HAL-Ecole des Ponts ParisTech
Not a member yet
42743 research outputs found
Sort by
Quel potentiel du développement des véhicules intermédiaires ? Quelles politiques d’accompagnement ? Réflexion à partir du cas de Tours Métropole
No full textInternational audienceLes véhicules intermédiaires (VI) semblent être une solution innovante et prometteuse pour décarboner la mobilité et réduire les externalités négatives de l’automobile. Ces véhicules offriraient une flexibilité proche de celle de la voiture, permettraient une réduction des impacts environnementaux, une meilleure gestion du trafic et une diminution des congestions routières (Jacquemin, 2024). Ils pourraient aussi favoriser l’accès à une mobilité électrique pour les ménages les plus défavorisés.Que ce soit l’Ademe avec le lancement depuis 2022 de l’« extrême défi », les industriels au travers de l’Association des acteurs des véhicules légers intermédiaires (Aveli) ou encore les associations d’usagers, ces véhicules apparaissent comme ayant un fort potentiel de développement pour les déplacements du quotidien des territoires péri-urbains et ruraux. Par exemple, l’Aveli estime dans son rapport Potentiels et impacts des VELIs en France (2024) que « 22 millions de voitures particulières pourraient être remplacées par des Véhicules Légers Intermédiaires » et que l’on pourrait « DIVISER PAR 2 les émissions globales de CO2 ». De plus, en s’appuyant sur l’enquête Mobilités des Personnes de 2019, le rapport souligne que « 94% des déplacements quotidiens font moins de 40km, un peu plus de la moitié entre 5 et 40km, terrain de prédilection de ces “nouveaux” véhicules du Quotidien ». Ainsi, le potentiel de demande attendu est très important pour les VI.Toutefois, plusieurs limites et contraintes peuvent expliquer le difficile développement des VI dans certains types de territoire. Une des limites est le besoin des ménages d’avoir une voiture pour les déplacements longues distances (Bigo A.), restreignant ainsi la possession du VI ou renforçant la multimotorisation. Ensuite, la vitesse limitée de ces véhicules semble un frein important dans les représentations si on les compare à des voitures qui sont uniquement contraintes par les vitesses limites autorisées. La difficile limitation des routes à 80 km/h en témoigne. On peut aussi parler des limites de sécurité et les conflits modaux dans les espaces urbains avec les piétons et les vélos et dans le périurbain ou les espaces ruraux avec les plus gros véhicules questionnant le besoin d’infrastructures dédiées (Héran, 2022).Cette communication a pour objectif de discuter du potentiel des VI. Après avoir donné notre définition des VI à partir de la littérature disponible, nous présenterons quelle est leur capacité réelle à se substituer aux déplacements du quotidien, selon les divers motifs de déplacement et les distances parcourues ? Quelles sont les politiques de mobilité qui pourraient favoriser ce développement ?Afin d’analyser le potentiel de demande des VI, nous mobiliserons le modèle 4 étapes de Tours Métropole. Ce modèle est un modèle multimodal calibré sur l’ensemble du département d’Indre-et-Loire sur la base de l’EMC² (Enquête Mobilité Certifiée Cerema) de 2019 et de l’enquête OD TCU réalisée en 2014. Le recours à ce modèle présente un double intérêt. Le premier est qu'il permet de tenir compte du chainage des activités, principale limite des analyses du potentiel actuelles. Cela permet ainsi d’avoir une analyse plus fidèle à la réalité du potentiel des véhicules intermédiaires. Le deuxième intérêt est qu’il permet de simuler différents types de politiques de mobilité qui pourraient renforcer le potentiel du VI. Aussi, nous simulerons différents types de politique de mobilité (réduction des vitesses, développement des infrastructures cyclables…) pour évaluer lesquelles paraissent les plus efficaces pour favoriser le développement des véhicules intermédiaires. Enfin, les analyses spatiales des déplacements simulés permettront de révéler de potentiels effets rebond et usage de VI pouvant se substituer à la marche ou aux transports en commun. Les limites de ce type de méthode seront finalement discutées pour évaluer le potentiel de diffusion d’un nouveau mode ou d’un mode qui est encore à l’échelle de niche
Spatially varying parameters improve carbon cycle modeling in the Amazon rainforest with ORCHIDEE r8849
No full textInternational audienceUncertainty in the dynamics of the Amazon rainforest poses a critical challenge for accurately modeling the global carbon cycle. Current dynamic global vegetation models (DGVMs), which use one or two plant functional types for tropical rainforests, fail to capture observed biomass and mortality gradients in this region, raising concerns about their ability to predict forest responses to global change drivers. Here we assess the importance of spatially varying parameters to resolve ecosystem spatial heterogeneity in the ORCHIDEE (ORganizing Carbon and Hydrology in Dynamic EcosystEms) DGVM. Using satellite observations of tree aboveground biomass (AGB), gross primary productivity (GPP), and biomass mortality rates, we optimized two key parameters: the alpha self-thinning (α), which controls tree mortality induced by light competition, and the nitrogen use efficiency of photosynthesis (η), which regulates GPP. The model incorporating spatially optimized α and η parameters successfully reproduces the spatial variability of AGB (R2 = 0.82), GPP (R2 = 0.79), and biomass mortality rates (R2 = 0.73) when compared to remote sensing observations in intact Amazon rainforests, whereas the model using spatially constant parameters has R2 values lower than 0.04 for all observations. Furthermore, the relationships between the optimized parameters and ecosystem traits, as well as climate variables, were evaluated using random forest regression. We found that wood density emerges as the most important determinant of α, which is in line with existing theory, while water deficit conditions significantly impact η. This study presents an efficient and accurate approach to enhancing the simulation of Amazonian carbon pools and fluxes in DGVMs by assimilating existing observational data, offering valuable insights for future model development and parameterization
Increasing awareness on geophysical environment: a multi-sensory experience of rainfall
No full textInternational audienceRainfall is very commonly experienced by most people, often seen as a constraint. Anyway, usually people are not really paying attention to it, being too busy with their daily life. As rainfall and hydrology scientists, we aim to reach out to the general public to increase knowledge in an area of widespread misinformation. More importantly, we aim to enhance curiosity and awareness of people in their geophysical environment. In order to contribute to this much needed efforts, we designed and implemented a series of multisensory experiences centered on rainfall with three purpose in mind: i) Actively engage people on geoscience topics by pushing them to pay attention to their environment ; ii) Create a simple and pleasant moment for people enabling to focus on geophysical environment. iii) Create some new knowledge on rainfall for them. With regards to the latter point, the involvement of one’s senses is a great tool to facilitate memorization.The experiences are simple and do not require any material, apart from an available mind and some rainfall. Three examples are feeling the drops and their sizes on the hand or face while walking; listening to the rain falling on something (tent, umbrella, sheet of metal…); looking at the rain falling near a lamppost at night. Each experience has a simple take home message. The first one is related to the various sizes of drops, the second one to the temporal variability of rainfall, while the third one enables to notice the temporal variability of both rainfall and wind. The process is designed as follows. A short description of the suggested experience is given to people. Once they have implemented them, they are asked to fill a rather open/free form to report their sensations and findings. After they are given some explanations on the take home messages we originally had in mind, which does not necessarily match their own feeling. If they are interested in doing it again, they are invited to provide new sets of feedback. In a first step, the whole process was tested with 10-15 people with various backgrounds and who have no expertise in rainfall. Results of this preliminary implementation will be presented in this poster. They are used to tune the process, i.e. the experiences, the short description and also the explanations of the take home message. In future investigations, it will be implemented with a larger number of people to obtain more quantitative and robust results
Multifractal singularity to bridge the scale gap between various rainfall measurement devices
No full textInternational audienceRainfall is known to exhibit extreme variability over wide range of space and time scale, which makes it challenging to characterize, model and even measure. Rainfall measurement devices have observation scales very different from one another ranging from roughly 20 cm in space and few tens seconds (or few minutes) in time for punctual measurement such as disdrometers (or rain gauge), to few hundreds meters in space and few minutes in time for operational weather radars, and up to few kilometres in space and few tens of minutes for satellite data. This very significant observation scale gap between these devices creates a challenge in the comparion simply because of the intrinsic variability of rainfall, even without considering instrumental biases associated to each device.This work focuses on the impact of the intrinsic rainfall variability on the comparison between punctual (disdrometer or rain gauge) and weather radar rainfall measurement. In order to achieve this, the physically based and mathematically robust framework of Universal Multifractals will be used. It relies on the assumption that rainfall is generated through an underlying multiplicative process. In such framework, the rain rate field can be written as the resolution (defined as the ratio between the outer scale of the phenomenon and the observation scale) to the power of a singularity. This singularity is preserved through scales.Rainfall data collected in UK and Taiwan are used. These include high-resolution radar composite products and ground gauge records. In the UK, C-band radar composite, Nimrod, at 5-min and 1-km resolutions is used to compare with 1-min rainfall records derived from tipping bucket gauge records, while, in Taiwan, S-band radar composite, QPESUM, at 10-min and 1-km resolutions is used to compare with 10-second disdrometer rainfall records.The concept of singularity is used to suggest an innovative comparison approach between rainfall measurement devices. More precisely, the local singularity along with the associated uncertainty is assessed using radar data on the range of available space time scales and then compared with the one of disdrometer or rain gauge accounting for the ratio between the observation scales. Results and interpretation of this novel comparison method on the available data will be discussed.Authors acknowledge the France-Taiwan Ra2DW project (supported by the French National Research Agency – ANR-23-CE01-0019-01 and Taiwan’s National Science and Technology Council – 113-2923-M-002-001-MY4) for partial financial support
Multifractal correlation of rainfall extremes and temperature
No full textInternational audienceMultifractal processes describe complex systems characterized by variability that spans across multiple scales and intensities, governed by scale-invariant distributions of extreme values. Universal Multifractals (UM) provide a robust framework for modelling and understanding the inherent extreme variability and scaling properties of various geophysical phenomena. It is a parsimonious framework that relies on only 3 parameters with physical interpretation, C1 the mean intermittency, α the multifractality index and H the non-conservation parameter. Rainfall, inherently variable across spatial and temporal domains, has been widely studied in the framework of UM, with techniques like Trace Moment (TM) and Double Trace Moment (DTM) applied to characterize its scaling properties. Based on this framework, this study aims to assess the correlation between rainfall scaling features and extremes, and temperature ones, relying on multifractal analysis such as DTM and TM. High resolution simultaneously collected rainfall data from disdrometers and temperature data from meteorological stations is used. Data was collected during various measurement campaigns operated by the TARANIS observatory of HM&Co laboratory of Enpc (https://hmco.enpc.fr/portfolio-archive/taranis-observatory/). Data collected both in an urban area and on a meteorological mast located on a wind farm is used. For the disdrometer data, it was collected with 30 seconds time steps, As for the temperature, the meteorological station measures the temperature at 1Hz, so to match their time series it was necessary to take averages of the temperature data at each 30s. Initially, the study explores the correlation between the primary multifractal parameters (C1, α, H) of rainfall and the average temperature at the rainfall event scale. Subsequently, a comparative analysis was conducted between these rainfall parameters and their counterparts derived from temperature fluctuations. This two-step approach aimed to uncover not only direct correlations between rainfall and temperature but also the extent to which the multifractal properties of rainfall mirror those observed in temperature dynamics. In a second part of the study, similar analysis on longer periods of typically one month are used to complement event based analysis by accounting for dry periods. Authors acknowledge the ANR PRCI Ra2DW project supported by the French National Research Agency – ANR-23-CE01-0019-01 for partial financial support
Influences of land use and depth profile on the characteristics of microplastics in agricultural soils
No full textInternational audienceTerrestrial soils are an environmental compartment in which microplastics are known to accumulate. Compared to the surface water of global oceans, soils contain more microplastics, however they are less well studied to date. In particular, the applications of wastewater and corresponding sludge as fertilizers are a major source of microplastics to agricultural soil, as they include washing machine effluent which is often concentrated in polyester fibres. Other relevant microplastic sources include plastic mulching, netting, greenhouses, plastic drainage pipes, and atmospheric deposition. The characteristics and transfer dynamics of microplastics between different environmental compartments including soil in the same agricultural watershed are not well understood. Additionally, very limited information is known on the stock of microplastics in soils. In this work, a long-term French research site, the Orgeval watershed (104 km2), was sampled for soil. This watershed, located slightly beyond the extremities of the Eastern Parisian suburbs, is composed largely of intensive cereal crops and minimal urban zones. Nine locations within the watershed were composite sampled at the soil surface including locations both upstream and at the watershed outlet. These soil samples were derived from various land use areas including agricultural zones such as tilled or undisturbed agricultural fields, greenhouses, and drainage canal riverbanks, plus soil in forested areas and an urban green space. Of these land use types, greenhouse soils demonstrated the highest concentrations of microplastics in surface soils up to 11,200 MPs/kg, where polyethylene and polypropylene made up the majority of the polymers identified. In comparison, forest soils contained far fewer microplastics up to a concentration of 880 MPs/kg. Soil cores were also collected from two of these sites down to a depth of 60 cm, the typical maximum tilling depth used in this watershed. The most noticeable concentration decrease was observed between soil samples collected at the soil surface versus a further 20 cm below it. This study helps better understand the sources of microplastics as well as their fate in agricultural soils
Quels enjeux de redistribution de l'offre urbaine sur les corridors ferroviaires des futurs SERM ? Une démarche exploratoire
No full textInternational audienceLe travail présenté ici pose la question des "transferts de masse" potentiels entre offre urbaine et offre des futurs SERM sur des corridors actuellement desservis prioritairement par les services urbains. Ces derniers peuvent passer à proximité de gares existantes sans les desservir (ou les points d'arrêt portent des noms différents), ce qui peut se justifier dans l'absolu par une très faible offre ferroviaire. Nous avons testé une méthode d'identification des doublons potentiels dans l'optique du développement des SERM, de la revalorisation des gares qui devrait en découler (rabattement possible, gains de temps à la clé vers le centre), dans trois contextes différents : la métropole lilloise, l'agglomération tourangelle et le continuum urbain Aix-les-Bains - Chambéry - Montmélian
An innovative method based on CFD to simulate the influence of photovoltaic panels on the microclimate in agrivoltaic conditions
No full textInternational audienceAssessing the impact of photovoltaic panels on solar and infrared radiation, wind speed, and turbulence is essential for understanding how these panels may affect crops or livestock in agrivoltaic (APV) systems, as well as water reservoirs in floating photovoltaic (FPV) installations. However, state-of-the-art numerical methods require huge computing resources and rarely account for many physical phenomena at the same time. This study suggests the implementation of source and sink terms within the Computational Fluid Dynamics (CFD) solver code_saturne, specifically in the Unsteady Reynolds-Averaged Navier-Stokes (U-RANS) equations and the Discrete Ordinate Radiation Model (DOM). It enables time-efficient simulations of solar and infrared radiation, wind speed, and turbulence in the presence of obstacles. First, this method is compared to wind tunnel measurements of velocity and turbulence fields for a downsized ground-mounted photovoltaic plant, RMSEvel<0.12 m/s, and RMSEturb<0.05 m(2)/s(2 ), for a flow with a wind speed of 2.5 m/s and a turbulent kinetic energy of 0.05 m(2)/s(2 )at the PV panel height. Then, it has been applied to an actual APV power plant to validate solar and infrared radiation simulations, on average RMSEsolar<61.0 W/m(2), and RMSEir<14.0 W/m(2), for a solar radiation reaching 500 W/m2 and an IR radiation of about 350 W/m(2). This innovative method allows for the examination of how obstacles affect the microclimate, and subsequently, key parameters such as evapotranspiration. It paves the way for comprehensive numerical studies of the influence of photovoltaic panels on their environment, with a particular focus on APV and FPV configurations
40 Hz light stimulation restores early brain dynamics alterations and associative memory in Alzheimer’s disease model mice
No full textInternational audienceAbstract Visual gamma entrainment using sensory stimuli (vGENUS) is a promising non-invasive therapeutic approach for Alzheimer’s disease (AD), showing efficacy in improving memory function. However, its mechanisms of action remain poorly understood. Using young AppNL-F/MAPT double knock-in (dKI) mice, a model of early AD, we examined brain dynamics alterations before amyloid plaque onset. High-density EEG recordings and metrics from fields outside neuroscience were used to assess brain dynamics fluidity—a measure of the brain’s ability to transition between activity states. We revealed that dKI mice exhibit early, awake state-specific reductions in brain dynamics fluidity associated with cognitive deficits in complex memory tasks. Daily vGENUS sessions over 2 weeks restored brain dynamics fluidity and rescued memory deficits in dKI mice. Importantly, these effects built up during the stimulation protocol and persisted after stimulation ended, suggesting long-term modulation of brain function. Based on these results, we propose a “brain dynamics repair” mechanism for vGENUS that goes beyond current amyloid-centric hypotheses. This dual insight—that brain dynamics are both a target for repair and a potential diagnostic tool—provides new perspectives on early Alzheimer’s disease pathophysiology
-error analysis of mixed-order hybrid high-order methods for elliptic problems on simplicial meshes
No full textWe present both -a priori and -a posteriori error analysis of a mixed-order hybrid high-order (HHO) method to approximate second-order elliptic problems on simplicial meshes. Our main result on the -a priori error analysis is a -order -suboptimal error estimate. This result is, to our knowledge, the first of this kind for hybrid nonconforming methods and matches the state-of-the-art for other nonconforming methods (as discontinuous Galerkin methods) with general (mixed Dirichlet/Neumann) boundary conditions. Our second main result is a residual-based -a posteriori upper error bound, comprising residual, normal flux jump, tangential jump, and stabilization estimators (plus data oscillation terms). The first three terms are -optimal and only the latter is -order -suboptimal. This result is, to our knowledge, the first -a posteriori error estimate for HHO methods. A novel approach based on the partition-of-unity provided by hat basis functions and on local Helmholtz decompositions on vertex stars is devised to estimate the nonconforming error. Finally, we establish local lower error bounds. Remarkably, the normal flux jump estimator is only -order -suboptimal, as it can be bounded by the stabilization owing to the local conservation property of HHO methods. Numerical examples illustrate the theory