Orientadores: Antonio J. Ramirez, Maria Clara F. Ierardi / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-09T21:56:05Z (GMT). No. of bitstreams: 1 Seraphim_RafaelMolena_M.pdf: 6485115 bytes, checksum: 380cfffee5fa982ec74a9cdc78c88e3a (MD5) Previous issue date: 2007 / Resumo: O avanço cientifico no estudo de átomos, moléculas e proteínas tem recebido uma contribuição significativa dos aceleradores de partículas, que em sua grande maioria são utilizados para a geração de radiação síncrotron. Por isso, o aprimoramento destas máquinas mostra-se de extrema importância para manter a ciência em seu contínuo avanço. O sistema de vácuo destas máquinas apresenta-se como um importante parâmetro para o seu bom funcionamento e melhorias neste promovem diretamente melhorias na qualidade da radiação síncrotron gerada. Logo, o desenvolvimento deste trabalho teve como principal objetivo o estudo das juntas soldadas das câmaras de vácuo que compõem o acelerador do Laboratório Nacional de Luz Síncrotron (LNLS). As juntas foram preparadas com o processo de soldagem GTAW (Gás Tungsten Arc Welding) mediante a utilização de diferentes gases de proteção, como Argônio, Hélio e Nitrogênio, e misturas entre estes. Os estudos concentraram-se na análise da influência dos gases de proteção na dessorção de gases das juntas soldadas. Para a caracterização destas utilizaram-se as técnicas de análise de superfícies Dessorção Estimulada por Elétrons (DEE) e Dessorção Estimulada por Fótons (DEF). Adicionalmente, realizou-se um estudo comparativo entre as duas técnicas buscando-se estabelecer relações entre os resultados fornecidos pelas mesmas. Os resultados mostraram que a dessorção de gases independe do gás de proteção de soldagem, mas depende sim do nível de oxidação das juntas soldadas, as quais podem apresentar altas taxas de dessorção caso estejam muito oxidadas e os óxidos não sejam camadas contínuas. Em conclusão pode-se dizer que as juntas soldadas para câmaras de vácuo de aceleradores de partículas devem apresentar baixos níveis de oxidação, e apesar das semelhanças encontradas entre a DEE e a DEF é aconselhável utilizar a DEF para a caracterização de superfícies para trabalharem com radiação síncrotron / Abstract: The scientific advance of atoms, molecules and proteins studies has received an important contribution from particle accelerators, which are mainly used to generate synchrotron radiation. Hence, the improvement of these machines is necessary to maintain the continuous advance of science. One of the key components for the adequate operation of these accelerators is the vacuum system. Thus, its improvement directly impacts on the quality of the generated synchrotron radiation. Therefore, the principal purpose of this work is to study the gas desorption from the welding joints on the particle accelerators vacuum chambers. The welds were prepared using the GTAW (Gas Tungsten Arc Welding) process with different shielding gases, as argon, helium and nitrogen, and some mixtures of them. The study concentrated on the analysis of the shielding gas influence on the gas desorption from the welded joints. The gas desorption of the joints was evaluated using Electron Stimulated Desorption (ESD) and Photon Stimulated Desorption (PSD). In addition, it was carried out a comparative study between both desorption techniques to establish relationships between the results provided by them. The results showed that the gas desorption from the welding joints does not depend on the welding shielding gas, but on the oxidation level of the joint, which can present high desorption yield if it is highly oxidized and these oxides are not a continuous film. Therefore, it is advisable to minimize the oxidation during welding of vacuum chambers for particle accelerators. Regarding the comparison between ESD and PSD they were found some similarities. However, PSD will have better performance characterizing surfaces that will be exposed to synchrotron radiation / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Made available in DSpace on 2014-07-29T15:13:39Z (GMT). No. of bitstreams: 1 Claudia peixoto bueno.pdf: 2154558 bytes, checksum: e3212e2f2e948a89b381b38c7ab473b7 (MD5) Previous issue date: 2009-02-20 / The deterioration of vacuum packed refrigerated meat accompanied by large gas production - a phenomenon called blown pack - is considered a major cause of economic losses of the meat industry in several regions of Brazil and the world. Several psychrophilic and psychrotrophic microorganisms may be involved, especially species of Clostridium. The objective of the present study was to perform the molecular characterization, through the use of the PCR technique, and the molecular isolation by conventional bacteriology, of the main microorganisms that cause blown pack in refrigerated meat from Brazil, New Zealand and the United Kingdom. Thus, typing techniques were used to differentiate the species and subspecies involved in this type of deterioration. Tirty-six samples of Brazilian blown pack meat, 6 samples from the UK and 12 experimental blown pack samples of venison from the North Island of New Zealand were analyzed. Three pairs of primers, the RFP / RRP, the 16SEF/16SER and the pair EISRF / EISRR were used for C. estertheticum estertheticum and Clostridium estertheticum like, and one for C. gasigenes (16DBF/16DBR). The samples with the PCR results were sent to a microbiology laboratory for conventional isolation of Clostridium estertheticum. It was concluded that Clostridium estertheticum estertheticum is responsible for the deterioration of meat and hence the blown pack in the UK. Samples of blown pack Brazilian meat have Clostridium estertheticum like as primary causal agent. The typing was carried out in isolates and strains - donated by Mirinz Center / Ruakura Agresearch / Hamilton / New Zealand - together with two isolates from Brazil, involved in this type of deterioration. The selected techniques AFLP and RFLP - PCR were able to distinguish species and subspecies of psychrophilic and psychrotrophic clostridia. However, the AFLP showed the highest discriminatory power, being able to distinguish 100% of the species - C. estertheticum, C. frigoris, C. bowmani, C. lacusfryxellense and C. psychrophylum - and also the subspecies C. estertheticum estertheticum, C. estertheticum laramiense, C. estertheticum like k21 and k24. Through the technique of RFLP, it was possible to differentiate the species of clostridia psychrotrophic, psichrophilic and also the subspecies C. estertheticum estertheticum and Clostridium estertheticum like, along with the use of four restriction endonucleases - AluI, CfoI, TaqI and HaeIII. The HaeIII provided greater variety of fragments and the ability to differentiate the species of clostridia psychrophilic and psychrotrophic, whereas TaqI was the only enzyme capable of differentiating the subspecies of C. estertheticum estertheticum and C. estertheticum laramiense of C. estertheticum like. The Brazilian samples isolated fit into the group of Clostridium estertheticum like, although there is no confirmation of the absence of Clostridium estertheticum estertheticum in the country. / A deterioração de carnes refrigeradas embaladas a vácuo acompanhada de grande produção de gás - fenômeno denominado tufamento de embalagens - é considerada uma das principais causas de perdas econômicas da indústria cárnea, em várias regiões do Brasil e do mundo. Diversos microrganismos psicrofílicos e psicrotróficos podem estar envolvidos, destacando-se espécies do gênero Clostridium. Objetivou-se com o presente estudo a caracterização molecular, por meio do emprego da técnica de PCR e o isolamento pela bacteriologia convencional, dos principais microrganismos causadores do tufamento de embalagens de carnes refrigeradas procedentes do Brasil, Nova Zelândia e Reino Unido. Para tanto, foram empregadas técnicas de tipagem visando a diferenciação das espécies e subespécies envolvidas neste tipo de deterioração. Foram analisadas 36 amostras tufadas de carnes brasileiras, 6 amostras tufadas oriundas do Reino Unido e 12 amostras experimentais tufadas de carne de cervo provenientes da Ilha Norte da Nova Zelândia. Foram utilizados três pares de primers, o RFP/RRP, o 16SEF/16SER e o par EISRF/EISRR para C. estertheticum estertheticum e Clostridium estertheticum like e um para C. gasigenes (16DBF/16DBR). As amostras com os resultados positivos ao PCR foram enviadas para a microbiologia convencional para isolamento do Clostridium estertheticum. Concluiu-se que o Clostridium estertheticum estertheticum é responsável pela deterioração das carnes e, consequentemente, pelo tufamento das embalagens no Reino Unido. As amostras tufadas de embalagens de carnes brasileiras têm como principal agente causador o Clostridium estertheticum like. A tipagem foi relizada em cepas e isolados doados pelo Mirinz Centre/ Ruakura AgResearch/ Hamilton/NZ - juntamente a dois isolados brasileiros, envolvidos nesse tipo de deterioração . As técnicas eleitas AFLP e RFLP PCR foram capazes de distinguir as espécies e subespécies de clostrídios psicrofílicos e psicrotróficos, porém, o AFLP apresentou maior poder discriminatório, sendo capaz de diferenciar 100% das espécies C. estertheticum, C. frigoris, C. bowmani, C. lacusfryxellense e C psychrophylum - e também as subespécies - Clostridium estertheticum estertheticum, Clostridium estertheticum laramiense, o Clostridium estertheticum like K21 e Clostridium estertheticum like K24. Por meio da técnica de RFLP foi possível diferenciar as espécies do clostrídio psicrofílicos e psicrotróficos e também as subespécies C. estertheticum estertheticum e Clostridium estertheticum like, utilizando em conjunto as quatro endonucleases de restrição AluI, CfoI, TaqI e HaeIII. A HaeIII proporciona maior variedade de fragmentos e capacidade de diferenciar as espécies de clostrídios psicrofílicos e psicrotróficos. Já a TaqI foi a única enzima capaz de diferenciar as subespécies C. estertheticum estertheticum e C. estertheticum laramiense do C. estertheticum like. As amostras brasileiras isoladas se enquadraram no grupo do Clostridium estertheticum like.

Dans l'industrie du raffinage, les procédés de craquage catalytique permettent la production de carburants à partir de coupes pétrolières lourdes, telles que les distillats sous vides (DSV). Pour optimiser ces procédés, un hydrotraitement préalable est nécessaire. Ces dernières années, les travaux conséquents de R&D ont considérablement amélioré l'activité des catalyseurs d'hydrotraitement. Par conséquent, le transfert de matière interne peut devenir limitant, il doit donc être quantifié.Une méthodologie utilisant la chromatographie inverse liquide a été développée afin de caractériser le transfert de matière dans des supports aluminiques de catalyseur. Le système a ensuite été déployé pour caractériser l'influence de l'adsorption, de la température et des précurseurs de la phase active. Dans des alumines mésoporeuses, le régime de diffusion est moléculaire pour des composés saturés allant des coupes essences au DSV. Ainsi, pour différentes alumines, des valeurs de tortuosité ont été estimées et corrélées aux propriétés texturales (porosité, surface spécifique et distribution en taille des pores). Ces relations montrent que les valeurs de tortuosité obtenues ne sont pas en accord avec un solide homogène vis-à-vis des propriétés de transfert de matière. Il y aurait donc une organisation dans la porosité des alumines.Un test catalytique en réacteur agité a aussi été développé pour étudier le transfert de matière en conditions réactives. L'impact de la taille des grains sur l'hydrodésulfuration d'une molécule synthétisée a été caractérisé et modélisé. Ces résultats ont été comparés aux expériences de chromatographie inverse avec un bon accord / The catalytic cracking has an important role in fuels production from heavy oil cuts like vacuum gas oil (VGO). To optimize these processes, a pre-hydrotreatment is required. The amount of work dealt by the research community in the last years has highly contributed to the enhancement of the catalyst’s activity. Therefore, the internal mass transfer can become the limiting step and it must be quantified.A methodology based on inverse liquid chromatography has been developed to characterize the mass transfer within alumina catalyst supports. The experimental setup was also used to study the influence of several parameters into mass transfer properties such as, adsorption, temperature, and active phase precursors. In mesoporous aluminas, the diffusion regime undertaken by saturated compounds, going from gasoline to VGO is the molecular regime. For different alumina supports, tortuosity values were estimated and correlated to the textural properties (porosity, specific surface area and pore size distribution). These results showed that the aluminas can not be considered as homogeneous supports given the estimated mass transfer properties. Thus, we assume that a hierarchical porous structure might be in cause. A catalytic test promoted in a stirred reactor was also developed to study the mass transfer properties under reactive conditions. The impact of the particle grains size into the hydrodesulphurization of a synthetized molecule was characterized and modeled. A good agreement was found between the data obtained using the inverse chromatography experiments and the catalytic tests

This work was aimed at studying lipid stability of silver catfish (Rhamdia quelen) fillets. The influence of the inclusion (5%) of soybean or rice oil in silver catfish diet and vacuum packaging on lipid and color stability of raw silver catfish fillets was evaluated during frozen storage (18 months). Besides, the influence of seven cooking methods (boiling, conventional baking, microwave baking, grilling, deep frying in soybean oil, canola oil, or partially hydrogenated vegetable oil) on the oxidation, proximate, and fatty acid composition of fillets was also evaluated. The different diets had no effect on the proximate composition of the fish fillets. The content of thiobarbituric acid reactive substances (TBARS, lipid oxidation index) of fillets from both diets increased after 12 months of storage with or without vacuum, but this increase was higher in fish fed with soybean oil. Color parameters were not affected by the vacuum storage or diet, but most parameters (a*, b*, chroma, and Hue values) were affected by the time of storage. Hue value showed that raw fillets tended to yellowness and after 18 months of frozen storage became greener. The content of various fatty acids in fillets was influenced by the type of vegetable oil used in the diet, but n-3/n-6 polyunsaturated fatty acids ratio and unsaturated/saturated ratio did not differ between diets. All cooking methods evaluated reduced moisture and increased protein content. Fat content was higher in the fried fillets. The free fatty acid content of fillets was significantly reduced by the different cooking methods, while conjugated dienes and peroxide values decreased for all fried samples, but remained constant in the samples submitted to the other cooking methods. Boiling and baking increased TBARS, while grilling and frying did not change TBARS. Boiling, baking, and grilling did not affect the silver catfish fillets fatty acid composition. Frying in canola oil increased n-3/n-6 ratio, in soybean oil increased general polyunsaturated fatty acid content, and in hydrogenated vegetable oil incorporated trans fatty acids in the fillets. Results indicated that fillets from silver catfish fed diets with soybean or rice oil have different lipid profile and lipid stability during frozen storage. Frying silver catfish fillets in canola oil could increase the low n-3/n-6 polyunsaturated fatty acids ratio of raw silver catfish fillets. / O presente trabalho teve por objetivo estudar a estabilidade lipídica de filés de jundiá (Rhamdia quelen). Foi avaliada a influência da inclusão (5%) de óleo de soja ou arroz na dieta do jundiá, e a embalagem a vácuo, sobre a estabilidade lipídica e a cor de filés crus congelados (18 meses). Avaliou-se também a influência de sete métodos de cocção (cozido em água, assado em forno convencional ou microondas, grelhado, ou frito em óleo de soja, arroz ou gordura vegetal hidrogenada) sobre a oxidação, a composição centesimal e de ácidos graxos de filés de jundiá. Não houve diferença na composição centesimal dos filés entre as dietas. O conteúdo de substâncias reativas ao ácido tiobarbitúrico (TBARS, índice de lipoperoxidação) aumentou nos filés dos peixes de ambas as dietas, após 12 meses de armazenamento congelado, tanto nos filés embalados com ou sem vácuo. Esse aumento foi mais acentuado nos filés dos peixes alimentados com dietas contendo óleo de soja. Os parâmetros de cor não foram afetados pela embalagem a vácuo ou pela dieta, mas a maioria dos parâmetros (a*, b*, croma e ângulo de matiz), foi afetada pelo tempo de estocagem. O valor de ângulo de matiz mostrou que os filés crus tendiam ao amarelo, e após 18 meses de armazenamento congelado tenderam ao verde. O conteúdo de vários ácidos graxos nos filés foi influenciado pelo tipo de óleo vegetal utilizado na dieta, porém a razão dos ácidos graxos poliinsaturados n-3/n-6 e insaturados/saturados não diferiu entre as dietas. Todos os métodos de processamento térmico avaliados reduziram a umidade e aumentaram o conteúdo de proteína dos filés. O teor de gorduras foi maior nos filés fritos. O conteúdo de ácidos graxos livres dos filés foi significativamente reduzido pelos diferentes métodos de processamento térmico, enquanto os teores de dienos conjugados e peróxidos diminuíram em todas as amostras submetidas à fritura, mas permaneceram constantes nas amostras submetidas aos demais métodos de processamento térmico. Nos filés cozidos e assados observou-se aumento dos teores de TBARS, enquanto os grelhados e fritos não sofreram alteração neste parâmetro. A composição de ácidos graxos dos filés de jundiá cozidos, assados e grelhados não foi alterada pelo tratamento térmico. A fritura em óleo de canola aumentou a razão n-3/n-6, enquanto que a fritura em óleo de soja aumentou o conteúdo total de ácidos graxos poliinsaturados, e a fritura em gordura vegetal hidrogenada incorporou ácidos graxos trans aos filés. Os resultados indicam que os filés de jundiá alimentados com dietas contendo óleo de soja ou de arroz tiveram perfil lipídico e estabilidade lipídica diferente durante o armazenamento congelado. A fritura dos filés de jundiá em óleo de canola poderia aumentar a razão de ácidos graxos poliinsaturados n-3/n-6, que é baixa nos filés de jundiá crus.

The theme of the master´s thesis is design a microphone preamplifier which uses vacuum tube as a main amplifying element. Part of the work is theoretical assumptions for the optimal design and implementation of peripheral involvement, comparing the properties of components used and the resulting parameters of modeled device. The thesis also includes a proposal of the source unit for supplying all parts of the preamplifier. The results are accompanied by circuit simulations and laboratory measurements of the main parameters of the designed device.

This thesis discusses vacuum deposited organic solar cells. It focuses on the investigation of new donor molecules blended with the standard electron acceptor C60. These donor-acceptor heterojunctions form the photoactive system of organic solar cells. In addition, the influence of the processing conditions on the morphology of the blend layers is investigated, as the morphology is crucial for an efficient generation of free charge carriers upon photon absorption. Bulk heterojunction solar cells with the donor DTDCTB are deposited at different substrate temperatures. We identify three substrate temperature regimes, discriminated by the behavior of the fill factor (FF ) as a function of the blend layer thickness. Devices deposited at RT have a maximum FF between 50 and 70 nm blend thickness, while devices deposited at 110 °C have a monotonically decreasing FF. At Tsub=85 °C, the devices have an S-kinked current-voltage curve. Grazing incidence wide angle X-ray scattering measurements show that this peculiar behavior of the FF is not correlated with a change in the crystallinity of the DTDCTB, which stays amorphous. Absorption measurements show that the average alignment of the molecules inside the blend also remains unchanged. Charge extraction measurements (OTRACE) reveal a mobility for the 110 °C device that is an order of magnitude higher than for the RT device. The difference in mobility can be explained by a higher trap density for the RT samples as measured by impedance spectroscopy. Despite slightly higher carrier lifetimes for the RT device obtained by transient photovoltage measurements, its mobility-lifetime product is still lower than for the 110 °C devices. Based on DTDCTB, three new donor materials are designed to have a higher thermal stability in order to achieve higher yields upon material purification using gradient sublimation. For PRTF, the thermal stability is increased demonstrated by a higher yield upon sublimation. However, all new materials have a reduced absorption as compared to DTDCTB, which limits the short current density, and the FF is more sensitive to an increase of the blend layer thickness. The highest power conversion efficiency is achieved for a PRTF:C60 solar cell with 3.8%. Interestingly, PRTF:C60 solar cells show exceptionally low nonradiative voltage losses of only 0.26 V. Another absorber molecule is the push-pull chromophore QM1. Scanning electron microscope (SEM) measurements show a growth of the molecule in nanowires on several substrates. The nanowires have lengths up to several micrometers and are several tens of nanometers wide. The formation of the nanowires is accompanied by a strong blue shift (650 meV) of the thin film absorption spectrum in comparison to the absorption in solution, which is attributed to H-aggregation of the molecules. Furthermore, the thin film absorption onset reaches up to 1100 nm, making the material a suitable candidate for a near infrared absorber in organic solar cells. For a solar cell in combination with C60, a power conversion efficiency of 1.9% was achieved with an external quantum efficiency of over 19% for the spectral range between 600 and 1000 nm. The method of “co-evaporant induced crystallization” as a means to increase the crystallinity of blend layers without increasing the substrate temperature during the deposition is investigated. Mass spectrometry (LDI-ToF-MS) measurements show that polydimethylsiloxane (PDMS), which is used as a co-evaporant, decomposes during the evaporation and only lighter oligomers evaporate. Quartz crystal microbalance (QCM) measurements prove that the detection of PDMS saturates at higher amounts of evaporated material. LDI-ToF-MS measurements show further that the determination of the volatilization temperature by QCM measurements is highly error prone. The method was applied to zinc phthalocyanine (ZnPc) :C60 solar cells, accepting the insertion of PDMS into the blend layer. Diffraction (GIXRD) measurements show a large increase in crystallinity. ZnPc:C60 solar cells produced by applying the method reveal a similar behavior as solar cells processed at a higher substrate temperature.

Es wird der Eigenschaftsbereich von thermisch modififizierter Kartoffelstärke erweitert und durch viele Proben sowie eine große Probenmenge verififiziert. Ziel ist es neue Möglichkeiten zur Optimierung der Stärke-Prozesskette zu erschließen und somit das industrielle Anwendungsspektrum für den Ausgangsstoff Stärke zu vergrößern. Native und konditionierte Kartoffelstärke werden auf neuartige Weise durch eine (Vakuum-)Mikrowellenbehandlung und durch eine konvektive Ofenbehandlung im Labormaßstab thermisch modififiziert. Um Einflussparameter auf die resultierende Eigenschaftsänderung zu identififizieren, werden das Quellungs- und Lösungsverhalten der Stärkeproben in wässriger Umgebung charakterisiert sowie das Stärkegel mikroskopisch untersucht. Eine Steigerung der variierten Behandlungsparameter (Behandlungsdauer und -temperatur bzw. -leistung) bewirkt unabhängig vom Behandlungsverfahren eine Zunahme der Quellung und der Löslichkeit. Die schlüssige grafifische Darstellung der Ergebnisse offenbart die Unterschiede zwischen den thermischen Verfahren. Bei der Mikrowellenbehandlung verursacht der ungehinderte Eintrag der Feldenergie in die Stärke eine erheblich schnellere Modififikation gegenüber der Ofenbehandlung. Bei der Vakuum-Mikrowellenbehandlung bewirkt der große Dampfdruck-Gradient eine intensivere Behandlung gegenüber der Mikrowellenbehandlung bei Atmosphärendruck. Mit den Verfahren können vorbestimmte Eigenschaften der Kartoffelstärke bewirkt werden, bspw. verursacht die Mikrowellenbehandlung eine geringere Löslichkeit als die Ofenbehandlung. Bei der Ofenbehandlung verringert eine Befeuchtung die Quellung und die Löslichkeit, was ähnlich dem Heat-Moisture-Effekt auf eine Modififikation der Stärkestruktur bei erhöhter Feuchte zusammen mit hoher Temperatur hindeutet. Die mikroskopische Geluntersuchung zeigt Unterschiede des Stärkegels für die verschiedenen Verfahren. Nach der Vakuum-Mikrowellenbehandlung brechen bei der Quellung einzelne Körner im Glasübergangsstadium auf und die Kornfragmente sind als Schlieren sichtbar.

L’apparition d’inclusions exogènes demeure un problème majeur pour les élaborateurs de titane. Afin d’améliorer la propreté inclusionnaire des lingots élaborés par le procédé de refusion à l’arc sous vide (Vacuum Arc Remelting), une étude numérique et expérimentale a été réalisée. La partie numérique de la thèse consiste à modéliser le comportement d’un défaut hard-α provenant de l’électrode consommable et tombant dans le puits liquide du lingot. Un modèle décrivant le processus de dissolution prédit l’évolution de la taille d’une inclusion durant son séjour dans le puits liquide. La trajectoire est déterminée à l’aide d’un modèle lagrangien tenant compte de la turbulence de l’écoulement en modifiant le coefficient de trainée. Les deux modèles ont été couplés et implémentés dans le logiciel SOLAR, qui simule la croissance d’un lingot VAR.Les résultats mettent en évidence la difficulté d’éliminer une inclusion hard-α avec une seule refusion, principalement à cause de la croissance d’une couche de phase β pendant les premiers moments de l’immersion. Le comportement global du défaut dépend fortement de l’hydrodynamique du puits et des caractéristiques de l’inclusion.Pour étudier la dissolution expérimentalement, des défautssynthétiques (hard-α et HDI) ont été immergés dans un bain de titane liquide chauffé dans un four à bombardement électronique. Les vitesses de dissolution ont été déterminées en mesurant les dimensions des défauts avant et après les expériences et ont été ensuite utilisées pour valider les modèles numériques. Par ailleurs, nous avons mis en évidence la grande influence de la température et de la vitesse de l’écoulement sur les cinétiques de dissolution / The presence of exogeneous inclusions has always been a major concern for the titanium industry. To help improve the inclusional cleanliness of VAR (Vacuum Arc Remelting) titanium ingots, a numerical and experimental study was undertaken.The numerical model is capable of predicting the motion and dissolution of a hard-α defect falling from the electrode tip into the ingot melt pool during vacuum arc remelting. It is implemented in SOLAR, a CFD code that simulates the ingot growth and solidification. The dissolution of the inclusion is governed by nitrogen diffusion from the defect towards the surrounding molten metal. A model describing this phenomenon predicts the particle size evolution and the nitrogen profile at each moment. The motion of the spherical particle is tracked using a Lagrangian model and the influence of turbulence is accounted for by a modification of the drag coefficient.Results show that inclusion removal is difficult with a single melt since the growth of a β-phase layer leads to an initial increase in the defect size. The inclusion behaviour is highly dependent on the pool hydrodynamics and on inclusion characteristics.In order to clarify dissolution aspects of these defects and to measure their dissolution kinetics, synthetically processed defects were introduced into molten titanium heated in an electron beam melting furnace. Dissolution rates were calculated by measuring the size of the defects before and after the experiments and the results were used to validate the numerical models. Furthermore, the experiments show that dissolution kinetics highly depend on fluid motion and temperature

Les principaux objectifs de cette thèse sont la fabrication et la caractérisation structurale à haute résolution de nanorubans de graphène à bords atomiquement lisses ainsi que leur intégration dans des composants et l'étude du transport électronique. En premier lieu, nous montrons que des nanorubans de graphène cristallins de largeur inférieure à 100 nm et avec des qualités structurales supérieures l'état de l'art peuvent être découpé par un faisceau électronique focalisé d'énergie modérée en présence d'oxygène. Les caractéristiques des rubans obtenus sont également supérieures à l'approche précédente utilisant la vapeur d'eau. Dans un deuxième temps, la structure des nanorubans est caractérisée jusqu'à l'échelle atomique par microscopie électronique en transmission corrigée des aberrations sphériques. Nous montrons que la cristallinité des nanorubans, tant en leur centre que le long des bords de découpe, est préservée. Les performances de notre approche atteignent l'état de l'art et sa reproductibilité permet de fabriquer des rubans longs de plusieurs centaines de nanomètres mais de largeur aussi fine que 16 nm. Ensuite, nous avons transposé la découpe de nanoruban suspendus à une configuration partiellement suspendue sur substrat SiO2/Si permettant de les intégrer dans des composants adaptés aux mesures de transport électronique à basse température et sous champ magnétique. Le transport électronique dans les rubans contactés de 60 x 300 nm présente un gap et des oscillations en balayage de grille arrière qui sont en accord avec un mécanisme de blocage de Coulomb dans un domaine de taille de l'ordre de la taille du ruban. Si ces résultats montrent la persistance de barrières tunnel, ses bords semblent de qualité suffisante pour ne pas induire de confinement supplémentaire. Au-delà des composants mésoscopiques, notre méthode de fabrication des rubans par gravure électronique sous oxygène ouvre des perspectives dans deux domaines en émergence. Elle est compatible avec l'ultravide et parfaitement adaptée au développement d'une technologie atomique à base de graphène. Une caractérisation de la contamination du graphène ainsi qu'une caractérisation électrique de dispositifs de graphène qui a été fait par microscopie à effet tunnel multisonde en ultra vide. Enfin, les rubans de graphène que nous produisons ont les dimensions et qualités structurales requises pour observer un comportement plasmonique du graphène dans le visible et ainsi interagir avec des structures plasmoniques métalliques. Ce couplage a été examiné en étudiant le signal Raman du graphène au voisinage de colloïdes d'or. / The main objectives of this thesis are the fabrication and high-resolution structural characterisation of graphene nanoribbons with atomically smooth edges as well as their device integration and electronic transport study. In first place, we show that crystalline graphene nanoribbons with width under 100 nm and structural properties better than the state of the art can be patterned by a focused electron beam in presence of oxygen. The structural characteristics of the ribbons are also better than the old process using water vapour. Secondly, nanoribbons structure is characterized down to the atomic scale by spherical aberration corrected transmission electron microscopy. We show that the nanoribbons crystallinity, of the centre as well as along the cut edges, is preserved. The performance of our process reaches the state of the art and its reproducibility allows to produce ribbons with length of hundreds of nanometer but as narrow as 16 nm. After that, we have transposed the suspended nanoribbon etching to a partially suspended configuration on a SiO2/Si substrate allowing the integration in devices suitable for electronic transport measurements at low temperature and under magnetic field. The electronic transport in contacted ribbons of 60x300 nm shows a gap and oscillations on backgate scanning measurements that are in agreement with a Coulomb blockade mechanism with dot sizes in the range of the ribbon surface. Even though those results show the persistence of tunnel barriers, the edges quality look good enough to avoid additional confinement. Other than mesoscopic devices, our ribbon fabrication process by electronic beam under oxygen atmosphere opens perspectives in two emergent fields. The process is ultra high vacuum compatible and perfectly adapted to the development of an atomic graphene based technology. A characterisation of contaminants of graphene samples as well as electrical characterisation of graphene devices has been performed in a multiprobe scanning tunnelling microscope in ultra high vacuum. Finally, our graphene nanoribbons have the right dimensions and structural qualities required for the observation of plasmonic behaviour of graphene in visible light and so interact with metallic plasmonic structures. This coupling has been analysed by studying the Raman signal of graphene at the close environment of gold colloids.

Ultra-relativisitic heavy ion collisions produce quark gluon plasma-a hot and dense soup of deconfined quarks and gluons akin to the early universe. We study two models in the context of these collisions namely, Polyakov Quark Meson Model (PQM) and Hadron Resonance Gas Model (HRGM).The PQM Model provides us with a simple and intuitive understanding of the QCD equation of state and thermodynamics at non zero temperature and baryon density while the HRGM is the principle model to analyse the hadron yields measured in these experiments across the entire range of beam energies. We study the effect of including the commonly neglected fermionic vacuum fluctuations to the (2+1) flavor PQM model. The conventional PQM model suffers from a rapid phase transition contrary to what is found through lattice simulations. Addition of the vacuum term tames the rapid transition and significantly improves the model’s agreement to lattice data. We further investigate the role of the vacuum term on the phase diagram. The smoothening effect of the vacuum term persists even at non zero . Depending on the value of the mass of the sigma meson, including the vacuum term results in either pushing the critical end point into higher values of the chemical potential or excluding the possibility of a critical end point altogether. We compute the fluctuations(correlations) of conserved charges up to sixth(fourth) order. Comparison is made with lattice data wherever available and overall good qualitative agreement is found, more so for the case of the normalised susceptibilities. The model predictions for the ratio of susceptibilities approach to that of an ideal gas of hadrons as in HRGM at low temperatures while at high temperature the values are close to that of an ideal gas of massless quarks. We examine the stability of HRGMs by extending them to take care of undiscovered resonances through the Hagedorn formula. We find that the influence of unknown resonances on thermodynamics is large but bounded. We model the decays of resonances and investigate the ratios of particle yields in heavy-ion collisions. We find that extending these models do not have much effect on hydrodynamics but the hadron yield ratios show better agreement with experiment. In principle HRGMs are internally consistent up to a temperature higher than the cross over temperature in QCD; but by examining quark number susceptibilities we find that their region of applicability seems to end even below the QCD cross over.