2007 MU dissertations - Freely available online
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Item Development of MURR flux trap model for simulation and prediction of sample loading reactivity worth and isotope production(University of Missouri--Columbia, 2007) Ma, Zhegang, 1968-; Miller, William Hughes, 1941-University of Missouri Research Reactor (MURR) is the highest power university research reactor in America. It has been supplying various radioisotopes for more than 20 years. The flux trap, locating in the center island tube, has the highest flux for sample irradiating with an ability of 6x1014 n/cm2/s. It is very important for the MURR to be able to predict the reactivity worth of sample loading in the flux trap, as well as the production of specific isotopes. The research develops MURR Flux Trap Model (MFTM) which simulates the reactor core and flux trap area, solves the neutron transport equation and calculates the loading worth based on the Monte Carol method, proceeds with burnup and decay calculation, and predicts the requested isotope production. MCNP part of the MFTM model carries out neutron transport calculations and predicts the reactivity worth of sample loading in the flux trap while MonteBurns part of the model calculates isotope production from the target sample irradiated in the flux trap by solving the general nuclide depletion equation. Different sample loadings and their measurement data have been provided by the MURR for benchmarking the model during the developing period. The discrepancy between the model and the corresponding experimental data has been analyzed. Over-prediction of the negative worth of KCl samples was determined to be the cause of most of the deviation between the model and experimentally measured results.The original MCNP model has been refined with the consideration of the self-shielding effect and burnup effect. The modified model has yielded better predictions approaching the experimental values. The MCNP and MonteBurns models were integrated into an automatic analytic tool with Visual Basic language for efficient usage by the MURR. The automated package has been successfully run on the MURR MCNP Server.Item The role of the P2Y₂ nucleotide receptor in inflammation: the mechanisms of P2Y₂ receptor-mediated activation of G proteins(University of Missouri--Columbia, 2007) Liao, Zhongji, 1978-; Erb, Laurie; Weisman, Gary A.The extracellular ATP/UTP receptor, i.e., the P2Y₂ receptor (P2Y₂R), mediates pro-inflammatory responses in the vasculature, including the endothelium-dependent infiltration of monocytes and their transmigration into sites of infection, injury, or stress. This dissertation concerns the mechanisms whereby the P2Y₂R mediates chemotaxis as well as the modulation of endothelial intercellular junctions. Since G proteins, such as heterotrimeric G₁₂ and Gi/o and the monomeric Rho family of GTPases, are responsible for regulating cellular actin dynamics and cytoskeletal changes that are central to chemotaxis, endothelial permeability and leukocyte transendothelial migration, this dissertation focuses on the mechanisms underlying the P2Y₂R-mediated activation of G proteins. The P2Y₂R is a G protein-coupled receptor with an extracellular integrin binding domain (RGD) that enables this receptor to directly interact with [alpha]v [beta]3/[beta]5 integrins. The integrin binding domain is required for P2Y₂R-mediated activation of G₁₂, G₀ and G₁₂, G₀₋mediated events, including RhoA and Rac activation, stress fiber formation and chemotaxis towards UTP. In human coronary artery endothelial cells (HCAEC), UTP causes a rapid and transient association of the P2Y₂R and the vascular endothelial growth factor receptor-2 (VEGFR-2) with VE-cadherin, a transmembrane component of endothelial adherens junctions. Inhibition of VEGFR-2 kinase activity, or siRNA-mediated down-regulation of VE-cadherin, inhibits Rac activation induced by UTP. Taken together, these data suggest that the P2Y₂R requires direct interactions with [alpha]v integrin, growth factor receptors and VE-cadherin to activate G proteins involved in chemotaxis and leukocyte transendothelial migration.Item Essays on security issuance(University of Missouri--Columbia, 2007) Olsen, Brett C.; Howe, John S.When a firm requires funds for financing operations, managers face several alternatives. Managers may raise funds through the public markets or the private sector. They may issue equity, debt, or a mix of equity and debt. The type of security issued, size of the offering, and the timing and pricing of the issue represent additional options for firm managers. Mangers must consider the costs and benefits for the firm related to each alternative. Influencing the assessment of the costs and benefits are the incentives of the managers, which may or may not align with those of the firm's other stakeholders. This dissertation addresses the decision making process of firm managers when faced with raising funds for firm operations. I examine three broad corporate finance issues by employing a comprehensive hand-collected dataset of firms issuing common stock purchase warrants. These securities, which provide holders the option of buying shares of stock in the issuing firm for an exercise price, possess features that allow me to evaluate research questions related to corporate governance, ownership and liquidity, and the market for corporate control.Item Optical stimulation of quantal exocytosis on transparent microchips(University of Missouri--Columbia, 2007) Chen, Xiaohui, 1973-; Gillis, Kevin D.Photorelease of caged Ca²⁺ is a uniquely powerful tool to study the dynamics of Ca²⁺-triggered exocytosis from individual cells. Using photolithography and other microfabrication techniques, we have developed transparent microchip devices to enable photorelease of caged Ca²⁺ together with electrochemical detection of quantal catecholamine secretion from individual cells or cell arrays as a step towards developing high-throughput experimental devices. A 110 nm - thick transparent Indium-Tin-Oxide (ITO) film was sputter-deposited onto glass coverslips, which were then patterned into 24 cell-sized working electrodes (2̃0 [mu]m by 20 [mu]m). We loaded bovine chromaffin cells with acetoxymethyl (AM) ester derivatives of the Ca²⁺ cage NP-EGTA and Ca²⁺ indicator dye Fura-4F, then transferred these cells onto the working ITO electrodes for amperometric recordings. Upon flash photorelease of caged Ca²+С uniform rise of [Ca²⁺]i within the target cell leads to quantal release of oxidizable catecholamines measured amperometrically by the underlying ITO electrode. We observed a burst of amperometric spikes upon rapid elevation of [Ca²⁺]i and a "priming" effect of sub-stimulatory [Ca²⁺]i on the response of cells to subsequent [Ca²⁺]i elevation, similar to previous reports using different techniques. We conclude that UV photolysis of caged Ca²⁺ is a suitable stimulation technique for higher-throughput studies of Ca²⁺-dependent exocytosis on transparent electrochemical microelectrode arrays.Item Maintaining cross-domain objects and features in working memory : implications for storage in models of working memory(University of Missouri--Columbia, 2007) Morey, Candice Coker, 1978-; Cowan, NelsonA great deal of evidence, both from behavioral studies of cross-domain interference and from neuroimaging, suggests the need for a domain-general store in models of working memory. Baddeley included such a store in an updated version of the influential multiple component model (2000), but it is still unknown how this new component interacts with better-known working memory components. Using cross-domain objects (letters in spatial locations) for memoranda, the following experiments aimed to learn whether domain-specific and domain-general stores can be used concurrently, and in doing so to better understand how components of a working memory system interact. A critical finding shows that concurrent articulatory suppression impairs memory for integrated cross-domain objects that include spatial location features, but does not affect spatial locations when they are represented as isolated features. This evidence is interpreted as support for a domain-general store capable of accommodating different representations for spatial materials and capable of interfacing with verbal rehearsal mechanisms, depending on memory demands.