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480 Matching Results
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Laser Processing of Metals and Polymers
A laser offers a unique set of opportunities for precise delivery of high quality coherent energy. This energy can be tailored to alter the properties of material allowing a very flexible adjustment of the interaction that can lead to melting, vaporization, or just surface modification. Nowadays laser systems can be found in nearly all branches of research and industry for numerous applications. Sufficient evidence exists in the literature to suggest that further advancements in the field of laser material processing will rely significantly on the development of new process schemes. As a result they can be applied in various applications starting from fundamental research on systems, materials and processes performed on a scientific and technical basis for the industrial needs. The interaction of intense laser radiation with solid surfaces has extensively been studied for many years, in part, for development of possible applications. In this thesis, I present several applications of laser processing of metals and polymers including polishing niobium surface, producing a superconducting phase niobium nitride and depositing thin films of niobium nitride and organic material (cyclic olefin copolymer). The treated materials were examined by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), atomic force microscopy (AFM), high resolution …
Date:
May 31, 2012
Creator:
Singaravelu, Senthilraja
System:
The UNT Digital Library
Precision Measurement of Electroproduction of pi{sup 0} near Threshold
Electromagnetic production of neutral pions near threshold is the most basic, lowest energy reaction in which a new hadron is created. The electromagnetic interaction is well understood so measurements of this reaction can yield direct insight into the hadronic production mechanism. During the past three decades there have been many developments in both the measurement and theory of threshold pion production, starting with measurements of photo-production at Saclay in 1986 and at Mainz in 1990. These measurements indicated a surprising discrepancy with so-called Low Energy Theorems (LETs) which are based on quite fundamental symmetries and considerations. Chiral Perturbation Theory (ChPT) is an e#11;ective #12;eld theoretic description of the nuclear force which contains the underlying symmetries of the force but deals with nucleons and pions rather than quarks and gluons. It has the advantage of being applicable at low energies but requires tuning some parameters to experimental data. Once these parameters have been determined ChPT predicts how the reaction should behave as a function of the kinematic variable. When applied to the reaction, p({gamma},{pi}{sup 0})p, near threshold it explained the discrepancy with the LETs and made predictions for electroproduction, p(e,e'p){pi}#25;{sup 0}. Electroproduction measurements at Mainz in the 1990's showed a clear …
Date:
May 1, 2012
Creator:
Chirapatpimol, Khem
System:
The UNT Digital Library
Controlling atomistic processes on Pb films via quantum size effects and lattice rotation
The two main techniques used to record the data in this dissertation were Spot Profile Analysis - Low Energy Electron Diffraction (SPA-LEED) and Scanning Tunneling Microscopy (STM). A specific data analysis technique for LEED data called G(S) curves is described in depth. G(S) curves can provide a great deal of structural information about the surface; including step heights, island size, and island separation. The effects of quantum size effects (QSE) on the diffusion and critical island sizes of Pb and In on Pb #12;films are reported. Pb depositions on the 2D In phases {radical}3 and {radical}31 to see how the phases affect the Pb growth and its strong QSE are reported.
Date:
June 14, 2012
Creator:
Binz, Steven
System:
The UNT Digital Library
First observation of the Charmless Decay B to K pi0pi0 and Study of its Dalitz Plot Structure
Results for the first measurement of the inclusive branching and CP asymmetry of the charmless 3-body decay B{sup +} {yields} K{sup +}{pi}{sup 0}{pi}{sup 0} are presented. The analysis uses a data sample with an integrated luminosity of 429.0 fb{sup -1}, recorded by the BABAR detector at the PEP-II asymmetric B Factory. This sample corresponds to 470.9 {+-} 2.8 million B{bar B} pairs. Measurements of the branching fractions (B) and CP asymmetries (A{sub CP}) of some of the intermediate resonances in the K{sup +}{pi}{sup 0}{pi}{sup 0} Dalitz plot are also presented.
Date:
March 21, 2012
Creator:
Puccio, Eugenia Maria Teresa Irene & /SLAC, /Warwick U.
System:
The UNT Digital Library
Structural and magnetic properties and superconductivity in Ba(Fe{sub 1-x}TM{sub x}){sub 2}As{sub 2}
We studied the effects on structural and magnetic phase transitions and the emergence of superconductivity in transition metal substituted BaFe{sub 2}As{sub 2}. We grew four series of Ba(Fe{sub 1-x}TM{sub x}){sub 2}As{sub 2} (TM=Ru, Mn, Co+Cr and Co+Mn) and characterized them by crystallographic, magnetic and transport measurements. We also subjected Ba(Fe{sub 1-x}Cr{sub x}){sub 2}As{sub 2} and Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} to heat treatment to explore what changes might be induced.
Date:
July 23, 2012
Creator:
Thaler, Alexander
System:
The UNT Digital Library
First principles analysis of lattice dynamics for Fe-based superconductors and entropically-stabilized phases
Modern calculations are becoming an essential, complementary tool to inelastic x-ray scattering studies, where x-rays are scattered inelastically to resolve meV phonons. Calculations of the inelastic structure factor for any value of Q assist in both planning the experiment and analyzing the results. Moreover, differences between the measured data and theoretical calculations help identify important new physics driving the properties of novel correlated systems. We have used such calculations to better and more e#14;ciently measure the phonon dispersion and elastic constants of several iron pnictide superconductors. This dissertation describes calculations and measurements at room temperature in the tetragonal phase of CaFe{sub 2}As{sub 2} and LaFeAsO. In both cases, spin-polarized calculations imposing the antiferromagnetic order present in the low-temperature orthorhombic phase dramatically improves the agreement between theory and experiment. This is discussed in terms of the strong antiferromagnetic correlations that are known to persist in the tetragonal phase. In addition, we discuss a relatively new approach called self-consistent ab initio lattice dynamics (SCAILD), which goes beyond the harmonic approximation to include phonon-phonon interactions and produce a temperature-dependent phonon dispersion. We used this technique to study the HCP to BCC transition in beryllium.
Date:
July 20, 2012
Creator:
Hahn, Steven
System:
The UNT Digital Library
A Comparison of "Total Dust" and Inhalable Personal Sampling for Beryllium Exposure.
In 2009, the American Conference of Governmental Industrial Hygienists (ACGIH) reduced the Beryllium (Be) 8-hr Time Weighted Average Threshold Limit Value (TLV-TWA) from 2.0 {micro}g/m{sup 3} to 0.05 {micro}g/m{sup 3} with an inhalable 'I' designation in accordance with ACGIH's particle size-selective criterion for inhalable mass. Currently, per the Department of Energy (DOE) requirements, the Lawrence Livermore National Laboratory (LLNL) is following the Occupational Health and Safety Administration (OSHA) Permissible Exposure Limit (PEL) of 2.0 {micro}g/m{sup 3} as an 8-hr TWA, which is also the 2005 ACGIH TLV-TWA, and an Action Level (AL) of 0.2 {micro}g/m{sup 3} and sampling is performed using the 37mm (total dust) sampling method. Since DOE is considering adopting the newer 2009 TLV guidelines, the goal of this study was to determine if the current method of sampling using the 37mm (total dust) sampler would produce results that are comparable to what would be measured using the IOM (inhalable) sampler specific to the application of high energy explosive work at LLNL's remote experimental test facility at Site 300. Side-by-side personal sampling using the two samplers was performed over an approximately two-week period during chamber re-entry and cleanup procedures following detonation of an explosive assembly containing Beryllium (Be). …
Date:
April 25, 2012
Creator:
Carter, C. M.
System:
The UNT Digital Library
Computational fluid dynamic modeling of fluidized-bed polymerization reactors
Polyethylene is one of the most widely used plastics, and over 60 million tons are produced worldwide every year. Polyethylene is obtained by the catalytic polymerization of ethylene in gas and liquid phase reactors. The gas phase processes are more advantageous, and use fluidized-bed reactors for production of polyethylene. Since they operate so close to the melting point of the polymer, agglomeration is an operational concern in all slurry and gas polymerization processes. Electrostatics and hot spot formation are the main factors that contribute to agglomeration in gas-phase processes. Electrostatic charges in gas phase polymerization fluidized bed reactors are known to influence the bed hydrodynamics, particle elutriation, bubble size, bubble shape etc. Accumulation of electrostatic charges in the fluidized-bed can lead to operational issues. In this work a first-principles electrostatic model is developed and coupled with a multi-fluid computational fluid dynamic (CFD) model to understand the effect of electrostatics on the dynamics of a fluidized-bed. The multi-fluid CFD model for gas-particle flow is based on the kinetic theory of granular flows closures. The electrostatic model is developed based on a fixed, size-dependent charge for each type of particle (catalyst, polymer, polymer fines) phase. The combined CFD model is first verified …
Date:
November 2, 2012
Creator:
Rokkam, Ram
System:
The UNT Digital Library
United abominations: Density functional studies of heavy metal chemistry
Carbonyl and nitrile addition to uranyl (UO{sup 2}{sup 2+}) are studied. The competition between nitrile and water ligands in the formation of uranyl complexes is investigated. The possibility of hypercoordinated uranyl with acetone ligands is examined. Uranyl is studied with diactone alcohol ligands as a means to explain the apparent hypercoordinated uranyl. A discussion of the formation of mesityl oxide ligands is also included. A joint theory/experimental study of reactions of zwitterionic boratoiridium(I) complexes with oxazoline-based scorpionate ligands is reported. A computational study was done of the catalytic hydroamination/cyclization of aminoalkenes with zirconium-based catalysts. Techniques are surveyed for programming for graphical processing units (GPUs) using Fortran.
Date:
April 2, 2012
Creator:
Schoendorff, George
System:
The UNT Digital Library
Beam Size Measurement by Optical Diffraction Radiation and Laser System for Compton Polarimeter
Beam diagnostics is an essential constituent of any accelerator, so that it is named as "organs of sense" or "eyes of the accelerator." Beam diagnostics is a rich field. A great variety of physical effects or physical principles are made use of in this field. Some devices are based on electro-magnetic influence by moving charges, such as faraday cups, beam transformers, pick-ups; Some are related to Coulomb interaction of charged particles with matter, such as scintillators, viewing screens, ionization chambers; Nuclear or elementary particle physics interactions happen in some other devices, like beam loss monitors, polarimeters, luminosity monitors; Some measure photons emitted by moving charges, such as transition radiation, synchrotron radiation monitors and diffraction radiation-which is the topic of the first part of this thesis; Also, some make use of interaction of particles with photons, such as laser wire and Compton polarimeters-which is the second part of my thesis. Diagnostics let us perceive what properties a beam has and how it behaves in a machine, give us guideline for commissioning, controlling the machine and indispensable parameters vital to physics experiments. In the next two decades, the research highlight will be colliders (TESLA, CLIC, JLC) and fourth-generation light sources (TESLA FEL, …
Date:
December 31, 2012
Creator:
Liu, Chuyu
System:
The UNT Digital Library
Measurement of the D_s Decay Constant f_Ds and Observation of New Charm Resonances Decaying to D^(*)\pi
The absolute branching fractions for the decays D{sub s}{sup -} {yields} {ell}{sup -}{bar {nu}}{sub {ell}} ({ell} = e, {mu}, or {tau}) are measured using a data sample corresponding to an integrated luminosity of 521 fb{sup -1} collected at center of mass energies near 10.58 GeV with the BABAR detector at the PEPII e{sup +}e{sup -} collider at SLAC. The number of D{sub s}{sup -} mesons is determined by reconstructing the recoiling system DKX{gamma} in events of the type e{sup +}e{sup -} {yields} DKXD*{sub s}{sup -}, where D*{sub s}{sup -} {yields} D{sub s}{sup -} {gamma} and X represents additional pions from fragmentation. The D{sub s}{sup -} {yields} {ell}{sup -}{nu}{sub {ell}} events are detected by full or partial reconstruction of the recoiling system DKX{gamma}{ell}. The following results are obtained: {Beta}(D{sub s}{sup -} {yields} {mu}{sup -}{nu}) = (6.02 {+-} 0.38 {+-} 0.34) x 10{sup -3}, {Beta}(D{sub s}{sup -} {yields} {tau}{sup -}{nu}) = (5.00 {+-} 0.35 {+-} 0.49) x 10{sup -2}, and B(D{sub s}{sup -} {yields} e{sup -}{nu}) < 2.8 x 10{sup -4} at 90% C.L., where the first uncertainty is statistical and the second is systematic. The branching fraction measurements are combined to determine the D{sub s}{sup -} decay constant f{sub D{sub s}} …
Date:
March 15, 2012
Creator:
Benitez, Jose
System:
The UNT Digital Library
Much Ado about Microbunching: Coherent Bunching in High Brightness Electron Beams
The push to provide ever brighter coherent radiation sources has led to the creation of correspondingly bright electron beams. With billions of electrons packed into normalized emittances (phase space) below one micron, collective effects may dominate both the preservation and use of such ultra-bright beams. An important class of collective effects is due to density modulations within the bunch, or microbunching. Microbunching may be deleterious, as in the case of the Microbunching Instability (MBI), or it may drive radiation sources of unprecedented intensity, as in the case of Free Electron Lasers (FELs). In this work we begin by describing models of microbunching due to inherent beam shot noise, which sparks both the MBI as well as SLAC's Linac Coherent Light Source, the world's first hard X-ray laser. We first use this model to propose a mechanism for reducing the inherent beam shot noise as well as for predicting MBI effects. We then describe experimental measurements of the resulting microbunching at LCLS, including optical radiation from the MBI, as well as the first gain length and harmonic measurements from a hard X-ray FEL. In the final chapters, we describe schemes that use external laser modulations to microbunch light sources of the …
Date:
May 25, 2012
Creator:
Ratner, Daniel & /SLAC, /Stanford U.
System:
The UNT Digital Library
Paralization and check pointing of GPU applications through program transformation
GPUs have emerged as a powerful tool for accelerating general-purpose applications. The availability of programming languages that makes writing general-purpose applications for running on GPUs tractable have consolidated GPUs as an alternative for accelerating generalpurpose applications. Among the areas that have bene#12;ted from GPU acceleration are: signal and image processing, computational uid dynamics, quantum chemistry, and, in general, the High Performance Computing (HPC) Industry. In order to continue to exploit higher levels of parallelism with GPUs, multi-GPU systems are gaining popularity. In this context, single-GPU applications are parallelized for running in multi-GPU systems. Furthermore, multi-GPU systems help to solve the GPU memory limitation for applications with large application memory footprint. Parallelizing single-GPU applications has been approached by libraries that distribute the workload at runtime, however, they impose execution overhead and are not portable. On the other hand, on traditional CPU systems, parallelization has been approached through application transformation at pre-compile time, which enhances the application to distribute the workload at application level and does not have the issues of library-based approaches. Hence, a parallelization scheme for GPU systems based on application transformation is needed. Like any computing engine of today, reliability is also a concern in GPUs. GPUs are vulnerable …
Date:
November 15, 2012
Creator:
Solano-Quinde, Lizandro Dami#19 & Laboratory], an
System:
The UNT Digital Library
Between Comancheros and Comanchería: a History of Fort Bascom, New Mexico
In 1863, Fort Bascom was built along the Canadian River in the Eroded Plains of Territorial New Mexico. Its unique location placed it between the Comanches of Texas and the Comancheros of the Sangre de Cristo Mountains. This post was situated within Comanchería during the height of the United States Army's war against the Southern Plains Indians, yet it has garnered little attention. This study broadens the scholarly understanding of how the United States Army gained control of the Southwest by examining the role Fort Bascom played in this mission. This includes an exploration of the Canadian River Valley environment, an examination of the economic relationship that existed between the Southern Plains Indians and the mountain people of New Mexico, and an account of the daily life of soldiers posted to Fort Bascom. This dissertation thus provides an environmental and cultural history of the Canadian River Valley in New Mexico, a social history of the men stationed at Fort Bascom, and proof that the post played a key role in the Army's efforts to gain control of the Southern Plains Indians. This study argues that Fort Bascom should be recognized as Texas' northern-most frontier fort. Its men were closer to …
Date:
August 2012
Creator:
Blackshear, James Bailey
System:
The UNT Digital Library
A Cell-Centered Multiphase ALE Scheme With Structural Coupling
None
Date:
January 17, 2012
Creator:
Dunn, T. A.
System:
The UNT Digital Library
Predictors of College Readiness: an Analysis of the Student Readiness Inventory
The purpose of this study was to better predict how a first semester college freshman becomes prepared for college. the theoretical framework guiding this study is Vrooms’ expectancy theory, motivation plays a key role in success. This study used a hierarchical multiple regression model. the independent variables of interest included high school percentile class rank, composite ACT scores, composite SAT scores, and the 10 themes as measured by the Student Readiness Inventory (SRI) to address two research questions: What are the psychosocial factors identified by the SRI are most relevant in predicting college success? What conventional academic indicators are most relevant in predicting college success? the sample size for this study was 5279 (n), including a stratified random sample of first semester college freshman enrolled in credit bearing courses; these participants were deemed college ready by the university. Academic Discipline accounted for 4.2% of the variance in first semester college GPA, General Determination accounted for 1.7% of the variance, and the remaining psychosocial factors of the SRI accounted for less than 1% of the variance. High school percentile class rank accounted for 10.7% of the variance, composite ACT accounted for 5.9% of the variance, and composite SAT accounted for 5.6% …
Date:
May 2012
Creator:
Wilson, James K., III
System:
The UNT Digital Library
Equivalence Classes of Subquotients of Pseudodifferential Operator Modules on the Line
Certain subquotients of Vec(R)-modules of pseudodifferential operators from one tensor density module to another are categorized, giving necessary and sufficient conditions under which two such subquotients are equivalent as Vec(R)-representations. These subquotients split under the projective subalgebra, a copy of ????2, when the members of their composition series have distinct Casimir eigenvalues. Results were obtained using the explicit description of the action of Vec(R) with respect to this splitting. In the length five case, the equivalence classes of the subquotients are determined by two invariants. In an appropriate coordinate system, the level curves of one of these invariants are a pencil of conics, and those of the other are a pencil of cubics.
Date:
August 2012
Creator:
Larsen, Jeannette M.
System:
The UNT Digital Library
Lind, James Meyer the Trumpet Concertos of Anthony Plog: a Performer’s Guide
Anthony Plog (b. 1947) has contributed several notable works for brass instruments. He is known for writing extremely technically challenging works that contain angular melodies, fast rhythms and a large degree of chromaticism. Though his music is difficult, it also conveys intense emotions. His music for trumpet, specifically Concerto no. 1 for Trumpet, Brass Ensemble and Percussion and Concerto no. 2 for Trumpet and Orchestra, represents a zenith in his compositional development. This dissertation examines Concerto no. 1 and Concerto no. 2 from a performer’s perspective to better understand the stylistic characteristics and challenges encountered in his music. Each concerto is examined in terms of rhythmic structure, intervallic structure, thematic material, motivic material and form.
Date:
August 2012
Creator:
Lind, James Meyer
System:
The UNT Digital Library
“The Way It Goes”: Stories
This collection of short stories attempts to examine the role of a changing and often indifferent world has in the way various characters achieve maturity. Though the past is not always obvious in each story, each protagonist is characterized as holding onto some aspect of his or her past life in a way that is detrimental to their growing as human beings. the stories attempt to portray the indifference of the world as it moves forward to the plight of these characters, and to portray the manner in which they each come to terms with such a world and with their own lives.
Date:
May 2012
Creator:
Wood, Joshua
System:
The UNT Digital Library
Implementing a Physical Activity Centered Education Program for Individuals with Brain Injury
Research has shown that health promotion programs (HPP) that incorporate education about physical activity (PA) are one mode of rehabilitation that can improve the health of individuals with disabilities. However, education-based PA curriculum is not included in the rehabilitation program for individuals with a brain injury, indicating a gap in services provided. Consequently, the purpose of this study was to create and deliver a physical activity centered education (PACE) program that supplemented the existing rehabilitation program for brain injury. PACE consists of an 8-week (16 session) program aimed to (1) increase self-efficacy for being physically active of PACE program participants, (2) increase PA stage of change in PACE program participants or the maintenance of adequate level of PA, and (3) improve the rehabilitation outcomes (i.e., abilities, participation, adjustment) of PACE program participants. Based on previous research, it is hypothesized that participation in PACE will result in (1A) increased self-efficacy for PA, (1B) greater self-efficacy for PA than the standard of care group, (2A) increased readiness to be physically active, (2B) greater readiness to change their PA behavior than the standard of care group, (3A) improved rehabilitation outcomes, and (3B) greater rehabilitation outcomes than the standard of care group. the PACE …
Date:
May 2012
Creator:
Woolsey, Anne-Lorraine T.
System:
The UNT Digital Library
Performance Rights in Sound Recordings: the Impact of the Performance Rights Act on Radio, Records, and Performing Artists
The original works of copyright holders included tangible creations, as music written on a page, thereby, extending copyright protection to songwriters and music publishers. Until 1995, absent from U.S. copyright law was protection for copyright owners of intangible sound recordings. the Performance Rights Act (PRA) seeks to amend the US copyright law in order to grant copyright holders of sound recordings the right to performance royalties from terrestrial broadcast radio. If passed, the legislation would be unprecedented in the United States. the PRA has implications for broadcast radio, record labels, and performing artists. This study includes historical and legal perspective of previous attempts at legislation of this nature and predicts outcomes of current legislation.
Date:
May 2012
Creator:
Wright-Harmon, Joy
System:
The UNT Digital Library
Repression, Civic Engagement, Internet Use, and Dissident Collective Action: the Interaction Between Motives and Resources
This dissertation investigates three questions: First, what conditions make dissident collective action such as protest, revolt, rebellion, or civil war more likely to happen in a country? Second, what conditions make citizens more likely to join in dissident collective action? Third, does Internet use play a role in dissident collective action, and if so, why? I argue that motives and resources are necessary rather than sufficient conditions for dissident collective action. I develop an analytical framework integrating motives and resources. Specifically, I theorize that state repression is an important motive, and that civil society is critical in providing resources. Four statistical analyses are conducted to test the hypotheses. Using aggregate level data on countries over time, I find that civil war is more likely to occur in countries where both state repression and civil society are strong. Moreover, the effect of civil society on civil war onset increases as the repression level rises. at the individual level using 2008 Latin American Public Opinion Project surveys from 23 Latin American and Caribbean countries, I find individuals more likely to join in protest when they experience both more repression and greater civic engagement. Moreover, civic engagement’s effect on protest participation increases as …
Date:
May 2012
Creator:
Wu, Jun-deh
System:
The UNT Digital Library
My Land, My Life
My Land, My Life is a documentary film about the woman, Jo Angela Lamb, who lives and works on Frying Pan Ranch in Texas Panhandle. the film explores the complexity of a ranch woman's experience that breaks the spell of the stereotyped image of American cowgirls. It also reflects on women ranchers’ relationship with their family members and their relationship with the land.
Date:
May 2012
Creator:
Zhang, Mingyun
System:
The UNT Digital Library
“What Are You?”: Racial Ambiguity and the Social Construction of Race in the Us
This dissertation is a qualitative study of racially ambiguous people and their life experiences. Racially ambiguous people are individuals who are frequently misidentified racially by others because they do not resemble the phenotype associated with the racial group to which they belong or because they belong to racial/ethnic groups originating in different parts of the world that resemble each other. the racial/ethnic population of the United States is constantly changing because of variations in the birth rates among the racial/ethnic groups that comprise those populations and immigration from around the world. Although much research has been done that documents the existence of racial/ethnic mixing in the history of the United States and the world, this multiracial history is seldom acknowledged in the social, work, and other spheres of interaction among people in the U.S., instead a racialized system based on the perception of individuals as mono-racial thus easily identified through (skin tone, hair texture, facial features, etc.). This is research was done using life experience interviews with 24 racially ambiguous individuals to determine how race/ethnicity has affected their lives and how they negotiate the minefield of race.
Date:
May 2012
Creator:
Smith, Starita
System:
The UNT Digital Library