Le cortex cérébral constitue l’une des structures les plus évoluées et complexes de notre cerveau. Sa surface est divisée en de nombreuses aires fonctionnelles. La mise en place des aires corticales dépend à la fois de facteurs intrinsèques comme la sécrétion de morphogènes ou l’expression en gradient de différents facteurs de transcription, mais elle dépend aussi de facteurs extrinsèques au cortex, en particulier l'innervation par le thalamus. Les ephrines et leurs récepteurs Eph constituent une famille multigénique de facteurs de signalisation impliqués dans divers événements clé du développement cortical où ils sont exprimés selon des profils spatio-temporels complexes. Aux stades tardifs du développement, EphA7 et l’ephrine-A5 sont exprimés en gradients complémentaires au sein de chaque territoire des aires présomptives, constituant ainsi les marqueurs les plus précoces de ces aires corticales. Par la combinaison d’approches in-vitro utilisant la technique d’électroporation focale de tranches corticales embryonnaires, puis in-vivo en utilisant la technique de transgénèse d’addition, nous avons identifié une séquence régulatrice de EphA7 appelée pA7, capable de mimer l’expression endogène de EphA7 au sein du télencéphale dorsal en développement. La lignée de souris pA7-GFP ainsi générée exprime la GFP spécifiquement au sein du télencéphale dorsal durant les stades précoces. Aux stades périnataux cette expression se régionalise au sein de la plaque corticale de chacune des aires présomptives selon des gradients récapitulant ceux observés pour EphA7. Nous avons ensuite purifié des neurones exprimant différents niveaux d’EphA7 par la technique de FACS «Fluorescence-Activated Cell Sorting » et l’analyse de leur transcriptome nous a permis de trouver un grand nombre de gènes différentiellement exprimés. Tous ceux testés par la technique d’hybridation in situ sont exprimés selon un gradient latéral fort et médial faible dans le cortex pariétal, similaire à celui d’EphA7. L’examination de leur profil au sein de cortex de souris dépourvus d’afférences thalamiques, nous a permis de conclure que l’expression de ces gènes incluant EphA7 s’établit indépendamment de celles-ci. Ainsi, notre étude a permis d'identifier un répertoire de gènes neuronaux, pouvant agir en amont ou en combinaison avec EphA7 pour contrôler les facteurs intrinsèques essentiels à l’établissement des aires corticales./ The cerebral cortex is subdivided into distinct cortical areas characterized by specific patterns of gene expression and neuronal connectivity. The patterning of cortical areas is thought to be controlled by a combination of intrinsic factors that are expressed in the cortex, and external signals such as inputs from the thalamus. EphA7 is a member of the ephrin/Eph family of guidance factors that is involved in key aspects of the development of the cortex, and is expressed in several gradients within developing cortical areas. By combining in vitro transcriptional assays and mouse transgenics, we identified a regulatory element of the EphA7 promoter, named pA7, that can recapitulate salient features of the pattern of expression of EphA7 in the developing forebrain, including gradients in the cortex. Using a mouse reporter line where GFP expression recapitulates EphA7 expression, we developed a GFP-based cell sorting procedure to isolate cortical neuron populations displaying different levels of EphA7 expression. Transcriptome analysis of these populations enabled to identify a specific array of differentially expressed genes. All genes validated further in vivo were confirmed to be expressed along distinct gradients in the developing cortical plate, similarly to EphA7. The expression of these genes was unchanged in mutant mice defective for thalamocortical projections, indicating that their graded pattern is largely intrinsic to the cortex. Our study identifies a novel repertoire of cortical neuron genes that may act upstream of, or together with EphA7, to control the intrinsic patterning of cortical areas.

Numerous studies have considered the ability of humans to perceive differences in forces and how this affects our ability to interpret the properties of materials. Previous research has not considered the effect of the rate of change of the material stiffness in our ability to perceive differences, however, an important factor in exploration processes such as a doctor’s palpation of the skin to examine tissues beneath. These effects are the topic of this research which attempts to quantify the effects of stiffness gradient magnitude and form on the discernment of changes in stiffness.

In this paper, we investigate the topology convergence problem for the gossip-based Gradient overlay network. In an overlay network where each node has a local utility value, a Gradient overlay network is characterized by the properties that each node has a set of neighbors containing higher utility values, such that paths of increasing utilities emerge in the network topology. The Gradient overlay network is built using gossiping and a preference function that samples from nodes using a uniform random peer sampling service. We analyze it using tools from matrix analysis, and we prove both the necessary and sufficient conditions for convergence to a complete gradient structure, as well as estimating the convergence time. Finally, we show in simulations the potential of the Gradient overlay, by building a more efficient live-streaming peer-to-peer (P2P) system than one built using uniform random peer sampling. / <p>© 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111124</p>

A key challenge in tissue engineering is overcoming cell death in the scaffold interior due to the limited diffusion of oxygen and nutrients therein. We hypothesized here that immobilizing a gradient of vascular endothelial growth factor (VEGF-165) would guide endothelial cells into the interior of the scaffold thereby enhancing angiogenesis. The protein was immobilized onto a collagen scaffold through carbodiimide chemistry by one of the three methods experimented: placing 5 µl of the solution at the center of the scaffold to create a ~2 ng/ml/mm gradient in a radial direction. D4T endothelial cells were observed to be guided by this VEGF-165 gradient deep into the center of the scaffold compared to both uniformly immobilized VEGF-165 and VEGF-free controls. We concluded that the VEGF-165 gradient scaffolds promoted the migration, and not proliferation, of cells deep into the scaffold. These gradient scaffolds provide the foundation for future in vivo tissue engineering studies.

A key challenge in tissue engineering is overcoming cell death in the scaffold interior due to the limited diffusion of oxygen and nutrients therein. We hypothesized here that immobilizing a gradient of vascular endothelial growth factor (VEGF-165) would guide endothelial cells into the interior of the scaffold thereby enhancing angiogenesis. The protein was immobilized onto a collagen scaffold through carbodiimide chemistry by one of the three methods experimented: placing 5 µl of the solution at the center of the scaffold to create a ~2 ng/ml/mm gradient in a radial direction. D4T endothelial cells were observed to be guided by this VEGF-165 gradient deep into the center of the scaffold compared to both uniformly immobilized VEGF-165 and VEGF-free controls. We concluded that the VEGF-165 gradient scaffolds promoted the migration, and not proliferation, of cells deep into the scaffold. These gradient scaffolds provide the foundation for future in vivo tissue engineering studies.

Preservation of cells and tissues by freezing at temperatures below 70°C has led to new possibilities for the storage of germ cells for fertility preservation. During the freezing process problems might occur, the greatest being ice crystallization which can cause membrane destruction and thus cell death. To minimize this risk, solutions that reduce the freezing point can be added to reduce crystallization and increase survival rates. These solutions are called cryoprotectants. The best method for freezing is still not known.The aim of this study was to analyze the effect of various parameters on the survival rate of human semen frozen with liquid nitrogen. The parameters investigated were thawing method (incubator or water bath) and container choice (straw or ampoule). In addition, two different cryoprotectants were tested.The method used was the instruction for preservation with Sperm CryoProtec™ II from Nidacon. In total 16 samples were collected for the first test and 13 samples for the second test. Sperm concentration and motility was measured.There seem to be no significant differences depending on container choice or thawing method leading to the conclusion that the most cost effective method of storage and thawing may be used. A small but significant difference was found in survival after thawing dependent on cryoprotectant p=0.041. However the study sample was limited and further studies might be of value.

This investigation will use this ability in a different way. Studies have shown that a category can create a grade structure of prototypical items. We will take a graded structure generated by a category, and see if we can recreate the category based on presenting prototypical examples in a variety of ways. Five different sampling techniques will be used to determine which one is the best for category reconstruction. Since the items themselves have bits of information about the category, the number of samples presented will also be manipulated to determine if this is a factor in determining the category. The independent variables investigated were: sampling technique, and prompt conditions. In determining the effect of the independent variables on matching a category, the independent variables were also considered as mediating variables of each other. The method of opportunistic sampling was used for the surveys. The main participants were undergraduate 3rd year students taking a MSci 311 course at the University of Waterloo. Results indicate that there was no statistical significance. Fluctuations in significance levels indicate some random findings. Participants are not discriminating the samples or prompts which were given. This research is a contribution to this field because little research has been conducted in this area and implications are drawn for future research on the saliency of a category or attribute that can vary by context or knowledge

Conservation biologists often use biological indicators to measure and monitor changes in biological diversity. This study examines butterflies as indicators using a gradient-based study approach. The urban gradient was characterized by Environmentally Sensitive Policy Areas (ESPAs), urban parks, golf courses, residential areas, and industrial areas. This thesis has been divided into two separate chapters. Chapter 1 summarizes an extensive review of existing data on butterfly presence/absence in the Region of Waterloo to determine what species are relatively uncommon or rare in the Region and examine how butterfly presence/absence has changed over the last 80 year. Each butterfly species that occurs in the region was assigned a regional status which resulted in the identification of 46 uncommon and rare species. Chapter 2 examines changes in butterfly abundance and diversity along a gradient of urbanization to determine how different land uses are potential affecting butterfly communities. Transects, 500 meters in length, were established at fifteen sites, each of which represented a land use within the urban gradient identified. Each transect was walked once a week for a total of 28 weeks over two years (2009 and 2010). Overall butterfly richness was observed to be highest within ESPAs, followed by urban parks and industrial areas and lowest within golf courses and residential areas. Shannon diversity scores were compared using a Kruskal Wallis test and indicated that species richness and evenness was significantly different between ESPAs and urban parks and compared to the remaining land uses, while species richness and evenness was not significantly different among residential areas, golf courses, and industrial areas in either 2009 or 2010. Significant differences in species richness and evenness was observed across the same land uses in 2009 and 2010 for all types except residential areas. Overall butterfly abundance was observed to be highest in industrial areas and lowest within golf courses and residential areas, a trend which was observed in both 2009 and 2010. Abundance was observed to be heavily influenced by counts of two non native species- the cabbage white (Pieris rapae) and European Skipper (Thymelicus lineola). ESPAs were identified as 1) supporting the most diverse butterfly community out of the 5 land uses examined and 2) providing habitat for the highest number of rare and uncommon species, indicating that current regional policies in place for protecting rare species are effective. Through an extensive literature review it was concluded that butterflies are effective indicators in temperate regions within a small geographic area such as the Region of Waterloo. Therefore it is expected that the results of this study indicate how other terrestrial taxonomic groups, which are known to show a similar response to urbanized land uses, may be impacted by urbanization in the Region. It is anticipated that the results of this study may be used to guide urban land use planning as it identifies rare and uncommon butterfly species within the region as well as what land uses need habitat enhancement to support more diverse communities.

When drilling offshore, shallow gas hazards are a major concern because of their potential to cause a major blowout. This is a special concern when drilling in shallower water, where the gas influx reaches the rig sooner. A common practice used to avoid the potential dangers of shallow gas is to drill a pilot hole through the shallow gas zone with the hope that the smaller diameter hole will prevent such a large influx. The use of dual-gradient top hole drilling technology would allow for a larger hole to be drilled and the possible gas influx to be killed dynamically, which I have simulated with the use of a top hole dual-gradient simulator.

Dual Gradient Drilling is an exciting technology which promises to solve the current technical hurdles and economic risks of Deepwater Drilling. Several techniques for Dual Gradient Drilling have been proposed to the industry. One such method involves installing a subsea booster pump at the seafloor with the aim of returning the drilling fluid back to the rig. The pump will manage annular pressures in the wellbore as circulation rates and mud weights vary and will permit early detection of wellbore influxes. Any such pump chosen to achieve this objective will be subjected to very high differential pressures and will be faced with the onerous task of lifting very abrasive and viscous mud slurries from the sea floor back to the drilling rig. This distance in deep water may be well within the range of about 4, 000 – 12,000 feet depending on the operating water depth of the rig. Several pump technologies available to the industry were examined. Piston pumps are very efficient and can withstand the high differential pressures encountered in the Mudlift Drilling System. However, their drawbacks are their large size and weight and high initial capital cost and maintenance costs. Centrifugal pumps on the other hand are relatively smaller than piston and diaphragm pumps and are generally less expensive. Disc pumps, with their non-impingement design are able to handle solids and fluids with a high gas volume fraction but, like centrifugal pumps, are generally less efficient than reciprocating pumps. Diaphragm pumps are capable of maintaining a constant rate regardless of pressure fluctuations. They can handle very abrasive solids with limited wear on the pump. They also excel at handling very viscous fluids and they can be modified to handle up to 95% gas volume fraction. Like piston pumps, they have very high efficiencies. The potential of each of these pump technologies to meet the requirements for the Mudlift Drilling System was examined in this thesis. The benefits and drawbacks of each of these pump technologies were highlighted and modifications to meet the demands of the mudlift system evaluated.