Scientific Publications of the University of Toulouse II Le Mirail
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Eigen-Value based Multivariate Selfsimilarity Analysis in Internet Traffic: A case study
No full textInternational audienceInternet traffic modeling and analysis is critical for network design and for cybersecurity. Internet time series are well characterized by scalefree temporal dynamics. However, scalefree analysis remained so far univariate, applied independently to directional counts of either bytes or packets while challenges in cybersecurity naturally call for multivariate analysis. Elaborating on recent theoretical developments on eigenvaluebased multivariate selfsimilarity analysis, this work provides evidence, for the first time, of multivariate selfsimilarity in 17 years of Internet traffic data from the MAWI repository. It discusses the potential use of multivariate selfsimilarity for regular background traffic characterization and anomaly detection
Bayesian Unsupervised Multifractal Image Segmentation using a Multiscale Graph Label Prior
No full textInternational audienceThis paper presents a Bayesian multifractal segmentation method that segments multifractal textures in regions with different multifractal properties. First, a computationally and statistically efficient model for wavelet leaderbased multifractal parameter estimation is developed, assigning wavelet leader coefficients associated with distinct parameters to different image regions. Next, a multiscale graph label prior is introduced to capture spatial and scale correlations among these labels. Gibbs sampling is used to generate samples from the posterior distribution. Numerical experiments on synthetic multifractal images demonstrate the effectiveness of the proposed method, outperforming traditional unsupervised and modern deep learning-based segmentation approaches
Multiscale approximate eigenvectors for multivariate self-similarity estimation
No full textInternational audienceMany real-world systems generate multivariate time series data, often exhibiting self-similarity and scale-invariance across different modalities. The estimation of Hurst exponents in such settings is crucial for analyzing long-range dependencies. Yet, traditional eigenanalysis-based methods suffer from scaledependent distortions, particularly in the presence of scaling amplitude discrepancies. In this work, we propose a novel multiscale eigenanalysis approach that leverages joint diagonalization of wavelet random matrices to improve estimation accuracy. By approximating a common eigenvector basis across multiple scales, our method mitigates the limitations of scale-wise eigenvalue regressions and provides robust estimation of multivariate selfsimilarity parameters. We demonstrate the effectiveness of our approach through extensive Monte Carlo simulations, showcasing improved performance over traditional methods in both orthogonal and non-orthogonal mixing scenarios. These findings establish joint eigenvector-based wavelet analysis as a powerful tool for multivariate self-similarity estimation
TorchGDM: A GPU-accelerated Python toolkit for multi-scale electromagnetic scattering with automatic differentiation
No full textInternational audienceWe present “torchGDM”, a numerical framework for nano-optical simulations based on the Green’s Dyadic Method (GDM). This toolkit combines a hybrid approach, allowing for both fully discretized nano-structures and structures approximated by sets of effective electric and magnetic dipoles. It supports simulations in three dimensions and for infinitely long, two-dimensional structures. This capability is particularly suited for multi-scale modeling, enabling accurate near-field calculations within or around a discretized structure embedded in a complex environment of scatterers represented by effective models. Importantly, torchGDM is entirely implemented in PyTorch, a well-optimized and GPU-enabled automatic differentiation framework. This allows for the efficient calculation of exact derivatives of any simulated observable with respect to various inputs, including positions, wavelengths or permittivity, but also intermediate parameters like Green’s tensor components, which can be interesting for physics informed deep learning applications. We anticipate that this toolkit will be valuable for applications merging nano-photonics and machine learning, as well as for solving nano-photonic optimization and inverse problems, such as the global design and characterization of metasurfaces, where optical interactions between structures are critical
Preliminary study of the anti-corrosion performance of different protection systems applied to two World War II aluminium alloy archaeological objects with different surface finishes
No full textInternational audienceThis article looks at the conservation of historic aircraft from the Second World War, testing different coatings to protect their aluminium alloy structures from corrosion. Five different protective protection systems, including ParaloidTM B72, wax, DinitrolTM , Multi Matt Clear LesonalTM and carboxylates, were evaluated by being applied to artefacts from WWII aircraft wrecks, in particular a wing fragment from a Supermarine Spitfire and a propeller blade from a P38 Lightning, which presented different surface condi- tions. The protected objects were exposed to real-life conditions (uncontrolled indoor environment). Ad- vanced analytical techniques such as electrochemical impedance spectroscopy (EIS), Fourier transform in- frared spectroscopy (FTIR), optical coherence tomography (OCT) and scanning electron microscopy (SEM) were used to characterize the evolution and effectiveness of the protection systems. The results showed different degrees of effectiveness for different coatings. DinitrolTM and LesonalTM demonstrated the best protective properties, forming thin but effective layers that enhance corrosion resistance. Carboxylates, on the other hand, proved ineffective, while ParaloidTM B72 and wax were not very effective and unsuitable for objects with original paint residues
Axiomatic Characterisations of Argumentation Semantics
No full textInternational audienceThe evaluation of argument strength lies at the core of any argumentation system. Numerous semantics have been proposed for this purpose, along with a variety of principles (or axioms) that such semantics are expected to satisfy. Most existing semantics in the literature have been analyzed and compared in light of these principles. While this body of work marks a significant step toward establishing the theoretical foundations of argumentation semantics, it remains incomplete. In particular, characterizations of entire classes of semantics that uniquely satisfy specific subsets of axioms are still lacking, leaving open questions on the kind of semantics that can still be defined and their added values. This paper addresses this gap by establishing representation theorems that explicitly relate subsets of principles to corresponding classes of semantics. These semantics are defined through two mathematical functions: an impact function and an aggregation operator, each satisfying specific structural properties. We demonstrate how these principles offer a uniform and concise explanatory framework for the identified semantics. Finally, we show that classical extension-based semantics do not belong to these classes.</div
Mission Préhistorique Franco-Angolaise - Rapport 2025
No full textLes activités de la Mission Préhistorique Franco-Angolaise (MPFA) en 2025 s’inscrivent dans la continuité des activités réalisées en 2023 et 2024, à savoir un programme annuel de 7 semaines qui s’ancre sur deux terrains principaux fédérant des équipes différentes avec pour but de développer une recherche pluridisciplinaire internationalisée en Angola et de former des étudiants d’Angola, de France ou d’ailleurs.La fouille programmée à Ndalambiri, municipalité de Ebo, province de Cuanza-Sul, a depuis 2023 un objectif double : démocratiser la fouille archéologique comme expérience pratique et apprentissage des modes d’acquisition des sources archéologiques dans la reconstitution du passé de l’Angola pour les étudiants du département d’Histoire de l’Instituto Superior de Ciências da Educação do Sumbe (ISCED-Sumbe) et collecter en contexte des séries d’artefacts pour développer une approche pluridisciplinaire sur la séquence de l’abri de Ndalambiri. Dans ce contexte, les activités sont conduites en collaboration avec l’ISCED de Sumbe, l’administration municipale de Ebo, Cuanza-Sul, et le Museu Nacional de Arqueologia de Benguela (MNAB), incluant un support financier et logistique important de leur part. Cette campagne de deux semaines a été conduite du 4 au 18 mai 2025 et a accueilli 39 étudiants et 9 encadrants de terrain. La participation aux activités de terrain permet désormais aux étudiants de valider des crédits universitaires pour le cours de méthodologie de terrain en archéologie pour les étudiants de deuxième année de licenciatura. Enfin, un projet ANR JCJC (projet RESIST) sera déposé le 14 octobre avec pour objectif d’intégrer Ndalambiri dans un réseau de sites de l’Holocène récent entre le Gabon et la Namibie. La première partie de ce rapport rappelle les objectifs et enjeux scientifiques, présente en détail les activités de terrain réalisées durant cette campagne, ainsi que l’état d’avancement de l’étude du matériel.Par ailleurs, les fouilles programmées au mois d’août sur les terrasses marines de la province de Benguela, à l’extrême nord du biome Karoo-Namib, donnent continuité au projet de recherche pluridisciplinaire initialement développé sur l’Earlier Stone Age en 2021 et aujourd’hui étendu à l’ensemble de la séquence sédimentaire exposée à Mormolo et Dungo, du Néogène, il y a plus de 3 000 000 d’années, aux amas coquilliers de l’Holocène récent. Cette approche diachronique et pluridisciplinaire a été récompensée en 2025 par le prix de la Fondation Engie, garantissant l’acquisition de certains équipements, des frais d’analyses ainsi que des gratifications de stage de Master 2 pour 2026. Le terrain inclut une approche large et diachronique des terrasses grâce au montage d’une carte archéologique qui se veut la plus exhaustive possible et une prospection méthodique où chaque période chronologique apporte des connaissances nouvelles. Chaque année, de nouvelles informations et matériaux sont collectés pour mettre en forme l’histoire évolutive du littoral de Benguela et de ses populations, soulignant le potentiel exceptionnel des terrasses de Mormolo pour la préhistoire et la paléoécologie marine. En 2025, on compte 9 chercheurs internationaux impliqués dans l’étude du matériel collecté. Le terrain est ouvert aux étudiants – notamment grâce au soutien de la Fondation Leakey pour la mobilité et l’expérience de terrain des étudiants africains. Les résultats du terrain et des analyses réalisées depuis l’automne 2024 sont présentés dans la deuxième partie du rapport.Ensemble, les terrains de Ndalambiri et de Mormolo ont permis de consolider une équipe chaque année plus large d’étudiants angolais et français et de fédérer nos activités autour d’objectifs communs de développement de la recherche, de récolte de données primaires et d’une contribution à la préservation et à la connaissance du patrimoine archéologique de l’Angola. Par conséquent, des activités de recherche sont également conduites sur d’autres terrains ou collections. Par exemple, une thèse de doctorat (Sofia Mateus, co-encadrée par G. de Saulieu (UMR PALOC) et I. Mesfin au Muséum national d’Histoire naturelle et financée par l’Ambassade de France en Angola) a été lancée dans le cadre d’une demande angolaise d’un programme d’archéologie de sauvetage, sur le développement d’une archéologie du paysage des vestiges architecturaux en pierre de Caculo Cabaça, province de Cuanza-Norte (photogrammétrie, LiDAR et approche spatiale des vestiges céramiques). Comme autre exemple, Raphaël Hanon (UMR PACEA) et Pierre Linchamps (Université de Witwatersrand, Afrique du Sud / UMR 7194) ont établi le programme d’activités de terrain qui sera conduit sur les brèches fossilifères de Humpata, province de Huila, entre 2025 et 2027, en partenariat avec l’ISCED-Lubango et le MNARQ, qui représenteront un pôle paléontologique important pour la mission à l’avenir. L’ensemble de cette dynamique émanant à la fois des universités angolaises et étrangères a permis de créer le projet FEF-R DIGARQ en 2024-2025, qui vient d’être reconduit pour un FEF de deux ans (DIGARQ-2, jusqu’en septembre 2027), permettant à l’équipe de bénéficier de formations, d’équipements, d’analyses et de frais relatifs à la divulgation, sur lesquels nous reviendrons dans la dernière partie du rapport.As atividades da Missão Pré-Histórica Franco-Angolana (MPFA) em 2025 inscrevem-se na continuidade das ações realizadas em 2023 e 2024, nomeadamente um programa anual de sete semanas que se baseia em dois principais terrenos, reunindo diferentes equipas com o objetivo de desenvolver uma investigação pluridisciplinar e internacionalizada em Angola, e de formar estudantes de Angola, de França e de outros países.A escavação programada em Ndalambiri, município do Ebo, província do Cuanza-Sul, tem desde 2023 um duplo objetivo: democratizar a escavação arqueológica como experiência prática e como aprendizagem dos modos de aquisição de fontes arqueológicas na reconstituição do passado de Angola para os estudantes do Departamento de História do Instituto Superior de Ciências da Educação do Sumbe (ISCED-Sumbe), e recolher, em contexto, séries de artefactos para desenvolver uma abordagem pluridisciplinar sobre a sequência do abrigo de Ndalambiri. Neste contexto, as atividades são realizadas em colaboração com o ISCED do Sumbe, a Administração Municipal do Ebo, Cuanza-Sul, e o Museu Nacional de Arqueologia de Benguela (MNAB), incluindo um importante apoio financeiro e logístico da parte destas instituições. Esta campanha de duas semanas foi conduzida de 4 a 18 de maio de 2025 e acolheu 39 estudantes e 9 supervisores de campo. A participação nas atividades de campo permite agora aos estudantes validar créditos universitários na unidade curricular de Metodologia de Campo em Arqueologia para os estudantes do segundo ano da licenciatura. Finalmente, um projeto ANR JCJC (projeto RESIST) será submetido a 14 de outubro com o objetivo de integrar Ndalambiri numa rede de sítios do Holoceno recente entre o Gabão e a Namíbia. A primeira parte deste relatório recorda os objetivos e desafios científicos, apresenta em detalhe as atividades de campo realizadas durante esta campanha, bem como o estado de avanço do estudo do material.Por outro lado, as escavações programadas para o mês de agosto nos terraços marinhos da província de Benguela, no extremo norte do bioma Karoo-Namib, dão continuidade ao projeto de investigação pluridisciplinar inicialmente desenvolvido sobre o Earlier Stone Age em 2021 e atualmente alargado a toda a sequência sedimentar exposta em Mormolo e Dungo, desde o Neogénico, há mais de 3 000 000 de anos, até aos amontoados concheiros do Holoceno recente. Esta abordagem diacrónica e pluridisciplinar foi premiada em 2025 com o Prémio da Fundação Engie, garantindo a aquisição de certos equipamentos, as despesas de análises, bem como bolsas de estágio de Mestrado 2 para 2026. O trabalho de campo inclui uma abordagem ampla e diacrónica dos terraços através da elaboração de uma carta arqueológica que se pretende o mais exaustiva possível e uma prospeção metódica em que cada período cronológico traz novos conhecimentos. Todos os anos, novas informações e materiais são recolhidos para construir a história evolutiva do litoral de Benguela e das suas populações, sublinhando o potencial excecional dos terraços de Mormolo para a Pré-História e a paleoecologia marinha. Em 2025, contam-se 9 investigadores internacionais envolvidos no estudo do material recolhido. O trabalho de campo está aberto aos estudantes – nomeadamente graças ao apoio da Fundação Leakey para a mobilidade e a experiência de campo de estudantes africanos. Os resultados do trabalho de campo e das análises realizadas desde o outono de 2024 são apresentados na segunda parte do relatório.Conjuntamente, os trabalhos de Ndalambiri e de Mormolo permitiram consolidar uma equipa cada vez mais ampla de estudantes angolanos e franceses e federar as nossas atividades em torno de objetivos comuns de desenvolvimento da investigação, recolha de dados primários e contribuição para a preservação e o conhecimento do património arqueológico de Angola. Consequentemente, atividades de investigação são também conduzidas noutros terrenos ou coleções. Por exemplo, foi iniciado um doutoramento (Sofia Mateus, coorientado por G. de Saulieu (UMR PALOC) e I. Mesfin no Muséum national d’Histoire naturelle e financiado pela Embaixada de França em Angola) no quadro de um pedido angolano de um programa de arqueologia de salvamento, sobre o desenvolvimento de uma arqueologia da paisagem dos vestígios arquitetónicos em pedra de Caculo Cabaça, província do Cuanza-Norte (fotogrametria, LiDAR e abordagem espacial dos vestígios cerâmicos). Como outro exemplo, Raphaël Hanon (UMR PACEA) e Pierre Linchamps (Universidade de Witwatersrand, África do Sul / UMR 7194) definiram o programa de atividades de campo que será conduzido nas brechas fossilíferas de Humpata, província da Huíla, entre 2025 e 2027, em parceria com o ISCED-Lubango e o MNARQ, que representarão um polo paleontológico importante para a missão no futuro.Esta dinâmica, emanando tanto das universidades angolanas como das estrangeiras, permitiu criar o projeto FEF-R DIGARQ em 2024-2025, recentemente renovado para um FEF de dois anos (DIGARQ-2, até setembro de 2027), permitindo à equipa beneficiar de formações, equipamentos, análises e despesas relacionadas com a divulgação, sobre as quais voltaremos na última parte do relatório
Déploiement de réseaux denses de suivi de la pression lumineuse pour des actions territoriales: les cas de l'île de La Réunion et de la Brière, France
No full textInternational audienceDense networks of photometric sensors offer high-frequency, high-resolution data at unprecedented spatial scales. Such arrays detect lighting variations across minutes to years, enabling both short- and long-term assessments, while also enhancing skyglow and radiative transfer modeling. Critically, they support fine-scale evaluation of lighting policies — such as LED transitions or dimming regulations — by tracking their effects on sky brightness. These systems also enable near-continuous monitoring of Artificial Light At Night (ALAN) changes with atmospheric conditions including aerosols and cloud cover, and help validate satellite-derived products while informing ecological and health impact assessments. In this contribution, we present high-resolution datasets from two dense TESS-W sensor networks deployed for long-term ALAN monitoring in: (1) Réunion Island, a French territory in the Indian Ocean with volcanic terrain, high biodiversity, and a rapidly urbanizing coast; and (2) the Brière region, a wetland near France’s Atlantic coast, home to a regional nature park and sensitive nocturnal ecosystems. These networks provide continuous, multi-year measurements of night-sky brightness at fine spatial (~km) and temporal (~minute) scales. We describe the network architecture, calibration procedures, data processing pipeline, and access details. By making these high-resolution ALAN datasets openly available, this work enhances our ability to monitor light pollution and evaluate the effectiveness of mitigation strategies. Designed as part of the Observatoire de l’Environnement Nocturne of the French National Centre for Scientific Research (CNRS), these datasets offer a robust empirical foundation for investigating the multifaceted dynamics of light pollution across ecological, atmospheric, sociocultural, and territorial contexts. They also contribute to publicengagement and educational initiatives, fostering broader awareness and collective action toward preserving the nocturnal environment
Experimental evidence of stress-induced critical state in schooling fish
No full textInternational audienceHow animal groups dynamically adjust their collective behavior in response to environmental changes remains an open and challenging question. Here we investigate the mechanisms that allow fish schools to tune their collective state under stress, testing the hypothesis that these systems operate near criticality, a state that maximizes sensitivity, responsiveness, and adaptability. We combine experiments and data-driven computational modeling to study how group size and stress influence the collective behavior of rummy-nose tetras (). We quantify the collective state of fish schools using polarization, milling, and cohesion metrics and use a burst-and-coast model to infer the social interaction parameters that drive these behaviors. Our results indicate that group size modulates stress levels, with smaller groups experiencing higher baseline stress, likely due to a reduced social buffering effect. Under stress, fish adjust the strength of their social interactions in a way that leads the group into a critical state, thus enhancing its sensitivity to perturbations and facilitating rapid adaptation. However, while large groups require an external stressor to enter the critical regime, small groups are already near this state. Our findings suggest that adjusting interaction strength is a simple yet effective mechanism that drives collective state transitions while minimizing individual cognitive load. By revealing how stress and group size drive self-organization toward criticality, our study provides fundamental insights into the adaptability of collective biological systems and the emergent properties in animal groups