There has been much interest in the use of therapeutics based on ribonucleic acid interference(RNAi) to inhibit synthesis of mutant proteins ever since Elbashir et al. (Elbashir, S. M., Harborth, J., Lendeckel, W., Yalcin, A., Weber, K. and Tuschl, T., 2001. Duplexes of 21-nucleotide RNAs mediate RNA interference in cultured mammalian cells. Nature. 411, 494-498.) found that synthetic double stranded small interfering ribonucleic acids (siRNAs) can initiate this evolutionarily conserved process in mammalian cells. Since RNAi is able to target single genes and therefore mitigate the underlying molecular pathology of diseases, RNAi-based therapeutics will most likely benefit monogenic neurodegenerative diseases such as Huntington’s disease. It is however particularly difficult to deliver exogenous materials such as siRNAs into neurons in vivo as the blood-brain barrier (BBB) isolates the brain from the vascular system and prevents permeation of most materials. Neurons also do not take up exogenous materials readily. Therefore, effective delivery of siRNAs into the brain remains one of the biggest challenges impeding their use as a potential neurotherapeutic. Layered double hydroxide (LDH) nanoparticles are a class of anionic clay materials that have demonstrated great potential as a DNA (deoxyribonucleic acid) delivery system for a variety of mammalian cell lines due to their unique physiochemical properties. This thesis examined the feasibility of LDH as a siRNA delivery system for cultured neurons and demonstrated that the delivered siRNAs are able to effectively down-regulate synthesis of a target protein with minimal toxicity. Experiments were conducted using double stranded DNAs (dsDNAs) initially, and siRNAs were then used to verify these results. It was shown that nucleic acids(dsDNAs and siRNAs) could successfully intercalate into pristine LDHs to form nucleic acid-LDH complexes that had properties suitable for use as a delivery system in mammalian cells. These studies established that LDHs and nucleic acid-LDH complexes were biocompatible with neurons isolated from embryonic day 17.5 mouse cerebral cortex, suggesting that LDH can be used for nucleic acid delivery into cultured neurons. LDHs were also shown to successfully deliver nucleic acids into a non-neural mammalian cell line (NIH 3T3 cells). Finally, this thesis demonstrated for the first time that LDHs were able to deliver siRNAs into neurons, providing encouraging preliminary evidence that sequence specific gene silencing of the Mus Musculus Deleted in Colorectal Cancer (DCC) gene had occurred. However, down-regulation of the DCC protein did not occur consistently, suggesting that further optimisation is needed to improve the efficacy of siRNA-LDH complexes to inhibit expression of target protein in neurons. In future, LDHs should be further developed as an efficient siRNA delivery system for therapeutic gene silencing in the central nervous system using a neurodegenerative disease model such as the Huntington’s disease mouse model, which closely phenocopies the human disease. This model will allow the in vivo efficacy of these nanoparticles to be tested and subsequently improved in order to deliver siRNAs locally and systematically into the brain.

Au vu d’une demande croissante pour un stockage d’énergie à grande échelle, il est préférable de se tourner vers des matériaux peu coûteux et répandus. De ce point de vue, le sodium, qui présente des caractéristiques très proches de celles du lithium, présente également l’avantage d’être peu coûteux, abondant et réparti uniformément dans le monde. Cette thèse porte sur l’étude d’un système complet Na-ion constitué d’un carbone dur à l’électrode négative et d’un oxyde lamellaire à l’électrode positive. Un volet sur l’électrolyte a également été abordé.Concernant l’électrode négative, l’influence de la température de pyrolyse de la cellulose sur la structure des carbones durs et sur les performances électrochimiques a été étudiée. Une graphitisation localisée, une fermeture des pores et une évolution de la porosité interne avec la température de pyrolyse ont pu être observées. Les meilleures performances électrochimiques ont été obtenues pour le matériau synthétisé à 1600 °C : une capacité réversible d’environ 300 mAh.g-1 stable sur 200 cycles est atteinte à 37,2 mA.g-1 avec une efficacité coulombique initiale de 84 %. Pour mieux comprendre les mécanismes d’insertion du sodium dans ces matériaux, des études par spectroscopie d’impédance, SAXS et EDX ont été réalisées sur des carbones durs cyclés à différents potentiels.Le matériau d’électrode positive choisi est l’oxyde lamellaire Na0,6Ni0,25Mn0,75O2. L’influence de la température de calcination a permis de faire varier le nombre de défauts d’empilement de type P3 au profit d’une phase P2 plus cristalline. Après avoir optimisé l’électrolyte à base de carbonates pour garantir la reproductibilité des tests oxyde lamellaire//sodium métal, une capacité d’oxydation de 130 mAh.g-1 a pu être atteinte au premier cycle avant de chuter fortement sur les 40 cycles suivants. Cette perte de capacité a pu être en partie expliquée par des études de DRX operando. Enfin, ces travaux ont permis d’aboutir à des systèmes complets Na-ion dont les premiers résultats sont prometteurs. / Because of the development of renewable energy and electric vehicles, the need for a large scale energy storage has increased. This type of storage requires a large amount of raw materials. Therefore low cost and abundant resources are necessary. Consequently the use of sodium batteries is of interest because sodium’s low cost, high abundance, and worldwide availability. This PhD thesis deals with the study of a full Na-ion cell containing a hard carbon negative electrode, and a layered oxide positive electrode. A shorter part concerns the electrolyte.Concerning the negative electrode, the first objective was to understand in detail the influence of the pyrolysis temperature of a hard carbon precursor, cellulose, on the final structure of the material and its consequences on the electrochemical performance. Many techniques were used to characterize the hard carbon structure as a function of the pyrolysis temperature. Localized graphitization, pore closure, and an increase in micropore size have been observed with increasing temperature. The best electrochemical performance has been reached with the hard carbon synthesized at 1600°C: a reversible capacity of around 300 mAh.g-1 stable over 200 cycles is obtained at 37.2 mA.g-1 with an initial coulombic efficiency of 84%. To deeper understand sodium insertion mechanisms in hard carbon structures impedance spectroscopy, SAXS and EDX were carried out on hard carbon electrodes cycled at different voltages.The layered oxide Na0.6Ni0.25Mn0.75O2 was investigated as the positive electrode. It was observed that with increasing calcination temperature the number of P3-type stacking faults decreases in favor of a more crystalline P2 phase. Then, the carbonate-based electrolyte has been optimized to guarantee the reproducibility of the electrochemical tests performed in a layered oxide//sodium metal configuration. A first oxidation capacity of around 130 mAh.g-1 is reached. However this value drops quickly after 40 cycles. Operando XRD analysis did partially explain the capacity decrease. Finally, the results of these investigations were used to design an optimized full cell which demonstrated promising performance during initial testing.

Ce travail porte sur la synthèse et la caractérisation de nouveaux matériaux afin de proposer une alternative dans le cadre de la dépollution nucléaire. Dans une première partie bibliographique, les principaux matériaux inorganiques utilisés pour ce procédé sont décrits en précisant leurs capacités de sorption. Les matériaux lamellaires apparaissent comme possédant un fort potentiel pour cette application. Deux solides ont retenu notre attention : les nanostructures à base de vanadates et de manganates.Des synthèses solvothermales sous flux micro-ondes de ces composés sont ensuite développées, afin d’obtenir une structuration sous forme de nanotubes de vanadates et de nanofleurs de manganates. Une optimisation des vanadates a ainsi été menée en évaluant l’impact de différents facteurs (par exemple, temps de maturation, temps de chauffage, nature et quantité de templates) sur les propriétés structurales et texturales des produits synthétisés. L’enroulement des feuillets est fortement influencé à la fois par la quantité d’amine et sa structure chimique. En effet, seules les amines à longue chaîne conduisent à l’obtention de nanotubes de façon homogène. Une analyse structurale a également été menée pour les deux types de composés en couplant les données expérimentales et celles obtenues par simulation.Les performances de sorption et la sélectivité des matériaux dans différents milieux (eau ultra-pure, eau de rivière) ont été évaluées vis-à-vis du césium et du strontium, seuls ou en mélange. Les résultats montrent clairement une sélectivité très forte des vanadates vis-à-vis du Cs+ et des manganates pour le Sr2+, même en milieu compétitif.La calorimétrie et la simulation moléculaire ont finalement été couplées pour mieux décrire les processus de sélectivité. / This work focuses on the synthesis and characterization of new nanostructured materials that can be potentially proposed as alternatives in the field of nuclear decontamination. The first part is devoted to the state of the art on the use of inorganic materials for decontamination purposes, with the emphasis placed on their sorption capacity and selectivity. The layer materials are considered as offering potential for such applications. In consequence, the main efforts in this work have been focused on manganate and vanadate nanostructures.Solvothermal synthesis of these materials was developed on the basis of micro-wave oven procedures to control the materials structuring, thus leading to vanadate nanotubes and manganate nanoflowers. The optimization of vanadates was carried out by taking into account the effect of various factors (e.g., duration of maturation and heating stages, nature and mass of the template) on both the structural and textural properties of the resulting substrates. It was demonstrated that the scrolling of the layers was strongly influenced by the amount of amine and its chemical structure. Indeed, only the amine templates possessing long chains allowed homogeneous nanotubes to be achieved. More information about the structuring process was inferred when coupling experimental and simulation approaches.The sorption performance of the resulting solid materials in terms of sorption capacity and selectivity was assessed in model and simulated systems obtained by using either ultrapure or river water with an adequate composition as solvent to prepare aqueous solutions of strontium or/and cesium. The results of sorption experiments clearly indicated strong selectivity of the vanadate structures toward Cs+ and that of the manganate ones toward Sr2+, even under conditions of competition among various ionic species.Direct calorimetry measurements of heat effects accompanying sorption were correlated with the results of molecular simulation studies to shed more light on the origin of the improved sorption selectivity.

Os constantes avanços nas áreas de transmissão e processamento de dados ao longo dos últimos anos permitiram a criação de diversas aplicações e serviços baseados em dados multimídia, como streaming de vídeo, videoconferências, aulas remotas e IPTV. Além disso, avanços nas demais áreas da computação e engenharias, possibilitaram a construção de uma enorme diversidade de dispositivos de acesso a esses serviços, desde computadores pessoais até celulares, para citar os mais utilizados atualmente. Muitas dessas aplicações e dispositivos estão amplamente difundidos hoje em dia, e, ao mesmo tempo em que a tecnologia avança, os usuários tornam-se mais exigentes, buscando sempre melhor qualidade nos serviços que utilizam. Devido à grande variedade de redes e dispositivos atuais, uma dificuldade existente é possibilitar o acesso universal a uma transmissão. Uma alternativa criada é utilizar transmissão de vídeo escalável com IP multicast e controlada por mecanismos para adaptabilidade e controle de congestionamento. O produto final dessas transmissões mulimídia são os próprios dados multimídia (vídeo e áudio, principalmente) que o usuário está recebendo, portanto a qualidade destes dados é fundamental para um bom desempenho do sistema e satisfação dos usuários. Este trabalho apresenta um estudo de avaliações subjetivas de qualidade aplicadas em sequências de vídeo codificadas através da extensão escalável do padrão H.264 (SVC). Foi executado um conjunto de testes para avaliar, principalmente, os efeitos da instabilidade da transmissão (variação do número de camadas de vídeo recebidas) e a influência dos três métodos de escalabilidade (espacial, temporal e de qualidade) na qualidade dos vídeos. As definições foram baseadas em um sistema de transmissão em camadas com utilização de protocolos para adaptabilidade e controle de congestionamento. Para execução das avaliações subjetivas foi feito o uso da metodologia ACR-HRR e recomendações das normas ITU-R Rec. BT.500 e ITU-T Rec. P.910. Os resultados mostram que, diferente do esperado, a instabilidade não provoca grandes alterações na qualidade subjetiva dos vídeos e que o método de escalabilidade temporal tende a apresentar qualidade bastante inferior aos outros métodos. As principais contribuições deste trabalho estão nos resultados obtidos nas avaliações, além da metodologia utilizada durante o desenvolvimento do trabalho (definição do plano de avaliação, uso das ferramentas como o JSVM, seleção do material de teste, execução das avaliações, entre outros), das aplicações desenvolvidas, da definição de alguns trabalhos futuros e de possíveis objetivos para avaliações de qualidade. / The constant advances in multimedia processing and transmission over the past years have enabled the creation of several applications and services based on multimedia data, such as video streaming, teleconference, remote classes and IPTV. Futhermore, a big variety of devices, that goes from personal computers to mobile phones, are now capable of receiving these transmissions and displaying the multimedia data. Most of these applications are widely adopted nowadays and, at the same time the technology advances, the user are becoming more demanding about the quality of the services they use. Given the diversity of devices and networks available today, one of the big challenges of these multimedia systems is to be able to adapt the transmission to the receivers' characteristics and conditions. A suitable solution to provide this adaptation is the integration of scalable video coding with layered transmission. As the final product in these multimedia systems are the multimedia data that is presented to the user, the quality of these data will define the performace of the system and the users' satisfaction. This paper presents a study of subjective quality of scalable video sequences, coded using the scalable extension of the H.264 standard (SVC). A group of experiments was performed to measure, primarily, the efeects that the transmission instability (variations in the number of video layers received) has in the video quality and the relationship between the three scalability methods (spatial, temporal and quality) in terms of subjective quality. The decisions taken to model the tests were based on layered transmission systems that use protocols for adaptability and congestion control. To run the subjective assessments we used the ACR-HRR methodology and recommendations given by ITU-R Rec. BT.500 and ITU-T Rec. P.910. The results show that the instability modelled does not causes significant alterations on the overall video subjective quality if compared to a stable video and that the temporal scalability usually produces videos with worse quality than the spatial and quality methods, the latter being the one with the better quality. The main contributions presented in this work are the results obtained in the subjective assessments. Moreover, are also considered as contributions the methodology used throughout the entire work (including the test plan definition, the use of tools as JSVM, the test material selection and the steps taken during the assessment), some applications that were developed, the definition of future works and the specification of some problems that can also be solved with subjective quality evaluations.

Dans un grand nombre d'applications industrielles, il est nécessaire d'inspecter des structures rayonnantes à l'aide de techniques de caractérisation et de localisation de sources acoustiques instationnaires. Ces dernières décennies, plusieurs techniques d'imagerie acoustique ont été développées, reposant sur l'utilisation de mesures d'un jeu de grandeurs acoustiques (pression et/ou vitesse particulaire) sur des antennes microphoniques, structurées ou non. Le travail réalisé durant cette thèse porte plus spécifiquement sur les techniques d'imagerie instationnaires par retournement temporel. Nous nous intéressons plus particulièrement aux optimisations permettant de rendre les performances de ces techniques d'imagerie instationnaires insensibles aux conditions de mesures (environnement réverbérant et bruité). Pour cela, différentes améliorations sont proposées dans ce manuscrit, grâce à des mesures réalisées sur une antenne hémisphérique double-couche. En particulier, nous détaillerons un processus d'imagerie acoustique quantitative par retournement temporel grâce au calcul de l'intégrale de Helmholtz-Kirchhoff retournée temporellement, grâce aux mesures "double données" réalisées sur l'antenne. Ensuite, nous détaillerons les optimisations pour supprimer les effets de salle et les contributions de sources perturbatrices grâce à une méthode de séparation de champs, qui consiste à projeter les données mesurées sur la base des harmoniques sphériques puis à séparer les contributions "entrantes" et "sortantes". Pour finir, la résolution d'imagerie par retournement temporel, intrinsèquement limitée, est améliorée grâce à la définition automatique d'un puits à retournement temporel dont la formulation analytique tire partie de la structure double-couche des données mesurées. Il est essentiel de noter que ces différentes stratégies d'optimisation sont possibles grâce à l'enregistrement d'un double jeu de données (pression-pression ou pression-vitesse). La qualité de reconstruction du champ de pression par le processus d'imagerie par retournement temporel double couche complet est illustré à travers des études numériques et des études expérimentales, allant d'une configuration idéale (environnement anéchoïque et non bruité) à un cas complexe (environnement fortement réverbérant et bruité). / For many industrial applications, it is necessary to inspect radiating structures using non-stationary sources localization and characterization techniques. In the last decades, many acoustical imaging methods have been developed. These techniques are based on the measurement of a set of acoustical quantities (pressure and/or particle velocity) on structured (or not) microphones antennas. In particular, this thesis work aims at studying and optimizing non-stationary imaging methods using time reversal. More particularly, we are interested in improvements following to assess precisely the acoustic field with good performances, by making these methods performances insensitive to the measurements conditions (reverberant and noisy environment). For purpose, several improvements are proposed in this manuscript, thanks to measurements realised on a hemispherical double layer antenna. In particular, we detail a quantitative time reversal acoustical imaging process thanks to the calculation of the time reversed version of the Helmholtz-Kirchhoff integral, using the "double data" measurements realised on the antenna. Then, we will detail improvements to suppress both room effects and the perturbative sources contributions thanks to a field separation method, which consists in expanding the measured data onto spherical harmonics functions basis. Then, the "incoming" and the "outgoing" contributions are separated. Finally, the time reversal imaging resolution, intrinsically limited, is improved thanks to the automatic definition of a time reversal sink. Its analytical formulation takes advantage of double layer measurement structure. This of crucial importance to note that all these improvements take advantage from the recording of a double data set (pressure-pressure or pressure-velocity). The quality of the pressure field reconstructed using the full double layer time reversal imaging process is illustrated through numerical and experimental studies, from an idealized situation (anechoic and not noisy environments) to a hard case (highly reverberant and noisy environment).

Dans le cadre de certaines applications militaires ou méthodologiques, on peut chercher à rendre un objet « invisible » vis-à-vis des ondes acoustiques. Différentes méthodes passives ont été proposées ces dernières années pour éviter ou atténuer la diffraction d'ondes acoustiques sur des obstacles rigides. Ces techniques reposent sur des phénomènes purement acoustiques, avec par exemple la présence de multiples résonateurs ou d'objets diffractants. L'étude présentée ici s'intéresse pour sa part aux effets que l'on pourrait obtenir au moyen d'un revêtement multicouche élastique fixé à un cylindre que l'on souhaite rendre indétectable. Le comportement vibro-acoustique d'un tel revêtement est d'abord modélisé. Par optimisation, on détermine les caractéristiques mécaniques et dimensionnelles des couches permettant une atténuation omnidirectionnelle de la diffraction. Des configurations réalistes de revêtements composés d'une couche orthotrope et d'une couche isotrope sont dégagées dans le cas d'un milieu extérieur constitué d'air. On montre que de tels dispositifs permettent d'atténuer la diffraction à une fréquence donnée ou sur une bande de fréquence. Le problème de la caractérisation expérimentale de ces revêtements est également abordé. Dans un second temps, le cas d'un milieu extérieur constitué d'eau est étudié. On met alors en évidence une réduction de la diffraction avec des revêtements composés de deux couches isotropes. L'influence des différents paramètres de la couche intérieure est analysée. Enfin, des exemples montrent que la bande de fréquence sur laquelle a lieu l'atténuation de la diffraction peut être élargie en augmentant le nombre de couches. / Making an object invisible to acoustic waves could prove useful for military applications or measurements in confined space. Different passive methods have been proposed in recent years to avoid acoustic scattering from rigid obstacles.These techniques are exclusively based on acoustic phenomena, and use for instance multiple resonators or scatterers. This thesis deals with a different method and studies the effects in terms of scattering reduction of an elastic multi-layered coating fixed to the object to conceal. Vibrations of the coating subject to acoustic waves are first modelled to compute the scattered pressure in the external fluid. Mechanical and dimensional properties of the layers leading to omnidirectional scattering reduction are optimised. Considering an external fluid consisting of air, realistic configurations of coatings emerge, composed of a thick internal orthotopic layer and a thin external isotropic layer. These coatings are shown to enable scattering reduction at a precise frequency or on a larger frequency band. The problem of experimental characterisation is also addressed.The study then focuses on a cylinder immersed in water. Bi-layer isotropic coatings can be used in such configuration. A parametric study is led on the characteristics of the internal layer. Finally, significant scattering reduction is achieved for alarger frequency range by increasing the number of layers. Examples of four-layer isotropic coatings are presented to highlight this result.

Orientador: Prof. Dr. Daniel Zanetti de Florio / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2014. / Motores a combustão flexíveis foram desenvolvidos para diversificar a utilização de combustíveis para a indústria da mobilidade, com o intuito de trazer benefícios econômicos, ganho em sustentabilidade e redução do impacto ambiental. Tal diversificação tem proporcionado o desenvolvimento de linhas de pesquisa que aperfeiçoem essa utilização, através de incentivo fiscal do governo, bem como injeção de recursos da indústria nas universidades como, por exemplo, o programa Inovar Auto. Dentre os novos combustíveis está o etanol que devido às suas características físico-químicas, como a sua pressão de vapor traz vantagens como ganho de torque e potência e desvantagens como aumento de desgaste e corrosão dos componentes metálicos a ele expostos. As bronzinas são partes de base metálica que promovem a redução do contato metal-metal entre as principais peças de um motor como bloco, virabrequim e biela, além de permitirem uma melhor hidrodinâmica do óleo lubrificante, aumentando a vida útil do motor. Significativamente expostas ao ambiente etanol, óleo, gases e água, as mesmas são suscetíveis ao fenômeno de corrosão. Análise de corrosão por espectroscopia de impedância eletroquímica é um método conhecido na literatura e motivou a caracterização eletroquímica de componentes cíclicos metálicos de motores, através da obtenção de espectros de impedância para três diferentes recobrimentos em bronzinas, expostos sistematicamente a condicionamentos e envelhecimentos, variando-se temperatura, tempo de exposição em mistura óleo e etanol comuns. Dentre os três recobrimentos está uma proposta cerâmica a partir de óxido de boro depositado por uma técnica comum denominada slurry, apresentada na literatura aeroespacial com vantagens tribológicas. As medições foram feitas em solução aquosa de cloreto de sódio a 0,1 M, utlizando-se um eletrodo de referência de prata e cloreto de prata, um eletrodo de medição de platina como contra eletrodo e um eletrodo de trabalho com amostras de aço embutidas e recobertas com três diferentes superfícies; metálica (VW1), polimérica (P1) e cerâmica (C1), dispostos em uma célula ligada a um impedancímetro e a um potenciostato de marca Solartron. A intersecção do semicírculo do espectro com o eixo das abcissas ou parte real da impedância, Z¿ é conhecida como resistência de polarização Rp. Da literatura sabe-se que esta grandeza é proporcional ao inverso da corrente e taxa de corrosão da superfície do eletrodo de trabalho. A obtenção desta variável pode ser feita através de aproximações, com modelos de circuitos equivalentes RC, que calculam as resistências e capacitâncias destes circuitos. A partir do tratamento dos dados acima descritos, foi possível estabelecer três diferentes tendências de comportamento da taxa de corrosão ao longo do tempo de exposição ao meio etanol mais óleo, a saber: amostra de superfície metálica tipo VW1 apresentou corrosão dinâmica e controlada com taxa de corrosão decrescente ao longo do tempo; amostra polimérica tipo P1 apresentou também redução da taxa de corrosão por passivação ao longo do tempo após penetração da camada polimérica e; amostra cerâmica de óxido de boro tipo C1 apresentou maior redução da taxa de corrosão ao longo do envelhecimento em óleo e etanol. / Flex fuel combustion engines were developed to diversify the use of fuels for the mobility industry, in order to bring economic benefits gain in sustainability and environment impact reduction. Such diversification has permitted the research line development which optimizes this use through government incentive as well as fund injection in universities such as Inovar Auto program. Ethanol is among the new fuels, which due to its physical-chemical characteristics (vapor pressure) presents advantages as power and torque and disadvantages, as waste increase and corrosion of the exposed metal components. The bearings are parts made of metal that promote the metal-metal contact reduction among the main engine parts like cylinder block, cranckshaft and connecting rods. Besides, they allow better hydrodynamics of the lubrication oil increasing the duration of a flex combustion engine. Exposed to the ethanol, oil, gases and water environment these bearings are prone to corrosion phenomenon. The corrosion analysis by impedance spectroscopy corrosion is a method known in the literature and has motivated the electrochemical characterization of metal cyclic components by obtaining impedance spectra for three different recovering in bearings. The third type of recovering was developed through bore oxide produced by slurry coating techniques, which was presented on a aerospacial research publication with tribologic gain. These are systematically exposed to conditionings and aging while varying temperature, exposure time and rotation of oil and ethanol common mixtures. The measurements were made on aquous solution of NaCl 0,1 M through a reference silver and silver cloride eletrode, a platine counter eletrode and the work eletrode with samples of the three different bearings surface, metallic (VW1), polymeric (P1) and ceramic (C1) all assembled in a eletrochemistry cell, switched to a potenciostat and an impedancimeter, both by Solartron. The intersection of the semicircle spectra with "X" axle or real part of the impedance Z¿ is known as polarization resistance Rp. From the bibliography review it is known that this resistance is proportional to the inverse of corrosion rate on the surface of the working electrodes. The obtention of this variable could be done through approximation of RC circuit models, which calculate the resistances and the capacitances. Through data treatment it was possible to establish three different tendencies of corrosion rate behavior during ethanol and oil exposure time: Metallic surface sample type VW1 presented dynamic controlled with descending corrosion rate during the aging processes. Polymeric recovery sample type P1 also presented reduction of corrosion rate after penetration of the polymeric recovering e less during the aging processes. Ceramic recovery sample type C1 presented major reduction of corrosion during the aging on oil plus ethanol.

Os constantes avanços nas áreas de transmissão e processamento de dados ao longo dos últimos anos permitiram a criação de diversas aplicações e serviços baseados em dados multimídia, como streaming de vídeo, videoconferências, aulas remotas e IPTV. Além disso, avanços nas demais áreas da computação e engenharias, possibilitaram a construção de uma enorme diversidade de dispositivos de acesso a esses serviços, desde computadores pessoais até celulares, para citar os mais utilizados atualmente. Muitas dessas aplicações e dispositivos estão amplamente difundidos hoje em dia, e, ao mesmo tempo em que a tecnologia avança, os usuários tornam-se mais exigentes, buscando sempre melhor qualidade nos serviços que utilizam. Devido à grande variedade de redes e dispositivos atuais, uma dificuldade existente é possibilitar o acesso universal a uma transmissão. Uma alternativa criada é utilizar transmissão de vídeo escalável com IP multicast e controlada por mecanismos para adaptabilidade e controle de congestionamento. O produto final dessas transmissões mulimídia são os próprios dados multimídia (vídeo e áudio, principalmente) que o usuário está recebendo, portanto a qualidade destes dados é fundamental para um bom desempenho do sistema e satisfação dos usuários. Este trabalho apresenta um estudo de avaliações subjetivas de qualidade aplicadas em sequências de vídeo codificadas através da extensão escalável do padrão H.264 (SVC). Foi executado um conjunto de testes para avaliar, principalmente, os efeitos da instabilidade da transmissão (variação do número de camadas de vídeo recebidas) e a influência dos três métodos de escalabilidade (espacial, temporal e de qualidade) na qualidade dos vídeos. As definições foram baseadas em um sistema de transmissão em camadas com utilização de protocolos para adaptabilidade e controle de congestionamento. Para execução das avaliações subjetivas foi feito o uso da metodologia ACR-HRR e recomendações das normas ITU-R Rec. BT.500 e ITU-T Rec. P.910. Os resultados mostram que, diferente do esperado, a instabilidade não provoca grandes alterações na qualidade subjetiva dos vídeos e que o método de escalabilidade temporal tende a apresentar qualidade bastante inferior aos outros métodos. As principais contribuições deste trabalho estão nos resultados obtidos nas avaliações, além da metodologia utilizada durante o desenvolvimento do trabalho (definição do plano de avaliação, uso das ferramentas como o JSVM, seleção do material de teste, execução das avaliações, entre outros), das aplicações desenvolvidas, da definição de alguns trabalhos futuros e de possíveis objetivos para avaliações de qualidade. / The constant advances in multimedia processing and transmission over the past years have enabled the creation of several applications and services based on multimedia data, such as video streaming, teleconference, remote classes and IPTV. Futhermore, a big variety of devices, that goes from personal computers to mobile phones, are now capable of receiving these transmissions and displaying the multimedia data. Most of these applications are widely adopted nowadays and, at the same time the technology advances, the user are becoming more demanding about the quality of the services they use. Given the diversity of devices and networks available today, one of the big challenges of these multimedia systems is to be able to adapt the transmission to the receivers' characteristics and conditions. A suitable solution to provide this adaptation is the integration of scalable video coding with layered transmission. As the final product in these multimedia systems are the multimedia data that is presented to the user, the quality of these data will define the performace of the system and the users' satisfaction. This paper presents a study of subjective quality of scalable video sequences, coded using the scalable extension of the H.264 standard (SVC). A group of experiments was performed to measure, primarily, the efeects that the transmission instability (variations in the number of video layers received) has in the video quality and the relationship between the three scalability methods (spatial, temporal and quality) in terms of subjective quality. The decisions taken to model the tests were based on layered transmission systems that use protocols for adaptability and congestion control. To run the subjective assessments we used the ACR-HRR methodology and recommendations given by ITU-R Rec. BT.500 and ITU-T Rec. P.910. The results show that the instability modelled does not causes significant alterations on the overall video subjective quality if compared to a stable video and that the temporal scalability usually produces videos with worse quality than the spatial and quality methods, the latter being the one with the better quality. The main contributions presented in this work are the results obtained in the subjective assessments. Moreover, are also considered as contributions the methodology used throughout the entire work (including the test plan definition, the use of tools as JSVM, the test material selection and the steps taken during the assessment), some applications that were developed, the definition of future works and the specification of some problems that can also be solved with subjective quality evaluations.

Ce travail de thèse se base sur quatre matériaux modèles, de composition LiNi1/3Mn1/3Co1/3O2, qui différent de par leur microstructure. Le lien entre leur morphologie et les performances électrochimiques est étudié par la combinaison de la caractérisation exhaustive de leur microstructure, l’étude de leur comportement en batterie et la modélisation de leur réponse électrochimique. L’étape limitant le processus électrochimique est identifiée par voltampérométrie cyclique et nous montrons que la transition attendue d’une limitation par le transfert de charge à une limitation par la diffusion en phase solide a lieu à différents régimes selon la microstructure. Ce comportement est expliqué par l’utilisation d’outils de simulations numériques. Selon leur forme et leur agglomération, les cristallites agissent collectivement ou indépendamment les unes des autres. Ces résultats rationalisent les performances en puissance obtenues sur nos matériaux. Les résultats de simulation montrent également qu’une faible fraction de la surface développée est électroactive, ce qui remet en question la large utilisation de la surface BET dans la littérature. Nous montrons également que, si les matériaux poreux sont les plus performants en puissance gravimétrique, la tendance est inversée pour la puissance volumique. Les stratégies de nanostructuration largement employées, qui se basent sur la capacité spécifique pour caractériser les matériaux, ne doivent pas oublier faire oublier le compromis nécessaire entre surface développée et volume. / Four NMC materials are synthesized by co-precipitation. They exhibit a hierarchical architecture made of reasonably spherical agglomerates. One is constituted of flake-shaped, spatially oriented, crystallites that leave large apparent void spaces in the agglomerate, while the other results from the tight agglomeration of micron-sized cuboids. Porous material exhibits the best power performances. It is impossible to identify a geometrical parameter that predict performances, even after achieving the full characterization of the microstructures. Cyclic voltammetry reveals two behaviours depending on the shape of crystallites: processes limited by solid-state diffusion (cuboids) and the ones limited by charge transfer even at high rates (flake-shaped). This observation challenges active materials design strategies that assume diffusion as the limiting process of lithium intercalation. Focusing on enhancing kinetics could be the way to increase performances. Charge-transfer is first investigated by measuring electronic conductivities over a wide range of frequencies, allowing to discriminate relaxations arising at various length scales. We show that flake-shaped crystallites facilitate the motion of electrons at all scale levels compared to cuboids. Charge-transfer limitations originate from the electrolyte/material interface in materials exhibiting high surface areas. Numerical simulations reveal that BET measurements largely overestimate the actual electroactive surface, which is understood by HRTEM images of flake-shaped crystallites. Only a small percentage, limited to the edge plane is truly electroactive.

Cette thèse présente un travail sur l’obtention d’aérogels d’HDL par séchage en conditions CO2 supercritique et l’élaboration de nouveaux bionanocomposites formés par la coprécipitation d’hydroxydes doubles lamellaire (HDL) dans l'espace confiné des billes d'alginate. Grâce à la combinaison d’une synthèse par coprécipitation Flash et d’un séchage en conditions supercritiques au CO2, des aérogels d’HDL possédant des surfaces spécifiques élevées sont élaborés. Parallèlement, l’alginate est utilisé comme une matrice de confinement pour la précipitation inorganique d’HDL. D’une part, les billes d'alginate sont synthétisées par complexation des ions Ca2+ et la coprécipitation des phases HDL s’effectue en réalisant des imprégnations successives de réactifs. D’autre part, des billes d'alginate sont formées directement en présence des cations divalents (Mg2+, Ni2++, Co2+, ...) et des cations des métaux trivalents (Al3+), précurseurs des composés inorganiques. La coprécipitation des HDL se produit dans ce cas lors d'une étape d'imprégnation dans une solution d'hydroxyde de sodium. Tous les composés HDL, aérogels ou encore bionanocomposites sont caractérisés en détail par DRX, spectroscopie IR, MEB/MET, adsorption/désorption d’azote et ATG/DTG, pour obtenir un meilleur aperçu de la structure des particules, de leur taille et de leur morphologie. Des études menées sur l’adsorption de la trypsine pour les aérogels ou encore sur les performances d’électrodes modifiées HDL-alginate ont permis de montrer qu’il était possible d'améliorer les performances des HDL en augmenter leur porosité et en élaborant des bionanocomposites. / In this work, we investigated both the use of CO2 supercritical drying conditions and the use of biopolymer to modify the growth and aggregation of inorganic Layered Double Hydroxide (LDH) particles. Indeed, one possibility to enhance their performances is to increase the LDH porosity and to design them as nanostructured open structure. Thanks to the combinaison of fast coprecipitation and CO2 supercritical drying, highly porous LDH aerogels were obtained with enhanced textural properties. In parallel, the coprecipitation of Layered Double Hydroxides (LDH) in the confined space of alginate beads is reported. In our approach, Alginate acts as a template to support and confined the inorganic precipitation. In one hand, beads made of Alginate are synthesized by complexation of Ca2+ ions and LDH phases are coprecipitated using successive impregnations of reactants. In another hand, Alginate beads are formed directly in presence of the divalent (Mg2+, Ni2+, Co2+,…) and trivalent metal cations (Al3+), precursors of the inorganic compounds. LDH coprecipitation then occurs during a further impregnation step in a sodium hydroxide solution. All the LDH aerogels and LDH nanocomposites beads are deeply characterized using XRD, SEM/TEM, FTIR spectroscopic, adsorption/desorption of nitrogen and TGA/DTG to get better insight on particle structure, size and morphology Aerogels display enhanced adsorption behavior toward trypsine immobilization whereas a net improvement of the electrochemical response is noticed for the NiAl based bionanocomposites prepared by confined coprecipitation into Alginate.