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Externally-forced and intrinsic variability of the Mediterranean surface and overturning circulations
No full textInternational audienceAbstract. Part of Mediterranean Sea variability is forced and paced by external drivers (e.g. atmosphere, river runoffs, Atlantic inflow); the other part has a random phase and spontaneously emerges due to chaotic intrinsic variability (CIV). This study quantifies across time scales the imprints of both variability components on the surface and zonal overturning circulations within the basin, from a 39-year 30-member ensemble ocean 1/12° simulation. We find that most of SSH variance is intrinsic over 17 % of the basin, in particular in the southern Ionian and Levantine basins, and most notably in the Algerian basin where CIV explains 80 % of the SSH variance at periods greater than 4 months. In contrast, 75 % of its interannual to decadal variance of the North Ionian Gyre circulation is paced by the atmosphere, suggesting an external triggering of the Adriatic-Ionian Bimodal Oscillating System (BiOS) reversal. Other gyres such as Rhodes, Bonifacio, and Alboran shows more balanced contribution of CIV. Fluctuations of the density-coordinate zonal overturning circulation (ZOCσ) and of associated transports are mostly paced by the forcing over most of the basin. However, CIV tends to explain a larger fraction of these transports variance in the intermediate and bottom layers near deep convection sites, in particular in the Levantine basin where this fraction exceeds 50 % between 27 and 30° E at submonthly periods, and 20–30 % at periods reaching 20 years locally. This partly random character of the multi-scale Mediterranean variability has consequences for evaluating model simulations, and the design of observation systems targeting the long-term monitoring of the basin
Étude en laboratoire de l'influence des cycles de geldégel sur du calcaire -projet PermaPyrenees
No full textInternational audienceDans le contexte de changement climatique, la dégradation du pergélisol, observée par l'approfondissement de sa couche active (qui gèle et dégèle de façon saisonnière), entraîne une modification de l’intensité et de la fréquence des cycles de gel-dégel au sein de cette dernière. Dans le cadre du Projet Interreg Poctefa PermaPyrénées (EFA 063/01), une étude expérimentale a été menée dans le but d’étudier le lien entre ces cycles de gel-dégel et la micro et macro fracturation des roches.Des cycles de 12h entre -10 et 20°C ont été réalisés dans une enceinte climatique sur des éprouvettes saturées et non saturées de calcaire de Saint-Maximin. La masse, les dimensions et les vitesses des ondes P et S à travers ces échantillons ont été mesurées chaque semaine pour évaluer l’évolution du volume des vides et donc la fissuration de l’échantillon. De plus, deux échantillons, un saturé et l’autre non saturé, ont été suivis par microtomographie à rayons X afin d’observer l’évolution de la microfissuration de la roche due à la succession de cycles de gel-dégel
A Census of Graph-Drawing Algorithms Based on Generalized Transversal Structures
No full textInternational audienceWe present two graph drawing algorithms based on the recently defined "grand-Schnyder woods", which are a far-reaching generalization of the classical Schnyder woods. The first is a straight-line drawing algorithm for plane graphs with faces of degree 3 and 4 with no separating 3-cycle, while the second is a rectangular drawing algorithm for the dual of such plane graphs.In our algorithms, the coordinates of the vertices are defined in a global manner, based on the underlying grand-Schnyder woods. The grand-Schnyder woods and drawings are computed in linear time. When specializing our algorithms to special classes of plane graphs, we recover the following known algorithms: (1) He's algorithm for rectangular drawing of 3-valent plane graphs, based on transversal structures, (2) Fusy's algorithm for the straight-line drawing of triangulations of the square, based on transversal structures, (3) Bernardi and Fusy's algorithm for the orthogonal drawing of 4-valent plane graphs, based on 2-orientations, (4) Barriere and Huemer's algorithm for the straight-line drawing of quadrangulations, based on separating decompositions. Our contributions therefore provide a unifying perspective on a large family of graph drawing algorithms that were originally defined on different classes of plane graphs and were based on seemingly different combinatorial structures
Large-scale destratification in the Eurasian Basin thermocline driving Atlantic Water spreading
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Microplastic dynamics along an extreme flood event in a peri-urban stream
No full textInternational audienceRecent studies have investigated the effects of hydrological conditions on the dynamics of microplastics (MPs) in rivers. However, no clear correlation is consistently observed. In addition, these studies focus on sampling before and after the event, neglecting the dynamics of MPs over the course of the event. Given the increased intensity of extreme events related to climate change, an understanding of fine temporal MP dynamics in rivers is required to better estimate the fluxes and their contribution to downstream contamination. To address this gap and enhance understanding of the impact of hydrological conditions on MP contamination, an intensive sampling campaign was conducted throughout hurricane Kirk. This event caused an extreme flood in October 2024 at the outlet of a small peri-urban catchment (Avenelles, 45 km², 70 km east of Paris). Sampling was performed using a plastic-free in-situ filtration pumping system coupled with in series filtration (300 and 10 µm). Analyses were carried out using Fourier transform infrared µ-spectroscopy (automated imaging and data processing with SiMPle software), enabling the characterization of MP particles down to 25 µm. In addition, total suspended solids (TSS) were characterized alongside the sampling campaign to investigate their potential role in the transport and dynamics of MPs. Throughout this campaign, 18 samples were collected throughout the 6-day flood event, including pre-event conditions, the increasing and decreasing water levels, and post-event base flow. The MP concentrations and flux increased twofold from pre-flood (669 MPs m-3 and 398 MPs s-1) to flood peak (10804 MPs m-3 and 56181 MPs s-1). Four days after the flood peak, the concentration and flux returned to levels similar to those observed pre-flood (977 MPs m-3 and 479 MPs s-1). In addition, the concentrations of MPs and TSS exhibited a similar trend, with a correlation coefficient of 0.66. These results highlight the limitations of interpreting hydrological effects based on data limited to pre- and post-flood sampling, underscoring the importance of studying the full progression of flood dynamics
Blockchain et Données de Santé : Enjeux Juridiques et Perspectives Régulatoires
No full textThe use of blockchain in healthcare is attracting growing interest due to its ability to guarantee the integrity, traceability, and transparency of sensitive data processing. However, its integration into a legal environment strictly regulated by the GDPR and French healthcare data law faces major tensions: immutability versus the right to erasure, decentralization versus legal responsibility, transparency versus medical confidentiality. After reviewing the legal obstacles, this article proposes a series of regulatory adjustments aimed at making the use of distributed ledgers in healthcare legally viable. It calls for dedicated governance, a functional interpretation of rights, and regulation by design in order to reconcile technological innovation with the protection of fundamental rights.L’usage de la blockchain dans le domaine de la santé suscite un intérêt croissant pour sa capacité à garantir l’intégrité, la traçabilité et la transparence des traitements de données sensibles. Toutefois, son intégration dans un environnement juridique strictement encadré par le RGPD et le droit français des données de santé se heurte à des tensions majeures : immuabilité versus droit à l’effacement, décentralisation versus responsabilité juridique, transparence versus confidentialité médicale. Cet article propose, après un état des lieux des obstacles juridiques, une série d’adaptations normatives visant à rendre juridiquement viable l’usage de registres distribués en santé. Il plaide pour une gouvernance dédiée, une interprétation fonctionnelle des droits et une régulation par le design, afin de réconcilier innovation technologique et protection des droits fondamentaux
Essais sur les inégalités sociales de santé
No full textSocial health inequalities emerge as early as pregnancy and childhood and persist throughout life: a more favorable socioeconomic situation leads to a longer and healthier life. In my research, I have focused on measuring (social) health inequalities using an axiomatic approach. I have also explored the relationship between socioeconomic status and health using econometric tools, in both France and the United Kingdom. Various population groups have drawn my attention -- for example, precarious workers, children and adolescents, adults, and older people. Some of my work is descriptive, measuring the association between socioeconomic status and health, while other studies aim to identify the causal effect of economic conditions on health. My research perspectives build on my previous work; they focus on students' diet and nutrition in the Île-de-France region, social health inequalities through the lens of gender in France, and the relationship between macroeconomic conditions and health status.Des inégalités sociales de santé apparaissent dès la grossesse et l’enfance et persistent tout au long de la vie : une situation socioéconomique plus favorable permet une vie plus longue et en meilleure santé. Dans mon travail de recherche, je me suis intéressée à la mesure des inégalités (sociales) de santé, dans une démarche axiomatique. J'ai aussi exploré le lien entre statut socioéconomique et santé, à l'aide d'outils économétriques, en France et au Royaume-Uni. Différents groupes de population ont retenu mon attention : par exemple, certains travailleurs et travailleuses précaires, les enfants et les adolescent(e)s, les adultes et les seniors. Certains de mes travaux sont descriptifs, mesurant l'association entre la situation socioéconomique et l'état de santé, alors que d'autres cherchent à identifier l'effet causal des conditions économiques sur la santé. Mes perspectives de recherche s'inscrivent dans la continuité de ce travail ; elles portent sur l'alimentation des étudiant(e)s en Île-de-France, les inégalités sociales de santé au prisme du genre en France, et le lien entre conditions macroéconomiques et état de santé
Simulating microplastics temporal dynamics, driving mechanisms and giving insights on sources
No full textInternational audienceAt the scale of a watershed, the microplastic (MP) fluxes within and between compartments contribute to the contamination of the air-soil-water continuum. The sources and fluxes of microplastics vary greatly depending on land use and human activities within the watershed. The quantifying of MP – sampling and analysis – is a time-consuming task which limits the monitoring of the fine temporal dynamics of MP. The objective of this work is to simulate the MP dynamics in the outlet of a peri-urban watershed and to gain insight into the sources. The study site is the Avenelles sub-catchment, 50 km east of Paris (France), and surface of ~50 km2, and it is an experimental site highly instrumented for physico-chemical parameters of the hydrographic network and meteorology. The subcatchment is dominated by agricultural activities, which account for 81% of its surface area, while 18% is forested, and 1% is urbanized. The arable land in the catchment is drained and its influence on the flow rate regime is characterized by flash floods. Samples of MP were collected at the watershed outlet during 2023 using a Universal Filtration Object and analysed using the micro Fourrier Transform Infra-Red. The main sources contributing to the MP dynamics are: loss of MP stocks in the soil via drainage system; remobilization of MP stocks in the sediments; the effluent of the water treatment plant (WWTP) and the stormwater overflows.The MP modelling approach is based on a multilinear model using hydrological variables. The hydrological variables used were (i) the baseflow and the quickflow, estimated from a conceptual automated process, and, (ii) the filling rate of routing reservoir and the production reservoir simulated by the hydrological model GR4H. Simulations evaluated at the MP dynamics at hourly timestep at annual and rainy season time scales. Besides the streamflow characteristics and storages, the precipitation, via the index of previous precipitation, the water conductivity and the total suspended solids are input variables as well. On an annual scale, the most significant variables in the regression appear to be the TSS, the filling rate of the routing reservoir and the water conductivity (R2=0.89). Isolating the hydrological variables, the baseflow and the total flow presented significancy (R2=0.64). For the rainy season, fast flow and total flow are the variables contributing to the MP dynamics (R2=0.86). These results can indicate the MP sources : at annual simulation, denoting TSS and base flow as significant variables, the WWTP discharge might be the main source as it is constant throughout the year; During the rainy season, presents quick flow as major contribution highlighting the drainage system and thus the MP stocks in the soil as major source. In conclusion, this simple model provides a better understanding of the sources of MP at a catchment and a better estimate of the dynamics and contamination of MP
Enforcing Colonial Rule: Blood Tax and Head Tax in French West Africa
No full textWe study the enforcement of two pillars of colonial rule in French West Africa—military conscription and head tax collection—using new district-level data from 1919 to 1949. Tax compliance was strikingly high, with about 80 percent of liable taxpayers meeting obligations despite limited administrative capacity. Military recruitment targets were likewise consistently met despite avoidance and poor health. Spikes in head tax rates significantly increased tax-related protests, prompting colonial authorities to moderate rates in times of crisis and adjust burdens to perceived district affluence. Yet local shocks such as droughts or crop price collapses were largely ignored
Mayors strike back: Evidence from upzoning in France
No full textTo address rising housing prices, national governments have increasingly sought to relax local land use rules through "upzoning" reforms. Yet the effectiveness of such top-down policies remains uncertain. This paper examines the impact of a reform in France that abolished floor area ratios (FAR) from unique zoning data in the Paris Urban area. We exploit within-municipality variation in pre-reform FAR coverage through a difference-indifferences strategy. We show that local governments opposed upzoning by tightening other regulatory tools -such as maximum heights and building coverage ratios -and denying more building permits. These countervailing responses undermined the deregulatory intent of the reform, resulting in negligible effects on real estate markets. Our findings highlight the political and institutional limits of central government efforts to override local zoning decisions.</div