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3D near-surface geophysics and geostatistics for heterogeneities characterization and water table monitoring on the Orgeval critical zone observatory
No full textInternational audienceGroundwater fluxes and interacting zones between groundwater and surface water are crucial for understanding the water dynamics of the critical zone. Groundwater within the critical zone plays a significant role in the ecosystem, biodiversity, and water supply. However, estimating these fluxes remains a key challenge because they are not directly measured in the field. Model calibration involves adjusting key parameters—such as saturated hydraulic conductivity and soil-water retention properties—using observed data like hydraulic head and river discharge, while initial and boundary conditions are prescribed to define the model l setup. That calibration is often done by comparing simulated soil water saturation and water table level to piezometers. Nevertheless, real flows occur in 3D in a complex medium containing heterogeneities with various lithologies, with different hydraulic parameters such as hydraulic conductivity and porosities.Geophysical methods such as electrical resistivity tomography (ERT), seismic refraction tomography (SRT), and multichannel analysis of surface wave (MASW), which are sensitive to lithology, content, and nature of fluid, represent helpful tools for hydrogeological modelling, both in terms of model parameterization and physical property characterization. ERT, which is particularly sensitive to lithology, allows us to identify and delineate heterogeneities, while seismic methods, which are sensitive to mechanical properties, will enable us to infer the water saturation and the piezometric surface in the near surface through the P-wave and S-wave velocities ratio (Poisson’s ratio, e.g. ) (Dangeard et al., 2021).We propose a workflow combining geophysics and geostatistics to reconstruct the heterogeneities and the piezometric surface in an alluvial plain context. We implemented the workflow in a 30 x 30 m area at the Avenelles site of the Orgeval Critical Zone Observatory (CZO), which is part of the French network of CZOs OZCAR. ERT, SRT, and MASW surveys were carried out along 7 profiles to obtain 2D sections of electrical resistivity, P and S wave velocities (6 profiles of 72 electrodes/geophones and one profile of 48 electrodes/geophones, with 0.40 m spacing leading to 12,708 apparent resistivity data, 33,888 first wave arrival picks, and 277 dispersion curves). Geophysics allows us to pass from punctual piezometer data to 2D vertical sections. However, carrying out 3D geophysical acquisition is cumbersome. To overcome these limitations, we then use geostatistics to get a distribution of our geophysical parameters in the 3D volume delineated by the geophysical survey. Once the 3D interpolation is done by kriging methods, we can retrieve a view of the heterogeneities distribution in the near surface as well as the water table position to inform hydrogeological inversion. Furthermore, with the addition of petrophysical relationships, it is possible to estimate saturation and porosity distribution for a future 3D hydrogeological physics-based model run to better characterise groundwater fluxes. Finally, all these workflows, including complementary methods, could be performed on different dates for time-lapse monitoring of the water table
Numerical optimization of the physical properties of thermochromic layers based on spin transition materials for cold coating applications
No full textInternational audienceThis article explores the theoretical potential for using spin-crossover (SCO) materials to insulate buildings against photothermal effects. While many works on their possible applications as memories, actuators, displays, sensors, etc. are often reported in the literature, the present theme is absent from the study of the properties of SCO materials. Our strategy is based on the use of the thermally-induced first-order transition of SCO solids, which is accompanied by thermochromic properties, to pave the way for their use as a protective layer improving the energy efficiency of buildings, notably by protecting them from photothermal effects caused by the sun’s heat. In this context, we propose detailed numerical simulations and parametric analysis of the physical properties of the SCO layer (thickness, heat diffusion, ligand field, …), which are key factors regulating their thermal performance. This work provides predictive guidelines for engineering applications and opens up new avenues for experimental investigations of SCO-based thermal protection systems. © 2026 The Author(s)
Pre-liver transplant assessment of patients with acute-on-chronic liver failure: an international survey
No full textInternational audienceBackground and aimsLiver transplantation (LT) is increasingly performed in the setting of acute-on-chronic liver failure (ACLF). In this context, pre-transplant evaluation must be completed rapidly while minimizing the risk of overlooking contraindications. We aimed to describe current practices for pre-transplant assessment in ACLF patients.Materials and MethodsWe conducted a survey across 34 European LT centers (including 16 French) and 22 French non-LT centers to assess pre-transplant evaluation practices, focusing on cardiopulmonary, addiction, oncological, and nutritional assessments. Practices were compared across three clinical scenarios: outpatients (OutPat), hospitalized decompensated patients without ACLF (Hosp), and ACLF patients admitted to intensive care units (ACLF-ICU). In parallel, we retrospectively evaluated post-transplant outcomes in patients with cirrhosis and severe ACLF transplanted in two high-volume centers.ResultsFifty-three centers (96%) responded. Cardiological stress testing was reported in 2% of ACLF-ICU patients vs. 21% of OutPat (p=0.002) vs. 17% of Hosp patients (p=0.008). Coronary angiography following abnormal noninvasive testing was less frequently performed in ACLF (42%) than in OutPat (76%, p=0.0004) or Hosp patients (66%, p=0.01). Alcohol abstinence requirements were more often decided on a case-by-case basis in ACLF (62%) than in OutPat or Hosp patients. Oncological screening, including colonoscopy and ENT consultation, was also less frequently performed in ACLF-ICU patients. Median time from assessment initiation to listing was 7 days in ACLF-ICU versus 45 days in OutPat and 18 days in Hosp patients (both p<0.0001). In the retrospective cohort (n=221), patients listed after ACLF onset had a higher 1-year incidence of cardiovascular events than those listed before ACLF onset (19% vs. 9%).ConclusionIn ACLF-ICU patients, pre-transplant evaluation is markedly abbreviated, with critical gaps—particularly in cardiological assessment—highlighting the need for dedicated, evidence-based guidelines.Impact and implicationsWe sent a questionnaire to centers with an expertise in the management of patients with ACLF to assess current practices in pre-transplant evaluation in patients with ACLF admitted in intensive care unit, as compared to patients without (outpatients and patients hospitalized in regular ward)According to the responses from 53 centers, cardiological stress test and coronary angiography were less commonly performed as part as pre-transplant evaluation in patients with ACLF admitted to the ICU, as well as colonoscopy and Ear Nose Throat consultation. Median timeframe from pre-LT workup initiation to listing was 7 days in patients with ACLF admitted to the ICU, which was significantly shorter than in patients without ACLF.These results suggest that pre-transplant workup is abbreviated in patients with ACLF, and might have an impact on post-transplant outcome, especially cardiovascular complications.Further dedicated studies are needed to specifically address the relation between pre-transplant workup and post-LT complications in patients with ACLF
Invasive aspergillosis in liver transplant recipients in France (2007–21): a nationwide, retrospective, matched case–control study
No full textInternational audienceBackgroundInvasive aspergillosis is a rare but severe complication of liver transplantation. Incidence varies from 1·2% to 5·6% and mortality is greater than 50%. Few studies have investigated this complication. We aimed to describe cases of, and identify the factors associated with, invasive aspergillosis occurrence and mortality.MethodsThis nationwide, retrospective, matched case–control study included cases of invasive aspergillosis occurring after liver transplantation between Jan 1, 2007, and Dec 31, 2021, matched 1:1 on centre and transplantation period to control individuals without invasive aspergillosis across 15 liver transplantation centres in France. Cases were patients aged 18 years or older who presented with proven or probable invasive aspergillosis. The matched control was the next patient who received a transplant at the same transplantation centre after the case. Cases were retrospectively identified in each centre using the mycology laboratory database and the French Medicalised Information System Programme. Data were retrieved from hospital charts. The primary outcome was the identification of risk factors associated with the development of invasive aspergillosis following liver transplantation. Multivariable analysis using conditional logistic regression with a random effect for study centres was done to establish risk factors.FindingsAmong 14 332 liver transplantations, 196 recipients with invasive aspergillosis (62 [32%] female and 134 [68%] male) were identified and matched with 196 control individuals (54 [28%] female and 142 [73%] male). Invasive aspergillosis occurred at a median of 29 days (IQR 7–173) after liver transplantation. Risk factors for developing invasive aspergillosis were history of chronic kidney disease (adjusted odds ratio 4·13 [95% CI 2·35–7·24]), liver transplantation for acute liver disease (3·41 [1·44–8·06]), post-liver transplantation renal replacement therapy (3·82 [1·96–7·42]), and post-liver transplantation vasopressor support for longer than 24 h (2·82 [1·70–4·68]).InterpretationThis study identifies three patient populations at risk of invasive aspergillosis after liver transplantation: patients with history of chronic kidney disease, those who have received a transplant for acute liver disease, and those who had a post-operative period marked by organ failure. This identification could lead to new invasive aspergillosis prophylactic strategies
Preliminary Results from the IWGSC Wheat Diversity Project
No full textcommunication orale faite par Joshua SteinInternational audienceGenetic diversity is essential for sustaining the future adaptive capacity of agriculture. In bread wheat, most genetic diversity is held within landrace varieties that were locally adapted over thousands of years by traditional farming prior to modern agriculture. While today’s high-yielding cultivars contain only a fraction of this available gene pool, landraces remain a key reservoir for adaptive traits that will be essential for meeting future demands for wheat improvement. The IWGSC Wheat Diversity Project addresses the critical need to preserve, discover, and mobilize these genetic resources by focusing on the sequencing of 12 wheat landraces that represent the worldwide diversity of bread wheat and by generating a platinum-quality reference for Chinese Spring (IWGSC CS RefSeq 3.0) using state-of-the-art sequencing, assembly, and annotation methods. Preliminary results of this work will be presented as well as the plans for completion of the wheat diversity project
Assimilation de données pour la prévision des débits d’étiage
No full textWithin the framework of WP3 of the ANR CIPRHES project, data assimilation techniques have been developed and/or evaluated at spatial scales ranging from watershed to the entire country of France. General conclusions common to all of these studies emerge. The first is that assimilating observed streamflows improves the simulation of river flows for historical periods. It appears to have a modest but present effect on low flow forecasts. The results from these studies show a very short persistence of the assimilation contribution in forecasting (less than 10 days). Moreover, the results demonstrate a real interest in terms of operational scores (e.g., anticipating the onset of drought periods). Finally, assimilating groundwater table levels does not seem to improve either the simulation of river flows for historical periods or future river flow forecasts.As a perspective, it is necessary to increase the number of assimilated observation points, either to improve the contribution of assimilation itself, or to enhance the method in order to improve its robustness in more varied hydrological contexts. Finally, the modalities for which a transition to operational use in the PREMHYCE platform could be considered in the future still need to be defined.Dans le cadre du WP3 du projet ANR CIPRHES, des techniques d’assimilation ont été développées et/ou évaluées à des échelles spatiales allant du bassin versant jusqu’à la France entière. Il en ressort des conclusions générales communes à l’ensemble de ces travaux. La première est que l’assimilation des débits observés permet d’améliorer la simulation des débits en périodes historiques. Elle semble avoir un effet modeste mais néanmoins présent sur la prévision des débits d’étiage. Les résultats issus de ces travaux montrent une persistance très courte de l’apport de l’assimilation en prévision (inférieure à 10 jours). De plus, les résultats montre un réel intérêt au regard de scores plus opérationnels (exemple : anticiper le démarrage des périodes de sécheresse). Enfin, l’assimilation des niveaux de nappe ne semble pas apporter d’amélioration ni sur la simulation des débits en période historique, ni sur la prévision future des débits.En perspectives de ces travaux, il est nécessaire d’augmenter le nombre de points d’observation assimilés, soit pour améliorer l’apport de l’assimilation en elle-même, soit pour améliorer la méthode pour qu’elle soit robuste dans des contextes hydrologiques plus variés. Enfin, il reste à définir les modalités pour lesquelles un passage en opérationnel dans la plate-forme PREMHYCE pourrait être envisagé dans le futur
A variational mean field game of controls with free final time and pairwise interactions
No full textThis article considers a mean field game model inspired by crowd motion models in which agents aim at reaching a given target set and wish to minimize a cost consisting of an individual running cost, an individual cost depending on the arrival time at the target set, and an interaction running cost, which takes the form of pairwise interactions with other agents through both positions and velocities. We subsume this game under a more general class of games on abstract Polish spaces with pairwise interactions, and prove that the latter games have a variational structure (in the sense that their equilibria can be characterized as critical points of some potential functional) and admit equilibria. We also discuss two a priori distinct notions of equilibria, providing a sufficient condition under which both notions coincide. The results for the games in abstract Polish spaces are applied to our mean field game model, and a numerical illustration concludes the paper
L’ennui des managers intermédiaires : une influence stratégique empêchée ?
No full textFNEGE 2International audienceÀ l’heure où le rôle des managers intermédiaires est remis en question, s’intéresser à leur expérience de l’ennui peut révéler une tout autre réalité. En adoptant une approche socialement située, notre objectif est de comprendre cette expérience dans le cadre de l’exercice de leurs rôles stratégiques. Une étude qualitative conduite auprès de trente managers intermédiaires du secteur bancaire souligne un ennui marqué par le sentiment d’être empêché d’exercer leur influence stratégique. Leur sortie de l’ennui dépend alors des interactions au cœur de leur métier
A fast powerful X-ray transient from possible tidal disruption of a white dwarf
No full textInternational audienceStars getting close enough to black holes (BHs) can be torn apart by strong tidal forces, producing electromagnetic flares. To date, more than 100 tidal disruption events (TDEs) have been observed, each involving invariably normal gaseous stars whose debris falls onto the BH, sustaining the flares over years. White dwarfs (WDs), which are the most prevalent compact stars and a million times denser–and therefore tougher–than gaseous stars, can only be disrupted by intermediate-mass black holes (IMBHs) of 102–105 solar masses. WD-TDEs are considered to generate more powerful and short-lived flares, but their evidence has been lacking. Here we report observations of a fast and luminous X-ray transient EP250702a detected by Einstein Probe. Its one-day-long X-ray peak as luminous as 1047-49ergs-1showed strong recurrent flares with hard spectra extending to several tens of MeV gamma-rays, as detected by Fermi/GBM and Konus-Wind, indicating relativistic jet emission. The jet’s X-rays dropped sharply from 3×1049ergs-1 to around 1044ergs-1within 20 days (10 days in the source rest frame). These characteristics are inconsistent with any previously known transient phenomena. We suggest that this fast-evolving event over the unprecedentedly short timescale arises likely from disruption of a WD by an IMBH. At late times, a soft component progressively dominates the X-ray spectrum, reaching a luminosity as high as 1044 erg s−1, which is consistent with being extreme super-Eddington emission from an accretion disk expected to form in an IMBH-WD TDE. WD-TDEs open a new window for investigating the elusive IMBHs and their surrounding stellar environments, and they are prime sources of gravitational waves in the band of space-based interferometers