HAL-Université de Bretagne Occidentale
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Majorization-Minimization Networks for Inverse Problems: An Application to EEG Imaging
No full textInverse problems are often ill-posed and require optimization schemes with strong stability and convergence guarantees. While learning-based approaches such as deep unrolling and meta-learning achieve strong empirical performance, they typically lack explicit control over descent and curvature, limiting robustness. We propose a learned Majorization-Minimization (MM) framework for inverse problems within a bilevel optimization setting. Instead of learning a full optimizer, we learn a structured curvature majorant that governs each MM step while preserving classical MM descent guarantees. The majorant is parameterized by a lightweight recurrent neural network and explicitly constrained to satisfy valid MM conditions. For cosine-similarity losses, we derive explicit curvature bounds yielding diagonal majorants. When analytic bounds are unavailable, we rely on efficient Hessian-vector product-based spectral estimation to automatically upper-bound local curvature without forming the Hessian explicitly. Experiments on EEG source imaging demonstrate improved accuracy, stability, and cross-dataset generalization over deep-unrolled and meta-learning baselines
Nontuberculous Mycobacterial Lymphadenitis in Children: A French Retrospective Multicenter Study on Epidemiology, Management Strategy and Outcome Over the Last Decade
No full textInternational audienceBackground: Nontuberculous mycobacterial (NTM) adenitis is increasingly recognized in children; however, optimal management strategies remain debated. The aim of this study was to describe the clinical characteristics, management and outcomes of pediatric NTM lymphadenitis in France. Methods: We conducted a multicenter retrospective descriptive study of culture-confirmed NTM lymphadenitis cases in children across 15 French hospitals participating in the MYCOMED network between 2010 and 2019. Results: A total of 279 patients were included, with a progressive increase in diagnoses over the study period, from 11 cases in 2010 to 33 in 2019, with peaks of 38 observed in 2015 and 2018. Most patients were female (64%) with a median age of 3 years. Mycobacterium avium was the most frequently isolated species (71%). Histologic examination revealed necrotizing granulomatous lymphadenitis in two-third of cases (71%, 112/115), and acid-fast bacilli staining was positive in 24.6% (68/276) of the cases. Of the 250 patients with available therapeutic data, 34.8% were treated with surgery alone, 24.8% with antibiotics alone, 28% with combined therapy and 12.4% received no treatment. Overall, 104 children were lost to follow-up. Among 175 patients with follow-up data, the overall cure rate was 96%, with no significant differences between therapeutic strategies. Relapse occurred in 6 children (3.4%). No cases of facial nerve palsy were reported; however, cosmetic sequelae related to scarring were observed. Conclusions: The incidence of pediatric NTM adenitis has increased over the last decade in France, with M. avium as the predominant species. The clinical outcome was favorable in most cases, irrespective of the management strategy. Surgery with complete excision should be considered when technically feasible and safe, while antibiotics or a “wait and see” strategy remain acceptable alternatives
Green's functions for the static curvature and deflection of two-phase peridynamic elastic Euler-Bernoulli beams with exponential kernels
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Antarctic Bottom Water contraction drives abyssal ocean warming along SAMBA-West line (34.5°S) in the Argentine basin
No full textInternational audienceWe present an updated assessment of abyssal temperature trends in the Argentine Basin using expanded hydrographic and moored observations from the SAMBA-West line. The study addresses two main questions: (1) What is the spatial distribution of the abyssal warming along the SAMBA-West line? (2) What mechanisms drive the observed changes? Using output from a high-resolution numerical simulation, we first characterize how the abyssal flow near 34.5 • S relates to the broader basin-scale circulation, providing context for interpreting the observations. Within this framework, we find that SAMBA-West is situated within a dynamically complex junction of deep boundary currents and recirculation pathways in the northwestern portion of the Argentine Basin. A coherent, statistically significant warming trend is found across most of the array and vertically throughout the AABW layer, primarily due to its vertical contraction, likely reflecting reduced formation or export of the AABW.</div
Encombrement de la sphère de coordination cuivre(I)-diimine par un groupe benzyle : impact sur la stabilité et les propriétés photoredox
No full textInternational audienceCu(I)-bisdiimine complexes, [Cu(NN)2] + (where NN represents a diimine such as phenanthroline or bipyridine derivatives), are considered promising photosensitizers for various photochemical applications. However, their effectiveness is subject to several key challenges. In particular, controlling steric strain around the copper(I) center by introducing appropriate substituents (R) at the α-position of the nitrogen atoms is crucial for optimizing the excited-state properties of the complex. In brief, increasing the size of R leads to longer emission lifetimes and higher quantum yields. Additionally, the energy of the singlet excited state rises with increasing steric bulk, enhancing photoinduced reactivity. However, excessive steric strain from bulky substituents can significantly destabilize the coordination sphere. To balance complex stability with increased steric bulk around the metal center, we have developed two novel non-symmetrical ligands featuring branched alkyl chains and benzyl groups at the α-position of the nitrogen atoms. Our findings demonstrate that intramolecular π-stacking interactions between the benzyl group and the opposing phenanthroline ligand contribute to stabilizing the coordination sphere. Furthermore, the flexibility of the benzyl group reinforces the tetrahedral geometry around copper(I), resulting in an increased singlet excitedstate energy compared to benchmark complexes. Notably, we show that this enhancement in excited-state energy translates into greater excited-state reactivity.</div
Corps productifs, mécaniques de contrôle et puissance du sabotage dans deux nouvelles de Richard Matheson
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L’histoire de Bretagne dans les ABPO : une approche historiographique
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Stationary internal waves in a two-dimensional aquarium at low viscosity
No full textWe prove the uniform solvability of a stationary problem associated to internal waves equation with small viscosity in a two dimensional aquarium with real-analytic boundary, under a Morse-Smale dynamical assumption. This is achieved by using complex deformations of the aquarium, on which the inviscid stationary internal wave operator is invertible
TGCAT — A Tool to Analyse the Content of Sea Level Data Portals
No full textInternational audienceThe volume of tide gauge data available to the sea level community has grown substantially, with information distributed across numerous global, national, and institutional data centres. As a result, the main challenge is no longer accessing data, but identifying the most relevant dataset for a given application. Currently, more than 15 global data centres provide sea level information, each tailored to different users and use cases (e.g., real‐time monitoring, delayed‐mode analysis, monthly means). For users unfamiliar with tide gauge data, selecting the appropriate source can be difficult. Tide Gauge CATalog (TGCAT) is a software tool developed to address this challenge. It helps users discover where specific tide gauge data are available and assists data providers and centres in identifying inconsistencies, such as misreferenced stations or discrepancies in metadata. TGCAT collects metadata from global and national sea level data centres to produce intercomparable catalogues. It also allows visualisation of data availability timelines across multiple sources. Written entirely in Python and linked to an online dashboard ( www.sonel.org/tgcat ), TGCAT is designed as an open, community‐based platform. Its goal is to improve data discoverability, support better referencing practices, and help users navigate the complex landscape of tide gauge data portals
Quarante ans après l'adhésion : l'Espagne, miroir et laboratoire de l'intégration européenne
No full textInternational audienceIntroductio