Conventional CMOS scaling has been the engine of the technology revolution in most application domains. This trend has changed as in each technology generation, transistor densities continue to increase while due to the limits on threshold voltage scaling, per-transistor energy consumption decreases much more slowly than in the past. The power scaling issues will restrict the adaptability of designs to operate in different power and performance regimes. Consequently, future systems must employ more efficient architectures for optimizing every thread in the program across different power and performance regimes, rather than architectures that utilize more transistors. One solution is composable or dynamic multicore architectures that can span a wide range of energy/performance operating points by enabling multiple simple cores to compose to form a larger and more powerful core. Explicit Data Graph Execution (EDGE) architectures represent a highly scalable class of composable processors that exploit predicated dataflow block execution and distributed microarchitectures. However, prior EDGE architectures suffer from several energy and performance bottlenecks including expensive intra-block operand communication due to fine-grain instruction distribution among cores, the compiler-generated fanout trees built for high-fanout operand delivery, poor next-block prediction accuracy, and low speculation rates due to predicates and expensive refills after pipeline flushes. To design an energy-efficient and flexible dynamic multicore, this dissertation employs a systematic methodology that detects inefficiencies and then designs and evaluates solutions that maximize power and performance efficiency across different power and performance regimes. Some innovations and optimization techniques include: (a) Deep Block Mapping extracts more coarse-grained parallelism and reduces cross-core operand network traffic by mapping each block of instructions into the instruction queue of one core instead of distributing blocks across all composed cores as done in previous EDGE designs, (b) Iterative Path Predictor (IPP) reduces branch and predication overheads by unifying multi-exit block target prediction and predicate path prediction while providing improved accuracy for each, (c) Register Bypassing reduces cross-core register communication delays by bypassing register values predicted to be critical directly from producing to consuming cores, (d) Block Reissue reduces pipeline flush penalties by reissuing instructions in previously executed instances of blocks while they are still in the instruction queue, and (e) Exposed Operand Broadcasts (EOBs) reduce wide-fanout instruction overheads by extending the ISA to employ architecturally exposed low-overhead broadcasts combined with dataflow for efficient operand delivery for both high- and low-fanout instructions. These components form the basis for a third-generation EDGE microarchitecture called T3. T3 improves energy efficiency by about 2x and performance by 47% compared to previous EDGE architectures. T3 also performs in a highly power efficient manner across a wide spectrum of energy and performance operating points (low-power to high-performance), extending the domain of power/performance trade-offs beyond what dynamic voltage and frequency scaling offers on state-of-the-art conventional processors. This high level of flexibility and power efficiency makes T3 an attractive candidate for future systems which need to operate on a wide range of workloads under varying power and performance constraints. / text

Μελετάται η Ολοκαινική εξέλιξη των βόρειων ακτών του Αμβρακικού κόλπου, με τη βοήθεια τεσσάρων γεωτρήσεων οι οποίες εντοπίζονται στον οδικό άξονα Αρτας-Σαλαώρας. / Studying the Holocene evolution of the northern coasts of Amvrakikos Gulf, by using four sediment cores, which are located along the main road that connects Arta to Salaora region.

A new whole-core transport method is described for 3-D hexagonal geometry. This is an extension of a stochastic-deterministic hybrid method which has previously been shown highly accurate and efficient for eigenvalue problems. Via Monte Carlo, it determines the solution to the transport equation in sub-regions of reactor cores, such as individual fuel elements or sections thereof, and uses those solutions to compose a library of response expansion coefficients. The information acquired allows the deterministic solution procedure to arrive at the whole core solution for the eigenvalue and the explicit fuel pin fission density distribution more quickly than other transport methods. Because it solves the transport equation stochastically, complicated geometry may be modeled exactly and therefore heterogeneity even at the most detailed level does not challenge the method. In this dissertation, the method is evaluated using comparisons with full core Monte Carlo reference solutions of benchmark problems based on gas-cooled, graphite-moderated reactor core designs. Solutions are given for core eigenvalue problems, the calculation of fuel pin fission densities throughout the core, and the determination of incremental control rod worth. Using a single processor, results are found in minutes for small cores, and in no more than a few hours for a realistically large core. Typical eigenvalues calculated by the method differ from reference solutions by less than 0.1%, and pin fission density calculations have average accuracy of well within 1%, even for unrealistically challenging core configuration problems. This new method enables the accurate determination of core eigenvalues and flux shapes in hexagonal cores with efficiency far exceeding that of other transport methods.

As part of an international cooperative research program, the U.S. Geological Survey (USGS) and researchers from the National Gas Hydrate Program (NGHP) of India are studying the physical properties of sediment recovered during the NGHP-01 cruise conducted offshore India during 2006. Here we report on index property, acoustic velocity, and triaxial shear test results for samples recovered from the Krishna-Godavari Basin. In addition, we discuss the effects of sample storage temperature, handling, and change in structure of fine-grained sediment. Although complex, sub-vertical planar gas-hydrate structures were observed in the silty clay to clayey silt samples prior to entering the Gas Hydrate And Sediment Test Laboratory Instrument (GHASTLI), the samples yielded little gas post test. This suggests most, if not all, gas hydrate dissociated during sample transfer. Mechanical properties of hydrate-bearing marine sediment are best measured by avoiding sample depressurization. By contrast, mechanical properties of hydrate-free sediments, that are shipped and stored at atmospheric pressure can be approximated by consolidating core material to the original in situ effective stress.

The recent development and deployment of HYACINTH and IODP PCS pressure cores on the JOIDES Resolution during Expedition 1 of the Indian National Gas Hydrate Program (NGHP-1) has provided some of the first “undisturbed” samples of gas hydrate in fine grained marine sediments. Some samples, once recovered from the seafloor, were subject to rapid depressurization and subsequent immersion in liquid nitrogen, at approximately -196oC, for use in subsequent laboratory test programs. This paper describes the techniques used at Southampton University, the difficulties encountered, and the results obtained from geotechnical testing of these samples. The original intention had been to pressurize and unfreeze the material before testing it in the Gas Hydrate Resonant Column (GHRC) Apparatus. Initial CT scanning of the samples showed that the sample quality might be too poor for such testing, and this proved to be the case. Instead a suite of geotechnical testing was carried out, the results of which are reported and interpreted in this paper.

Recent advances in pressure coring techniques, such as the HYACINTH and IODP PCS pressure cores deployed during Expedition 1 of the India National Gas Hydrate Program using the JOIDES Resolution have enabled the recovery of fine grained sediments with intact gas hydrates contained within the sediments. This has provided the opportunity to study the morphology of gas hydrates within fine grained sediments which until now has been hindered due to the long transit times during core recovery leading to the dissociation of the gas hydrates. Once recovered from the seafloor, rapid depressurization and subsequent freezing of the cores in liquid nitrogen has enabled the near complete fine fracture filling nature of the gas hydrates to be largely preserved. High resolution X-ray CT (computer tomography), which has a pixel resolution of approx. 0.07mm, has been used to provide detailed images showing the 3-dimensional distribution of hydrates within the recovered fine grained sediments. Results have shown that in fine grained sediments gas hydrates grow along fine fracture faults within the sediment. Although the fractures were predominantly sub-vertical and continuous through the cores, stranded fractures were also observed suggesting that hydrate formation is episodic. However, within the cores open voids were observed which were not evident in low resolution CT images taken before the depressurization step suggesting that during depressurization either finely disseminated gas hydrate was dissociated or that gas exsolving from solution created these voids in the sample prior to freezing in liquid nitrogen. These detailed observations of gas hydrate in fine grained sediments will help us understand the differing morphology of gas hydrates in sediments. They also show that sample disturbance is still a major concern and further techniques are required to restrict these effects so that meaningful laboratory tests can be undertaken on recovered samples.

L'étude et l'analyse des réseaux sociaux attirent l'attention d'une variété de sciences (psychologie, statistiques, sociologie). Parmi elles, le domaine de la fouille de données offre des outils pour extraire automatiquement des informations utiles sur les propriétés de ces réseaux. Plus précisément, la fouille de graphes répond au besoin de modéliser et d'étudier les réseaux sociaux en particulier dans le cas des grandes communautés que l'on trouve habituellement dans les médias en ligne oú la taille des réseaux sociaux est trop grande pour les méthodes manuelles. La modélisation générale d'un réseau social est basée sur des structures de graphes. Les sommets du graphe représentent les individus et les arêtes des actions différentes ou des types de liens sociaux entre les individus. Une communauté est définie comme un sous-graphe (d'un réseau social) et se caractérise par des liens denses. Plusieurs mesures ont été précédemment proposées pour l'évaluation des divers aspects de la qualité de ces communautés mais la plupart d'entre elles ignorent diverses propriétés des interactions entre individus (par exemple l'orientation de ces liens). Dans la recherche présentée ici, le concept de "k-core" est utilisé comme un moyen d'évaluer les communautés et d'en extraire des informations. La structure de "k-core" mesure la robustesse d'un réseau non orienté en utilisant la dégénérescence du graphe. En outre, des extensions du principe de dégénérescence sont introduites pour des réseaux dont les arêtes possèdent plus d'informations que celles non orientées. Le point de départ est l'exploration des attributs qui peuvent être extraits des graphes non orientés (réseaux sociaux). Sur ce point, la dégénérescence est utilisée pour évaluer les caractéristiques d'une collaboration entre individus et sur l'ensemble de la communauté - une propriété non capturée par les métriques sur les sommets individuels ou par les métriques d'évaluation communautaires traditionnelles. Ensuite, cette méthode est étendue aux graphes pondérés, orientés et signés afin d'offrir de nouvelles mesures d'évaluation pour les réseaux sociaux. Ces nouvelles fonctionnalités apportent des outils de mesure de la collaboration dans les réseaux sociaux oú l'on peut attribuer un poids ou un orientation à une interaction et fournir des moyens alternatifs pour capturer l'importance des individus au sein d'une communauté. Pour les graphes signés, l'extension de la dégénérescence permet de proposer des métriques supplémentaires qui peuvent être utilisées pour modéliser la confiance. De plus, nous introduisons une approche de partitionnement basée sur le traitement du graphe de manière hiérarchique, hiérarchie fournie par le principe de "core expansion sequence" qui partitionne le graphe en différents niveaux ordonnés conformément à la décomposition "k-core". Les modèles théoriques de graphes sont ensuite appliqués sur des graphes du monde réel pour examiner les tendances et les comportements. Les jeux de données explorés incluent des graphes de collaborations scientifiques et des graphes de citations (DBLP et ARXIV), une instance de graphe interne de Wikipédia et des réseaux basés sur la confiance entre les individus (par exemple Epinions et Slashdot). Les conclusions sur ces ensembles de données sont significatives et les modèles proposés offrent des résultats intuitifs.

In 2005, box cores were collected throughout the Hudson Bay and Strait. A detailed micropaleontological data set has been generated from these cores for this study and is combined with geochemical and geochronological data to observe temporal and spatial oceanographic changes throughout the bay and strait. All of the cores show an increase in tintinnid species and agglutinated foraminifera, and coincident decreases in calcareous foraminifera in younger core sections. In general, these microfossil trends are correlated with higher organic matter content of the younger core sections. This results from a more extensive freshwater plume that causes lowered pH in the superficial sediments and conditions less favourable for the preservation of calcareous tests. Furthermore, with a 14C age constraint in one of the cores, the mid-Holocene depositional and paleoceanographic history is represented, and provides evidence of marine invasion by 7100 cal yrs BP.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 151-167).

Thesis (doctoral)-Universität, Tübingen, 2003. / Folded plate in pocket. Includes bibliographical references (p. 399-427; 691-692).