HAL-uB
Not a member yet
73989 research outputs found
Sort by
Generalized Heterodyne Interferometry in Kerr Materials
No full textInternational audienceInterferometry has long been used to measure the phase of light signals. Combined with a heterodyne detection scheme, it allows to simultaneously record amplitude and phase variations. In this work, these well‐known techniques are exploited to evaluate the nonlinear phase induced by the optical Kerr effect during the propagation of a laser pulse in a nonlinear medium. It is shown that the nonlinear index can easily be retrieved when the accumulated phase remains small, but counter‐intuitive results can be observed at higher powers. In particular, the combination of pulsed excitation and Kerr nonlinearity results in nonlinear variations of the amplitude of the interference pattern, whose shape depends on the pulse profile and the dispersion of the propagation medium
FAlen–Zn Complexes for the Cycloaddition of CO<sub>2</sub> to Epoxide and the Ring-Opening Polymerization of Lactide
No full textInternational audienceWe report the synthesis of four bis(o,p-tBu-phenoxy-amidine) ligands (FAlen) with dimethylamino-, pyrrolidine-, and piperidine-substituted amidines and a phenylene or a maleonitrile amidine bridge. We examined the coordination chemistry of these ligands toward Zn and the potential of this combination as a catalyst in the cycloaddition of CO2 to epoxide and in the ROP of rac-LA. FAlen ligands were shown to greatly differ from their parent bis(salicylaldimine) ligands (aka salen) in how they coordinate to Zn. In the solid state, the complexes were found as dinuclear tetracoordinated Zn complexes with the two FAlen ligands bridging the metal centers in an asymmetric μ-κ1,κ3 manner. In solution, these dinuclear structures most often vanished even in noncoordinating solvent to afford mononuclear tetracoordinated species. The FAlen–Zn complexes were found to be less active than their salen–Zn counterparts in the catalytic cycloaddition of CO2 with styrene epoxide. Conversely, the FAlen–Zn complexes were shown to be highly active for the ROP of rac-LA, whereas the parent salen–Zn complex exhibited no activity. A kinetic study performed with the most active complex 1 showed a first order in rac-LA, Zn complex, and iPrOH. DFT calculations revealed two possible low-energy-barrier ROP mechanisms: an amidine-assisted activated monomer mechanism or a very unusual zincate-amidinium hydrogen-bonding mechanis
Rethinking Traffic Prediction in Mobile Network Digital Twins: A flexible inductive graph-based learning model for data-scarce scenarios
No full textInternational audienceNetwork Digital Twins (NDTs) are increasingly relying on data-driven approaches for modeling complex network dynamics. Traffic forecasting is crucial for NDTs to provide timely insights for automated network reconfiguration. Existing spatiotemporal forecasting methods, while effective, often rely on pre-constructed graphs, limiting their flexibility in dynamic network environments. This paper introduces Flex+, an inductive graph-based learning model designed for traffic prediction in data-scarce scenarios. Flex+ focuses on individual eNodeB traffic prediction by extracting local spatial correlations from k-hop subgraphs, combined with temporal information. Its inductive design allows it to operate on unseen nodes during training, enabling adaptability to evolving network topologies. Empirical studies on a large-scale cellular traffic dataset demonstrate that Flex+ achieves a 5.9% improvement in accuracy in inductive settings and a 22% reduction in error in data-scarce scenarios when trained with only 3 days of traffic data. Notably, a Knowledge Distillation (KD) framework is introduced to reduce model size and accelerate inference time up to 10 times while maintaining prediction accuracy
Degré de Bourbaki de paires de surfaces projectives
No full textThe logarithmic tangent sheaf associated to an algebraically independent sequence of homogeneous polynomials - defined as the kernel of the associated Jacobian matrix - naturally generalizes the classical logarithmic tangent sheaf of a divisor in a projective space to the case of subvarieties defined by more than one equation. As is the case for divisors, one may investigate the freeness of such sequences, and other weaker notions.The present work focuses on sequences of two homogeneous polynomials in four variables. We introduce two positive discrete invariants: the invariant m and the Bourbaki degree of a sequence, inspired by the framework of the Bourbaki degree recently developed for projective plane curves by Jardim-Nejad-Simis. The invariant m plays the role of the Tjurina number of plane projective curves and is bounded by a quadratic relation. We establish results concerning the interplay of minimal degree for syzygies of the Jacobian matrix and the introduced discrete invariants. Our approach uses tools from foliation theory, taking advantage of the fact that the logarithmic sheaf is, up to a twist, the tangent sheaf of a codimension one foliation in projective three-space.We provide examples and classification results for pencils of cubics and for pairs of a quadric and a cubic polynomials, relating stability and Chern classes with the discrete invariants introduced, while classifying free and nearly-free cases. In particular, one of the nearly-free examples induces an unstable, non-split tangent sheaf for a codimension one foliation of degree 3, answering, in the negative, a conjecture of Calvo-Andrade, Correa and Jardim from 2018.Le faisceau tangent logarithmique associé à une suite algébriquement indépendante de polynômes homogènes – défini comme le noyau de la matrice jacobienne associée – généralise naturellement le faisceau tangent logarithmique classique d'un diviseur dans un espace projectif au cas des sous-variétés définies par plusieurs équations. Comme pour les diviseurs, on peut étudier la liberté de telles suites, ainsi que d'autres notions plus faibles.Ce travail porte sur les suites de deux polynômes homogènes à quatre variables. Nous introduisons deux invariants discrets positifs : l'invariant m et le degré de Bourbaki d'une suite, inspirés du cadre du degré de Bourbaki récemment développé pour les courbes planes projectives par Jardim-Nejad-Simis. L'invariant m joue le rôle du nombre de Tjurina des courbes planes projectives et est borné par une relation quadratique. Nous établissons des résultats concernant l'interaction entre le degré minimal des syzygies de la matrice jacobienne et les invariants discrets introduits. Notre approche utilise des outils de la théorie des feuilletages, en tirant parti du fait que le faisceau logarithmique est, à une torsion près, le faisceau tangent d'un feuilletage de codimension un dans l'espace projectif tridimensionnel.Nous fournissons des exemples et des résultats de classification pour des faisceaux de polynômes cubiques et pour des paires de polynômes quadriques et cubiques, en reliant la stabilité et les classes de Chern aux invariants discrets introduits, tout en classant les cas libres et quasi-libres. En particulier, un des exemples quasi-libres induit un faisceau tangent instable et non scindé pour un feuilletage de codimension un de degré 3, réfutant ainsi une conjecture de Calvo-Andrade, Correa et Jardim de 2018
Social Promotion Through Teaching? A Socio-Historical Approach to Early Remuneration Schemes (France, 1957-2024)
No full textInternational audienc
Manœuvres et désordres informationnels dans l’espace public numérique : identification, rôle et narratif des « bots »
No full textInternational audienceThis article explores truth regimes in the digital public space in the era of bots and AI. It aims to understand how bots identified on X manipulate public opinion and weaken democracy. Based on the Beelzebot project, the analysis combines quantitative and qualitative methods applied to a corpus of tweets related to the 2022 French presidential election.Cet article interroge les régimes de vérité dans l’espace public numérique à l’ère des bots et de l’IA. Il vise à comprendre comment des bots identifiés sur X manipulent l’opinion publique et fragilisent la démocratie. L’analyse, issue du projet Beelzebot, combine méthodes quantitative et qualitative sur un corpus de tweets liés à l’élection présidentielle française de 2022
Selecting, cooking, serving and eating food with sufficiency – introducing restobriety as a new paradigm
No full textInternational audienceRestaurants significantly impact the environment, yet their sustainability role is under- researched. This paper introduces restobriety, a new paradigm integrating ecological sufficiency into restaurant management, from selecting to eating food. Grounded in environmental ethics and the experience economy, restobriety follows five principles: constraint as creative force, sufficiency as luxury, transparent hedonism, systemic integration, and cultural contextuality. This approach holistically transforms logistics, marketing, finance, and human resources, prioritizing quality and responsible resource management. This study aims to investigate practical conditions for implementing restobriety, examining how stakeholders—including managers, chefs, customers, and suppliers—perceive and enact this approach across diverse cultural and gastronomic contexts
