OF–CEAS laser spectroscopy to measure water isotopes in dry environments: example of application in Antarctica

International audienceWater vapour isotopes are important tools to better understand processes governing the atmospheric hydrological cycle. Their measurement in polar regions is crucial to improve the interpretation of water isotopic records in ice cores. In situ water vapour isotopic monitoring remains challenging, especially in dry places of the East Antarctic Plateau, where water mixing ratios can be as low as 10 ppm. We present in this article new commercial laser spectrometers based on the optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) technique, adapted for water vapour isotopic measurements in dry regions. We characterise a first instrument adapted for Antarctic coastal monitoring with an optical cavity finesse of 64 000 (ring-down time of 54 µs), installed at Dumont d'Urville Station during the summer campaign 2022-2023, and a second instrument with a high finesse of 116 000 (98 µs ring-down time), to be deployed inland of East Antarctica. With a drift calibration every 24 h, the stability demonstrated by the high-finesse instrument allows one to study isotopic diurnal cycles down to 10 ppm humidity for δD and 100 ppm for δ 18 O.</div

Modèle statistique apprenable de mélange de distributions et fusion de données multivariées pour l'imagerie d'exoplanètes

International audienceExoplanet imaging is a major challenge in astrophysics due to the high star-planet contrast. This paper presents a multi-scale statistical model for the nuisance component corrupting multivariate image series. Integrated into a learnable architecture, it leverages the physics of the problem and enables the fusion of multiple observations of the same star. Applied to real data, the method significantly improves the detection sensitivity and the accuracy of exoplanet position and flux estimation.L'imagerie des exoplanètes est un défi majeur en raison du fort contraste étoile-planète. Cet article propose un modèle statistique multi-échelle de la nuisance affectant des séries d’images multivariées. Intégré à une architecture apprenable, il exploite la physique du problème et permet la fusion de plusieurs observations d’une même étoile. Appliquée à des données réelles, la méthode améliore significativement la sensibilité de détection et la précision de l’estimation de la position et du flux des exoplanètes

Biodiversity-dependent invasiveness of naive river epilithic biofilms

International audienceWith more than 1 million deaths attributed each year, antibiotic resistance has become a major societal issue. The emergence and dissemination of antibiotic resistance in bacteria rests on two pillars, the enrichment of resistant variants upon selection and the contagion of the resistant bacteria and their resistance genes within and across the human, animal and environmental spheres. Although poorly described, this contagion process necessarily implies the persistence of invading resistant bacteria from one microbiome to another. In this study, we carefully selected a series of headwater streams located in the Vosges Mountains (North-eastern, France), with a clear pristine-like upstream part and well identified prime-exposure to modest anthropic activities, to explore invasion processes while avoiding multiple pollution effect. Using high-throughput qPCR for 45 resistance genes and mobile genetic elements we showed that one third of the markers were already widespread, while another third massively invaded the river epilithic biofilm communities at prime-exposure to anthropic activities, with the concomitant entry of fecal pollution. We used 16S rRNA gene metabarcoding to explore the structure of the bacterial biofilm communities along river continuums and showed that the extent of the invasion process was inversely correlated with the level of biodiversity, but positively correlated with the magnitude of propagule pressure

Optimization and performance analysis of novel waste EPS bead-sand composite cushions for rockfall mitigation: An integrated experimental and numerical study

International audienceOrthogonal Experimental Design (OED) and Response Surface Methodology (RSM) optimized waste Expanded Polystyrene (EPS) bead-sand composite cushions, identifying an optimal EPS content of 38.79 % by volume for superior energy absorption and load distribution. The novel SE-S-F layered configuration (EPS-sand mixture over pure sand) reduced RC slab tension damage by 79.7 % compared to traditional sand cushions and crack width by 92.3 % relative to the EPS-sand mixture, surpassing monolithic designs. It minimized transmitted forces, accelerations, and energy dissipation while promoting flexural cracking for enhanced structural protection. Validated numerical simulations accurately modeled impact dynamics, enabling reliable performance predictions. Successive impact tests confirmed the SE-S-F configuration's multi-impact resistance, achieving a nondimensional factor (Ω) of 1.47 by the fifth impact, outperforming geofoam-based designs. Repurposing waste EPS, this approach delivers lightweight, sustainable, and cost-effective rockfall protection systems, enhancing safety in mountainous regions and transportation corridors

Floodplain and channel restoration challenges in the Middle Ebro River.

International audienceThe Ebro River is a large Iberian watercourse that develops an extensive floodplain in its middle reach with frequent floods and flooding processes. Fluvial dynamics have been stabilised by regulation and defence works. The flood risk management paradigm has now been changed and some nature-based solutions are being implemented within the framework of the LIFE+ Ebro Resilience strategy and project. With a large interdisciplinary scientific team, the SEDEXCHARE Project evaluates this change in flood risk management from a hydromorphological and river restoration perspective. The achievements so far are scarce in restoration, but important in risk management. It is explained in which line actions should be increased to recover the river dynamics, proposing a territory of freedom for the river. Learning lines are also defined from the current diagnosis for a context of climate emergency and increase in extreme events. The recovered health of the river will provide territorial resilience to the floodable space, which includes population centres, agricultural uses and natural spaces

AN INTRODUCTION TO SOLVING THE LEAST-SQUARES PROBLEM IN VARIATIONAL DATA ASSIMILATION

Variational data assimilation is a technique for combining measured data with dynamical models. It is a key component of Earth system state estimation and is commonly used in weather and ocean forecasting. The approach involves a large-scale generalized nonlinear least-squares problem. Solving the resulting sequence of sparse linear subproblems requires the use of sophisticated numerical linear algebra methods. In practical applications, the computational demands severely limit the number of iterations of a Krylov subspace solver that can be performed and so high-quality preconditioners are vital. In this paper, we introduce variational data assimilation from a numerical linear algebra perspective and review current solution techniques, with a focus on the challenges that arise in large-scale geophysical systems.</div

Crust (unified) tool for equation-of-state reconstruction (CUTER) v2

International audienceThe equation of state (EoS) is a needed input to determine the neutron-star global properties and to relate them. It is thus important to provide thermodynamically consistent and unified EoSs to avoid possible biases in the analyses coming from the use of inconsistent EoSs. We propose a numerical tool, CUTER, allowing the user to consistently match a nuclear-physics informed crust to an arbitrary higher density EoS. We present here the second version of this tool, CUTER v2. Two functionalities are available with the CUTER v2 tool, allowing the user to reconstruct either the whole (outer and inner) crust, or the outer crust only. We show that the code, that has been tested and validated for use by the astrophysical community, is able to efficiently perform both tasks, allowing the computation of neutron-star global properties in a consistent way

Peculiar Rainbows in Saturn's E Ring: Uncovering Luminous Bands Near Enceladus

International audienceWe report observations of stripe-like features in Enceladus' plumes captured simultaneously by Cassini's VIMS-IR and ISS NAC instruments during flyby E17, with similar patterns seen in VIMS-IR data from flyby E13 and E19. These parallel stripes, inclined at approximately 16° to the ecliptic and 43° to Saturn's ring plane, appear continuous across images when projected in the J2000 frame. A bright stripe, most visible at wavelengths around 5 μm, acts as the zeroth-order diffraction peak of a reflection grating with an estimated groove spacing of 0.12-2.60 mm, while adjacent stripes are attributed to higher-order diffraction peaks. We suggest that this light-dispersing phenomenon originates from an inclined periodic structure within Saturn's E ring. This structure, constrained between Saturn's G-ring and Rhea's orbit, likely consists of fresh ice particles supplied by Enceladus' plumes

Life after death: Hidden diversity of orchids across European cemeteries

International audienceHabitats sensitive to anthropogenic pressures are growing in conservation importance in the protection and perpetuation of rare animal and plant species. Although natural habitats sensitive to disturbance in urban areas have mostly declined in availability, patches offer conservation opportunities for wildlife that are fundamental to maintaining biodiversity. Human burial sites can contribute to this: they are more numerous and greater in extent in more urbanized areas, but their significance in the maintenance and promotion of biodiversity has not been considered across Europe and other continents. Because of their high sensitivity to even minor disturbance to natural habitats, orchid diversity is a key bioindicator of terrestrial ecosystem function. We evaluated orchid diversity in cemeteries of 13 European countries. Comprehensive field surveys of orchid flora in 2079 locations revealed that they occurred in every country visited and in high variability in both the number of taxa (n = 65) and individual plant counts (n = 44680). We propose that cemeteries are of major importance as refugia in conserving orchids in most of the visited European countries; however, one of the most urgent issues is to identify the many anthropogenic factors determining biodiversity of cemeteries, and to eliminate some newly emerged management practices in cemeteries that undermine biodiversity, including the orchid flora. Human burial grounds are therefore not just important in preserving the history of humankind; they are key in protecting biodiversity in this modern era of unprecedente

Quantum confinement and carbon nanodots: A conceptual view for the origin of diffuse interstellar bands

International audienceThe nature of the Diffuse Interstellar Band (DIB) carriers is perhaps the most studied, longest standing, unresolved problem in astronomy. While four bands have been associated with the fullerene cation (C^+_60) the vast majority (> 550) remain unidentified. This works is an attempt to provide a conceptual framework for the typical energy transitions that are central to explaining the origin of DIBs, however, it does not make an association between these transitions and any particular DIBs. The effect of quantum confinement on excitons is used, including charge transfer excitons, to construct a generic basis for the electronic transitions that could, in principle, be coherent with the energies associated with DIBs. In this model the carriers are carbon nanodots (CNDs) modelled as nanodiamonds and a-C(:H) nanoparticles. These preliminary results seem to show that particle size dependent effects in nanodiamond and a-C(:H) CNDs could be consistent with the positions of, and intervals between, some of the DIBs. One particular strength of the model is that predicts single bands from the majority of single-size particles and, at most, two bands from some of these same carriers. In the latter case the two bands come from different transitions and may or may not inter-correlate, depending upon the local environment. This generic framework indicates that the size dependent fundamental transitions in CNDs could provide a viable scenario for the origin of some DIB-type bands. While this work does not identify a single DIB, it furnishes a conceptual view for the DIB origin, and suggests that a more refined exploration of quantum confinement size effects, and exciton physics within the astronomical domain might prove fruitful. This work also hints at the requirement for stable configurations for particular size domains in order to explain DIB wavelength stability