Σ3{111} coherent twin boundary (CTB) in face-centered-cubic (FCC) metals and alloys have been regarded as an efficient way to simultaneously increase strength and ductility at the nanoscale. Extensive study of dislocation-CTB interaction has been carried out by a combination of computer simulations, experiments and continuum theory. Most of them, however, are based on the perfect CTB assumption. A recent study [Wang YM, Sansoz F, LaGrange T, et al. Defective twin boundaries in nanotwinned metals. Nat Mater. 2013;12(8):697-702.] has revealed the existence of intrinsic kink-like defects in CTBs of nanotwinned copper through nanodiffraction mapping technique, and has confirmed the effect of these defects on deformation mechanisms and mechanical behavior. One of the deformation mechanisms proposed therein, i.e. general hard dislocation slip intersecting with kink line is studied here in detail by molecular dynamics (MD) simulation. Simulations are performed using copper bicrystal models with a particular focus on the interaction of a screw dislocation with 0 degree and 60 degree kinked CTBs. It is found that kink-like defects have a profound impact on screw dislocation - CTB interaction mechanisms, resulting in significant strengthening or softening effects.

This study aimed to understand the processes that govern free surface behaviour in depth-limited turbulent flows. Experimental data has shown that the turbulence properties at a point near the free surface relate directly to the properties of the free surface pattern. This would suggest a direct linkage between the free surface and the underlying turbulence field, but this cannot be true since the free surface pattern is strongly dynamic while the sub-surface turbulence field is relatively persistent. An oscillatory spatial correlation function was derived which explains the de-linkage, showing that the turbulence-generated surface pattern periodically inverts as it advects downstream. A model was developed, which shows that the observed free surfaces can be considered as an ensemble of overlapping but behaviourally independent oscillons. These are shown to influence a zone of fluid beneath the surface and invert at a frequency which is a function of the root-mean-square roughness height of the free surface. The spatial frequency of free surface oscillation relates strongly to the spatial frequency of turbulent structures, suggesting that the oscillon motion may form the trigger for near-bed bursting events. Given these relationships, it is proposed that measurement of the free surface behaviour may allow remote measurement of flow conditions. An acoustic wave probe was developed, which is able to remotely recover the key features of the water surface pattern. An array of such probes is proposed for the accurate measurement of temporal and spatial properties of turbulent free surfaces and hence the underlying bulk flow conditions.

<p>This work focuses on the construction and application of coded apertures to compressive X-ray tomography. Coded apertures can be made in a number of ways, each method having an impact on system background and signal contrast. Methods of constructing coded apertures for structuring X-ray illumination and scatter are compared and analyzed. Apertures can create structured X-ray bundles that investigate specific sets of object voxels. The tailored bundles of rays form a code (or pattern) and are later estimated through computational inversion. Structured illumination can be used to subsample object voxels and make inversion feasible for low dose computed tomography (CT) systems, or it can be used to reduce background in limited angle CT systems. </p><p>On the detection side, coded apertures modulate X-ray scatter signals to determine the position and radiance of scatter points. By forming object dependent projections in measurement space, coded apertures multiplex modulated scatter signals onto a detector. The multiplexed signals can be inverted with knowledge of the code pattern and system geometry. This work shows two systems capable of determining object position and type in a 2D plane, by illuminating objects with an X-ray `fan beam,' using coded apertures and compressive measurements. Scatter tomography can help identify materials in security and medicine that may be ambiguous with transmission tomography alone.</p> / Dissertation

La diffraction cohérente est une technique étonnante par sa simplicité expérimentale : une source XUV cohérente illumine un échantillon unique, isolé, et la figure de diffraction de l’objet est enregistrée sur une caméra CCD. Une inversion de la figure de diffraction à une image dans l’espace réel est possible grâce à une approche basée sur des algorithmes itératifs. Les techniques d’holographie par transformée de Fourier, pour lesquelles une référence est placée à proximité de l’objet que l’on veut imager, permettent-elles la reconstruction directe de l’image, même lorsque la qualité des données expérimentales est moindre. Nous disposons dans notre laboratoire d’une source compacte XUV suffisamment intense pour réaliser ce type d’expérience. Les impulsions XUV ultrabrèves (femtoseconde à attoseconde) sont produites en sélectionnant les harmoniques d’ordre élevé d’un laser infra-rouge femtoseconde focalisé dans une cellule de gaz rare. Nous avons récemment démontré la possibilité d’utiliser cette source pour l’imagerie par diffraction cohérente avec une résolution spatiale de 78 nm. De plus, nous avons démontré expérimentalement une technique d’holographie avec référence étendue, et obtenu une résolution de 110 nm en simple tir (soit un temps d’intégration de 20 femtosecondes). Une perception d’un objet en trois dimensions nous donne une meilleure compréhension de celui-ci. A l’échelle nanométrique, les techniques d’imagerie 3D sont issues de techniques tomographiques autour de la microscopie électronique. Cependant, les nombreuses prises de vue nécessaires (sous des angles différents) rendent ces techniques caduques lors de l’étude résolue en temps de phénomènes irréversibles sur des échantillons non reproductibles. Dans ce contexte, le but de ma thèse est d’étendre les techniques d’imagerie 2D à une perception 3D d’objets nanométriques (physiques, biologiques), tout en préservant l’aspect ultrarapide. Le développement d’une nouvelle technique d’imagerie cohérent 3D en seul vue, l’ankylographie, proposée par le professeur J. Miao de UCLA [Raines et al., Nature 2010] a été effectué. Cette technique permet de reconstruire l’image 3D d’un échantillon d’après une unique image de diffraction. Son principe basique est de retrouver la profondeur d’un objet 3D par l’interférence constructive longitudinale. Cependant, cette technique d’imagerie cohérent 3D est plus exigeante en termes de qualité de données expérimentales comme en moyen informatique d’analyse et d’inversion. L’autre idée en imagerie 3D est de mimer la vision humaine en utilisant deux faisceaux X cohérents arrivant simultanément sur l’échantillon mais avec un petit angle. Dans ce schéma, on utilise des références à coté de l’objet mire (holographie) pour améliorer le rapport signal sur bruit dans la figure de diffraction (soit hologramme). On recueille ensuite deux hologrammes sur le même détecteur. L’inversion Fourier de chacun des hologrammes forme deux images issues d’une vision différente de l’objet. La parallaxe est ainsi réalisée. La reconstruction stéréo de l’objet est effectuée numériquement. Enfin, des applications de démonstration seront envisagées après ma thèse. Il s’agit d’imager des objets biologiques (nanoplanktons déjà collectés et préparés au CEA). Et nous nous intéresserons également à l’étude du mouvement 3D d’objets nanométriques (azo-polymères) sur des temps ultracourts. Une autre application importante sera d’étudier la transition de phase ultra-rapide tel que le nano-domaine magnétique où des phénomnes de désaimantation induite par des impulsion femtoseconde ont lieu. / Coherent diffraction is an amazing art by its experimental simplicity: a coherent XUV source illuminates a single, isolated sample, and the diffraction pattern of the object is recorded by a CCD camera. An inversion of the diffraction pattern to an image in real space is possible through an approach based on iterative algorithms. The techniques for Fourier transform holography, for which reference is placed near the object to be imaged, allow the direct reconstruction of the image, even when the quality of the experimental data is worse. We have a laboratory sufficiently intense compact XUV source for this type of experience. The ultrashort XUV pulses (from femtosecond to attosecond) are produced by selecting high order harmonics of a femtosecond infrared laser which is focused into a cell of rare gas. We recently demonstrated the feasibility of using this source for coherent diffraction imaging with a spatial resolution of 78 nm. Furthermore, we demonstrated experimentally a holographic technique with extended reference and obtained a resolution of 110 nm in single shot (i.e. an integration time of 20 femtoseconds). A perception of an object in three dimensions gives us a better understanding thereof. A nanoscale 3D imaging techniques are from tomographic techniques of electron microscopy. However, many shots required (from different angles) make these techniques obsolete during the study time-resolved irreversible phenomena on non-reproducible samples. In this context, the aim of my thesis is to extend the 2D imaging techniques for 3D perception of nanoscale (physical, biological ) objects, while preserving the ultrafast appearance. The development of a new technology of 3D coherent imaging in single view, named ‘ankylography’, proposed by Professor Miao J. UCLA [Raines et al., Nature 2010] was made in progress. This technique allows reconstructing a 3D image of the sample after a single diffraction image. Its basic principle is to find the depth of a 3D object by the longitudinal constructive interference. However, this technique is more requested in both the quality of experimental data and the computer hardware and analysis. The other idea for 3D imaging is to imitate human vision using two coherent beams X arriving simultaneously on the sample but with a small angle. In this scheme, we use references near the target object (i.e. holography) to improve the signal to noise ratio in the diffraction pattern (hologram). Two holograms are then collected on the same detector. The inverse Fourier of each hologram forms two images from different views of the object. Parallax is thus produced. The stereo reconstruction of the object is performed by computer. Finally, the demonstration of applications will be considered after my thesis. This imaging of biological objects (such as nanoplanktons already collected and prepared CEA). And we are also interested in the study of 3D nanoscale objects (azo-polymers) movement on ultrashort time. Furthermore, another important application will be to study the ultra-fast phase transition such as nano-magnetic field where demagnetization phenomena induced by femtosecond pulse occurs.

La manipulation des propriétés physiques des nanostructures, telles que leur forme ou leur composition, suscite de plus en plus l’intérêt des recherches à cause des propriétés exceptionnelles des matériaux à cette échelle. L’ingénierie des contraintes a pour objet d’utiliser la déformation pour contrôler les propriétés. Cela est particulièrement intéressant dans les nano-objets car ils peuvent supporter des déformations élastiques élevées. Dans ce travail, nous étudions la déformation et l’influence de la température dans des nanofils uniques de type coeur/coquille. Ceci est possible en utilisant la diffraction cohérente des rayons X (CDI) en condition de Bragg, une technique d’imagerie qui remplace les lentilles optiques par des algorithmes d’inversion capables de reconstruire l’amplitude (densité électronique) et la phase (projection du champ de déplacement atomique) de l’échantillon à partir des clichés de diffraction. Cette méthode a également été appliquée à des particules facettées de platine qui ont des propriétés catalytiques exceptionnelles. Des expériences CDI in situ ont permis d’étudier l’évolution du champ de déformation dans les particules pendant des réactions chimiques et donc de progresser vers le découplage entre leur déformation intrinsèque et leur activité chimique. / Manipulating the physical and chemical properties of nanostructures by changing their characteristics (such as shape, strain or composition) is a vivid field of research spurred by the numerous applications that may take advantage of the unique properties that materials offer at this scale.Strain engineering aims to tune the strain in order to control the properties of materials. This is particularly interesting in nano-objects because they can sustain much higher elastic strains before the occurrence of defects. In this work, we study the strain and the influence of temperature in single core/shell nanowires. This is possible thanks to X-ray coherent diffraction (CDI) in Bragg condition, an imaging technique that replaces the optical lenses by inversion algorithms that are able to reconstruct the amplitude (electronic density) and the phase (projection of the atomic displacement field) of the sample from the experimental diffraction patterns. In addition to nanowires, the method is applied to metallic particles of platinum with exceptional catalyticproperties. In situ CDI experiments allowed to study the strain evolution within particles during chemical reactions, thereby moving forward in the understanding of important relationships such as the intrinsic strain and chemical activity of the nanoparticles.

Dans cette thèse, nous étudions le transport quantique d’ondes de matière avec des atomes ultrafroids. Ces systèmes d’atomes ultrafroids fournissent un très bon contrôle et une grande flexibilité pour les paramètres du système tels que les interactions, sa dimensionnalité et les potentiels externes. Cela les rend un excellent outil pour l’étude de plusieurs concepts fondamentaux de la physique de la matière condensée. Nous nous concentrons sur le transport quantique dans les milieux désordonnés. Il diffère du transport classique par le rôle fondamental joué par les phénomènes d’inférence, qui peuvent éventuellement conduire à la suppression du transport; connu comme la Localisation d’Anderson. Nous étudions l’expansion d’un condensat de Bose-Einstein dans un désordre fort et montrons des signes de localisation d’atomes ultrafroids à trois dimensions. Dans la dernière partie de ce manuscrit, nous discutons l’observation de la rétrodiffusion cohérente d’atomes ultrafroids, ce qui est un signal direct du rôle de la cohérence quantique dans le transport quantique dans les milieux désordonnés. Nous observons l’évolution temporelle de la distribution d’impulsions d’un nuage de atomes ultrafroids, lancé avec une distribution de vitesse étroite dans un potentiel désordonné. Un pic émerge dans le sens rétrograde, correspondant au signal de CBS. / In this thesis we study the quantum transport of matter waves with ultracold atoms. Such ultracold atom systems provide a very good control and a high flexibility of the parameters of the systems like the interactions, its dimensionality and the external potentials. This makes them a great tool for the investigation of several fundamental concepts of condensed matter physics. We focus on the quantum transport in disordered media. It differs to classical transport by the fundamental role played by inference phenomena, which can eventually lead to the suppression of transport; known as Anderson Localization. Observing the expansion of a Bose-Einstein condensate in a strong light disorder, we show evidence for Localization of ultracold atoms in three dimensions. In the last part of this manuscript we discuss the observation of Coherent Backscattering of ultracold atoms, which is a direct signal of the role of quantum coherence in quantum transport in disordered media. We observe the time evolution of the momentum distribution of a cloud of ultra-cold atoms, launched with a narrow velocity distribution in a disordered potential. A peak emerges in the backwards direction, corresponding to the CBS signal.

Após a excitação de uma amostra semicondutora por um pulso ultracurto, os fotoporadores interagem com a rede excitando modos longitudinais ópticos. Essa interação provoca variações no índice de refração do material, produzindo modulações na resposta óptica do meio (efeito eletro-óptico). Por outro lado, esta dinâmica origina polarizações dependentes do tempo o que gera emissão de radiação terahertz. Experimentos recentes (pump-probe) observaram modulações do campo através de medidas da refletividade resolvidas no tempo. A refletividade e o campo estão relacionados segundo o efeito eletro-óptico. Também se resolve temporalmente o campo irradiado pela amostra, através de antenas que operam na faixa de terahertz. Tanto as medidas eletro-ópticas quanto de emissão terahertz fornecem informações sobre a interação dinâmica do plasma com a rede após a excitação óptica. Nesse trabalho simulamos a interação dinâmica de plasma e fônons em n-GaAs e Telúrio (\"bulk\") após estes serem excitados por um pulso ultracurto. Utilizamos equações hidrodinâmicas para descrever transporte de cargas e uma equação fenomenológica de oscilador harmônico forçado, para descrever oscilações longitudinais ópticas da rede. Complementando nossa descrição temos a equação de Poisson, com a qual calculamos o campo gerado pelo plasma e pela polarização da rede semicondutora. Essas equações constituem um sistema de seis equações diferencias (quatro parciais) acopladas. Para resolvê-las utilizamos o método das diferenças finitas. Do cálculo numérico obtemos a evolução temporal do campo elétrico no interior do material. Com esse campo determinamos as freqüências de oscilação do sistema e calculamos o campo irradiado. Nossos resultados apresentam acordo qualitativo com os experimentos / Above-band-gap optical excitation of semiconductors generates highly non-equilibrium photocarriers which interact with phonons thus exciting vibrational modes in the system. This interaction induces refractive-index changes via the electro-optic effect. Moreover it gives rise to electromagnetic radiation at characteristic frequencies (terahertz). Both effects have been measured by time-resolved ultra fast spectroscopy. Recent pump-probe experiments have found strong modulations of the internal electric field through electro-optic measurements. The emitted electromagnetic radiation has also been detected by a terahertz dipole antenna. Both electro-optic and terahertz emission measurements provide information about the coupled dynamics of photocarriers and phonons. In this work we simulate the dynamics of plasmon-phonon coupled modes in n-GaAs and Tellurium (bulk) following ultrafast laser excitation. The time evolution of the photocarrier densities and currents is described semi classically in terms of the moments of the Boltzmann equation. Phonon effects are accounted for by considering a phenomenological driven-harmonic-oscillator equation, which is coupled to the electron-hole plasma via Poisson\'s equation. These equations constitute a coupled set of differential equations. We use finite differencing to solve these equations. From the numerical results for the evolution of internal fields we can calculate both the characteristic frequencies of system and its terahertz radiation spectrum. Our results are consistent with recent experimental data

O objetivo desta Tese foi a aplicação da teoria dos estados coerentes para sistemas quânticos não-triviais. A partir da definição de estados coerentes para grupos de Lie compactos em geral, nos dedicamos a uma investigação detalhada da construção de tais estados e de suas propriedades no caso do grupo simplético unitário Sp(4), que é extremamente importante tanto em mecânica quântica quanto em mecânica clássica. Esse grupo possui uma complexidade intermediária, que permite um tratamento analítico ainda que apresente propriedades não-triviais do ponto de vista de teoria de representação de álgebras de Lie. Os estados coerentes obtidos nos permitiram uma investigação do limite clássico para sistemas com simetria Sp(4) e uma conexão com a teoria do caos em mecânica quântica. Além disso, tratamos uma proposta recente de generalização do conceito de estados coerentes para sistemas de espectro discreto não-degenerado, os estados de Gazeau-Klauder. Esses estados foram aplicados a um problema de magnetização bidimensional e também ao potencial unidimensional de mínimos duplos, onde observamos o aparecimento dos estados chamados \"Gatos de Schrödinger\", que consistem na superposição de dois estados de mínima incerteza. / The subject of the Thesis was the aplication of the coherent states theory to non-trivial quantum systems. Starting from the general definition of coherent states for compact Lie groups, we made a detailed investigation of the construction of these states and its properties in the case of the unitary symplectic group Sp(4), which is extremely important in both quantum and classical mechanics. This group has an intermediate complexity, allowing an analytic treatment while presenting non-trivial properties from the point of view of represention theory of Lie algebras. The coherent states so obtained allowed us an investigation of the classical limit of systems with Sp(4) symmetry and a conection with the theory of chaos in quantum mechanics. Besides that, we have treated a recent generalization of the concept of coherent states for systems with discrete and nondegenerate spectrum, the Gazeau-Klauder states. These states were applied to a twodimensional magnetization problem and also to the onedimensional double-well potential, where we have observed the appearence of the so-called \"Schrödinger cats\", which consist in the superposition of two minimum-uncertainty states.

<p>Conventional rocket propellants such as monomethyl hydrazine (MMH) and hydrazine have been used for decades due to their high specific impulse and performance. However, interest in greener alternatives, including HAN or HAN-based propellants, has grown due to high levels of toxicity and difficulties in the handling and storage of conventional fuels. Included among potential propellants are monopropellants nitromethane (NM) and isopropyl nitrate (IPN) and their blends. Though large-scale investigations on the ignition and combustion of these fuels have been done, the ignition and combustion processes of these monopropellant fuels are still not well understood. Droplet studies have been traditionally and extensively employed to decipher the influence of ambient conditions and fuel properties on ignition and combustion of different fuels. These fundamental studies allow for the isolation of different factors such as ambient temperature and initial droplet size among others, to provide a deeper understanding of their effects in overall spray combustion.</p> <p> </p> <p>The research described here seeks to add to the knowledge on the ignition and combustion processes of NM and IPN through single droplet ignition and combustion studies. To this end, the first effort has been to establish a suitable method of studying the ignition and combustion of droplets in conditions similar to those in practical systems. Droplet ignition delay measurements for NM and IPN droplets have also been conducted, and the influence of ambient temperature and droplet size has been studied. The double flame structures of NM and IPN, representative of hybrid combustion, have also been observed. In addition, the applicability of the hybrid combustion model, developed to predict mass burning rates for hypergolic fuels exhibiting hybrid burning including MMH, UDMH and hydrazine, has been assessed. Lastly, the ability of the quasi-steady droplet ignition model to predict ignition delays of IPN and NM monopropellant droplets is also discussed.</p>

Questões ambientais estão no centro das discussões nas últimas décadas. A poluição atmosférica, causada pela expansão pós-revolução industrial fez surgir a necessidade de aprender a descrever, usando modelos matemáticos, esse fenômeno. Com esse conhecimento pode-se propor soluções que mitiguem a poluição e os danos colaterais causados ao ambiente. A dispersão de poluentes modelada por soluções analíticas, a partir das equações de advecção-difusão oferecem um conhecimento sobre cada componente que constrói a equação, característica inexistente em outras abordagens, como a numérica. Entretanto ela era incapaz de descrever propriedades que se referem à turbulência, as estruturas coerentes, causadas por componentes não-lineares suprimidas por construção das equações governantes do modelo. Este trabalho estudou uma forma de recuperar características associadas à turbulência através de uma componente fundamental em estruturas coerentes, a fase. Essa é incluída no modelo que passa a descrever manifestações da turbulência em processos de dispersão através de flutuações de pequena escala na concentração da solução do modelo sesquilinear, que é determinístico-estocástico. No decorrer do trabalho há um estudo através de variações de parâmetros para compreender os efeitos da fase no modelo. Ele também foi aplicado ao experimento de Copenhagen e a dois cenários reais com a intenção de compreender o modelo frente à variáveis micrometeorológicas assim como aprimorá-lo para simular a dispersão de poluentes oriundos de fontes de forma realística. / Environmental issues have been at the center of discussions in the last few decades. Atmospheric pollution, caused by post-industrial revolution, has increased the necessity to describe, using mathematical models, this phenomenon. With this knowledge is possible to propose solutions mitigating the pollution and collateral damages caused in the environment. The pollutant dispersion modeled by analytical solutions, from advection-diffusion equations, offers a knowledge about each component that constructs the equation, a characteristic that does not exist in other approaches, such as numerical. However it was unable to describe properties that refer to turbulence, coherent structures, caused by nonlinear components suppressed by constructing the model governing equations. This work studied a way to recover characteristics associated with turbulence through a fundamental component in coherent structures, the phase. This is included in the model which describes manifestations of turbulence in the dispersion process through the presence of small-scale concentration fluctuations in the sesquilinear model, which is deterministicstochastic. In the course of this work there is a study through variations of parameters to understand the phase effects in the model. It was also applied to Copenhagen experiment and to two real scenarios with the intention of understanding the model regarding micrometeorological variables as well as improving it to simulate the pollutant dispersion from sources in a realistic way.