Ce travail de thèse a porté sur le développement de membranes céramiques pour la filtration de colloïdes issus de la corrosion dans le circuit primaire des REP. La voie des polymères précéramiques a été mise en œuvre par la synthèse d’un polyborocarbosilane (PBC) à partir d’allylhydridopolycarbosilane conduisant à une céramique de type SiBC. Des billes de PMMA mono disperses d’une taille de 1,5 et 0,3 µm ont été préparées pour servir d’agent porogène pour créer une porosité contrôlée. Des objets micro-cellulaires 3D de forme circulaire ont été élaborés par pressage uni-axial avec ajout de billes de PMMA commercial pour servir de support macroporeux. Une étude de cristallinité à haute température (> 1000 °C) a été réalisée, montrant son influence sur la stabilité du matériau. La couche sélective a été préparée par dip-coating à partir de différentes formulations de barbotine contenant du PBC et les billes de PMMA élaborées. La stabilité physico-chimique des supports micro-cellulaires a été étudiée grâce à des essais de vieillissement en micro-autoclave en milieu primaire simulé. La résistance à la filtration a été testée grâce à un essai sur un dispositif de filtration connecté à un moyen d’essai de laboratoire permettant de simuler les conditions des REP. / This work has been focused on the development of ceramic membranes for the filtration of colloids resulting from corrosion in the primary loop of PWR. SiBC ceramics were synthesized by the preceramic polymers route from a polyborocarbosilane (PBC) obtained from allylhydridopolycarbosilane. Single-dispersed PMMA beads with a size of 1.5 and 0.3 μm were prepared to be used as a porogen agent to lead to a controlled porosity of the selective layer. 3D micro-cellular objects with a circular shape were developed by uni-axial pressing with the addition of commercial PMMA beads to serve as a macroporous support. A crystallinity study at high temperature (> 1000 ° C) was carried out showing its influence on the stability of the material. The selective layer was prepared by dip-coating from various slurry formulations containing PBC and the prepared PMMA beads. The chemical and physical stability of the microcellular supports was studied by ageing tests in a simulated primary water chemistry. The filtration resistance was tested by means of tests on a filtration device connected to a laboratory loop which simulates the conditions of the PWRs.

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Resumo: O presente trabalho teve como objetivo avaliar a agressividade de linhagens de Ralstonia solanacearum provenientes de solanáceas, plantas ornamentais e eucalipto, em plantas de batata, tomate e fumo, bem como caracterizar as linhagens por meio de técnicas moleculares. Vinte e duas linhagens foram utilizadas nos ensaios de avaliação da agressividade, em experimentos conduzidos em casa-de-vegetação evidenciaram alta severidade da doença pelas linhagens de R. solanacearum quando inoculadas em plantas de tomate e batata, sendo a batata mais afetada nas inoculações. Todas as linhagens mostraram-se agressivas, sendo que o fumo mostrou baixa suscetibilidade ao ataque das bactérias. As linhagens mais agressivas em plantas de tomate foram IBSBF 309, IBSBF 1712, IBSBF 1839, IBSBF 1882, IBSBF 1883 e IBSBF 2000, pertencentes às biovares I, II e III. As linhagens mais agressivas às plantas de fumo foram IBSBF 309, IBSBF 2131 e IBSBF 292T, pertencentes à biovar I. Foi efetuado também ensaio de microbiolização in vitro em sementes de eucalipto, a fim de se identificar possíveis linhagens patogênicas a esta espécie vegetal e concluiu-se que todas as linhagens utilizadas infectaram plantas de eucalipto ou afetaram seu crescimento. A caracterização molecular de 41 linhagens de Ralstonia solanacearum, provenientes de diversas plantas hospedeiras, incluindo solanáceas, bananeira, helicônia, plantas ornamentais e eucalipto, foi efetuada empregando-se ERIC e BOX-PCR e os resultados mostraram grande diversidade genética entre as linhagens. A análise de PCR-RFLP da região espaçadora 16S-23S DNAr permitiu distinguir os isolados pertencentes à biovar III das demais biovares (I, II, IIA e IIT), quando digeridos com as enzimas Taq I e Hin6 I. A análise de sequenciamento de parte dos genes Endoglucanase (Egl) e MutS possibilitou a classificação em filotipos e os resultados... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This study aimed to evaluate the aggressiveness of strains of Ralstonia solanacearum from solanaceus, ornamental and eucalyptus plants, on potato, tomato and tobacco, and to characterize the strains through molecular techniques. Twenty-two strains were used in this study to evaluate the aggressiveness and, the experiments conducted in a greenhouse revealed the high susceptibility of tomato and potato plants, with the potato being the most affected on through the inoculations. All isolates proved to be aggressive and higher tolerance to the attack of bacteria was verified on tobacco plants. Strains more aggressive on tomato were IBSBF 309, IBSBF 1712, IBSBF 1839, IBSBF 1882, IBSBF 1883 and IBSBF 2000, belonging to biovars I, II and III. The more aggressive strains on the tobacco plants were IBSBF 309, IBSBF 292T and IBSBF 2131 belonging to biovar I. Tests in vitro of microbiolization of eucalyptus seeds were also performed in order to identify possible pathogenic strains to this species and the results showed that all strains used cause infection on emerging plants or affected their growth. To molecular characterization of 41 strains of Ralstonia solanacearum from several host plants including solanaceous, banana, heliconia, ornamentals and eucalyptus were employed to ERIC and BOX-PCR, and the results showed high genetic diversity among strains. The analysis of PCR-RFLP of 16S-23S spacer region rDNA allowed us to distinguish the isolates belonging to biovar III from the others (biovars I, II, IIA and IIT) when digested with enzymes Taq I and Hin6 I. The sequence analysis of the partial of Endoglucanase (Egl) and MutS genes allowed the classification in phylotypes and the results revealed a predominance of the phylotype II in Brazil, and four isolates were classified in the phylotype I, all belonging to biovar III / Orientador: Antonio Carlos Maringoni / Coorientador: Suzete Aparecida Lanza Destéfano / Banca: Valdemar Atilio Malavolta Junior / Banca: Ivan Paulo Bedendo / Mestre

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-05-09T19:31:56Z No. of bitstreams: 1 UbiratanNascimentoDeAlencarJunior_DISSERT.pdf: 777766 bytes, checksum: 69ddb442856cc32d92e8b803a53d873b (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-05-09T22:46:06Z (GMT) No. of bitstreams: 1 UbiratanNascimentoDeAlencarJunior_DISSERT.pdf: 777766 bytes, checksum: 69ddb442856cc32d92e8b803a53d873b (MD5) / Made available in DSpace on 2016-05-09T22:46:06Z (GMT). No. of bitstreams: 1 UbiratanNascimentoDeAlencarJunior_DISSERT.pdf: 777766 bytes, checksum: 69ddb442856cc32d92e8b803a53d873b (MD5) Previous issue date: 2015-03-27 / A pesquisa define-se como um Estudo de Caso que toma como objeto central o programatelevisivo Profiss?o Rep?rter, exibido semanalmente pela Rede Globo, ?s ter?as-feiras, nafaixa de hor?rio das 23h40min. A meta foi identificar, em tr?s epis?dios do programa, sempreju?zo da observa??o criteriosa de outras edi??es, a presen?a ou n?o das teorias deautorreferencialidade, a for?a do contrato midi?tico, bem como quais as representa??essociais. O objetivo foi perceber, fazendo uso de metodologias complementares, qual, de fato,? o ?nordeste? apresentado pelo programa, sempre com a preocupa??o de discutir o que aunidade ou parte considerada (o corpus) sugere a respeito do ?todo? e n?o a formata??o deconceitos que generalizem o tema, ao considerar a abrang?ncia da produ??o televisiva e seussentidos. / Research is defined as a Case Study that central object the TV show Profession Reporter, appears weekly by Rede Globo, on Tuesdays, in the 23:40 time range. Empirical basis, the research makes the questioning of journalism and social representations through it articulated for the construction of approaches to what is defined as "Brazilian Northeast." In this goal, the study seeks to drive a multiplicity of angles and methods to illuminate specific aspects of the case study, as well as areas that intersect in the production of meaning. The Job Reporter is built, as well as the appropriate object to analyze the theories of self-referentiality and the strength of the media contract, given the overlap in the derived logical not factual genres and related entertainment that format or feed back what is established in the course of time, as the "real" features of this regional space.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-01-12T15:34:48Z No. of bitstreams: 1 MarceloPereiraPaivaMelo_DISSERT.pdf: 1188162 bytes, checksum: 5982046a3466d54e95d1d627fd59897e (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-01-20T13:17:10Z (GMT) No. of bitstreams: 1 MarceloPereiraPaivaMelo_DISSERT.pdf: 1188162 bytes, checksum: 5982046a3466d54e95d1d627fd59897e (MD5) / Made available in DSpace on 2017-01-20T13:17:10Z (GMT). No. of bitstreams: 1 MarceloPereiraPaivaMelo_DISSERT.pdf: 1188162 bytes, checksum: 5982046a3466d54e95d1d627fd59897e (MD5) Previous issue date: 2015-12-18 / Esta disserta??o tem por objetivo a reflex?o acerca dos sentidos de Justi?a encontrados no Livro 1 d?A Rep?blica, particularmente aqueles inseridos entre os trechos 336c e 354c. Analisa-se tamb?m a possibilidade de que o conceito de Tras?maco da Justi?a como conveni?ncia do mais forte ? uma forma pr?-plat?nica de entendimento da Justi?a que, apropriada por Plat?o, passa a ser v?lida quando se considera o mais forte como sendo virtuoso e orientado ao Bem, situa??o apenas encontrada no contexto da Rep?blica. Desse modo, defende-se que Tras?maco n?o est? inteiramente errado quanto ao seu conceito de Justi?a. Tamb?m se considera a no??o de que a Justi?a, ao longo d?A Rep?blica, seja a harmonia entre os elementos da alma e da Cidade-Estado. / This thesis intends to ponder the concepts of Justice found in The Republic?s book 1, mostly on those between excerpts 336c and 354c. It also considers the possibility that Thrasymachus? concept of Justice ? the convenience of the stronger ? is a pre-Platonic view of Justice that is appropriated by Plato, who makes it valid when considering the stronger to be virtuous and oriented to the Good: such condition of the stronger can only be found on Plato?s Republic. Therefore, this thesis states that Thrasymachus may not be entirely wrong on his concept of Justice. Moreover, this thesis also considers the possibility that Justice, throughout The Republic, is harmony among the soul?s elements and the city?s.

Submitted by Erika Demachki (erikademachki@gmail.com) on 2014-10-21T17:26:17Z No. of bitstreams: 2 Dissertação - Aline Assis Cardoso - 2014.pdf: 1764081 bytes, checksum: e25295d0c53ab008ce92f6d68f628db7 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Jaqueline Silva (jtas29@gmail.com) on 2014-10-21T18:17:40Z (GMT) No. of bitstreams: 2 Dissertação - Aline Assis Cardoso - 2014.pdf: 1764081 bytes, checksum: e25295d0c53ab008ce92f6d68f628db7 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-10-21T18:17:40Z (GMT). No. of bitstreams: 2 Dissertação - Aline Assis Cardoso - 2014.pdf: 1764081 bytes, checksum: e25295d0c53ab008ce92f6d68f628db7 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2014-02-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Research on biological nitrogen fixation (BNF) in common bean had a great progress in recent years, especially in the knowledge of microsimbiont and exploring new approaches seeking greater variability in macrosimbiont for efficiency of BNF. Studies of bacterial diversity and taxonomy, especially applied to common bean symbionts showed a great evolution due to new molecular methodologies for evaluation and characterization. This study aimed to evaluate the tolerance to salinity and temperature, to characterize based on molecular markers and to evaluate the symbiotic efficiency of bacterial isolates obtained from nodules of common bean cultivated on soil samples from the States of Goiás, Minas Gerais and Paraná. The isolates were evaluated for salinity and temperature on YMA medium with different NaCl concentrations (0%, 1%, 2%, 4% and 6%) at different temperatures (28ºC, 33ºC, 38ºC, 43ºC and 48ºC). For molecular characterization based on BOX-PCR and REP-PCR profiles the isolates were grown in liquid YMA for 24 hours and then DNA extraction was performed. Evaluation of symbiotic efficiency of the isolates was conducted under greenhouse conditions in Leonard jars. Seeds of common bean (var. Pérola) were inoculated with different isolates selected in the previous analysis. Nodule number (NN), dry mass of nodules (DMN), specific mass of nodules (SMN), root dry weight (RDW), dry matter of aerial part (DMAP), relation root/shoot (R/S), total nitrogen (N) and leaf area (LA) were evaluated. It was observed that 41.12% of the isolates grew in more restrictive conditions than standard strains SEMIA 4077, SEMIA 4080 and SEMIA 4088, and 29.90% of the isolates grew in less restrictive conditions than SEMIAs strains.BOX-PCR and REP-PCR profiles showed high genetic diversity among the evaluated isolates, demonstrating a high degree of polymorphism. JPrG8A7 and JPrG8A6 isolates exhibited superior performance compared to standard strains when compared the NN , SMN and DMN. The latter showed a positive correlation with the DMAP, Total-N and LA. It was observed that some isolates showed competitive features equal or superior than commercial standards strains, with results that can improve the process of symbiosis between plant and bacteria, thereby generating greater productivity for the common bean cultivation. / A pesquisa sobre a fixação biológica de nitrogênio (FBN) no feijoeiro teve bastante progresso nos últimos anos, especialmente no conhecimento do microsimbionte e no estudo de novas abordagens buscando maior variabilidade no macrosimbionte para maior eficiência da FBN. Os estudos da diversidade e taxonomia bacteriana, especialmente aplicados aos simbiontes do feijoeiro-comum apresentou uma grande evolução devido às novas metodologias moleculares de avaliação e caracterização. Este trabalho teve como objetivo avaliar a resistência à salinidade e temperatura, caracterizar molecularmente e avaliar a eficiência simbiótica de isolados de nódulos de feijoeiro-comum oriundos dos estados de GO, MG e PR. Os isolados foram avaliadas quanto à salinidade e temperatura em meio YMA com diferentes concentrações de NaCl (0%; 1%; 2%; 4% e 6%) em diferentes temperaturas (28ºC; 33ºC; 38ºC; 43ºC e 48ºC). Para a caracterização molecular os isolados foram crescidos em meio YMA líquido por 24 horas e logo em seguida foi realizada a extração do DNA. Foram avaliados perfis BOX-PCR e REP-PCR. A avaliação da eficiência simbiótica dos isolados foi conduzida em casa-de-vegetação com vasos tipo Leonard com a cultivar Pérola inoculada com diferentes isolados selecionados na análise anterior. Foi avaliado o número de nódulos (NN), massa seca de nódulos (MSN), massa específica de nódulos (MEN), massa seca de raiz (MSR), matéria seca da parte aérea (MSPA), relação raiz/parte aérea (R/PA), nitrogênio total (N) e área foliar (AF). Observou-se que 41,12% dos isolados cresceram em condições mais restritivas que as estirpes padrão SEMIA 4077, SEMIA 4080 e SEMIA 4088, e 29,90% dos isolados cresceram em condições menos restritivas que as SEMIAs. Os perfis BOX-PCR e REP-PCR apresentaram grande diversidade genética entre os isolados avaliados, demonstrando um alto grau de polimorfismo. Os isolados JPrG8A7 e JPrG8A6 apresentaram desempenho superior as estirpes padrão quando comparados o NN, MEN e MSN. Esta última apresentou correlação positiva com a MSPA, N-Total e AF. Foi observado que alguns isolados apresentaram características competitivas iguais ou superiores as estirpes-padrões comerciais, apresentando resultados que podem melhorar o processo de simbiose entre a planta e a bactéria, gerando assim uma maior produtividade para a cultura do feijoeiro-comum.

La Corrosion Sous Contrainte (CSC) est un des principaux modes de dégradation des composants assemblés par soudage dans Réacteurs à Eau Pressurisée (REP). Le retour d’expérience de 2007 sur les soudures en alliage à base de nickel a présenté 3 cas de fissuration par CSC sur l’Alliage 82 sur les 300 cas recensés dans le circuit primaire. L’objectif de cette étude est alors d’identifier des paramètres microstructuraux et mécaniques à l’échelle de la microstructure impliqués dans l’amorçage de fissures. Les caractérisations du matériau pour identifier ces paramètres sont composées d’une part, d’analyses de la composition chimique et d’analyses EBSD (Electron Back-Scattered Diffraction) pour la morphologie et les orientations cristallographiques des grains pour la microstructure et, d’autre part, de mesures expérimentales de déformation en surface et de calculs numériques de champs de contrainte autour des joints de grains par éléments finis pour le comportement mécanique. La corrélation de ces informations avec les sites d’amorçage de fissures de CSC obtenus avec les essais d’amorçage entrepris sur des éprouvettes U-bend en milieu vapeur d’eau hydrogénée à 400°C, 188 bar a confirmé la sensibilité de l’Alliage 82 en CSC avec une fissuration intergranulaire des joints de grains dont la particularité première est d’être perpendiculaire à la sollicitation (mode I). Les autres paramètres concernent celui de la chimie locale au niveau des joints de grains, de leur nature (généraux ou spéciaux) et du chargement mécanique appliqué à ces derniers (contrainte et différence de déformation). Cette méthodologie, applicable à d’autre matériau, a permis de mieux comprendre quels sont les paramètres microscopiques sensibilisent la cohésion du joint de grains et à quels degré d’importance doivent-il être pris en compte dans le mécanisme d’amorçage de fissures de CSC. / In Pressurize Water Reactors (PWR), Stress Corrosion Cracking (SCC) is the mean degradation mode of components pieced together by welding. Nickel based alloys are, among others, used in dissimilar metal welding (DMW). International report showed only 3 cracking cases in Alloy 82 out of 300 cracking cases concerned on nickel based alloys DMW in primary water circuit. The aim of this study is to identify which microstructural and local mechanism parameters at microstructure scale provide the initiation of SCC cracks. Characterizations performed on specimen surface to identify those parameters are composed ofchemical composition analysis and EBSD analysis (Electron Back-Scattered Diffraction) to know the morphology and the crystallography of grains for microstructure features on one hand, and experimental strain fields measured by Digital Imaging Correlation (DIC) of gold microgrids deposed by electronic lithography on U-bend specimen surface and stress fields calculated along grains boundaries by finite element for local mechanical features on the other hand. The correlation between those characterizations and localization of initiation sites of SCC cracks, obtained on U-bend specimens tested in autoclave in hydrogen steam water at 400°C and 188 bar for 3500 hours, confirmed the susceptibility of the Alloy 82 in SCC conditions with intergranular SCC cracks. The perpendicular position to the loading direction (mode I) is the worst conditions for grains boundary in SCC. The others points concern the chemical composition (precipitation, impurities) around grain boundary and the grain boundary type which is more susceptible when it is a High Angle Grain Boundary. It is following by the mechanical characterization (stress and strain gradient) along grain boundary. This methodology can be used to other material and helped to define which microstructural and mechanical parameter can be define the initiation of SCC cracks.

Unmanned Aerial Vehicles (UAV) have been heavily studied in the past decade, where autonomous flights have been a popular subject. More complex applications have led to higher requirements on the autonomous flight algorithms and the absence of performance data complicates the selection of what algorithm to use for various applications. Therefore, this thesis focused in analyzing the performance difference between two methods, Simultaneous Localization AndMapping (SLAM) and Artificial Potential Field Approach (APFA), which are planning and reactive algorithms, respectively. Fundamental dynamics were applied, Feedback Linear Controllers (FBLC)s for stabilization and an odometry position model combined with an inverse dynamics technique that linearizes the non-linear odometry model. The SLAM approach was set up in four steps: landmark extraction which uses a point distance based method for segment separation, combined with a Split-And-Merge algorithm for extracting linear landmarks, data association that validates the landmarks, Extended Kalman Filter (EKF) that uses the landmarks together with the odometry model for estimating the position of the UAV, and a modified TangentBug as the reactive algorithm. The APFA was constructed of two functions, an attractive and a repulsive function. The two methods were implemented on the robotics simulation platform Virtual Robot Experimentation Platform (V-REP), where a quadcopter was used as the model for the UAV. All theory was implemented onto the quadcopter model and embedded scripts were used for communication within V-REP, mainly through internal Application Programming Interface (API)-functions. Furthermore, a script was written that randomly generates three different types of simulation environments. The implementation of both methods was analyzed in reaching an arbitrary goal position in terms of: the most successful, the most time efficient and the safest navigation path. Another thing analyzed was the time- and space-complexity of both implemented methods. The results stated that the implemented APFA and the SLAM approach had approximately equal success rate, SLAM had the safest navigation, was the most time efficient, and had the highest time- and space-complexity for a worst case scenario. One of the conclusions were that improvements could be done in the implementations. Future work includes adding a proper damping method, improving the flaws in the implemented methods as well as to use V-REP as a Robot Operating System (ROS)-node for creating a Software In The Loop (SITL)-simulation, in order to achieve more realistic simulations.

Le dimensionnement en fatigue des composants de centrales nucléaires prend en compte l’influence de nombreux paramètres tels que l’état de surface, les effets d’échelle, la variabilité du matériau, … Afin d’optimiser ce dimensionnement, il est nécessaire de comprendre le rôle joué par ces différents facteurs et d’identifier leurs interactions potentielles avec le milieu eau primaire REP (Réacteur à Eau Pressurisée). Dans cette étude, l’influence de l’environnement sur un acier inoxydable austénitique 304L en fatigue oligocyclique, mise en évidence par des essais conduits sous vide, dans l’air et en milieu eau primaire REP, est analysée en fonction de l’état de surface initial (état poli ou meulé) et de la nature du signal de chargement considéré (signaux triangulaires à différentes vitesses de déformation ou signaux complexes représentatifs de chocs thermiques successifs rencontrés en service). Une diminution de la durée de vie et l’accélération de l’endommagement provoquées par le milieu eau primaire REP ont été constatées quels que soient l’état de surface ou le signal de chargement considérés. L’influence néfaste de l’état de surface meulé sur les durées de vie en fatigue est mise en évidence puis expliquée par des essais interrompus à l’aide d’analyses qualitatives et quantitatives de l’endommagement. L’importance de la géométrie des fissures est révélée par des observations fractographiques et sa prise en compte au sein de lois de propagation permet d’expliquer la réduction de durée de vie liée à l’état de surface meulé. Enfin, l’influence dela forme du signal sur le comportement cyclique, l’endommagement du matériau et les durées de vie est détaillée. L’influence du positionnement des parties à faible vitesse de déformation au sein des cycles de chargement complexes est analysée en prenant en compte le temps d’exposition des fissures à l’environnement. / The fatigue design of Pressurized Water Reactor (PWR) components takes into account many parameters suchas the surface finish, the scale effects, the material variability, etc. To optimise this design, it is necessary tounderstand the role of those parameters and to identify their possible interactions with PWR waterenvironment.This work is focused on the low cycle fatigue behaviour of a 304L austenitic stainless steel in threeenvironments, namely vacuum, air and PWR water, through fatigue lifetimes, cracking mechanisms and crackgrowth characterisations. In addition, the roles of both surface finish (polished or ground) and load signal form(triangular signals with different strain rates or complex signals representative of successive thermal shocks)were investigated.The PWR water environment causes a fatigue life reduction and a crack propagation rate enhancement,regardless of surface finish or load signal shape. The deleterious effect of ground surface finish observed onfatigue life is explained by means of interrupted tests through qualitative and quantitative damage analysis. Theimportance of the crack geometry is revealed by fractographic characterisations and its integration inpropagation laws is used to account for fatigue life reductions induced by ground surface finish. Finally thesignal shape effects on cyclic behaviour, damage kinetics and fatigue life are discussed. The influence of theposition of the low strain rate parts within a complex cycle is analysed taking into account the time of crackexposure to the environment.

Les génomes bactériens contiennent de nombreuses séquences répétées qui ont un rôle majeur dans la plasticité et l'évolution des génomes. Parmi elles, les séquences REP sont de courtes séquences d'ADN, trouvées en grand nombre dans des régions intergéniques de plusieurs espèces bactériennes. Ces séquences ont la particularité de présenter des structures en tige boucle précédées par un tétranucléotide conservé. Elles peuvent exister seules mais sont majoritairement groupées dans des clusters consécutifs appelés BIME. De nombreux rôles ont été attribués aux REP/BIME dans la physiologie de la cellule : elles sont notamment impliquées dans la régulation de l'expression des gènes et elles constituent des sites de fixation pour plusieurs protéines de l'hôte. Toutefois, leur origine et le mécanisme de leur dissémination dans les génomes ne sont pas connus. Récemment, un gène codant une protéine (TnpAREP) apparentée aux transposases de la famille des séquences d'insertions IS200/IS605 a été identifiée en association avec des REP/BIME au sein de structures appelées REPtron. Il a été alors proposé que les REP/BIME pourraient être des éléments transposables non-autonomes mobilisables par la protéine TnpAREP. Cette protéine fait partie de la superfamille des enzymes HuH comprenant des Relaxases, des protéines Rep des phages/plasmides à réplication en cercle roulant et certaines transposases. Elles utilisent le motif HuH (Histidine - résidu hydrophobe - Histidine) pour coordonner des cofacteurs métalliques ainsi que des résidus tyrosines pour leur activité catalytique. Comme pour les transposases HuH de la famille IS200/IS605, TnpAREP reconnait spécifiquement des substrats ADN simple brin. Elle est active in vitro sur des séquences structurées contenant des REP/BIME sous forme simple brin et celle-ci clive au niveau d'un dinucléotide spécifique. Des données cristallographiques suggèrent que TnpAREP serait monomérique, contrairement aux transposases d'IS200/IS605 qui sont des dimères obligatoires. Cela pose de nombreuses questions sur le site catalytique de l'enzyme ainsi que sur le mécanisme de prolifération des REP/BIME dans les génomes bactériens, d'autant plus qu'aucune activité de TnpAREP n'a été décrite in vivo. Mes premiers résultats portent sur la caractérisation du site catalytique de TnpAREP d'E. coli et ont permis d'exclure la possibilité d'un site catalytique hybride comme dans le cas des protéines Rep de certains plasmides. J'ai pu mettre en évidence une activité in vivo de TnpAREP : son expression sous contrôle d'un promoteur inductible à un effet toxique et induit la réponse SOS chez E. coli. J'ai également développé un test pour cartographier des sites de clivage de TnpAREP in vivo et montré que l'enzyme est capable de cliver les deux brins des plasmides et de l'ADN chromosomique. De plus, une excision d'un BIME a pu être observée dans ces conditions. J'ai aussi construit des souches bactériennes permettant d'étudier l'évolution expérimentale des REP/BIME in vivo dont les résultats sont en cours d'analyse. Enfin, nous avons élargi notre étude à un sous-groupe de TnpAREP associées à un autre type de REP/BIME. Cette analyse comparative nous a permis non seulement de généraliser des propriétés observées avec TnpAREP d'E. coli, mais aussi de révéler des caractéristiques spécifiques de ce sous-groupe. / In spite of their compact size, bacterial genomes carry many repetitive sequences, often important for genome function and evolution. Among them, REPs are short DNA found at high copy number in intergenic regions in many bacterial species. These sequences can form stem-loop structures preceded by a conserved tetranucleotide. They can exist as individual units but also as complex consecutive clusters called BIMEs. REP/BIMEs are known to interact with different proteins and several important roles have been attributed to these sequences in cell physiology. However, their origin and dissemination mechanisms are poorly understood. Recently, a first example of prokaryotic domesticated transposases (TnpAREP) was found associated with REP/BIME sequences in structure called REPtron. REP/BIMEs might represent a special type of non-autonomous transposable element mobilizable by TnpAREP. TnpAREP is member of the HuH enzymes superfamily including Relaxases, Rep proteins of RCR plasmids/ss phages and some transposases. These transposases are fundamentally different from classical transposases. They use HuH motif (Histidine-hydrophobe-Histidine) to coordinate metal cofactor and tyrosine residues (Y) as nucleophile for catalysis. TnpAREP shares certain similarities to Y1 HuH transposases encoded by the IS200/IS605 family which processes only ssDNA substrates. Analysis of E. coli TnpAREP activity in vitro also shown the strict requirement of structured single stranded REP/BIME DNA substrates. Cleavage in vitro occurs at a specific dinucleotide. In contrast to Y1 HuH transposases which are obligatory dimers, E. coli TnpAREP is a monomer as shown by structural studies. Furthermore, TnpAREP activities have never been described in vivo. This raises questions about its catalytic sites and also the way by which it promotes REP/BIME proliferation within their host genomes. The first objective of my PhD was to characterize the TnpAREP catalytic site. My results exclude the possibility of a second catalytic site as observed for REP protein of some plasmid families. Here I show that in vivo, expression of TnpAREP under control of an inducible external promoter is toxic to E. coli cells and induces SOS response, the effect depending on catalytic activity of the protein. I have developed an assay to map TnpAREP cleavage sites in vivo and show that it can cleave both DNA strands on plasmid and bacterial chromosome. In these conditions, an excision of BIME could be observed. I also constructed bacterial strains to perform REP/BIME experimental evolution, results are under analysis. Finally, we are extending our analysis to a subgroup of TnpAREP that are associated with another type of REP/BIME. This comparative analysis not only permitted to generalize some properties observed with E. coli TnpAREP but also revealed some interesting distinct characteristics of this subgroup.