Dans les télécommunications, le débit-fiabilité et la complexité de l’encodage et du décodage (opération à virgule flottante-flops) sont largement reconnus comme représentant des facteurs limitant interdépendants. Pour cette raison, tout tentative de réduire la complexité peut venir au prix d’une dégradation substantielle du taux d’erreurs. Cette thèse traite de l’établissement d’un compromis limite fondamental entre la fiabilité et la complexité dans des systèmes de communications « outage »-limités à entrées et sorties multiples (MIMO), et ses scénarios point-à-point, utilisateurs multiple, bidirectionnels, et aidés de feedback. Nous explorons un large sous-ensemble de la famille des méthodes d’encodage linéaire Lattice, et nous considérons deux familles principales de décodeurs : les décodeurs à maximum de vraisemblance (ML) et les décodeurs Lattice. L‘analyse algorithmique est concentrée sur l’implémentation de ces décodeurs ayant comme limitation une recherche bornée, ce qui inclue une large famille de sphère-décodeurs. En particulier, le travail présenté fournit une analyse à haut rapport Signal-à-Bruit (SNR) de la complexité minimum (flops ou taille de puce électronique) qui permet d’atteindre a) une certaine performance vis-à-vis du compromis diversité-gain de multiplexage et b) une différence tendant vers zéro avec le non-interrompu (optimale) ML décodeur, ou une différence tendant vers zéro comparé à l’implémentation exacte du décodeur (régularisé) Lattice. L’exposant de complexité obtenu décrit la vitesse asymptotique d’accroissement de la complexité, qui est exponentielle en terme du nombre de bits encodés. / In telecommunications, rate-reliability and encoding-decoding computational complexity (floating point operations - flops), are widely considered to be limiting and interrelated bottlenecks. For this reason, any attempt to significantly reduce complexity may be at the expense of a substantial degradation in error-performance. Establishing this intertwined relationship constitutes an important research topic of substantial practical interest. This dissertation deals with the question of establishing fundamental rate, reliability and complexity limits in general outage-limited multiple-input multiple-output (MIMO) communications, and its related point-to-point, multiuser, cooperative, two-directional, and feedback-aided scenarios. We explore a large subset of the family of linear lattice encoding methods, and we consider the two main families of decoders; maximum likelihood (ML) based and lattice-based decoding. Algorithmic analysis focuses on the efficient bounded-search implementations of these decoders, including a large family of sphere decoders. Specifically, the presented work provides high signal-to-noise (SNR) analysis of the minimum computational reserves (flops or chip size) that allow for a) a certain performance with respect to the diversity-multiplexing gain tradeoff (DMT) and for b) a vanishing gap to the uninterrupted (optimal) ML decoder or a vanishing gap to the exact implementation of (regularized) lattice decoding. The derived complexity exponent describes the asymptotic rate of exponential increase of complexity, exponential in the number of codeword bits.

Les extensions bifluides des méthodes Lattice Boltzmann à frontière libre utilisent généralement des pseudopotentiels microscopiques pour modéliser l'interface. Nous avons choisi d'orienter nos recherches vers une méthode Lattice Boltzmann à capture d'interface où la fraction massique d'un des deux fluides, inconnue, est transportée. De nombreux travaux ont montré les difficultés des méthodes Lattice Boltzmann à traiter des systèmes bifluides, et ce d'autant plus que le ratio de densité est important. Nous expliquerons l'origine de ces problèmes en mettant en évidence le manque de diffusion numérique pour capturer précisément les discontinuités de contact. Pour régler cet obstacle, nous proposerons une formulation Arbitrary Lagrangian Eulerian (ALE) des méthodes Lattice Boltzmann. Cela permet de séparer le traitement des ondes matérielles de celui des ondes de pression. Une fois l'étape ALE terminée, une phase de projection ramène les variables sur la grille eulérienne de calcul initiale. Nous expliquons comment obtenir une procédure de projection ayant une précision d'ordre 2 et une interface fine et dépourvue d'oscillations. Il sera montré que la fraction massique satisfait un principe du maximum discret et qu'elle reste donc entre 0 et 1. Les simulations numériques sont en accord avec la théorie. Même si notre méthode n'est pour le moment utilisée que pour simuler des écoulements de fluides non visqueux (Equations d'Euler), nous sommes convaincus qu'elle pourra être étendue à des simulations d'écoulements bifluides visqueux. / Two-fluid extensions of Lattice Boltzmann methods with free boundaries usually consider ``microscopic'' pseudopotential interface models. In this paper, we rather propose an interface-capturing Lattice Boltzmann approach where the mass fraction variable is considered as an unknown and is advected. Several works have reported the difficulties of LBM methods to deal with such two-fluid systems especially for high-density ratio configurations. This is due to the mixing nature of LBM, as with Flux vector splitting approaches for Finite Volume methods. We here give another explanation of the lack of numerical diffusion of Lattice Boltzmann approaches to accurately capture contact discontinuities. To fix the problem, we propose an arbitrary Lagrangian-Eulerian (ALE) formulation of Lattice-Boltzmann methods. In the Lagrangian limit, it allows for a proper separated treatment of pressure waves and advection phenomenon. After the ALE solution, a remapping (advection) procedure is necessary to project the variables onto the Eulerian Lattice-Boltzmann grid.We explain how to derive this remapping procedure in order to get second-order accuracy and achieve sharp stable oscillation-free interfaces. It has been shown that mass fractions variables satisfy a local discrete maximum principle and thus stay in the range $[0,1]$. The theory is supported by numerical computations of rising bubbles (without taking into account surface tension at this current state of development).Even if our methods are currently used for inviscid flows (Euler equations) by projecting the discrete distributions onto equilibrium ones at each time step, we believe that it is possible to extend the framework formulation for multifluid viscous problems. This will be at the aim of a next work.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19479号 / 理博第4139号 / 新制||理||1595(附属図書館) / 32515 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 戸塚 圭介, 教授 川上 則雄, 教授 石田 憲二 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20892号 / 理博第4344号 / 新制||理||1624(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 高橋 義朗, 教授 川上 則雄, 教授 田中 耕一郎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

In the course of experiments using uniaxial double alignment channeling to investigate radiation damage in single crystals, an anomalously large ion-scattering yield from the near surface of disordered or simulated disordered solid targets was observed. The chronology of the discovery of this new ion-solid effect and its explanation are presented along with experiments detailing the dependence of the new effect upon ion type and energy, as well as target atomic number and density. Targets included a spectrum of polycrystalline elemental targets in a range Z = 29 to Z = 82. Also, the influence of the effect upon scattering yields from an aligned Au(110) single crystal is demonstrated.

This thesis discusses some of the invariants of rational elliptic surfaces, namely the Mordell-Weil Group, Mordell-Weil Lattice, and another lattice which will be called the Shioda Lattice. It will begin with a brief overview of rational elliptic surfaces, followed by a discussion of lattices, root systems and Dynkin diagrams. Known results of several authors will then be applied to determine the groups and lattices associated with a given rational elliptic surface, along with a discussion of the uses of these groups and lattices in classifying surfaces.

We present comparative results from simulations of a lattice and an off-lattice model of a homopolymer, in the context of kinetics of the collapse transition. Scaling laws related to the collapse time, cluster coarsening and aging behavior are compared. Although in both models the cluster growth is independent of temperature, the related exponents turn out to be different. Conversely, the aging and associated scaling properties are found to be universal, with the nonequilibrium autocorrelation exponent obeying a recently derived bound.

The intention with this thesis is to investigate a dimer in a spin chain. Inorder to do that, a model from Z2-gauge theory is taken as the theoretical motivation to construct a discrete lattice with Ising spin properties. A dimer is then allowed to exist indirectly in the empty space between sites. We choose to tackle the problem through a quantum mechanical approach in 1+1-dimensions, distancing ourselves from the original description in quantum field theory. The exposition begins by reviewing the spatial construction of the entire chain as well as its components, and ends with a discussion of time development where the main concern is dispersion in addition to reflection against a static charge.

No description available.

This thesis project evaluates and compares different deep learning based segmentation tools for acquiring 3D segmentations of mitochondria. These segmentations could then hopefully be used in the future to quantify the mitochondria dynamics, which is vital for the survival of human cells. Four different models were evaluated and compared using the metrices Intersection over Union (IoU) and Dice, and a measurement of the quantity and area of the segmented mitochondria. The four different models were from the Fiji U-Net plugin, MitoSegNet, EmbedSeg 2D and EmbedSeg 3D. The data used was microscopic images of transfected MDCKII cells taken using a Lattice light-sheet microscope. Processing of the data was done in Fiji, which included manual annotation of the images in order to acquire ground truth segmentations. The results showed that the most suited model for this task was the model from the Fiji U-Net plugin. The other models also generated adequate segmentations, but could not adapt to images from a different cell. It was also concluded that stacking together 2D segmentations in order to achieve a 3D segmentations was successful. / Detta examensarbete utvärderar och jämför olika djupinlärningsbaserade segmenteringsverktyg för att få 3D-segmenteringar av mitokondrier. Dessa segmenteringar kan sedan förhoppningsvis användas i framtiden för att kvantifiera mitokondriernas dynamik, vilken är avgörande för de mänskliga cellernas överlevnad. Fyra olika modeller utvärderades och jämfördes med hjälp av måtten IoU och Dice, samt en mätning av kvantiteten och arean av de segmenterade mitokondrierna. De fyra olika modellerna var från en Fiji U-Net-plugin, MitoSegNet, EmbedSeg 2D och EmbedSeg 3D. Datan som användes var mikroskopbilder av transfekterade MDCKII-celler tagna med ett Lattice light-sheet mikroskop. Processeringen av datan gjordes i Fiji, som inkluderade manuell annotering av bilderna för att få ground truth segmenteringar. Resultaten visade att modellen som var bäst lämpad för denna uppgift var modellen från Fiji U-Net-pluginen. De andra modellerna genererade också adekvata segmenteringar, men kunde inte anpassa sig till bilder av en annan cell. En slutsats var också att stapla samman 2D-segmenteringar för att få 3D-segmenteringar var en lyckad metod.