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French ARGONAUT project: Inferring pollutants (NOx, CO, NMVOCs) and CO2 emissions at high resolution over France using Sentinel-5P and the CIF-CHIMERE inversion system
No full textInternational audienc
Problème de Helmholtz intérieur : formulation modale couplée à une représentation intégrale Version définitive
No full textInternational audienceLet Ω be an opened domain of R3 with a boundary Γ. The problem numbered (1) in the text has a unique solution in H1(Ω), if k ∈ R, Re( 1/ζ ) > 0 on a part of Γ the area S of which is different from zero and g(k, y, ε) ∈ H 1/2 (Γ): ε is the damping of an elastic structure and ζ is the normalised acoustic impedance of the internal wall of the cavity. Parameters ε et 1/ζ are small and real. Thanks to a proper modal expansion, an integral relation between u, ζ, ε and g is built to the first order ϑ( 1/ζ , ε) in 1/ζ and ε, using the residues theorem. The result is the solution to problem (1). A less elaborate version is included in the publication [6] relating to the transmission of sound inside a cavity.Soit Ω un domaine ouvert de R3 de frontière Γ. Le problème numéroté (1) dans le texte admet une solution unique dans H1(Ω), si k ∈ R, Re( 1/ζ ) > 0 sur une portion de Γ d’aire S non nulle et g(k, y, ε) ∈ H 1/2 (Γ) : ε correspond à l’amortissement d’une structure élastique et ζ est l’impédance acoustique normalisée de la paroi interne de la cavité. Les paramètres ε et 1/ζ sont petits et réels. Par une décomposition modale adaptée, une relation intégrale entre u, ζ, ε et g, est construite au premier ordre ϑ( 1/ζ , ε) en 1/ζ et ε, par l’intermédiaire du théorème des résidus. Le résultat est la solution du problème (1). Une version moins élaborée est incluse dans la publication [6] relative à la transmission du son à l’intérieur d’une cavité
Decoding dynamic molecular interactions in cells
No full textInternational audienceVisualization of specific molecules and their interactions in space and time is essential toinvestigate how cellular plasticity and dynamics are regulated, as perturbation of these processesis detrimental to health. The 1st International Conference on Cellular Dynamics and ChemicalBiology (CDCB), which was held in Hefei, China in 2008, united scientists in the fields ofphotonics, chemistry, and biology, to provide synergism between these different disciplines (Yao& Fang, 2009; Yao, 2013). The 8th CDCB conference was held in Hefei, China from July 23 to26, 2024, in a joint meeting with the Chinese Society for Cell Biology, the American Society forCell Biology, and the Asian Pacific Organization for Cell Biology (Figure 1). About 200 scientistsand students gathered in Hefei to discuss the recent advances in cellular dynamics, mesoscaleimaging, and chemical interrogation of cell fate plasticity
Nuclear waste glass alteration under the influence of iron, claystone, and cementitious grout: an integral study
No full textInternational audienceTo prepare for the future deep geological disposal of high-level waste, the alteration of two inactive nuclear glasses was studied in the presence of claystone, iron, and cementitious grout at 50 °C for a period of 4 years. The materials were immersed together in a synthetic water representative of claystone solution composition. Blank experiments were also carried out to study the independent behaviors of iron and glass in the synthetic water. The evolution of the solutions’ chemistry was monitored. At the end of the experiments, the glass and iron, as well as the neoformed phases, were characterized. Results showed that Si, Ca, Mg, and Fe are key elements. A competition exists between the retention/integration of species into glass gels and clay-like neoformations. Magnesium tends to be leached from glasses and form Mg-silicates. It would only integrate into the gel if it was widely available in the solution. Furthermore, iron could form Fe-silicates. Whether for Mg or Fe, the formation of silicates was detrimental to the glass since it involved the creation of a silicon sink and thus the conservation of a high alteration rate. Concerning calcium, in these experiments it appeared that this species tends to be integrated/retained within the gels. In the pH conditions existing here, it seems that there is no competition with a neoformation. The specific impact of the cementitious grout was also studied, and the results showed that the presence of this material in the system had a beneficial effect on glass alteration due to a significant Si supply in the solution, enabling a reduction in the glass alteration rate
Numerical analysis of an enriched beam model
No full textNational audienceThe finite element for a thin-walled tube developped in [1] is considered. A classical EulerBernoulli beam element has been enriched in order to take into account the influence of the rotations of the mid-surface on the local deformations of the tube cross-sections. The latter is a semi-analytical model using a Fourier expansion based on the circumferential variable. A grid convergence study of the enriched model is carried out for different mesh discretisations. Next, the stability of the explicit time integration is studied using the lumped mass matrix and the critical time steps associated to the mass matrix lumping are estimated
Développement d'un modèle de simulation numérique du soudage pour l'optimisation de dimensionnement d'essais expérimentaux
No full textNational audienceCette étude présente une nouvelle approche basée sur un modèle numérique de simulation thermique par éléments finis pour dimensionner des essais expérimentaux. Un essai instrumenté est réalisé pour l’étalonnage des paramètres du modèle thermique. Cet étalonnage est effectué par la résolution d’un problème inverse bayésien, couplé à la construction d’un modèle de substitution. Le modèle numérique calibré et validé est ensuite utilisé afin d’optimiser le dimensionnement d’essais expérimentaux
An innovative method for measuring the convective cooling of photovoltaic modules
No full textInternational audienceThe temperature of photovoltaic (PV) cells is a critical factor in evaluating energy yield and predicting system degradation. Although thermo-electrical models allows predicting the evolution of the system over time, precise understanding of the thermal exchanges between the system and its environment is needed as they are implemented in the yield assessment using thermal correlations. These empirical correlations are based on heat transfer magnitudes undergone by similar PV set-ups.The aim of this study is to introduce a non-intrusive experimental methodology for precisely determining the convective heat transfer coefficient (CHTC) at the front of photovoltaic modules using two setups. The method integrates a heat flux sensor glued to the PV surface coupled with environmental data (e.g., irradiance, ambient temperature). This experimental method is applied to PV modules on a roof in an urban area and to a floating photovoltaic (FPV) system. It is demonstrated that the method significantly improves the accuracy of prediction of PV module temperatures in operating conditions compared to the conventional method based on the energy balance of a PV module. By using quantile regression, an empirical forced convection correlation is found based on the average wind speed. Compared to the traditional approach which relies on global transmittance, the CHTC is mainly dependent on the wind, whereas the global transmittance includes the radiative heat transfer which depends on the module temperature. The correlation for CHTC tailored for the floating photovoltaic system shows sensitivity to wind speed that is slightly higher compared to the inland setup in the literature
Spectrum of the Laplacian with mixed boundary conditions in a chamfered quarter of layer
No full textInternational audienceWe investigate the spectrum of a Laplace operator with mixed boundary conditions in an unbounded chamfered quarter of layer. This problem arises in the study of the spectrum of the Dirichlet Laplacian in thick polyhedral domains having some symmetries such as the so-called Fichera layer. The geometry we consider depends on two parameters gathered in some vector κ = (κ_1,κ_2) which characterizes the domain at the edges. We identify the essential spectrum and establish different results concerning the discrete spectrum with respect to κ. By exchanging the axes and/or modifying their orientations if necessary, it is sufficient to restrict the analysis to the cases κ_1\ge0 and κ_2∈ [−κ_1,κ_1]. We identify the essential spectrum and establish different results concerning the discrete spectrum with respect to κ. In particular, we show that for a given κ_1 > 0, there is some h(κ_1) > 0 such that discrete spectrum exists for κ_2 ∈ (−κ_1,0) ∪ (h(κ_1),κ_1) whereas it is empty for κ_2 ∈ [0; h(κ_1)]. The proofs rely on classical arguments of spectral theory such as the max-min principle. The main originality lies rather in the delicate use of the features of the geometry
Lignes directrices d’un cadre de spécification pour contrôler les systèmes basés sur de l’apprentissage machine profond utilisant la théorie de le modélisation et de la simulation et un héritage nécessairement revisité de la philosophie de la technique.
No full textThe aim of our contribution is to share the guidelines of our work aimed at defining a formal specification framework for systems based on deep learning, in order to ensure a rigorous and systematic control of these systems. To achieve this, we are working on an adaptation of the Theory of Modeling and Simulation (TMS) for this type of systems, guided by our previous work on the epistemological clarification of the concepts of explanation and understanding applied to machine learning. Establishing an explanation requires firstly to formalize the system, which we propose to do by instantiating the concepts of target phenomenon, model, simulator and experimental protocol issued from the TMS. The experimental protocol is particularly important because it allows the system to be embedded in a use case, in a context that allows judgement based on predicted decisions. Understanding is a matter of hermeneutics, as proposed in support theory, which states that knowledge is the result of a mechanism for interpreting the material properties of the inscription. This process requires us to overcome the epistemic ruptures induced by the deep machine learningNotre contribution a pour objectif de partager les lignes directrices de nos travaux visant à définir un cadre de spécification formelle de systèmes basés sur de l’apprentissage machine profond afin d’assurer un contrôle rigoureux et systématique de ces systèmes. Pour cela, nous mettons en oeuvre une adaptation de la théorie de la modélisation et de la simulation pour ces types de systèmes, guidée par notre travail de clarification épistémologique des concepts d'explication et de compréhension appliqués à l’apprentissage machine. Le résumé est organisé comme suit. Nous commençons par établir dans le prochain paragraphe une mise en perspective historique de l’évolution des techniques d’apprentissage machine permettant une confrontation avec certaines théories philosophiques portant sur la technique. Nous indiquons ensuite la stratégie retenue par la Commission Européenne pour réglementer les systèmes basés sur de l’apprentissage machine profond. Le dernier paragraphe présente les lignes directrices du cadre de spécification que nous proposons pour mener un contrôle systématique des systèmes conçues avec des techniques d’apprentissage machine quelque soit son supposé impact
About the structural stability of Maxwell fluids: convergence toward elastodynamics
No full textInternational audienceMaxwell's models for viscoelastic flows are famous for their potential to unify elastic motions of solids with viscous motions of liquids in the continuum mechanics perspective. But rigorous proofs are lacking. The present note is a contribution toward well-defined viscoelastic flows proved to encompass both solid and (liquid) fluid regimes. In a first part, we consider the structural stability of particular viscoelastic flows: 1D shear waves solutions to damped wave equations. We show the convergence toward purely elastic 1D shear waves solutions to standard wave equations, as the relaxation time λ and the viscosity µ grow unboundedly λ ≡ µ/G → ∞ in Maxwell's constitutive equation λ τ +τ = 2 µD(u) for the stress τ of viscoelastic fluids with velocity u. In a second part, we consider the structural stability of general multi-dimensional viscoelastic flows. To that aim, we embed Maxwell’s constitutive equation in a symmetric-hyperbolic system of PDEs which we proposed in our previous publication [ESAIM:M2AN 55 (2021) 807-831]so as to define multi-dimensional viscoelastic flows unequivocally. Next, we show the continuous dependence of multi-dimensional viscoelastic flows on λ ≡ μ/ G using the relative-entropy tool developped for symmetric-hyperbolic systems after C. M. Dafermos. It implies convergence of the viscoelastic flows defined in [ESAIM:M2AN 55 (2021) 807-831] toward compressible neo-Hookean elastodynamics when λ → ∞