The metabolism of 5'-AMP by 5'-nucleotidase, adenylate deaminase and adenylate kinase was examined in heart homogenates of rat, rabbit, dog, pigeon and turtle. The study was conducted in consideration of the possibility that adenosine, a catabolic product of 5'-AMP, may control vasotone for the autoregulation of coronary blood flow. The relative activities of homogenates of hearts from various species to form adenosine by the action of 5'-nucleotidase generally supported such a role for this nucleoside. Those species anticipated to have the largest potential requirements for coronary vasodilation, i.e. those whose oxygen consumption is known to increase significantly during physical exertion, had the highest levels of cardiac 5'-nucleotidase. An exception to this was the pigeon which had no detectable cardiac 5'-nucleotidase; the order of levels of this enzyme in hearts of the other species tested was: rat > dog > rabbit > turtle. The turtle ventricle, by virtue of its high content of adenylate deaminase and low content of 5'-nucleotidase appeared to catabolize 5'-AMP largely by deamination to IMP. Homogenates of pigeon ventricle contained the greatest activity of adenylate kinase, indicating that the heart of this species is equipped for preservation of ATP by resynthesis from ADP. Enzyme histochemistry revealed that most 5'-nucleotidase of mammalian hearts was localized in the endothelial cells of capillaries. Therefore, if adenosine is involved in regulation of coronary perfusion, its source may be capillary endothelial cells rather than cardiac muscle cells. 5'-Nucleotidase was partially purified from an acetone powder of rat heart. It was active over a broad range of pH with an optimum at pH 8.5. The enzyme was stimulated up to 5-fold by Mg(++) [formula omitted]; Mn(++) and Ni(++) also stimulated activity. The K for 5'-AMP was 2.1 x 10(-5)M in the absence of 16Mg and 2.3 x 10 M in the presence of 16 mM MgCl(2). Certain of its properties indicated that the production of adenosine might be favoured under conditions in which coronary vasodilation would be required and vice-versa. For example, the enzyme was inhibited by ATP, whose levels are greatest in well oxygenated hearts in which energy charge is high. Not all properties of 5'-nucleotidase were consistent with enhanced adenosine formation at reduced energy charge. Both ADP and orthophosphate, the levels of which increase when energy charge decreases, inhibited the enzyme; in fact ADP was a more powerful inhibitor than ATP. In addition, the enzyme was not specific for 5'-AMP but hydrolyzed a variety of nucleoside 5'-monophosphates; and the hydrolysis of 5'-AMP was competitively inhibited by UMP. In the absence of Mg(++) , inhibition by ADP was of the mixed (competitive- non-competitive) type. In the presence of 16 mM MgCl(2), inhibition was non-competitive. On the basis of these data and Dixon plots of inhibition as a function of ADP concentration, it is suggested that two conformations of the enzyme are possible; one which is competitively inhibited by ADP. The simple non-competitive inhibition by ADP, observed in the presence of 16 mM MgCl(2), is attributed to Mg(++) -induced preference for the latter conformation. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate

No description available.

High-speed planing craft slamming into waves can cause structural damage to the vessel as well as hinder or injure personnel onboard. As a result, it is one of the primary constraints that limit the operating envelope of high-speed surface vessels. The controlled motion experiments presented in this thesis were designed to be an intermediate step between vertical water entry tests of a wedge and a traditional tow tank experiment of a planning hullform in waves. This allowed a deeper study of the hydrodynamic loads that occur during slamming. A planing hull model was subjected to controlled motions in the vertical plane to replicate the types of slamming motions that a vessel may experience in the ocean. The slamming events investigated were chosen based on towing tank experiments previously conducted at the U.S. Naval Academy. Hydrodynamic forces were measured globally and also at particular locations near the bow. The vertical motions were programmed into a pair of linear actuators that were rigidly mounted to the towing carriage. The towing carriage prescribed the horizontal motion. Each actuator was independently controlled and capable of moving at 1.3 m/s and 15 m/s^2. Pressure sensors were used to measure the pressure time history at discrete points on the model. Force sensors mounted beneath the actuators were used to compute the overall slamming load and moments induced by the slam event. A combination of other sensors were used to verify the accuracy of the prescribed motion profile. The results suggested that total impact velocity is correlated with the load growth rate. In addition, the velocity normal to the keel was found to be most impactful on the magnitude of the peak force. / Master of Science / The goal of this thesis was to understand the effect of high-speed boats impacting waves. These wave slamming events can harm the boat and make people sea sick onboard. Consequently, the top speed at which these high-speed boats can operate safely is often limited by these wave impacts. The approach taken for this study involved using a model boat that had similar features to high-speed boats seen in the real world. The model underwent specific movements to replicate the impact that occurs when a real boat encounters waves at sea. This method sought to identify important parameters that determine the severity of the slam event. A Vertical Planar Motion Mechanism simulated the slamming motion, allowing the model boat to move at high speeds relative to its size. A variety of sensors located throughout the model collected data on the slam event. The combination of these sensors helped paint a picture of what is occurring during the entire slam event. This study focused on the dynamics that are measured by the sensors. This included the pressure at important locations, the force on the whole model, and the way that the model moves. The Office of Naval Research provided both financial and intellectual support that makes this research possible. Beyond the ONR, many other academic, commercial, and military groups had given their support for this work.

Mounted ill. Bibliography: leaves [221-240]

This investigation seeks to perform a comparative study between the combined effects of internal pressure and piping loads versus external pressure and piping loads on a pressure vessel. There are currently several well-known and widely-used procedures for predicting the stress situation and the structural stability of pressure vessels under internal pressure when external piping loads (due to thermal expansion, weight, pressure, etc.) are applied at the nozzles. This project familiarises one with several international pressure vessel design Codes and standards, including AS ME (American Society of Mechanical Engineers) pressure vessel code sections and WRC (Welding Research Council) bulletins. It has been found that many vessels are designed to operate under normal or steam-out conditions (in vacuum). The combined effect of the external atmospheric pressure and the piping loads at the nozzle could be catastrophic if not addressed properly - especially when the stability of the structure is a crucial consideration, i.e. when buckling is a concern. The above-mentioned codes and standards do not directly address procedures or provide acceptance criteria for external loads during vacuum conditions. The approach to the study was, firstly, to investigate the effects of internal pressure and piping loads at the shell-to-nozzle junction. Theoretical stresses were compared with Finite Element results generated using the software package MSC PATRAN. Finite Element Methods provide a more realistic approach to the design of pressure vessels as compared to theoretical methods. It was necessary to determine if the theoretical procedures currently used were adequate in predicting the structural situation of a pressure vessel. Secondly, the buckling effects of vessels subjected to external atmospheric pressure and piping loads were also investigated. Buckling of the shell-to-nozzle region was explored with the aid of Finite Element software. The results gained were used to develop appropriate procedures for the design of vessels under external atmospheric pressure and piping loads. The design is such that it indicates if buckling will occur at the shell-to-nozzle junction. These design procedures form the basis for future exploration in this regard. / Thesis (M.Sc.Eng)-University of Natal, Durban, 2003.

Thesis (Ph. D.)--University of Missouri--Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves [174]-186). Also available on the Internet.

No description available.

published_or_final_version / Physiology / Master / Master of Philosophy

published_or_final_version / Surgery / Doctoral / Doctor of Philosophy

Throughout much of the blood circulatory system, supply vessels (arteries and arterioles) are situated adjacent to corresponding draining vessels (veins and venules), which flow in the opposite direction. In this dissertation, mathematical models are developed to describe diffusive exchange of heat, oxygen and inert gases between such paired countercurrent blood vessels and surrounding tissue. In preliminary analyses, exchange between a single vessel and surrounding tissue is considered. The concept of equilibration length is developed. Then a well-known solution for two-dimensional diffusion between two vessels situated in an infinite domain is presented. This provides a basis for developing semianalytic solutions for two vessels situated in a cylindrical tissue region with Dirichlet or zero-flux conditions at the outer boundary. A general approach is then developed for obtaining semianalytic solutions for domains with non-circular cross-sections, and applied to the case of a rectangular domain. The governing equations for paired blood vessels are then solved to obtain the axial variation of temperature or concentration for a variety of cases, including Dirichlet and zero-flux boundary conditions, with and without deposition or consumption of heat or gas. For the Dirichlet case, the equilibration length is compared to that for a single vessel, showing that equilibrium is achieved more rapidly when a single vessel is replaced by two vessels with the same diameter as the single vessel. For the zero-flux case, particular solutions to the full three-dimensional diffusion equation in the tissue are obtained from the two-dimensional solutions. The total transport (convective and diffusive) in the axial direction is evaluated, with and without consumption/deposition, and the results are interpreted in terms of an enhanced diffusivity. Finally, the complementary roles of convection and diffusion in mass and heat transport in the axial direction are considered. It is shown that as vessel diameter decreases, countercurrent exchange eventually results in a reduction of convective transport. Axial diffusion becomes significant at approximately the same range of diameters. This finding is interpreted in terms of the efficiency by which a branching network can transport heat and mass to its extremities.