HAL-Ecole des Ponts ParisTech
Not a member yet
42743 research outputs found
Sort by
Aerial perspective on the large city. Subjectivities and unthought aspects of anthropization
No full textInternational audienceThe construction of an aerial gaze has a long history, well before the beginnings of aviation, well before the invention of balloons, when from the top of medieval belvederes one could discover the panorama of the city and its surroundings. However, the context of the evolution of the greater city with its ever-fading limits gradually gave meaning to the aerial apprehension of space, that of a stable, free and autonomous movement in the third dimension, equipped with visual prostheses (photography, cinema), which allowed to grasp a reality that constantly escapes human perception. The quest for figurability of the large city crossed a bundle of inventions and appropriations, opportunities and contexts, allowing the development of an aerial thought of the space whose interferences did not cease to work the architecture and the urbanism. Representations, projections, realizations: this paper will question the functions of this imaginary that has influenced urban futures, pointing out its subjectivities and its unthinking, while cities and territories are confronted with the critical stakes of the anthropocene: ecology, globalization, digitalization
Par-delà l’anthropocène. Projeter l’infrastructure comme relation socio-politique au vivant
No full textInternational audienceTimes of crisis call into question the value of the infrastructure that supports our worlds – its materiality, its arrangements, its representations. Symptoms of an Anthropocene whose critical perspective provides a prism for analysis, they reveal the divergences of infrastructural futures. In order to envisage the project of habitability on Earth, we must seek to understand what the Anthropocene controversy, in its current state and beyond, does to infrastructure as a problem of the contemporary world, heir to thermo-industrial modernization, and a promise of a future coexistence of societies with living beings. The article explains the reasons and temporalities that shape the Anthropocene and, in doing so, examines conceptions of “strong” infrastructure. It proposes to reverse the perspective from the strong to the weak in order to reconsider infrastructure dialectically, conceived not as the dominant structure of human activity but as the foundation of the socio-political relationship with the living, beyond or (entirely) against the Anthropocene. This direction outlines an agenda for a project practice that articulates the knowledge and professions of the Landscape Territory. In support of this position, three urban situations are examined that mobilize the figure of the park as infrastructure.Les temps de crises interrogent la valeur des infrastructures qui soutiennent nos mondes - leurs matérialités, leurs agencements, leurs représentations. Symptômes d’un anthropocène dont la perspective critique constitue un prisme d’analyse, ils manifestent les divergences des futurs infrastructurels. Pour envisager le projet d’une habitabilité terrestre, il convient de s’attacher à saisir ce que la controverse de l’anthropocène, dans son état et son dépassement, fait à l’infrastructure, comme problème du monde contemporain héritier de la modernisation thermo-industrielle et promesse d’une coexistence à venir des sociétés avec le vivant. L’article explicite les raisons et les temporalités qui façonnent l’anthropocène et ce faisant travaillent les conceptions de l’infrastructure « forte ». Il propose de renverser la perspective du fort au faible pour reconsidérer l’infrastructure de manière dialectique, conçue non comme la structure dominante de l’activité humaine, mais comme le socle de la relation socio-politique au vivant, au-delà ou (tout) contre l’anthropocène. Cette direction esquisse un agenda pour une pratique du projet qui articule les savoirs et les professions du Landscape Territory. À l’appui de cette position, trois situations urbaines qui mobilisent la figure du parc comme infrastructure sont évoquées
Citation Context Analysis of Retracted Articles: Leveraging Retraction Reasons to Track Unreliability in Citing Literature
No full textInternational audienceObjectiveTo address the challenge of tracking the use of unreliable sources in scientific literature, we analyzed citations to retracted articles (CRAs) using retraction reasons (RRs) and citation context (CC) analysis. Our aim was to inform the development of automated tools for postpublication peer review (PPPR) by identifying instances in which a CRA is not only an unreliable source, but may also introduce unreliability into the citing work itself, depending on the way it is cited. We examined the degree to which the content of the citation context aligns with the RR, indicating potential risk for the integrity of the citing article.DesignRRs were obtained from the Retraction Watch database1 for a set of 22,558 publications that cite retracted sources accessed from the Problematic Paper Screener.2 We selected 29 of 108 retraction reasons that directly relate to scientific content of the article (eg, unreliable or fabricated data or results). To ensure access to CCs, we limited our dataset to open access citing articles and excluded those that had themselves been retracted. This yielded 4979 citing articles and 7424 unique CRA instances; 88% of these were preretraction citations. We then limited the rest of the analysis to a subset of 3049 CCs from the PubMed Central Open Access corpus.3 We used regular expressions to search for terms referencing concepts related to the retraction reasons (eg, “data,” “results,” “findings”) and manually validated their use in the CCs.ResultsOf 3049 CCs, we identified 57 that explicitly mentioned the exact issue mentioned in the RR. Among these, 12 emphasized similarity or consistency with the retracted findings, which are instances we interpret as potential indicators of unreliability in the citing paper, meriting PPPR. These 57 CCs span 18 research fields and involve 60 distinct RRs (some overlapping with the selected 29). The cases are distributed across a range of publishers and fields, offering a basis to be used in the development of automatic systems.ConclusionsWhile retracted publications are unreliable sources, we argue that how the retracted work is used and why it was retracted matter more than the fact that a retracted reference is found in a publication. If the retracted source is used to support the citing work, this calls for a secondary assessment when it is detected. By combining RRs with CC analysis, our approach informs a practical method to flag such cases for PPPR and supports the development of tools for large-scale CRA assessment.References1. The Center for Scientific Integrity. Retraction Watch Database.2. Cabanac G, Labbé C, Magazinov A. The ‘Problematic Paper Screener’ automatically selects suspect publications for post-publication (re)assessment. arXiv. Preprint posted online October 7, 2022. doi:10.48550/arXiv.2210.048953. National Library of Medicine. PMC Open Access Subset. Accessed January 30, 2025. https://pmc.ncbi.nlm.nih.gov/tools/openftlist/1Univ. Grenoble Alpes, CNRS, Grenoble INP, LIG, Grenoble, France, [email protected]; 2Ecole Nationale des Ponts et Chaussées, Institut Polytechnique de Paris, Marne-la-Vallée, France; 3LISIS, INRAE, Univ Gustave Eiffel, CNRS, Marne-la-Vallée, France.Conflict of Interest DisclosuresNone reported.Funding/SupportWe acknowledge the NanoBubbles project that has received Synergy grant funding from the European Research Council within the European Union’s Horizon 2020 program (grant agreement number 951393) (https://cordis.europa.eu/project/id/951393)
First estimates of Tropical Tropopause Cirrus lifetimes using balloon-borne lidar observations
No full textInternational audienceTropical tropopause layer (TTL) cirrus clouds play a key role in the Earth climate system, yet the relative role of the various processes shaping them remains poorly known. Characterizing the temporal evolution of cloudy structures from observations is essential to address this issue, but represents a challenge. Indeed, space- and air-borne platform are not well-suited for this task: moving much faster than the air, they only provide instantaneous snapshots. In boreal winter 2021-2022, two balloon-borne lidars flew over the Equatorial Pacific Ocean, slowly drifting above the clouds. We use those unique observations of truncated (nighttime only) lifetime distribution to quantify the underlying continuous distribution of cloud lifetime above this homogeneous region. While most clouds are short-lived (mean lifetime estimated at about 6 h, a median value of 1 h), the temporal cloud cover is still dominated by the few long-lived ones (24 h or more). These results are compared to cirrus lifetimes in ERA5 reanalysis, showing a fair agreement between the reanalysis and the observations, and demonstrating the value of our approach to evaluate cirrus representation in global models
Citoyenneté et infrastructures urbaines : L'État, les médiations non étatiques et les pratiques quotidiennes
No full textThis Special Issue on “Citizenship and Urban Infrastructures: The State, Non-State Mediations and Everyday Practices”, which brings together contributions that critically examine how infrastructures shape, mediate, and complicate the formation of citizenship. Building on current debates that move beyond normative and legal definitions of citizenship, this Special Issue expands these discussions by examining the varied roles infrastructures play in the interplay between state and non-state actors, material arrangements, and everyday practices. Drawing on empirical cases from cities in Latin America, Europe, the Middle East, and South Asia, the articles explore how infrastructures - from transport and sanitation systems to digital identification technologies - mediate citizenship through daily interactions. The diversity of contexts reveals important conceptual variations in how infrastructure and citizenship intersect, shaped by differing political conditions, historical trajectories, and spatial configurations.Across the articles, citizenship emerges as multiple and contingent, shaped by diverse contexts. Infrastructures appear variously : as instruments of the state used to promote both inclusion and exclusion, and to enforce norms of belonging and governmentality; as systems appropriated by non-state actors to assert political power and create alternative political spaces; and as arenas through which rights are claimed and contested. Moreover, the Special Issue calls for examining citizenship formation across multiple spatial and temporal registers—attending to historical trajectories, and the everyday temporalities through which infrastructural governance is experienced and negotiated. This introduction concludes by outlining three directions for future research : (1) comparative analysis that engages with diverse sociopolitical and material conditions; (2) critical explorations of the politics of everyday infrastructural practices as sites where citizenship is enacted; and (3) sustained attention to the dynamic and heterogeneous nature of infrastructures as constitutive of both governance and political subjectivity
Rethinking volatility scaling in firm growth
No full textWe revisit the size-volatility relationship in firm growth using administrative data on French manufacturing firms. Departing from the log-log linear decay commonly reported by other studies, we find a two-regime pattern: volatility declines steeply with size for small firms, but flattens for larger ones. We relate this new fact to the presence of resources misallocation as captured by imperfect correlation be- tween size and productivity at the firm level. To explain the nexus between these two facts, we develop a stochastic model where firms face a number of risky business opportunities for which they compete. Two key features characterize this competition process.First, larger firms are more intensively exposed to competition dynamics. Second, firms with higher productivity are more likely to see business opportunities turning into positive, rather than negative, growth episodes. We analytically show that only when the correlation between firm size and productivity is lower than 1 the model is able to reproduce the volatility scaling we observed in the data. Simulations suggest that finite sample approximations of our asymptotic result are satisfactory in a reasonable portion of the parameter space. We conclude showing that in France industries populated by firms with higher correlation between size and productivity are associated with steeper average size-volatility decays consistent with the model’s main prediction. Our findings suggest that the existence of resources misallocation, shaping the size-volatility relation, affects the relevance of the granularity channel in explaining aggregate fluctuations (Gabaix, 2011)
A general Monte Carlo sampling strategy for the adjoint Boltzmann equation in continuous energy
No full textFor neutron transport problems where the detector region is 'smaller' than the source region, solving the adjoint Boltzmann equation by Monte Carlo methods might prove a more efficient computational strategy, compared to solving the standard (forward) Boltzmann equation. Despite intensive research efforts over the last decades, a robust and effective implementation of adjoint Monte Carlo sampling strategies in continuous-energy configurations remains elusive, due to inherent issues encompassing numerical instabilities and explosive variance growth. In view of these considerations, in this paper we investigate the reasons behind such behavior and propose a general sampling strategy that can be tailored in order to achieve a satisfactory compromise between computational complexity and resulting variance of the sought observables. We focus in particular on the sampling of the collision events, in the context of neutron transport in infinite media, as a stepping stone towards the treatment of the full adjoint Boltzmann equations by Monte Carlo methods
Memory and oblivion:how the past obliterated the 1929 crisis in France
No full textInternational audienceOral presentation duringe session "Financial Crises: Analyses, Perceptions, Memories in a Long-run Historical Perspective (Part 1/2)" (id 66211
To Bubble or Not to Bubble: Asset Price Dynamics and Optimality in OLG Economies
No full textWe study an overlapping generations (OLG) exchange economy with an asset that yields dividends. First, we derive general conditions, based on exogenous parameters, that give rise to three distinct scenarios: (1) only bubbleless equilibria exist, (2) a bubbleless equilibrium coexists with a continuum of bubbly equilibria, and (3) all equilibria are bubbly. Under stationary endowments and standard assumptions, we provide a complete characterization of the equilibrium set and the associated asset price dynamics. In this setting, a bubbly equilibrium exists if and only if the interest rate in the economy without the asset is strictly lower than the population growth rate and the sum of per capita dividends is finite. Second, we establish necessary and sufficient conditions for Pareto optimality. Finally, we investigate the relationship between asset price behaviors and the optimality of equilibria
IA : Les déserts médicaux autrement.Vision prospective du rôle disruptif de l’IA et des soins à domicile: IA : Les déserts médicaux autrement
No full texthttps://finances-hospitalieres.frLe système de santé français, longtemps structuré autour de l’hôpital comme pilier central, traverse une mutation profonde. Sous l’effet conjugué du vieillissement démographique, de la pénurie de professionnels et des avancées technologiques, l’offre de soins se réinvente en déplaçant son centre de gravité vers le domicile des patients. Cette évolution, accélérée par la crise sanitaire, remet en question la notion traditionnelle de « déserts médicaux » – ces zones géographiques où l’accès aux soins est limité – en proposant une approche plus flexible, ancrée dans le numérique et l’intelligence artificielle (IA). Historiquement, la France a construit son modèle sur une logique d’équité territoriale, avec un maillage serré d’hôpitaux et de cliniques. Pourtant, depuis les années 2000, la réduction du nombre de lits (-9,4 % entre 2013 et 2022) et la fermeture de structures locales ont exacerbé les disparités. Aujourd’hui, 7 millions de Français résident dans une zone sous-dotée en médecins généralistes, selon la DREES (2023) . Mais cette réalité statique est bousculée par l’émergence de nouveaux paradigmes : l’hospitalisation à domicile (HAD), la télémédecine et les objets connectés transforment la géographie des soins, redistribuant les cartes entre urbain et rural, jeunes et seniors, précarité et aisance technologique. L’HAD incarne cette révolution silencieuse. En 2023, 168 000 patients – principalement âgés ou en soins palliatifs – ont bénéficié de prises en charge complexes à domicile, évitant des séjours hospitaliers prolongés . Soutenue par des protocoles coordonnés (infirmiers, médecins, aides-soignants), cette pratique réduit les coûts structurels et améliore le confort des patients. Toutefois, son déploiement reste inégal : seuls 1 % des séjours en soins aigus concernent l’HAD, et les technologies de surveillance à distance y sont encore marginales, contrairement à des modèles étrangers comme la Mayo Clinic (États-Unis) ou le CHUV@home (Suisse), où capteurs connectés et IA optimisent le suivi en temps réel. Parallèlement, l’hospitalisation ambulatoire (53% des hospitalisations en 2023) et la téléconsultation (11 millions d’actes de généralistes, libéraux et en centres de santé ; et 8 millions de téléconsultations/télé expertises de spécialistes en 2024) redessinent les parcours de soins . Si ces innovations désengorgent les hôpitaux, elles soulèvent des enjeux d’équité : le reste à charge pour les soins en ville – 35 % non remboursés – pénalise les ménages modestes, tandis que la fracture numérique exclut les populations âgées ou rurales des avancées technologiques. En témoigne le département du Tarn, où seulement 2 % des plus de 80 ans ont recours à la téléconsultation par un praticien libéral, contre 15 % des 18-25 ans. Dans ce contexte, l’IA apparaît à la fois comme une promesse et un défi. D’un côté, elle permet de prédire des crises (diabète, AVC) via l’analyse de données massives, de superviser l’observance des traitements (ex. : comprimés équipés de capteurs) ou d’assister les aidants. De l’autre, elle interroge la place du lien humain, pilier de la relation soignant-patient, et nécessite une refonte complète des formations médicales pour intégrer ces outils. Face à ces bouleversements, le concept de « désert médical » semble obsolète. La question n’est plus seulement de combler un vide géographique, mais de garantir un accès équitable à une offre de soins hybride, mêlant présence physique et solutions digitales. Ce rapport explore comment la France, à l’aune des expériences internationales, peut réinventer son modèle pour concilier innovation technologique, justice sociale et qualité des soins – sans sacrifier l’humain au profit de la machine