Les oscillateurs sont des blocs qui figurent dans presque tous les circuits. En effet,ils sont utilisés pour générer les signaux de synchronisation (les horloges), les signauxmodulés et démodulés ou récupérer des signaux noyés dans du bruit (détection synchrone).Les caractéristiques de ces oscillateurs dépendent de l'application. Dans le cas des boucles àverrouillage de phase (PLL), il existe de fortes exigences en matière de stabilité et de bruitde phase. En outre, face aux avancées des technologies nanométriques, il est égalementnécessaire de prendre en compte les effets liés à la variabilité des procédés de fabrication.Aujourd'hui, de nombreuses études sont menées sur les oscillateurs asynchrones en anneauqui présentent des caractéristiques bien adaptées à la gestion de la variabilité et qui offrentune structure appropriée pour limiter le bruit de phase. A ce titre, les anneaux asynchronessont considérés comme une solution prometteuse pour générer des horloges.Cette thèse étudie les avantages et les potentiels offerts par les oscillateursasynchrones en anneau. Deux applications principales ont été identifiées. D’une part, cesoscillateurs sont une solution prometteuse pour la génération d’horloges polyphasées àhaute fréquence et à faible bruit de phase. D’autre part, ils constituent une alternativesimple, dans une certaine mesure aux oscillateurs plus conventionnels et aux DLLs, car ilssont programmables en fréquence numériquement et sont susceptibles de fournir lesfonctionnalités d’arrêt de type gated clock de façon native. Plusieurs oscillateurs ont étéconçus, implémentés, fabriqués en technologie CMOS 65 nm de STMicroelectronics et,finalement, caractérisés sous pointes. Ces travaux ont notamment permis de démontrer lapertinence de ces oscillateurs, qui constituent une alternative sérieuse aux très classiquesoscillateurs en anneau à base d’inverseurs. / Oscillators are essential building blocks in many applications. For instance, they arebasic blocks in almost all designs: they are part of PLLs, clock recovery systems andfrequency synthesizers. The design of a low phase-noise multi-phase clock circuitry isespecially crucial when a large number of phases is required. There are plenty of workscovering the design of multiphase clocks. High frequency oscillators can be implementedusing ring structures, relaxation circuits or LC circuits. Ring architectures can easily providemultiple clocks with a small die size. With the advanced nanometric technologies, it is alsorequired to deal with the process variability, stability and phase noise. Today many studiesare oriented to Self-Timed Ring (STR) oscillators which present well-suited characteristicsfor managing process variability and offering an appropriate structure to limit the phasenoise. Therefore, self-timed rings are considered as promising solution for generatingclocks.This thesis studies the benefits and potential offered by Self-Timed Ring oscillators.Two main applications have been identified. On the one hand, these oscillators are apromising solution for the generation of high-frequency multi-phase low phase noise clocks.On the other hand, they are a simple alternative to some extent to the conventionaloscillators and DLLs, because they are digitally programmable. Several oscillators havebeen designed, implemented, manufactured in 65 nm CMOS technology fromSTMicroelectronics, and characterized. This work has demonstrated the relevance of theseoscillators, which are a serious alternative to the conventional ring oscillators based oninverters.

La chaleur dégagée par des dispositifs à différentes échelles (microprocesseurs, automobiles, habitations, usines) constitue une source quasi inexploitée d’énergie. La conversion de cette énergie thermique en énergie électrique est possible via l’emploi de générateurs thermoélectriques. Cependant actuellement leur usage est peu répandu du fait de leur faible rendement, de la toxicité et du coût des matériaux. L’objectif de cette thèse qui fait suite à la thèse théorique de Kinga Niedziolka (Université Montpellier, 2014) était l’obtention de nouveau matériaux thermoélectriques performants à base de ZnSb sur la base des résultats obtenus par modélisation. Conformément aux calculs réalisés et en accord avec le partenaire industriel (Hutchinson), les dopants choisis pour ZnSb ont été l’aluminium (1% en substitution du zinc), le tellure (1% en substitution de l’antimoine, le titane (1% en substitution du zinc) et l’yttrium (1% en substitution du zinc). L’objectif ici est de synthétiser et de caractériser les matériaux qui ont été calculés de type n (conduction électrique assurée par les électrons). Les matériaux ont été synthétisés par fusion, trempe et recuit et ont été obtenus sous forme de lingot polycristallin. Ils ont été caractérisés par diffraction des rayons X, microscopie électronique à balayage et microsonde de Castaing. Leur mise en forme pour les caractérisations thermoélectriques a ensuite été mise au point. C’est en utilisant la technique du Spark Plasma Sintering (SPS) que nous avons atteint des densités très intéressantes de l’ordre de 98% pour tous les matériaux contenant un dopant. Les caractérisations thermoélectriques ont été conduites en fonction de la température jusqu’à 600 K au moyen d’un appareillage de type ZEM-3.Les travaux de dopage se sont concentrés sur les matériaux dopés au tellure présentant les résultats les plus prometteurs. Cependant les caractérisations thermoélectriques des matériaux synthétisés n’ont pas permis de mettre en évidence le passage au type n souhaité. Cependant, une avancée a été réalisée en ce qui concerne ZnSb non dopé qui est naturellement un matériau de type p (conduction électrique assurée par les trous): grâce à la mise en œuvre de la mécanosynthèse nous avons obtenu un matériau présentant de meilleurs propriétés que ceux existants. Des analyses de ce matériau au microscope électronique en transmission ainsi que des analyses par la méthode XPS ont conduit à l’identification de certains précipités responsables de l’amélioration de ses propriétés thermoélectriques. De plus, le matériau ZnSb obtenu, présente une grande stabilité en température ce qui renforce d’autant plus son intérêt d’utilisation par rapport à d’autres matériaux dans la même gamme de température. / The heat loss from different sources at different scales (microprocessors, cars, houses, factories) is an almost untapped source of energy. The conversion of this thermal energy into electrical energy is possible through the use of thermoelectric generators. However at the present time their use is not widespread due to their low efficiency, toxicity and because of the cost of the existing materials. The aim of this thesis that follows the DFT calculations previously made during Kinga Niedziolka’s thesis, (University of Montpellier, 2014) was to obtain new efficient thermoelectric materials based on ZnSb relying on the calculation results. Based on the calculations and in agreement with the industrial partner Hutchinson, aluminum (1 % at. in substitution of Zn), tellurium (1 % at. in substitution of Sb), titanium (1 % at. in substitution of Zn) and yttrium (1 % at. in substitution of Zn) were selected as dopants. The objective, was to synthesize and characterize the materials which were calculated as n type semiconductors (electron conduction). The materials were synthesized by melting, quenching and annealing. They were obtained in the form of polycrystalline ingots. They were characterized by X-ray diffraction, scanning electron microscopy and EDS and WDS microanalysis. Their shaping for thermoelectric characterization was then developed. The technique of Spark Plasma Sintering (SPS) was chosen to this aim and we achieved very interesting densities of around 98% for all doped materials. Thermoelectric characterizations were carried out up to 600 K by means of a ZEM-3 type apparatus. Only tellurium doped materials with the most promising results were thoroughly studied. However, the thermoelectric characterization of the synthesized doped materials didn’t show the expected transition to an n-type conduction. However, progress was made regarding ZnSb as a p-type material. The optimization of the mechanical alloying process led to a very promising ZnSb material. The analyses of this material by transmission electron microscopy and XPS analysis led to the identification of some precipitates which give rise to improved thermoelectric properties compared to existing p-type ZnSb. Furthermore the obtained material has a high thermal stability reinforcing its interest compared to other materials for applications in the same temperature range.

Comprendre la supraconductivité des pnictures et séléniures de fer nécessite de bien connaître leurs propriétés électroniques et magnétiques. Dans ce cadre, j'ai aidé à réaliser et j'ai automatisé un dispositif cryogénique capable d'étudier ces propriétés, à basse température (jusqu'à ~1 K) et sous application d'un champ magnétique statique (jusqu'à 2 T) ou oscillant. Les techniques implémentées sont la spectroscopie de pointe et la microscopie à sonde de Hall, et le dispositif est conçu de sorte qu'il soit possible de basculer de l'une à l'autre sans manipuler l'échantillon.J'ai ensuite utilisé ce dispositif pour étudier par spectroscopie de pointe les gaps supraconducteurs du pnicture Ba(Fe,Ni)2As2, puis rechercher la signature du couplage de ses électrons de conduction à des modes bosoniques. Ce faisant, il a été observé dans la conductance différentielle de jonctions métal-supraconducteur un signal oscillant dont la période varie en température comme le gap supraconducteur de l'échantillon. Ce signal dépend de la résistance de contact de la jonction d'une façon qui prouve clairement qu'il est issu d'effets hors équilibre.J'ai modélisé ce signal en étudiant théoriquement la physique de jonctions métal-métal-supraconducteur, dont la seconde région métallique serait formée par transition locale du supraconducteur vers l'état normal. Le modèle que j'ai ainsi construit permet de prédire la conductance différentielle d'une telle jonction, moyennant une connaissance préalable de la loi L(V) reliant la taille de la seconde région métallique à la tension aux bornes de la jonction. J'ai ensuite proposé plusieurs modèles pour cette loi.Après comparaison avec l'expérience, il semble possible que la région métallique se forme par dépassement local de la densité de courant critique Jd du supraconducteur associée à la brisure de paires de Cooper, ou "courant de depairing". Mais il serait aussi vraisemblable que l'injection d'électrons perturbe localement la distribution électronique f(E) de l'échantillon, au point de déstabiliser l'état supraconducteur. Cette dernière interprétation suppose une forte dépendance en température du couplage électron-boson à basse énergie.Enfin, je présente en annexe les fonctionnalités de microscopie magnétique du dispositif réalisé, ainsi que les premiers résultats scientifiques qu'elles ont permis d'obtenir : la mise en évidence du rôle joué par le fluage quantique dans la relaxation des vortex piégés au sein de Fe(Se,Te). / Reaching a good understanding of the superconductivity of iron pnictides and selenides requires an accurate knowledge of their electronic and magnetic properties. To this end, I helped building and I automated a cryogenic device that is suitable for the study of these properties, at low temperatures (down to ~1 K) and under the application of a magnetic field, either static (up to 2 T) or oscillating. The device implements the experimental techniques of point contact spectroscopy and scanning hall probe microscopy, and it allows switching between them without requiring sample manipulations.I subsequently used this device to study the superconducting gaps of Ba(Fe,Ni)2As2 by point contact spectroscopy, before I began looking for signatures of the coupling of conduction electrons to bosonic modes. However, in this process, the differential conductance of metal-superconductor junctions turned out to exhibit oscillating features, whose period evolves in temperature like the superconducting gap of the sample. This signal also depends on a junction's contact resistance in such a manner that it appears unmistakably out-of-equilibrium in nature.I derived a model of this signal by undertaking a theoretical study of metal-metal-superconductor junctions. In these junctions, the second metallic region would emerge from a local transition of the superconductor to the normal state. The resulting model is able to predict the differential conductance of such a junction, given prior knowledge of the L(V) law linking the size of the second metallic region to the voltage being applied across the junction. I subsequently derived several models for this law.Comparing these models to experimental data, it appears that the observed phenomenology could emerge from a local increase of current density above the "depairing current" Jd associated to Cooper pair breaking in the superconductor. Alternatively, electron injection could also locally alter the electron energy distribution f(E) of the sample to the point of destabilizing the superconducting state. This last explanation requires a strong temperature dependence of the electron-boson coupling at low energies.Finally, in an appendix, I describe the magnetic microscopy capabilities of the experimental device. Those capabilities enabled us to understand the role played by quantum creep in the relaxation of trapped vortices within Fe(Se,Te).

Made available in DSpace on 2014-10-09T12:24:21Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:27Z (GMT). No. of bitstreams: 1 00404.pdf: 1111146 bytes, checksum: f2492669cbf68883695a8c4243057513 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

Fundando-se em argumentos de equilíbrio e estabilidade termodinâmica, a solubilidade de soluto em um solvente é definida pelo limiar de existência da mistura como sistema homogêneo. De fato, entende-se tal grandeza sobre a coexistência de fases. A noção de solubilidade apresentada é desenvolvida através de modelos simples, que incluem resultados na rede bem como a extensão do modelo de van der Waals ao caso de duas componentes. Desta extrai-se uma condição genérica à observação de mínimos na solubilidade incidente sobre a topologia de seu diagrama de fases e de evidente correspondência física. / Concerning the equilibrium and stability in thermodynamics, the solubility of solute in a solvent is defined as the threshold of the mixture existing as a homogeneous system. Indeed, such quantity meets its meaning when understood on the coexistence surface. The idea of solubility presented is developed following the discussion of simple models, including results on the lattice as well as the van der Waals model extended to include two components. From these results we extract a general condition which connects the occurence of a minimum in solubility to the topological structure of the phase diagram.

Les propriétés mécaniques du combustibles nucléaire sont un problème complexe qui fait intervenir de nombreux mécanismes différents à des échelles diverses. Afin de faire progresser notre connaissance de ce matériau, nous avons effectué des simulations utilisant des modèles de Dynamique Moléculaire. Ces simulations permettent l'étude de différents mécanismes de déformation du dioxyde d'uranium à l'échelle atomique. Nous avons mis en place une procédure permettant de calculer les chemins de transition entre différents polymorphes de l'UO2 de manière statique et dynamique. Ces calculs ont confirmé la stabilité des structures fluorine à pression ambiante et cotunnite en compression, vers laquelle une transition reconstructive a été observée. Ils ont aussi montré l'importance de la direction de sollicitation principale pour déterminer la transition activée en tension, soit vers une structure scrutinyite, soit vers une structure rutile. D'autre part, les propriétés élastiques de l'UO2 ont été déterminées en température à partir d'une approche multi-modèles. L'accord relatif entre les potentiels existants pour l'UO2 a été utilisé pour déterminer des paramètres pour des modèles mésoscopiques. La propagation d’une fissure dans un monocristal a ensuite été étudié. Lors de ces simulations nous avons mis en évidence l'apparition de phases secondaires en pointe de fissure. Ce mécanisme prédit par les modèles atomistiques pourrait jouer un rôle important lors de la propagation d’une fissure aux échelles supérieures. Finalement, certaines propriétés des dislocations coin stabilisées dans le cristal UO2 ont été étudiées. La structure de cœur de ces dislocations dans différents plans de glissements a été comparée. Leur contrainte critique de glissement en fonction de la température a été calculée. Ces derniers calculs suggèrent un lien direct entre le désordre chimique observé au cœur de dislocations et leur mobilité. / Mechanical properties of nuclear fuel are a complex problem, involving many coupled mechanisms occurring at different length scales. We used Molecular Dynamics models to bring some light on some of these mechanisms at the atomic scale. We devised a procedure to calculate transition pathways between some UO2 polymorphs, and then carried out dynamics simulations of these transitions. We confirmed the stability of the cotunnite structure at high pressure using various empirical potentials, the fluorite structure being the most stable at room pressure. Moreover, we showed a reconstructive phase transition between the fluorite and cotunnite structures. We also showed the importance of the major deformation axis on the kind of transition that occur under tensile conditions. Depending on the loading direction, a scrutinyite or rutile phase can appear. We then calculated the elastic behaviour of UO2 using different potentials. The relative agreement between them was used to produce a set of parameters to be used as input in mesoscale models. We also simulated crack propagation in UO2 single crystals. These simulations showed secondary phases nucleation at crack tips, and hinted at the importance thereof on crack propagation at higher length-scales. We then described some properties of edge dislocations in UO2. The core structures were compared for various glide planes. The critical resolved shear stress was calculated for temperatures up to 2000 K. These calculations showed a link between lattice disorder at the dislocations core and the dislocations mobility

Dans ce travail, nous avons étudié l’effet des contraintes extérieures et des inhomogénéités locales sur les propriétés diélectriques et structurales des cristaux ferroélectriques- relaxeurs à base de plomb PZN-x%PT avec 0%≤x≤12%. Dans une première partie, nous avons déterminé les propriétés diélectriques et structurales du système PZN-6%PT. Pour l’état vierge, ce composé subit la séquence de transition de phase C  T  R, où C, T et R sont, respectivement, les phases cubique, quadratique et rhomboédrique. En appliquant un champ électrique statique, une phase orthorhombique est induite entre les phases T et R. Dans la deuxième partie, nous avons montré la présence d’une anomalie diélectrique à basse température observée sur le PZN-x%PT avec 0%≤x≤12%. Dans ce domaine de température, l’étude structurale ne montre aucune transition de phase. L’ensemble de ces résultats sont interprétés moyennant un modèle basé sur la présence des nano-régions polaires. En troisième partie nous avons déterminé les propriétés diélectriques et piézoélectrique du PZN-12%PT dopé au manganèse dans son état monodomaine. Le dopage affecte, principalement, la permittivité transverse et le coefficient piézoélectrique de cisaillement. Le dopage induit aussi la stabilité de la structure monodomaine et l’effet de mémoire de la microstructure. Ces résultats sont expliqués en utilisant le modèle de symétrie des défauts. Dans la dernière partie, nous nous sommes intéressés à la simulation de l’effet de la présence des dipôles-défaut (dopage) sur les propriétés physiques de BaTiO3. Nous avons mis en évidence l’induction d’un champ électrique interne responsable du décalage du cycle d’hystérésis vers les champs électriques négatifs. / In this work, we studied the effect of external constraints and local inhomogeneities on dielectric and structural properties of the lead-based ferroelectric-relaxor system PZN-x%PT with 0%≤x≤12%. In the first part, we determined phase transformations of [001], [110] and [111] oriented PZN-6%PT single crystals. The un-poled samples undergo C  T  R, phase transitions sequence, where C, T and R, and are rhombohedral, tetragonal and cubic phases, respectively. Under electric field, an intermediate orthorhombic phase is induced between T and R phases. The second part was devoted to the study of the electromechanical and structural properties at cryogenic temperature of the PZN-x%PT system (0%≤x≤12%.). These characterizations show the presence of a dielectric anomaly at low temperatures. In the same temperature range, the structural study does not show any phase transition. These behaviors are interpreted through a model based on the presence of polar nano-regions. In the third part we study the influence of manganese doping on the electromechanical properties of PZN-12%PT single crystal in a single domain state. Doping leads to a decrease of the dielectric transverse permittivity  T 11 and of the shear piezoelectric coefficient d15. This intrinsic effect is discussed by using a volume effect model based on the symmetry conforming principle of point defects. This model explains also the stability of the single domain structure and the memory effect observed during this work. In the last part, we simulated, using molecular dynamics method, the effect of doping (defects-dipoles) on the physical properties of BaTiO3. The introducing of defects-dipoles induces an internal electric field, responsible for the shift of the hysteresis loop.

Made available in DSpace on 2014-10-09T12:24:21Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:27Z (GMT). No. of bitstreams: 1 00404.pdf: 1111146 bytes, checksum: f2492669cbf68883695a8c4243057513 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

Orientadores: Maria Aparecida Azevedo Pereira da Silva, Maria Regina Bueno Franco / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-09T03:53:03Z (GMT). No. of bitstreams: 1 Sampaio_KarinadeLemos_D.pdf: 3249314 bytes, checksum: c77f7bb03d18a2359d110d8fa3068a70 (MD5) Previous issue date: 2007 / Resumo: Durante a etapa de concentração de sucos, juntamente com a água, são também perdidos compostos voláteis responsáveis pelo aroma e sabor característicos da fruta. Esses voláteis podem, no entanto, ser recuperados por condensação, gerando um subproduto conhecido como water phase. Quando submetida à destilação fracionada, a water phase recuperada durante o processamento de sucos pode gerar essências naturais (GRAS), de alto valor agregado, as quais, ao serem incorporadas a sucos e refrescos, aumentam a qualidade sensorial desses produtos. Infelizmente, as water phases geradas por empresas brasileiras de sucos tropicais como caju, maracujá, etc são subaproveitadas. Isso ocorre devido ao conhecimento insuficiente tanto da composição dos voláteis presentes nas mesmas, como das condições de destilação a que devem ser submetidas para a elaboração de essências. Assim, os objetivos do presente estudo foram: i) identificar por cromatografia gasosaespectrometria de massas (CG-EM) o perfil de voláteis presentes em waterphase de caju gerada por indústria nacional de suco, determinando por CG-olfatometria (CGO), a importância odorífera de cada volátil identificado e, ii) através de destilação fracionada de water phase de caju gerada por empresa nacional, elaborar essências naturais, caracterizando a qualidade sensorial das mesmas, bem como o perfil de voláteis. Três tipos de materiais foram analisados: i) water phase de caju gerada durante a concentração de suco utilizando-se recuperador de aromas; ii) um condensado aquoso obtido por simples condensação da água evaporada durante a etapa de concentração do suco de caju e, iii) nove essências naturais GRAS geradas através da destilação fracionada de uma water phase de caju, utilizando-se coluna de fracionamento a 1 atm de pressão atmosférica e temperatura de 98 ºC, com condensação a ¿ 6 ºC. Os compostos voláteis presentes nas amostras foram isolados através de extração líquido-líquido com diclorometano e concentrados sob fluxo de nitrogênio. Após avaliação sensorial por equipe treinada, os isolados foram analisados por cromatografia gasosa (CG) utilizando-se um cromatógrafo gasoso Varian modelo 3600, equipado com detector de ionização de chama (DIC) e coluna capilar com fase estacionária DB-Wax. A identificação dos compostos foi conduzida através de um cromatógrafo gasoso da marca SHIMADZU modelo 17-A, equipado com detector de massas QP-5000 e operando nas seguintes condições: voltagem de ionização de 70eV (ionização por impacto de elétrons), velocidade de scan de 1 scan s ¿1 e varredura realizada entre 35 e 350 m/z. Os isolados da water phase e de uma das essências foram submetidos à CG-olfatometria (CGO), onde cinco julgadores treinados utilizando a técnica tempo-intensidade Osme, avaliaram os odores presentes nos efluentes cromatográficos dos citados isolados. Os resultados revelaram na water phase a presença de 64 compostos voláteis, dos quais 52 apresentaram impacto odorífero no efluente cromatográfico. Cerca de 38% dos compostos voláteis eram ésteres, 23% álcoois e 15% ácidos. Os voláteis de maior impacto odorífero presentes na water phase foram: ácido 3-metil butanóico (descrito como vômito, chulé), 2- metil butanóico (vômito, chulé), ácido acético (abacaxi cozido, remédio), acetofenona (queijo, cera), 2-hidroxi hexanoato de etila (caju), 2-metil-4-pentenal (verde, fruta), heptanol (caju, fruta), trans-3-hexen-1-ol (verde, fruta), 3-metil-1-butanol (chulé, álcool isoamílico); trans-2-butenoato de etila (fruta, caju), 2-metil butanoato de etila (fruta, caju), octanol (perfume, flor), trans-2-hexenal (maria fedida, verde), cis-3-hexen-1-ol (grama, doce), 2-etil-1-hexanol (verde, erva), isovalerato de etila (caju, doce) , 2-etil acrilato de metila (maria fedida, verde) e octanoato de etila (grão, terra molhada). Assim, a presente water phase, por conter muitos voláteis odoríferos de aromas desejáveis em uma essência de fruta, possuía grande potencial para gerar essências naturais de caju de boa qualidade sensorial. No condensado aquoso foram identificados 27 compostos voláteis, sendo 40% álcoois, 27% ácidos e 23% ésteres. A grande quantidade de álcoois e ácidos aliado a pequena quantidade e concentração de ésteres presentes no condensado aquoso demonstram que o mesmo é uma matéria prima menos favorável para a produção de essências, mas ainda assim, passível de ser explorada para esse fim. Todas as essências elaboradas apresentaram baixa intensidade de aroma de caju. O isolado da essência com maior intensidade de aroma de caju entre as 9 elaboradas possuía 61 compostos voláteis, dos quais 36 apresentaram importância odorífera no efluente cromatográfico. Dos 32 voláteis identificados, 33% eram álcoois, 23% terpenos, 14% ésteres, 11% aldeídos. Dentre eles, os de maior impacto odorífero foram: carvona (descrita como grama, sauna), 2-metil- 1-butanol (caju fermentado, fermentado), linalol (mamão, perfume), 2-hidroxi-4-metil pentanoato de etila (caju, fruta), cis-geraniol (essência de caju, fruta, flor), nonanal (grama, verde), 3-metil-1-butanol (caju fermentado, ardido), octanol (perfume, fruta), 2-etil-1- hexanol (grão, óleo de amêndoa), crotonoato de etila (caju, fruta). O alto caráter ¿doce/alcoólico¿ reportado nesta essência pela equipe sensorial, em detrimento do aroma característico de caju, pode ser atribuído à grande proporção de álcoois e terpenos presentes na mesma, em detrimento dos ésteres, que normalmente são responsáveis por notas de aromas ¿frutais¿ em essências. Dentre outros fatores, a baixa proporção de ésteres nesta essência, pode ser atribuída à perda, degradação, ou oxidação dos mesmos durante o processo de destilação fracionada da essência, realizada a alta temperatura e pressão atmosférica. A temperatura de condensação utilizada durante o processo de destilação (-6°C) também pode não ter sido suficientemente baixa para recuperar estes compostos na essência. De um modo geral, os resultados da presente pesquisa revelam que ainda que empresas brasileiras estejam gerando water phase com grande potencial para elaboração de essências naturais de caju, o processo de destilação fracionada dessas water phases, embora não possa ser considerado complexo, não é trivial, e requer otimização. Pesquisas adicionais explorando condições de destilação a menores temperaturas e pressões são cruciais para a adequada transformação das water phases nacionais em essências GRAS de alta qualidade sensorial / Abstract: During the juice concentration step, volatile compounds responsible for the aroma and flavour characteristics of the fruit are lost together with the water. These volatiles can however be recovered by condensation, producing a sub-product known as the water phase. When submitted to fractionated distillation, the water phase recovered during juice processing can produce natural essence (GRAS), of high economic value, which, on being incorporated into juices and soft drinks, can increase the sensory quality of these products. Unfortunately, the water phases produced by Brazilian companies producing tropical juices such as cashew and passion fruit juices are under-used, due to a lack of knowledge of the composition of the volatiles present and of the distillation conditions to which they should be submitted to elaborate the essences. Thus the objectives of the present study were: i) identify the profile of the volatiles present in the cashew water phase produced by a national juice industry using gas chromatography-mass spectrometry (GC-MS), determining the odoriferous importance of each volatile identified using GC-olfactometry, and ii) elaborate natural essences by way of fractionated distillation of the cashew water phase produced by a national company, characterising their sensory quality and the profile of the volatiles. Three types of material were analysed: i) the cashew water phase produced during juice concentration using an aroma recovery unit; ii) an aqueous condensate obtained by the simple condensation of the water evaporated off during the cashew juice concentration step, and iii) nine natural GRAS essences produced by the fractionated distillation of a cashew water phase, using a fractionation column at 1 atm of atmospheric pressure and a temperature of 98ºC, with condensation at ¿6ºC. The volatile compounds present in the samples were isolated by liquid-liquid extraction using dichloromethane and concentrated in a flow of nitrogen. After a sensory evaluation by a trained panel, the isolates were analysed by gas chromatography (GC) using a Varian model 3600 gas chromatograph equipped with a flame ionisation detector (FID) and a capillary column with a DB-Wax stationary phase. The compounds were then identified using a Shimadzu model 17-A gas chromatograph equipped with a QP-5000 mass detector operating under the following conditions: ionisation voltage of 70eV (ionisation by electron impact), scanning velocity of 1 scan s-1 scanning between 35 and 350 m/z. Compounds isolated from the water phase and from one of the essences were submitted to GC-olfactometry (GC-O), where five trained judges evaluated the odours present in the chromatographic effluent of the above cited isolates using the Osme time-intensity technique. Sixty-four volatile compounds were found in the water phase, of which 52 presented an odoriferous impact on the chromatographic effluent. About 38% of the volatile compounds were esters, 23% alcohols and 15% acids. The following volatiles of the water phase showed the greatest odoriferous impact: 3-methyl butanoic acid (described as smelling of vomit, smelly feet), 2- methyl butanoic acid (vomit, smelly feet), acetic acid (cooked pineapple, medicinal), acetophenone (cheese, wax), ethyl 2-hydroxy hexanoate (cashew), 2-methyl-4-pentenal (greens, fruity), heptanol (cashew, fruity), trans-3-hexen-1-ol (greens, fruity), 3-methyl-1- butanol (smelly feet, isoamyl alcohol); ethyl trans-2-butenoate (fruity, cashew), ethyl 2- methyl butanoate (fruit, cashew), octanol (perfume, flowery), trans-2-hexenal (stinky insect, greens), cis-3-hexen-1-ol (grass, sweet), 2-ethyl-1-hexanol (greens, herbal), ethyl isovalerate (cashew, sweet), methyl 2-ethyl acrylate (stinky insect, greens) and ethyl octanoate (grainy, wet earth). Thus since the water phase contained so many odoriferous volatiles with desirable aromas for a fruit essence, it showed considerable potential to produce natural cashew essence with good sensory quality. Twenty-seven volatile compounds were identified in the aqueous condensate, of which 40% were alcohols, 27% acids and 23% esters. The larger amounts of alcohols and acids allied to the smaller amount and concentration of esters present in the aqueous condensate, indicated that this was a less favourable raw material for the production of essences, although possibly still of some use for such ends. All the essences elaborated presented a low intensity of cashew aroma. The isolate from the essence with the greatest intensity of cashew aroma amongst the 9 elaborated had 61 volatile compounds, of which 36 presented odoriferous importance in the chromatographic effluent. Of the 32 volatiles identified, 33% were alcohols, 23% terpenes, 14% esters and 11% aldehydes. Amongst these, those with greater odoriferous impact were: carvone (described as smelling of grass, sauna), 2-methyl-1-butanol (fermented cashew, fermented), linalool (papaya, perfume), ethyl 2-hydroxy-4-methyl pentanoate (cashew, fruity), cis-geraniol (cashew essence, fruity, flowery), nonanal (grass, greens), 3-methyl-1- butanol (fermented cashew, pungent), octanol (perfume, fruit), 2-ethyl-1-hexanol (grainy, almond oil), ethyl crotonoate (cashew, fruit). The highly ¿sweet/alcoholic¿ character of this essence as reported by the sensory panel, in detriment of a characteristic cashew aroma, can be attributed to the high proportion of alcohols and terpenes present, in detriment of esters, which are the compounds normally responsible for the fruity notes of essences. Amongst other factors, the low proportion of esters in this essence could be attributed to their loss during the fractionated distillation of the essence, carried out at high temperatures and atmospheric pressure. In general the results of the present study revealed that even if Brazilian companies are producing cashew water phase with great potential for the elaboration of natural cashew essences, the fractionated distillation process of these water phases, although not complex, is not trivial and requires optimisation. Additional research is crucial, exploring distillation conditions at lower temperatures and pressures for an adequate transformation of these national water phases into GRAS essences with high sensory quality / Doutorado / Consumo e Qualidade de Alimentos / Doutor em Alimentos e Nutrição

Ligas de Urânio são candidatas ao uso como combustível nuclear em reatores avançados, dentre essas ligas se destacam as ligas de Urânio com Nióbio e com Zircônio. Este trabalho investigou como os teores de Nb e Zr, assim como a processamento termomecânico afetam as microestruturas e as propriedades mecânicas de 3 ligas U-XNb-YZr onde X+Y=12. Duas amostras contendo 50g cada, foram fabricadas através de fusão à plasma nos teores U-3Nb-9Zr (liga 39), U- 6Nb-6Zr (liga 66) e U-9Nb-3Zr (liga 93). Uma das amostras de cada liga foi tratada termicamente por 5h a 1000°C para a realização de homogeneização química. A amostra homogeneizada e a amostra bruta de fusão de cada liga foram conjuntamente encapsuladas em aço para a realização de laminação a quente seguida de um recozimento final a 1000°C por 2h. À rota adotada pela amostra bruta de fusão chamou-se \" Rota C\" e a rota adotada pela amostra homogeneizada chamou-se \"Rota H\". A caracterização microestrutural foi feita por microscopia óptica e eletrônica de varredura. Todas as amostras, independente do processamento, apresentaram precipitados ricos em Nióbio e Zircônio em adição a uma matriz rica em Urânio. A caracterização das amostras brutas de fusão mostra que os teores de elementos de liga influenciam diretamente a morfologia das dendritas evidentes na microestrutura assim como das demais fases presentes em cada amostra. A liga 39 apresentou predominantemente fase ?\', a liga 66 a fase ?\" com traços de fase y e a liga 93 a fase y com traços de fase ?\". Após o tratamento térmico de homogeneização, a liga 39 apresentou fase ?\" na forma celular enquanto a liga 66 apresentou as fases y0 e y e a liga 93 apresentou apenas fase y. As propriedades mecânicas das ligas foram avaliadas por ensaios de dureza e de dobramento simples. As amostras da Rota C apresentaram redução de dureza em relação à condição inicial. Todas as microestruturas das amostras laminadas a quente exibiram duas fases ricas em U. A liga 39 apresentou as fases ?\" na forma celular e ?\' após a laminação a quente. Após o recozimento final na rota C, a liga 39 apresentou fase ?\" na forma acicular enquanto as ligas 66 e 93 apresentaram as fases ?\" e y após a laminação e fase y. A fração de área da amostra pobre em U elevou-se nas ligas 39 e 66 e reduziu-se na liga 93. As amostras da Rota H apresentaram redução de dureza em relação à condição bruta de fusão. A liga 39 apresentou fase ?\" na forma celular com orientação e traços da fase ?, a liga 66 exibiu as fases y0 e y e a liga 93 as fases y e y0. Após o recozimento final, a liga 39 mostrou-se novamente na forma ?\" na forma celular, mas sem orientação. A liga 66 apresentou fase y e a liga 93 fase y0. Os testes de dobramento simples mostraram que as ligas da Rota C exibem plasticidade, retendo parte da deformação plástica após a ruptura das amostras testadas. Já as amostras da Rota H mostraram comportamento super elástico, possibilitando maiores deformações mas sem reter deformação plástica após a ruptura das amostras. A melhor relação entre deformação total e residual foi observada na liga 93 fabricada pela Rota C. As análises nos perfis de fratura das amostras da Rota C mostram fraturas transgranulares em todas as amostras. O perfil de fratura de na amostra recozida liga 39 mostra que a fase ?\" na forma acicular tende a deforma-se por deslizamento. As análises dos perfis de fratura nas amostras da Rota H confirmaram a ausência de deformação plástica mesmo em escala microscópica. Para essa condição, a fase ?\" na forma celular com orientação (liga 39) aparenta deformar-se por maclação. As análises de superfície de fratura indicam que a fase pobre em U tem participação durante o processo de crescimento e propagação da fratura na Rota H, atuando como caminho para bifurcação de trincas acelerando o processo de ruptura, enquanto na Rota C, a fase pobre em U deforma-se conjuntamente com a matriz de U. Em uma segunda etapa do trabalho, a estabilidade das microestruturas resultantes na amostras processadas foi investigada por Ensaios de Calorimetria Diferencial Exploratória (DSC) e por calorimetria de queda livre (esta apenas para a amostra 93 da rota H). O teor de Nb e Zr também afeta a estabilidade das fases presentes em cada amostra. foram realizados com as amostras da condição homogeneizada e laminada. A quantidade de transformações assim como o estado final de cada liga diferiu de acordo com a razão Nb/Zr. Após o ciclo de aquecimento e resfriamento da análise térmica, a liga 39 apresentou fase ?\', a liga 66 fase ?\" e a liga 93 fase y. No ensaio de calorimetria por queda livre foi possível observar as diferentes etapas de reação de envelhecimento da matriz g, correspondendo a à transformação y -> y0 (entre 525 e 530 K), a transformação y -> ?\". (entre 623 e 651 K) e à transformação y\' -> y3+? (entre 825 e 925 K). / Uranium alloys are candidates to be used as nuclear fuel in research reactors, among the U alloys, the Nb and Zr containing alloys are promising. This work evaluated how the Nb and Zr content and the thermomechanical processing affects the microstructure and mechanical properties of 3 alloys U-XNb-YZr were X+Y=12. Two 50g slugs of each sample were fabricated using plasma arc melting according to U-3Nb-9Zr (alloy 39), U-6Nb-6Zr (alloy 66) and U-9Nb-3Zr (alloy 93). One slug of each alloy was heat treated for 5h at 1000°C to perform the chemical homogenization. The homogenized sample and the as-cast one were encapsulated in the same steel frame in order to perform hot rolling. After the rolling process, the samples were annealed by 2h at 1000°C. The route that uses only as-cast samples was nominated \"Route C\" and the route that uses the homogenized sample was nominated \"Route H\". The microstructural characterization was performed by optical and scanning electron microscopy. All samples, regardless the processing route, presented Nb and Zr rich precipitates in addition to U rich matrix. The characterization of as-cast samples shows that the content of the alloying element has a direct influence on dendrite morphology as in the phases presented for each alloy. The alloy 39 presented predominantly ?\' phase, the alloy 66 the ?\" phase with a small quantity of ? phase and the alloy 93 presented the ? phase with small quantity of ?\" phase. Afte the homogenization, the alloy 39 presented cellular ?\" phase, the alloy 66 presented ?0 and ?, the alloy 93 presented only ? phase. The mechanical properties were evaluated by hardness measurements and free bending tests. The Route C samples presented hardness reduction in comparison to the initial condition. All microstructures of hot-rolled samples of this route exhibit two U rich phases. The alloy 39 exhibited cellular ?\" and ?\', after the final annealing the alloy 39 presented acicular ?\". The alloys 66 and 93 exhibited ?+?\" after hot rolling and ? phase after the final annealing. The area fraction of poor U phase increased in the alloys 39 and 66, but reduced in alloy 93. The Route H samples presented hardness reduction in comparison to as-cast samples. The alloy 39 presented cellular oriented ?\" phase and a small quantity of ? phase. The alloy 66 exhibited ?0 and ?, the alloy 93 ? and ?0. After the final annealing, the alloy 39 presented the ?\" again, but without orientation. The alloy 66 presented ? phase and the alloy 93 presented ?0. The free bending tests show that Route C samples have real plasticity, retaining part of deformation after rupturing as plastic strain. The Route H samples exhibited superelastic behavior, allowing higher deformations but retaining no plastic strain after sample breaking. The better balance between total and residual strain was observed in alloy 93 fabricated by Route C. The cracking profile analysis of Route C samples shows transgranular fractures in all samples. The Cracking profile of final 39 sample shows that acicular ?\" tends to deform by slipping. The cracking profile analysis of Route H samples confirmed the absence of plasticity even on the microscopic scale. This condition, the oriented cellular ?\" phase (alloy 39) apparently deforms by twinning. The crack surface analysis indicates that the U poor phase has a direct participation in crack growing and propagation, acting as forking points to the fracture and accelerating the fracture process. In the Route C samples, the poor U phase deforms alongside the U matrix. The stability of resulting microstructures of homogenized and hot rolled samples was investigated by Differential Scanning Calorimetry (DSC) and Drop Differential Scanning Calorimetry (only for the homogenized hot rolled 93 sample). The Nb and Zr also affect the stability of present phases in each sample. The number of transformations and the final structure is directly influenced by the Nb/Zr ratio. After the thermal cycle imposed by the DSC analysis, the alloy 39 exhibited ?\' phase, the alloy 66 exhibited ?\" phase and the alloy 93 exhibited ? phase. The Drop-DSC allowed observing the different stages of reaction in ? matrix, corresponding to ? -> ?0 (between 525 and 530 K), ? -> ?\" transformation (between 623 and 651 K) and ?\' -> ?3+? transformation (between 825 and 925 K).