Archive ouverte de Centrale Lyon
Not a member yet
32420 research outputs found
Sort by
AI-assisted identification of nonmelanoma skin cancer structures based on combined line-field confocal optical coherence tomography and confocal Raman microspectroscopy
No full textInternational audienceSignificance: Morpho-chemical characterization of skin cancers provides valuable insights for early diagnosis, classification, and treatment response assessment.Aim: We introduce a compact, noninvasive system combining high-resolution morphological imaging and chemical characterization of skin tissues. The system integrates line-field confocal optical coherence tomography for cellular-level imaging and confocal Raman microspectroscopy to analyze the chemical composition of specific targets identified within the morphological images.Approach: We present results obtained from the system installed in a clinical setting over the course of 1 year. More than 330 nonmelanoma skin cancer specimens were imaged ex vivo, with different structures targeted for Raman microspectroscopy, resulting in over 1300 spectral acquisitions. To evaluate the system's ability to accurately identify cancerous structures, an artificial intelligence model was trained on the spectral data.Results:The model demonstrated high classification performance, achieving an area under the ROC curve of 0.95 for basal cell carcinoma structures and 0.92 when including structures from both basal and squamous cell carcinomas.Conclusions: Spectral attention scores derived from Raman data revealed key chemical differences among the various cancerous structures, offering deeper insights into their composition
Influence of eddies-waves interactions on structure functions in 2D stably stratified turbulence
No full textInternational audienc
Analyse multi-échelle d'un élément de paroi biosourcé mécaniquement renforcé
No full textThe building sector is a crucial lever in the ecological transition. It significantly contributes to the exploitation of natural resources, energy consumption, and CO₂ emissions. To mitigate this impact, it is essential to move toward more sustainable solutions and prioritize materials with a low environmental footprint. The use of bio-based materials, such as hempcrete, represents a relevant alternative for certain applications, particularly due to its hygrothermal properties, which help reduce energy needs while ensuring good occupant comfort.In this context, the research work presented in this thesis aims to develop a self-supporting wall element, mechanically reinforced, using hempcrete formulated with a lime-based binder and hemp shiv serving as insulation, coupled with a mineral-based composite (Textile Reinforced Cement, TRC). The resulting compound is designated by the acronym BTC-TRC.The first part of this work involved studying and characterizing hempcrete at the material scale, with the goal of improving its mechanical performance. To this end, particular attention was paid to the influence of surface treatment and particle size of the hemp shiv. Two treatment approaches were explored and analyzed: an alkaline treatment with caustic soda (NaOH) applied to coarse hemp shiv, and a treatment with a bio-based epoxy resin applied to both coarse and fine shiv. The physicochemical effects induced by these treatments on the hemp particles were investigated. The mechanical, hygric, and thermal performances of the different formulations were compared, and the relevance of these enhancement strategies was discussed.The second part of the study focused on the uniaxial tensile behavior of TRC composites composed of a matrix that remains relatively uncommon in the scientific literature (lime-based). Beyond identifying the impact of key factors governing the performance of conventional TRCs (such as the nature and ratio of reinforcement and its impregnation), the addition of short fibers and the influence of sand substitution were analyzed and discussed, particularly in relation to the behavior of the textile-matrix interface.Finally, the performance assessment of BTC-TRC compounds (self-supporting panels) was carried out on a mechanical basis prior to validation under more realistic thermo-mechanical conditions. Although only partially representative of in-service conditions, the results obtained on small-scale panels highlight the potential of this concept both at the element scale and in terms of localized behavior. This reinforcement concept could thus open credible perspectives for integration at the building scale, provided that its thermal performance is further establishedLe secteur du bâtiment est un levier crucial dans la transition écologique. Il contribue fortement à l'exploitation des ressources naturelles, aux consommations d'énergie et aux émissions de CO₂. Pour limiter cet impact, il est essentiel de s'orienter vers des solutions plus durables et de privilégier des matériaux à faible impact environnemental. L'utilisation de matériaux biosourcés, tels que le béton de chanvre, constitue une alternative pertinente pour certaines applications notamment grâce à ses propriétés hygrothermiques, qui permettent de réduire les besoins énergétiques tout en assurant un bon confort des occupants.Dans ce contexte, le travail de recherche présenté dans cette thèse a pour objectif de développer un élément de paroi autoportant, mécaniquement renforcé mobilisant du béton de chanvre, formulé à partir d'un liant à base de chaux et de chènevottes, jouant le rôle d'isolant, couplé à un composite à base minérale (Textile Reinforced Cement, TRC). Le composé ainsi obtenu est désigné par l'acronyme BTC-TRC.Le premier volet de ce travail a consisté à étudier et caractériser, à l'échelle du matériau, le béton de chanvre avec pour finalité l'amélioration de ses performances mécaniques. Dans cette optique, l'attention s'est particulièrement focalisée sur l'incidence du traitement de surface et la granulométrie des chènevottes. Ainsi, deux approches de traitement ont été explorés et analysés : un traitement alcalin à la soude caustique (NaOH), appliqué aux chènevottes de grande taille, et un traitement par résine époxy d'origine végétale, appliquée aux chènevottes de grande et de petite dimension. Les effets physico-chimiques induits par ces traitements sur les chènevottes ont été exploré. Les performances mécaniques, hygriques et thermiques des différentes formulations ont pu être confrontées et l'intérêt du recours à ces leviers discutés.Le deuxième volet de ce travail a porté sur l'étude du comportement en traction uniaxiale des composites TRC, constitués d'une matrice peu usitée à ce stade dans la littérature scientifique (chaux). Ainsi, par-delà l'identification de l'impact de certains facteurs considérés pour majeurs dans la tenue des TRC traditionnels, (nature et taux de renfort, son imprégnation,) l'adjonction de fibres courtes et l'influence de la substitution du sable ont été analysées et discutées notamment à la lumière de la tenue de l'interface textile-matrice.En dernier lieu, l'évaluation performantielle de composés BTC-TRC (panneau autoportant) a été conduite sur une base mécanique préalable à une validation dans des conditions thermo-mécaniques plus réalistes. Bien que partiellement fidèles aux conditions d'exploitation les résultats obtenus sur la base de panneaux de petite échelle permettent de souligner les potentialités tant à l'échelle de l'élément qu'au regard du comportement plus localisé. Ainsi, ce concept de renforcement est susceptible de paver la voie à des perspectives crédibles pour son intégration à l'échelle du bâtiment sous réserve de performances thermiques à établir
Heterotopic energy for Sobolev mappings
No full textWe study the notion of heterotopic energy defined as the limit of Sobolev energies of Sobolev mappings in a given homotopy class approximating almost everywhere a given Sobolev mapping. We show that the heterotopic energy is finite if and only if the mappings in the corresponding homotopy classes are homotopic on a codimension one skeleton of a triangulation of the domain. When this is the case, the heterotopic energy of a mapping is the sum of its Sobolev energy and its disparity energy, defined as the minimum energy of a bubble to pass between these homotopy classes. At the more technical level, we rely on a framework that works when the target and domain manifolds are not simply connected and there is no canonical isomorphism between homotopy groups with different basepoints.</div
Electro-Optic Probe for Real Time and Vectorial Analysis of Partial Discharges and Breakdown
No full textInternational audienceThe comprehensive analysis of the processes involved in discharges requires theunderstanding of the associated electric field behavior. We here demonstrate thepotentialities of a pigtailed electro-optic (EO) probe to perform the experimentalassessment of the transients associated to discharges in several configurations. The EOprobe is entirely dielectric and millimeter sized, thus leading to very low invasivemeasurements and allowing near field analysis. Moreover, its frequency bandwidthexceeds several gigahertz and its measurement dynamics allows measurement from lessthan 1 V/m up to the breakdown field. All these properties make the EO probe suitablefor real time characterization of discharges.We firstly compare the temporal behavior of the field of corona and dielectric barrierdischarges, both induced by a AC voltage. In these configurations, the voltage isdelivered by a tuneable high voltage transformer ( in the 10kV range) and applied oncentimeter sized discharge configuration. Specific signatures of discharges have beenidentified and are compared to simultaneous measurements using a high frequencycurrent transformer and UHF antenna.The second experimental campaign concerns single shot artificial lightnings induced bythree lightning rods. The single pulsed voltage is delivered thanks to a Marx generator (1MV–50 kJ) and applied to an upper electrode consisting in a 2 m diameter circularplateau separated by 1m of air from the top of the lightning rod. The behavior of theelectric field at the top of the lightning rod is analyzed as a function of voltagemagnitude and polarity. Indeed, their non linear electric field generation with respectthe the applied voltage exhibit specific figures. Advantages and limitations ofthe vectorial EO probe, will be explained. A lot of experimental results, concerning verylocalized partial discharge as well as meter sized leader discharges, will be presentedduring the conference and will be analyzed.AcknowledgmentThis work has been supported financially within the program: France Relance. Authorswould like to thank the French ministry of higher education, research and innovation(MESRI), and the national research agency (ANR) for the support
Hybrid Ge/Sb 2 S 3 /SiGe waveguide for tunable Mid-IR supercontinuum generation
No full textInternational audienceWe demonstrate supercontinuum generation in the mid-IR using a hybrid Ge/Sb2S3/SiGe-on-Si waveguide. By changing the Sb2S3 state, we modify the waveguide's dispersion regime and therefore the properties of generated spectra
On a repulsion model with Coulomb interaction and nonlinear mobility
No full textWe study a scalar conservation law on the torus in which the flux j is composed of a Coulomb interaction and a nonlinear mobility: j = -u m ∇g * u. We prove existence of entropy solutions and a weak-strong uniqueness principle. We also prove several properties shared among entropy solutions, in particular a lower barrier in the fast diffusion regime m < 1. In the porous media regime m ≥ 1, we study the decreasing rearrangement of solutions, which allows to prove an instantaneous growth of the support and a waiting time phenomenon. We also show exponential convergence of the solutions towards the spatial average in several topologies.</div
Masures et théorie de Kazhdan-Lusztig affine pour les groupes de Kac-Moody
No full textWe explore the applications of twin masures in the development of an affine Kazhdan-Lusztig theory for Kac-Moody groups. Loop groups of Kac-Moody groups admit a partial Iwahori-Bruhat decomposition indexed by a semigroup W^a_+, called its affinized Weyl semigroup. This object is not a Coxeter group, but Braverman Kazhdan and Patnaik defined a partial order leq on W^a_+, which plays the role of a Bruhat order.The first part of this memoir is dedicated to the study of (W^a_+,leq). In particular, we prove that the integral length defined by Muthiah and Orr is a grading of (W^a_+,leq), and we give an explicit classification of the covering relations. In order to obtain several finiteness properties of (W^a_+,leq), we also completely classify quantum roots of general Kac-Moody root systems.In a second time, we present the building theoretic approach to the study of Kac-Moody groups and of the associated Schubert cells. We then generalize this approach to study affine Schubert cells, which live in loop groups of Kac-Moody groups, using the theory of twin masures. In particular, we construct a family of affine Kazhdan-Lusztig R-polynomials, indexed by pairs of comparable elements in W^a_+.Nous explorons les applications des masures jumelées au développement d'une théorie de Kazhdan-Lusztig affine pour les groupes de Kac-Moody. Les groupes de lacets des groupes de Kac-Moody admettent une décomposition de Iwahori-Bruhat partielle indexée par un semi-groupe W^a_+, appelé son semi-groupe de Weyl affinisé. Cet objet n'est pas un groupe de Coxeter, mais Braverman Kazhdan et Patnaik ont défini une relation d'ordre leq sur W^a_+ jouant un rôle analogue à l'ordre de Bruhat sur un groupe de Coxeter. La premère partie de ce mémoire est dédiée à l'étude combinatoire de (W^a_+,leq), et à sa comparaison avec la combinatoire des groupe de Coxeter. Nous montrons d'abord que la longueur entière introduite par Muthiah et Orr est une graduation du semi-groupe de Weyl affinisé, et nous obtenons une classification explicite des couvertures. Certaines racines du système de racines associé jouent un rôle particulier, les racines quantiques. Nous classifions les racines quantiques et nous en déduisons que tout système de racines, même infini, possède un nombre fini de racines quantiques. Nous utilisons ce résultat pour prouver certaines propriétés de finitude de l'ordre de Bruhat affinisé, en particulier que chaque élément admet un nombre fini de couvertures, et que les intervalles sont toujours finis.Dans un second temps, nous présentons une approche immobilière à l'étude des groupes de Kac-Moody et aux cellules de Schubert associées. Grâce aux masures jumelées introduites par Bardy-Panse, Hébert et Rousseau nous généralisons cette approche pour étudier les cellules de Schubert affines, qui vivent dans les groupes de lacets des groupes de Kac-Moody. En particulier, nous construisons une famille de polynômes R de Kazhdan-Lusztig affine, indexés par les paires d'éléments comparables dans W^a_+. Nous établissons ensuite plusieurs relations entre ces polynômes R et l'ordre de Bruhat affinisé
A Weighted Loss Approach to Robust Federated Learning under Data Heterogeneity
No full textFederated Learning (FL) enables multiple data holders (workers) to collaboratively train a machine learning model without sharing their private data. A central server orchestrates this process by distributing the global model and aggregating local updates. However, faulty or malicious (Byzantine) workers can compromise training. Additionally, in heterogeneous settings, even honest gradients may deviate significantly, making them difficult to distinguish from Byzantine updates. To address this, we propose the Worker Label Alignment Loss (WoLA), a weighted loss that locally rebalances sample errors to simulate similar label distributions across workers, thereby aligning their gradients and enhancing the detection of Byzantine behavior. Through extensive evaluation, we show in this paper that WoLA outperfoms stateof-the-art approaches in empirical evaluations and is supported by theoretical analysis. Our approach is particularly strong when the number of Byzantine participants is large, achieving improvements of up to +21.4 on MNIST, +16.6 on Fashion-MNIST, and +11.3 on CIFAR-10 over the best competing methods. Moreover, when combined with other robustness techniques, its performance improves even further. Code is available at: https://github.com/anonymous14031992/WoLA.</div
Moments and non-vanishing of L-functions over subgroups
No full textWe obtain an asymptotic formula for all moments of Dirichlet -functions modulo when averaged over a subgroup of characters of size with . Assuming the infinitude of Mersenne primes, the range of our result is optimal and improves and generalises the previous result of S.~Louboutin and M.~Munsch (2022) for second moments. We also use our ideas to get an asymptotic formula for the second moment of over subgroups of characters of similar size. This leads to non-vanishing results in this family where the proportion obtained depends on the height of the smallest rational number lying in the dual group. Additionally, we prove that, in both cases, we can take much smaller subgroups for almost all primes . Our method relies on pointwise and average estimates on small solutions of linear congruences which in turn leads us to use and modify some results for product sets of Farey fractions