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Habiter la terre agricole, entre transitions et conflictualités - Regards croisés, géographie et droit
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Quantifying how nutrient and carbon inputs from land affect Arctic Ocean acidification
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Multiphysics modelling of 3D concrete printing: From material model to process simulation and optimisation
No full textInternational audiencePredictive simulation of 3D concrete printing is important to warrant printability and durability of print pieces and to optimise printing parameters, yet tedious due to the complexity of the material behaviour and printing process. From a constitutive model allowing a continuous description of the coupled chemothermo-poro-mechanical behaviour of cement-based materials from the early-age to the hardened state, a comprehensive finite element simulation framework is designed. It aims at modelling extrusion-based 3D printing processes, taking into account the sequential deposition of material. Study of the onset of plastic collapse on specific geometries at different printing speeds show the complexity of collapse prediction as well as the importance of process-related effects. An optimisation scheme is proposed to determine optimal printing speed modulations from numerical simulations with the perspective of increasing productivity in 3D concrete printing. The model shows good predicting capabilities when compared with experimental printing failures, and is able to extrapolate to other accelerator dosages without model re-calibration
En finir avec la responsabilité individuelle ? Associations de consommateurs et réglementation des véhicules aux Etats-Unis
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Forecasting the solar cycle using variational data assimilation: Validation on cycles 22 to 25
No full textInternational audienceContext. Forecasting future solar activity has become crucial in our world today, where intense eruptive phenomena, mostly occurring during solar maximum, are likely to exert a highly detrimental effect on satellites and telecommunications. However, forecasting such events is a very difficult task owing to the highly turbulent flows existing in the solar interior.Aims. We present a 4D variational assimilation technique (4D-Var) applied for the first time to real solar data, consisting of the time series of the sunspot number and the line-of-sight surface magnetic field from 1975 to 2024. We tested our method against observations of past cycles 22, 23, 24, as well as the ongoing cycle 25. For the latter, we offer an estimate of the imminent maximum value and timing, along with a first forecast of the next solar minimum.Methods. We used a variational data assimilation technique applied to a solar mean-field Babcock-Leighton (BL) flux-transport dynamo model. This translates to a minimization of an objective function with respect to the control vector, defined here as a set of coefficients representing the meridional flow and the initial magnetic field. Ensemble predictions were produced to obtain uncertainties on the timing and value of the maximum of cycle n + 1, when the data on cycle n were assimilated. In particular, we have studied the influence of the phase during which the data were assimilated into the model and that of the weighting of various terms in the objective function.Results. Our method was validated on cycles 22, 23, and 24 with very satisfactory results. We found a particularly good convergence of our predictions (both in terms of accuracy and precision) when the assimilation window encompassed more and more of the rising phase of cycle n + 1. For cycle 25, predictions varied, again depending on the extent of the assimilation window; however, they were seen to start converging past 2022 to a solar maximum reached between mid-2024 up to the beginning of 2025, with a sunspot number value of 143.1 ± 15.0. Relatively close values of the maximum have been found in both hemispheres within a time lag of a few months. We also offer a forecast for the next minimum to occur around late 2029 (with significant error bars).Conclusions. The data assimilation technique presented here combines a physics-based model and real solar observations, offering promising results for future solar activity forecasting
Agriculture, aquaculture et pêche : impacts des modes de production labellisés sur la biodiversité. Synthèse du rapport scientifique de l'étude
No full textLa loi Climat et résilience de 2021 a instauré la mise en place d’un affichage environnemental sur les produits alimentaires afin d’informer les consommateurs du coût environnemental de leurs achats. La construction de cet affichage a suscité un important travail méthodologique ouvert aux acteurs. Un bilan intermédiaire a souligné la difficulté à appréhender toutes les dimensions de la biodiversité. C’est dans ce cadre que les ministères en charge de la transition écologique, et de l’agriculture et de l’alimentation, ainsi que l’ADEME, ont sollicité INRAE et l’Ifremer courant 2022 pour mieux documenter ce volet biodiversité, en se focalisant sur les pratiques de production. Afin d’éclairer plus largement les politiques publiques, les pouvoirs publics ont choisi de s’appuyer sur les labels dont les cahiers des charges certifient des pratiques et parce que leur développement les place au cœur de nombreux débats sur les relations entre production et consommation durables. L’étude, intitulée « BiodivLabel », a été menée par un comité pluridisciplinaire d’experts scientifiques issus d’organismes publics de recherche et d’enseignement supérieur
Assessing climate change impacts on the March 2024 compound floods and Saharan dust outbreak in Europe
No full textInternational audienceThis study examines the impact of climate change on the compound extreme weather event that caused simultaneous floods in Portugal and an African dust outbreak (ADO) across the Mediterranean region at the end of March 2024. The event was primarily driven by a large low-pressure system near Western Europe. We use circulation analogs to identify similar weather patterns and evaluate the potential influence of climate change on this event over the past 45 years. Our findings indicate that such events have become more frequent and are associated with deeper depressions. Specifically, they feature more intense precipitation over the Western Iberian Peninsula and increased dust transport over the Central-Western Mediterranean, highlighting the role of climate change in amplifying this particular event