HAL-Ecole des Ponts ParisTech
Not a member yet
42743 research outputs found
Sort by
A triple‐microstructure hydro‐mechanical constitutive damage model for compacted MX80 bentonite pellet/powder mixture
No full textInternational audienceA triple‐microstructure hydro‐mechanical constitutive damage model was proposed to describe the hydro‐mechanical behaviour of MX80 bentonite pellet/powder mixture, based on the results from a series of suction‐controlled oedometer tests and microstructure observations. Emphasis was put on the pellet damage behaviour. The model parameters were determined essentially based on these results. The model response was firstly verified with the obtained oedometer tests. Then, the results of Molinero‐Guerra et al. and Darde who carried out suction‐controlled oedometer tests and swelling pressure tests on similar bentonite pellet/powder mixture were employed to validate the proposed model. It appeared that the global volume behaviour and the development of swelling pressure with suction of the bentonite mixture could be well reproduced. The model allowed gaining insights into the microstructural evolutions under oedometer loading. The global compression behaviour was governed by the filling of inter‐grain pores at unsaturated state, but by the compression of grains themselves at saturated state. Conversely, when wetted under constant‐volume condition, inter‐grain pores and intra‐grain macro‐pores were closed, by the swelling of intra‐grain micro‐pores. Examination of the water‐retention property showed that water saturated the intra‐grain micro‐pores at suction 19 MPa, and then started filling intra‐grain macro‐pores. When inter‐grain pores and intra‐grain macro‐pores were all closed at suction 0.1 MPa, water finally came back to intra‐grain micro‐pores. On the whole, the hydro‐mechanical behaviour of the bentonite pellet/powder mixture can be well described by the proposed model
Le nouvel Agenda du Comité international olympique pour l’accueil des Jeux olympiques et paralympiques : un tournant durable ?
No full textInternational audienceThe almost systematic contestation of the Olympic and Paralympic Games has reduced the number of cities potentially able to host them, particularly in so-called democratic countries where organized citizens can succeed in thwarting cities' ambitions. This fact has forced the International Olympic Committee (IOC) to modify its hosting requirements. So, after presenting the IOC's new guidelines, we'll look at the extent to which the Olympic Games can serve as a lever for the sustainable development of host cities.La contestation quasi systématique des Jeux Olympique et Paralympique a réduit le nombre de villes potentiellement en mesure de les accueillir, en particulier dans les pays dits démocratiques où les citoyens organisés peuvent parvenir à contrarier les ambitions des villes. Ce fait a contraint le Comité international olympique (CIO) à modifier ses exigences en matière d’ accueil. Aussi, après avoir présenté les nouvelles orientations du CIO, nous nous demanderons dans quelle mesure les JOP peuvent servir de levier au développement durable des villes hôtes
The Future of the Network Metropolis
No full textInternational audienceIn the landscape of the words that describe urban ecosystems, both the terms “metropolis” and “network” occupy a particular place. Dense networks help cities distinguish themselves, whilst metropolises, to exist at national and international levels, encourage the creation of global networks—from high-speed travel by ground or air, to intermodal platforms, ports or hubs, just to mention transportation. As concepts that fluctuate in their meanings and framework, they require to, as the historian Bernard Lepetit (1996: 10–11) argues, “escape the two symmetrical risks of opacifying complexification and blurring of the subject”. We will here focus our efforts on defining the French network metropolis, while exposing the specific characteristics built over the long term
Existence of minimizers for the Dirac-Fock model of crystals
No full textInternational audienceWhereas many different models exist in the mathematical and physics literature for ground states of non-relativistic crystals, the relativistic case has been much less studied and we are not aware of any mathematical result on a fully relativistic treatment of crystals. In this paper, we introduce a mean-field relativistic energy for crystals in terms of periodic density matrices. This model is inspired both from a recent definition of the Dirac-Fock ground state for atoms and molecules, due to one of us, and from the non-relativistic Hartree-Fock model for crystals. We prove the existence of a ground state when the number of electrons per cell is not too large
Statistical distributions of free surface elevation and wave height for out-of-equilibrium sea-states provoked by strong depth variations
No full textInternational audienc
On the existence of Monge maps for the Gromov-Wasserstein problem
No full textInternational audienceThe Gromov–Wasserstein problem is a non-convex optimization problem over the polytope of transportation plans between two probability measures supported on two spaces, each equipped with a cost function evaluating similarities between points. Akin to the standard optimal transportation problem, it is natural to ask for conditions guaranteeing some structure on the optimizers, for instance if these are induced by a (Monge) map. We study this question in Euclidean spaces when the cost functions are either given by (i) inner products or (ii) squared distances, two standard choices in the literature. We establish the existence of an optimal map in case (i) and of an optimal 2-map (the union of the graphs of two maps) in case (ii), both under an absolute continuity condition on the source measure. Additionally, in case (ii) and in dimension one, we numerically design situations where optimizers of the Gromov–Wasserstein problem are 2-maps but are not maps. This suggests that our result cannot be improved in general for this cost. Still in dimension one, we additionally establish the optimality of monotone maps under some conditions on the measures, thereby giving insight on why such maps often appear to be optimal in numerical experiments
Variabilité temporelle et influences régionales des PM 2,5 dans les villes ouest africaines d'Abidjan (Côte d'Ivoire) et d'Accra (Ghana)
No full textInternational audienceParticulate Matter (PM) Low-Cost Sensors (LCS) can be used to monitor air quality in regions with limited access to reference monitors. This study carried out within the framework of the Improving Air Quality in West Africa (IAQWA) project provides high temporal resolution of data on fine aerosol (PM2.5) mass concentrations in Abidjan (Cote d'Ivoire) and Accra (Ghana) through the deployment of field calibratedReal-time Affordable Multi-pollutant (RAMP) monitors. From February 2020 to June 2021, RAMPs were deployed at five sites in Abidjan and four sites in Accra. Using a temporal resolution of 15 seconds, the datasets provided by RAMPs allowed a comparative analysis of diurnal, daily and seasonal variability of PM2.5 concentrations for different urban sites with distinct pollution sources, over an extended period oftime. Diurnal variations in PM2.5 concentrations showed prominent morning peaks related to traffic rush hours reaching up to 50 mg m−3 . Evening peaks were significant for sites in residential neighborhoods, and pointed to residential type pollution sources. Seasonal differences are analysed over a yearly cycle and maximum values are found during the so-called long dry season (Harmattan), between December and February. During a prominent pollution episode in January 2021 observed by the ground network,analysis of 3D satellite data, revealed Saharan dust transport as an additional source of (fine) aerosol pollution significantly increasing PM2.5. The same episode also revealed a limitation of LCS – an inability to adequately capture dust-dominated pollution, which can be quantified by reference monitors. Annual average PM2.5 concentrations vary between 17 and 26 mg m−3 . PM2.5 differences between sites within a city, especially between traffic impacted and urban background sites, are larger than the differencesbetween the two cities. These annual averages exceed World Health Organization (WHO) annual pollution thresholds from the 2005 (10 mg m−3) and 2021 (5 mg m−3) guidelines.Les capteurs de particules (PM) à faible coût (LCS) peuvent être utilisés pour surveiller la qualité de l'air dans les régions ayant un accès limité aux moniteurs de référence. Cette étude réalisée dans le cadre du projet d'amélioration de la qualité de l'air en Afrique de l'Ouest (IAQWA) fournit des données à haute résolution temporelle sur les concentrations massiques d'aérosols fins (PM 2,5 ) à Abidjan (Côte d'Ivoire) et à Accra (Ghana) grâce au déploiement de moniteurs RAMP (Real Time Affordable Multi-polluants) étalonnés sur le terrain. De février 2020 à juin 2021, des RAMP ont été déployés sur cinq sites à Abidjan et quatre sites à Accra. Utilisant une résolution temporelle de 15 secondes, les ensembles de données fournis par RAMP ont permis une analyse comparative de la variabilité diurne, quotidienne et saisonnière des concentrations de PM 2,5 pour différents sites urbains avec des sources de pollution distinctes, sur une période de temps prolongée. Les variations diurnes des concentrations de PM 2,5 ont montré des pics matinaux importants liés aux heures de pointe de la circulation, atteignant jusqu'à 50 μg m −3 . Les pointes nocturnes étaient significatives pour les sites situés dans des quartiers résidentiels et pointaient vers des sources de pollution de type résidentiel. Les différences saisonnières sont analysées sur un cycle annuel et les valeurs maximales sont trouvées pendant la longue saison sèche (Harmattan), entre décembre et février. Lors d'un épisode de pollution important en janvier 2021 observé par le réseau terrestre, l'analyse des données satellitaires 3D a révélé que le transport de poussières sahariennes était une source supplémentaire de pollution par aérosols (fins) augmentant considérablement les PM 2,5 . Le même épisode a également révélé une limitation du LCS – une incapacité à capturer de manière adéquate la pollution dominée par la poussière, qui peut être quantifiée par des moniteurs de référence. Les concentrations annuelles moyennes de PM 2,5 varient entre 17 et 26 μg m −3 . Les différences de PM 2,5 entre les sites d’une même ville, en particulier entre les sites impactés par la circulation et les sites urbains, sont plus importantes que les différences entre les deux villes. Ces moyennes annuelles dépassent les seuils de pollution annuels de l'Organisation mondiale de la santé (OMS) des lignes directrices de 2005 (10 μg m −3 ) et 2021 (5 μg m −3 )
-robust equivalence of global continuous constrained and local discontinuous unconstrained approximation, a -stable local commuting projector, and optimal elementwise approximation estimates in
No full textLet an open bounded Lipschitz polygon or polyhedron , a function in the Sobolev space , and a simplicial mesh of be given. We prove the equivalence of two piecewise (Raviart--Thomas) polynomial best approximations of in the -norm: 1) globally on the whole computational domain , with the normal trace continuity requirement and a divergence constraint; 2) locally on each mesh element, without any interelement continuity requirement and without any constraint on the divergence. The former (global-best continuous constrained piecewise polynomial approximation) arises in numerical methods for partial differential equations related to the space, whereas the latter (local-best discontinuous unconstrained piecewise polynomial approximation) is a key quantity in approximation theory. Crucially, we establish -robustness in that the equivalence constant only depends on the mesh shape regularity and the spatial dimension. This improves the recent result of [IMA J. Numer. Anal. {\bf 42} (2022), 1023--1049], where the equivalence constant was possibly dependent on the underlying polynomial degree. Consequently, we obtain fully - and - (mesh-size- and polynomial-degree-) optimal approximation estimates under the minimal Sobolev regularity only requested separately on each mesh element. These two results immediately follow by our construction of an operator from the infinite-dimensional Sobolev space to its finite-dimensional Raviart--Thomas subspace that has the following properties: 1) it is defined over the entire and preserves boundary conditions imposed on a part of the boundary of ; 2) it is defined locally in a neighborhood of each mesh element; 3) it is based on elementwise -orthogonal polynomial projections; 4) it is a projector, i.e., it leaves intact objects that are already in the Raviart--Thomas piecewise polynomial space; 5) it is locally and -robustly stable in the -norm, up to data oscillation; 6) its approximation property is locally and -robustly equivalent to that of the discontinuous unconstrained (elementwise -orthogonal) projection; 7) it satisfies the commuting property with the -orthogonal projection onto piecewise polynomials
Dynamique du blocage atmosphérique et son lien avec les températures extrêmes températures extrêmes
No full textAtmospheric blocking is a large-scale anticyclonic system that disrupts the westerly flow in mid-latitudes, often leading to extreme weather events. Despite its significance, the processes behind blocking remain poorly understood. This thesis aims to improve our understanding of blocking and its link to temperature extremes. It first examines the roles of dry and moist processes, showing that the dry models with realistic wave and mean flow energy very well capture the basic features of blocking. The moist processes, such as diabatic heating are a source of extra energy in the systems. The study then explores how moisture fluxes from the Gulf Stream help in reinforcing the blocking, particularly in winter. Finally, the research investigates the connection between blocking and heatwaves, it shows that longer blocked days significantly correlate with heatwave features. This study also highlights some discrepancies in blocking definitions, which overlook less amplified ridges that can trigger extreme heatwaves.Le blocage atmosphérique est un système anticyclonique à grande échelle qui perturbe le flux d’ouest dans les latitudes moyennes, entraînant souvent des phénomènes météorologiques extrêmes. Malgré son importance, les processus à l’origine du blocage restent mal compris. Cette thèse vise à améliorer notre compréhension du blocage et de son lien avec les températures extrêmes. Elle examine d’abord les rôles des processus secs et humides, montrant que les modèles secs avec une énergie d’onde réaliste capturent très bien les caractéristiques de base du blocage. Les processus humides, tels que le chauffage diabatique, sont une source d’énergie supplémentaire dans les systèmes. L’étude examine ensuite comment les flux d’humidité provenant du Gulf Stream contribuent à renforcer le blocage, en particulier en hiver. Enfin, l’étude examine le lien entre le blocage et les vagues de chaleur, et montre qu’il existe une corrélation significative entre les jours de blocage plus longs et les caractéristiques des vagues de chaleur. Cette étude met également en évidence certaines différences dans les définitions du blocage, qui négligent des crêtes moins amplifiées susceptibles de déclencher des vagues de chaleur extrêmes