WorldCat Identities

Laboratoire J.-A. Dieudonné (Nice)

Overview
Works: 84 works in 85 publications in 2 languages and 87 library holdings
Roles: Other, Degree grantor, Editor
Publication Timeline
.
Most widely held works by Laboratoire J.-A. Dieudonné (Nice)
Étude par méthode spectrale de sillages tridimensionnels en fluides stratifiés by Marc Forestier( Book )

2 editions published in 2000 in French and held by 2 WorldCat member libraries worldwide

Notre principal objectif est l'étude numérique des sillages en fluides stratifiés en température, phénomène physique qui se rencontre fréquemment à l'état naturel. Une approche bibliographique apporte les connaissances de base nécessaires. Une méthode spectrale multidomaine Tchebychev-Tchebychev-Fourier est proposée et développée sur calculateur parallèle. Un gain en stabilité est obtenu en traitant implicitement une partie des termes d'advection et l'implémentation algorithmique utilise une technique de triangularisation de Schur. À chaque pas de temps, la résolution des équations de Navier-Stokes se ramène à un problème d'Oseen généralisé. La difficulté des conditions de sortie est surmontée grâce à des conditions originales de non réflexion : "u - [oméga]". Une méthode de pénalisation permet de modéliser l'obstacle dans l'écoulement et son emploi est justifié par le calcul du sillage tridimensionnel d'un cylindre. Enfin, le code numérique a permis la résolution spatio-temporelle du sillage tridimensionnel d'une sphère pour différentes stratifications au nombre de Reynolds de 300. On donne une description des différents phénomènes physiques et on étudie le rôle de la stratification sur les structures tourbillonnaires. Son caractère inhibitoire est identifié, notamment pour le cas de plus forte stratification par le phénomène d'effondrement du sillage
Contributions théoriques en optimisation et modélisation des structures by Zeine Ould Mohamed Ould Zeidane( Book )

1 edition published in 1995 in French and held by 2 WorldCat member libraries worldwide

CE TRAVAIL TRAITE QUELQUES PROBLEMES D'OPTIMISATION ET DE MODELISATION DE STRUCTURES MINCES ELASTIQUES. LE DEPLACEMENT D'UNE STRUCTURE SOUMISE A UN CHARGEMENT EST SOLUTION D'UNE EQUATION OU D'UN SYSTEME D'EQUATIONS AUX DERIVEES PARTIELLES FAISANT INTERVENIR OUTRE LES CARACTERISTIQUES PHYSIQUES DU MATERIAU LA GEOMETRIE DE LA STRUCTURE QUI EST CONSIDEREE COMME VARIABLE DE CONCEPTION. L'OBJECTIF DU CONSTRUCTEUR EST DE DETERMINER LA MEILLEURE STRUCTURE AU SENS D'UN CRITERE DONNE QUANTIFIE PAR UNE FONCTION COUT. IL CHERCHE A DETERMINER DONC LA VALEUR DE LA VARIABLE DE CONCEPTION QUI MINIMISE CETTE FONCTION. LE PROBLEME DE L'EXISTENCE DE CET OPTIMUM EST BIEN SOUVENT DIFFICILE VOIRE IMPOSSIBLE A RESOUDRE ET IL EXISTE DE NOMBREUX CAS OU IL N'ADMET PAS DE SOLUTION. CEPENDANT, ON MONTRE DANS CE TRAVAIL, L'EXISTENCE D'UNE ARCHE ET D'UNE POUTRE OPTIMALES POUR DE LARGES CLASSES DE FONCTIONS COUTS. DE MEME, ON MONTRE L'EXISTENCE D'UNE FINE DISTRIBUTION OPTIMALE DE MATERIAU MOU, ENTOURANT UNE PLAQUE, QUI MINIMISE L'ENERGIE GLOBALE. DANS LA PARTIE MODELISATION, ON DONNE UNE JUSTIFICATION DU MODELE D'ASSEMBLAGE D'ARCHES AVEC CHARNIERE RIGIDE. EN EFFET, CELUI-CI APPARAIT COMME LIMITE, DANS UN CERTAIN SENS, DU MODELE UTILISE POUR LES ARCHES REGULIERES. ENFIN, ON PRESENTE UNE ETUDE COMPARATIVE ENTRE LES MODELES DE TYPE KIRCHHOFF-LOVE ET LE MODELE DE NAGHDI POUR LES COQUES EN EXPLICITANT, DANS LE CAS PARTICULIER D'UNE ARCHE, DES CONDITIONS NECESSAIRES ET SUFFISANTES SUR LE CHARGEMENT POUR QU'IL Y AIT IDENTITE DES DEUX FAMILLES DE MODELES
Interaction entre symbolique et numérique : application à la vision artificielle by Didier Bondyfalat( Book )

1 edition published in 2000 in French and held by 2 WorldCat member libraries worldwide

"Les motivations initiales de ce travail proviennent de l'étalonnage de caméras en vision artificielle. Nous nous sommes surtout intéressés aux manières d'exploiter des mesures dans les images (détection d'objets) et des considérations géométriques formelles. Nous avons élargi nos recherches à la problématique suivante :"l'interaction entre symbolique et numérique ". Ce travail se divise en trois parties. La première partie traite de la résolution d'équations polynomiales avec des coefficients approchés. Nous étudions des méthodes matricielles qui transforment la résolution en la recherche des valeurs et des vecteurs propres d'une matrice. Ces transformations et et les calculs de valeurs et vecteurs propres sont continues par rapport aux coefficients et permettent donc de résoudre des équations à coefficients approchés. La deuxième partie présente un cadre algébrique permettant d'exprimer simplement des contraintes géométriques. Ce formalisme nous a permis de modéliser de manière fine l'étalonnage d'une ou plusieurs caméras avec l'aide d'un plan. L'étalonnage ne peut être effectué pratiquement qu'avec des résolutions numériques de systèmes linéaires. La troisième partie est consacrée à l'étude et surtout à l'utilisation des outils de démonstration automatique en géométrie pour la construction de modèles 3D articulés. Par des optimisations numériques, nous déterminons les paramètres des modèles articulés qui permettent aux images de ces modèles de coïncider avec les données extraites des photographies"
Sur la synchronisation et la désynchronisation des systèmes dynamiques. Applications by Camille Poignard( )

1 edition published in 2013 in English and held by 1 WorldCat member library worldwide

This thesis deals with the synchronization and desynchronization of dynamical systems. In a first part we tackle (under a biological viewpoint) the desynchronization problem, which consists in the induce- ment of a chaotic behavior in a stable dynamical system. We study this problem on a gene regulatory network called V-system, invented in order to couple in a very simple way, a Hopf bifurcation and a hysteresis-type dynamics. After having proved that a vector field on Rn admitting such a coupling may, under some condi- tions, show a chaotic dynamics, we give a set of parameters for which the associated V-system satisfies these conditions and verify numerically that the mechanism responsible of the chaotic motion occurs in this system. In a second part, we take interest in the synchronization of hierarchically organized dynamical systems. We first define a hierarchical structure for a set of 2^n systems by a matrix representing the steps of a matching process in groups of size two. This leads us naturally to the case of a Cantor set of systems, for which we obtain a global synchronization result generalizing the finite case. Finally, we deal with the situation where some defects appear in the hierarchy, that is to say when some links between certain systems are broken. We prove we can afford an infinite number of such broken links while keeping a local synchronization, providing they are only present at the first N stages of the hierarchy (for a fixed integer N) and they are enough spaced out in these stages
Approche multiéchelle pour le comportement vibratoire des structures avec un défaut de rigidité by Nadia Ben Brahim( )

1 edition published in 2014 in French and held by 1 WorldCat member library worldwide

We consider small solutions of a vibrating mechanical system with smooth non-linearities for which we provide an approximate solution by using multiple scale analysis; we first use a double scale analysis; in order to improve the approximation, then we perform a triple scale analysis; a rigorous proof of convergence of the triple scale method is included; for the forced response, a stability result is needed in order to prove convergence in a neighborhood of a primary resonance. The amplitude of the response with respect to the frequency forcing is described and it is related to the frequency of a free periodic vibration
Groupes projectifs et arrangements de droites by Zhenjian Wang( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

The objective of this thesis is to investigate various questions about projective groups and line arrangements in the projective plane. A projective group is a group which is isomorphic to the fundamental group of a smooth complex projective variety. To study projective groups, sophisticated techniques in algebraic topology and algebraic geometry have been developed in the passed decades, for instance, the theory of cohomology jump loci, together with Hodge theory, has been proven a powerful tool. Line arrangements in the projective plane are of special interest in the study of projective groups. Indeed, there are many open questions related to projective groups, and the theory of hyperplane arrangements, and in particular that of line arrangements, which is quite an active area of research, may provide insights for these problems. Furthermore, problems concerning the fundamental groups of the complements of hyperplane arrangements can be reduced to the case of line arrangements, due to the celebrated Zariski theorem of Lefschetz type. Very often, in the study of projective groups or quasi-projective groups, one usually considers line arrangements first to get some intuitive ideas. In this thesis, we also prove some theorems that are of independent interest and can be used elsewhere, for instance, we prove properties concerning morphisms from products of projective spaces in Chapter 4, we show that some morphisms have generic connected fibers in Chapter 5 and we give criteria for a projective surface to be of general type in Chapter 7
La stabilité du filtre non-linéaire en temps continu by Van Bien Bui( )

1 edition published in 2016 in French and held by 1 WorldCat member library worldwide

The filtering problem consists of estimating the state of a dynamic, called signal which is often a Markov process, from the noisy observation of the past states. In this thesis, we consider a filtering model in continuous time for the diffusion process. The aim is to study the stability of the optimal filter with respect to its initial condition beyond the mixing (or quasi - mixing) hypothesis for the transition kernel
Optimisation automatisée de scénarios pour le système de champ magnétique poloïdal dans les tokamaks by Xiao Song( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

Cette thèse concerne le développement et l'application d'outils numériques permettant d'optimiser l'utilisation du système de champ magnétique poloïdal dans les tokamaks. Ce dernier est constitué d'un ensemble de bobines et d'alimentations électriques dont le rôle est de contrôler la forme et la position du plasma ainsi que de générer le courant plasma. Le contexte général de notre travail est décrit dans le Chapitre 1. Le Chapitre 2 présente notre approche du problème, qui consiste à appliquer des méthodes de contrôle optimal au problème d'Equilibre à Frontière Libre (EFL). Ce dernier est composé d'une équation d'équilibre des forces dans le plasma couplée aux équations de Maxwell dans l'ensemble du tokamak. L'outil numérique employé ici est le code FEEQS.M, qui peut être utilisé soit (dans le mode dit « direct ») pour résoudre le problème EFL soit (dans le mode dit « inverse ») pour minimiser une certaine fonction-coût sous la contrainte que les équations d'EFL soient satisfaites. Chacun de ces deux modes (« direct » et « inverse ») se subdivise en un mode « statique » (qui s'applique à un instant donné) et un mode « évolutif » (qui s'applique sur un intervalle de temps). Le code est écrit en langage Matlab et utilise la méthode des éléments finis. La nature non-linéaire du problème d'EFL est traitée au moyen d'itérations de Newton, et une méthode de type programmation séquentielle quadratique est appliquée pour les modes inverses. Nous soulignons que le mode « inverse évolutif » est, à notre connaissance, une caractéristique unique de FEEQS.M. Après avoir décrit les problèmes d'EFL ainsi que les méthodes numériques utilisées et quelques tests de FEEQS.M, nous présentons deux applications. La première, décrite dans le Chapitre 3, concerne l'identification du domaine opérationnel en termes d'équilibre plasma pour le tokamak ITER. Ce domaine est contraint par les limites du système de champ poloïdal portant par exemple sur les courants, forces ou champ magnétiques dans les bobines. Nous avons implémenté des termes de pénalisation dans la fonction-coût du mode « statique inverse » de FEEQS.M pour prendre en compte ces limites. Ceci nous a permis de calculer de façon rapide, rigoureuse et automatique le domaine opérationnel, ce qui représente un progrès substantiel par rapport aux méthodes « traditionnelles » qui impliquent une intervention humaine beaucoup plus lourde. La seconde application, présentée au Chapitre 4, concerne le développement d'une transition rapide d'une configuration plasma « limitée » à une configuration « divergée » au début d'une décharge dans le tokamak WEST. La motivation est ici la réduction de la contamination du plasma par les impuretés de tungstène. A cette fin, le code FEEQS.M est utilisé dans son mode « inverse évolutif ». Des données expérimentales de WEST sont utilisées pour paramétrer la simulation. Le calcul FEEQS.M fournit alors des trajectoires optimales pour les courants des bobines poloïdales et les voltages de leurs alimentations afin d'obtenir une transition « limité »-« divergé » rapide. Ces trajectoires sont testées d'abord sur le « simulateur de vol » WEST (qui embarque FEEQS.M en mode « direct évolutif » couplé à un système de rétroaction identique à celui utilisé dans WEST) et ensuite expérimentalement sur WEST. Ceci a permis de passer d'une transition durant 1s à une transition durant 200ms
Développements autour de la méthode d'interactions de configurations en champ moyen by Amine Ilmane( )

1 edition published in 2015 in French and held by 1 WorldCat member library worldwide

In this thesis we developed new theoretical tools for molecular rovibrational spectra for a better description of the excited vibrational states and movements with large amplitudes using mean field configuration interaction method. First, we discussed the choice of modal basis and different trade-off to overcome the possible shortcomings of potential energy surfaces. In this context we have also developed selection criteria to improve the quality of rovibrational wave functions. These approaches have been successfully applied to the methane molecule (CH4). Secondly, we have implemented a formal algorithm for calculating the kinetic energy operators in arbitrary coordinates that allows the derivation of exact expressions and their Taylor and Fourier series, using, in a very efficient way, the capabilities of the software MATHEMATICA which yield to the derivation of rovibrational Hamiltonians in valence coordinated. Finally, we have generalized the mean-field configuration interaction method by adding perturbatively a second order effective field. We applied this generalization to the hydrogen peroxide molecule (HOOH), which has shown an improvement for both energy levels and the associated wave functions, when dealing with groups of degrees of freedom that are energetically well separated
Modèles cinétiques de particules en interaction avec leur environnement by Arthur Vavasseur( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

The goal of this PhD is to study a generalisation of a model describing the interaction between a single particle and its environment. We consider an infinite number of particles represented by their distribution function. The environment is modelled by a vibrating scalar field which exchanges energy with the particles. In the single particle case, after a large time, the particle behaves as if it were subjected to a linear friction force driven by the environment. The equations that we obtain for a large number of particles are close to the Vlasov equation. In the first chapter, we prove that our new system has a unique solution. We then care about some asymptotic issues; if the wave velocity in the medium goes to infinity, adapting the scaling of the interaction, we connect our system with the Vlasov equation. Changing also continuously a function that parametrizes the model, we also connect our model with the attractive Vlasov-Poisson equation. In the second chapter, we add a diffusive term in our equation. It means that we consider that the particles are subjected to a friction force and a Brownian motion. Our main result states that the distribution function converges to the unique equilibrium distribution of the system. We also establish the diffusive limit making the wave velocity go to infinity at the same time. We find a simpler equation satisfied by the spatial density. In chapter 3, we prove the validity of both equations studied in the two first chapters by a mean field limit. The last chapter is devoted to studying the large time asymptotic properties of the equation that we obtained on the spatial density in chapter 2. We prove some weak convergence results
Une étude comparative de méthodes d'assimilation de données pour des modèles océaniques by Giovanni Abdelnur Ruggiero( )

1 edition published in 2014 in English and held by 1 WorldCat member library worldwide

This thesis developed and implemented iterative data assimilation algorithms for a primitive equation ocean model, and compared them with other well established DA methods such as the 4Dvar and the Singular Evolutive Extended Kalman (SEEK) Filter/Smoother. The new proposed iterative algorithms, similarly to the Back and Forth Nudging (BFN), are all based on a sequence of alternating forward and backward model integrations. Namely, they are the Backward Smoother (BS), which uses the backward model to freely propagate “future” observations backward in time, and the Back and Forth Kalman Filter, which also uses the backward model to propagate the observations backward in time but, at every time an observation batch is available, an update step similar to the SEEK filter step is carried out. The Bayesian formalism was used to derive these methods, which means that they may be used with any algorithm that estimates the “a posteriori” conditional probability of the model state by means of sequential methods. The results show that the main advantage of the methods based on the BFN is the use of the backward model to propagate the observation informations backward in time. By this way, it avoids the use of the adjoint model, needed by the 4Dvar, and of unknown temporal correlations, needed by the Kalman Smoother, to produce initial states or past model trajectories. The advantages of using the Back and Forth (BF) idea rely on the implicit use of the unstable forward subspace, which became stable when stepping backwards, that allows the errors components projecting onto this subspace to be naturally damped during the backward integration
Modèles cinétiques, de Kuramoto à Vlasov : bifurcations et analyse expérimentale d'un piège magnéto-optique by David Métivier( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

Long-range interacting systems are known to display particular statistical and dynamical properties.To describe their dynamical evolution, we can use kinetic equations describing their density in the phase space. This PhD thesis is divided into two distinct parts. The first part concerns our collaboration with an experimental team on a Magneto-Optical Trap. The physics of this widely-used device, operating with a large number of atoms, is supposed to display effective Coulomb interactions coming from photon rescattering. We have proposed experimental tests to highlight the analog of a Debye length, and its influence on the system response. The experimental realizations do not allow yet a definitive conclusion. In the second part, we analyzed the Vlasov and Kuramoto kinetic models. To study their infinite dimensional dynamics, we looked at bifurcations around unstable steady states. The goal was to obtain reduced equations describing the dynamical evolution. We performed unstable manifold expansions on five different kinetic systems. These reductions are in general not exact and plagued by singularities, yet they predict correctly the nature and scaling of the bifurcation, which we tested numerically. We conjectured an exact dimensional reduction (obtained using the Triple Zero normal form) around the inhomogeneous states of the Vlasov equation. These results are expected to be very generic and could be relevant in an astrophysical context. Other results apply to synchronization phenomena through the Kuramoto model for oscillators with inertia and/or delayed interactions
Interaction houle-courant : application à la physique des trous noirs : mémoire de Master 2 : [soutenu au] Laboratoire J-A Dieudonné, Nice by Jennifer Chaline( )

1 edition published in 2010 in French and held by 1 WorldCat member library worldwide

Modèle simplifié de changement de phase en présence de convection et rayonnement : application à un mur translucide associant superisolation et stockage d'énergie thermiques by Farah Souayfane( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

This thesis aims to study the exploitation of solar radiation thanks to a new concept of passive sensor wall. In this context, the thermal behavior of a novel semi-transparent solar wall has been studied. The wall is composed of glazing, silica aerogel (TIM) and glass bricks filled with fatty acids (PCM). This wall provides storage and restitution of heat, thermal-acoustic insulation and daylighting. The thermal performance of the TIM-PCM wall is tested in a full-sized test cell located in Sophia, PERSEE center. In winter, particularly in sunny cold days, the PCM absorbs solar radiation, melts, and then releases the stored heat to the building at night. During summer, overheating is encountered, the PCM remains in its liquid state and is unable to release the stored heat. A simplified model for PCM melting in presence of natural convection and radiation is developed and validated using a CFD model, and benchmark solutions. Then, a numerical model describing the heat transfer mechanisms through the wall is developed. This model is linked to TRNSYS to assess the thermal performance of the whole building. The MATLAB-TRNSYS model is then validated experimentally. The thermal behavior of the wall is tested under different climates, and passive solutions are proposed to ensure thermal comfort in summer. Finally, the validated model is used to study the annual thermal behavior of a building integrating TIM-PCM wall and an economic study is conducted. These studies confirm the interest of the wall vis-à-vis the improvement of energy performance of the building. The economic feasibility of applying the TIM-PCM wall depends mainly on climate, energy costs, and investment cost
L'histoire des mathématiques au service d'une nouvelle didactique de la discipline dans les cursus scolaires au Sénégal : approches théoriques et applications by Oumar Sagna( )

1 edition published in 2019 in French and held by 1 WorldCat member library worldwide

Our experience as a mathematics teacher has led us to explore a way that is still underused in Senegal, introducing a historical perspective into mathematics education, to check if it could interest students and motivate them to scientific studies.This thesis, which consists of seven chapters; the first five of which deal with the state of the art and the theoretical approaches. The last two describe and analyze the experimentation carried out in class of “Quatrième” at a College in the suburbs of Dakar.Chapter I is devoted on the one hand to the nature and specificity of mathematics to better understand the difficulties related to its teaching, and on the other hand to a review of the literature on the introduction of a historical perspective into teaching of mathematics, which clarified the use of history in the mathematics classroom. In this chapter are also defined the didactic framework of the thesis and the methodology used to carry out an experimentation in class of “Quatrième”.The context of our research was then detailed in Chapter II through a thorough description of the Senegalese educational system characterized by good results in the construction of classrooms and new scientific and technical blocks (BST), the parity index favorable to girls in primary school and high schools, but also by insufficiencies with the plethoric numbers of students, the weakness of the pedagogic supervision, the desertion of the scientific disciplines, the poor results in examinations certifications and external evaluations in mathematics.The presence of the History of Mathematics in curricula, textbooks and teacher training schemes is examined in Chapter III and compared to France, which has enormous potential in the field.These historical informations served as the subject for the didactic analysis proposed in Chapter IV, which also contains another input to the analysis: the illustrated description of the different types of use of the History of Mathematics. The didactic analysis inspired us in the development of a repertoire integrating the History of Mathematics, proposed to evolve the Senegalese programs.Chapter V, quizzes mathematics students and teachers, prior to the experiment, to collect and analyze their opinions and practices regarding the introduction of a historical perspective. The President of the National Commission of Mathematics (CNM) of Senegal is also put to contribution, through an interview, to give his opinion on the question and to bring us clarifications on some options of the program.The experimentation that we have done is discussed in Chapter VI and concerns six sessions in class of "Quatrième" which relate to the intersection of a circle and a line, the condition of existence of a triangle, the history of numbers, the equation modelling, the resolution of equations of the type ax + b = 0, and the theorem of Pythagoras. We have conceived their didactic engineering. They were then tested by a teacher in our presence. The sequences in the classroom were filmed and transcribed.The last chapter focuses on the analysis of experimentation, which was based on Chevallard's Anthropological Theory of Didactics (TAD) through praxeology and didactical moments to study students'tasks and filmed sequences. Barbin's three hypothetical arguments, namely replacement, disorientation, and cultural understanding, were also used in this chapter, along with the analysis of questionnaire responses and interviews submitted to students one year after the experiment, to measure positive effects of experimentation on students.The general conclusion provides information on the results of the experiment which are on the whole very promising in the framework of the improvement of the teaching lessons of the mathematics in Senegal despite the difficulties noted in the management of the time and related to the large number of students in the class where the experiment took place
Théorie de Hodge non-abélienne et des spécialisations by Pengfei Huang( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

La premiére partie de cette thèse est la géométrie de la théorie de Hodge non-Abélienne, en particulier l'étude des propriétés géométriques des espaces de modules.Le premier résultat principal de cette partie est la construction d'un système dynamique sur l'espace de modules des fibrés de Higgs, nous montrons que les points fixes de ce système dynamique sont exactement ceux fixés par l'action de C* sur l'espace de modules des fibrés de Higgs, c'est-àdire tous les C-VHS dans l'espace de modules. Dans le même temps, nous étudions sa première variation et son comportement asymptotique.Le deuxième résultat principal de cette partie est la preuve d'une conjecture (forme faible) par Simpson sur la stratification de l'espace de modules des fibrés plats, nous prouvons que la strata d'opérateurs est la strata fermée unique de dimension minimale en étudiant l'espace de modules des chaînes holomorphes de type donné.Le troisième résultat principal de cette partie est une généralisation de la construction par Deligne en l'espace de twistor de Hitchin dans le cas de surface de Riemann, nous construisons des sections holomorphes pour ce nouvel espace de twistor, c'est-à-dire les sections de de Rham. Nous calculons les fibrés normals de ces sections, et nous avons constaté que les sections de de Rham dans l'espace de twistor de Deligne-Hitchin ont également la propriété wight 1, donc ce sont des courbes rationnelles amples. Dans le même temps, nous montrons le théorème de type Torelli pour l'espace de twistor.La deuxième partie de cette thèse est l'étude de certaines spécialisations de la correspondance de Hodge non-Abélienne. Celui-ci comprend principalement deux chapitres, le premier est une preuve fondamentale d'une conjecture liée aux représentations de carquois proposée par Reineke en 2003, nous montrons pour les représentations de carquois de type An , il existe un système de poids tel que les représentations stables par rapport à ce système de poids sont précisément celles indécomposables. Pour la deuxième, nous construisons la correspondance de Kobayashi-Hitchin pour les fibrés de carquois sur les variétés Kähleriennes généralisées
Modélisation et discrétisation des écoulements diphasiques en milieux poreux avec réseaux de fractures discrètes by Mayya Groza( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

Les travaux de cette thèse portent sur la modélisation et la discrétisation des écoulements diphasiques dans les milieux poreux fracturés. On se place dans le cadre des modèles dits dimensionnels hybrides couplant l'écoulement dans la matrice 3D à l'écoulement dans un réseau de fractures modélisées comme des surfaces 2D. La discrétisation s'appuie sur le cadre abstrait des schémas gradients. Dans cette étude nous présentons deux classes de schémas de types Gradient Schemes sur ces modèles en monophasique et en diphasique. Les objectifs sont motivés par l'application cible de la thèse qui concerne les procédés de récupération assistée de gaz par fracturation hydraulique dans les réservoirs de très faibles perméabilités
Influence de la ventilation sur les propriétés de transport dans un poumon sain et enflammé by Frédérique Noël( )

1 edition published in 2021 in English and held by 1 WorldCat member library worldwide

The main function of the lung is to supply the blood with oxygen and to drain the carbon dioxide from it. The lung captures the oxygen present in the ambient air where it rejects the carbon dioxide taken from the blood. This exchange results from the process of the lung's ventilation that repeatedly makes a volume of ambient air enter and leave the lung. In an idealized view, the ventilation can be characterized by two parameters: the maximum air velocity in the trachea (the amplitude) and the breathing frequency (the period). The goal of this thesis is to study and model the process of oxygen and carbon dioxide transport and exchanges in the lung. Gas transport is modeled by convection-diffusion-reaction equations in an idealized lung. A mathematical analysis of the model has been performed to prove the existence of a unique solution along with an asymptotic periodicity in time. Numerical simulations were performed to study a wide range of physiological configurations. In the healthy human case, the amounts of gas exchanged predicted by our model are close to physiology. The viscous and elastic energies spent during inspiration were then minimized assuming that our body needs in oxygen can be represented in our model by a constraint on the oxygen flow exchanged with the blood. Simulations were carried out for humans but also for any mammals using allometric scaling laws. The predictions of our model show that the ventilation parameters in mammals might be optimized to cost as little energy as possible. Then, we focused on the lung's ventilation of a human subject suffering from a pulmonary infection. The spread of a bronchial infection has been modeled in an idealized way and we studied how the ventilation is affected by the response of the immune system through bronchi wall inflammation. Our results show that the location of the transition zone between convection and diffusion mainly influence the quantity of oxygen exchanged with the blood. The location of this transition can be affected by the infection and hence alter the efficiency of the ventilation and modify its optimal configuration. Finally, to better understand the efficiency of a drug treatment delivered by aerosol, we modeled the deposit of aerosol particles in the first bifurcation of the bronchi of the human lung. Our model takes into account the evolution of the radius of the particles due to the exchange of water vapor and the evolution of the temperature of the particles due to the change of the surrounding environment. Our results show that the modeling of these parameters is important to represent more accurately the deposit of the particles on the walls of the bronchi. This work allows to better understand how the process of lung's ventilation is adjusted and how it is affected by lung's pathologies. Moreover, it highlights how ventilation can be used efficiently as a way to deliver drugs in the body
Exemples de restauration d'unicité et de sélection d'équilibres dans les jeux à champ moyen by Rinel Foguen Tchuendom( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

The purpose of this thesis is to present several results on the restoration of uniqueness and selection of equilibria when uniqueness fails in mean field games. The theory of mean field games was initiated in the 2000s by two groups of researchers, Lasry and Lions in France, and Huang, Caines, and Malhamé in Canada. The aim of this theory is to describe the Nash equilibria in stochastic differential games involving a large number of players interacting with each other through their common empirical measure, under sufficient symmetry hypothesis. If the existence of equilibria in mean field games is now well understood, uniqueness remains known in a very limited number of cases. In this respect, the most well-known condition is the monotony hypothesis, due to Lasry and Lions. In this thesis, we demonstrate that for a certain class of mean field games, uniqueness can be restored by means of a random and common forcing, acting on all the players. Such a forcing is called “common noise”. We also show that in some cases it is possible to select equilibria in the absence of common noise by letting the common noise tend towards zero. Finally, we show how these results apply to “principal-agent” .problems, with a large number of interacting agents
Étude de méthodes précises d'approximation d'équations différentielles stochastiques ou d'équations aux dérivées partielles déterministes en Finance by Lord Bienvenu Youmbi Tchuenkam( )

1 edition published in 2016 in French and held by 1 WorldCat member library worldwide

The work presented in this thesis is devoted to the study of precise methods forapproximating stochastic differential equations (SDE) or deterministic partialdifferential equations (PDE). The first part is devoted to the development ofbias correction methods in parametric diffusion processes. Three models arestudied in particular : Ornstein-Uhlenbeck, auto-regressive and Movingaverage. At the end of this work, several approximations of bias have beenproposed following two approaches : the first consists in a Taylor developmentof the obtained estimator while the second one relies on a stochastic expansionof the latter.The second part of this thesis deals with the approximation of the heatequation obtained after changing variables from the Black-Scholes model. Likethe vast majority of PDE, this equation does not have an exact solution, sosolutions must be approached using explicit or implicit time schemes. Itis often customary to prefer the use of implicit methods to solve parabolic PDEsuch as the heat equation, but in the past few years, the stabilized explicitRunge-Kutta methods which have the largest possible domains of stabilityalong the negative real axis, are increasingly used. We show that the useof this type of explicit methods and in particular the ROCK (Runge-Orthogonal-Chebyshev-Kutta) schemes give very good results even if the initial conditionsare not very regular, which is the case in the financial models
 
moreShow More Titles
fewerShow Fewer Titles
Audience Level
0
Audience Level
1
  Kids General Special  
Audience level: 0.92 (from 0.88 for Interactio ... to 0.94 for Étude par ...)

Alternative Names
Centre national de la recherche scientifique (France). Unité associée (168)

Centre national de la recherche scientifique (France). Unité mixte de recherche (6621)

Centre national de la recherche scientifique (France). Unité mixte de recherche (7351)

JAD

Laboratoire de mathématiques Jean-Alexandre Dieudonné (Nice)

Laboratoire de mathématiques (Nice)

Laboratoire J. A. Dieudonné (Nice)

Laboratoire Jean-Alexandre Dieudonné facility in Nice, France

Laboratoire Jean-Alexandre Dieudonné (Nice)

LJAD

Université Côte d'Azur. Laboratoire de mathématiques

Université Côte d'Azur. Laboratoire J.-A. Dieudonné

Université de Nice. Laboratoire de mathématiques

Université de Nice-Sophia Antipolis. Laboratoire de mathématiques

Université de Nice-Sophia Antipolis. Laboratoire J.-A. Dieudonné

Languages
English (11)

French (10)