<div>We propose an order parameter theory of the quantum Hall nematic in high fractional Landau levels in terms of an Ising description. This new model solves a couple of extant problems in the literature: (1) The low-temperature behavior of the measured resistivity anisotropy is captured better by our model than previous theoretical treatments based on the electron nematic having XY symmetry. (2) Our model allows for the development of true long-range order at low temperature, consistent with the observation of anisotropic low-temperature transport.<br></div><div><div> We furthermore propose new experimental tests based on hysteresis that can distinguish whether any two-dimensional electron nematic is in the XY universality class (as previously proposed in high fractional Landau levels), or in the Ising universality class (as we propose). Given the growing interest in electron nematics in many materials, we expect our proposed test of universality class to be of broad interest.</div><div> </div><div> Whereas the XY model in two dimensions does not have a long-range ordered phase, the addition of uniaxial random field disorder induces a long-range ordered phase in which the spontaneous magnetization points perpendicular to the random field direction, via an order-by-disorder transition. We have shown that this spontaneous magnetization is robust against a rotating driving field, up to a critical driving field amplitude. Thus we have found evidence for a new non-equilibrium phase transition that was unknown before in this model. Moreover, we have discovered an incredible anomaly at this nonequilibrium phase transition: the critical region is accompanied by a cascade of period multiplication events. This physics is reminiscent of the period bifurcation cascade signaling the transition to chaos in nonlinear systems, and of the approach to the irreversibility transition in models of yield in amorphous solids~\cite{reichhardt-dahmen,leishangthem_yielding_2017}. This period multiplication cascade is surprising to be present in a statistical mechanics model, and suggests that the non-equilibrium transition as a function of driving field amplitude is part of a larger class of transitions in dynamical systems.</div><div> Moreover, we show that this multi-period behavior represents a new emergent classical discrete time-crystal, since the new period is robust against changes to initial conditions and low-temperature fluctuations over hundreds of driving period cycles.</div><div><br></div><div> We expect this work to be of broad interest, further encouraging cross-fertilization between the rapidly growing field of time-crystals with the well-established fields of nonequilibrium phase transitions and dynamical systems.</div><div> </div><div> Geometrical configurations gave us a better understanding of the multi-period behavior of the limit-cycles.</div><div> Moreover, surface probes are continually evolving and generating vast amounts of spatially resolved data of quantum materials, which reveal a lot of detail about the microscopic and macroscopic properties of the system. <br></div><div> Materials undergoing a transition between two distinct states, phase separate.</div><div> These phase-separated regions form intricate patterns on the observable surface, which can encode model-specific information, including interaction, dimensionality, and disorder. </div><div> While there are rigorous methods for understanding these patterns, they turn out to be time-consuming as well as requiring expertise. </div><div> We show that a well-tuned machine learning framework can decipher this information with minimal effort from the user.</div><div> We expect this to be widely used by the scientific community to fast-track comprehension of the underlying physics in these materials.</div><div><br></div></div>

Ce travail concerne l'étude du polymorphisme, de la dynamique et des transitions de phases de cinq dérivés de l' adamantane : 1-fluoroadamantane, 1-adamantaneméthanol, 1,3-diméthyladamantane, 1,3-dibromoadamantane et 1,3-adamantanediol.Les diagrammes pression -température ont été établis pour la majorité de ces dérivés. Ces matériaux peuvent présenter une, voire plusieurs, transitions de phases. Le 1-fluoroadamantane, le 1,3-diméthyladamantane et le 1,3-adamantanediol possèdent une phase plastique avant fusion.Les structures de toutes les phases non plastiques ont été résolues principalement à partir de diagrammes de diffraction des rayons X sur poudre. Celles du 1,3-dibromoadamantane, et du 1,3-diméthyladamantane sont ordonnées. L'existence d'un désordre statistique concernant l'occupation du site d'un atome a été montrée pour les autres phases. L'atome de fluor du 1-fluoroadamantane peut occuper 4 (phases III et II) ou 8 sites (phase I). Dans le cas de la phase I du 1-adamantaneméthanol et de la phase II du 1,3-adamantanediol, la symétrie du réseau implique que l'atome d'hydrogène lié à l'oxygène se partage sur deux sites.Deux mécanismes de transition ordre-désordre par une relation de groupe à sous-groupe ont été montrés pour le cas du 1-fluoroadamantane et du 1-adamantaneméthanol en utilisant des techniques expérimentales complémentaires (DSC, DRX, RAMAN, GSH...). Le paramètre d'ordre de la transition résulte de la variation continue en fonction de la température de l'inclinaison du dipôle C-F pour le premier et, de la diminution de l'angle beta de la phase monoclinique jusqu'à 90°, pour le second.La dynamique moléculaire dans le cas du 1-fluoroadamantane a été étudiée par spectroscopie diélectrique. L'existence d'une double relaxation associée à deux mouvements de réorientations compatibles avec le réseau et la symétrie a été révélée. / This work deals with the study of the polymorphism, dynamics and phases transitions of five adamantane derivatives : 1-fluoroadamantane, 1-adamantanemethanol, 1,3-dimethyladamantane, 1,3-dibromoadamantane and 1,3-adamantanediol.Pressure-Temperature phase diagrams have been established for the majority of these derivatives. These materials may have one or more phase transitions. Plastic phases are observed before melting for 1-fluoroadamantane, 1,3-dimethyladamantane and 1,3-adamantanediol.The structures of all the non plastic phases have been solved, mainly from powder X-ray diffraction patterns. It is shown that 1,3-dibromoadamantane and 1,3-dimethyladamantane structures are ordered. Statistical disorder concerning the occupation of the site of one atom has been revealed in the other structures. The fluorine atom in 1-fluoroadamantane has four (phase III and II) or eight (phase I) possible equivalent sites. Due to the crystal symmetry of 1-adamantanemethanol (phase I ) and 1,3-adamantanediol (phase II), the hydrogen atom related to the oxygen atom is spitted on two sites.Two mechanisms of continuous order-disorder transitions through a group-subgroup relationship have been shown for the case of 1-fluoroadamantane and 1-adamantanemethanol using complementary experimental techniques (DSC, XRD, RAMAN, SHG ...). The order parameter of the transition results, by a continuous variation of the orientation of the C-F dipole for the first and, for the second, the continuous variation of the beta monoclinic angle down to 90°.Molecular dynamics in the case of 1-fluoroadamantane has been studied using dielectric spectroscopy. We have highlighted the existence of a double relaxation associated with two movements of reorientations compatible with the network and the symmetry.

A fosfatase Cdc25B atua na progressão do ciclo celular através da ativação de complexos Cdk/Ciclina. Atualmente, nos modelos estruturais propostos do domínio catalítico da Cdc25B não estão incluídos os últimos 16 resíduos da região C-terminal. Este segmento tem importante papel no reconhecimento do substrato proteico e pode estar envolvido na complexação de pequenas moléculas com a Cdc25B. Assim, o principal objetivo desta tese foi avaliar a flexibilidade conformacional do domínio catalítico completo da Cdc25B em solução através de simulações computacionais e por medidas experimentais de ressonância magnética nuclear (RMN). A similaridade entre as estruturas cristalográficas e em solução foi confirmada pela previsão de ângulos diedrais &#966;/&#968; da cadeia principal a partir dos deslocamentos químicos (CS) e pela concordância entre os acoplamentos dipolares residuais (RDC) medidos e calculados a partir da geometria cristalina. Medidas de parâmetros de relaxação de 15N e RDC evidenciaram a presença de desordem conformacional na região C-terminal, em acordo com a ausência de densidade eletrônica desse segmento no experimento de difração de raios-X. Através da comparação entre CS experimentais e previstos de simulações de dinâmica molecular (DM) longas (total de 6&#181;s de duração) foram apontados artefatos de cristalização, possíveis erros nos campos de força usados nas simulações, falhas na composição do sistema simulado e estados conformacionais populados pela Cdc25B em solução distintos da geometria cristalográfica. De maneira geral, os CS previstos a partir das simulações para a flutuação estrutural dos resíduos da região C-terminal desordenada estão em acordo com os valores experimentais, sugerindo que os estados conformacionais deste segmento foram razoavelmente bem amostrados nas simulações. Em particular, verificou-se que o contato tipo cátion-&#960; entre as cadeias laterais dos resíduos 550W do C-terminal desordenado e 482R do núcleo proteico, ausente na estrutura cristalográfica, pode ser importante em solução. A formação desse contato na simulação de DM também está de acordo com medidas experimentais de perturbação de deslocamentos químicos (CSP) entre construções completa e truncada do domínio catalítico da Cdc25B. Assim, através do uso conjunto de simulações computacionais e medidas experimentais foi possível obter uma representação mais completa e realista da flexibilidade conformacional do domínio catalítico da Cdc25B em solução, incluindo a determinação de possíveis contatos intramoleculares entre a região C-terminal desordenada e o núcleo proteico. Essas informações poderão ser usadas na construção de um ensemble conformacional da Cdc25B. / Cdc25B phosphatase acts on the progression of cell cycle through the activation of Cdk/Cyclin complexes. Currently, the proposed structural models of Cdc25B catalytic domain lack the last 16 residues from the C-terminal region. This segment is important for protein substrate recognition and might be involved in small molecule binding to Cdc25B. Thus, the main goal of this thesis was to evaluate the conformational flexibility of the complete catalytic domain from Cdc25B through computer simulations and experimental nuclear magnetic resonance (NMR) measurements. Similarity between crystal and in solution structures was confirmed by the prediction of backbone &#966;/&#968; dihedral angles from chemical shifts (CS) and by the agreement between observed and back-calculated residual dipolar couplings (RDC). 15N relaxation and RDC measurements pointed to the conformational disorder of the C-terminal region, in agreement with the X-ray diffraction experiment where this segment showed no electronic density. Comparison between experimental and predicted CS from long molecular dynamics (MD) simulations (6&#181;s total running time) pointed to the presence of crystallographic artifacts, possible deficiencies in simulation force fields, inaccurate composition of the simulated system and conformational states visited by Cdc25B in solution that were not observed in the crystallographic geometry. Generally, CS predicted from simulations for the structural fluctuation of the disordered C-terminal region were in agreement with experimental values, suggesting that the simulations sampled the conformational states populated by this segment reasonably well. In particular, a cation-&#960; contact not observed in the crystal structure between side chains of residue 550W from the disordered C-terminal tail and residue 482R from the protein core might be important in solution. This contact is also in agreement with experimental chemical shift perturbations (CSP) measured between complete and truncated constructs of Cdc25B catalytic domain. Therefore, the joint use of computer simulations and experimental measurements allowed the achievement of a more complete and realistic representation of the conformational flexibility of the Cdc25B catalytic domain in solution, including intramolecular contacts between the disordered C-terminal region and the protein core. This information might be used to obtain a conformational ensemble of Cdc25B.

Ternary lipid mixtures composed of cholesterol, saturated (frequently with sphingosine backbone), and unsaturated phospholipids show stable phase separation and are often used as model systems of lipid rafts. Yet, their ability to reproduce raft properties and function is still debated. We investigated the properties and functional aspects of three lipid raft model systems of varying degrees of biological relevance – PSM/POPC/Chol, DPPC/POPC/Chol, and DPPC/DOPC/Chol – using 2H solidstate nuclear magnetic resonance (NMR) spectroscopy, fluorescence microscopy, and atomic force microscopy. While some minor differences were observed, the general behavior and properties of all three model mixtures were similar to previously investigated influenza envelope lipid membranes, which closely mimic the lipid composition of biological membranes. For the investigation of the functional aspects, we employed the human N-Ras protein, which is posttranslationally modified by two lipid modifications that anchor the protein to the membrane. It was previously shown that N-Ras preferentially resides in liquid-disordered domains and exhibits a time-dependent accumulation in the domain boundaries of influenza envelope lipid membranes. For all three model mixtures, we observed the same membrane partitioning behavior for N-Ras. Therefore, we conclude that even relatively simple models of raft membranes are able to reproduce many of their specific properties and functions.

Made available in DSpace on 2015-05-14T12:14:00Z (GMT). No. of bitstreams: 1 parte1.pdf: 2310445 bytes, checksum: 3cfca25ce861a7301fea8d5aa8526310 (MD5) Previous issue date: 2011-02-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this work, we study the collective behaviour of living systems whose aggregates form organized groups such as flocks of birds, herds of mamals and schools of fishes. Through numerical simulations, we model the collective movement of a school of fishes using behavioural rules similar to the ones proposed by Couzin et al. [23], that investigates the spatial dynamics of animals groups. The model presents three interaction zones: repulsion, orientation and attraction. Our results for the distributions of nearest neighbour distance, the diference of orientation between the velocities of neighbour fishes and the cooperativeness of the school are in good agreement with experimental measurements. A simpler way to describe the collective motion of several groups of organisms was introduced by Vicsek et al. [10]. This model presents only one interaction region, called orientation zone and considers point particles moving off lattice at constant speed adjusting their direction of motion to that of the average velocity of their neighbors, being subject to some noisy term. A second-order transition between an ordered state and a disordered regime was found. However, Gregoire and Chate [12] contest the nature of such phase transition as being of first order. Indeed, this transition is related to the way of introducing the noise into the system. In this sense, we present a comparative study on noise in two system of self-propelled particle (Vicsek model and Gregoire model) with the aim of understanding the role of the noise on some observables such as polarization, distributions of the nearest neighbour distances, difference of orientations between neighbour particles, the order parameter and the Binder cumulant. / Neste trabalho, estudamos o comportamento coletivo de sistemas vivos cujos agregados formam grupos organizados tais como bandos de pássaros, rebanhos de mamíferos e cardumes de peixes. Através de simulações numéricas, modelamos o movimento coletivo de cardumes de peixes usando regras comportamentais similares áquelas propostas por Cousin et al.[23], que investigam a dinâmica espacial de grupos de animais. O modelo apresenta três zonas de interação: repulsão, orientação e atração. Nossos resultados para as distribuições das distâncias entre vizinhos mais próximos, a diferença de orientação entre as velocidades de peixes vizinhos e a cooperatividade do cardume estão de bom acordo com medidas experimentais. Uma maneira mais simples para descrever o movimento coletivo de vários grupos de organismos foi introduzido por Vicsek et al. [10]. Este modelo apresenta somente uma região de interação, chamada zona de orientação e considera partículas pontuais movendo na rede com uma velocidade constante ajustando sua direção de movimento à velocidade média de seus vizinhos, estando sujeita a algum termo ruidoso. Uma transição de segunda ordem entre um estado ordenado e um regime desordenado foi encontrado. Porém, Gregoire e Chaté [12] contestam a natureza da transição de fase como sendo de primeira ordem. Na verdade, está transição está relacionada à forma de introduzir o ruído no sistema. Neste sentido, apresentamos um estudo comparativo sobre o ruído em dois sistemas de partículas auto-propelidas (modelo de Vicsek e modelo de Gregoire) com o objetivo de compreender o papel do ruído em alguns observáveis tais como a polarização, distribuições das distâncias entre vizinhos mais próximos, diferença de orientação entre partículas vizinhas, o parâmetro de ordem e o cumulante de Binder.

A fosfatase Cdc25B atua na progressão do ciclo celular através da ativação de complexos Cdk/Ciclina. Atualmente, nos modelos estruturais propostos do domínio catalítico da Cdc25B não estão incluídos os últimos 16 resíduos da região C-terminal. Este segmento tem importante papel no reconhecimento do substrato proteico e pode estar envolvido na complexação de pequenas moléculas com a Cdc25B. Assim, o principal objetivo desta tese foi avaliar a flexibilidade conformacional do domínio catalítico completo da Cdc25B em solução através de simulações computacionais e por medidas experimentais de ressonância magnética nuclear (RMN). A similaridade entre as estruturas cristalográficas e em solução foi confirmada pela previsão de ângulos diedrais &#966;/&#968; da cadeia principal a partir dos deslocamentos químicos (CS) e pela concordância entre os acoplamentos dipolares residuais (RDC) medidos e calculados a partir da geometria cristalina. Medidas de parâmetros de relaxação de 15N e RDC evidenciaram a presença de desordem conformacional na região C-terminal, em acordo com a ausência de densidade eletrônica desse segmento no experimento de difração de raios-X. Através da comparação entre CS experimentais e previstos de simulações de dinâmica molecular (DM) longas (total de 6&#181;s de duração) foram apontados artefatos de cristalização, possíveis erros nos campos de força usados nas simulações, falhas na composição do sistema simulado e estados conformacionais populados pela Cdc25B em solução distintos da geometria cristalográfica. De maneira geral, os CS previstos a partir das simulações para a flutuação estrutural dos resíduos da região C-terminal desordenada estão em acordo com os valores experimentais, sugerindo que os estados conformacionais deste segmento foram razoavelmente bem amostrados nas simulações. Em particular, verificou-se que o contato tipo cátion-&#960; entre as cadeias laterais dos resíduos 550W do C-terminal desordenado e 482R do núcleo proteico, ausente na estrutura cristalográfica, pode ser importante em solução. A formação desse contato na simulação de DM também está de acordo com medidas experimentais de perturbação de deslocamentos químicos (CSP) entre construções completa e truncada do domínio catalítico da Cdc25B. Assim, através do uso conjunto de simulações computacionais e medidas experimentais foi possível obter uma representação mais completa e realista da flexibilidade conformacional do domínio catalítico da Cdc25B em solução, incluindo a determinação de possíveis contatos intramoleculares entre a região C-terminal desordenada e o núcleo proteico. Essas informações poderão ser usadas na construção de um ensemble conformacional da Cdc25B. / Cdc25B phosphatase acts on the progression of cell cycle through the activation of Cdk/Cyclin complexes. Currently, the proposed structural models of Cdc25B catalytic domain lack the last 16 residues from the C-terminal region. This segment is important for protein substrate recognition and might be involved in small molecule binding to Cdc25B. Thus, the main goal of this thesis was to evaluate the conformational flexibility of the complete catalytic domain from Cdc25B through computer simulations and experimental nuclear magnetic resonance (NMR) measurements. Similarity between crystal and in solution structures was confirmed by the prediction of backbone &#966;/&#968; dihedral angles from chemical shifts (CS) and by the agreement between observed and back-calculated residual dipolar couplings (RDC). 15N relaxation and RDC measurements pointed to the conformational disorder of the C-terminal region, in agreement with the X-ray diffraction experiment where this segment showed no electronic density. Comparison between experimental and predicted CS from long molecular dynamics (MD) simulations (6&#181;s total running time) pointed to the presence of crystallographic artifacts, possible deficiencies in simulation force fields, inaccurate composition of the simulated system and conformational states visited by Cdc25B in solution that were not observed in the crystallographic geometry. Generally, CS predicted from simulations for the structural fluctuation of the disordered C-terminal region were in agreement with experimental values, suggesting that the simulations sampled the conformational states populated by this segment reasonably well. In particular, a cation-&#960; contact not observed in the crystal structure between side chains of residue 550W from the disordered C-terminal tail and residue 482R from the protein core might be important in solution. This contact is also in agreement with experimental chemical shift perturbations (CSP) measured between complete and truncated constructs of Cdc25B catalytic domain. Therefore, the joint use of computer simulations and experimental measurements allowed the achievement of a more complete and realistic representation of the conformational flexibility of the Cdc25B catalytic domain in solution, including intramolecular contacts between the disordered C-terminal region and the protein core. This information might be used to obtain a conformational ensemble of Cdc25B.

Cette thèse porte sur différents aspects géométriques et morphologiques concernant des problèmes de mouillage et d'empilement de sphères. Nous proposons tout d'abord une nouvelle méthode de simulation pour étudier le mouillage et le glissement d'un liquide sur une surface nanostructurée: un modèle de champ de phase en lien avec la théorie de la fonctionnelle de la densité dynamique. Nous étudions grâce à cette méthode la possibilité de transformer une surface quelconque en surface omniphobe (c'est à dire qui repousse tous les liquides). Nous montrons que contrairement à la théorie classique de Cassie-Baxter-Wenzel, il est possible d'inverser la mouillabilité d'une surface en la texturant, et nous montrons qu'une surface monovaluée, i.e. sans constrictions, peut produire un comportement omniphobe c'est à dire repousser tous les liquides grâce à un effet de pointe. La géométrie a également un effet considérable dans les milieux vitreux ou bloqués. Les empilements aléatoires de sphères conduisent par exemple à des état bloqués ("jamming") et nous montrons que la structure locale de ces systèmes est universelle, c'est à dire indépendante de la méthode de préparation. Pour cela, nous introduisons des paramètres d'ordre - les tenseurs de Minkowski - qui suppriment les problèmes de robustesse qu'ont les paramètres d'ordre utilisés classiquement. Ces nouveaux paramètres d'ordre conduisent à une vision unifiée, basée sur des principes géométriques. Enfin, nous montrons grâce aux tenseurs de Minkowski que les empilements de sphères se mettent à cristalliser au delà du point d'empilement aléatoire le plus dense ("random close packing") / This thesis is devoted to several aspects of geometry and morphology in wetting problems and hard sphere packings. First, we propose a new method to simulate wetting and slip on nanostructured substrates: a phase field model associated with a dynamical density theory approach. We showed omniphobicity, meaning repellency, no matter the chemical properties of the liquid on monovalued surfaces, i.e. surfaces without overhangs, which is in contradiction with the macroscopic Cassie-Baxter-Wenzel theory, can produce so-called We checked systematically the impact of the surface parameters on omniphobic repellency, and we show that the key ingredient are line tensions, which emerge from needle shaped surface structures. Geometrical effects have also an important influence on glassy or jammed systems, for example amorphous hard sphere systems in infinite pressure limit. Such hard sphere packings got stuck in a so-called jammed phase, and we shall demonstrate that the local structure in such systems is universal, i.e. independent of the protocol of the generation. For this, robust order parameters - so-called Minkowski tensors - are developed, which overcome robustness deficiencies of widely used order parameters. This leads to a unifying picture of local order parameters, based on geometrical principles. Furthermore, we find with the Minkowski tensor analysis crystallization in jammed sphere packs at the random closed packing point

Ternary lipid mixtures composed of cholesterol, saturated (frequently with sphingosine backbone), and unsaturated phospholipids show stable phase separation and are often used as model systems of lipid rafts. Yet, their ability to reproduce raft properties and function is still debated. We investigated the properties and functional aspects of three lipid raft model systems of varying degrees of biological relevance – PSM/POPC/Chol, DPPC/POPC/Chol, and DPPC/DOPC/Chol – using 2H solidstate nuclear magnetic resonance (NMR) spectroscopy, fluorescence microscopy, and atomic force microscopy. While some minor differences were observed, the general behavior and properties of all three model mixtures were similar to previously investigated influenza envelope lipid membranes, which closely mimic the lipid composition of biological membranes. For the investigation of the functional aspects, we employed the human N-Ras protein, which is posttranslationally modified by two lipid modifications that anchor the protein to the membrane. It was previously shown that N-Ras preferentially resides in liquid-disordered domains and exhibits a time-dependent accumulation in the domain boundaries of influenza envelope lipid membranes. For all three model mixtures, we observed the same membrane partitioning behavior for N-Ras. Therefore, we conclude that even relatively simple models of raft membranes are able to reproduce many of their specific properties and functions.

[pt] Esse trabalho apresenta uma abordagem baseada em programação matemática para a solução de problemas de valor inicial de contorno constitutivo elastoplástico. Considerando a plasticidade associativa, as equações constitutivas locais, em sua forma discreta, são formuladas como problemas de otimização cônica. Especificamente, é demonstrado que métodos implícitos de retorno a superfície para os critérios mais conhecidos da literatura, como o de Rankine, von Mises, Tresca, Drucker-Prager e Mohr Coulomb, podem ser expressos como problemas de otimização cônica de segunda ordem e semidefinida. Além disso, um novo método numérico para a determinação do operador elastoplástico consistente, baseado na derivada paramétrica de primeira ordem das soluções ótimas, é proposto. / [en] This work presents a mathematical programming approach for elastoplastic constitutive initial boundary value problems. Considering associative plasticity, the local discrete constitutive equations are formulated as conic programs. Specifically, it is demonstrated that implicit return-mapping schemes for well-known yield criteria, such as the Rankine, von Mises, Tresca, Drucker-Prager, and Mohr-Coulomb criteria, can be expressed as secondorder and semidefinite conic programs. Additionally, a novel scheme for the numerical evaluation of the consistent elastoplastic tangent operator, based on a first-order parameter derivative of the optimal solutions, is proposed.

No description available.