Parmi la diversité des types microstructuraux que l’on peut trouver dans les coquilles des Mollusques, les architectures entrecroisées (lamellaire-croisé, lamellaire-croisé complexe, folié-croisé) sont de loin les plus abondantes. Mais elles restent, de par leurs organisations tridimensionnelles complexes, peu documentées : la majorité des études de biominéralisation, et les différents modèles qui en découlent, sont en effet essentiellement basés sur des architectures plus simples (telles que les couches nacrées ou prismatiques). Or il convient, si l'on souhaite aboutir à une meilleure compréhension des mécanismes fondamentaux qui dirigent la minéralisation de ces biocarbonates, de vérifier dans quelle mesure les modèles développés à partir de coquilles ”simples” sont aussi applicables à des organisations microstructurales plus complexes. Cette étude se focalise donc sur les couches entrecroisées des coquilles de quelques Mollusques, dans le but de mettre en évidence les différents niveaux du contrôle biologique que l'organisme exerce sur leur formation et leur croissance. À cette fin, des techniques de caractérisation in-situ des assemblages organiques sont privilégiées, en relation étroite avec l’analyse des organisations microstructurales et des mécanismes de biocristallisation à fine échelle. Quelques aspects de la diagénèse de ces microstructures seront aussi abordés, à travers l’étude de coquilles fossiles de Patella sp (~100 ka) et Velates perversus (~50 Ma). / Among the variety of microstructural types that can be found within Molluscs shells, intercrossed structures (crossed-lamellar, complex crossed-lamellar and cross-foliated) are by far the most commonly found. They are, however, still poorly documented - mainly due to their complex 3D organization. The majority of biomineralization studies, and the resulting models, are indeed essentially based on simple architectures (such as nacreous or prismatic layers). In order to achieve a better understanding of the fundamental mechanisms that drive the mineralization of such biocarbonates, it is therefore mandatory to check to which extent models developed from « simple » shells stay consistent when applied to more complex microstructural organizations. The present study focuses on intercrossed layers of several Mollusk shells, in order to highlight the various levels of biological control exerted by the organism on their formation and growth. In-situ techniques are used to characterize biochemical compositions, in close correlation with microstructural patterns, as well as fine-scale biocrystallization processes. Some peculiar features of the diagenesis of these microstructures are illustrated, through the study of fossil shells from Patella sp (~100 ky) and Velates perversus (~50 My).

Este trabalho tem o intuito de fazer uso do processamento paralelo na análise não linear de cascas pelo método dos elementos finitos. O elemento finito de casca é obtido com o acoplamento de um elemento de placa e um de chapa. O elemento de placa utiliza formulação de Kirchhof (DKT) para placas delgadas e o elemento de chapa faz uso da formulação livre (FF), introduzindo um grau de liberdade rotacional nos vértices. A análise não-linear com plasticidade utiliza o modelo de plasticidade associada com algoritmo de integração explícito, modelo de escoamento de von Mises com integração em camadas (modelo estratificado), para materiais isotrópicos. A implementação em paralelo é realizada em um sistema com memória distribuída e biblioteca de troca de mensagens PVM (Parallel Virtual Machine). O procedimento não-linear é completamente paralelizado, excetuando a impressão final de resultados. As etapas que constituem o método dos elementos finitos, matriz de rigidez da estrutura e resolução do sistema de equações lineares são paralelizadas. Para o cálculo da matriz de rigidez utiliza-se um algoritmo com decomposição de domínio explícito. Para resolução do sistema de equações lineares utiliza-se o método dos gradientes conjugados com implementação em paralelo. É apresentada uma breve revisão bibliográfica sobre o paralelismo, com comentários sobre perspectivas em análise estrutural / This work aims at using parallel processing for nonlinear analysis of shells through finite element method. The shell finite element is obtained by coupling a plate element with a membrane one. The plate element uses Kirchhoff’s formulation (DKT) for thin plates and the membrane element makes use of the free formulation (FF), introducing a rotational degree of freedom at the vertexes. Nonlinear plastic analysis uses associated plasticity model with explicit integration algorithm, von Mises yelding model with layer integration (stratified model) for isotropic materials. Parallel implementation is done on a distributed memory system and message exchange library PVM (Parallel Virtual Machine). Nonlinear procedure is completely parallelised, but final printing of results. The finite element method steps, structural stifness matrix and solution of the linear equation system are parallelised. An explicit domain decomposition algorithm is used for the stifness matrix evaluation. To solve the linear equation system, one uses conjugated gradients method, with parallel implementation. A brief bibliography about parallelism is presented, with comments on structural analysis perspectives

The total wind power capacity installed in the world has substantially grown during the last few years, mainly due to the increasing number of horizontal axis wind turbines (HAWT). Consequently, a big effort was employed to increase HAWT\'s power capacity, which is directly associated to the size of blades. Then, novel designs of blades may lead to very fexible structures, susceptive to large deformation, not only during extreme events, but also for operational conditions. In this context, this thesis aims to compare two geometrically nonlinear structural modeling approaches that handle large deformation of blade structures: 3D geometrically-exact beam and shell finite element models. Regarding the beam model, due to geometric complexity of typical cross-sections of wind turbine blades it is adopted a theory that allows creation of arbitrary multicellular cross-sections. Two typical blade geometries are tested, and comparisons between the models are done in statics and dynamics, always inducing large deformation and exploring the accuracy limits of beam models, when compared to shells. Results showed that the beam and shell models present very similar behavior, except when violations occur on the beam formulation hypothesis, such as when shell local buckling phenomena takes place. / A capacidade total de energia eólica instalada no mundo cresceu substancialmente nos últimos anos, principalmente devido ao número crescente de turbinas eólicas de eixo horizontal. Consequentemente, um grande esforço foi empregado com o intuito de aumentar a capacidade de produção das turbinas eólicas, que está diretamente associada ao tamanho das pás. Assim, surgiram projetos inovadores quanto à concepção de pás de turbinas eólicas levando a estruturas bastante flexíveis, susceptíveis a grandes deslocamentos, não apenas em eventos extremos, mas também em condições normais de operação. Nesse contexto, a presente dissertação tem por objetivo comparar duas abordagens de modelos estruturais geometricamente não-lineares capazes de lidar com grandes deslocamentos de pás de turbinas eólicas: elementos finitos geometricamente exatos 3D de vigas e cascas. Em relação ao modelo de viga, devido à complexidade geométrica das seções transversais típicas de pás de turbinas eólicas, adota-se uma teoria que permite a criação de seções transversais arbitrárias multicelulares. Duas geometrias de pás s~ao testadas e comparações entre os modelos s~ao feitas em análises estáticas e dinâmicas, sempre induzindo grandes deslocamentos e explorando os limites de precisão do modelo de viga, quando comparado ao modelo de cascas. Os resultados indicam que os modelos de viga e casca apresentam comportamento muito similar, exceto quando ocorrem violações em hipóteses do modelo de viga, tal como quando ocorre flambagem local do modelo de casca.

The environmental conditions in the center of the Milky Way galaxy (Central Molecular Zone; CMZ) are much more extreme than in the disk of the galaxy with molecular gas properties similar to those seen in galaxies at z~2. While the CMZ hosts several massive star clusters, the formation of stars from these dense molecular clouds and the feedback of these massive stars on the ISM is not well understood. I present in my thesis a case study of a few regions in the CMZ using VLA continuum and spectral line observations. I explore feedback eects of recent star formation (a young massive stellar cluster) on the surrounding ISM (molecular and ionized gas). Using the kinematic information of molecular and ionized gas, obtained dierent species of spectral lines, I will determine the line of sight geometry of the dierent gas components. I will then establish the relationship of these components to the larger structure of molecular gas in the CMZ.

Extensive shell ridges frame the edges of marsh platforms in parts of the Biloxi Marsh of southeast Louisiana. The exact sources of the shells in these accumulations have not been clearly identified but the most likely source is a combination of shells from modern offshore and shells excavated from buried St. Bernard delta deposits. Larger or fetch-protected ridges remain stable through time, whereas ridges facing open water are more mobile, moving as much as 38 m inland from July 2017 to January 2018. Behind stable ridges, marsh platform biomass is relatively unaffected. When ridges are mobile, vegetation is smothered, leaving an exposed platform that lacks aboveground vegetation to dampen wave energy and fragments into “blocks” along its terraced edge, which in turn are deposited onshore. In the future, marshes will likely erode fastest in areas where shell ridges are mobile and remain resistant where shell ridges are stable.

In recent years, employing advanced oxidation processes (AOPs) as a means of wastewater remediation has emerged as a promising route towards maintaining a sustainable global water management program. The heterogeneous photocatalytic oxidation process has been of particular interest due to the prospective of utilizing solar radiation as the driving force behind the degradation of pollutants. Of the photocatalyst studied to date, TiO2 remains the most attractive material for environmental applications due to its affordability, stability, biocompatibility and high quantum yield. A key draw back however is roughly only 5% of solar radiation incident on earth can provide the energy required (3.0-3.2 eV) to generate the electron-hole pairs necessary for photo-oxidation. As a means to improve the process under solar irradiance, optical properties such as surface plasmon resonance of metallic nanoparticles and upconversion luminescence of rare earth ions have been exploited for improved light harvesting as well as the generation of more usable UV light from lower energy photons. In order to explore these phenomena and their role in the enhancement of this AOP, the photocatalytic degradation of organic dyes was studied under various conditions employing Degussa P25 TiO2 as the photocatalyst. Ag nanocubes, Ag-Pd core-shell nanoparticles and YAG:Yb+3,Er+3 served as the dopants for the various studies which resulted in enhanced degradation rates, insight into the applicability of utilizing Yb+3 as sensitizing ion under solar radiation and a novel core-shell nanoparticle synthesis.

During the last two decades, a broad spectrum of short- and long-term studies on different taxonomic groups has enriched our understanding about how dynamics of taxonomic and ecological diversification have changed through geologic time. There are two major issues that have impacted these studies: the quality and quantity of data used are often insufficient in various ways and the methods used may produce results that are more equivocal than supposed. To investigate these issues more fully, this dissertation focuses on studies on two major aspects: 1) short-term studies examining the nature of successful and unsuccessful predatory attacks on Plio-Pleistocene bivalves; and 2) a Phanerozoic-scale project examining trends in bivalve richness and ecological differentiation. The short-term studies, focusing on shell-breaking predation on bivalves, have shown that the existing methodologies which only study either successful or unsuccessful component of predation in isolation are fraught with potential issues in developing effective interpretations. When these two components (i.e., successful and unsuccessful) are studied in tandem as was done here, however, traces of predation can be used to better constrain potential paleoecological interpretations related to predation intensity, predator's attack strategies, and predator-prey dynamics. The long-term project includes two Phanerozoic studies on bivalves' taxonomic and ecological richness. The taxonomic study has shown how the elements included in various datasets used can affect the Phanerozoic richness trajectory of bivalves. The revised and newly compiled dataset developed here reveals that bivalves showed three major episodes of diversification - a Ordovician radiation of orders and families, a Mesozoic diversification of families, and a dramatic Cenozoic rise in the total number of genera - all of which were synchronous with ecological diversification in terms of appearances of new life forms capable of colonizing new ecospace (i.e., cubes). However, these synchronous changes in taxonomic-ecologic richness were influenced by many biotic (e.g., predation, competition, and adaptive innovations) and abiotic (e.g., nutrient availability, sea level, and temperature) components, for which I propose a multilevel mixed model such that all these components can be studied in tandem.

Injection attacks are the top two causes of software errors and vulnerabilities, according to the MITRE Common Vulnerabilities list [1]. This thesis presents a threat analysis of injection attacks on applications built for Android, a popular but not rigorously studied operating system designed for mobile devices. The following thesis is argued: Injection attacks are possible on off-the-shelf Android systems, and such attacks have the capacity to compromise the device through resource denial and leaking private data. Specifically, we demonstrate that injection attacks are possible through the OS shell and through the SQLite API. To mitigate these attacks, we augment the Android OS with a taint-tracking mechanism to monitor the flow of untrusted character strings through application execution. We use this taint information to implement a mechanism to detect and prevent these injection attacks. A good denition of an attack being critical to preventing it, our mechanism is based on Ray and Ligatti's formalized “NIE" property, which states that untrusted inputs must only insert or expand noncode tokens in output programs. If this property is violated, an injection attack has occurred. This definition's detection algorithm, in combination with our taint tracker, allow our mechanism to defend against these attacks.

This cultural history of paua shell jewellery redresses the lack of visibility of such objects as a significant part of 20th century New Zealand material culture and provides a basis for a more balanced interpretation beyond its stereotyping as tourist kitsch. It questions why quality paua shell jewellery made before the late 1960s failed to gain recognition with most New Zealanders until fairly recently as anything other than tourist souvenirs. Over 1,500 items of paua shell jewellery, mainly in private collections, formed the basis for this multidisciplinary research project that incorporates historical, anthropological and material culture studies approaches to write a cultural history of such jewellery. The objects were photographed and where available, their provenance recorded. A visual analysis of the items - paying attention to details of design and construction - established various, often overlapping categories that facilitated the dating and identification process. Gradually, a picture of the production of paua shell jewellery over the decades emerged. The wider socio-cultural context was then built using archival sources, various publications, conversations with one-time industry representatives, and discussions with original owners of paua shell jewellery. Interpretation of the material established multiple roles for paua shell jewellery over the decades for various groups of people. Changes over time provided insights into aspects of identity creation by New Zealanders. Until the 1920s, the shell�s main role had been as a European applied arts material and as inlay for Maori woodcarvings. Paua shell as a commercial souvenir material developed during the Depression and was shaped by the interaction between an emerging nationalism and a democratising of travel in New Zealand. Paua shell native bird brooches functioned as affordable alternatives to greenstone souvenirs for the working-class tourists that began exploring their own country. In addition to its role as emblems of nationhood in the interwar years, paua shell jewellery had meaning as souvenirs for American servicemen stationed in New Zealand during the War, and as patriotic tokens for its own population due to its association with disabled servicemen. Paua shell jewellery functioned as acknowledgement of settlement for European immigrants in the post war era, and as travel memento for trans-Tasman tourists from the mid 1950s. New Zealand girls received paua shell items as first jewellery, and women wore it as dress or costume jewellery. Until the increase of tourism in the 1960s, paua shell jewellery had existed on a number of planes. The exploitation of paua shell by the tourist industry, however, upset the balance and its dominance as souvenir forced a retreat of alternative uses. Other than as tourist souvenir, paua shell jewellery became invisible to the local population. Their withdrawal from an association with paua shell as a cultural marker of national identity explains why so many New Zealanders were uncertain about liking or disliking paua shell jewellery until recently.

The subject of free vibration analysis of thin cylindrical shells is one that extends well back into the last century. In general, the computational methods can be classified as analytical methods and numerical methods. Based on the Flugge thin shell theory, this thesis presents exact solutions for vibration of closed and open cylindrical shells. The state-space technique is adopted to derive the homogenous differential equations for a shell segment and the domain decomposition method is employed to impose the equilibrium and compatability requirements along the interfaces of the shell segments. Extensive analytical and numerical results have been obtained in this thesis for vibration of open/closed cylindrical shells with different boundary conditions, step-wise thickness variations, and multiple intermediate ring supports. The results can serve as useful benchmark values for researchers and engineers to validate their numerical method for shell analysis. / Doctor of Philosophy (PhD)