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No description available.

No description available.

The research and development of zinc selenide (ZnSe) based wide-gap II¡VVI materials and related blue/green light-emitting devices have significantly progressed since 1990. ZnSe is also a promising material for use in windows, lenses, output couplers, beam expanders, optically controlled switching, visible transmission and giant photo-resistivity. Recently, ZnSe has become an important material used as the window layer of CuInSe2-based solar cells . To improve device performance, it is necessary to reduce interface defects and improve epitaxial layer quality. However, ZnSe thin films on glass substrates with high reliability and applicability have not yet been developed. In this study, a ZnSe buffer layer was firstly grown by SME during the initial stage of film growth; the film crystallinity could gradually be improved layer by layer with smaller thicknesses. While the lattice disorder of the buffer layer decreased rapidly after several cycles of SME growth, the interfacial lattice mismatch between the buffer layer and the ZnSe film deposited by MBD was reduced. Thus, ZnSe films with buffer layers demonstrated better crystallinity. Initial growth stage evaluation of high-quality ZnSe films deposited on glass substrate was investigated. The self-limiting monolayer epitaxial (SME) process was used to pre-growth the buffer layer for a zinc selenide (ZnSe) film deposited. After alternating depositions for several cycles, the growth mode was changed to the molecular beam deposition (MBD) mode under growth conditions. Films deposited at substrate temperatures of 250¡V350¢XC and Se/Zn beam equivalent pressure (BEP) ratios of 0.77¡V1.87 were investigated. The crystal structure and preferred orientation of as-grown ZnSe films were examined using X-ray diffraction (XRD) patterns. The optical properties of the ZnSe films were revealed by photoluminescence spectra. The structure properties of as-deposited ZnSe films have been measured by X-ray diffraction (XRD) technique. The optimum film growth condition has been determined rapidly by comparing and analyzing the relative full width at half-maximum (FWHM) and peak intensity of XRD spectra. The composition of ZnSe films is determined by energy dispersive spectroscopic (EDS) analysis. Optical properties of ZnSe films are characterized by photoluminescence spectra. In addition, the structural parameters, crystallinity, lattice constant, grain size, strain, dislocation density and orientation of ZnSe film calculated are correlated with their growth conditions. The characteristics of the ZnSe films with and without a buffer layer were compared and discussed in detail. Finally, our results demonstrate that how the quality of ZnSe film can be improved on glass substrates for application to various devices.

Nitroalkane oxidase (NAO) catalyzes the oxidation of neutral nitroalkanes to aldehydes and ketones with oxygen consumption and the production of hydrogen peroxide and nitrite. The enzyme is a flavoprotein from the fungus Fusarium oxysporum. The active site base, Asp402, abstracts one proton from the substrate to give a carbanion which then attacks the flavin adenine dinucleotide (FAD). The three dimensional crystal structure of NAO shows that Arg409 is 3.6 Å from Asp402. When Arg409 is mutated to Lys, the rate constant for proton abstraction decreases 100-fold. The three-dimensional structure of NAO also reveals the existence of a tunnel which extends from the protein exterior and terminates at the FAD N5 atom and the residues Asp402 and Phe401. We mutated amino acids in the tunnel into tryptophan, phenylalanine and leucine. The L99W, S276W and S276A enzymes showed the biggest decreases in both kcat and kcat/Km; these amino acids are closest to the FAD molecule and the active site. Mutation of amino acids farther away from the active site showed very small changes in the kinetic parameters. Ser276 is hydrogen bonded to Asp402 in the wild-type enzyme. When this amino acid is mutated to alanine or tryptophan, k3, the rate constant for proton abstraction, decreases around 35 fold. Asp402, Arg409 and Ser276 constitute a catalytic triad in the active site of nitroalkane oxidase, and both Arg409 and Ser276 are important for positioning Asp402 and catalysis.

published_or_final_version / Botany / Master / Master of Philosophy

Peat moss is a major component of many plant growing substrates but is quickly becoming a limited resource. To reduce the reliance on peat moss a number of composted products, including pine mulch, manure, yard waste and aged bark - in combination with peat moss and/or coconut coir, were mixed in various combinations as growing substrates for greenhouse potted Gerbera (Gerbera jamesonii) production. Four new substrates were developed and compared to a commercial mix, BM6 in greenhouse production trials. Experiments were conducted to (1) compare the plant growth and quality of potted Gerbera in the newly developed substrates to BM6, (2) determine whether a pre-charge fertilizer was needed for the newly developed substrates, (3) determine appropriate rates of a pre-charge fertilizer for the newly developed substrates, and (4) determine the nitrogen drawdown index over the time of production and determine if there is a relationship between the NDI values and the nitrogen availability measured by pour through values. Two of the newly developed peat reduced substrates were successful in producing acceptable quality potted Gerbera. One of the substrates contained a low percentage of peat moss and the other contained coir fines. Fertilizer pre-charge rates, and some nutrient and irrigation management protocols were recommended for these two substrates.

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No description available.