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The original Ilizarov frame is a form of circular external fixation in which bone fragments are supported by tensioned fine wires; the wires give the frame a nonlinear axial stiffness which is one of its key qualities. However, as the wires deform plastically in response to loads imposed by functional weight bearing, the stiffness of frame gradually decreases with time. To circumvent this problem the modified Ilizarov frame was conceived in which half pins rather than wires are used for bone support. As fractures managed with Ilizarov fixation tend to unite with little radiographic evidence, monitoring the progression of fracture healing is difficult. The study described in this dissertation had three primary objectives. The first was to investigate the significance of the plastic deformation which occurs in the tensioned fine wires to the long term performance of the original frame. The second was to investigate the biomechanics of the modified frame. The third objective was to conduct a in-vivo feasibility study on the use of fracture axial stiffness measurements as method of monitoring the progression of fracture healing. Plastic deformation of the wires in the original frame readily occurs at moderate load levels because stress concentrations arise at the wire-clamp and wire-bone interfaces. The reduction in frame stiffness is typically 20-30%; re-tensioning only temporarily restores the original frame stiffness. In contrast to the original frame, the modified frame displays a linear stiffness and, as the half pins act as cantilevers, shearing of the bone ends can occur under axial loading. The in-vivo study showed that the technique of relative stiffness measurement, which has been successfully applied to uniaxial fixators, is not directly applicable to Ilizarov fixation. However, it was noted that the standardd eviation of repeatm easurementsd ecreasedw ith the progressiono f healing. It is suggestedt hat this may arise as a result of decreasedm icromovement at the fracture site and might provide a means of monitoring fracture healing itself

In oligotrophic systems, where primary production is low and nitrogen is in short supply, nitrogen fixation process is intense. Although a few diazotrophs (eg. Trichodesmium) have been widely-studied, the rest of the diazotrophic community is still poorly understood. Furthermore, the global distribution of diazotrophs are yet to be clearly resolved. This dissertation assessed the distribution of diazotrophs in oligotrophic systems, particularly in the tropical and subtropical oceans, using genomics tools including next-generation sequencing. We first tested out a pair of nifH-specific primer that previously performed well in silico, but found that its application on seawater samples was biased towards paralogous, non-functional nitrogenase nifH genes. Instead, we found that the use of a nested PCR method using different primers sets to be more effective in amplifying functional nifH genes. Trichodesmium sp., UCYN-A and Pseudomonas sp. forms the core of the diazotrophic communities in oligotrophic oceans. Temperature is the primary driver of the abundances and distributions of these organisms in the Pacific, Atlantic and Indian Oceans, as well as in the oligotrophic Red Sea. Trichodesmium tends to dominate warm, surface waters, while UCYN-A prefers cooler environments and dwell in sub-surface waters in the Red Sea. Due to the dominance of Pseudomonas in the large-sized fraction samples, they are believed to be part of the Trichodesmium-associated consortia, although this requires further investigations. We also found non-cyanobacterial species of diazotrophs to be dominant previously-described hotspots of nitrogen fixation, and found evidence for the widespread of alternative nitrogenases (Cluster II). Using the Red Sea as an exemplar for future warming ocean, we found patterns of niche partitioning in the Red Sea diazotrophs, based on their distribution along seasons, latitude and depth. Our one-year observation of Red Sea Trichodesmium population witnessed the collapse of the population at temperatures above 32°C. This dissertation not only improve our understanding of the effects of future rising temperature on the natural populations of diazotrophs, but it also helps to establish a baseline understanding of the structure, spatial and temporal dynamics of Red Sea diazotrophs, which has not been discussed elsewhere.

Seagrasses are key coastal ecosystems, providing many ecosystem services. Seagrasses increase biodiversity as they provide habitat for a large set of organisms. In addition, their structure provides hiding places to avoid predation. Seagrasses can grow in shallow marine coastal areas, but several factors regulate their growth and distribution. Seagrasses can uptake different kinds of organic and inorganic nutrients through their leaves and roots. Nitrogen and phosphorous are the most important nutrients for seagrass growth. Biological nitrogen fixation is the conversion of atmospheric nitrogen into ammonia by diazotrophic bacteria. This process provides a significant source of nitrogen for seagrass growth. The nitrogen fixation is controlled by the nif genes which are found in diazotrophs. The main goal of the project is to measure nitrogen fixation rates on seagrass sediments, in order to compare among various seagrass species from the Red Sea. Moreover, we will compare the fixing rates of the Vegetated areas with the bare sediments. This project will help to ascertain the role of nitrogen fixing bacteria in the development of seagrass meadows.

<p> This thesis is concerned with the systematic variation of stimulus movement and complexity in order to investigate developmental changes in visual fixation. It was shown that there is a developmental transition in the way in which infants extract visual information from the environment, with younger infants responding primarily through length of fixation, and older infants through the number of fixations. It was demonstrated that the faster a stimulus moves, the more fixation it elicits from infants; that older infants appear to be more responsive to differences in speed than younger infants; and that the more complex the stimulus, the greater the visual response to it. Percent measures were found to be more reliable than absolute measures in making age comparisons. </p> / Thesis / Doctor of Philosophy (PhD)

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No description available.

In this study, participants performed a change detection task. Specifically we examined whether participants had to fixate on a difference between two images before they could detect it. Thirty-six participants performed a change detection task in either a 3 minute or a 1.5 minute condition. We found a significant interaction between task duration and fixation type (whether the participant had fixated on the difference in both, one, or neither image). Participants found a greater number of differences given more time only when they fixated on the difference in both images. The number of differences which were detected by participants with a fixation on only one image or on neither image did not increase with a corresponding increase in time, indicating that some mechanical error may be involved. This suggests that participants need to fixate on a difference before being able to detect it.

Un mécanisme évolutif très important pour l'acquisition de nouvelles fonctions protéiques est la duplication génique. Les protéines paralogues résultantes subissent une divergence fonctionnelle permettant à leur gène d'être retenus dans le génome. Les événements de duplication étant à l'origine de l'expansion de la famille des domaines SH3, une compréhension de la divergence des propriétés de liaison de ceux-ci sur les protéines paralogues est essentielle pour saisir leur implication dans diverses fonctions cellulaires. La liaison des domaines SH3 peut être très spécifique ou elle peut reconnaître des groupes canoniques de peptides riches en proline. Ainsi, l'objectif de ce projet de maîtrise est d'améliorer notre compréhension sur l'évolution des propriétés de liaison des domaines SH3 portés par des paralogues. En utilisant des données sur les interactions physiques entre les protéines in vivo, nous avons établi que les domaines SH3 des myosines de type I de Saccharomyces cerevisiae, un organisme modèle, montraient une divergence fonctionnelle. Puis, les domaines SH3 ont été échangés entre les paralogues et les domaines ancestraux pré-duplications ont été insérés dans les paralogues. Cette expérience a révélé que le domaine SH3 présent au moment de la duplication montre le même profil d'interaction que les SH3 existants, mais que les SH3 plus anciens perdent graduellement leurs interactions. Ensuite, l'arrimage moléculaire des SH3s avec leurs peptides de liaison prédits ainsi que la caractérisation des interactions des SH3s libres montrent que l'affinité ne diminue pas avec le domaine ancestral. Ces résultats sont confirmés par le patron de PPIs des domaines SH3 libre de contexte protéique. Cela a permis de déterminer que la propriété de liaison n'est pas le facteur principal qui influence sur les interactions des domaines SH3 présent sur des paralogues, mais que c'est leur protéine hôte. Nos résultats s'accordent avec la recherche récente qui suggère que les domaines protéiques ne sont pas des éléments isolés dans une protéine, contrairement à la croyance répandue. / A very important evolutionary mechanism for the acquisition of new protein functions is gene duplication. The resulting paralogous proteins undergo functional divergence allowing them to be retained in the genome. Since duplication events are responsible for the expansion of the SH3 domain family, an understanding of the divergence of the binding properties of SH3 domains on paralogous proteins is essential to grasp their involvement in various cellular functions. The binding of SH3 domains can be very specific or it can recognize canonical groups of proline-rich peptides. The objective of this master project is to improve our understanding of the evolution of the binding properties of SH3 domains carried by paralogs. Using data on physical interactions between proteins in vivo, we established that the SH3 domains of the type I myosins from Saccharomyces cerevisiae, a model organism, show functional divergence. Then, the SH3 domains were exchanged between paralogs and the pre-duplication ancestral domains were inserted into the paralogs. This experiment showed that the SH3 domain at the time of duplication displays the same interaction profile as the extant SH3s, but, as the SH3s get older, they gradually lose their interactions. Next, molecular docking of the SH3s with their predicted binding peptides and characterization of the free SH3s PPIs shows that the affinity does not decrease with the ancestral domain. Those results are confirmed by the PPI network of the SH3 domains free of a protein context. These experiments determined that the host protein is the primary factor influencing paralogous SH3 domain interactions instead of the SH3 binding preferences. Our results are consistent with recent research suggesting that protein domains are not isolated elements in a protein, contrary to popular belief.