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Intégration de la précarité numérique dans la RSE : quelles responsabilités pour lesentreprises face à l’illectronisme ?
No full textInternational audienceThis article examines how major French companies integrate digital vulnerabilityinto their corporate social responsibility (CSR) strategies. Based on a qualitative study conducted with five organizations (SFR, Bouygues, La Poste, EDF, SNCF), it analyzes the perceptions, mechanisms, and limitations of their engagement in this domain. The findings reveal often fragmented approaches, largely outsourced to nonprofit partners. Building on the frameworks of Selwyn (2004), Van Dijk (2005), and Gond et al. (2009), the article highlights the tensions between image management, authenticity, and transformative impact. From a managerial perspective, it advocates for a more integrated governance of digital inclusion and the strategic evaluation of einclusion within CSR policies.Cet article interroge la manière dont les grandes entreprises françaises intègrent laprécarité numérique dans leur stratégie RSE. À partir d’une enquête qualitative menée auprès de cinq groupes (SFR, Bouygues, La Poste, EDF, SNCF), il analyse les perceptions, dispositifs et limites de ces engagements. Les résultats mettent en évidence des démarches souvent fragmentées et en grande partie confiées à des partenaires associatifs. S’inspirant de Selwyn (2004), Van Dijk (2005) et Gond et al. (2009), l’article met en lumière les tensions entre image, sincérité et transformation. Sur le plan managérial, il plaide pour une gouvernance plus intégrée de l’inclusion numérique et pour l’évaluation stratégique de l’e-inclusion au sein des politiques RSE
Some stability results for frictionless contact problems in elastodynamics formulated with Nitsche's method
No full textThis work focuses on the numerical performance of the Nitsche-based Finite Element Method for dynamic unilateral contact problems combined with two implicit one-step time-marching schemes. The non-linear contact boundary conditions cause irregularities, which may lead to unstable performance and potential divergence during simulations. By focusing on the discontinuities inherent in dynamic contact problems, we provide new stability results for the proposed methods
A neural operator framework for solving inverse scattering problems
No full textWe present a neural operator framework for solving inverse scattering problems. A neural operator produces a preliminary indicator function for the scatterer, which, after appropriate rescaling, is used as a regularization parameter within the Linear Sampling Method to validate the initial reconstruction. The neural operator is implemented as a DeepONet with a fixed radial-basis-function trunk, while the noise level required for rescaling is estimated using a dedicated neural network. A neural tangent kernel analysis guides the architectural design, reducing the network tuning to a single discretization parameter, adjustable according to the wavelength. Two-dimensional numerical experiments demonstrate the method's effectiveness, with a Python toolbox provided for reproducibility
Effect of directionality on extreme wave formation during nonlinear shoaling
No full textInternational audienceRecent studies have shown that, in coastal waters where water depth decreases significantly due to rapid bathymetric changes, the non-equilibrium dynamics (NED) substantially increases the occurrence probability of extreme (rogue) waves. Nevertheless, research on depth-induced NED has been predominantly confined to unidirectional irregular waves, while the role of directionality remains largely unexplored. The scarce studies on multidirectional waves mainly rely on numerical simulations and have yielded conflicting results. In this work, we report on an experimental investigation of wave directionality on the depth-induced non-equilibrium wave statistics. High-order statistical moments, skewness and kurtosis, are used as proxies for the non-equilibrium wave response. Our results indicate that the directional spreading has a minor effect on decreasing the maximum values of these statistical moments. In contrast, the incidence direction plays a significant role in the non-equilibrium wave response, which is attributed to the effective bottom slope
Exploring low-rank structure for an inverse scattering problem with far-field data
No full textInternational audienceThe inverse scattering problem exhibits an inherent low-rank structure due to its ill-posed nature; however developing low-rank structures for the inverse scattering problem remains challenging. In this work, we introduce a novel low-rank structure tailored for solving the inverse scattering problem. The particular low-rank structure is given by the generalized prolate spheroidal wave functions, computed stably and accurately via a Sturm-Liouville problem. We first process the far-field data to obtain a post-processed data set within a disk domain. Subsequently, the post-processed data are projected onto a low-rank space given by the low-rank structure. The unknown is approximately solved in this low-rank space, by dropping higher-order terms. The low-rank structure leads to a H\"{o}lder-logarithmic type stability estimate for arbitrary unknown functions, and a Lipschitz stability estimate for unknowns belonging to a finite dimensional low-rank space. Various numerical experiments are conducted to validate its performance, encompassing assessments of resolution capability, robustness against randomly added noise and modeling errors, and demonstration of increasing stability
Monitoring of Riverine Aquatic Vegetation Using Satellite PlanetScope Imagery: Feasibility, Limitations and Prospects
No full textInternational audienceSpectral interference induced by the water and the spatial resolution of many satellite images (≥ 10 m) limit the efficiency of remote sensing for monitoring riverine aquatic plant stands. In this study, the potential of using PlanetScope satellite images (3 m in spatial resolution, ~daily acquisition) for monitoring seasonal and interannual aquatic vegetation surface area was evaluated. Airborne images (≤ 0.2 m) acquired on four dates on three aquatic plant stands were used to create, through visual interpretation, reference maps indicating whether the pixels of each PlanetScope image acquired at ±8 days correspond to aquatic vegetation or nonvegetated aquatic areas. For each PlanetScope image, the green normalized difference vegetation index (GNDVI) was calculated and centred on the mean (GNDVI centred ) to distinguish aquatic vegetation from nonvegetated aquatic areas while minimizing variations in their spectral signature over time. Reference maps from the date when aquatic vegetation was the least developed were used to calculate the GNDVI centred classification threshold. To reduce classification errors from radiometric inconsistencies, the frequency at which pixels of PlanetScope images acquired at ±8 days from airborne images were classified as aquatic vegetation was also calculated. Aquatic vegetation was then empirically defined as pixels with a frequency ≥ 85%. Although the classification of PlanetScope images indicates that low abundances of aquatic vegetation cannot be detected, our results show that large changes in stand surface area can be monitored using a multidate classification threshold, thus providing new opportunities for the monitoring of riverine aquatic vegetation on large scales
Normal form computation of nonlinear dispersion relationship for locally resonant metamaterial
No full textInternational audienceThis article is devoted to the application of the parametrisation method for invariant manifold with a complex normal form style (CNF), for the derivation of higher-order approximations of underdamped nonlinear dispersion relationships for periodic structures, more specifically by considering the case of a locally resonant metamaterial chain incorporating damping and various nonlinear stiffnesses. Two different strategies are proposed to solve the problem. In the first one, Bloch's assumption is first applied to the equations of motion. The nonlinear change of coordinates provided by the complex normal form style in the parametrisation method is applied. This direct procedure, which applies first the wave dependency to the original physical coordinates of the problem, is referred to as CNF-BP (for CNF applied with Bloch's assumption on physical coordinates). In the second strategy, the nonlinear change of coordinates provided by the parametrisation method, which relates the physical coordinates to the so-called normal coordinates, is first applied. Then the periodic assumption is used, thus imposing a Bloch wave ansatz on the normal coordinates. This method will be referred to as CNF-PN (for CNF with a periodic assumption on normal coordinates). In the conservative case, the two CNF calculation strategies are first verified by comparing with the results from existing literature. Subsequently, two carefully selected examples demonstrate that the CNF-PN strategy exhibits superior capability in capturing complex wave propagation phenomena, whereas the CNF-BP strategy encounters limitations in handling non-fundamental harmonics and the nonlinear interactions between host oscillators. The influence of truncation order on the accuracy of CNF-PN is further examined, demonstrating its effectiveness in extending the validity limit. For underdamped systems, the CNF-PN is systematically compared against numerical techniques, a classical analytical perturbation technique (the method of multiple scales), and direct numerical time integration of annular chain structures. The results confirm the exceptional accuracy of the CNF-PN in predicting nonlinear dispersion relationships, damping ratios, invariant manifolds, and wave attenuation characteristics, as long as the validity limit of the asymptotic expansion is not reached. This advancement provides a novel and efficient analytical and numerical tool for studying nonlinear metamaterials
Boundary-layer parameterization for assessing temperature and evaporation in floating photovoltaics at the utility-scale
No full textInternational audienceA precursor model for parameterizing the effects of photovoltaic powerplants on the atmospheric boundary layer is developed using computational fluid dynamics. The method allows one to compute the surface roughness lengths, aerodynamical resistances of covered surfaces and convective heat transfer coefficients, adapted for any photovoltaic module layouts and wind directions. It has been applied for two setups: a wind tunnel system and a utility-scale floating photovoltaic installation. In these cases, the altitude-based velocity profiles was reproduced over the arrays; and we found that the turbulence generated by the photovoltaic/atmosphere interaction is greater for head-and tailwinds than sidewinds, therefore affecting the environment and the photovoltaic system. Constructing a digital twin of the floating array using large-scale meteorological fields and the parameters of the precursor model, the temperature of a monitored module was calculated and a spatial variation of 1.3 °C∕km and 5.8 °C∕km was estimated at the utility scale. Moreover, the waterbody evaporation was reduced by 40%-50% due to the photovoltaic panels blocking the vapour removal processes. This result decreased to 14%-20% when considering the flow spatial variations across the waterbody. Further research is necessary to adapt the parameterization to scenarios with low wind velocity
Advanced modeling of gas chemistry and aerosol dynamics with SSH-aerosol v2.0
No full textInternational audienceSSH-aerosol is developed to represent the evolution of primary and secondary pollutants in the atmosphere by processes linked to gas-phase chemistry, aerosol dynamics (coagulation, condensation/evaporation and nucleation) and intra-particle reactions. The representation of process complexity can be adjusted based on the user's choices. The model uses a sectional size distribution, and offers the capability to discretize chemical composition to account for the mixing state of particles. The algorithms are designed to represent the evolution of ultrafine particles: conservation of mass and number during numerical resolution, taking into account the Kelvin effect, the condensation dynamics of nonvolatile compounds, and nucleation. Different parameterizations are provided for nucleation: binary, ternary, heteromolecular and organic nucleation depending on the compounds involved. For gas-phase chemistry, schemes of different complexities can be handled: from simple schemes to model ozone, oxidants and inorganic chemistry (e.g. CB05, RACM2, Melchior2), to more complex schemes, e.g. from the Master Chemical Mechanism (MCM). The complexity of the schemes used for secondary organic aerosol (SOA) formation may also be adjusted: from schemes built from chamber data to near-explicit schemes from MCM. SOA schemes reduced using the GENOA algorithm are also provided for several precursors (toluene, a sesquiterpene and three monoterpenes), together with their evaluation against chamber or flow-tube experiments. A wall-loss module has also been added for easier comparisons to chamber experiments. Specific developments were made in version 2.0 to automatically link the chosen gas-phase mechanism to SOA formation by using the SMILES structure of organic compounds, allowing for the determination of their hydrophilic and hydrophobic properties and for the partitioning in both organic and aqueous phases. The gas/particle partitioning may also be represented with different complexities. For the organic phase, viscosity may be modelled, adapting the aerosol viscosity to its composition, and coupling organic and inorganic thermodynamics. The dynamic evolution of the partitioning may be computed explicitly or thermodynamic equilibrium may be assumed. Different options are also provided to simulate the chemistry of organic compounds inside the particles with different types of reactions: irreversible 1st order reactions, bulk oligomerization, hydratation of aldehydes and reactions of organic compounds with inorganic ions. The SSH-aerosol model may be installed with a docker for standalone use. It has also been coupled to several 3D models to represent gas and aerosol concentrations: from the local scale with computational fluid dynamic and street network models to the regional scale with chemistry-transport models
Analysis of a two-level domain decomposition preconditioner for the time-harmonic Maxwell equations in anisotropic media
No full textInternational audienceWe analyze a domain decomposition preconditioner, namely a two-level additive Schwarz method, for the time-harmonic Maxwell equations in anisotropic media. The material law is described by a tensor-valued electric permittivity ε, magnetic permeability µ and conductivity σ which are assumed to be uniformly symmetric positive definite in the physical domain. Convergence estimates for the preconditioned GMRES solver are obtained through bounds on the norm and the field-of-values (FOV) of the preconditioned operator. Our purpose is to extend the convergence analysis available for scalar and constant coefficients established in Bonazzoli et al. [5] to this tensorial setting. While the overall argument follows the additive Schwarz framework therein, the anisotropic case requires substantial new ingredients. Among these are a coefficient-weighted discrete Helmholtz decomposition, regularity estimates adapted to the anisotropic setting, and a stronger "high frequency regime" assumption. The latter allows control of unsigned terms that vanish via orthogonality in the scalar case. These tools are crucial for the main technical result: bounding the FOV away from the origin through estimates explicit in the frequency and anisotropy parameters, under suitable resolution assumptions