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Notre compréhension de la structuration des chaînes trophiques pélagiques du Paléozoïque inférieur, mise en place lors des évènements d’« explosion Cambrienne » et de « Grande Biodiversification Ordovicienne » et qui a abouti à la mise en place des écosystèmes marins à « caractère moderne », reste encore très fragmentaire. Nous nous intéressons ici à comprendre les origines et la dynamique de paléobiodiversité des Radiolaires polycystines, composantes biotiques clefs du plancton hétérotrophe, dans le but de mieux comprendre le calendrier et la dynamique de diversification du plancton au cours du Paléozoïque inférieur. La découverte de nouveau matériel provenant des montagnes de l’Altaï (Sibérie) apporte de nouvelles données sur l’enregistrement fossilifère des premiers radiolaires biominéralisés avec l’identification des plus anciens représentant de la famille des Archéoentactinidae d’âge Botomien. Des études menées sur du matériel de Terre-Neuve et d’Australie ont permis de caractériser l’ensemble des changements biotiques intervenus au sein des assemblages à radiolaires à l’aube de la révolution planctonique mais également de préciser la répartition paléogéographique des radiolaires au Cambrien supérieur. Une étude taxonomique menée sur un échantillon provenant du Kazakhstan a également permis la découverte d’un nouvel assemblage à radiolaire enrichissant considérablement notre connaissance de la diversité des radiolaires à l’Ordovicien moyen. / Our understanding of the structuration of Lower Paleozoic pelagic trophic chains during the ‘Cambrian Explosion’ and the ‘Great Ordovician Biodiversification Event’, which has lead to the establishment of modern marine ecosystems, is still very fragmentary. We are here interested in understanding the paleodiversity dynamics of polycystines Radiolaria planctonic group, a key biotic component of the heterotrophic plankton, in order get a better idea of the timing and dynamics of plankton diversification at the Lower Paleozoic. The discovery of new material from the Altai Mountains (Siberia) brings new data on the fossil record of the first biomineralized radiolarians with the identification of the oldest representatives of the Archeoentactinidae family dated of a Botomian age. Study conducted on Newfoundland and Australian material allowed us to characterize precisely the various biotic changes undergone by radiolarians during the Cambrian-Ordovician transition, at the dawn of the planktonic revolution but also to precise their paleogeographic distribution at the Late Cambrian. A detailed taxonomic study conducted on a Kazakhstanian sample has allowed us to describe a new radiolarian assemblage enriching considerably our knowledge on the radiolarian diversity at the middle Ordovician.

"For industrial explosion protection, residual risk analysis determines the likelihood that a given protection scheme will fail to mitigate an explosion occurrence, where one or more points of a system are subject to failure. Current design practice for providing explosion protection measures for industrial hazards follows a process where, although the designer satisfies accepted industry codes and standards, the result is a system where the risk of failure remains unknown. This thesis proposes and demonstrates the use of a methodology to assist design engineers in constructing an explosion protection system that meets a specified quantifiable level of risk. This new methodology can assist building owners and decision makers in selecting a design that best meets their risk-based goals and objectives."

Two experiments were performed to investigate the interaction of a combustion wave with porous media. The first experiment was performed in a 1.22m long, 76mm wide, and 152mm high horizontal channel with a nitrogen-diluted stoichiometric methane-oxygen mixture at initial pressures of 20-50kPa. A layer of 12.7mm diameter ceramic-oxide spheres was placed along the bottom to partially obstruct the channel, leaving a gap of free space above. For a fixed gap height the bead layer thickness had very little effect on explosion propagation. For a fixed bead layer thickness the explosion propagation was strongly influenced by the gap height. For example, a 31% nitrogen diluted mixture at room temperature resulted in DDT for a gap height of 38mm at initial pressures of 30-50 kPa, but not for 109mm over the same pressures. The gap above the bead layer permits DDT as long as the gap height is larger than one detonation cell width. Propagation of the detonation wave over the bead layer is possible if the gap height can accommodate at least two detonation cells. For a 38mm gap, velocity measurements and sooted foil imprints indicate that the detonation undergoes successive failure and re-initiation, referred to as “galloping” in the literature. In the second experiment, the head-on collision of a combustion front with a layer of 3 and 12.7mm diameter ceramic-oxide spheres was investigated in a 61cm long, 76.2mm diameter vertical tube for a nitrogen-diluted stoichiometric ethylene-oxygen mixture at initial pressures of 10-100kPa. Four orifice plates were placed at the ignition end to accelerate the premixed flame to a “fast-flame” or a detonation wave. For fast-flames pressures recorded at the bead layer face were up to five times the reflected CJ detonation pressure. This explosion iv developed by two distinct mechanisms: a) shock reflection off the bead layer face and b) shock transmission into the bead layer and subsequent explosion therein. The measured explosion delay time (time after shock reflection from the bead layer face) was found to be independent of the incident shock velocity. Thus, it was shown that explosion initiation is not the direct result of shock reflection but is more likely due to the interaction of the reflected shock with the trailing flame. The bead layer was found to be very effective in attenuating the explosion and isolating the tube endplate. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2008-08-15 17:57:22.213

With the advent of automated sequencing, sequence data are now available to help us understand the functioning of our genome, as well as its history. To date,powerful methods such as maximum likelihood have been used to estimate its mode and tempo of evolution and its branching pattern. However, these methods appear to have some limitations. The purpose of this thesis is to examine these issues in light of Bayesian modelling, taking advantage of some recent advances in Bayesian computation. Firstly, Bayesian methods to estimate divergence dates when rates of evolution vary from lineage to lineages are extended and compared. The power of the technique is demonstrated by analysing twenty-two genes sampled across the metazoans to test the Cambrian explosion hypothesis. While the molecular clock gives divergence dates at least twice as old as those indicated by the fossil records, it is shown (i) that modelling rate change gives results consistent with the fossils, (ii) that this improves dramatically the fit to the data and (iii) that these results are not dependent on the choice of a specific model of rate change.Results from this analysis support a molecular explosion of the metazoans about 600 million years (MY) ago, i.e. only some 50 MY before the morphological Cambrian explosion. Secondly, two new Bayesian tests of phylogenetic trees are developed. The first aims at selecting the correct tree, while the second constructs confidence sets of trees. Two other tests are also developed, in the frequentist framework. Based on p-values adjusted for multiple comparisons,they are built to match their Bayesian counterparts. These four new tests are compared with previous tests. Their sensitivity to model misspecification and the problem of regions is discussed. Finally, some extensions to the models examined are made to estimate divergence dates from data of multiple genes, and to detect positive selection.

The design of buildings for extreme loads has traditionally been conducted on a life safety basis. As a result, buildings often need to be demolished after an extreme event since the cost of repairing the extensive damage is too great. For many buildings, especially critical infrastructure, continued operation after an explosive attack is essential. The use of energy-dissipating methods in a componentized system will enable the protection of a structure and occupants from a blast and permit the rapid repair and re-occupation of the building after an explosive attack. This study focuses on the characterization of a componentized system utilizing energy-dissipating component assemblies. From this characterization, a predictive theory, based on a single degree of freedom model, is developed and a general design method proposed. The predictive theory and design method are evaluated in field blast tests.

The design of buildings for extreme loads has traditionally been conducted on a life safety basis. As a result, buildings often need to be demolished after an extreme event since the cost of repairing the extensive damage is too great. For many buildings, especially critical infrastructure, continued operation after an explosive attack is essential. The use of energy-dissipating methods in a componentized system will enable the protection of a structure and occupants from a blast and permit the rapid repair and re-occupation of the building after an explosive attack. This study focuses on the characterization of a componentized system utilizing energy-dissipating component assemblies. From this characterization, a predictive theory, based on a single degree of freedom model, is developed and a general design method proposed. The predictive theory and design method are evaluated in field blast tests.

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No description available.