HAL UVSQ
Not a member yet
57319 research outputs found
Sort by
Constraining the origins of terrestrial stratospheric solid aerosols over the 1981-2020 period
No full textInternational audienceThe injection of materials into the Earth's atmosphere has both a natural and an anthropogenic component. Natural solid aerosols that reach the stratosphere can come from Earth—like ash from volcanic eruptions and biomass fires, pollens, spores, etc. —or from space, such as interplanetary dust, asteroids and comets. Anthropogenic stratospheric solid aerosols exclusively come from space activities, including rocket launches (alumina and black-carbon during propellant combustion) and the re-entry of space objects (rocket bodies, payloads and associated debris) into the atmosphere. Since 2000, the number of rocket launches has increased by a factor of 3 and the number of satellites launched into orbit has increased by a factor of 30 (Lasue et al., 2024). Over the same period, the mass of alumina ejected by Solid Rocket Motors is estimated to have decreased by a factor 2 without accounting for black-carbon emissions (Fig. 1). At the same time, the total mass re-entered into the atmosphere from payloads (excluding manned space flight capsules), rocket bodies, boosters and their debris has increased by more than a factor 2 (Fig. 2). Space debris accounts for only 1% of the total mass re-entered into the atmosphere, while payloads and rocket bodies (and upper stages) account for 7% and 9% respectively. Most of the re-entered mass (83%) comes from boosters and core stages in suborbital flight. Overall, an average of 3.4 kt/year of anthropogenic materials enters Earth’s atmosphere. Whereas the estimated total re-entered mass from cosmic particles ranges between 8.4 and 33.4 kt/year (Schulz et al., 2021, Fig. 1 and Tab. A.7)
The vertical distribution of water vapour isotopes on Mars from the Atmospheric Chemistry Suite aboard the ExoMars Trace Gas Orbiter
No full textInternational audienceIsotope ratios in water vapour provide key insights about the history of water on Mars and can help us unravel the fate of the large amounts of liquid water that once existed on the surface of early Mars [1]. A five-fold enrichment of the deuterium-to-hydrogen (D/H) ratio in Martian water vapour with respect to Earth suggests that a substantial amount of the water inventory escaped to space, but more quantitative estimates rely on a rigorous understanding of the relative escape between the light and heavy isotopes (e.g., [2]).Atmospheric processes such as condensation or photolysis shape the vertical distribution of the water vapour isotopes [3,4] and in turn impact the relative supply of isotopes to the upper atmosphere, where they can escape through thermal and non-thermal processes [5]. Therefore, an in-depth understanding of the vertical distribution of the water vapour abundance and its isotopic fractionation is crucial for reconstructing the escape history of water on Mars.In this study, we measure and model the vertical distribution of D/H and 18O/16O on Martian water vapour using infrared solar occultation observations from the Atmospheric Chemistry Suite (ACS) aboard the ExoMars Trace Gas Orbiter (TGO), together with simulations of the D/H and 18O/16O cycles on Mars from the Mars Planetary Climate Model (PCM)
Water Vapor Vertical Distribution on Mars after Six Years of TGO/NOMAD Solar Occultations. Part II: Cross-validation within TGO and comparison with models
No full textInternational audienceThis is the second part of an investigation of water vapor in the Martian atmosphere using solar occultation observations by the spectrometer NOMAD on board the ExoMars Trace Gas Orbiter. Following the analysis performed in the first part, hereafter named as Paper I, a cross-validation exercise between NOMAD and ACS results is presented, showing global as well as profile-by-profile comparisons. The results reveal an overall good agreement between different teams and instruments, taking into account the different retrieval methodologies. In order to compare with model predictions, we perform an exhaustive analysis of the water vapor simulated by Mars Planetary Climate Model (MPCM). It shows that the MPCM reproduces most of the water vapor climatological features observed in the atmosphere. However, several discrepancies between model and observations are noticed. Some of these are possibly related to the vertical distribution of dust and its effect on the global circulation and on the water vapor vertical transport. Other data-model differences found at 60 km seem to be related to discrepancies on the water ice cloud formation in the MPCM. In addition, we include a cluster analysis of Martian water vapor vertical profiles for the first time. This technique applied to MPCM and NOMAD water vapor retrievals reveal distinct groups of profiles being representative of specific seasons and latitudinal regions, similarly distributed in both model and observations. Moreover, it allows us to provide a simplified water vapor climatology, useful to detect out-of-season events and biases in the retrieval processes
Circulations linguistiques et culturelles: L'étude de l'espagnol en France à l'époque moderne
No full textInternational audienc
Surface modification of nanocatalysts via ion beam techniques for enhanced activity
No full textInternational audienceInterface science is at the forefront of advanced materials design, particularly in catalysis, where surface properties critically determine performance. Among emerging techniques, ion beam irradiation has shown strong potential for modifying the catalytic behavior of solid materials by introducing surface and sub-surface defects. In this study, the effect of nitrogen ion irradiation on the catalytic and redox properties of a ceria–zirconia-based oxidation catalyst (Ce₀.₆₈Zr₀.₃₂O₂), both in its unmodified form and when combined with supported Pt nanoparticles, was systematically investigated through a series of catalytic tests (TPO/TPR), operando FTIR, HRTEM, and XPS analyses. Ion bombardment was found to induce significant modifications to nanoparticle distribution, surface morphology, and defect structure—most notably the formation of oxygen vacancies and enhanced oxygen mobility. These changes resulted in improved catalytic performance for the oxidation of light alkanes and CO, with consistent reductions in T₅₀ values and a notable increase in aging resistance. The enhanced reducibility observed, particularly in Pt-containing systems, suggests a strong impact at the metal/support interface. Overall, this work highlights post-synthesis ion irradiation as an effective tool for activating and stabilizing redox catalysts, providing new opportunities for designing durable materials for environmental and energy applications
Advection, diffusion and linear transport in a single path-sampling Monte-Carlo algorithm: Getting insensitive to geometrical refinement
No full textInternational audienceWe address the question of numerically simulating the coupling of diffusion, advection and one-speed linear transport, with a specific focus on managing geometrical complexity. We base our work on recent advances from the computer graphics community, which has developed Monte Carlo algorithms simulating linear radiation transport in physically realistic scenes, with numerical costs that remain unaffected by geometrical refinement: adding more details to the scene description does not impact the computation time. The resulting benefits in terms of engineering flexibility are already fully integrated into the cinema industry and are gradually being adopted by the video game industry. Here we demonstrate that the same insensitivity to the geometric complexity can be achieved when considering not only one-speed linear transport, but also its coupling with diffusion and advection. In this case, pure linear-transport paths are replaced with advection-diffusion/linear-transport paths, which are composed of subpaths. Each subpath represents one of the three physical phenomena, and coupling is handled by switching from one subpath (i.e. phenomenon) to another. This approach is illustrated using a porous medium involving up to 10,000 pores, with the computation time being strictly independent of the number of pores, showing its ability to facilitate engineering calculations in complex geometries
Parental engagement in an early intervention program for anorexia nervosa : a qualitative study
No full textInternational audienceAnorexia nervosa (AN) is a severe chronic condition requiring early and effective intervention. Family involvement is considered a cornerstone of adolescent treatment, yet the specific dynamics of early parental engagement into care remain poorly understood. This study aimed to explore the processes underlying parental involvement in early care for adolescents with AN, within the context of a family-based day program (EVAFAM) in France. We conducted a qualitative study using semi-structured interviews with 15 parents (7 fathers, 8 mothers) whose adolescents participated in the EVAFAM program between January 2023 and June 2024. We identified three main processes that lead to parental engagement in care: (1) a grieving process, where parents recognized the chronic nature of the illness and their emotional responses to the diagnosis; (2) an active reconstruction process, where parents adapted their attitudes and behaviors to become therapeutic partners; and (3) the relationship to the institutional care framework, which provided both authority and support, while sometimes generating ambivalence. Engagement was supported by increased knowledge and structured interventions but challenged by emotional strain and uncertainty. Notably, early intervention enabled families to shift from denial to active participation, suggesting that engagement is a progressive construction, not an initial precondition. Understanding the trajectories of parental engagement during early intervention highlights key levers for supporting families, including acknowledging emotional transitions, providing practical tools, and reinforcing institutional alliances. These insights can inform tailored interventions and enhance family-centered care for adolescents with AN
The Carlitz module and a differential Ax-Lindemann-Weierstrass theorem for the Euler gamma function
No full textWe prove an Ax-Lindemann-Weierstrass differential transcendence result for Euler's gamma function, namely that the functions are differentially independent over the field of rational functions in the variable , with coefficients in the field of -periodic meromorphic functions over , as soon as determine a set of algebraic functions over , stable by conjugation and pairwise distinct modulo . \par To prove this result we use both the Galois theory of difference equations and the theory of a characteristic zero analog of the Carlitz module introduced by the second author in 2013. As an intermediate result we give an explicit description of the Picard-Vessiot rings and of the Galois groups associated to the operators in the image of the Carlitz module, using techniques inspired by the Carlitz-Hayes theory
