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J-groupes généralisés, J-groupes de tresses et groupes d'entrelacs de Seifert
No full textThe family of J-groups was introduced by Achar and Aubert with the goal of providing Coxeter-like combinatorial tools for studying rank 2 complex reflection groups. However, J-groups lack an explicit presentation with abstract reflections as generators. This gap was filled by Gobet, and later by the second author, for the subfamily of so-called J-reflection groups. The obtained presentations then gave rise to a concept of J-braid group, which coincides with the link groups of torus necklaces.In this paper we study a generalization of J-groups. We determine which of these groups are finitely generated. We show that, as for classical J-groups, the family of finite generalized J-groups coincides with the family of rank 2 complex reflection groups. We also show that finitely generated generalized J-groups coincide with what we call the torsion quotients of J-braid groups. We deduce explicit presentations for all finitely generated generalized J-groups, where the generators are abstract reflections. We also complete the classification of these groups up to reflection isomorphism.As a byproduct of these results, we obtain that a quotient of a Seifert link group obtained by adding torsion to meridians somehow determines the link up to isotopy. Moreover, such a quotient is finite if and only if it is isomorphic to a complex reflection group of rank two.Les J-groupes ont été introduits par Achar et Aubert dans le but de fournir une combinatoire similaire à celle des groupes de Coxeter pour les groupes de réflexions complexes de rang 2. Cependant, les J-groupes ne sont pas défini via une présentation de réflexions explicite. Ce vide à été comblé par Gobet, puis par le second auteur pour la sous-famille dite des J-groupes de réflexions. Les présentations obtenues alors ont ensuite donné la définition des J-groupes de tresses, qui coïncide avec la famille des groupes d'entrelacs des entrelacs toriques. Dans cet article nous étudions une généralisation des J-groupes. Nous déterminons lesquels de ces groupes sont finiment engendrés. Nous montrons que, comme pour les J-groupes classiques, la famille des J-groupes généralisés finis coïncide avec la famille des groupes de réflexions complexes de rang 2. Nous montrons également que la famille des J-groupes généralisés finiment engendrés coincide avec les quotients de torsions des J-groupes de tresses. Nous en déduisons des présentations explicites pour tous les J-groupes généralisés finiment engendrés. Nous complétons également la classification de ces groupes à isomorphisme de réflexions près. Comme conséquence de ces constructions, nous obtenons que le quotient d'un groupe d'entrelac de Seifert obtenu en ajoutant de la torsion au méridiens détermine d'une certaine manière l'entrelacs à isotopie près. De plus, un tel quotient est fini si et seulement si il est isomorphe à un groupe de réflexions complexe de rang 2
Agree to disagree? Making sense of vagueness in International Environmental Agreements
No full textInternational audienc
Influence of Free-Stream Turbulence on the Swirling Wake of a Porous Disc
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Visites de jardins et expériences muséales : médiation, participation et inclusion au prisme de la multimodalité
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An Archaeometric Study of Silver Elite Jewelry from Grave H82, Lumbe's Garden Cemetery, Prague Castle
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Demo: Exploring Utility and Attackability Trade-offs in Local Differential Privacy
No full textInternational audienceLocal Differential Privacy (LDP) provides strong, formal privacy guarantees without requiring a trusted curator, making it a promising approach for privacy-preserving data collection and analysis. However, despite extensive research, practitioners may struggle to understand how to tune LDP parameters and anticipate the impact on data utility and attack risks for their specific scenarios. To address this gap, we demonstrate LDP-Toolbox, the first interactive, web-based toolbox (implemented in Python) that enables practical, analytical visualization of trade-offs between privacy loss (ε), utility loss, and vulnerability to attacks. The toolbox supports exploration of these trade-offs using real-world datasets from different domains; in this demonstration, we focus on discrete personal attributes and location-based scenarios. By providing intuitive, visual insights, LDP-Toolbox lowers the barrier to deploying LDP in real applications and helps bridge the gap between theoretical guarantees and practical adoption. The toolbox is open-source on PyPI (https://pypi.org/project/ldp-toolbox) and a video is available on our GitHub repository (https://github.com/hharcolezi/ldp-toolbox)
PM2.5 Pollution Decrease in Paris, France, for the 2013–2024 Period: An Evaluation of the Local Source Contributions by Subtracting the Effect of Wind Speed
No full textInternational audienceMeasuring the long-term trend of PM2.5 mass-concentration in urban environments is essential as it has a direct impact on human health. PM2.5 levels depend not only on the intensity of local emission sources and on imported pollution, but also on meteorological conditions (e.g., anticyclonic versus windy conditions), which leads to yearly variations in mean PM2.5 values. Two datasets available for Paris, France, are considered: measurements from Airparif air quality agency network and from the Pollutrack network of mobile car-based sensors. Also, meteorological parameters coming from ERA5 analysis (ECMWF) are considered. Annual values are calculated using three different statistical methods, which yield different results. For the 2013–2024 period, a clear relationship between wind speed and PM2.5 mass-concentration levels is established. The results show a linear decrease in both concentration and standard deviation for wind speeds in the 0–6 m·s−1 range, followed by nearly stable values for wind speed above 6 m·s−1. This behavior is explained by the dispersive effect of strong winds on air pollution. Under such conditions, which occur about 10% of the time in Paris, the contribution of persistent background sources can be isolated. Using the 6 m·s−1 threshold, the average annual linear decrease in emissions from local sources is estimated at 4.1 and 4.3% per year for the Airparif and Pollutrack data, respectively. Since 2023, the annual background value attributed to emission has been close to 5 µg·m−3, in agreement with WHO recommendations. This approach could be used to monitor the effects of regulations on traffic and heating emissions and could be applied to other cities for estimating background pollution levels. Finally, future studies should therefore prioritize number concentrations and size distributions, rather than mass-concentrations
Usage du sol et érosion hydrique : application de l’EPM de Gavrilović au bassin d’Abou Al-Aswad (sud-ouest du Liban, milieu méditerranéen semi-aride)
No full textInternational audienceThe Abou Al-Aswad watershed, covering 148 km² in southwestern Lebanon, experiences intensified water erosion due to deforestation, inappropriate agricultural practices, and a semi-arid climate. To quantify soil losses, this study employs Gavrilović’s Erosion Potential Method (EPM) (1962). Soil erodibility was further assessed using the Universal Soil Loss Equation (USLE), while erosion dynamics were determined via the Bare Soil Index. Within the GIS environment, the combination of model parameters indicates that soil losses may reach up to 13000 m³·km⁻², particularly in areas lacking protective vegetation cover and erosion-control measures. Conversely, the slopes cultivated along contour lines show losses of less than 1000 m³·km⁻² (a thickness of 1 mm). To validate these estimates, the computed volumes were converted to equivalent thickness in millimeters. Comparison with in situ measurements, obtained using metal rods, confirms the model’s overall reliability, although localized discrepancies remain owing to variations in slope and vegetation cover. The EPM proves to be a robust tool for assessing erosion risk at the watershed scale, provided its parameters are precisely calibrated to local conditions. A regular monitoring program, combining field measurements and remote-sensing observations, is essential to continuously update and refine soil-management strategies.Le bassin versant d’Abou Al-Aswad, d’une superficie de 148 km² et situé au sud-ouest du Liban, est soumis à une érosion hydrique exacerbée par la déforestation, des pratiques culturales inadaptées et un climat semi-aride. Afin de quantifier les pertes de sol, cette étude mobilise la Méthode du Potentiel d’Érosion (EPM) de Slobodan Gavrilović (1962). Par ailleurs, l’érodibilité du sol a été évaluée à l’aide de l’équation universelle des pertes en sol (USLE), tandis que l’évolution de l’érosion a été calculée grâce à la formule de l’Indice de Sol Nu (BSI). Dans l’environnement SIG, la combinaison des paramètres du modèle révèle que les pertes de sol peuvent atteindre 13000 m³·km⁻², en particulier dans les zones dépourvues de couvert végétal protecteur et de dispositifs antiérosifs. À l’inverse, les versants cultivés selon les courbes de niveau présentent des pertes inférieures à 1000 m³·km⁻² (1mm d’épaisseur). Afin de valider ces estimations, les volumes obtenus ont été convertis en millimètres d’épaisseur équivalente. La comparaison avec les mesures in situ, réalisées à l’aide de tiges métalliques, confirme globalement la fiabilité du modèle, même si des divergences localisées subsistent en raison des variations de pente et de couverture végétale. La méthode EPM se révèle robuste pour évaluer le risque d’érosion à l’échelle du bassin, dès lors que ses paramètres sont calibrés avec précision selon le contexte local. Un suivi régulier, associant mesures de terrain et observations par télédétection, est par ailleurs indispensable pour actualiser et améliorer en continu les stratégies de gestion des sols
Experimental constraints on shallow differentiation of high-Mg andesite at Whakaari, New Zealand
No full textInternational audienceAbstract Phase equilibrium experiments were used to determine conditions of melt evolution and phenocryst growth in high-Mg andesite magmas that were erupted at Whakaari (White Island) in New Zealand between 1976 and 2000. The high-Mg andesites are both mafic (7.21–10.3 wt% MgO) and silica-rich (55.3–58.6 wt% SiO 2 ) with phenocrysts of plagioclase, orthopyroxene, clinopyroxene, olivine, Cr-spinel and Fe–Ti oxides contained in a glassy to fine-grained matrix of mostly dacitic composition. Experiments were conducted on one of the most primitive samples available (the high-Mg andesite TRW34) at conditions ranged from 1 atm to 500 MPa at temperatures of 950 to 1200 °C with total water concentrations of 0 to 10 wt%. Except for the 500 MPa experiments, ƒO 2 was buffered at 1 or 2 log units above Ni–NiO. Consistent with earlier thermodynamic modelling, our results demonstrate that residual Whakaari melts (now represented by matrix glasses) evolved along a plagioclase + two-pyroxene cotectic (± magnetite ± ilmenite) under comparatively low-pressure, shallow conditions (< 200 MPa or < 6 km) and were relatively hot (> 950 °C) and dry (≤ 3 wt% melt-H 2 O), with oxygen fugacities either at, or slightly above Ni–NiO + 1 log unit. Although the bulk-rock trends of Whakaari volcanic rocks are clearly calc-alkaline, those of the residual matrix glasses are only weakly so. A likely explanation for this contrast is that the primary magmas were relatively hydrous, but became dehydrated when intruded at shallow depths. The effectiveness of water in this role, combined with the demonstrable presence of primitive calc-alkaline magmas in the upper-crust, highlights the importance of magmatic water, in place of deep crustal fractionation, for shaping the calc-alkaline evolutionary trend
Design, synthesis and immunological evaluation of CRM 197 -based immunogens functionalized with synthetic scaffolds displaying a tumor-associated MUC1 glycopeptide
No full textInternational audienceA generalizable semisynthetic vaccine approach to increase antigen presentation and immune recognition of poorly immunogenic tumor-associated MUC1 glycopeptides