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Modalités d'action et conditions pour un investissement de transition
No full textInternational audienc
Slip localization and grain boundary sliding analysis at sub-voxel resolution using phase contrast tomography
No full textInternational audienceMicroplasticity of a polycrystalline Ni-based superalloy was investigated using phase contrast tomography (PCT) and laser scanning confocal microscopy (LSCM). Incremental tensile testing was performed on three miniaturized specimens to investigate strain localization at low plastic deformation at room temperature and 650 ∘C. Microplasticity events, such as slip activity, deformation twinning, and grain boundary sliding, are free to emerge at the specimen surface and generate sub-micrometer topographic features. High resolution digital image correlation was conducted using LSCM to have a description of the in-plane and out-of-plane kinematics of the specimen surface. Despite slip amplitudes substantially smaller than the voxel size, PCT was capable to evidence the out-of-plane component of slip traces at the onset of plasticity. The technique was also used at 650 ∘C, a temperature at which grain boundary sliding occurs, but surface reactivity is severe enough not to allow for topographic measurements using LSCM. Therefore, PCT was found particularly adapted to evidence “surface” microplasticity events hidden by an extra surface oxidation layer
Lyapunov-Based Online Optimal Control of a Class of Cascaded Systems with an Infinite Horizon Time-Average Performance Guarantee
No full textIn this letter, we investigate the optimal control of a class of cascaded systems, where mass and/or energy flow through subsystems connected in series. In a stochastic setting, model predictive control (MPC) is a widely adopted approach for tackling this problem. However, it can be computationally intensive and, perhaps more importantly, relies on the characterization of uncertainty. To overcome these potential limitations, we propose a Lyapunov-based online optimal control method, which operates in real time without requiring prior characterization of the uncertainty. By relaxing time-coupling constraints, the proposed online method becomes suboptimal compared to offline optimization with perfect foresight, i.e., the ideal solution to the optimal control problem. Our main result establishes an infinite horizon time-average performance guarantee, demonstrating bounded suboptimality of the proposed method. We apply the Lyapunov-based online optimal control method to the economic dispatch of cascaded hydropower plants, and show that it can outperform both greedy online control and popular MPC
Vers une modélisation des émissions du transport maritime et de leur déposition en Méditerrannée
No full textNational audienc
Confinement to deterministic manifolds and low-dimensional solution formulas for continuously measured quantum systems
No full textInternational audienceQuantum systems under continuous weak measurement follow stochastic differential equations (SDE). Depending on the stochastic measurement results indeed, the quantum state can progressively diffuse, a priori in all directions of state space. This note draws attention to the observation that, in several settings of interest for quantum engineering, this diffusion in fact takes place in low dimension. Namely, the state remains confined in a low-dimensional nonlinear manifold, often time-dependent, but independent of the measurement results. The note provides the corresponding low-dimensional expressions for computing the stochastically evolving state in several such settings: quantum non-demolition measurement in arbitrary dimensions; quadrature measurements on a harmonic oscillator (linear quantum system); and subsystem measurement in multi-partite quantum systems. An algebraic criterion is proposed to directly check when such low-dimensional manifolds exist or survive under additional dynamics
Incorporating Purpose: The New Legal Foundations for the Corporation and its Management
No full textInternational audienceIn this Element, emerging legal forms of purpose-driven corporations are analyzed, revealing two important insights. First, within the traditional corporate law, a purpose is neither protected nor enforceable over time. While companies can have goals beyond profit, these are controlled by shareholders, who also appoint corporate managers. To protect social or environmental ambitions, especially during shareholder changes, a legal commitment from the company is essential. Second, these new legal forms highlight the need to redefine the corporation's legal foundations. In an era when management decisions impact entire populations and the planet, the law inadequately conceptualizes the conditions necessary for responsible management. The Element argues that embedding a purpose in the constitution of corporations can provide these new legal foundations. Ultimately, the Element suggests that purpose provides a unified theoretical framework for understanding the variety of corporate legal forms and for discussing their respective potentials and limitations in holding corporations accountable in the face of upcoming transitions
Valley bottom geometry withing the Seine catchment (France): constraining ages of the depositional alluvial infills based on ESR and OSL dating methods
No full textInternational audienceValleys bottoms and alluvial terraces in their edges hold sedimentary archives that are valuable for reconstructing past environmental conditions, particularly in relation to external perturbations such as climate fluctuations (base-level or water discharge changes in relation with glacial/interglacial cycles) and tectonic forcing. These valleys bottoms have an important impact on human settlements and their interactions with the environment over time. Consequently, the areas of valleys bottoms, where many archeological artifacts may be preserved, remain important to better understand the migration of both humans and animals.There is a significant need to reconstruct the geometry and determine the age of alluvial infill in valley bottoms. To achieve this, a detailed study of the current valley bottom geometry isessential to understand the relationship between its shape, its maximum width and their underlaying bedrock that it crosses. Based on this model, it will eventually be possible to apply it to ancient landforms, thereby enabling their reconstruction and allowing for a more precise alignment of human occupations within this fluvial environment. Direct or indirect dating of alluvial infill of the valleys bottoms provides knowledge on geomorphology and evolution of occupations. The first restitution of valley bottom geometry using the kriging method has been applied along the Seine catchment. This reconstruction was determined using 4817 boreholes from the Banque du Sous-Sol (BSS) that intersect the alluvium at the bottom of the valleys. These boreholes were used to quantify the volume stored in the valley bottom and to determine the geometry of the valley using the kriging. Alluvium thickness distributions estimated from the kriging show contrasted geometries along the valley bottom. The estimated thickness of the alluvial deposits varies from 0 to approximately 30 m. To reconstruct the evolution of the Seine catchment and the timing of sediment deposition, the ESR and OSL dating methods was applied in the fluvial deposits. The obtained results suggest that at least two Marine Isotopic Stage are recorded MIS 6 and MIS 2 along the valley bottom of the Seine catchment, highlighting that MIS 6 deposits in valley bottoms were not entirely removed during the Weichselian glaciation MIS 2. Thus, the valley bottom age could be used to better understand human and animal migrations over time
À la conquête des qubits
No full textBDEt si on vous disait que derrière les concepts plutôt intimidants de la physique quantique, il y avait une aventure passionnante où chaque étape rapproche un peu plus la science de l’impossible ?Grâce au projet Hamroqs, on vous embarque dans une exploration unique pour mieux comprendre et maîtriser l’information quantique. Dans cette bande dessinée : À travers une aventure visuelle ludique et pédagogique, vous découvrirez comment des chercheurs simplifient le complexe et transforment le potentiel scientifique en solutions concrètes. - Les qubits décryptés : Contrairement aux bits classiques, qui oscillent entre 0 et 1, les qubits peuvent adopter une infinité d’états intermédiaires. Une vraie gymnastique scientifique pour les contrôler efficacement !- Les défis à relever : Comment créer des modèles simplifiés, tant au niveau des mathématiques que des signaux physiques, afin de rendre cette technologie plus accessible ?- Les solutions innovantes : Grâce à des signaux optimisés et des approches créatives, Hamroqs ouvre la voie à une manipulation plus fiable de l’information quantique.C’est quoi l’enjeu ?Les qubits sont une clé pour débloquer un futur dans lequel des calculs aujourd’hui impossibles deviendront réalité. Mais pour y arriver, il faut d’abord réussir à "dompter" ces unités d’information aux comportements encore trop instables
Fabrication additive par fil et laser (WLAM) : simulation numérique multiphysique du transfert thermique, de l'écoulement du fluide et de la formation de la microstructure : Application à l'alliage IN718
No full textWire Laser Additive Manufacturing (WLAM) is an additive manufacturing technique that produces large, high-value metallic parts from a metallic wire continuously melted by a laser. Its efficiency and high deposition rate make it an attractive alternative to powder-bed processes for manufacturing structural components in the aeronautics and energy sectors. However, controlling the geometric quality and microstructure of the deposits remains a major challenge, as these characteristics are strongly influenced by the thermal and hydrodynamic conditions within the melt pool, which themselves depend on the operating process parameters.In this context, the doctoral work presented here, conducted within the ANR COLUMBO project, aims to develop a comprehensive numerical model for predicting thermo-hydraulic and microstructural evolution at the scale of a WLAM-deposited bead. The material studied is Inconel 718, a nickel-based alloy of industrial interest, selected for its excellent mechanical properties, its resistance to high-temperature corrosion, and its high elastic anisotropy coefficient—a parameter that strongly conditions the controllability of ultrasonic (US) methods. In addition, an original heating device using three converging laser beams, developed by the LURPA partner, was also implemented and investigated in this project.A volumetric source model, without explicit representation of the wire, is proposed to describe the mass and heat transfer associated with material addition. The thermo-hydraulic solution strategy, based on the finite element method, reproduces temperature distributions and melt-pool morphology as a function of process parameters (laser power, travel speed, wire feed rate, etc.). Its principal advantage is a significant reduction in computation time—from about one month to a few days—relative to studies reported in the literature for equivalent configurations, while maintaining a satisfactory level of accuracy. The thermal solution is coupled with a cellular automaton approach for predicting solidification microstructures, providing access to grain morphology and crystallographic orientation.A parametric analysis on several single-track deposit configurations was carried out to assess the influence of process parameters on bead morphology and the resulting grain structure. The results showed good consistency with experimental observations for these simple deposition cases. The approach was then extended to multi-track configurations representative of industrial practice. In these more complex cases, larger discrepancies with experiments were observed, particularly regarding bead morphology, highlighting the model's sensitivity to thermal interactions between passes as well as to wire delivery conditions.Nevertheless, the methodology developed provides a robust and efficient numerical basis for predictive analysis and optimization of the WLAM process, offering an in-depth understanding of thermal mechanisms and microstructural evolution and thereby contributing to the progressive improvement of the process and the quality of the parts produced.Le procédé Wire Laser Additive Manufacturing (WLAM) est une technique de fabrication additive permettant de produire des pièces métalliques de grande dimension à haute valeur ajoutée à partir d'un fil métallique continument fondu par laser. Son efficacité et son taux de dépôt élevé en font une alternative intéressante aux procédés sur lit de poudre pour la production de pièces structurelles dans les domaines de l'aéronautique et de l'énergétique. La maîtrise de la qualité géométrique et microstructurale des dépôts reste toutefois un enjeu majeur, ces caractéristiques étant fortement influencées par les conditions thermiques et hydrodynamiques au sein du bain de fusion, elles-mêmes dépendantes des paramètres procédé exploités.Dans ce contexte, le travail de doctorat présenté ici, réalisé dans le cadre du projet ANR COLUMBO, vise à développer un modèle numérique complet pour la prédiction des évolutions thermo-hydrauliques et microstructurales, à l'échelle du cordon de matière déposé par procédé WLAM. Le matériau étudié est l'Inconel 718, alliage base nickel d'intérêt industriel, retenu pour ses excellentes propriétés mécaniques, sa résistance à la corrosion à haute température et son fort coefficient d'anisotropie élastique, paramètre qui conditionne fortement la contrôlabilité des méthodes ultrasonores (US). Par ailleurs, un dispositif original de chauffage par trois faisceaux laser convergents, développé par le partenaire LURPA, a également été mis en œuvre et étudié dans le cadre de ce projet.Un modèle de source volumique, sans représentation explicite du fil, est proposé pour décrire les transferts de masse et de chaleur associés à l'apport de matière. La résolution thermo-hydraulique mise en œuvre, basée sur la méthode des éléments finis, permet de reproduire les distributions de température et la morphologie du bain de fusion en fonction des paramètres de procédé (puissance laser, vitesse de déplacement, débit de fil, etc.). Son principal avantage est de réduire significativement le temps de calcul d'environ un mois à quelques jours par rapport aux études documentées dans la littérature pour des configurations équivalentes, tout en conservant un niveau de précision satisfaisant. La résolution thermique est couplée à une méthode automate cellulaire permettant la prédiction des microstructures de solidification, et donnant accès, en particulier, à la morphologie et l'orientation cristallographique des grains.Une analyse paramétrique sur plusieurs configurations de dépôts monocordon a permis d'évaluer l'influence des paramètres procédé sur la morphologie du cordon et la structure de grains obtenue. Les résultats ont montré une bonne cohérence avec les observations expérimentales sur ces cas de dépôts simples. L'approche proposée a ensuite été étendue à des configurations multi-cordons, représentatives du procédé industriel. Dans ces cas complexes, des écarts plus marqués avec l'expérience sont observés, notamment sur la morphologie des cordons, soulignant la sensibilité du modèle aux interactions thermiques entre passes mais également aux conditions d'arrivée du fil.La méthodologie développée constitue néanmoins une base numérique robuste et efficace pour l'analyse prédictive et l'optimisation du procédé WLAM, offrant une compréhension approfondie des mécanismes thermiques et évolutions microstructurales, et contribuant en cela à l'amélioration progressive du procédé et de la qualité des pièces produites
