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Microplastiques dans les sédiments fluviaux : une importante hétérogénéité à l’échelle de la bande de sédimentation active
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On the dynamics of equatorial excited dipolar systems
No full textInternational audienceWe consider the two-layer moist-convective thermal rotating shallow water equations and design a flux globalization-based, well-balanced, path-conservative central-upwind numerical scheme for the studied model. We use the developed scheme to conduct a series of numerical simulations and report the observation of eastward-propagating excited dipolar systems. These systems are characterized by one or more convectively coupled, poorly isolated dipolar fronts, primarily driven by the equatorial adjustment of large-scale localized positive buoyancy or potential temperature anomalies on the equatorial beta plane. A formation of these dynamic structures is triggered when disturbances exceed a critical threshold in a moist-convective environment. Notably, during the evolution of cyclones, secondary counter-rotating anticyclones develop in the lower layer, while oppositely signed structures emerge in the upper layer, highlighting the system's vertical coupling. A significant finding of our experiments is the identification of a time lag mechanism, observable even under weaker moist-convective conditions, between the initial state and the system reaching the excited threshold required for eastward propagation. This time lag underscores a critical build-up phase, during which the system accumulates the necessary energy and momentum to transition into a dynamically active state.</div
WindSightNet: The Inter‐Annual Variability of Martian Winds Retrieved From InSight's Seismic Data With Machine Learning
No full textInternational audienceAbstract Wind measurements from landed missions on Mars are vital to characterize the near surface atmospheric behavior on Mars and improve atmospheric models. These winds are responsible for aeolian change and the mixing of dust in and out of the atmosphere, which has a significant effect on global circulation. The NASA InSight mission recorded wind data for around 750 sols. The seismometer, however, recorded data for around 1400 sols. The dominant source of energy in the seismic data is in fact due to winds. To this end, we propose a machine learning model, dubbed WindSightNet, to map the seismic data to wind speed and direction. The trained network achieves wind speed and direction measurements with errors of 0.932 m/s and 32.6°. We use WindSightNet to retrieve winds from the entire time the seismometer was recording to compare year‐to‐year wind variations at InSight. The continuous nature of the data set enables the extraction of periodic behavior. We observe a pattern of waves due to baroclinic activity with periods of 2–3, 4, 5–7 and 9–20 sols occurring 180–360°. We also observe periodicity during the day due to convective cells. This is used to estimate the boundary layer height, yielding values between 2.3 and 7.7 km. A data‐science based metric is proposed to provide a quantification of the year‐to‐year differences in the wind speeds. This highlights variations linked to dust activity as well as other transient differences. On the whole, the seismic‐derived winds confirm the dominance of the global circulation leading to repeatable weather patterns
Coarsening of bubble assemblies: From dry foams to dilute bubbly liquids
No full textInternational audienceHypothesis: Experimental data on bubble coarsening in a liquid are sparse, limited to relatively narrow ranges of liquid volume fractions, and do not encompass the full range relevant to the numerous applications of these systems. Our objective is to leverage recent data obtained aboard the International Space Station and to integrate these with dedicated measurements to produce a comprehensive coarsening rate diagram across the entire range of liquid fractions.Experiment: The objective of new coarsening measurements is to eliminate gravity effects, which can make these systems highly inhomogeneous. We achieve this by using clinostat-type coarsening cells capable of maintaining the homogeneity of foams with low aqueous solution content, i.e. between 2% and 8%. For liquid fractions above 45%, we replace the aqueous solution with a concentrated emulsion of oil droplets in an aqueous solution, possessing a low yield stress to counteract gravitational effects without impacting coarsening kinetics.Findings: For the first time, by combining our results with recent data obtained aboard the International Space Station using the same surfactant, we achieve coverage of the full range of liquid fractions characterizing liquid foam coarsening, from 2% to 38%, significantly expanding the range studied to date. This leads us to propose a model that describes coarsening over this entire range, accounting for both osmotic pressure effects and contact adhesion effects at higher liquid fractions. Similarly, for the first time, we have data covering the full range of liquid fractions characterizing the coarsening of bubbly liquids, from 45% to 96%, allowing us to compare existing models and identify the most robust ones. Finally, we can map the evolution of coarsening rates over a broad range, from 2% to 96%, thereby highlighting the overall impact of dispersed phase fraction on coarsening. This provides a valuable new tool to tackle coarsening effects in diphasic systems
Dam-break flow over various obstacles configurations
No full textInternational audienceFast floods resulting from the failure of hydraulic structures can be characterized by ‘dam-break’ type waves. They pose catastrophic risks to downstream populations and result in severe structural damage, especially in urban areas. To assess and mitigate these risks, it is essential to forecast the influence of urban forms on flooding severity at a global scale. This paper provides datasets from reduced-scale physical experiments of transient flow through various obstacles configurations. The experiments are conducted in a rectangular horizontal open channel, where flow conditions are achieved by rapidly opening a gate holding a volume of water. To assess the impact of obstacle configurations on flow behaviour, two obstacle sizes are investigated, along with one idealized city layout. The experiments provide complete water hydrographs upstream and downstream of the gate. Additionally, the good performance of the code_saturne computational fluid dynamics (CFD) solver and the volume-of-fluid (VOF) method in numerically simulating the experiments is demonstrated
Optimizing UAV Path Planning and Energy Management Using Reinforcement-Learning and Digital Twins Simulation
No full textInternational audienceIn many industrial applications, optimizing the path planning and energy management of unmanned aerial vehicles (UAVs) is crucial for efficient and sustainable operations. This work presents a framework that integrates Reinforcement Learning (RL) and Digital Twin (DT) technologies to optimize UAV trajectory planning while managing energy resources. The framework aims to minimize energy consumption and maximize operational efficiency by dynamically adjusting the UAV’s path and recharging schedule. The UAVs operate in an industrial environment where they must visit multiple checkpoints and avoid obstacles while adhering to battery constraints. A deep reinforcement learning approach, specifically Q-learning, is used to optimize the UAVs’ decision-making processes in real-time. The proposed solution significantly improves energy efficiency and adaptability when compared to traditional path-planning algorithms such as A* and Dijkstra. Experimental results demonstrate the effectiveness of the proposed framework in achieving 100% checkpoint coverage with minimal battery usage, highlighting its potential for large-scale, real-time industrial applications
Quantitative analysis of sheared unsaturated wet granular materials using X-ray micro-tomography and advanced segmentation techniques
No full textInternational audienceThe microstructure of sheared unsaturated wet granular materials, comprising solid particles, liquid phases, and void spaces, is explored using X-ray micro-tomography. Advanced segmentation techniques are employed to overcome challenges in distinguishing phases within the material, utilizing a combination of Random Forest and U-Net models for accurate segmentation of the X-ray images. This methodology enables the quantification of the solid and liquid fractions within the sample, revealing the effects of shear deformation on their distribution. Additionally, an automated tool is designed to characterize the local geometry of small liquid domains, classified according to the number of connected liquid bridges joining grain pairs and the shape of such clusters. It is shown that deformation redistributes the liquid phase, which tends to be excluded from the strongly sheared regions. Coordination number estimates agree with published numerical simulation results. The study also addresses some limitations related to voxel size. The robust tools to analyse complex three-phase microstructure of wet granular materials are expected to improve the modeling of their rheology under different conditions
Water Vapor Spectroscopy and Thermodynamics Constrain Earth's Tropopause Temperature
No full textInternational audienceAs Earth warms, the tropopause is expected to rise, but predictions of its temperature change are less certain. Longstanding theories employing "gray" radiation tie the tropopause temperature to outgoing longwave radiation (OLR), but this is in contrast to recent work in which simulations exhibit a Fixed Tropopause Temperature (FiTT) even as OLR increases. The FiTT is thought to result from the interaction between upper tropospheric moisture and radiation, but a predictive theory for FiTT has not yet been formulated. Here, we build on a recent explanation for the temperature of anvil clouds and argue that tropopause temperature, defined by where radiative cooling becomes negligible, is set by water vapor's maximum spectroscopic absorption and Clausius-Clapeyron scaling. This "thermospectric constraint" makes quantitative predictions for tropopause temperature that are borne out in single column and general circulation model experiments where the spectroscopy is modified and both the radiative and lapse-rate tropopause change in response. This constraint provides a theoretical foundation for the FiTT hypothesis and a more refined explanation for why the tropopause rises with surface warming, shows how tropopause temperature can decouple from OLR, suggests a way to relate the temperatures of anvil clouds and the tropopause, and shows how spectroscopy manifests in Earth's general circulation.</div
Les risques d'une standardisation de la gestion des risques
No full textInternational audienceCe chapitre concerne la régulation des grands systèmes techniques, en particulier de l'industrie à "risques majeurs" , par des normes internationales et des sociétés de certification indépendantes dites tierce-partie. La première mondialisation des échanges, au XIXème siècle, a généré l'essor des sociétés de classification (Lloyd's Register, Bureau Veritas), organismes experts privés en charge de la sécurité maritime. La seconde mondialisation, en cours depuis les années 1980, a généré entre autres l'apparition d'Organismes Notifiés, en charge d'attester de la conformité des produits circulant en Europe à des normes de sécurité transnationales. La cybersécurité et l'Intelligence Artificielle sont en passe d'être régulées par des mécanismes similaires en Europe. Enfin, la seconde mondialisation a aussi généré toutes sortes de normes sociales et environnementales, elles aussi produites et certifiées par le secteur privé. Au moment du constat d'un déficit chronique des finances publiques, au moins en France, il y a lieu de s'inquiéter d'une possible substitution progressive des services d'inspections nationaux traditionnels (ICPE, Inspecteurs du Travail) par une régulation plus "souple" et moins coûteuse pour le contribuable, via des normes et des dispositifs de certification privés
The Low-Hanging Fruit of the Single European Market: New Methods and Measures
No full textWe propose and construct novel measures of the effectiveness and potential of trade blocs, combining estimation with granular data and simulation with a New Quantitative Trade Model. We deploy our methods and new indexes to quantify the potential benefits from (i) further integration within the largest and most successful trade liberalization effort in the world -the Single European Market -and (ii) a possible enlargement. Three main results and implications stand out from our analysis. First, European integration has been very effective in promoting trade among its members, with heterogeneous effects across industries and member states. Second, and most novel and important, our estimates reveal that only half of the potential benefits from EU membership have been realized to date. Third, EU accession will generate very large gains from trade for the new joiners and moderate gains for existing members, with larger benefits for some small and peripheral EU members. Importantly, our methods enable us to construct confidence bounds for the effects of EU enlargement