Les mousses de carbone vitreux à très forte porosité, qui résultent de la pyrolyse de mousses polymères, ont des propriétés mécaniques et thermiques inadaptées pour certaines applications structurales (absorption de choc, piles à combustible...). Lors de cette étude, des revêtements de pyrocarbone (PyC, à partir de propane) et de carbure de silicium (SiC, issu du mélange CH3SiCl3/H2) ont été mis en oeuvre par dépôt chimique en phase vapeur (CVD) et les conditions expérimentales ont été optimisées afin d’améliorer les propriétés des mousses. Les caractéristiques mécaniques, thermiques et de transport gazeux ont été évaluées respectivement grâce à des tests de compression uniaxiale et des mesures sur bancs de diffusivité flash et de perméabilité. Les propriétés physiques varient dans une grande proportion avec la densité relative. Grâce au contrôle de la composition, de la structure, de l’homogénéité d’épaisseur des dépôts et de la densité relative des mousses, le procédé de CVD permet d’adapter précisément leurs propriétés à une application précise. / High porosity open cell carbon foams, resulting from the pyrolysis polymeric foams, have inadequate properties for structural applications such as shock absorbers or fuel cells. In this study, pyrocarbon (PyC derived from propane) and silicon carbide (SiC from CH3SiCl3/H2 mixtures) coatings were prepared by Chemical Vapour Deposition (CVD) and the experimental conditions were optimized to improve the properties of the foams. The mechanical, thermal and gas transport properties were respectively assessed by uniaxial crushing tests, flash diffusivity and gas permeability measurements. The physical properties vary significantly with the relative density. The CVD process allows the tailoring of the foam properties, for a specific application, through an accurate control of the structure, the composition, the thickness uniformity of the coatings and the relative density of the foams.

Le nombre grandissant de véhicules électriques implique une grande quantité d’accumulateurs devant être alimentés par le réseau électrique. Le principe d’échange d’énergie véhicule-réseau (V2G) permet des transferts énergétiques bidirectionnels entre le réseau et les véhicules électriques. Il est ainsi possible de compter sur ces accumulateurs pour alimenter le réseau. Le chargeur intégré assure l’interface entre le réseau et ces accumulateurs. Son rendement constitue un élément majeur de la viabilité du principe V2G. Son caractère mobile est tout aussi important puisque cet appareil est intégré au véhicule. Les semi-conducteurs au carbure de silicium (SiC) présentent une percée substantielle pour atteindre le rendement et la densité énergétiques nécessaires pour un tel convertisseur. Les impacts de l’utilisation du SiC dans la conception et la mise en œuvre d’un chargeur bidirectionnel seront démontrés dans ce mémoire. La topologie du convertisseur est initialement déterminée puis dimensionnée pour les paramètres de l’étude, soit en tension et puissance. Les simulations du convertisseur exposent les différences entre une solution n’utilisant que des composants au SiC à une seconde n’utilisant que des composant au silicium (Si) traditionnellement utilisés. Une dernière solution combinant les deux types de composant a aussi été évaluée. Finalement, la mise en œuvre d’un chargeur bidirectionnel prototype démontre des phénomènes distincts entre les solutions exposant l’impact des semi-conducteurs au carbure de silicium sur le rendement du convertisseur bidirectionnel.

Submitted by Celso Magalhaes (celsomagalhaes@ufrrj.br) on 2018-08-02T15:53:51Z No. of bitstreams: 1 2017 - Ana Carolina Mendes Bezerra.pdf: 1946898 bytes, checksum: 5eac08b2a62141f12ea8b97452156ae3 (MD5) / Made available in DSpace on 2018-08-02T15:53:54Z (GMT). No. of bitstreams: 1 2017 - Ana Carolina Mendes Bezerra.pdf: 1946898 bytes, checksum: 5eac08b2a62141f12ea8b97452156ae3 (MD5) Previous issue date: 2017-02-16 / Irrigation acts as an important factor to reduce risks and increase productivity in agricultural crops. However, due to increasing water scarcity and the waste of water practiced by many farmers, there is great concern about the negative impacts of this technique on the productive sector, generating the need to establish a balance between agricultural productivity and the preservation of natural resources. In this scenario, studies related to water economics are inserted through more sustainable types of irrigation management. The objective of this study was use the Simplified Irrigation Controller sensor positioned in the atmosphere, to control the irrigation of lettuce seedlings based on the variation of water vapor pressure. The performance of the adaptation was evaluated by monitoring plant parameters, as well as, water use efficiency (WUE). The device was evaluated with the ceramic sensor positioned outside the substrate, in the atmosphere adjacent to the production trays, seeking to correlate the applied water with the vapor pressure deficit (VPD) observed at the experiment site. The seeds of the Regina cultivar were sown in polystyrene trays (200 cells) with substrate used in organic cultivation. A randomized block design was used in a factorial scheme where factor A were four adjustments of the SIC (3.5; 5, 6.5 and 8kPa) and factor B were the two evaluation periods (from July 8 to August 8 and September 16 to October 16, both in 2016) with four replications, totaling 32 plots (experimental units). Parameters related to the growth and physiology of the crop was evaluated, such as: fresh mass, dry mass, water use efficiency, chlorophyll fluorescence parameters and stomatal conductance. The results were submitted to analysis of variance and in the presence of significant interaction a Sliced- analysis was carried out for each factor. Scott-Knott test was used to determine significance with the cut off at 5%.Biometric and physiological variables tested showed a decrease as the tested tensions were increased. The 3.5 kPa tension showed a higher potential for producing more vigorous seedlings, presenting WUE with an average value of 1.37 g L-1 and producing a seedling with approximately 32.4 mL of water in the second experimental period. The cultivation of lettuce seedlings is possible in both experimental periods. The results show the availability of the use of the SIC with atmospheric sensor and compatibility of the applied water volume applied with the observed VPD / A irriga??o atua como importante fator de redu??o de risco e incremento na produ??o de culturas agr?colas. Por?m, devido ? crescente escassez h?drica e ao desperd?cio de ?gua praticado por grande parte dos agricultores, h? uma grande preocupa??o em rela??o aos impactos negativos dessa t?cnica, gerando a necessidade de se estabelecer um equil?brio entre a produtividade agr?cola e a preserva??o dos recursos naturais. Nesse cen?rio se inserem estudos relacionados com efici?ncia h?drica por meio de tipos de manejo da irriga??o mais sustent?veis. O objetivo desse estudo foi utilizar o sensor do Acionador Simplificado de Irriga??o (ASI) na atmosfera para controlar a irriga??o de mudas de alface baseando-se na varia??o de press?o de vapor da ?gua. O desempenho da adapta??o foi avaliado por meio do monitoramento de par?metros na planta, bem como, da efici?ncia de uso da ?gua (EUA). O acionador foi avaliado com o sensor cer?mico posicionado fora do substrato, na atmosfera adjacente superior as bandejas de produ??o, buscando correlacionar a ?gua aplicada com o d?ficit de press?o de vapor observado nesse local. As sementes da cultivar Regina foram semeadas em bandejas de isopor (200 c?lulas) com substrato utilizado em cultivo org?nico. Foi utilizado o delineamento experimental de blocos casualizados, em esquema fatorial, onde o fator A foi quatro regulagens do acionador (3,5; 5; 6,5 e 8 kPa) e o fator B as duas ?pocas de avalia??o (de 8 de julho a 8 de agosto e 16 de setembro ? 16 de outubro, ambas no ano de 2016), com quatro repeti??es, totalizando 32 parcelas. Foram avaliados par?metros referentes ao crescimento e fisiologia da cultura, quais sejam: massa fresca, massa seca, par?metros de cin?tica da fluoresc?ncia da clorofila a e condut?ncia estom?tica, al?m da EUA. Os resultados foram submetidos ? an?lise de vari?ncia e na presen?a de intera??o significativa foi realizada nova an?lise de vari?ncia com desdobramento dos graus de liberdade. Teste de Scott-Knott foi usado para determina??o de signific?ncia a 5% de probabilidade. As vari?veis biom?tricas e fisiol?gicas avaliadas apresentaram decr?scimo conforme foram aumentadas as tens?es de acionamento. A tens?o 3,5 kPa mostrou maior potencial para produ??o de mudas mais vigorosas, apresentando EUA com valor m?dio de 1,37 g L-1 e produzindo uma muda com aproximadamente 32,4 mL de ?gua na segunda ?poca experimental. O cultivo de mudas de alface mostra-se poss?vel nas duas ?pocas experimentais. Os resultados mostram a viabilidade do uso do acionador com sensor atmosf?rico e compatibilidade do volume de ?gua aplicado com o d?ficit de press?o de vapor da atmosfera observado.

Esta dissertação tem como tema a onerosidade excessiva no direito civil brasileiro. Primeiramente, fazem-se necessários uma noção inicial da figura, uma delimitação conceitual do problema e uma síntese de seu desenvolvimento histórico no direito civil brasileiro. Feito isso, são apresentadas as teorias utilizadas para sua fundamentação pela doutrina e pela jurisprudência brasileiras antes do advento de texto legal expresso sobre a matéria. Concluída essa fase preparatória, adentra-se no direito positivo vigente, precisamente no Código Civil, para explicar o conteúdo da onerosidade excessiva, de seus pressupostos e de suas conseqüências. São diretamente estudados os artigos 478, 479, 480, 317 e ainda outros específicos de alguns tipos contratuais. São abordados ainda alguns tópicos correlatos que finalizam o entendimento da matéria, como os pressupostos negativos da figura, sua incidência em contratos de sinalagma indireto e nos contratos aleatórios e as diferenças nos pressupostos para sua configuração no Código de Defesa do Consumidor. / The theme of this dissertation is known in english as hardship, which means the fundamental alteration of the equilibrium of the contract. Firstly, it is necessary to make an introductional notion of the figure, a conceptual delineation of the problem and a summary of its historical evolution in the brazilian civil law. After that, it is presented the theories used by authors and courts to reason the solution of the problem before the existence of legal text about the issue. Then, we study the related articles of the Brazilian Civil Code to explain the content of hardship, the content of its requirements, and the content of its consequences. The articles 478, 479, 480, 317 are directly studied, and also other articles from particular named contracts. Some related issues finalize the understanding of the theme, as the negative requirements of the figure, its incidence in some particular categories of contracts, and the difference of its requirements in the Consumer Defense Code.

Silicon carbide (SiC) has been used for centuries as an industrial abrasive and has been actively researched since the 1960's as a robust material for power electronic applications. Despite being the first semiconductor to emit blue light in 1907, it has only recently been discovered that the material has crucial properties ideal for long-term, implantable biomedical devices. This is due to the fact that the material offers superior biocompatibility and hemocompatibility while providing rigid mechanical and chemical stability. In addition, the material is a wide-bandgap semiconductor that can be used for optoelectronics, light delivery, and optical sensors, which is the focus of this dissertation research. In this work, we build on past accomplishments of the USF-SiC Group to develop active SiC-based Brain Machine Interfaces (BMIs) and develop techniques for coating other biomaterials with amorphous SiC (a-SiC) to improve device longevity. The work is undertaken to move the state of the art in in vivo biomedical devices towards long term functionality. In this document we also explore the use of SiC in other bio photonics work, as demonstrated by the creation of the first reported photosensitive capacitor in semi-insulating 4H-SiC, thus providing the mechanism for a simple, biocompatible, UV sensor that may be used for biomedical applications. Amorphous silicon carbide coatings are extremely useful in developing agile biomaterial strategies. We show that by improving current a-SiC technology we provide a way that SiC biomaterials can coexist with other materials as a biocompatible encapsulation strategy. We present the development of a plasma enhanced chemical vapor deposition (PECVD) a-SIC process and include material characterization analysis. The process has shown good adhesion to a wide variety of substrates and cell viability tests confirm that it is a highly biocompatible coating whereby it passed the strict ISO 10993 standard tests for biomaterials and biodevices. In related work, we present a 64-channel microelectrode array (MEA) fabricated on a cubic 3C-SiC polytype substrate as a preliminary step in making more complex neurological devices. The electrode-electrolyte system electrical impedance is studied, and the device is tested against the model. The system is wire-bonded and packaged to provide a full neural test bed that will be used in future work to compare substrate materials during long-term testing. Expanding on this new MEA technology, we then use 3C-SiC to develop an active, implantable, BMI interface. New processes were developed for the dry etching of SiC neural probes. The developed 7 mm long implantable devices were designed to offer four channels of single-unit electrical recording with concurrent optical stimulation, a combination of device properties that is indeed at the state-of-the-art in neural probes at this time. Finally, work in SiC photocapacitance is presented as it relates to radio-frequency tuning circuits as well as bio photonics. A planar geometry UV tunable photocapacitor is fabricated to demonstrate the effect of below-bandgap optical tuning. The device can be used in a number of applications ranging from fluorescence sensing to the tuning of antennas for low-power communications. While technology exists for a wide variety of in vivo interfaces and sensors, few active devices last in the implantable environment for more than a few months. If these devices are going to reach a long-term implant capability, use of better materials and processing strategies will need to be developed. Potential devices and strategies for harnessing the SiC materials family for this very important application are reviewed and presented in this dissertation to serve as a possible roadmap to the development of advanced SiC-based biomedical devices.

The present thesis is a study of the evolution of defect states in devices based on wide bandgap semiconductors. The attention has been focused on light-emitting diodes based on GaN and Schottky diodes based on SiC, these latter a basic structure for the fabrication of high-power rectifiers and ionising particle detectors. In both cases, we studied the defects and their electronic properties by means of the following experimental techniques: current-voltage (I-V) measurements, in order to investigate the effect of imperfections on the transport properties of the material/device; capacitance-voltage (C-V) measurements, yielding the profile of concentration of charge carriers, and giving information on the influence of defects on this concentration; deep level transient spectroscopy (DLTS), a technique allowing for the identification and characterization of defect-originated electron levels in the gap. I also employed techniques, such as photocurrent spectroscopy (PC), allowing for the characterization of light absorption by the material and/or device versus varying photon energy. In both cases of SiC and GaN, the defect characterization was always interpreted in the framework of its influence on device operation. In the analysed LEDs the defect evolution was connected to the evolution of quantum efficiency, and in the SiC diodes we studied the effects of defect introduction on the charge collection efficiency (CCE) and on the leakage current of the device. Furthermore, for the interpretation of photocurrent spectra, I developed a model describing the generation of photocurrent considering the dispersion relations for the absorption coefficient and refractive index in the various device layers, as well as the internal reflection, transmission and interference phenomena involving the optical field within the device. The research yielded various interesting results: I detected many deep levels introduced by proton- and electron-irradiation in SiC. From the study of their annealing behaviour I concluded that one of these levels is related to a particular lattice defect, the carbon interstitial. By means of the analysis of the introduction rates of the levels and comparisons between proton and electron irradiation, I was able to distinguish between deep levels related to simple intrinsic defects and to defect complexes. In the case of the GaN LED, I found that the evolution of several independent properties are strongly correlated, meaning that a single degradation mechanism is responsible for the observed changes. In particular, I concluded that the degradation of the light emission intensity is due to the generation of defects in the active region of the device.

Les applications potentielles du carbure de silicium (SiC) en microélectronique ont motivé de nombreuses études sur les défauts ponctuels, qui jouent un rôle important dans la compensation électrique. Ce matériau possède en outre de nombreux atouts pour participer au confinement des matières fissiles dans les réacteurs à caloporteur gazeux du futur (4ème génération). Dans cette thèse, nous avons utilisé la Résonance Paramagnétique Electronique et la Spectroscopie d'Annihilation de Positons pour étudier les propriétés (nature, taille, état de charge, migration et agglomération sous recuit) des défauts ponctuels natifs et induits par irradiation avec différentes particules (H+, e-, ions carbone) dans les polytypes 3C et 6H de SiC. L'étude par annihilation de positons des défauts natifs dans 6H-SiC a permis de mettre en évidence une forte concentration de pièges non lacunaires de type accepteur, qui ne sont pas présents dans les cristaux 3C-SiC. La nature des défauts détectés après irradiation aux électrons de basse énergie (190keV) dépend du polytype. En effet, si des paires de Frenkel de silicium et des monolacunes de carbone sont détectées dans les cristaux 6H, seules des monolacunes de carbone sont détectées dans les cristaux 3C. Nous proposons que ces différences quant aux populations de défauts ponctuels détectés résultent de valeurs différentes des énergies de seuil de déplacement du silicium dans les deux polytypes (environ 20eV pour 6H et 25eV pour 3C). Par ailleurs, les irradiations avec des protons de 12MeV et des ions carbone de 132MeV créent des monolacunes de silicium ainsi que des bilacunes VSi-VC. Ni la particule (protons ou ions carbone), ni le polytype (3C ou 6H) n'influent sur la nature des défauts générés. Enfin l'étude du recuit de monocristaux 6H-SiC irradiés avec des protons de 12MeV a permis de mettre en évidence plusieurs processus successifs. Le résultat le plus original est l'agglomération des monolacunes de silicium avec les bilacunes VSi-VC qui mène à la formation de trilacunes VSi-VC-VSi.

Cette thèse relate une recherche-action en didactique de l'anglais de spécialité en lien avec les environnements d'apprentissage multimédias. Le versant “recherche” fait appel aux disciplines connexes de la philosophie de l'éducation, de la psychologie de l'apprentissage, de la linguistique appliquée et des sciences cognitives pour forger des outils théoriques. Nous revisitons les modèles ternaires de la situation pédagogique, d'abord pour y redéfinir la place du processus d'enseignement puis pour y introduire les instruments d'enseignement, ce qui nous amène à proposer un modèle nouveau, le carré pédagogique. Les concepts de médiatisation et de médiation sont redéfinis à la lumière de la théorie des situations d'activités instrumentées de Rabardel. Les conceptions et approches de la didactique des langues étrangères de la seconde moitié du XXe siècle sont examinées du point de vue de la situation pédagogique et de la place qu'elles font aux instruments didactiques. Le versant “action” de la recherche conduit au développement d'un didacticiel multimédia dont on fait l'hypothèse qu'il amènera une amélioration de la motivation et des stratégies d'apprentissage de la population cible. On formule une deuxième hypothèse selon laquelle la valeur de la médiation exercée par l'instrument multimédia est fonction de l'action de médiatisation exercée par l'enseignant. Le dispositif a fait l'objet d'une expérimentation in situ pendant six ans, période au cours de laquelle des données ont été recueillies a) par enquêtes et questionnaires, b) par enregistrement informatique de la trace du parcours des utilisateurs et c) par enregistrement audio d'interactions verbales. Les données des types a) et b) ont été analysées par l'analyse factorielle de correspondances et celles de type c) par les méthodes de l'analyse du discours.

Le Carbure de Silicium, par ses propriétés intrinsèques, offre des perspectives dans le domaine de l'électronique de puissance à même de supplanter le Silicium aujourd'hui sollicité à ses limites. En particulier, le Carbure de Silicium (SiC) permet la réalisation de diodes réunissant la technologie Schottky et supportant une haute tension. Après avoir resitué la filière du SiC dans son contexte, on présente dans ce travail les éléments de physique du semiconducteurappliqués à la diode Schottky SiC et justifiant les propriétés et le dimensionnement du composant. Le comportement électrique statique et dynamique des diodes Schottky SiC est ensuite comparé à l'état de l'art des diodes bipolaires en Silicium, et une simulation fine de la cellule de commutation est présentée. Le comportement électrothermique des diodes Schottky SiC est analysé dans la partie suivante à l'aide d'un outil de simulation dédié, permettant d'intégrer à la fois les phénomènes d'emballement thermique propres aux composants majoritaires et les propriétés de haute tenue en température du SiC, pour fournir une évaluation de la densité de courant utile des diodes. Enfin, la dernière partie propose une évaluation de la technologie Schottky SiC DANS UNE APPLICATION pfc, suivant le régime de fonctionnement du convertisseur. Une amélioration visant à exploiter au mieux les propriétés de cette nouvelle diode dans le PFC est ensuite présentée.

<p>This report is the result of a diploma work made at Linköping University from August 2006 till September 2007 by Erik Lundin, under the guidance of Doctor Mike Andersson and Professor Anita Lloyd Spetz. Its purpose was to find suitable materials for the construction of an oxygen sensor. The hope was not to construct such a sensor, but to investigate materials that may be suitable in creating one. In the preparatory time period of the diploma work, different papers and books were studied in order to get a proper understanding of the sensor mechanism. During this period of time, a design proposal was made and the theory behind it is presented in this thesis. The main objective in this thesis has been to investigate the response of field effect devices to oxygen and other gases that are compounds in exhaust or flue gases. Devices were created by employing the materials which were investigated. Special material combinations were proposed for field effect devices suitable for oxygen detection by Doctor Mike Andersson. One material combination showed promising results for selective detection of the oxygen concentration in exhaust gases.</p> / This diploma work has been confidential