Dissertations / Theses: 'Modes de Bloch'

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Ratcliffe, Keith. "Trapped modes in the presence of thin obstacles." Thesis, Loughborough University, 2002. https://dspace.lboro.ac.uk/2134/34725.

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In this thesis we use various techniques to investigate the occurrence of trapped modes in the presence of thin obstacles. Physically trapped modes are oscillations of finite energy in a fluid which is unbounded in at least one direction. These oscillations mainly occur locally to some structure and decay to zero at large distances away from it. Trapped modes are important as they have been found to exist in a wide range of physical situations. We consider a number of problems in two and three dimensions including waveguides containing bodies and arrays of identical structures. A modified residue calculus technique, a variational technique and a method based on the truncation of matched eigenfunction expansions are used to solve the problems, with numerous results presented.

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Gerelli, Emmanuel. "Nanopinces optiques à base de modes de Bloch lents en cavité." Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00838792.

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Ce travail de thèse s'inscrit dans les efforts actuellement réalisés, pour améliorer l'efficacité des pinces optiques conventionnelles qui permettent de manipuler sans contact des objets de quelques dizaines de nanomètres à quelques dizaines de micromètres avec une extrême précision et trouvent de nombreuses applications en biophysique et sciences de colloïdes.L'objectif de cette thèse a été d'explorer une nouvelle approche pour la réalisation de Nanopinces Optiques. Elle s'appuie sur l'utilisation de cavités à cristaux photoniques à modes de Bloch lents. Ces cavités peuvent être efficacement et facilement excitées par un faisceau Gaussien à incidence normale. Contrairement aux pinces optiques conventionnelles, des objectifs à faibles ouvertures numériques peuvent être utilisés. Les performances attendues en termes de piégeage vont bien au-delà de limitations imposées par la limite de diffraction pour les pinces conventionnelles. Ce travail démontre expérimentalement l'efficacité de l'approche. Cette thèse comporte deux parties principales. Dans un premier temps, il a fallu monter un banc expérimental pour mener nos études. Nous avons construit un banc optique, interfacé les instruments, et développé des applications logicielles pour analyser les données. Deux éléments importants ont présidé à sa construction : - Le développement d'un système optique permettant d'exciter les nanostructures photoniques - la conception d'un système d'imagerie pour suivre les nanoparticules. La seconde partie de ce travail a porté sur la mise en évidence du piégeage optique à l'aide de nanostructure à base de cristaux photonique. Nous avons d'abord montré que même des cavités possédant des coefficients de qualités modérés (quelques centaines) permettait d'obtenir des pièges optiques dont l'efficacité est d'un ordre de grandeur supérieur à celui de pinces conventionnels. Fort de ce résultat, nous avons exploré un nouveau type de cavité à cristaux photoniques s'appuyant sur une approche originale : des structures bi-périodiques. Nous avons montré qu'à l'aide de cette approche des facteurs de qualités de l'ordre de plusieurs milliers étaient facilement atteignable. A l'aide de ces nouvelles structures, nous sommes arrivés aux résultats le plus important de ce travail : le piégeage de nanoparticules de 250nm de rayon avec une puissance optique incidente de l'ordre du milliwatt. Une analyse fine du mouvement de la nanoparticule, nous a permis de trouver la signature du mode de Bloch lent.

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Manga, Etoungh Dimitri. "Application de la réfraction négative à l'imagerie acoustique à l'aide de cristaux phononiques bidimensionnels." Phd thesis, Université François Rabelais - Tours, 2012. http://tel.archives-ouvertes.fr/tel-00785442.

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La propagation des ondes ultrasonores à travers des cristaux phononiques CP à deux dimensions 2D constitués de diffuseurs solides dans des matrices solide et fluide est ici étudiée, ainsi que la caractérisation de ces milieux et leur application à l'imagerie acoustique. Les techniques expérimentales utilisées permettent une mesure complète des champs transmis à travers les cristaux. Les études sont menées dans des bandes fréquentielles autorisant les effets de réfraction négative indispensables à l'obtention d'une résolution inférieure à la limite de diffraction (super-résolution). De manière à compléter les analyses, différents outils théoriques sont exploités : Décomposition en Ondes Planes et Éléments Finis, notamment. La première partie du document concerne la réalisation et la caractérisation de cristaux phononiques possédant des propriétés nécessaires à la réalisation de systèmes d'imagerie acoustique : réfraction négative, contours équi-fréquences circulaires, accord d'indice, accord d'impédance. Cette première étude est menée sur un cristal à matrice solide, elle met en relief la possibilité de générer différents modes de Bloch au cours de la propagation. L'accord d'indice avec l'eau n'étant cependant pas obtenu, la seconde partie porte sur la réfraction négative et la focalisation des ondes à travers un CP à matrice fluide. Les propriétés du CP déterminées, le dernier chapitre s'attache à évaluer les performances des systèmes d'imagerie développés : dynamique et résolution.

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Duan, Yuting. "Trapped modes and acoustic resonances." Thesis, Loughborough University, 2004. https://dspace.lboro.ac.uk/2134/12860.

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The scattering of waves by a finite thin plate in a two-dimensional wave guide and an array of finite thin plates, in the presence of subsonic mean flow, are formulated using a mode matching technique. The influence of mean flow on trapped modes in the vicinity of a finite thin plate in a two-dimensional wave guide is then investigated by putting the amplitude of the forcing term to zero in the scattering problem. The conditions for complex resonances are found, and numerical results are computed. The influence of mean flow on Rayleigh-Bloch modes is investigated by using a similar methodology. The condition for embedded trapped modes to exist is introduced next, and then numerical results for embedded trapped modes without mean flow are presented. Complex resonances without mean flow are then found by fixing the geometry of the waveguide. The influence of mean flow on complex resonances and embedded trapped modes is investigated subsequently. In addition, the investigation of scattering coefficients is discussed when the frequency of an incident wave is near the real part of the frequency of complex resonances or embedded trapped modes. Embedded trapped modes near an indentation in a strip wave guide, which may correspond to a two-dimensional acoustic wave guide or a channel of uniform water depth in water waves, are also found. Modes are sought which are either symmetric or anti-symmetric about the centreline of the guide and the centre of the indentation. In each case, a simple approximate solution is found numerically. Full solutions are then found by using a Galerkin approach in which the singularity near the indentation edge is modelled by choosing proper special functions. The final part of the thesis is devoted to spinning modes (Rayleigh-Bloch modes) in a cylindrical waveguide in the presence of radial fins. A mode matching technique is used to obtain the potential, and the coefficients in the expansion are found numerically by using an efficient Galerkin procedure. In addition, an existence proof for modes symmetric about the centre of the guide and the centre of the section with radial fins is given by applying a variational approach. The connection between Rayleigh-Bloch modes and trapped modes is discussed thereafter, and numerical results for a number of geometric configurations are presented.

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Crouzil, Thomas. "Modélisation de structure dynamique dans un champ optique." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0043/document.

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Le piégeage optique se présente maintenant, depuis quelques décennies, comme une thématique majeure à l'intersection de diverses disciplines. Depuis les résultats d'Ashkin, de nombreux travaux ont été effectués dans le piégeage et le guidage d'objets physiques (particules, molécules, bactéries, etc.) de toutes tailles. Ces derniers caractériseront alors, devant la longueur d'onde, le domaine optique dans lequel nous nous placerons (Rayleigh, Mie, Optique géométrique).Notre travail porte donc sur l'étude des propriétés de chaînes linéaires périodiques de gouttelettes (huile), placées dans l'eau, et soumises à deux faisceaux laser horizontaux contra-propageants de profil gaussien. Nous démontrons qu'il est possible d'établir un ordre spatial sur un ensemble de grosses gouttes (devant la longueur d'onde) suivant une structure périodique. L'originalité d'un tel système réside dans le fait que la lumière peut alors être refocalisée par l'ensemble des gouttes espacées périodiquement. Cette périodicité peut ainsi, dans certains cas, conférer au faisceau une refocalisation périodique au sein du réseau. Cette première étude, en limite statique, nous permet ainsi de mettre en évidence les conditions de couplage des modes liés aux chaînes de gouttes. En particulier, nous caractérisons la présence de modes de Bloch où le faisceau se propage avec une périodicité équivalente à celle du réseau. Cela nous amène à remarquer que ces conditions modales sont soumises au paramètre de phase gaussien "Thêta" (phase de Gouy). Ainsi, bien que structuré à une échelle largement supérieure, nous mettons en évidence théoriquement des propriétés analogues à celle des cristaux photoniques, conférées par la périodicité des chaînes de gouttes. Ce qui nous permet, en conséquence, de démontrer l'existence de bandes interdites, nous amenant à définir un ensemble de modes guidants/nonguidants de cette chaîne. Cette étude statique est, par la suite, étendue d'un point de vue dynamique en considérant l'effet des forces optiques sur les gouttes. Nous démontrons ainsi qu'il est possible de piéger optiquement de telles gouttes sur des états d'équilibres stables. Au-delà desquels nous mettons en évidence, à travers une étude paramétrique, l'existence de modes oscillants périodiques ou pseudo-périodiques. Enfin, nous prenons en compte les phénomènes de collisions par coalescence, entraînant une réorganisation des répartitions de champs optiques qui peuvent se traduire par de nouvelles configurations de piégeage
Optical trapping appears now, since a few decades, as a major theme at the intersection of variousdisciplines. Since the results of Ashkin, many works were made in the trapping and the guidance of physical objects (particles, molecules, bacteria, etc.) of any sizes. The latter will characterize then, in front of the wavelength, the optical domain in which we shall take place (Rayleigh, Mie, Geometrical Optics).Our work thus concerns the study of the properties of periodic linear chains of droplets (oil), placed in water, and submitted to two counter-propagating horizontal laser beams of gaussian profile. We show that it is possible to establish a spatial order of a set of large drops (in front of the wavelength) in a periodic structure. The originality of such a system lies in the fact that the light can then be refocused by the set of periodically spaced drops. This periodicity may thus, in some cases, confer on the beam a periodic refocusing within the network. This first study, in static limit, allows us to identify the conditions of coupling modes associated with drop channels. In particular, we characterize the presence of Bloch modes where the beam propagates with similar frequency to that of the network. This leads us to note that these modal conditions are submitt to the gaussian phase parameter "Thêta" (Gouy phase). Thus, although structured at a widely higher scale, we highlight theoretically similar properties to that of the photonic crystals, conferred by the periodicity of the chains of drops. This allows us, consequently, to demonstrate the existence of bandgaps, leading us to define a set of guiding/not-guiding modes of this chain. This static study, thereafter, is extended from a dynamic point of view by taking into account the effect of the optical forces on the drops. We show that it is possible to optically trap such drops on stable equilibrium states. Beyond of which we highlight, through a parametric study, the existence of periodic or pseudo-periodic oscillating modes.Finally, we take into account the phenomena of collisions by coalescence, involving a reorganization of the distributions of optical fields which can result in new configurations of trapping

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Vo, Thanh Phong. "Optical near-field characterization of Slow-Bloch Mode based photonic crystal devices." Phd thesis, Ecole Centrale de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00758323.

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2D-Photonic crystal (PC) structures have enabled the fabrication of a wide variety of nanophotonic components. In perfect PCs, the exploitation of the enhanced local density of states at critical points of the band diagram has attracted considerable attention. Near these points, where the group velocity vanished, low curvature flat bands give rise to delocalized and stationary optical slow Bloch modes (or slow light modes). Properties of slow light make them good candidates to enhance Purcell or various non-linear effects or to design low-threshold lasers. Among these modes, slow Bloch modes (SBMs) emitting in the vertical direction, i.e. located at the Γ- point of the Brillouin zone are particularly interesting for integrating 2D PC architectures with free space optics. In particular, some SBMs proved to be suitable for achieving strong vertical emission with peculiar polarization properties. Other promising applications concern disorder: by introducing a controlled randomness into the PC structure, it is possible to induce a transition from slow Bloch mode (in ordered PC) to Anderson's localization (in disordered PC) as a function of disorder degree. In this PhD dissertation, Slow Bloch modes have been studied and characterized by the means of Near-field Scanning Optical microscopy (NSOM). We particularly focused on Slow Bloch laser mode at Γ- point of a honeycomb 2DPC. This NSOM technique enables to visualize the evanescent component of the mode with a spatial resolution below the diffraction limit. In this work, we showed that the far-field and the near-field image of the mode at the 2D-PC surface are different and that near-field results yield a better insight in the real mode structure inside the PC slab in agreement with theoretical prediction. The importance of the probe selection (bare silica, metallized tip and bow-tie aperture nanoantenna) for studying III-V photonic crystal structures was also demonstrated. Besides intensity measurement of the electromagnetic field, the polarization of the electric field has been measured at the nanoscale for the first time by using a bow-tie nano-antenna probe. These results enable the unambiguous identification of the modes with the 3D-FDTD simulations.In this work is also reported the first observation of two-dimensional localization of light in two types of 2D random photonic crystal lasers, where Slow Bloch Mode (SBM) is scattered by artificial structural randomness in triangular PCs. The structural randomness is introduced whether by nanometer displacements in the positions of lattice elements (air holes), whether by variation of the hole diameters. The direct near-field imaging of the lasing mode by use of NSOM for the first time, allowed us to observe the transition of the extended planar SBM to be Anderson localized.

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Zang, Xiaorun. "Lumière lente dans les guides à cristaux photoniques pour l'interaction renforcée avec la matière." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0172/document.

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Dans cette thèse, nous avons étudié l'impact considérable de désordre aléatoire sur le transport de la lumière lente dans les guides à cristaux photoniques 1D, c'est-à-dire la localisation de la lumière. Les mesures en champ proche, les simulations statistiques et le modèle théorique révèlent l'existence d'une limite inférieure de l’extension spatiale des modes localisés. Nous avons également présenté que le niveau de désordre et l’extension spatiale de mode localisé individuelle sont liés par la masse effective de photons plutôt que la vitesse de groupe considérant en général.Deuxièmement, les systèmes hybrides d'atomes froids et des guides à cristaux photoniques ont été reconnus comme un approche prometteuse pour l'ingénierie grande interaction lumière-matière au niveau des atomes et des photons individuels. Dans cette thèse, nous avons étudié la physique, à savoir le transport de la lumière dans des guides de nanophotonique périodiques couplées à des atomes à deux niveaux. Notre expression semi-analytique développée est générale et peut rapidement caractériser le couplage entre les atomes froids et les photons guidées. Pour surmonter les difficultés techniques considérables existent dans les systèmes hybrides atomique et photonique, nous avons conçu un guide nanophotonique qui supporte un mode de Bloch lente guidée avec grande queue évanescente dans l'espace libre pour les atomes froids de piégeage. Pour adapter précisément la région de fréquence de la lumière lente du mode guidé à la ligne de transition atomique, nous avons conçu la bande photonique et de la courbe de dispersion du mode guidé afin que la force de l'interaction est robuste contre imprévisible fabrication imperfection
In this thesis, we firstly investigated the striking influence of random disorder on light transport near band edges in one dimensional photonic crystal wave guides, i.e. light localization. Near-field measurements, statistical simulations and theoretical model revealed the existence of a lower bound for the spatial extent of localized modes. We also showed that the disorder level and the spatial extent of individual localized mode is linked by the photon effective mass rather than the generally considered group velocity. Secondly, hybrid cold atoms and photonic crystal wave guides system have been recognized as a promising paradigm for engineering large light-matter interaction at single atoms and photons level. In this thesis, we studied the basic physics, i.e. light transport in periodic nanophotonic wave guides coupled to two-level atoms. Our developed general semi-analytical expression can quickly characterize the coupling between cold atoms and guided photons. Aim to overcome the significant technical challenges existed for developing hybrid atom-photonic systems, we designed a nanophotonic waveguide, which supports a slow guided Bloch mode with large evanescent tail in free space for cold atoms trapping (release the limitation imposed by Casmir Polder force and technical challenge of nanoscale manipulation of cold atoms). To match precisely the slow light region of the guided mode to the atomic transition line, we carefully engineered the photonic band and the dispersion curve (i.e.flatness) of the guided mode so that the interaction strength is robust against unpredictable fabrication imperfection

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Salemeh, Elie. "Periodic structures : transmission invariance and symmetry effects." Electronic Thesis or Diss., Le Mans, 2024. http://www.theses.fr/2024LEMA1010.

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Une caractéristique du régime localisé dans un milieu désordonné est l’insensibilité du speckle transmis à l’ondeincidente. En optique, l’image sur un écran du champ transmis à travers un milieu désordonné opaque - le speckle- est la même quelles que soient les conditions d’éclairage. Ce phénomène remarquable peut être expliqué parl’analyse des modes propres de transmission du matériau étudié. Le régime localisé se caractérise par laprédominance d’un unique mode, la transmission de tous les autres étant significativement plus faible. Le motifdu champ transmis est alors déterminé par ce seul mode, indépendamment de la source. Un phénomène analogueest possible dans un milieu ordonné, périodique, lorsque l’onde propagée dans le milieu est principalement portéepar un unique mode de Bloch. L’onde propagée dans le milieu périodique est alors progressivement « gelée »,présentant un même motif, quelque soit la source qui l’a générée. Le travail présenté vise à caractériser etobserver expérimentalement ce phénomène dans le cas de la propagation dans un guide d’onde périodique. Il viseaussi à caractériser ce phénomène dans le cas de la transmission à travers un réseau de diffraction. Finalementnous nous intéressons aux effets de la symétrie lorsqu’une barrière opaque est placée dans un guide d’ondespériodique, en particulier au gain de la transmission induit par la symétrie
A characteristic of the localized regime in a disordered medium is the insensitivity of the transmitted speckle tothe incident wave. In optics, the image on a screen of the transmitted field through an opaque disordered medium- the speckle - remains the same regardless of the lighting conditions. This remarkable phenomenon can beexplained by analyzing the eigenmodes of transmission of the studied material. The localized regime ischaracterized by the predominance of a single mode, with the transmission of all other modes being significantlyweaker. The pattern of the transmitted field is then determined by this single mode, regardless of the source. Asimilar phenomenon is possible in an ordered, periodic medium, when the wave propagated in the medium ismainly carried by a single Bloch mode. The wave propagated in the periodic medium is then gradually "frozen",presenting the same pattern, regardless of the source that generated it. The presented work aims to characterizeand to observe experimentally this phenomenon in the case of propagation in a periodic waveguide. It also aims tocharacterize this phenomenon in the case of transmission through a diffraction grating. Finally, we are interestedin the effects of symmetry when an opaque barrier is placed in a periodic waveguide, specifically focusing on thetransmission enhancement induced by symmetry

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Roth, Paul [Verfasser], Philip St J. [Akademischer Betreuer] Russell, Philip St J. [Gutachter] Russell, Fabio [Gutachter] Biancalana, and Markus A. [Gutachter] Schmidt. "Helical Bloch Modes in Twisted Photonic Crystal Fibers / Paul Roth ; Gutachter: Philip St.J. Russell, Fabio Biancalana, Markus A. Schmidt ; Betreuer: Philip St.J. Russell." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2021. http://d-nb.info/1228627622/34.

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Liu, Wei. "The Effective Spin Concept to Study the Properties of the Shannon Entropy of Arrays of Elastic Scatterers." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1331300313.

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Silberstein, Eric. "Généralisation de la méthode modale de Fourier aux problèmes de diffraction en optique intégrée. Application aux convertisseurs modaux par ingénierie des modes de Bloch." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2002. http://tel.archives-ouvertes.fr/tel-00003101.

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Cette thèse s'inscrit dans la mouvance entourant les matériaux nanostructurés pour la photonique. Ces nouveaux composants, structurés à l'échelle de la longueur d'onde, offrent la possibilité de confiner le champ électromagnétique à une échelle très petite, ouvrant ainsi la voie à des composants optiques compacts. En outre, ces matériaux offrent également la possibilité de contrôler l'émission spontanée d'atomes émetteurs, et donc de concevoir des lasers à très bas seuil par exemple. Bien que les premières étapes visant à leur réalisation aient déjà été franchies, de nombreux problèmes subsistent. D'une part, ces matériaux étant structurés à l'échelle de la longueur d'onde, il est nécessaire pour les modéliser de résoudre les équations de Maxwell sans approximation. D'autre part, pour que ces composants puissent être utilisés en pratique, il faut parvenir à les connecter à d'autres composants optiques plus classiques. Malheureusement, le confinement du champ étant très différent entre ces deux types de composants, il survient immédiatement des pertes d'insertion élevées qui sont pressenties comme un verrou à lever pour les applications futures. C'est précisément sur ces deux problèmes que porte ma thèse. Dans la première partie, nous présentons une méthode originale de calcul de structures diffractives en optique guidée dérivée de la méthode modale de Fourier (RCWA). Cette nouvelle approche permet, en périodisant numériquement la structure que nous voulons étudier, d'appliquer des codes numériques développés à l'origine pour l'étude des réseaux de diffraction. Nous étendons ainsi de façon importante le champ d'application de la RCWA, lui permettant par exemple de calculer les caractéristiques de miroirs de Bragg ou de cavités intégrées. Dans la seconde partie, nous nous attaquons au problème des pertes d'insertion en développant des convertisseurs modaux efficaces pour des miroirs de Bragg intégrés courts. Pour ce faire, nous déformons progressivement le mode de Bloch fondamental du miroir en imposant au convertisseur un gradient d'indice complexe. Nos calculs numériques montrent que ces convertisseurs modaux peuvent être très courts, ouvrant ainsi la voie à la réalisation pratique de cavités courtes et à faibles pertes. Cette approche est validée pour des cavités fabriquées dans un substrat de silicium sur isolant.

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Silberstein, Éric. "Généralisation de la méthode modale de Fourier aux problèmes de diffraction en optique intégrée : application aux convertisseurs modaux par ingénierie des modes de Bloch." Paris 6, 2002. https://pastel.archives-ouvertes.fr/tel-00003101.

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Afdideh, Fardin. "Block-sparse models in multi-modality : application to the inverse model in EEG/MEG." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAT074/document.

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De nombreux phénomènes naturels sont trop complexes pour être pleinement reconnus par un seul instrument de mesure ou par une seule modalité. Par conséquent, le domaine de recherche de la multi-modalité a émergé pour mieux identifier les caractéristiques riches du phénomène naturel de la multi-propriété naturelle, en analysant conjointement les données collectées à partir d’uniques modalités, qui sont en quelque sorte complémentaires. Dans notre étude, le phénomène d’intérêt multi-propriétés est l’activité du cerveau humain et nous nous intéressons à mieux la localiser au moyen de ses propriétés électromagnétiques, mesurables de manière non invasive. En neurophysiologie, l’électroencéphalographie (EEG) et la magnétoencéphalographie (MEG) constituent un moyen courant de mesurer les propriétés électriques et magnétiques de l’activité cérébrale. Notre application dans le monde réel, à savoir le problème de reconstruction de source EEG / MEG, est un problème fondamental en neurosciences, allant des sciences cognitives à la neuropathologie en passant par la planification chirurgicale. Considérant que le problème de reconstruction de source EEG /MEG peut être reformulé en un système d’équations linéaires sous-déterminé, la solution (l’activité estimée de la source cérébrale) doit être suffisamment parcimonieuse pour pouvoir être récupérée de manière unique. La quantité de parcimonie est déterminée par les conditions dites de récupération. Cependant, dans les problèmes de grande dimension, les conditions de récupération conventionnelles sont extrêmement strictes. En regroupant les colonnes cohérentes d’un dictionnaire, on pourrait obtenir une structure plus incohérente. Cette stratégie a été proposée en tant que cadre d’identification de structure de bloc, ce qui aboutit à la segmentation automatique de l’espace source du cerveau, sans utiliser aucune information sur l’activité des sources du cerveau et les signaux EEG / MEG. En dépit du dictionnaire structuré en blocs moins cohérent qui en a résulté, la condition de récupération conventionnelle n’est plus en mesure de calculer la caractérisation de la cohérence. Afin de relever le défi mentionné, le cadre général des conditions de récupération exactes par bloc-parcimonie, comprenant trois conditions théoriques et une condition dépendante de l’algorithme, a été proposé. Enfin, nous avons étudié la multi-modalité EEG et MEG et montré qu’en combinant les deux modalités, des régions cérébrales plus raffinées sont apparues
Three main challenges have been addressed in this thesis, in three chapters.First challenge is about the ineffectiveness of some classic methods in high-dimensional problems. This challenge is partially addressed through the idea of clustering the coherent parts of a dictionary based on the proposed characterisation, in order to create more incoherent atomic entities in the dictionary, which is proposed as a block structure identification framework. The more incoherent atomic entities, the more improvement in the exact recovery conditions. In addition, we applied the mentioned clustering idea to real-world EEG/MEG leadfields to segment the brain source space, without using any information about the brain sources activity and EEG/MEG signals. Second challenge raises when classic recovery conditions cannot be established for the new concept of constraint, i.e., block-sparsity. Therefore, as the second research orientation, we developed a general framework for block-sparse exact recovery conditions, i.e., four theoretical and one algorithmic-dependent conditions, which ensure the uniqueness of the block-sparse solution of corresponding weighted mixed-norm optimisation problem in an underdetermined system of linear equations. The mentioned generality of the framework is in terms of the properties of the underdetermined system of linear equations, extracted dictionary characterisations, optimisation problems, and ultimately the recovery conditions. Finally, the combination of different information of a same phenomenon is the subject of the third challenge, which is addressed in the last part of dissertation with application to brain source space segmentation. More precisely, we showed that by combining the EEG and MEG leadfields and gaining the electromagnetic properties of the head, more refined brain regions appeared

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Ferrier, Lydie. "Micro-nano structures à base de cristaux photoniques pour le contrôle 3D de la lumière." Phd thesis, Ecole Centrale de Lyon, 2008. http://tel.archives-ouvertes.fr/tel-00625602.

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Le contrôle 3D de la lumière est réalisé, à l'échelle de la longueur d'onde, dans des circuits photoniques intégrés. La brique élémentaire choisie dans cette étude est le cristal photonique (CP) membranaire qui, par ses propriétés de dispersion, permet un contrôle de la lumière à la fois dans le plan (optique guidée) et hors du plan (dispositifs adressables par la surface). En particulier, l'exploitation de modes de Bloch situés au point Gamma de la courbe de dispersion (k//=0) permet l'émission de la lumière dans la direction verticale. Dans cette étude, nous nous sommes focalisés sur des cristaux photoniques à réseaux de micropiliers, comme alternative aux réseaux de trous, mais également en envisageant la possibilité d'intégrer ces structures dans des systèmes microfluidiques, les fluides ayant la capacité de circuler au travers des réseaux de piliers. Nous décrirons dans une première partie, des dispositifs à CP à émission par la surface. Nous démontrerons, pour la première fois, que l'utilisation de modes fortement résonants permet de réaliser des microlasers à réseaux de piliers en InP. Les modes faiblement résonants peuvent être utilisés pour la réalisation de miroirs à CP et de microcavités Fabry-Pérot constituées uniquement de tels miroirs. Les facteurs de qualité obtenus (>10000) rendent possible la fabrication de nouveaux types de VCSEL. Dans une seconde partie, nous nous intéresserons à la problématique de l'intégration de ces dispositifs dans un circuit photonique 3D. Tout d'abord, nous expliquerons comment il est possible d'optimisation le diagramme de rayonnement des composants. Ensuite, nous étudierons le couplage de dispositifs à cristaux photoniques avec un ou deux guides d'onde ruban en silicium. De fortes efficacités de couplage sont obtenues en simulation FDTD 3D (95%). Ces dispositifs en cours de fabrication en collaboration avec le LETI-CEA de Grenoble permettront de démontrer expérimentalement ce couplage.

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Boutami, Salim. "MICROCAVITES OPTIQUES VERTICALES A BASE DE CRISTAUX PHOTONIQUES MEMBRANAIRES." Phd thesis, Ecole Centrale de Lyon, 2007. http://tel.archives-ouvertes.fr/tel-00341736.

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Ce travail de thèse est axé sur l'utilisation de modes de Bloch lents à pertes rayonnées verticales, dans des cristaux photoniques membranaires 1D (réseau de fentes) et 2D (réseaux de trous) en InP, pour la réalisation de réflecteurs en espace libre. L'intérêt premier de tels réflecteurs réside dans leur compacité verticale (une seule couche épitaxiée), comparés aux miroirs de Bragg traditionnels, mais également dans le contrôle de la polarisation qu'ils autorisent. Les règles de conception de ces réflecteurs, ainsi que leurs procédés de fabrication et de caractérisation sont présentés. Les résultats expérimentaux obtenus sont en bon accord avec la théorie.

Ces réflecteurs membranaires à cristaux photoniques ont ensuite été intégrés dans des cavités Fabry-Pérot verticales, où ils remplacent le miroir de Bragg supérieur. Un dispositif passif (filtre MOEMS accordable électriquement, compact et polarisé) et un dispositif actif (VCSEL à puits quantiques, émettant à 1.55µm, compact et polarisé) ont été réalisés.

Enfin, des cavités Fabry-Pérot ultimes, uniquement à base de ces réflecteurs à CP, sont étudiées. Le concept est validé en utilisant deux échantillons différents placés en vis-à-vis à l'aide d'un montage piézo-électrique. Ensuite, un démonstrateur passif monolithique, montrant une sélectivité et une compacité verticale sans précédents.
En outre, une étude théorique démontre la capacité des miroirs à CP à influer très fortement sur la vitesse d'expansion latérale de la lumière dans les cavités Fabry-Pérot, ce qui ouvre la voie à de toutes nouvelles applications.

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Sciancalepore, Corrado. "Intégration hétérogène III-V sur silicium de microlasers à émission par la surface à base de cristaux photoniques." Phd thesis, Ecole Centrale de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00915280.

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La croissance continue et rapide du trafic de données dans les infrastructures de télécommunications, impose des niveaux de débit de transmission ainsi que de puissance de traitement de l'information, que les capacités intrinsèques des systèmes et microcircuits électroniques ne seront plus en mesure d'assurer à brève échéance : le développement de nouveaux scenarii technologiques s'avère indispensable pour répondre à la demande de bande passante imposée notamment par la révolution de l'internet, tout en préservant une consommation énergétique raisonnable. Dans ce contexte, l'intégration hétérogène fonctionnelle sur silicium de dispositifs photoniques à émission par la surface de type VCSEL utilisant des miroirs large-bandes ultra-compacts à cristaux photoniques constitue une stratégie prometteuse pour surmonter l'impasse technologique actuelle, tout en ouvrant la voie à un développement rapide d'architectures et de systèmes de communications innovants dans le cadre du mariage entre photonique et micro-nano-électronique.

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Berrier, Audrey. "InP-based photonic crystals : Processing, Material properties and Dispersion effects." Doctoral thesis, KTH, Mikroelektronik och tillämpad fysik, MAP, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4734.

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Photonic crystals (PhCs) are periodic dielectric structures that exhibit a photonic bandgap, i.e., a range of wavelength for which light propagation is forbidden. The special band structure related dispersion properties offer a realm of novel functionalities and interesting physical phenomena. PhCs have been manufactured using semiconductors and other material technologies. However, InP-based materials are the main choice for active devices at optical communication wavelengths. This thesis focuses on two-dimensional PhCs in the InP/GaInAsP/InP material system and addresses their fabrication technology and their physical properties covering both material issues and light propagation aspects. Ar/Cl2 chemically assisted ion beam etching was used to etch the photonic crystals. The etching characteristics including feature size dependent etching phenomena were experimentally determined and the underlying etching mechanisms are explained. For the etched PhC holes, aspect ratios around 20 were achieved, with a maximum etch depth of 5 microns for a hole diameter of 300 nm. Optical losses in photonic crystal devices were addressed both in terms of vertical confinement and hole shape and depth. The work also demonstrated that dry etching has a major impact on the properties of the photonic crystal material. The surface Fermi level at the etched hole sidewalls was found to be pinned at 0.12 eV below the conduction band minimum. This is shown to have important consequences on carrier transport. It is also found that, for an InGaAsP quantum well, the surface recombination velocity increases (non-linearly) by more than one order of magnitude as the etch duration is increased, providing evidence for accumulation of sidewall damage. A model based on sputtering theory is developed to qualitatively explain the development of damage. The physics of dispersive phenomena in PhC structures is investigated experimentally and theoretically. Negative refraction was experimentally demonstrated at optical wavelengths, and applied for light focusing. Fourier optics was used to experimentally explore the issue of coupling to Bloch modes inside the PhC slab and to experimentally determine the curvature of the band structure. Finally, dispersive phenomena were used in coupled-cavity waveguides to achieve a slow light regime with a group index of more than 180 and a group velocity dispersion up to 10^7 times that of a conventional fiber.
QC 20100712

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18

Eichenauer, Florian. "Analysis for dissipative Maxwell-Bloch type models." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17661.

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Die vorliegende Dissertation befasst sich mit der mathematischen Modellierung semi-klassischer Licht-Materie-Interaktion. Im semiklassischen Bild wird Materie durch eine Dichtematrix "rho" beschrieben. Das Konzept der Dichtematrizen ist quantenmechanischer Natur. Auf der anderen Seite wird Licht durch ein klassisches elektromagnetisches Feld "(E,H)" beschrieben. Wir stellen einen mathematischen Rahmen vor, in dem wir systematisch dissipative Effekte in die Liouville-von-Neumann-Gleichung inkludieren. Bei unserem Ansatz sticht ins Auge, dass Lösungen der resultierenden Gleichung eine intrinsische Liapunov-Funktion besitzen. Anschließend koppeln wir die resultierende Gleichung mit den Maxwell-Gleichungen und erhalten ein neues selbstkonsistentes, dissipatives Modell vom Maxwell-Bloch-Typ. Der Fokus dieser Arbeit liegt auf der intensiven mathematischen Studie des dissipativen Modells vom Maxwell-Bloch-Typ. Da das Modell Lipschitz-Stetigkeit vermissen lassen, kreieren wir eine regularisierte Version des Modells, das Lipschitz-stetig ist. Wir beschränken unsere Analyse im Wesentlichen auf die Lipschitz-stetige Regularisierung. Für regularisierte Versionen des dissipativen Modells zeigen wir die Existenz von Lösungen des zugehörigen Anfangswertproblems. Der Kern des Existenzbeweises besteht aus einem Resultat von ``compensated compactness'''', das von P. Gérard bewiesen wurde, sowie aus einem Lemma vom Rellich-Typ. In Teilen folgt dieser Beweis dem Vorgehen einer älteren Arbeit von J.-L. Joly, G. Métivier und J. Rauch.
This thesis deals with the mathematical modeling of semi-classical matter-light interaction. In the semi-classical picture, matter is described by a density matrix "rho", a quantum mechanical concept. Light on the other hand, is described by a classical electromagnetic field "(E,H)". We give a short overview of the physical background, introduce the usual coupling mechanism and derive the classical Maxwell-Bloch equations which have intensively been studied in the literature. Moreover, We introduce a mathematical framework in which we state a systematic approach to include dissipative effects in the Liouville-von-Neumann equation. The striking advantage of our approach is the intrinsic existence of a Liapunov function for solutions to the resulting evolution equation. Next, we couple the resulting equation to the Maxwell equations and arrive at a new self-consistent dissipative Maxwell-Bloch type model for semi-classical matter-light interaction. The main focus of this work lies on the intensive mathematical study of the dissipative Maxwell-Bloch type model. Since our model lacks Lipschitz continuity, we create a regularized version of the model that is Lipschitz continuous. We mostly restrict our analysis to the Lipschitz continuous regularization. For regularized versions of the dissipative Maxwell-Bloch type model, we prove existence of solutions to the corresponding Cauchy problem. The core of the proof is based on results from compensated compactness due to P. Gérard and a Rellich type lemma. In parts, this proof closely follows the lines of an earlier work due to J.-L. Joly, G. Métivier and J. Rauch.

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Huang, Jici. "Sorting by Block Moves." UNF Digital Commons, 2015. http://digitalcommons.unf.edu/etd/576.

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The research in this thesis is focused on the problem of Block Sorting, which has applications in Computational Biology and in Optical Character Recognition (OCR). A block in a permutation is a maximal sequence of consecutive elements that are also consecutive in the identity permutation. BLOCK SORTING is the process of transforming an arbitrary permutation to the identity permutation through a sequence of block moves. Given an arbitrary permutation π and an integer m, the Block Sorting Problem, or the problem of deciding whether the transformation can be accomplished in at most m block moves has been shown to be NP-hard. After being known to be 3-approximable for over a decade, block sorting has been researched extensively and now there are several 2-approximation algorithms for its solution. This work introduces new structures on a permutation, which are called runs and ordered pairs, and are used to develop two new approximation algorithms. Both the new algorithms are 2-approximation algorithms, yielding the approximation ratio equal to the current best. This work also includes an analysis of both the new algorithms showing they are 2-approximation algorithms.

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Wang, Xiaopei. "Multi-Way Block Models." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1342716695.

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21

Vallès, Català Toni. "Network inference based on stochastic block models: model extensions, inference approaches and applications." Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/399539.

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L'estudi de xarxes ha contribuït a la comprensió de sistemes complexos en una àmplia gamma de camps com la biologia molecular i cel·lular, l'anatomia, la neurociència, l'ecologia, l'economia i la sociologia. No obstant, el coneixement disponible sobre molts sistemes reals encara és limitat, per aquesta raó el poder predictiu de la ciència en xarxes s'ha de millorar per disminuir la bretxa entre coneixement i informació. Per abordar aquest tema fem servir la família de 'Stochastic Block Models' (SBM), una família de models generatius que està guanyant gran interès recentment a causa de la seva adaptabilitat a qualsevol tipus de xarxa. L'objectiu d'aquesta tesi és el desenvolupament de noves metodologies d'inferència basades en SBM que perfeccionaran la nostra comprensió de les xarxes complexes. En primer lloc, investiguem en quina mesura fer un mostreg sobre models pot millorar significativament la capacitat de predicció que considerar un únic conjunt òptim de paràmetres. Un cop sabem quin model és capaç de descriure millor una xarxa determinada, apliquem aquest mètode en un cas particular d'una xarxa real: una xarxa basada en les interaccions/sutures entre els ossos del crani en nounats. Concretament, descobrim que les sutures tancades a causa d'una malaltia patològica en el nounat humà son menys probables, des d'un punt de vista morfològic, que les sutures tancades sota un desenvolupament normal. Recents investigacions en xarxes multicapa conclou que el comportament de les xarxes d'una sola capa són diferents de les de múltiples capes; d'altra banda, les xarxes del món real se'ns presenten com xarxes d'una sola capa.
El estudio de las redes del mundo real han empujado hacia la comprensión de sistemas complejos en una amplia gama de campos como la biología molecular y celular, la anatomía, la neurociencia, la ecología, la economía y la sociología . Sin embargo, el conocimiento disponible de muchos sistemas reales aún es limitado, por esta razón el poder predictivo de la ciencia en redes se debe mejorar para disminuir la brecha entre conocimiento y información. Para abordar este tema usamos la familia de 'Stochastic Block Modelos' (SBM), una familia de modelos generativos que está ganando gran interés recientemente debido a su adaptabilidad a cualquier tipo de red. El objetivo de esta tesis es el desarrollo de nuevas metodologías de inferencia basadas en SBM que perfeccionarán nuestra comprensión de las redes complejas. En primer lugar, investigamos en qué medida hacer un muestreo sobre modelos puede mejorar significativamente la capacidad de predicción a considerar un único conjunto óptimo de parámetros. Seguidamente, aplicamos el método mas predictivo en una red real particular: una red basada en las interacciones/suturas entre los huesos del cráneo humano en recién nacidos. Concretamente, descubrimos que las suturas cerradas a causa de una enfermedad patológica en recién nacidos son menos probables, desde un punto de vista morfológico, que las suturas cerradas bajo un desarrollo normal. Concretamente, descubrimos que las suturas cerradas a causa de una enfermedad patológica en recién nacidos son menos probables, desde un punto de vista morfológico, que las suturas cerradas bajo un desarrollo normal. Recientes investigaciones en las redes multicapa concluye que el comportamiento de las redes en una sola capa son diferentes a las de múltiples capas; por otra parte, las redes del mundo real se nos presentan como redes con una sola capa. La parte final de la tesis está dedicada a diseñar un nuevo enfoque en el que dos SBM separados describen simultáneamente una red dada que consta de una sola capa, observamos que esta metodología predice mejor que la metodología de un SBM solo.
The study of real-world networks have pushed towards to the understanding of complex systems in a wide range of fields as molecular and cell biology, anatomy, neuroscience, ecology, economics and sociology. However, the available knowledge from most systems is still limited, hence network science predictive power should be enhanced to diminish the gap between knowledge and information. To address this topic we handle with the family of Stochastic Block Models (SBMs), a family of generative models that are gaining high interest recently due to its adaptability to any kind of network structure. The goal of this thesis is to develop novel SBM based inference approaches that will improve our understanding of complex networks. First, we investigate to what extent sampling over models significatively improves the predictive power than considering an optimal set of parameters alone. Once we know which model is capable to describe better a given network, we apply such method in a particular real world network case: a network based on the interactions/sutures between bones in newborn skulls. Notably, we discovered that sutures fused due to a pathological disease in human newborn were less likely, from a morphological point of view, that those sutures that fused under a normal development. Recent research on multilayer networks has concluded that the behavior of single-layered networks are different from those of multilayer ones; notwhithstanding, real world networks are presented to us as single-layered networks. The last part of the thesis is devoted to design a novel approach where two separate SBMs simultaneously describe a given single-layered network. We importantly find that it predicts better missing/spurious links that the single SBM approach.

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Böhm, Julian. "Phénomènes de transport originaux dans des expériences micro-ondes via la mise en forme spatiale et spectrale." Thesis, Université Côte d'Azur (ComUE), 2016. http://www.theses.fr/2016AZUR4048/document.

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Le transport des ondes joue un rôle majeur dans les systèmes de communication comme le Wifi ou les fibres optiques. Les principaux problèmes rencontrés dans ces systèmes concernent la protection contre les intrusions, la consommation d’énergie et le filtrage modal. Nous proposons différentes expériences micro-ondes mettant toutes en œuvre une mise en forme des ondes, pour traiter ces problèmes. Dans une cavité micro-ondes, des états de diffusion particuliers sont générés en s’appuyant uniquement sur des mesures de transmission et sur le formalisme du temps de retard de Wigner-Smith. Ces états sont capables d’éviter une région déterminée de la cavité, de se concentrer sur un point particulier, ou de suivre une trajectoire d’une particule classique. Le filtrage de mode est mis en œuvre dans un guide d’ondes aux frontières ondulées et en présence de pertes dépendant de la position. Le profil du guide est choisi de façon à ce que les deux modes de Bloch qui se propagent encerclent un point exceptionnel. Cette trajectoire s’accompagne d’une transition non-adiabatique entre les deux modes et d'un filtrage asymétrique de ces modes. La thèse présente également des travaux liés à la problématique des algorithmes de « recherche quantique », notamment l’algorithme de Grover. Cette recherche est mise en œuvre dans un réseau en nid d’abeilles de résonateurs micro-ondes couplés, bien décrits par un modèle de liaisons fortes (le système constitue un analogue micro-ondes du graphène). Une expérience de preuve de principe propose la recherche de deux résonateurs distincts reliés au réseau. La loi d’échelle attendue pour cet algorithme est expérimentalement obtenue dans une chaîne linéaire
Transport of waves plays an important role in modern communication systems like Wi-Fi or optical fibres. Typical problems in such systems concern security against possible intruders, energy consumption, time efficiency and the possibility of mode filtering. Microwave experiments are suited to study this kind of problems, because they offer a good control of the experimental parameters. Thus we can implement the method of wave shaping to investigate atypical transport phenomena, which address the mentioned problems. Wave front shaping solely based on the transmission together with the Wigner-Smith time delay formalism allows me to establish special scattering states in situ. These scattering states avoid a pre-selected region, focus on a specific spot or follow trajectories of classical particles, so called particle-like scattering states. Mode filtering is induced inside a waveguide with wavy boundaries and position dependent loss. The boundary profiles are chosen in such a way that the two propagating modes describe an encircling of an exceptional point in the Bloch picture. The asymmetric mode filtering is found due to the appearing non-adiabatic transitions. Another part of my work deals with Grover’s quantum search. I put such a search into practice in a two-dimensional graphene-lattice using coupled resonators, which form a tight-binding analogue. In this proof of principle experiment we search for different resonators attached to the graphene-lattice. Furthermore, the scaling behaviour of the quantum search is quantified for a linear chain of resonators

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Tabouy, Timothée. "Impact de l’échantillonnage sur l’inférence de structures dans les réseaux : application aux réseaux d’échanges de graines et à l’écologie." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS289/document.

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Dans cette thèse nous nous intéressons à l’étude du modèle à bloc stochastique (SBM) en présence de données manquantes. Nous proposons une classification des données manquantes en deux catégories Missing At Random et Not Missing At Random pour les modèles à variables latentes suivant le modèle décrit par D. Rubin. De plus, nous nous sommes attachés à décrire plusieurs stratégies d’échantillonnages de réseau et leurs lois. L’inférence des modèles de SBM avec données manquantes est faite par l’intermédiaire d’une adaptation de l’algorithme EM : l’EM avec approximation variationnelle. L’identifiabilité de plusieurs des SBM avec données manquantes a pu être démontrée ainsi que la consistance et la normalité asymptotique des estimateurs du maximum de vraisemblance et des estimateurs avec approximation variationnelle dans le cas où chaque dyade (paire de nœuds) est échantillonnée indépendamment et avec même probabilité. Nous nous sommes aussi intéressés aux modèles de SBM avec covariables, à leurs inférence en présence de données manquantes et comment procéder quand les covariables ne sont pas disponibles pour conduire l’inférence. Finalement, toutes nos méthodes ont été implémenté dans un package R disponible sur le CRAN. Une documentation complète sur l’utilisation de ce package a été écrite en complément
In this thesis we are interested in studying the stochastic block model (SBM) in the presence of missing data. We propose a classification of missing data into two categories Missing At Random and Not Missing At Random for latent variable models according to the model described by D. Rubin. In addition, we have focused on describing several network sampling strategies and their distributions. The inference of SBMs with missing data is made through an adaptation of the EM algorithm : the EM with variational approximation. The identifiability of several of the SBM models with missing data has been demonstrated as well as the consistency and asymptotic normality of the maximum likelihood estimators and variational approximation estimators in the case where each dyad (pair of nodes) is sampled independently and with equal probability. We also looked at SBMs with covariates, their inference in the presence of missing data and how to proceed when covariates are not available to conduct the inference. Finally, all our methods were implemented in an R package available on the CRAN. A complete documentation on the use of this package has been written in addition

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24

Zhang, Xusheng. "Mesoscopic models of block copolymer rheology." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=96823.

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We develop a mesoscopic theoretical framework to study viscoelastic response of block copolymers in the vicinity of their order-disorder transition point. We use it to study orientation selection of lamellar phases of diblock copolymers under oscillatory shears. We examine the effect of hydrodynamics on the relaxation of lamellar phases, and include anisotropic viscous stresses that follow from the uniaxial nature of the phase. We also introduce network viscoelastic effects that model chain entanglements, also made consistent with the symmetry of the phase. A numerical algorithm has been developed to solve the governing equations, which has been implemented on a parallel computer architecture. Simple cases involving the relaxation of small transverse perturbations, or viscoelasticity arising from diffusive relaxation of the order parameter have been investigated, and used to validate the numerical code. We also address the issue of spontaneous orientation selection from an initially disordered state due to an imposed oscillatory shear. In the absence of hydrodynamic coupling, we observe that the so called parallel orientation is selected for small shear frequency and amplitude, crossing over to a perpendicular orientation at higher shear frequencies and amplitudes. Hydrodynamic effects are seen to shift this crossover region. We have also examined the effect of network entanglement at finite frequencies. We find that network entanglement can lead to faster alignment, and that anisotropic network stresses can significantly influence the orientation selection process.
Nous developpons un cadre theorique propre a l'echelle me oscopique dans le but d'etudier la reponse viscoelastique des blocs de copolymeres pres du point de transition entre leur etat ordonne et desordonne. Nous utilisons cette theorie pour e tudier la selection de l'orientation des phases de lamelles des blocs de copolymeres subissant des cisaillements oscillatoires. Nous examinons les effets hydrodynamiques de la relaxation des phases lamellaires et nous incluons les stress visqueux anisotropes, dues a la nature uniaxiale des phases. Nous introduisons aussi les effets viscoelastique relatifs aux r eseaux modelisant l'enchevetrement des chaines dans une approche consistante avec la symetrie des phases. Un algorithme nume rique sous implementation parallele a ete developpe pour resoudre les equations relatives a cette etude. Des cas simples impliquant la relaxation diffuse du parametre relatif a l'ordre ont ete examines et utilises pour verifier le code numerique. Nous adressons aussi la question de la selection de l'orientation spontane d'un etat initialement desordonne due a un cisaillement oscillatoire impose au systeme. Dans l'absence d'interaction hydrodynamique, nous observons que l'orientation denomme e parallele est selectionnee pour des petites frequences et amplitudes de cisaillement mais adopte une orientation perpendiculaire pour de grandes frequences et amplitudes de cisaillement. Les effets hydrodynamiques changent la region de transition. Nous avons aussi examin e l'effet d'enchevetrement du reseau pour des frequences finies. Nous trouvons que l'enchevetrement du reseau mene a un alignement plus rapide et que les stress des reseaux anisotropes peuvent influencer de maniere significative le processus de se lection d'orientation.

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Mekkaoui, Imen. "Analyse numérique des équations de Bloch-Torrey." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI120/document.

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L’imagerie par résonance magnétique de diffusion (IRMd) est une technique non-invasive permettant d’accéder à l'information structurelle des tissus biologiques à travers l’étude du mouvement de diffusion des molécules d’eau dans les tissus. Ses applications sont nombreuses en neurologie pour le diagnostic de certaines anomalies cérébrales. Cependant, en raison du mouvement cardiaque, l’utilisation de cette technique pour accéder à l’architecture du cœur in vivo représente un grand défi. Le mouvement cardiaque a été identifié comme une des sources majeures de perte du signal mesuré en IRM de diffusion. A cause de la sensibilité au mouvement, il est difficile d’évaluer dans quelle mesure les caractéristiques de diffusion obtenues à partir de l’IRM de diffusion reflètent les propriétés réelles des tissus cardiaques. Dans ce cadre, la modélisation et la simulation numérique du signal d’IRM de diffusion offrent une approche alternative pour aborder le problème. L’objectif de cette thèse est d’étudier numériquement l’influence du mouvement cardiaque sur les images de diffusion et de s’intéresser à la question d’atténuation de l’effet du mouvement cardiaque sur le signal d’IRM de diffusion. Le premier chapitre est consacré à l’introduction du principe physique de l'imagerie par résonance magnétique(IRM). Le deuxième chapitre présente le principe de l’IRM de diffusion et résume l’état de l’art des différents modèles proposés dans la littérature pour modéliser le signal d’IRM de diffusion. Dans le troisième chapitre un modèle modifié de l’équation de Bloch-Torrey dans un domaine qui se déforme au cours du temps est introduit et étudié. Ce modèle représente une généralisation de l’équation de Bloch-Torrey utilisée dans la modélisation du signal d’IRM de diffusion dans le cas sans mouvement. Dans le quatrième chapitre, l’influence du mouvement cardiaque sur le signal d’IRM de diffusion est étudiée numériquement en utilisant le modèle de Bloch-Torrey modifié et un champ de mouvement analytique imitant une déformation réaliste du cœur. L’étude numérique présentée, permet de quantifier l’effet du mouvement sur la mesure de diffusion en fonction du type de la séquence de codage de diffusion utilisée, de classer ces séquences en terme de sensibilité au mouvement cardiaque et d’identifier une fenêtre temporelle par rapport au cycle cardiaque où l’influence du mouvement est réduite. Enfin, dans le cinquième chapitre, une méthode de correction de mouvement est présentée afin de minimiser l’effet du mouvement cardiaque sur les images de diffusion. Cette méthode s’appuie sur un développement singulier du modèle de Bloch-Torrey modifié pour obtenir un modèle asymptotique qui permet de résoudre le problème inverse de récupération puis correction de la diffusion influencée par le mouvement cardiaque
Diffusion magnetic resonance imaging (dMRI) is a non-invasive technique allowing access to the structural information of the biological tissues through the study of the diffusion motion of water molecules in tissues. Its applications are numerous in neurology, especially for the diagnosis of certain brain abnormalities, and for the study of the human cerebral white matter. However, due to the cardiac motion, the use of this technique to study the architecture of the in vivo human heart represents a great challenge. Cardiac motion has been identified as a major source of signal loss. Because of the sensitivity to motion, it is difficult to assess to what extent the diffusion characteristics obtained from diffusion MRI reflect the real properties of the cardiac tissue. In this context, modelling and numerical simulation of the diffusion MRI signal offer an alternative approach to address the problem. The objective of this thesis is to study numerically the influence of cardiac motion on the diffusion images and to focus on the issue of attenuation of the cardiac motion effect on the diffusion MRI signal. The first chapter of this thesis is devoted to the introduction of the physical principle of nuclear magnetic resonance (NMR) and image reconstruction techniques in MRI. The second chapter presents the principle of diffusion MRI and summarizes the state of the art of the various models proposed in the litera- ture to model the diffusion MRI signal. In the third chapter a modified model of the Bloch-Torrey equation in a domain that deforms over time is introduced and studied. This model represents a generalization of the Bloch-Torrey equation used to model the diffusion MRI signal in the case of static organs. In the fourth chapter, the influence of cardiac motion on the diffusion MRI signal is investigated numerically by using the modified Bloch-Torrey equation and an analytical motion model mimicking a realistic deformation of the heart. The numerical study reported here, can quantify the effect of motion on the diffusion measurement depending on the type of the diffusion coding sequence. The results obtained allow us to classify the diffusion encoding sequences in terms of sensitivity to the cardiac motion and identify for each sequence a temporal window in the cardiac cycle in which the influence of motion is reduced. Finally, in the fifth chapter, a motion correction method is presented to minimize the effect of cardiac motion on the diffusion images. This method is based on a singular development of the modified Bloch-Torrey model in order to obtain an asymptotic model of ordinary differential equation that gives a relationship between the true diffusion and the diffusion reconstructed in the presence of motion. This relationship is then used to solve the inverse problem of recovery and correction of the diffusion influenced by the cardiac motion

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26

Qahur, Al Mahri Hassan Musallam Ahmed. "Analysis of selected block cipher modes for authenticated encryption." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/119361/1/Hassan%20Musallam%20Ahmed_Qahur%20Al%20Mahri_Thesis.pdf.

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Information assets stored or transmitted electronically require protection from unauthorised disclosure or modification. Authenticated encryption provides both confidentiality and integrity assurance services. This research examines the security of four authenticated encryption block cipher modes submitted to the recent cryptographic competition CAESAR: ++AE, OTR, XEX/XE and AEZ. Flaws in these designs were identified and forgery attacks exploiting these flaws were proposed. Certain modes were shown to be vulnerable to fault attacks. This work contributes to both the CAESAR evaluation process and the development of future ciphers. Finally, an online authenticated encryption block cipher mode resilient to side channel attacks was proposed.

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27

Healy, Timothy M. "Multi-block and overset-block domain decomposition techniques for cardiovascular flow simulation." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/15622.

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Wang, Baolin. "A block-spring model for jointed rocks." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/7521.

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A numerical method called the Block-Spring Model for analyzing heavily jointed rocks has been developed from first principles. The model simulates the jointed rock mass by an assemblage of rigid blocks interacted through contacts. The contact forces between blocks are determined in terms of the relative displacements between the blocks. By introducing the contact forces and the boundary conditions into the equilibrium equations of the blocks, a wet of stiffness equations are obtained in which the unknown variables are the displacements of the blocks. The displacements of the blocks can therefore be determined by solving the stiffness equations. The contact forces between blocks are calculated after the displacements are obtained. The discontinuities of the jointed rock mass are automatically modelled as the interfaces between the blocks. The deformation behaviour of the joints are governed by a non-tension rule in normal direction. Patton's bi-linear criterion is used to describe the shear failure behaviour of the rock joints. An interaction procedure is applied to describe the progressive failure along the joints. The positions of the blocks are continuously updated based on the displacements obtained after each step of iteration. Therefore, the large scale displacements of the blocks are modelled incrementally with the iteration procedure. During evolution of the block movement, the blocks are allowed to rearrange. The block system may become statically stable or unstable after undergoing large scale displacements. The proposed model therefore identifies unstable blocks by considering the rearrangement of the blocks. A numerical procedure for simulating the rock bolts has been proposed. The rockbolts are modelled by a series of one dimensional elements interacted with the rock blocks through nodal points. The effect of the rockbolts on the rock masses is evaluated by relating the bolt forces to the displacements of the blocks and by introducing the bolt forces into the equilibrium equations of the blocks. The model can be used to analyze both the end-anchored rock bolts and the fully grouted rock bolts either pre-tensioned or untensioned. A procedure for modelling the groundwater pressure has also been developed. It has been considered that groundwater may affect the stability of the jointed rock masses by reducing the effective stresses between the rock blocks. In simulating the groundwater effect on the rock masses, the water pressures imposed on the surfaces of the rock blocks are calculated. These water pressures are introduced into the equilibrium equations of the blocks. The contact forces between blocks determined after solving the equations are the effective forces across the rock joints. A FORTRAN program, BLOSMER, has been entirely written by the Author based on the procedures of the Block-Spring Model developed during this study. The program can be used to analyze the stability of the surrounding rock masses of either open pits or underground excavations at the shallow depth. It has been applied to several examples to demonstrate the capability of the proposed model. Two case histories have been analyzed in detail with the Block-Spring Model. The numerical results have been compared with the field instrumentation data. Good agreement has been observed between the results from the back analyses with the proposed model and the field measurements in both cases. The proposed model can be applied for analysis of rock excavations by practicing civil and mining engineers.

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29

Karim, Ali Abdul Jabbar, Johan Lessner, and Mehrdad Moridnejad. "Model calibration of a wooden building block." Thesis, Linnéuniversitetet, Institutionen för bygg- och energiteknik (BE), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-26271.

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Constructing multi floor buildings by light weight material have increased recently. There are many advantages of using light weight material, such as wood, for the environment. However, one of the deficiencies of lightweight material is the acoustic performance. Transmission of sound and vibration through floors in multi floor buildings in wood is a drawback to be considered. There are many studies that have addressed this issue. It is most common to make a finite element models well as experiments in laboratory. In these studies the material properties in the FE model are probably often adjusted to correlate to the laboratory experiments, since there is a large spread in material properties found in literature. This thesis however tries to elaborate on the actual material properties of the included wooden elements. Dynamic testing is done to determine the spread (here spread means gap between material properties) in material properties of wooden elements. The materials tested are chipboards and two types of wooden beams. The examined beams are both normal wooden beams and laminated veneer lumber beams. When the dynamic behaviour is known for the wooden parts, they are assembled to two small floor systems. The floor systems consist of four beams and one wooden board. The assembly is dynamically tested in laboratory and in FE software. The FE model used the known material properties for each individual building part. The results from the FE model correlate well with the laboratory tests. This shows that when material properties are known a FE model can predict the real behaviour. However, the examined material properties show a large spread from beam to beam, etc and a better knowledge about the material properties of used wooden parts is needed.
Att bygga flervåningshus med lätta byggmaterial har blivit allt vanligare. Det finns många fördelar med att använda lätta material, såsom trä. En av fördelarna är att det är skonsamt för miljön. Emellertid är en av bristerna i lättviktsmaterial den akustiska prestandan. Överföring av ljud och vibrationer genom golv i flervåningshus i trä är en nackdel att överväga. Det finns flera studier som har behandlat denna fråga. Ofta görs finita element modeller samt tester i laboratorium. I dessa studier justerar man materialegenskaperna i FE-modellen för att korrelera mot laboratorieexperiment. Detta eftersom det finns en stor spridning i materialegenskaperna för trä i litteraturen. Med detta examensarbete, undersöks de faktiska materialegenskaperna hos träelementen genom försök. Dynamiska tester utförs för att bestämma spridningen i materialegenskaper. De testade materialen är spånskivor och två typer av träbalkar. De undersökta balkarna är både normala träreglar och laminerade faner balkar. När det dynamiska beteendet är känt för trädelarna, monteras de ihop till två små golvsystem. Golvsystemen består av fyra balkar och en träskiva. Den assemblerade modellen testas både dynamiskt i ett praktiskt försök och i ett FE program. I FEmodellen används de tidigare framtagna faktiska materialegenskaper för varje ingående enskild byggnadsdel. Resultaten från FE-modellen korrelerar väl med de praktiska experimenten. Med detta examensarbete visas att när materialegenskaperna är kända kan FE-modellen förutsäga det verkliga beteendet. De undersökta materialegenskaperna visar dock en stor spridning från balk till balk, etc. och mer kunskap om materialegenskaper hos trädelar behövs.

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30

Sharp, Melissa Ann. "Using block copolymers to solubilise model adjuvants." Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440053.

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Keenan, David Wayne 1955. "BLOCK PLAN CONSTRUCTION FROM A DELTAHEDRON-BASED ADJACENCY GRAPH." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/292025.

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32

Bezerra, Victor Hugo Ferreira. "Estudo de colisÃes de paredes de Bloch e localizaÃÃo de modos ferminÃnicos." Universidade Federal do CearÃ, 2005. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=2918.

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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
Neste trabalho estudamos numericamente o processo de colisÃo de paredes de domÃnio em um modelo de dois campos escalares acoplados que geram paredes com estrutura interna, as chamadas paredes de Bloch. Percebemos que os objetos resultantes da colisÃo pertencem a um setor topolÃgico diferente dos setores escolhidos no inÃcio do processo, ou seja, o sistema passou de um setor do tipo AA para um setor do tipo AB. Para a velocidade inicial acima de 0, 57..., percebemos a aniquilaÃÃo dos objetos. As ondas solitÃrias refletidas possuem aproximadamente metade da energia inicial. AlÃm do decaimento do setor AA para um tipo AB, verificou-se que parte da energia Ã convertida numa estrutura coerente oscilante no centro da rede, com aproximadamente metade da energia inicial do sistema. Estudamos ainda estados ligados a partir de duas paredes inicialmente prÃximas com velocidade nula. A estrutura formada perde energia em forma de radiaÃÃo. Entretanto, a perda de energia se dÃ lentamente, assim como os breathers do modelo Ã4. Estudou-se ainda a presenÃa de fÃrmions acoplados nas paredes de domÃnio tipo Bloch. O acoplamento entre o campo fermiÃnico e os campos Ã e Ã Ã do tipo Yukawa. Mostrou-se que o modo zero fermiÃnico Ã localizado em x = 0 no campo x, ou seja, o campo fermiÃnico Ã localizado dentro da parede. A massa fermiÃnica no setor de vÃcuo Ã a mesma para o modelo Ã4, uma vez que a massa do campo Ã no setor de vÃcuo Ã nula.
In this work we numerically study the collision process of domain-walls in a system with two coupled scalar fields, which generates a wall with internal structures, the so called Bloch Walls. If the initial velocity is less than 0, 57... occurs inelastic scattering and part of the energy is lost as radiation. We realize that the objects resulting from the collision belong to a topological sector which is different from those chosen in the beginning of the process. In other words, the system transit from a sector AA-like to a sector AB-like one. The reflected solitary waves have approximately half of the initial energy. Besides of the decay of the sector AA to AB one, we note that part of the energy is converted into a coherent structure which oscillates in the center of the net, with approximately half of the initial energy of the system. We have studied also bound states of the system in the case of two walls which initially are close and with null velocity. The resulting structure lose energy as radiation. However, the energy loss is gradual, like in the case of the breathers of the Ã4 model. On the other hand, we have studied the coupling of fermions to the Bloch domainwall. The coupling between the fermionic field and two different scalar fields named Ã and Ã it is a Yukawa-type coupling. We have showed that the fermionic zero mode is localized at x = 0 in the scalar field Ã, which means that the ferminonic field is localized inside wall. The fermionic mass in the vacuum sector is the same obtained for the Ã4 model, since that the mass of the scalar field Ã in the vacuum sector is zero.

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Bezerra, Victor Hugo Ferreira. "Estudo de colisões de paredes de Bloch e localização de modos ferminônicos." reponame:Repositório Institucional da UFC, 2005. http://www.repositorio.ufc.br/handle/riufc/12924.

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BEZERRA, Victor Hugo Ferreira. Estudo de colisões de paredes de Bloch e localização de modos ferminônicos. 2005. 90 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2005.
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In this work we numerically study the collision process of domain-walls in a system with two coupled scalar fields, which generates a wall with internal structures, the so called Bloch Walls. If the initial velocity is less than 0, 57... occurs inelastic scattering and part of the energy is lost as radiation. We realize that the objects resulting from the collision belong to a topological sector which is different from those chosen in the beginning of the process. In other words, the system transit from a sector AA-like to a sector AB-like one. The reflected solitary waves have approximately half of the initial energy. Besides of the decay of the sector AA to AB one, we note that part of the energy is converted into a coherent structure which oscillates in the center of the net, with approximately half of the initial energy of the system. We have studied also bound states of the system in the case of two walls which initially are close and with null velocity. The resulting structure lose energy as radiation. However, the energy loss is gradual, like in the case of the breathers of the Á4 model. On the other hand, we have studied the coupling of fermions to the Bloch domainwall. The coupling between the fermionic field and two different scalar fields named Á and Â it is a Yukawa-type coupling. We have showed that the fermionic zero mode is localized at x = 0 in the scalar field Â, which means that the ferminonic field is localized inside wall. The fermionic mass in the vacuum sector is the same obtained for the Á4 model, since that the mass of the scalar field Â in the vacuum sector is zero.
Neste trabalho estudamos numericamente o processo de colisão de paredes de domínio em um modelo de dois campos escalares acoplados que geram paredes com estrutura interna, as chamadas paredes de Bloch. Percebemos que os objetos resultantes da colisão pertencem a um setor topológico diferente dos setores escolhidos no início do processo, ou seja, o sistema passou de um setor do tipo AA para um setor do tipo AB. Para a velocidade inicial acima de 0, 57..., percebemos a aniquilação dos objetos. As ondas solitárias refletidas possuem aproximadamente metade da energia inicial. Além do decaimento do setor AA para um tipo AB, verificou-se que parte da energia é convertida numa estrutura coerente oscilante no centro da rede, com aproximadamente metade da energia inicial do sistema. Estudamos ainda estados ligados a partir de duas paredes inicialmente próximas com velocidade nula. A estrutura formada perde energia em forma de radiação. Entretanto, a perda de energia se dá lentamente, assim como os breathers do modelo Á4. Estudou-se ainda a presença de férmions acoplados nas paredes de domínio tipo Bloch. O acoplamento entre o campo fermiônico e os campos Á e Â é do tipo Yukawa. Mostrou-se que o modo zero fermiônico é localizado em x = 0 no campo x, ou seja, o campo fermiônico é localizado dentro da parede. A massa fermiônica no setor de vácuo é a mesma para o modelo Á4, uma vez que a massa do campo Â no setor de vácuo é nula.

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34

Paltrinieri, Federico. "Modeling temporal networks with dynamic stochastic block models." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18805/.

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Osservando il recente interesse per le reti dinamiche temporali e l'ampio numero di campi di applicazione, questa tesi ha due principali propositi: primo, di analizzare alcuni modelli teorici di reti temporali, specialmente lo stochastic blockmodel dinamico, al fine di descrivere la dinamica di sistemi reali e fare previsioni. Il secondo proposito della tesi è quello di creare due nuovi modelli teorici, basati sulla teoria dei processi autoregressivi, dai quali inferire nuovi parametri dalle reti temporali, come la matrice di evoluzione di stato e una migliore stima della varianza del rumore del processo di evoluzione temporale. Infine, tutti i modelli sono testati su un data set interbancario: questi rivelano la presenza di un evento atteso che divide la rete temporale in due periodi distinti con differenti configurazioni e parametri.

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35

Kendall, Toby. "Theoretical models of trade blocs and integrated markets." Thesis, University of Warwick, 2000. http://wrap.warwick.ac.uk/4014/.

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This thesis consists of four main chapters, together with a general introduction and conclusion. The thesis examines, both separately and together, the formation of trade blocs and global market integration. All the models use a partial equilibrium framework, with firms competing as Cournot oligopolists. Chapter 2 presents two models of trade bloc formation under segmented markets. In the first model, with common constant marginal costs, global free trade is optimal for all countries when there are no more than four countries, but with five or more countries there is an incentive to form a trade bloc containing most countries, but excluding at least one. The second model introduces a cost function where a firm's marginal cost is lower when it is located in a larger trade bloc, with little effect on the results. Chapter 3 analyses the formation of trade blocs between countries with different market sizes under segmented markets. The formation of a two country customs union or free trade area will always raise the smaller country's welfare, while the larger country will usually lose from a free trade area, and sometimes from a customs union. Chapter 4, which is joint work with David R. Collie and Morten Hviid, presents a model of strategic trade policy under integrated markets, under complete and incomplete information. In the former case, a low cost country will give an export subsidy which is fully countervailed by the high cost country's import tariff. In the simultaneous signalling game, each country's expected welfare is higher than under free trade. Chapter 5 considers models of trade bloc formation under integrated markets. With common constant costs, there is no incentive for blocs to form. When costs are decreasing in membership of a bloc, either global free trade is optimal or countries would prefer to belong to the smaller of two blocs.

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Fletcher, William P. Jr. "The Development of A Block Scheduling Evaluation Model." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/29833.

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The purpose of the study was to develop and test a block scheduling evaluation model. Conceptual development of the model was based on a review of the literature which targeted the components of the school program most consistently identified with scheduling type: instruction, school climate, student outcomes, and operating efficiency. The model included an interview with the principal, analysis of documents, survey of teachers, and survey of students. The model was pilot tested in three high schools in Western Virginia. The principals of the three pilot schools and the researcher evaluated the model according to preestablished evaluation criteria. The evaluation identified several improvements including: instrumentation refinements aimed at providing more detailed information on teacher concerns about preparation and planning on the block schedule; data analysis refinements centering on technology; inclusion of other indicators such as standardized test scores and cost analysis; and, expansion of data collection techniques centering on systematic observation over an extended period of time.
Ed. D.

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37

Qin, Shanlin. "Fractional order models: Numerical simulation and application to medical imaging." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/115108/1/115108_9066888_shanlin_qin_thesis.pdf.

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This thesis is primarily concerned with developing new models and numerical methods based on the fractional generalisation of the Bloch and Bloch-Torrey equations to account for anomalous MRI signal attenuation. The two main contributions of the research are to investigate the anomalous evolution of MRI signals via the fractionalised Bloch equations, and to develop new effective numerical methods with supporting analysis to solve the time-space fractional Bloch-Torrey equations.

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Norton, Kevin M. "Parameter optimization of seismic isolator models using recursive block-by-block nonlinear transient structural synthesis." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02sep%5FNorton.pdf.

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39

Samoylova, M. "STABILIZATION OF BLOCH OSCILLATIONS OF ULTRACOLD ATOMS IN A RING CAVITY." Doctoral thesis, Università degli Studi di Milano, 2015. http://hdl.handle.net/2434/274589.

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The work presented in this thesis is dedicated to studies of stabilization of Bloch oscillations of ultracold atoms in a one-dimensional vertical optical lattice under the influence of the gravitational force. The atoms simultaneously interact with both the lattice potential and a unidirectionally pumped optical ring cavity whose vertical arm is collinear with the optical lattice. In the proposed scheme, the atoms not only exchange photons between the optical lattice laser beams, but also collectively scatter light from the pump into the reverse cavity mode. The initial investigation of the system without the cavity allows understanding of the importance of the perfectly adiabatic atomic motion in the observation of stable Bloch oscillations and how easily the adiabaticity can be broken due to a very fast switch-on of the lattice or its amplitude and phase modulation. Under certain parameter regimes, adding the ring cavity to the system provides a surprisingly positive feedback on the atomic dynamics. It is found that, while acting back on the atoms, the cavity field establishes a mode-locking mechanism which assists adiabatic rapid passages between adjacent momentum states. Thus, the cavity-induced feedback mechanism enforces the adiabaticity of the process and reveals a regime where the Bloch oscillations are self-synchronized for long times. This stabilization technique is shown to steer the atoms to the lowest Bloch band preventing the problem of interband tunneling. A demonstration is also made of the ability of the system to stabilize the atomic Bloch oscillations against technical amplitude or phase noise and even suppress dephasing due to the atom-atom interactions. Furthermore, the response of the system to the atomic motion is generated in the form of perfectly detectable periodic bursts of light emitted into the counter-propagating cavity mode. Thus, the system offers a continuous and reliable non-destructive method to monitor the Bloch oscillations dynamics without perturbing their periodicity by detecting the scattered light transmitted through the cavity. All features studied in this work may be crucial for future improvements of the design of atomic gravimeters based on recording Bloch oscillations.

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Bagheri, Mehdi. "Model uncertainty of design tools to analyze block stability." Licentiate thesis, KTH, Civil and Architectural Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10580.

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Block failure is one of the most common failure modes in tunnels. Design tools have some simplifications and, therefore, they also have some model uncertainties. The purpose of this licentiate thesis is to assess the model uncertainty for different design tools in order to estimate block stability.

Different approaches of kinematic limit equilibrium (KLE) including conventional KLE, limited joint length, limited joint length and stress field consideration and probabilistic KLE were compared to that of DFN-DEM. In this approach, the results of the calibrated DFN-DEM with field mapping were considered to be of true value. The results show that the conventional KLE is overdesign due to it’s over simplification. By considering fracture length and stress field, the volume of predicted unstable blocks is reduced. The probabilistic approach of KLE by considering finite joint length and stress field predicts the volume of unstable blocks to be lower than DFN-DEM approach. Therefore there is a great model uncertainty of our standard design tools for block stability analysis.

The assumption made in this study is that the results from DEM were considered to have a true value; the results from analytical solution based on joint relaxation process were compared to those of DEM in a different condition of depth, K0, apical and friction angle, Kn and Ks value, and ratio of Kn/Ks. The comparison shows that for shallow depth with K0 less than 1, analytical solution leads to an overestimation of block stability. The analytical solution predicts that the block is stable, while the analyses from numerical solution show the block is unstable. The analyses show that by increasing K0, accuracy of analytical solution also increases. Moreover, for the cases with close value of friction angle to semi-apical angle, the use of analytical solution is not recommended. As the ratio of Kn/Ks increases, the accuracy of analytical solution decreases. Increasing the angle ratio (ratio between semi-apical angle to friction angle) is one source of increasing uncertainty in the model. The analytical solution is very uncertain in cases with a low value of K0, and a high value of stiffness ratio and angle ratio. On the other hand, the analytical solution is more certain in conditions with a high value of K0 and a low value of stiffness ratio and angle ratio. According to current information (K0, angle ratio, stiffness ratio), one can determine the value of model uncertainty by using the diagrams presented in Chapter 6 of the thesis. The analyses show that by having more information about the key parameters, the model uncertainty could be identified more precisely. However, having more information means spending more money, and this increase in cost must be compared to the cost of failure or delay in the project or overdesign.

Blockutfall är en av de vanligaste brottformerna i tunnlar. Dimensioneringsverktyg har förenklingar och därför har de viss modelosäkerhet. Syftet med licentiat avhandlingen är att bedöma modelosäkerhet för olika dimensioneringsverktyg för att uppskatta blockstabilitet.

I Olika metoder av KLE inkluderad konventional KLE, begränsad spricklängd och insitu spänning och sannolikhetsbasserad KLE är jämförda med DFN-DEM. I den här metoden kalibreras DFN-DEM med fältkartläggning som är betraktad som sanna värden. Resultat visar att konventionell KLE ger starkt konservative resultat. Genom att betrakta spricklängden och spänningsfältet, så minskar volymen på uppskattade instabila block. Den sannolikhetsbaserade metoden för KLE genom att betrakta finit spricklängd, och spänningsfältet förutser att volymen av de instabila blocken är mindre än de som bedöms med DFN-DEM metoden. Det finns mycket osäkerhet i vår standard dimensioneringsverktyg att uppskatta block stabilitet.

Antagande som gjorts i den studien är att resultatet från DEM är betraktade som sanna värden och resultaten från analytiska lösningar baserad på sprickavlastning är jämförda med resultatet från DEM. Jämförelse visar att för grunda djup och med K0 mindre än 1, den analytiska lösningen leder till en överestimering av blockstabiliteten. Den analytiska lösningen förutsäger att blocket är stabilt medan analys av den numeriska lösningen visar att blocket är instabilt. Analysen visar attgenom en ökning av K0 så ökar tillförlitligheten av den analytiska lösningen. Det visar sig att även att för fall med friktionsvinkel nära semitoppvinkeln så kan den analytiska lösningen inte rekommenderas. Vidare leder en ökning av förhållandet Kn/Ks till att tillförlitligheten av den analytiska lösningen minskar. En ökning av vinkelförhållandet mellan semitoppvinkeln och friktionsvinkeln är källa till en ökning av osäkerhet i modellen. En analytisk lösning är mer osäker i fall av lågt värde på K0 och högt värde på styvhetsförhållandet och vinkelnförhållandet. Å andra sidan, så är den analytiska lösningen mer säker i fall av högt värde på K0, och lågt värde på vinkel förhållandet och styvhetsförhållandet.

Vid given information (K0, styvhetsvärde och vinkel förhållande) kan man bestämma värdet på modellosäkerheten genom att använda diagrammen i avhandlingen. Analysen visar att vid ökad information om nyckelparametrarna, så kan modelosäkerheten identifieras mer exakt. Hur som helst så betyder mer tillgång till information att mer pengar måste satsas och denna kostnad måste gemföras med kostnader för blockinstabilitet eller överdesign.

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Enoiu, Eduard. "Model Checking-Based Software Testing for Function-Block Diagrams." Licentiate thesis, Mälardalens högskola, Inbyggda system, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-26003.

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Software testing becomes more complex, more time-consuming, and more expensive. The risk that software errors remain undetected and cause critical failures increases. Consequently, in safety-critical development, testing software is standardized and it requires an engineer to show that tests fully exercise, or cover, the logic of the software. This method often requires a trained engineer to perform manual test generation, is prone to human error, and is expensive or impractical to use frequently in production. To overcome these issues, software testing needs to be performed earlier in the development process, more frequently, and aided by automated tools. We devised an automated test generation tool called COMPLETETEST that avoids many of those problems. The method implemented in the tool and described in this thesis, works with software written in Function Block Diagram language, and can provide tests in just a few seconds. In addition, it does not rely on the expertise of a researcherspecialized in automated test generation and model checking. Although COMPLETETEST itself uses a model checker, a complex technique requiring a high level of expertise to generate tests, it provides a straightforward tabular interface to the intended users. In this way, its users do not need to learn the intricacies of using this approach such as how coverage criteria can be formalized and used by a model checker to automatically generate tests. If the technique can be demonstrated to work in production, it could detect and aid in the detection of errors in safety-critical software development, where conventional testing is not always applicable and efficient. We conducted studies based on industrial use-case scenarios from Bombardier Transportation AB, showing how the approach can be applied to generate tests in software systems used in the safety-critical domain. To evaluate the approach, it was applied on real-world programs. The results indicate that it is efficient in terms of time required to generate tests and scales well for most of the software. There are still issues to resolve before the technique can be applied to more complex software, but we are already working on ways to overcome them. In particular, we need to understand how its usage in practice can vary depending on human and software process factors.

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Ludkin, Matthew Robert. "The autoregressive stochastic block model with changes in structure." Thesis, Lancaster University, 2017. http://eprints.lancs.ac.uk/125642/.

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Network science has been a growing subject for the last three decades, with sta- tistical analysis of networks seing an explosion since the advent of online social networks. An important model within network analysis is the stochastic block model, which aims to partition the set of nodes of a network into groups which behave in a similar way. This thesis proposes Bayesian inference methods for problems related to the stochastic block model for network data. The presented research is formed of three parts. Firstly, two Markov chain Monte Carlo samplers are proposed to sample from the posterior distribution of the number of blocks, block memberships and edge-state parameters in the stochastic block model. These allow for non-binary and non-conjugate edge models, something not considered in the literature. Secondly, a dynamic extension to the stochastic block model is presented which includes autoregressive terms. This novel approach to dynamic network models allows the present state of an edge to influence future states, and is therefore named the autoregresssive stochastic block model. Furthermore, an algorithm to perform inference on changes in block membership is given. This problem has gained some attention in the literature, but not with autoregressive features to the edge-state distribution as presented in this thesis. Thirdly, an online procedure to detect changes in block membership in the au- toregresssive stochastic block model is presented. This allows networks to be monitored through time, drastically reducing the data storage requirements. On top of this, the network parameters can be estimated together with the block memberships. Finally, conclusions are drawn from the above contributions in the context of the network analysis literature and future directions for research are identified.

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Elmahalawy, Yasser Reda Ahmed Abdelhamid. "Ricci Time in Lemaître-Tolman Model and Block Universe." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13373.

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Includes bibliographical references.
It is common to think of our universe according to the "block universe" idea, which says that spacetime consists of many "stacked" 3-surfaces varied as a function of some kind of proper time Ƭ. Standard ideas do not distinguish past and future, but Ellis' "evolving block universe" tries to make a fundamental distinction. One proposal for this proper time is the proper time measured along the timelike Ricci eigenlines, starting from the big bang. The main idea of this work is to investigate the shape of the {Ƭ=constant} surfaces relative to the the null surfaces, and determine what makes these surfaces timelike or spacelike. We use the Lemaître-Tolman metric as our inhomogeneous spacetime model, and we find the necessary and sufficient conditions for these {Ƭ=constant} surfaces to be spacelike or timelike. Furthermore, we indicate whether or not timelike surfaces appear inside black holes and other strong gravity domains, by determining the location of the timelike regions relative to the apparent horizon. Based on this idea, we find that the regions where these surfaces become timelike are often close to the apparent horizons, but always outside them, and in particular timelike regions occur outside black holes. They are always spacelike near the big bang, and at late times (near the crunch or the extreme far future), they are only timelike under special circumstances.

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Cheng, Xiang. "TFTs circuit simulation models and analogue building block designs." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/271853.

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Building functional thin-film-transistor (TFT) circuits is crucial for applications such as wearable, implantable and transparent electronics. Therefore, developing a compact model of an emerging semiconductor material for accurate circuit simulation is the most fundamental requirement for circuit design. Further, unique analogue building blocks are needed due to the specific properties and non-idealities of TFTs. This dissertation reviews the major developments in thin-film transistor (TFT) modelling for the computer-aided design (CAD) and simulation of circuits and systems. Following the progress in recent years on oxide TFTs, we have successfully developed a Verilog-AMS model called the CAMCAS model, which supports computer-aided circuit simulation of oxide-TFTs, with the potential to be extended to other types of TFT technology families. For analogue applications, an accurate small signal model for thin film transistors (TFTs) is presented taking into account non-idealities such as contact resistance, parasitic capacitance, and threshold voltage shift to exhibit higher accuracy in comparison with the adapted CMOS model. The model is used to extract the zeros and poles of the frequency response in analogue circuits. In particular, we consider the importance of device-circuit interactions (DCI) when designing thin film transistor circuits and systems and subsequently examine temperature- and process-induced variations and propose a way to evaluate the maximum achievable intrinsic performance of the TFT. This is aimed at determining when DCI becomes crucial for a specific application. Compensation methods are reviewed to show examples of how DCI is considered in the design of AMOLED displays. Based on these design considerations, analogue building blocks including voltage and current references and differential amplifier stages have been designed to expand the analogue library specifically for TFT circuit design. The $V_T$ shift problem has been compensated based on unique circuit structures. For a future generation of application, where ultra low power consumption is a critical requirement, we investigate the TFT’s subthreshold operation through examining several figures of merit including intrinsic gain ($A_i$), transconductance efficiency ($g_m/I_{DS}$) and cut-off frequency ($f_T$). Here, we consider design sensitivity for biasing circuitry and the impact of device variations on low power circuit behaviour.

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Robert, Valérie. "Classification croisée pour l'analyse de bases de données de grandes dimensions de pharmacovigilance." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS111/document.

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Cette thèse regroupe des contributions méthodologiques à l'analyse statistique des bases de données de pharmacovigilance. Les difficultés de modélisation de ces données résident dans le fait qu'elles produisent des matrices souvent creuses et de grandes dimensions. La première partie des travaux de cette thèse porte sur la classification croisée du tableau de contingence de pharmacovigilance à l’aide du modèle des blocs latents de Poisson normalisé. L'objectif de la classification est d'une part de fournir aux pharmacologues des zones intéressantes plus réduites à explorer de manière plus précise, et d'autre part de constituer une information a priori utilisable lors de l'analyse des données individuelles de pharmacovigilance. Dans ce cadre, nous détaillons une procédure d'estimation partiellement bayésienne des paramètres du modèle et des critères de sélection de modèles afin de choisir le modèle le plus adapté aux données étudiées. Les données étant de grandes dimensions, nous proposons également une procédure pour explorer de manière non exhaustive mais pertinente, l'espace des modèles en coclustering. Enfin, pour mesurer la performance des algorithmes, nous développons un indice de classification croisée calculable en pratique pour un nombre de classes élevé. Les développements de ces outils statistiques ne sont pas spécifiques à la pharmacovigilance et peuvent être utile à toute analyse en classification croisée. La seconde partie des travaux de cette thèse porte sur l'analyse statistique des données individuelles, plus nombreuses mais également plus riches en information. L'objectif est d'établir des classes d'individus selon leur profil médicamenteux et des sous-groupes d'effets et de médicaments possiblement en interaction, palliant ainsi le phénomène de coprescription et de masquage que peuvent présenter les méthodes existantes sur le tableau de contingence. De plus, l'interaction entre plusieurs effets indésirables y est prise en compte. Nous proposons alors le modèle des blocs latents multiple qui fournit une classification croisée simultanée des lignes et des colonnes de deux tableaux de données binaires en leur imposant le même classement en ligne. Nous discutons des hypothèses inhérentes à ce nouveau modèle et nous énonçons des conditions suffisantes de son identifiabilité. Ensuite, nous présentons une procédure d'estimation de ses paramètres et développons des critères de sélection de modèles associés. De plus, un modèle de simulation numérique des données individuelles de pharmacovigilance est proposé et permet de confronter les méthodes entre elles et d'étudier leurs limites. Enfin, la méthodologie proposée pour traiter les données individuelles de pharmacovigilance est explicitée et appliquée à un échantillon de la base française de pharmacovigilance entre 2002 et 2010
This thesis gathers methodological contributions to the statistical analysis of large datasets in pharmacovigilance. The pharmacovigilance datasets produce sparse and large matrices and these two characteritics are the main statistical challenges for modelling them. The first part of the thesis is dedicated to the coclustering of the pharmacovigilance contingency table thanks to the normalized Poisson latent block model. The objective is on the one hand, to provide pharmacologists with some interesting and reduced areas to explore more precisely. On the other hand, this coclustering remains a useful background information for dealing with individual database. Within this framework, a parameter estimation procedure for this model is detailed and objective model selection criteria are developed to choose the best fit model. Datasets are so large that we propose a procedure to explore the model space in coclustering, in a non exhaustive way but a relevant one. Additionnally, to assess the performances of the methods, a convenient coclustering index is developed to compare partitions with high numbers of clusters. The developments of these statistical tools are not specific to pharmacovigilance and can be used for any coclustering issue. The second part of the thesis is devoted to the statistical analysis of the large individual data, which are more numerous but also provides even more valuable information. The aim is to produce individual clusters according their drug profiles and subgroups of drugs and adverse effects with possible links, which overcomes the coprescription and masking phenomenons, common contingency table issues in pharmacovigilance. Moreover, the interaction between several adverse effects is taken into account. For this purpose, we propose a new model, the multiple latent block model which enables to cocluster two binary tables by imposing the same row ranking. Assertions inherent to the model are discussed and sufficient identifiability conditions for the model are presented. Then a parameter estimation algorithm is studied and objective model selection criteria are developed. Moreover, a numeric simulation model of the individual data is proposed to compare existing methods and study its limits. Finally, the proposed methodology to deal with individual pharmacovigilance data is presented and applied to a sample of the French pharmacovigilance database between 2002 and 2010

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46

Santos, Carla Maria Lopes da Silva Afonso dos. "Error Orthogonal Models: Structure, Operations and Inference." Doctoral thesis, Universidade da Beira Interior, 2012. http://hdl.handle.net/10400.6/1742.

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In this thesis, we develop the theory of Error-Orthogonal Models availing ourselves of the identity of these models and those with Commutative Orthogonal Block Structure. Thus our treatment will rest on the algebraic structure of the models. In our development we consider: the estimation of variance components; crossing and nesting of models; model joining, in which observations vectors obtained separately are jointly analyzed; step nesting which require much less observations than the corresponding usual models. To broaden our treatment we also consider L Extensions of Error-Orthogonal models. In this way, we may consider interesting cases such as models otherwise balanced with different numbers of replicates for the treatments. Last we include normality. We will be interested in obtaining sufficient statistics as well as conditions for them to be complete. We will carry out inference and consider orthogonal L extensions.
Nesta tese é desenvolvida a teoria dos modelos Error-orthogonal recorrendo à identidade entre estes modelos e os modelos com estrutura ortogonal de blocos comutativos. Desta forma, o tratamento apresentado irá assentar na estrutura algébrica dos modelos. No desenvolvimento considera-se: a estimação das componentes de variância; o cruzamento e aninhamento de modelos; a junção de modelos, na qual vectores das observações obtidos separadamente são analisados conjuntamente; aninhamento em escada, que requer muito menos observações do que os modelos correspondentes. Para alargar o tratamento apresentado consideram-se também Extensões L de modelos Error-orthogonal. Desta forma, poderemos considerar casos interessantes como o dos modelos com número diferente de repetições para os vários tratamentos. Por fim, inclui-se o caso normal. Com base no pressuposto da normalidade pretende-se obter estatísticas suficientes assim como condições para que estas sejam completas. É realizada inferência e consideram-se extensões L ortogonais.

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47

Hinds, Raynard Orin. "Robust mode selection for block-motion-compensated video encoding." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80081.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.
Includes bibliographical references (p. 129-132).
by Raynard O. Hinds.
Ph.D.

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48

Chang, Hao-Chi. "Sliding mode control design based on block control principle /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486461246815228.

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49

Nikkhah, Hamdam. "Enhancing the Performance of Si Photonics: Structure-Property Relations and Engineered Dispersion Relations." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37144.

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The widespread adoption of photonic circuits requires the economics of volume manufacturing offered by integration technology. A Complementary Metal-Oxide Semiconductor compatible silicon material platform is particularly attractive because it leverages the huge investment that has been made in silicon electronics and its high index contrast enables tight confinement of light which decreases component footprint and energy consumption. Nevertheless, there remain challenges to the development of photonic integrated circuits. Although the density of integration is advancing steady and the integration of the principal components – waveguides, optical sources and amplifiers, modulators, and photodetectors – have all been demonstrated, the integration density is low and the device library far from complete. The integration density is low primarily because of the difficulty of confining light in structures small compared to the wavelength which measured in micrometers. The device library is incomplete because of the immaturity of hybridisation on silicon of other materials required by active devices such as III-V semiconductor alloys and ferroelectric oxides and the difficulty of controlling the coupling of light between disparate material platforms. Metamaterials are nanocomposite materials which have optical properties not readily found in Nature that are defined as much by their geometry as their constituent materials. This offers the prospect of the engineering of materials to achieve integrated components with enhanced functionality. Metamaterials are a class of photonic crystals includes subwavelength grating waveguides, which have already provided breakthroughs in component performance yet require a simpler fabrication process compatible with current minimum feature size limitations. The research reported in this PhD thesis advances our understanding of the structure-property relations of key planar light circuit components and the metamaterial engineering of these properties. The analysis and simulation of components featuring structures that are only just subwavelength is complicated and consumes large computer resources especially when a three dimensional analysis of components structured over a scale larger than the wavelength is desired. This obstructs the iterative design-simulate cycle. An abstraction is required that summarises the properties of the metamaterial pertinent to the larger scale while neglecting the microscopic detail. That abstraction is known as homogenisation. It is possible to extend homogenisation from the long-wavelength limit up to the Bragg resonance (band edge). It is found that a metamaterial waveguide is accurately modeled as a continuous medium waveguide provided proper account is taken of the emergent properties of the homogenised metamaterial. A homogenised subwavelength grating waveguide structure behaves as a strongly anisotropic and spatially dispersive material with a c-axis normal to the layers of a one dimensional multi-layer structure (Kronig-Penney) or along the axis of uniformity for a two dimensional photonic crystal in three dimensional structure. Issues with boundary effects in the near Bragg resonance subwavelength are avoided either by ensuring the averaging is over an extensive path parallel to boundary or the sharp boundary is removed by graded structures. A procedure is described that enables the local homogenised index of a graded structure to be determined. These finding are confirmed by simulations and experiments on test circuits composed of Mach-Zehnder interferometers and individual components composed of regular nanostructured waveguide segments with different lengths and widths; and graded adiabatic waveguide tapers. The test chip included Lüneburg micro-lenses, which have application to Fourier optics on a chip. The measured loss of each lens is 0.72 dB. Photonic integrated circuits featuring a network of waveguides, modulators and couplers are important to applications in RF photonics, optical communications and quantum optics. Modal phase error is one of the significant limitations to the scaling of multimode interference coupler port dimension. Multimode interference couplers rely on the Talbot effect and offer the best in-class performance. Anisotropy helps reduce the Talbot length but temporal and spatial dispersion is necessary to control the modal phase error and wavelength dependence of the Talbot length. The Talbot effect in a Kronig-Penny metamaterial is analysed. It is shown that the metamaterial may be engineered to provide a close approximation to the parabolic dispersion relation required by the Talbot effect for perfect imaging. These findings are then applied to the multimode region and access waveguide tapers of a multi-slotted waveguide multimode interference coupler with slots either in the transverse direction or longitudinal direction. A novel polarisation beam splitter exploiting the anisotropy provided by a longitudinally slotted structure is demonstrated by simulation. The thesis describes the design, verification by simulation and layout of a photonic integrated circuit containing metamaterial waveguide test structures. The test and measurement of the fabricated chip and the analysis of the data is described in detail. The experimental results show good agreement with the theory, with the expected errors due to fabrication process limitations. From the Scanning Electron Microscope images and the measurements, it is clear that at the boundary of the minimum feature size limit, the error increases but still the devices can function.

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Garkusha, Sergey, Aymen Al-Dulaimi, and Haider Al-Janabi. "Result Research Model of Scheduling Block Allocation in Downlink LTE." Thesis, TCSET'2014, 2014. http://dspace.puet.edu.ua/handle/123456789/1954.

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Result of the model of time and frequency resource scheduling in downlink LTE development was applied. The given model is directed upon securing the wireless network users being served by the allocation to user equipment required transmission rates. Comparative analysis of the offered model with existing methods from the point of view of securing the common productivity of downlink, level of bandwidth balancing, possibility of allocation to users' equipment required transmission rate are completed

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Dissertations / Theses on the topic 'Modes de Bloch'

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