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Damage created by abrasive waterjet and conventional drilling in open-hole and assembled 3D interlock woven carbon fiber-reinforced plastic composites examined by fatigue testing and linear regression analysis
No full textInternational audienc
4-port Microwave sensor and electrical model for 3D object mapping
No full textInternational audienceThe characterization of biological objects with microwave spectroscopy is getting increasing interests, as it is label-free and noninvasive. To perform their analysis, 2-port sensors are present in the literature, enabling only partial investigations of 3D biological samples, without taking their structural heterogeneity into account. Within this context, a 4-port microwave-based biosensor dedicated to microtissue characterization is proposed, in order to extend the sensing capabilities of microwave dielectric spectroscopy and provide electrical responses of 3D biological models subdivisions. An electrical model suitable for such a multiport device is established to extract the characteristics of the different sections of the 3D entity. The modeling methodology exploits the symmetry of the microwave component, while applying a common and differential modes approach derived from the measured 4 ports scattering parameters. After the mathematical validation of this approach, different elementary models are evaluated. Ethanol-based aqueous solutions are first used for their homogeneity within the fluidic channel. Polystyrene beads exhibiting two different diameter sizes are then numerically and experimentally investigated due to their 3D configuration and their uniform and known permittivity. This study demonstrates that the 4-port sensor and associated electrical model enable to consider electrical subdivisions of the 3D entity under test, based on the localization of the object on the different microwave electrodes. This constitutes the first step toward the analyses of complex and heterogeneous 3D biological models such as microtissues
Shock-induced evolution: Tracing the fate of coronene in astrophysical environments
No full textInternational audiencePolyclic aromatic hydrocarbons (PAHs) are considered ubiquitous in the interstellar medium. There is now solid evidence for their presence. The mechanisms that lead to their formation and their destruction, remain debated, however. Of the processes that drive their evolution, the shock-induced alteration of PAHs has received little attention. Our objective is to explore the gaseous volatiles and solid residues generated by shock-processing of coronene C_24H_12, which is a prototypical compact PAH with seven aromatic rings. A pressure-driven shock tube was employed to sublimate and heat coronene up to 4000,K. The time evolution of the shock products was probed in situ by optical emission spectroscopy on a microsecond timescale. Solid residues were collected and analyzed ex situ by a variety of methods, including infrared microspectroscopy, Raman spectroscopy, X-ray diffraction, transmission electron microscopy, and laser desorption laser ionization mass spectrometry. The experiments were supported by molecular dynamics (MD) simulations. The experiments revealed a dominant dehydrogenation pathway for coronene under shock conditions. In situ spectroscopy confirmed the presence of C_2 radicals and a broad continuum emission attributed to large carbon clusters (C_n) and small, weakly hydrogenated hydrocarbons (C_nH_x). The ex situ analysis of solid residues indicates the formation of graphitic and graphenic nanostructures, including carbon nano-onions, nanotubes, and nanoribbons in the cooling phase . Laser desorption laser ionization mass spectrometry analysis validates the carbonization of the shock products, while MD simulations support the dehydrogenation and fragmentation processes of the rapid-heating phase. Shock waves drive the transformation of PAHs into small hydrocarbons and carbon clusters that recombine in the cooling phase into graphene-like structures. This affects the carbon life cycle of the interstellar medium. The identification of C_nH_x species as potential carriers of the broad green emission seen in the laboratory suggests a possible link to the łambda5450 diffuse interstellar band. This study underscores the value of shock tubes as a tool for simulating astrophysical environments and investigating the chemical evolution of large molecules and small particles in space
Impact of protein fining agents and bentonite on rotundone concentration in red wine made from <i>Vitis vinifera</i> L. cv. Tardif
No full textInternational audienceRotundone, the main aroma compound responsible for peppery notes in red wine, has a strong affinity with solids and may be affected by wine fining. This work aimed to study the impact of several fining agents on this compound using a red wine made from Tardif. Egg albumin, gelatine, vegetable protein (pea protein) and sodium bentonite were investigated at the same dosage (D1, 20 g/hL) to compare their effect under similar conditions and at a second dosage, which corresponds, depending on the agents, either to half of D1 or twice D1 to reflect more common winemaking practices. Overall, the fining agents had a minor, although significant effect on rotundone, with the greatest impact, which might not be detectable sensorily speaking, observed for vegetable protein (pea protein) used at 40 g/hL (–12.1 %). At D1, although not statistically different from gelatine and vegetable protein (pea protein), egg albumin induced the largest decrease in rotundone, which could be attributable to its higher surface charge density. A correlation (R2 = 0.85) was noticed between mean values of rotundone concentrations (3 replicates) and A620, suggesting that this proxy can be used to predict the impact of fining on rotundone in Tardif red wines. Though further work is necessary to investigate the impact of additional fining agents and to better understand the mechanisms involved, notably using computational chemistry, our results encourage winemakers to use fining agents in their wine if required, without having to fear excessive rotundone losses
Spin-polaron fingerprints in the optical conductivity of iridates
No full textAs a consequence of their spin-orbit entangled ground state, many iridate materials display a peculiar double peak structure in optical transport quantities, such as absorption and conductivity. Their common interpretation is based on the presence of Hubbard subbands in the half-filled manifold. Herein, we challenge this picture, proposing a scenario based on the presence of spin-polaron (SP) quasiparticles, and assigning a dominant SP character to the first peak. We illustrate it by taking the materials BaIrO and SrIrO as paradigmatic examples, which we investigate within the dynamical mean-field theory and the self-consistent Born approximation. Both theories reproduce nontrivial features revealed by angle-resolved photoemission spectroscopy and optical transport measurements, supporting our interpretation. In the case of SrIrO, we show how the SP scenario survives in the low-doped regime. Similar optical transport fingerprints are expected to be found in the wider class of iridates and more generally in strongly correlated antiferromagnetic regimes, such as those found in cuprates
Sequential Conformal Risk Control for Safe Railway Signaling Detection
No full textInternational audienceAs machine learning becomes a more common tool in industry, its needs for certification increase. Conformal Prediction (Vovk et al., 2005), a framework for construction of prediction sets with tight coverage guarantees at any desired error rate, is an ideal tool for this purpose. However, adapting conformal methods to complex computer vision pipelines and providing appropriate guarantees is still a challenging task. Indeed, conformal approaches to object detection are often restricted to subtasks: often localization, and sometimes classification. In this study, we apply the comprehensive framework from Andéol et al. (2025) to the safety-critical task of railway signaling detection
Algorithmic curation of News on YouTube: Evidence from the 2022 French Presidential Campaign
No full textDebate is growing over how algorithmic recommendations influence news visibility, particularly regarding interest and ideological bias. This study examines YouTube's News Recommender System (NRS), focusing on the French "News" section of the homepage through a large-scale audit using automated browsing agents.Our findings show that the NRS prioritises platform-native creators over established news outlets, favouring content that aligns with YouTube's features rather than traditional editorial standards. Politically charged, opinion-based videos, especially those from prominent figures affiliated with extreme political parties, receive ongoing algorithmic promotion. While centrist and moderate political figures remain underrepresented, the algorithm boosts their visibility once users interact with this type of content. This two-part mechanism, which amplifies already prominent content and appears to overcompensate for rare content, does not just reflect engagement-based optimisation, but is driven by the algorithm's tendency to maintain coherence in a highly unbalanced content landscape. However, this compensatory logic does not counteract the algorithm's broader tendency to promote content from radical political figures while marginalising institutional news outlets. Through this process, the NRS actively reshapes news exposure within the "News" section, privileging political expression over journalistic authority and reproducing structural hierarchies of visibility
A modified Crank-Nicolson scheme for the Vlasov-Poisson system with a strong external magnetic field
No full textWe propose and study a Particle-In-Cell (PIC) method based on the Crank-Nicolson time discretization for the Vlasov-Poisson system with a strong and inhomogeneous external magnetic field with fixed direction, where we focus on the motion of particles in the plane orthogonal to the magnetic field. In this regime, the time step can be subject to stability constraints related to the smallness of Larmor radius and plasma frequency [21]. To avoid this limitation, our approach is based on numerical schemes [9, 10, 12], providing a consistent PIC discretization of the guiding-center system taking into account variations of the magnetic field.We carry out some theoretical proofs and perform several numerical experiments to validate the method and its underlying concepts.</p
Modélisation numérique d’un instrument à vent réel et confrontation à la mesure expérimentale
No full textWind instruments making has long relied on traditional craftsmanship, associated with an empirical knowledge of the mechanics that govern their functioning. Although the latter involves many coupled physical phenomena, it is mainly modelled by a purely acoustic approach based on the impedance at the input of the instrument. To access this quantity, the use of exclusively numerical methods is currently limited, either by the accuracy - semi-analytical models - which does not meet the requirements of professional musicians, or by the computational time - highly predictive models based on the numerical resolution of partial differential equations - which are not compatible with industrial time-to-market , because of the multi-resolution context. This work proposes two levels of model reduction for the 3D finite element simulation (FEM) of the Helmholtz problem, which allow to integrate the fine geometric details of the complex air column designed by the maker, with limited computational costs (time and memory). The first level is based on the reduction of the studied domain by static condensation, combined with parallel and distributed modelling and resolution strategies, combining frequency interpolation and low-rank approximations for the storage of Schur complements. The second level is based on a non-invasive Free Form Deformation (FFD) method, based on B-Splines functions, which allows to restricted the analysis to be a regular subspace of the finite element approximation space, significantly reducing the number of degrees of freedom in the problem. This reduced 3D FEM-FFD modelling offers an overall cost saving in computational time of at least two orders of magnitude compared to a standard 3D FEM approach, and is validated by comparison with experimental measurements. As part of a modelling approach for the real instrument, the influence of the thermodynamic aspects of the playing was investigated experimentally, and an impedance measurement setup was specifically designed to allow acquisitions under controlled flow and temperature conditions. Finally, a image-based model based on tomographic data was proposed to analyse the influence of metallurgical operations on geometric and surface defects.La facture des instruments de musique à vent a longtemps reposé sur le savoir-faire artisanal, associé à une connais- sance empirique de la mécanique qui en régit le fonctionnement. Si ce dernier implique de nombreux phénomènes physiques couplés, il est principalement modélisé par une approche purement acoustique basée sur l’impédance à l’entrée de l’instrument. Pour accéder à cette quantité, l’utilisation des méthodes exclusivement numériques est actuellement limitée, soit par leur précision — modèles semi-analytiques — qui ne satisfait pas les exigences des musiciens professionnels, soit par leurs temps de calcul — modèles hautement prédictifs basés sur la résolution nu- mérique des équations aux dérivées partielles — qui, en raison du contexte multi-résolution, ne sont pas compatibles avec les délais industriels. Ce travail propose deux niveaux de réduction de modèle pour la simulation par éléments finis (FEM) 3D du problème de Helmholtz non-convecté, qui permettent au facteur d’intégrer les fins détails géomé- triques de la perce complexe de ses objets, pour des coûts de calcul (temps et mémoire) limités. Le premier niveau s’appuie sur la réduction du domaine d’étude par condensation statique, associée à des stratégies de modélisation et de résolution parallèle et distribuée, combinant interpolation fréquentielle et approximations de faible rang pour le stockage des compléments de Schur. Le second niveau repose sur une méthode de Free Form Deformation (FFD), non-intrusive, basée sur des fonctions B-Splines, qui permet de restreindre l’analyse à un sous-espace régulier de l’espace d’approximation des éléments finis et donc de réduire considérablement le nombre de degrés de liberté du problème. Cette modélisation FEM-FFD 3D réduite est validée par comparaison à la mesure expérimentale et offre un gain total d’au moins deux ordres de grandeur sur les temps de calcul comparativement à une approche FEM 3D standard. Dans une démarche de modélisation de l’instrument réel, l’influence des conditions thermodynamiques du jeu a été investiguée expérimentalement et un pont d’impédance permettant des acquisitions sous écoulement, de dé- bit et température contrôlés, a été spécifiquement développé. Pour analyser l’influence des opérations métallurgiques sur les défauts géométriques et de surface, une modélisation basée sur les images tomographiques est finalement proposée