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 Collection: UNT Theses and Dissertations
Investigations in the Mechanism of Carbothermal Reduction of Yttria Stabilized Zirconia for Ultra-high Temperature Ceramics Application and Its Influence on Yttria Contained in It

Investigations in the Mechanism of Carbothermal Reduction of Yttria Stabilized Zirconia for Ultra-high Temperature Ceramics Application and Its Influence on Yttria Contained in It

Date: May 2014
Creator: Sondhi, Anchal
Description: Zirconium carbide (ZrC) is a high modulus ceramic with an ultra-high melting temperature and, consequently, is capable of withstanding extreme environments. Carbon-carbon composites (CCCs) are important structural materials in future hypersonic aircraft; however, these materials may be susceptible to degradation when exposed to elevated temperatures during extreme velocities. At speeds of exceeding Mach 5, intense heating of leading edges of the aircraft triggers rapid oxidation of carbon in CCCs resulting in degradation of the structure and probable failure. Environmental/thermal barrier coatings (EBC/TBC) are employed to protect airfoil structures from extreme conditions. Yttria stabilized zirconia (YSZ) is a well-known EBC/TBC material currently used to protect metallic turbine blades and other aerospace structures. In this work, 3 mol% YSZ has been studied as a potential EBC/TBC on CCCs. However, YSZ is an oxygen conductor and may not sufficiently slow the oxidation of the underlying CCC. Under appropriate conditions, ZrC can form at the interface between CCC and YSZ. Because ZrC is a poor oxygen ion conductor in addition to its stability at high temperatures, it can reduce the oxygen transport to the CCC and thus increase the service lifetime of the structure. This dissertation investigates the thermodynamics and kinetics of the YSZ/ZrC/CCC ...
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Investigations of neuronal network responses to electrical stimulation in murine spinal cultures.

Investigations of neuronal network responses to electrical stimulation in murine spinal cultures.

Date: December 2001
Creator: Sparks, Christopher A.
Description: Spontaneous activity in neuronal networks in vitro is common and has been well documented. However, alteration of spontaneous activity in such networks via conditioning electrical stimulation has received much less experimental attention. Two different patterns of electrical stimulation were used to enhance or depress the level of spontaneous activity in spinal cord cultures. High-frequency stimulation (HFS), a method routinely shown to increase the efficacy of synaptic transmission, was employed to augment spontaneous activity. Low-frequency stimulation (LFS), the technique often applied to depress synaptic efficacy, was employed to decrease spontaneous activity. In addition, LFS was used to reverse the effect of HFS on spontaneous activity. Likewise, HFS was applied to counter the effect of LFS. Because these networks were grown on multi-microelectrode plates (MMEPs), this allowed the simultaneous stimulation of any combination of the 64 electrodes in the array. Thus, the possible differences in response to single versus multi-electrode stimulation were also addressed. Finally, test-pulses were delivered before and after the conditioning stimulation on the same stimulation electrode(s) in order to assess the change in mean evoked action potentials (MEAPs). Dissociated spinal tissue from embryonic mice was allowed to mature into self-organized networks that exhibited spontaneous bursting activity after two weeks ...
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Investigations of Thermochemistry and the Kinetics of H Atom Radical Reactions

Investigations of Thermochemistry and the Kinetics of H Atom Radical Reactions

Access: Use of this item is restricted to the UNT Community.
Date: December 2002
Creator: Peebles, Lynda Renee
Description: The thermochemistry of several species, and the kinetics of various H atom radical reactions relevant to atmospheric and combustion chemistry were investigated using ab initio theoretical techniques and the flash photolysis / resonance fluorescence technique. Using ab initio quantum mechanical calculations up to the G3 level of theory, the C-H bond strengths of several alkanes were calculated. The bond strengths were calculated using two working reactions. From the results, it is apparent that the bond strengths decrease as methyl groups are added to the central carbon. The results are in good agreement with recent experimental halogenation kinetic studies. Hydrogen bond strengths with sulfur and oxygen were studied via CCSD(T) theory, together with extrapolation to the complete basis set limit. The results for the bond dissociation energies (ground state at 0 K, units: kJ mol-1) are: S-H = 349.9, S-D = 354.7, HS-H = 376.2, DS-D = 383.4, and HO-H = 492.6. These data compare well with experimental literature. The rate constants for the isotopic reactions of H + H2S, D + H2S, H + D2S, and D + D2S are studied at the QCISD(T)/6-311+G(3df,2p) level of theory. The contributions of the exchange reaction versus abstraction are examined through transition state ...
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Investing and Hedging Techniques in the Convertible Bond Market

Investing and Hedging Techniques in the Convertible Bond Market

Date: June 1969
Creator: Vinson, Charles E. (Charles Eldred)
Description: This study was designed to yield three types of information: (1) The degree of perfection prevailing in the parimary and secondary convertible bond markets; (2) the profit potential of various investing and hedging techniques in the convertible bond market; and (3) a judgment on whether each technique can be classified as rational or irrational.
Contributing Partner: UNT Libraries
Investment decisions: Influence of an Internet stock message board.

Investment decisions: Influence of an Internet stock message board.

Date: December 2007
Creator: Pleis, Letitia Meier
Description: The Internet provides many sources of financial information that investors can use to help with investment decisions and in interpreting companies' accounting information. One source of information is Internet stock message boards such as those at Yahoo! Finance. This source allows for anonymous postings and information exchange. Despite the possibility of the information being incorrect many individuals visit these message boards. The purpose of this study is to investigate Internet stock message boards and address the primary question: From an individual investor perspective, do message boards, which contain accounting information, influence investment decisions? The question is addressed using psychology rumor literature and attitude theories. Message board postings are a type of rumor, since not all the information is verified and is usually intended to persuade a belief or influence a decision. Further, the messages may influence an investor by causing a change in attitude about the investment. Using an experiment, message board influence on an investment decision and attitude was tested. The results indicated that individuals that received negative message board postings did have a significantly higher change in investment amount as compared to a control group that did not receive any message postings. The positive message board group and ...
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The Invisible Dragon

The Invisible Dragon

Date: December 2012
Creator: Boutwell, Nathan
Description: This collection of memoir essays chronicles the author's 19 year struggle with chronic depression. "The Invisible Dragon" explores the onset of the disease and its cure. "The Silent Typewriter" looks at how it affected the author as a writer. "Roses for Trish" discusses how it affected his wife. "My Mother's Son" explores the possibility that he inherited depression from his mother. The final essay, "The Dragon Returns" probes the author's life in 2012 with the probability that he has a personality disorder. The preface examines several depression memoirs and explores the strategies used by William Styron, Elizabeth Wurtzel and Kay Redfield Jamison to prevent sliding into the pitfalls inherent in a linear structure. Among these are the use of alternative structures, language, characterization, focus and imagery.
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Involvement in Admission to Two Homes for the Aged

Involvement in Admission to Two Homes for the Aged

Date: August 1963
Creator: Howze, Glenn Ray
Description: The study reported in the thesis attempted to examine the decision-making process for the institutionalization of older people in homes for the aged. More specifically, it sought to determine who was responsible for the decisions, to discover if this responsibility was related to selected social factors, and to ascertain if it affected the adjustment of older people to the institutional setting.
Contributing Partner: UNT Libraries
Ion Beam Synthesis of Carbon Assisted Nanosystems in Silicon Based Substrates

Ion Beam Synthesis of Carbon Assisted Nanosystems in Silicon Based Substrates

Date: May 2011
Creator: Poudel, Prakash Raj
Description: The systematic study of the formation of β-SiC formed by low energy carbon ion (C-)implantation into Si followed by high temperature annealing is presented. The research is performed to explore the optimal annealing conditions. The formation of crystalline β-SiC is clearly observed in the sample annealed at 1100 °C for a period of 1 hr. Quantitative analysis is performed in the formation of β-SiC by the process of implantation of different carbon ion fluences of 1×1017, 2×1017, 5×1017, and 8×1017 atoms /cm2 at an ion energy of 65 keV into Si. It is observed that the average size of β-SiC crystals decreased and the amount of β-SiC crystals increased with the increase in the implanted fluences when the samples were annealed at 1100°C for 1 hr. However, it is observed that the amount of β-SiC linearly increased with the implanted fluences up to 5×1017 atoms /cm2. Above this fluence the amount of β-SiC appears to saturate. The stability of graphitic C-C bonds at 1100°C limits the growth of SiC precipitates in the sample implanted at a fluence of 8×1017 atoms /cm2 which results in the saturation behavior of SiC formation in the present study. Secondly, the carbon cluster formation process ...
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Ion-Induced Damage In Si: A Fundamental Study of Basic Mechanisms over a Wide Range of Implantation Conditions

Ion-Induced Damage In Si: A Fundamental Study of Basic Mechanisms over a Wide Range of Implantation Conditions

Date: May 2006
Creator: Roth, Elaine Grannan
Description: A new understanding of the damage formation mechanisms in Si is developed and investigated over an extended range of ion energy, dose, and irradiation temperature. A simple model for dealing with ion-induced damage is proposed, which is shown to be applicable over the range of implantation conditions. In particular the concept of defect "excesses" will be discussed. An excess exists in the lattice when there is a local surplus of one particular type of defect, such as an interstitial, over its complimentary defect (i.e., a vacancy). Mechanisms for producing such excesses by implantation will be discussed. The basis of this model specifies that accumulation of stable lattice damage during implantation depends upon the excess defects and not the total number of defects. The excess defect model is validated by fundamental damage studies involving ion implantation over a range of conditions. Confirmation of the model is provided by comparing damage profiles after implantation with computer simulation results. It will be shown that transport of ions in matter (TRIM) can be used effectively to model the ion-induced damage profile, i.e. excess defect distributions, by a simple subtraction process in which the spatially correlated defects are removed, thereby simulating recombination. Classic defect studies ...
Contributing Partner: UNT Libraries
Iranian Access Television of Dallas: Cultural Issues, Preservation, and Community Formation

Iranian Access Television of Dallas: Cultural Issues, Preservation, and Community Formation

Date: August 1997
Creator: Karimi, Mohammad, 1959-
Description: This study focused on the televisual and cultural practices of Iranians via public access television in Dallas, Texas. It includes analysis of format and content. It combines demographic, structural, and statistical information with a culturalist and interpretive viewpoint in examining the efforts of Iranians, via access television programs, in preserving their culture and the formation of a coherent and active community in the Dallas/Fort Worth Metroplex.
Contributing Partner: UNT Libraries