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Stabilisation d'une classe de systèmes non linéaires avec propriétés de passivité
No full textIn this thesis we address the problem of stabilization of nonlinear systems. In particular, we focus on models where the energy plays a fundamental role. This energy-based framework is suitable to capture the phenomena of several physical domains, such as mechanical systems, electrical systems, hydraulic systems, etc. The starting point in the proposed controllers are the concepts of passive system, passive outputs and energy (storage) functions. In this work we study two classes of dynamical systems, namely port-Hamiltonian (PH) and Euler-Lagrange (EL), which are suitable to represent many physical processes. A first step towards the controller design is to show the passivity of the PH systems and the characterization of their passive outputs. Thereafter, we explore the use of the different passive outputs in two well-known passivity-based control (PBC) techniques, that is control by interconnection (CbI) and energy balancing (EB), and we compare the obtained results in both approaches. In addition, we propose a novel methodology in which the controller consists in a proportional (P), an integral (I) and, possibly, a derivative (D) term of the passive output. In this approach the energy of the closed-loop system is shaped without the necessity of solving partial differential equations (PDEs). We analyze the scenario of the PID controller using the different passive outputs previously characterized. Finally, we apply a PID-PBC scheme recently proposed in the literature to a complex mechanical system, namely an ultra flexible inverted pendulum, which is represented as a constrained EL model. The controller design, the stability proof, as well as simulations and experimental results are presented to show the applicability of this technique to physical systems.Dans cette thèse, nous abordons le problème de la stabilisation des systèmes non linéaires. En particulier, nous nous concentrons sur les modèles où l'énergie joue un rôle fondamental. Ce cadre énergétique est adapté pour capturer les phénomènes de plusieurs domaines physiques tels que les systèmes mécaniques, les systèmes électriques, les systèmes hydrauliques, etc. Le point de départ des contrôleurs proposés sont les concepts de système passif, des sorties passives et des fonctions d'énergie (ou stockage). Dans ce travail, nous étudions deux classes de systèmes dynamiques, à savoir les Hamiltoniens à ports (PH) et les Euler-Lagrange (EL), qui conviennent pour représenter de nombreux processus physiques. Une première étape vers la construction des contrôleurs est de montrer la passivité des systèmes PH et la caractérisation de leurs sorties passives. Par la suite, nous explorons l'utilisation des différentes sorties passives dans deux techniques bien connues de contrôle par passivité (PBC), c'est-à-dire le contrôle par interconnexion (CbI) et l'équilibrage énergétique (EB), et nous comparons les résultats obtenus dans les deux approches. De plus, nous proposons une nouvelle méthodologie dans laquelle la loi de commande est composée d'un terme proportionnel (P), un terme intégral (I) et, éventuellement, un terme dérivatif (D) de la sortie passive. Dans cette stratégie, l'énergie du système en boucle fermée est façonnée sans qu'il soit nécessaire de résoudre des équations différentielles partielles (PDE). Nous analysons le scénario du régulateur PID à l'aide des différentes sorties passives précédemment caractérisées. Enfin, nous appliquons un schéma PID-PBC récemment proposé dans la littérature à un système mécanique complexe, à savoir un pendule inversé ultra flexible, représenté sous la forme d'un modèle contraint EL. La conception du contrôleur, la preuve de stabilité, ainsi que les simulations et les résultats expérimentaux sont présentés pour montrer l'applicabilité de cette technique aux systèmes physiques
Towards energy-proportional Clouds partially powered by renewable energy
No full textInternational audienceWith the emergence of the Future Internet and the dawning of new IT models such as cloud computing, the usage of data centers (DC), and consequently their power consumption, increase dramatically. Besides the ecological impact, the energy consumption is a predominant criterion for DC providers since it determines the daily cost of their infrastructure. As a consequence, power management becomes one of the main challenges for DC infrastructures and more generally for large-scale distributed systems. In this paper, we present the EpoCloud prototype, from hardware to middleware layers. This prototype aims at optimizing the energy consumption of mono-site Cloud DCs connected to the regular electrical grid and to renewable-energy sources
Stability Verification and Timing Contract Synthesis for Linear Impulsive Systems using Reachability Analysis
No full textInternational audienceThis paper deals with stability analysis for a class of linear impulsive systems subject to a timing contract specifying bounds on the time between two consecutive impulses. We consider the problem of stability verification, which consists in proving stability for a particular timing contract, and the problem of timing contract synthesis, which consists in synthesizing a set of timing contracts that guarantee the stability of the linear impulsive system. Our approach is based on a reformulation using parameterized difference inclusions. We derive theoretical necessary and sufficient conditions for stability based on the propagation of a set by the system dynamics. For linear impulsive systems, this allow us to design a stability verification algorithm using reach-ability analysis. We then propose an approach to timing contract synthesis, which exploits the monotonicity of stability with respect to timing contract parameters to design an algorithm based on adaptive sampling of the parameter space. Several examples are provided, which allow us to compare our algorithm with several existing techniques, and show the effectiveness of our approach
A modified block Lanczos algorithm with fewer vectors
No full textInternational audienceThe block Lanczos algorithm proposed by Peter Montgomery is an efficient means to tackle the sparse linear algebra problem which arises in the context of the number field sieve factoring algorithm and its predecessors. We present here a modified version of the algorithm, which incorporates several improvements: we discuss how to efficiently handle homogeneous systems and how to reduce the number of vectors stored in the course of the computation. We also provide heuristic justification for the success probability of our modified algorithm. While the overall complexity and expected number of steps of the block Lanczos is not changed by the modifications presented in this article, we expect these to be useful for implementations of the block Lanczos algorithm where the storage of auxiliary vectors sometimes has a non-negligible cost. 1 Linear systems for integer factoring For factoring a composite integer N , algorithms based on the technique of combination of congruences look for several pairs of integers (x, y) such that x 2 ≡ y 2 mod N. This equality is hoped to be non trivial for at least one of the obtained pairs, letting gcd(x − y, N) unveil a factor of the integer N. Several algorithms use this strategy: the CFRAC algorithm, the quadratic sieve and its variants, and the number field sieve. Pairs (x, y) as above are obtained by combining relations which have been collected as a step of these algorithms. Relations are written multiplicatively as a set of valuations. All the algorithms considered seek a multiplicative combination of these relations which can be rewritten as an equality of squares. This is achieved by solving a system of linear equations defined over F 2 , where equations are parity constraints o
Biophotonique : Sondes de lumières résonantes intégrées sur puce pour la détection d'espèces biologiques et le diagnostic dynamique en bio-métrologie des processus de la matière molle
No full textCommunication - Highlight :Site UFR SPM - Sciences et Propriétés de la MatièreNos recherches se situent dans le domaine des nanotechnologies à base de photonique intégrée et senseurs en métrologie pour la biodétection d’espèce biologique (comme le glucose), la santé (interaction lipides/protéines au niveau cellulaire), l’étude des processus fondamentaux de la matière molle (sédimentation en matière molle) et est bâti sur un socle fédérateur de compétences fortes existant au sein d’Instituts de Recherche CNRS et INRA rennais (IPR-CNRS, https://ipr.univ-rennes1.fr/ ; STLO-INRA, http://www6.rennes.inra.fr/stlo/UMR-STLO et IETR-CNRS, https://www.ietr.fr/)
Time-reversal in diffusive media
No full textInternational audienceA chapter dealing with the peculiarities of time reversal in diffusive media and its application
Continuous-fiber-reinforced thermoplastic composites: influence of processing on fire retardant properties
No full textInternational audienceFiber-reinforced thermoplastic composite materials can find numerous applications in the transportation sector and replace thermoset composites. However, they have to comply with strict standards, particularly with those concerning their fire behavior. In this frame, composites based on an acrylic resin Elium ® (Arkema), a woven fiberglass, (taffetas tissue Chomarat G-Weave 600 P/A) and Exolit OP930 (Clariant) as fire retardant were prepared using three processes. The thermal stability and fire behavior was studied by means of thermogravimetric analysis and cone calorimetry. The obtained results allowed to highlight the drawbacks of each processing method and to select the most appropriate. The improvement of the fire behavior by combining post-curing of the composites, addition of a cross-linking agent and addition of aluminum trihydroxide (ATH) was also investigated
L p -norm Sauer-Shelah Lemma for Margin Multi-category Classifiers
No full textInternational audienceIn the framework of agnostic learning, one of the main open problems of the theory of multi-category pattern classification is the characterization of the way the complexity varies with the number C of categories. More precisely, if the classifier is characterized only through minimal learnability hypotheses, then the optimal dependency on C that an upper bound on the probability of error should exhibit is unknown. We consider margin classifiers. They are based on classes of vector-valued functions with one component function per category, and the classes of component functions are uniform Glivenko-Cantelli classes. For these classifiers, an L p-norm Sauer-Shelah lemma is established. It is then used to derive guaranteed risks in the L ∞ and L 2-norms. These bounds improve over the state-of-the-art ones with respect to their dependency on C, which is sublinear
Parameter estimation of perfusion models in dynamic contrast-enhanced imaging: a unified framework for model comparison
No full textInternational audiencePatients follow-up in oncology is generally performed through the acquisition of dynamic sequences of contrast-enhanced images. Estimating parameters of appropriate models of contrast intake diffusion through tissues should help characterizing the tumour physiology. However, several models have been developed and no consensus exists on their clinical use. In this paper, we propose a unified framework to analyse models of perfusion and estimate their parameters in order to obtain reliable and relevant parametric images. After defining the biological context and the general form of perfusion models, we propose a methodological framework for model assessment in the context of parameter estimation from dynamic imaging data: global sensitivity analysis, structural and practical identifiability analysis, parameter estimation and model comparison. Then, we apply our methodology to five of the most widely used compartment models (Tofts model, extended Tofts model, two-compartment model, tissue-homogeneity model and distributed-parameters model) and illustrate the results by analysing the behaviour of these models when applied to data acquired on five patients with abdominal tumours
Random Numbers for Parallel Computers: Requirements and Methods, with emphasis on GPUs
No full textInternational audienceWe examine the requirements and the available methods and software to provide (or imitate) uniform random numbers in parallel computing environments. In this context, for the great majority of applications, independent streams of random numbers are required, each being computed on a single processing element at a time. Sometimes, thousands or even millions of such streams are needed. We explain how they can be produced and managed. We devote particular attention to multiple streams for GPU devices