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Caractérisation des irrégularités ionosphériques par mesure Radar à Synthèse d'Ouvertures
No full textInternational audienceThis work is dedicated to the characterization of ionospheric irregularities using measurements performed by Synthetic Aperture Radar (SAR)
Investigation on the evaporation of respiratory droplet surrogates with acoustic levitation and modeling using sorption isotherms measurements
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Large-Eddy simulation of solid/fluid heat and mass transfer applied to the thermal degradation of composite materials
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Miniature antenna for GNSS satellite constellation reception
No full textInternational audienceThis paper presents the design, simulation, and real-world validation of a compact, dual-band, right-hand circularly polarized antenna for Global Navigation Satellite System (GNSS) applications. The antenna operates in the L1 (1575 MHz) and L5 (1176 MHz) bands, utilizing a stacked patch structure on low-cost FR4 substrates to achieve compactness and circular polarization. The design ensures axial ratio values below 3 dB, with peak gains of 2.59 dBi (L1) and -0.89 dBi (L5), while maintaining wide radiation coverage. Unlike many recent proposals based on Rogers substrates or complex geometries, our design focuses on cost-effectiveness and manufacturing simplicity. The prototype was validated using a Quectel LC29HAAMD GNSS receiver during the 2024 French National Microwaves Days (JNM), successfully acquiring over 40 satellites within 60 seconds in a real-world suburban environment. These results demonstrate the antenna’s suitability for space-constrained and low-cost GNSS platforms in the “New Space” era
Comparative Analysis of Tropospheric Water Isotope Distributions on Mars and Earth: Insights into Ice Cloud Microphysical Processes and Storm Dynamics
No full textInternational audienceIsotopic analysis is a critical tool for understanding planetary water cycles and quantifying the role of distinct atmospheric processes. This study investigates the spatio-temporal distribution and controlling factors of the HDO/H₂O ratio in water vapor within the tropospheres of Earth and Mars, highlighting the similarities and differences in water vapor transport and phase changes on both planets.We found significant isotopic enrichment from ice sublimation on both planets, with a stronger effect observed on Mars due to longer ice-crystal residence times, lower atmospheric pressures, and substantial temperature fluctuations. In contrast, Earth's near-surface oceans buffer these isotopic variations. Quantifying ice sublimation effects through observational data could help improve the microphysical parameterization in atmospheric models.Moreover, during Mars's global dust storm, the D/H ratio markedly increased and propagated upward due to reduced condensation and the absence of liquid precipitation. In contrast, Earth-based observations during typhoon events indicate isotopic depletion propagating northward from tropical regions, driven primarily by raindrop evaporation within convective systems. Thus, storm events lead to opposite isotopic responses on Earth (depletion) and Mars (enrichment). Consequently, isotopic signals have considerable potential as proxies for reconstructing storm history and intensity across planetary environments.This comparative analysis underscores both shared and planet-specific aspects of tropospheric water cycling, supporting a unified conceptual framework that effectively explains isotopic distributions under differing planetary conditions. Our results may enhance climate and weather models by improving representations of cloud microphysics and atmospheric water transport, while offering new tools for interpreting past climate events based on isotopic evidence
Maximum principle preserving and entropy stable time implicit DGSEM for nonlinear scalar conservation laws
No full textInternational audienceThis work concerns the analysis of the discontinuous Galerkin spectral element method (DGSEM) with implicit time stepping for the numerical approximation of nonlinear scalar conservation laws in multiple space dimensions. First we consider the DGSEM with a backward Euler time stepping, then a space-time DGSEM discretization to remove the restriction on the time step. We design firstorder graph viscosities in space, and in time for the space-time DGSEM, to make the schemes maximum principle preserving and entropy stable for every admissible convex entropy. We also establish wellposedness of the discrete problems by showing existence and uniqueness of the solutions to the nonlinear implicit algebraic relations that need to be solved at each time step. We then use these low-order schemes as building blocks to design a two-step limiter that successfully captures the physical solution, imposes the maximum principle and entropy stability for any convex entropy imposed by the user on the high-order DGSEM scheme, while keeping its accuracy in smooth regions. These properties hold at any approximation order in space and time and without any constraint on the time step. Numerical experiments in one and two space dimensions are presented to illustrate the properties of these schemes
Sentinel-2 Time Series For Vegetation Mapping and Monitoring In A Former Ore Processing Site
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Adaptive Gaussian process-based strategies for solving the NASA-DNV UQ challenge 2025
No full textInternational audienceThis paper describes a dedicated approach to solve the 2025 NASA-DNV UQ challenge problem using adaptive Gaussian process strategies. The uncertainty model is determined through a calibration problem using an optimization approach to identify the aleatory variable joint distribution and the epistemic variable uncertainties. The estimation of the prediction interval for the model output components consists of a quantile estimation problem based on an adaptive Gaussian process strategy. Eventually, the design optimization problems are solved using Bayesian optimization controlling the noise level involved in the estimation of the objective and constraint functions
A gradient-based method for concurrent layout and topology optimization of modular lattice structures
No full textInternational audienceThe design of modular lattice structures, known for their adaptability and damage tolerance, has become increasingly significant with advancements in additive manufacturing and aerospace applications. This study introduces an innovative methodology to minimize structural weight by concurrently optimizing the layout of the structure and the topology of the repeating modules in such structures. The structure layout is parameterized using continuous design variables, enabling the use of a gradient descent optimizer. A two-step optimization strategy is implemented: an initial relaxed optimization phase addresses layout design and initial module topology, followed by a refinement phase that incorporates advanced mechanical constraints into the topology.Applications span 2D and 3D structures, including benchmark cases such as cantilever beams and modular truss bridges. The results highlight the framework’s capability to simultaneously handle stress and local buckling constraints, as well as its modularity. In the best case, it produces designs comparable in volume to monolithic structures, with a weight penalty of only up to 2.8 %. Furthermore, the algorithm demonstrates its efficiency for medium-scale applications, achieving optimized configurations within minutes on a standard laptop computer.<br /
Road Patrol with Traveling Salesman Formulation
No full textInternational audienceTraffic jams and accidents are one of the biggest problems in road traffic. The most agile way to monitor trafficpatrols and detect incidents is to use a fleet of drones. We propose an approach based on a fleet of drones to maximize firstlythe patrol task, secondly the traffic observation and thirdly the Point of Interest (PoI) observation. While maximizing the trafficobservation, our system keeps a probability map of the traffic condition updated. For this purpose, the multi-TravelingSalesman (mTSP) formulation coupled with a selection criterion of (PoI) and a probabilistic formula for keeping the probabilitymap updated are used to solve our problem. The control strategy is ensured by pursuit law. Compared to a systematic patrolling,namely the scanning approach, the performance of our method surpasses the scanning approach and is designed tobe real-time