We study the electronic band structure of no-common-atom InAs-GaSb superlattice within a nearest-neighbor bond-orbital model. The effect of interfacial asymmetry is also taken into account. This model can reproduce fairly accurate bulk band structures near the center of the Brillouin zone. We find that interfacial asymmetry, which is first included in bond-orbital model, can yield spin splitting. We also find that a negative indirect band gap appears for long period superlattice, due to interfacial asymmetry and band anisotropy of the heavy hole band in GaSb material. This indicates that the semiconductor-semimetal transition, which occurs when the period d reach a critical value dC, does exist in InAs-GaSb superlattice. In our calculation, the critical period dC is about 150 Å.

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This dissertation consists of two independent topics: (1) a molecular loop with interstitial channels in a chiral environment; (2) study of formation of metal-metal bonds in dinickel, dipalladium and dititanium complexes On the first topic, a study of the reaction products of the interaction of cis- Mo2(DAniF)2(CH3CN)4 2+ corner pieces with ortho-, meta- and para- isomers of enatiomerically pure –O2CCH(CH3)C6H4CH(CH3)CO2 – dicarboxylate was performed. First, an enantiomerically pure molecular loop based on two dimolybdenum units and two para-dic arboxylate linkers was synthesized and structurally characterized. Similar reactions with isomeric ortho- and meta- dicarboxylate linkers, as well as with some nonchiral ligands, showed that the structure of the obtained products depends on the geometry of the ligand. Meta- dicarboxylate linker favors the formation of the chelated product and ortho- dicarboxylate linker produces the mixture of chelated molecules and loops. On the second topic, an investigation of the formation of metal-metal bonds was performed. Study of the one-electron bond obtained upon oxidation of Ni2 4+ and Pd2 4+ to Ni2 5+ and Pd2 5+, respectively, was made. The compounds synthesized were studied with various physical methods, such as X-ray crystallography, UV-visible spectroscopy and EPR spectroscopy. The nature of oxidized species as well as the dependence of metalmetal interactions on electron-donating abilities of bridging ligands was studied. It was shown that oxidation takes place on a metal center. The formation of one-electron bond in oxidized species is proposed. Finally formation of Ti2 6+ single bonded compounds by the reduction of two Ti4+ monomers to Ti2 6+ dimer was studied. The nature of the species obtained in solution and in solid state is discussed. The crystal structure shows the presence of two types of hpp ligands – chelating and bridging. NMR study of this compound in solution proposes the rearrangement of this structure to a paddlewheel.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Supervisor: Raul G. Longoria. Vita. Includes bibliographical references. Also available from UMI.

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As new adhesive products become available in restorative dentistry, investigating their potential application for orthodontic use is warranted. Vertise Flow (Kerr) is a self-adhering flowable resin and is being marketed for use as a sealant, porcelain repair and small class I restorations. It has potential for use as an orthodontic adhesive. Objective: Determine if Vertise Flow (Kerr) is suitable for bonding fixed orthodontic appliances to enamel, restorative resin composite and porcelain with minimal surface preparation. Methods: Shear Bond Strengths (SBS) from six (6) groups of fifteen (15) bonded stainless steel lingual buttons (Ormco) were obtained over three time points (24hr, 7 days, and 3 months). The six test groups were: 1.Vertise Flow to enamel (Tt) with coarse pumice debridement, 2. Transbond XT (3M, Unitek) to enamel (Tc) with phosphoric acid etching [control], 3.Vertise Flow to Herculite Ultra (Kerr) (Cc) with coarse pumice debridement, 4. Vertise Flow to Filtek Supreme Ultra (3M, ESPE) (Ct) with coarse pumice debridement, 5. Vertise Flow (Kerr) to porcelain (Pt) with diamond bur roughening, and 6. Transbond XT (3M Unitek) to porcelain (Pc) with hydrofluoric acid etching. Samples were stored in distilled water and incubated at 37C. The buttons were then debonded with a Zwick Universal Testing machine using a 10 kN load cell with a crosshead speed of 0.5mm/min. Debonded buttons were evaluated based on a modified Adhesive Remnant Index (ARI). Statistical assessment of the data was performed using parametric and non-parametric tests, with p<0.05 as the threshold for statistical significance. Results: The mean SBS obtained in all groups at each time point were >4MPa and varied between 8.69MPa and 27.44MPa. Statistical differences were found within the composite and porcelain groups at T1, and the enamel and composite groups at both T2 and T3. Nearly half of the sample (47.2%) achieved an ARI score of 5 (100% adhesive left on button base). Conclusion: Vertise Flow potentially provides clinically acceptable bond strengths to enamel, restorative resin composite and porcelain with minimal surface preparation. Furthermore, upon removal, minimal adhesive clean-up is required thus saving valuable chair time. Based on the results in this study, future in vivo investigation is suggested.

Objective: Evaluate the effect of crosshead speed, load cell configuration and curing time on shear bond strengths. Methods: 160 human molars were divided into equal groups of 20 second and 40 second photopolymerization times and then into 1kN or 10kN load cell groups. Each of the groups were divided into 0.5mm/min or 5mm/min crosshead speeds. Results: Regarding photopolymerization time (20s vs. 40s) and crosshead speeds (0.5mm/min vs. 5.0mm/min) there were no significant differences in SBS (p>0.05). The load cell configuration (1kN vs. 10kN) however showed statistically significant differences (p<0.05) with the 1kN producing higher bond strengths.

The work described in this thesis is principally concerned with the measurement of the anharmonicity associated with 'isolated' CH stretching frequencies, and the prediction of individual bond dissociation energies from these values. In addition, CHC1F₂ was the subject of an extended anharmonic vibrational analysis, and CHD₂C1 of a similar vibration-rotation one. In the first of these studies, the IR gas phase spectra of the two isotopic species: CH³⁵C1F₂ and CH³⁷C1F₂, were recorded in the range 15000 - 300 cm^-1. The frequencies of all fundamental vibrations have been accurately determined and analysis of the 800 cm^-1 region Fermi resonance dyad between v4 and 2v6 by the method of isotope shifts yielded an initial estimate of the k₄₆₆ potential energy term. This value enabled the complex pattern of 'hot' bands observed here and in the 1200, 1400, 1600 and 2000 cm^-1 regions, where related Fermi resonances occur, to be analysed, yielding several X<i>ij</i> (i,j = 4,5,6,9) values for both isotopic species. An initial refinement calculation on the data for the ³⁵C1 species from these regions resulted in more accurate X_ij values and a superior estimate of K₄₆₆. A subsequent refinement using data up to 10000 cm^-1 for the vibrational modes v1, v4, and v6 enabled further X_ij (i,j = 1,4,6) values to be determined and several features associated with the CH stretching overtones to be successfully explained. However, the unexpected doublet observed in the region of the CH stretching fundamental could not be unambiguously assigned beyond that one component results from a 'hot' transition. Finally, several more X_ij values were determined from the many overtone and combination bands of other vibrational modes observed in this study, thus defining in total 32 of the 45 anharmonicity constants for this molecule. Secondly, the CH stretching and CH bending modes, their overtones and combinations, in a series of tri-halogenated methanes were studied. The observed spectral features of interests were explained by application of simple second order perturbation theory. However, this approach failed to account for the spectra above approximately 10000 cm^-1 at which point it apparently becomes necessary to apply first order perturbation theory. During the course of this study several ωi and X_ij values were determined. In addition, the inclusion of terms of the type ωey_evi + 1/2)³ when treating an 'isolated' CH bond in a polyatomic molecule as a simple diatomic was investigated. In the next two groups of studies the technique of partial deuteration was employed in order to obtain information on individual CH bond strengths in methyl groups. Firstly, some molecules having symmetrical methyl groups are discussed, specifically CHD₂X (X = C1, Br, I). For the bromide and the iodide the CH stretching mode, v1, and its first two overtones were recorded whilst the entire spectrum of the chloride in the region 12000 - 400 cm^-1 was observed. The bands of these compounds are amenable to both rotational and vibrational analysis in many instances. Thus, for each molecule a value of A_o was determined along with the anharmonicity constant X₁₁. In CHD₂C1 the analysis led to a number of harmonic frequencies, ωi.

No description available.

This thesis develops a model of closed end bond funds that helps us better understand a recent finding in the literature. In 2012 Elton et al. published an empirical study of closed end bond funds (CEBFs) and they suggested that the use of leverage in CEBFs could explain the fact that these funds had higher returns than those of comparable open end funds. This thesis provides a framework for estimating the impact of leverage on expected return and risk in this context. We use a Merton type approach to model both unlevered and levered CEBFs. The assets of a CEBF are primarily risky bonds. Each of these risky bonds can be analysed in terms of options under the Merton approach. We create an unlevered CEBF model by extending Merton's model to a multi-firm framework to represent a CEBF composed of several risky bonds. We then add leverage by assuming the CEBF issues debt. This permits us to model the securities of a levered closed end bond fund as compound options. The equity and debt of the CEBF can be decomposed into options on a portfolio of options. This framework enables us to compute the expected rate of return and standard deviation of an unlevered and levered CEBF. We obtain results that are comparable to those observed in Elton et al.