Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2006. / Additional advisors: Renato Camata, Richard Fork, Andrei Stanishevsky, Charles L. Watkins, Mary Ellen Zvanut. Dissertation not released until Fall 2007. Description based on contents viewed Oct. 6, 2007; title from title screen. Includes bibliographical references (p. 94-102).

No description available.

An automated ellipsometer was used to study field-induced optical anisotropy in anodic niobium oxide films. The oxide films were found to change from the optically isotropic state to the optically anisotropic state when an electric field was applied normal to the film surface. The anisotropic refractive indices of the oxide films decreased quadratically while the thickness of the films increased quadratically with the applied field. The quadratic electro-optic coefficients were determined. The changes in refractive indices and in thickness of the oxide films were found to be independent of time. Field recrystallization of the anodic niobium oxide films was investigated using a scanning electron microscope. The results are compared with those reported for anodic tantalum oxide films in the published literature. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Internal waves are ubiquitous features in coastal marine environments and have been observed to mediate vertical distributions of zooplankton in situ. Internal waves create fine-scale hydrodynamic cues that copepods and other zooplankton are known to sense, such as fluid density gradients and velocity gradients (quantified as shear deformation rate). The role of copepod behavior in response to cues associated with internal waves is largely unknown. The objective is to provide insight to the bio-physical interaction and the role of biological versus physical forcing in mediating organism distributions. We constructed a laboratory-scale internal wave apparatus to facilitate fine-scale observations of copepod behavior in flows that replicate in situ conditions of internal waves in a two-layer stratification. Three cases were chosen with density jump of 0.75, 1.0, and 1.5 sigma-t units. Analytical analysis of the two-layer system provided guidance to the target forcing frequency needed to generate a standing internal wave with a single dominate frequency of oscillation. Flow visualization and signal processing of the interface location were used to quantify the wave characteristics. The results show a close match to the target wave parameters. Marine copepod (mixed population of Acartia tonsa, Temora longicornis, and Eurytemora affinis) behavior assays were conducted for three different physical arrangements: (1) no density stratification, (2) stagnant two-layer density stratification, and (3) two-layer density stratification with internal wave motion. Digitized trajectories of copepod swimming behavior indicate that in the control (case 1) the animals showed no preferential motion in terms of direction. In the stagnant density jump treatment (case 2) copepods preferentially moved horizontally, parallel to the density interface. In the internal wave treatment (case 3) copepods demonstrated orbital trajectories near the density interface. Further analysis showed that the copepods swim closer to the interface in the presence of internal waves.

Master of Science / Department of Civil Engineering / Mustaque A. Hossain / Due to budget constraints, many highway agencies are becoming interested in pavement preservation or rehabilitation rather than reconstruction to ensure pavement is in serviceable condition. Thin whitetopping (TWT) is the process of rehabilitation of distressed asphalt concrete (AC) pavements using a concrete overlay. This study was done to develop a design catalog for existing AC pavements to be overlaid with TWT. The finite element (FE) analysis was performed with SolidWorks, a 3-D FE software program to develop this design catalog. The design considered different TWT thicknesses, existing AC layer thicknesses and modulus, bonding conditions between TWT and existing AC layer, shoulder conditions and temperature differentials. Each model was built as a three-layer pavement system—concrete (TWT), asphalt layer, and subgrade soil. The traffic load was modeled as a constant pressure with a rectangular area applied at the surface and with intensity equal to the tire inflation pressure of 100 psi. The expected lives of TWT overlays were estimated using fatigue equations developed by the Portland Cement Association (PCA). Results obtained from this study show that interface bonding condition is the most important factor affecting the behavior of TWT. With the increase of TWT thickness or existing AC thickness or AC modulus, and addition of paved shoulder, concrete tensile stress decreases. Curling stress increases with the increase of TWT thickness and is not a function of AC properties. A design catalog was developed in terms of service life of the pavement. Unlike unbonded TWT with unpaved shoulder that results in catastrophic loss of rehabilitated pavement life, bonded TWT is expected to last 10 years, assumed in design. Thus, proper bonding must be ensured in order to have extended pavement life.

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Call number: LD2668 .T4 1962 B45

Sputter deposition is one of the vapour quenching methods used to produce alloying compounds in thin film form. The alloying compounds produced by this method have a chemically homogeneous, non-equilibrium structure which is dill'erent from that of alloys produced by solid quenching, liquid quenching, or mechanical alloying methods. In the present investigation the Fe 1-:x.A1x alloy thin films were prepared using multisource magnetron sputtering. The samples were deposited onto a water cooled substrate and their thickness was kept constant at t- 300nm. To investigate the effect of the deposition parameters on the properties of the films, the samples were deposited at various argon gas pressures PAr I, 3, or 4 mtorr. The effect of gas pressure is consistent with the thermalization of the deposited material by collisions with gas atoms in the chamber. The composition range of the samples varied from pure iron to pure aluminium. The composition, structure and morphology of the films was obtained using Transmission Electron Microscopy (TEM). X-ray diffraction patterns were also used to obtain the structure of the films. Structure analysis showed that a bcc crystalline structure was obtained in samples of composition range x= 0 to - 50%, an amorphous structure in samples of composition range x- 55% to - 83%, and a fcc crystalline structure in samples of composition range x- 85% to 100%. These composition ranges are affected by altering the deposition gas pressure. The morphology of the deposited films was observed to be affected by the deposition gas pressure. The samples deposited at low gas pressure Par=1 mtorr consist of a fibrous structure with densely packed boundaries, while the samples deposited at high gas pressure Par=4 mtorr consist of columnar structures separated by open boundaries. Room temperature resistivity measurements show a drop in resistivity in the composition range x- 30% to 50%. This drop is thought to be due to the formation of chemically ordered Fe3Al and FeAI compounds. Also the resistivity increases with increasing argon gas pressure. The effect of altering the argon gas pressure is to change the morphology of these alloys, and this has a significant effect on the magnetic properties. The effect of annealing on the magnetisation and morphology was also studied in the samples. A low temperature resistivity measurement system was constructed. A closed cycle helium refrigerator, which provided a working temperature range of T= l5°K to 3000K was used for the cooling process. The resistivity measurements revealed three distinct characteristics dependent on composition :- 1. x= 0 to 46%: The samples in this range exhibit a metallic behaviour, with the samples in the composition range x= 27% to 46% showing a resistivity minimum at low temperature which is thought to be due to spin glass formation. 2. x= 48% to 83%: These samples have a semiconductor or metallic glass-like behaviour. 3. x= 85% to 100%: These samples show a metallic behaviour. The above properties are associated with the change in the structure of the fiIrns as the composition varies. A computer controlled AC susceptometer was designed and constructed to measure the AC susceptibility of the samples in the temperature range T= 20 OK to T= 300 OK. A closed cycle helium refrigerator was used to provide the cooling process. The AC susceptibility measurements for the samples with resistivity minima show a sharp peak at low temperature which confirms the presence of spin glass in these samples at low temperature. The results of magnetic and transport properties can be related to the structure and morphology of the filrns. The results have been compared with those obtained from bulk samples with the same composition.

No description available.