Abstract In the repair of complex congenital heart defects or in surgery of the aortic arch, normal circulation may be temporarily halted to ensure a clean, bloodless operation field. The brain is the organ most vulnerable to ischemic injury during this no-flow period, and the mortality and morbidity of these procedures today consists mostly of neurological complications. Hypothermia decreases the need for oxygen and other metabolites, and cooling the patient with an extracorporeal heart-lung machine can provide enough time to perform the necessary surgical procedures during a circulatory standstill. This procedure is referred to as hypothermic circulatory arrest (HCA). Sometimes the cerebral circulation can be maintained even if the rest of the body undergoes circulatory arrest, and this strategy, involving separate catheterization of brain-destined vessels, is referred to as selective cerebral perfusion (SCP). In this work, four separate brain protection strategies were evaluated. Two studies were performed on a surviving porcine model (I, II) to evaluate neurological recovery as well as cerebral metabolism and histopathology, and two were acute in design (III, IV), employing the modern technology of intravital microscopy to examine cerebral microcirculation. The first study (I) showed that the administration of hypertonic saline dextran (HSD) led to a decrease in intracranial pressure, improved brain metabolism, better neurological recovery and less histopathological injury of the brain tissue in association with HCA. In the second study (II) a novel pharmacological molecule, levosimendan, reduced the intracranial pressure during the operation, but no improvement in terms of cerebral metabolism, neurological recovery or histopathological brain injury was observed after HCA. In the third study (III), real-time intravital microscopy showed that in association with HCA, a leukocyte depleting filter (LDF) attached to the cardiopulmonary bypass circuit reduces the number of activated leukocytes in cerebral microcirculation. In the fourth study (IV), cerebral metabolism and microcirculation were similar during SCP independent of the acid-base management strategy. The results of this work suggest that HSD could be assessed in human trials, that levosimendan needs further studies to optimize its potential, that the LDF functions as designed and that the differences between the α- and the pH-stat acid-base management strategies with SCP did not differ in moderate hypothermia.

Master of Science / Department of Mechanical and Nuclear Engineering / Kirby S. Chapman / In the natural gas production industry, recent legislation has mandated new emission regulations for low horsepower reciprocating internal combustion engines. One method to achieve compliance of the new regulations is the use of non-selective catalytic reduction. Nonselective catalytic reduction utilizes a three-way catalyst and an air-to-fuel ratio controller to oxidize carbon monoxide and unburned fuel while reducing oxides of nitrogen. Testing of a non-selective catalytic reduction system was preformed on a typical exploration and production engine, a Compressco GasJack. To fully test the unit, exhaust gas samples were taken with an ECOM gas analyzer both before and after the catalyst over typical engine speeds and powers. By sampling the exhaust gas concentration before and after the catalyst, the catalyst efficiency or percent reduction in exhaust gas specific concentrations were calculated. Additionally by testing throughout the engine's typical operation range, conditions under which the non-selective catalyst reduction system fails were determined. After testing, it was found that the three-way catalyst was effective at reducing oxides of nitrogen by 98% at all speeds and power conditions. Carbon monoxide was reduced by 90% under all conditions except for maximum speed and power. At maximum speed and power, the conversion efficiency for carbon monoxide was recorded as low as 32%. One reason for the low conversion efficiency at maximum speed and power was that the oxygen concentration entering the catalyst was not sufficient to oxidize the carbon monoxide to carbon dioxide. These results indicate the three-way catalyst was effective at reducing emissions when the controller correctly maintained the pre-catalyst oxygen concentration. However, the controller was unable to maintain engine operation at the ideal airto- fuel ratio at all test conditions. The controller failed to keep the pre-catalyst oxygen concentration in the correct range because the oxygen sensor was not accurate and consistent in its output. Future work on the development of a more robust oxygen sensor is recommended.

Deforming a complex generic shape into a representation of another complex shape is investigated. An initial study is done on the effect of cranial shape variation on masticatory induced stress. A finite element analysis is performed on two different skull geometries. One skull geometry has a prognathic shape, characterised by jaws protruding forward, while the other has a non-prognathic form. Comparing the results of the initial nite element analyses, the effect of an undesired variation in shape and topology on the resulting stress field is observed. This variation in shape and topology can not be attributed to the cranial shape variation that is investigated. This means that the variation in the masticatory induced stress field that is due to the relative degree in prognathism can not be quantified effectively. To best compare results, it would be beneficial to have a computational domain for the different skull geometries that have one-to-one correspondence. An approach to obtain a computational domain that represents various geometries with the exact same mesh size and connectivity between them does exist. This approach involves deforming a generic mesh to represent different target shapes. This report covers an introductory study to register and deform a generic mesh to approximately represent a complex target geometry. Various procedures are investigated, implemented and combined to specifically accommodate complex geometries like that of the human skull. A surface registration procedure is implemented and combined with a feature registration procedure. Feature lines are extracted from the surface representation of each skull as well as the generic shape. These features are compared and an initial deformation is applied to the generic shape to better represent the corresponding features on the target. Selective feature preserved elastic surface registration is performed after the initial feature based registration. Only the registration to surfaces of featureless areas and matched feature areas are allowed along with user selected areas during surface registration. The implemented procedures have various aspects that still require improvement before the desired study regarding prognathism's effect on masticatory induced stress could truly be approached pragmatically. Focus is only given to the use of existing procedures while the additional required improvements could be addressed in future work. It is however required that the resulting discretised domain obtained in this initial study be of sufficient quality to be used in a finite element analysis (FEA). The implemented procedure is illustrated using the two original skull geometries. Symmetric versions of these geometries are generated with a one-to-one correspondence map between them. The skull representations are then used in a finite element analysis to illustrate the appeal of having computational domains with a consistent mapping between them. The variation in the masticatory induced stress field due to the variation in cranial shape is illustrated using the consistent mapping between the geometries as part of this example. / Dissertation (MEng)--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

This dissertation presents an investigation of the modifying role of attention and awareness in human learning and decision making. A series of experiments showed that performance in a range of tests of unconscious cognition can be better explained as resulting from conscious attention rather than from implicit processes. The first three experiments utilised a modification of the Serial Reaction Time task in order to measure the interaction of implicit and explicit learning processes. The results did not show evidence for an interaction, but did exhibit an effect of explicit knowledge of the underlying rules of the task. Subsequent studies examined the role of selective attention in learning. The investigation failed to provide evidence that learning inevitably results from the simple presentation of contingent stimuli over repeated trials. Instead, the learning effects appeared to be modulated by explicit attention to the association between stimuli. The following study with a novel test designed to measure the role of selective attention in prediction learning demonstrated that learning is not an obligatory consequence of simultaneous activation of representations of the associated stimuli. Rather, learning occurred only when attention was drawn explicitly to the association between the stimuli. Finally, the Deliberation without Attention Paradigm was tested in a replication study along with two novel versions of the task. Additional assessment of the conscious status of participants' judgments indicated that explicit deliberation and memory could best explain the effect and that the original test may not be a reliable measure of intuition. In summary, the data in these studies did not require explanation in terms of unconscious cognition. These results do not preclude the possibility that unconscious processes could occur in these or other designs. However, the present work emphasises the role conscious attention plays in human learning and decision making.

Due to the attractive advantages of wireless communication technologies, wireless networking and mobile computing has developed expeditiously and gained ample prevalence. Thereby, many practical applications are being designed for the use of wireless ad hoc networks in both military and civilian scenarios. However, some security concerns have arisen from such networks, especially in that misbehaving nodes pose a major threat during the construction of a trusted network. Therefore, security is one of the key challenges in wireless ad hoc networks, requiring significant attention due to their own features and concerns. This thesis presents several computational models and security strategies for the design of secure, trustworthy networks, which are able to make rational decisions when encountering potential threats. In this thesis, we first propose a distributed network management model for secure group communication. Our approach simplifies the complexity of traditional group management and supports the inclusion of other security mechanisms for the purpose of secure communications. As a decentralized management method, trust can perform well in a dynamic and agile environment. Our proposed trust system defines the concept of trust, establishes the trust relationship between distributed nodes, involves the novel and effective computational model, and specifies a set of trust-based rules in this system for wireless nodes. We also propose a hybrid cryptosystem through the application of both symmetric and asymmetric key algorithms to provide reliable and secure protection of data confidentiality. With the design of selective encryption, uncertainty is incorporated into data encryption and the overhead spent on the data protection is significantly reduced. Thus, the communicating parties not only obtain reliable security protection, but also improve the efficiency of data communication. Through security analysis and simulation experiments, we have shown how decentralized management is useful in wireless and ad hoc scenarios, how trust provides feasible solutions for misbehavior detection, and how our proposed strategies offer security properties.

The discovery of stem and progenitor cells capable of ongoing neurogenesis in the adult mammalian brain has raised hope that we will one day be able to harness their intrinsic regenerative capacity following injury. Development of such therapeutic strategies relies on a comprehensive understanding of the underlying regulation of the neurogenic process. To this end, I show, in this thesis, that cultured post-natal hippocampal neural progenitor cells (NPCs) express a specific repertoire of connexins (Cx), a family of channel forming proteins critical for communication prior to the development of functional chemical synapses. I show that this pattern of Cx expression, specifically Cx43 and Cx45, is modulated by interaction with the extracellular matrix component laminin providing evidence of extracellular matrix-cell interaction in the regulation of intrinsic Cx expression and function in postnatal NPCs. In adult brain, I show, for the first time, that Cx45 localizes to all cell types of the neuronal lineage with the exception of the type 3 doublecortin (DCX)-positive NPCs. Using a loss of function approach, I show that this expression is required for the normal proliferation of type 1 nestin and glial fibrillary acidic protein-positive stem like NPCs but not for the differentiation or survival of their progeny in the adult hippocampus. With respect to exogenous pharmacological cues that influence hippocampal neurogenesis, this thesis also demonstrates that chronic treatment with a sub-set of selective serotonin reuptake inhibitor antidepressants, fluoxetine and escitalopram, increases the proliferation but not the survival of adult NPCs in healthy, non-depressed mice. Further, standard post-operative analgesia with the opiate buprenorphine inhibits the proliferation of DCX-positive adult NPCs and increases the survival of their progeny. Finally, over the course of the research for this thesis, it became clear that exposing research animals to even very subtle environmental changes can influence the basal neurogenic process. Ultimately this work further highlights the exquisite sensitivity of the regulation of what is already recognized to be a highly dynamic process and provides important insight into the neurogenic process that can be used to inform future therapeutic development and application.

Background: In September 2005, scientific journals began requiring trial protocol registration to increase transparency and accountability. Objective: My primary objectives were: develop a database of linked protocols and publications for surgical randomized control trials (RCTs); estimate the proportion published; and determine the proportion exhibiting selective outcome reporting. Methods: A systematic search of the clinicaltrials.gov database was conducted identifying surgical RCTs, completed between 2006 and 2012. Protocols were linked with publications. Primary outcomes were compared. Results: We identified a cohort of 743 surgical RCT protocols. The proportion of registered trials which published their primary results was 0.49 (n=364). The proportion of selective outcome reporting was estimated to be 0.244, significantly lower than the previous estimate (p<0.001). Conclusion: More than half of the completed surgical RCTs were unpublished, and one quarter of those published selectively reported their primary outcome. This supports the notion that significant bias is present in the surgical literature.

No description available.

The optical properties of the absorber pipe in a parabolic trough collector isessential for the performance of the solar collector. The desirable propertiesare high absorptance (α) of solar radiation and low emittance (ε) of thermalradiation. A surface with these properties is known as a solar selective surface. There are several techniques used to produce selective surfaces, but one of the most common ones is electroplating. Research done by Vargas, indicates that optical properties of α = 0.98 and ε = 0.03 [1], which is superior to the best commercial alternatives (α = 0.95 and ε = 0.04 [2]), can be achieved by electroplating a Co-Cr coating on a stainless steel substrate. Additionally, Vargas used an electrolyte of trivalent chromium dissolved in a deep eutectic solvent, as opposed to the traditionally used aqueous electrolytes containing hexavalent chromium, which is toxic and carcinogenic. In this project, a coating of Co-Cr was electroplated on a stainless steel substratewith a method similar to that of Vargas in order to obtain a solar selective surface. The electrolyte was composed of ethylene glycol, choline chloride, CrCl3•6H2O and CoCl2•6H2O in a molar ratio of 16:1:0.4:0.2. The plating process was conducted using chronoamperometric electrodeposition with an applied potential of -1.2 V (against an Ag/AgCl reference electrode) for 15 min. The system was investigated using Cyclic Voltammetry (CV). The total absorptance was measured using UV-Vis spectroscopy, while the emittance was measured using an IR-thermometer. The microstructure and chemical composition was investigated using Scanning ElectronMicroscopy (SEM), Focused Ion Beam (FIB), Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy. The thermal stability of the coating was investigated by exposingit to 400°C in air for 24 h. The electroplated coating is approximately 2.8 μm thick and exhibits a porousstructure with a surface of fine fiber-like flakes. The coating consists largely of Co hydroxides with low concentrations of Cr compounds, Co oxides and metallic Co. Hence, a satisfactory co-deposition was not accomplished, as the Cr concentration is low. The coating is not thermally stable up to 400°C, exhibiting signs of at least partially melting in the annealing process. The compounds in the coating were largely oxidized in the process. The electroplated surface does however exhibits strong selectivity, with a total solar absorptance of α = 0.952 and total emittance of ε = 0.32 at 160°C.

Pulmonary embolism (PE) is a common clinical problem affecting 600,000 patients per year in the United States. Although the diagnosis can be easily confirmed by imaging techniques, such as computed tomographic angiography of the chest, the identification of underlying mechanism leading to PE is important for appropriate duration of anticoagulation, and prevention of subsequent episodes. The differential diagnosis of underlying mechanism is broad and must include careful review of medication history. Drug-related thromboembolic disease can be easily missed and may have catastrophic consequences. The identification of the culprit drug is important for prevention of subsequent episodes and choosing appropriate duration of anticoagulation. We report a case of a middle-aged man who developed PE after administration of intravenous immunoglobulin.