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European Union's Experiments for Sustainability Transition: The Disappointing Case of Real-Life Trials for Electric Vehicle Charging Infrastructure
No full textThis paper explores the European Union’s practice of sustainability transition experiments. It specifically examines how, in the 2010s, the EU promoted “real-life trials” to encourage private investment in electric vehicle charging infrastructure (EVCI) and advance electromobility across the Union. Based on a longitudinal and multi-level field research, we analyse this new experimental approach from its initial conception to its implementation through local projects, and the resulting learning outcomes. In the light of the EU policy turn to challenge-oriented innovation and experimentalist governance, we illuminate the paradoxical nature of the real-life trial approach, which fostered local experiments as a new innovation tool, but overlooked governance experimentation, thereby limiting the EU’s learning and the experimentation’s overall impact. We recommend refining the real-life trial approach, applying it consistently over time and expanding it to address a broader array of issues to help governing sustainability transitions efficiently within the EU and beyond
Real-World Asphalt Pavement Emissions: Combining Simulation Chamber Measurements and City Scale Modeling to Elucidate the Impacts on Air Quality
No full textInternational audienceIn this paper, the role of asphalt pavement emissions in urban air quality was assessed combining laboratory experiments and city-scale air-quality modeling. In particular, the emission factors (EFs) of volatile and intermediate volatility organic compounds (VOCs and IVOCs) of asphalt pavements were determined in an atmospheric simulation chamber. Relative humidity (RH) and simulated solar light UV-A radiation were found to play a key role in the emission of VOCs and IVOCs. RH significantly increased the EFs, and predominantly those of oxygenated VOCs, due to changes in the microphysical properties of the materials. Under UV-A radiation, EFs were enhanced, due to the photochemical process induced on the asphalt–air interface. IVOCs were found to account for up to 30% of the Total EFs measured. Considering Paris as a case study, asphalt emissions in air-quality simulations lead to an increase in organic aerosol concentrations of at least 3%, during average summer daytime conditions. We estimate this impact significantly higher, in case all the IVOCs emissions are included in the model. This highlights the significant influence of solar radiation on emissions from old asphalt when exposed to UV radiation and the impact on air quality during the summer
La diffusion des services de e-hailing dans les villes d’Afrique
No full textInternational audienceDepuis l’introduction d’Uber en Afrique du Sud en 2013, les services de e-hailing se sont diffusés au sein des systèmes de mobilité de nombreuses villes en Afrique. Cette évolution donne lieu à une littérature croissante, mais qui s’est encore peu intéressée aux populations jeunes. Ces dernières rencontrent pourtant des difficultés de mobilité importantes, liées à des ressources limitées et des services de transport largement défaillants. Cet article s’intéresse aux jeunes usagers du service de e-hailing Gozem à Lomé (Togo), en étudiant leur profil, leurs logiques d’adoption de ce service, les effets sur leurs pratiques de mobilité et, plus largement, sur leur accès à la ville. Il se base sur une enquête par questionnaire auprès de 266 personnes âgées de 15 à 34 ans, complétée par 10 entretiens approfondis. Les résultats montrent que les jeunes usagers du e-hailing dans le grand Lomé sont généralement instruits et disposent de ressources financières et d’un accès à un mode de transport motorisé (souvent une moto et rarement une voiture) souvent supérieurs à la moyenne des habitants. Le service de e-hailing est adopté essentiellement pour son aspect pratique et ses qualités en termes de sécurité, de confort mais aussi de prestige social. Il apporte aussi des améliorations en termes de mobilité et facilite globalement l’accès des jeunes Loméens aux aménités urbaines « ordinaires » (travail, études, lieux de loisirs et de consommation), notamment aux heures de pointe et la nuit. Toutefois, en raison de son coût, son usage demeure peu fréquent, et sert des déplacements, individuels ou à plusieurs, qui n’auraient pas pu être réalisés autrement ou qui auraient été effectués en taxi-moto, taxi collectif ou moto personnelle. Dans ces conditions, le e-hailing apparaît comme un vecteur de consolidation de la place de la voiture dans les pratiques de mobilité et les imaginaires des jeunes Loméens
French Market Design in Practice: Some Lessons from the 2022 Energy Crisis
No full textBetween 2005 and 2021, France has generated more electricity from fossil-free resources (491 TWh/year on average) than its gross domestic consumption (481 TWh/year). Therefore, in terms of total surplus, the French electricity sector should have been barely hit, if at all, by the surge in fossil fuel prices during the 2022 energy crisis. In practice, however, the French government spent billions of euros in subsidies to electricity consumers, the incumbent utility – who operates the whole nuclear fleet – recorded its worst yearly financial result to date, and total electricity imports exceeded exports for the first time in more than 40 years. Although these outcomes can largely be attributed to bad luck, the extent to which they could have been mitigated through better market design and public policies is an open question. This article argues that existing policies, through their implied incentives to share and manage long-term risks, played a critical role in how France navigated the energy crisis. Consistently, reforming long-term risk-sharing mechanisms has emerged as the most pressing issue to address. Looking forward, however, updating short-term wholesale market design so as to better support a low-cost and reliable energy transition will likely prove increasingly important
Comment surveiller et prévoir la qualité microbiologique des sites de baignade dans les cours d'eau urbains ? Le site d'étude du bassin de la Villette (Paris)
No full textInternational audienceSwimming in urban rivers is becoming increasingly popular. In order to limit the health risks to bathers, a warning system can be used to anticipate episodes of microbiological contamination and thus better manage any bathing closures. This article presents a short-term (24 hours) forecasting system developed at La Villette bathing site in Paris, where a public bathing area was opened in 2017. It is based on the measurement of physico-chemical and hydraulic variables and on the in situ measurement of faecal indicator bacteria (FIB) upstream of the bathing area. The functioning of this early warning system is illustrated during 2021 summer. The data collected from the 1st June to the 31st August 2021 showed a major contamination event following heavy rainfall in mid-July. This event led to the closure of the bathing facility. By integrating these measurements with a hydrodynamic model, TELEMAC-3D, the transport of bacteria and their spatial distribution were simulated. The observations coupled with the simulations also highlighted the thermal stratification and its impact on the velocity and flow direction, which can significantly alter the transfer time of FIB. The results demonstrate the ability of this approach to anticipate contamination peaks, providing useful information to manage closure and reopening of urban bathing areas.La baignade dans les cours d’eau urbains bénéficie d’un attrait grandissant. Afin de limiter les risques sanitaires pour les baigneurs, un système d’alerte permet d’anticiper des épisodes de contamination microbiologique et ainsi de mieux gérer l’éventuelle fermeture à la baignade. Cet article présente un système prédictif à court terme (48 heures) développé sur le site d’étude du bassin de La Villette à Paris, où une baignade publique est ouverte en été depuis 2017. Il s’appuie sur la mesure de variables physico-chimiques, hydrauliques et sur la mesure in situ de bactéries indicatrices fécales (BIF) en amont de l’espace de baignade. Le fonctionnement de ce système de suivi et d’alerte est illustré sur l’été 2021. Les données collectées du 1er juin au 31 août 2021 ont révélé un événement de forte contamination microbiologique, ayant entrainé une fermeture du site de baignade, après de fortes précipitations survenues à la mi-juillet. L'intégration de ces mesures à un modèle hydrodynamique, TELEMAC-3D, a permis de simuler le transport des bactéries et leur distribution spatiale. Les mesures, ainsi que la modélisation, ont aussi permis de montrer les effets de la stratification thermique sur la vitesse et la direction de l’écoulement, modifiant alors fortement le temps de transfert des BIF. Les résultats mettent en évidence la capacité de cette approche à anticiper les pics de contamination, fournissant ainsi des informations utiles pour décider de la fermeture et la réouverture des zones de baignade
Geometry of Sparsity-Inducing Norms
No full textInternational audienceSparse optimization seeks an optimal solution with few nonzero entries. To achieve this, it is common to add to the criterion a penalty term proportional to the ℓ1-norm, which is recognized as the archetype of sparsity-inducing norms. In this approach, the number of nonzero entries is not controlled a priori. By contrast, in this paper, we focus on finding an optimal solution with at most~k nonzero coordinates (or for short, k-sparse vectors), where k is a given sparsity level (or ``sparsity budget''). For this purpose, we study the class of generalized k-support norms that arise from a given source norm. When added as a penalty term, we provide conditions under which such generalized k-support norms promote k-sparse solutions. The result follows from an analysis of the exposed faces of closed convex sets generated by k-sparse vectors, and of how primal support identification can be deduced from dual information. Finally, we study some of the geometric properties of the unit balls for the k-support norms and their dual norms when the source norm belongs to the family of ℓp-norms
Unraveling Lake Geneva's hypoxia crisis in the Anthropocene
No full textInternational audienceRecent decades have witnessed widespread deoxygenation of temperate lakes. The intricate interplay between climate change and nutrient loading and its impact on oxygen dynamics still lacks clear understanding. We develop a paleo-data-model coupling approach to investigate long-term variations of dissolved oxygen conditions in Lake Geneva over the period 1850-2100. Our approach provides first estimates of oxygen baseline conditions and quantifies duration of hypoxia since pre-disturbance. Over the 19 th and 20 th centuries, an increase in DO consumption rates (from 0.3 to 2.5 g O 2 m À2 d À1 ) following nutrient over-enrichment caused the onset of hypoxia, and its intensity and duration were governed by the combined influence of climatic forcing and high phosphorus concentration. In the future, hypoxia will be primarily disrupted by reduced frequency of full mixing events
Asymptotic optimality of the edge finite element approximation of the time-harmonic Maxwell's equations
No full textInternational audienceWe analyze the conforming approximation of the time-harmonic Maxwell's equations using Nédélec (edge) finite elements. We prove that the approximation is asymptotically optimal, i.e., the approximation error in the energy norm is bounded by the bestapproximation error times a constant that tends to one as the mesh is refined and/or the polynomial degree is increased. Moreover, under the same conditions on the mesh and/or the polynomial degree, we establish discrete inf-sup stability with a constant that corresponds to the continuous constant up to a factor of two at most. Our proofs apply under minimal regularity assumptions on the exact solution, so that general domains, material coefficients, and right-hand sides are allowed
Open-Canopy: Towards Very High Resolution Forest Monitoring
No full text22 pages, 8 figures, Submitted to NeurIPS 2024 Datasets and Benchmarks TrackInternational audienceEstimating canopy height and its changes at meter resolution from satellite imagery remains a challenging computer vision task with critical environmental applications. However, the lack of open-access datasets at this resolution hinders the reproducibility and evaluation of models. We introduce Open-Canopy, the first open-access, country-scale benchmark for very high-resolution (1.5 m) canopy height estimation, covering over 87,000 km² across France with 1.5 m panchromatic resolution satellite imagery and aerial LiDAR data. Additionally, we present Open-Canopy-, a benchmark for canopy height reduction detection between images from different years at tree level---a difficult task for current computer vision models. We evaluate state-of-the-art architectures on these benchmarks, highlighting significant challenges and opportunities for improvement. Our datasets and code are publicly available at \url{https://github.com/fajwel/Open-Canopy}
Vertical Structure of the Martian Atmosphere: The View from Mars Express
No full textInternational audienceLaunched in 2003, the European Space Agency’s Mars Express (MEX) has been orbiting Mars for 20 years and its instruments have performed continuous monitoring of the conditions in the Martian atmosphere, providing one of the most complete datasets of atmospheric parameters ever collected for Mars. This article provides an overview of the observations of the vertical structure of the Martian atmosphere performed by MEx, which led to the identification of peculiar phenomena that affect the atmospheric circulation and dynamics on different scales, from local to regional and global