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Synthesis and characterization of ternary nanolaminated carbide Ti2NbAlC1.82
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VIVALDy: AI-Driven Low-Order Modeling of Vortex-Induced Vibrations via β-Variational Autoencoders, Transformers, and Adversarial Training
No full textInternational audienceVortex-induced vibration (VIV) systems offer a promising path to harvest renewable energy from water currents; however, efficently modelling their turbulent flow fields remains a significant challenge. This paper introduces VIVALDy, an AI-driven framework that integrates β-variational autoencoders (β -VAE) and a bidirectional transformer to predict flow fields from minimal input: the displacement signal of a cylinder. The autoencoder incorporates masked convolutions to preserve interface fidelity at the solid-fluid boundary, while an adversarial-training stage enhances data-distribution alignment in the reconstructed flows. Using an experimental dataset that spans a range of Reynolds numbers relevant to VIV energy-harvesting applications, VIVALDy demonstrates substantial gains over standard reduced-order models (ROMs) in terms of both reconstruction accuracy and preservation of flow data distribution. The results highlight the potential of this data-driven approach to facilitate efficient surrogate modelling of VIV flows for future energy-harvesting devices, enabling more accurate control and optimization strategies
Global versus local schedulability analysis of a two-level hierarchical system
No full textInternational audienceAircraft systems manage resource sharing among several uniprocessor modules operating under the ARINC 653 specification. This standard, based on a two-level hierarchical architecture, guarantees function isolation within partitions. Partitions are scheduled on the processor according to an infinitely repeated offline statically defined cycle. During each cycle, a partition may be accessed either once or multiple times. This study focuses on the case where each partition is granted a single processor access per cycle.We propose an approach that involves transforming a two-level hierarchical scheduling model into a conventional uni-level system. This transformation enables the application of existing results from non-hierarchical uniprocessor scheduling for analysis. We establish a correlation between the schedulability properties of both systems and derive an exact schedulability criterion for fully harmonic task sets. Additionally, we extend this approach to compute precise worst-case response times of tasks within a two-level hierarchical system, leveraging established uniprocessor schedulability results. Finally, we evaluate the scalability of this method
L’empreinte du corps en mémoire épisodique : le rôle du répertoire moteur dans l’observation d’actions chez les adultes jeunes et âgés
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Transport sédimentaire d'un apport local de sédiments visant à la restauration de frayères : étude couplée laboratoire/terrain/numérique
No full textInternational audienceThis project, supported by le pôle de R&D en écohydraulique OFB-IMFT-Pprime et la région Nouvelle Aquitaine, aims to gain a better understanding of the remobilization of a local input of sediment as part of the restoration of spawning grounds for large salmonids, under unsteady flow conditions, particularly during floods. A methodology combining laboratory studies, field measurements and numerical simulations is used to study a specific site on the Marrone River (Corrèze). This site, located on the short-circuited section downstream of the Hautefage dam, is subject to highly variable hydrographs during dam overflows. These hydrographs are modeled in a laboratory flume using a scaling technique that takes into account sediment properties and hydrodynamic criteria based on Froude and Shields numbers. The data obtained in the laboratory, in addition to providing fundamental knowledge of sediment transport under unsteady conditions, enable transport simulations to be validated without the same conditions. These simulations are then extended to the study site and coupled with field measurements to propose a complete methodology for assessing sediment transport processes and their impact on habitat restoration in a specific case.Ce projet, porté par le pôle de R&D en écohydraulique OFB-IMFT-Pprime et la région Nouvelle Aquitaine, vise à mieux comprendre la remobilisation d’un apport local de sédiments dans le cadre de la restauration de frayères de grands salmonidés, sous des conditions de débits instationnaires, notamment lors de crues. Une méthodologie intégrée combinant études en laboratoire, mesures de terrain et simulations numériques est mise en oeuvre pour étudier un site spécifique de la rivière Marrone (Corrèze). Ce site, situé sur le tronçon court-circuité en aval du barrage d’Hautefage, est soumis à des hydrogrammes fortement variables lors des débordements du barrage. Ces hydrogrammes sont modélisés dans un canal de laboratoire à partir d’une mise à l’échelle respectant les propriétés des sédiments ainsi que les critères hydrodynamiques basés sur les nombres de Froude et de Shields. Les données obtenues en laboratoire permettront non seulement d'apporter des connaissances fondamentales sur le transport de sédiments sous conditions instationnaires, mais aussi de valider des simulations de transport sans les mêmes conditions. Ces simulations seront ensuite étendues au site d’étude et couplées à des mesures de terrain afin de proposer une méthodologie complète pour évaluer les processus de transport sédimentaire et leur impact sur la restauration des habitats dans le cas spécifique étudié
Physics-regularized data augmentation for effects on local mechanical properties of an epoxy resin ageing under thermo-oxidative environment
No full textInternational audienceNanoindentation tests are an effective experimental approach to characterize the effects on local mechanical properties of epoxy resins undergoing thermo-oxidative ageing. However, there is currently no physical model capable of accurately representing these effects. In this work, we propose a hybrid methodology combining experimental nanoindentation data with a chemical kinetic model of oxidation through Physics-Regularized Neural Networks (PRNNs). By using the thickness of the oxidized layer as a physically meaningful and common metric between mechanical data and chemical models, we augment limited nanoindentation data. The developed hybrid model demonstrates good generalization capability across different oxygen partial pressures and ageing times. Finally, the resulting hybrid twin is used to produce a reduced order separated representation of the solution field
Distributed alternating direction method of multipliers approach for the power distribution network reconfiguration
No full textInternational audienceThe electrical network reconfiguration problem aims to minimize losses in a distribution system by adjusting switches while ensuring radial topology. The growing use of renewable energy and the complexity of managing modern power grids make solving the reconfiguration problem crucial. Distributed algorithms help optimize grid configurations, ensuring efficient adaptation to changing conditions and better utilization of renewable energy sources. This paper introduces a distributed algorithm designed to tackle the problem of power distribution network reconfiguration with a radiality constraint. This algorithm relies on ADMM (Alternating Direction Method of Multipliers), where each agent progressively updates its estimation based on the information exchanged with neighboring agents. We show that every agent is required to solve a linearly constrained convex quadratic programming problem and a Minimum Weight Rooted Arborescence Problem (MWRAP) with local weights during each iteration. Through numerical experiments, we demonstrate the performance of the proposed algorithm in various scenarios, including its application to a 33-bus test system and a real-world network
Tribo-charging Characteristics of Poly-styrene with varying BFR Concentrations in view of Electrostatic Separation from Mixed Granular Waste Plastics
No full textInternational audienceThe increasing volume of waste electrical and electronic equipment (WEEE) has led to growing concern about the efficient and environmentally friendly recovery of plastic materials containing brominated flame retardants (BFRs). BFRs, commonly added to polymeric materials to meet flammability standards, are now classified as persistent organic pollutants (POPs) due to their toxicity and persistence in the environment. Among the plastics widely used in electrical and electronic applications, polystyrene (PS) is frequently associated with varying levels of BFRs. However, the safe and efficient recovery of brominated PS from mixed waste streams remains a significant challenge, mainly due to the similar physical properties between brominated and non-brominated polymers. This paper aims at evaluating the potential for extracting bromine-containing flame retardant (BFR) polymers from mixed granular waste plastics using triboelectric charging and electrostatic separation. It examines the triboelectric charging characteristics of polystyrene (PS) polymers with three different BFR concentrations: 0%, 0.23%, and 4.6%. The experiments consisted of charging the PS samples by triboelectric effect using a sieve machine operating at 400 revolutions per minute, the acquisition of the charge being measured continuously for 40 minutes. The results reveal a strong correlation between BFR content and charge build-up. Notably, the PS sample containing 4.6% BFR exhibited the highest charging levels. It showed an exponential increase in surface loading during the first 30 minutes of agitation before reaching a plateau marking sample saturation. The sample containing 0.23% BFR also showed a significant increase in charge compared to pure PS (0% BFR), but to a lesser extent. These results suggest that the incorporation of RFBs modifies the surface triboelectric properties of PS, probably through alterations in electron affinity or conductivity, thus influencing triboelectric behavior. The exponential nature of the charge accumulation observed in all samples can be attributed to the number of contact events between the PS particles and the walls of the tribocharge device. For samples containing BFR, the charge saturation point appeared earlier, suggesting that the presence of brominated compounds improves the efficiency of the triboelectric charge. This behavior is crucial for separation processes, as it indicates a stronger response to the electric fields during the downstream electrostatic separation phase. From these observations it can be inferred that triboelectric measurements may serve as an indicator to assess the feasibility of selective sorting of RFB-charged polymers. Since tribo-electrostatic separation operates on the basis of differences in net surface charge acquired by particles, the marked charge contrasts between samples indicate a high potential to selectively isolate brominated PS from mixed granular plastic waste. These findings make the case for the integration of filler-based separation technologies into recycling chains, especially for materials with low density contrast and overlapping melting points, where traditional mechanical methods fail. From a broader perspective, this work contributes to the optimization of pre-treatment steps in WEEE recycling lines. The differentiation of triboelectric performance according to BFR concentration allows the development of treatment parameters that can be adjusted according to the level of contamination of the incoming waste streams. In addition, understanding the influence of chemical composition on charge dynamics could help design more efficient triboelectric chargers tailored to specific types of plastics and additives. In conclusion, the study demonstrates that BFR concentration has a significant effect on the triboelectric charging behavior of PS, with higher bromine content leading to more efficient charge build-up. These results reinforce the viability of tribo-electrostatic separation as a sustainable method for the recovery of polymers containing BFRs from complex waste mixtures. Future work will focus on extending these results to more heterogeneous plastic waste scenarios, including real mixtures derived from WEEE, and assessing the impact of other additives and environmental parameters such as moisture
The counter-rotating mechanism makes a substantial contribution to balance-movement coordination during the anticipatory period of gait initiation
No full textInternational audienceMaintaining balance during gait initiation is essential for mobility and functional independence. The transition from a postural state to steady-state gait relies on two mechanisms to accelerate the whole-body centre of mass (WBCoM): moving centre of pressure (CoP); and counter-rotating segments to modulate internal whole-body angular momentum (HM). While the moving CoP mechanism is well-understood and known to generate mechanical instability, the role of the counter-rotating mechanism is less clear. Therefore, the present study quantified the contribution of the counter-rotating mechanism and explored its coordination with the moving CoP mechanism during the anticipatory period of gait initiation. Based on a sample of 13 healthy participants, we computed the time evolution of CoP, HM, the coefficient of cancellation (i.e., the extend to which segmental angular momenta counterbalance each other), and the relative contribution of each mechanism to WBCoM acceleration. We tested whether the contribution of the counter-rotating mechanism was significantly different from zero using a Statistical Parametric Mapping t-test. In the frontal plane, the counter-rotating mechanism did not appear to play a substantial role. However, in the sagittal plane, we found that: (1) the period of mechanical instability was longer than the period that have been identified based on the moving CoP mechanism alone; (2) rotational instability was reduced in anticipation of unipedal support; and (3) the counter-rotating mechanism significantly contributed to WBCoM forward acceleration. Overall, our findings emphasise the critical role of the counter-rotating mechanism in the sagittal plane for balance-movement coordination. Considering the counter-rotating mechanism appears important for understanding, assessing, and developing interventions for individuals with balance impairments
