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A Cascade of Mesostrophy in Turbulence with Reduced Vortex-Stretching
No full textIn three-dimensional turbulence, vortex stretching is the central mechanism enabling the transfer of kinetic energy toward smaller scales. If vortex stretching is absent in three-dimensional turbulence, energy is no longer conserved and enstrophy cascades to smaller scales. In this paper we propose a system which interpolates between these two cases by reducing the strength of vortex stretching in the Navier-Stokes equations. The resulting dynamics yield a cascade that is neither a pure energy cascade nor a pure enstrophy cascade. We refer to this process as a mesostrophy cascade. We formulate a consistent picture describing this cascade and the characteristic scales involved in the mesostrophy balance. We illustrate this picture via numerical integrations of the EDQNM model with reduced vortex stretching
Fitting the Chrono Urbanism of 15-Minute City Principles into the City of Semarang, Jawa-Indonesia: A GIS-Based Identification
No full textInternational audienceThe concept of chrono-urbanism, particularly embodied in Carlos Moreno's '15-Minute City' model, advocates for urban environments where residents can fulfill their daily needs within a 15-minute walk from their homes. Achieving such short-distance mobility necessitates the integration of micromobility solutions-small vehicles powered either electrically or manually. This study spatially analyzes the residential zones of Banyumanik District and Central Semarang District in Semarang City, Indonesia, utilizing GIS-based methods to assess the feasibility of adopting the 15-Minute City framework in these areas. The selected districts represent both a central urban residential area and a secondary urban center. Employing techniques such as Kernel Density estimation, GIS Closest Facility, GIS Isochrones, and GIS Urban Network Analysis, the research quantifies the accessibility of public facilities within a 15-minute radius. Findings indicate that both districts are characterized by low-density residential development and a limited concentration of public facilities within the target proximity. From the perspective of the 15-Minute City concept, Semarang City faces morphological challenges, as the prevalence of expansive landed housing undermines the necessary clustering of services and amenities. Consequently, the study underscores the importance of reinforcing policies that promote mixed-use zoning and the development of vertical housing within residential areas as crucial measures to counteract urban sprawl and enhance the efficiency of public facility provision.Le concept de chrono-urbanisme, notamment incarné par le modèle « Ville du quart d'heure » de Carlos Moreno, prône des environnements urbains où les habitants peuvent satisfaire leurs besoins quotidiens à moins de 15 minutes de marche de leur domicile. Réaliser une telle mobilité sur de courtes distances nécessite l'intégration de solutions de micromobilité : des petits véhicules électriques ou manuels. Cette étude analyse spatialement les zones résidentielles des districts de Banyumanik et de Semarang-Centre, dans la ville de Semarang, en Indonésie, en utilisant des méthodes SIG pour évaluer la faisabilité de l'adoption du modèle « Ville du quart d'heure » dans ces zones. Les districts sélectionnés représentent à la fois une zone résidentielle centrale et un centre urbain secondaire. À l'aide de techniques telles que l'estimation de la densité par noyau, l'installation la plus proche (SIG), les isochrones (SIG) et l'analyse des réseaux urbains (SIG), la recherche quantifie l'accessibilité des équipements publics dans un rayon de 15 minutes. Les résultats indiquent que les deux districts se caractérisent par un développement résidentiel de faible densité et une concentration limitée d'équipements publics à proximité de la cible. Du point de vue du concept de « Ville du Quart d'Heure », la ville de Semarang est confrontée à des défis morphologiques, la prédominance de vastes ensembles résidentiels compromettant le regroupement nécessaire des services et des équipements. Par conséquent, l'étude souligne l'importance de renforcer les politiques favorisant le zonage mixte et le développement de logements verticaux au sein des zones résidentielles, des mesures cruciales pour contrer l'étalement urbain et améliorer l'efficacité de la fourniture d'équipements publics
Espaces de Sobolev à valeurs variétés
No full textThis thesis is concerned with several properties of Sobolev spaces of mappings between manifolds. An important amount of research has been carried out on these spaces since the beginning of the 80's, notably motivated by their strong connection with problems arising from geometry, from physics, or from numerical methods. Although they are defined as metric subspaces of classical Sobolev spaces of vector-valued mappings, spaces of mappings with values into a manifold exhibit striking qualitative differences with the former ones. A typical instance of such a difference is the fact that smooth maps into a given manifold need not be dense among the Sobolev mappings with values into the same target, in strong contrast with the classical density result in real-valued functions spaces. Following this observation, a whole area of research was initiated, focused notably on the four following questions: (I) characterize those values of the parameters s and p, the domains, and the targets for which strong density of smooth maps does occur; (II) find a suitable class of almost smooth maps which is always dense among Sobolev mappings; (III) when strong density fails, characterize the closure of smooth maps; and (IV) determine what happens if strong convergence is replaced by a weaker notion. This thesis aims at presenting a contribution in the study of each of these questions. First, we solve the missing case s > 1 noninteger in the first two questions, where the main difficulty is the combination of the rigidity of higher order spaces with the nonlocal character in fractional order, hence concluding the complete answer to the strong density problem. We also push further the study of the second question by establishing the strong density of an improved class of almost smooth maps. Then, we construct two families of analytical obstructions to the weak approximation property, showing that, for any p in N {0,1} — the only case to be left open — there exist targets so that the weak approximation property fails. Finally, we construct integral invariants allowing to characterize the closure of smooth maps for a large class of target manifolds in the range 0 1 non entier des deux premières questions, où la difficulté principale est la combinaison de la rigidité des espaces d'ordre supérieur et du caractère non local propre à l'ordre fractionnaire, finalisant ainsi la réponse complète au problème de la densité forte. Par ailleurs, on pousse plus avant l'étude de la deuxième question en établissant la densité forte d'une classe améliorée d'applications presque lisses. Ensuite, on construit deux familles d'obstructions analytiques à la propriété d'approximation faible, montrant que pour tout p dans N {0,1} — le seul cas encore ouvert — il existe des cibles pour lesquelles la propriété d'approximation faible échoue. Enfin, on construit des invariants intégraux permettant de caractériser la clôture des fonctions lisses pour une grande famille de variétés cibles dans la gamme 0 < s < 1, correspondant au cas où la construction même de tels invariants est une tâche délicate
Une contribution à la connaissance des professionnel·les de l’APA et des dynamiques du secteur
No full textInternational audienceLes politiques publiques de santé, depuis 2001, ont largement façonné l’organisation de l’APA. Celle-ci est également traversée de logiques marchandes complexes (Belorgey, 2010 ; Collinet, Delalandre, 2016) ; au point que cette activité peut être appréhendée comme un quasi-marché (Nyssens, 2015). Cette configuration se traduit notamment par une séparation entre le financement et la régulation menés par l’État d’une part, et d’autre part, la prestation des services assurée par d’autres acteurs publics et privés - à but lucratif ou non (Prescapp, 2023). Les enjeux de définition et de délimitation de l’AP à des fins de santé (dont l’APA), de formation, de qualification et de légitimation des professionnel·les (Perrin, 2016) témoignent de la difficulté à saisir cette sphère d’activité (Brier, 2021). Alors que le référentiel professionnel des enseignants en APA (Barbin et al., 2016), issue d’une enquête sociologique, considère uniquement les secteurs sanitaire, médico-social et social, nous avons fait le choix, dans une enquête mixte menée en France entière, d’intégrer également le secteur sportif (Handisport, Sport adapté, fédérations sportives et affinitaires), et de considérer la diversité des professionnel·les susceptibles de s’identifier au secteur de l’APA, incluant formé·es en STAPS et ailleurs.Les résultats présentés sont principalement issus du traitement des réponses à un questionnaire auto-administré à destination des professionnel·les de l’activité physique à des fins de santé [N=930 questionnaires complétés] diffusé entre juin et décembre 2024, complétés par des éléments d’analyse d’entretiens (enquête en cours) conduits avec des professionnel·les de l’APA. Après avoir présenté les modes de diffusion du questionnaire, nous souhaitons soumettre à la discussion la représentation de la structure de l’espace des professionnel·les issue de ce travail, et les premiers résultats quant aux effets, sur les conditions d’emploi et les pratiques des professionnel·les de l’APA, de leur inscription dans des domaines d’activité distincts. Si les résultats font apparaître un espace dans lequel les EAPA sont majoritaires, l’acception volontairement élargie de l’APA permet de saisir un centre (bénéficiant certainement du travail de légitimation de la filière universitaire et de certains effets des politiques publiques de santé) sans invisibiliser pour autant d’autres profils professionnels situés en périphérie et dans les segments limitrophes (déclarant par exemple exercer dans le domaine du sport-santé et effectuer quelques heures d’APA) dont les situations illustrent le caractère flou et mouvant du secteur de l’APA en même temps qu’ils participent à la diffusion et la légitimation de ce principe d’intervention
ROBIN: Reference observatory of basins for international hydrological climate change detection
No full textInternational audienceHuman-induced warming is modifying the water cycle. adaptation to posed threats requires an understanding of hydrological responses to climate variability. Whilst these can be computationally modelled, observed streamflow data is essential for constraining models, and understanding and quantifying emerging trends in the water cycle. to date, the identification of such trends at the global scale has been hindered by data limitations -in particular, the prevalence of direct human influences on streamflow which can obscure climate-driven variability. By removing these influences, trends in streamflow data can be more confidently attributed to climate variability. Here we describe the Reference Observatory of Basins for INternational hydrological climate change detection (ROBIN) -the first iteration of a global network of streamflow data from national reference hydrological networks (RHNs) -comprised of catchments which are near-natural or have limited human influences. This collaboration has established a freely available global RHN dataset of over 3,000 catchments and code libraries, which can be used to underpin new science endeavours and advance change detection studies to support international climate policy and adaptation
High and low similarity backbone extraction using similarity-based link prediction
No full textInternational audienceAbstract Complex networks are fundamental to understanding systems across diverse domains. However, their increasing size and complexity pose challenges for analysis and scalability. Backbone extraction simplifies networks by preserving key structures while reducing complexity. Traditional methods include statistical and structural approaches, with statistical methods often lacking interpretability and structural methods offering limited flexibility. This paper introduces a novel framework for backbone extraction using similarity-based link prediction methods in weighted and unweighted networks. It aligns Low Similarity backbones (LS-backbones) with traditional statistical methods and High Similarity backbones (HS-backbones) with structural methods. LS-backbones retain edges with low similarity scores, emphasizing weak or unexpected connections. HS-backbones preserve edges with high similarity scores, focusing on strong and cohesive structures. In this study we employ three similarity functions: Preferential Attachment (local), Local Path Index (quasi-local), and Shortest Path Index (global). Quantitative evaluation across 18 networks shows that: LS-backbones preserve more nodes and highlight peripheral structures but struggle with fragmentation at lower edge retention levels. HS-backbones maintain superior connectivity and interconnectivity, making them ideal for robust and cohesive networks. A qualitative evaluation using the global air transportation network highlights the framework’s versatility. While the LS-methods aligns with statistical methods they are more interpretable due to their clear and well-defined similarity assumptions. Similarly, although the High Salience Skeleton is interpretable, the framework demonstrates greater flexibility by varying the similarity function to capture diverse network complexities. For instance, the Low Similarity Preferential Attachment backbone uncovers weak peripheral links, enhancing regional connectivity. Low Similarity Shortest Path backbone identifies critical connections vital for maintaining isolated regions, while Low Similarity Local Path backbone highlights non-redundant connections in constrained areas. High Similarity Preferential Attachment backbone emphasizes robust global links between major hubs, High Similarity Shortest Path backbone ensures efficient direct paths, and High Similarity Local Path backbone reveals redundant connections that strengthen localized cohesion. This study demonstrates the versatility of similarity-based link prediction for extracting meaningful backbones. Future research will explore the synergy between LS-backbones and HS-backbones, alongside advanced link prediction methods, to further expand the framework’s applicability
Algebraic combinatorics around a problem in enumerative geometry
No full textThe research presented in this habilitation thesis falls within the field of algebraic combinatorics, and consists of several original contributions. It was initially motivated by an enumerative geometry problem: namely, the explicit computation of the number of intersection points between the permutahedral variety and a Schubert subvariety within the flag variety.The first part introduces the original problem and describes classical cohomological techniques that allow for the derivation of two distinct formulas for . The first formula, based on Klyachko’s work, establishes the strict positivity of the numbers and highlights several of their structural properties. The second formula, obtained through substantial algebraic and combinatorial developments, provides an explicit combinatorial interpretation of these numbers.The second part gathers various contributions that emerged during the resolution of the initial problem. In particular, -analogues of the quantities appearing in the first formula, named remixed Eulerian numbers, are introduced and studied. This rich family encompasses many classical combinatorial sequences, and the combinatorial and algebraic aspects of this -deformation are studied in depth. Additionally, in connection with the second formula, a variant of the theory of -partitions is developed, along with a theory of bilateral parking functions which sheds light on certain combinatorial aspects of the formula.The third and final part focuses on quasisymmetric polynomials, an important family playing a central role in the derivation of the second formula for . A new operator-based approach is introduced, simplifying and extending classical methods for studying these polynomials. This construction is directly inspired by the theory of symmetric polynomials, with forest polynomials playing a role analogous to that of Schubert polynomials
Red blood cells rheology measured using AFM. A comparison with other studies
No full textInternational audienc
MorphoCellSorter is an Andrews plot-based sorting approach to rank microglia according to their morphological features
No full textInternational audienceMicroglia exhibit diverse morphologies reflecting environmental conditions, maturity, or functional states. Thus, morphological characterization provides important information to understand microglial roles and functions. Most recent morphological analysis relies on classifying cells based on morphological parameters. However, this classification may lack biological relevance, as microglial morphologies represent a continuum rather than distinct, separate groups, and do not correspond to mathematically defined clusters irrelevant of microglial cells function. Instead, we propose a new open-source tool, MorphoCellSorter, which assesses microglial morphology by automatically computing morphological criteria, using principal component analysis and Andrews plots to score cells. MorphoCellSorter properly ranked cells from various microglia datasets in mice and rats of different ages, from in vivo , in vitro , and ex vivo models, that were acquired using diverse imaging techniques. This approach allowed for the discrimination of cell populations in various pathophysiological conditions. Finally, MorphoCellSorter offers a versatile, easy, and ready-to-use method to evaluate microglial morphological diversity that could easily be generalized to standardize practices across laboratories
bench-MIA: Towards automatic multi-lever benchmark construction for MIA evaluation
No full textInternational audienceThe lack of transparency in large language models (LLMs) training data has created concerns regarding unauthorized data use. Membership Inference Attacks (MIA) offer a method for detecting potential copyright violations and privacy breaches by determining whether specific data points were included during training. However, existing MIA methods face reliability and generalization challenges due to biases in validation datasets. Since various LLMs are trained on different, often proprietary datasets, creating a single universal dataset and evaluation framework is not feasible. In this work-in-progress paper, we introduce bench-MIA, an approach that automatically constructs tailored benchmarks for MIA evaluation. Bench-MIA leverages the concept of lever to systematically generate evaluation datasets addressing key sources of bias. By providing appropriate evaluation baselines for each dataset, bench-MIA facilitates more accurate and fair MIA assessments. Preliminary experimental results demonstrate the impact of these levers on MIA evaluation and motivate further validation