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The Role of Misfit Strain and Oxygen Content on Formation and Evolution of Omega Precipitate in Metastable Beta-titanium Alloys
β-Ti alloys are widely used in airframe and biomedical applications due to their high ductility, high hardenability, and low elastic modulus. The phase transformations in β-Ti alloys are rather complex due to formation of metastable phases during various thermo-mechanical treatments. One such critical metastable phase, the hexagonal omega (ω) phase, can form in β-Ti alloys under quenching from the high temperature β phase and/or isothermal aging at intermediate temperature. Despite a substantial amount of reported works on the ω phase, there are several critical issues related to the ω formation need to be resolved, e.g. role of alloying elements and oxygen content. Therefore, this dissertation has attempted to provide insights into ω transformation in low misfit (Ti-Mo) and high misfit (Ti-V) binary systems as well as multicomponent (Ti-Nb-Zr-Ta) alloys. The evolution of ω structure, morphology and composition from the early stage (β-solution+quenched) to later stages after prolonged aging are systematically investigated by coupling transmission electron microscopy (TEM), atom probe tomography (APT) and high-energy synchrotron X-ray diffraction techniques. The influence of aging temperature and duration on characteristic of ω phase in Ti-Mo, and Ti-V alloys is addressed in details. It is found that compositional changes during aging can alter the structure, …
Date:
December 2016
Creator:
Hendrickson, Mandana
System:
The UNT Digital Library
A Study of Mechanisms to Engineer Fine Scale Alpha Phase Precipitation in Beta Titanium Alloy, Beta 21S
Metastable b-Ti alloys are titanium alloys with sufficient b stabilizer alloying additions such that it's possible to retain single b phase at room temperature. These alloys are of great advantage compared to a/b alloys since they are easily cold rolled, strip produced and can attain excellent mechanical properties upon age hardening. Beta 21S, a relatively new b titanium alloy in addition to these general advantages is known to possess excellent oxidation and corrosion resistance at elevated temperatures. A homogeneous distribution of fine sized a precipitates in the parent b matrix is known to provide good combination of strength, ductility and fracture toughness. The current work focuses on a study of different mechanisms to engineer homogeneously distributed fine sized a precipitates in the b matrix. The precipitation of metastable phases upon low temperature aging and their influence on a precipitation is studied in detail. The precipitation sequence on direct aging above the w solvus temperature is also assessed. The structural and compositional evolution of precipitate phase is determined using multiple characterization tools. The possibility of occurrence of other non-classical precipitation mechanisms that do not require heterogeneous nucleation sites are also analyzed. Lastly, the influence of interstitial element, oxygen on a precipitation …
Date:
August 2013
Creator:
Behera, Amit Kishan
System:
The UNT Digital Library
Titanium Boride Formation and Its Subsequent Influence on Morphology and Crystallography of Alpha Precipitates in Titanium Alloys
Over the last two decades there has been an increased interest in understanding the influence of trace boron additions in Ti alloys. These additions refine the prior β grain size in as-cast Ti alloys along with increasing their modulus and yield strength due to the precipitation of TiB. TiB also acts as a heterogeneous nucleation site for α precipitation and has been shown to influence the α phase morphology. B is completely soluble in liquid Ti but has a negligible solubility in both body centered cubic β and hexagonal close packed α phases of Ti. Thus, during solidification of hypoeutectic B containing alloys, B is rejected from β into the liquid where it reacts with Ti to form pristine single crystal whiskers of TiB. Despite a substantial amount of reported experimental work on the characterization of TiB precipitates, its formation mechanism and influence on α phase precipitation are still not clear. The current work is divided into two parts – (i) understanding the mechanism of TiB formation using first principles based density functional theory (DFT) calculations and (ii) elucidating how TiB influences the α phase morphology and crystallography in titanium alloys using electron microscopy techniques. TiB exhibits anisotropic growth morphology …
Date:
December 2013
Creator:
Nandwana, Peeyush
System:
The UNT Digital Library
Cellular Mechanisms of Ocular Hypotensive Effects of a₂-Adrenergic Agonists
Th ocular bilateral hypotensive effect after unilateral topical administration of medetomidine and 4 analogs was demonstrated in a dose-response study (0.5%-2%) in NZW rabbits (bilateral IOP-lowering efficacy: medetomidine>detomidine and MPV-1440>MPV-1441 and MPV-305BIII).
Date:
May 1993
Creator:
Verstappen, Annita A. (Annita Apollonia)
System:
The UNT Digital Library
Phase Separation and Second Phase Precipitation in Beta Titanium Alloys
The current understanding of the atomic scale phenomenon associated with the influence of beta phase instabilities on the evolution of microstructure in titanium alloys is limited due to their complex nature. Such beta phase instabilities include phase separation and precipitation of nano-scale omega and alpha phases in the beta matrix. The initial part of the present study focuses on omega precipitation within the beta matrix of model binary titanium molybdenum (Ti-Mo) alloys. Direct atomic scale observation of pre-transition omega-like embryos in quenched alloys, using aberration-corrected high resolution scanning transmission electron microscopy and atom probe tomography (APT) was compared and contrasted with the results of first principles computations performed using the Vienna ab initio simulation package (VASP) to present a novel mechanism of these special class of phase transformation. Thereafter the beta phase separation and subsequent alpha phase nucleation in a Ti-Mo-Al ternary alloy was investigated by coupling in-situ high energy synchrotron x-ray diffraction with ex-situ characterization studies performed using aberration corrected transmission electron microscopy and APT to develop a deeper understanding of the mechanism of transformation. Subsequently the formation of the omega phase in the presence of simultaneous development of compositional phase separation within the beta matrix phase of a …
Date:
May 2011
Creator:
Devaraj, Arun
System:
The UNT Digital Library
Development of the Knowledge and Attitudes Toward Near-death Experiences Scale
The purpose of this study was to develop an instrument to measure healthcare professionals’ knowledge and attitudes about near-death experiences (NDEs) that would demonstrate acceptable psychometric properties. In consultation with a focus group of six NDE experts, I developed the 50-item Knowledge and Attitudes toward Near-Death Experiences Scale (KANDES), including the 24-item KANDES–Attitude subscale (KANDES-A) and the 26-item KANDES–Knowledge subscale (KANDES-K). Including a pilot administration in which feedback indicated no need for revision, a total of 256 professional and student counselors completed the KANDES. Separate reliability and validity analyses were conducted for each subscale. For the KANDES–A, Cronbach’s alpha was .909, and Pearson’s r for test-retest was .748, both indicating acceptable reliability. An exploratory factor analysis indicated four factors to retain and yielded a factor solution that explained 54.87% of the variance, an acceptable amount of variance to substantiate construct validity. For the KANDES–K, Cronbach’s alpha was .816, indicating acceptable reliability. For each of the scale’s three domains, Cronbach’s alpha was .816 for Domain 1: NDE Content, .817 for Domain 2: NDE Aftereffects, and .631 for Domain 3: Experiencer Characteristics, indicating acceptable reliability. Pearson’s r for test-retest on the total KANDES–K was .812, further demonstrating acceptable reliability.
Date:
August 2013
Creator:
Pace, Laura
System:
The UNT Digital Library
Laser Deposition, Heat-treatment, and Characterization of the Binary Ti-xmn System
The present research seeks to characterization of an additively manufactured and heat-treated Ti-xMn gradient alloy, a binary system that has largely been unexplored. In order to rapidly assess this binary system, compositionally graded Ti-xMn (0<x<15 wt%) specimens were fabricated using the LENS (Laser Engineered Net Shaping) and were subsequently heat-treated and characterized using a wide range of techniques. Microstructural changes with respect to the change in thermal treatments, hardness and chemical composition were observed and will be presented. These include assessments of both continuous cooling, leading to observations of both equilibrium and metastable phases, including the titanium martensites, and to direct aging studies looking for composition regimes that produce highly refined alpha precipitates – a subject of great interest given recent understandings of non-classical nucleation and growth mechanisms. The samples were characterized using SEM, EDS, TEM, and XRD and the properties probed using a Vickers Microhardness tester.
Date:
August 2013
Creator:
Avasarala, Chandana
System:
The UNT Digital Library
Combat Near-Death Experiences: An Exploratory, Mixed-Methods Study
This mixed-methods study’s purpose was a systematic comparison of contents and aftereffects of near-death experiences (NDEs) occurring in a variety of circumstances with those occurring in combat. They completed an online survey: a demographic questionnaire, the Near-Death Experience Scale, the Life Changes Inventory-Revised (LCI-R), and four narrative response items. Survey completers were 68 participants: 20 combat near-death experiencers (cNDErs) and 48 non-NDErs (nNDErs). The 29% of participants who met NDE Scale criterion for an NDE was comparable to NDE incidence findings from previous retrospective studies. For statistical analyses, significance was set at p < .05, and effect size (Cohen’s d) was calculated. Mean total NDE Scale scores were significantly lower for cNDErs than variety-of-circumstance NDErs from one of two comparable studies (t = 5.083, p < .0001, d = -1.26), possibly suggesting cNDEs may have “less depth” than other-variety NDEs. Regarding cNDE aftereffects, absence of previous LCI-R data made comparison impossible. Cronbach’s alpha analysis yielded acceptable reliability on the total scale and seven of nine subscales, a finding that matched Schneeberger’s (2010); however, factor analytic results did not support the hypothesized subscale structure of the LCI-R. Although cNDErs did not score significantly higher than nNDErs on the total scale or …
Date:
August 2011
Creator:
Goza, Tracy H.
System:
The UNT Digital Library
Effects of a Self-care Intervention for Counselors on Compassion Fatigue and Compassion Satisfaction
This study investigated the impact of a psychoeducational and experiential structured counselor self-care curriculum, developed by Drs. Charles and Kathleen Figley, on compassion fatigue and the prevention of professional impairment as measured by the Professional Quality of Life (ProQOL), Version 5. Volunteer licensed professional counselors, supervisors, and interns from four children's advocacy centers in Texas were assigned to treatment group (n = 21; 20 females, 1 male; mean age 34.4 years) or waitlist control group (n = 21; 19 females, 2 males; mean age 34.6 years). Participating counselors identified themselves ethnically as 64% Caucasian, 26% Hispanic, 7% African-American, and 2% Native-American. Employing a quasi-experimental design, three reliability-corrected analysis of covariance (ANCOVA) were utilized to analyze the data with an alpha level of .05 to assess statistical significance and partial eta squared to assess effect size. With pre-test scores as the covariate, results revealed in the experimental group a statistically significant reduction with large treatment effect for burnout (p = .01; partial ?2 = .15), a statistically nonsignificant reduction with a medium effect for secondary traumatic stress (p = .18; partial ?2 = .05), and a statistically nonsignificant increase with a medium effect for compassion satisfaction (p = .06; partial ?2= …
Date:
December 2012
Creator:
Koehler, Christine Marie Guthrie
System:
The UNT Digital Library
Precession Electron Diffraction Assisted Characterization of Deformation in α and α+β Titanium Alloys
Ultra-fine grained materials with sub-micrometer grain size exhibit superior mechanical properties when compared with conventional fine-grained material as well as coarse-grained materials. Severe plastic deformation (SPD) techniques have been shown to be an effective way to modify the microstructure in order to improve the mechanical properties of the material. Crystalline materials require dislocations to accommodate plastic strain gradients and maintain lattice continuity. The lattice curvature exists due to the net dislocation that left behind in material during deformation. The characterization of such defects is important to understand deformation accumulation and the resulting mechanical properties of such materials. However, traditional techniques are limited. For example, the spatial resolution of EBSD is insufficient to study materials processed via SPD, while high dislocation densities make interpretations difficult using conventional diffraction contrast techniques in the TEM. A new technique, precession electron diffraction (PED) has gained recognition in the TEM community to solve the local crystallography, including both phase and orientation, of nanocrystalline structures under quasi-kinematical conditions. With the assistant of precession electron diffraction coupled ASTARÔ, the structure evolution of equal channel angular pressing processed commercial pure titanium is studied; this technique is also extended to two-phase titanium alloy (Ti-5553) to investigate the existence of …
Date:
August 2015
Creator:
Liu, Yue
System:
The UNT Digital Library
Charged Particle Transport and Confinement Along Null Magnetic Curves and in Various Other Nonuniform Field Configurations for Applications in Antihydrogen Production
Comparisons between measurements of the ground-state hyperfine structure and gravitational acceleration of hydrogen and antihydrogen could provide a test of fundamental physical theories such as CPT (charge conjugation, parity, time-reversal) and gravitational symmetries. Currently, antihydrogen traps are based on Malmberg-Penning traps. The number of antiprotons in Malmberg-Penning traps with sufficiently low energy to be suitable for trappable antihydrogen production may be reduced by the electrostatic space charge of the positrons and/or collisions among antiprotons. Alternative trap designs may be needed for future antihydrogen experiments. A computational tool is developed to simulate charged particle motion in customizable magnetic fields generated by combinations of current loops and current lines. The tool is used to examine charged particle confinement in two systems consisting of dual, levitated current loops. The loops are coaxial and arranged to produce a magnetic null curve. Conditions leading to confinement in the system are quantified and confinement modes near the null curve and encircling one or both loops are identified. Furthermore, the tool is used to examine and quantify charged particle motion parallel to the null curve in the large radius limit of the dual, levitated current loops. An alternative to new trap designs is to identify the effects …
Date:
May 2016
Creator:
Lane, Ryan A.
System:
The UNT Digital Library
Establishing Criterion on a Personality-Based Assessment for Employment: A Latent Class Analysis of Faking Behavior
Personality assessments have a long history in psychology and have become the backbone of the human capital management industry, with the Big-Five model being the most prevalent. The central criticism of personality assessments for employment decisions is validity of responses since applicants for employment often endorse items to make themselves more desirable for hire, referred to as faking behavior. The present study examined faking behavior using the Assess Personality Survey (APS). Using a sample of applicant and incumbent data (N = 8,020), the objective was to identify response difference between applicant and incumbents, and the prevalence of faking behavior in applicants. Latent class analysis (LCA) was used to compare groups. Results indicate a clear distinction between applicant and incumbent response patterns. Additional analyses suggest 6 classes of testing patterns among applicants, and results are compared with previous faking identification procedures to improve criteria used to establish faking behavior in respondents.
Date:
December 2018
Creator:
Johnson, Casey W.
System:
The UNT Digital Library
Passionate transformation in vernicle images.
This thesis will examine the iconography of late-thirteenth- through fifteenth-century images of St. Veronica's veil, also known as vernicles. In the late Middle Ages, vernicle iconography changed from iconic representations of Christ's face toward graphic imagery of Christ's suffering during his Passion. These passionate transformations, as I have called them, were affected by the Roman Sudarium relic, popular devotion to Christ's suffering and humanity during his Passion, and the Catholic ritual of Mass. This thesis will consider how the function of vernicle images during Mass was reflected in their iconography throughout Europe between 1250 and 1500.
Date:
December 2004
Creator:
Hoffman, J. Starr
System:
The UNT Digital Library
Edvard Munch's Fatal Women: A Critical Approach
This study is the first comprehensive analysis of the fatal woman motif in the writings and art of Edvard Munch from the early 1890s to 1909. It uses a background of the women in the artist's life as well as the literary and artistic worlds in which Munch participated. Following separate accounts of Munch's relationships with five women, the manner in which the artist characterizes each as a fatal woman in his writings and art is discussed and analyzed. Next, the study describes the fatal woman motif in late nineteenth century art and literature. It begins with a discussion of the origin of the Symbolist and Decadent Movements and an ideological examination of the fatal woman motif as it is manifested in the writing and art of these two groups. In addition, it compares Munch's visual manifestations of the femme fatale with the manner in which the artist's contemporaries depicted her. Finally, this study describes two groups of men with whom Munch was particularly close: the Christiania Bohéme and the Schwarzen Ferkel Circle. An examination of the literary works of these men helps to determine the way in which they affected Munch's pictorial perception of the fatal woman.
Date:
December 1985
Creator:
Bimer, Barbara Susan Travitz
System:
The UNT Digital Library
A Survey of the Growth and the Development of Extra-Curricular Activities in North Texas State Teachers College, 1919-1939
"This survey of extra-curricular activates in North Texas State Teachers College from 1919 to 1939 was made to determine when and how extra-curricular activates made their appearances and developed in this institution."--v.
Date:
August 1940
Creator:
Davis, Dorothy Marie
System:
The UNT Digital Library
Attitudes of Selected Resident Undergraduate Military Veterans Toward Selected Campus Organizations at a State University
The problem of this study was to determine and report the attitudes of selected undergraduate military veterans toward selected campus organizations at North Texas State University. The purpose of this study was to provide a basis for evaluating and possibly improving the campus organizations at this university. As a result of this study, it was concluded that the majority of responding veterans had very little knowledge concerning the majority of campus organizations. It was concluded that the majority of responding veterans preferred the miscellaneous type of organizations as opposed to the national honorary and professional, departmental, and social types. It was also concluded that all the responding veterans stated the overall groups of campus organizations were between "good" and "fair," and felt they needed help from their advisors about the organizations on this campus.
Date:
May 1975
Creator:
Nelson, Bill Monta
System:
The UNT Digital Library
An Analysis and Production Book for a Staging of Jerry Bock's and Sheldon Harnick's The Apple Tree
The problem with which this study is concerned is that of critically analyzing and producing the musical comedy The Apple Tree. The study attempts to adapt some of the major unifying elements of this production and, in addition, unite the show through the use of color. The study also attempts to update the production through an extension of symbolism based on the style of Peter Max; to produce a major musical comedy in a stylized and symbolic style, and to show how a stylized and symbolic method of production can be used to achieve simplicity and unity within the confines of a limited budget.
Date:
May 1971
Creator:
Foard, Robert B.
System:
The UNT Digital Library
Academic Achievement of National Social Fraternity Pledges Compared to Non-Fraternity Students
This study examined the academic achievement of national social fraternity pledges compared to non-fraternity students at the University of Texas at Arlington. It was done to determine whether significant differences existed between the grade point averages of pledges of social fraternities and those of students who did not pledge a social fraternity, and to determine whether significant differences existed among fraternities when compared with each other with respect to academic achievement. This study was meant to provide a research design that could be used by other colleges and universities with fraternities to conduct the same comparison of academic performance. In the fall semester of 1989, 164 pledges were selected as the population for the study to be matched with non-fraternity students based on Scholastic Aptitude Test (SAT) scores, age, sex, classification, academic major, and number of hours attempted. A T-test of like groups was performed on the entire population with no significant difference found at the .05 level between all the fraternity pledges and all the matched pairs. A T-test of like groups was performed on the pledges from each separate organization and there was a significant difference among three of the fraternities. Two of the fraternities had significantly higher …
Date:
August 1990
Creator:
Gardner, Kent Lee
System:
The UNT Digital Library
The Light, for Two Narrators and Chamber Ensemble
The Light is a twenty-four minute composition for two narrators and chamber orchestra. The two narrators perform the roles of the Apostle John and Moses. After an overview of the piece and a brief history of pieces incorporating narrators, the essay focuses on my compositional process, describing how orchestration, drama, motive, and structure work together in the piece. The Light is organized as a series of five related scenes. In the first scene, God creates light. In the second scene, God places Adam and Eve into the Garden of Eden to tend it, allowing them to eat from any tree except the tree of the knowledge of good and evil. The serpent appears, Adam and Eve succumb to his evil influence, and God banishes them from the Garden of Eden. Many generations have passed when Scene Three begins. Moses relates a story from Israel's journey in the wilderness after leaving Egypt. The people had become frustrated with Moses and with God. When God sent serpents among them as punishment, they appealed to Moses to pray for them. God's answer was for Moses to make a bronze serpent and place it on a pole. Whoever looked at the serpent would live. …
Date:
May 2003
Creator:
Feezell, Mark Brandon
System:
The UNT Digital Library
History and Current State of Performance of the Literature for Solo Trombone and Organ
More than 200 compositions have been written for solo trombone and organ since the nineteenth century, including contributions from notable composers such as Franz Liszt, Gustav Holst, Gardner Read, Petr Eben, and Jan Koetsier. This repertoire represents a significant part of the solo literature for the trombone, but it is largely unknown to both trombonists and organists. The purpose of this document is to provide a historical perspective of this literature from the nineteenth century to the present, to compile a complete bibliography of compositions for trombone and organ, and to determine the current state of performance of this repertoire. This current state of performance has been determined through an internet survey, a study of recital programs printed in the ITA Journal, a study of recordings of this literature, and interviews and correspondence with well-known performers of these compositions. It is the intention of this author that this document will serve to make the repertoire for trombone and organ more accessible and more widely known to both trombonists and organists.
Date:
August 2008
Creator:
Pinson, Jr., Donald Lynn
System:
The UNT Digital Library
A Study of Nonprofit Governance through the Lens of Stewardship Theory
This dissertation examines the association between independent governance structure and various measures of good governance. The evaluation draws on observations of a dataset of 101 Texas public charities, in particular the organization's self-disclosed governance-related activities as reflected in the transparency, monitoring, and strategic tools available to the public. The study reveals that two measures of good governance are associated with an identified independent governance structure at the organizational level. In managing the governance of the organization, the study finds evidence that less emphasis is placed on the constituted strategic direction clauses listed in the articles of incorporation of the organization. The research suggests that each of the fiduciary stewardship concerns need to be addressed by the legal governing body in order to fulfill good governance as an outcome quality measure.
Date:
May 2020
Creator:
Humphrey, Duchess Deidre
System:
The UNT Digital Library
A History of the Speech and Drama Department at North Texas State University as it Relates to General Trends in Speech Education, 1890-1971
"The purpose of this study is to record an accurate account of this development at North Texas State University and to correlate it to general trends in speech education in the United States. The hypothesis for such a study is that historical comparisons may be beneficial to scholars as indicative of those methods that have met with the greatest success."--2.
Date:
August 1971
Creator:
Sandel, Mildred J.
System:
The UNT Digital Library
Construct Validation and Measurement Invariance of the Athletic Coping Skills Inventory for Educational Settings
The present study examined the factor structure and measurement invariance of the revised version of the Athletic Coping Skills Inventory (ACSI-28), following adjustment of the wording of items such that they were appropriate to assess Coping Skills in an educational setting. A sample of middle school students (n = 1,037) completed the revised inventory. An initial confirmatory factor analysis led to the hypothesis of a better fitting model with two items removed. Reliability of the subscales and the instrument as a whole was acceptable. Items were examined for sex invariance with differential item functioning (DIF) using item response theory, and five items were flagged for significant sex non-invariance. Following removal of these items, comparison of the mean differences between male and female coping scores revealed that there was no significant difference between the two groups. Further examination of the generalizability of the coping construct and the potential transfer of psychosocial skills between athletic and academic settings are warranted.
Date:
May 2017
Creator:
Sanguras, Laila Y., 1977-
System:
The UNT Digital Library
First Principles Study of Metastable Beta Titanium Alloys
The high temperature BCC phase (b) of titanium undergoes a martensitic transformation to HCP phase (a) upon cooling, but can be stabilized at room temperature by alloying with BCC transition metals such as Mo. There exists a metastable composition range within which the alloyed b phase separates into a + b upon equilibrium cooling but not when rapidly quenched. Compositional partitioning of the stabilizing element in as-quenched b microstructure creates nanoscale precipitates of a new simple hexagonal w phase, which considerably reduces ductility. These phase transformation reactions have been extensively studied experimentally, yet several significant questions remain: (i) The mechanism by which the alloying element stabilizes the b phase, thwarts its transformation to w, and how these processes vary as a function of the concentration of the stabilizing element is unclear. (ii) What is the atomistic mechanism responsible for the non-Arrhenius, anomalous diffusion widely observed in experiments, and how does it extend to low temperatures? How does the concentration of the stabilizing elements alter this behavior? There are many other w forming alloys that such exhibit anomalous diffusion behavior. (iii) A lack of clarity remains on whether w can transform to a -phase in the crystal bulk or if it …
Date:
August 2015
Creator:
Gupta, Niraj
System:
The UNT Digital Library