Dissertations / Theses on the topic 'Phénomènes de concentration'
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Druet, Olivier. "Asymptotiques géométriques, phénomènes de concentration et inégalités optimals." Cergy-Pontoise, 2001. http://www.theses.fr/2001CERG0134.
We study sharp Sobolev inequalities on manifolds. The limit case is the Cartan-Hadamard conjecture. A study of elliptic concentration phenomena is also done
Mesmar, Hussein. "Phénomènes de concentration pour des équations elliptiques surcritiques." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0338.
In this manuscript, we present several aspects of the resolution of nonlinear elliptic partial differential equations with supercritical Sobolev exponent. We are considering the context of a compact Riemannian manifolds and we fix a subgroup of the isometries of this manifold. Taking a problem invariant under the action of this group permits to get a reasonable supercritical problem. More precisely, if the action of such a group is free, the quotient is also a smooth manifold: this transforms a supercritical problem on the initial manifold into a critical problem on the quotient manifold. Therefore, under this free-action hypothesis, the problem is artificially supercritical. In our work, we consider the more intricate case of a group that does not act freely, so that the quotient space is not necessarily a manifold, and the preceding method fails. We make explicit hypothesis on the group to be able to perform some analysis. In the first part, we compute the best constant in the Hardy-Sobolev supercritical inequalities with invariance under such a group: this constant depends on the corresponding Euclidean best constant. This constant allows us to get solutions to a supercritical Hardy-Sobolev equation with perturbation via the Mountain-Pass Lemma of Ambrosetti-Rabinowitz. In the second part, we perform an analysis of the concentration phenomenon associated with a supercritical problem, still invariant under the action of an isometry group. The main novelty we have to face is that we have to work on a piece of the quotient which is a manifold, but it has a boundary, and we do not have conditions like Dirichlet or Neumann here. However, we overcome this problem by proving a concentration of the mass that allows to get a good control far from the concentration orbit. Under suitable nondegeneracy assumptions, we show that the concentration orbit converges very fast to a limiting orbit. This allows to get a relation between the potential and the geometry at the concentration orbit, so that we get a localization of the concentration. Despite they are geometric in nature, our technique enjoy applications to the more classical context of nonlinear equations on a domain of the flat space
Mirrahimi, Sepideh. "Phénomènes de concentration dans certaines EDPs issues de la biologie." Paris 6, 2011. http://www.theses.fr/2011PA066165.
Vanderschaeve, Frédérique. "Influence de l'azote en forte concentration sur les phénomènes de précipitation dans les aciers." Lille 1, 1993. http://www.theses.fr/1993LIL10120.
Cini, Emmanuel. "Contribution à l'étude de phénomènes de germination, de démixtion et de métastabilité morphologique." Grenoble INPG, 1997. http://www.theses.fr/1997INPG0004.
A thermodynamic approach of homogeneous nucleation in binary liquid alloys is presented. It postulates that concentration fluctuations in the liquid state can provide favoured sites for nucleation. This mechanism considers local chemical order fluctuations and structure fluctuations as separated events. A statistical analysis shows that the efficiency of the transformations of liquid fluctuations into solid nuclei increases with the amount of undercooling and reaches a maximum for a relative level of undercooling equal to 2/3. Spinodal decomposition is also considered. Particular emphasis is laid upon the topological aspects of phase separation, which provide evidence for a continuous transition from metastability to instability in the case of short range atomic interactions. Furthermore, a critical size for the mother phase appears, below which spinodal decomposition is thermodynamically impossible. This critical size, brought to the fore in the frame of the capillary formalism, becomes identical to that obtained by the continuous theories of phase transitions when physico-chemical constraints at the interface are relaxed. The stabilising effect of the mother phase size is also demonstrated for nucleation. Finally, grain refinement phenomena encountered in non equilibrium solidification processes are reviewed. In addition to a critical assessment of the main explanatory mechanisms, a new approach is proposed, which is based on the kinetic undercooling at the solidification front. At high supercooling levels, planar front stabilisation may be preceded by a transient unstable regime which could cause the solidification structure to be refined. Similar structures can also result when kinetic anisotropy interferes with surface tension anisotropy. Highly undercooled metallic samples processed in the 48 meter high Grenoble drop tube undergo a recrystallization phenomenon that is likely related to the existence of metastable phases. Besides, morphological instabilities are noticeable, which support the kinetic approach
Calesso, Teixeira Elba. "Étude des phénomènes relatifs à la concentration et à la lixiviation des éléments-traces dans les cendres volantes produites lors de la combustion du charbon pulvérisé." Vandoeuvre-les-Nancy, INPL, 1988. http://www.theses.fr/1988NAN10024.
Aissaoui, Rached. "Contribution à l'étude des couches minces de l'alliage germanium-sélénium, avec une concentration de germanium inférieure à trente-trois pour cent : élaboration, relaxation, conduction." Rouen, 1986. http://www.theses.fr/1986ROUES046.
Jing, Ruihua. "Phénomène de concentration pour des équations avec nonlinéarités surcritiques." Paris 12, 2005. https://athena.u-pec.fr/primo-explore/search?query=any,exact,990003940560204611&vid=upec.
Mahmoudi, Fethi. "Phénomène de concentration pour desproblèmes non linéaires issus de la géométrie." Phd thesis, Université Paris XII Val de Marne, 2005. http://tel.archives-ouvertes.fr/tel-00011695.
courbure principale de l'hyersurface). Nous donnons dans cette thèse quelques résultats d'existence de telles hypersurfaces. En outre, les exemples que nous construisons mettent en évidence un phénomène de concentration le long de sous variétés, phénomène
associé à un phénomène de résonance qui rend l'analyse de ces objets particulièrement délicate et que l'on rencontre dans l'étude de nombreux autres problèmes non-linéaires, équation de Schrödinger non linéaire, problème de perturbations singulière,
système de réaction-diffusion,...
Mahmoudi, Fethi. "Phénomène de concentration pour des problèmes non linéaires issus de la géométrie." Paris 12, 2005. https://athena.u-pec.fr/primo-explore/search?query=any,exact,990002286080204611&vid=upec.
In this thesis, we study concentration phenomenom for geometrical elliptic equations : the existence of constant r-curvature hypersurfaces in Riemannian manifolds. We give some results of existence of such submanifolds. Moreover, the examples we give present a phenomenom of concentration along submanifolds, which is associated with a resonance phenomenom. This makes particulary delicate the analysis of these objects and which shows up in the study of many other nonlinear problems : nonlinear Schrödinger equations, singularly perturbed problems,. .
Atmani, Hassane. "Investigations dans le domaine des comportements thermiques de matériaux désordonnés : application au sélénium et aux mélanges Se-Bi à faible concentration en bismuth." Rouen, 1988. http://www.theses.fr/1988ROUES009.
Joulin, Aldéric. "Concentration et fluctuations de processus stochastiques avec sauts." Phd thesis, Université de La Rochelle, 2006. http://tel.archives-ouvertes.fr/tel-00115724.
Dans la première partie de la thèse, nous explorons le
phénomène de concentration des processus de naissance et de mort. Les différentes approches considérées sont d'une part les inégalités fonctionnelles ainsi que la méthode de
Herbst, et d'autre part l'étude des propriétés du semigroupe associé et des techniques de martingales. En particulier, nous
sommes amenés à introduire diverses notions de courbures de ces processus, analogues discrets du critère de courbure de Bakry-Emery dans le cadre des processus de diffusion.
Dans la deuxième partie de la thèse, nous étudions le
comportement du processus supremum d'une intégrale stable stochastique en établissant des inégalités maximales que nous appliquons à des problèmes de temps de passage de
processus symétriques stables. Enfin, nous démontrons un principe de domination convexe pour des intégrales stochastiques brownienne et stable corrélées.
Buffet-Bataillon, Sylvie. "Relation épidémiologique et génétique entre la résistance aux antibiotiques et des concentrations minimales inhibitrices élevées d'Escherichia coli isolés de bactériémies vis-à-vis d'ammoniums quaternaires." Rennes 1, 2011. http://www.theses.fr/2011REN1B085.
Quaternary ammonium compounds (QACs) are used as a preservative in the composition of cosmetics and pharmaceuticals products. They are also widely used as detergents, disinfectants. The increasing use of AQs may be one factor responsible for the emergence of multidrug resistance in clinical bacterial strains. A prospective study was conducted in 153 patients with Escherichia coli bacteremia at the University Hospital of Rennes. This study showed an epidemiological link between high values of minimum inhibitory concentrations (MIC) of QACs in E. Coli and resistance to antibiotics (ATB). Secondarily, the mechanisms of co-resistance has been studied showing the involvement of the Class 1 integrons, the AcrAB multi-drug efflux pump and mar regulon in E. Coli strains resistant to ATB and with high MICs of QACs. A review finally reported the role of QACs in the acquisition of antibiotic resistance. It appears important that this mechanism can be identified by microbiology laboratories
Ben-Hamou, Anna. "Concentration et compression sur alphabets infinis, temps de mélange de marches aléatoires sur des graphes aléatoires." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC197/document.
This document presents the problems I have been interested in during my PhD thesis. I begin with a concise presentation of the main results, followed by three relatively independent parts. In the first part, I consider statistical inference problems on an i.i.d. sample from an unknown distribution over a countable alphabet. The first chapter is devoted to the concentration properties of the sample's profile and of the missing mass. This is a joint work with Stéphane Boucheron and Mesrob Ohannessian. After obtaining bounds on variances, we establish Bernstein-type concentration inequalities and exhibit a vast domain of sampling distributions for which the variance factor in these inequalities is tight. The second chapter presents a work in progress with Stéphane Boucheron and Elisabeth Gassiat, on the problem of universal adaptive compression over countable alphabets. We give bounds on the minimax redundancy of envelope classes, and construct a quasi-adaptive code on the collection of classes defined by a regularly varying envelope. In the second part, I consider random walks on random graphs with prescribed degrees. I first present a result obtained with Justin Salez, establishing the cutoff phenomenon for non-backtracking random walks. Under certain degree assumptions, we precisely determine the mixing time, the cutoff window, and show that the profile of the distance to equilibrium converges to the Gaussian tail function. Then I consider the problem of comparing the mixing times of the simple and non-backtracking random walks. The third part is devoted to the concentration properties of weighted sampling without replacement and corresponds to a joint work with Yuval Peres and Justin Salez
Compain, Séverine. "Pharmacologie intracellulaire des antirétroviraux utilisés contre le VIH : développement et méthodes analytiques et intérêt de la mesure des concentrations intracellulaires pour la compréhension des phénomènes d'efficacité et d'échappement thérapeutique." Paris 11, 2006. http://www.theses.fr/2006PA114806.
Several analytical methods were developed using LC/MS/MS and LC/UV for the determination of the antiretroviral drugs used against HIV in plasma and intracellular medium. In particular, these analytical lethods enabled to study the transformation of AZT that leads to the formation of d4TP-TP, compound thaty was formally identified. Some information concerning the step of this transformation, and the intracellular pharmacocinetik profile of d4TP-TP from AZT was given. We showed that intracellular concentrations could be a predictive tool for efficient treatment and allowed understanding treatment failure phenomena. Thus d4TP-TP from AZT did not participate to effectiveness of AZT and in contrary d4TP-TP decreased its. The use of plasmatic and intracellular concentrations is an essential tool for the pharmacology of antiviral drugs used against HIV and will allow setting up an effective treatment
Uzhegov, Sergey. "Capital concentration and petroleum abundance in economies of Eurasia - Russia, Kazakhstan, and Azerbaijan : microeconomic performance and macroeconomic dynamics." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC182/document.
Present research is an inquiry into implications of emergence of billionaires and petroleum-abundance on development trajectory of Russia, Kazakhstan, and Azerbaijan. Highly-controversial accumulation of massive fortunes is going in parallel with economic downturn and transformation of collective owners of state assets into low-paid labor-force, with thousands of street-protesters in Russia in 2017, who 100 years after 1917 Revolution raise the same questions: ‘who owns what?’ and ‘how efficiently?’ In order to contribute ‘hard data’ to debate, current investigation: first, explores a process of formation of billionaires, focusing on legitimacy and social fairness; and second, evaluates their comparative performance. Analyzing 9-year 2007-15 timespan, it considers 300 legal entities, comprised by 3 groups of companies: 100 of billionaires, 100 of government, and 100 of entrepreneurs. To elicit performance differences this study refers to 25 financial metrics, composed by 2 categories – 5 core accounting parameters and 20 financial ratios. Alongside, a paradox of economic underperformance of these 3 petronations of Eurasian Continent is explored. To overcome adversities of resource-based path, the study suggests: 1. novel analytical framework: diagnosis algorithm and process model; 2. growth model’s setup, embracing petronational and institutional dimensions; and 3. empirical model, exposing links of analysis’ elements with macroeconomic dynamics
Gil, Marie-Ève. "Analyse d'équations intégro-différentielles et d'EDP non locales issues de la modélisation de dynamiques adaptatives." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0346.
This manuscript is devoted to the mathematical analysis of integro-differential models from population genetics. Both models are reaction-dispersion equations of the form ∂tp(t,m) = UD[p](t,m)+ f[p](t,m). They describe the dynamics of fitness distribution in an asexual population under the effect of mutation and selection. These two processes are represented by the nonlocal terms UD[p](t,m) and by f[p](t,m) respectively. The difference between the models rests on the mutation term. Indeed, in the first model, the mutation effects on fitness do not depend on the fitness of the parent. Thus, the mutation term is a standard convolution product: D[p](t,m) =RR J(m−y)p(t,y)dy −p(t,m). When a mutation occurs, the function J(m − y) represents the density of probability for an individual with fitness y to have an offspring with fitness m. The mutation rate is given by the constant U. In the second model, the mutation effects on fitness depend on the fitness of the parent. In this case, an individual with fitness y has an offspring with fitness m with a probability density Jy(m−y). This type of dependence naturally arises when the existence of an optimal fitness (or a phenotypic optimum) is assumed. For both models, we first establish existence and uniqueness results as well as decay properties of the solution. The decay property allows us to define the cumulant generating function (CGF). The CGF obeys a nonlocal transport equation. In the first model, we compute the analytical solution of this transport equation and thus, we obtain a complete description of the distribution p(t,m) through its moments. Then, we study the stationary states for both models, and establish sufficient conditions for the existence and non-existence of a concentration phenomenon corresponding to an accumulation of individuals with best possible phenotype. The results are compared to the results of stochastic individual based models which represent the same kind of evolutionary dynamics
Rossignol, Raphaël. "Largeur du seuil dans les lois du Zéro-Un." Phd thesis, Paris 5, 2005. http://www.theses.fr/2005PA05S010.
This thesis further develops some recent results due to Talagrand , Friedgut and Kalai on the study of general conditions under which threshold phenomena occur. In a first part, we contribute to the unification of the general framework of the threshold phenomena, firstly by connecting the original setting of the "thresholds functions" due to Erdös and Renyi, the one of Friedgut and Kalai's work and the concentration of the hittig time of the property for which the threshold phenomenon holds ; secondly, by originating a research on the stability of the threshold phenomena under three kind of operations : union, intersection and tensor product. We obtain thus a simple way to construct threshold widths of various orders. In a second part, we optimize the general upper bound on the threshold width of a monotone symmetric property by using the logarithmic Sobolev inequality on the discrete cube
Robert, Marianne. "Le comportement des thons tropicaux autour des objets flottants : de l’étude des comportements individuels et collectifs à l’étude du piège écologique." Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20118/document.
Research in fisheries science aims at investigating the functioning of fish population with the objective of using this knowledge to propose sustainable management measures. This PhD thesis relies on a collection of experiments and modelling designed to further our knowledge on the aggregative behaviour of large pelagic fish with floating structures at the surface of the ocean. The overall objective is to test whether the thousands of man-made floating structures deployed by fishermen (also referred as Fish Aggregating Device –FAD) act as ecological traps for tropical tunas. To archive this main objective, it was first necessary to characterize the individual behaviour of tuna in a network of FAD. In the first chapter, the analysis of 96 acoustically tagged yellowfin tuna (Thunnus albacares) between 30-96 cm FL in the array of anchored FADs around Oahu (Hawaii, US) shows that individuals tuna exhibited behavioural plasticity while in the array and that behaviour around FAD is size dependent. In order to assess the impact of the increasing density of FAD, the major habitat modification, it is essential to understand the factors that influence the residence time at FADs. In the second chapter, binary choice experiments suggest that the aggregated biomass under the FAD play a role in the aggregative process. Nonetheless, quantification of arrival and departure dynamics of fish to FAD are required to validate the assumptions we proposed on the underlying social mechanism. Such model would, then, allow testing the effect of FAD density and environmental conditions on individual residence time and spatial distribution of population. In the third chapter, the comparison of skipjack tuna (Katsuwonus pelamis) condition between individual associated with logs and in free swimming schools in the Mozambique Channel, an area known to be naturally enriched with logs with few FADs, highlights the need for estimating reference points prior to assessing the impacts of anthropogenic modifications to habitats on animals.Combining the different chapters, our results tend to favour a social rather than a trophic role of floating objects in the ecology of tunas. More generally, we discuss what novel insight our results bring up on the ecological trap hypothesis. Tropical tunas represent an interesting model species on which we focused. However, the theoretical framework of the questions we addressed, the observation and analytical tools we developed are generic enough to be applied to the others species that are encountered around floating structures. In a broader extent, this work meets the general topic of studying behavioural strategies and distribution of population in multi-patch environment
De, Wals Pierre-Yves. "Analyses mutationnelles et cinétiques de la [bêta]-lactamase TEM-1 de Escherichia coli : vers une meilleure compréhension du phénomène de résistance aux antibiotiques." Thèse, 2007. http://hdl.handle.net/1866/15245.