Nowadays liquid crystals have widely used for optical devices, even are attractive in display. But a major problem for nematic phase is its long response time, which hinders the phase to be used in high quality displays. Surface Stabilized Ferroelectric Liquid Crystal¡]SSFLC¡^is a thin device which has fast response time and exhibits excellent bistability. It can be applied in display. But it is difficult for SSFLC to achieve alignment without zigzag defects. This defect will reduce contrast ratio of display and cause image irregularities and flickering. This article discusses zigzag defects in SSFLC device. In experiment, we use convenient rubbing method to alignment FLC with high pre-tilt PI film. And we investigate the surface properties of polyimide (PI) films rubbed with different rubbing strength. We fabricate the SSFLCs without zigzag defects, and confirm that the great rubbing strength produce more zigzag defects for FLC alignment. In addition, we discuss the topography of smooth surface results in fewer defects. Finally, with the relationship between surface energy and different rubbing strength in PI film, we show the polarity of surface energy is a important role for FLC alignment.

No description available.

ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California / In this paper, a novel zigzag scanning concept of quantized coefficients for H.264/AVC is introduced. In order to scan the quantized coefficients efficiently, the statistical occurrence values of the quantized coefficients after the final mode decision are utilized. We develop a zigzag scanning pattern by reordering the statistical occurrence values in descending order. In addition, we consider the temporal and spatial correlation among the frames to classify the zigzag scanning pattern. In particular, we focus on the macroblock level zigzag scanning so that the proposed method will have the different zigzag scanning pattern based on the macroblock. Experimental results show that the proposed scheme reduces the total bits up to 4.05% and 3.67% while introducing either negligible loss of video quality for intra- and inter mode, respectively.

No description available.

La présente thèse doctorale traite de la formulation et l'évaluation élément fini d'un model variationel de Mindlin discret et modifié pour l'analyse du comportement statique et dynamique, linéaire et non linéaire des plaques et coques composites. Incluant des termes additionnels de type zigzag, en vue d'améliorer la précision de contraintes, le modèle a été reformulé afin de prendre en considération la variation linéaire par couche du déplacement. En conséquence, deux éléments finis de plaques et coques à quatre nœuds, baptisés respectivement DMQP et DMQS (Discret Mindlin Quadrilateral Plates/ Shells), améliorés par un champ de rotations quadratique ont été développés et validés sur les codes de calcul REFLEX et ABAQUS. Dans une seconde version, les deux éléments avec un effet de zigzag ont été développés et validés à travers quelques tests statiques et dynamiques connus de la littérature. Les résultats montrent une indépendance vis-à-vis de la correction du cisaillement transverse et une précision des contraintes meilleure à celle obtenue par rapport le modèle initial (sans l'effet de zigzag).Les résultats satisfaisants de ce modèle constatés à travers les cas-tests linéaires de coque isotropes, nous ont motivés à étendre la présente approche aux applications non-linéaires géométriques. Un élément isoparamétrique courbe de coque a été développé à cet effet, avec l'hypothèse des petites déformations élastiques et grands déplacements et rotations modérées. Il est géométriquement simple et ne possède que quatre nœuds aux sommets et 6 ddl/nœud. Le calcul élémentaire de la matrice de rigidité tangente consiste à associer la partie linéaire du modèle de coque courbe (DMQS) avec celle non linéaire de l'élément standard Q4 de membrane. Une formulation lagrangienne actualisée à chaque itération (FLAI) a été utilisée avec la méthode de résolution de Newton-Raphson. Quelques tests standards non-linéaires des structures coques sont présentés, ils montrent un très bon comportement global et une convergence meilleure que celle d'éléments pareils. / This doctoral thesis deals with the finite element formulation and evaluation of a modified Mindlin's discrete variational model for static, dynamic, linear and non-linear composite plates and shells analysis. Including additional terms of zigzag type, in order to improve the accuracy of stress, the model has been reformulated to take into account the linear picewise of displacement variation. Consequently, two finite plate and shell elements with four nodes, called DMQP and DMQS (Discrete Quadrilateral Mindlin Plates and Shells respectively), enhanced by quadratic field rotations, have been developed and validated under REFLEX and ABAQUS codes.Both elements including the zigzag effect have been also developed in a second version, and validated through several static and dynamic test problems known from the literature, highlighting the independence towards the transverse shear correction and in particular the stress accuracy with respect to the initial model without the zigzag effect.The satisfactory results of this model found through cases of linear isotropic shell tests, motivated us to extend this approach to the non-linear geometric applications. An isoparametric curve element of shell has been developed for this purpose, where small elastic deformation assumptions of and large displacements and moderate rotations are adopted. It is geometrically simple and has only four nodes at corners and 6 DOF/node. The elementary calculation of the tangent stiffness matrix consists in combining the linear part of the curved shell element (DMQS) with that of the membrane Q4 non-linear part. An Updated Lagrangian Formulation at each Iteration (ULFI) is used with Newton-Raphson resolution Method. Some standard tests of nonlinear geometrical shell structures are presented; they show a very good convergence and global behavior better than such elements.

La croissance de l’Internet en tant que plateforme d’approvisionnement à grande échelled’approvisionnement de contenus multimédia a été une grande success story du 21e siécle.Toutefois, les applications multimédia, avec les charactéristiques spécifiques de leur trafic ainsique les les exigences des nouveaux services, posent un défi intéressant en termes de découverte,de mobilité et de gestion. En outre, le récent élan de l’Internet des objets a rendu très nécessairela revitalisation de la recherche pour intégrer des sources hétérogènes d’information à travers desréseaux divers. Dans cet objectif, les contributions de cette thèse essayent de trouver un équilibreentre l’hétérogénéité et l’interopérabilité, pour découvrir et intégrer les sources hétérogènesd’information dans le contexte de l’Internet du Futur.La découverte de sources d’information sur différents réseaux requiert une compréhensionapprofondie de la façon dont l’information est structurée et quelles méthodes spécifiques sontutilisés pour communiquer. Ce processus a été régulé à l’aide de protocoles de découverte.Cependant, les protocoles s’appuient sur différentes techniques et sont conçues en prenant encompte l’infrastructure réseau sous-jacente, limitant ainsi leur capacité à franchir la limite d’unréseau donné. Pour résoudre ce problème, le première contribution dans cette thèse tente detrouver une solution équilibrée permettant aux protocoles de découverte d’interagir les uns avecles autres, tout en fournissant les moyens nécessaires pour franchir les frontières entre réseaux.Dans cet objectif, nous proposons ZigZag, un middleware pour réutiliser et étendre les protocolesde découverte courants, conçus pour des réseaux locaux, afin de découvrir des servicesdisponibles dans le large. Notre approche est basée sur la conversion de protocole permettant ladécouverte de service indépendamment de leur protocole de découverte sous-jacent. Toutefois,dans les réaux de grande échelle orientée consommateur, la quantité des messages de découvertepourrait rendre le réseau inutilisable. Pour parer à cette éventualité, ZigZag utilise le conceptd’agrégation au cours du processus de découverte. Grâce à l’agrégation, ZigZag est capabled’intégrer plusieurs réponses de différentes sources supportant différents protocoles de découverte.En outre, la personnalisation du processus d’agrégation afin de s’aligner sur ses besoins,requiert une compréhension approfondie des fondamentaux de ZigZag. À cette fin, nous proposonsune seconde contribution: un langage flexible pour aider à définir les politiques d’unemanière propre et efficace. / The growth of the Internet as a large scale media provisioning platform has been a great successstory of the 21st century. However, multimedia applications, with their specific traffic characteristicsand novel service requirements, pose an interesting challenge in terms of discovery,mobility and management. Furthermore, the recent impetus to Internet of things has made it verynecessary, to revitalize research in order to integrate heterogeneous information sources acrossnetworks. Towards this objective, the contributions in this thesis, try to find a balance betweenheterogeneity and interoperability, to discovery and integrate heterogeneous information sourcesin the context of Future Internet.Discovering information sources across networks need a through understanding of how theinformation is structured and what specific methods they follow to communicate. This processhas been regulated with the help of discovery protocols. However, protocols rely on differenttechniques and are designed taking the underlying network infrastructure into account. Thus,limiting the capability of some protocols to cross network boundary. To address this issue, thefirst contribution in this thesis tries to find a balanced solution to enable discovery protocols tointeroperate with each other as well as provide the necessary means to cross network boundaries.Towards this objective, we propose ZigZag, a middleware to reuse and extend current discoveryprotocols, designed for local networks, to discover available services in the large. Our approachis based on protocol translation to enable service discovery irrespectively of their underlyingdiscovery protocol. Although, our approach provides a step forward towards interoperability inthe large. We needed to make sure that discovery messages do not create a bottleneck for thenetwork.In large scale consumer oriented network, service discovery messages could render the networkunusable. To counter this, ZigZag uses the concept of aggregation during the discoveryprocess. Using aggregation ZigZag is able to integrate several replies from different servicesources supporting different discovery protocols. However, to customize the aggregation processto suit once needs, requires a through understanding of ZigZag fundamentals. To this end, wepropose our second contribution, a flexible policy language that can help define policies in aclean and effective way. In addition, the policy language has some added advantages in terms ofdynamic management. It provides features like delegation, runtime time policy management andlogging. We tested our approach with the help of simulations, the results showed that ZigZag canboth reduce the number of messages that flow through the network, and provide value sensitiveinformation to the requesting entity.Although, ZigZag is designed to discover media services in the large. It can very well be usedin other domains like home automation and smart spaces. While, the flexible pluggable modulardesign of the policy language enables it to be used in other applications like for instance, e-mail.

L’état local de la chromatine joue un rôle crucial dans tous les processus génétiques comme le contrôle de la transcription, de la réplication et de la réparation de l’ADN, de la signalisation, etc... La structure précise de l’organisation 3D du deuxième ordre de compaction de la chromatine, aussi appelé fibre de 30 nm, a été le sujet d’intenses débats durant les 40 dernières années. En se basant sur les données in vitro, deux modèles concurrents se distinguent: le solénoïde et le zigzag. Dans le modèle solénoïde, des nucléosomes consécutifs interagissent pour former une trajectoire hélicoïdale avec courbure de l’ADN de liaison. Dans le modèle zigzag, deux hélices d’empilement de nucléosomes se forment, reliées par l’ADN de liaison qui peut être droit ou tordu. Durant ma thèse, j’ai développé une nouvelle approche expérimentale biochimique, appelée ICNN (Identification of the Closest Neighbor Nucleosome), permettant de déchiffrer les interactions entre nucléosomes voisins au sein de la fibre et ainsi de définir sous quelle forme la chromatine se compacte. Nous avons démontré que dans une fibre compactée H1-dépendante, les nucléosomes N+2 sont les plus proches voisins d’un nucléosome N arbitrairement choisit. Ces résultats montrent, sans ambiguïté, l’organisation zigzag de la fibre de 30 nm. De plus, cette organisation reste indépendante de la longueur de l’ADN de liaison, démontrant ainsi que la longueur des nucléosomes (177-227 bp) n’affecte pas la structure de la chromatine et ne peut donc pas être responsable de l’hétérogénéité structurale décrite dans la littérature. La dynamique et la structure de la chromatine peuvent être affectées par l’incorporation de variants d’histones. Nos expériences utilisant des assemblages H2A.Z ne montrent aucune différence de repliement entre les fibres contenant H2A.Z et H2A. Ces données suggèrent que le mécanisme de régulation de la transcription spécifique de H2A.Z est indépendant du repliement de la chromatine. CENP-A est un élément de la chromatine centromérique indispensable à la division cellulaire. Les images cristallographiques montrent que les nucléosomes contenant CENP-A sont plus ouverts que le nucléosomes conventionnels à cause d’une hélice α-NCENP-A plus courte. Parallèlement, des résultats récents de notre laboratoire ont montré que H1 ne se lie pas d’une façon stable aux nucléosomes contenant CENP-A, ne conduisant à aucune organisation de l’ADN de liaison (données non publiées). Notre étude au niveau de la chromatine a confirmé l'absence de repliement de la fibre contenant CENP-A en présence de H1. De manière intéressante, le remplacement de CENP-A par un mutant α-NH3-CENP-A restaure la bonne liaison de H1 et le repliement de la fibre avec une conformation habituelle en zigzag comme dans une fibre contenant H3. / The local chromatin state plays a crucial role in all fundamental DNA-templated processes, such as transcription control, DNA replication or repair, signaling, etc. The precise 3D organization of the second level folding, the so-called 30 nm fiber, has been a matter of intense speculations and debates over the past 40 years. Two competing models have been proposed on the basis of in vitro data, the solenoid and zigzag arrangements. In the solenoid model, consecutive nucleosomes interact with each other and follow a helical trajectory with bent DNA linker. In the zigzag model, alternate nucleosomes interact with each other with straight, twisted or coiled linker DNA. During my thesis, I developed a new biochemical approach, called ICNN (Identification of the Closest Neighbor Nucleosomes), allowing a direct “visualization” of the neighboring nucleosomes within H1-dependent compacted chromatin. We showed that within H1-compacted regular nucleosomal array, N±2 nucleosomes are the nearest neighboring interaction partners of any arbitrary nucleosome N. This finding provides an unambiguous evidence for the zigzag two-start helix conformation of the 30 nm fiber. Furthermore, this organization remains independent on the DNA linker length, demonstrating that the nucleosome repeat length (177-227 bp) does not affect the chromatin structure and therefore cannot be a reason for chromatin structural heterogeneity as suggested in the literature. Chromatin structure and dynamics might be affected by the incorporation of histone variants. Our ICNN experiments with H2A.Z arrays showed no difference of folding between H2A.Z- and H2A-containing fibers. This finding suggests that the H2A.Z-specific transcriptional regulation involves mechanisms other than chromatin folding. CENP-A is a hallmark for centromeric chromatin that is indispensable for cell division. X-ray scattering in crystals showed that CENP-A-containing nucleosomes are more “open” than conventional ones due to the shorter α-NCENP-A helix. Besides, recent results in our lab showed that H1 does not stably bind to the CENP-A nucleosomes and that no stem organization of the linker is formed (not published). Our ICNN study at the chromatin level confirmed the absence of H1-induced folding of a regular CENP-A array. Interestingly, replacement of CENP-A with the α-NH3-CENP-A mutant restored proper H1 binding and folding of the fiber into the usual zigzag conformation, as does the conventional H3-containing fiber.

Graphene is a single layer of carbon atoms arranged in honeycomb lattice. Over a long period of time it was treated as a hypothetical material to understand the properties of other allotropes of carbon, such as graphite, carbon nanotube etc. Half decade back, a single layer of graphene was finally isolated and since then the field has observed a flurry of activities. Low energy excitations in graphene are massless Dirac Fermions and quantum electrodynamic effects can be observed at room temperature in graphene, which makes it very popular among the condensed matter community. In addition graphene also shows many interesting mesoscopic effects, which is the focus of the present work. We study the electronic, magnetic and structural properties of the graphene nanostructures. The entire thesis based on the results and findings obtained from the present investigation is organized as follows. Chapter 1: provides a general introduction to the properties of graphene and graphene based nanostructures. Chapter2:describes the theoretical tools used in this thesis to investigate the properties of graphene nanoribbons. The first two chapters are meant to give the reader an overview about the field of graphene and a few of the computational techniques commonly used to investigate the properties of graphene. The following chapters are the new findings reported in this thesis. Chapter3:shows how zigzag graphene nanoribbons respond in a non-linear fashion when edges are subjected to some external potential such as magnetic field. Such response originates from the edge states present in zigzag ribbons and thus not observed in armchair nanoribbons. In the limit of ribbon width W→∞, an edge magnetic field produces a moment of ~ 1/3 per edge atom even for an infinitesimally small field, which is clearly a signature of non-linear response. Response of a finite width nanoribbon is size dependent and also depends on ln(V), the applied field. This is akin to Weber-Fechner law of audio visual perceptions. It is interesting to note that nature does provide a “quantum realization” of this in the form of biological sensing organs like the ear and eye. The magnetic response is found to scale inversely with the ribbon width. Chapter4:deals with the magnetic properties of the zigzag graphene nanoribbon. This is also a special property of the geometry of the zigzag edges and not observed in armchair nanoribbons. Our investigation reveals that the electron-electron repulsion (Hubbard U) energy creates a delta function like edge magnetic field in zigzag graphene nanoribbons. Starting from this, magnetic properties of zigzag graphene nanoribbons can be qualitatively and quantitatively explained from the non-linear response of zigzag nanoribbons. Zigzag graphene nanoribbons can exist in two possible ‘magnetic states’: antiferro (AF) where the two opposite edges have antiparallel magnetic moment and ferro (FM) where moment is parallel in the two opposite edges. First we describe the properties of undoped zigzag nanoribbons. They have AF ground state. Continuum theory can explain the size dependent bandgap and magnetic moment of the ground state. We present the first explicit derivation of the gap. Then we show that hole doping can change the ground state to FM, which is metallic. Thus the system has the property of magnetoresistance, which can be exploited by doping zigzag graphene nanoribbons externally with some gate voltage or internally by some electron acceptor element, such as boron. The critical doping for transition depends inversely with the ribbon width. We have found that the ‘phase transition’ on hole doping is a common phenomena for zigzag terminated nanostructures, such as hexagonal nanodots. Chapter5:discusses the effects of random edge shapes and random potential (Anderson disorder) on the magnetic properties of zigzag graphene nanostructures. Defects and disorders in the form of edge shape randomness and random potentials arising from substrate are very common in graphene. Our study reveals that edge state magnetism is very robust to shape randomness of the terminating edges of nanostructures; as long as there are three to four repeat units of a zigzag edge, the edge state magnetism is preserved. We also discover some “high energy” edges (ones where the edge atoms have only one nearest neighbor) can have very large moments compared to even the zigzag edges. Edge magnetism is also found to be robust to relatively small Anderson disorders, because a slowly varying small potential does not scatter the edge states. Chapter6:reveals how edge functionalization by O atom and OHgroup changes the properties of the zigzag graphene nanoribbons. Functionalization by various different molecules is a very popular method of tuning the properties of graphene. We have shown that it is possible to tune the properties of zigzag graphene nanoribbons by edge functionalization. Further, we have found that structures with clustered functionalization leads to “spatially” varying electronic structure, which can lead to interesting possibilities for electronic devices. Chapter7:describes structural stability, electronic and magnetic properties of graphene nanoribbons in presence of topological defects such as Stone-Wales defects. Our study reveals that the sign of stress induced by a SW defect in a graphene nanoribbon depends on the orientation of the SW defect with respect to the ribbon edge and the relaxation of the structure to relieve this stress determines its stability. Local warping or wrinkles arise in graphene nanoribbon when the stress is compressive, while the structure remains planar otherwise. The specific consequences to armchair and zigzag graphene nanoribbon can be understood from the anisotropy of the stress induced by a SW defect embedded in bulk graphene. We also have found localized electronic states near the SW defect sites in a nanoribbon. However, warping results in delocalization of electrons in the defect states. We have observed that, in zigzag graphene nanoribbons magnetic ordering weakens due to the presence of SW defects at the edges and the ground state is driven towards that of a nonmagnetic metal.

Orientadores: Peter Alexander Bleinroth Schulz, Ana Luiza Cardoso Pereira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-18T12:03:32Z (GMT). No. of bitstreams: 1 BahamonArdila_DarioAndres_D.pdf: 15568018 bytes, checksum: 6b550b7e0291945e86b0152735b9ea2c (MD5) Previous issue date: 2011 / Resumo: Neste trabalho analisamos os efeitos das bordas nas propriedades eletrônicas e de transporte em estruturas finitas de grafeno, como nanofitas, pontos quânticos e anéis quânticos de grafeno. Nós focamos essencialmente no acoplamento entre os estados localizados nas bordas externas e estados localizados nas bordas internas, tais como as bordas internas dos anéis, vacâncias ou defeitos estendidos gerados pelas fronteiras de grão. Os cálculos são abordados no formalismo tight-binding para a rede hexagonal do grafeno. Para calcular as propriedades de transporte utilizamos o formalismo de Landauer-Buttiker e as funções de Green da rede. Para anéis quânticos observamos que a evolução dos estados localizados nas bordas internas, em função do campo magnético é oposta à dos estados localizados nas bordas externas. Tanto para anéis quânticos quanto para nanofitas, quando a magnitude do campo magnético gera um comprimento magnético maior do que a metade da separação entre as bordas internas e externas, os estados se acoplam levando à criação de gaps no espectro de auto-energias e ressonâncias de Fano na condutância. Este cenário é enriquecido pelo fato do grafeno ter duas sub-redes (novo grau de liberdade), identi cando que uma mudança na sub-rede dos átomos mais externos ou mais internos dos braços vizinhos de um anel muda a distribuição de carga e que a sub-rede de uma vacância fortemente modifica a forma de linha da condutância em uma nanofita. O mapeamento da densidade local de estados, diferenciada por sub-rede, nos leva a propor uma possível imagem experimental da força de acoplamento, que caracteriza a forma de linha das ressonâncias Fano. Quando consideramos um defeito estendido na rede do grafeno (defeito linear como os recentemente observados experimentalmente) foi encontrado que ele age como uma borda interna, que adiciona um novo canal para elétrons de baixa energia, e que tem aplicações promissórias como um o metálico quântico. Todos os nossos resultados são robustos quando a desordem nas bordas é incluído / Abstract: This work is concerned with the effects of the edges in the electronic and transport properties of nite structures of graphene, such as quantum dots, quantum rings and graphene nanoribbons. We primarily focus on the coupling between states located at the outer edges and states located at the inner edges, as internal edges of rings, vacancies or extended defects generated by the grain boundaries. The calculations are addressed within the tight-binding formalism for the hexagonal lattice. To calculate the transport properties we use the Landauer-B uttiker formalism and the recursive lattice Green's functions. For quantum rings we observed that the evolution of the states located at the inner edges, as a function of magnetic eld is opposite to that of the states located on the outer edges. For quantum rings as well as graphene nanoribbons when the magnitude of the magnetic eld creates a magnetic length larger than a half of the separation between the inner and outer edges, the states are coupled creating gaps in the self-energy spectrum and Fano resonances in the conductance of the graphene nanoribbons. This scenario is enriched when the sublattice is added as a new degree of freedom, identifying that a change in sublattice of the most external or most internal atoms of neighboring arms of a ring changes the charge distribution and the sublattice of a vacancy strongly modify the lineshape of the conductance. Sublattice differentiated Local density of states mapping for different lineshapes leading us to propose a possible experimental imaging of the coupling strength, which characterizes the lineshape of the Fano resonances. When we considered the recently experimentally observed extended defect, we found that it acts as an internal edge, which adds a new channel for low energy electrons, and would have promissory applications as metallic wire. All of our results are robust when edge disorder is included / Doutorado / Física da Matéria Condensada / Doutor em Ciências

Décrire la diffusion d'objets browniens corrélés est un problème non trivial en physique statistique. La présence de corrélations à longue portée induit en effet une diffusion "anormale", par définition non décrite par les lois usuelles de la physique statistique et devant être étudiée au cas par cas. Cette thèse est consacrée à l'un de ces exemples, la Single-File Diffusion, désignant la diffusion d'une chaîne ordonnée de particules ne pouvant pas se croiser. Nous présentons des études numériques de dynamique moléculaire ainsi que des études expérimentales nous permettant de mettre en évidence et de caractériser plusieurs régimes de diffusion longitudinale et transverse rencontrés lors de ce phénomène de transport. L'ensemble de nos résultats numériques et expérimentaux est expliqué par un modèle analytique basé sur la décomposition des fluctuations thermiques sur les modes propres de vibration d'un système. Ce modèle s'applique aux systèmes physiques réels car il est valable pour des interactions entre particules à longue portée et tient compte de la dissipation, de la taille du système et des propriétés du potentiel de confinement. L'analyse en modes propres nous permet également de caractériser l'évolution des fluctuations thermiques transverses lors de la transition zizag et de prévoir la structure du système après la transition. Enfin, l'étude de la transition zigzag nous renseigne plus généralement sur les effets d'un bruit thermique sur une bifurcation.