No description available.

Master of Science / Department of Biochemistry / Qize Wei / Proper regulation of mitosis and cytokinesis is fundamentally important for all living organisms. During anaphase, antiparallel microtubules are bundled between the separating chromosomes, forming the central spindle (also called the spindle midzone), and the myosin contractile ring is assembled at the equatorial cortex. Regulators of central spindle formation and myosin contractile ring assembly are mostly restricted to the interdigitated microtubules of central spindles and they can be collectively called midzone components. It is thought that characteristic microtubule configurations during mitosis and cytokinesis are dictated by the coordinated action of microtubule-stabilizing and -destabilizing factors. Although extensive investigations have focused on understanding the roles of microtubule-bundling/stabilizing factors in controlling central spindle formation, efforts have been lacking in aiming to understand how microtubule-destabilizing factors regulate the assembly of central spindles. This dissertation describes the role of a novel microtubule-destabilizing factor termed CCDC69 (coiled-coil domain-containing protein 69) in controlling the assembly of central spindles and the recruitment of midzone components. Endogenous CCDC69 was localized to the nucleus during interphase and to the central spindle during anaphase. Exogenous expression of CCDC69 in HeLa cells destabilized microtubules and disrupted the formation of bipolar mitotic spindles. RNA interference (RNAi)-mediated knockdown of CCDC69 led to the formation of aberrant central spindles and interfered with the localization of midzone components such as aurora B kinase, protein regulator of cytokinesis 1 (PRC1), MgcRacGAP/HsCYK-4, and pololike kinase 1 (Plk1) at the central spindle. CCDC69 knockdown also decreased equatorial RhoA staining, indicating that CCDC69 deficiency can impair equatorial RhoA activation and ultimately lead to cytokinesis defects. Four coiled-coil domains were found in CCDC69 and the C terminal coiled-coil domain was required for interaction with aurora B. Disruption of aurora B function in HeLa cells by treatment with a small chemical inhibitor led to the mislocalization of CCDC69 at the central spindle. Further, vitro kinase assay showed that Plk1 could phosphorylate CCDC69. Taken together, we propose that CCDC69 acts as a scaffold and a microtubule-destabilizing factor to control the recruitment of midzone components and the assembly of central spindles.

L'utilisation des informations proprioceptives pour le contrôle de l’équilibre à la marche est encore mal comprise chez les sujets en santé ou hémiparétiques suite à un accident vasculaire cérébral. Le but de cette étude était d’évaluer le rôle des informations proprioceptives dans le maintien de l'équilibre à la marche chez les patients en santé et hémiparétiques. Une analyse de mouvement en trois dimensions a été faite chez treize participants en santé et six hémiparétiques qui marchaient sur un tapis roulant instrumenté pour déterminer leur difficulté à maintenir l’équilibre postural et dynamique, évaluée respectivement par les forces stabilisante et déstabilisante. Des vibrations étaient appliquées en continu ou pendant la phase d’appui sur les muscles postérieurs du cou et sur le triceps sural du côté non-dominant/parétique. La vibration continue ou à l’appui du triceps sural a diminué, chez les sujets en santé, la difficulté à maintenir l’équilibre dynamique et postural (p< 0,01), avec une position du corps plus en arrière, sans changement des paramètres temporels de marche. L'équilibre et les paramètres temporels de la marche n'étaient pas modifiés significativement par la vibration à la nuque (p>.17). Aucun effet des vibrations n'a été mesuré chez les patients hémiparétiques (p> 0,45). Les informations proprioceptives sont donc bien utilisées lors de la marche, mais leur rôle dépendrait des conditions de marche et des afférences visuelles disponibles. Un changement dans les capacités d’intégration expliquerait l'absence d'effet des vibrations chez les patients hémiparétiques. D’autres études sont nécessaires pour comprendre l’intégration des informations proprioceptives et visuelles dans le contrôle de l’équilibre à la marche. / Proprioceptive information is important for balance control, but little is known about how it is used during gait, or how stroke affects this use. The aim of this study was to evaluate the role of neck and ankle proprioception in balance during gait in healthy participants and after stroke. Thirteen healthy and 6 hemiparetic participants walked on an instrumented treadmill in a fully lit room, while whole-body three-dimension kinematics was quantified. Vibration was applied on the posterior neck muscles and triceps surae tendon on the non-dominant/paretic side, continuously or during the stance phase only. Difficulty to maintain dynamic and postural balance was evaluated using the stabilizing and destabilizing forces, respectively. Summary data of gait kinematics and kinetics were also reported. Continuous and stance phase vibration of the triceps surae decreased, in healthy patients, the difficulty to maintain both dynamic and postural balance in healthy participants (p<.01), with a longer distance between the centre of mass and centre of pressure and the limit of the base of support, indicating a more backward body position, and no change in temporal gait parameters. No effect of neck muscle vibration was observed (p>.17). None of the vibration conditions affected balance or gait parameters in stroke participants. The results confirmed that proprioception information is used for control balance during gait. Its importance depends on the walking and visual conditions. Changes in sensory integration capacities likely explain the results after stroke. Further study is needed to understand the integration of proprioception and vision information to control balance during gait.

Inclined planes and stairs are current in the environment and represent a barrier for seniors and people with mobility problems. Slower progression, alteration in gait pattern likely explains the high rate of fall on these surfaces, but their effect on balance is not well known. Our objective was thus to compare the difficulty in maintaining dynamic stability during the ascent and descent of an inclined plane and stairs at natural and slow walking speed in healthy individuals. Ten young healthy participants ascended and descended an inclined plane and stairs, instrumented with force- platforms to record ground reaction forces. Whole-body kinematics was also recorded to determine balance difficulty using the stabilizing and destabilizing forces, center of mass velocity and step length. Analyses of variance were used to compare the effect of surface (inclined plane vs. stairs), direction (ascent vs. descent) and speed (natural vs. slow). The stabilizing force was higher on the inclined plane than on the stairs, with a higher velocity of the center of mass. Stabilizing force was higher and destabilizing force was lower during descent than ascent only in the inclined plane but destabilizing force was lower during ascent than descent on the stairs. Slower gait speed reduced balance difficulty on both surfaces. Step length was shorter in the stairs than on the inclined plane, and particularly during descent, and at slow gait speed. Balance difficulty was higher on the inclined plane than on the stairs and at natural speed than at slow speed. The effect of direction was opposite between surfaces with higher difficulty during descent of the inclined plane, but during ascent of the stairs. Further studies are necessary in older adults or individuals with balance deficits. / La présence d’un escalier ou d’un plan incliné constitue souvent un obstacle sérieux à la réalisation des habitudes de vie des personnes ayant des incapacités physiques et même chez les personnes âgées. L’objectif général de cette étude était de quantifier l’équilibre dynamique lors de la négociation (montée et descente) d’un escalier et d’un plan incliné chez des sujets en santé. Dix sujets en santé ont été recrutés pour participer à l’évaluation. Les participants ont effectué la montée et la descente du plan incliné et de l’escalier à vitesse naturelle puis à vitesse lente. L’évaluation a compris un enregistrement de la cinématique de l’ensemble du corps. L’ensemble des données ont servi à analyser la force déstabilisante, la force stabilisante, la vitesse du centre de masse et la longueur de pas. Des ANOVAs et des tests t de Student ont permis de comparer l’effet de la surface (plan incliné vs. Escalier), de la direction (montée vs. Descente) et de la vitesse (naturelle vs. lente). La force stabilisante était plus élevée sur le plan incliné qu’à l’escalier, avec une vitesse de centre de masse plus élevée. La force stabilisante était plus élevée et la force déstabilisante était plus basse durant la descente en comparaison avec la montée sur le plan incliné. Par contre, à l’escalier, la force déstabilisante était plus basse lors de la montée en comparaison avec la descente. La vitesse de marche lente a réduit la difficulté en termes d’équilibre sur les deux surfaces. Les pas étaient plus courts sur l’escalier en comparaison avec le plan incliné, particulièrement lors de la descente à vitesse naturelle. L’effet de direction était opposé entre les surfaces, avec une difficulté plus élevée durant la descente du plan incliné et durant la montée de l’escalier. Des études approfondies seront nécessaires chez les personnes âgées et les personnes ayant des déficits de la balance.

No description available.

Both insect parasitic/entomopathogenic nematodes and plant parasitic nematodes are of great economic importance. Insect parasitic/entomopathogenic nematodes provide an environmentally safe and effective method to control numerous insect pests worldwide. Alternatively, plant parasitic nematodes cause billions of dollars in crop loss worldwide. Because of these impacts, it is important to understand how these nematodes evolve, and, in the case of entomopathogenic nematodes, how their bacterial symbionts evolve. This dissertation contains six chapters. Chapter one is a review of DNA markers and their use in the phylogenetic systematics of entomopathogenic and insect-parasitic nematodes as well as a review of phylogenetic, co-phylogenetic, and population genetic methodologies. Chapter two characterizes positive destabilizing selection on the luxA gene of bioluminescent bacteria. Our data suggests that bacterial ecology and environmental osmolarity are likely driving the evolution of the luxA gene in bioluminescent bacteria. Chapter 3 examines relationships among bacteria within the genus Photorhabdus. Our analyses produced the most robust phylogenetic hypothesis to date for the genus Photorhabdus. Additionally, we show that glnA is particularly useful in resolving specific and intra-specific relationships poorly resolved in other studies. We conclude that P. asymbiotica is the sister group to P. luminescens and that the new strains HIT and JUN should be given a new group designation within P. asymbiotica. Chapter 4 characterizes the morphology of the head and feeding apparatus of fungal feeding and insect infective female morphs of the nematode Deladenus siricidicola using scanning electron microscopy. Results showed dramatic differences in head, face, and stylet morphology between the two D. siricidicola female morphs that were not detected in previous studies using only light microscopy. Chapter five utilizes comparative transciptomics to identify putative plant and insect parasitism genes in the nematode Deladenus siricidicola. Results from this study provide the first transcriptomic characterization for the nematode Deladenus siricidicola and for an insect parasitic member of the nematode infraorder Tylenchomorpha. Additionally, numerous plant parasitism gene homologues were discovered in both D. siricidicola libraries suggesting that this nematode has co-opted these plant parasitism genes for other functions. Chapter six utilizes a phylogenomic approach to estimate the phylogeny of the nematode infraorder Tylenchomorpha.

Cette thèse porte sur le processus de décision, exécution, régulation et évaluation des projets d'école réalisés par des enseignants des écoles en France. Cette recherche, géographiquement située dans le département du Val d'Oise, a été menée sous les principes de la recherche ethnographique. Toutes les informations recueillies ont été analysées selon les préceptes de la méthode de la Théorie enracinée. Cela a permis de décrire la portée des travaux des enseignants lors de l'exécution de cette tâche imposée par le ministère de l'Education nationale depuis 1989. Ainsi l’usage que les enseignants font de ce dispositif révèle de nombreux paradoxes. Alors que pour beaucoup d’enseignants, il n’est rien de plus qu'un exercice bureaucratique, le projet est également une opportunité pour innover sur le plan pédagogique et d’installer de nouvelles formes d'interaction sociale au sein de la communauté éducative. La principale difficulté réside dans le fait que le processus projet d'école met en lumière un certain nombre de questions transversales pours lesquelles les enseignants ne se considèrent guère compétents. Cela motive, dans de nombreux cas, une série d'initiatives, une sorte d’activisme, que par la suite les enseignants ne parvenaient plus à évaluer. Le sentiment d’expérimenter en aveugle et de ne pas alimenter les processus de changement laisse chez les enseignants une forte frustration professionnelle et une grande démotivation à l’heure d’envisager des nouvelles actions. Le projet d’école met en évidence la nécessité des enseignants de disposer des outils professionnels pour, d’une part, interpréter les différents aspects de phénomènes éducatifs auxquels ils sont confrontés et, d'autre part, être en mesure de construire leurs propres dispositifs pédagogiques et évaluatifs. L'autonomie des enseignants est plus que l’autorisation institutionnelle à entreprendre des actions au sein de chaque école, elle revient plutôt à la capacité à comprendre et à rendre intelligibles leurs propres processus de travail pour améliorer la qualité de l'apprentissage et la vie à l'école. Cette thèse prône la nécessité d'associer la formation continue des enseignants et les activités réelles – la réflexion et la prise de décisions - qui concourent dans le lieu de travail des enseignants. / This thesis deals with the process of decision, execution, control and evaluation of educational projects in schools - les projets d'école - conducted by French primary education teachers. This research, geographically located in the department of Val d'Oise, was conducted under the principles of ethnographic research. The data collected was analyzed according to the precepts of the Grounded Theory Method. This allows describing the scope of teachers work when performing this mandatory task imposed by the Ministry of National Education since 1989. The teacher’s use of this obligation reveals many paradoxes. While for many teachers it is nothing more than a bureaucratic exercise, the project is also an opportunity to innovate pedagogically and install new forms of social interaction within the educational community. The main difficulty lies in the fact that the school project process brings to light a number of cross-cutting issues in which teachers do not feel competent. This motivates, in many cases, a series of initiatives, a kind of activism which teachers aren't able to later evaluate. The feeling of experimenting blindly not to feed the change process and leaves a strong professional frustration that declines motivation when teacher are to consider to engage in new activities. The educational project highlights the need for teachers to have professional tools, in order to both interpret the various aspects of the educational phenomena they face, and be able to build their own pedagogical and evaluative settings. The teacher’s autonomy is fare more than the mere institutional authorization to take action, it rather refers to the ability to understand their own work processes to improve the quality of learning and life at school. This thesis advocates the need to associate the continuous training of teachers to the actual activities - reflection and decision-making-that take place in the teacher’s workplace. / Esta tesis aborda el proceso de realización, ejecución, regulación y evaluación de los proyectos educativos de las escuelas – les projets d’école - llevados a cabo por los profesores de la educación primaria en Francia. Esta investigación situada geográficamente en el departamento de Val d'Oise, se realizó bajo los principios de la investigación etnográfica. El conjunto de las informaciones recogidas fueron analizadas según los preceptos de la metodología fundamentada en los hechos. Esto permite describir el panorama de trabajo de los profesores a la hora de realizar esta tarea impuesta por el ministerio de la Educación nacional desde el año 1989. La utilización que los profesores hacen de este dispositivos revela numerosas paradojas. Si bien para muchos no es más que una actividad burocrática, el proyecto es también la oportunidad de innovar a nivel pedagógico y de instalar nuevas formas de interacción social en el seno de la comunidad educativa. La principal dificultad reside en el hecho que el proceso projet d'école saca a luz una serie de problemáticas transversales para las cuales los profesores no se consideran competentes. Esto motiva, en numerosas ocasiones, una serie iniciativas, una especie de activismo, que posteriormente los docentes logran apenas evaluar. El sentimiento de experimentar a ciegas y de no retroalimentar los procesos de cambio dejan en los profesores una fuerte frustración profesional y una consecuente desmotivación para emprender nuevas acciones. El proyecto educativo pone en relieve la necesidad de los profesores de contar con las herramientas profesionales que les permitan por un lado interpretar las distintas dimensiones de los fenómenos educativos a los que se enfrentan y por otro, ser capaces de construir sus propios dispositivos pedagógicos y evaluativos. La autonomía de los docentes es más que la autorización institucional para realizar acciones, ésta se refiere más bien a la capacidad de entender y volver inteligibles sus propios procesos de trabajo para la mejora de la calidad de los aprendizajes y de la vida en la escuela. Esta tesis preconiza la necesidad de asociar la formación continua de los profesores a las actividades reales - a la reflexión y a la toma de decisiones- que se llevan a cabo en el lugar de trabajo de los maestros.

Made available in DSpace on 2014-12-17T14:20:17Z (GMT). No. of bitstreams: 1 LeninaLSS_TESE.pdf: 2389924 bytes, checksum: be98cf3c8ee6fa1fe09ca9da91183afc (MD5) Previous issue date: 2010-11-30 / This thesis is a translation of work of the Brazilian doctor, Pedro da Silva Nava (1903-1984), in particular, his memoirs and chronicles, articulated with the writings of medicine history, aiming to defend that the autobiographical narratives are sources of research capable of promoting discussions on the expansion of the present at the confluence of complex and unequal society in constant changing process as the Brazilian. The theoretical and methodological support circulates around studies, proposals and thesis by Boaventura Santos about empowering past, destabilizing subjectivity, sociology of absences, cosmopolitan reason and translation work. The empirical support drawn from the literature produced by Nava were analyzed with reference this reasoning and studies that have facilitated the flow of translation among others, the studies of Antonio Candido, Arrigucci Jr., Boris Cyrulnik, Beatriz Sarlo, Ecl?a Bosi, ?talo Calvino, Jos? Willington Germano, Jos? Maria Can?ado, Lev Vygotsky, Marilena Chau?, Paul Ric?eur and Walter Benjamim, without neglecting what we consider indispensable to scientific research, the production of relevant knowledge and prudent, in view of a decent life. The initial inflections reflect the subject of the Memoirs and its education/training, to then place the Memoir subject in the literary context, scientific, historical and Brazilian poetic (1972-2010), bringing great interpreters and discussing the rationale used by the Narrator that we defend stand closer to the cosmopolitan, showing the formation of narratives whose presence insert itself beforehand to modernist verve, linked to the discursive array against the literature as domination space, disseminated in Brazil in the early twentieth century. So, it articulate with those in which the concerns adjust the construction of the social formation of Brazil as a national heritage through literary narrative that focuses on a historical principle that becomes the past empowering, allowing his rereading, whose converge to memory, the lifestyles, the plurality of language and Brazilian culture, formed by several people, converging into a design not of culture but multiculturalism in Brazil. The memory issue was addressed in the space-time of experiences of being that narrates, shaped by a destabilizing subjectivity that sought to order the testimony of a time, a history and society, retelling them by creative imagination, almost fictional, to make circulate his knowledge about Brazil attached to his medical knowledge, as well as other subjects in his living group and other groups with whom they maintained contact. Thus, he portrayed both tangible and intangible cultural assets of the country as a form of preservation, giving them meanings and sense. It approaches, therefore, from the perspective of sociology of absences, the expansion of the present and by the logic inherent in his narratives of self and Brazil / Consiste, este trabalho de tese, de uma tradu??o da obra do m?dico brasileiro, Pedro da Silva Nava (1903-1984), em particular, de seus escritos memorial?sticos e das cr?nicas, articulados com os de hist?ria da medicina, objetivando-se defender que as narrativas autobiogr?ficas s?o fontes de pesquisas capazes de promover discuss?es sobre a dilata??o do presente na conflu?ncia de uma sociedade desigual e complexa, em constante processo de mudan?a, como a brasileira. A fundamenta??o te?rica e metodol?gica circula no entorno dos estudos, propostas e teses de Boaventura Santos sobre passado capacitante, subjetividade desestabilizadora, sociologia das aus?ncias, raz?o cosmopolita e trabalho de tradu??o. As bases emp?ricas, extra?das da literatura produzida por Nava, foram analisadas tendo como referentes esta fundamenta??o e estudos que possibilitaram o fluir da tradu??o, entre outros, de Antonio Candido, Arrigucci Jr., Boris Cyrulnik, Beatriz Sarlo, Ecl?a Bosi, ?talo Calvino, Jos? Willington Germano, Jos? Maria Can?ado, Lev Vygotsky, Marilena Chau?, Paul Ric?eur e Walter Benjamim, sem descurar daquilo que consideramos imprescind?vel ? pesquisa cient?fica, ? produ??o de conhecimentos prudentes e pertinentes, na perspectiva de uma vida decente. As inflex?es iniciais traduzem o sujeito das Mem?rias e sua educa??o/forma??o, para, em seguida, situar as Mem?rias do sujeito no contexto liter?rio, cient?fico, hist?rico e po?tico brasileiro (1972-2010). Trazem seus principais int?rpretes, discutindo a racionalidade empregada pelo Narrador, que defendemos aproximar-se da cosmopolita, evidenciando a constitui??o de narrativas cujas presen?as inserem-se de antem?o ? verve modernista, vinculada ? matriz discursiva contr?ria ? literatura como espa?o de domina??o, disseminada no Brasil no in?cio do S?culo XX. Desse modo, articula-se ?quela na qual as preocupa??es conformam a constru??o da forma??o social do Brasil, como patrim?nio nacional, atrav?s da narrativa liter?ria com enfoque em um princ?pio hist?rico que torna o passado capacitante. Permite, assim, sua releitura, para cujas tramas convergem ? mem?ria, os modos de vida, a pluralidade da linguagem e da cultura brasileira, formada por v?rios povos, confluindo para uma concep??o, n?o de cultura, mas de multiculturalidade brasileira. A quest?o da mem?ria foi tratada no espa?otempo das experi?ncias do ser que narra, moldado por uma subjetividade desestabilizadora que buscou ordenar os testemunhos de um tempo, de uma hist?ria e de uma sociedade, recontando-os pela imagina??o criadora, quase ficcional, para fazer circular seus conhecimentos sobre o Brasil, unidos aos seus conhecimentos m?dicos, bem como aos de outros sujeitos de seu grupo de conviv?ncia e de outros grupos com os quais manteve contato. Assim, retratou bens culturais materiais e imateriais do pa?s como forma de preserva??o, atribuindo-lhes significados e sentidos. Aproxima-se, portanto, da perspectiva de sociologia das aus?ncias, pela dilata??o do presente e pelas l?gicas a ela inerentes em suas narrativas de si e do Brasil

Les grands effondrements de flanc sont des phénomènes récurrents dans l'évolution géologique des îles océaniques. Parfois catastrophiques. les épisodes de déstabilisation sont capables de générer d'importants tsunamis, et représentent donc des événements dangereux. Le îles des Açores à l’est de la Dorsale Médio-Atlantique sont situées sur la frontière de plaques diffuse entre l’Eurasie (Eu) et la Nubie (Nu), et donc sous l'influence d’un contrôle structural et d’une activité sismique importante (événements historiques de magnitude jusqu'à environ 7). Avant le projet MEGAHazards (PTDC/CTE-GIX /108149/2008, financé par FCT, Portugal), les effondrements de flanc à grande échelle étaient considérés inexistants aux Açores, principalement à cause de la petite dimension des édifices volcaniques. Ici, nous concluons sans équivoque que de tels événements se sont bien produits dans les Açores. La thèse de doctorat porte sur l'évolution de la ride volcanique escarpée de Pico-Faial, qui se trouve sur une faille normale majeur associée à la limite diffuse Nu/Eu, et particulièrement sur les grands effondrements de flanc qui ont affecté l'île de Pico. A partir de modèles numériques de terrain à haute-résolution, de nouvelles données structurales, stratigraphiques, et de datations K-Ar, nous avons: (1) calibré la stratigraphie volcanique de Pico; (2) reconstruit les phases majeures de croissance et de destruction des îles de Pico durant les derniers 200 kyr; (3) reconstruit l'évolution du slump actif du SE d'île de Pico, au cours des derniers 125 kyr; (4) fourni de nouvelles interprétations concernant l'escarpement qui coupe le flanc S du stratovolcan de Pico; (5) montré l’existence d’effondrements catastrophiques des flancs N et S de l'île de Pico entre ca. 125 et 70 ka, qui ont généré d'importants débris sous-marins; et (6) proposé que l’accommodation de l' extension associé à la limite des plaques Nu/Eu le long de la ride Pico-Faial, a été consolidée dans les derniers ca. 125 ka. De nombreux facteurs favorisant le développement des instabilités de flanc sur les îles volcaniques ont été proposés dans la littérature, mais leur rôle exact et leur contribution mutuelle restent mal compris. Nous présentons ici une solution analytique pour la théorie du Prisme Critique de Coulomb cohésif, appliquée à des instabilités gravitaires, et des simulations analogiques complémentaires pour tester certaines implications structurales du modèle. Nous étudions l'impact de variables comme: la géométrie et les dimensions du prisme, la cohésion, le coefficient de friction interne et le rapport de surpression de fluide (surpression de fluide divisé par la pression lithostatique).Nous concluons que: (1) l’augmentation de la pente des flancs du volcan et du décollement basal conduit à une diminution du rapport de surpression de fluide nécessaire pour produire la rupture; (2) la diminution de l'effet stabilisateur de la cohésion avec la profondeur du décollement basal favorise l'occurrence de déstabilisation gravitaire profonde à grande échelle pour des décollements plus profonds que 2000-2500 m. Pour des décollements basales plus superficiels, les rapports de surpression de fluide nécessaires pour induire la rupture sont relativement supérieurs. Pour les décollements moins profonds, des flancs très inclinés et des matériaux très résistants, la rupture superficielle parallèle à la surface du flanc est favorisée, par rapport à la rupture profonde; (3) Pour des profondeurs supérieures à 2500 m (cas des grands édifices volcaniques), tandis que l'impact de la cohésion diminue, l'effet de la friction interne le long du décollement basal devient relativement plus importante. L’étude des grands effondrements de flanc dans les îles des Açores, et la modélisation des variables qui contrôlent la stabilité des édifices volcaniques demeurent cependant incomplets, et seront approfondis dans un futur proche. / Large-scale flank collapses are recurrent in the geological evolution of volcanic ocean islands. Such catastrophic episodes of destabilization can be voluminous and generate large tsunamis, which may cause considerable damage and thus represent extremely hazardous events. The Azores islands east of the Mid-Atlantic Ridge are located on the Eurasia(Eu)/Nubia(Nu) plate boundary, and therefore subject to structural control and seismic activity (historical events of magnitude up to ca. 7). However, prior to MEGAHazards Project (PTDC/CTE-GIX/108149/2008, funded by FCT, Portugal), large-scale flank collapses in the Azores were considered to be lacking, mainly due to the small dimension of the volcanic edifices. Here, we conclude unequivocally on the occurrence of such events in the Azores. The present PhD thesis addresses the evolution of the Pico-Faial steep volcanic ridge, which sits on a major normal fault associated with the Eu/Nu diffuse boundary, focusing especially on the large-scale flank failures in Pico Island. Based on high-resolution sub-aerial and submarine Digital Elevation Models, new structural and stratigraphic data, and high-resolution K-Ar dating on separated volcanic groundmass, we: (1) constrain the volcano stratigraphy of Pico; (2) reconstruct the major phases of growth and destruction in Pico and Faial islands in the last 200 kyr; (3) reconstruct the ca. 125 kyr evolution of the currently active large-scale slump in the SE of Pico Island; (4) provide new structural data/interpretations regarding the scarp that sharply cuts the S flank of Pico Stratovolcano; (5) report on the occurrence of large-scale failures in the N and S flanks of the Pico Island between ca. 125 and 70 ka, which generated large submarine debris deposits; and (6) propose that the role of the Pico-Faial ridge as a structure accommodating part of the extension on the diffuse Nu/Eu boundary has been consolidated in the last ca. 125 kyr. Many factors favouring the development of such large-scale flank instabilities have been proposed in the literature, but their exact role and mutual contribution remain poorly understood. We here present an analytical solution for the cohesive Coulomb Critical Wedge theory applied to gravitational instabilities, and associated analogue simulations to test some structural implications of the model. We investigate the impact of several variables on the stability of volcanic flanks, including: wedge slope and dimensions, cohesion, internal friction along the basal detachment, and fluid overpressure. We conclude that: (1) the steepening of the volcanic flanks and basal detachment lead to a decrease in the fluid overpressure ratio (fluid overpressure divided by lithostatic pressure) necessary to produce failure. (2) The decrease of the stabilizing effect of cohesion with increasing depth of the basal detachment favours the occurrence of deep-seated large-scale gravitational destabilization in basal detachments deeper than ca. 2000-2500 m (in volcanic edifices necessarily higher than 2500 m). For shallower basal detachments, the overpressure ratios required to induce failure are comparatively larger. For shallower basal detachments, steeper flanks and stronger edifice materials, shallow failure parallel to the edifice flank surface is favoured, instead of deep-seated deformation. (3) With increasingly deeper basal detachments (possible in larger volcanic edifices), while the impact of cohesion diminishes, the relative importance of basal internal friction for the stability of the edifice increases. The investigation of the occurrence of large-scale mass-wasting in the Azores islands, and the modelling of the variables controlling the stability of the volcanic edifices are only at their first steps and will be further developed in the future.