Les phénomènes de diffusion se produisant lors du frittage des oxydes mixtes d'uranium et deplutonium (MOX) dépendent du potentiel d'oxygène de l'atmosphère du four, qui détermine lanature et la concentration des défauts ponctuels dans le matériau. Les travaux de thèse ont porté surune meilleure compréhension de l'influence du potentiel d'oxygène sur la densification, la formationde la solution solide et l'interdiffusion U-Pu lors du frittage des combustibles MOX. Pour cela, unlarge domaine de potentiel d'oxygène a été étudié, entre -600 et -100 kJ.mol-1 à 1700°C, afin demettre en évidence les différents mécanismes diffusionnels et leur impact sur la microstructurelorsqu'on s'éloigne de la composition stoechiométrique i.e. lorsque la concentration en défautsaugmente.Les études ont montré que plus le potentiel d'oxygène augmente, plus la densification du mélange70 % UO2+x + 30 % PuO2 s'effectue à basse température. Lors du chauffage, les oxydes de départ(UO2+x et PuO2-x) densifient dans un premier temps puis la solution solide se forme à une températureplus élevée d'environ 200°C. La solution solide apparaît à plus basse température quand le potentield'oxygène augmente, avec une cinétique de formation plus rapide. L'étude de l'interdiffusion U-Puindique qu'un traitement thermique avec un potentiel d'oxygène supérieur à -150 kJ.mol-1 à 1700°Cpermet d'obtenir un coefficient d'interdiffusion supérieur d'un à deux ordres de grandeur à ceuxobtenus entre -550 et -350 kJ.mol-1 à 1700°C et conduit donc à une homogénéisation U-Pu accrue.Cette étude permet de donner des recommandations sur le choix de l'atmosphère et de proposer uncycle de frittage optimisé en fonction de l'application ou de la caractéristique souhaitée.

Une méthode de couplage continu-discret a été développée pour simuler les mécanismes complexes d'endommagement de la silice soumise à un choc laser de haute puissance. Dans un premier temps, une classification des méthodes numériques existantes a été faite pour choisir celles les mieux adaptées à la simulation du comportement sous choc de la silice. Comme résultat de cette classification, deux méthodes ont été retenues: la méthode des éléments discrets (DEM) et la méthode des éléments naturels contraints (CNEM). Ces méthodes sont alors couplées en se basant sur la technique dite "Arlequin". Puis, un modèle numérique permettant de tenir compte des différents phénomènes qui caractérise le comportement de la silice sous haute pression a été développé. Pour bien caractériser les mécanismes de fissuration de la silice à l'échelle microscopique, un nouveau modèle de rupture a été développé dans ce travail. Finalement, ces deux modèles, modèle de comportement et modèle de rupture, ont été intégrés dans la méthode du couplage pour simuler d'un point de vue mécanique le choc laser sur un échantillon en silice.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Thermomechanical treatments seek to increase the wood density, throught of the temperature and pressure combination, which results in a material with improved physical and mechanical properties. Thus, the study aimed to evaluate the influence of thermomechanical treatments in Pinus elliottii Engelm and Eucalyptus grandis W. Hill ex Maiden wood. So, were prepared from five trees of each species, wood pieces that have been submitted to six different thermomechanical treatments. For this purpose, we used a laboratory oil bath to perform preheating of wood and a hydraulic press with the temperatures of the dishes ranging from 150 to 190°C. Compression time used was between 30 and 60 min. After, physical (compression rate, weight loss, equilibrium moisture content, density, dimensional stability and hygroscopicity), mechanical (static bending, dynamic bending and Janka hardness), surface (colorimetry and roughness) and infrared spectroscopy (ATR-IR) tests were performed. For statistical analysis, we used qualitative factorial 3 x 2, with three temperature levels and two compression time and Tukey test. Furthermore, it was performed to compare the treatments with the control. The main results for the technological properties showed that the degree of compression and mass loss increased with the temperature increase. The equilibrium moisture content decreased and the density obtained increases. For the dimensional stability was observed that there was a reduction of the effect of the return densified wood, and hygroscopicity was increased in both wood species. The mechanical properties showed increases with the densification, except for the Janka hardness and dynamic flexion in E. grandis wood treated with high temperatures. Infrared spectroscopy showed degradation of the amorphous cellulose and hemicellulose, providing a proportional increase of crystalline cellulose and lignin. The color of the densified wood was changed presenting surface browning, measured by decrease in brightness L* parameter. Roughness was reduced, making the surface softer wood. Before the alterations, it is indicated using thermomechanical treatment with temperature of 150°C and the compression time of 60 min. In this respect, it is recommended the use of densified wood floors and coatings, even for softwoods (conifers). / Os tratamentos termomecânicos visam aumentar a densidade da madeira, por meio da combinação entre temperatura e pressão, o que resulta em um material com as propriedades físico-mecânicas melhoradas. Nesse sentido, o presente estudo teve como objetivo avaliar a influência dos tratamentos termomecânicos na madeira. Para tanto, foram confeccionadas peças de madeira, a partir de cinco árvores de Pinus elliottii Engelm e Eucalyptus grandis W. Hill ex Maiden que foram submetidas a seis tratamentos termomecânicos. Para tal, foi utilizado um banho de óleo laboratorial para realizar o pré-aquecimento da madeira e uma prensa hidráulica com a temperatura dos pratos variando de 150 a 190°C e o tempo de compressão entre 30 e 60 min. Na sequência, foram realizados os ensaios físicos (grau de compressão, perda de massa, teor de umidade de equilíbrio, densidade, estabilidade dimensional e higroscopicidade), mecânicos (flexão estática, flexão dinâmica e dureza Janka), de superfície (colorimetria e rugosidade) e espectroscopia no infravermelho (ATR-IR). Para a análise estatística foi utilizado o arranjo fatorial qualitativo 3 x 2, com três níveis de temperatura (150, 170 e 190°C) e dois de tempo de compressão (30 e 60 min) e comparados pelo teste de Tukey. Além disso, foi realizado a comparação dos tratamentos com o controle pelo teste de Dunnett. Os principais resultados encontrados para as propriedades tecnológicas mostraram que o grau de compressão, a perda de massa e a densidade aumentaram com o acréscimo da temperatura, já o teor de umidade de equilíbrio apresentou decréscimo com a elevação da temperatura. Para a estabilidade dimensional foi observado que houve redução pelo efeito do retorno da madeira densificada e a higroscopicidade foi aumentada na madeira de ambas as espécies. As propriedades mecânicas apresentaram acréscimo com a densificação, com exceção para a dureza Janka e flexão dinâmica da madeira de E. grandis tratada com altas temperaturas. Por meio da espectrometria no infravermelho foi verificado a partir da razão de pico que houve degradação de hemiceluloses e celulose amorfa, proporcionando aumento proporcional de celulose cristalina e lignina. A coloração da madeira densificada foi alterada apresentando escurecimento superficial, quantificado pelo decréscimo do parâmetro de claridade L*. Já a rugosidade foi reduzida, tornando a superfície da madeira mais suave. Diante das alterações ocorridas é indicado utilizar tratamento termomecânico com a temperatura de 150°C e o tempo de compressão de 60 min. Nesse aspecto, é recomendado a utilização da madeira densificada como assoalhos e revestimentos, mesmo para as madeiras macias (coníferas).

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-11-11T16:39:02Z No. of bitstreams: 0 / Made available in DSpace on 2016-11-11T16:39:02Z (GMT). No. of bitstreams: 0 / O reator de pesquisas IEA-R1 opera em regime de 40 h semanais à potência de 4,5 MW. Nestas condições, os cestos disponíveis para o armazenamento dos elementos combustíveis irradiados possuem menos de metade da sua capacidade inicial. Assim, nestas condições de operação, teremos apenas cerca de seis anos de capacidade para armazenamento. Considerando que a vida útil desejada do IEA-R1 seja de pelo menos mais 20 anos, será necessário aumentar a capacidade de armazenamento de combustível irradiado. Dr. Henrik Grahn, especialista da Agência Internacional de Energia Atômica sobre o armazenamento molhado (em piscinas de estocagem), ao visitar o reator IEA-R1 (setembro/2012) fez algumas recomendações. Entre elas, a concepção e instalação de cestos fabricados com aço inoxidável borado e internamente revestidos com uma película de alumínio, de modo que a corrosão dos elementos combustíveis não ocorresse. Após uma revisão da literatura sobre opções de materiais disponíveis para esse tipo de aplicação chegamos ao BoralcanTM fabricado pela 3M devido suas propriedades. Este trabalho apresenta estudos sobre a análise de criticalidade com o código computacional MCNP-5 utilizando duas bibliotecas americanas de dados nucleares avaliados (ENDF/B-VI e ENDF/B-VII) comparativamente. Estas análises demonstraram a possibilidade de dobrar a capacidade de armazenamento de elementos combustíveis, no mesmo espaço ocupado pelos cestos atuais, atendendo a demanda do reator de pesquisas IEA-R1 e também satisfazendo os requisitos de segurança da Comissão Nacional de Energia Nuclear (CNEN) e da Agência Internacional de Energia Atômica (IAEA). / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The densification mechanisms of polycrystalline α-alumina by spark plasma sintering are highly contradictory, with different research groups suggesting diffusion to dislocation controlled mechanisms to be rate controlling. The specific objective of this work was to investigate densification mechanisms of α-alumina during the intermediate and final stages of sintering by SPS, analyze the microstructural development and establish sintering trajectories. In addition, zirconia and yttria were added in different weight percentages to study the effect of solute concentration on the densification kinetics of spark plasma sintered alumina. The present work adopts a different approach from the classical method adopted previously to analyze the sintering kinetics and densification mechanisms of alumina in SPS, although existing models for hot pressing were adopted for the basic analysis. The densification behavior was investigated in the temperature range 1223-1573 K under applied stresses of 25, 50 and 100 MPa and grain sizes between 100 and 250 nm. The SEM micrographs reveal equiaxed grains with no abnormal grain growth in the dense samples. The ‘master sintering curve’ shows grain size to be primarily dependent on density, irrespective of the applied stresses or temperature. The stress exponent of 1 along with an inverse grain size exponent of 3 and activation energy of 320-550 kJ mol-1 suggests Al3+ grain boundary diffusion as the rate controlling densification mechanism in alumina. The densification rates are marginally slower in compositions with 0.1% Y2O3 and ZrO2 content possibly due to the smaller grain sizes used in this study which leads to faster rates compared to earlier reports. However, higher Y2O3 and ZrO2 content led to decrease in densification rate by more than an order of magnitude possibly due to presence of a second phase which increases the effective path length for diffusion, thereby reducing the densification rates. Presence of Y2O3 and ZrO2 in the compositions with 0.1% Y2O3 and ZrO2 were confirmed by TEM studies. The Y3Al5O12 (YAG) phase developed between 1223 and 1273 K and suppressed densification and grain growth in alumina. In spite of higher temperatures required for alumina-YAG and alumina-zirconia composites to attain density ~99%, the alumina grain size in the composites was smaller than that in pure alumina due to the Zener drag effect. The stress exponents obtained for Y2O3 and ZrO2 composites at both the concentrations yield a value of n~ 2, which indicates a change in densification mechanism from pure alumina. The higher stress dependence of these composites could be due to presence of solute and second phase formation, both of which retard densification rates. The inverse grain size exponents obtained are between 1 and 2; both stress exponent and grain size exponent values suggest an interface reaction controlled diffusion mechanism occurring in these composites, independent of the Y2O3 and ZrO2 content. Higher activation energies are obtained with the Y2O3 and ZrO2 composites of higher content, respectively, due to presence of second phase particles at grain boundaries. The presence of solutes at grain boundaries hinders grain boundary diffusion of alumina, leading to interface reaction controlled process; this is confirmed by superimposing standard aluminum grain boundary and lattice diffusion data on to stress-densification rate data obtained in this work. A comparison of stress exponents using current experimental data adopting the present and the classical approaches show a wide difference in their values indicating a change in the rate controlling diffusion path, necessitating a review of the assumptions made on the basic equations used in previous SPS studies.

Density is more about an experienced nearness to functions and activities than buildingsbeing physically close to each other. Density is interaction, and the intensity of itdepends on accessibility to the functions and activities of the built environment. The current planning, continuing the thoughts of the modernist, are a threat to publichealth and the environment, as sprawling settlements demand more resources forinfrastructure and time spent commuting between home and work, taking up the timeto spend with family and friends. The suburban planning principles of the Swedish housing estate unit have graduallytransformed the suburban neighbourhoods into dispersed, disconnected islands, wheresocial life is inhibited in the mere configuration of space. Legibility of the urban environment is important regarding orientation and navigation,but also to understand the underlying meanings of spaces and places. The urbanstructure should be easily read to be understandable in the choices of everyday life. How we understand the boundaries and transitions of our surrounding affects howspaces are used. Unclear territorial interfaces, like the open space landscape ofmodernist planning feels too exposed to be appropriated. If activities should take placein the outdoor environment, there must be a certain quality to the spaces that areinviting and promote interaction between people. The suburban housing estate neighbourhoods can be developed to promote thisinteraction, providing spaces where the different layers of social life can take place, fromthe private home – through mediating interfaces of front yards, indoor collective spaceand collective gardens – to the public realm of the streets, pathways and parks. The thesis studies the suburban neighbourhood Årsta in eastern Uppsala, whichshows the signs of a disperse suburban housing estate in its configuration of buildings,withdrawn from the streets, turning inward away from the public spaces. By adding built volume within the existing structure of the open yards, the boundariesbetween the public and the private spaces can be clearly defined and new activatedspaces can be created. Many fronts towards the streets and paths make people meet inevery-day life and new types of spaces can be used to set a framework for interactionbetween residents as well as outsiders. Such spaces can also work as a buffer betweenpublic life and the private dwelling, e.g. a collective garden mediates the space inbetween a pedestrian path and an inner yard.

Densification is a well-known method for improving the mechanical properties of wood. In the present study, unmodified and furfurylated wood samples were densified and submitted to cyclic water storage tests and cyclic alternating climate tests. Swelling coefficients and spring-back data were determined for the evaluation of the quality of densification. The study shows that results depend on the test method applied. Simple water storage tests do not reflect the behavior of densified wood in the high humidity range. The spring-back data of unmodified samples are more influenced by the testing method than those of the furfurylated ones.

The diploma thesis deals with the construction and activation of the territory in connection with the historical center of Kyjov. Part of the proposal was to work with an existing urban brownfield and an extensive park, which accounts for almost half the area under consideration. The goal, as I set out in my work, is to activate the territory and design an urban sprawl with a suitable functional structure. The proposed design respects the context and character of the site in a modern and sustainable manner. The principles followed in my work are based on the current urban and city-forming rules. I have put an emphasis on the human scale, the priority of pedestrians over traffic, and especially the shortcomings and needs in the territory that arise from the analysis. The draft concept is based on the permeability and interconnection of the individual parts of the city, the insertion of a new public space and the completion of the city block. The new urban sprawl clearly defines the street, completes the boundaries and makes the most of the area on the released land. The newly designed buildings are residential and multi-functional houses with active parterres. Part of the proposal is the revitalization of the city park, which explores its hidden potential. The basic step is to remove obstacles in the permeability of the park and to highlight its strengths, such as the flowing river Kyjovka, healthy large trees and the size of the park itself.

The main goal of the project is to design a city house near the central part of Brno as an alternative for the existing monofunctional zones and finding out the most suitable functions for the area. The idea is based on a compact city block which communicates with the events on the streets and connects them together to the house via inner atrium. Within the intensive urban structure, housing was chosen for the most important component because nowadays it disappears from the city centres. As the prerequisite for the high-quality living, the residential floors were raised on a three-storey platform which integrates the culture, offices and the commercial use. The roof of the platform is also used as a green roof terrace with a lot of vegetation which protects the living against the polution and noise from the traffic. So it becomes a safe and calm place for the relaxation and children´s games in a busy part of the city. The important point of view where the emphasis was placed was connecting all the functions together not only within the house itself, but also within the range of the whole city. The house functions and the street area are mutually connected via inner public atrium which becomes the important people meeting site. The residential floors are connected to the rest of the house through the large roof skylight which allows the sun rays to reach the lower floors. So the city house doesn´t hide its purpose on its own, but rather "lives together with the city".

Studien grundar sig i den ständigt ökade stadsbefolkningen vilket bidrar till att städerna behöver utvecklas. En lösning på detta kan vara förtätning. Det kan leda till konsekvenser i de befintliga kvarteren med nya byggnader som oftast ska placeras i känsliga miljöer som i detta fall är ett kulturhistoriskt värdefullt område. För att inte förvanska kulturhistoriska miljöer är det viktigt att förtätning sker varsamt. Studien behandlar ett kvarter i centrala Växjö som är av högt kulturhistoriskt värde. Syftet i följande studie är att undersöka vilka prioriteringar som sker vid utformning av nybyggnation vid förtätning av kulturhistoriska miljöer. Målet är att ta fram ett förslag på hur en förtätning i ett kulturhistoriskt område kan gå till. Undersökningen baseras på en enkätundersökning och områdesanalyser samt litteraturstudier. Resultatet visar att exploatering kan genomföras om det sker på ett varsamt sätt. Det sätter synnerligen höga krav på fasadutformning, detaljer, material, kulörval, markanslutningar, volym, skala och proportioner samt samspelet med omkringliggande byggnader och miljöer. Att visa respekt för de befintliga områdena och ha ett varsamt förhållningssätt vid förtätningsprojekt för nutida och framtida behov är väsentligt. / The study is based on the ever-increasing urban population, which contributes to the development needs of cities. A solution to this can be densification. This can lead to consequences in the existing neighborhoods with new buildings, which will often be placed in a sensitive environment, which in the case of this study is a cultural-historical area. In order not to distort cultural-historical areas, it is important that densification takes place with care. The study deals with a current area in central Växjö which is of high cultural and historical value. The purpose of the following study is to examine what priorities take precedence while designing new constructions during densifying in cultural-historical environments. The goal is to suggest how densification in a cultural-historical area can look like. The study is based on a survey and observations. The results show that exploitation can be achieved gently. It places truly high demands on facade design, details, materials, color choices, ground connections, volume, scale and proportions as well as interaction with surrounding buildings and environments. Showing respect for existing areas and maintaining a gentle approach when developing cities for contemporary and future needs is essential.