{pi}{sup -} mass. In the mass region 1.1 to 1.9 GeV we measure the fraction of longitudinal polarization of the D*{sup +} to be {Lambda}{sub L}/{Lambda} = 0.654 {+-} 0.042(stat.) {+-} 0.016(syst.). This is in agreement with the expectations from heavy-quark effective theory and factorization assuming that the decay proceeds as {bar B}{sup 0} {yields} D*{sup +} {rho}(1450){sup -}, {rho}(1450){sup -} {yields} {omega}{pi}{sup -}. Furthermore, we present the results on the time-dependent CP asymmetry in neutral B meson decays to …
Date: January 16, 2008
Creator: Dahmes, Bryan
System: The UNT Digital Library
Virtual tool mark generation for efficient striation analysis in forensic science (open access)

Virtual tool mark generation for efficient striation analysis in forensic science

In 2009, a National Academy of Sciences report called for investigation into the scienti#12;c basis behind tool mark comparisons (National Academy of Sciences, 2009). Answering this call, Chumbley et al. (2010) attempted to prove or disprove the hypothesis that tool marks are unique to a single tool. They developed a statistical algorithm that could, in most cases, discern matching and non-matching tool marks made at di#11;erent angles by sequentially numbered screwdriver tips. Moreover, in the cases where the algorithm misinterpreted a pair of marks, an experienced forensics examiner could discern the correct outcome. While this research served to con#12;rm the basic assumptions behind tool mark analysis, it also suggested that statistical analysis software could help to reduce the examiner's workload. This led to a new tool mark analysis approach, introduced in this thesis, that relies on 3D scans of screwdriver tip and marked plate surfaces at the micrometer scale from an optical microscope. These scans are carefully cleaned to remove noise from the data acquisition process and assigned a coordinate system that mathematically de#12;nes angles and twists in a natural way. The marking process is then simulated by using a 3D graphics software package to impart rotations to the tip …
Date: November 16, 2012
Creator: Ekstrand, Laura
System: The UNT Digital Library
Scattering of Positive Pions on Protons at 310 Mev: Recoil-Nucleon Polarization and Phase-Shift Analysis (open access)

Scattering of Positive Pions on Protons at 310 Mev: Recoil-Nucleon Polarization and Phase-Shift Analysis

None
Date: September 16, 1960
Creator: Foote, J. H.
System: The UNT Digital Library
International Legal Framework for Denuclearization and Nuclear Disarmament – Present Situation and Prospects (open access)

International Legal Framework for Denuclearization and Nuclear Disarmament – Present Situation and Prospects

This thesis is the culminating project for my participation in the OECD NEA International School of Nuclear Law. This paper will begin by providing a historical background to current disarmament and denuclearization treaties. This paper will discuss the current legal framework based on current and historical activities related to denuclearization and nuclear disarmament. Then, it will propose paths forward for the future efforts, and describe the necessary legal considerations. Each treaty or agreement will be examined in respect to its requirements for: 1) limitations and implementation; 2) and verification and monitoring. Then, lessons learned in each of the two areas (limitations and verification) will be used to construct a proposed path forward at the end of this paper.
Date: December 16, 2012
Creator: Gastelum, Zoe N.
System: The UNT Digital Library
Measurement of CP Violation in B Anti-B Mixing on the Recoil of Partially Reconstructed Anti-B0 to D* L- Anti-Nu/L Using Kaon Tags (open access)

Measurement of CP Violation in B Anti-B Mixing on the Recoil of Partially Reconstructed Anti-B0 to D* L- Anti-Nu/L Using Kaon Tags

After its formulation in 1960's the Standard Model of Fundamental Interactions has gone through an impressive series of successes, begun with the discovery of neutral weak currents [1] and the experimental observations of the massive carriers of weak interactions, the W{sup {+-}} and Z{sup 0} bosons [2], [3]. High precision measurements performed at LEP and SLAC test the validity of the theory to an unprecedented level of accuracy and do not show any significant deviations with respect to the Standard Model predictions. One of the attractive features of the Standard Model is the description of the phenomena which violate the matter-antimatter symmetry (CP), and this violation uniquely depends (in the quark sector) on a weak phase in the matrix describing the couplings among different quark flavors. CP-violation was discovered in 1964 as a tiny effect in the mixing of the K{sup 0} - {bar K}{sup 0} system [12] but, after a few decades of study of the physics of K mesons, no strong confirmation of the Standard Model can be obtained on the mechanism which generates CP-violation. On the other hand the physics of B mesons is suitable for a pretty large number of measurements which can confirm or disprove …
Date: November 16, 2011
Creator: Gaz, Alessandro & U., /Padua
System: The UNT Digital Library
Measurement of the top quark pair production cross section in proton-antiproton collisions at a center of mass energy of 1.96 TeV, hadronic top decays with the D0 detector (open access)

Measurement of the top quark pair production cross section in proton-antiproton collisions at a center of mass energy of 1.96 TeV, hadronic top decays with the D0 detector

Of the six quarks in the standard model the top quark is by far the heaviest: 35 times more massive than its partner the bottom quark and more than 130 times heavier than the average of the other five quarks. Its correspondingly small decay width means it tends to decay before forming a bound state. Of all quarks, therefore, the top is the least affected by quark confinement, behaving almost as a free quark. Its large mass also makes the top quark a key player in the realm of the postulated Higgs boson, whose coupling strengths to particles are proportional to their masses. Precision measurements of particle masses for e.g. the top quark and the W boson can hereby provide indirect constraints on the Higgs boson mass. Since in the standard model top quarks couple almost exclusively to bottom quarks (t {yields} Wb), top quark decays provide a window on the standard model through the direct measurement of the Cabibbo-Kobayashi-Maskawa quark mixing matrix element V{sub tb}. In the same way any lack of top quark decays into W bosons could imply the existence of decay channels beyond the standard model, for example charged Higgs bosons as expected in two-doublet Higgs …
Date: January 16, 2009
Creator: Hegeman, Jeroen Guido
System: The UNT Digital Library
Observation of forward peaks in $pi$$sup +$n $Yields$ K$sup 0$Y*$sup +$(1385) and in related single-meson-exchange-forbidden reactions (open access)
Photodissociation spectroscopy and dynamics of free radicals, clusters, and ions (open access)

Photodissociation spectroscopy and dynamics of free radicals, clusters, and ions

The photodissociation spectroscopy and dynamics of free radicals and ions is studied to characterize the dissociative electronic states in these species. To accomplish this, a special method of radical production, based on the photodetachment of the corresponding negative ion, has been combined with the technique of fast beam photofragment translational spectroscopy. The photofragment yield as a function of photon energy is obtained, mapping out the dissociative and predissociative electronic states. Branching ratios to various product channels, the translational energy distributions of the fragments, and bond dissociation energies are then determined at selected photon energies. The detailed picture of photodissociation dynamics is provided with the aid of ab initio calculations and a statistical model to interpret the observed data. Important reaction intermediates in combustion reactions have been studied: CCO, C{sub 2}H{sub 5}O, and linear C{sub n} (n = 4--6).
Date: December 16, 1999
Creator: Hyeon, Choi
System: The UNT Digital Library
A Search for B+ to K+ Nu Anti-Nu (open access)

A Search for B+ to K+ Nu Anti-Nu

A search for the rare, flavour-changing neutral current decay B{sup +} {yields} K{sup +} {nu}{bar {nu}} is presented using 81.9 fb{sup -1} of data collected at the {Upsilon}(4S) resonance by the BABAR experiment. Signal candidate events are selected through the identification of a high momentum charged kaon and significant missing energy, where the companion B{sup -} in the event has decayed semileptonically via B{sup -} {yields} D{sup 0}{ell}{sup -}{bar {nu}} X and X is kinematically constrained to be either nothing or a low momentum transition photon or {pi}{sup 0}. The analysis was performed blind and 6 candidates were selected with a background expectation of 3.4 {+-} 1.2. This leads to a limit on the branching fraction of {Beta} (B{sup +} {yields} K{sup +} {nu}{bar {nu}}) < 7.2 x 10{sup -5} at 90% confidence level. We also search for the reaction B{sup +} {yields} {pi}{sup +}{nu}{bar {nu}} and extract a limit on the branching fraction of {Beta}(B{sup +} {yields} {pi}{sup +}{nu}{bar {nu}}) < 2.5 x 10{sup -4} at 90% confidence level.
Date: January 16, 2008
Creator: Jackson, Paul D.
System: The UNT Digital Library
Photon and Neutral Pi 0 production in (197)Au + (197)Au collisions at sqrt S(NN) = 130 GeV (open access)

Photon and Neutral Pi 0 production in (197)Au + (197)Au collisions at sqrt S(NN) = 130 GeV

Inclusive transverse momentum spectra of photons and {pi}{sup 0}s at mid-rapidity are studied as a function of collision centrality for {sup 197}Au+ {sup 197}Au collisions at {radical}s{sub NN} = 130 GeV. Photon pair conversions have been reconstructed from charged tracks measured by the main Time Project Chamber of the STAR experiment at the RHIC heavy ion facility. The transverse momentum resolution of photons with this method is estimated to be {Delta}p{sub t}/p{sub t} = 2% at 0.125 GeV/c and 5% at 2.5 GeV/c. Photon spectra were measured up to a transverse momentum of 2.4 GeV/c between {+-} 0.5 units of rapidity. The dominant photon production mechanism, the {pi}{sup 0} {yields} {gamma}{gamma} decay, was measured between 0.25-2.5 GeV/c and {+-} 1 units of rapidity. Spectra are reported for the top 11%, 11-34% and 34-85% centrality classes. It was observed that in mid-central and central collisions the relative contribution of the {pi}{sup 0} {yields} {gamma}{gamma} decay to the inclusive photon spectrum decreases above a transverse momentum of 1.65 GeV/c. In central collisions the magnitude of the decrease from p{sub t} = 1.65 GeV/c to 2.4 GeV/c is 20%. It is unlikely that contributions from other {pi}{sup 0} decay channels and other particle …
Date: September 16, 2002
Creator: Johnson, Ian J.
System: The UNT Digital Library
Single-Mode VISAR (open access)

Single-Mode VISAR

High energy-density physics (HEDP) experiments examine the properties of materials under extreme conditions. These experiments rely on the measurement of one or two velocities. These velocities are used to obtain Hugoniot relationships and thermodynamic equations of state. This methodology is referred to as 'velocimetry' and an instrument used to measure the shock wave is called a 'velocimeter' or a '(velocity) diagnostic'. The two most-widely used existing velocity diagnostics are; photonic Doppler velocimetry (PDV) and velocity interferometer system for any reflector (VISAR). PDV's advantages are a fast rise-time and ease of implementation but PDV has an upper velocity limit. Traditional implementations of VISAR have a rise time 10 times slower than PDV and are not easily implemented but are capable of measuring any velocity produced during HEDP experiments. This thesis describes a novel method of combining the positive attributes of PDV and VISAR into a more cost effective diagnostic called a Single-Mode VISAR (SMV). The new diagnostic will consist of PDV parts in a VISAR configuration. This configuration will enable the measurement of any velocity produced during shock physics experiments while the components used to build the diagnostic will give the diagnostic a fast rise time and make it easy to …
Date: November 16, 2007
Creator: Krauter, K
System: The UNT Digital Library
A Simultaneous Measurement of the Branching Fractions of Ten B to Double Charm Decays (open access)

A Simultaneous Measurement of the Branching Fractions of Ten B to Double Charm Decays

This dissertation presents a simultaneous measurement of the branching fractions of ten B {yields} D{sup (*)}{bar D}{sup (*)} decays. The measurements are derived from a sample of 2.32 x 10{sup 8} B{bar B} pairs collected by the BABAR detector at the PEP-II B Factory located at Stanford Linear Accelerator Center. The branching fractions (x 10{sup -4}) are: -0.10 {+-} 0.44 {+-} 0.15 (<0.59) for B{sup 0} {yields} D{sup 0}{bar D}{sup 0}; 1.01 {+-} 1.07 {+-} 0.35 (<2.92) for B{sup 0} {yields} D*{sup 0}{bar D}{sup 0}; -1.31 {+-} 1.05 {+-} 0.41 (<0.92) for B{sup 0} {yields} D*{sup 0}{bar D}*{sup 0}; 2.81 {+-} 0.43 {+-} 0.45 for B{sup 0} {yields} D{sup +}D{sup -}; 5.72 {+-} 0.64 {+-} 0.71 for B{sup 0} {yields} D*{sup +}D{sup -}; 8.11 {+-} 0.57 {+-} 0.97 for B{sup 0} {yields} D*{sup +}D*{sup -}; 3.76 {+-} 0.57 {+-} 0.45 for B{sup -} {yields} D{sup -}D{sup 0}; 3.56 {+-} 0.52 {+-} 0.39 for B{sup -} {yields} D*{sup -}D{sup 0}; 6.30 {+-} 1.32 {+-} 0.93 for B{sup -} {yields} D{sup -}D*{sup 0}; and 8.14 {+-} 1.17 {+-} 1.11 for B{sup -} {yields} D*{sup -}D*{sup 0}. The first uncertainty is statistical while the second is systematic. The number in parentheses is the …
Date: January 16, 2008
Creator: Lae, Chung Khim
System: The UNT Digital Library
Measuring the Weak Charge of the Proton and the Hadronic Parity Violation of the N -> {Delta} Transition (open access)

Measuring the Weak Charge of the Proton and the Hadronic Parity Violation of the N -> {Delta} Transition

Qweak will determine the weak charge of the proton, Q{sup p}{sub W}, via an asymmetry measurement of parity-violating elastic electron-proton scattering at low four momentum transfer to a precision of 4%. Q{sup p}{sub W} has a firm Standard Model prediction and is related to the weak mixing angle, sin{sup 2} {Theta}{sub W}, a well-defined Standard Model parameter. Qweak will probe a subset of new physics to the TeV mass scale and test the Standard Model. The details of how this measurement was performed and the analysis of the 25% elastic dataset will be presented in this thesis. Also, an analysis of an auxiliary measurement of the parity-violating asymmetry in the N -> {Delta} transition is presented. It is used as a systematic inelastic background correction in the elastic analysis and to extract information about the hadronic parity violation through the low energy constant, d{sub Delta}. The elastic asymmetry at Q{sup 2} = 0.0252 ± 0.0007 GeV{sup 2} was measured to be A{sub ep} = -265 ± 40 ± 22 ± 68 ppb (stat., sys., and blinding). Extrapolated to Q{sup 2} = 0, the value of the proton's weak charge was measured to be Q{sup p}{sub W} = 0.077 ± 0.019 …
Date: October 16, 2012
Creator: Leacock, John
System: The UNT Digital Library
Fabrication of Yttria stabilized zirconia thin films on poroussubstrates for fuel cell applications (open access)

Fabrication of Yttria stabilized zirconia thin films on poroussubstrates for fuel cell applications

A process for the deposition of yttria stabilized zirconia (YSZ) films, on porous substrates, has been developed. These films have possible applications as electrolyte membranes in fuel cells. The films were deposited from colloidal suspensions through the vacuum infiltration technique. Films were deposited on both fully sintered and partially sintered substrates. A critical cracking thickness for the films was identified and strategies are presented to overcome this barrier. Green film density was also examined, and a method for improving green density by changing suspension pH and surfactant was developed. A dependence of film density on film thickness was observed, and materials interactions are suggested as a possible cause. Non-shorted YSZ films were obtained on co-fired substrates, and a cathode supported solid oxide fuel cell was constructed and characterized.
Date: June 16, 2003
Creator: Leming, Andres
System: The UNT Digital Library
Growth of a Au-Ni-Sn intermetallic compound on the solder-substrate interface after aging (open access)

Growth of a Au-Ni-Sn intermetallic compound on the solder-substrate interface after aging

Au/Ni metallization has become increasingly common in microelectronic packaging when Cu pads are joined with Pb-Sn solder. The outermost Au layer serves to protect the pad from corrosion and oxidation and the Ni layer provides a diffusion barrier to inhibit detrimental growth of Cu-Sn intermetallics. As a result of reflowing eutectic Pb-Sn on top of Au/Ni metallization, the as-solidified joints have AuSn{sub 4} precipitates distributed throughout the bulk of the solder joint, and Ni{sub 3}Sn{sub 4} intermetallics at the interface. Recent work has shown that the Au-Sn redeposits onto the interface during aging, compromising the strength of the joint. The present work shows that the redeposited intermetallic layer is a ternary compound with stoichiometry Au{sub 0.5}Ni{sub 0.5}Sn{sub 4}. The growth of this intermetallic layer was investigated, and results show that the ternary compound is observed to grow after as little as 3 hours at 150 C and after 3 weeks at 150 C has grown to a thickness of 10 {micro}m. Additionally, methods for inhibiting the growth of the ternary layer were investigated and it was determined that multiple reflows, both with and without additional aging can substantially limit the thickness of the ternary layer.
Date: December 16, 1999
Creator: Minor, Andrew M. & Morris, J. W., Jr.
System: The UNT Digital Library