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<p>Microorganisms inhabiting silica solute-rich environments often show various degrees of Si02 mineralization as a consequence of exposure to SiOrsaturated waters. As such, it has been thought that microorganisms exert a prominent role in the immobilization of amorphous silica phases. While this intimate spatial relationship of microorganisms and amorphous Si02 phases are almost always observed in hot springs, the exact mechanisms by which microbes affect Si02 secondary mineral precipitation is still poorly understood. Further, available laboratory investigations to date consistently showed that microbes do not significantly impact Si02 immobilization, suggesting that microbial silicification is a mere consequence of exposure to a largely abiogenically-driven Si02 precipitation. </p> <p>This study demonstrates that discernible microbially-mediated silicification can occur under conditions where the potential for microbial opportunity to biomineralize is promoted. Identification of the key geochemical requirements for biosilicification to occur include thermodynamically favorable, but sluggish silica reaction kinetics associated with acidic conditions, and the necessity for colloidal silica rather than dissolved silicic acid species. This work provides the first results to bridge the apparent literature discrepancy between widespread, in-situ observations of microbial silicification, and the inability to demonstrate a detectable microbial effect in this process under well-constrained laboratory conditions.</p> <p>Acid conditions promote microbial silicification by overriding the dominant repulsive forces arising from charge similarities between Si02 and cell surfaces, via neutralization of deprotonated surface silanol and carboxylic groups, respectively. Mechanistic consideration for Si02 coordination to cell surfaces suggests direct chemical bonding of silanol to carboxylic groups forming stable inner-sphere complexes largely insensitive to environmental perturbations. This result indicates that microbially immobilized Si02 are more tenaciously-coordinated on cell surfaces and not simply electrostatically-held.</p> <p>Surface-dependent silicification showed higher Si02 mineralization propensities for unmineralized microbial cells compared to silica-encrusted cell matrices. Moreover, the extent and style of microbial Si02 mineralization is impacted by cellular level of metabolic activity. These results suggest that a biological overlay may be discernible in microbially induced biosilicification. </p> / Thesis / Doctor of Philosophy (PhD)

<p> The products of the reaction between oxomethoxodichlorobistriphenylphosphinerhenium(V) and acetylacetone are determined, characterized and correlated in terms of a reaction scheme. A series of rhenium(III) compounds, characteristic of reactions analogous to the one mentioned above, with other β-ketoenols is prepared and characterized. The syntheses and properties of tris-1,1,1-5,5,5-hexafluoropentane-2,4-dionatorhenium(III) and trispentane-2,4-dionatorhenium(III) are described. A new nitrido-rhenium complex, nitridochloro-1,1,1-5,5,5-hexafluoropentane-2,4-dionatobistriphenylphosphinerhenium(V) complex is prepared and characterized. A synthetic route to pyridine-acetylacetonate complexes of rhenium is described. </p> / Thesis / Doctor of Philosophy (PhD)

<p> The following thesis comprises the study of six resonances in the Na^23(p,γ)Mg^24 reaction, using a 40 cu. cm. Ge(Li) detector. These resonances are at proton energies, Ep = 512 Kev, 987 Kev, 1020 Kev, 1174 Kev, 1318 Kev and 1416 Kev. The decay scheme and branching ratios have been found for each of these resonances. Also the gamma transition widths have been found for all of these resonances, except the 1416 Kev resonance, and these transition widths have been employed in calculating the reduced gamma transition strengths for the above decays.</p> / Thesis / Master of Science (MSc)

<p> This dissertation describes an experimental study of the simultaneous mass transfer and chemical reaction at a plane liquid-liquid interface involving the saponification of simple esters transferring into aqueous caustic solutions. The transfer experiments were carried out with both liquid phases stirred and unstirred respectively.</p> <p> Special emphasis was placed on the stagnant-phase systems. Turbulent reaction layer propagation rates were measured for ester phases (pre-saturated with water) in contact wiith aqueous caustic solutions (at various concentration levels). The distortion of the moire pattern was used to indicate the position of the propagating layer front. The cause and nature of the turbulent layer were elucidated. An apparatus, capable of withdrawing small samples of the liquid with probes precisely located in the aqueous phase, was constructed. Experimental techniques were developed to measure the abnormal concentration profiles of the reactants and the products within the turbulent layer. From the component concentration distribution data, the turbulent layer thicknesses, the reaction zone (within the turbulent layer) thicknesses, the mass transfer rates, and the enhancement factors were deduced. The effects of turbulence in the aqueous phase were estimated in terms of the derived eddy diffusivities and of the differences between the experimentally measured and the theoretically predicted (by molecular diffusion with reaction equation) enhancement factors.</p> <p> In the steady state transfer study using stirring in both phases, transfer rate data and enhancement factor data were obtained for three formate-sodium hydroxide systems.</p> <p> In addition to the mass transfer studies, a preliminary investigation on the diffusion coefficient measurement in binary and ternary liquid systems employing the moire pattern method was carried out. A diffusion cell was designed and built to enable the quick acquisition of the experimental data with reasonable accuracy.</p> / Thesis / Doctor of Philosophy (PhD)

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