Les cellules souches embryonnaires (cellules ES) sont capables de se multiplier de façon autonome en l’absence de facteurs de croissance et de cytokines, un état appelé “état fondamental de pluripotence”. Le cycle cellulaire des cellules ES se caractérise : (i) par une expression élevée et uniforme de la cycline E et des complexes Cycline E-CDK2 au cours de la progression dans le cycle cellulaire et (ii) par une phase G1 très courte (1 heure) dont la traversée ne dépend ni des MAPK ni des points de contrôles régulés par la protéine du rétinoblastome (RB) et p53. Ces observations soulèvent la question de l’existence d’un lien de cause à effet entre ce phénomène de réplication autonome et la pluripotence. Mon projet de thèse se construit autour de trois axes qui montrent que : 1/ la phase G1 des cellules ES de souris est une phase de sensibilité accrue aux inducteurs de différenciation. 2/ la balance entre autorenouvellement et différenciation est perturbée, (i) quand l’expression de la cycline E est altérée, ou (ii) quand l’association de la cycline E avec la kinase CDK2 et le centrosome est bloquée. 3/ La signalisation par le LIF contrôle la formation et l’activation des complexes Cycline E/CDK2. Dans les cellules ES naïves Rex1+, l’allongement de la durée de la phase G1 induit par la privation de LIF précède, ou est concomitante, à la diminution de l’expression de marqueurs de pluripotence et à l’activation des marqueurs les plus précoces de la différenciation. Finalement, nous proposons un modèle dans lequel la signalisation par le LIF régule la transition G1/S et permet le maintien de l’autorenouvellement des cellules ES murines / Pluripotency can be captured and propagated in vitro from the epiblast of the pre-implantation blastocysts in the form of embryonic stem cells (ESCs). ESCs are capable of unlimited proliferation in an undifferentiated state while maintain the potential to differentiate into cells of all three germ layers in the embryo, including the germline. Two key features the ES cell mitotic cycle are (i) a vastly elevated and uniform expression of Cyclin E and Cyclin E/CDK2 complexes throughout the cell cycle and (ii) a short G1 phase characterized by the lack of RB- and p53-dependent checkpoints, and reduced dependency on MAPK signalling. During my PhD project, we explored whether and how the regulation of the cell cycle actively sustains self-renewal of mouse ESCs (mESCs). We demonstrated that: 1/ the G1 phase of mESCs is a phase of increased susceptibility to differentiation inducers. Thus shortening of G1 might shield undifferentiated cells from differentiation inducers and help ESCs to self-renew in the pluripotent state. 2/ Cyclin E opposes differentiation and supports self-renewal of mESCs by two independent mechanisms, one of which being independent of CDK2 activation. 3/ LIF signalling regulates Cyclin E/CDK2 kinase activity therefore accelerating the G1 to S phase transition. Finally, we propose a model in which LIF signalling stimulates the G1 to S phase transition to shield mESCs from undesired differentiation signals and help them to self-renew in the pluripotent state

Dans cette thèse, nous discutons l'influence d'un réseau qui possède une topologie non triviale sur les propriétés collectives d'un modèle hamiltonien pour spins,le modèle $XY$, défini sur ces réseaux.Nous nous concentrons d'abord sur la topologie des chaînes régulières et du réseau Petit Monde (Small World), créé avec le modèle Watt- Strogatz.Nous contrôlons ces réseaux par deux paramètres $\gamma$, pour le nombre d' interactions et $p$, la probabilité de ré-attacher un lien aléatoirement.On définit deux mesures, le chemin moyen $\ell$ et la connectivité $C$ et nous analysons leur dépendance de $(\gamma,p)$.Ensuite,nous considérons le comportement du modèle $XY$ sur la chaîne régulière et nous trouvons deux régimes: un pour $\gamma<1,5$,qui ne présente pas d'ordre longue portée et un pour $\gamma>1,5$ où une transition de phase du second ordre apparaît.Nous observons l'existence d'un état ​​métastable pour $\gamma_ {c} = 1,5$. Sur les réseaux Petit Monde,nous illustrons les conditions pour avoir une transition et comment son énergie critique $\varepsilon_{c}(\gamma,p)$ dépend des paramètres $(\gammap$).Enfin,nous proposons un modèle de réseau où les liens d'une chaîne régulière sont ré-attachés aléatoirement avec une probabilité $p$ dans un rayon spécifique $r$. Nous identifions la dimension du réseau $d(p,r)$ comme un paramètre crucial:en le variant,il nous est possible de passer de réseaux avec $d<2$ qui ne présentent pas de transition de phase à des configurations avec $d>2$ présentant une transition de phase du second ordre, en passant par des régimes de dimension $d=2$ qui présentent des états caractérisés par une susceptibilité infinie et une dynamique chaotique. / In this thesis we discuss the influence of a non trivial network topology on the collective properties of an Hamiltonian model defined on it, the $XY$ -rotors model. We first focus on networks topology analysis, considering the regular chain and a Small World network, created with the Watt-Strogatz model. We parametrize these topologies via $\gamma$, giving the vertex degree and $p$, the probability of rewiring. We then define two topological parameters, the average path length $\ell$and the connectivity $C$ and we analize their dependence on $\gamma$ and $p$. Secondly, we consider the behavior of the $XY$- model on the regular chain and we find two regimes: one for $\gamma<1.5$, which does not display any long-range order and one for $\gamma>1.5$ in which a second order phase transition of the magnetization arises. Moreover we observe the existence of a metastable state appearing for $\gamma_{c}=1.5$. Finally we illustrate in what conditions we retrieve the phase transition on Small World networks and how its critical energy $\varepsilon_{c}(\gamma,p)$ depends on the topological parameters $\gamma$ and $p$. In the last part, we propose a network model in which links of a regular chain are rewired according to a probability $p$ within a specific range $r$. We identify a quantity, the network dimension $d(p,r)$ as a crucial parameter. Varying this dimension we are able to cross over from topologies with $d<2$ exhibiting no phase transitions to ones with $d>2$ displaying a second order phase transition, passing by topologies with dimension $d=2$ which exhibit states characterized by infinite susceptibility and macroscopic chaotic dynamical behavior.

Dans cette thèse intitulé "Dynamique quantique de la phase et de la charge dans des chaînes des jonctionsJosephson", une étude expérimentale et une description théorique des effets quantiques des phases et descharges dans les chaînes de jonctions Josephson est présenté.La dynamique des chaînes de jonctions est dominé par deux échelles d'energie: l'energie Josephsonrelié a la superposition des fonctions d'ondes de deux électrodes et l'energie de charge relié a l'énergieélectrostatique des charges sur les deux électrodes. La réalisation d'un état quasi-classique de la chargenécessite une énergie de charge importante pour diminuer lesfluctuation quantique de la charge. En plus,le temps de relaxations de la jonctions dois être augmenté par un environnement a haute impédance.Un état de charges localisé a été réalisé sur une jonctions Josephson dans un environnement inductiveréalisé par une chaîne de jonction Josephson. L'état de charge localisé se manifeste par l'apparition d'undomaine a haute résistances dans les caractéristques courant-tension.Une chaînes des jonctions n'est pas une inductances parfaite. Des résonances electro-magnétique lié a lacapacité vers la masse des îlots supra-conducteurs altèrent la localisation de charge.Une characterisation des effets de pertes et des non-lineartés de ces résonances a été effectué. / In this thesis entitled ' Quantum phase and charge dynamics in Josephson junction chains ' an experimental study and theoretical description of quantum effects of phases and charges in chains of Josephsonjunctions is presented.The dynamics of Josephson junction chains are dominated by two different energy scales: the Josephsonenergy, which is related to the overlap of the superconducting wave functions of the two superconductorsforming the junction and the charging energy that is related to the electrostatic energy of the Cooper-pairs on the islands. The realization of a well-defined charge state on a Josephson junction requires a highcharging energy to suppress the quantumfluctuations of the charge. In addition, the charge relaxationtimes must be increased by inserting the junction in a high impedance environment.We have realized such a well-defined charge state on a Josephson junction in an inductive environmentthat is formed by a Josephson junction chain. The localized charge state manifest itself by the appearanceof a high resistive regime in the current-voltage characteristic.A Josephson junction chain is however not a perfect inductor. Electromagnetic resonances related withthe finite ground capacitance of the superconducting islands influence the charge localization.We have characterized the effect of losses and nonlinearities on the electromagnetic resonances of Josephson junction chains in microwave spectroscopy measurements.

Cette thèse concerne l'étude du diagramme de phase du fer en conditions extrêmes de pression et température. La Terre possède un noyau interne solide et un noyau externe liquide, qui sont principalement composés de fer. Une détermination fiable de la température de fusion du fer à 330 GPa, pression au-delà de laquelle le noyau terrestre est solide, permet de contraindre la température du noyau, ce qui est essentiel pour comprendre la dynamique terrestre. Le diagramme de phase du fer a été étudié jusqu'à 200 GPa en cellule à enclumes de diamant chauffée par laser utilisant la diffraction par rayon X comme diagnostic de l¿apparition de la fusion. Les températures obtenues sont en accord avec celles mesurées par compression dynamique, aux incertitudes expérimentales près, et sont plus élevées que celles obtenues lors de précédentes expériences statiques utilisant un critère de fusion différent. L'appareil, les méthodes et la métrologie utilisés pour les expériences en cellule à enclume de diamant chauffée par laser sont présentées ainsi que les problèmes rencontrés dans les expériences statiques à de telles conditions extrêmes. La possibilité d'utiliser le signal de diffraction des rayons X du joint en Re à des fins d'étalonnage de la pression pour l'expérimentation dans le domaine du multi-Mbar est aussi abordée. Dans ce but, l'équation d¿état du Re a été mesurée à 144 GPa. En fin, un test préliminaire a été effectué pour vérifier la possibilité d'utiliser la spectroscopie d'absorption des rayons X en dispersion d'énergie comme une technique complémentaire à la diffraction des rayons X pour la détermination de la courbe de fusion du fer. / This thesis concerns the study of the phase diagram of iron at extreme conditions of pressure and temperature. Iron is the main constituent of the terrestrial planetary cores. In particular, the Earth has a solid inner core and a liquid outer core which are mainly composed of iron. The accurate determination of the melting temperature of iron at the inner core boundary pressure, 330 GPa, would provide an important constraint on the temperature of the core, which is essential to understand how the dynamic Earth works. The phase diagram of iron has been investigated in laser-heated diamond anvil cell experiments up to 200 GPa using synchrotron-based fast X-ray Diffraction as a primary melting diagnostic. The obtained melting temperatures agree within the experimental uncertainties with the ones obtained from shock wave experiments and are higher than those reported by previous static experiments, where a different melting criterion was used. The apparatus, methods and metrology used in the static laser heated diamond anvil cell are discussed together with the issues encountered in static experiments at such extreme conditions. The possibility of using the X-ray diffraction signal of Re gasket for pressure calibration purpose for experiment in the multi-Mbar range is also discussed. For this purpose, Re equation of state has been measured up to 144 GPa. Finally, a preliminary test has been performed to check the possibility of using energy dispersive X-ray absorption spectroscopy as a technique complementary to fast X-ray diffraction in the investigation of the melting curve of iron.

L'interaction d'une impulsion laser intense (~10¹⁴ W /cm²) et de courte durée (femtoseconde) avec un gaz rare induit une polarisation hautement non-linéaire dans le domaine spectral XUV; les harmoniques d'ordre élevés. En raison des propriétés spécifiques du rayonnement harmonique et de ses applications, cette thématique est particulièrement riche et fertile. La production efficace d'harmoniques d'ordres élevés repose à la fois sur la réponse non-linéaire de l'atome unique et un comportement collectif.Le fil directeur des études présentées dans cette thèse est la compréhension et le contrôle de l'accord de phase ou du quasi accord de phase en présence d'une ionisation substantielle du gaz générateur. Dans ce contexte, nous montrons l'importance de la longueur de cohérence sur l'accord de phase en génération d'harmoniques. Nous étudions sa dépendance en fonction de la focalisation du laser, de la pression mais aussi sa dépendance temporelle liée à l'ionisation, effet que nous avons mis en évidence lorsqu'on a cherché à optimiser une double impulsion harmonique. Le travail de développement, sur la station LASERIX, de la source à double impulsion harmonique générée à partir d'un même milieu gazeux et avec un délai picoseconde variable est présenté. Cette source possède un véritable potentiel d'applications scientifiques, injectée dans un milieu amplificateur plasma qu'on appelle laser X, la double impulsion permettra de sonder la réponse temporelle de ce type de milieu. Par ailleurs, des expériences et des simulations menées sur la génération d'harmoniques en propagation guidée visent ainsi à étendre les spectres harmoniques vers les courtes longueurs d'ondes, zone spectrale pour laquelle le laser X à plasmas est émis. Ceci donnera l'accès à une source offrant des caractéristiques complémentaires des lasers X, sources développées en parallèle sur la station LASERIX. / The interaction of an intense laser pulse of short duration with a rare gas induces a highly non-linear polarization in the XUV spectral range: the high order harmonics. Due to the specific properties of the harmonic radiation and its applications, this issue is particularly rich and fertile. The efficient production of high order harmonics is based both on the non-linear response of the single atom and on collective behavior.The principle of the research presented in this thesis is the understanding and control of phase matching or quasi-phase matching in the presence of substantial ionization in the generating gas. In this context, we show the importance of the coherence length on the phase matching in High harmonic generation. We study its dependence on laser focusing, pressure but also its time dependence related to ionization. Moreover, experiments and simulations aim at extending harmonic spectra towards shorter wavelengths, a spectral range for which the X Ray Laser is emitted. This will give access to a source with complementary characteristics as regards to X-ray lasers. This source shall be developed in parallel on the LASERIX station or injected in soft X-ray laser amplifiers.

En cas d’accident grave dans un réacteur nucléaire à eau sous pression, l’alliage absorbant Ag-Cd-In est susceptible d’interagir à haute température avec leurs tubes guides en zircaloy. L’étude thermodynamique du liquide et des équilibres impliquant cette phase dans les systèmes Ag-Zr et Ag-Cd-In est une étape pour une estimation des relâchements de produits de fission. Le système Ag-Zr est difficile à étudier en raison de la réactivité du zirconium, à l’état liquide et avec l’oxygène, et de la difficulté à atteindre l’équilibre et enfin car les stabilités des phases intermédiaires AgZr et AgZr2 sont faibles. Après la mise en place de protocoles expérimentaux, les réactions invariantes du système sont établies en couplant l’analyse thermique différentielle avec des caractérisations par MEB. Un diagramme de phases Ag-Zr est proposé. Des mesures de calorimétrie de dissolution en bain aluminium sont effectuées à 723°C dans le but de déterminer l’enthalpie de formation de AgZr et AgZr2. Les résultats montrent la difficulté de dissoudre le zirconium dans l’aluminium liquide. Un modèle est développé pour quantifier la cinétique de dissolution. L’enthalpie de formation de AgZr est déterminée par calorimétrie de dissolution en bain acide à 25°C. L’extension dans le diagramme Ag-In-Cd du domaine de stabilité de la phase liquide est précisée en combinant une méthode isotherme de recuit et trempe d’échantillons biphasés solide/liquide avec la calorimétrie différentielle à balayage . La cohérence de ces nouveaux résultats entre eux et avec les données de la littérature est testée par le biais d’une optimisation thermodynamique suivant la méthode CALPHAD. / During a severe accident in a Pressurized Water Reactor, the Ag-In-Cd absorbing alloy is likely to interact at a high temperature with their guide tubes or with the fuel rod cladding, both in Zry. The thermodynamic study of liquid phase and its equilibria in the Ag-Zr and Ag-Cd-In systems is a necessary step for an estimate of the fission product release and of the corium progression. The aim is to bring an experimental contribution to this thermodynamic study. The Ag-Zr system is difficult to study experimentally for various reasons. Zirconium, especially when liquid, is reactive with oxygen. Equilibria often prove difficult to reach. Last, the stabilities of AgZr and AgZr2 are low. After the establishment of experimental protocols, the invariant transformations of the system were established by coupling differential thermal analysis with characterization by metallography and scanning electron microscopy. A Ag-Zr phase diagram is proposed. Solution calorimetry measurements in an Al bath were performed at 723°C to determine the enthalpy of formation of AgZr and AgZr2. Results show the difficulty of dissolving solid zirconium in aluminum. A model was developed to quantify the dissolution kinetics. The formation enthalpy of AgZr was determined by solution calorimetry in an acid bath at 25°C. In the Ag-In-Cd system, the extension of the liquid phase stability domain is specified by combining an isothermal method of annealing and quenching of biphasic solid / liquid samples with differential scanning calorimetry. The consistency of the new results between them and compared to the literature has been tested by means of a thermodynamic optimization following the CALPHAD method.

A four quadrant general single-phase bi-directional DC/DC converter was designed and constructed for high effect systems. The target application for the DC/DC converter was to be used to transfer energy between different energy storages, a miniature DC power grid and the high voltage AC power city grid. The converter is capable of step-up and step-down operations in both directions i.e. it is bi-directional at varying voltage levels. Different DC/DC topologies were investigated, and thereafter simulations were performed in LTspice and Simulink to ensure its capabilities and functionalities. The result of the simulations was a two layered PI-regulator, controlling both the external DC-grid voltage and inductor current through the converter. Once a suitable topology and control strategy was found, a suitable power transistor investigated and a PCB driver card were developed with KiCad. The final converter is capable to seamlessly change between its four modes and controlling voltages up to 1200 V and currents up to 200 A.

Computer simulations of the growth of binary alloy thin films in two and three dimensions were performed using an extension of the Solid on Solid model. Snapshots for a range of interactions and diffusion rates are presented and critically compared to experiment. A wide variety of distinct phases is identified and their growth conditions analyzed. These findings are summarized in a phase diagram. In addition, a fractal analysis of the domains is performed. It is found that for negative interactions the islands are two-dimensional, while for positive interactions, regardless of diffusion rate, a fractal dimension of 1.78 is obtained. / by Mark R. Bouwens. / Thesis (Ph.D.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.

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).

This Thesis proposes phase modulating interferometry as an alternative to phase stepping and phase-shifting interferometry for use in the shape and displacement characterization of microelectromechanical systems (MEMS) [Creath, 1988; de Groot, 1995a; Furlong and Pryputniewicz, 2003]. A phase modulating interferometer is developed theoretically with the use of a stroboscopic illumination source and implemented on a Linnik configured interferometer using a software control package developed in the LabVIEWâ„¢ programming environment. Optimization of the amplitude and phase of the sinusoidal modulation source is accomplished through the investigation and minimization of errors created by additive noise effects on the recovered optical phase. A spatial resolution of 2.762 µm over a 2.97x2.37 mm field of view has been demonstrated with 4x magnification objectives within the developed interferometer. The measurement resolution lays within the design tolerance of a 500Ã… ±2.5% thick NIST traceable gold film and within 0.2 nm of data acquired under low modulation frequency phase stepping interferometry on the same physical system. The environmental stability of the phase modulating interferometer is contrasted to the phase stepping interferometer, exhibiting a mean wrapped phase drift of 40.1 mrad versus 91 mrad under similar modulation frequencies. Shape and displacement characterization of failed µHexFlex devices from MIT's Precision Compliant Systems Laboratory is presented under phase modulating and phase stepping interferometry. Shape characterization indicates a central stage displacement of up to 7.6 µm. With a linear displacement rate of 0.75 Ã…/mV under time variant load conditions as compared to a nominal rate of 1.0 Ã…/mV in an undamaged structure [Chen and Culpepper, 2006].