A finite element model of a fracture test specimen is developed using the STAGS computer code (STructural Analysis of General Shells). The test specimen was an internally pressurized, aluminum cylindrical shell reinforced with two externally bonded aluminum tear straps around its circumference. The shell contained an initial, axial through-crack centered between the straps. The crack propagated slowly in the axial direction as the pressure increased above a certain value until a maximum pressure was attained, and then the crack propagated dynamically. The tear straps sufficiently toughened the shell such that the dynamic crack path bifurcated near the edges of the straps. The bifurcated crack branches ran circumferentially, parallel to the straps causing the shell wall to flap open. The STAGS analysis for the static equilibrium configurations of the fractured shell include geometric nonlinearity and elastic-plastic material behavior. The crack tip opening angle (CTOA) is used in the criterion for ductile crack growth, and the critical value of the CTOA is determined by correlating the STAGS predictions of the stable portion of the crack growth curve (internal pressure versus half crack length) to the test. With the employment of a new STAGS algorithm, the complete axial crack growth curve, including both the stable and unstable portions, through the tear strap is obtained. The complete axial crack growth curve indicates that crack growth through the strap is unlikely. STAGS models with long cracks which bifurcate at various half crack lengths are developed to assess the location of crack bifurcation. Three different stress based crack turning criteria are investigated from the axial crack growth results as a second method for assessing a location of bifurcation. The bifurcation analyses and stress based turning criteria corroborate the experimentally measured bifurcation point. A parametric study is then conducted to determine the influence of tear strap thickness and width on the location of crack bifurcation. / Master of Science

Circadian rhythms are the endogenous, roughly 24-hour rhythms that coordinate an organism's interaction with its cycling environment. The molecular mechanism underlying this physiological process is a cell-autonomous oscillator comprised of a complex regulatory network of interacting DNA, RNA and proteins that is surprisingly conserved across many different species. It is not a trivial task to understand how the positive and negative feedback loops interact to generate an oscillator capable of a) maintaining a 24-hour rhythm in constant conditions; b) entraining to external light and temperature signals; c) responding to pulses of light in a rather particular, predictable manner; and d) compensating itself so that the period is relatively constant over a large range of temperatures, even for mutations that affect the basal period of oscillation. Mathematical modeling is a useful tool for dealing with such complexity, because it gives us an object that can be quickly probed and tested in lieu of the experiment or actual biological system. If we do a good job designing the model, it will help us to understand the biology better by predicting the outcome of future experiments. The difficulty lies in properly designing a model, a task that is made even more difficult by an acute lack of quantitative data. Thankfully, our qualitative understanding of a particular phenomenon, i.e. the observed physiology of the cell, can often be directly related to certain mathematical structures. Bifurcation analysis gives us a glimpse of these structures, and we can use these glimpses to build our models with greater confidence. In this dissertation, I will discuss the particular problem of the circadian clock and describe a number of new methods and tools related to bifurcation analysis. These tools can effectively be applied during the modeling process to build detailed models of biological regulatory with greater ease. / Ph. D.

We investigate the relative equilibria of a gyrostat with a spring-mass-dashpot damper to gain new insights into the dynamics of spin-stabilized satellites. The equations of motion are developed using a Newton-Euler approach, resulting in equations in terms of system momenta and damper variables. Linear and nonlinear stability methods produce stability conditions for simple spins about the nominal principal axes. We use analytical and numerical methods to explore system equilibria, including the bifurcations that occur for varying system parameters for varying rotor momentum and damper parameters. The equations and bifurcations for zero rotor absolute angular momentum are identical to those for a rigid body with an identical damper. For the more general case of non-zero rotor momentum, the bifurcations are complex structures that are perturbations of the zero rotor momentum case. We examine the effects of spring stiffness, damper position, and inertia properties on the global equilibria. Stable equilibria exist for many different spin axes, including some that do not lie in the nominally principal planes. Some bifurcations identify regions where a jump phenomenon is possible. We use Liapunov-Schmidt reduction to determine an analytic relationship between parameters to determine if the jump phenomenon occurs. Bifurcations of the nominal gyrostat spin are characterized in parameter space using two-parameter continuation and the Liapunov-Schmidt reduction technique. We quantify the effects of rotor or damper alignment errors by adding small displacements to the alignment vectors, resulting in perturbations of the bifurcations for the standard model. We apply the global bifurcation results to several practical applications. We relate the general set of all possible equilibria to specific equilibria for dual-spin satellites with typical parameters. For systems with tuned dampers, where the natural frequency of the spring-mass-damper matches the gyrostat precession frequency, we show numerically and analytically that the existence of certain equilibria are related to the damper tuning condition. Finally, the global equilibria and bifurcations for varying rotor momentum provide a unique perspective on the dynamics of simple rotor spin-up maneuvers. / Ph. D.

Fertilized frog eggs (and cell-free extracts) undergo periodic oscillations in the activity of "M-phase promoting factor" (MPF), the crucial triggering enzyme for mitosis (nuclear division) and cell division. MPF activity is regulated by a complex network of biochemical reactions. Novak and Tyson, and their collaborators, have been studying the qualitative and quantitative properties of a large system of nonlinear ordinary differential equations that describe the molecular details of this system as currently known. Important clues to the behavior of the model are provided by bifurcation theory, especially characterization of the codimension-1 and -2 bifurcation sets of the differential equations. To illustrate this method, I have been studying a system of 9 ordinary differential equations that describe the frog egg cell cycle with some fidelity. I will describe the bifurcation diagram of this system in a parameter space spanned by the rate constants for cyclin synthesis and cycling degradation. My results suggest either that the cell cycle control system should show dynamical behavior considerably more complex than the limit cycles and steady states reported so far, or that the biochemical rate constants of the system are constrained to avoid regions of parameter space where complex bifurcation points unfold. / Ph. D.

Dans cette thèse, nous étudions un système à temps discret de dimension N, dont les paramètres varient périodiquement. Le système de dimension N est construit à partir de n sous-systèmes de dimension un couplés symétriquement. Dans un premier temps, nous donnons les propriétés générales du système de dimension N. Dans un second temps, nous étudions le cas particulier où le sous-système de dimension un est défini à l’aide d’une transformation logistique. Nous nous intéressons plus particulièrement à la structure des bifurcations lorsque N=1 ou 2. Des zones échangeurs centrées sur des points cuspidaux sont obtenues dans le cas de courbes de bifurcation de type fold (noeud-col).Ensuite, nous nous intéressons au comportement de circuits de type Chua couplés lorsqu’un paramètre varie lui aussi périodiquement, la période étant celle d’une des variables d’état interne au système. A partir de l’étude des bifurcations du système, la non existence de cycles d’ordre impair et la coexistence de plusieurs attracteurs est mise en évidence. D’autre part, on peut mettre en évidence la coexistence de différents attracteurs pour lesquels les états de synchronisation sont distincts. Le cas continu est comparé avec le cas discret. Des phénomènes tout à fait similaires sont obtenus. Il est important de noter que l’étude d’un système à temps discret est plus facile et plus rapide que celle d’un système à temps continu. L’étude du premier système permet donc d’avoir des informations sur ce qui peut se produire dans le cas continu. Pour terminer, nous analysons le comportement d’un autre système couplé à temps continu, basé lui aussi sur le circuit de Chua, mais pour lequel la commutation qui contrôle la variation du paramètre s’effectue différemment du premier système. Ce type de commutation génère une augmentation du nombre d’attracteurs / In this thesis, we propose a N-dimensional coupled discrete-time system whose parameters are forced into periodic varying, the N-dimensional system being constructed of n same one-dimensional subsystems with mutually influencing coupling and also coupled continuous-time system including periodically parameter varying which correspond to the periodic varying in the discrete-time system.Firstly, we introduce the N-dimensional coupled parametrically forced discrete-time system and its general properties. Then, when logistic maps is used as the one-dimensional subsystem constructing the system, bifurcations in the one or two-dimensional parametrically forced logistic map are investigated. Crossroad area centered at fold cusp points regarding several order cycles are confirmed.Next, we investigated behaviors of the coupled Chua's circuit whose parameter is forced into periodic varying associated with the period of an internal state value. From the investigation of bifurcations in the system, non-existence of odd order cycles and coexistence of different attractors are observed. From the investigation of synchronizations coexisting of many attractors whose synchronizations states are different are observed. Observed phenomena in the system is compared with the parametrically forced discrete-time system. Similar phenomena are confirmed between the parametrically forced discrete-time system and the parametrically forced Chua's circuit. It is worth noting that this facilitates to analyze parametrically forced continuous-time systems, because to analyze discrete-time systems is easier than continuous-time systems. Finally, we investigated behaviors of another coupled continuous-time system in which Chua's circuit is used, while, the motion of the switch controlling the parametric varying is different from the above system. Coexisting of many attractors whose synchronizations states are different are observed. Comparing with theabove system, the number of coexisting stable state is increased by the effect of the different switching motion

O objetivo desta tese é estudar a dinâmica de mesoescala do sistema de correntes de contorno oeste ao largo da costa leste brasileira entre 10o -20o S. Esta é a área em que a Corrente Sul Equatorial (CSE) se bifurca, no escopo da circulação de larga escala forcada pelo vento associado ao giro subtropical do Atlântico Sul. Este sistema de bifurcação, somado à circulacao equatorial, tem uma estrutura tri-dimensional complexa que implica na formação de diversas correntes de contorno oeste (CCOs) que fluem ao largo da costa brasileira. Este sistema de CCOs tem sido reconhecido na literatura como de extrema importância nos últimos anos, por estar embebido nos padrões de larga escala da Célula de Revolvimento Meridional no Atlântico Sul. Transportes de calor e volume entre hemisférios em diferentes profundidades são parcialmente controlados pela média de longo termo da atividade de mesoescala na região supracitada, seja esta gerada localmente ou forçada remotamente. Esta tese objetiva estudar a dinâmica do oceano superior nesta região em dois capítulos independentes. Cada um destes capítulos são auto-suficientes em seu conteúdo, descrevendo suas hipóteses, metodologia, resultados, discussões e implicações. O conteúdo de cada um destes capítulos é sumarizado nos parágrafos seguintes. A Corrente do Brasil (CB) se origina com a chegada e bifurcação da CSE em superfície, entre 10-20o . A CB é uma CCO centrada em superfície e transporta águas quentes e salinas em direção ao pólo sul. Estudos climatológicos prévios descrevem a bifurcação da CSE como um fenômeno estratificado vertical e horizontalmente, e que o ramo sul da CSE dá origem a CB - uma corrente de contorno oeste fraca e rasa. A origem da CB é atualmente um dos aspectos menos explorados da circulação regional e sua atividade de mesoescala na parte oeste do giro subtropical do Atlântico Sul. O Capítulo 1 deste trabalho objetiva preencher esta lacuna de conhecimento descritivo na porção entre 10o-20o S ao largo da costa brasileira. A análise de três cruzeiros quase-sinóticos recentes em conjunto com padrões inferidos por altimetria e modelos de circulação global, confronta a descrição da CB como uma corrente de contorno oeste contínua. De acordo com nossas análises, o sinal da bifurcação da CSE próximo à costa não é claro, e os campos de velocidade são dominados por estruturas vorticais de mesoescala. Anticiclones recorrentes que aparentam estar associados ao meandramento da CB, nos conduzem a estabelecer um cenário de escoamento fortemente influenciado pela topografia e possivelmente instável. Diante desde cenário, sugerimos que a CB se caracteriza por um escoamento dominado por vórtices ao norte do paralelo de 20o S. O Capítulo 2 parte do pressuposto enunciado no Capítulo 1 e objetiva estudar os papéis do cisalhamento vertical e da topografia na formação dos vórtices observados na região de origem da CB. Apresentamos simulações numéricas de estudo de processo que mostram que as principais feições realísticas de mesoescala nas imediações da origem da CB podem ser reproduzidas com sucesso a partir da interação dinâmica entre versões parametrizadas do escoamento médio de dois jatos de contorno oeste e fluindo em sentido oposto (CB e Sub-corrente Norte do Brasil - SNB) e a topografia local, sem influência de dinâmica remota ou forçantes atmosféricas. Três extensos anticiclones reportados no Capítulo 1 são reproduzidos e apresentam um comportamento estacionário durante um ano de simulação. Dois experimentos de sensitividade adicionais são conduzidos. Quando a SNB é suprimida do contexto físico, a interação entre CB e topografia não é suficiente para reproduzir tais feições anticiclônicas, e em geral, o padrão obtido exibe pouca semelhança aos dados observacionais. Quando uma topografia idealizada, livre de bancos e montes submarinos é adotada, a interação CB-SNB é também insuficiente para produzir as estruturas realísticas de mesoescala. Nossa análise sugere que vórtices anticlônicos de borda de promontório ocorrem nos níveis verticais da SNB (cerca de 400 m) e que estes estão forçando o aparecimento de anticiclones em superfície (CB) cerca de 10 dias depois. Esta tese tem estrutura baseada em dois artigos científicos pré-existentes, ambos de autoria do presente aluno, com co-autoria de seu orientador, co-orientador e colegas. O Capítulo 1 destina-se aos resultados de um artigo publicado no periódico científico denominado Geophysical Research Letters [Soutelino et al., 2011] e o Capítulo 2 refere-se a um artigo atualmente submetido ao periódico científico denominado Continental Shelf Research [Soutelino et al., subm]. O conteúdo de ambos os capítulos estão expandidos em relação as versões originais para permitir maior nível de detalhamento das diversas partes que compõem o trabalho. Mais detalhes relativos às técnicas metodologicas são apresentados, bem como um maior numero de gráficos, buscando maximizar a clareza do documento. O Capítulo 3 compila e sumariza os resultados oriundos de ambos os artigos científicos, e consequentemente desta tese, finalizando com sugestões para trabalhos futuros. / This dissertation addresses the mesoscale dynamics of the western boundary current system off Brazilian coast easternmost portion (10o -20o S). This is the area where the South Equatorial Current (SEC) of the Atlantic Ocean bifurcates, in the scope of the large scale wind driven subtropical gyre. This bifurcation, summed to the Equatorial circulation, has a complex tri-dimensional structure that leads to the formation of several different western boundary currents (WBCs) flowing in different directions and in different depths off the entire Brazilian coast. This system have been recognized to have major scientific importance in the last few years, because it is embedded in the South Atlantic Meridional Overturning Circulation (SAMOC) large scale pathways. Inter-hemisphere volume and heat net transports in different depths are partly controlled by the time-averaged effect of mesoscale features occurring in the region cited above, being these generated locally or remotely. This dissertation intends to address the upper ocean regional dynamics of this area in two self-contained chapters. Each of these chapters can stand alone, independently describing the problem, the methods, the results, and their implications. The contents of each chapter are summarized in the next paragraphs. The Brazil Current (BC) originates with the arrival and bifurcation of the southernmost branch of the South Equatorial Current (sSEC) at the surface between 10-20o. The BC is a surface-cored feature and it transports warm and salty waters poleward. Previous climatological studies showed a stratified sSEC bifurcation and that the resulting southern branch formed a shallow BC - a weak western boundary current. The site of origin of the BC is currently one of the less explored aspects of regional circulation and mesoscale activity in the South Atlantic Subtropical gyre westernmost portion. Chapter 1 of this work aims to fill this gap in the 10o -20o S zone off the Brazilian coast. The analysis of three recent synoptic surveys and global model outputs challenge the description of a continuous BC. According to our analysis, The sSEC bifurcation signal near the continental margin is unclear, and the velocity fields are dominated by mesoscale eddies. Recurrent anticyclones that seem to be related to the meandering BC leads us to construct a picture of a flow strongly influenced by topography and probably very unstable. Given this new emerging scenario, we hypothesize that the Brazil Current is eddy-dominated to the north of 20o S. Chapter 2 of this dissertation assumes the hypothesis formulated in Chapter 1 to be true, and studies the roles of vertical shear and topography on the eddy formation near the site of origin of the BC. We present numerical simulations that show that the main realistic mesoscale features in the eddy-rich vicinities of the BC site of origin can be successfully modeled through the dynamical interaction between parameterized versions of two opposing mean western boundary currents (BC and North Brazil Undercurrent - NBUC) and local topography, with no influence of remote dynamics or atmospheric forcing. Three large BC-related anticyclones described in Chapter 1 are reproduced and present a steady behavior during one year run. Two additional sensitivity experiments are performed. When NBUC is removed from the physical context, BC interaction with topography is not sufficient to generate such eddies, and the overall pattern shows considerably less resemblance with real data. When an idealized flat-bottom and no-banks topography is considered, BC-NBUC interaction is also not capable of developing realistic mesoscale structures. Our analyses suggest that leeward anticyclonic eddy generation mechanism is occurring at NBUC vertical levels (around 400 m) at the lee of bathymetric promontories and that this is driving the appearance of these eddies in the surface levels (BC domain) with a 10 days time lag. This dissertation structure is based on two existing scientific papers, both having the current PhD candidate as the first author, and co-authorship of his advisor, co-advisor and colleagues. Chapter 1 refers to the results of an article published at the Geophysical Research Letters scientific journal [Soutelino et al., 2011] and the Chapter 2 refers to an article currently submitted to Continental Shelf Research [Soutelino et al., subm]. The contents of both Chapter 1 and Chapter 2 are expanded in respect to the publication versions. More details regarding the applied methods and additional graphics and computations are shown. Finally, Chapter 3 ends the dissertation with final remarks.

O objetivo desta tese é estudar a dinâmica de mesoescala do sistema de correntes de contorno oeste ao largo da costa leste brasileira entre 10o -20o S. Esta é a área em que a Corrente Sul Equatorial (CSE) se bifurca, no escopo da circulação de larga escala forcada pelo vento associado ao giro subtropical do Atlântico Sul. Este sistema de bifurcação, somado à circulacao equatorial, tem uma estrutura tri-dimensional complexa que implica na formação de diversas correntes de contorno oeste (CCOs) que fluem ao largo da costa brasileira. Este sistema de CCOs tem sido reconhecido na literatura como de extrema importância nos últimos anos, por estar embebido nos padrões de larga escala da Célula de Revolvimento Meridional no Atlântico Sul. Transportes de calor e volume entre hemisférios em diferentes profundidades são parcialmente controlados pela média de longo termo da atividade de mesoescala na região supracitada, seja esta gerada localmente ou forçada remotamente. Esta tese objetiva estudar a dinâmica do oceano superior nesta região em dois capítulos independentes. Cada um destes capítulos são auto-suficientes em seu conteúdo, descrevendo suas hipóteses, metodologia, resultados, discussões e implicações. O conteúdo de cada um destes capítulos é sumarizado nos parágrafos seguintes. A Corrente do Brasil (CB) se origina com a chegada e bifurcação da CSE em superfície, entre 10-20o . A CB é uma CCO centrada em superfície e transporta águas quentes e salinas em direção ao pólo sul. Estudos climatológicos prévios descrevem a bifurcação da CSE como um fenômeno estratificado vertical e horizontalmente, e que o ramo sul da CSE dá origem a CB - uma corrente de contorno oeste fraca e rasa. A origem da CB é atualmente um dos aspectos menos explorados da circulação regional e sua atividade de mesoescala na parte oeste do giro subtropical do Atlântico Sul. O Capítulo 1 deste trabalho objetiva preencher esta lacuna de conhecimento descritivo na porção entre 10o-20o S ao largo da costa brasileira. A análise de três cruzeiros quase-sinóticos recentes em conjunto com padrões inferidos por altimetria e modelos de circulação global, confronta a descrição da CB como uma corrente de contorno oeste contínua. De acordo com nossas análises, o sinal da bifurcação da CSE próximo à costa não é claro, e os campos de velocidade são dominados por estruturas vorticais de mesoescala. Anticiclones recorrentes que aparentam estar associados ao meandramento da CB, nos conduzem a estabelecer um cenário de escoamento fortemente influenciado pela topografia e possivelmente instável. Diante desde cenário, sugerimos que a CB se caracteriza por um escoamento dominado por vórtices ao norte do paralelo de 20o S. O Capítulo 2 parte do pressuposto enunciado no Capítulo 1 e objetiva estudar os papéis do cisalhamento vertical e da topografia na formação dos vórtices observados na região de origem da CB. Apresentamos simulações numéricas de estudo de processo que mostram que as principais feições realísticas de mesoescala nas imediações da origem da CB podem ser reproduzidas com sucesso a partir da interação dinâmica entre versões parametrizadas do escoamento médio de dois jatos de contorno oeste e fluindo em sentido oposto (CB e Sub-corrente Norte do Brasil - SNB) e a topografia local, sem influência de dinâmica remota ou forçantes atmosféricas. Três extensos anticiclones reportados no Capítulo 1 são reproduzidos e apresentam um comportamento estacionário durante um ano de simulação. Dois experimentos de sensitividade adicionais são conduzidos. Quando a SNB é suprimida do contexto físico, a interação entre CB e topografia não é suficiente para reproduzir tais feições anticiclônicas, e em geral, o padrão obtido exibe pouca semelhança aos dados observacionais. Quando uma topografia idealizada, livre de bancos e montes submarinos é adotada, a interação CB-SNB é também insuficiente para produzir as estruturas realísticas de mesoescala. Nossa análise sugere que vórtices anticlônicos de borda de promontório ocorrem nos níveis verticais da SNB (cerca de 400 m) e que estes estão forçando o aparecimento de anticiclones em superfície (CB) cerca de 10 dias depois. Esta tese tem estrutura baseada em dois artigos científicos pré-existentes, ambos de autoria do presente aluno, com co-autoria de seu orientador, co-orientador e colegas. O Capítulo 1 destina-se aos resultados de um artigo publicado no periódico científico denominado Geophysical Research Letters [Soutelino et al., 2011] e o Capítulo 2 refere-se a um artigo atualmente submetido ao periódico científico denominado Continental Shelf Research [Soutelino et al., subm]. O conteúdo de ambos os capítulos estão expandidos em relação as versões originais para permitir maior nível de detalhamento das diversas partes que compõem o trabalho. Mais detalhes relativos às técnicas metodologicas são apresentados, bem como um maior numero de gráficos, buscando maximizar a clareza do documento. O Capítulo 3 compila e sumariza os resultados oriundos de ambos os artigos científicos, e consequentemente desta tese, finalizando com sugestões para trabalhos futuros. / This dissertation addresses the mesoscale dynamics of the western boundary current system off Brazilian coast easternmost portion (10o -20o S). This is the area where the South Equatorial Current (SEC) of the Atlantic Ocean bifurcates, in the scope of the large scale wind driven subtropical gyre. This bifurcation, summed to the Equatorial circulation, has a complex tri-dimensional structure that leads to the formation of several different western boundary currents (WBCs) flowing in different directions and in different depths off the entire Brazilian coast. This system have been recognized to have major scientific importance in the last few years, because it is embedded in the South Atlantic Meridional Overturning Circulation (SAMOC) large scale pathways. Inter-hemisphere volume and heat net transports in different depths are partly controlled by the time-averaged effect of mesoscale features occurring in the region cited above, being these generated locally or remotely. This dissertation intends to address the upper ocean regional dynamics of this area in two self-contained chapters. Each of these chapters can stand alone, independently describing the problem, the methods, the results, and their implications. The contents of each chapter are summarized in the next paragraphs. The Brazil Current (BC) originates with the arrival and bifurcation of the southernmost branch of the South Equatorial Current (sSEC) at the surface between 10-20o. The BC is a surface-cored feature and it transports warm and salty waters poleward. Previous climatological studies showed a stratified sSEC bifurcation and that the resulting southern branch formed a shallow BC - a weak western boundary current. The site of origin of the BC is currently one of the less explored aspects of regional circulation and mesoscale activity in the South Atlantic Subtropical gyre westernmost portion. Chapter 1 of this work aims to fill this gap in the 10o -20o S zone off the Brazilian coast. The analysis of three recent synoptic surveys and global model outputs challenge the description of a continuous BC. According to our analysis, The sSEC bifurcation signal near the continental margin is unclear, and the velocity fields are dominated by mesoscale eddies. Recurrent anticyclones that seem to be related to the meandering BC leads us to construct a picture of a flow strongly influenced by topography and probably very unstable. Given this new emerging scenario, we hypothesize that the Brazil Current is eddy-dominated to the north of 20o S. Chapter 2 of this dissertation assumes the hypothesis formulated in Chapter 1 to be true, and studies the roles of vertical shear and topography on the eddy formation near the site of origin of the BC. We present numerical simulations that show that the main realistic mesoscale features in the eddy-rich vicinities of the BC site of origin can be successfully modeled through the dynamical interaction between parameterized versions of two opposing mean western boundary currents (BC and North Brazil Undercurrent - NBUC) and local topography, with no influence of remote dynamics or atmospheric forcing. Three large BC-related anticyclones described in Chapter 1 are reproduced and present a steady behavior during one year run. Two additional sensitivity experiments are performed. When NBUC is removed from the physical context, BC interaction with topography is not sufficient to generate such eddies, and the overall pattern shows considerably less resemblance with real data. When an idealized flat-bottom and no-banks topography is considered, BC-NBUC interaction is also not capable of developing realistic mesoscale structures. Our analyses suggest that leeward anticyclonic eddy generation mechanism is occurring at NBUC vertical levels (around 400 m) at the lee of bathymetric promontories and that this is driving the appearance of these eddies in the surface levels (BC domain) with a 10 days time lag. This dissertation structure is based on two existing scientific papers, both having the current PhD candidate as the first author, and co-authorship of his advisor, co-advisor and colleagues. Chapter 1 refers to the results of an article published at the Geophysical Research Letters scientific journal [Soutelino et al., 2011] and the Chapter 2 refers to an article currently submitted to Continental Shelf Research [Soutelino et al., subm]. The contents of both Chapter 1 and Chapter 2 are expanded in respect to the publication versions. More details regarding the applied methods and additional graphics and computations are shown. Finally, Chapter 3 ends the dissertation with final remarks.

Cette thèse décrit l’insertion professionnelle d’enseignants stagiaires du second degré ayant déjà un vécu professionnel hors système éducatif. Elle retrace les expériences, les ressentis,les activités de ces enseignants lors de leur année de stage professionnel et tente d’identifier les effets de leur vécu professionnel antérieur dans leurs façons de percevoir le travail enseignant et d’intervenir en classe.L’étude a été conduite afin de comprendre leur parcours professionnel antérieur (typique ou atypique), leur motivation, l'(ou les) élément(s) déclencheur(s) de leur bifurcation professionnelle, les difficultés rencontrées, les attentes à l’égard du système… mais aussi lors de leur première année d'entrée dans le métier d'enseignant : les professionnalités antérieures de nouveau mobilisées, leurs expectatives professionnelles, les deuils à faire, l'adéquation ou non à ce nouveau métier… et les remaniements identitaires que cette bifurcation professionnelle a provoqués pour l’intégrer.Une cohorte initialement constituée de 20 enseignants fonctionnaires stagiaires, dans l’académie de Clermont-Ferrand, a été suivie durant l’année scolaire 2011/2012. La diversité des matières enseignées, couplée à la pluralité des lieux d’enseignement contribue à la richesse des matériaux recueillis, mais aussi limite les tentatives de généralisation à partir des monographies étudiées. Le recueil des données, s’est effectué en plusieurs phases : a) des entretiens individuels ont permis de mieux comprendre la trajectoire professionnelle de l'enseignant, reconstituée d’un point de vue chronologique, conduisant à son second métier ;b) un à deux enregistrements audiovisuels de l'enseignant concerné en activité devant ses élèves ; c) un à deux entretiens d'autoconfrontation sur la base de ces enregistrements ; d) en parallèle, la tenue par chaque débutant d’un carnet de bord dans lequel il a pu exprimer son ressenti de la semaine ; e) un bilan de fin d’année établi avec chaque enseignant volontaire de l’étude comportant un retour sur les évènements saillants de son point de vue.Les principaux résultats de la thèse montrent : a) les tensions identitaires vécues par ces nouveaux enseignants ; b) l’existence de typicalités de parcours conduisant à des processus de reprofessionnalisation ; c) la présence de phénomènes d’hystérésis ou au contraire de rejets des anciennes pratiques professionnelles ; d) la convocation de gestes professionnels issus de l’ancien métier.Au final, notre recherche met l’accent sur les similitudes et les différences d’entrée dans le métier entre celle des membres de notre cohorte et celle (décrite dans la littérature) des débutants ayant suivi un cursus normal, c’est-à-dire directement issus de l’université. Ce travail peut contribuer à offrir une aide potentielle aux formateurs pour mieux comprendre les tensions et les transformations identitaires que ces « nouveaux enseignants seconde carrière » issus de l’entreprise vivent afin de mieux les aider à s’adapter à leur nouveau métier. / This thesis describes the employability of secondary school trainee teachers who already have professional experience outside of the educational system. It traces the experiences, feelings, activities of these teachers during their year of internship and tries to identify the effects of their previous professional experience on their perception of teaching methods and on their classroom work. The study was conducted in order to understand their previous career (typical or atypical), their motivation, the initiating that led to their professional bifurcation, their difficulties and expectations towards the system... but also in their first year into the teaching profession: the former professional skills once again mobilized, their professional expectations, their grieving over losses, their suitability or not to this new job... and the professional identity related challenges that this bifurcation has generated. A cohort initially comprised of 20 teachers probationers in the region of Clermont-Ferrand, was followed during the school year 2011/2012. The diversity of the subjects taught, coupled with the plurality of educational places contributes to the richness of the materials gathered, but also limits the generalization attempts from the studied monographs. The collection of data was carried out in several phases: a) individual interviews helped to understand better the professional route of the teacher, reconstructed from a chronological point of view, leading to his second job; b) one or two audiovisual recordings of the teacher interacting with his students; c) one or two self-confrontation conversations based on these recordings; d) in parallel, each beginner had to write a professional diary in which he could express his feelings during the week; e) a year-end balance sheet made by volunteering teachers of the study with their feedback on what they considered salient events. The main results of the thesis have shown: a) the identity tensions experienced by these new teachers; b) the existence of course typicalities leading to re-professionalisation process; c) the presence of hysteresis phenomena or on the contrary the rejection of former professional practices; d) the calling for professional acts inherited from their past job experience. In the end, our research focuses on the similarities and differences in entering the teaching profession between the members of our cohort and the beginners (described in the literature) who have followed a regular curriculum, that is, ie directly from the university. This work may help provide potential assistance to trainers to better understand the tensions and identity transformations that these "new second career teachers" coming from the private sector live through and help them adapt to their new profession.

La fragmentation d’enveloppes métalliques en expansion dynamique intéresse tant l’industrie civile que celle de la défense. Pour les deux domaines d’application, il s’agit de pouvoir prédire la taille et la vitesse des fragments, résultant de la destruction des enveloppes, afin de mesurer les conséquences que ceux-ci peuvent avoir sur des structures de sécurité. Les modèles de prédiction existants étudient le développement d’un défaut au sein du matériau et arrivent à déterminer une taille caractéristique des fragments. Néanmoins, ces modèles nécessitent une hypothèse dont la validité est remise en cause lorsque la vitesse de déformation est importante. Dans ce travail, nous proposons un nouveau modèle analytique pour des cylindres (sollicitation en traction plane) permettant de s’affranchir de cette hypothèse et d’étudier l’influence du défaut initial en suivant son évolution. Le modèle développé est comparé avec succès à des résultats issus de simulations numériques par éléments finis. Nos travaux permettent notamment de préciser les cadres d’application et de validité des approches classiques. Comme résultats majeurs, la nouvelle approche permet d’analyser les évolutions des perturbations aux faibles déformations mais aussi d’estimer le temps d’apparition des premières décharges élastiques, synonymes de strictions localisées. / This work deals with the fragmentation of dynamically expanding metal shells and covers a problem of interest for both civil and military industries. For both fields of application, it is crucial to predict the size and the speed of fragments, resulting from the destruction of shells in order to measure the consequences that it could have on structures. Current models study the growth of a defect within the material and are able to determine a characteristic size of fragments. Nevertheless, these models require a hypothesis whose validity is questionable when the rate of deformation is important. In this work, we propose a new analytical model for cylinders (equivalent to the dynamic extension of a plate) to overcome this hypothesis and study the influence of the initial defect by following its time evolution. The model is compared successfully with results performed with a finite element method. Our work notably expands the framework of classical linear stability analyses. As a major outcome, the proposed approach is able to track the evolution of a perturbation even for small plastic strain, when the flow may be stable. In addition it is shown that the present approach can predict accurately the time where the elastic unloading is observed in finite element simulations.

Thesis (Ph.D) - University of Queensland, 2006. / Includes bibliography.