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Simplicity of the automorphism group of fields with operators
No full textWe adapt a proof of Lascar in order to show the simplicity of the group of automorphisms fixing pointwise all non-generic elements for a class of uncountable models of suitable theories of fields with operators
Analytical obstructions to the weak approximation of Sobolev mappings into manifolds
No full textFor any integer , we construct a compact Riemannian manifold such that if , there is a map in the Sobolev space of mappings which is not a weak limit of smooth maps into due to a mechanism of analytical obstruction. For , the target manifold can be taken to be the sphere thanks to the construction by Whitehead product of maps with nontrivial Hopf invariant, generalizing the result by Bethuel for . The results extend to higher order Sobolev spaces , with , , , and .</div
RED2Hunt: an Actionable Framework for Cleaning Operational Databases with Surrogate Keys
No full textSurrogate keys are now extensively utilized by database designers to implement keys in SQL tables. They are straightforward, easy to understand, and enable efficient access, despite lacking any real-world semantic meaning. In this context, complex redundancy issues might emerge and often go unnoticed as long as they do not affect the operational applications built on top of the databases. These issues become evident when organizations seek to leverage data science, posing significant challenges to the implementation of analytical projects. This paper, grounded in real-world applications, defines the concept of artificial unicity and proposes RED2Hunt (RElational Databases REDundancy Hunting), a human-in-the-loop framework for identifying hidden redundancy and, if problems occur, cleaning relational databases implemented with surrogate keys. We first define the central and intricate notion of artificial unicity and then the RED2Hunt framework to address it. We rely on simple abstractions easy to visualize based on the so-called redundancy profile associated to some relations and the notion of attribute stability. Quite interestingly, those profiles can be computed very efficiently in quasi-linear time. We have devised different metrics to guide the domain expert and an actionable framework to generate new redundancy-free databases. The proposed framework was implemented on top of PostgreSQL. From the publicly available IMDB database, we have generated synthetic databases, implementing different redundancy scenarios, on which we tested RED2Hunt to study its scalability. RED2Hunt has also been tested on operational databases implemented with surrogate keys. Lessons learned from these real-life applications are discussed
Reliability is Blind: Collective Incentives for Decentralized Computing Marketplaces without Individual Behavior Information
No full textInternational audienceIn decentralized cloud computing marketplaces, ensuring fair and efficient interactions among asset providers and end-users is crucial. A key concern is meeting agreed-upon service-level objectives like the service's reliability. In this decentralized context, traditional mechanisms often fail to address the complexity of task failures, due to limited available and trustworthy insights into these independent actors' individual behavior. This paper proposes a collective incentive mechanism that blindly punishes all involved parties when a task fails. Based on ruin theory, we show that Collective Incentives improve behavior in the marketplace by creating a disincentive for faults and misbehavior even when the parties at fault are unknown, in turn leading to a more robust marketplace. Simulations for small and large pools of marketplace assets show that Collective Incentives enable to meet or exceed a reliability target, i.e., the success-rate of tasks run using marketplace assets, by eventually discarding failure-prone assets while preserving reliable ones
Generalised class groups in dihedral and fake Z_p-extensions
No full textInternational audienceWe study restricted ramification in dihedral extensions of number fields, with a focus on its ℓ-adic properties along fake Z_p-extensions, for p and ℓ distinct odd primes. Our results generalise previous works in the (pro)-dihedral setting, with applications to the study of more general fake Iwasawa theories beyond the classical case of standard class groups
-Graph: A Graph Embedding for Interpretable Time Series Clustering
No full textInternational audienceTime series clustering poses a significant challenge with diverse applications across domains. A prominent drawback of existing solutions lies in their limited interpretability, often confined to presenting users with centroids. In addressing this gap, our work presents k-Graph, an unsupervised method explicitly crafted to augment interpretability in time series clustering. Leveraging a graph representation of time series subsequences, k-Graph constructs multiple graph representations based on different subsequence lengths. This feature accommodates variable-length time series without requiring users to predetermine subsequence lengths. Our experimental results reveal that k-Graph outperforms current state-of-the-art time series clustering algorithms in accuracy, while providing users with meaningful explanations and interpretations of the clustering outcomes
An ageing study of twenty 18650 lithium-ion Graphite/LFP cells in first and second life use
No full textInternational audienceThe dataset gives a comprehensive data collection focusing on the ageing of twenty 18650 Graphite/LFP 1.1 Ah commercial cells in first and second life. The ageing from a pristine state up to 40% of capacity loss is uncommon due to the extensive testing time required. Therefore, this new data collection provides insights on long-term ageing of lithium-ion batteries. The initial aim of the study was to comprehend the ageing in first and second-life applications, with a special focus on the sudden acceleration of capacity loss that can occur after a long-term use. The ageing experiment was designed to assess the impact of various test conditions: electric vehicle use, high current charge and discharge, full or partial discharge and a reduced operating voltage window. The cells were characterised every 100 cycles to measure the remaining capacity and the pseudo-open-circuit-voltage. This dataset can help the research community in studying second-life applications or any other study on long-term ageing of Graphite/LFP batteries: new diagnosis and prognosis techniques, AI, battery modelling, and more.Le jeu de données propose une collection complète axée sur le vieillissement de vingt cellules commerciales 18650 Graphite/LFP de 1,1 Ah en première et seconde vie. Le vieillissement, depuis un état initial jusqu'à une perte de capacité de 40 %, est rarement étudié en raison du temps de test requis pour un usage standard. Cette nouvelle collection de données apporte ainsi des informations sur le vieillissement à long terme des batteries lithium-ion. L'objectif initial de l'étude était de mieux comprendre le vieillissement dans les applications de première et seconde vie, avec une attention particulière portée à l’accélération soudaine de la perte de capacité pouvant survenir après une utilisation prolongée. L'expérience de vieillissement a été conçue pour évaluer l'impact de diverses conditions de test : utilisation en véhicule électrique, charge et décharge à courant élevé, décharge totale ou partielle, ainsi qu'une réduction de la fenêtre de tension de fonctionnement. Les cellules ont été caractérisées tous les 100 cycles afin de mesurer la capacité restante et la tension pseudo-circuit-ouvert. Ce jeu de données peut aider la communauté scientifique à étudier les applications de seconde vie ou toute autre recherche sur le vieillissement à long terme des batteries Graphite/LFP, notamment dans le développement de nouvelles techniques de diagnostic et de pronostic, l'intelligence artificielle, la modélisation des batteries, et bien plus encore
Darboux type theorems in multisymplectic geometry
No full textWe give a survey of Darboux type theorems in multisymplectic geometry. These theorems establish when a closed differential form of a certain type admits a constant-coefficient expression in some local coordinate system. Beyond the classical cases of symplectic and volume forms, 0-deformability (i.e. constancy of linear type) is typically not automatic and has to be imposed, leading to distinct theorems 'per linear type'
Socially aware robot for reward, effort, and risk distribution
No full textInternational audienceIn this work we address the problem of designing a straightforward resource allocation decision making robot. We developed a model that accurately makes decisions to distribute risk, effort and reward between two humans or a human and a robot, considering their age, sex and humanness. To assess the model's alignment with social norms, we conducted a Turing test which showed that our model is perceived as making socially acceptable decisions, similar to those of human participants. Furthermore we demonstrated our model by embodying it in a robot negotiator that automatically distributed reward, effort and risk tokens among participant dyads by perceiving their physical characteristics
Extreme vertical drafts as drivers of Lagrangian dispersion in stably stratified turbulent flows
No full textInternational audienceThe dispersion of Lagrangian particle pairs is a fundamental process in turbulence, with implications for mixing, transport, and the statistical properties of particles in geophysical and environmental flows. While classical theories describe pair dispersion through scaling laws related to energy cascades, extreme events in turbulent flows can significantly alter these dynamics. This is especially important in stratified flows, where intermittency manifests itself also as strong updrafts and downdrafts. In this study, we investigate the influence of extreme events on the relative dispersion of particle pairs in stably stratified turbulence. Using numerical simulations we analyze the statistical properties of pair separation across different regimes, and quantify deviations from classical Richardson scaling. Our results highlight the role of extreme drafts in accelerating dispersion. These findings have important implications for turbulent mixing in natural systems, including atmospheric and oceanic flows, as well as applications in cloud microphysics and pollutant transport