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9-Lipoxygenase Oxylipin Pathway in Plant Response to Biotic Stress
The activity of plant 9-lipoxygenases (LOXs) influences the outcome of Arabidopsis thaliana interaction with pathogen and insects. Evidence provided here indicates that in Arabidopsis, 9-LOXs facilitate infestation by Myzus persicae, commonly known as the green peach aphid (GPA), a sap-sucking insect, and infection by the fungal pathogen Fusarium graminearum. in comparison to the wild-type plant, lox5 mutants, which are deficient in a 9-lipoxygenase, GPA population was smaller and the insect spent less time feeding from sieve elements and xylem, thus resulting in reduced water content and fecundity of GPA. LOX5 expression is induced rapidly in roots of GPA-infested plants. This increase in LOX5 expression is paralleled by an increase in LOX5-synthesized oxylipins in the root and petiole exudates of GPA-infested plants. Micrografting experiments demonstrated that GPA population size was smaller on plants in which the roots were of the lox5 mutant genotype. Exogenous treatment of lox5 mutant roots with 9-hydroxyoctadecanoic acid restored water content and population size of GPA on lox5 mutants. Together, these results suggest that LOX5 genotype in roots is critical for facilitating insect infestation of Arabidopsis. in Arabidopsis, 9-LOX function is also required for facilitating infection by F. graminearum, which is a leading cause of Fusarium head …
Date:
May 2012
Creator:
Nalam, Vamsi J.
System:
The UNT Digital Library
Abelian Group Actions and Hypersmooth Equivalence Relations
We show that any Borel action on a standard Borel space of a group which is topologically isomorphic to the sum of a countable abelian group with a countable sum of lines and circles induces an orbit equivalence relation which is hypersmooth. We also show that any Borel action of a second countable locally compact abelian group on a standard Borel space induces an orbit equivalence relation which is essentially hyperfinite, generalizing a result of Gao and Jackson for the countable abelian groups.
Date:
May 2019
Creator:
Cotton, Michael R.
System:
The UNT Digital Library
Absorptive Capacity: An Empirical Examination of the Phenomenon and Relationships with Firm Capabilities
The field of strategic management addresses challenges that firms encounter in an attempt to remain competitive. The ability to explain variation in firm success through examination of knowledge flows has become a prominent focus of research in the strategic management literature. Specifically, researchers have sought to further examine how firms convert knowledge, a phenomenon conceptualized as absorptive capacity. Absorptive capacity is the firm’s ability to acquire, assimilate, transform, and exploit knowledge. Few studies have captured the richness and multi-dimensionality of absorptive capacity, and it remains to be understood how the dimensions of the phenomenon convert knowledge. Furthermore, how absorptive capacity influences the firm remains to be understood. To address these research gaps, this dissertation seeks to (1) determine how absorptive capacity converts knowledge, and (2) determine how absorptive capacity influences firm capabilities. The research questions are investigated using structural modeling techniques to analyze data collected from software-industry firms. The findings offer contributions to the absorptive capacity and capability literatures. For example, absorptive capacity is hypothesized to consist of complex relationships among its internal dimensions. However, findings of this study suggest the relationships among the dimensions are linear in nature. This finding is in line with the theoretical foundations of and …
Date:
May 2012
Creator:
Daspit, Josh
System:
The UNT Digital Library
Academic Advising Professional Characteristics and Standards: Do Academic Advisors Follow Recognized Professional Standards in Their Work?
There were two main purposes of this quantitative study. The first purpose was to identify characteristics associated with the selected sample of academic advisors that comprise study. Secondly, the study sought to determine how well work related activities of a selected population of academic advisors correlate with professional characteristics constructs and professional standards constructs of academic advising as a profession. The study used Habley’s (1986) characteristics of a profession to derive the studies professional characteristic construct, education activities, research activities, and professional development activities as it relates to a selected group of academic advisors work related activities. The studies professional standards construct was derived from five Council for the Advancement of Standards (CAS) professional standards for academic as it relates to a selected group of academic advisors work related activities. The study of 78 out of 210 identified full-time academic advisors at two-and four-year public colleges and universities in the North Texas Region utilized a multidimensional researcher-developed Web survey instrument designed to measure professional standards and characteristic within the field of academic advising. Study results reinforced current criticism of research and education activities within the field of academic advising showing that the lack of scholarly research and education activities among …
Date:
May 2014
Creator:
Shelton, Kiesha R.
System:
The UNT Digital Library
Academic Reading Online: Digital Reading Strategies of Graduate-level English Language Learners
English language learners (ELLs) face many linguistic and cultural challenges in their attempts to succeed academically. They encounter complex academic text, which is increasingly presented online. Although some research has addressed the challenges that university-level ELLs face when reading online texts, almost all of this prior work has focused on undergraduates. The purpose of the current study was to investigate the reading strategies employed by graduate-level ELLs when reading an academic English text online. Participating in the study were four foreign-born doctoral students from different first-language backgrounds—Arabic, Korean, Urdu, and Vietnamese—and the focus was on commonalities as well as differences among them. All four were enrolled in the same doctoral-level course, which included the reading of a specific online academic article as a course requirement. When reading this text individually, each student participated in a think-aloud procedure, followed by post-reading and discourse-based interviews. Analyses included unitizing data from the think-aloud protocols, coding units for strategies employed, and considering related interview commentary and classroom contributions. In their reading, these students made major use of problem-solving strategies, especially reading segments aloud and questioning. They also employed evaluative strategies as well as metacognitive strategies, which included affirming their understanding or indicating lack of …
Date:
May 2015
Creator:
Knezek, Lois Ann
System:
The UNT Digital Library
Accelerated Degree Program Faculty: Motivation to Teach
Adult educators are a growing part of American higher education. Because of their increasing prominence in adult education, it is essential to understand what roles these educators play and what motivates them to remain in the profession despite poor work prospects and conditions. Research to date, however, focuses primarily on the adult learner and not the adult educator. The purpose of this qualitative, multiple-case study was to explore the role and motivation for teaching of adult educators employed as adjunct faculty in an accelerated degree program at a small, liberal arts college in the northwest United States. Purposeful sampling was used to select the five participants for the study. All participants taught in the program for more than five years and were considered to be successful in their positions by peers, students, and administrators. The study employed a preliminary demographic survey to solicit initial background data on the instructors. Other data collection included in-depth, open-ended, face-to-face interviews, document analysis, and classroom observation. The results showed that all five participants identified the following roles and assumed them in the classroom: (a) facilitator, (b) listener, (c) specialist, (d) guide, (e) adviser, and (f) co-learner or colleague. Further results showed that all five …
Date:
May 2016
Creator:
Grishkevich, Hanna H.
System:
The UNT Digital Library
The Acceptance and Use of Cloud Computing Services by Small and Medium Enterprises in Lagos, Nigeria
This study explored the acceptance of cloud computing (CC) services by small and medium enterprises (SMEs) in Lagos, Nigeria, which has been missing from CC services literature. It aimed to understand the motivations for adoption, the uses of the services, and the benefits they derive from it. The uses and gratification theory was applied as the theoretic framework for this endeavor. An online survey with close-ended and open-ended questions was distributed to 1200 randomly selected participants through email. In total, 392 valid responses were collected and analyzed using descriptive statistics and categories. The results found that SMEs in Lagos, Nigeria had a low level of awareness and appreciation of CC services. The adoption rate was also low. Unlike their counterparts in other regions, SMEs primary concerns were service downtime, stable power supply, and better internet access. The study found that SMEs were not taking full advantage of the capabilities of CC services. Some sections, however, were doing better than others, such as the information and communications sub-sector. This study suggested that targeted interventions should be conducted to raise the awareness of CC services in SMEs, and to improve their efficient and effective use of CC services. The uses and gratification …
Date:
May 2017
Creator:
Azogu, Olajumoke Oluwaseye
System:
The UNT Digital Library
Access to Health Care and Rates of Mortality and Utilization for the Elderly in Rural America
The aging experience of men and women in rural America is different than that of their urban counterparts. In this study, I identified key disparities in access to health care, mortality, and utilization of health care that result from geographic location. Foundational theories are discussed to illustrate that disparities can originate from historical societal behaviors. Secondary data and literary reviews create a combined qualitative and quantitative approach to explore the rural/urban divide, concluding that the potential for increased disparities as the aging population grows is very real and rural residents remain vulnerable to a poor(er) aging experience. Recommendations for policy and practice, as well as additional research, are made to address the conclusion.
Date:
May 2018
Creator:
Johnson, Barbara Ann
System:
The UNT Digital Library
Accomplished Teachers' Instructional Decisions About Shakespeare
Teachers' decisions are a powerful influence on student learning and it is important to fully document accomplished teachers' instructional decisions, as well as to investigate possible influences on those decisions. Shakespearean dramas are central to high school curricula across the U.S. and pose particular instructional challenges, therefore teachers' decisions about teaching these texts are of particular interest. There is limited empirical research, however, about these instructional decisions. Thus, the purpose of this study was to describe how four accomplished high school English teachers working on a single campus make instructional decisions about teaching a Shakespearean play. Specifically, research questions addressed teachers' decisions regarding the teaching of a Shakespearean play and various influences on those decisions (self-reports and inferences from the data). Case study methodology was used, including an inductive analysis of individual teacher interviews, classroom observations, focus group, instructional artifacts, and researcher's journal. The findings revealed that instructional activities described by these teachers addressed support for meaning-making during four stages of reading instruction: (a) before, during, and after; (b) before; (c) during; and (d) after. Comparison of these cases suggests that, although each teacher brings personal preferences and unique background knowledge to her instructional decisions, all make decisions to promote …
Date:
May 2013
Creator:
Parris, Sheri Rene’
System:
The UNT Digital Library
Accreditation Facilitation Projects: Supporting High Quality Early Childhood Education and Care
High-quality early childhood education and care (ECEC) are linked to positive developmental outcomes for children. Systems have been created to define, measure and promote high-quality ECEC. National accreditation status is deemed the gold standard of a high-quality program, yet many centers are unable to achieve this without assistance. With the help of Accreditation Facilitation Projects (AFPs), many low-income centers are able to achieve accreditation. Centers collaborating with an AFP reap many benefits including financial support, ongoing training and mentoring, and guidance through the accreditation process. AFPs invest greatly in the centers they collaborate with and the longer the center takes to achieve accreditation, the more resources an AFP must expend. The purposes of this study were to understand if the educational level of center director, the total enrollment of a center, or the percentage of children receiving government subsidies could predict the time it takes for a center to complete the accreditation process while receiving assistance from an AFP, and to determine if there are differences in attitudes about program accreditation between center directors and early learning specialists who serve as accreditation mentors to the directors. Findings revealed that a) the higher educational level of program directors is associated with …
Date:
May 2013
Creator:
Reinke, Stephanie L.
System:
The UNT Digital Library
Accurate Joint Detection from Depth Videos towards Pose Analysis
Joint detection is vital for characterizing human pose and serves as a foundation for a wide range of computer vision applications such as physical training, health care, entertainment. This dissertation proposed two methods to detect joints in the human body for pose analysis. The first method detects joints by combining body model and automatic feature points detection together. The human body model maps the detected extreme points to the corresponding body parts of the model and detects the position of implicit joints. The dominant joints are detected after implicit joints and extreme points are located by a shortest path based methods. The main contribution of this work is a hybrid framework to detect joints on the human body to achieve robustness to different body shapes or proportions, pose variations and occlusions. Another contribution of this work is the idea of using geodesic features of the human body to build a model for guiding the human pose detection and estimation. The second proposed method detects joints by segmenting human body into parts first and then detect joints by making the detection algorithm focusing on each limb. The advantage of applying body part segmentation first is that the body segmentation method narrows …
Date:
May 2018
Creator:
Kong, Longbo
System:
The UNT Digital Library
An Action Research Study of Community Building with Elementary Students in a Title I School
“In what ways does teaching with folk arts inspired visual arts-based instruction enhance community building among elementary students in a Title I school?” was the primary research question in this study. Agreeing with past and present day research that the construct of community is vital to social and cultural capital, this research attempts to determine how the notion of community benefits both students and teachers in the elementary art classroom. Folk art was utilized because this genre was accessible in terms of locality and familiarity among students and teachers. The purpose of this investigation was to produce teaching strategies and methods that show how community can be formed in the art classroom. The participants were elementary students, Grades 2 and 3, in a Title I school located in Denton, Texas. This investigation was conducted under an action research methodology. This approach to research is intended to be transformational, emergent, and accommodating. I recorded observations, field notes, and conversations from the participants. Emergent themes were discovered through content analysis and conceptual maps. Results from this investigation concluded transformation is only possible if the person wants change to happen. Data also showed that community and art education are symbiotic. Transformation, growth, and …
Date:
May 2014
Creator:
Dew, SaraBeth
System:
The UNT Digital Library
Actions Taken by Texas School Districts to Prevent Fraud
This research is a descriptive analysis answering the question, what measures are currently taken by the leadership―boards of trustees and superintendents of schools―of Texas school districts to prevent embezzlement? The research perspective utilized was quantitative with a descriptive, cross-sectional design. Data collection was accomplished through a survey with questions constructed from the most commonly recommended strategies discovered through the review of literature. The survey was distributed to the 1031 superintendents of school districts in Texas via email. The response rate was 33% or 339 returned surveys. The data set created concentrates on the four most common preventive measures: policy and procedure, management, auditing, and ethics. These measures are considered as they function to interrupt the principles of the fraud triangle. Comparisons were completed regarding region, district size, superintendent tenure and superintendent experience. Policy adoption was found to be extremely widespread. Procedures written to fully implement policy were less prevalent. Review of management practices found problems concerning credit cards, personnel evaluations, and password access to multiple computer finance recordkeeping systems concentrated in one employee. External auditing programs were universal due to statutory mandate but internal auditors and internal audit committees were few. Ethics training for business office personnel existed but with …
Date:
May 2011
Creator:
Taylor, Gordon Douglas
System:
The UNT Digital Library
Adequacy and Equity: How the Texas Supreme Court's Perceptions Have Changed Over the Past 50 Years
The purpose of this study identifies state court cases involving public school finance specifically related to adequacy and equity in funding. Results address how state court cases have challenged the constitutionality of school finance in the United States, including Texas, over the last 50 years. The study further shows how the decisions from previous cases have influenced the Supreme Court of Texas decision in the Texas Taxpayer & Student Fairness litigation.
Date:
May 2017
Creator:
Ford, Daniel William
System:
The UNT Digital Library
The Adoption, Management, and Performance of Local Government Investment Pools: A Comparative Analysis of State Practices
This dissertation examines the factors influencing a state’s decision to adopt a local government investment pool (LGIP), the institutional arrangements used in managing them, and the effect of the institutional types on LGIP performance. The dissertation extends the policy adoption theory with insights from investment theory to demonstrate that management credibility influences the likelihood of a state’s LGIP adoption. The study finds that the quality of financial management, the quality of professional leadership, proximate state neighbors who have previously adopted an LGIP, and economic factors determine a state’s proclivity to policy adoption. The dissertation also describes the institutional arrangements used in managing LGIPs and develops typologies based on their institutional arrangements. The dissertation compares LGIPs depending on the risk aversion of their institutional arrangements. The research extends the risk-return tradeoff in investment theory to LGIP institutional arrangements. The empirical findings show that LGIP institutional arrangement that has greater risk report higher performance. The dissertation also finds that competition in the LGIP market due to multiple vendors, and periods of economic recession account for higher performance because of higher risk-taking behaviors associated with them. This dissertation promotes public funds investment laws that emphasize prudent management of government finances and guides managers …
Date:
May 2016
Creator:
Nukpezah, Julius Atsu
System:
The UNT Digital Library
The Adoption of Open Source Software in Uganda: a Pragmatist Approach to the Formation of a National Information Policy for a New Technology
This exploratory research examined an information policy formation process for the adoption of open source software (OSS) in Uganda. Grounded in a pragmatist tradition, this theoretical and empirical study pursued a qualitative research approach with a triangulation of theoretical concepts, data collection, and analysis techniques in an iterative and interactive process. The design provided a powerful context to develop and conduct field activities in Kampala with a purposeful sample of 22 participants, 20 in interviews and 5 in a focus group discussion. The research design enhanced consistency in the evidence from the data, increased robustness in the results, and confidence in the findings. The results highlighted a vibrant ICT sector in Uganda, underlined the multiple stakeholders and their competing interests in the policy, revealed a lack of consensus between the government and OSS promoters on the meaning of OSS, and illuminated the benefits in the OSS model over proprietary software. The stakeholders' conflicting perceptions appear to be too far apart to allow meaningful progress and are derailing the policy. Unless their conflicting perceptions are resolved, the OSS policy will continue stagnating. The study fills critical information gaps in Uganda’s policy formation processes, provides timely and relevant information to holistically understand …
Date:
May 2014
Creator:
Muwanguzi, Samuel
System:
The UNT Digital Library
The Affect of Mobile Performance Support Devices on Anxiety and Self-Efficacy of Hospital Float Staff
Floating describes the act of staff moving from one unit to another based on the needs of the patients in a hospital. Many staff who float to different units express negative feelings, including anxiety and lack in self-efficacy. However, floating is both an economical and efficient method to use staff across the hospital, especially with current staffing shortages in the United States. This study investigated how the use of mobile performance support devices may help reduce anxiety and increase self-efficacy for those staff who float to different units. with access to multiple resources available on the mobile device, Bandura's social learning theory and self-efficacy concept set the framework through modeling, observing, and imitating others in order to reproduce certain behaviors and tasks and believe in one's capability to perform. a quantitative study incorporating the retrospective pretest-posttest design was conducted using the population of float staff, including both nurses and respiratory therapists, from Children's Medical Center of Dallas. Both the State-Trait Anxiety Inventory and General Self-Efficacy Scale, along with a basic demographic tool, were used to explore anxiety and self-efficacy in relation to the usage of mobile performance support devices. Findings can be used to impact the negative feelings of staff …
Date:
May 2012
Creator:
McKee, Megan Riley
System:
The UNT Digital Library
After the Planes
The dissertation consists of a critical preface and a novel. The preface analyzes what it terms “polyvocal” novels, or novels employing multiple points of view, as well as “layered storytelling,” or layers of textuality within novels, such as stories within stories. Specifically, the first part of the preface discusses polyvocality in twenty-first century American novels, while the second part explores layered storytelling in novels responding to World War II or the terrorist attacks of 9/11. The preface analyzes the advantages and difficulties connected to these techniques, as well as their aptitude for reflecting the fractured, disconnected, and subjective nature of the narratives we construct to interpret traumatic experiences. It also acknowledges the necessity—despite its inherent limitations—of using language to engage with this fragmentation and cope with its challenges. The preface uses numerous novels as examples and case studies, and it also explores these concepts and techniques in relation to the process of writing the novel After the Planes. After the Planes depicts multiple generations of a family who utilize storytelling as a means to work through grief, hurt, misunderstanding, and loss—whether from interpersonal conflicts or from war. Against her father’s wishes, a young woman moves in with her nearly-unknown grandfather, …
Date:
May 2012
Creator:
Boswell, Timothy
System:
The UNT Digital Library
Age Friendly Cities: The Bureaucratic Responsiveness Effects on Age Friendly Policy Adoption
Challenging a long-held attachment to the medical model, this research develops a cultural model placing local governments at the center of policy making and refocusing policy attention on mobility, housing, the built environment and services. To examine the phenomenon of age friendly policy adoption by cities and the magnitude of adoption, a 21-question web-based survey was administered to a sample of 1,050 cities from the U.S. Census having a population over 10,000 and having at least 14% of their population aged 65 years and over. The goal of the questionnaire was to help identify what kind of policy objectives cities establish to facilitate the opportunity for older adults to live healthy and independent lives in their communities as they age. Multiple linear and ordinal regression models examined the likelihood of policy action by cities and provide evidence as to why some cities support more age friendly policy actions than others. Evidence illustrates theoretical advancement providing support for a cultural model of aging. The cultural model includes multiple factors including bureaucratic responsiveness reflected in the management values of the administration. Findings show variation in the integration of a cultural awareness of aging in the municipality's needs assessment, strategic goals, citizen engagement …
Date:
May 2017
Creator:
Keyes, Laura Marie
System:
The UNT Digital Library
Aging Is a Determinant in Anoxia Stress Tolerance in Caenorhabditis Elegans
Oxygen availability is critical for survival for most organisms. The nematode, C. elegans, has been useful for studying genetic regulation of anoxia tolerance due to the oxygen deprivation response mechanisms shared with other metazoans. Studies examining long-term anoxia (72h, LTA) tolerance have only been conducted at adult day 1. To investigate the effect of aging on anoxia tolerance wild-type and mutant strains were exposed to LTA between adult day 1 and day 9. Wild-type isolates and daf-16(mu86) (FOXO transcription factor regulated by insulin-signaling) and aak-2(gt33) (catalytic subunit of AMP-activated protein kinase) strains were anoxia sensitive at day 1 and displayed increased LTA tolerance with aging correlated with reproductive senescence followed by a decline in survivorhsip through day 9. The daf-2(e1370) (insulin receptor homologue of C. elegans), glp-1(e2141) (a lin-12/Notch receptor) and fog-2(q71) (required for spermatogenesis) strains were LTA-tolerant through day 5. I conclude that aging influences LTA-tolerance in a strain- and age-dependent manner. In addition to being LTA-tolerant the daf-2(e1370) and glp-1(e2141) strains have a longevity phenotype that is suppressed by loss of kri-1 or daf-12. While loss of kri-1 did not suppress the LTA-tolerant phenotype of glp-1(e2141) at day 1 the portion of impaired survivors increased at day 3 …
Date:
May 2013
Creator:
Goy, Jo M.
System:
The UNT Digital Library
Alfredo Casella's Serenata, op. 46, A Performance Guide for the Ensemble and Trumpet Part
Alfredo Casella's Serenata, op. 46 for clarinet, bassoon, trumpet, violin and cello is a composition that received great acclaim at the time of its conception, it is all but unknown to modern audiences and performers. The Serenata has several historical influences from the French and Italian Baroque and Classical periods. At present, there is limited scholarship regarding the Serenata op. 46. The first section of this study presents a survey of historical information, current literature and methods of examination. The second section compares movements of the Serenata op. 46 to other historical forms of similar design. The third section provides a performance guide for the trumpeter and ensemble. Implications and suggestions for performance of the composition are provided for the trumpeter. This performance guide provides the trumpeter and ensemble with performance information to help facilitate an informed performance.
Date:
May 2011
Creator:
Walker, Brian Matthew
System:
The UNT Digital Library
Algebraically Determined Semidirect Products
Let G be a Polish group. We say that G is an algebraically determined Polish group if given any Polish group L and any algebraic isomorphism from L to G, then the algebraic isomorphism is a topological isomorphism. We will prove a general theorem that gives useful sufficient conditions for a semidirect product of two Polish groups to be algebraically determined. This will smooth the way for the proofs for some special groups. For example, let H be a separable Hilbert space and let G be a subset of the unitary group U(H) acting transitively on the unit sphere. Assume that -I in G and G is a Polish topological group in some topology such that H x G to H, (x,U) to U(x) is continuous, then H x G is a Polish topological group. Hence H x G is an algebraically determined Polish group. In addition, we apply the above the above result on the unitary group U(A) of a separable irreducible C*-algebra A with identity acting transitively on the unit sphere in a separable Hilbert space H and proved that the natural semidirect product H x U(A) is an algebraically determined Polish group. A similar theorem is true …
Date:
May 2011
Creator:
Jasim, We'am Muhammad
System:
The UNT Digital Library
Algorithmic Music Analysis: a Case Study of a Prelude From David Cope’s “From Darkness, Light”
The use of algorithms in compositional practice has been in use for centuries. With the advent of computers, formalized procedures have become an important part of computer music. David Cope is an American composer that has pioneered systems that make use of artificial intelligence programming techniques. In this dissertation one of David Cope’s compositions that was generated with one of his processes is examined in detail. A general timeline of algorithmic compositional practice is outlined from a historical perspective, and realized in the Common Lisp programming language as a musicological tool. David Cope’s compositional output is summarized with an explanation of what types of systems he has utilized in the analyses of other composers’ music, and the composition of his own music. Twentieth century analyses techniques are formalized within Common Lisp as algorithmic analyses tools. The tools are then combined with techniques developed within other computational music analyses tools, and applied toward the analysis of Cope’s prelude. A traditional music theory analysis of the composition is provided, and outcomes of computational analyses augment the traditional analysis. The outcome of the computational analyses, or algorithmic analyses, is represented in statistical data, and corresponding probabilities. From the resulting data sets part of …
Date:
May 2015
Creator:
Krämer, Reiner
System:
The UNT Digital Library
Alloy Development and High-Energy X-Ray Diffraction Studies of NiTiZr and NiTiHf High Temperature Shape Memory Alloys
NiTi-based shape memory alloys (SMAs) offer a good combination of high-strength, ductility, corrosion resistance, and biocompatibility that has served them well and attracted the attention of many researchers and industries. The alloys unique thermo-mechanical ability to recover their initial shape after relatively large deformations by heating or upon unloading due to a characteristic reversible phase transformation makes them useful as damping devices, solid state actuators, couplings, etc. However, there is a need to increase the temperature of the characteristic phase transformation above 150 °C, especially in the aerospace industry where high temperatures are often seen. Prior researchers have shown that adding ternary elements (Pt, Pd, Au, Hf and Zr) to NiTi can increase transformation temperatures but most of these additions are extremely expensive, creating a need to produce cost-effective high temperature shape memory alloys (HTSMAs). Thus, the main objective of this research is to examine the relatively unstudied NiTiZr system for the ability to produce a cost effective and formable HTSMA. Transformation temperatures, precipitation paths, processability, and high-temperature oxidation are examined, specifically using high energy X-ray Diffraction (XRD) measurements, in NiTi-20 at.% Zr. This is followed by an in situ XRD study of the phase growth kinetics of the favorable …
Date:
May 2018
Creator:
Carl, Matthew A
System:
The UNT Digital Library