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Séminaire Institut Jean le Rond d'Alembert - Modèles dynamiques équivalents de structures complexes et caractérisations vibroacoustiques en large bande fréquentielle
No full textNational audienceJe présenterai dans ce séminaire mes activités de recherche qui s'articulent autour des problématiques de modélisation et de caractérisation dynamique de structures complexes sur une large bande fréquentielle avec un intérêt particulier pour l'identification précise de l'amortissement. Le premier volet, « expérimental », sera consacré à ma thématique de recherche principale qui porte sur la caractérisation de structures anisotropes dans les différents domaines fréquentiels d’intérêt pour les problématiques vibroacoustiques industrielles. Quelques applications concrètes en vibroacoustique de la méthode d’analyse modale haute résolution (HRMA) que j’ai développée seront détaillées puis les avancées majeures obtenues sur les techniques d'identification des nombres d'ondes et des propriétés matériaux seront exposées : méthode de corrélation par fonction de Hankel pour des structures isotropes et orthotropes elliptiques, méthode RIC anisotrope pour l'identification de force et la caractérisation (thèse de Fabien Marchetti, 2019). Les structures sandwichs stratifiées feront office de cas d'école pour l'application des différentes techniques expérimentales exposées en portant une attention particulière à vérifier la comparaison et la superposition des méthodologies malgré les différentes formulations théoriques sous-jacentes. Des applications possibles des méthodologies d’identification des courbes de dispersion pour le Contrôle Non Destructif et la détection de défauts (Internoise 2024, thèse CIFRE Saint-Gobain Research Paris en cours de Théodore Braule) seront évoquées.Dans le second volet « modélisation » je synthétiserai mes différents apports et mes contributions au développement de modèles équivalents en vibroacoustique large bande fréquentielle. On s'intéressera ainsi aux structures planes orthotropes raidies avec application à la vibroacoustique de la table d'harmonie du piano : structure complexe en épicéa périodiquement raidie. Puis je présenterai l'axe majeur de ma recherche théorique actuelle qui traite de la modélisation équivalente de structures multicouches (composites, anisotropes) en large bande fréquentielle. En se basant sur ce formalisme un modèle dynamique équivalent de matériaux multicouches anisotropes a été développé. Deux verrous scientifiques ont pu être levés : étendre à l'anisotropie (angles d’orientation des couches quelconques) l'approche équivalente plaque mince et unifier les définitions de l'amortissement dynamique de la littérature en corrigeant celle implicite au modèle équivalent plaque mince. Je terminerai en présentant les perspectives de développement de mes thématiques de recherches exposées, notamment l’étude théorique et expérimentale visant à modéliser, concevoir et mesurer des structures multicouches à interfaces complexes (thèse de Nicolas Auquier 2020-2023 et postdoc en cours d’Antoine Demiquel), ainsi que les travaux collaboratifs en cours entre le CRASH-UdeS (Alain Berry et Olivier Robin) et le LVA portant sur l’identification des paramètres mécaniques de table d’harmonie en bois de lutherie, et le développement de la méthode des champs virtuels pour l’identification des propriétés matériaux de panneaux complexes par la technique de mesure de déflectométrie optique
Real-Time Simulation of Deformable Tactile Sensors and Objects in Robotic Grasping using Graph Neural Networks with Inductive Biases
No full textInternational audiencePhysical simulation of deformable bodies is crucial for robotic manipulation, particularly for applications involving deformable objects and deformable tactile sensors. While Finite Element Method (FEM) simulations provide high accuracy for modeling deformable objects and tactile sensors, they are prohibitively expensive for real-time applications, with simulation times often exceeding practical limits for robotic control and learning. This paper presents a novel Graph Neural Network (GNN) framework that accelerates the simulation of tactile sensors by factors of - compared to FEM, while maintaining high physical accuracy. Our approach addresses limitations in existing GNN-based physics learning through inductive biases. The key contributions include: (1) extending FEM simulation to deformable tactile sensors in grasping scenarios, (2) incorporating novel inductive biases through tetrahedral features and global graph features to improve information propagation and training stability, and (3) demonstrating the first successful application of GNN simulation for tactile sensors with generalization to unseen objects. Additionally, the inductive biases reduce prediction errors by up to 45% compared to baseline approaches. This work enables real-time soft tactile sensors of soft object simulation for robotic applications with stress prediction. All simulation and training code will be released
Unrolled Multiplicative Updates for Nonnegative Matrix Factorization applied to Hyperspectral Unmixing
No full textHyperSpectral Unmixing (HSU), the problem of separating mixed spectra of overlapping materials in a hyperspectral image, has motivated dedicated algorithmic developments in the last two decades. On the one hand, traditional model-based algorithms frequently guarantee interpretable results. On the other hand, deep-learning-based approaches are often faster at inference time and may obtain better empirical results. This work utilizes the strengths of both approaches by building on the deep unrolling paradigm. Our contribution is twofold. First, we propose two new algorithms based on deep unrolling of the well-known Multiplicative Updates. The first, coined Non-Adaptive Learned Multiplicative Updates (NALMU), adopts a simple element-wise multiplicative scheme. The second, called Recursive Adaptive Learned Multiplicative Updates (RALMU), has more flexible updates and better take into account the spatial correlations in the abundances. Second, we relate NALMU to the minimization of an explicit cost function under some assumptions. Such guarantees are unique in the HSU field. NALMU and RALMU are tested on astrophysics and remote sensing datasets. They outperform the other deep learning-based HSU algorithms and classical iterative schemes for the endmember estimates and obtain competitive results for the abundance estimates, even when trained in a self-supervised way. The code used in this paper will be made available upon publication
End-To-End Multi-View Multi-Modal Detection-Driven Image Fusion: One Method to Fuse them all
No full textWe present EDIF, an end-to-end detection-driven framework designed to unify multi-modal and multi-view image fusion within a single architecture. While most existing fusion methods address either spectral complementarity (multi-modal) or viewpoint variability (multi-view) in isolation, real-world perception systems increasingly require both. EDIF formulates fusion as an object-level alignment problem: heterogeneous images are encoded as sets of keypoints, which are matched and aggregated through a graph attention mechanism to form object-centric representations directly optimized for detection. To stabilize training across heterogeneous components, we introduce a three-stage task-driven strategy that progressively aligns keypoint extraction, object localization, and cross-sensor grouping. In addition, we release the Multi-Modal and Multi-View Object Detection Dataset (MMDOD), a new benchmark designed to study detection-driven fusion under strong modality–view dependencies. MMDOD contains over 10,000 images of transparent objects captured under four complementary modalities (visible, NIR, low-contrast, polarization shift) and six viewpoints, with detailed object-level annotations. Experiments on RGB–thermal, multi-camera, and joint multi-modal multi-view benchmarks show that EDIF achieves performance competitive with recent specialized methods, while uniquely operating within a unified framework. On MMDOD, EDIF significantly outperforms adapted multi-modal multi-view baselines, highlighting the benefits of detection-driven, object-level fusion. The proposed MMDOD dataset is publicly available at https://datasets.liris.cnrs.fr/mmdod-version1
Quand, où et comment (dé)centraliser la prise de décisions pour une Industrie 4.0 durable
No full text(De)centralising the organisation of decision-making to a greater or lesser level should be based on quantified evidence. I am particularly interested in the (de)centralisation of decision-making organisation (rather than its physical or informational structuring) in production systems of goods and services, e.g., how many decision-makers should be there and how should they interact? This is an old question that I address with recent digital tools. From a technical point of view, this organisational issue corresponds to the choice of decision support technologies (de)centralised to a more or lesser degree. Indeed, Industrial Engineering employs various such decision-making methods, initially centralised and often based on Mixed Integer Linear Programming (MILP, or PLNE in French) and, more recently, decentralised through MultiAgent Systems (MASs, or SMAs in French). Each of both approaches is developed independently by its community with little overlap. These approaches seem complementary to me. For instance, MILP finds the optimal decision if it has sufficient computation time available, whereas MASs are not only more reactive but also take the autonomy of decision-makers into account. In this context, the core of my research aims to optimise the organisation of decision-making by studying when, where and how to use MILP within a MAS. To this end, I quantitatively compare, using simulation, the efficiency of more or less (de)centralised decision-making organisations when agents are more or less selfish, hence my inspiration from game theory.This basic research contributes in multiple ways to support the making of decisions in Industry 4.0. A first example is my ongoing work on applying agent-based simulation as an engine for a digital twin. Next, I am starting to work on the transport of people and goods in sparsely populated areas, taking my inspiration from the physical internet (interconnection of logistics networks). In the longer term, I would like to study how to improve the sustainability of production systems in our increasingly VUCA (Volatility, Uncertainty, Complexity & Ambiguity) environment thanks to the lack of a single point of failure in a MAS.(Dé)centraliser plus ou moins l'organisation de la prise de décisions devrait être basé sur des preuves quantifiées. Je m'intéresse plus particulièrement à la (dé)centralisation de l'organisation de la prise de décisions (plutôt qu'à sa structuration physique ou informationnelle) dans des systèmes de production de biens et de services, par exemple, combien devrait-il y avoir de décideurs et comment devraient-ils interagir ? Il s'agit d'une vieille question que j'aborde avec les outils récents du numérique. Du point de vue technique, ce problème organisationnel se traduit par le choix de technologies plus ou moins (dé)centralisées d'aide à la décision. En effet, le Génie Industriel emploie différentes méthodes de prise de décisions, d'abord centralisées et souvent à base de Programmation Linéaire en Nombres Entiers (PLNE) et, plus récemment, décentralisées grâce aux Systèmes Multi-Agents (SMAs). Chacune de ces deux approches est développée indépendamment l’une de l’autre par sa communauté avec peu d’intersections. Ces approches me semblent complémentaires. Par exemple, la PLNE trouve la décision optimale si elle a suffisamment de temps de calcul disponible, alors que les SMAs sont non seulement plus réactifs, mais tiennent compte de l'autonomie des décideurs. Dans ce contexte, le cœur de mes recherches vise à optimiser l'organisation de la prise de décisions en étudiant quand, où et comment utiliser de la PLNE dans un SMA. A cet effet, je compare, de manière quantitative grâce à la simulation, l'efficience d'organisations plus ou moins (dé)centralisées de la prise de décision lorsque les agents sont plus ou moins égoïstes, d'où mon inspiration par la théorie des jeux.Cette recherche amont contribue de multiples façons à l'aide à la décision dans l'Industrie 4.0. Un premier exemple est mon travail en cours sur l'application de la simulation à base d'agents comme moteur d'un jumeau numérique. Ensuite, je commence à travailler sur le transport de personnes et de biens en zones peu denses, inspiré par l'internet physique (interconnexion de réseaux logistiques). A plus long terme, je souhaiterais étudier l'amélioration de la durabilité des systèmes de production dans notre environnement de plus en plus VUCA (Volatility, Uncertainty, Complexity & Ambiguity) grâce à l'absence de point de défaillance unique d'un SMA
Comparison of methods for the estimation of Young’s moduli and structural loss factor of wood, applied to guitar soundboards made of Adirondack spruce
No full textInternational audienceStandardised methods for characterising the mechanical properties of materials were mainly developed for metals or alloys with isotropic behaviour. They are consequently poorly suited to characterising materials that exhibit orthotropic and space-varying behaviour, such as polymers, composites, and natural materials like wood. The focus of this work is on guitar soundboards made of Adirondack spruce (Picea rubens, also known as red spruce). Tests are conducted on 12 quarter-sawn plates. This work compares the practicality of methods to estimate the Young's modulus and the structural loss factor of these soundboards, while the variability of results for each method is outlined. A first interest of this work is to determine the trade-off between measurement methods and systems of variable cost and complexity. In addition, the viability of an asymptotic method is demonstrated for such structures (a technique based on mobility measurement and the assumption of an infinite structure). At the same time, the importance of considering the sensor mass is confirmed for low-density structures by comparison with measurements on aluminum and medium-density fibre board panels
Renaming in distributed certification
No full textInternational audienceLocal certification is the area of distributed network computing asking the following question: How to certify to the nodes of a network that a global property holds, if they are limited to a local verification? In this area, it is often essential to have identifiers, that is, unique integers assigned to the nodes. In this short paper, we show how to reduce the range of the identifiers, in three different settings. More precisely, we show how to rename identifiers in the classical local certification setting, when we can (resp. cannot) choose the new identifiers, and we show how a global certificate can help to encode very compactly a new identifier assignment that is not injective in general, but still useful. We conclude with a number of applications of these three results
Filtrations and asymptotic geometry of non-Archimedean norms on section rings
No full textThis article is concerned with the metric study of a construction of Gérardin of the action of the boundary at infinity of the space of norms on a non-Archimedean vector space, and its generalisation to graded algebras. Namely, given (X,L) a polarised variety over an arbitrary non-Archimedean field, we show that there is a jointly d_1-contracting action of the space of filtrations of the section ring R(X,L) on the space of graded norms on R(X,L). This naturally yields non-Archimedean geodesic rays and infinite-dimensional flats in this setting, generalising previous work of the author and Witt Nyström. It is further shown that relative limit measures converge along geodesic rays, providing a result on the d_p-radial geometry of graded norms, analogous to a recent result of Finski in the Archimedean case
Evolution of multicellular reproduction through co-option of ecological interactions
No full textDuring the transition to multicellularity, cells evolved novel regulatory mechanisms to coordinate cell division and differentiation, which enabled the emergence of group reproduction. These mechanisms were repurposed from molecular and cellular traits that once mediated interactions between single-celled organisms. However, it remains unclear how these traits were evolutionarily integrated to form the first developmental programs in multicellular life. To address this issue, we developed a spatially structured evolutionary model in which cells can migrate, divide, and adhere to their neighbors — behaviors common to most unicellular eukaryotes. When coupled to a selective pressure driven by food scarcity, the model reveals that the ecological context plays a central role in the evolution of multi-cellular reproduction. Depending on the spatial distribution of food in the environment, both unicellular and multicellular life cycles with diverse modes of reproduction could evolve. Among these were multicellular life cycles that reproduce through unicellular propagules, the most prevalent reproductive strategy in multicellular life, which emerged spontaneously as a dispersal strategy in some environments. We show that these propagules are genetically homologous to the lineage’s unicellular ancestors, which were co-opted and repurposed as reproductive structures during evolution. Furthermore, after multicellular lineages with propagules evolved, they could colonize environments that were previously dominated by unicellular life. Altogether, our results show how ecological interactions between single cells can transform into developmental processes during the evolutionary transition towards multicellularity. Significance statement Reproduction is a universal feature of life. Yet, the evolution of multicellularity transformed it fundamentally: while single-celled organisms reproduce via cell division, reproduction in multicellular organisms is a complex process involving the coordination of many cells. How these new forms of multicellular reproduction first evolved is currently unknown. Using a computational model, we study how group reproduction emerges from the collective dynamics of individual cells. The model shows that unicellular ancestral life cycles can be repurposed as propagules used for reproduction in multicellular species, suggesting that genetic co-option is a key mechanism through which early development evolves
Opportunities from energy-loss near-edge fine structure analysis to track chemical and structural damage in zircon
No full textInternational audienceZircon (ZrSiO4) is the oldest-known mineral of Earth and an ubiquitous silicate in geochronology. More specifically, the accumulation of alpha decay damage in zircon over time significantly affects its physical and chemical properties, and can lead to a disturbance of the ages measured in this mineral. Therefore, analytical tools that enable comprehensive structural and chemical information at the nanoscale in this compound are highly sought after. In this context, we explore the electron energy-loss fine structures resulting from the excitation of O1s and Si2p core electrons in zircon, which are interpreted from ab initio calculations in a single-particle framework. An excellent agreement is obtained between the experimental and calculated fine structures, emphasizing the large distortion of the final electronic states induced by the core-hole potential. The O-K edge is particularly rich in information, with intense peaks dominated by O2p - Zr4d and O2p - Si3sp hybrids. This work suggests that the near-edge structures from the O1s and Si2p excitations accessible from electron energy-loss spectroscopy or X-ray absorption spectroscopy could be used as tools to follow, interpret and understand structural and chemical modifications in zircon subject to natural radiation damage. We illustrate the potential of this approach through the evolution of near-edge fine structures in a zircon sample that exhibits a locally amorphized zone formed by ultrafast laser excitation