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HREM imaging was performed using the Jeol 4000ex microscope on specimens prepared from an as-grown ingot of semi-insulating Gallium Arsenide. Various low angle grain boundaries were imaged in the [110] orientation, misorientations varying between 4°-13°. Detailed study of a grain boundary of 11.5° misorientation about the [110] rotation axis has been carried out. Burgers vector analysis showed the presence of perfect 60° and [001] dislocations. Modelling of the [001] dislocation has been carried out using the Tersoff potential, Bond Order Potential and a tight binding Hamiltonian for GaAs, using Chadi (1984) parameters. The dislocation core was associated with an 8-membered and two 5-membered rings. Assum- ing there is a minimum of wrong bonds, we predict that the core has two wrong bonds, one being Ga-Ga, and the other As-As, both in equivalent positions where the two 5-membered rings were appended to the 8-membered ring. The Ga-Ga bond is considerably shorter and hence stronger than the As-As bond. Band structure calculations performed using a Vogl (1983) sp³s* Hamiltonian revealed deep states in the gap, which are associated with atoms in the core only. Using Stadelmann's (1987) EMS program, successful image matching of calculated images of the [001] dislocation has been achieved with the experimental image, using the atomic structure generated by tight binding relaxation. Ga and As being only two atomic numbers apart have similar scattering factors and cannot be easily distinguished in the experimental image. The equivalence of the position of the two wrong bonds greatly eases image matching as it is no longer necessary to know which is the Ga-Ga , and which is the As-As bond. This is the first suggested model of the [001] dislocation in GaAs, to the best of my knowledge. It is found to be similar to the atomic structure of the 90° partial dislocation in silicon (Bigger et al., 1992). No account of segregation of impurities to the grain boundary, or the [001] dislocation core is taken here, though it is very likely that an impurity atom would sit itself in this large space. The relaxed atomic structure for the 60° dislocation showed a doubling of periodicity along the dislocation line, similar to that found in the 30° partial in Si. The core consists of a 7-membered and a 5-membered ring with a minimum of two wrong bonds. In addition to this, quantitative comparisons of the [001] HREM image and simulated structures have been made and an iterative structure refinement carried out in order to achieve the best image matching. The resultant 'experimental-best-fit' structure was not found to be physically or chemically plausible.

Biopolymers are polymers produced by certain microorganisms, that are readily degradable in the environment. These biodegradable plastics have the potential to be used as substitutes for conventional petroleum based plastic provided that the production costs can be greatly reduced. The high cost of biopolymer production is due to the cost of substrate which mainly is glucose. / The enzymatic hydrolysis of potato processing wastes was to produce glucose as a least expensive feedstock substrate for the production of biopolymers of polyhydroxybutirate (PHB) from the bacterium Alcaligenes eutrophus was studied. The enzymatic hydrolysis experiments were carried out using $ alpha$-amylase liquefaction enzymes from Aspergillus oryzae and barley-malt, and amyloglucosidase saccharification enzyme from Rhizopus. / The results indicated that the production of glucose from potato starch waste to be used as a substrate to produce biopolymers was both technically and economically feasible. A 10 to 90 ratio of barley-malt to potato starch waste gave the highest conversion of starch to glucose of 194.30 gL$ sp{-1}$ (96.56%), and the lowest liquefaction enzyme cost ($0.054) to hydrolyze one kg of potato starch waste. { it A. eutrophus /} produced PHB of 5.0 gL$ sp-1$ (76.9 % of biomass) using the glucose substrate generated from the potato starch waste.

A beta-galactosidase gene from Bifidobacterium breve B24 which showed the higher hydrolytic and synthetic activity was cloned in E. coli. The complete beta-galactosidase gene contained 2076 bp nucleotides and encoded 691 amino acids which had a high homology to the other Bifidobacterium species. This beta-galactosidase was homologous to that of the LacA family. The galA gene was successfully over-expressed in E. coli ER2566. To observe any change in the recombinant enzyme, beta-galactosidases from Bifidobacterium breve B24 and recombinant E. coli ER2566 were purified to homogeneity by ion exchange chromatography (Mono-Q) and gel-filtration chromatography (Superose-12 and Superdex 200) columns. The molecular mass of both beta-galactosidases was estimated to be 75 kDa on SDS-PAGE. Activity staining on non-denaturing Native-PAGE and Superose-12 gel-filtration chromatography showed that the enzymes are composed of a dimer with a molecular mass of 150 kDa. / The optimum pHs of the native and recombinant enzymes for hydrolyzing O-nitrophenyl-beta-D-galactopyranose (ONPG) were pH 6.0 and 7.0, respectively, and they were stable over the pH range of 5-8 and 6-9, respectively. The optimum temperature of both enzymes for hydrolyzing ONPG was similar at 45 °C and they were stable over the temperature range of 20-45 °C. Both enzymes were stable up to 45 °C during 5 h of incubation at pH 6.5. The recombinant enzyme was slightly activated by bivalent metal ions, Mg2+, Mn2+, and Zn2+ at 1 mM but strongly inhibited by Hg2+ and p-chloromercuribenzoic acid (PCMB). The K m values of both native and recombinant beta-galactosidases for ONPG were 2.77 and 1.82 mM, respectively, and the Vmax values were 1.02 and 1.39 mM/min, respectively. / The two beta-galactosidase activities were also tested with lactose as substrate. The optimum pH of the native and recombinant enzymes for hydrolyzing lactose was similar at pH 6.0. Both enzymes had more than 80 % of their activity in the range of pH 6-8, indicating that the enzymes were stable at neutral pH. However, the native beta-galactosidase had around 40 % of its activity at pH 5.0, whereas the recombinant enzyme had no activity at this pH. On the other hand, the recombinant enzyme had over 50 % of its activity at pH 9.0, while the native beta-galactosidase showed lower than 5 % of its activity. The optimum temperature of both enzymes was at 45 °C. The profiles of both enzyme activities were very similar except at the temperature of 10 °C. The recombinant beta-galactosidase still had around 20 % of its enzyme activity at 10 °C, while no enzyme activity from the native enzyme was detected at this temperature.

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 56-58). / xiii, 58 leaves, bound ill. 29 cm

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