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Influence de la présence de la ripisylve sur la thermie des cours d’eau : étude de terrain dans le département du Tarn-et-Garonne
No full textInternational audienceRiparian forests, forest formations areas along watercourses, are key for the thermal regulation of aquatic ecosystems by providing shade that reduces water warming. This study investigated the effect of riparian cover density, measured using the Leaf Area Index (LAI), on water temperature, in rivers with alternating vegetated and open segments. Results indicate that dense riparian cover significantly lowers water temperatures during warm periods, particularly in summer. However, hypotheses suggest that factors such as stream width and flow rate may influence the effects of shading on stream temperature, warranting further investigation. Conducted during a rainy year, the study highlights the need for multi-year research, including drier conditions, to better assess riparian impacts under diverse hydroclimatic conditions. Our results already support the prioritization of conservation and restoration of riparian zones in climate adaptation strategies.Les ripisylves, formations forestières bordant les cours d’eau, jouent un rôle crucial dans la régulation thermique des écosystèmes aquatiques en limitant le réchauffement des eaux par leur ombrage. Cette étude a examiné l’effet de la densité des ripisylves, mesurée par l’indice de surface foliaire (LAI), sur la température de l’eau, dans des cours d’eau alternant tronçons avec et sans couverture végétale. Les résultats montrent qu’une ripisylve dense réduit significativement la température de l’eau pendant les périodes chaudes, notamment en été. Cependant, des hypothèses émergent concernant l’influence de facteurs comme le débit ou la largeur du cours d’eau, qui pourraient moduler l’effet de l’ombrage et justifient des recherches plus approfondies. Réalisé lors d’une année pluvieuse, ce suivi souligne la nécessité d’études pluriannuelles, incluant des années plus sèches, pour évaluer pleinement l’impact des ripisylves dans des contextes climatiques variés. Les résultats obtenus soutiennent d’ores et déjà la priorisation de la préservation et de la restauration des ripisylves dans les stratégies d’adaptation au dérèglement climatique
Molecular representation of benzene SOA for 3D modelling
No full textInternational audienceAromatic compounds account for a significant proportion of anthropogenic volatile organic compounds emissions, and their atmospheric ageing is a key driver of the formation and growth of organic aerosols. In this study, the benzene oxidation scheme extracted from the Master Chemical Mechanism (MCM) 3.3.1 was revised and improved by the implementation of several new oxidation pathways, including multigeneration oxidation, peroxy radical rearrangement, formation of di-bridged species and autoxidation. These updates lead to the formation of various compounds that can partition into organic and aqueous aerosol phases. Comparisons to chamber experiments of benzene and phenol oxidation show that the addition of these pathways provides a better representation of the formation (aerosol mass yields) and chemical composition of secondary organic aerosols.While near-explicit schemes provide greater details, their computational complexity makes them difficult to directly implement in chemistry-transport models. To address this, the near-explicit scheme of benzene is reduced using the GENerator of Reduced Organic Aerosol Mechanisms (GENOA) algorithm under representative atmospheric conditions. Using reduction strategies and evaluation criteria, GENOA trains and reduces the SOA mechanism under atmospheric conditions commonly encountered over Europe. The trained benzene SOA mechanism preserves the main characteristic of the near-explicit mechanism (e.g., chemical pathways, molecular structures of crucial compounds, the effect of non-ideality and hydrophilic/hydrophobic partitioning of aerosols), with a size (in terms of reaction and species numbers) that is manageable for three-dimensional aerosol modelling (e.g., regional chemical transport models)
Hybrid high-order approximations of div-curl systems on domains with general topology
No full textInternational audienceWe devise and analyze hybrid polyhedral methods of arbitrary order for the approximation of div-curl systems on three-dimensional domains featuring non-trivial topology. The div-curl systems we are interested in stem from magnetostatics, and can either be first-order (field formulation) or second-order (vector potential formulation). The well-posedness of the resulting discrete problems essentially hinges on recently established, topologically generic, hybrid versions of the (first and second) Weber inequalities. Our error analysis covers the case of regular solutions. Leveraging (co)homology computation techniques from the literature, we perform an in-depth numerical assessment of our approach, covering, in particular, the case of non-simply-connected domains
AI for Industry: Transforming the Daily Lives of Maintenance Operators
No full textInternational audienceIn a highly constrained industrial environment, AI is gradually moving into a field where it was not expected: that of maintenance assistance. In the following, we will discuss this low-key innovation, the conditions of its acceptance and the dialogical processes in which it is involved. It is the fruit of several years of industrial cooperation and innovation. Genesis of this innovationMaintenance support has long been a key area for AI. This applies to expert systems and, more specifically, diagnostic support systems, event memorization and retrieval systems, and trend interpretation systems for predictive maintenance. AI focuses on the exploitation of large masses of data, or on "specialized", targeted expert knowledge, depending on the era, research fields or technological opportunities. Hybrid AI has yet to be developed in this field.Our innovation, which combines expert knowledge and the latest AI techniques, is a real case study and the fruit of a dynamic R&D program involving several industrial partners: EDF R&D, FRAMATOME, SPIE Nucléaire and TECHNICATOME, Boost Conseil and ASSYSTEM. The results are tangible thanks to a demonstration by SPIX Industry.Its history is part of a panorama of successful projects, some of which are cited in Mercier-Laurent (Mercier-Laurent 2011), with:Chapter written by Anne DOURGNON, Eunika MERCIER LAURENT and Alain ANTOINE.</div
Statistical modelling of combined sewer overflow
No full textInternational audienceRivers are at the heart of human activity. They provide many ecosystem services: drinking water, agriculture, transport, hydropower, bathing, freshness, etc. They are also hotspots for biodiversity. However, the water quality of these rivers is deteriorated as a result of human activity. The current work focuses on fecal contamination, which is a discriminating criterion for bathing. In urban watersheds, fecal bacteria contamination comes from point sources related to the operation of the drainage network. During rainy weather, the combined sewer network, mixingboth wastewater and stormwater, can become saturated. As a consequence, part of the flow is discharged directly into the river via combined sewer overflows (CSOs). This is the case for the city of Paris. The possible CSO overflow can be modeled by a function linking its discharge toprecipitation. This relationship is currently poorly understood, with little related work, and even less for the Seine river.To build such linking function, we rely on a dataset that includes location and hourly discharged volume of the monitored CSOs in the Seine River within Paris. Urban watersheds have been delineated within the study site. Rainfall height over these watersheds have been obtained from eather radar. We broke down the data timeseries into events. An event begins with the cause, the rain, and ends with the consequence, the overflow. To link rainfall to CSOs a directional graph based on the drainage network map, was created. It represents the wastewater transport from one watershed to another. This highlights which rainfall variables to consider regarding the CSO location. Principal component analysis (PCA) is used to assess for rain characteristics selection. An unsupervised non-linear technique (Isomap) is then used to build linking function structure.The overflow volume in time can be modeled by a triangular shape. This shape is described by the overflow initial time, its total and maximum volume and the time of the maximum. We expect to retrieve these overflow variables by reducing the number of rainfall event characteristics to single indicators using sequentially PCA and Isomap.Modeling and forecasting source discharges would enable better management of bathing and water supply risks, and better evaluation of mitigation infrastructures
"Chez nous". La réception sociale des compteurs communicants Linky et leur usage au prisme de l'intimité domestique et du partage des données
No full textInternational audienceEn se concentrant sur le cas du suivi de la consommation d’énergie et des outils de suivi de la consommation d'électricité, ce chapitre apporte un éclairage empirique au débat sur la protection de la vie privée et des données dans le domaine de l’électricité. Basée sur deux terrains menés auprès de 104 consommateurs dans le cadred’expérimentations commerciales et lors du déploiement des compteursLinky, l’analyse s’attache à décrire les pratiques et à comprendre les discourset les positionnements qui accompagnent la réception et l'usage du compteur Linky en écho à un impératif moral énergétique qui ne cesse de sediffuser dans l’espace public. Sensibles ou pas à cette préoccupation desobriété énergétique publique, les individus ajustent toutefois, chez eux,dans leur intimité, leurs modes de consommation de façon personnelle, enlien avec les rythmes sociaux, leurs équipements et leurs normes de bien-être.En fouillant les manières de lire, d’analyser, de produire, voire de dénoncerles traces des volumes d’électricité, l’enquête montre quatre formes d’engagementdes individus au croisement de leur rapport à l’accès aux donnéesde consommation d’énergie et à l’intimité qui constituent des lignes de conduite domestique : « suivre à la trace », « rester au chaud », « économiser coûts et attention », « agir en toute sobriété »
Numerical hydrodynamic characterization for the design of a lab-scale jet-loop reactor
No full textInternational audienceThe jet-loop reactor is a powerful tool for analyzing the kinetics of heterogeneous catalytic reactions due to its high mixing degree. Indeed, the high momentum gas flow injected within the loop induces a large gas recycling flow, minimizing concentration and temperature gradients. The purpose of this numerical study is to optimize the geometric features of the reactor (injection nozzle diameters and length, and outlet pipe diameter) to improve the gas recycle ratio. Its hydrodynamic behavior is predicted by using multi-fluid solver, with an immersed boundary method to model the injector and easily vary its geometry. The effects of the operating parameters such as the injection flowrate, the pressure and the temperature are also assessed. In addition, a residence time distribution analysis allows for the evaluation of the Péclet number as a function of the geometric and operating parameters of the reactor. Then, a zero-dimensional hydrodynamic model, based on a macroscopic momentum balance, is finally developed. After fitting specific terms thanks to separated numerical CFD simulations, it enables a rapid optimization of the reactor design and provides insights into its behavior
Enhanced remediation of diesel-contaminated soils using a novel biopolymer-based emulsion
No full textInternational audienceConventional in-situ light non-aqueous phase liquid (LNAPL) remediation techniques often face challenges of high costs and limited efficiency, leaving residual hydrocarbons trapped in soil pores. This study investigates the efficiency of an alcohol-in-biopolymer emulsion for enhancing diesel-contaminated soil remediation. The emulsion, formulated with xanthan gum biopolymer, sodium dodecyl sulfate surfactant, and the oil-soluble alcohol 1-pentanol, was evaluated through rheological tests, interfacial tension measurements, and onedimensional sand-column experiments under direct injection and post-waterflooding scenarios. The emulsion exhibited non-Newtonian shear-thinning behavior with high viscosity, ensuring stable propagation and efficient delivery of 1-pentanol to mobilize trapped diesel ganglia. It achieved 100 % diesel recovery within 1.2 PV during direct injection, outperforming shear-thinning polymer-only and polymer-surfactant solutions, which achieved recovery factors of 83.4-92.9 %. Post-waterflooding experiments also demonstrated 100 % diesel recovery within 1.3 PV, regardless of initial diesel saturation. Key mechanisms include reduced interfacial tension, diesel swelling and mobilization induced by 1-pentanol, and uniform displacement facilitated by the emulsion’s viscosity. Additionally, the emulsion required lower injection pressures compared to more viscous alternatives, enhancing its injectability into the soil and reducing energy demands. These findings highlight the emulsion’s potential to overcome conventional remediation limitations, offering a highly effective and sustainable solution for diesel-contaminated soils and groundwater
Microstructural evolution of neutron irradiated ultrafine-grained austenitic stainless steel
No full textInternational audienceAustenitic stainless steels utilized in-core components of pressurized water reactors are prone to radiation-induced segregation, which leads to the degradation of microstructure and mechanical properties. To improve irradiation resistance, one possible solution is to increase the number density of point defect sinks, such as grain boundaries. For this purpose, ultrafine-grained or nanostructured microstructures are recommended due to their high density of grain boundaries. This paper investigates the microstructural changes in ultrafine-grained 316 austenitic stainless steel exposed to neutron radiation up to 3.9 dpa in irradiation conditions representative of light water reactors. The microstructure at different length scales was analyzed using electron backscattered diffraction, transmission electron microscopy, and atom probe tomography before and after neutron irradiation. The study compares its findings with those of existing literature on coarse-grained austenitic stainless steels to evaluate the benefit of ultrafine-grained 316 austenitic stainless steels regarding irradiation ageing in representative conditions of light water reactors
Analyse de convergence des préconditionneurs de décomposition de domaine avec recouvrement pour problèmes non linéaires
No full textNumerical simulations of nonlinear partial differential equations often involve solving large nonlinear systems, for which Newton's method is widely employed due to its fast convergence near the solution. However, its performance can deteriorate in the presence of strong nonlinearities or poor initial guesses. Nonlinear overlapping domain decomposition methods, such as RASPEN and Substructured RASPEN (SRASPEN) , have proven effective in addressing these challenges. Because SRASPEN reduces the problem size by restricting computations to a substructure, it does not update the solution outside the substructure, so that no natural initial guesses for the nonlinear local solution exists that might lead to additional inner subdomain nonlinear iterations or even prevent the local solvers to converge. In this study, we analyze the convergence of RASPEN. We show how domain decomposition improves the convergence rate of the Newton's method by highlighting the key role of the substructure on the global error contraction. Moreover, our analysis provides insight into an inexpensive modification to SRASPEN that mitigates the lack of iterations outside the substructure. The proposed variant significantly reduces computational cost while improving overall efficiency compared to existing techniques in the literature. Numerical experiments confirm the computational performance and robustness of the improved SRASPEN, establishing it as a reliable approach for solving large-scale nonlinear systems.Les simulations numériques d'équations aux dérivées partielles non linéaires impliquent souvent la résolution de grands systèmes non linéaires, pour lesquels la méthode de Newton est largement utilisée en raison de sa convergence rapide près de la solution. Cependant, ses performances peuvent se détériorer en présence de fortes non-linéarités ou de mauvaises suppositions initiales. Les méthodes de décomposition de domaines non linéaires par chevauchement, telles que RASPEN et Substructured RASPEN (SRASPEN), se sont avérées efficaces pour relever ces défis. Comme SRASPEN réduit la taille du problème en limitant les calculs à une sous-structure, il ne met pas à jour la solution en dehors de la sous-structure, de sorte qu'il n'existe pas de suppositions initiales naturelles pour la solution locale non linéaire qui pourraient conduire à des itérations non linéaires supplémentaires dans le sous-domaine intérieur ou même empêcher les solveurs locaux de converger.Dans cette étude, nous analysons la convergence de RASPEN. Nous montrons comment la décomposition du domaine améliore le taux de convergence de la méthode de Newton en mettant en évidence le rôle clé de la sous-structure sur la contraction de l'erreur globale. En outre, notre analyse donne un aperçu d'une modification peu coûteuse de SRASPEN qui atténue le manque d'itérations en dehors de la sous-structure.La variante proposée réduit considérablement les coûts de calcul tout en améliorant l'efficacité globale par rapport aux techniques existantes dans la littérature. Des expériences numériques confirment les performances de calcul et la robustesse de la SRASPEN améliorée, l'établissant comme une approche fiable pour la résolution de systèmes non linéaires à grande échelle