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Multi-domain encoder–decoder neural networks for latent data assimilation in dynamical systems
No full textInternational audienceHigh-dimensional dynamical systems often require computationally intensive physics-based simulations, making full physical space data assimilation impractical. Latent data assimilation methods perform assimilation in reduced-order latent space for efficiency but struggle with complex, nonlinear state-observation mappings. Recent solutions like Generalized Latent Data Assimilation (GLA) and Latent Space Data Assimilation (LSDA) address heterogeneous latent spaces by incorporating surrogate mapping functions but introduce computational costs and uncertainties. Furthermore, current algorithms that integrate data assimilation and deep learning still face limitations when it comes to handling non-explicit mapping functions. To address these challenges, this paper introduces a novel deep-learning-based data assimilation scheme, named Multi-domain Encoder–Decoder Latent Data Assimilation (MEDLA), capable of handling diverse data sources by sharing a common latent space. The proposed approach significantly reduces the computational burden since the complex mapping functions are mimicked by the multi-domain encoder–decoder neural network. It also enhances assimilation accuracy by minimizing interpolation and approximation errors. Extensive numerical experiments from three different test cases assess MEDLA’s performance in high dimensional dynamical systems, benchmarking it against state-of-the-art latent data assimilation methods. The numerical results consistently underscore MEDLA’s superiority in managing multi-scale observational data and tackling intricate, non-explicit mapping functions
La planification des transports et des mobilités en Île-de-France au prisme du référentiel de transition : outils, enjeux, impensés
No full textInternational audienc
Viscous effects in sheared unsaturated wet granular materials
No full textInternational audienceWe report on experiments and discrete element simulations of homogeneous, simple, normal stress-controlled, shear flows of model unsaturated granular materials: assemblies of frictional spherical particles bonded by a small quantity of a wetting liquid. The rheology of such unsaturated granular materials in the dense flow regime was characterized in recent publications of our group, in terms of internal friction coefficient μ∗ and solid fraction Φ, depending on the reduced pressure P∗ comparing capillary forces to controlled normal stress, and on inertial number I. The present study extends this description to the influence of the liquid viscosity on material rheology in the low saturation regime. The quantitative agreement of simulations with experiments is confirmed for the quasistatic limit, and our numerical results, despite some quantitative differences, capture the correct trends in the regime dominated by viscous forces. Rheological properties are then determined, to a large extent, by the same viscous numberIv as used to formulate constitutive laws in saturated, dense suspensions. More precisely, a visco-inertial numberJ, combining Iv with inertial number I as J=Iv+2I2, appears apt to describe the rheological laws, as expressed by the internal friction coefficient and the solid fraction, measured in the laboratory or in the simulations, as well as the numerically investigated internal state of the flowing material. Simulations provide insight into the role of viscous forces: predominantly tensile, they contribute to the increase with shear rate of the macroscopic friction coefficient μ∗ through a direct positive contribution to shear stress, a negative contribution to normal stresses (enhancing the strength of the contact network), and microstructural changes affecting the network of contacts and liquid bridges
Enseignants à l’université : quand l’enrichissement des missions déstabilise le cœur de métier
No full textNational audienceAvec l’arrivée de publics scolaires « fragiles » à l’Université, la réussite des étudiants s’est progressivement imposée comme un enjeu majeur des politiques publiques de l’enseignement supérieur. Dans ce contexte, nous montrons que la prise en charge de ces étudiants et de leur réussite s’est traduite, pour les personnels enseignants à l’Université, par l’apparition de missions supplémentaires conduisant à l’élargissement de leurs fonctions et à la transformation de leur identité professionnelle
Wastewater treatment with performic acid (PFA): Efficiency on antimicrobial resistance
No full textInternational audienc
Lobbying for Globalisation
No full textUsing detailed information from lobbying reports filed under the Lobbying Disclosure Act, we construct a unique dataset that allows us to identify which firms lobby on Free Trade Agreements (FTAs) negotiated by the United States, their position (in favour or against) and their lobbying effort on the ratification of each trade agreement. Using this dataset, we show that lobbying on FTAs is dominated by large multinational firms, which are in favour of these agreements. On the intensive margin, we exploit exogenous variation across FTAs to show that individual firms put more effort supporting agreements that generate larger potential gains -larger improvements in their access to foreign consumers and suppliers and smaller increases in domestic competitionand that are more likely to be opposed by politicians. To rationalise these findings, we develop a new model of endogenous lobbying on trade agreements. In this model, heterogeneous firms select into trade and choose whether and how much to spend lobbying on the ratification of an FTA, and politicians may be biased in favour of or against the agreement
Constructing narratives and counter-narratives of the future in a context of climate change: the case of 'megabassines' in western France
No full textInternational audienceWith the succession of heatwaves and growing difficulties in obtaining water in quantity and quality, water is at the centre of many tensions. Scientific forecasts are highly uncertain. Farmers are organising themselves around new water management infrastructures, while citizens are worried and make their concerns known.In western France, government consultation has led to the creation of water replacement reservoirs (also called as "megabassines" by their critics) (Carrausse 2022). These infrastructures enable surplus water to be stored in the water tables in winter, to be used when agricultural irrigation needs are greatest in summer. However, the social and environmental impacts are widely decried by opponents, backed by numerous scientists (Azam et al., 2023). Since 2022, there has been an increase in the number and variety of events linked to these protests, including demonstrations, juridical actions and damages to infrastructure. Many scientists are taking sides in the debate but are also committed to producing new data, whether this concerns the capacity of soils to retain water, the groundwater hydrogeology, naturalistic knowledge or legal remedies. From a STS (Science and Technology Studies) perspective, this paper aims to show how different narratives, including scientific narratives, participate in the fabrication of futures (Granjou, Walker, and Salazar 2017). I will show how farmers are placed at the heart of action in the face of the risks of climate change in the imaginaries associated with the implementation of these infrastructures and what alternative narratives are constructed
Attribution of summer 2022 extreme wildfire season in Southwest France to anthropogenic climate change
No full textInternational audienceSummer 2022 was exceptionally hot and dry in Europe and especially in Southwest France, where the most important wildfires since 1949 had serious environmental and socio-economic impacts. Here we conduct an impact-oriented climate change attribution study by first investigating which climate indices are the most correlated with the burnt area between 2003 and 2022. We find that an index combining soil moisture integrated over 6 months and temperature and vapour pressure deficit integrated over 3 months is correlated with large burnt areas. Using the index developed, we estimate that anthropogenic climate change made climate conditions propitious for wildfire development, such as the ones of July 2022, two times more likely, with a return period of 13 years in the current climate. Our study raises the question of the sustainability of the Landes Forest and stresses the urgent need to mitigate greenhouse gas emissions and adapt to climate change
Stratospheric aerosols and C6H6 in Jupiter’s south polar region from JWST/MIRI observations
No full textInternational audienceContext. The polar atmosphere of Jupiter is significantly affected by auroral activity, which can induce both thermal and chemical differences compared to the rest of the atmosphere. In particular, auroral activity enhances the production of various hydrocarbons, including benzene. Benzene could be a potential precursor to the formation of the stratospheric hazes.Aims. We investigated the spatial distribution of the benzene abundance across latitudes ranging from 50°S to 81°S and 17°S to 25°S. Additionally, we examined the chemical origin of polar aerosols and their latitudinal distribution.Methods. We employed James Webb Space Telescope (JWST) Mid InfraRed Instrument (MIRI) observations to measure the benzene abundance based on its emission at 674 cm−1. Additionally, we examined the spectral dependence of the aerosol opacity within the 680–760 and 1380–1500 cm−1 spectral ranges, and mapped their distribution from 80°S–50°S.Results. At latitudes lower than 60°S, benzene is found to be up to ten times more abundant compared to lower latitudes. This enhancement of C6H6 is well mixed longitudinally and not particularly concentrated inside the auroral oval. Photochemical models predict a decrease in the abundance as we approach the mid latitudes, but fail at polar latitudes as they do not include ion-neutral chemistry. Moreover, we find that the southern polar atmosphere is enriched with aerosols at ~10 mbar. The optical depth of the aerosols increases at latitudes poleward of ~60°S, similar to the enhancement of C6H6. These aerosols have spectral features similar to the aerosols of Titan and Saturn, and the mass loading is of ~1.2 ± 0.2 × 10−4 g cm−2. Finally, we quantified the impact of these aerosols on the retrieved temperature structure, causing a decrease in the temperature at pressure levels deeper than 10 mbar.Conclusions. We find that the auroral precipitation produces abundant stratospheric aerosols, which must play an important role in the chemistry and dynamics of the planet
