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 Language: English
 Collection: UNT Theses and Dissertations
Laser Deposition, Heat-treatment, and Characterization of the Binary Ti-xmn System

Laser Deposition, Heat-treatment, and Characterization of the Binary Ti-xmn System

Date: August 2013
Creator: Avasarala, Chandana
Description: 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.
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Laser Modified Alumina: a Computational and Experimental Analysis

Laser Modified Alumina: a Computational and Experimental Analysis

Date: December 2012
Creator: Moncayo, Marco Antonio
Description: Laser surface modification involves rapid melting and solidification is an elegant technique used for locally tailoring the surface morphology of alumina in order to enhance its abrasive characteristics. COMSOL Multiphysics® based heat transfer modeling and experimental approaches were designed and used in this study for single and multiple laser tracks to achieve densely-packed multi-facet grains via temperature history, cooling rate, solidification, scanning electron micrographs, and wear rate. Multi-facet grains were produced at the center of laser track with primary dendrites extending toward the edge of single laser track. The multiple laser tracks study indicates the grain/dendrite size increases as the laser energy density increases resulting in multiplying the abrasive edges which in turn enhance the abrasive qualities.
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Laser Surface Modification on Az31b Mg Alloy for Bio-wettability

Laser Surface Modification on Az31b Mg Alloy for Bio-wettability

Date: December 2013
Creator: Ho, YeeHsien
Description: Laser surface modification of AZ31B Magnesium alloy changes surface composition and roughness to provide improved surface bio-wettability. Laser processing resulted in phase transformation and grain refinement due to rapid quenching effect. Furthermore, instantaneous heating and vaporization resulted in removal of material, leading the textured surface generation. A study was conducted on a continuum-wave diode-pumped ytterbium laser to create multiple tracks for determining the resulting bio-wettability. Five different laser input powers were processed on Mg alloy, and then examined by XRD, SEM, optical profilometer, and contact angle measurement. A finite element based heat transfer model was developed using COMSOL multi-physics package to predict the temperature evolution during laser processing. The thermal histories predicted by the model are used to evaluate the cooling rates and solidification rate and the associated changes in the microstructure. The surface energy of laser surface modification samples can be calculated by measuring the contact angle with 3 different standard liquid (D.I water, Formamide, and 1-Bromonaphthalen). The bio-wettability of the laser surface modification samples can be conducted by simulated body fluid contact angle measurement. The results of SEM, 3D morphology, XRD, and contact angle measurement show that the grain size and roughness play role for wetting behavior of ...
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Laser Surface Treatment of Amorphous Metals

Laser Surface Treatment of Amorphous Metals

Date: May 2014
Creator: Katakam, Shravana K.
Description: Amorphous materials are used as soft magnetic materials and also as surface coatings to improve the surface properties. Furthermore, the nanocrystalline materials derived from their amorphous precursors show superior soft magnetic properties than amorphous counter parts for transformer core applications. In the present work, laser based processing of amorphous materials will be presented. Conventionally, the nanocrystalline materials are synthesized by furnace heat treatment of amorphous precursors. Fe-based amorphous/nanocrystalline materials due to their low cost and superior magnetic properties are the most widely used soft magnetic materials. However, achieving nanocrystalline microstructure in Fe-Si-B ternary system becomes very difficult owing its rapid growth rate at higher temperatures and sluggish diffusion at low temperature annealing. Hence, nanocrystallization in this system is achieved by using alloying additions (Cu and Nb) in the ternary Fe-Si-B system. Thus, increasing the cost and also resulting in reduction of saturation magnetization. laser processing technique is used to achieve extremely fine nanocrystalline microstructure in Fe-Si-B amorphous precursor. Microstructure-magnetic Property-laser processing co-relationship has been established for Fe-Si-B ternary system using analytical techniques. Laser processing improved the magnetic properties with significant increase in saturation magnetization and near zero coercivity values. Amorphous materials exhibit excellent corrosion resistance by virtue of their atomic ...
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The Last Laugh: Selected Edwardian Punch Cartoons of Edward Linley Sambourne

The Last Laugh: Selected Edwardian Punch Cartoons of Edward Linley Sambourne

Date: May 2001
Creator: Larson, Alison
Description: The illustrative work of Edward Linley Sambourne for Punch magazine during the period 1901-1910 addresses a myriad of political topics prevalent during the Edwardian period in British history. This thesis examines two of those topics - Women's Suffrage and Socialism - through their artistic treatment by one of Britain's most influential periodicals. Through a study of the historical context and iconography of selected cartoons-of-the-week, one is better equipped to understand and appreciate the meaning, message, and humor in the cartoons. Chapter 1 introduces the Sambourne, Punch magazine, and the Edwardian period in general. Chapters 2 and 3 discuss four Women's Suffrage cartoons and four Socialism cartoons respectively. Chapter 4 draws conclusions regarding Sambourne's techniques as a cartoonist as well as the relationship between the text and image in his illustrations.
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Late adolescents' parental, peer, and romantic attachments as they relate to affect regulation and risky behaviors.

Late adolescents' parental, peer, and romantic attachments as they relate to affect regulation and risky behaviors.

Date: August 2008
Creator: Ingle, Sarah J.
Description: The current study examined the relationships among attachment styles to parent, peer, and romantic partner, ability to regulate emotion, as well as engagement in sexual behaviors and substance use. Attachment theory and previous research suggests that an individual learns how to manage emotions through the modeling of appropriate techniques and a stable sense of self-worth. These two aspects develop through a secure attachment bond with an important figure. When an individual does not have a secure attachment bond in which to practice adaptive affect regulation strategies, he/she may attempt to manage emotions through external means, such as sexual behaviors or substance use. Overall, results supported these associations, with some notable exceptions. Across attachment sources a secure attachment style was related to lower levels of psychological distress and less engagement in substance use. In contrast to the findings from earlier studies, affect regulation did not mediate the relationship between attachment and substance use, and engagement in sexual behaviors was not significantly related to either attachment style or affect regulation.
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Latent Transition Analysis of Pre-service Teachers' Efficacy in Mathematics and Science

Latent Transition Analysis of Pre-service Teachers' Efficacy in Mathematics and Science

Date: December 2009
Creator: Ward, Elizabeth Kennedy
Description: This study modeled changes in pre-service teacher efficacy in mathematics and science over the course of the final year of teacher preparation using latent transition analysis (LTA), a longitudinal form of analysis that builds on two modeling traditions (latent class analysis (LCA) and auto-regressive modeling). Data were collected using the STEBI-B, MTEBI-r, and the ABNTMS instruments. The findings suggest that LTA is a viable technique for use in teacher efficacy research. Teacher efficacy is modeled as a construct with two dimensions: personal teaching efficacy (PTE) and outcome expectancy (OE). Findings suggest that the mathematics and science teaching efficacy (PTE) of pre-service teachers is a multi-class phenomena. The analyses revealed a four-class model of PTE at the beginning and end of the final year of teacher training. Results indicate that when pre-service teachers transition between classes, they tend to move from a lower efficacy class into a higher efficacy class. In addition, the findings suggest that time-varying variables (attitudes and beliefs) and time-invariant variables (previous coursework, previous experiences, and teacher perceptions) are statistically significant predictors of efficacy class membership. Further, analyses suggest that the measures used to assess outcome expectancy are not suitable for LCA and LTA procedures.
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Latin Mass for Choir, Orchestra, Soprano and Mezzo-Soprano Soloists

Latin Mass for Choir, Orchestra, Soprano and Mezzo-Soprano Soloists

Date: May 2003
Creator: Bonneau, Paul G.
Description: The Latin Mass is a musical composition in five movements, scored for large choir, standard orchestra, and two soloists. The movements are the standard parts of the Roman Catholic Mass Ordinary. The language is set mainly in Latin with two exceptions: the Kyrie movement is set in Greek (which is the standard Roman Catholic setting), and the Credo is simultaneously recited in English and sung in Latin. The work is scored using conventional notation techniques and employs rather conservative technical demands on both the choir and orchestra. No extended techniques are required of any of the performers. It is set in a modal harmonic language.
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Latin Vocabulary Acquisition : An Experiment Using Information-processing Techniques of Chunking and Imagery

Latin Vocabulary Acquisition : An Experiment Using Information-processing Techniques of Chunking and Imagery

Date: August 1997
Creator: Carter, Terri Gay Manns
Description: The purpose of the study was to determine the effect on student performance and attitude toward high school Latin by Latin I students when provided with vocabulary instruction through chunking and imagery.
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Latino Students’ School Counseling Needs: an Exploratory Needs Assessment

Latino Students’ School Counseling Needs: an Exploratory Needs Assessment

Date: August 2012
Creator: Morganfield, Maggie Garris
Description: The purpose of this study was to examine Latino/a student preferences for school counselor activities. The primary focus of research was to determine what school counseling activities Latino/a students perceived as important and which school counseling activities Latino/a high school students perceived as satisfying. The researcher pursued this purpose through administration of a survey instrument developed by the researcher. The instrument consisted of 14 demographic items and 42 5-point Likert scale items based on the domains described in the ASCA’s national model and current literature on experiences of Latino/a adolescents. The sample was comprised of 210 Latino/a high school students from five high schools in three school districts in the suburbs of a large Southwestern U.S. metroplex. The study population consisted of 94 female and 115 male participants ranging in age from 14 to 20 years old with the median age of 17.54 years. Overall, students preferred school counseling activities focusing on college and career readiness. According to the results of this study, students indicated that although they believed college and career activities to be important, they were not satisfied with how their school counselors provided those activities. Multiple regression analyses were utilized to determine which demographic variables were significant ...
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