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L’approche par compétences dans le cadre d’un projet à l’université : des rôles attribués au positionnement des enseignants et enseignants-chercheurs, Bulletin de l'Association des Sociologues de l'Enseignement Supérieur ASES Approche par compétences. Anatomie d’une réforme silencieuse, n°44
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Effects of predictions robustness and object-based predictions on subjective visual perception
No full textInternational audienceLearned regularities about contextual associations between objects and scenes allow to form predictions about the likely features of the environment, facilitating perception of noisy visual inputs. Studies showed that blurred objects that can be predicted based on their scene context appear subjectively sharper than the same objects that cannot. Experiment 1 addressed whether this effect could be modulated by the robustness of context-based predictions.Participants performed a blur matching task between two images, each depicting a blurred object in context. They had to adjust the blur level of the right object to match that of the left object (Target). Robustness of context-based predictions was manipulated via phase-coherence alteration in scene contexts. Results showed that robustly-predicted objects were subjectively perceived as sharper than less predictable objects when the Target object was noisy.Experiment 2 addressed whether object-based predictions also sharpen the perception of scene contexts. Participants performed a blur matching task between two scenes and had to adjust the blur level of the right scene context to match that of the left one (Target). One scene contained an intact object (predictable context), while the other had a phase-scrambled object (unpredictable context). Results showed that at objectively equal blur levels participants perceived predictable scenes as sharper than unpredictable ones, again only when the Target scene was noisy. These results suggest that perceptual sharpening mainly occurs when the visual signal is noisy and predictions are robust enough to disambiguate it, and reveal reciprocal influences between context-and object-based predictions in shaping visual perception.</div
WMSAN Python Package: From Oceanic Forcing to Synthetic Cross-correlations of Microseismic Noise
No full textInternational audienceSeismic ambient noise spectra ubiquitously show two amplitude peaks corresponding to distinct oceanic wave interaction mechanisms called primary (seismic period (T) ~ 14 s) and secondary (T ~ 7 s) microseism. Seismic noise records are used in a wide range of applications including crustal monitoring, imaging of the Earth's deep interior using noise correlations, and studies on the coupling between oceans and solid Earth. All of these applications could benefit from a robust knowledge of spatiotemporal dynamics of microseismic sources. Consequently, seismologists have been studying how to model microseismic sources of ambient noise with the recent improvements in ocean wave models. Global sea state and its derivative products are now covering the past decades in models such as the WAVEWATCHIII hindcast. This paper introduces the Wave Model Sources of Ambient Noise (WMSAN, pronounced [wam-san]) Python package. This modular package uses standardized wave model outputs to visualize ambient noise source maps and efficiently compute synthetics of seismic spectrograms and cross-correlations for surface waves (Rayleigh) and body waves (P, SV), in a user-friendly way
A composite gradient index lens for wideband elastic waves focusing: Design approach and experimental validation at constant thickness
No full textInternational audienceVibrational energy focusing is of significant interest in fields such as energy harvesting, particularly with the emergence of smart structures and self-powered technologies. This paper presents the design and manufacturing approach for Gradient-Index (GRIN) lenses using composite materials. As a proof of concept, the strategy implemented here focuses on controlling the fiber mass ratio of a unidirectional (UD) composite at constant thickness. Mechanical properties must be carefully controlled throughout a dedicated manufacturing process to achieve a gradient of phase velocity for focusing elastic flexural waves. Numerical calculation have demonstrated the efficiency of energy focusing within a frequency range from 2 kHz to 8 kHz. A manufacturing process has been developed to prototype a composite structure that integrates the designed GRIN lens. Additionally, the comparison of a numerical model with experimental results from a manufactured lens structure reveals that the energy density in a defined focusing zone can be increased sevenfold using a gradient lens composite structure, with an incident wave of 8 kHz
Quantitative analysis of flames generated by Li-ion battery thermal runaway
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Dépenses périodiques futures : le juge est libre de sa méthode, mais la capitalisation ne peut se faire dans le passé (Cass. crim., 14 janvier 2025, n° 23-84.994 )
No full textInternational audienceLe juge est libre de capitaliser les rentes correspondant à des dépenses périodiques au jour du premier renouvellement, ou au jour de la liquidation ; en revanche, toute capitalisation dans le passé est à proscrire
Mineral fertilization reduces the drought resistance of soil multifunctionality in a mountain grassland system through plant-soil interactions
No full textInternational audienceIncreasing droughts threaten soil microbial communities and the multiple functions they control in agricultural soils. These soils are often fertilized with mineral nutrients, but it remains unclear how this fertilization may alter the capacity of soil multifunctionality (SMF) to be maintained under drought, and how plant-soil interactions shape these effects. In this study, we used a mountain grassland soil to test the interactive effect of mineral nutrient (Nitrogen and Phosphorous) addition and drought on SMF with and without plants (Lolium perenne) in a mesocosm experiment. We calculated SMF based on 8 microbial properties associated with the capacity of soil microbes to store carbon (C), nitrogen (N) and phosphorous (P) in their biomass, and to process these elements through organic matter depolymerization, mineralization, nitrification and denitrification processes. To investigate mechanisms underlying the SMF response we characterized the associated changes in soil stoichiometry and microbial community composition using 16S and 18S rRNA amplicon sequencing. Our results showed that fertilization decreased the SMF drought resistance when plants were present, but the opposite was observed in the unplanted mountain grassland soil. Our analysis suggested this was due to the interaction of plants, fertilization and drought in influencing four coupled properties related to high SMF: high soil moisture, low microbial C limitation, high bacterial diversity and low bacteria gram positive:gram negative ratio. Altogether, our results suggested that reducing the use of mineral fertilizer for plant production in mountain grassland could improve the ability of their soils to maintain their multifunctionality during drought period. Finally, our study clearly further demonstrated the importance of plant in the complex responses of SMF to global changes and showed that combining stoichiometric and microbial diversity assessment represents a powerful approach to disentangle the underlying mechanisms
Numerical Modeling of Premixed Combustion and Flame Acceleration of Li-ion Battery Thermal Runaway Gases
No full textInternational audienceINTRODUCTIONLi-ion battery safety is of primal concern in an expanding market for this technology's wide range of applications. Fire and explosions are consequential of the thermal and electrochemical chain reactions that affect battery components after mechanical, thermal, or electrical abuse. This thermal runaway triggers the production of flammable gases and a significant temperature and pressure rise within the battery cells. Scientific literature extensively covered the characterization of the gas mixture emitted by faulty batteries and its fundamental flame properties. On one side, some studies focused on the sustained venting and the ignition of non-premixed battery vent gases after opening to assess the propagation of thermal runaway between cells of the same module. On the other side, as done in this work, the severity of premixed combustion of thermal runaway gases was quantified in the scenario of an accumulation of a reactive mixture inside a confined space mixing with ambient air [1], leading to an increased risk for the integrity of structures and safety of people. To this end, numerical modeling should account for flame acceleration and deflagration to detonation transition, as previous works did on hydrogen safety in large-scale volumes, typically of several tens of cubic meters. Therefore, selecting a representative thermal runaway mixture and adapting existing models to this specific composition is necessary to deal with these phenomena adequately. RESULTS AND DISCUSSIONPrevious reviews and meta-analyses of studies revealed a wide dispersion of numerical and experimental results on thermal runaway gas composition and flame properties quantification, depending on cathode chemistry, state of charge and more [2]. Thus, this work selects a gas mixture representing a “worst-case” scenario regarding fire and explosion hazards, notably based on high laminar burning velocity and maximum overpressure. It results from NCA-18650-cells at 100% State of Charge gas composition measurements, and experimental and numerical research on this specific mixture [3]. At first, this work computes fundamental combustion properties with the GRI-Mech 3.0 reaction mechanism. The numerical model relies on Euler equations and the hypothesis of infinitely fast reaction to solve Reactive Riemann problems at the interfaces between burnt and unburnt mixtures to handle large-scale problems [4]. Using the Reactive Discrete Equation Method, the code covers all premixed combustion regimes (slow or fast deflagration and detonation) and the flame front propagation. Nevertheless, the closure of the model requires knowledge of the laminar flame speed as a function of space and time. This parameter primarily depends on the local pressure and temperature, turbulence, and flame wrinkling. Large experimental data sets served as validation cases for current parameters of the model with H2/air. However, adaptation is necessary for mixtures emitted by the faulty batteries, mainly composed of H2, CH4, CO and CO2. Thermodynamic dependence of flame speed on pressure and temperature is directly determined from CANTERA with freely-propagating premixed laminar flames initialized over a range of pressures and temperatures expected in the numerical simulation. Besides, a second simulation environment with a high-order numerical scheme solves the compressible reactive multicomponent Navier-Stokes equation [5]. This Roe Approximate Riemann solver is extended at high order with a One Step Monotonicity-Preserving scheme and cured from carbuncle instabilities. Adaptive mesh refinement performs computational cost reduction and immersed boundary methods model fluid-structure interaction. Previous simulations of hydrodynamic instabilities, flame acceleration, and detonation structure validated the code [5]. It also captured the effect of vortices in the wake of obstacles to accelerate the flame through turbulence. It is, therefore, a reliable reference for computing the turbulent flame velocity of the battery gas mixture after passing through a series of obstacles. Finally, simulation results using the large-scale numerical model [4] with updated turbulence correlation are compared with the reference accurate solver [5] in the same case study.REFERENCES[1] A. Cellier, Simulation aux Grandes Echelles de Feux de Batteries Lithium-ion pour Diagnostic de l’Emballement Thermique. PhD Thesis, Institut National Polytechnique de Toulouse – INPT, France, 2023[2] P.J. Bugryniec, E. G. Resendiz, S. M. Nwophoke, S. Khanna, C. James, S.F. Brown, Review of Gas Emissions from Lithium-ion Battery Thermal Runaway Failure — Considering Toxic and Flammable Compounds. Journal of Energy Storage 87 (2024)[3] M. Henriksen, K. Vaagsaether, J. Lundberg, S. Forseth, D. Bjerketvedt, Numerical Study of Premixed Gas Explosion in a 1-m Channel Partly Filled with 18650 Cell-like Cylinders with Experiments, Journal of Loss Prevention in the Process Industries 77 (2022)[4] A. Velikorodny, E. Studer, S. Kudriakov, A. Beccantini, Combustion Modeling in Large Scale Volumes using EUROPLEXUS Code, Journal of Loss Prevention in the Process Industries 35 (2015) 104–116[5] L. Lecointre, R. Vicquelin, S. Kudriakov, E. Studer, C. Tenaud, High-order Numerical Scheme for Compressible Multi-component Real Gas Flows using an Extension of the Roe Approximate Riemann Solver and Specific Monotonicity-Preserving Constraints. Journal of Computational Physics 450 (2022
Understanding the Operation of a Gas Diffusion Electrode Setup for the Oxygen Reduction Reaction: Experiment versus 3D Multiphysics Modeling
No full textInternational audienceProton exchange membrane fuel cells (PEMFC) require highly efficient oxygen reduction reaction (ORR) electrocatalysts. The intrinsic ORR performance of advanced ORR catalysts (measured in rotating disk electrode, RDE) is often not obtained in membrane electrode assembly (MEA), which denotes for RDE inability to forecast intrinsic activity at large current density/low potential, owing to severe mass-transport limitation. The gas diffusion electrode (GDE) is a relevant tool to assess the intrinsic ORR activity of catalysts at high current density/low potential, so it enables to better forecast their performance in PEMFC MEA. Herein, ORR kinetics is studied in a GDE via cyclic voltammetry and electrochemical impedance spectroscopy; the polarization curve is modeled using multiphysics and multicomponent 3D simulations. The model allows to investigate the interplay between the electrochemical kinetics and the mass-transport of reactant and products in the flow channels of the monopolar plate, gas diffusion layer, porous electrode, and solution. The simulations highlight the significant impact of partial water flooding in the catalyst layer-even at a minimal thickness of 0.6 μm-on the shape of the GDE polarization curves and suggest that mass-transport limitation inside the catalyst layer may be limiting in a GDE setup, specifically at high current density
Motor Aspects of Handwriting Acquisition and Developmental Dysgraphia
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