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Influence du vieillissement sur les performances en étanchéité de joints toriques élastomères
No full textThis study focuses on the sealing performance of elastomeric O-rings and the influence of thermo-oxidative aging on the evolution of their performance. It specifically aims to examine traditional aging study methods and propose new approaches. Aging analysis methods using tracer monitoring are implemented on industrial EPDM. Classical time-temperature equivalence methods are applied, and sealing tests are conducted on aged seals to establish a link with the tracers. A numerical modeling approach is proposed with an initial hypothesis on the homogeneity of the material. The Bergström-Boyce viscoelastic model is used to create a database of behavior law parameters for different aging conditions. The numerical model is then compared to leakage measurements after establishing a relevant performance criterion. The final part is dedicated to studying the gradients of mechanical properties induced by thermo-oxidative aging. A robust nanoindentation protocol is developed and implemented to characterize the gradients on aged seals. A simplified approach to identifying behavior law parameters is adopted, and a numerical simulation model of seals incorporating property heterogeneity is proposed. This model is then compared to homogeneous seal simulations to estimate the criticality of the gradients for the application.Cette étude porte sur l’étanchéité par joint torique élastomère et l’influence du vieillissement thermo-oxydatif sur l’évolution des performances. Elle consiste plus particulièrement à étudier des démarches classiques d’étude du vieillissement et à proposer des approches nouvelles. Les démarches d’analyse du vieillissement par le suivi de traceurs sont mises en place sur un EPDM industriel. Des méthodes classiques d’équivalence temps-température sont appliquées et des contrôles d’étanchéité sont réalisés sur des joints vieillis afin d’établir un lien avec les traceurs. Une approche de modélisation numérique est proposée avec une première hypothèse sur l’homogénéité du matériau. Le modèle viscoélastique de Bergström-Boyce est utilisé afin de constituer une base de données de paramètres de loi de comportement pour différentes conditions vieillissement. Le modèle numérique est ensuite confronté aux mesures de fuite après avoir établi un critère de performance pertinent. Une dernière partie est dédiée à l’étude des gradients de propriétés mécaniques induits par le vieillissement thermo-oxydatif. Un protocole robuste de nanoindentation est développé et mis en oeuvre afin de caractériser les gradients sur des joints vieillis. Une approche simplifiée d’identification de paramètres de loi de comportement est adoptée et un modèle de simulation numériques de joints intégrant l’hétérogénéité de propriétés est proposé. Ce modèle est ensuite confronté aux simulations homogènes de joints afin d’estimer la criticité des gradients pour l’application
Electrical Activity in Arithmetic Operations vs Security
No full textInternational audienceElectrical activity in circuits, including processors running codes, partly comes from transitions of signals used during arithmetic operations. Some side channel attacks can analyze this activity to deduce internal information. The talk will present some links between arithmetic algorithms, representations of numbers, circuit architecture and information leakage
Etudes semi-analytiques et numériques d'une plaque rigide unidimensionnelle soumise à une explosion sous-marine avec prise en compte de la cavitation
No full textInternational audienceEtudes semi-analytiques et numériques d'une plaque rigide unidimensionnelle soumise à une explosion sous-marine avec prise en compte de la cavitatio
A 4 foils hydrofoiler regulation solution and experiments
No full textInternational audienceThis paper introduces the Black Pearl, a novel 4-foil electric hydrofoiler, by presenting its design, control structure, and experimental findings. The innovative aspect of our approach lies in the redundant design of the sustentation structure, which utilizes four independent foils to control three degrees of freedom: roll, pitch, and altitude above the water. This redundancy improves actuation efficiency, significantly reducing the risk of actuation saturation. Moreover, the explicit management of this redundancy ensures robust actuation performance, even in scenarios where one foil becomes locked at a fixed angle. The paper also presents experimental trials conducted on the Black Pearl prototype, as well as the proposal and simulation testing of novel guidance laws designed to enhance the hydrofoiler's flight performance
Un cadre paraconsistant pour l'évaluation de similarité dans les bases de connaissances
No full textInternational audienceThis article proposes a paraconsistent framework for evaluating similarity in knowledge bases. Unlike classical approaches, this framework explicitly integrates contradictions, enabling a more robust and interpretable similarity measure. A new measure is introduced, which penalizes inconsistencies while rewarding shared properties. Paraconsistent super-categories are defined to hierarchically organize knowledge entities. The model also includes a contradiction extractor and a repair mechanism, ensuring consistency in the evaluations. Theoretical results guarantee reflexivity, symmetry, and boundedness of . This approach offers a promising solution for managing conflicting knowledge, with perspectives in multi-agent systems.Cet article propose un cadre paraconsistant pour l'évaluation de la similarité dans les bases de connaissances. Contrairement aux approches classiques, ce cadre intègre explicitement les contradictions, permettant une mesure de similarité plus robuste et interprétable. Une nouvelle mesure S * est introduite, pénalisant les incohérences tout en valorisant les propriétés partagées. Des super-catégories paraconsistantes Ξ * K sont définies pour organiser hiérarchiquement les entités de connaissances. Le modèle inclut également un extracteur de contradictions E et un mécanisme de réparation, garantissant la cohérence des évaluations. Les résultats théoriques assurent la réflexivité, la symétrie et les bornes de S * . Cette approche offre une solution prometteuse pour la gestion des connaissances conflictuelles, avec des perspectives dans les systèmes multiagent
Split-step framelet: leveraging wavelet frames for tropospheric long-range propagation
No full textInternational audienceModeling electromagnetic wave propagation over long distances is crucial for radar systems and navigation applications. This work introduces a split-step method based on wavelet frames to model tropospheric long-range propagation. This approach capitalizes on a fully wavelet-towavelet framework, designed to enhance computational efficiency, accuracy, and ease of implementation on GPUs. Numerical experiments demonstrate the effectiveness and advantages of the proposed method
Modelling the influence of environmental factors on the acoustic presence of blue whale populations in the southern Indian Ocean
No full textInternational audienceBlue whales in the Indian Ocean have been severely depleted by previous extensive commercial whaling. A good understanding of their spatio-temporal distribution is crucial for conservation. The songs of three blue whale acoustic populations - Antarctic blue whales (Balaenoptera musculus intermedia, ANT BW) and pygmy blue whales (B. musculus brevicauda) from the Southeast (SEIO PBW) and Southwest Indian Ocean (SWIO PBW) - were analyzed using 13 years of passive acoustic recordings from 10 sites in the southwest Indian Ocean. Although blue whale vocalizations comprise both songs and non-song calls (e.g., D-calls), the present study concentrates on the examination of songs. Generalized additive models (GAMs) were used to relate acoustic presence, measured by the number of positive minutes per day (averaged weekly), to environmental drivers such as sea surface temperature (SST), chlorophyll-a concentrations, and sea ice extent. These models allowed predictions of blue whale acoustic presence across the region. Empirical orthogonal functions (EOFs) were applied for dimensionality reduction to identify key habitats, including the Kerguelen Plateau and Madagascar Basin, which may serve as important feeding and resting zones based on acoustic presence and environmental data. Antarctic blue whales were predominantly detected in austral winter and spring, associated with lower SST and higher chlorophyll-a. In contrast, SEIO and SWIO pygmy blue whales were more frequent in summer and autumn, with some overlap suggesting ecological interactions. These findings lay the groundwork for targeted conservation efforts to protect critical blue whale habitats in a rapidly changing ocean
Diaphragmatic Breathing Guidance Using a Humanoid Robot with a Soft Robotic Haptic Interface for Anxiety Reduction
No full textInternational audienc
On the breathing of spectral bands in periodic quantum waveguides with inflating resonators
No full textInternational audienceWe are interested in the lower part of the spectrum of the Dirichlet Laplacian A^ε in a thin waveguide Π^ε obtained by repeating periodically a pattern, itself constructed by scaling an inner field geometry Ω by a small factor ε > 0. The Floquet-Bloch theory ensures that the spectrum of A^ε has a band-gap structure. Due to the Dirichlet boundary conditions, these bands all move to +∞ as O(ε^{-2}) when ε → 0^+. Concerning their widths, applying techniques of dimension reduction, we show that the results depend on the dimension of the so-called space of almost standing waves in Ω that we denote by X_†. Generically, i.e. for most Ω, there holds X_† = {0} and the lower part of the spectrum of A^ε is very sparse, made of bands of length at most O(ε) as ε → 0^+. For certain Ω however, we have dim X_† = 1 and then there are bands of length O(1) which allow for wave propagation in Π^ε. The main originality of this work lies in the study of the behaviour of the spectral bands when perturbing Ω around a particular Ω_⋆ where dim X_† = 1. We show a breathing phenomenon for the spectrum of A^ε : when inflating Ω around Ω_⋆ , the spectral bands rapidly expand before shrinking. In the process, a band dives below the normalized threshold π^2 /ε^2 , stops breathing and becomes extremely short as Ω continues to inflate
Not all sub-Riemannian minimizing geodesics are smooth
No full textA longstanding open question in sub-Riemannian geometry is the following: are sub-Riemannian length minimizers smooth? We give a negative answer to this question, exhibiting an example of a C 2 but not C 3 length-minimizer of a real-analytic (even polynomial) sub-Riemannian structure