HAL-INSA Toulouse
Not a member yet
34325 research outputs found
Sort by
A linearly-implicit energy-momentum preserving scheme for geometrically nonlinear mechanics based on non-canonical Hamiltonian formulations
No full textInternational audienceThis work presents a novel formulation andnumerical strategy for the simulation of geometricallynonlinear structures. First, a non-canonical Hamilto-nian (Poisson) formulation is introduced by includ-ing the dynamics of the stress tensor. This frame-work is developed for von-Kármán nonlinearities inbeams and plates, as well as geometrically nonlin-ear elasticity with Saint-Venant material behavior. Inthe case of plates, both negligible and non-negligiblemembrane inertia are considered. For the former casethe two-dimensional elasticity complex is leveragedto express the dynamics in terms of the Airy stressfunction. The finite element discretization employs amixed approach, combining a conforming approxima-tion for displacement and velocity fields with a dis-continuous stress tensor representation. A staggered,linear implicit time integration scheme is proposed,establishing connections with existing explicit-implicitenergy-preserving methods. The stress degrees of free-dom are statically condensed, reducing the compu-tational complexity to solving a system with a pos-itive definite matrix. The integration strategy pre-serves energy and angular momentum exactly. Themethodology is validated through numerical experi-ments on the Duffing oscillator, a von-Kármán beam,and a column undergoing finite deformations. Com-parisons with fully implicit energy-preserving methodand the leapfrog scheme demonstrate that the pro-posed approach achieves superior accuracy while main-taining energy stability. Additionally, it enables largertime steps compared to explicit schemes and exhibitscomputational efficiency comparable to the leapfrogmethod.<br /
Une nouvelle approche au problème des valeurs propres pour l'opérateur de Monge-Ampère
No full textWe study the eigenvalue problem for the complex Monge-Ampère operator in bounded hyperconvex domains in C^n , where the right-hand side is a non-pluripolar positive Borel measure. We establish the uniqueness of eigenfunctions in the finite energy class introduced by Cegrell, up to positive multiplicative constants, and provide a Rayleigh quotient type formula for computing the eigenvalue. Under a natural continuity assumption on the measure, we further show that both the eigenvalue and eigenfunctions can be obtained via an iterative procedure starting from any negative finite energy function. Our approach relies on the fine properties of plurisubharmonic envelopes, which allow a partial sublinearization of the nonlinear problem. As far as we know, this method is new, even in the linear case, and not only yields new results but also significantly simplifies existing arguments in the literature. Moreover, it extends naturally to the setting of complex Hessian operators. Finally, by translating our results from the complex Monge-Ampère setting via a logarithmic transformation, we also obtain several interesting analogues for the real Monge-Ampère operator.Nous étudions le problème des valeurs propres pour l'opérateur complexe de Monge-Ampère dans les domaines hyperconvexes bornés en C^n , où le membre droite est une mesure de Borel positive non multipolaire. Nous établissons l'unicité des fonctions propres dans la classe d'énergie finie introduite par Cegrell, à constantes multiplicatives positives près, et fournissons une formule de type quotient de Rayleigh pour le calcul de la valeur propre. Sous une hypothèse de continuité naturelle sur la mesure, nous montrons en outre que la valeur propre et les fonctions propres peuvent être obtenues par une procédure itérative à partir de toute fonction d'énergie finie négative. Notre approche s'appuie sur les propriétés fines des enveloppes plurisubharmoniques, qui permettent une sous-linéarisation partielle du problème non linéaire. À notre connaissance, cette méthode est nouvelle, même dans le cas linéaire, et non seulement produit de nouveaux résultats, mais simplifie aussi considérablement les arguments existants dans la littérature. De plus, il s'étend naturellement au cadre des opérateurs hessiens complexes. Enfin, en traduisant nos résultats du cadre complexe de Monge-Ampère via une transformation logarithmique, nous obtenons également plusieurs analogues intéressants pour le véritable opérateur de Monge-Ampère
Définition d'un essai de matage dans une structure bi-composant composite/métal.
No full textInternational audienceDecarbonization of transports represents a key action for reducing carbon emissions. Therefore, solutions for lightweight rail infrastructures in composite materials are investigated. During the design stage, a structural issue about a composite/metal bi-component happened. An experimental set-up was set up to study the diffusion of bearing stresses in this structure. Five material configurations were studied. Parts in 0/90 fabric, biaxial braid and triaxial braid, glass and basalt fibers, Elium® thermoplastic and Epoxy thermoset resin were studied. Loads from 10 to 70 kN were applied to the samples using an indenter. Finally, an X-ray tomography analysis is used to identify damage phenomena in the composite.Décarboner le transport humain et matériel représente un levier important pour la réduction des émissions de C02. Dans cet objectif, le développement de nouvelles infrastructures ferroviaires en matériaux composites adaptées à des trains légers est étudié. Lors de la conception de ces équipements, une problématique structurelle sur un bi-composant composite/métal est soulevée. Afin d'étudier la diffusion des contraintes de matage dans une telle structure, un montage expérimental est mis en place. Cinq configurations matériaux différentes sont étudiées, comprenant des parties en tissu 0/90, en tresse biaxiale et triaxiale. Des fibres de verre et de basalte ainsi qu'une résine thermoplastique Elium ® et thermodurcissable Epoxy sont étudiées. Des charges de 10 à 70 kN sont appliquées sur les échantillons par l'intermédiaire d'un indenteur. Enfin, une analyse par tomographie RX est utilisée afin d'identifier les phénomènes d'endommagement du composite
Revealing the Fe doping effect on Ni catalysts for low alkalinity OER: from three-electrode systems to continuous flow anion exchange membrane water electrolyser
No full textInternational audienceHere, we report the use of magnetic induction heating as a rapid and efficient synthesis method to produce Fe@Ni nanoparticles (NPs) with tunable surface coverage and their application as catalysts in the oxygen evolution reaction (OER). This approach enables localized thermal decomposition of precursors, offering improved control over catalyst phase formation. To bridge the gap between lab-scale materials and practical electrolyser integration, the catalysts were deposited onto commercially available Ni-mesh supports suitable for Anion Exchange Membrane Water Electrolyser (AEMWE) operation. The influence of iron content on OER activity was evaluated, and the catalyst performance was validated in a full-cell electrolyser, highlighting the potential of this synthesis route for scalable green hydrogen technologies.</div
IA : comment les grands modèles de langage peuvent devenir des super méchants… entre de mauvaises mains
No full text[VULGARISATION SCIENTIFIQUE]Avec l’arrivée des grands modèles de langage (LLM), les attaques informatiques se multiplient. Il est essentiel de se préparer à ces LLM entraînés pour être malveillants, car ils permettent d’automatiser le cybercrime. En mai, un LLM a découvert une faille de sécurité dans un protocole très utilisé… pour lequel on pensait que les failles les plus graves avaient déjà été décelées et réparées.Pour rendre un LLM malveillant, les pirates détournent les techniques d'apprentissage à la base de ces outils d'IA et contournent les garde-fous mis en place par les développeurs.Avec l’arrivée des grands modèles de langage (LLM), les attaques informatiques se multiplient. Il est essentiel de se préparer à ces LLM entraînés pour être malveillants, car ils permettent d’automatiser le cybercrime. En mai, un LLM a découvert une faille de sécurité dans un protocole très utilisé… pour lequel on pensait que les failles les plus graves avaient déjà été décelées et réparées.Pour rendre un LLM malveillant, les pirates détournent les techniques d'apprentissage à la base de ces outils d'IA et contournent les garde-fous mis en place par les développeurs
Unexpected softening in helical compression springs: Experimental Characterization and numerical modeling of longitudinal wire cracks
No full textInternational audienceCylindrical helical compression springs were experimentally found to exhibit significant softening — up to 40% loss in stiffness — despite having passed all conventional quality control procedures, including tensile tests, chemical analysis, wire and spring coiling trials, and visual inspections. Unlike documented failure modes that typically involve wire rupture under static or fatigue loading, these springs remained intact, making the anomaly difficult to identify. A multi-technique investigation combining optical and electron microscopy, dye penetrant testing, eddy current inspection, and X-ray tomography revealed a continuous longitudinal crack along the wire. This axial defect, introduced during wire drawing, had a depth close to the wire radius and a sub-micrometric width, placing it at the edge of detectability. Numerical simulations confirmed that such cracks do not affect the wire’s response in tensile or bending loading — explaining why traditional inspections failed — but significantly reduce torsional stiffness. Analytical models from the literature were compared with simulations; some were validated, and a simplified model was proposed. The role of torsional warping in setting the softening limit was also clarified. Finally, a parametric study on crack positioning along the wire’s circumference showed that while overall stiffness was only slightly affected, internal stress flow was notably disrupted when the crack lay on highly stressed fibers. This study is the first to report and explain the mechanical effects of longitudinal cracking in compression springs. The findings offer practical insights for improving defect detection and mechanical prediction in drawn wire products
MODULE COTANGENT RELATIF
No full textFor any object x in a category C it is possible to define the category of Beck modules over x as the category Ab(C/x) of abelian group objects in the category C/x. We can deduce from this construction, at least for any locally presentable category, the notion of cotangent module or module of differentials Ωx of x in Ab(C/x).In the case of the category Algk of commutative k-algebras over a ring k, the category of Beck modules Ab(Algk/A) over a k-algebra A is equivalent to the category ModA of A-modules and the cotangent module is equal to the module of Kähler differentials of A.The aim of this article is to prove for any locally presentable category some results which generalize the classical properties of modules of Kähler differentials.Pour tout objet x dans une catégorie C il est possible de définir la catégorie des modules de Beck au dessus de x, comme la catégorie Ab(C /x) des objets en groupe abélien de la catégorie C /x. Nous pouvons en déduire, au moins pour toute catégorie localement présentable, la notion de module cotangent ou de module des différentielles Ωx de x dans Ab(C /x). Dans le cas de la catégorie Alg k des k-algèbres commutatives au-dessus d'un anneau k, la catégorie des modules de Beck Ab(Alg k /A) au-dessus d'une k-algèbre A est équivalente à la catégorie Mod A des A-modules et le module des différentielles est égal au module des différentielles de Kähler de A. Le but de cet article est de montrer pour toute catégorie localement présentable des résultats qui généralisent les propriétés classiques des modules des différentielles de Kähler
Dibenzothiophene S-Oxide Molecules investigated on metallic and insulating substrates by LT-SPM
No full textInternational audienceDue to their rich in-solution chemistry, sulfoxide derivatives are promising reagents for the development of new chemical tools for on-surface synthesis. Among them, dibenzothiophene S-oxide (DBTO) is known to undergo S=O bond cleavage under UV irradiation in the solvent.[1] This following work provides a comprehensive analysis of these compounds on metallic and insulating surfaces.First the molecules were deposited on Au(111) surface. Non-contact AFM intramolecular imaging of an isolated molecule with a CO-functionalized tip at 9.8 K allows identification of its configuration adsorption (Fig.1a), which is later confirmed by X-ray standing wave photoemission spectroscopy and DFT calculations. A thermal analysis of these molecules' behavior on Au(111) at different temperatures ̶ from the supramolecular regime to the Ullmann polymerization reaction (Fig.1b), passing by the deoxygenation ̶ was also carried out by combining SPM and XPS observations.The supramolecular phase of molecules was then investigated upon deposition on two mono-layers of NaCl/Au(111) under illumination (UV 280 nm) (Fig.1c). Successful deoxygenation of the molecules was put in evidence by statistical analysis of high-resolution images. The deoxygenation rate increases with time and reaches a plateau after six hours of illumination, at which point approximately 40% of the molecules were deoxygenated. Structural characterization was further completed by bias spectroscopies acquired on a statistical set of pristine/deoxygenated molecules. Deoxygenated molecules exhibit increased contact potential difference (CPD), indicating a more negative charge state at the sulfur atom, consistent with the loss of oxygen.[2]References[1]Mrinmoy Nag and William S. Jenks, J. Org. Chem. 70 (9), 3458-3463 (2005).[2]Mélissa Hankache et al., Nature Comm. 16, 4841 (2025)
Photoinduced Modulation of the Oxidation State of Dibenzothiophene S-Oxide Molecules on an Insulating Substrate
No full textInternational audienceDue to their rich in-solution chemistry, sulfoxide derivatives are promising reagents for the development of new chemical tools for on-surface synthesis. Among them, dibenzothiophene S-oxide (DBTO) is known to undergo S=O bond cleavage under UV irradiation in the solvent [1], along with the generation of dibenzothiophene and atomic triplet oxygen O(3P). This study provides evidence of on-surface deoxygenation of a dibrominated sulfoxide derivative (ortho-Br)2-DBTO under UV irradiation [2]. Therefore, it proves that chemical transformations of small molecules can be transposed from diluted solutions to surfaces.The molecules were first deposited on the Au(111) surface. Non-contact AFM intramolecular imaging of an isolated molecule with a CO-functionalized tip at 9.8 K allows identification of its configuration adsorption (Fig.1), which is confirmed by X-ray standing wave photoemission spectroscopy and DFT calculations.The behavior of a supramolecular phase of molecules adsorbed on two mono-layers of NaCl / Au(111) under illumination (UV 280 nm) was then investigated. Successful deoxygenation of the molecules was put in evidence by statistical analysis of high-resolution images. The deoxygenation rate increases with time and reaches a plateau after six hours of illumination. Then, 40% of molecules are deoxygenated (Fig.2a). The structural characterization is completed by bias spectroscopies acquired on a statistical set of pristine/deoxygenated molecules, both in a grid mode and directly on top of the S atom of several molecules. Deoxygenated molecules exhibit increased contact potential difference (CPD), pointing towards a less positive partial charge of the S atom, consistently with a deoxygenated state (Fig.2b)
Unit inclusion in a non-semisimple braided tensor category and non-compact relative TQFTs
No full text35 pages. To appear in Geometry&TopologyInternational audienceThe inclusion of the unit in a braided tensor category V induces a 1-morphism in the Morita 4-category of braided tensor categories BrTens. We give criteria for the dualizability of this morphism.When V is a semisimple (resp. nonsemisimple) modular category, we show that the unit inclusion induces, under the cobordism hypothesis, a (resp. noncompact) relative 3-dimensional topological quantum field theory. Following Jordan, Reutter and Safronov, we conjecture that these relative field theories together with their bulk theories recover Witten–Reshetikhin–Turaev (resp. De Renzi–Gainutdinov–Geer–Patureau-Mirand–Runkel) theories, in a fully extended setting. In particular, we argue that these theories can be obtained by the cobordism hypothesis