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STEM Professional Volunteers in K-12 Competition Programs: Educator Practices and Impact on Pedagogy

Description: This mixed methods dissertation study explored how secondary school educators in specific K-12 competition programs recruited and deployed STEM professional volunteers. The study explored which practices were viewed as most important, and how practices related to constructivist pedagogy, all from the viewpoint of educators. The non-positivist approach sought new knowledge without pursuing generalized results. Review of the literature uncovered extensive anecdotal information about current practices, and suggested that large investments are made in engaging volunteers. One National Science Foundation-sponsored study was identified, and its recommendations for a sustained research agenda were advanced. Three study phases were performed, one to explore practices and operationalize definitions, a second to rate practice's importance and their relation to pedagogy, and a third to seek explanations. Educators preferred recruiting local, meaning recruiting parents and former students, versus from industry or other employers. Most educators preferred volunteers with mentoring skills, and placing them in direct contact with students, versus deploying volunteers to help with behind-the-scenes tasks supporting the educator. Relationships were identified between the highest-rated practices and constructivism in programs. In STEM professional volunteers, educators see affordances, in the same way a classroom tool opens affordances. A model is proposed which shows educators considering practicality, pedagogy, knowledge and skills, and rapport when accessing the affordances opened by STEM professional volunteers. Benefits are maximized when programs align with strong industry clusters in the community.
Date: December 2016
Creator: Zintgraff, Alfred Clifton

The Museum is the Object: An Action Research Study in How Critical Theory Curriculum Influences Student Understanding of an Art Museum

Description: The purpose of this action research study was to determine how a critical theory curriculum implemented in a college-level art appreciation course impacted student understanding of an encyclopedic art museum. A critical theory-based curriculum unit was designed and implemented, and students were given assignments to assess their learning. The most significant assignment centered on a self-guided student visit to the art museum in which students made detailed observations of the museum spaces and responded to articles critiquing museum practices. These documents, together with class discussions and my personal observations, were analyzed and described in this research study. The data revealed that students had a high level of regard for and interest in art museums, were capable of understanding how history and context influences museum practices, detected multiple instances of bias in art museum galleries, and self-reported high levels of cognition and empowerment based on their experiences. The data suggested that, in college students, both art appreciation instructors and museum educators have an ideal audience in which to facilitate sustained, higher-level, critical theory-based museum learning experiences.
Date: December 2016
Creator: Elizondo, Kristina Kay

Adult Learning: Evaluation of Preferences for Technology and Learning Sources for Workplace Learning

Description: The purpose of this research was to provide an initial investigation of the preferences for both technology and learning sources that are available today in the modern workplace at a large financial institution with a national presence in the USA. In addition to the preferences of the participants, the research includes insights about the culture of the learning organization by using the Dimension of Learning Organization Questionnaire (DLOQ) and two preference surveys. The research methods used in this study are categorized as mixed methods and include both quantitative and qualitative methods. This study is nonpositivist and descriptive. It is based on a triangulation design method which is comprised of analysis from data obtained from the DLOQ and preference surveys, as well as semi-structured interviews with several survey participants. The results of the studies provide the foundational information for an extended quantitative analysis.
Date: December 2016
Creator: Kaiser, Robert Cresswell

Framework to Evaluate Entropy Based Data Fusion Methods in Supply Chain Management

Description: This dissertation explores data fusion methodology to deduce an overall inference from the data gathered from multiple heterogeneous sources. Typically, if there existed a data source in which the data were reliable and unbiased, then data fusion would not be necessary. Data fusion methodology combines data form multiple diverse sources so that the desired information - such as the population mean - is improved despite redundancies, inaccuracies, biases, and inflated variability in the data. Examples of data fusion include estimating average demand from similar sources, and integrating fatality counts from different media sources after a catastrophe. The approach in this study combines "inputs" from distinct sources so that the information is "fused." Another way of describing this process is "data integration." Important assumptions are 1. Several sources provide "inputs" for information used to estimate parameters of a probability distribution. 2. Since distributions for the data from the sources are heterogeneous, some sources are less reliable. 3. Distortions, bias, censorship, and systematic errors may be more prominent in data from certain sources. 4. The sample size of sources data, number of "inputs," may be very small. Examples of information from multiple sources are abundant: traffic information from sensors at intersections, multiple economic indicators from various sources, demand data for product using similar retail stores as sources, polling data from various sources, and disaster count of fatalities from different media sources after a catastrophic event. This dissertation seeks to address a gap in the operations literature by addressing three research questions regarding entropy base data fusion (EBDF) approaches to estimation. Three separate, but unifying, essays address the research questions for this dissertation. Essay 1 provides an overview of supporting literature for the research questions. A numerical analysis of airline maximum wait time data illustrates the underlying issues involved in EBDF methods. This ...
Date: December 2016
Creator: Tran, Huong Thi

Simulink Based Modeling of a Multi Global Navigation Satellite System

Description: The objective of this thesis is to design a model for a multi global navigation satellite system using Simulink. It explains a design procedure which includes the models for transmitter and receiver for two different navigation systems. To overcome the problem, where less number of satellites are visible to determine location degrades the performance of any positioning system significantly, this research has done to make use of multi GNSS satellite signals in one navigation receiver.
Date: December 2016
Creator: Mukka, Nagaraju

Musical Ekphrasis in the Poetry of Nicolás Guillén, Federico García Lorca, and Langston Hughes

Description: Musical ekphrasis was occurring in the twentieth century in different centers around the world, Cuba: Andalusia, Spain; and Harlem, New York, simultaneously. The writers at the heart of this movement used poetry about music as a means to celebrate the cultures of the marginalized people in their lands, los negros, los gitanos, and African-Americans. The purpose of this study is to define musical ekphrasis and identify it in the works of Nicolás Guillén, Federico García Lorca, and Langston Hughes. Also explored are the common characteristics in ekphrastic poetry by the three poets and the common themes found in their ekphrastic poetry, as well as common influences. Each author is considered in the context of his surroundings and his respective culture, and how that influenced his musical tastes as well as his writing style.
Date: December 2016
Creator: Divett, Andrew Brennan

Associations between Collaborative Learning and Personality/Cognitive Style among Online Community College Students

Description: This research study investigated associations between online community college students' personal characteristics and experiences in online courses (n = 123). Specifically, students' personalities and cognitive styles were examined alongside the perceived quality and outcomes of collaboration. Negative correlations were found between the conscientiousness personality style and both the quality of collaboration (p = .09) and the outcome of collaboration (p = .05). This finding indicates that conscientious students who, according to the literature tend to have higher academic achievement than other students, perceive negative experiences in online collaborative environments. Conversely, a positive correlation was discovered between the extraversion personality type and the perceived outcomes of collaboration (p = .01). Thus, students with a strongly extraverted personality tend to perceive that they benefits from collaborative learning. Approximately 11% of the variance in the collaborative experience was explained by the combined personal characteristics. The reported frequency of collaboration was positively correlated with both the quality (p < .01) and the outcomes of collaboration (p < .01). While not generalizable, these results suggest that not all students perceive benefits from online collaborative learning. It may be worthwhile to teach students traits associated with the extraversion type like flexibility which is important for collaborative learning. Also, teaching students to adopt traits associated with conscientiousness that improve academic achievement like self-regulation may help improve perceptions of collaborative experiences.
Date: December 2016
Creator: Sheffield, Anneliese

Assessing the Older Diabetic Population in the US: A Descriptive Look at This Population from 2001-2010 Focusing upon Education and Clinical Behaviors

Description: The focus of this research study was to gain needed information on the older adult population in the United States who have diabetes. The research method was quantitative retrospective study of American diabetes obtained from the National Health Interview Survey database from 2001 through 2010. The study results confirmed more than one-third of the U.S. diabetics are aged 65 and older. More than 75% of the older diabetic population report clinical limitations or comorbidities. Based on surrogate markers of education, it appears the older diabetic cohort did receive more preventative care visits than did the older nondiabetic population; however, the difference was not robust. I found a slight negative trend between age and emergency room visits in the older diabetic population; in addition, there was a negative association between age and smoking in this population. There continues to be a need for scientific research in this population. Greater numbers need education and more clinical trials specific to the older diabetic should be encouraged.
Date: December 2016
Creator: Parker, Patti Annette

An Evaluation of the Effects of Effort on Resistance to Change

Description: Behavioral momentum theory (BMT) has become a prominent method of studying the effects of reinforcement on operant behavior. BMT represents a departure from the Skinnerian tradition in that it identifies the strength of responding with its resistance to change. Like in many other operant research paradigms, however, responses are considered to be momentary phenomena and so little attention has been paid to non-rate dimensions of responding. The current study takes up the question of whether or not the degree of effort defining a discriminated operant class has any meaningful effect on its resistance to change. Using a force transducer, rats responded on a two-component multiple VI 60-s VI 60-s schedule where each component was correlated with a different force requirement. Resistance to change was tested through prefeeding and extinction. Proportional declines in response rate were equal across components during all disruption tests. Differentiated response classes remained intact throughout. The negative result suggests several future research directions.
Date: December 2016
Creator: Foss, Erica K

Defect Behaviors in Zinc Oxide and Zinc Titanates Ceramics from First Principles Computer Simulations

Description: ZnO and ZnO-TiO2 ceramics have intriguing electronic and mechanical properties and find applications in many fields. Many of these properties and applications rely on the understanding of defects and defect processes in these oxides as these defects control the electronic, catalytic and mechanical behaviors. The goal of this dissertation is to systematically study the defects and defects behaviors in Wurtzite ZnO and Ilmenite ZnTiO3 by using first principles calculations and classical simulations employing empirical potentials. Firstly, the behavior of intrinsic and extrinsic point defects in ZnO and ZnTiO3 ceramics were investigated. Secondly, the effect of different surface absorbents and surface defects on the workfunction of ZnO were studied using DFT calculations. The results show that increasing the surface coverage of hydrocarbons decreased the workfunction. Lastly, the stacking fault behaviors on ilmenite ZnTiO3 were investigated by calculating the Generalized Stacking Fault (GSF) energies using density functional theory based first principles calculations and classical calculations employing effective partial charge inter-atomic potentials. The gamma-surfaces of two low energy surfaces, (110) and (104), of ZnTiO3 were fully mapped and, together with other analysis such as ideal shear stress calculations.
Date: December 2016
Creator: Sun, Wei

A Multidimensional Polymetric Analysis of Excerpts from the Wind Band Music of Dan Welcher and Yo Gotō

Description: Polymetric writing is an integral technique in contemporary compositional practice. Dan Welcher and Yo Goto are principal employers of this practice in the wind band medium. Their methods endure even the results of modern scholarship showing limited human perception of polyrhythmic events. This dissertation provides a comprehensive metric analysis of excerpts from the music of Welcher and Goto. Five examples are explored from major band works of each of the two composers. The analytical process in the study utilizes the metrical concept set forth by Maury Yeston, so that a comparison can be made between the rhythmic components of the competing meters. The results of the study show that both Welcher and Goto, in all ten excerpts, create polymetric sections containing elements that surpass the aural limits proposed by modern scholarship. Additionally, through identification of the misaligned metric layers causing each polymeter, pedagogical considerations are offered to aid performance of each identified excerpt.
Date: December 2016
Creator: Robinson, David

An Evaluation of Correspondence between Preference and Performance under a Progressive Ration Schedule with College Students

Description: Preference assessments are used in clinical settings to identify stimuli with reinforcing potential. The progressive-ratio schedule has shown to be useful in clinical assessments in identifying stimuli with stronger reinforcer efficacy that corresponds to formalized assessments.The current study utilized a progressive-ratio schedule to compare videos of high and low preference assessed by verbal reports of preference with college students. Results indicated breakpoints were higher for high preferred videos than low preferred videos for three out of five participants, but preference was not indicative of performance.
Date: December 2016
Creator: Johnson, Jamarious

Ethiopian Coffee Stories: Applied Research with Sidama Coffee Farmers Combining Visual and Ethnographic Methods

Description: The purpose of this study is to demonstrate the value of visual research methods to applied anthropology in the context of exploratory research with farmers in Ethiopia. The three methods of photo-elicitation, participatory photography, and ethnographic film, enrich and expand ethnographic methods to support the client's objective of supporting farmers. The applied project constructs a narrative from the local perspective to help consumers learn more about farmers' lives. The research focuses on specific farmers, and their experiences with direct fair trade and coffee farming. The client sees the application of research produced by ethnographic and visual methods as a good direction not only for his company, but the Fair Trade Industry as a whole.
Date: December 2016
Creator: Suter, Paula Jean

Dissimilar Friction Stir Welding Between Magnesium and Aluminum Alloys

Description: Joining two dissimilar metals, specifically Mg and Al alloys, using conventional welding techniques is extraordinarily challenging. Even when these alloys are able to be joined, the weld is littered with defects such as cracks, cavities, and wormholes. The focus of this project was to use friction stir welding to create a defect-free joint between Al 2139 and Mg WE43. The stir tool used in this project, made of H13 tool steel, is of fixed design. The design included an 11 mm scrolled and concave shoulder in addition to a 6 mm length pin comprised of two tapering, threaded re-entrant flutes that promoted and amplified material flow. Upon completion of this project an improved experimental setup process was created as well as successful welds between the two alloys. These successful joints, albeit containing defects, lead to the conclusion that the tool used in project was ill fit to join the Al and Mg alloy plates. This was primarily due to its conical shaped pin instead of the more traditional cylindrical shaped pins. As a result of this aggressive pin design, there was a lack of heat generation towards the bottom of the pin even at higher (800-1000 rpm) rotation speeds. This lack of heat generation prohibited the material from reaching plastic deformation thus preventing the needed material flow to form the defect free joint.
Date: December 2016
Creator: Reese, Gregory A

Maternal Transfer of Dietary Methylmercury and Implications for Embryotoxicity in Fathead Minnows (Pimephales promelas)

Description: Mercury (Hg) is a ubiquitous environmental contaminant, which is capable of global atmospheric transport. As a result, even the most pristine aquatic ecosystems are affected by atmospheric Hg deposition, following which microbial transformation yield organic Hg forms, the most concerning of which is methylmercury (MeHg). Methylmercury is capable of bioaccumulation and biomagnification in food webs, resulting in potentially toxic body burdens due to regular dietary exposure in long-lived organisms at higher trophic levels. It is also a molecular mimic of some endogenous amino acids, providing a route of transfer from mother to offspring via large amino acid transporters. Exposure during neurodevelopment can lead to serious, irreversible neurological dysfunction, associated with a variety of cognitive and motor abnormalities across species. The present studies evaluate the effects of maternally-transferred dietary MeHg, at environmentally relevant concentrations on early life stage fathead minnows (Pimephales promelas). Embryos were collected from adult fatheads exposed to one of three diets with varying concentrations of MeHg for 30 days. Adult reproductive metrics were also monitored over the course of the study, with results indicating no effects on spawning frequency, clutch size, or total egg output. In embryos, Hg concentration was a function of female diet and the duration (number of days) of female exposure. Offspring spawned in tanks administered the low Hg diet displayed altered embryonic movement patterns (hyperactivity), decreased time to hatch, decreased mean larval size, and alterations to several metabolite abundances when compared with controls. Significantly altered metabolites include those associated with cellular energetics, fatty acid metabolism, and polyamine synthesis, indicating current environmental exposure scenarios are sufficient to disrupt important cellular pathways. Dysregulation of the dopaminergic system of embryos is also characterized, and may be a possible mechanism by which hyperactive behaviors are observed in these embryos. Offspring from tanks administered the high Hg diet exhibited ...
Date: December 2016
Creator: Bridges, Kristin

Western Spruce Budworm Effects on Throughfall C, N, and P Fluxes in a Central Washington Forest

Description: Western spruce budworm (Choristoneura occidentalis) outbreaks periodically disturb Western US conifer forests by defoliating canopies, which could alter the quantity and chemistry of throughfall delivered to the forest floor. Our objectives were to: i) quantify throughfall water, carbon (C), nitrogen (N), and phosphorus (P) fluxes under budworm-impacted canopies, and ii) examine the influence of herbivore intensity on flux magnitudes. In June 2015, we installed throughfall collectors in two watersheds experiencing high and background levels of herbivory. In each watershed, four plots, each with three throughfall collectors, were established (n=24) collectors), and two bulk rainfall collectors were installed in areas without canopy cover. Throughfall and rainfall were collected from late June to early November 2015. Samples were analyzed for dissolved organic carbon (DOC), ammonium (NH4-N), and soluble reactive phosphorus (SRP). Over the sampling period, throughfall fluxes ranged 8.57 to 47.59 kg/ha for DOC, 0.004-0.011 kg/ha for NH4-N, and 007 - 0.29 kg/ha for SRP. Percent throughfall was slightly, but not significantly, higher in the high (48%) compared to the background watershed (42%). There were no differences in solute concentrations among the watersheds. Net throughfall fluxes, the sum of canopy uptake and leaching and dry/fog deposition, differed significantly for NH4-N by herbivory level and through time for NH4-N and DOC but not SRP. Over time, net NH4-N throughfall fluxes showed a clear transition from net uptake of NH4-N to net leaching of NH4-N in the high herbivory watershed. There was also a clearn NH4-N pulse in the high herbivory watershed after the first, but not subsequent, rainfall events. In this N-limited forest, altered throughfall N may affect soil nutrient cycling and downstream water quality.
Date: December 2016
Creator: Bailey, Jennifer Meghan

Negotiated Living: An Ethno-Historical Perspective of Punta Allen

Description: Situated within the jurisdiction of the Municipality of Tulum and within the Sian Ka'an Biosphere gives the village of Punta Allen a distinctive agency in determining their role in the on-going development of tourism in the region that is not given to other communities in the state. This unique circumstance facilitates a dialogue between the reserve, the municipality, and the business cooperatives of Punta Allen that produce a negotiated living. Through the negotiations with the reserve and Tulum, the lobster fishing and tourism cooperatives are given the opportunity to have a relatively significant role in determining the future of Punta Allen in regards to tourism.
Date: December 2016
Creator: McRae, David Thomas

A Decomposition of the Group Algebra of a Hyperoctahedral Group

Description: The descent algebra of a Coxeter group is a subalgebra of the group algebra with interesting representation theoretic properties. For instance, the natural map from the descent algebra of the symmetric group to the character ring is a surjective algebra homomorphism, so the descent algebra implicitly encodes information about the representations of the symmetric group. However, this property does not hold for other Coxeter groups. Moreover, a complete set of primitive idempotents in the descent algebra of the symmetric group leads to a decomposition of the group algebra as a direct sum of induced linear characters of centralizers of conjugacy class representatives. In this dissertation, I consider the hyperoctahedral group. When the descent algebra of a hyperoctahedral group is replaced with a generalization called the Mantaci-Reutenauer algebra, the natural map to the character ring is surjective. In 2008, Bonnafé asked whether a complete set of idempotents in the Mantaci-Reutenauer algebra could lead to a decomposition of the group algebra of the hyperoctahedral group as a direct sum of induced linear characters of centralizers. In this dissertation, I will answer this question positively and go through the construction of the idempotents, conjugacy class representatives, and linear characters required to do so.
Date: December 2016
Creator: Tomlin, Drew E

Teaching Water Safety Skills to Children with Autism Using Behavioral Skills Training

Description: Behavioral skills training (BST) and in situ training (IST) have been evaluated as methods to teach different safety skills to individuals with developmental disabilities. Research on BST has examined topics such as gun safety, abduction prevention, poison avoidance, and sexual abuse prevention. A large safety issue that is missing from the literature is drowning prevention and water safety skills. Drowning is one of the most prevalent issues facing facing children with Autism Spectrum Disorder (ASD), particularly those who elope from their homes or caregivers. The current study aimed the effectiveness of using BST+IST to teach three water safety skills to three children with ASD. The intial form of intervention was BST with total task presentation of the skill, using verbal instruction, modeling, rehearsal, and feedback. If this intervention did not result in an increase in performance, the skill was broken down into individual component presentation, in which each component of the skill was taught using the same procedures. Results from the current study showed that BST+IST was effective in teaching all skills to all participants.
Date: December 2016
Creator: Tucker, Marilyse

Ion Beam Synthesis of Binary and Ternary Transition Metal Silicide Thin Films

Description: Among the well-known methods to form or modify the composition and physical properties of thin films, ion implantation has shown to be a very powerful technique. In particular, ion beam syntheses of binary iron silicide have been studied by several groups. Further, the interests in transition metal silicide systems are triggered by their potential use in advanced silicon based opto-electronic devices. In addition, ternary silicides have been by far less studied than their binary counterparts despite the fact that they have interesting magnetic and electronic properties. In this study, we investigate ion beam synthesis of Fe-Si binary structures and Fe-Co-Si ternary structures. This work involves fundamental investigation into development of a scalable synthesis process involving binary and ternary transitional metal silicide thin films and Nano-structures using low energy ion beams. Binary structures were synthesized by implanting Fe- at 50 keV energy. Since ion implantation is a dynamic process, Dynamic simulation techniques were used in these studies to determine saturation fluences for ion implantation. Also, static and dynamic simulation results were compared with experimental results. The outcome of simulations and experimental results indicate, dynamic simulation codes are more suitable than static version of the TRIM to simulate high fluence, low energy and, heavy ion implantation processes. Furthermore, binary Fe-Si phase distribution was determined at different implantation fluences and annealing temperatures. A higher fluence implantation at 2.16×1017 atoms/cm2 and annealing at 500 oC showed three different Fe-Si phase formations (β-FeSi2, FeSi and Fe3Si) in substrate. Further, annealing the samples at 800 oC for 60 minutes converted the Fe3Si phase into FeSi2 and FeSi phases. As an extension, a second set of Fe- ion implantations was carried with the same parameters while the substrate was placed under an external magnetic field. External magnetic fields stimulate the formation of magnetic phase centers in the ...
Date: December 2016
Creator: Lakshantha, Wickramaarachchige Jayampath

Analysis of Students' Knowledge, Perceptions, and Interest in Engineering Post Teacher Participation in a National Science Foundation (NSF) Research Experience for Teachers (RET) Professional Development

Description: This study examined the impact of the National Science Foundation's Research Experience for Teachers (RET) in engineering at University of North Texas on students after their teachers' participation in the program. Students were evaluated in terms of self-efficacy, knowledge of engineering, perceptions of engineering, and interest in engineering. A 22-item Likert pre/post survey was used for analysis, and participants included 589 students from six high schools, one middle school, and one magnet school. Paired surveys were analyzed to determine if there was a statistically significant difference in attitudes and knowledge after teachers implemented lessons from their time at the RET. Surveys were also analyzed to determine if there was a statistically significant difference in student response based on gender or student school type. Results showed no statistically significant difference in the self-efficacy of students, however there was a statistically significant difference in knowledge, perceptions, and interest in engineering. In addition, there was a statistically significant difference between genders on an isolated question, and seven out of the 22 Likert questions showed a statistically significant difference between student school types.
Date: December 2016
Creator: Reeder, Christina

Modeling of Fracture Toughness of Magnesium Alloy WE43 Before and After Friction Stir Processing

Description: Magnesium alloys are a popular research topic for structural applications because they have a lower density than conventional structural materials, including steel, titanium, and aluminum; however, the reliability and safety of their mechanical properties must be further proven. An important mechanical property for this purpose is fracture toughness, which is the measure of the material's resistance to crack propagation. In this study, a model of an experiment to investigate the fracture toughness of a magnesium alloy WE43 before and after friction stir processing (FSP) is developed, and the results are compared to those produced by a digital image correlation (DIC) system during an experiment from another paper. The model results of the material before FSP matched well with the DIC results, but the model of the material after FSP only partially matches the DIC results. In addition, a theoretical approach to calculating the standard fracture toughness value, KIc, from the modeling results is proposed, and is found to be a conservative approach.
Date: December 2016
Creator: Lipscomb, Celena Andrea

Women Chief Housing Officers at State Universities in the Northwest United States

Description: Hyatt, Jennifer Leigh. Women Chief Housing Officers at State Universities in the Northwest United States. Doctor of Education (Higher Education), December 2016, 89 pp., 1 table, 3 figures, 48 references, titles. This qualitative study explored the experiences of women chief housing officers (CHOs) at state universities within the northwest region of the United States. The study used narrative inquiry methodology with a thematic analysis approach to investigate how seven female CHOs experience and make meaning of their professional career progression and journey toward becoming and remaining a CHO. Five core themes emerged from the study: (a) understanding housing operations, (b) self-efficacy, (c) gender inequities, (d) relationships with staff, and (e) mentorship. The theme of gender identity suggests that gender does influence how these female CHOs make meaning of their professional experience. The overall results suggest that although the perception of many is that the field of student affairs is wide open to women, in some senior-level positions, such as CHO, gender inequity is prevalent. A factor that may contribute to this inequity is the privatization of housing which calls for a greater understanding of business and housing operations, areas dominated by males. An implication from this study is that an increase in the number of women in the CHO position may only occur when university housing personnel expand professional preparation for mid-level housing positions to include more business-related practices. The mid-level position could then be seen as a step toward desired CHO competencies and toward making the position of CHO more inclusive.
Date: December 2016
Creator: Hyatt, Jennifer

The Role of Misfit Strain and Oxygen Content on Formation and Evolution of Omega Precipitate in Metastable Beta-titanium Alloys

Description: 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, size and morphology of ω precipitates. In low misfit alloys, the ellipsoidal morphology of ω phase was retained during isothermal aging, while in high misfit alloys it changed from ellipsoidal to cuboidal morphology after prolonged aging. Secondly, ω transformation in biomedical Ti-Nb-Zr-Ta alloy is probed in which the micro-hardness was sensitive to microstructural changes. Furthermore, the evolution of oxygen concentration in ω precipitates during various aging conditions in binary Ti-Mo and Ti-V alloys are reported. It has been accepted that interstitial elements such as oxygen can largely alter mechanical behavior and the microstructure of Ti-alloys. Recently, oxygen is intentionally added ...
Date: December 2016
Creator: Hendrickson, Mandana