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De l'essor de la lenteur dans le sport contemporain...
No full textInternational audienceThis paper examines the development of sporting, leisure, physical and recreational activities that are based on a logic of slowness, or at least slowing down. After situating the movement historically, it goes on to propose a common characterisation of the five major internal logics of these activities (flow, distraction, landscape kinaesthetics, resonance and ecosophy), using a wealth of illustrations to suggest the diversity of activities that have been won over by this movement. Finally, it explains the extent to which this ‘sporting slowness’, as a societal groundswell, can be seen as a heterotopia aspiring to renew the order of things, in terms of ethical responsibility and iteration.Cet article questionne le développement d’activités sportives, ludiques, physiques et récréatives qui s’inscrivent dans une logique de lenteur, du moins de ralentissement. Après l’avoir situé historiquement, il propose, avec force illustrations suggérant la diversité des activités conquises par ce mouvement, un effort de caractérisation commune des cinq logiques internes majeures de ces activités (flow, distraction, kinesthésique paysagère, résonance et écosophie). Dans un troisième temps, il explicite dans quelles mesures de responsabilité éthique et d’itération cette « lenteur sportive », comme lame de fond sociétale, peut apparaître comme une hétérotopie aspirant à renouveler l’ordre des choses
Évolution décennale de la composition fonctionnelle du phytoplancton dans la Manche orientale : effets majeurs possibles du changement climatique à venir
No full textInternational audienceGlobal change is known to exert a considerable impact on marine and coastal ecosystems, affecting various parameters such as sea surface temperature (SST), runoff, circulation patterns and the availability of limiting nutrients (like nitrogen, phosphorus and silicon), with each influencing phytoplankton communities differently. This study is based on weekly to fortnightly in vivo fine-spatial-resolution (∼ 1 km) phytoplankton observations along an nearshore–offshore gradient in the French waters of the Eastern English Channel in the Strait of Dover. The phytoplankton functional composition was addressed by automated “pulse-shape recording” flow cytometry, coupled with the analysis of environmental variables over the last decade (2012–2022). This method allows for the characterization of almost the entire phytoplankton size range (from 0.1 to 800 µm width) and the determination of the abundance of functional groups based on optical single-cell signals (fluorescence and scatter). We explored seasonal, spatial and decadal dynamics in an environment strongly influenced by tides and currents. Over the past 11 years, the SST has shown an increasing trend at all stations, with nearshore waters warming faster than offshore waters (+1.05 °C vs. +0.93 °C). Changes in nutrient concentrations have led to imbalances in nutrient ratios () relative to reference nutrient ratios. However, a return to balanced ratios has been observed since 2019. The phytoplankton total abundance has also increased over the aforementioned decade, with a higher contribution of small-sized cells (picoeukaryotes and picocyanobacteria) and a decrease in microphytoplankton, particularly near the coast. Based on an analysis of environmental parameters and phytoplankton abundance, the winters of 2013–2014 and 2019–2020 were identified as shifting periods in this time series. These changes in the phytoplankton community, favoring the smallest groups, could lead to a reduction in the productivity of coastal marine ecosystems, which could, in turn, affect higher trophic levels and the entire food web.Il est connu que le changement global exerce un impact considérable sur les écosystèmes marins et côtiers, affectant divers paramètres tels que la température de surface de la mer (SST), le ruissellement, les schémas de circulation et la disponibilité des nutriments limitants (comme l'azote, le phosphore et le silicium), chacun influençant différemment les communautés phytoplanctoniques. Cette étude est basée sur des observations in vivo hebdomadaires à bimensuelles de phytoplancton à résolution spatiale fine ( ∼ 1 km) le long d'un gradient littoral-hauturier dans les eaux françaises de la Manche orientale dans le détroit du Pas de Calais. La composition fonctionnelle du phytoplancton a été étudiée par cytométrie de flux automatisée « enregistrement de la forme des impulsions », couplée à l'analyse des variables environnementales sur la dernière décennie (2012-2022). Cette méthode permet de caractériser la quasi-totalité de la gamme de taille du phytoplancton (de 0,1 à 800 µ m de large) et de déterminer l'abondance des groupes fonctionnels à partir de signaux optiques unicellulaires (fluorescence et diffusion). Nous avons exploré la dynamique saisonnière, spatiale et décennale dans un environnement fortement influencé par les marées et les courants. Au cours des 11 dernières années, la température de surface de la mer (SST) a affiché une tendance à la hausse à toutes les stations, les eaux littorales se réchauffant plus rapidement que les eaux du large ( + 1,05 °C contre + 0,93 °C). Les variations des concentrations en nutriments ont entraîné des déséquilibres dans les ratios de nutriments () par rapport aux ratios nutritifs de référence. Cependant, un retour à des ratios équilibrés a été observé depuis 2019. L'abondance totale du phytoplancton a également augmenté au cours de la décennie susmentionnée, avec une contribution plus élevée des cellules de petite taille (picoeucaryotes et picocyanobactéries) et une diminution du microphytoplancton, en particulier près de la côte. Sur la base d'une analyse des paramètres environnementaux et de l'abondance du phytoplancton, les hivers 2013-2014 et 2019-2020 ont été identifiés comme des périodes de décalage dans cette série chronologique. Ces changements dans la communauté phytoplanctonique, favorisant les plus petits groupes, pourraient entraîner une réduction de la productivité des écosystèmes marins côtiers, ce qui pourrait, à son tour, affecter les niveaux trophiques supérieurs et l'ensemble du réseau trophique
The number system in rational base 3/2 and the 3x + 1 problem
No full textTo appear in Comptes Rendus. Mathématique. Académie des Sciences, ParisThe representation of numbers in rational base p/q was introduced in 2008 by Akiyama, Frougny and Sakarovitch, with a special focus on the case p/q = 3/2. Unnoticed since then, natural questions related to representations in that specific base turn out to intimately involve the Collatz 3x+1 function. Our purpose in this note is to expose these links and motivate further research into them
Cointeraction on noncrossing partitions and related polynomial invariants
No full text34 pagesWe study the structure of two cointeracting bialgebras on noncrossing partitions appearing in the theory of free probability. The first coproduct is given by separation of the blocks of the partitions into two parts, with respect to the nestings, while the second one is given by fusion of blocks. This structure implies the existence of a unique polynomial invariant respecting the product and both coproducts.We give a combinatorial interpretation of this invariant, study its values at -1 and use it for the computation of the antipode. We also give several results on its coefficients when applied to noncrossing partitions with no nesting. This leads to unexpected links with harmonic nested sums, Riordan arrays, composition of formal series and generalized Stirling numbers. This polynomial invariant is shown to be related to other ones, counting increasing or strictly increasing maps for the nesting order on noncrossing partitions, through the action of several characters
Les défis sanitaires liés à l'eau
No full textInternational audienceCette présentation, sous forme de poster, se concentra sur certaines problématiques liées à l’élévation du niveau des eaux ou aux catastrophes naturelles, notamment dans des régions vulnérables telles que Mayotte ou notre région. L’eau étant une ressource indispensable, sa gouvernance repose sur un système complexe de régulation de plus en plus impacté par les catastrophes naturelles
Noncrossing arithmetic
No full textHigher-order notions of Kreweras complementation have appeared in the literature inthe works of Krawczyk, Speicher, Mastnak, Nica, Arizmendi, Vargas, and others. Whilethe theory has been developed primarily for specific applications in free probability, it alsopossesses an elegant, purely combinatorial core that is of independent interest. The presentarticle aims at offering a simple account of various aspects of higher-order Kreweras complementation on the basis of elementary arithmetic, (co)algebraic, categorical and simplicialproperties of noncrossing partitions. The main idea is to consider noncrossing partitions asproviding an interesting noncommutative analogue of the interplay between the divisibilityposet and the multiplicative monoid of positive integers. Just as the divisibility poset can beregarded as the decalage of the multiplicative monoid, we exhibit the lattice of noncrossingpartitions as the decalage of a partial monoid structure on noncrossing partitions encodinghigher-order Kreweras complements. While our results may be considered familiar, severalof the viewpoints can be regarded as novel, offering an efficient approach both conceptuallyand computationally
La justice à soi-même en matière civile et commerciale
No full textInternational audienceContracting parties who cannot agree on one or more points of their contract must endeavor to find a joint solution. Otherwise, they must refer the matter to a judge, who will decide between them, ruling in favor of one and against the other. Neither party may impose their own solution. Except perhaps by using one of the following legal mechanisms: compensation; exception of non-performance; right of retention; unilateral termination; unilateral cancellation.Les cocontractants qui ne s’entendent pas sur un ou plusieurs points de leur contrat doivent s’efforcer d’y trouver une solution en commun. Sinon, ils leur font s’adresser à un juge qui les départage en donnant raison à l’un, et tort à l’autre. Aucun des deux ne saurait imposer sa propre solution. Sauf peut-être en utilisant l’un des mécanismes juridiques suivants : la compensation ; l’exception d’inexécution ; le droit de rétention ; la résolution unilatérale ; l’annulation unilatérale
La difficulté de calcul de l’ancienneté lucrative
No full textInternational audienceL’ancienneté du travailleur présente une incidence sur ses droits patrimoniaux et extrapatrimoniaux à l’égard de son employeur. Mais il y a parfois des difficultés à mesurer cette ancienneté ; en particulier dans les hypothèses de travail à temps partiel, en cas de suspension du travailleur ; voire en cas d’absentéisme. L’étude ci-dessous aide à la maîtrise de ces questions
On extended associative semigroups
No full textPublished version in SIGMAWe study extended associative semigroups (briefly, EAS), an algebraic structure used to define generalizations of the operad of associative algebras, and the subclass of commutative extended diassociative semigroups (briefly, CEDS), which are used to define generalizations of the operad of pre-Lie algebras. We give families of examples based on semigroups or on groups, as well as a classification of EAS of cardinality two. We then define linear extended associative semigroups as linear maps satisfying a variation of the braid equation. We explore links between linear EAS and bialgebras and Hopf algebras. We also study the structure of nondegenerate finite CEDS and show that they are obtained by semidirect and direct products involving two groups
A baseline for biodiversity: spatio-temporal variability of fish assemblages in the pristine and little-known Iguela Lagoon, Gabon
No full textInternational audienceCoastal lagoons in tropical regions are recognized for their high ecological value, functioning as critical nursery, feeding, and transitional habitats for a wide range of fish species. Despite their importance, data on fish assemblage structure and dynamics remain scarce for many systems in Central Africa. This study investigates the spatial and temporal variability of ichthyofaunal assemblages in the Iguela Lagoon, a relatively pristine estuarine ecosystem located in southwestern Gabon, protected under the Ramsar Convention and flanked by Loango National Park and the Iguela Mouth Marine Park. Seasonal fish sampling was conducted across nine stations using trammel nets over four hydrological seasons. A total of 59 species distributed among 30 families were identified during the present study. However, a comprehensive bibliographic synthesis, based on the available grey literature, made it possible to identify 118 species belonging to 46 families within the Iguéla lagoon. Multivariate analyses revealed four distinct assemblage groups shaped by seasonal and salinity gradients: (i) a rainy season-dominated freshwater migrant group, (ii) a dry season transitional estuarine group, (iii) a generalist assemblage occurring year-round, and (iv) a marine-influenced downstream group. Ecological guild analysis confirmed the strong influence of freshwater inputs and salinity fluctuations on species distribution and habitat use. Commercially important species, including Parachelon grandisquamis, Chrysichthys nigrodigitatus, Ethmalosa fimbriata, as well as Lutjanidae and Haemulidae species were abundant, although most individuals were juveniles, underscoring the lagoon's essential nursery function. The structural complexity of the lagoon, including mangroves and seagrass beds, provides key habitats for juvenile development and contributes to the high biodiversity observed. This study fills a major gap in ichthyological knowledge for Gabonese coastal systems and provides a scientific baseline for conservation planning. The clear spatio-temporal differentiation in fish assemblages highlights the need for adaptive, spatially explicit management strategies to preserve the ecological integrity and fisheries productivity of the Iguela Lagoon in the face of ongoing environmental change