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Parallel geodesics and minimal stable length of random groups
No full text21 pagesWe show that for any pair of long enough parallel geodesics in a random group G(m, d) with m generators at density d < 1/6, there is a van Kampen diagram having only one layer of faces. Using this result, we give an upper bound, depending only on d, of the number of pairwise parallel geodesics in G(m, d) when d < 1/6. As an application, we show that the minimal stable length of a random group at density d < 1/6 is exactly 1
Existence of a solution of the TV Wasserstein gradient flow
No full textOn the flat torus in any dimension we prove existence of a solution to the TV Wasserstein gradient flow equation, only assuming that the initial density is bounded from below and above by strictly positive constants. This solution preserves upper and lower bounds of the densities, and shows a certain decay of the BV norm (of the order of for -- if , otherwise the BV norm is of course bounded -- and of the order of as ). This generalizes a previous result by Carlier and Poon, who only gave a full proof in one dimension of space and did not consider the case .The main tool consists in considering an approximated TV-JKO scheme which artificially imposes a lower bound on the density and allows to find a continuous-in-time solution regular enough to prove that the lower bounds of the initial datum propagates in time, and study on this approximated equation the decay of the BV norm
Hybrid nonlinear energy sink, a tunable device for vibration mitigation : Theorical and experimental demonstration
No full textInternational audienceHybridization is a powerful and recent technology that combines passive and active componentsto enhance system performance. The central idea behind this approach is to improve the respon-siveness and adaptability of the passive energy absorption mechanism by integrating a control lawsupported by actuator/sensor pairs. This combination enables the system to dynamically adapt it-self to varying excitation conditions, thereby significantly improving overall performance. Mean-while, nonlinear energy sinks (NES) are well known for their frequency robustness. The weakpoint of a nonlinear energy sink lies in its activation threshold, i.e.: the absorber is inactive atlow or high levels of external force applied to the primary structure. Additionally, under a sig-nificant shift in the primary structure’s natural frequencies, the absorber becomes ineffective orinactive. Furthermore, the reactivity of passive absorbers may be insufficient depending on theapplication. For these reasons, a new device for vibration mitigation called the hybrid nonlinearenergy sink is introduced. The latter is designed to overcome the limitations of passive linearand nonlinear absorbers and hybrid linear absorbers. It enhances the non-linear passive energysink by integrating sensor-actuator pairs and a specially designed control law to modify the sys-tem dynamics in real time. This ensures that the absorber remains effective even when externalconditions change. This paper presents theoretical and experimental demonstrations of this newdevice, applied to a one-storey building. By introducing control laws within the hybrid nonlinearenergy sink, it becomes possible to adjust its parameters, e.g., the nonlinear stiffness, to shift theactivation threshold and ensure consistent performance of the absorber in real-time
Air Gaps Fabrication for Sub-100 nm GaN HEMTs by Novel SF6 Plasma Etching
No full textInternational audienceWe demonstrate the fabrication of air gaps in a PECVD SiN interlayer through lateral recess by employing two consecutive plasma etch steps on an AlN/SiN/Al2O3 stack. This approach enables the preservation of sub-100 nm openings in Al2O3, offering a potential optimization for the GaN-HEMT gate stack in RF applications while retaining low gate foot dimensions. A low-power, SF6-based plasma etch is introduced, and time-dependent etch profiles reveal the formation of a skirt-like profile. The process exhibits excellent selectivity between SiN and Al2O3 etch rates. Furthermore, low-power SF6 plasma produces a small self-bias voltage, and surface fluorine contamination which can subsequently be eliminated by annealing
HARMONY: A Holistic Auto-Scaling Resilient Model for Multi-Objective Adaptation in Microservices Using HPPNs—A Case Study on E-Business Platforms
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On the relaxation towards mechanical equilibrium for two-pressure compressible flows
No full textWe introduce a symmetrization of a one-velocity two-pressures Baer-Nunziato type model for mixtures of barotropic compressible fluids. It allows us to justify the zero compaction viscosity limit and to recover a solution of the so-called Kapila model. On the other hand, the symmetrization highlights a pressure-induced stabilization mechanism which allows us to recover a global-in-time existence result for initial data close to constant states
« Des collectes de mémoires à la nostalgie des mondes à venir. Recueillir, inventorier, archiver en temps de crise »
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Santé environnementale et transition écologique du système de santé
No full textInternational audienceFace à l’urgence climatique et aux effets de l’environnement sur la santé, la transition écologique du système de santé est devenue un enjeu majeur. Cet ouvrage propose une synthèse structurée et opérationnelle des fondements de la santé environnementale et de leur application au champ sanitaire et médico-social.Il réunit les définitions essentielles des notions clés (santé environnementale, transition écologique, décarbonation des activités…), un état des lieux du cadre juridique, des politiques publiques et des connaissances actuelles (PNSE 4, feuille de route de planification écologique du système de santé), ainsi que des exemples concrets de démarches de transition mises en œuvre dans les établissements de santé et médico-sociaux.Une annexe méthodologique dédiée aux concours administratifs complète l’ouvrage, avec des conseils pratiques et des exemples de sujets.Initialement conçu pour les candidats aux concours d’entrée à l’EHESP, ce livre s’adresse également aux professionnels du système de santé souhaitant intégrer les enjeux environnementaux dans leurs pratiques, leurs décisions et leurs engagements, ainsi qu’à toutes celles et ceux désireux de concilier expertise sanitaire et responsabilité écologique
Modélisation de trajectoires à partir de données non longitudinales à l'aide de l'analyse formelle de concepts
No full textInternational audienceLa modélisation des trajectoires permet de suivre l'évolution d'un phénomène au fil du temps et d'identifier des profils communs d'évolution, notamment dans le contexte des maladies neurodégénératives. Les méthodes classiques reposent sur des données longitudinales, mais leur collecte est souvent complexe et coûteuse. Dans cet article, nous proposons une approche innovante pour extraire des trajectoires à partir de données cross-sectional en utilisant l'Analyse Formelle des Concepts (FCA). Notre méthode transforme les données statiques en une représentation pseudo-temporelle, regroupe les patients en concepts significatifs et génère des trajectoires linéaires sur plusieurs étapes. La progression est ensuite modélisée sous forme d'un graphe de concepts et d'un processus de Markov, où les états sont décrits par les attributs cliniques partagés (intension) et les transitions sont pondérées par une similarité de Jaccard sous contraintes.</div
Closed-form solutions for contact pressure distribution generated by 2D rough profiles
No full textThis study investigates the influence of surface roughness on contact mechanics, addressing the limitations of existing models that often rely on idealized and symmetric asperity shapes. We introduce a generalized representation of asperity geometries, including non-symmetric profiles, to better capture the diversity of surface characteristics encountered in real-world applications. By applying this parametric asperity model, we perform numerical simulations to analyze the impact of different parameters on contact behavior, effectively identifying various interaction regimes. The analysis is based on the assumption of elastic contact and focuses on two-dimensional roughness profiles characterized by surfaces that remain invariant along the axis orthogonal to the rolling direction. This approach effectively simulates geometries that display sufficient invariance along this axis, thereby representing realistic asperities in the form of streaks. Our theoretical framework quantifies the resulting analytical pressure distribution as a function of both geometric and mechanical parameters of the generalized asperities. By accommodating non-symmetric asperity geometries, our approach enhances model accuracy while significantly reducing computational time and resource requirements compared to traditional numerical methods