Silicone hydrogels haves been widely utilized in many in ophthalmic and other biomedical applications due to the its comfort of hydrogels, their excellent biocompatibility, high oxygen permeability and transparency. For use as a contact lens, the silicone hydrogel with interacts with the tear film, cornea, and eyelid;, thus surface properties of the gel are crucial to be considered. The highly oxygen permeabilitye performance of the silicone hydrogel contact lens materials mainly relies on the incorporationng of the siloxane functional groups., Hhowever these groups are extremely mobile and surface active, which can result in an increase in the of lens surface hydrophobicity, as well as protein and lipid deposition. Therefore, there is a need for surface modification of silicone hydrogel contact lenses. Otherwise users may might have to choose to decrease the frequency and length of wearing duration of silicone contact lenses due to dryness or bio-fouling related issues. A novel biomimetic methacrylate monomer which contains a phosphorylcholine group, 2-mMethacryloyloxyethyl pPhosphorycholine (MPC) is was grafted onto the surface of novel silicone hydrogel materials surface to create a thick hydration layer in order to enhance the protein resistance and surface wettability. Low temperature air plasma has beenwas chosen to initiate grafting polymerization of MPC monomers onto silicone hydrogel substrates. Hydrogels were treated with plasma and exposed to air flow to yield hydroperoxides on the surface; the, and peroxides group acted as a photo-initiators for further thermal MPC grafting polymerization. After surface modification, the silicone hydrogels were characterized by XPS and ATR-FTIR to confirm the structure and elemental composition. A significant amount of phosphorus element was found shown on the XPS spectra of the modified materialsum,, demonstrating that so the MPC monomers were successfully grafted onto the gel surface. According to water contact measurement results, the modified samples possessed very hydrophilic surfaces, with advancing angles of about 27°, while compared the unmodified samples at around 110°. After surface grafting, between a around 20% and to 50%’s reduction in protein deposition was also observed, which aligned with water contact angle results. Other properties such as oxygen permeability, transparency, water equilibrium, and elastic modulus remained unchanged after the air plasma exposure and thermal MPC polymerization. / Thesis / Master of Applied Science (MASc)

The primary purpose of this research is to investigate the effectiveness of a scaled roller rig for accurately assessing the contact mechanics and dynamics between a profiled steel wheel and rail, as is commonly used in rail vehicles. The established creep models of Kalker and Johnson and Vermeulen are used to establish correction factors, scaling factors, and transformation factors that allow us to relate the results from a scaled rig to those of a tangent track. �Correction factors, which are defined as the ratios of a given quantity (such as creep coefficient) between a roller rig and a track, are derived and used to relate the results between a full-size rig and a full-size track. Scaling factors are derived to relate the same quantities between roller rigs of different scales. Finally, transformation factors are derived by combining scaling factors with correction factors in order to relate the results from a scaled roller rig to a full-size tangent track. Close-end formulae for creep force correction, scaling, and transformation factors are provided in the thesis, along with their full derivation and an explanation of their limitations; these formulae can be used to calculate the correction factors for any wheel-rail geometry and scaling. For Kalker's theory, it is shown that the correction factor for creep coefficients is strictly a function of wheel and rail geometry, primarily the wheel and roller diameter ratio. For Johnson and Vermeulen's theory, the effects of creepage, scale, and load on the creep force correction factor are demonstrated. �It is shown that INRETS' scaling strategy causes the normalized creep curve to be identical for both a full-size and a scaled roller rig. �It is also shown that the creep force correction factors for Johnson and Vermeulen's model increase linearly with creepage, starting with the values predicted by Kalker's theory. �Therefore, Kalker's theory provides a conservative estimate for creep force correction factors. �A case study is presented to demonstrate the creep curves, as well as the correction and transformation factors, for a typical wheel-rail configuration. �Additionally, two studies by other authors that calculate the correction factor for Kalker's creep coefficients for specific wheel-rail geometries are reviewed and show full agreement with the results that are predicted by the formulae derived in this study. �Based on a review of existing and past roller rigs, as well as the findings of this thesis, a number of recommendations are given for the design of a roller rig for the purpose of assessing the wheel-rail contact mechanics. �A scaling strategy (INRETS') is suggested, and equations for power consumption of a roller rig are derived. Recommendations for sensors and actuators necessary for such a rig are also given. Special attention is given to the resolution and accuracy of velocity sensors, which are required to properly measure and plot the creep curves. / Master of Science

La curiethérapie à haut débit de dose (HDR pour High Dose Rate) est une modalité de traitement du cancer qui délivre au volume cible la dose prescrite avec un débit de dose élevé. Malgré les distributions de doses hautement conformes obtenues avec cette modalité de traitement, le traitement lui-même n’est pas exempt d’erreurs. En raison des forts gradients de dose, typique de la curiethérapie, de petites erreurs dans le positionnement de la source peuvent entraîner des conséquences néfastes pour les patients. L’utilisation systématique de systèmes de vérification en temps réel est le seul moyen de savoir quelles doses ont été réellement données à la tumeur et aux organes à risque. Cette thèse présente les démarches effectuées pour créer et valider un système de dosimétrie à scintillateurs plastiques multipoints (mPSD pour Multipoint Plastic Scintillation Detector) capable d’effectuer avec précision des mesures in vivo en curiethérapie HDR. Un prototype a été optimisé, caractérisé et testé dans des conditions typiques de la curiethérapie HDR. Une analyse exhaustive a été réalisée pour obtenir un modèle optimisé du détecteur, capable de maximiser la collection de lumière de scintillation produite par l’interaction des photons ionisants. Il a été constaté que le scintillateur de longueur d’onde plus courte devrait toujours être placé plus près du photodétecteur, alors que le scintillateur émettant dans la longueur d’onde la plus élevée doit être en position distale. Si la configuration, comme mentionnée précédemment, n’est pas utilisée, des effets d’excitation et d’auto-absorption entre les scintillateurs peuvent se produire, et en conséquence, la transmission de la lumière à travers la fibre collectrice n’est pas optimale. Le détecteur a été rendu étanche à la lumière. Son noyau de 1 mm de diamètre permet son utilisation dans la majorité des applicateurs utilisés pour le parcours de la source en curiethérapie HDR avec l’192Ir. Pour la meilleure configuration du détecteur multipoints (3 mm de BCF10, 6 mm de BCF12, 7 mm BCF60), une optimisation numérique a été effectuée pour sélectionner les composants optiques (miroir dichroïque, filtre et tube photomultiplicateur (PMT pour Photomultiplier Tube)) qui correspondent le mieux au profil d’émission recherché. Ceci permet la déconvolution du signal en utilisant une approche multispectrale, en extrayant la dose de chaque élément tout en tenant compte de l’effet de tige Cerenkov. Le système de luminescence optimisé a été installé dans une boîte protectrice pour assurer la stabilité des composantes optiques lors de la manipulation. Les performances dosimétriques du système IViST (In Vivo Source Tracking) ont été évaluées en curiethérapie HDR, sur une plage clinique réaliste allant jusqu’à 10 cm de distance entre la source et les capteurs du mPSD. IViST peut simultanément mesurer la dose, trianguler la position et mesurer le temps d’arrêt de la source. En effectuant 100 000 mesures/s, IViST échantillonne suffisamment de données pour effectuer rapidement des tâches QA / QC clés, telles que l’identification d’un mauvais temps d’arrêt individuel ou des tubes de transfert interchangés. En utilisant 3 capteurs colinéaires et des informations planifiées pour une géométrie d’implant provenant des fichiers DICOM RT, la plateforme peut également trianguler la position de la source en temps réel avec une précision de positionnement de 1 mm jusqu’à 6 cm de la source. Le détecteur ne présentait aucune dépendance angulaire. Un essai clinique est actuellement en cours avec ce système. / High Dose Rate (HDR) brachytherapy is a cancer treatment modality that delivers to the target volume high doses in short amount of time in a few fractions. Despite the highly conformal dose distributions achieved with this treatment modality, the treatment itself is not free from errors. Because of the high dose gradient characteristics of the brachytherapy techniques, small errors in the source positioning can result in harmful consequences for patients. The routine use of a real-time verification system is the only way to know what dose was actually delivered to the tumor and organs at risk. This thesis presents the investigation done to obtain a Multi-point Plastic Scintillation Detector (mPSD) system capable of accurately performing in vivo dosimetry measurements in HDR brachytherapy. A first system’s prototype was optimized, characterized, and tested under typical HDR brachytherapy conditions. An exhaustive analysis was carried out to obtain an optimized mPSD design that maximizes the scintillation light collection produced by the interaction of ionizing photons. We found that the shorter wavelength scintillator should always be placed closer to the photodetector and the longer wavelength scintillator in the distal position for the best overall light-yield collection. If the latter configuration is not used, inter-scintillator excitation and self-absorption effects can occur, and as a consequence, the light transmission through the collecting fiber is not optimal. The detector was made light-tight to avoid environmental light, and its 1 mm diameter core allows their usage in most applicator channel used in 192Ir HDR brachytherapy. For the best mPSD design (3 mm of BCF10, 6 mm of BCF12, 7 mm BCF60), a numerical optimization was done to select the optical components (dichroic mirror, filter and Photomultiplier Tube (PMT)) that best match the light emission profile. It allows for signal deconvolution using a multispectral approach, extracting the dose to each element while taking into account the Cerenkov stem effect. The optimized luminescence system was enclosed into a custom-made box to preserve the optical chain stability and easy manipulation. The In Vivo Source Tracking (IViST) system’s dosimetric performance has been evaluated in HDR brachytherapy, covering a range of 10 cm of source movement around the mPSD’s sensors. IViST can simultaneously measure dose, triangulate source position, and measure dwell time. By making 100 000 measurements/s, IViST samples enough data to quickly perform key QA/QC tasks such as identifying wrong individual dwell time or interchanged transfer tubes. By using 3 co-linear sensors and planned information for an implant geometry (from DICOM RT), the platform can also triangulate source position in real-time with 1 mm positional accuracy up to 6 cm from the source. The detector further exhibited no angular dependence. A clinical trial is presently on-going using the IViST system.

L'homologie de contact est un invariant homologique pour variétés de contact dont la définition est basée sur l'utilisation de courbes holomorphes. Ce travail de thèse concerne l'étude de cet invariant dans le cas des produits de contact. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

For efficient transportation in either trains, busses or passenger cars, rolling elements such as wheels, tyres, bearings and transmission elements are fundamental. The energy efficiency and the generation of noise and vibrations in rolling contacts depend on the surface roughness of contacting bodies. In order to optimize the surfaces of rolling elements, prediction of its impact on the dynamic response from rolling excitation is required. A computationally efficient method to include surface roughness in the modelling of rolling contacts is presented. More specifically, nonlinear effects on the contact force due to the threedimensional shape and roughness of the contacting surfaces are introduced in a moving point force formulation. As a consequence of the point force approximation follows the assumption that any dynamic wave motion within the contact area is negligible.The rolling contact force is nonlinear due to a varying relative displacement between contacting bodies and is therefore referred to as state-dependent. A study case for the state-dependent method consisting of a steel ball rolling on a steel beam showed good agreement between numerical predictions and measured beam vibrations. Furthermore, an application to the wheel-rail interaction show that roughness-induced contact nonlinearities have a significant impact on the dynamic response caused by rolling excitation. / <p>QC 20141103</p> / ECO2 Vehicle Design

Depuis l'utilisation des boulons au XVème siècle pour assembler deux pièces, les assemblages boulonnés posent des questions quant à la compréhension de leur fonctionnement et de leurs défaillances, telles que la variation de la tension de serrage entrainant, le desserrage, le dévissage, la perte d'étanchéité, l'initialisation de fissures, ... Pour comprendre leur fonctionnement, une méthodologie d'analyse tribologique a été mise en place, permettant de démonter un assemblage boulonné sans le desserrer, afin de ne pas modifier les conditions de contact lors du desserrage. Ainsi, toutes les interfaces d'assemblages (‘‘filets’’ écrou/vis et ‘‘autres que filets’’) formant des triplets tribologiques, ont été étudiées durant les trois phases de leur cycle de vie (fabrication, serrage, service) par le biais de cas-tests de matériaux différents. Un dialogue interactif entre les expérimentations (corrélations d'images, expertises) et la simulation numérique (Eléments Finis, Eléments Discrets) a permis de dégager des interprétations, notamment concernant les trois phases. Lors de la fabrication, le roulage des vis engendre des transformations tribologiques superficielles au niveau des sous-surfaces des filets formés. Le cœur des vis (noyau) restant non-déformé, ce procédé crée ainsi une différence de microstructure au sein de ces vis, ce qui est une source d'altération de leurs propriétés en fatigue. Lors du serrage, il se forme à l'interface ‘‘filets’’ une mixture de troisièmes corps ‘‘sec-solide’’, accommodant la vitesse entre la vis et l'écrou. Cette mixture résulte d'une réactivité entre une graisse utilisée pour le serrage et des particules, détachées d'un revêtement appliqué sur les filets d'écrous et/ou de vis. En fin de serrage, une partie de la mixture reste piégée entre les filets, jouant le rôle de maintien de la tension de serrage. Dans ces conditions, il apparaît que le frottement varie en fonction de la rhéologie de la mixture, conditionnant la variation de la tension de serrage. En service, des instabilités de contact (glissement, décollement, ...) ont été identifiées au niveau des interfaces. Ces instabilités engendrent dans les interfaces ‘‘autres que filets’’ la formation d'un troisième corps oxydé. Ce dernier constitue un surplus de matière qui peut entrainer l'augmentation des contraintes mécaniques dans les assemblages. A l'interface ‘‘filets’’ écrou/vis, il a été constaté que si la mixture de troisièmes corps piégée en serrage n'est pas cohésive, elle est extrudée des contacts, initialisant la perte de la tension de serrage. A partir de ces interprétations, des interactions entre plusieurs circuits tribologiques conduisent à converger vers un scénario de fonctionnement des assemblages boulonnés, permettant de solutionner leurs défaillances par la re-conception (mise en place de gorge de décharge, ...). / Since the use of bolts in the fifteenth century to assemble two parts, the bolted assemblies have the interrogations according to the understanding of their operating and failures occurring, such as the variation of the clamping force leading to, self-loosening, loss of sealing performance, cracks initialization, ... In order to understand their operating, a methodology focused on tribological approach was established, enabling to disassemble a bolted assembly without loosen its, allowing to not change the contact conditions during loosening. So, all the bolted assemblies interfaces (nut/screw ‘‘threads’’ and ‘‘others than threads’’) constituting tribological triplets, have been studied according to the three stages of their full life-cycle (manufacturing, tightening and service) using configurations of different materials. An interactive dialogue between the experiments (fields measuring by digital images correlation, tribological analysis) and the numerical simulation (Finite Element Method, Discrete Element Method) has led to interpretations about the three stages. During the manufacturing, the rolling of screws generates tribological superficial transformations in subsurfaces of machined threads. Contrariwise, inside the volume of these machined screws, there is no tribological transformation. So, this manufacturing process creates a difference of microstructure in these screws, that could be a source of their fatigue properties destruction. During the tightening, it produces at ‘‘threads’’ interface a ‘‘dry-solid’’ mixture of third bodies, accommodating the speed jump between the screw and the nut. This mixture is the result of a reactivity between a grease used for bolted tightening and the particles, detached by plastic flow from a coating initially applied on the threads of nuts and/or bolts. At the end of the process, a part of the mixture remains trapped in the threads, playing the role of maintaining the clamping force. In these conditions, it appears that the friction varies depending of the rheology of the mixture, conditioning the variation of the clamping force. In service, contact instabilities (slip, peeling off, ...) have been identified in the interfaces. These instabilities lead to the formation of an oxidized third body in ‘‘others than threads’’ interfaces. This oxidized third body represents a surplus of material and can increase mechanical stresses in the assemblies. In the nut/screw ‘‘threads’’ interface, it was found that if the mixture of third bodies trapped during the tightening stage is not cohesive, it is extruded, initializing the loss of clamping force. Based on the findings, the interactions between multiple tribological circuits lead to converge to a scenario of bolted assemblies operating, allowing to solve their failures by re-designing (create discharge grooves, ...).

Contact resistance is the most important and universal characteristic of all types of electrical and thermal contacts. Accurate measurement of contact resistance is important, because it serves as a measure for judging the performance and operational life span of contacts. Rise in contact temperature is one of the major factors that pose a big threat to the stability of electrical contacts. Dissipation of heat by solid conduction through a contact interface is governed by its thermal contact conductance (TCC). This emphasizes the need to study the TCC of an electrical contact along with its electrical contact resistance (ECR). Simultaneous measurement of ECR and TCC is important for understanding the interconnection between these two quantities and the possible influence of one over another. Real time experimental data and analytical correlations can be extremely helpful in developing electrical contacts with improved thermal management capabilities. As a part of the experimental investigation, a test facility has been developed for making simultaneous measurement of ECR and TCC across flat contacts. The facility has the capability of measuring ECR and TCC over a wide range of operating parameters, such as contact pressure, contact temperature, interstitial gaseous media, ambient pressure, etc. It is also capable of determining the electrical resistivity and thermal conductivity of materials as a function of temperature, which is very helpful in analyzing the generated contact resistance data. Using this facility, simultaneous ECR and TCC measurements are made across bare and gold plated contacts of OFHC Cu (oxygen free high conductivity copper) and brass. Simultaneous ECR and TCC measurements are made on nominally flat contacts in the contact pressure range of 0 – 1 MPa and the interface temperature range of 20 – 120 °C. Effect of contact pressure and interface temperature on ECR and TCC is studied on bare and gold coated contacts in vacuum, N2, Ar, and SF6 environments. TCC strongly depends on the thermophysical properties of the interstitial media and shows a significant enhancement in gaseous media, because of the increased interfacial gap conductance compared to vacuum. The gas pressure is varied in the range of 1 – 2.6 bar to study its effect on the gap conductance at different contact pressures and interface temperatures. Minor increase in the ECR observed in gaseous media is found to be independent of the properties of the media. Experimental results indicated that ECR depends on the gas pressure as well as on the applied contact load. Effect of gold coating and its thickness on the ECR and TCC across OFHC Cu and brass contacts is studied. Measurements on electroplated gold specimens having different gold layer thicknesses (0.1, 0.3, and 0.5 µm) indicated that ECR decreases and TCC increases with increasing gold coating thickness. Effect of gold coating on the substrate properties, contact surface tomography, and microhardness is analyzed and correlated to the observed behavior of ECR and thermal gap conductance. An attempt is made to understand and quantify the changes in the contact surface characteristics due to contact loading and heating, by measuring various surface topography parameters before and after the experimentation. Effect of thermal stresses (generated due to temperature variations) on ECR and TCC is studied and inclusion of an experimentally measured temperature dependent load correction factor is suggested in the theoretical models to take into account the effect of thermal stresses in contact assemblies.

No presente trabalho foi desenvolvida uma teoria de característica elétrica da estrutura metal-isolante-metal considerando uma camada fina de óxido entre o metal e o isolante, sendo o óxido um outro isolante de banda de energia proibida mais larga. Foi considerada uma distribuição energética uniforme de estados de impurezas à interface óxido-isolante. Estudamos a distribuição real do potencial na região de carga espacial usando a equação de Poisson. Através desta distribuição obtemos a relação entre o potencial de contato e a carga positiva na região de depleção e assim a característica capacitância-voltagem da estrutura. Este tipo de característica é útil para se calcular as características corrente em função do potencial e corrente em função do tempo para um dado potencial e deste modo é importante para o entendimento das estruturas MIM e MOIM. / In this work we have developed a theory of electric characteristic of the metal-oxide-insulator-metal structure, considering a thin film of oxide between metal and insulator; the oxide is another insulator of wider forbidden energy gap. A uniform energy distribution of impurity states at the oxide-insulator interface was considered. W e have studied the actual distribution of potential in the region of spatial charge using the Poisson equation. With this distribution we obtain the relation between the contact potential and the charge in the depletion region and then the characteristic potential - capacitance of t his structure. This type of characteristic is useful to calculate the characteristic current - potential, and current-time at a given potential . In this manner it is important to the understanding of MIM and MOIM structures.

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In this thesis, we study Legendrian and transverse isotopy problem for cabled knot types. We give two structural theorems to describe when the (r,s)- cable of a Legendrian simple knot type K is also Legendrian simple. We then study the same problem for cables of the positive trefoil knot. We give a complete classification of Legendrian and transverse cables of the positive trefoil. Our results exhibit many new phenomena in the structural understanding of Legendrian and transverse knots. we then extend these results to the other positive torus knots. The key ingredient in these results is to find necessary and sufficient conditions on maximally thickened contact neighborhoods of the positive torus knots in three sphere.