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Le mystère de la maladie des pêcheurs (2020-2021) sénégalais levé [Note politique AWA]
No full text1 : otherIl aura fallu quatre années d'investigations, la mobilisation d'une quarantaine de scientifiques à travers une vingtaine d'équipes de recherche situées dans une quinzaine de laboratoires à travers le monde, pour venir àbout de l'énigme de la maladie mystérieuse qui a sévit au Sénégal en 2020 et 2021 chez les pêcheurs artisans. Cette maladie mystérieuse a touché plus d'un millier de pêcheurs sénégalais, suscitant l'inquiétude et l'attentioninternationale, est une dermatite aiguë. Les mêmes symptômes sont apparus sur des pêcheurs artisans en Guinée en 2023. Une étude menée par un consortium scientifique international (article publié en février 2025)dévoile l'origine de cette maladie : une toxine, la Portimine A, produite par la microalgue marine Vulcanodinium rugosum, jusqu'ici inconnu au Sénégal et dans sa sous-région CSRP. Cette toxine, qui perturbe les cellules de la peau humaine, déclenche une inflammation sévère. Cette étude met en lumière une problématique plus large : l'impact croissant des toxines environnementales sur la santé humaine, dans un contexte du changementglobal, notamment le changement climatique et l'accroissement des flux de transport maritime qui favorisent la prolifération et la redistribution de certains micro-organismes marins, comme les dinoflagellés toxiques.Le trafic maritime favorise la dissémination d'espèces marines d'un écosystème à un autre, notamment par les eaux de ballast. L'épidémie de dermatite associée à la Portimine A illustre les risques imprévisibles queles transformations subies par les écosystèmes marins peuvent entraîner. Elle souligne également l'urgence de surveiller, de manière coordonnée interdisciplinaire à une échelle sous-régionale, les espèces marinesproductrices de toxines, de comprendre leurs mécanismes d'action et d'adaptation, et de développer des solutions pour prévenir et traiter les menaces qui pèsent sur la santé humaine et les écosystèmes marins
Interpretability of deep-learning methods applied to large-scale structure surveys
No full textInternational audienceDeep learning and convolutional neural networks in particular are powerful and promising tools for cosmological analysis of large-scale structure surveys. They are already providing similar performance to classical analysis methods using fixed summary statistics, are showing potential to break key degeneracies by better probe combination and will likely improve rapidly in the coming years as progress is made in the physical modelling through both software and hardware improvement. One key issue remains: unlike classical analysis, a convolutional neural network's decision process is hidden from the user as the network optimises millions of parameters with no direct physical meaning. This prevents a clear understanding of the potential limitations and biases of the analysis, making it hard to rely on as a main analysis method. In this work, we explore the behaviour of such a convolutional neural network through a novel method. Instead of trying to analyse a network a posteriori, i.e. after training has been completed, we study the impact on the constraining power of training the network and predicting parameters with degraded data where we removed part of the information. This allows us to gain an understanding of which parts and features of a large-scale structure survey are most important in the network's prediction process. We find that the network's prediction process relies on a mix of both Gaussian and non-Gaussian information, and seems to put an emphasis on structures whose scales are at the limit between linear and non-linear regimes
Is OSSO a Significant Contributor to the Unknown UV Absorber in Venus' Atmosphere?
No full textInternational audienceIt has been proposed that two isomers of the SO dimer (cis-and trans-OSSO) are candidates for the unknown UV absorber in Venus' atmosphere because they have a good spectral match with the absorber, despite the low concentrations predicted by 1D photochemical models. Here OSSO chemistry (production from SO and loss by photolysis, thermal decomposition, and reaction with O and Cl) has been included in the photochemistry scheme of a 3D planetary climate model (PCM-Venus) along with sulfur injection due to meteoric ablation. 1D multiple scattering radiative transfer modeling is then used to predict the resulting top-ofthe-atmosphere reflectance produced by OSSO. The modeled OSSO concentrations are shown to be ∼3 orders of magnitude too low to explain the observed absorbance levels, and the predicted ratio of the OSSO isomers provides an unsatisfactory match to the spectral shape of the unknown absorber
Holocene paleoenvironmental reconstructions in western Brittany (Bay of Brest): Part II – A 7 kyr human-environment story with a focus on the Neolithic-Bronze Age transition
No full textInternational audienceThe Bay of Brest (BB, NW France) is a semi-enclosed basin of 180 km² subject to macro-tidal dynamics and to the fluvial influences of the rivers Aulne and Elorn, which combined drain watersheds of 2600 km². This coastal environment is subject to natural climate oscillations overlaid on the long-term landscape transformations inherited from the post-glacial sea level rise and increasing anthropogenic forcing since the Neolithic (6.9 ka BP), and especially from the Bronze Age (4.2 ka BP) onwards. The BB therefore appears suitable for the reconstruction of the interactions between climate, environment and human dynamics across the Holocene. In this study, a palynological stack was created based on five cores (including two new cores PALM-KS05 and PALM-KS06 from the Brest harbour), allowing us to discuss vegetation dynamics over the last 7 kyrs. Since the Neolithic period, the forest cover has decreased in favour of open and agro-pastoral landscapes. This trend is not uniform, however: forest cover first declined slowly around 4 ka BP, then strongly decreased at the end of the Iron Age, before experiencing a revival of about five centuries at the end of the Roman period (1.7–1.2 ka BP). Finally, a drastic fall of tree pollen taxa is recorded at the start of the Middle Ages. This study is the first on long-term Holocene trends that allows discussion of both climatic and anthropogenic forcing at an unprecedent average study resolution of 35 years. We also place this local evolution in a wider context to detail interactions between natural and anthropic forcings over the last 7 kyrs BP at a regional-scale and we discuss paleoenvironments and human dynamics thanks to the incorporation of an up-to-date corpus of archaeological data
A dataset of annotated ground-based images for the development of contrail detection algorithms
No full textInternational audienceAll economic sectors must understand, measure and mitigate their contributions to climate change. The aviation sector is no exception and has to reduce its CO2 emissions while also addressing its non-CO2 effects which are responsible for a significant radiative impact on climate. The most important of these effects is due to the formation of contrails and their transformation into induced cirrus. Many studies have focused on detecting contrails onto satellite images because, taken together, meteorological geostationary and sun-synchronous satellites provide a good monitoring of the Earth's atmosphere, but unfortunately the spatial resolution and temporal sampling of such satellite images are often insufficient to detect contrails right after their formation and attribute a particular contrail to a given flight. The use of ground-based cameras, especially as part of a network, is therefore complementary to satellite imagery and currently represents an important avenue of research for contrail monitoring. In this article we describe a dataset of annotated ground-based hemispheric sky images that can serve as a basis for the training and validation of contrail detection algorithms, in particular those aiming at segmenting contrails using machine learning methods
La chimie réactive de la troposphère
No full textInternational audienceL'observation globale des espèces réactives dans l'atmosphère s'est améliorée au cours de la dernière décennie, notamment grâce au lancement de nombreuses missions satellitaires dans le monde entier et à l'amélioration des méthodes de détection et d’inversion. Dans ce chapitre, nous examinons les principales espèces réactives organiques et inorganiques qui alimentent la chimie atmosphérique dans la troposphère
Industrial applications of Cannabis sativa (L.): Exploring its biological and nanotechnological potential
No full textInternational audienc
L'oeuvre scientifique de Benjamin Baillaud (1848-1934) : la structuration institutionnelle au service des savoirs astronomiques
No full textBenjamin Baillaud's publications, mainly in celestial mechanics, had a modest impact. His scientificachievements are essentially in the administration of astronomical research, above all the develop-ment of research activities at Toulouse Observatory and the construction of a telescope at the sum-mit of the Pic du Midi. In addition to his duties as director, he continued to teach and participated inscientific work, getting involved in measurements and their analysis. During his terms as dean ofthe Faculty of Sciences of Toulouse, he improved teaching conditions by recruiting quality teachersand material expansions. As director of Paris Observatory, he led a project to create a branch farfrom urban pollution, which did not succeed. Finally, he increased the international visibility ofFrench astronomy through his participation in the Carte du Ciel project, through his direction of theInternational Time Bureau and by hosting international conferences at the Paris Observatory whenhe was its director.Les publications de Benjamin Baillaud, principalement en mécanique céleste, ont eu un impact modeste. Son oeuvre scientifique est essentiellement dans l'administration de la recherche en astronomie, avant tout le développement des activités de recherche à l'Observatoire de Toulouse et la construction d'un télescope au sommet du pic du Midi. Outre sa charge de directeur, il a continué d'enseigner et a participé aux travaux scientifiques, s'impliquant dans les mesures et leur analyse. Pendant ses mandats de doyen de la Faculté des Sciences de Toulouse, il a amélioré les conditions d'enseignement par le recrutement d'enseignants de qualité et des agrandissements matériels. En tant que directeur de l'Observatoire de Paris, il a mené un projet de création d'une succursale loin de la pollution urbaine, qui n'a pas abouti. Enfin, il a accru la visibilité internationale de l'astronomie française par sa participation au projet de la Carte du Ciel, par sa direction du Bureau international de l'Heure et par l'accueil de conférences internationales à l'Observatoire de Paris lorsqu'il en était directeur
Development of Permeability Heterogeneity During Compaction of Porous Sandstone
No full textInternational audienceWe aimed to establish how permeability heterogeneities develop in relation to compaction deformation in sandstone. Three sandstones were tested in the compactant regime: Locharbriggs sandstone, which is initially heterogeneous with beds of lower initial permeability; a low porosity (22%) Bleurswiller sandstone, which is initially homogeneous and produces localized compaction bands; a high porosity (24%) Bleurswiller sandstone, also homogeneous but producing compaction in a more diffused pattern. We monitored acoustic emission locations and elastic wave speed variations throughout deformation. In addition, at regular stages during each test, a constant pore pressure difference was imposed at the boundaries of the samples, and steady-state flow was established. Internal pore pressure measurements at four locations allowed us to derive local permeability estimates. In all samples, progressive compaction produced overall reductions in permeability. In addition, localized compaction also produced internal reorganization of the permeability structure. Strong permeability reductions in the direction perpendicular to flow, by up to two orders of magnitude, are only observed when fully connected compaction bands grow across samples. Compaction and permeability reduction preferentially impacted the more porous and permeable regions of the samples, which lead to an overall homogenization of the transport properties of the samples during deformation. Compaction results from grain crushing, and is directly linked to progressive reductions in elastic wave speed. However, the impact of compaction on permeability depends strongly on the spatial connectivity of the compacted regions
Commissioning of ThomX Compton source subsystems and demonstration of 10 X-rays/s
No full textInternational audienceThomX is a compact x-ray source based on Compton scattering, installed at IJCLab (Laboratoire de physique des 2 infinis-Irène Joliot-Curie) in Orsay. The machine uses a small electron storage ring and an intense laser pulse stored in a high-finesse optical cavity. This article describes the various subsystems of the machine and their initial results of the commissioning, which began in mid-2021. This first commissioning phase led to the production of 10 x-rays/s with an on-axis energy of 45 keV. The main steps to be taken to reach the nominal flux are outlined at the end.ThomX est une source compacte de rayons X basée sur la diffusion Compton, installée à IJCLab (Laboratoire de physique des 2 infinis - Irène Joliot-Curie) à Orsay. La machine utilise un petit anneau de stockage et un laser impulsionnel intense stocké dans une cavité de haute finesse. Cet article décrit les différents sous-systèmes de la machine, et leurs premiers résultats lors de la mise en service, entamée mi-2021. Cette première phase de mise en service a débouché sur la production de 10 rayons X/s, avec une énergie sur l'axe de 45 keV. Les principales étapes requises pour atteindre le flux nominal sont soulignées en conclusion