Thesis (Ph.D.)--Stanford University, 2006. / Adviser: Krishna C. Saraswat. Includes bibliographical references (p. 160-177)

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The UNderstanding Severe Thunderstorms and Alberta Boundary Layer Experiment (UNSTABLE) in July 2008 was a field project to investigate the initiation of thunderstorms in southern Alberta. Special field observations included an enhanced surface network augmented with instrumented vehicles. Upper air observations were taken from four sites every two hours. This thesis focuses on the case study day of 17 July 2008 when a dryline formed parallel to the Rocky Mountains at 1030 MDT and persisted for up to nine hours. The vapour mixing ratio changed from 4.5 to 8.5 g/kg over 5 km. We documented the spatial and temporal distribution of cloud and precipitation relative to the dryline. Initially, extensive cloud formed over the dry air to the west of the dryline, while the capping inversion at 800 mb inhibited cloud formation in the moist air. In the afternoon, convection was triggered along the dryline and severe thunderstorms were observed.

In polymer electrolyte membrane (PEM) fuel cells one of the most important components is the flow field. The flow field distributes reactant gasses to the active area and also delivers electrons from the outer circuit so that the electrochemical reaction may be completed. Optimizing flow field design is extremely important in order to increase the overall power density of the fuel cell. It is particularly important to understand the ways in which the different portions of the flow field, namely the land and channel sections, interact with the gas diffusion layer (GDL), catalyst layer and membrane; this study focuses on those interactions. The most common type of flow field design currently used in PEM fuel cells is the serpentine flow field. It is used for its simplicity of design, its effectiveness in distributing reactants and its water removal capabilities. The knowledge about where current density is higher, under the land or the channel, is critical for flow field design and optimization. Yet, no direct measurement data are available for serpentine flow fields. In this study a fuel cell with a single channel serpentine flow field is used to separately measure the current density under the land and channel, which is either catalyzed or insulated on the cathode. In this manner, a systematic study is conducted under a wide variety of conditions and a series of comparisons are made between land and channel current density. Results show that under most operating conditions, current density is higher under the land than that under the channel. However, at low voltage, a rapid drop off in current density occurs under the land due to concentration losses. The mechanisms for the direct measurement results and general guidelines for serpentine flow field design and optimizations are provided. In addition the same technique is utilized to separately measure current density under the land and channel on a variety of serpentine flow field geometries. Each flow field is tested under a wide variety of operating conditions thereby providing guidance for the optimum design geometry. Experimental results show that generally flow fields with both thinner lands and thinner channels provide better overall performance. However, the optimal flow field designs are highly dependent on fuel cell operating parameters. Finally, it is critical not only to know where the current density is greater, under the land or under the channel, but to understand the fundamental mechanisms driving these differences. Resistance was measured, ex-situ, between the GDE and flow plate under the land of the flow field and under the channel separately. The contact resistance between the gas diffusion electrode (GDE) and the graphite flow plate were measured using an ex-situ technique. The resistance was measured under different land and channel widths. Cyclic Voltammetry tests were also conducted in order to determine if there is any different in electrochemically active area(ECA) under the land and under the channel and what the cause of this difference might be. Results show that the compression of the gas diffusion electrode not only affects the electronic resistance but the ECA as well and that these are key factors in current density variations under the land and channel.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 159-164).

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The prevention and control of salmonellae in commercial swine operations are becoming increasingly important. The current approach focuses on identifying sources and/or origins of salmonellae contamination before swine are processed for human consumption. The objective of the current study was to assess strain variability among salmonellae grouped by serotype and to determine common origins of contamination (farm or slaughter plant). Salmonellae were previously collected from swine at slaughter, serotyped by the National Veterinary Services Laboratory and stored at - 70??C. Pulsed-field gel electrophoresis (PFGE) was performed to genotypically characterize serotypic isolates using restriction endonuclease XbaI. Dendrogram comparisons were also used to assess genotypic similarity when multiple genotypes existed. This study found PFGE to be more discriminatory than serotyping indicating that multiple genotypic strains existed among selected serotypes. On the basis of PFGE results alone, origins of contamination could not be determined in this study. It is suggested by the author, that origins of contamination could be further defined pending future research, in which in-depth longitudinal studies are included. When used as an adjunct to conventional typing methods, PFGE may prove to be a substantial subtyping system in epidemiologic investigations to identify point-of-entry contaminants to the food chain.