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Mesures et modélisations de BRDF hyperspectrales : Application pour la prédiction de signatures de véhicules et satellites
No full textFor several decades, the number of objects in Earth's orbit has been steadily increasing, highlighting the need for tools tailored to space surveillance. These tools, essential for detecting and tracking satellites and other orbiting devices, also enable the characterization of their state, use, and composition. Among these sources of information, the optical signature of materials represents a valuable resource, provided it is correctly interpreted. Advances in image synthesis algorithms, combining optics and computer science, have opened new opportunities to simulate these signatures with a high degree of realism. These techniques rely on detailed modeling of object geometry, materials, light sources, and their environment. However, existing data or models of material reflectivity are often insufficient, especially when it comes to capturing angular and spectral variations. The scientific literature continues to face significant gaps in the availability of physically realistic hyperspectral bidirectional models.In this context, the work presented in this manuscript focuses on developing innovative approaches for measuring and modeling the hyperspectral bidirectional reflectivity of materials. The first step involved using a spectro-gonioreflectometer and developing a processing pipeline to perform precise measurements of material reflection properties across extensive angular and spectral domains. The proposed processing chain includes specific contributions for this type of setup, such as adaptive sampling of observation directions and a method for correcting alignment errors. Following these experimental measurements, new tools for critical analysis were introduced. Validation criteria, such as verifying Helmholtz reciprocity, were proposed, along with approaches to separate the spectral and angular contributions of the measured bidirectional spectral reflectivities.In the second phase, this work focused on modeling the measured bidirectional spectral reflectivities. Two complementary approaches were explored. The first, analytical, led to the proposal of a parametric model based on spherical Gaussians, designed to comply with physical constraints and faithfully represent the measured materials. The second approach involves interpolating experimental data using radial basis functions. A robust methodology was developed, integrating reciprocity constraints and leveraging a parameterization suited to the definition domain of bidirectional reflectivity functions. This technique provides a practical solution for reconstructing sparse data and integrating them into rendering engines for realistic simulations.Depuis plusieurs décennies, le nombre d’objets en orbite terrestre ne cesse de croître, témoignant de la nécessité d’outils adaptés à la veille spatiale. Ces outils, essentiels pour la détection et le suivi de satellites et autres engins en orbite, permettent également de caractériser leur état, leur utilisation et leur composition. Parmi ces vecteurs d’information, la signature optique des matériaux constitue une source précieuse, à condition d’être correctement interprétée. Les avancées en algorithmes de synthèse d’image, combinant optique et informatique, ont ouvert de nouvelles perspectives pour simuler ces signatures avec un haut degré de réalisme. Ces techniques reposent sur une modélisation fine de la géométrie des objets, de leurs matériaux, des sources lumineuses, ainsi que de leur environnement. Cependant, les données ou modèles existants de réflectivité des matériaux sont souvent insuffisants, notamment lorsqu’il s’agit de capturer les variations angulaires et spectrales. Le littérature scientifique demeure confrontée à d’importantes lacunes dans la disponibilité de modèles bidirectionnels hyperspectraux physiquement réalistes.Dans ce contexte, les travaux présentés dans ce manuscrit se sont focalisés sur le développement d’approches innovantes pour mesurer et modéliser la réflectivité bidirectionnelle hyperspectrale de matériaux. Une première étape a consisté à utiliser un spectro-gonioréflectomètre et développer une chaîne de traitement pour réaliser des mesures précises des propriétés de réflexion de matériaux dans des domaines angulaire et spectral étendus. La chaîne de traitement proposée comporte des propositions spécifiques à ce type de banc telles qu'un échantillonnage adaptatif des directions d’observation ou une méthode de correction des erreurs d’alignement. A la suite de ces mesures expérimentales, nous avons introduit de nouveaux outils d’analyse critique. Des critères de validation, comme la vérification de la réciprocité de Helmholtz, ont été proposés, tout comme des approches pour séparer les contributions spectrales et angulaires des réflectivité bidirectionnelles spectrales mesurées.Dans un second temps, ces travaux ont porté sur la modélisation des réflectivités bidirectionnelles spectrales mesurées. Deux approches complémentaires ont été explorées. La première, analytique, a conduit à la proposition d’un modèle paramétrique basé sur des gaussiennes sphériques, conçu pour respecter les contraintes physiques et capable de représenter fidèlement les matériaux mesurés. La seconde approche repose sur l’interpolation des données expérimentales grâce à des fonctions à base radiale. Une méthodologie robuste a été développée, intégrant les contraintes de réciprocité et exploitant une paramétrisation adaptée au domaine de définition des fonctions de réflectivité bidirectionnelle. Cette technique offre une solution pratique pour reconstruire des données éparses et les intégrer dans des moteurs de rendu pour des simulations réalistes
Eras of Monetary and Financial Dominance: A Copernican-Type Model of Multilayered Network with Endogenous Regimes
No full textInternational audienc
Experimental detection of long-distance interactions between biomolecules through their diffusion behavior: Numerical study
No full textInternational audienceThe dynamical properties and diffusive behavior of a collection of mutually interacting particles are numerically investigated for two types of long-range interparticle interactions: Coulomb-electrostatic and dipole-electrodynamic. It is shown that when the particles are uniformly distributed throughout the accessible space, the self-diffusion coefficient is always lowered by the considered interparticle interactions, irrespective of their attractive or repulsive character. This fact is also confirmed by a simple model to compute the correction to the Brownian diffusion coefficient due to the interactions among the particles. These interactions are also responsible for the onset of dynamical chaos and an associated chaotic diffusion which still follows an Einstein-Fick like law for the mean square displacement as a function of time. Transitional phenomena are observed for Coulomb-electrostatic (repulsive) and dipole-electrodynamic (attractive) interactions considered both separately and in competition. The outcomes reported in this paper clearly indicate a feasible experimental method to probe the activation of resonant electrodynamic interactions among biomolecules
Catching homologies by geometric entropy
No full textInternational audienceA geometric entropy is defined as the Riemannian volume of the parameter space of a statistical manifold associated with a given network. As such it can be a good candidate for measuring networks complexity. Here we investigate its ability to single out topological features of networks proceeding in a bottom-up manner: first we consider small size networks by analytical methods and then large size networks by numerical techniques. Two different classes of networks, the random graphs and the scale--free networks, are investigated computing their Betti numbers and then showing the capability of geometric entropy of detecting homologies
Why a special issue on definitions and concepts in biolaw?
No full textInternational audienceConcepts and definitions play a central role in law as they allow, respectively, to name and describe, as well as delimit a real or fictional entity, and ensure a common understanding of it, with a view to legally qualifying it in order to associate it with a legal regime. By focusing on the conceptual dimension, we intend to go beyond an approach based purely on notions. As far as possible, the discussion will focus on concepts, rather than notions, the latter being regarded here as a necessary preliminary step to any reflection on the former. We offer to consider that a notional analysis entails the identification of all criteria that may be used to recognize an element of reality, in an exhaustive manner, by identifying and examining each criterion, without necessarily determining their relative relevance for identifying that reality. In contrast, a conceptual analysis requires selecting only those criteria that are relevant for identifying the element of reality, and assigning to each selected criterion its proper weight and position in order to reveal the typical features of the object described. For the science of law—as a scholarly discourse on law—the act of conceptualization lies at the core of the scientific approach. Numerous studies in legal theory, or more broadly in fundamental legal research, have addressed this topic. In the field of biolaw—understood here as the body of legal norms and legal questions pertaining to the biological domain and/or arising from technological advances in biomedicine, and more broadly in biotechnology—definitions and concepts present particular challenges that have rarely been addressed directly and transversally within legal scholarship. Yet, definitions and concepts are of critical importance in this area, given the continuously evolving and unpredictable nature of scientific practices, and the absence of consensus around many scientific definitions. The establishment of definitions thus constitutes a fundamental concern for biolaw, as it enables the law to apprehend and orient such practices in a coherent and effective manner. While biolaw may itself be approached as a concept within the science of law, it is considered here, first and foremost, as a domain of legal inquiry, forming the subject matter of the present study. Nevertheless, the scholarly work produced within this domain contributes to the conceptual framing of biolaw, whose usage—as a doctrinal category—would benefit from greater consistency and theoretical refinement.This thematic raises a series of concrete and pressing legal questions: Can legislation or regulation meaningfully define emerging innovations in biomedicine or biotechnology while these developments remain in flux, or in fields characterized by scientific and technological uncertainty? To what extent may legal or regulatory definitions diverge from those adopted by the scientific community, and under what conditions is such divergence justified? What normative legitimacy does the legal scholar or legislator possess in departing from scientific definitions? Is it preferable, in certain contexts, to refrain from defining a given object of regulation, due to the inherent difficulties in tracking developments within dynamic and highly technical fields? Under what circumstances, and for what reasons, have legislators or regulatory authorities chosen to define—or to abstain from defining—biomedical innovations or biotechnologies? When and why has the law opted to regulate on the basis of the intended use of a given technology rather than the intrinsic nature of the object itself?While legal literature generally focuses on the legal or regulatory frameworks to be adopted and on the challenges posed to such regulation by biomedical and biotechnological innovations, this special issue focuses instead on how legislation—or regulation more broadly—defines or fails to define these innovations, and on the consequences that definitions and concepts may have for their development
« Démocratie représentative et participation citoyenne : le cas de la France »
No full textInternational audienceFrench politicians have been thinking for several years about ways to overcome mistrust of representative institutions. In this context, developing citizen participation is a crucial issue in the face of a representative model that is running out of steam. The traditional method of referendums is increasingly criticised and rejected in favour of new, more deliberative and participatory mechanisms. However, these mechanisms are subject to very flexible rules and do not offer the same prospects in terms of influencing political choices. The most innovative methods, such as citizens' conventions, are still at an experimental stage. Intermediate citizens' initiative procedures could be introduced and given constitutional and legislative backing to guarantee, at the very least, the possibility of bringing a subject to the attention of Parliament by requesting its inclusion on the agenda. Existing mechanisms could also be enhanced by deliberative processes to clarify the issues at stake in a vote or consultation. In view of the development of deliberative and participatory democracy tools within the Council of Europe, France still has considerable room for improvement, which would give new impetus to representative democracy.Les responsables politiques français réfléchissent depuis plusieurs années aux moyens de surmonter la défiance envers les institutions représentatives. Dans ce contexte, le développement de la participation citoyenne constitue un enjeu crucial face à un modèle représentatif qui s’essoufle. La méthode classique de référendum est de plus en plus critiquée et délaissée au profit de nouveaux mécanismes plus délibératifs et participatifs. Ces derniers cependant font l’objet d’un encadrement très souple et n’offrent pas les mêmes perspectives en termes d’influence sur les choix politiques effectués. Les méthodes les plus innovantes, telles que les conventions citoyennes, sont encore à un stade expérimental. Des procédures intermédiaires d’initiative citoyenne pourraient être introduites et bénéficier d’un ancrage constitutionnel et législatif permettant de garantir a minima la possibilité de porter un sujet à la connaissance du Parlement en demandant son inscription à l’ordre du jour. Les mécanismes existants pourraient également être enrichis par des processus délibératifs permettant de clarifier les enjeux lors d’un vote ou d’une consultation. Au regard du développement des outils de démocratie délibérative et participative au sein du Conseil de l’Europe, la marge de progression de la France reste donc importante et permettrait de donner un nouveau souffle à la démocratie représentative
Faster and objective Level Set-DEM mechanical simulations of discrete systems with convex particles from contact history and particle surface considerations
No full textARTICLE IN PRESSInternational audienceAiming for versatile simulations of the mechanics of discrete systems with arbitrary convex particles, an extended Level Set (LS) description of particle shape is proposed in the framework of the Discrete Element Method (DEM). The LS shape description as a discrete field of the signed distance function is first obtained with a faster initial generation and then proposed to directly output particle surface in a validated workflow. It mostly includes an innovative optimization for the surface nodes discretization which combines with the LS distance field for DEM contact treatment. In their optimized definition, surface nodes locate in a nearly uniform fashion over a particle and are handled in a sparse manner during contact treatment, thanks to an original consideration of contact history. As such, computation speed gains are reported with a factor of more than 3 during simulations of quasistatic mechanical loading. The proposed nodes definition is also shown to be instrumental to insure objectivity of the LS contact model and DEM simulations. The present LS approach is finally applied to a preliminary study of the residual shear strength of various packings made of superquadrics all sharing the same shape. After a justification of the chosen particle number to form a Representative Elementary Volume, the shear strength is shown to lack a clear relationship with Wadell's true sphericity as a shape index, while being possibly 73% higher than the one obtained with spherical particles
De l’urgence à l’état de nécessité climatique
No full textJulien Giudicelli, Sylvie Schmitt (dir.), La désobéissance civile : regard croisé entre la France et l'Italie, Paris, L'Harmattan, 202
Introduction: An Emerging Research Field at the Intersection of the Sociology of Work and Sociology of Language
No full textInternational audienceThe introduction of “International Perspectives on Language and Work: Analysing the Impact of Mutual Influences” sets foundational elements of this specific encounter in the field, between the sociology of work and the sociology of language, from the perspective of looking at language rather than solely through it. After a presentation of how language and work intersect in today’s dynamic language-labour landscape, it addresses the evolving nature of labour markets due to economic and geopolitical challenges, emphasising the importance of understanding how language shapes work environments, and how language in return is processed too. The aim is to bridge the sociology of language and the sociology of work, examining how language influences organisational dynamics, professionalisation processes, new forms of work and employment and power relations. International perspectives support the elucidation of the reciprocal impacts of language and work across various contexts: case studies from four continents and with quotations in the original language as with an English translation are briefly presented to outline the thematic contributions of each chapter
