La cavitation est un phénomène de changement de phase dans les zones de basses pressions des machines hydrauliques. Ses conséquences sont souvent néfastes : pertes de performances, génération de bruit et de vibrations, abrasion des matériaux... Ces effets deviennent une préoccupation importante dans la conception des machines hydrauliques. Ce travail a pour objectif principal de développer un modèle de simulation numérique pour la simulation de la cavitation à haut ordre de précision, pour des écoulements compressibles visqueux, et pour des géométries complexes. Le modèle adopté pour la modélisation de la cavitation est le modèle de mélange homogène. Cette formulation ne dépend d'aucun paramètre empirique et peut être aisément étendu à du multi-espèce. Nous utilisons un code de volumes finis, dont le haut ordre de reconstruction est assuré par la méthode des moindres carrés mobiles.

Therapeutic strategies of stroke can take two directions: to prevent brain damage from stroke or aid in its repair after a stroke. In this thesis, a rat stroke model, which mimics the human small vessel stroke, was used. Two potential repair strategies were investigated with this model, reduction of inflammatory processes with the aid of minocycline treatment and replacing necrotic neurons with new ones with the aid of neurogenesis of endogenous progenitor cells. <p>The stroke model is induced by disrupting the medium-size pial vessels within a 5mm-circular brain surface of adult Wistar rats. This leads to a cone-shaped cortical lesion. Therefore it mimics the clinical situation of lacunar infarction, the most frequent outcome of small vessel stroke. <p>Minocycline, a second-generation tetracycline, prevented cavitation and facilitated the repopulation of the lesion by reactive astrocytes. However, I could not identify the molecular target as the number of activated microglia, infiltrating leukocytes and CD3+ lymphocytes as well as interleukin-1β expression were not significantly altered. Doublecortin (DCX) is a microtubule-associated protein expressed by migrating neuroblasts and immature neurons. After injury, DCX-positive cells appeared in the neocortex at the base of the lesion. These cells exhibit a morphology resembling differentiated post-migratory neurons with long branched processes. Some of the DCX-positive cells were also immunoreactive for βIII-tubulin, another marker of immature neurons. This might indicate a migratory pathway for developing neuroblasts from the subventricular zone (SVZ) through the corpus callosum to the lesion. SVZ cells were labeled with carboxyfluorescein diacetate, succinimidyl ester (CFSE) stereotaxical injections. Although rostral migratory stream and olfactory bulb were intensely labeled, no CFSE containing cells were found in the cortex underneath the lesion. These results suggest that the DCX-positive cells may not originate from neural precursors from the SVZ, but might be generated from local progenitor cells. In summary, using the PVD II model, which mimics the lacunar stroke, I found that neuroblasts appeared spontaneously near the lesion in the cerebral cortex and were attempting to upregulate neuronal properties. Reducing inflammation with post-stroke minocycline treatment prevented cavitation. I think both findings open up exciting new avenues for treatment of lacunar infarctions.

Firing an underwater spark discharge generates an expanding plasma which causes a spherical shockwave to propagate through the surrounding water. The shockwave can have many effects, including resonance effects on bubbles, mechanical destructive effects on solid surfaces and living organisms, and sonochemical oxidative effects on particles and chemical species present in the water. This phenomenon has been shown to improve the efficiency of ink removal in a laboratory flotation deinking cell, while simultaneously decreasing fiber loss. These process improvements are attributed to the sonochemical oxidation of ink particle surfaces, caused by shockwave-induced cavitation. This finding is supported by zeta potential measurements. Sparking was found to reduce the zeta potential of ink particles by up to 20 mV. When sparking was performed during deinking, no effect was found on either ink removal or solids loss. However, when the pulp was pretreated with sparking before flotation, a significant improvement was seen in the brightness gain. Further, fiber loss was decreased by up to 25% in a single flotation stage. The economics of this process are attractive; payback is on the order of three months based on fiber savings alone. Also, at about 1.5 kJ per spark, the power requirements are minimal with respect to the benefit derived.

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Thèse de doctorat : Sciences. Thermique et énergétique : Ecole centrale de Lyon : 2003. / Bibliogr. 116 réf.

Thèse de doctorat : Sciences. Thermique et énergétique : Ecole centrale de Lyon : 2003. / Titre provenant de l'écran-titre. Bibliogr. 116 réf.

Reproduction de : Thèse de doctorat : Dynamique des fluides : Toulouse, INPT : 2006. / Titre provenant de l'écran-titre. Bibliogr. 74 réf.

Reproduction de : Thèse de doctorat : Dynamique des fluides : Toulouse, INPT : 2005. / Titre provenant de l'écran-titre. Bibliogr. 182 réf.

Thèse doctorat : Chimie-Physique : Strasbourg 1 : 2006. / Titre provenant de l'écran-titre. Bibliogr. p8 .

Thesis (Ph. D.)--Mississippi State University. Department of Computational Engineering. / Title from title screen. Includes bibliographical references.