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Un modèle de transfert radiatif Monte Carlo 3D pour le PCM Titan
No full textInternational audienceWe present a comparison of two radiative transfer models in the context of improving the Titan Planetary Climate Model (PCM). In one hand, we have access to the results from the current 2-stream model incorporated in the Titan PCM and in the other hand, we use a 3D backward Monte Carlo model to estimate the heating rates. Our results demonstrate that the sphericity and heterogeneity effects, not accounted with 2-stream models, have major effects on the radiative budget of Titan atmosphere. We conduct this study at equinoxe and solstice, demonstrating the radiative effects of various phenomenon.Nous présentons une comparaison entre deux modèles de transfert radiatif dans le cadre de l'amélioration du modèle climatique planétaire (PCM) de Titan. D'une part, nous avons accès aux résultats du modèle à deux flux actuellement intégré au PCM de Titan et, d'autre part, nous utilisons un modèle Monte Carlo 3D pour estimer les taux de réchauffement. Nos résultats montrent que les effets de sphéricité et d'hétérogénéité, qui ne sont pas pris en compte dans les modèles à deux flux, ont des effets majeurs sur le bilan radiatif de l'atmosphère de Titan. Cette étude se focalise sur l'équinoxe et le solstice, montrant les effets radiatifs de divers phénomènes.Traduit avec DeepL.com (version gratuite
On the determination of pore size distribution by nitrogen Adsorption and Mercury intrusion Porosimetry for claystone
No full textInternational audienceUnderstanding the evolution of Callovo-Oxfordian (COx) claystone porosity under alkaline conditions is crucial for assessing its role as a geological barrier for nuclear waste deep geological disposal facility. This study evaluates the pore size distribution of COx claystone using two experimental techniques: nitrogen adsorption and mercury intrusion porosimetry (MIP). The nitrogen adsorption data were analysed using the Barrett-Joyner-Halenda (BJH) model and the non-local density functional theory (NLDFT). These were further combined in a Total Pore Volume (TPV) approach to better describe the full pore size spectrum. Results show significant discrepancies between the methods. BJH overestimates mesopore volume (~3.8 nm) due to the cavitation and pore blocking artifacts, while MIP underestimate total porosity due to the compression effects and its inability to detect micropores. DFT provides a more reliable micropore and mesopore characterization, yet its detection range (<50 nm) remains limited, requiring high- resolution data at low relative pressures for accurate analysis. To overcome these limitations, the TPV method combine DFT and MIP data, offering a more continuous and accurate pore size distribution. The results indicate that alkaline exposure increases macroporosity while reducing microporosity, potentially affecting the permeability and self-sealing capacity of COx claystone
Stone masonry floor systems for low environmental impact structures
No full textInternational audienceStone masonry structures are relevant solutions to tackle buildings embodied impacts as they are low-processed materials. Although floor systems contribute to a large part of the greenhouse gas emissions of new constructions, stone floor systems are still little explored in recent constructions and their environmental impact has yet to be thoroughly assessed. This study integrates parametric design with Life Cycle Assessment for four stone floor typologies: Abeille vault, groin vault, stone floor with post-stressed stone beams, and post-stressed stone slabs. A comparison of stone structures with conventional floor systems, made using discernibility analysis, finds that stone floor systems can achieve up to a 60% reduction in embodied carbon compared to typical concrete floors. This result proves that stone floor systems can mitigate climate impacts. Further results indicate that stone masonry floor systems perform better than concrete and steel floors for human health, and better than wood floors for ecosystem quality. A sensitivity analysis highlights parameters such as transport logistics, energy usage in quarries, and stone cutting losses, suggesting that the structural design starting point should be the investigation of locally available material resources. Future work taking into account seismic and fire resistance as well as including detailed quarry impact on ecosystems could constitute relevant additions. This study shows the potential of stone floor systems for the decarbonisation of new building structures and highlights transport and production energy as key parameters to pilot GHG emissions of such structures
Mesurer la pluie et sa variabilité à travers les échelles d'espace et de temps
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Bivariate asymptotics via random walks: application to large genus maps
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Density of Rational Languages Under Shift Invariant Measures
No full textInternational audienceWe study density of rational languages under shift invariant probability measures on spaces of two-sided infinite words, which generalizes the classical notion of density studied in formal languages and automata theory. The density for a language is defined as the limit in average (if it exists) of the probability that a word of a given length belongs to the language. We establish the existence of densities for all rational languages under all shift invariant measures. We also give explicit formulas under certain conditions, in particular when the language is aperiodic. Our approach combines tools and ideas from semigroup theory and ergodic theory
Microplastic dynamics at the outlet of a peri-urban catchment over a year of sampling: Effects of hydrological conditions, including an extreme flood event
No full textInternational audienceIn the context of climate change some territories are experiencing reduced episodes of rainfall but increasing intensity of these events. At the watershed level, it results in increasing frequency of flood events. Such events modulate not only the water quantity but also water quality. Among the contaminants driven by these hydrological events there are the microplastics (MPs). This contaminant is present in all environmental compartments and poses potential toxicological and ecotoxicological risk. The influence of hydrological variability on this type of pollution remains poorly understood, particularly during flood events. One major reason is that sampling is typically conducted before and after floods, for practical reasons, thereby neglecting the flow rate variability during the event, increase, peak and decrease.To address this gap, an extensive sampling campaign was conducted between 2023 and 2025 at the outlet of a peri-urban watershed: the Avenelles catchment. This small watershed (45 km²) is part of the ORACLE observatory and the OZCAR network. The campaign covered both low and high-flow periods, as well as different flood events, including one extreme event (65 mm of rainfall in 48 hours) that was fully monitored (18 samples collected). In parallel with every MPs sample, total suspended solids (TSS) concentrations were also measured.MPs were sampled using a pumping system coupled with in-situ filtration (10 µm). Quantification and characterization analyses were performed using Fourier-transform infrared microspectroscopy (µ-FTIR) coupled to the siMPle database. Throughout the monitoring period, MPs concentrations and fluxes showed significant variability in response to hydrological conditions. On a seasonal scale, the median MPs concentration during low-flow periods was approximately tenfold lower (median = 666 MPs m⁻³, n = 11) than during high-flow periods (median = 6136 MPs m⁻³, n = 19). During high-flow periods, MPs concentrations ranged from a minimum of 193 MPs m⁻³ (129 MP s-1) to a maximum of 32,941 MPs m⁻³ (21,576 MPs s⁻¹), highlighting the strong influence of hydrological conditions on MPs dynamics. This pattern was confirmed during the extreme flood event, with MPs concentrations and fluxes substantially increasing from pre-flood levels (669 MPs m⁻³ and 398 MPs s⁻¹) to peak flood values (17,343 MPs m⁻³ and 63,197 MPs s⁻¹). Four days after the peak, when flow rate decreased to pre-flood rate, the MPs concentrations also returned to pre-flood levels (977 MPs m⁻³ and 479 MPs s⁻¹).These results emphasize the role of flood events in the transport and flux of MPs in streams, as well as the importance of capturing the full range of hydrological conditions when assessing the transport and dynamics of microplastics in rivers. This high-resolution monitoring revealed the key role of flood events in driving microplastic transfer through freshwater systems
When Many Trees Go to War
No full textIt is known that any two trees on the same n leaves can be displayed by a network with n -2 reticulations, and there are two trees that cannot be displayed by a network with fewer reticulations. But how many reticulations are needed to display multiple trees? For any set of t trees on n leaves, there is a trivial network with (t -1)n reticulations that displays them. To do better, we have to exploit common structure of the trees to embed non-trivial subtrees of different trees into the same part of the network. In this paper, we show that, for t ∈ o((log n)^0.5), there is a set of t trees with virtually no common structure that could be exploited. More precisely, we show for any t ∈ o((log n)^0.5) , there are t trees such that any network displaying them has (t -1 - o(1))n reticulations. For t ∈ o(log n), we obtain a slightly weaker bound. We also prove that already for t = c log n, for any constant c > 0, there is a set of t trees that cannot be displayed by a network with o(n log n) reticulations, matching up to constant factors the known upper bound of O(n log n) reticulations sufficient to display all trees with n leaves. These results are based on simple counting arguments and extend to unrooted networks and trees
A variational method for curve extraction with curvature-dependent energies
No full textWe introduce a variational approach for extracting curves between a list of possible endpoints, based on the discretization of an energy and Smirnov's decomposition theorem for vector fields. It is used to design a bi-level minimization approach to automatically extract curves and 1D structures from an image, which is mostly unsupervised.We extend then the method to curvature-dependent energies, using a now classical lifting of the curves in the space of positions and orientations equipped with an appropriate sub-Riemanian or Finslerian metric
Corporate Tax Avoidance and Sales: Micro Evidence and Aggregate Implications
No full textInternational audienceThis paper examines the effect of corporate tax avoidance (CTA) on U.S. firmlevel sales and its aggregate implications. In theory, CTA gives a competitive edge to avoiding firms, which affects the distribution of sales in the economy. In practice, we find a causal impact of CTA on firm-level sales using a broad set of measures of tax avoidance and different identification strategies. Combining micro-estimates and the model, we assess how changes in CTA over the past two decades have shaped the distribution of sales across U.S. industries. While the effects vary by sector, rising CTA among large firms has reinforced their dominant positions, contributing to increased concentration, in several key industries