HAL-Ecole des Ponts ParisTech
Not a member yet
42743 research outputs found
Sort by
Stock and vertical distribution of microplastics and tire and road wear particles into the soils of a high-traffic roadside biofiltration swale
No full textInternational audienceUrban highways are a central infrastructure in megacities and represent diverse sources of microplastic pollution. Understanding the relative contribution of these microplastic sources, including the abrasion of macrolitter and the generation of tire and road wear particles (TRWP) is necessary to better assess the sources and fate of microplastics in terrestrial environments. This study focuses on microplastic (MP) and TRWP infiltration in the soil of a biofiltration swale alongside a high-traffic highway in the north of Paris, France. First, using manual core sampling, soil samples were collected and analysed by micro-Fourier Transformed Infrared (micro-FTIR) imaging and Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC/MS) to determine the stock and vertical distribution of microplastics and TRWP. Secondly, the relative contribution of major microplastics and TRWP sources into the soils were estimated. Finally, these field results were then used to provide an estimate of the mass balance of microplastics and TRWP on that site. Results revealed a median concentration of 5.4 μg MP g−1, three orders of magnitude lower than the median TRWP concentration of, 1.16 mg TRWP g−1. In both types of contaminations, surface samples presented a significantly higher microplastic abundance than deeper layers, with 90 % of the overall stock located in the surface layers. The major contributors to microplastics accumulation in the soils were found to be fragmentation of macrolitter found on-site, followed by road runoff. The TRWP accumulation on-site was significantly lower than the TRWP production from the local traffic, suggesting TRWP may either remain trapped in the road or are deposited away from the road. To better understand the distance around a road that is affected by TRWP and microplastic emissions, further studies should be conducted at varying distances around highways. The present study focusing on a site highly exposed to microplastic and TRWP pollution helps prioritize the sources and improves the understanding of the short scale transfer dynamics of the plastic pollution stemming from an urban road
The distribution of minimal fractions on the Stern-Brocot tree
No full textThe Stern-Brocot (SB) tree enumerates all irreducible rationals, uniquely positioned with ties to continued fractions and Christoffel words. In this work, we study a quotiented SB tree, focusing on fractions at levels multiple of 3 and their presence on minimal paths defined by the second-order balancedness of Christoffel words. We describe the distribution of all fractions belonging to a minimal path at these levels, detailing their positions, and provide a comprehensive study of the gaps between consecutive fractions, revealing structural patterns tied to the quotiented tree. In prior work, fractions Fn F n+1 with Fn from the Fibonacci sequence were found to be on a minimal path (zigzag path). Analogously, we study four other minimal paths that define the boundary of the set of all minimal paths.</div
La restauration socio-écologique, une transposition concrète du concept normatifdes solutions fondées sur la nature
No full textInternational audienceLes « solutions fondées sur la nature » (SfN) sont aujourd’hui largement mentionnées pour rendre les écosystèmes anthropisés plus durables. Les SfN émanent des principes de l’ingénierie écologique tels que conceptualisés par H. T. Odum (1962), c’est-à-dire reposant sur une approche centrée sur les flux énergétiques et l’autorégulation des écosystèmes. Malgré leur popularité croissante, la mise en œuvre de ces SfN reste complexe et souvent orientée vers les seuls bénéfices sociétaux, avec de faibles bénéfices pour la biodiversité.La crise climatique et écologique actuelle nécessite une reconsidération de notre relation à la nature, en intégrant à la fois des objectifs sociaux et écologiques dans une nouvelle mobilisation des sociétés et des écosystèmes en crise. C’est ce que prône la restauration socio-écologique, un récent concept développé lors de la reconstruction de villes côtières après le tsunami de 2011 au Japon. Ce concept propose la réparation conjointe des écosystèmes et d’une cohésion sociale humaine. Il utilise les éléments de l’écosystème pris comme repères historiques avant perturbation, ce qui permet un ancrage local et la reprise d’une trajectoire sociale et écologique viable. La restauration socio-écologique ne constitue pas une activité classique d’un programme, mais un processus social dans lequel plusieurs acteurs s’impliquent en s’appuyant les uns sur les autres.Nous proposons de généraliser cette restauration socio-écologique, au-delà des situations post-catastrophe ou post-conflit, pour modifier les pratiques d’aménagement et créer de vraies synergies entre vivants humains et non-humains. À ce titre, nous utilisons la réouverture de la rivière Bièvre dans la région de Paris comme un exemple de restauration socio-écologique pertinente, car elle implique la communauté locale et répond à des enjeux écologiques. Pour conclure, nous formulons cinq recommandations visant à adapter les principes de la restauration socio-écologique à la mise en œuvre de SfN, dans le but de rendre plus résilients face aux changements globaux non seulement nos environnements, mais aussi les environnements qui concernent l’ensemble du monde vivant non humain, souvent oubliés dans les pratiques sur le terrain. En optant ainsi pour une approche plus écocentrée, les SfN pourraient être en phase avec la définition initiale de l’IUCN, et devenir finalement des solutions fondées pour et par la nature, à la hauteur des enjeux d’une transition écologique effective sur le terrain dans les pratiques des acteurs
Transformations Preserving the Effective Spectral Radius of a Matrix
No full textInternational audienceWe discuss transformations on matrices that preserve the effective spectrum and/or the effective spectral radius
A logarithm law for nonautonomous systems fastly converging to equilibrium and mean field coupled systems
No full textInternational audienceWe prove that if a nonautonomous system has in a certain sense a fast convergence to equilibrium (faster than any power law behavior) then the time τ_r(x,y) needed for a typical point x to enter for the first time in a ball B(y,r) centered in y, with small radius r scales as the local dimension of the equilibrium measure μ at y, i.e.lim(r→0) log [τ_r(x,y)]/ [-log(r)]We then apply the general result to concrete systems of different kind, showing such a logarithm law for asymptotically authonomous solenoidal maps and mean field coupled expanding maps
Spatialized and Prospective LCA of Agrivoltaism in the Mediterranean basin under Climate Change
No full textInternational audienc
Long-term thermo-mechanical behaviour of an energy pile installed in clay: Field experiments and numerical simulations
No full textInternational audienceThis study investigates the long-term thermo-mechanical behaviour of an energy pile installed in clay using field experiments and numerical simulations, aiming both to understand its response under sustained mechanical loads and cyclic thermal loading, and to develop a novel numerical model that can provide practical guidance for the design of energy piles. Firstly, full-scale experiments were performed on energy piles (0.42 m in diameter and 12 m in length) subjected to constant axial loads combined with three or five cyclic thermal loads. One pile was loaded to 30 % of its bearing capacity, and another to 50 %. Under these constant axial loads, the piles were subjected to several thermal loading cycles. Mechanical loading was finally applied to these piles after thermal cycles. A third pile was only mechanically loaded until the pile’s bearing capacity was reached. Results for the pile temperature and axial strain, pile head displacement, and axial load are shown. Secondly, a numerical model was developed based on a one-dimensional nonlinear finite element approach to investigate the long-term thermomechanical behaviour. This model was validated against the experimental results. It was then used to simulate 30 thermal cycles, revealing that the irreversible settlement of the pile head increases with higher axial loads, and that the first thermal cycle induces the largest irreversible settlement
Water Isotope Model Intercomparison Project (WisoMIP): Present-day Climate
No full textInternational audienceWe present the first results of the Water Isotope Model Intercomparison Project (WisoMIP), with Phase 1 focused on modern simulations (1979–2023) from a suite of isotope-enabled atmospheric general circulation models nudged to ERA5 reanalyses. Water sources, mixing, and rainout history influence the isotopic composition of vapor and precipitation, making these simulations powerful tools for tracing the global water cycle. By prescribing identical winds, sea surface temperatures, and sea ice conditions, we isolate differences in water isotope behavior across models, controlling for variability in atmospheric dynamics and mean climate. Our analyses show that the ensemble mean best matches observations, as individual model errors cancel out to yield a more accurate representation of Earth’s isotope distributions. We also evaluate trends and responses to major climate modes during the recent warming period, highlighting regional and temporal sensitivities in the isotope signals. These diagnostics extend beyond traditional model evaluation metrics (e.g., temperature, precipitation) to reveal uncertainties in physical processes and guide improvements in model parameterizations. The resulting modern nudged ensemble dataset serves as a benchmark for isotope-enabled model development, satellite product comparison, and understanding of water cycle changes in a warming climate. Given its standardized design and broad participation, WisoMIP provides a valuable “isotope reanalysis’ product for applications ranging from paleoclimate reconstruction to model tuning. Our work demonstrates the importance of coordinated isotope model evaluation in advancing the use of water isotopes as a diagnostic tool in climate science
Cellules solaires à pérovskite avec électrodes à base de carbone, suivies sous différents modes de fonctionnement, en conditions réelles extérieures et en conditions contrôlées
No full textInternational audienceThe best-performing devices all use gold or silver as the back contact which limits perovskite solar cells large-scale application. However, the use of such noble metals is a source of instability in these devices. Performance and stability of triple mesoscopic perovskite solar cells with a carbon electrode, a promising architecture for the next generation of photovoltaics will be disclosed. Comparative study between indoor and outdoor tests is motivated by the lack of data on real conditions of use. This communication describes the manufacture of the PSCs and the indoor (under constant illumination and regulated temperature) and outdoor (on the SIRTA observatory, with monitoring and measurements of environmental conditions) test platforms. The initial results, collected between July and November 2024, have shown differences in performance and lifetime according to the operating mode
Elasto-acoustic wave propagation in geophysical media using hybrid high-order methods on general meshes
No full textHybrid high-order (HHO) methods are numerical methods characterized by several interesting properties such as local conservativity, geometric flexibility and high-order accuracy. Here, HHO schemes are studied for the space semi-discretization of coupled elasto-acoustic waves in the time domain using a first-order formulation. Explicit and singly diagonal implicit Runge-Kutta (ERK & SDIRK) schemes are used for the time discretization. We show that an efficient implementation of explicit (resp. implicit) time schemes calls for a static condensation of the face (resp. cell) unknowns. Crucially, both static condensation procedures only involve blockdiagonal matrices. Then, we provide numerical estimates for the CFL stability limit of ERK schemes and present a comparative study on the efficiency of explicit versus implicit schemes. Our findings indicate that implicit time schemes remain competitive in many situations. Finally, simulations in a 2D realistic geophysical configuration are performed, illustrating the geometrical flexibility of the HHO method: both hybrid (triangular and quadrilateral) and nonconforming (with hanging nodes) meshes are easily handled, delivering results of comparable accuracy to a reference spectral element software based on tensorized elements