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Introduction: Le pas de deux de la race et de l’ethnicité. Débats théoriques et variabilité des usages
No full textInternational audienc
Non-unique self-similar blowups in shell models: insights from dynamical systems and machine-learning
No full textInternational audienceStrong numerical hints exist in favor of a universal blowup scenario in the Sabra shell model, a popular cascade model of 3D turbulence, which features complex velocity variables on a geometric progression of scales ℓ n ∝ λ − n . The blowup is thought to be of self-similar type and characterized by the finite-time convergence towards a universal profile with non-Kolmogorov (anomalous) small-scale scaling ∝ ℓ n x . Solving the underlying nonlinear eigenvalue problem has however proven challenging, and prior insights mainly used the Dombre–Gilson renormalization scheme, transforming self-similar solutions into solitons propagating over infinite rescaled time horizon. Here, we further characterize Sabra blowups by implementing two strategies targeting the eigenvalue problem. The first involves formal expansion in terms of the bookkeeping parameter δ = ( 1 − x ) log λ , and interpretes the self-similar solution as a (degenerate) homoclinic bifurcation. Using standard bifurcation toolkits, we show that the homoclinic bifurcations identified under finite-truncation of the series converge to the observed Sabra solution. The second strategy uses machine-learning optimization to solve directly for the Sabra eigenvalue. It reveals an intricate phase space, with the presence of a continuous family of non-universal blowup profiles, characterized by various number N of pulses and exponents x N ⩾ x
Pupil plane intensity interferometry with imaging air Cherenkov telescopes
No full textInternational audienceThe Intensity Interferometry Imaging Telescope (I3T) concept illustrated how a single imaging air Cherenkov telescope (IACT) can be transformed into a multi-element intensity interferometer. This is achieved by segmenting the light collecting surface into many sub-apertures via active control of individual mirror facets. Here, we propose an alternative method applicable to all IACTs that we refer to as pupil plane intensity interferometry. Principally, the re-imaged pupil of an IACT can be subdivided with a multipixel detector to enable extremely dense uv-plane sampling. Ray tracing of an IACT based on one of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) light collectors was performed as a proof of principle. Several unique science cases could be investigated and, in particular, we performed a case study that indicates the ability to strongly constrain the angular brightness distribution of the extended disc of the Be star Gamma Cassiopeia. The proposed design could be used as an alternative to current intensity interferometry instruments as it mitigates several inherent limitations of IACTs when used as intensity interferometers, namely temporal dispersion and large angular point spread functions
Oser l’expérimentation collective pour transformer l’organisation vers plus de flexibilité : Le cas d’une PME dans les services numériques
No full textInternational audienceCe chapitre vise à répondre à la question suivante : comment mener un projet de transformation radicale visant à développer des modes d’organisation flexibles ? Son objectif est de contribuer à une meilleure compréhension de la génération de nouvelles formes d’organisation en mettant en lumière l’interaction entre l’inspiration et la motivation d’un leader, d’une part et les capacités d’expérimentation de ses équipes, d’autre part.Pour apporter des éléments de réponse à cette question, une étude qualitative exploratoire d’un cas unique a été menée sur une entreprise de services numériques, Aepsilon, dont le directeur fondateur et dirigeant a initié une transformation en décidant de « libérer » l’entreprise
EPOS-GNSS Data Gateway: News and Novelties
No full textInternational audienceThe EPOS-GNSS Data Gateway (DGW) is the European thematic gateway to GNSS data distributed within the European Plate Observing System - EPOS framework. Thanks to this portal, all interested parties have free access to metadata and data from over 2,000 European GNSS stations.The information system is based on a network of servers, the nodes, connected to a main server, the DGW. The main showcase is the DGW's graphical interface (https://gnssdata-epos.oca.eu/), which enables all the data and metadata in the EPOS-GNSS data infrastructure to be browsed and downloaded. It conceals a complex system of multiple software enabling the integration and synchronization of metadata between the DGW and the nodes. The development and population of this system is the result of a team effort involving the development team, node managers and the node infrastructure and DGW operation coordination team (https://gnss-epos.eu).New features for 2024 include the integration of two new nodes (CEGNxEPOS, Italy and SONEL, France), filling a gap in Central Europe (Northern Italy, Austria, Slovenia) and opening up to other scientific communities, such as those working on long-term sea level trends as part of GLOSS (Global Sea Level Observing System). Their deployment and population, at record speed, demonstrate the commitment of the new partners, the robustness of the system and the efficiency of the procedures. Next, the level of data completeness at the DGW in relation to the stations proposed to EPOS is becoming very good. Finally, the number of files not validated at the nodes, according to the EPOS-GNSS procedure, and therefore not transmitted to the DGW, is now very low.On the other hand, there are some important novelties worth highlighting. All the monitoring tools needed to check that the entire system is working properly are now operational. These tools focus on monitoring all system elements and their interaction at the DGW, comparing metadata between the DGW and the nodes that highlights metadata and synchronization issues, monitoring availability statistics for each DGW-hosted service and user statistics. The system also now gives the opportunity to publish hourly High-Rate GNSS data that are accessible at both the DGW and the EPOS multidisciplinary platform. In early 2025, a new version of the graphical interface, developed using a different technology, will be deployed, enabling easier customization of the interface by node managers, in particular to better acknowledge all contributors to the EPOS-GNSS system
On Sparse Representations of 3-Manifolds
No full text3-manifolds are commonly represented as triangulations, consisting of abstract tetrahedra whose triangular faces are identified in pairs. The combinatorial sparsity of a triangulation, as measured by the treewidth of its dual graph, plays a fundamental role in the design of parameterized algorithms. In this work, we investigate algorithmic procedures that transform or modify a given triangulation while controlling specific sparsity parameters. First, we describe a linear-time algorithm that converts a given triangulation into a Heegaard diagram of the underlying 3-manifold, showing that the construction preserves treewidth. We apply this construction to exhibit a fixed-parameter tractable framework for computing Kuperberg's quantum invariants of 3-manifolds. Second, we present a quasi-linear-time algorithm that retriangulates a given triangulation into one with maximum edge valence of at most nine, while only moderately increasing the treewidth of the dual graph. Combining these two algorithms yields a quasi-linear-time algorithm that produces, from a given triangulation, a Heegaard diagram in which every attaching curve intersects at most nine others
Control of an NV center as a two-qubit system
No full textNitrogen-vacancy (NV) centers are promising experimental platforms for quantum information processing. In this paper, we investigate their controllability and fundamental quantum speed limit for two-qubit gates. Such a quantum system consists of two coupled spins, an electronic and a nuclear spin, where only the former can be controlled directly via microwave pulses. We discuss the various physical approximations that lead to the system model before studying its controllability. We use this control issue as an example to demonstrate how standard geometric control tools can be applied to spin networks. We complete this analysis with a computation of the quantum speed limit using known analytical techniques on Lie groups and their algebras. We finally demonstrate, thanks to preliminary optimal control numerical experiments, that this limit can be approached while keeping a reasonable energy of the control field
Unsupervised Machine Learning Analysis to Enhance Risk Stratification in Patients with Asymptomatic Aortic Stenosis
No full textInternational audienceAims: There is a lack of studies investigating the pathophysiologic and phenotypic distinctiveness of aortic stenosis (AS). This heterogeneity has important implications for identifying optimal intervention timing and potential medical management. This study seeks to identify phenogroups of AS using unsupervised machine learning to improve risk stratification. Methods and results: A total of 349 patients with asymptomatic AS from the PROGRESSA study were included in this analysis. Echocardiographic, clinical and blood sample data were used in the unsupervised clustering process. Longitudinal echocardiographic data were used to evaluate AS progression. Five clusters of patients were revealed using 18 variables selected by an unsupervised machine learning algorithm. Amongst them, aortic valvular phenotype, mean gradient, peak jet velocity (Vpeak), and left ventricle stroke volume were selected as discriminatory variables. Following the clustering process, characteristics differed between clusters, including age, body mass index, and sex ratio (all P < 0.001). Of note, cluster 1 showed higher AS severity at baseline with significantly higher initial Vpeak (344 [314; 376] cm/s) and calcium score (1257 [806; 1837] UA) (P < 0.001). Patients from cluster 1 had a faster AS progression (progression of Vpeak = 22 [9; 39] cm/s/year), and calcium score (213 [111; 307] UA/year) (P < 0.001). Cluster 1 was also associated with a higher composite risk of mortality and aortic valve replacement when adjusted for age, sex, and baseline AS severity (P < 0.001).Conclusion: Artificial intelligence-guided phenotypic classification revealed 5 distinct groups and enhanced risk stratification of patientswith AS. This approach may be useful to optimize and individualize medical and interventional management of AS
La contribution du commerceéquitable à la transition écologique :des modes de production soutenablesvers des actions marketing durables ?
No full textInternational audienceCet article traite de la contribution du commerce équitable envers la transition écologique. Il est discuté de la relation entre les modes de production soutenables et la transition écologique. La demande des consommateurs de produits équitables s’est désormais modifiée avec la transition écologique en incluant davantage les problématiques sociales et des préoccupations environnementales. Cette demande se heurte toutefois à des limites comportementales et historiques. Le marketing peut jouer un rôle pour valoriser la consommation éthique à travers des actions durables. Nous montrons que le commerce équitable contribue à la transition écologique en répondant aux attentes des consommateurs et aux acteurs du marché en mobilisant des actions de marketing durable.La première partie est consacrée aux enjeux de la transition écologique et aux attentes des consommateurs sur le marché du commerce équitable. La seconde partie présente les actions menées par les acteurs du terrain dont les organisations de producteurs (en Afrique de l’Ouest) en faveur de la transition écologique. En discussion, nous analysons l’apport du marketing durable pour promouvoir la transition écologique et sociale
Q²Forge : Générer des Collections de Questions de Compétences et Requêtes SPARQL pour Interroger des Graphes de Connaissances en Langue Naturelle
No full textLe langage de requêtes SPARQL constitue la méthode standard pour accéder aux graphes de connaissances (KGs). Cependant, la formulation de requêtes SPARQL reste une tâche difficile pour les utilisateurs non experts, et chronophage même pour les plus expérimentés. Les bonnes pratiques recommandent de documenter les KGs avec des questions de compétence (CQs) et des requêtes d’exemple afin de contextualiser les connaissances qu’ils contiennent et d’illustrer leurs applications potentielles. En pratique, cela est rarement fait, ou seulement avec un nombre limité d’exemples. Les grands modèles de langage (LLMs) sont de plus en plus utilisés dans les agents conversationnels et démontrent un large éventail d’applications, allant du question-réponse simple à la génération de code dans un langage spécifique. Néanmoins, l’entraînement et l’évaluation de ces modèles pour produire des requêtes SPARQL de haute qualité à partir de questions en langage naturel nécessitent des collections importantes d'exemples de paires question–requête. Cet article présente Q²Forge, une approche visant à générer automatiquement de nouvelles questions de compétence pour un graphe de connaissances et leurs requêtes SPARQL correspondantes. Q²Forge valide ces requêtes de manière itérative grâce à une évaluation humaine et à un LLM agissant comme un juge. L’outil est open source, générique, extensible et modulaire : ses différents modules (génération de CQs, génération et raffinement de requêtes) peuvent être utilisés séparément ou comme un pipeline intégré. Le résultat est un workflow complet allant de la formulation des questions de compétence jusqu’à l’évaluation des requêtes, facilitant la création d’ensembles de référence question–requête pour tout KG cible