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A framework for expressing general constitutive models in FEniCSx
No full textNational audienceMany important problems in solid mechanics involve non-trivial constitutive models that are difficult to express in variational form. It is therefore challenging to express these problems in domainspecific languages that work at the variational form level. We introduce a framework for FEniCSx / DOLFINx that allows for the straightforward implementation of a wide range of constitutive models. The application of the framework is demonstrated by implementing a von Mises elastoplastic material model with hardening using JAX and Numba software.Many important problems in solid mechanics involve non-trivial constitutive models that aredifficult to express in variational form. It is therefore challenging to express these problems in domainspecific languages that work at the variational form level.We introduce a framework for FEniCSx / DOLFINx that allows for the straightforward implementation of a wide range of constitutive models. The application of the framework is demonstrated by implementing a von Mises elastoplastic material model with hardening using JAX and Numba software
Booléens en programmation : une analyse à destination des enseignants
No full textNational audienceThe notion of boolean is fundamental in computer science. Even if it seems simple at first sight, its introduction in the first stages of programming education reveals a number of difficulties related to the fact that it is linked to several general concepts of computer science: data types, truth values, invariants, control structures... Starting from this observation, the point of this article is to propose a reflection on the role of booleans in programming. We elaborate on some points concerning possible “good practices”, especially in the context of computer science teaching. In particular, we focus on boolean as a data type and on the main control structures using booleans. We also discuss the general notion of boolean expression used in programming. Finally through a few examples, we illustrate some typical uses of boolean variables.La notion de booléen est fondamentale en informatique. Même si elle paraît simple à première vue, son introduction dans les premiers apprentissages de la programmation révèle un certain nombre de difficultés liées au fait qu'elle est associée à plusieurs concepts généraux de l'informatique : types de données, valeurs de vérité, invariants, structures de contrôle... Partant de ce constat, l'objectif de cet article est de proposer quelques réflexions sur le rôle des booléens en programmation. On détaille certains points relatifs aux « bonnes pratiques » possibles, en particulier dans le cadre de l'enseignement de l'informatique. On s'intéresse notamment au booléen comme type de données et aux principales structures de contrôle faisant appel à des booléens ainsi qu'à la notion générale d'expression booléenne utilisée en programmation. On identifie enfin quelques usages emblématiques des variables booléennes par l'intermédiaire d'exemples variés
Reduced Basis method for finite volume simulations of parabolic PDEs applied to porous media flows
No full textNumerical simulations are a highly valuable tool to evaluate the impact of the uncertainties of various modelparameters, and to optimize e.g. injection-production scenarios in the context of underground storage (of CO2typically). Finite volume approximations of Darcy’s parabolic model for flows in porous media are typically run many times, for many values of parameters like permeability and porosity, at costly computational efforts. We study the relevance of reduced basis methods as a way to lower the overall simulation cost of finite volume approximations to Darcy’s parabolic model for flows in porous media for different values of the parameters such as permeability. In the context of underground gas storage (of CO2 typically) in saline aquifers, our aim is to evaluate quickly, for many parameter values, the flux along some interior boundaries near the well injection area—regarded as a quantity of interest—. To this end, we construct reduced bases by a standard POD-Greedy algorithm. Our POD-Greedy algorithm uses a new goal-oriented error estimator designed from a discrete space- time energy norm independent of the parameter. We provide some numerical experiments that validate the efficiency of the proposed estimator
Au nom du père : ressources et limites d’une enquête sur le syndicalisme par le truchement d’un parent
No full textInternational audienc
Economic growth with brown or green capital
No full textThis paper explores a growth model with capital that can be "brown" or "green," impacting other firms’ total factor productivity (TFP). Brown capital acts as a negative externality, lowering productivity, while green capital, either human or natural, spills over and generates positive externalities, boosting productivity. We prove the existence of a competitive equilibrium with these externalities and demonstrate the occurrence oftwo-period cycles through local and global stability analysis. Notably, cycles in the case of negative externalities require strong intertemporal income effects, while positive externalities lead to cycles with significant substitution effects
Extensive coverage of ultrathin tropical tropopauselayer cirrus clouds revealed by balloon-bornelidar observations
No full textInternational audienceTropical tropopause layer (TTL) clouds have a significant impact on the Earth’s radiative budgetand regulate the amount of water vapor entering the stratosphere. Estimating the total coverage of tropical cir-rus clouds is challenging, since the range of their optical depth spans several orders of magnitude, from thickopaque cirrus detrained from convection to sub-visible clouds just below the stratosphere. During the Strateole-2observation campaign, three microlidars were flown on board stratospheric superpressure balloons from October2021 to late January 2022, slowly drifting only a few kilometers above the TTL. These measurements have un-precedented sensitivity to thin cirrus and provide a fine-scale description of cloudy structures both in time and inspace. Case studies of collocated observations with the spaceborne Cloud-Aerosol Lidar with Orthogonal Polar-ization (CALIOP) show very good agreement between the instruments and highlight the Balloon-borne Cirrusand convective overshOOt Lidar’s (BeCOOL) higher detection sensitivity. Indeed, the microlidar is able to de-tect optically very thin clouds (optical depth τ < 2 × 10−3) that are undetected by CALIOP. Statistics on cloudoccurrence show that TTL cirrus appear in about 50 % of the microlidar profiles and have a mean geometricaldepth of 1 km. Ultrathin TTL cirrus (τ < 2 × 10−3) have a significant coverage (23 % of the profiles), and theirmean geometrical depth is 0.5 km
Vers un changement d’échelle de la séparation à la source ? Focus sur le lisain : une analyse des conditions d’utilisation en agriculture et de diffusion de la pratique
No full textNational audienc
Airborne observations of fast-evolving ocean submesoscale turbulence
No full textInternational audienceOcean images collected by astronauts onboard the Apollo spacecraft more than 50 years ago revealed a large number of ocean eddies, with a size between 1 and 20 km. Since then, satellite infrared, ocean color, sun glitter and synthetic aperture radar images, with high spatial resolution, have confirmed the ubiquitous presence of these small eddies in all oceans. However, observing the dynamical characteristics and evolution of these eddies has remained challenging. An experiment was recently carried out in the California Current system using the new airborne Doppler Scatterometer (National Aeronautics and Space Administration-Jet Propulsion Laboratory DopplerScatt) instrument that observes surface velocities. Here, with DopplerScatt, we mapped a 30 × 100 km domain over multiple days to unveil numerous 1–20 km ocean eddies, called submesoscale eddies, that evolve over a period of a few hours. The strong interactions between eddies generate horizontal velocity divergence, implying vertical velocities reaching 250 m day‑1 at 40 m depth. The velocity field also produces horizontal dispersion of particles over a distance of 50 km within 12 h, which rapidly fills the turbulent eddy field. These observations suggest that submesoscale ocean turbulence may profoundly affect the vertical transport of heat, carbon, and important climatic gases between the atmosphere and the ocean interior, as well as the horizontal dispersion of tracers and particles. As such, submesoscale ocean eddies are a critical element of Earth's climate system
Basic Physics Predicts Stronger High Cloud Radiative Heating With Warming
No full textInternational audienceRadiative heating of clouds, particularly those in the upper troposphere, alters temperature gradients in the atmosphere, affecting circulation and precipitation in today's and future climates. However, the response of cloud radiative heating to global warming remains largely unknown. We study changes to high cloud radiative heating in a warmer climate, identify physical mechanisms responsible for these changes, and develop a theory based on well-understood physics to predict them. Our approach involves a stepwise procedure that builds upon a simple hypothesis of an upward shift in cloud radiative heating at constant temperature and gradually incorporates additional physics. We find that cloud radiative heating intensifies as clouds move upward, suggesting that the role of high clouds in controlling atmospheric circulations increases in a warmer climate
: Restarting the nuclear power project: Revisiting IAEA's handbook
No full textNational science and technology magazine.The article analyzes IAEA's nuclear infrastructure development framework in the context of Vietnam restarting its nuclear program. The framework comprises 19 infrastructure elements developed through 3 milestones. The author compares this process to temple construction, requiring solid foundations and careful architecture. It assesses Vietnam's progress before the 2016 project suspension and current conditions, proposing 6 specific steps for systematically restarting the program.L'article analyse le cadre de développement des infrastructures nucléaires de l'AIEA dans le contexte du redémarrage du programme vietnamien. Le cadre comprend 19 éléments d'infrastructure à développer à travers 3 jalons. L'auteur compare ce processus à la construction d'un temple, nécessitant des fondations solides et une architecture soignée. Il évalue les progrès du Vietnam avant la suspension du projet en 2016 et les conditions actuelles, proposant 6 étapes spécifiques pour relancer systématiquement le programme.Bài báo phân tích khung phát triển hạ tầng điện hạt nhân của IAEA trong bối cảnh Việt Nam tái khởi động dự án này. Khung này gồm 19 yếu tố hạ tầng cần phát triển qua 3 cột mốc. Tác giả so sánh tiến trình này với việc xây dựng một ngôi đền, đòi hỏi nền móng vững chắc và kiến trúc cẩn thận. Bài viết đánh giá tiến độ của Việt Nam trước khi dừng dự án năm 2016 và các điều kiện hiện tại, đề xuất 6 bước cụ thể để tái khởi động chương trình một cách có hệ thống