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Mandelbrojt, Juliette. "How do transcription and chromosomal context interfere with an efficient replication origin ?" Electronic Thesis or Diss., Université Paris Cité, 2024. https://wo.app.u-paris.fr/cgi-bin/WebObjects/TheseWeb.woa/wa/show?t=7639&f=73688.
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La réplication fidèle du génome des vertébrés est un processus essentiel au maintien de son intégrité. Elle est initiée selon un programme temporel bien orchestré de déclenchement des origines de réplication. En condition de stress réplicatif, deux types de régions chromosomiques sont susceptibles de subir une instabilité génomique. Les sites fragiles de réplication précoce (ERFS) sont caractérisés par une forte densité en gènes courts fortement transcrits contenant des R-loops ainsi qu'en origines de réplication efficaces. Au contraire, les sites fragiles communs (SFC) sont localisés dans des régions tardives contenant des gènes très longs et modérément exprimés. Dans ces régions, l'instabilité est associée à un appauvrissement des événements d'initiation corrélé à la transcription. Ces observations ont conduit à une hypothèse sur la formation des SFC, selon laquelle la transcription peut activement éliminer les complexes de pré-réplication, limitant le déclenchement d'origines dans ces longs gènes. Nous avons étudié comment la transcription interfère avec l'initiation de la réplication au niveau d'un SFC et d'une région ayant certaines propriétés des ERFS dans des lignées cellulaires aviaires DT40 modifiées. Nous avons d'abord analysé l'activité d'une origine de réplication minimale et efficace insérée au milieu de la zone dépourvue d'événements d'initiation du gène de la dystrophine (DMD), couvrant 1 Mb et se répliquant tardivement. Le gène DMD, naturellement silencieux et non fragile dans la DT40, devient fragile lorsqu'il est placé sous le contrôle d'un promoteur TetOn inductible. Lorsque la transcription est induite, celle-ci progresse à travers l'origine, diminuant drastiquement son activité. Ce résultat est en accord avec le modèle proposé de formation des SFC. Nous avons ensuite analysé l'effet du passage de la transcription induite par le promoteur fort b-actine sur la même origine minimale dans une région répliquée en milieu de phase S. Nous avons observé que le passage de la machinerie de transcription n'inhibe pas son déclenchement. La transcription progresse au-delà de l'origine minimale, suggérant que les deux machineries peuvent coexister sur le même substrat. De plus, des analyses du moment de réplication ont montré que l'origine minimale coopère avec l'origine présente dans le promoteur b-actine pour avancer le moment de réplication de la région qui devient précoce. Cette configuration ressemblant aux ERFS, nous avons testé la stabilité de la région modifiée. Contrairement aux ERFS précédemment décrits dans la DT40, cette configuration n'induit pas le recrutement de g-H2AX lors d'un stress réplicatif. Ces résultats suggèrent que la transcription affecte différemment l'initiation de la réplication dans deux contextes génomiques distincts. Le contexte de réplication tardive est répressif, alors que le contexte précoce ne l'est pas. Pour approfondir cette question, nous avons testé un troisième contexte, une région de réplication tardive non génique. Des résultats antérieurs ont montré que la combinaison de l'origine complète b-globine avec l'origine b-actine avançait de manière significative le moment de réplication. Nous avons montré que l'origine minimale modèle insérée seule dans ce troisième contexte chromosomique est réprimée, alors que l'origine b-actine est active. Lorsque les deux origines modèles sont insérées à proximité, l'origine minimale devient fonctionnelle. Globalement, ce dernier contexte chromosomique se comporte différemment des deux précédents. L'origine minimale efficace ne peut fonctionner dans ce contexte très répressif que lorsqu'elle est associée à une transcription active. Ce dernier résultat confirme la forte influence de l'environnement chromosomique sur la fonction d'une origine. Ce travail contribue à une meilleure compréhension des mécanismes moléculaires qui régissent la formation des sites fragiles et l'établissement des domaines chromosomiques du moment de réplicationThe faithful duplication of vertebrate genomes is essential for maintaining genome integrity. DNA replication is initiated at thousands of replication origins following a well-orchestrated temporal programme of origin firing. Under replication stress, two main types of chromosomal regions are prone to chromosomal instability. Early replicating fragile sites (ERFSs) are characterised by a high density of short and highly transcribed genes containing R-loops and efficient replication origins. In contrast, common fragile sites (CFSs) are located in late-replicating regions containing very long, moderately expressed genes. In these late regions, instability has been shown to be associated with a transcription-induced depletion of initiation events. This leads to the current main hypothesis for CFS formation, that ongoing transcription may actively remove pre-replication complexes, thereby limiting origin firing within these long genes. In this study, we investigated how transcription interferes with replication initiation at CFSs and in a context similar to ERFSs using engineered avian DT40 cell lines. First, we analysed the consequences of introducing an efficient minimal model replication origin in the centre of the region depleted of initiation events of the 1Mb long and late replicating dystrophin (DMD) gene. The DMD gene, which is naturally silent and non-fragile in DT40 cells, becomes fragile under the control of an inducible TetOn promoter. We observed a dramatic decrease in the minimal efficient origin activity after tetracycline induction. This result supports the commonly accepted model of CFS formation. Next, we analysed the effect of transcription induced by the strong b-actin promoter through the same efficient minimal origin in a mid-late replicating region. We observed that the passage of the transcriptional machinery does not inhibit origin firing in this context. Transcription proceeds beyond the minimal origin, suggesting that the two types of machinery can coexist on the same substrate. Furthermore, replication timing analyses showed that the minimal origin cooperates with the origin present in the b-actin promoter to advance the replication timing of the region. Since this configuration shares many features with ERFSs, we tested whether this organisation affects chromosome stability. Interestingly, unlike the previously described DT40 ERFS, this configuration does not induce gH2AX recruitment upon replication stress induction, suggesting that it does not cause fragility. Our results demonstrate that transcription differentially affects replication initiation in two distinct genomic contexts. The late-replicating timing context is repressive, whereas the early context is not. To investigate this further, we tested a third context, a non-genic late-replicating region. Previous results showed that the combination of the full-length b-globin origin next to the b-actin origin significantly advanced replication timing. Single-cell RT analyses revealed that this late region, which is closely associated with the nuclear lamina, is under tight control to ensure late replication. We showed that the minimal model origin alone inserted into this third chromosomal context is repressed, whereas the b-actin promoter/origin is active. Furthermore, when the two model origins are inserted in close proximity, the minimal origin becomes functional suggesting a cooperative interaction. Overall, this last chromosomal context behaves differently from the two previously studied. We found that the minimal efficient origin can only function in this very repressive context when associated with active transcription. This last result confirms the strong influence of the chromosomal environment on origin function. Overall, this work contributes to a better understanding of the molecular mechanisms that govern the formation of fragile sites and the establishment of chromosomal domains of replication timing
2
Barbault, Florent. "Etude par RMN et modélisation moléculaire des structures de la séquence ARN initiant la dimérisation chez VIH-1Lai et de son analogue ADN". Phd thesis, Université d'Orléans, 2001. http://tel.archives-ouvertes.fr/tel-00009954.
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Le génome du virus de l'immunodéficience humaine (VIH) est constitué, comme tous les rétrovirus, de deux copies identiques d'ARN génomique. Celles-ci sont liées de manière non covalente au niveau de leur région 5'-terminale. Ce phénomène de dimérisation interfère avec différentes étapes clés du cycle rétroviral. C'est pourquoi, l'inhibition de la dimérisation représente une nouvelle voie de traitement potentiel du VIH. La première partie de ce travail porte sur la séquence d'ARN SL1 initiant la dimérisation chez VIH-1Lai. Nous nous sommes intéressés à la détermination structurale, par RMN et modélisation moléculaire, des espèces présentes dans le processus de dimérisation sous forme instable. Après avoir isolé les deux différents dimère d'ARN, nous avons mis en évidence la structure du dimère stable qui permet d'avancer des hypothèses quant à leur stabilité relative. La seconde partie de ce travail porte sur l'étude du fragment désoxyribose de SL1. Là encore, deux conformères de stabilité différente sont isolables. Le dimère instable s'organise sous forme de “kissing-complex” et représente la première structure de ce type élucidée pour un ADN. La structure du dimère stable demeure de type “kissing-complex” bien que présentant des différences à l'origine du changement de stabilité. La présence du groupement hydroxyle distinguant l'ADN de l'ARN explique cette différence de comportement. Ces investigations structurales constituent une solide base d'étude dans les stratégies de “drug-design” impliquant le développement d'inhibiteurs susceptibles d'interférer avec le phénomène de dimérisation.
3
Pollès, Rémi. "Structures exotiques en nanophotonique, théorie et approche numérique". Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2011. http://tel.archives-ouvertes.fr/tel-00646673.
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Dans la perspective d'un contrôle ultime de la lumière, les arrivées récentes des cristaux photoniques et des métamatériaux constituent des avancées majeures. Ces matériaux nano-structurés présentant des propriétés optiques inédites nous ouvrent tout un champ de possibilités encore inexploré. En particulier, des milieux d'indice effectif négatif sont rendus concevables. L'objectif de cette thèse est d'étudier d'un point de vue électromagnétique, à l'aide d'outils analytiques et numériques, le comportement de la lumière dans ces structures exotiques. Nous nous penchons sur les boucles de lumières, qui sont des modes localisés d'une structure multi-couches, émergeant du couplage contra-directionnel entre deux guides distincts. Une analyse physique est proposée et un modèle basé sur la théorie des modes couplés est développé. Cela nous permet de décrire avec précision l'excitation d'une boucle de lumière par une source lumineuse, et d'envisager des applications pour la mise en forme de faisceau. Dans une seconde partie, nous étudions des cristaux photoniques unidimensionnels formés par une alternance de milieux d'indices positif et négatif. Lorsque l'indice moyen est nul, une bande interdite aux propriétés nouvelles apparait. Nous montrons que le caractère dispersif des milieux transforme des pics étroits de transmission en larges bandes. Pour caractériser la propagation d'un faisceau dans un tel cristal, nous développons et validons alors un modèle qui nous permet de démontrer le potentiel en matière de mise en forme de faisceau (auto-collimation, focalisation).
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Diamantoudi, Effrosyni. "Coalition structures". Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36762.
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The first chapter introduces the topic of coalition structures and stresses its importance and impact on game theory. Additionally, it presents and motivates the significance of the three following chapters.The second chapter investigates how rational individuals partition themselves into different coalitions. We propose a notion that determines simultaneously the coalition structures that are likely to prevail in a game, as well as the feasible payoff configurations associated with them. Our solution concept is built in the spirit of von Neumann and Morgenstern stability, but it overcomes the overoptimism associated with it when employed in our context. Moreover, in doing so, we achieve consistency and resolve the problem of myopia embedded in previous notions. We prove existence for a general class of games, and investigate the efficiency of our solution.
The third chapter ascertains which partitions of players will emerge and what actions will these players choose under each partition, when they can negotiate with each other and their actions have externalities. Naturally, the environment is depicted by a normal form game. The solution is a collection of pairs, each consisting of a coalition structure and a strategy profile. Although this chapter addresses the same question the Ray and Vohra (1997) paper did, it does so in a manner that overcomes the problems embedded in their approach. In particular, we assume that once a coalition deviates it fears the worst, given that the non-members do the best for themselves. In doing so, we improve upon previous solution concepts (e.g. strong and coalition-proof Nash equilibria) by NOT assuming that all other players will stay put. Yet, unlike the Ray and Vohra approach, we do not endow the deviating coalition with the power of imposing its will on all of the other players. A general solution concept is defined and its properties (efficiency, etc.) and applications are discussed.
The fourth chapter analyzes cartel stability when firms are farsighted. It studies a price leadership model a la D'Aspremont et al. (1983), where the dominant cartel acts as a leader by determining the market price, while the fringe behaves competitively. According to D'Aspremont et al.'s notion of cartel stability, a firm will not remain in a cartel as long as it prefers the outcome where it is the only member leaving the cartel for the fringe. Such an approach implies that the firm is myopic since it ignores whether the outcome of its deviation is stable itself. Our notion captures foresight by employing a solution concept built in the spirit of von Neumann and Morgenstern stable set, yet adopting an indirect dominance a la Harsanyi. We show that there always exists a unique, non-empty set of stable cartels.
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McCune, David Thomas. "Manufacturing Quality of Carbon/Epoxy IsoTruss (R) Reinforced Concrete Structures". Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd753.pdf.
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Anarella, Mateo. "Submanifolds of the nearly Kähler SL(2,R) x SL(2,R)". Electronic Thesis or Diss., Valenciennes, Université Polytechnique Hauts-de-France, 2024. http://www.theses.fr/2024UPHF0024.
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Le but de cette thèse est d’élargir la compréhension de la variété presque kählerienne SL(2,R) × SL(2,R) et de ses sous-variétés. Les variétés presquekähleriennes sont une relaxation riemannienne de la définition de variété Kähler : une variété presque hermitienne (M, g, J) est presque kählerienne si la dérivée covariante de la structure presque complexe est antisymétrique. De plus, afin d’éviter une éventuelle intersection avec les variétés de Kähler, nous exigeons que ∇J soit non dégénéré, ce que nous appelons une variété stricte presque Kähler. Les sous-variétés presque kähleriennes sont l’une des seize classes de variétés presque hermitiennes classées par Gray et Hervella dans [27]. Selon Gray, la classe la plus intéressante, les variétés presque kähleriennes, possèdent de nombreuses propriétés intéressantes. Par exemple, d’un point de vue physique, ce sont les seules variétés à six dimensions à admettre un spineur Killing [23, 28]. De plus, les variétés strictes presque kähleriennes sont intéressantes en géométrie multiplectique car elles sont 2-plectiques [37]. Ils possèdent également de nombreuses propriétés de division utiles. À savoir, étant donné une variété presque kählerienne M, il existe une variété presque kählerienne stricte M1 et une variété de Kähler M2 telle que M = M1 ×M2. Dans les dimensions deux et quatre, variétés presque kähleriennes sont automatiquement variétés de Kähler. Par conséquent, nous trouvons les plus petits exemples intéressants de variétés presque kählerienne en dimension six. En dimension huit, Gray [26] a prouvé qu’une variété presque kählerienne est toujours de Kähler ou le produit d’une variété presque kählerienne stricte à six dimensions avec une surface de Kähler. En dimension dix, Nagy [41] a prouvé qu’une variété presque Kähler est soit Kähler, un produit d’une variété Kähler stricte à six dimensions avec une variété Kähler à quatre dimensions, soit une variété Kähler stricte, qu’il a classée comme espaces de twisteurs au-dessus de variétés Kähler-quaternioniques avec constante d’Einstein positive. [etc]A strict nearly Kähler manifold is an almost Hermitian manifold for which thecovariant derivative of the almost complex structure is non-degenerate and skewsymmetric. Strict nearly Kähler manifolds are quite rare. In six dimensions,there are only four homogeneous strict nearly Kähler manifolds: S6, S3 × S3,CP 3 and F (C3). In the pseudo-Riemannian setting, there are six analogues.We consider SL(2, R) × SL(2, R), the analogue of S3 × S3.We first study the strict nearly Kähler structure of SL(2, R) × SL(2, R). Themetric and almost complex structure of are both induced from a pseudo-Riemannian submersion π : SL (2, R)×SL (2, R)×SL(2, R) → SL (2, R)×SL (2, R).We give an expression for the full isometry group.In this space we study different types of submanifolds, such as surfaces,Lagrangian submanifolds or hypersurfaces. We divide Lagrangian submanifoldsinto four different types, which depend on their behavior with respect to analmost product structure P.We classify all totally geodesic and extrinsically homogeneous Lagrangiansubmanifolds. Moreover, we study totally geodesic surfaces and hypersurfaces with constant sectional curvature
Een strikte nagenoeg-Kählervariëteit is een bijna-Hermitische variëteit waarvoor de covariante afgeleide van de bijna-complexe structuur niet-ontaard en scheefsymmetrisch is. Dergelijke variëteiten zijn vrij zeldzaam. In dimensie zes zijn er slechts vier homogene strikte nagenoeg-Kählervariëteiten: S6, S3 × S3,CP3 en F(C3). In de pseudo-Riemannse setting bestaan er zes analogen. We beschouwen SL(2,R) × SL(2,R), analoog aan S3 × S3.We bestuderen eerst de strikte nagenoeg-Kählerstructuur van SL(2,R)×SL(2,R). De metriek en bijna-complexe structuur zijn beide geïnduceerd door een pseudo-Riemannse submersie SL(2,R)×SL(2,R)×SL(2,R) → SL(2,R)×SL(2,R). We geven een uitdrukking voor de volledige isometriegroep. In deze ruimte bestuderen we verschillende soorten deelvariëteiten, zoals oppervlakken, Lagrangiaanse deelvariëteiten en hyperoppervlakken. Lagrangiaanse deelvariëteiten verdelen we in vier verschillende types, afhankelijk van hun gedrag ten opzichte van een bijna-productstructuur. We classificeren alle totaal geodetische en extrinsiek homogene Lagrangiaanse deelvariëteiten. Bovendien bestuderen we totaal geodetische oppervlakken en hyperoppervlakken met constante sectionele kromming
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Ruppert, Wolfgang A. F., Brigitte E. Breckner i Andreas Cap@esi ac at. "On Asymptotic Behaviour and Rectangular Band structures in SL(2,R)". ESI preprints, 2000. ftp://ftp.esi.ac.at/pub/Preprints/esi919.ps.
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Al, Hamidi Yasser. "Multivariable feedforward control of vibrations in multi-axes flexible structures : applications to multi-axes piezoelectric actuators". Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD016/document.
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Les actionneurs multi-axes sont de plus en plus prisés par les concepteurs de systèmes de nanopositionnement car ils permettent une réduction de l'espace occupé et de l'énergie consommée, une dextérité plus grande et une modularité avec peu de contraintes pour les applications. Certains de ces actionneurs et systèmes multi-axes sont cependant caractérisés par des oscillations mal-amorties qui compromettent de manière drastique leurs performances générales. Cette thèse concerne l'exploitation des techniques de commande en boucle-ouverte input-shaping classiquement utilisées pour amortir de manière sans capteurs les oscillations dans les systèmes mono-axes et les étendent pour qu'ils soient utilisables pour les systèmes multi-axes. Les résultats proposés dans la thèse qui sont des techniques input-shaping multivariables sont ensuite appliquées sur des actionneurs piézoélectriques classiquement dédiés pour les applications de nanopositionnementMulti-axes actuators are becoming more and more tempting to nanopositioning system designers as they enable them to save space, reduce energy consumption, increase dexterity and offer more modularity and freedom with fewer constraints to their applications. Some of these multi-axes actuators and systems exhibit however badly damped vibrations which strongly compromise their global performances. This thesis work exploits the advantages of the well-known feedforward input shaping techniques usually used to damp vibrations in monovariable (SISO) systems to present a new multivariable (MIMO) input shaping technique that can be used to damp vibrations in multi-axes systems. The approach that was used in this study is to extend a previous work that was done on multiple-input single-output (MISO) systems and generalize it for MIMO systems. The study demonstrates also the application of this newly developed technique on different piezoelectric actuators commonly used in nanopositioning systems
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Zouari, Rafik. "Détection précoce d’instabilité aérolélastique des structures aéronautiques". Rennes 1, 2008. ftp://ftp.irisa.fr/techreports/theses/2008/r-zouari.pdf.
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L'objectif de cette thèse est de concevoir des nouvelles méthodes statistiques de détection capables d'améliorer la surveillance du flottement aéroélastique lors des essais en vol. La surveillance du flottement est étudiée comme un problème de détection des déviations d'indicateurs d'instabilité. On s'appuie sur la combinaison d'une méthode d'identification sous-espaces pour définir un vecteur résidu sensible à un indicateur de flottement et d'un test CUSUM pour surveiller en ligne ses déviations par rapport à une valeur de référence. Trois méthodes de détection sont proposées dans cette thèse. La première réalise une détection du flottement par rapport à un état de référence prédit au voisinage de l'instabilité en utilisant la connaissance a priori d'un modèle aéroélastique et/ou des mesures expérimentales des essais en vol. La deuxième méthode utilise une surveillance adaptative du flottement en actualisant l'état de référence au cours du temps. La troisième méthode proposée vise à suivre l'amortissement en déterminant des intervalles de confiance par des tests de détectionThe goal of this thesis is to design useful statistical detection approaches to improve the aeroelastic flutter monitoring during the flight testing process. Flutter monitoring is investigated as a detection problem regarding the deviations of instability indicators. It consists of a combination of a subspace-based identification method to define a residual vector sensitive to a flutter indicator and a statistical CUSUM test for an on-line deviations monitoring with respect to a fixed reference value. This thesis proposes three approaches. The first performs a flutter detection with respect to a reference modal state predicted close to instability using the a priori knowledge of an aeroelastic model and/or experimental flight testing data. The second approach uses an adaptive flutter monitoring through updating the reference state during the on-line test. The third approach exploits detection tests for damping assessment with confidence bounds determination
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Zouari, Rafik Basseville Michèle Mevel Laurent. "Détection précoce d'instabilité aérolélastique des structures aéronautiques". Rennes : [s.n.], 2008. ftp://ftp.irisa.fr/techreports/theses/2008/r-zouari.pdf.
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Palmieri, Benoit. "Diffusion in channeled structures". Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18269.
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The theory of Ronis and Vertenstein [J. Chem. Phys. vol. 85, 1628, (1986)] is used to calculate the permeability of Xenon in Theta-1 and of Argon in alpha-quartz, both crystalline sodalites containing large, one-dimensional channels in the first case and narrow interconnected channels in the second. The simulated dynamics of a small part of the crystal atoms exactly reproduce those of the full crystal by the means of a generalized Langevin classical equation of motion. An approximate expression for the potential of mean force inside the crystal is derived. The Theta-1 energy landscape is smooth with small energy barriers while the alpha-quartz has large energy barriers to diffusion. The permeability is reported for both systems and compared in detail with that obtained from transition state theory. The role of the lattice vibrations is also investigated. For Xenon in Theta-1, transition state theory does not properly describe the diffusion process and the lattice vibrations do not play a large role. For Argon in alpha-quartz, transition state theory is more appropriate but there, the lattice vibrations cannot be neglected. For systems where the lattice vibrations play a role, the quantum mechanical corrections to the diffusion are computed. The diffusion is studied using the path integral formalism. Forward-Backward path integrals are combined and, using the MSR [Phys. Rev. A., vol. 8, 423 (1973)] formalism, are transformed to a set of generalized Langevin equations that reduce to the classical equations of motion at high temperatures. The quantum mechanical treatment of the lattice vibrations results in a decreased permeability. The quantum corrections to the potential of mean force are computed from an approximate density matrix. A modification to the original Feynman-Kleinert variational method[Phys. Rev. A., vol. 34, 5080 (1986)] to calculate quantum mechanical partition functions is suggesLa méthode dévelopée par Ronis et Vertenstein [J. Chem. Phys. vol. 85, 1628, (1986)] est utilisée pour calculer la perméabilité du Xénon à l'intérieur du zéolite Theta-1 et de l'Argon à l'intérieur d'un cristal d'alpha-quartz. Ces deux sodalites contiennent des canaux qui sont larges et unidimensionnels dans le premier cas et étroits et interconnectés dans le deuxième. La dynamique d'une petite partie des atomes du cristal est explicitement simulée. Cette dynamique est décrite à partir d'équations de Langevin généralisées qui reproduisent l'effet du reste du cristal. L'énergie libre du gaz absorbé à l'intérieur du cristal est approximée. Le profil énergétique à l'intérieur du zéolite Theta-1 est presque plat et contient des barrières énergétiques peu élevées. Celui à l'intérieur du quartz contient de larges barrières à la diffusion. La perméabilité des deux systèmes est rapportée et comparée en détail avec celle obtenue à partir de la théorie dite des états de transitions. Le rôle qu'ont les modes de vibrations du cristal sur la diffusion est aussi étudié. Pour le Xénon à l'intérieur du zéolite Theta-1, la théorie des états de transitions ne décrit pas adéquatement la diffusion du gaz et les vibrations du cristal ne jouent pas un grand rôle. Pour l'argon dans le quartz, la théorie des états de transitions est plus appropriée et les vibrations du cristal ne peuvent être négligées. Pour les systèmes où les vibrations du cristal jouent un rôle, les premières corrections quantiques sont calculées. Dans ce cas, la diffusion est étudiée à partir de la formulation des intégrales de chemins. Les intégrales de chemins sont combinées et, en utilisant la théorie développée par Martin, Siggia et Rose [Phys. Rev. A., vol. 8, 423 (1973)], réduites à un système d'équations de Langevin généralisées q
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Aloupis, Greg. "Reconfigurations of polygonal structures". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85114.
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This thesis contains new results on the subject of polygonal structure reconfiguration. Specifically, the types of structures considered here are polygons, polygonal chains, triangulations, and polyhedral surfaces. A sequence of vertices (points), successively joined by straight edges, is a polygonal chain. If the sequence is cyclic, then the object is a polygon. A planar triangulation is a set of vertices with a, maximal number of non-crossing straight edges joining them. A polyhedral surface is a three-dimensional structure consisting of flat polygonal faces that are joined by common edges.For each of these structures there exist several methods of reconfiguration. Any such method must provide a well-defined way of transforming one instance of a structure to any other. Several types of reconfigurations are reviewed in the introduction, which is followed by new results. We begin with efficient algorithms for comparing monotone chains. Next, we prove that flat chains with unit-length edges and angles within a wide range always admit reconfigurations, under the dihedral model of motion. In this model, angles and edge lengths are preserved. For the universal model, where only edge lengths are preserved, several types of hexagons that cannot be reconfigured are exhibited. New bounds are provided for the number of operations required to reconfigure between triangulations, using "point moves" and "edge flips". Finally, unfolding motions are proven to always be possible for specific slices of polyhedra.
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Ghosh, Soham. "Compact multiple-antenna structures". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110651.
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Multiple-Input-Multiple-Output (MIMO) communications, which employ multiple antennas at the transmitter and receiver, have become quite ubiquitous today due to its capability to increase the system spectral efficiency and reliability. With the current niche of miniaturization of communication devices, one of the key problems is the design of low-profile multi-antennas. Moreover, when the antenna elements are too close to each other, the inherent problem of mutual coupling can greatly reduce the system capacity. Addressing these two issues at the same time remains an engineering challenge given the spatial constraints inside the device. This thesis investigates antenna miniaturization, mutual coupling reduction and antenna performance characterization for various realistic channel scenarios. Electromagnetic Band-Gap structures are used to reduce the size and mutual coupling of multi-element Microstrip Patch Antennas (MPAs), which can be envisioned to be incorporated in WLAN/LTE base-stations. Furthermore, ultra-miniaturized multi-element Planar Inverted-F Antennas (PIFAs) exploiting pattern and polarization diversity are proposed for receiver terminals, such as a handheld device. The capacity and diversity performance of these multi-antennas have been evaluated in free-space and various fading environments.Les systèmes de communication à entrée multiple sortie multiple, utilisant plusieurs antennes à l'émetteur et au récepteur, sont devenus omniprésents de nos jours en raison de leur capacité d'augmenter le rendement spectral et la fiabilité du système. Avec le marché de niche actuelle dans la miniaturisation des périphériques de communication, l'un des principaux problèmes est la conception d'antennes multiples avec un profile modéré. De plus, quand les antennes sont trop proche les uns des autres, le problème inné de couplage mutuel peut réduire substantiellement la capacité du système. Trouver une solution qui résout deux problèmes simultanément demeure un défi d'ingénierie compte tenu des contraintes d'espace à l'intérieur des périphériques. Ce mémoire examine la miniaturisation des antennes, la réduction du couplage mutuel, et la caractérisation de la performance des antennes dans divers scénarios avec des voies de transmissions réalistes. Les structures de bande interdite électromagnétique sont utilisées pour réduire les dimensions et le couplage mutuel dans les antennes planaires à microrubans (MPA) multiples. Ces structures peuvent être envisagées pour être incorporées dans les stations de base de technologie d'évolution à long terme (LTE) et de réseau local sans fil (WLAN). De plus, des antennes planaires F inversées (PIFA) ultra-miniatures à éléments multiples qui exploitent les diversités du motif et de la polarisation sont proposées pour les terminaux récepteurs tels que les périphériques de poche. La capacité et la performance de la diversité de ces antennes multiples sont évaluées dans l'espace libre et dans divers environnements d'évanouissement.
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Sinn, Thomas. "Smart deployable space structures". Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28327.
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Nowadays, space structures are often designed to serve only a single objective during their mission life, examples range from solar sail for propulsion over shields for protection to antennas and reflectors for communication and observation. By enabling a structure to deploy and change its shape to adapt to different mission stages, the flexibility of the spacecraft can be greatly increased while significantly decreasing the mass and the volume of the system. Inspiration was taken from nature. Various plants have the ability to follow the sun with their flowers or leaves during the course of a day via a mechanism known as heliotropism. This mechanism is characterized by the introduction of pressure gradients between neighboring motor cells in the plant’s stem,enabling the stem to bend. By adapting this bio-inspired mechanism to mechanical systems, a new class of smart deployable structures can be created. The shape change of the full structure can be significant by adding up these local changes induced by the reoccurring cell elements. The structure developed as part of this thesis consists of an array of interconnected cells which are each able to alter their volume due to internal pressure change. By coordinated cell actuation in a specific pattern, the global structure can be deformed to obtain a desired shape. A multibody code was developed which constantly solves the equation of motion with inputs from internal actuation and external perturbation forces. During the inflation and actuation of the structure, the entities of the mass matrix and the stiffness matrix are changed due to changing properties of the cells within the array based on their state and displacement. This thesis will also give an overview of the system architecture for different missions and shows the feasibility and shape changing capabilities of the proposed design with multibody dynamic simulations. Furthermore, technology demonstrator experiments on stratospheric balloons and sounding rockets have been carried out to show the applicability and functionality of the developed concepts.
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Mohammed, Aslam. "Neurovascular structures at risk from proximal locking of retrograde femoral nails". Thesis, University of Glasgow, 2002. http://theses.gla.ac.uk/5921/.
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The Richards retrograde femoral nail (Smith and Nephew 1997) is inserted into the medullary canal of the femur via an entry point in the intercondylar fossa, just anterior the anterior cruciate ligament. This particular implant requires insertion of both proximal and distal interlocking screws for maximal axial and rotational stability. The distal screws are inserted lateral to medial in a relatively safe area of the lower thigh using an external guide. The proximal locking screws by contrast are inserted 'freehand' at the level of the lesser trochanter in an anteroposterior direction using X-Ray control. The proximal thigh contains many vital neurovascular structures and it is the proximity of the femoral nerves and vessels which is of significant concern due to the relative inaccuracy of the freehand technique (Riina et al 1998). Hypothesis This led me to my first null hypothesis that 'proximal anteroposterior locking screws of retrograde femoral nails can be inserted in the proximal end of the femur through the proximal thigh without damage to the nerves and vessels'. To test this hypothesis we proposed to: 1). Dissect the main nerves and vessels of the thigh and describe their position and relation to the lesser trochanter. 2). Place investigative drill holes in a modified anatomical procedure to imitate insertion of the proximal anteroposterior locking screws. 3). Dissect the proximal thigh to determine whether important anatomical structures are at risk of being damaged by the proximal anteroposterior locking screws. The preliminary results of this first investigation lead to a second null hypothesis:- That the nerves and vessels of the upper thigh are at risk from proximal locking screws inserted in a lateral to medial direction in the upper thigh. To test this hypothesis we propose to; 4). Plan dissections to compare lateral to medial locking with anteroposterior locking, for use with a redesigned nail. 5). Finally we proposed a modified clinical trial of the redesigned nail. This would involve attaching the redesigned nail to the side of a volunteer's thigh and taking X-Rays in theatre to determine whether the redesigned nail could be adequately screened to allow its use in practice.
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Theußl, Stefan, Uwe Ligges i Kurt Hornik. "Prospects and Challenges in R Package Development". Institute for Statistics and Mathematics, WU Vienna University of Economics and Business, 2010. http://epub.wu.ac.at/866/1/document.pdf.
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R, a software package for statistical computing and graphics, has evolved into the lingua franca of (computational) statistics. One of the cornerstones of R's success is the decentralized and modularized way of creating software using a multi-tiered development model: The R Development Core Team provides the "base system", which delivers basic statistical functionality, and many other developers contribute code in the form of extensions in a standardized format via so-called packages. In order to be accessible by a broader audience, packages are made available via standardized source code repositories. To support such a loosely coupled development model, repositories should be able to verify that the provided packages meet certain formal quality criteria and "work": both relative to the development of the base R system as well as with other packages (interoperability). However, established quality assurance systems and collaborative infrastructures typically face several challenges, some of which we will discuss in this paper.Series: Research Report Series / Department of Statistics and Mathematics
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Angelchev, Shiryaev Artem, i Johan Karlsson. "Estimating Dependence Structures with Gaussian Graphical Models : A Simulation Study in R". Thesis, Umeå universitet, Statistik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-184925.
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Graphical models are powerful tools when estimating complex dependence structures among large sets of data. This thesis restricts the scope to undirected Gaussian graphical models. An initial predefined sparse precision matrix was specified to generate multivariate normally distributed data. Utilizing the generated data, a simulation study was conducted reviewing accuracy, sensitivity and specificity of the estimated precision matrix. The graphical LASSO was applied using four different packages available in R with seven selection criteria's for estimating the tuning parameter. The findings are mostly in line with previous research. The graphical LASSO is generally faster and feasible in high dimensions, in contrast to stepwise model selection. A portion of the selection methods for estimating the optimal tuning parameter obtained the true network structure. The results provide an estimate of how well each model obtains the true, predefined dependence structure as featured in our simulation. As the simulated data used in this thesis is merely an approximation of real-world data, one should not take the results as the only aspect of consideration when choosing a model.
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Goulet, Jean 1939. "Data structures for chess programs". Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65427.
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Dandurand, Alain. "Seismic upgrading of existing structures". Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=64072.
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Capocci, Michael Sean. "Conformal structures and symmetries". Thesis, University of Aberdeen, 1994. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU070087.
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The purpose of this thesis is to study methods by which conformal vector fields on pseudo-Riemannian manifolds can be simplified. A vector field on a manifold M with metric g is conformal if its local flows preserve the metric g up to a scaling and unlike Killing vector fields, which preserve g exactly, it cannot in general be linearised in a neighbourhood of any given point. The difference is that a Killing vector field is affine, that is it preserves a connection on the manifold. In this case the connection is the canonical (Levi-Civita) connection associated with g, but affine vector fields with respect to any connection are linearisable. The task is to find new connections with respect to which the set of conformal vector fields, or some subset of them, are affine. Suppose that we have a manifold M with a pseudo-Riemannian conformal structure and an orthogonal splitting of the tangent bundle. We construct, for a natural choice of torsion, a unique connection in the principal bundle of frames adapted to the splitting. Moreover this connection is preserved by any transformations which preserve the splitting of the tangent bundle. Thus any conformal vector field which preserves the splitting is affine. The splitting can be chosen to reflect the tangent to the orbits of a subalgebra of conformal vector fields, the principal null directions of the Weyl tensor or the flow of a perfect fluid. We also give a study of conformal vector fields in three-dimensional Lorentzian manifolds. An equivalent of the Cotton-York tensor is used to investigate the behaviour of these vector fields at their fixed points in the same spirit as the Weyl tensor is used in four dimensions.
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Beltz, Hervé. "Etude par fluorescence de l'importance des structures primaires et secondaires de la séquence cTAR et de la protéine NCp7 lors du premier saut de brin de la transcription inverse de VIH-1". Phd thesis, Université Louis Pasteur - Strasbourg I, 2004. http://tel.archives-ouvertes.fr/tel-00007730.
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La NCp7 est impliquée dans de nombreuses étapes du cycle viral notamment la rétrotranscription. Ceci en fait une cible potentielle pour un traitement anti-HIV. Par son activité chaperonne, elle permet de stimuler le premier saut de brin. Ce dernier consiste en la déstabilisation et l'hybridation des séquences TAR et cTAR du génome viral. C'est à l'aide de séquences cTAR marquées à leurs extrémités 3' et 5' par des chromophores et différentes techniques de spectroscopie de fluorescence et d'absorption que nous avons pu mettre en évidence l'importance des structures primaire et secondaire de la NCp7 et de cTAR dans le premier saut de brin. L'activité déstabilisatrice est fortement dépendante des bulges et de la boucle interne de cTAR. D'autre part, cette activité dépend également de la présence du Trp37 ainsi que de la présence des deux doigts de zinc de la NCp7 dans leur conformation native. Ensuite, nous avons pu mettre en évidence que la NCp7 favorisait la formation de l'homodimère de mutants de la partie haute de cTAR par formation d'un complexe boucle-boucle. Finalement, nous avons étudié une nouvelle sonde fluorescente analogue à l'adénine (la 8-vinyl-déoxyadénosine) qui est une solution alternative à la 2-aminopurine.
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Chang, Lieh-Jeng. "Neutron diffraction studies of the magnetic structures of R-Ni-B-C compounds". Thesis, University of Warwick, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245934.
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Yoshioka, Satoru. "Structures and phase relations of ZnO-R2O3 (R=Al, Ga, In) pseudobinary systems". 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136187.
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Mehrzad, Khosrow. "Torsional behaviour of framed-tube structures". Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61920.
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Cruvellier, Mark R. (Mark Richard). "Planar modelling for tall building structures". Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74627.
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In this thesis, methods are developed for representing in planar computer models the full behaviour of complex three dimensional tall building structural systems. Simple models capable of duplicating the simultaneous bending and torsional response to loading of progressively more complex systems are described and justified. In contrast with previously existing planar techniques, a geometrical approach is used here throughout so that no pre- or post-analysis transformations of structural properties or of analysis results are required. The development culminates in a planar model for the static and dynamic analysis of asymmetrical structures composed of intersecting structural bents whose properties and configurations may vary throughout the height.
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Pan, Jin 1959. "Characteristics of selenium schottky diode structures". Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61722.
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Yoon, Young-Soo. "Translational-torsional coupling in asymmetric structures". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39378.
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An approximate method for predicting the degree of translational-torsional coupling of mixed-bent type multi-storey building structures subject to dynamic loading is presented. The method uses the parametric approach and is based on the generalized representation of asymmetric wall-frame structures by shear-flexure, torsion-warping cantilevers. It is applicable to structures consisting of any combinations of walls and frames that are uniform with height.Simple methods for predicting the uncoupled translational-torsional period ratio and the equivalent eccentricity, which require a knowledge of only the preliminary design information, are developed. The actual coupled period ratio can then be estimated in terms of these two quantities. The concepts of shear centres and centres of resistance of mixed-bent type multi-storey building structures are clarified, and the significance of the uncoupled and coupled period ratios in the assessment of the coupling effect is discussed. The derivation of the method and comparisons of results with those obtained by 3-D finite element dynamic analyses of discrete member models, are given. Numerical examples are worked to illustrate the application of the method.
The applicability of the method to non-uniform wall-frame structures having changes in the stiffness through the height is demonstrated; a non-uniform distribution of mass over the floor is also taken into account.
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Wang, Enhao. "Vortex-induced vibration of cylindrical structures". Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28871.
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Vortex-induced vibration (VIV) of cylindrical structures is a classical topic within fluid-structure interaction (FSI). In offshore engineering, it often causes the fatigue of slender structures, such as risers, mooring lines and pipelines. Detailed understanding of this FSI phenomenon and an efficient prediction of such self-excited and self-sustained oscillations are required for the reliable estimation of the fatigue damage and the development of VIV suppression techniques. Over the past few decades, VIV has been extensively studied and the majority of the existing publications in the literature are experiments or semi-empirical modelling. In contrast, FSI simulations by combining high-fidelity computational fluid dynamics (CFD) and computational structural dynamics (CSD) solvers have received less attention. The main objective of this thesis is to investigate VIV of elastically mounted rigid cylinders and flexible cylinders using fully three-dimensional (3D) FSI simulations. Apart from important VIV aspects, such as response amplitude, response frequency and fatigue damage etc., the present research is also focussed on the aspects which have not been fully addressed by previous studies such as correlation lengths and time-dependent 3D flow structures. Two-degree-of-freedom (2DOF) VIV of an elastically mounted circular cylinder with varying in-line (IL) to cross-flow (CF) natural frequency ratios (f* = fnx/fny) is first studied using a 3D CFD approach. Numerical simulation is carried out for a constant mass ratio m* = 2 at a fixed Reynolds number Re = 500. The reduced velocity Vr ranges from 2 to 12. Three natural frequency ratios are considered, i.e., f* = 1, 1.5 and 2. The structural damping is set to zero to maximise the response of the cylinder. The main objective of the first study is to investigate the effect of f* on the 2DOF VIV responses and the 3D characteristics of the flow. It is discovered that there is a significant increase in the vibration amplitude and the peak amplitude shifts to a higher reduced velocity when f* increases from 1 to 2. A single-peak cross-flow response is observed for the identical in-line and cross-flow mass ratios when f* = 2. Dual resonance is found to exist over the range of f* studied. The preferable trajectories of the cylinder in the lock-in range are counterclockwise figure-eight orbits, whereas clockwise orbits primarily occur in the initial branch. The number of clockwise orbits decreases as f* increases from 1 to 2. Oblique figure-eight trajectories appear at Vr = 6, 7 and 8 when f* = 1. The third harmonic component which is observed in the lift fluctuation increases with f*. The correlation decreases in the lock-in range and reaches its minimum value around the transition region between the lock-in and post-lock-in ranges. Three vortex shedding modes (2S, P + S and 2P) appear in the present simulation. A dominant P + S mode is associated with the oblique figure-eight trajectories. Variation of vortex shedding flows along the cylinder is observed leading to the poor correlation of the sectional lift forces. Then, a numerical investigation of VIV of a vertical riser subject to uniform and linearly sheared currents is presented. The model vertical riser tested at the MARINTEK by ExxonMobil is considered. The predicted numerical results are in good agreement with the experimental data. It is found that the dominant mode numbers, the maximum root mean square amplitudes, the dominant frequencies and the fatigue damage indices increase with the flow velocity. Dual resonance is found to occur at most of the locations along the riser. At some locations along the riser, a third harmonic frequency component is observed in the CF response and a frequency component at the CF response frequency is found in the IL response apart from the frequency component at twice the CF response frequency. The majority of the vortex shedding shows a clear 2S pattern, whereas a 2P mode is observed near the position where the maximum vibration amplitude appears. The higher IL fatigue damage in the second study emphasises the importance of the IL fatigue damage analysis especially in the design of low flow velocity or low mode number applications. The third study is on VIV of two tandem flexible cylinders at different spacing ratios (Sx/D) at a fixed Reynolds number Re = 500 using a two-way FSI method. The main objective is to investigate the effect of spacing on the hydrodynamic interactions and the VIV responses of these cylinders. It is found that the responses of the two tandem flexible cylinders are similar to the classical VIV responses when Sx/D is small. Once Sx/D is large enough for the vortices to be completely detached from the upstream cylinder, the response of the upstream cylinder is similar to the typical VIV response whereas the downstream cylinder undergoes wake-induced vibration (WIV). The characteristics of the response of the downstream cylinder in the present study are similar to those of the first two response regimes. The third response regime is not observed for the flexible downstream cylinder with both ends fixed. The two changes in the phase relation between the cross-flow displacements of the two tandem flexible cylinders are discovered to be linked with the initial-upper branch transition and the upper-lower branch transition, respectively. The correlation lengths of the two tandem flexible cylinders decrease significantly in the transition range between the upper and lower branches. Three vortex shedding modes (2S, P + S and 2P) have been identified in the present study. It is found that the upper-branch 2P mode is associated with large-amplitude vibration of the upstream cylinder and the P + S mode is related to large-amplitude vibration of the downstream cylinder for Sx/D = 3.5 and 5. On the other hand, the lower-branch 2P mode leads to small-amplitude vibration of the downstream cylinder in the post-lock-in range at Sx/D = 2.5. The relative phase shifts of the sectional lift coefficients on different spanwise cross sections can be attributed to the variation of the vortex shedding flow along the flexible cylinders and these phase shifts result in poor phasing between the forces and the displacements which is related to the decrease of the correlation lengths.
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Norelius, Jenny, i Antonello Tacchi. "Evaluating data structures for range queries in brain simulations". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-229767.
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Our brain and nervous system is a vital organ to us, since it is from there our thoughts, personalities, and other mental capacities originate. Within this field of neuroscience a common method of study is to build and run large scale brain simulations where up to hundred thousand neurons are used to produce a model of a brain in three dimensional space. To find all neurites within a specific area is to perform a range query. A vast number of range queries are required when running brain simulations which makes it important that the data structure used to store the simulated neurons is efficient. This study evaluate three common data structures, also called spatial index; the R-tree, Quadtree and R*-tree (Rstar-tree). We test their performance for range queries with regards to execution time, incurred reads, build time, size of data and density of data. The data used is models of a typical neuron so that the characteristics of the data set is preserved. The results show that the R*-tree outperforms the other indices by being significantly more efficient compared to the others, with the R-tree having slightly worse performance than the Quadtree. The time it takes to build the index is to be almost identical for all implementations.Vår hjärna och nervsystem är ett grundläggande organ för oss. Det är där ifrån våra tankar, personligheter och mentala kapaciteter kommer ifrån. Inom neurovetenskap är en vanlig forskningsmetod att köra storskaliga hjärnsimuleringar där hundratusentals neuroner används för att skapa en modell av hjärnan i 3D. För att hitta alla neuroner inom en viss area används en så kallad intervallfråga. En stor mängd intervallfrågor behövs för hjärnsimuleringar vilket gör det viktigt att datastrukturerna som används för detta är kostnadseffektiva. Denna studie har som mål att jämföra tre stycken vanliga datastrukturer som används för intervallfrågor. Dessa är R-tree, Quadtree och R*-tree. Deras prestanda testas för exekveringstid, antal läsningar, konstruktionstid, samt storlek och densitet på neuroner. För att skapa hjärnsimuleringen används en typisk neuron som standard sådant att dess karakteristiska egenskaper bevaras. Resultaten från studien visar att R*-tree hade den tydligt bästa prestandan för de givna kriterierna, och att Quadtree har en något bättre prestanda än R-tree. Tiden det tar att mata in neuronerna i datastrukturerna är i stort sett densamma.
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Nollet, Marie-José. "Behaviour of wall-frame structures : a study of the interactive behaviour of continuous and discontinuous wall-frame structures". Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74683.
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The horizontal interaction between the walls and frames in wall-frame structures is investigated to determine its role in stiffening the structure against lateral, wind or earthquake loading. Discontinuous wall-frame structures are studied to assess the effects of the discontinuities on the horizontal interaction, and on the structures' lateral stiffness. The discontinuities include stepped walls or frames, curtailed walls, and different configurations of stiffened-storey frames.In each case, a continuum solution is developed and used to describe the behaviour of the structure, and to evaluate the effects of the discontinuities. Corresponding discrete finite elements analyses are also performed to verify the accuracy of the algebraic solutions and to determine the nature and magnitude of the resulting effects.
For stepped and curtailed wall-frame structures, it is found that the walls can be reduced or curtailed without modifying significantly the overall horizontal interaction and lateral stiffness. It is found that for stiffened-storey frame structures, the horizontal interaction and lateral stiffness are significantly increased. This constitutes an entirely new type of high-rise wall-frame structure of greater efficiency.
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Martinez, André. "Étude microlocale de problèmes semi-classiques : structures de contact dans R³ d'après D. Bennequin". Paris 11, 1988. http://www.theses.fr/1988PA11A001.
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Cette thèse concerne l’étude de l’opérateur de Schrödinger P=h² Δ+V dans la limite semi-classique h →0. On s’intéresse, dans la première partie, à l’effet tunnel créé entre deux puits de potentiel, dégénérés ou non, ainsi qu’à l’approximation de Born-Oppenheimer. La seconde partie est relative au spectre continu de P, et notamment aux effets liés à la présence de résonnancesThis thesis is concerned with the study of the Schrödinger operator P=h² Δ+V in the semi-classical limit with h →0. In the first part we are interested in the tunnel effect created by two potential wells, degenerated or not, and also in the Born-Oppenheimer approximation. The second part is about the continuous spectrum of P , and more precisely the effects which are related to the presence of resonances
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D'Argenzio, Domenic. "Inspection and repair of underwater concrete structures". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69790.
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The service life of any concrete marine structure is influenced by the physical condition of both the above water and below water portions of structure. This requires implementing an adequate inspection, maintenance, and repair program for the entire structure. To develop an effective maintenance and repair program for the submerged portion of the structure, the causes and extent of concrete distress or deterioration must be clearly understood. This requires a selective underwater condition survey, using a range of in-situ and laboratory testing and inspection techniques, to obtain the necessary information to assess the condition of the submerged portion of the structure. The cause and extent of deterioration, site logistics, and the clients needs will dictate the methods of inspection and repair. Recent developments in concrete admixtures has made it possible to place higher quality concrete suitable for underwater repairs. This thesis provides a summary of the most common forms of concrete distress found in a marine environment, along with a state-of-the-art review of existing and recently developed underwater inspection and repair techniques.In addition, four case studies are presented to illustrate the application of the above knowledge. The first case study describes the special aspects of underwater repairs to a concrete storm surge barrier damaged during construction. The second case study summarizes the procedures used for repairing a cracked concrete gravity dam by polyurethane resin injection methods. The third case study presents the various procedures used for repairing concrete railway bridge piers in a marine environment which were damaged by severe alkali-aggregate reaction. The final case study describes underwater repair procedures and concrete investigation techniques used in repairing the piers of a highway bridge.
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Sinn, Peter M. K. (Peter Man Kin). "A performance comparison of switched-current structures". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26418.
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In 1989 a new analog IC sampled-data circuit technique was proposed called the Switched-Current (SI) technique. Unlike other IC circuit techniques, the SI technique can realize analog functions using only MOS transistors without the need of any resistor, capacitor or other linear component. This is beneficial to the IC community at large, as mixed-signal IC's can now be realized using a standard digital CMOS process. SI circuits are classified into two groups: first or second-generation, duly named to correspond to the time of their introduction. On account of circuits that have been proposed over the past five years, this thesis will attempt to determine which circuits are better and what design strategy IC designers should follow when working with SI circuits.Specifically, this thesis will investigate the linear and non-linear behaviors of the various SI circuits using a relatively new frequency-domain analysis technique.
Finally, to verify the simulation results, two second-order SI filters were designed, laid-out and fabricated using first and second-generation cells in a 1.2 $ mu$m CMOS process. (Abstract shortened by UMI.)
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Nicholson, Karen. "Des structures mytho-initiatiques chez Michel Tournier". Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69654.
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According to the structuralist Claude Levi-Strauss, all myth has but one same structure. The purpose of this study is to expose the mythico-initiatory edifice that informs Vendredi ou les limbes du Pacifique, Le Roi des Aulnes, as well as Les Meteores, Michel Tournier's "trilogy".To write, according to Tournier, cannot be a matter of literary creation, but simply of literary renewal. Vendredi ou les limbes du Pacifique, Le Roi des Aulnes and Les Meteores represent literary reflections on the primordial importance of Myth, for the Artist and above all, for Man; it is this mythic dimension that makes Tournier's entire oeuvre an "autobiography", or rather an autohagiography, according to Tournier's neologism. The three protagonists, Robinson, Tiffauges and Paul Surin, literary avatars of Tournier as Author, embark on a Quest for this lost mythic Unity; we will see that the voyage each makes is but one and the same, an allegorical odyssey toward the light$ ...$ of the City of the Sun.
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Maciejko, Joseph. "Time-dependent quantum transport in mesoscopic structures". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99346.
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In this thesis, we present a theory to calculate the time-dependent current flowing through an arbitrary noninteracting nanoscale phase-coherent device connected to arbitrary noninteracting external leads, in response to sharp step- and square-shaped voltage pulses. Our analysis is based on the Keldysh nonequilibrium Green's functions formalism, and provides an exact analytical solution to the transport equations in the far from equilibrium, nonlinear response regime. The essential feature of our solution is that it does not rely on the commonly used wideband approximation where the coupling between device scattering region and leads is taken to be independent of energy, and as such provides a way to perform transient transport calculations from first principles on realistic systems, taking into account the detailed electronic structure of the device scattering region and the leads. As an illustration of the general theory, we perform a toy model calculation for a quantum dot with Lorentzian linewidth and show how interesting finite-bandwidth effects arise in the time-dependent current dynamics. Finally, we describe possible generalizations of our theory to the cases of superconducting leads (an example of broken symmetry) and one-dimensional leads in the Luttinger liquid regime (an example of an interacting system).
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Hanna, Elie M. "RNA secondary structures : generation and motif searching". Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=27332.
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The first part of this thesis discusses graph grammars as a tool to generate RNA secondary structures from sequences. Secondary structures are viewed as graphs of relations and an experimental eNCE graph grammar is hand-coded based on stereochemical constraints. Then, given a sequence, all secondary structures represented by graphs of relations that are parsed by the grammar are returned, with a free energy measure that indicates the structure's stability.The second part of this thesis discusses searching for motifs in RNA secondary structures. A script language is defined to encode secondary structures as graphs of relations. These graphs allow for rapid identification of all occurences of a given pattern, also encoded as a graph of relations. Then, analysing the results obtained by running the search engine on all known RNA secondary structures, motifs might be identified.
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Zhu, Yingchun 1968. "Optimizing parallel programs with dynamic data structures". Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36745.
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Distributed memory parallel architectures support a memory model where some memory accesses are local, and thus inexpensive, while other memory accesses are remote, and potentially quite expensive. In order to achieve efficiency on such architectures, we need to reduce remote accesses. This is particularly challenging for applications that use dynamic data structures.In this thesis, I present two compiler techniques to reduce the overhead of remote memory accesses for dynamic data structure based applications: locality techniques and communication optimizations. Locality techniques include a static locality analysis, which statically estimates when an indirect reference via a pointer can be safely assumed to be a local access, and dynamic locality checks, which consists of runtime tests to identify local accesses. Communication techniques include: (1) code movement to issue remote reads earlier and writes later; (2) code transformations to replace repeated/redundant remote accesses with one access; and (3) transformations to block or pipeline a group of remote requests together. Both locality and communication techniques have been implemented and incorporated into our EARTH-McCAT compiler framework, and a series of experiments have been conducted to evaluate these techniques. The experimental results show that we are able to achieve up to 26% performance improvement with each technique alone, and up to 29% performance improvement when both techniques are applied together.
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Khajooeizadeh, Arash. "Metal-insulator-semiconductor (MIS) slow-wave structures". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99773.
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Metal-insulator-semiconductors (MIS) are one of the most basic elements in the digital and microwave circuits. Theoretical and experimental investigation has shown that the dominant mode of propagation in MIS is not a quasi-TEM mode at all frequencies. It has been shown that an MIS transmission line is in fact a slow-wave structure in a certain frequency range. Slow-wave structures offer a large effective permittivity, therefore, can be employed to create large propagation delay and to reduce the guided wavelength. These characteristics can be utilized to design compact passive elements such as delay lines, phase shifters and filters. MIS structures can be easily fabricated using the current semiconductor technology. As well, they can be designed to operate in the slow-wave region for implementation of miniaturized passive components. In this thesis, first, an MIS interconnect is designed, fabricated and measured. Then, the transmission line characteristics are extracted from simulated and measured results. Subsequently, the MIS line parameters are used in designing a compact slow-wave meander line structure, which is compatible with silicon-based-packaging (SBP) solutions used in modern system-in-package/system-on-package (SIP/SOP) technologies.
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Toussaint, Richard. "Data structures and operations for geographical information". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23945.
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The topic of this thesis revolves around the organization of geographical information in permanent memory. Our premise is that a recognized and fully documented direct access storage technique called Multidimensional Paging or Multipaging would provide a well balanced storing structure for this category of data. Since multipaging uses a multidimensional perspective on the information to allocate it to pages in secondary storage then spatial data, which is fundamentally multidimensional by nature, would surely offer a suitable profile.First, we attempt to evaluate the efficiency of multipaging on static files and to suggest possible modifications to the standard algorithm to better serve spatial data.
Our solution to this problem consists in compressing the pages that overflow. Because geographical information is often a representation of occurences of Nature, we hypothesize that Fractal Geometry, which serves to formalize a mathematical description of such elements, could provide the theoretical background to derive an efficient fractal-based compression algorithm. An appreciable improvement is obtained by compressing the pages of the multipaged administrative regions data that exceed their capacity: $ alpha=0.7272$ and $ pi=1.0$.
The outcome of these experiments led us to elaborate a mixed system based on two relatively different approaches: multipaging and fractal-based data compression. The first part consisted in the implementation of the standard static multipaging algorithm using a relational database management system named Relix. The other approach was developed using the C programming language to accommodate some particularities of the multipaged spatial data. The preliminary results were encouraging and allowed us to establish the parameters for a more formal implementation. Also, it brought out the limits of the compression method in view of the intended usage of the data. (Abstract shortened by UMI.)
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Tavallaee, Amir Ali. "On the stopband characterization of periodic structures". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99542.
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Electromagnetic band-gap (EBG) structures, often termed frequency selective surfaces (FSSs) or photonic band-gap (PBG) materials, have found widespread applications as filters for microwaves and optical signals. Due to their frequency selective features and ease of implementation in printed circuit board (PCB) technology, EBG structures are utilized in power distribution networks (PDNs) to induce wide stopband and to provide global power/ground noise suppression. Attenuation characteristic of EBG structures within their forbidden frequency regions is examined in this thesis which ultimately provides the insertion loss obtained by inserting the EBG structure in the PDN. Bandgap characterization is efficiently achieved by applying the Bloch analysis to only one unit-cell of the EBG structure. For that purpose, two approaches have been investigated: the transmission-line (TL) technique and the finite element method (FEM). Printed-circuit EBG structures can be efficiently modeled by transmission-line circuits; thus TL techniques are widely used for their fast characterization. The developed TL model is exploited to investigate the power attenuation within the band-gap regions of PDNs containing EBG structures. A full-wave finite element code has been developed for accurate prediction of the stopband characteristics of periodic media. A number of simple periodic geometries are examined by the finite element code showing unique spectral properties of EBG structures, such as existence of evanescent and/or complex modes within their stopbands.
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Zane, Wallace W. (Wallace Wayne). "Surfers of southern California : structures of identity". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=22499.
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This thesis analyzes the structure of identity among surfers in Southern California, who constitute a subculture of American society. Surfer identity is shown to be derived from the act and the setting of surfing itself, from the individual's personal background and motivation for surfing, and from the social interaction among surfers on and off the water.Influences on the identity of surfers as a group include the surfers' own feeling of separateness from American society, surfer communication via the surf economy, the strong association of surfing with adolescence, and the portrayal of surfer symbols in the national media. The outward form of the "surf culture" changes in response to these influences, but the basic identity of surfers remains the same over time.
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Govind, Niranjan. "First principles calculations of atomic scale structures". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39910.
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Atomic scale structures are studied using first principles or ab initio simulations. We first review the formalism required for a typical calculation and then proceed to examine a few applications. All the simulations were performed using plane wave based pseudopotential methods and by a direct minimization of the Kohn-Sham total energy functional.Using this method, we have investigated the effect of impurity atoms like boron, sulphur and phosphorous on the adhesive properties of two aluminium minimum slabs. We found that both sulphur and phosphorous (both substitutional impurities) decreased the adhesive energy and the interfacial strength, while boron (an interstitial impurity) increased the interfacial strength marginally. It was also found that the impurities act as spacers and increase the interfacial spacing. This increase was found to increase with atomic size. These observations are consistent with experimental work.
We have also investigated the possibility of using orbital-free kinetic energy functionals in ab initio simulations. Various functionals, their limiting forms and response properties were studied. The results obtained using this method agree well with full Kohn-Sham calculations. This was demonstrated using a variety of systems (Si clusters, H$ vert$Si(100), c-Si). The excellent scaling properties of the method was illustrated with a simulation of the interactions between a tip and substrate (150 atoms). The normal forces experienced by the small cluster serving as the tip were used to map out the top surface of the substrate. An ad hoc scheme to incorporate pseudopotential non-locality into the orbital-free formalism was also proposed and tested.
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Bisaillon, Eric. "Distributed diffractive structures for micro-optical systems". Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103366.
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In modern communications systems, the components supporting wavelength division for increased density are rapidly becoming small compared with the wavelength of light being manipulated. As the size of these devices shrinks there comes a point when the features of interest become smaller than the wavelength and thereby the fundamental properties of light interaction with such structures change dramatically. In these structures and materials, resonances, effective properties, and band-gaps arise and offer designers a new realm of possibilities for the design of high quality factor resonators, filters and switches.The study of structures comprising two different scales compared with the wavelength of light promises interesting optical possibilities for future devices. In these structures a subwavelength size feature is used in conjunction with a super-wavelength size feature. This thesis will show how the resulting optical behavior for such structures arises from the combination of the sub- and super-wavelength diffractive effects.
Two application examples of these two-scale devices will be studied: the distributed echelle grating and the subwavelength based Fabry-Perot cavity. Both of these applications can be thought, of as distributed diffractive structures, a structure in which diffraction and subwavelength scale interference combine to produce high efficiency and versatile new devices.
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Puri, Manpreet Singh. "Design and analysis of inflatable space structures". Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28497.
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This thesis gives the conceptualization of inflation of inflatable membrane space structures. Although there has been little study using software simulation and the majority of documented research is based on theoretical numerical calculations. This research advanced the prior understanding of wrinkling within inflated membranes by using complex structures subjected to deformation loads. Within this thesis, a computational framework for the numerical analysis of the interaction between acting forces on the membrane and the membrane structure dynamics is presented. Moreover, in the case with thin membrane deformations, the synergy between the membrane wrinkling and structural forces has to be examined. This membrane structure-anatomical forces correlation results in a dynamic wrinkling problem, which can only be modelled easily and effectively by a simulation software that can integrate each assumption and attribute within the analysis. In the structural simulation within Abaqus FEA software, key consideration has to be given in modelling the geometric non-linearity behaviour of the membrane. By using the existing continuum expression for the virtual internal work in curvilinear coordinates. This is used to derive the modified fundamental formulation in which all subsequent analysis is established on and the initial equilibrium shape of the membrane. A critical feature of the new formulation is the prospect of adding pre-stressed forces to the membrane structure. The approach developed, established on an alteration of the material stiffness matrix to integrate the effects of wrinkling and deformation, can be utilized to calculate the behaviour of the membrane within a finite element simulation. In the wrinkling model, the state of the membrane element (taut, wrinkled or slack) is characterized by a mixed wrinkling criterion. Once it has been identified that the membrane element is wrinkled, an iterative scheme looks for the wrinkled orientation angle and the precise stress distribution, including only uni-axial tension in the wrinkle direction, is then derived. The wrinkling model has been verified and validated by contrasting the simulated conclusions with documented results for the instance of a time-independent isotropic membrane subjected to shear and axial loading. Utilizing the time integration method, a time-dependant pseudo-elastic stiffness matrix was represented and therefore, rather than calculating the convolution integral all through the Abaqus simulation, then we can calculate the behaviour of a membrane structure by superposition of a series of step by step increments in basic finite element software. The theoretical computations from the Abaqus/Explicit analysis were compared with documented results for the shear and axial loading. The results agreed very well, assuming friction and any relativistic dynamic effects were excluded. The discrepancy between the shear loading solution is 7% while the discrepancy between the axial loading is only 5% between the Abaqus modeland the documented model. This discrepancy could be the resultant of the source of energy dissipation from the visco-elastic behaviour during the loading and unloading of forces. It can be stated that for the Kapton HN membrane, this result falls within acceptable range but to increase accuracy, the load and unloading will be carried out on a set steady amplitude to inhibit in shock effects within the model. A three-dimensional finite element model which integrates wrinkling and frictionless contact has been developed to simulate the adaptive smart cell and cylindrical membrane structure. The loading of both structures is given by a non-uniform differential inflation pressure with a continual gradient adjacent to height. The resultant solutions are computed using Abaqus/Explicit software, with an integrated user-defined material subroutine to account for elastic wrinkling deformation that administers a combined stress-strain criterion. Frictionless contact within the membrane structure is prescribed for both complex structures (Adaptive Smart Structures Model and Inflatable Beam Model) in order to prohibit the penetration of the membrane structure through itself. Both the complex inflatable membrane wrinkling models accomplish the purpose of exceptional subgrid scale performance in relation to accuracy, competency, computing hardware & software expense, complexity and the model convergence rate. The numerical algorithm is created in general context and is flexible for a large variety of material models. For a closed membrane structure, the skew symmetric constraint parameters vanish, while the existing symmetric domain variables mirror preservation of the system. This procedure does not demand the discretization of the fluid (gas) domain or the link between coupling of fluid (gas) and membrane. As a result of this basic fact, the computation is drastically simplified. The adaptive structures model introduces a novel approach in harnessing solar power for reuse on the ground as a stable source of power. The simulations were based on the space part of the stiff structure created of hexagonal membrane cells. Simulations are carried out in Abaqus Finite Element Analysis software for simplicity & a comparison for validation purposes is tested against an experimental inflatable cell within a vacuum chamber. It was showcased that the final configuration could be achieved regardless of the packaging shape of the inflatable cell array. The inflatable beam model is comprised of two sections, the bending & buckling of the inflated beam and the post-inflation of the bent and buckled beam. Abaqus software was used to simulate the inflatable beam during each configuration utilizing the integration of a modified VUMAT subroutine. A comparison is showcased representing the importance of the integration of the VUMAT subroutine within our Abaqus model.
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Zhang, Jiaying. "Reconfiguring smart structures using approximate heteroclinic connections". Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=29529.
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The term smart structures is commonly used to describe structures which have the ability to actively change their geometry or mechanical properties. Potential applications can be found in the aerospace, energy and marine sectors, e.g. use of MEMS-type devices which require frequent switching of compliant components and morphing of advanced aerofoils to generate additional lift. Traditional reconfigurable smart structures are designed with multi-stable characteristics. In particular, such structures can use stored strain energy to enable motion from one stable position to another stable position. However, the means of reconfiguring smart structures between stable con-figurations requires the input of, and then dissipation of energy to cross the potential barrier separating the stable configurations. Therefore, the accumulated work done for frequently actuated devices in reconfiguring between stable states can be significant. Considering reconfigurable smart structures for power and energy constrained applications, this thesis investigates a novel concept of reconfiguring smart structures between unstable states. The vision is to take advantage of modern dynamical system theory to develop entirely new devices that use the instability of mechanical systems to deliver energy-efficient shape-changing structures. This thesis indicates that theoretically in a simple model, transitioning between unstable states (so-called heteroclinic connections) can be more energy-efficient than traditional structures which transition between stable states and so need to cross a potential barrier. However, further experimental work will be required to verify this initial finding for real engineering systems. Clearly, energy is required to stabilize the unstable configurations, but if the energy required for active control of the instability is sufficiently small, or devices need to be frequently switched between different states, this concept is likely to be of benefit. The concept of using instability for reconfiguration is demonstrated first by controlling a mass-spring chain model through a simple cubic nonlinearity, which is sufficient to provide the required qualitative behaviour of the system. A sufficiently smooth set of functions is then used to generate a path to approximate the heteroclinic connection, which is then used as reference trajectory for reconfiguring between different unstable configurations. Moreover, the model is extended to a smart surface as a two-dimensional spring-mass array without dissipation. It is shown that the activere configuration scheme can be used to connect equal-energy unstable (but actively controlled) configurations for the purpose of energy-efficient morphing of the smart surface. However, in consideration of the difference between the cubic and real spring model, a spring-mass model with fully geometric non-linearity is also developed to verify the possibility of using heteroclinic connections to reconfigure future real smart structures. Furthermore, by considering a compliant mechanism, the concept of reconfiguration of a four-bar mechanism using heteroclinic connections is also investigated. Different models varying from fully rigid to purely elastic are employed to be controlled for reconfiguring between different unstable configurations. In addition, a continuous buckled beam model has been investigated with its characteristics based on the Euler-Bernoulli beam theory. An experimental beam was fabricated with shape memory alloy actuators for active control. Although the shape memory alloy was a slow response to time, it illustrates the possibility of reconfiguration of smart structures by using heteroclinic connections. In summary, this thesis demonstrates the potential of using heteroclinic connection to reconfigure smart structures with both numerical investigation and experimental validation. This entirely new approach to smart structures offers potentially significant benefits for power and energy constrained applications which require frequent reconfiguration.
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Sun, Xing. "Estimation of residual stresses in marine structures". Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18980.
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A finite element model that is capable of simulating the thermo-mechanical welding process was developed by using full thermal-elasto-plastic computational analysis and validated by comparison with experimental data. It shows that distortions predicted by the finite element model agree well with measured data from previous literature and that the numerically obtained residual stress distribution is compared and agreed by both ANSYS and VrWeld software. After that, a simple method for predicting butt-welding residual stresses based on force and moment equilibrium was derived in this section. The results calculated from this simple method were a good match with the FE results. Then the author performed detailed analysis for the distribution of transverse and longitudinal residual stresses of 2D butt welding process by using 3D elements, which illustrated how the butt-welding residual stresses were distributed and accumulated during the welding process and how the boundary conditions affect the final results. A detailed parametric study for butt welding residual stresses based on 2D butt-welding by using 3D element was demonstrated. The factors carried out in the parametric study involved cut-off temperature effect, welding power effect, welding velocity effect, plate length effect and plate width effect. Lastly, the author also presented a simulation and an optimization of welding sequences for residual stress and distortion of a typical, fatigue sensitive, ship's side shell connection detail under different welding sequences.
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Diyaroglu, Cagan. "Peridynamics and its applications in marine structures". Thesis, University of Strathclyde, 2016. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26573.
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Prediction of fracture and failure is a challenging research area. There are various methods available in the literature for this purpose including well-known finite element (FE) method. FE method is a powerful technique for deformation and stress analysis of structures. However, it has various disadvantageous in predicting failure due to its mathematical structure since it is based on classical continuum mechanics (CCM). CCM has governing equations in the form of partial differential equations. These equations are not valid if the displacement field is discontinuous as a result of crack occurance. In order to overcome this problem, a new continuum mechanics formulation was introduced and named as Peridynamics. Peridynamics uses integrals equations as opposed to partial differential equations of CCM. Moreover, it does not contain any spatial derivatives. Hence, its equations are always valid regardless of discontinuities. In this thesis, the applications of Peridynamics for marine structues are demonstrated. Particularly, the Peridynamic equations are rederived for simplified structures commonly used in marine structures including beams and plates. Furthermore, underwater shock response of marine composites is investigated. Finally, the peridynamic formulation for contact analysis which can be used for collision and grounding of ship structures is demonstrated. In order to reduce the computational time, several solution strategies are explained.
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Fortaleza, Eugênio. "Contrôle actif de structures offshores : positionnement et réduction des vibrations induites par vortex". Phd thesis, École Nationale Supérieure des Mines de Paris, 2009. http://pastel.archives-ouvertes.fr/pastel-00006011.
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L'exploration pétrolière en eaux profondes crée des nouveaux défis technologiques. Certains de ces problèmes sont liés à des très longues structures servant à relier la plate-forme à la tête de puits. L'augmentation de la profondeur implique des structures plus longues et, par conséquent, plus souple. Deux problèmes liés à ce type de structure sont étudiés dans ce rapport : le positionnement de la structure pour sa connexion à la tête de puits (opération de rentrée), et les vibrations induites par vortex. La première partie de ce rapport est consacrée au contrôle de l'opération de rentrée. Deux stratégies différentes de planification du mouvement sont proposées. La première est basée sur un modèle obtenu par approche modale. L'autre stratégie approxime le comportement de la structure par l'équation d'un câble de Bernoulli avec amortissement. Les solutions approximées de cette EDP sont directement utilisées dans la conception du contrôleur. Deux types de contrôle en boucle fermée sont proposées: un système de suivi de trajectoire en utilisant une fonction de Lyapunov, et un autre qui utilise l'inverse du système. La deuxième partie de ce rapport est consacrée à l'étude des vibrations induites par vortex (VIV) et à leur contrôle. Elle présente une première stratégie de contrôle afin de réduire les VIV. Cette stratégie est basée sur une analyse modale des équations du système. La loi de commande génère un déplacement en opposition de phase par rapport au VIV, l'atténuation résultant d'un effet d'antirésonance. Les résultats de simulation sont confirmés par des expériences réalisées sur une maquette en modèle réduit.
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Lisboa, Osni. "Two-mode optical fiber sensors for concrete structures". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37692.
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An optical fiber bending sensor and a quasi-distributed optical fiber sensor, where isolated sensing regions can be designed to sense strain, bending, etc., are developed as sensor candidates for smart civil engineering materials and structures. Both sensors use two-mode fibers. With the same two-mode fibers, acousto-optic frequency shifters are developed as the main components to accomplish these sensors. Elliptical-core two-mode fibers are chosen to improve the stability and sensitivity of the sensors. A perturbation theory approach is used to investigate the sensing mechanism of the bending sensor. A system to simultaneously measure all the sensing regions of the quasi-distributed sensor is also demonstrated.Because conventional polymer-based fiber coatings often do not adequately protect the fibers themselves nor the fiber sensors during their installations into the concrete or metallic structures, two different processing methods are introduced. They provide superior protection to the fibers and sensors for the installation. The first method is to coat the fiber with a thick metallic layer (aluminum or tin) using a continuous casting process. Coating thicknesses of 0.5 to 1.5 mm and length up to 3 m are presented. Using a birefrigent fiber coated with such a thick metallic layer, a sensor for dynamic load or pressure was also implemented. The second method uses the thermal spray technology for directly embedding optical fibers and sensors into or surface attaching them onto concrete and metallic plates.
Finally, a sol-gel based process is used for coating optical fibers with piezoelectric lead zirconate titanate films. Coating thicknesses up to 120 mum have been achieved. Piezoelectric-coated fibers can be used as in-line optical fiber signal processing components for various fiber sensors relevant for smart structure applications. As an example, an in-line fiber phase modulator is also developed. Theoretical analysis is carried out based on an axial-symmetrical multi-layer structure operated in a radially resonant configuration. The phase modulation induced by radial acoustic modes excited on optical fibers, with a coating thickness of 120 mum and length of 5.8 cm, ranges from 100 kHz to 25 MHz.
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Pinsonneault, Luc. "Data structures for a fragment based programming environment". Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63848.
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