Un système à commutation est la donnée d’une famille de champs de vecteurs et d’une loi indiquant à chaque instant le champ de vecteurs responsable de l’évolution du système. Cette loi est en général donnée par une fonction du temps constante par morceaux. Ce type de systèmes différentiels alliant dynamiques continues et événements discrets permet de modéliser des phénomènes complexes, souvent rencontrés en automatique. Dans cette thèse, nous nous intéressons au problème de la stabilité des systèmes à commutation qui a largement été étudié ces deux dernières décennies. Un tel système est dit asymptotiquement stable en un point d’équilibre si le système est peu sensible aux perturbations au voisinage de ce point et toute solution converge vers cet équilibre. Dans la pratique, la loi de commutation n’étant pas connue, il est capital de trouver des conditions garantissant la stabilité asymptotique quelle que soit la loi de commutation. La principale difficulté réside dans le fait qu’une propriété partagée par tous les sous-systèmes n’est pas nécessairement satisfaite par le système commuté. Les fonctions de Lyapunov, qui jouent le rôle de l’énergie du système, restent un outil puissant dans l’analyse de la stabilité des systèmes à commutation. Dans ce travail, nous étudions principalement les systèmes à commutation donnés par une famille de champs de vecteurs admettant une fonction de Lyapunov faible commune. Nous présentons un résultat qui peut être vu comme une généralisation aux systèmes à commutation du principe d’invariance de LaSalle, puis nous en déduisons des conditions suffisantes de stabilité. Nous établissons un lien entre la stabilité des systèmes à commutation et l’observabilité d’un sous-système dont la dimension est en général beaucoup plus petite. Ensuite, nous tournons notre attention vers les taux de convergence des solutions de tels systèmes.

This book discusses various methods for designing different kinds of observers, such as the Luenberger observer, unknown input observers, discontinuous observers, sliding mode observers, observers for impulsive systems, observers for nonlinear Takagi-Sugeno fuzzy systems, and observers for electrical machines. A hydraulic process system and a renewable energy system are provided as examples of applications.

This volume contains the proceedings of the Colloquium "Analysis, Manifolds and Physics" organized in honour of Yvonne Choquet-Bruhat by her friends, collaborators and former students, on June 3, 4 and 5, 1992 in Paris. Its title accurately reflects the domains to which Yvonne Choquet-Bruhat has made essential contributions. Since the rise of General Relativity, the geometry of Manifolds has become a non-trivial part of space-time physics. At the same time, Functional Analysis has been of enormous importance in Quantum Mechanics, and Quantum Field Theory. Its role becomes decisive when one considers the global behaviour of solutions of differential systems on manifolds. In this sense, General Relativity is an exceptional theory in which the solutions of a highly non-linear system of partial differential equations define by themselves the very manifold on which they are supposed to exist. This is why a solution of Einstein's equations cannot be physically interpreted before its global behaviour is known, taking into account the entire hypothetical underlying manifold. In her youth, Yvonne Choquet-Bruhat contributed in a spectacular way to this domain stretching between physics and mathematics, when she gave the proof of the existence of solutions to Einstein's equations on differential manifolds of a quite general type. The methods she created have been worked out by the French school of mathematics, principally by Jean Leray. Her first proof of the local existence and uniqueness of solutions of Einstein's equations inspired Jean Leray's theory of general hyperbolic systems.

This book studies observation and control operators for linear systems where the free evolution of the state can be described by an operator semigroup on a Hilbert space. It includes a large number of examples coming mostly from partial differential equations.

Notes and Reports in Mathematics in Science and Engineering, Volume 3: On the Cauchy Problem focuses on the processes, methodologies, and mathematical approaches to Cauchy problems. The publication first elaborates on evolution equations, Lax-Mizohata theorem, and Cauchy problems in Gevrey class. Discussions focus on fundamental proposition, proof of theorem 4, Gevrey property in t of solutions, basic facts on pseudo-differential, and proof of theorem 3. The book then takes a look at micro-local analysis in Gevrey class, including proof and consequences of theorem 1. The manuscript examines Schrödinger type equations, as well as general view-points on evolution equations. Numerical representations and analyses are provided in the explanation of these type of equations. The book is a valuable reference for mathematicians and researchers interested in the Cauchy problem.

This book is a collection of essays which examine how the properties of aggregate variables are influenced by the actions and interactions of heterogenous individuals in different economic contexts. The common denominator of the essays is a critique of the representative agent hypothesis. If this hypothesis were correct, the behaviour of the aggregate variable would simply be the reproduction of individual optimising behaviour. In the methodology of the hard sciences, one of the achievements of the quantum revolution has been the rebuttal of the notion that aggregate behaviour can be explained on the basis of the behaviour of a single unit: the elementary particle does not even exist as a single entity but as a network, a system of interacting units. In this book, new tracks in economics which parallel the developments in physics mentioned above are explored. The essays, in fact are contributions to the analysis of the economy as a complex evolving system of interacting agents.

The essays in this edited volume, written in English and French, tackle the intriguing problems of fear and safety by analysing their various meanings and manifestations in literature and other narrative media. The articles bring forth new, cross-cultural interpretations on fear and safety through examining what kinds of genre-specific means of world-making narratives use to express these two affectivities. The articles also show how important it is to study these themes in order to understand challenges in times of global threats, such as the climate crisis. The main themes of the book are approached from various theoretical perspectives as related to their literary and cultural representations. Recent trends in research, such as affect and risk theory, serve as the basis for the discussion. The articles in the volume also draw from disciplines such as gender studies and trauma studies to examine the threats posed by collective fears and aggression on individuals' lives and propose ways of coping with fear. These themes are addressed also in articles analysing new adaptations of old myths that retell stories of the past. Many of the articles in the volume discuss apocalyptic and dystopian narratives that currently permeate the entire cultural landscape. Dystopian narratives do not only deal with future threats, such as totalitarianism, technocracy, or environmental disasters, but also suggest alternative ways of being and new hopes in the form of political resistance.