Nous étudions la transition de phase entre un superfluide et un isolant de Mott dans le cadre du modèle de Bose-Hubbard, décrivant des bosons sur réseau avec interactions sur site. Nous implémentons une formulation sur réseau du groupe de renormalisation non-perturbatif, dont la condition initiale est la limite locale (limite de sites découplés). Les résultats obtenus sont en accord quantitatif à la fois pour les quantités universelles (existence de deux classes d'universalité, exposants critiques comparables à ceux attendus) mais aussi non-universelles (diagramme de phase en accord avec les meilleurs approches numériques). La transition de Mott avec change- ment de densité appartient à la classe d'universalité de la transition vide-superfluide d'un gaz de Bose dilué. En caractérisant les excitations élémentaires au point critique quantique, des quasi-particules bosoniques de masse effective m∗, de poids de quasi- particule ZQP et dont les interactions sont décrites par une "longueur de diffusion" effective a∗, nous décrivons la thermodynamique universelle à proximité de la tran- sition de Mott grâce aux fonctions d'échelle du gaz dilué. Nous calculons également les fonctions d'échelle, non triviales, en dimension deux et à température finie et les comparons à des expériences récentes, démontrant ainsi l'universalité dans les gaz de Bose dilués avec ou sans réseau optique.

Esta tesis es un trabajo teórico, en el que estudiamos la física de los átomos dipolares bosónicos ultrafríos en retículos ópticos. Éstos gases consisten de átomos o moléculas bosónicas, enfriados bajo la temperatura de degeneración cuántica, típicamente del orden de nK. En éstas condiciones, en una trampa armónica tridimensional (3D), los bosones que interaccionan débilmente condensan y forman un Condensado de Bose Einstein (BEC). Cuando se carga un BEC en un retículo óptico producido por ondas estacionarias de luz láser, se producen nuevos fenómenos físicos. Estos sistemas entonces realizan modelos de tipo Hubbard y pueden ser llevados a regimenes fuertemente correlacionados.En 1989, M. Fisher et. al. predecían que el modelo de Bose-Hubbard homogéneo (BH) presenta la transición de fase cuántica Superfluid-Mott insulator (SF-MI). En 2002, la transición entre éstas dos fases fue observada experimentalmente por primera vez en el grupo de T. Esslinger e I. Bloch. La realización experimental de un BEC dipolar de cromo en el grupo de T. Pfau, y los progresos recientes en las técnicas de enfriamiento y atrapamiento de moléculas dipolares en los grupos de D. Jin e J. Ye, han abierto el camino hacia los gases cuánticos ultra-fríos dominados por la interacción dipolar. La evolución natural, y el reto de hoy en día por parte experimental, es de cargar BEC dipolares en retículos ópticos y estudiar los gases dipolares fuertemente correlacionados.Antes de éste trabajo de doctorado, estudios sobre modelos de BH con interacciones extendidas a los primeros vecinos mostraron la evidencia de nuevas fases cuánticas, como el supersólido (SS) y la fase checkerboard (CB). Debido al carácter de largo alcance de la interacción dipolo-dipolo, que decae con la potencia cúbica inversa de la distancia, es necesario incluir más de un primer vecino para obtener una descripción fiel y cuantitativa de los sistemas dipolares. De hecho, al incluir más vecinos se permiten y se estabilizan aún más nuevas fases.En esta tesis estudiamos modelos de BH con interacciones dipolares, investigando más allá del estado fundamental. Estudiamos un retículo bidimensional (2D) donde los dipolos están polarizados en dirección perpendicular al plano 2D, dando lugar a una interacción dipolar repulsiva e isotrópica. Utilizamos aproximaciones de campo-medio y un ansatz Gutzwiller, que son suficientemente correctos y adecuados para describir este sistema. Encontramos que los gases dipolares en 2D presentan una multitud de estados metaestables de tipo MI, que compiten con el estado fundamental, de modo parecido a sistemas desordenados. Estudiamos en detalle el destino de estos estados metaestables: como pueden ser preparados de manera controlada, como pueden ser detectados, cual es su tiempo de vida debido al tunnelling, y cual es su rol en los procesos de enfriamiento. Además, encontramos que el estado fundamental está caracterizado por estados MI de tipo checkerboard con coeficiente de ocupación n fraccionario (numero medio de partículas por sitio) que depende del cut-off utilizado en el radio de alcance de la interacción. Confirmamos esta predicción estudiando el mismo sistema con métodos Quantum Monte Carlo (worm algorithm). En este caso no utilizamos ningún cut-off en el radio de alcance de la interacción, y encontramos pruebas de una "Devil's staircase" en el estado fundamental, i.e. donde las fases MI aparecen en todos los n racionales del retículo subyacente. Encontramos además, regiones de los parámetros donde el estado fundamental es supersólido, obtenido drogando los sólidos con partículas o con agujeros.En este trabajo, investigamos también como cambia la estructura precedente en 3D. Nos focalizamos en el retículo 3D más sencillo compuesto de dos planos 2D, en el cual los dipolos están polarizados perpendicularmente a los planos; la interacción dipolar es entonces repulsiva por partículas del mismo plano, mientras es atractiva por partículas en el mismo sitio de dos planos diferentes. En cambio suprimimos el tunnelling entre los planos, lo cual hace el sistema equivalente a una mezcla bosónica en un retículo 2D. Nuestros cálculos muestran que las partículas se juntan en parejas, y demostramos la existencia de la nueva fase cuántica Pair Super Solid (PSS).Actualmente estamos estudiando un retículo 2D donde los dipolos están libres de apuntar en ambas direcciones perpendicularmente al plano, lo cual resulta en una interacción a primeros vecinos repulsiva (atractiva) por dipolos alineados (anti-alineados). Encontramos regiones de parámetros donde el estado fundamental es ferromagnético u anti-ferromagnético, y encontramos pruebas de la existencia de la fase cuántica Counterflow Super Solid (CSS).Las nuestras predicciones tienen directas consecuencias experimentales, y esperamos que vengan pronto controladas en experimentos con gases dipolares atómicos y moleculares ultra-fríos. / This thesis is a theoretical work, in which we study the physics of ultra-cold dipolar bosonic gases in optical lattices. Such gases consist of bosonic atoms or molecules, cooled below the quantum degeneracy temperature, typically in the nK range. In such conditions, in a three-dimensional (3D) harmonic trap, weakly interacting bosons condense and form a Bose-Einstein Condensate (BEC). When a BEC is loaded into an optical lattice produced by standing waves of laser light, new kinds of physical phenomena occur.These systems realize then Hubbard-type models and can be brought to a strongly correlated regime. In 1989, M. Fisher et. al. predicted that the homogeneous Bose-Hubbard model (BH) exhibits the Superfluid-Mott insulator (SF-MI) quantum phase transition. In 2002 the transition between these two phases were observed experimentally for the first time in the group of T. Esslinger and I. Bloch. The experimental realisation of a dipolar BEC of Chromium by the group of T. Pfau, and the recent progresses in trapping and cooling of dipolar molecules by the groups of D. Jin and J. Ye, have opened the path towards ultra-cold quantum gases with dominant dipole interactions. A natural evolution and present challenge, on the experimental side is then to load dipolar BECs into optical lattices and study strongly correlated ultracold dipolar lattice gases.Before this PhD work, studies of BH models with interactions extended to nearest neighbours had pointed out that novel quantum phases, like supersolid (SS) and checkerboard phases (CB) are expected. Due to the long-range character of the dipole-dipole interaction, which decays as the inverse cubic power of the distance, it is necessary to include more than one nearest neighbour to have a faithful quantitative description of dipolar systems. In fact, longer-range interactions tend to allow for and stabilize more novel phases.In this thesis we study BH models with dipolar interactions, going beyond the ground state search. We consider a two-dimensional (2D) lattice where the dipoles are polarized perpendicularly to the 2D plane, resulting in an isotropic repulsive interaction. We use the mean-field approximations and a Gutzwiller ansatz which are quite accurate and suitable to describe this system. We find that dipolar bosonic gas in 2D exhibits a multitude of insulating metastable states, often competing with the ground state, similarly as in a disordered system. We study in detail the fate of these metastable states: how can they be prepared on demand, how they can be detected, what is their lifetime due to tunnelling, and what is their role in various cooling schemes. Moreover, we find that the ground state is characterized by insulating checkerboard-like states with fractional filling factors v(average number of particles per site) that depend on the cut-off used for the interaction range. We confirm this prediction by studying the same system with Quantum Monte Carlo methods (the worm algorithm). In this case no cut-off is used, and we find evidence for a Devil's staircase in the ground state, i.e. where insulating phases appear at all rational of the underlying lattice. We also find regions of parameters where the ground state is a supersolid, obtained by doping the solids either with particles or vacancies.In this work, we also investigate how the previous scenario changes in 3D. We focus on the simplest 3D lattice composed of two 2D layers in which the dipoles are polarized perpendicularly to the planes; the dipolar interaction is then repulsive for particles laying on the same plane, while it is attractive for particles at the same lattice site on different layers. Instead we consider inter-layer tunnelling to be suppressed, which makes the system analogous to a bosonic mixture in a 2D lattice. Our calculations show that particles pair into composites, and demonstrate the existence of the novel Pair Super Solid (PSS) quantum phase.Currently we are studying a 2D lattice where the dipoles are free to point in both directions perpendicularly to the plane, which results in a nearest neighbour repulsive (attractive) interaction for aligned (antialigned) dipoles. We find regions of parameters where the ground state is ferromagnetic or antiferromagnetic, and find evidences for the existence of a Counterflow Super Solid (CSS) quantum phase.Our predictions have direct experimental consequences, and we hope that they will be soon checked in experiments with ultracold dipolar atomic and molecular gases.

Ce travail porte sur l'étude du comportement protecteur vis-à-vis de la corrosion de revêtements amorphes base Si élaborés par dépôt chimique en phase vapeur.<br />Le caractère protecteur de revêtements de type SiOx et SiOxNy a été analysé sur différents types de substrats. La tenue à la corrosion résulte de la faible porosité et de la nature très isolante de ces couches. <br />La protection fournie par des dépôts SiCx et SiCxNy utilisés comme couche d'accrochage au DLC (“Diamond Like Carbon”) a ensuite été étudiée. L'influence du taux d'incorporation d'azote de films SiCxNy a révélé une corrélation entre la structure chimique, déterminée par XPS, et le caractère semi-conducteur de la couche, établi par Mott-Schottky. La tenue à la corrosion a été directement associée à la densité de porteurs de charge.<br />L'étude a été complétée par une caractérisation électrochimique et une approche tribocorrosion du caractère protecteur fourni par des revêtements duplex SiCxNy / DLC.

Cette these aborde diverses problematiques concernant les electrons fortement correles dans des systemes bidimensionnels (composes a frustration geometrique, phases a liens de valence resonants), decrits a l'aide de modeles de dimeres. Une partie de la these concerne des modeles classiques sur un reseau triangulaire anisotrope, presentant des phases critiques qu'on peut decrire a l'aide de theories conformes; en se basant sur ces theories, l'analyse numerique de ce modele par matrice de transfert a permis de caracteriser les conditions d'existence de la criticalite, et plus generalement le diagramme de phases du modele en fonction d'interactions a courte portee et de l'anisotropie du reseau.<br />Une autre partie de la these traite un systeme d'electrons sur un reseau pyrochlore bidimensionnel (ou damier) a remplissage commensurable, en interactions a courte portee. Dans une limite de fortes interactions les electrons subissent des contraintes qui se traduisent par un modele effectif de dimeres quantiques (se differentiant par rapport au modele dit de Rokhsar-Kivelson, motive par les etats a liens de valence resonants, par un degre de liberte supplementaire, de spin). Une etude par diagonalisation exacte, completee par une approche variationnelle et des arguments perturbatifs, a permis d'identifier une phase cristalline a singulets resonants; une extension de ce modele a une mobilite finie des electrons a ete consideree pour caracteriser la transition de cette phase isolante vers un etat metallique en fonction du rapport de la mobilite des electrons et de leurs interactions.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1999. / Title from electronic submission form. Vita. Abstract. Includes bibliographical references.

Würzburg, Univ., Diss., 2009. / Zsfassung in engl. Sprache.

abstract: The formation of dendrites in materials is usually seen as a failure-inducing defect in devices. Naturally, most research views dendrites as a problem needing a solution while focusing on process control techniques and post-mortem analysis of various stress patterns with the ultimate goal of total suppression of the structures. However, programmable metallization cell (PMC) technology embraces dendrite formation in chalcogenide glasses by utilizing the nascent conductive filaments as its core operative element. Furthermore, exciting More-than-Moore capabilities in the realms of device watermarking and hardware encryption schema are made possible by the random nature of dendritic branch growth. While dendritic structures have been observed and are well-documented in solid state materials, there is still no satisfactory theoretical model that can provide insight and a better understanding of how dendrites form. Ultimately, what is desired is the capability to predict the final structure of the conductive filament in a PMC device so that exciting new applications can be developed with PMC technology. This thesis details the results of an effort to create a first-principles MATLAB simulation model that uses configurable physical parameters to generate images of dendritic structures. Generated images are compared against real-world samples. While growth has a significant random component, there are several reliable characteristics that form under similar parameter sets that can be monitored such as the relative length of major dendrite arms, common branching angles, and overall growth directionality. The first simulation model that was constructed takes a Newtonian perspective of the problem and is implemented using the Euler numerical method. This model has several shortcomings stemming majorly from the simplistic treatment of the problem, but is highly performant. The model is then revised to use the Verlet numerical method, which increases the simulation accuracy, but still does not fully resolve the issues with the theoretical background. The final simulation model returns to the Euler method, but is a stochastic model based on Mott-Gurney’s ion hopping theory applied to solids. The results from this model are seen to match real samples the closest of all simulations. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016

Made available in DSpace on 2016-06-02T19:10:07Z (GMT). No. of bitstreams: 1 3977.pdf: 12520615 bytes, checksum: 497a1cab19fc5cc6bb11416d048f7316 (MD5) Previous issue date: 2011-03-03 / Universidade Federal de Sao Carlos / In this work, the corrosion behavior of three Fe-Mn-Si-Cr-Ni (Co) shape memory stainless steels (SMSS) in aggressive environments was characterized. The electrochemical corrosion behavior in 0.5 M H2SO4 solution was obtained by potentiodynamic polarization, linear polarization, potential decay curves, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analyses. Localized corrosion resistance was evaluated by potentiodynamic polarization measurements in 3.5% NaCl solution. The corrosion performance in highly oxidizing environments was evaluated based on immersion tests in boiling HNO3 solution. The passive film composition was analyzed by X-ray photoelectron spectroscopy (XPS). The test results were compared with that of a type 304 (SS 304) austenitic stainless steel. The three SMSSs exhibited a passive behavior in 0.5 M H2SO4 solution; however, their anodic behavior in the active dissolution region was markedly different. The passive current densities of the SMSSs were similar to that of SS 304, although the critical anodic current required for passivation was higher. The corrosion rate of the SMSSs in 0.5 M H2SO4 solution was much higher than that of SS 304. It was observed that the amount of Cr and Mn plays an important role in the corrosion behavior of SMSS. The XPS analyses indicated substantial Si content (in the chemical form of a silicate) in the anodic passive films formed on SMSS. Mott-Schottky analyses suggested that the Si acts as a dopant in the films, making them less defective and thicker than the films formed on SS 304. Due to their high manganese content, SMSSs are highly prone to pitting corrosion in chloride environments. SMSSs exhibit better corrosion resistance than SS 304 in highly oxidizing environments. / Neste trabalho, a resistência à corrosão de três ligas inoxidáveis Fe-Mn-Si-Cr-Ni-(Co) com efeito de memória de forma (EMF) foi caracterizada em ambientes corrosivos. O comportamento eletroquímico em solução de ácido sulfúrico (H2SO4) 0,5 M foi obtido por polarização potenciodinâmica, polarização linear, curvas de decaimento de potencial, impedância eletroquímica e gráficos de Mott-Schottky. A resistência à corrosão localizada foi avaliada por testes potenciodinâmicos em solução de cloreto de sódio (NaCl) 3,5%. A resistência à corrosão em ambiente fortemente oxidante foi avaliada por ensaios de imersão em solução de ácido nítrico (HNO3) em ebulição. A composição do filme passivo foi analisada por espectroscopia de fotoelétrons excitados por raios X (XPS). Os resultados foram comparados com o de um aço inoxidável AISI 304. As três ligas com EMF apresentaram passividade em solução de H2SO4 0,5 M, no entanto, o comportamento anódico das ligas na região de dissolução ativa foi notavelmente diferente. Os valores de densidade de corrente passiva das ligas foram próximos ao do aço inoxidável AISI 304, no entanto a densidade de corrente crítica necessária para o início da passivação foi maior. A taxa de corrosão da ligas com EMF foi muito maior do que a do aço inoxidável AISI 304 em solução de H2SO4 0,5 M. Os teores de Cr e Mn têm grande influência na resistência à corrosão dessas ligas. As análises por XPS revelaram um filme passivo rico em Si4+ (na forma química de silicato). Os gráficos de Mott-Schottky sugerem que a alta proteção dos filmes passivos formados anodicamente em solução de H2SO4 0,5M está associada à incorporação de Si4+. O Si4+ age como um dopante nos filmes, tornando-os menos defeituosos e mais espessos do que os filmes formados no aço inoxidável AISI 304. Devido ao elevado teor de Mn (8-14 % em peso), as ligas inoxidáveis com EMF são muito propensas à corrosão por pites em ambientes com cloretos. As ligas inoxidáveis com EMF exibem melhor resistência à corrosão do que o aço inoxidável AISI 304 em ambientes fortemente oxidantes.

Dominick Argento's Miss Havisham's Wedding Night is the least explored of his artistic output. A monodrama in one act for soprano, Miss Havisham's Wedding Night contains some of Argento's most beautiful and challenging music of his compositional output. The purpose of a detailed analysis of the structure and content of Argento's Miss Havisham's Wedding Night is to facilitate the solo vocal performer's interpretation. Argento's setting of Miss Havisham's Wedding Night is unique in that he musically translates the manic psychological state of the literary character. Argento structured the one act opera in such a manner that the music would illuminate the text and the audience might connect with the unstable psychological episodes and outbursts demonstrated by Miss Havisham. To that end, each section and phrase has its own psychological motivation, which in turn demands a varied musical and dramatic interpretation. Utilizing selected scenes from Miss Havisham's Wedding Night, the researcher will analyze Argento's musical manifestation of Dickens's literary work. This research will include an investigation into the manner in which Argento uses the shape of melody and the musical phrase along with the harmonic materials to enhance the text and dramatic content. The author will explore the musical nuances Argento incorporates in an effort to develop and portray Miss Havisham's psychological state. Through an analysis of the orchestral writing the author will show how Argento's aesthetic balance between the music and text represents the emotional and psychological implications of the monodrama.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20161号 / 理博第4246号 / 新制||理||1611(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 高橋 義朗, 教授 田中 耕一郎, 教授 川上 則雄 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM