abstract: This dissertation describes the work on two projects which involves measuring molecular conductance and studying their properties on the nanoscale using various Scanning Tunneling Microscopy (STM) techniques. The first molecule studied was a porphyrin-fullerene moiety known as a molecular Dyad for photovoltaic applications. This project is further divided into two section, the first one involving the characterization of the Dyad monolayers and conductance measurement in the dark. The Dyads are designed to form charge separated states on illumination. The lifetime of the charged states have been measured efficiently but the single-molecule conductance through the molecules have yet to be characterized. The second part of the project describes the set-up of a novel sample stage which enables the study of molecular conductance under illumination. This part also describes the subsequent study of the molecule under illumination and the observation of a unique charge-separated state. It also contains the verification of the presence of this charge-separated using other characterization techniques like transient absorption spectroscopy. The second project described in the dissertation was studying and comparing the predicted rectifying nature of two molecules, identical in every way except for one stereocenter. This project describes the formation of monolayers of the molecule on gold and then studying and analyzing the current-voltage characteristics of the molecules and looking for rectification. Both the molecules proved to be rectifying, one more than the other as predicted by theoretical calculations. / Dissertation/Thesis / Ph.D. Chemistry 2011

The first chapter considers the asymptotic validity of bootstrap methods in a linear trend model with a change in slope at an unknown time. Perron and Zhu (2005) analyzed the consistency, rate of convergence, and limiting distributions of the parameter estimates in this model. I provide theoretical results for the asymptotic validity of bootstrap methods related to forming confidence intervals for the break date. I consider two bootstrap schemes, the residual (for white noise errors) and the sieve bootstrap (for correlated errors). Simulation experiments confirm that confidence intervals obtained using bootstrap methods perform well in terms of exact coverage rate. The second chapter extends Perron and Zhu's (2005) analysis to cover more general fractionally integrated errors with memory parameter d in the interval (-0.5,1.5). My theoretical results uncover some interesting features. For example, with a concurrent level shift allowed, the rate of convergence of the estimate of the break date is the same for all values of d in the interval (-0.5,0.5), a feature linked to the contamination induced by allowing a level shift. In all other cases, the rate of convergence is decreasing as d increases. I also provide results about the spurious break issue. The third chapter considers constructing confidence intervals for the break date in linear regressions. I compare the performance of various procedures in terms of the exact coverage rates and lengths: Bai's (1997) based on the asymptotic distribution with shrinking shifts, Elliott and Müller's (EM) (2007) based on inverting a test locally invariant to the magnitude of the change, Eo and Morley's (2013) based on inverting a likelihood ratio test, and various bootstrap procedures. In terms of coverage rates, EM's approach is the best but with a high cost in terms of length. With serially correlated errors and a change in intercept or in the coefficient of a regressor with a high signal-to-noise ratio, or when a lagged dependent variable is present, the length approaches the whole sample as the magnitude of the change increases. This drawback is not present for the other methods. Theoretical results are provided to explain the drawbacks of EM's method.

abstract: Studying charge transport through single molecules tethered between two metal electrodes is of fundamental importance in molecular electronics. Over the years, a variety of methods have been developed in attempts of performing such measurements. However, the limitation of these techniques is still one of the factors that prohibit one from gaining a thorough understanding of single molecule junctions. Firstly, the time resolution of experiments is typically limited to milli to microseconds, while molecular dynamics simulations are carried out on the time scale of pico to nanoseconds. A huge gap therefore persists between the theory and the experiments. This thesis demonstrates a nanosecond scale measurement of the gold atomic contact breakdown process. A combined setup of DC and AC circuits is employed, where the AC circuit reveals interesting observations in nanosecond scale not previously seen using conventional DC circuits. The breakdown time of gold atomic contacts is determined to be faster than 0.1 ns and subtle atomic events are observed within nanoseconds. Furthermore, a new method based on the scanning tunneling microscope break junction (STM-BJ) technique is developed to rapidly record thousands of I-V curves from repeatedly formed single molecule junctions. 2-dimensional I-V and conductance-voltage (G-V) histograms constructed using the acquired data allow for more meaningful statistical analysis to single molecule I-V characteristics. The bias voltage adds an additional dimension to the conventional single molecule conductance measurement. This method also allows one to perform transition voltage spectra (TVS) for individual junctions and to study the correlation between the conductance and the tunneling barrier height. The variation of measured conductance values is found to be primarily determined by the poorly defined contact geometry between the molecule and metal electrodes, rather than the tunnel barrier height. In addition, the rapid I-V technique is also found useful in studying thermoelectric effect in single molecule junctions. When applying a temperature gradient between the STM tip and substrate in air, the offset current at zero bias in the I-V characteristics is a measure of thermoelectric current. The rapid I-V technique allows for statistical analysis of such offset current at different temperature gradients and thus the Seebeck coefficient of single molecule junctions is measured. Combining with single molecule TVS, the Seebeck coefficient is also found to be a measure of tunnel barrier height. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012

The frequency, magnitude, and atmospheric drivers of winter hydroclimatic conditions conducive to snowmelt in western Canada were evaluated. These hydroclimatic variables were linked to the mid-winter break-up of river ice that included the creation of a comprehensive database including 46 mid-winter river ice break-up events in western Canada (1950-2008) and six events in Alaska (1950-2014). Widespread increases in above-freezing temperatures and spatially diverse increases in rainfall were detected over the study period (1946-2012), particularly during January and March. Critical elevation zones representing the greatest rate of change were identified for major river basins. Specifically, low-elevation (500-1000 m) temperature changes dominated the Stikine, Nass, Skeena, and Fraser river basins and low to mid-elevation changes (700-1500 m) dominated the Peace, Athabasca, Saskatchewan, and Columbia river basins. The greatest increases in rainfall were seen below 700 m and between 1200-1900 m in the Fraser and at mid- to high-elevations (1500-2200 m) in the Peace, Athabasca, and Saskatchewan river basins. Daily synoptic-scale atmospheric circulation patterns were classified using Self-Organizing Maps (SOM) and corresponding hydroclimatic variables were evaluated. Frequency, persistence, and preferred shifts of identified synoptic types provided additional insight into characteristics of dominant atmospheric circulation patterns. Trend analyses revealed significant (p < 0.05) decreases in two dominant synoptic types: a ridge of high pressure over the Pacific Ocean and adjacent trough of low pressure over western Canada, which directs the movement of cold, dry air over the study region, and zonal flow with westerly flow from the Pacific Ocean over the study region. Conversely, trend analyses revealed an increase in the frequency and persistence of a ridge of high pressure over western Canada over the study period. However, step-change analysis revealed a decrease in zonal flows and an increase in the occurrence of high-pressure ridges over western Canada in 1977, coinciding with a shift to a positive Pacific Decadal Oscillation regime. A ridge of high pressure over western Canada was associated with a high frequency and magnitude of above-freezing temperatures and rainfall in the study region. This pattern is highly persistent and elicits a strong surface climate response. A ridge of high pressure and associated above-freezing temperatures and rainfall was also found to be the primary driver of mid-winter river ice break-up with rainfall being a stronger driver west of the Rocky Mountains and temperature to the east. These results improve our understanding of the drivers of threats to snowpack integrity and the generation of extreme hydrologic events. / Graduate

Esta dissertação, a partir da linha de pesquisa Estudos sobre Infâncias, propõe investigar e problematizar o modo como vivem e o que pensam as crianças entre nove e dez anos de idade sobre o seu recreio, ocorrido no interior de uma escola fundamental pública localizada na cidade de Porto Alegre. Trata-se, portanto, de uma Pesquisa com Crianças, na qual as falas, as ações, os questionamentos e as proposições dos alunos participantes da investigação envolvendo o seu recreio, constituem os dados produzidos e analisados por esta dissertação. A metodologia utilizada envolveu observação participante, conversas informais com os alunos no recreio, encontros sistemáticos em grupos fora do recreio e diário de campo. As contribuições de Corsaro (2009 e 2011), Kohan (2004 e 2008), Elias (1998), Frago e Escolano (2001 e 2005) e Bauman (1998, 2001, 2007, 2010 e 2011) constituíram-se no aporte teórico principal para a análise dos dados produzidos, pois possibilitaram questionar, discordar, mas também compreender os funcionamentos e a importância do recreio para estas crianças, tendo em vista que os tempos e os espaços do recreio são por elas pensados e vividos de modo singular, diferentemente do que é proposto pela escola fundamental. Através de histórias de reivindicação, insistência, resistência e (re)invenção, as crianças mostram aos adultos, os modos pelos quais se organizam e funcionam no interior dos seus recreios ao viverem suas infâncias, e, deste modo, esta dissertação intenciona também sensibilizar o adulto/educador ao problematizar os tempos e os espaços ao recreio destinados, visto que esta escolha realizada pela escola influencia na produção das múltiplas infâncias vividas por seus alunos. / This essay, in the realm of the Studies on Childhoods research line, aims to investigate and question the way children in the bracket age of nine to ten years old live and think their breaks in a Public Elementary School in the city of Porto Alegre, Rio Grande do Sul, Brazil. It is, therefore, a Research with Children, in which the speeches, the actions, the questions and propositions of the involved students about their break time, are part of the data produced and analyzed in this work. The methodology used here involved participant observation, informal talks with the students in their break time, systematic group meetings extra-break and a field journal. Contributions from Corsaro (2009 and 2011), Kohan (2004 and 2008), Elias (1998), Frago and Escolano (2001 and 2005) and Bauman (1998, 2001, 2007, 2010 and 2011) were the theoretical support to the analysis of the achieved data, enabling not only questionings, disagreements and agreements, but also the possibility of understanding the functioning and importance of the break to these children, owing to the fact that the times and spaces are thought and lived by them in a singular way, differently from what has been proposed by the Elementary School. Through stories of claims, insistence, opposition and (re)invention, children show adults the ways they organize themselves and work within their break time moments as they live their childhoods, and, thus, this work also aims to touch the adult/educator as it questions the granted times and spaces to the children, once this choice made by the school affects the development of the multiple childhoods lived by its students.

O objetivo desta Dissertação é analisar como determinadas práticas culturais, ocorridas no recreio escolar, atuam na produção e no tensionamento de processos de pertencimentos identitários juvenis. Foram observados jovens alunos de turmas de sexta, sétima e de oitava séries em sua rotina escolar no ano letivo de 2007, em uma escola municipal de ensino fundamental do município de São Leopoldo/RS. Foram consideradas suas diferentes maneiras de estar no recreio escolar, sejam através das múltiplas, simultâneas e às vezes descartáveis formas de sociabilidade, ou mesmo do fortalecimento de amizades. Os caminhos teórico-metodológicos para o estudo partiram de referenciais teóricos inscritos no campo dos Estudos Culturais e na etnografia pós-moderna, tendo nos diários de campo, na transcrição das conversas realizadas, bem como nos registros fotográficos, a base para a construção dos dados. Observou-se que, durante o momento do recreio escolar, esses jovens percorriam diferentes espaços da escola destinados a tal prática, transbordando conversas, respingando inconstâncias, contornando obstáculos, inundando espaços, compondo temporariamente lugares, como se fossem vitrinas dinâmicas que se dissolviam ao término do período destinado para se recrear. Os jovens observados constituíam grupos, comunidades fundidas por ideias, produzindo práticas, lugarizando espaços nos quais alguns sujeitos eram incluídos e/ou excluídos dentre seus pares. Nesse sentido, infere-se que o momento do recreio escolar, apesar de estar inserido num contexto institucionalizado, atrelado a um espaço específico e com tempo estabelecido, constitui-se em importante lugar de socialização, de tensionamentos, de processos de pertencimentos, que ultrapassam o espaço da sala de aula e do currículo formal, ou seja, através das práticas culturais ocorridas nesse período de recrear, pode-se observar um 'borramento de fronteiras', alguns 'escapes' que permeiam esse espaço/tempo, local de produção e fortalecimento de identidades. / The aim of this study is analyzing how specific cultural practices, occurred during break time in a school environment, may affect the production and the stressing points in teenagers' identity and membership processes. Sixth, seventh and eighth graders of an elementary public school in São Leopoldo/RS were observed during their school routine along the 2007 school term. Students' different postures during break time were analyzed, considering the multiple, simultaneous and sometimes dischargeable ways of sociability, or even of friendship enhancement. The theoretical and methodological paths taken in this study belong to the Sociocultural Studies field and to the Post-modern Ethnography. Data are constituted by field notes, transcription of conversations and photographic registers. It was observed that during break time these kids used different spaces of the school dedicated to such practice, overflowing colloquies, showing inconstancies, skirting obstacles, flooding spaces, temporarily occupying places, as if they were dynamic display windows that dissolved at the ending of the specific recreation time. The observed teenagers formed groups, communities formed by ideas, producing practices, and selecting arenas in which some individuals were included by or excluded from their peers. Thus, it is inferred that break time, although inserted in an institutionalized structure and related to the context of a specific space and with a defined duration, consists of an important arena for socialization, for stress, and for processes of social inclusion that are not limited to the classroom and the formal curriculum. In other words, it means that through the cultural practices occurred during break time a blurring of borders can be observed, as well as some escapes that permeate this space/time, an arena for the production of identities.

Rayons ionisants, dessiccation, ou encore métabolites secondaires exogènes sont autant de facteurs qui peuvent engendrer des dommages à l’ADN chez les bactéries du sol, notamment en provoquant la formation de cassures double-brin (DSB), préjudice majeur pour une cellule. Chez les procaryotes, l’évolution a sélectionné deux principaux mécanismes de réparation des DSB, à savoir la recombinaison homologue (RH) et le non-homologous end joining (NHEJ). La RH est un mécanisme quasi-ubiquiste dans le monde bactérien qui repose sur l’utilisation d’une copie intacte de la molécule endommagée comme matrice pour la réparation de la DSB. Contrairement à la RH, le NHEJ n’est présent que chez 20 à 25% des bactéries et est considéré comme un mécanisme mutagène puisque la réparation de la DSB se fait sans matrice homologue et peut entrainer l’ajout ou la délétion de nucléotides au site de cassure. Chez la bactérie modèle Mycobacterium, seuls deux acteurs sont nécessaires pour la réparation par NHEJ. Ainsi, un dimère de protéine Ku se fixe sur la cassure puis recrute la protéine multifonctionnelle LigD, qui catalyse le traitement puis la ligation des extrémités grâce à ses domaines polymérase, nucléase et ligase. Les mécanismes de réparation des DSB chez les Streptomyces étaient peu connus à l’initiation de ce travail. Cette bactérie présente des caractéristiques génomiques remarquables avec notamment un chromosome linéaire de grande taille (6 à 12 Mb). En ce qui concerne la RH, nous avons focalisé nos recherches sur les étapes tardives (post-synaptiques) et étudié le rôle du complexe RuvABC et de RecG impliqués chez Escherichia coli dans la migration de la croix de Holliday et de sa résolution. La construction de mutants simples et multiples a montré que bien que les gènes codant ces protéines soient très conservés chez les Streptomyces, leur déficience ne se traduit chez Streptomyces ambofaciens que par une faible baisse de la recombinaison suite à un événement de conjugaison. Aucune baisse de l’efficacité de recombinaison intrachromosomique n’a en revanche été observée. Ces résultats suggèrent que des acteurs alternatifs majeurs sont encore à découvrir chez les Streptomyces. Le décryptage du mécanisme de NHEJ chez S. ambofaciens constitue une première dans ce genre bactérien. Une étude génomique exhaustive a permis de révéler la très grande diversité du nombre d’acteurs potentiels de ce mécanisme (Ku, LigDom, PolDom, NucDom) et de l’organisation des gènes qui les codent.. L’analyse fonctionnelle a révélé que l’ensemble des acteurs étaient impliqués dans la réponse à l’exposition à un faisceau d’électrons accélérés, connus pour induire, entre autre, la formation de DSB. La génération de DSB, par coupure endonucléasique I-SceI, a par ailleurs permis de mettre en évidence au niveau moléculaire des réparations de type NHEJ (délétions ou insertions de quelques nucléotides, intégration de fragments d’ADN). Les cassures dans les régions terminales du chromosome sont accompagnées de grandes délétions (jusqu’à 2,1 Mb) et de réarrangements de grande ampleur incluant circularisations du chromosome et amplifications d’ADN. Les conséquences de la réparation de DSB chez S. ambofaciens sont en tous points similaires aux réarrangements observés spontanément ou par comparaison des génomes des espèces types. Ainsi, il est possible de lier la plasticité du génome à la réparation de DSB. En outre, l’intégration de matériel génétique exogène serait favorisée au cours de la réparation NHEJ ce qui donnerait à ce système de réparation une place importante dans le processus de transfert horizontal, mécanisme d’évolution majeur chez les bactéries / Ionizing radiation, desiccation or exogenous secondary metabolites are all factors that can cause DNA damage in soil bacteria, especially by triggering double strand breaks (DSB), the most detrimental harm for the cell. In prokaryotes, evolution selected two main DSB repair pathways, namely homologous recombination (HR) and non-homologous end joining (NHEJ). HR is almost ubiquitous in bacteria and relies on an intact copy of the damaged DNA molecule as a template for DSB repair. In contrast to HR, NHEJ is only present in 20 to 25% of bacteria and is considered as a mutagenic pathway since DSB repair is performed without the need of any template and can lead to nucleotide addition or deletion at DSB site. In the bacterial model Mycobacterium, two partners are sufficient for a functional NHEJ pathway. Thus, Ku protein dimer recognizes and binds the DSB and then recruits the multifunctional LigD protein for extremities treatment and ligation thanks to its polymerase, nuclease and ligase domains. At the beginning of this work, few informations on DSB repair in Streptomyces were available. This bacteria exhibits remarkable genomic features including a large linear chromosome (6 to 12 Mb). Regarding HR, we focused on the late stage (post-synaptic step) in studying the role of RuvABC complex and RecG, involved in branch migration and Holliday junction resolution in E. coli. Construction of single and multiple mutants showed that although the genes encoding these proteins are highly conserved in Streptomyces, their deficiency in Streptomyces ambofaciens only results in a mild decrease of recombination after conjugation events. Besides, no decrease of intrachromosomal recombination efficiency could be observed. These results suggest that major alternative factors are still to be discovered in Streptomyces. This work was also the first occasion to decipher a NHEJ pathway in Streptomyces. An exhaustive genomic study revealed a great diversity in the number of factors potentially implicated in this pathway (Ku, LigDom, PolDom, NucDom) and in the organization of their encoding genes. Functional analyses revealed that all the factors, whatever they are conserved or not between species, were involved in the response to electron beam exposure, known to induce, amongst other things, DSB formation. Generation of DSB by I-SceI endonuclease cleavage was also used to evidence at a molecular level NHEJ type DSB repair (deletions or insertions of several nucleotides, integration of DNA fragments). Targeted breaks in the terminal regions of the chromosome were accompanied by large deletions (up to 2.1 Mb) and major rearrangements including chromosome circularizations and DNA amplifications. Consequences of DSB repair in S. ambofaciens are in all points similar to chromosome rearrangements observed spontaneously or by comparing genomes of different species. Thus, it is possible to link the genome plasticity to DSB repair. In addition, the integration of exogenous genetic material would be favoured during NHEJ repair which would give this repair system a major role in the horizontal transfer process, known to be a main evolution mechanism in bacteria

O objetivo desta Dissertação é analisar como determinadas práticas culturais, ocorridas no recreio escolar, atuam na produção e no tensionamento de processos de pertencimentos identitários juvenis. Foram observados jovens alunos de turmas de sexta, sétima e de oitava séries em sua rotina escolar no ano letivo de 2007, em uma escola municipal de ensino fundamental do município de São Leopoldo/RS. Foram consideradas suas diferentes maneiras de estar no recreio escolar, sejam através das múltiplas, simultâneas e às vezes descartáveis formas de sociabilidade, ou mesmo do fortalecimento de amizades. Os caminhos teórico-metodológicos para o estudo partiram de referenciais teóricos inscritos no campo dos Estudos Culturais e na etnografia pós-moderna, tendo nos diários de campo, na transcrição das conversas realizadas, bem como nos registros fotográficos, a base para a construção dos dados. Observou-se que, durante o momento do recreio escolar, esses jovens percorriam diferentes espaços da escola destinados a tal prática, transbordando conversas, respingando inconstâncias, contornando obstáculos, inundando espaços, compondo temporariamente lugares, como se fossem vitrinas dinâmicas que se dissolviam ao término do período destinado para se recrear. Os jovens observados constituíam grupos, comunidades fundidas por ideias, produzindo práticas, lugarizando espaços nos quais alguns sujeitos eram incluídos e/ou excluídos dentre seus pares. Nesse sentido, infere-se que o momento do recreio escolar, apesar de estar inserido num contexto institucionalizado, atrelado a um espaço específico e com tempo estabelecido, constitui-se em importante lugar de socialização, de tensionamentos, de processos de pertencimentos, que ultrapassam o espaço da sala de aula e do currículo formal, ou seja, através das práticas culturais ocorridas nesse período de recrear, pode-se observar um 'borramento de fronteiras', alguns 'escapes' que permeiam esse espaço/tempo, local de produção e fortalecimento de identidades. / The aim of this study is analyzing how specific cultural practices, occurred during break time in a school environment, may affect the production and the stressing points in teenagers' identity and membership processes. Sixth, seventh and eighth graders of an elementary public school in São Leopoldo/RS were observed during their school routine along the 2007 school term. Students' different postures during break time were analyzed, considering the multiple, simultaneous and sometimes dischargeable ways of sociability, or even of friendship enhancement. The theoretical and methodological paths taken in this study belong to the Sociocultural Studies field and to the Post-modern Ethnography. Data are constituted by field notes, transcription of conversations and photographic registers. It was observed that during break time these kids used different spaces of the school dedicated to such practice, overflowing colloquies, showing inconstancies, skirting obstacles, flooding spaces, temporarily occupying places, as if they were dynamic display windows that dissolved at the ending of the specific recreation time. The observed teenagers formed groups, communities formed by ideas, producing practices, and selecting arenas in which some individuals were included by or excluded from their peers. Thus, it is inferred that break time, although inserted in an institutionalized structure and related to the context of a specific space and with a defined duration, consists of an important arena for socialization, for stress, and for processes of social inclusion that are not limited to the classroom and the formal curriculum. In other words, it means that through the cultural practices occurred during break time a blurring of borders can be observed, as well as some escapes that permeate this space/time, an arena for the production of identities.

Depuis sa première adoption en 1990, la politique de ciblage de l'inflation est devenue la politique monétaire la plus adoptée par les banques centrales aussi bien dans les économies développées ou émergentes. Cette priorité stratégique des autorités monétaires nous a conduits à réfléchir sur l'efficacité de ce choix. L'objectif de cette thèse est alors étudier la performance économique de cette politique économique surtout en cas de ruptures structurelles. Le premier chapitre présente l'approche théorique de ce travail en mettant l'accent sur ce débat de performance et l'intérêt à adopter cette politique de ciblage d'inflation afin de maitriser sa volatilité. L'approche empirique de cette thèse cherche à vérifier la performance de ce passage. Le second chapitre traduit l'efficacité du nouveau régime en étudiant son effet sur la dynamique de l'inflation, la croissance et certains indicateurs agissant sur la conjoncture macroéconomique. Ce travail explore également l'existence des différents points de ruptures structurelles. Le troisième chapitre illustre l'existence de ces dates de changement correspondant au changement de régime. La présente étude montre d'un côté qu'il y a performance économique suite au changement de régime. D'un autre côté, les résultats prouvent l'existence de multitude points de changement de rupture structurelle qui coïncident avec la mise en œuvre de la nouvelle politique de ciblage d'inflation. / Since its first introduction in 1990, the policy of inflation targeting has become the most adopted monetary policy by central banks in both developed and emerging economies. This strategic priority of monetary policy has led us to think the effectiveness of this choice. The objective of this thesis is then to study the economic performance of this economic policy especially in the case of structural interruptions. The first chapter presents the theoretical approach of this work focusing on performance and the necessity of adopting this policy in order to control its volatility. The empirical approach of this thesis aims to verify the performance of this transition. The second chapter shows the effectiveness of the new system by studying its effect on the inflation dynamics, the growth and indicators which affect the macroeconomic environment. This work also explores the existence of different points of structural interruptions. The third chapter illustrates the existence of these date changes corresponding to the regime switching. The present study reveals on one side that there is economic performance following the regime change. On the other hand, the results confirm the existence of many structural break points which coincide with the implementation of the new policy of inflation targeting.

Made available in DSpace on 2014-06-11T19:23:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-12-02Bitstream added on 2014-06-13T18:50:59Z : No. of bitstreams: 1 leite_lob_me_ilha.pdf: 7876959 bytes, checksum: 679218273f75952f4df0237622251b57 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Rompimentos de Barreira são fenômenos caracterizados por um campo de escoamento inicialmente represado e submetido nos instantes subseqüentes a uma liberação abrupta. Diversos modelos matemáticos e leis de comportamento reológico podem ser associados a este problema e cada um deles deve ser estudado e compreendido de maneira a predizer, a partir de testes físicos e numéricos, sua adequação à descrição da evolução espaço-temporal de frentes resultantes deste fenômeno, tipo ruptura de barragem, retendo água , rejeitos ou materiais de reologia complexa. O desenvolvimento de técnicas analíticas possibilitou entender de maneira impar o desenvolvimento desses fenômenos, porém, a difícil obtenção de dados que alcançassem consonância com aqueles obtidos experimentalmente, demonstrava a fragilidade desse tipo de análise perante a descrição de sistemas dinâmicos complexos. Sendo assim, optou-se pela tentativa de recriar estes fenômenos a partir de técnicas que utilizassem a manipulação de equações governantes completas. Sistemas contínuos podem ser analisados através de aproximações discretas, resultando em valores realísticos, muito próximos aos obtidos experimentalmente, e a capacidade computacional atual, permite diminuir sensivelmente os erros envolvidos, aumentando cada vez mais a consistência física destes métodos. Neste trabalho utilizou-se o software comercial ANSYS-CFX para simular os fenômenos de ruptura de barreira, configurando a reologia de dois materiais, o Carbopol 940 representando um material de reologia complexa (Herschel-Bulkley) e o Glicerol (Newtoniano), esses dados foram então confrontados com os obtidos experimentalmente através de um modelo em escala reduzida. Campos de velocidade, pressão e evolução temporal das frentes foram analisadas, verificando-se valores com grande consonância entre numérico e experimental, mostrando uma grande consistência física dos métodos utilizados / The Dam Break problem is a phenomenon characterized by a flow field initially dammed and submitted in the subsequent moments of an abrupt release. Various mathematical models and laws of rheological behavior may be associated with this type of problem and each must be studied and understood in order to predict from physical and numerical tests the temporal evolution of their fronts resulting from this phenomenon, type Dan Break problems, retaining water or rheology complex materials. The development of analytical techniques enabled the understanding the development of these phenomena, however, the difficulty to obtain a reach agreement data with those obtained experimentally, showed the fragility of this type of analysis to the description of complex dynamic systems. But, it was decided by attempt of recreate these phenomena from techniques that use the manipulation of complete government equations. Continuous systems can be analyzed by discrete approximations, leading to realistic values, very close to those obtained experimentally, and current computational capacity, enables to reduce the errors involved significantly, increasing the consistency of these physical methods. This work used the commercial software ANSYSCFX to simulate the phenomena of breaking the barrier, setting the rheology of two materials, the Carbopol 940 representing a material of complex rheology (Herschel-Bulkley) and glycerol (Newtonian), these data were then compared with those obtained experimentally using a model in scale. Fields of velocity, pressure and temporal evolution of the fronts were analyzed. Found very similar values between numerical and experimental simulations, showing the physical consistency of the methods used