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The flavin-containing monoamine oxidases (MAO) A and B catalyze the oxidative deamination of primary and secondary amines. The overall process involves a two electron oxidation of the amine to the iminium with concomitantreduction of the flavin. Based on extensive studies with a variety of chemical probes, Silverman and colleagues have proposed a catalytic pathway for the processing of amine substrates and inactivators by MAO-B that is initiated by a single electron transfer (SET) step from the nitrogen lone pair to the oxidized flavin followed by α-proton loss from the resulting amine radical cation that leads to a carbon radical. Subsequent transfer of the second electron leads to the reduced flavin and the iminium product. In the case of N-cyclopropylamines, the initially formed amine radical cation is proposed to undergo rapid ring opening to form a highly reactive primary carbon centered radical that is thought to be responsible for inactivation of the enzyme. In this thesis we have exploited the unique substrate and inactivator properties of 1,4-disubstituted tetrahydropyridine derivatives to probe the mechanism of MAO-B catalysis. Reports of the parkinsonian inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a structurally unique substrate of MAO-B initiated these studies. Consistent with the SET pathway, the N-cyclopropyl analog of MPTP proved to be an efficient time and concentration dependent inactivator but not a substrate of MAO-B. On the other hand, the 4-benzyl-1-cyclopropyl analog is both a substrate and inactivator of MAO-B. These properties may not be consistent with the obligatory formation of a cyclopropylaminyl radicalcation intermediate. In an attempt to gain further insight into the mechanism associated with the MAO catalyzed oxidation of 1,4-disubstituted tetrahydropyridines, deuterium isotope effects studies on both the substrate and inactivation properties of the 4-benzyl-1- cyclopropyl derivative were undertaken. A series of 1-methyl- and 1-cyclopropyltetrahydropyridine derivatives bearing various heteroaro-matic groups at C-4 also have been examined. The MAO-B substrate properties, inactivator properties and partition ratios for these compounds together with preliminary results from chemical model studies are discussed in terms of the MAO-B catalytic pathway. / Ph. D.

Detailed heat transfer coefficient distributions have been obtained for narrow converging and diverging channels with and without enhancement features. The enhancement feature considered for this study is dimples (inline and staggered) on the main heat transfer surfaces. All the measurements are presented at Reynolds numbers of 3500, 8900, 18000, and 7000, 14000, 28000 for converging and diverging channels respectively. Pressure drop measurements for the overall channel are also presented to evaluate the heat transfer enhancement geometry with respect to pumping power requirements. The test models were studied for wall heat transfer coefficient measurements using the transient liquid crystal technique. The modeled wall inner surfaces were sprayed with thermochromic liquid crystals, and a transient test was used to obtain the local heat transfer coefficients from the measured color change. Analysis of results shows that dimples, in general, have very good enhancement capabilities and staggered dimpled surfaces provide considerably higher heat transfer coefficients and a reasonable pressure drop compared to inline dimpled configuration. Additionally, this study was extended to understand the effect of strategic placement of dimples (staggered) at various locations along the channel to understand regions that contribute significantly to the overall enhancement. / Master of Science

An electropolymerizable zinc porphyrin carrying eight entities of peripheral bithiophene, 4 was newly designed and synthesized. In this design, the bithiophene entities were separated by a biphenyl spacer to minimize ground state interactions perturbing porphyrin π-electronic structure. By multi-cyclic voltammetry, thin-films of 4 were formed on transparent FTO electrode and were characterized by optical, electrochemical and STM measurements. Further, the ability of zinc porphyrin in 4 to axially coordinate phenyl imidazole functionalized fullerene, C60Im both in solution and on the film interface was performed and characterized. Fluorescence quenching of zinc porphyrin both in solution and in the film was observed upon binding of C60Im. Femtosecond transient absorption studies revealed excited state charge separation for the dyad in solution wherein the measured rate of charge separation, kCS and charge recombination, kCR were found to be 2 x 1010 s−1 and 1.2 x 109 s−1, respectively. In contrast, transient absorption studies performed on the dyad in the film were suggestive of energy transfer with minimal contributions from electron transfer. The present study brings out the importance of modulating photochemical reactivity of donor-acceptor dyad in film as compared to that in solution. The electro- and photocatalytic reduction of molecular nitrogen to ammonia (nitrogen reduction reaction, NRR) is of broad interest as an environmentally- and energy-friendly alternative to the Haber–Bosch process for agricultural and emerging energy applications. Herein, we review our recent findings from collaborative electrochemistry/surface science/theoretical studies regarding transition metal oxides, oxynitrides and sulfides as NRR catalysts. We found that, for all metal oxides and oxynitrides specifically, there is no Mars–van Krevelen mechanism and that the reduction of lattice nitrogen and N2 to NH3 occurs by parallel reaction mechanisms at O-ligated metal sites without incorporation of N into the oxide lattice. Additionally, the results highlight the importance of both O-ligation and the importance of N in stabilizing the transition metal cation in an intermediate oxidation state, for effective N≡N bond activation. For transition metal sulfides, various exfoliation treatments are known to yield Sulfur vacancies and DFT calculations corroborate N2 binding to S-vacancies, with substantial π-backbonding to activate dinitrogen. Most of our NRR catalysts were selective to ammonia production without appreciable competing production of H2.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1959 Y36

Call number: LD2668 .T4 1962 A35

Thesis (M.Sc.(Agric, Science and Tech) North-West University, Mafikeng Campus, 2012

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / The Consultative Committee for Space Data Systems (CCSDS) developed the CCSDS File Delivery Protocol (CFDP) to provide reliable delivery of files across space links. Space links are typically intermittent, requiring flexibility on the part of CFDP. Some aspects of that flexibility will be highlighted in this paper, which discusses the planned use of CFDP on the Global Precipitation Measurement (GPM) mission. The operational scenario for GPM involves reliable downlink of science data files at a high datarate (approximately 4 megabits per second) over a space link that is not only intermittent, but also one-way most of the time. This paper will describe how that scenario is easily handled by CFDP, despite the fact that reliable delivery requires a feedback loop.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Reliable delivery of data products is often required across space links. For example, a NASA mission will require reliable delivery of images produced by an on-board detector. Many missions have their own (unique) way of accomplishing this, requiring custom software. Many missions also require manual operations (e.g. the telemetry receiver software keeps track of what data is missing, and a person manually inputs the appropriate commands to request retransmissions). The Consultative Committee for Space Data Systems (CCSDS) developed the CCSDS File Delivery Protocol (CFDP) specifically for this situation. CFDP is an international standard communication protocol that provides reliable delivery of data products. It is designed for use across space links. It will work well if run over the widely used CCSDS Telemetry and Telecommand protocols. However, it can be run over any protocol, and will work well as long as the underlying protocol delivers a reasonable portion of the data. The CFDP receiver will autonomously determine what data is missing, and request retransmissions as needed. The CFDP sender will autonomously perform the requested transmissions. When the entire data product is delivered, the CFDP receiver will let the CFDP sender know that the transaction has completed successfully. The result is that custom software becomes standard, and manual operations become autonomous. This paper will consider various ways of achieving reliable file delivery, explain why CFDP is the optimal choice for use over space links, explain how the core protocol works, and give some guidance on how to best utilize CFDP within various mission scenarios. It will also touch on additional features of CFDP, as well as other uses for CFDP (e.g. the loading of on-board memory and tables).