One of the major technical challenges towards a viable H2S//Air SOFC is to identify and develop anode materials that are electronically conductive, chemically and electrochemically stable, and catalytically active when exposed to H2S-rich environments. The corrosive nature of H2S renders most traditional state-of-the-art SOFC anode materials (Ni, Pt, Ag) useless for long-term cell performance even at very low sulfur concentrations. In my doctoral thesis work, a new class of perovskite-based anodes was developed for potential use in SOFCs operating with H2S and sulfur-containing fuels. Cermets from this family of materials have shown excellent chemical stability and electrochemical performance at typical SOFC operating conditions. As an added benefit, they appear to preferentially oxidize H2S over hydrogen, as suggested by open circuit voltage, impedance spectra, and cell performance measurements obtained using various H2S-H2-N2 fuel mixtures. Cell power output values were among the highest reported in the literature and showed no significant deterioration during 48-hour testing periods. Impedance measurements indicated overall cell resistances decreased with increasing temperature and H2S content of the fuel. This behavior is starkly different from that of contemporary SOFC anodes, where the presence of H2S usually increases overall polarization resistance and ultimately destroys the cell. Results are promising due to the drastic improvement in sulfur tolerance compared to the current generation of SOFC power systems.

Hydrogen peroxide (H2O2), a membrane-permeable reactive oxygen species, is continuously produced by mitochondrial respiration, the membrane-associated NADPH oxidase complex, xathine oxidase catalyzed reaction. Although the cytotoxic effect of H2O2 is well documented, the role of H2O2 in synapse formation if still in its infancy. Here we test the role of H2O2 on the frequency of spontaneous synaptic currents (SSCs) at developing Xenopus neuromuscular synapse by using whole-cell patch clamp recording. Bath application of H2O2 dose-dependently enhances the frequency of spontaneous synaptic currents (SSC frequency). Treatment of the culture with membrane-permeable antioxidants N-acetylcysteine and sodium pyruvate significantly decreased SSC frequency, indicating endogenous reactive oxygen species play important roles in the regulation of spontaneous ACh release. Bath application of membrane non-permeable catalase, which breaks down H2O2 specifically, has no significant effect on SSC frequency, suggesting H2O2 is not an intercellular signaling molecule being produced and released from postsynaptic myocyte and affects the neurotransmitter release of presynaptic motoneuron. Much to our surprise is that the SSC frequency was significantly decreased while catalase was vii loaded into the myocyte through recording pipette. Furthermore, the SSC frequency facilitation induced by exogenously applied H2O2 was completely hampered while catalase was loaded into the myocyte. These results indicate although endogenous H2O2 in myocyte plays a crucial role on SSC frequency facilitation, this facilitation on the neurotransmitter release of presynaptic motoneuron is achieved through a retrograde factor other than H2O2 itself. Treatment of the culture with inhibitor of either NADPH oxidase does not have significant effect on SSC frequency. Bath application of mitochondria complex I, II and xanthine oxidase inhibitor significantly decreased SSC frequency, suggesting H2O2 derived from xanthine oxidase and mitochondria is responsible for the regulation of SSC frequency. Bath application of translation blocker anisomycin and cycloheximide could not attenuate the facilitation of H2O2. Addition of IGF-1 receptor inhibitor JB-1 to the culture significantly attenuated SSC frequency. Overall, our current results suggest that xanthine oxidase activity-derived H2O2 in myocyte induce the release of IGF-1 which retrogradely enhance the spontaneous neurotransmitter release from presynaptic motoneuron. Since synaptic activity is crucial in synaptogenesis and synapse maturation, results form viii our studies have shed some light on the molecular mechanism of the formation of developing neuromuscular synapse.

The circadian oscillator of the cyanobacterium Synechococcus elongatus is composed of only three proteins, KaiA, KaiB, and KaiC, which together with ATP can generate a self-sustained ~24 hour oscillation of KaiC phosphorylation for several days. KaiA induces KaiC to autophosphorylate whereas KaiB blocks the stimulation of KaiC by KaiA, which allows KaiC to autodephosphorylate. We propose and support a model in which the C-terminal loops of KaiC, the “A-loops”, are the master switch that determines overall KaiC activity. When the A-loops are in their buried state, KaiC is an autophosphatase. When the A-loops are exposed, however, KaiC is an autokinase. The data suggest that KaiA stabilizes the exposed state of the A-loops through direct binding. We also show evidence that if KaiA cannot stabilize the exposed state KaiC remains hypophosphorylated. We propose that KaiB inactivates KaiA by preventing it from stabilizing the exposed state of the A-loops. Thus, KaiA and KaiB likely act by shifting the dynamic equilibrium of the A-loops between exposed and buried states, which shifts the balance of autokinase and autophosphatase activities of KaiC. A-loop exposure likely moves the ATP closer to the sites of phosphorylation and we show evidence in support of how this movement may be accomplished. Density functional theory calculations of isolated Watson–Crick A:U and A:T base pairs predict that adenine 13C2 trans-hydrogen bond deuterium isotope shifts due to isotopic substitution at the pyrimidine H3, 2hΔ13C2, are sensitive to the hydrogen-bond distance between the N1 of adenine and the N3 of uracil or thymine, which supports the notion that 2hΔ13C2 is sensitive to hydrogen-bond strength. Calculated 2hΔ13C2 values at a given N1–N3 distance are the same for isolated A:U and A:T base pairs. Replacing uridine residues in RNA with 5-methyl uridine and substituting deoxythymidines in DNA with deoxyuridines do not statistically shift empirical 2hΔ13C2 values. Thus, we show experimentally and computationally that the C7 methyl group of thymine has no measurable affect on 2hΔ13C2 values. Furthermore, 2hΔ13C2 values of modified and unmodified RNA are more negative than those of modified and unmodified DNA, which supports our hypothesis that RNA hydrogen bonds are stronger than those of DNA. It is also shown here that 2hΔ13C2 is context dependent and that this dependence is similar for RNA and DNA.

Thesis(M.S.)--Case Western Reserve University, 2009 / Title from PDF (viewed on 2009-11-23) Department of EMC - Aerospace Engineering Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 156-162). Available also in a digital version from Dissertation Abstracts.

Dissertation : Physics : Chicago : 1917. / Notes bibliographiques.

Thesis (M.Sc.)--York University, 2007. Graduate Programme in Physics and Astronomy. / Typescript. Includes bibliographical references (leaves 77-79). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR38785

Thesis (M.S.) -- University of Texas at Arlington, 2008.

Thesis (Ph. D.)--Columbia University, 1928. / Vita. Reprinted from the Transactions of the American electrochemical society, v. 51, 1927.

Thesis (Ph. D.)--University of Oregon, 2003. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 140-147). Also available for download via the World Wide Web; free to University of Oregon users.