La thèse s’inscrit dans le contexte de sûreté nucléaire relatif à l'hydruration des gainages combustibles en Zircaloy, en modélisant, à l’échelle atomique, les phénomènes d’ordre chimique hydrogène - lacune atomique, sur le sous-réseau interstitiel tétraédrique des hydrures de zirconium CFC. Une telle démarche s’est déclinée en deux étapes : en premier lieu, le développement d’un modèle énergétique atomistique à la fois précis et peu coûteux numériquement, puis l’implémentation d’approches thermostatistiques de type Monte-Carlo à l’aide de ce modèle. En prenant pour point de départ un Hamiltonien de Liaisons Fortes (TB), la construction du modèle énergétique a reposé sur la dérivation d’interactions multiatomiques entre atomes d’hydrogène, à l’aide de la méthode des perturbations généralisée (GPM) basée sur une représentation de l’état de désordre interstitiel dans l’Approximation du Potentiel Cohérent (CPA). La démarche a permis de réduire l'énergie d'ordre à un modèle d'Ising effectif dérivé des liaisons fortes (TBIM), basé sur les interactions de paires effectives entre atomes d’hydrogène. Le TBIM a ensuite été validé, en comparant les énergies de structures ordonnées d’une part reconstruites en TBIM, et d’autre part obtenues par des calculs directs d’énergie totale effectués soit en Liaisons Fortes, soit par des méthodes ab initio (DFT). L'implémentation d'une approche Monte-Carlo canonique par le TBIM a permis de caractériser les différentes transitions ordre-désordre, et d'établir un diagramme de phase de l’ordre chimique hydrogène - lacune atomique, sur le sous-réseau interstitiel tétraédrique des hydrures de zirconium CFC. / The thesis addresses the nuclear safety issue of Zircaloy fuel cladding hydruration, by modelling, at atomistic scale, chemical ordering processes between hydrogen and atomic vacancies on tetrahedral interstitial sublattice of CFC zirconium hydrides. This has been achieved into two steps : first the development of an atomistic energetic model sufficiently precise and not too much CPU time consuming, and secondly its implementation in Monte-Carlo thermostatistical simulations. Starting from a Tight-Binding (TB) Hamiltonian, the energetic model has been derived from the calculation of multiatomic interactions between hydrogen atoms, using the Generalized Perturbation Method (GPM) applied to an interstitial disorder described within the Coherent Potential Approximation (CPA). The path allows us to reduce the ordering energy to a Tight-Binding Ising Model (TBIM), based on effective pairwise interactions between hydrogen atoms. The TBIM has been validated by comparing ordering energies of ordered structures either reconstructed using TBIM, or directly obtained from total energy calculations perfor- med both within TB and ab initio (DFT) methods.By implementing a canonical Monte-Carlo with TBIM, we obtain different order-disorder phase transitions, and a phase diagram of H-vacancy chemical ordering, on the tetrahedral interstitial sublattice of CFC zirconium hydrides.

Foi feito o estudo da propagação de pulsos laser através de um sistema amplificador de pulsos ultracurtos com meios dispersivos e modificadores de banda espectral. Deu-se ênfase à concepção de um alargador (ou alongador) de pulsos ultracurtos para substituir o já existente no sistema CPA híbrido de Ti:Safira/Cr:LiSAF em operação no Centro de Lasers e Aplicações do IPEN/CNEN-SP. Fez-se o desenvolvimento teórico e o estudo de um alongador temporal do tipo Öffner, livre de aberrações esféricas, objetivando obter uma razão de alargamento superior à existente no sistema em operação. Estudou-se também a influência das componentes de fase do sistema na duração final dos pulsos amplificados, e o sistema atual teve seus componentes limitantes de largura de banda mapeados, com o objetivo de conhecer as condições nas quais um novo alongador temporal deve ser inserido no sistema. Com base nessas medidas, foram implementadas rotinas computacionais para se determinar as consequências da passagem de um pulso por um componente limitante de largura de banda. / The study of laser pulses propagation through an ultrashort pulses amplifying system containing dispersive and spectral modifying media was performed. The study emphasis was the development of an ultrashort pulse stretcher to replace the one inside a hybrid Ti:Sapphire/Cr:LiSAF CPA system operating at the Center for Lasers and Applications at IPEN/CNEN-SP. A spherical aberration free Öffner stretcher was theoretically studied, aiming to obtain a stretching ratio larger than the one available in our system. The influence of the phase components in the amplified pulse final duration was also studied, and the bandwidth limiting elements of the system in operation were mapped, with the purpose of determining the conditions under which a new stretcher should be implemented. Based on the actual measurements, computing routines were implemented in order to determine the consequences of an ultrashort pulse travelling through a bandwidth limiting component.

Foi feito o estudo da propagação de pulsos laser através de um sistema amplificador de pulsos ultracurtos com meios dispersivos e modificadores de banda espectral. Deu-se ênfase à concepção de um alargador (ou alongador) de pulsos ultracurtos para substituir o já existente no sistema CPA híbrido de Ti:Safira/Cr:LiSAF em operação no Centro de Lasers e Aplicações do IPEN/CNEN-SP. Fez-se o desenvolvimento teórico e o estudo de um alongador temporal do tipo Öffner, livre de aberrações esféricas, objetivando obter uma razão de alargamento superior à existente no sistema em operação. Estudou-se também a influência das componentes de fase do sistema na duração final dos pulsos amplificados, e o sistema atual teve seus componentes limitantes de largura de banda mapeados, com o objetivo de conhecer as condições nas quais um novo alongador temporal deve ser inserido no sistema. Com base nessas medidas, foram implementadas rotinas computacionais para se determinar as consequências da passagem de um pulso por um componente limitante de largura de banda. / The study of laser pulses propagation through an ultrashort pulses amplifying system containing dispersive and spectral modifying media was performed. The study emphasis was the development of an ultrashort pulse stretcher to replace the one inside a hybrid Ti:Sapphire/Cr:LiSAF CPA system operating at the Center for Lasers and Applications at IPEN/CNEN-SP. A spherical aberration free Öffner stretcher was theoretically studied, aiming to obtain a stretching ratio larger than the one available in our system. The influence of the phase components in the amplified pulse final duration was also studied, and the bandwidth limiting elements of the system in operation were mapped, with the purpose of determining the conditions under which a new stretcher should be implemented. Based on the actual measurements, computing routines were implemented in order to determine the consequences of an ultrashort pulse travelling through a bandwidth limiting component.

Accounting professors will now be accountable for teaching their students to think critically, analyze, and evaluate information. The pressure to change accounting higher education cannot be ignored with the new version of the CPA exam, released in April 2017, which now tests analysis and evaluation skills. Have the professors made the changes in their classrooms that will help their students to be successful with this format of questioning? This research seeks to find whether professors have indeed embraced pedagogy that will enhance students’ ability to develop higher order thinking skills. The study begins by explaining changes to the CPA exam. The study provides literature review of the accounting education process, traditional methods of teaching accounting, suggested methods of teaching accounting for enhancement of critical thinking, and identified reasons for resistance to changing teaching methods. The survey is designed to identify current teaching methods in accounting classrooms. The survey seeks to discover what methods are being used to develop higher order thinking skills. The results show that lecture and demonstration of problems are still the predominant method of instruction in accounting classrooms, and these methods are not typically endorsed by research in terms of developing critical thinking, analysis and evaluation skills.

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The cooperativism executed in the CPA (Land-production Cooperatives), stimulated by the MST (Movimento dos Trabalhadores Rurais Sem Terra Movement of Landless Workers), where possession of land and production are under the control of the cooperative, represents a model which is scarcely employed and, throughout the years these CPAs presented internal conflicts among some of its members, that preferred to work individually. The goal of this research is to analyze the subjectivity of rural settlement members located in the county of Charqueadas (RS), divided in two groups: i) those that are working under the integral perspective, (CPA) and ii) those who choose to work individually. The idea was to know the general point of view of these groups in relation to the individual and collective use of land. For this, we used the Q methodology that combines qualitative techniques such as in-depth interviews and qualified informers and quantitative techniques such as factorial statistical analyses of data. In the implementation of the methodology people were interviewed as qualified informers, where the most important set of 41 statements were selected and presented to 40 members of the rural settlement, divided between 20 from the integral model (CPA) and 20 from the individual model. The 41 statements were classified according to their importance in a pre-determined table and the data was analyzed and interpreted using a special statistical software program called PCQ. The results of the factorial analysis show that 5 factors emerged: i) one factor completely in favor of the individual approach, and ii) four factors in favor of collective approaches, with differences among them. In this sense, one factor was completely pro collective, and three factors were pro collective but with criticism to the model. According to the affirmations, the pro individual group believes the CPA experience was a mistake. For the other 4 pro collective groups, 1 of them was satisfied with the organization, and the other 3 groups demonstrated criticism and safeguard to collective model. The pro collective group and the pro individual group selected the same statements but were ranked inversely. It was also observed that in the other three collective groups there were insatisfactions in some aspects of the functioning of the CPA and that improvements could be made in these areas: i) solidarity among members, ii) inducement and centralization in the decision making process, and iii) encouragement to productivity. / O cooperativismo praticado nas CPA (Cooperativas de Produção Agropecuária) estimuladas pelo MST (Movimento dos Trabalhadores rurais Sem Terra), onde a posse da terra e a organização da produção estão sob controle da cooperativa, representa um modelo de assentamento pouco praticado, e com o passar dos anos as CPAs existentes enfrentaram conflitos como desagregações e divisões no quadro de associados, com uma parcela preferindo trabalhar individualmente. O objetivo desta pesquisa é analisar a subjetividade dos assentados no município de Charqueadas - RS, que estão divididos entre dois grupos: i) os que produzem coletivamente em uma CPA e ii) os atuais individuais que preferiram sair da mesma. A idéia foi saber o ponto de vista destes grupos sobre o modelo coletivo e individualizado de produção da terra. Para isso empregando a metodologia Q, a qual combina técnicas qualitativas como entrevistas em profundidade com informantes qualificados e técnicas quantitativas como as análises estatísticas do tipo fatorial sobre os dados. Na execução da metodologia foram entrevistados informantes qualificados de onde foram selecionadas as 41 afirmações mais importantes, apresentadas a uma amostra de 40 assentados, divididos entre 20 que estão no coletivo e 20 que passaram a trabalhar individualmente. As 41 afirmações foram classificadas de acordo com sua importância em uma grade pré-estabelecida e suas respostas foram analisadas e interpretadas mediante um programa estatístico especial de software chamado PCQ. Os resultados da análise fatorial mostram que 5 fatores emergiram: i) um fator totalmente favorável ao modo de trabalho individual, e ii) quatro fatores favoráveis ao modo de trabalho coletivo, mas com diferenças entre estes. Neste sentido, um fator totalmente favorável ao modo de trabalho coletivo e os outros três fatores coletivos, porém com críticas ao modelo. Pelas afirmações selecionadas, para o grupo do fator favorável ao trabalho individual a experiência na CPA foi um engano. Para os outros 4 grupos favoráveis ao trabalho coletivo, 1 totalmente pró-coletivo está muito satisfeito pela organização e conquistas adquiridas, e outros 3 grupos apresentam críticas e ressalvas ao coletivismo. O grupo favorável ao trabalho individual e o grupo totalmente prócoletivo selecionaram as mesmas afirmações, porém selecionadas completamente inversas sobre as que mais concordam e mais discordam. Foi constatado nos outros 3 grupos favoráveis ao coletivo que existem insatisfações em alguns aspectos no funcionamento da CPA e que poderiam ser melhorados como: i) maior solidariedade entre membros, ii) sobre decisões, alguns consideraram que as vezes ocorrem processos de induções e centralização na administração, e iii) um incentivo a produtividade.

La demande en énergies fossiles a connu une forte croissance au cours du vingtième siècle et représente aujourd'hui 80% de la consommation énergétique mondiale. Pour répondre à la demande, les industries pétrolières et gazières s'orientent vers de nouvelles sources. 40% des réserves de gaz contiennent un pourcentage important (jusqu'à 20%) de gaz acides (dioxyde de carbone et sulfure d'hydrogène). La production de ces gaz à forte teneur en gaz acides représente un défi pour les industries, étant donné la toxicité du sulfure d'hydrogène et la forte probabilité de corrosion des pipelines en présence d'eau (naturellement produite avec le gaz naturel). D'autre part, l'utilisation des énergies fossiles conduit au changement climatique avec des émissions importantes de dioxyde de carbone dans l'atmosphère. Le captage et le stockage du CO2 semble être un procédé prometteur. De l'eau est souvent présente lors du transport du gaz naturel et du CO2 capturé. Lors des étapes de production et de transport, les conditions de température et de pression sont sujettes au changement. La condensation de l'eau (à l'origine de la corrosion et donc d'une rupture possible des pipelines) et à la formation de glace et/ou d'hydrates en sont les conséquences principales. Or la formation d'hydrates est un sérieux problème avec un risque de blocage des pipelines. Pour éviter la formation des hydrates, des inhibiteurs chimiques sont utilisés. Il est donc indispensable de bien connaitre les équilibres entre phases pour les différents mélanges considérés pour un fonctionnement et une production en toute sécurité. / The twentieth century has seen an important increase of the fossil energy demand, representing today 80% of world energy consumption. To meet the request, oil and gas companies are interested in new gas fields. 40% of these reserves are acid and sour gases, i.e. the percentage of carbon dioxide and hydrogen sulphide is significant, sometimes over 20% of CO2 or H2S. Natural gas production with high content of acid gases can be a challenge, due to their corrosiveness potential in pipelines in the presence of water and H2S toxicity. On another hand, as a result of world's dependence on fossil energies, the release of carbon into atmosphere is increasing and leads to climate changes. Carbon Capture and Storage (CCS) is one of the most promising ways to reduce CO2 emissions in the atmosphere. Whether in natural gas or carbon dioxide transport, water may be present. During production, transportation and processing, changes in temperature and pressure can lead to water condensation (cause of corrosion, and consequently a possible pipeline rupture), ice and/or gas hydrates formation. Hydrates are a serious flow assurance problem and may block pipelines. To avoid hydrates formation, chemical inhibitors are used. Therefore accurate knowledge of mixtures phase equilibria are important for safe operation of pipelines and production/processing facilities.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Experimental data show that the dissolved impurities of the Mn presents a magnetic moment when substitute the Ni atom in pseudoquaternary borocarbide Y (Ni(1−x)Mx)2B2C, this is not observed if the impurities are Fe and Co. In this work we do a theoretical study of the superconducting order parameter variation and a possible formation of impurities magnetic moment to T < Tc. We have used the LAPW method, based in Density Functional Theory, to calculate the density of state of pure compound. To describe the superconductor system it was used the attractive Hubbard model. To describe the effects of the disorder induced by the dissolved impurities was used the coherent potential approximation. Using the Nambu s formalism to represent the Hamiltonian and the Green s functions of the effective medium (g) and of the perturbed system (G), we calculate the magnetic moment of the impurities from the diagonal terms and the variation of the order parameter from the off-diagonal one. The calculated date to magnetic moment show a qualitative agreement with the experimental results to Mn impurities. To the Fe and Co cases no magnetic moment was observed, in agreement with the experimental results too. The calculated order parameter shows a decrease with concentration to the Mn and Fe atoms. We investigate, through of the a calculation first principles (LAPW), the possible formation of the magnetic moment in this compound to concentration of 25 and 12.5%. The obtained results show that to concentration of 25%, both the impurities, Mn and Fe, presents a magnetic moment. The magnetization on the Co site was small when compared with the above cases. In this way we conclude that the Co atom not present a magnetic moment in this system. / Medidas experimentais mostram que impurezas de Mn formam momento magnético quando substituem o Ni no borocarbeto pseudoquaternário Y (Ni(1−x)Mx)2B2C, enquanto que as impurezas de Fe e de Co não exibem tal comportamento. Neste trabalho foi feito um estudo teórico da variação do parâmetro de ordem supercondutor e da possível formação de momento magnético nos sítios dessas impurezas para T < Tc. Para isso, utilizamos o m´etodo LAPW, baseado na Teoria do Funcional da Densidade, para calcular a densidade de estados do composto puro. Para descrever o sistema supercondutor foi utilizado o modelo de Hubbard atrativo. Os efeitos de desordem induzidos pela adição de impurezas de metais de transição M no material, foram tratados dentro da aproximação do potencial coerente. Usando o formalismo de Nambu para representar o hamiltoniano e as funções de Green associadas aos propagadores do sistema efetivo (g) e do sistema perturbado (G), calculamos o momento magn´etico das impurezas através dos termos diagonais e as variações do parâmetro de ordem efetivo a partir do termo fora da diagonal. Os resultados obtidos comprovam o que é observado experimentalmente, ou seja, o Mn forma momento magn´etico que aumenta com a concentração, enquanto que nas impurezas de Fe e Co nenhuma magnetização foi observada. Além disso, o parâmetro de ordem diminui com a concentração de Mn e Fe. Além desse estudo, também investigamos, através de um cálculo de primeiros princípios (LAPW), a possível formação de momento magnético neste composto para concentrações de 25 e 12.5%. Os resultados obtidos mostraram que para x = 25%, tanto as impurezas de Mn quanto as de Fe, apresentaram um momento magnético. A magnetização no síıtio do Co foi bastante pequena comparada com as duas anteriores e dessa forma pode-se concluir que esta impureza não forma momento quando diluída neste sistema.

Dans les applications industrielles et lors des opérations de transport du gaz naturel, la présence d'eau sous forme liquide ou en phase vapeur peut entraîner la formation d'hydrates provoquant le colmatage des unités industrielles et des lignes de conduites et il est indispensable de définir précisément les seuils de déshydratation à réaliser, afin d'éviter la formation d'hydrates. Cela est réalisé à l'aide d'un modèle thermodynamique qui prédit la stabilité des hydrates, en fonction de la température, de la pression et de la composition du gaz.Les modèles thermodynamiques classiques, développés uniquement sur la base de données expérimentales de formation d'hydrates en présence d'eau liquide, surestiment fortement la température de dissociation des hydrates en l'absence d'une phase aqueuse.Dans le but de définir un modèle thermodynamique capable de représenter convenablement les équilibres de phases vapeur-hydrate et prédire ainsi la température de dissociation des hydrates que l'on soit en présence ou en l'absence d'eau liquide, nous avons mis au point une méthodologie originale pour la détermination de la température de dissociation des hydrates de corps purs et de mélanges en l'absence d'eau liquide. Cette méthodologie, basée sur le suivi de la teneur en eau de phase vapeur, en fonction de la température par coulométrie Karl Fischer, a permis la détermination de la température de dissociation de plusieurs hydrates simples et mixtes à des teneurs en eau et pressions différentes ainsi que les quantités d'hydrates formées dans ces conditions.Sur la base de ces nouvelles données, nous avons défini un modèle thermodynamique basé sur l'utilisation de l'approche de Dharmawardhana pour le calcul de la fugacité de l'eau dans l'hydrate vide,le potentiel de Kihara pour le calcul de la constante de Langmuir et l'équation d'état CPA (Cubic Plus Association) pour la modélisation des phases fluides. Nous avons montré que l'utilisation de l'équation d'état CPA, capable de prendre en compte l'auto association de l'eau apporte une amélioration très significative.Le développement d'un flash biphasique hydrate-fluide nous a permis de calculer les quantités d'hydrates mixtes formées et de les comparer à nos données expérimentales. / In industrial applications and during natural gas transport, the presence of water under liquid form or within a vapour phase can lead to gas hydrate formation causing the blockage of industrial units and transport lines. Hence, in order to avoid such situation, it is very important to well determine its formation conditions. It is occurred by using a rigorous thermodynamic model. Due to the lack of data in the literature concerning gas hydrates formation in the absence of an aqueous phase,usual thermodynamic models predict correctly gas hydrate dissociation temperature only in the presence of aqueous water. Our purpose is to propose a thermodynamic model with hydrate phase that can predict gas hydrate dissociation temperature in both cases: with and without water liquid phase.At first, using an existing apparatus, we have developed a new experimental protocol in order tomeasure gas hydrate dissociation temperature in the absence of liquid water. It consists in measuring the water content in the vapour phase as a function of the temperature by using a Karl Fischer coulometer. We have measured the dissociation temperature of many simple and mixture hydrates.We have also developed a thermodynamic model that is able to predict correctly gas hydrate dissociation temperature, in the absence and in the presence of liquid water. This model is based onthe use of Dharmawardhana's approach for the calculation of hydrate fugacity in the empty hypothetical hydrate, Kihara potential for the calculation of the Langmuir constant and CPA EoS forfluid phases modelling. We have shown that the use of CPA EoS improves the prediction of gas hydrate dissociation temperature. We have also developed a biphasic flash (hydrate-fluid) allowing the calculation of the formed mixture hydrate amounts. The calculated amounts are in agreement with the experimental ones.

Es wird eine selbstkonsistente, approximative L\"osung f\"ur das verd\"unnte, ungeordnete Kondo-Gitter-Modell (KLM) vorgeschlagen, um die miteinander verkn\"upften elektronischen und magnetischen Eigenschaften von sogenannten ''local moment''-Systemen wie den verd\"unnten magnetischen Halbleitern zu diskutieren. Untersucht werden Verbindungen der Form $A_{1-x}M_x$, in denen magnetische ($M$) und nicht-magnetische Atome ($A$) statistisch \"uber das Kristallgitter verteilt sind. Die Kopplung zwischen den lokalisierten Momente und den quasi-freien Elektronen (L\"ocher) wird im Rahmen einer modifizierten RKKY-Theorie behandelt, die das KLM auf ein effektives Heisenberg-Modell abbildet. Die Unordnungen in dem elektronischen Teilsystem und in dem magnetischen Momentensystem werden nach Methoden behandelt, die der ''coherent potential approximation'' (CPA) angepa{\ss}t sind. Es wird eine Erweiterung der CPA zur Berechnung der sich wechselseitig bedingenden elektronischen und magnetischen Eigenschaften verd\"unnter ''local moment''-Systeme vom Typ $A_{1-x}M_x$ f\"ur die Situation vorgeschlagen, in der eine durch Kristallfeldparameter bedingte Unordnung in der N\"{a}chste-Nachbar-Schale des Aufatoms ber\"ucksichtigt werden mu\ss. Dabei werden Kristallfeldparameter zwischen zwei nicht-magnetischen Atomen ($\lambda^{AA}$), zwischen einem magnetischen und einem nicht-magnetischen Atom ($\lambda^{AM}$) und zwischen zwei magnetischen Atomen ($\lambda^{MM}$) unterschieden. Schl\"usselgr\"o{\ss}en wie die langreichweitigen und oszillierenden effektiven Austauschintegrale und die Curie-Temperatur und die elektronischen und magnonischen Quasiteilchen-Zustandsdichten werden im Detail in Abh\"angigkeit der Konzentration $x$ der magnetischen Ionen, der Ladungstr\"ager-Konzentration $n$, der Interband-Austauschkopplung $J$, der Temperatur und der Kristallfeldparameter untersucht. / We propose a self-consistent approximate solution of the disordered Kondo-lattice model (KLM) to get the interconnected electronic and magnetic properties of ''local-moment'' systems like diluted ferromagnetic semiconductors. Aiming at $(A_{1-x}M_x)$ compounds, where magnetic (M) and non-magnetic (A) atoms are distributed randomly over a crystal lattice, we present a theory which treats the subsystems of itinerant charge carriers and localized magnetic moments in a homologous manner. The coupling between the localized moments due to the itinerant electrons (holes) is treated by a modified RKKY-theory which maps the KLM onto an effective Heisenberg model. The disordered electronic and magnetic moment systems are both treated by coherent potential approximation (CPA) methods. An extension of CPA to perform a self-consistent model calculation of the electronic and magnetic properties of diluted local-moment systems $A_{1-x}M_x$ described by ferromagnetic Kondo-lattice model ($s-f$ model), where we included disorder in the first environment shell by use of crystal field parameters between two non-magnetic, one magnetic and non-magnetic, and two magnetic atoms, respectively $\lambda^{AA},\lambda^{AM},\lambda^{MM}$, and to get the interconnected electronic and magnetic properties of systems like diluted ferromagnetic semiconductors (DMS) is proposed. We discuss in detail the dependencies of the key-terms such as the long range and oscillating effectice exchange integrals and the Curie temperature as well as the electronic and magnonic quasiparticle densities of states on the concentration $x$ of magnetic ions, the carrier concentration $n$, the exchange coupling $J$ and the crystal field parameters.