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Roman-Egyptian mummy portraits and panels of gods from the Louvre: renewed historical and material knowledge
No full textInternational audienceSummation of the results of the material study conducted on the collection of Fayum portraits and panels of gods from the Louvre Museum between 2020 and 202
Engineering MgFe<sub>2</sub>O<sub>4</sub> nanoparticles to enhance magnetic, optical, and dielectric performance
No full textInternational audienceThis research investigated the effects of solution pH during synthesis and annealing on the structural, magnetic, optical, and dielectric properties of MgFe2O4 synthesised using the citric acid-assisted sol-gel auto-combustion method. Structural data showed that crystallinity, lattice parameters, and cation distribution were strongly influenced by both pH and annealing temperature. Optimal morphology and crystallinity were achieved at pH 7 and an annealing temperature of 550 °C for 3 h, under which cation ordering and defect reduction were effectively achieved. Magnetic characterisation revealed a significant improvement in saturation magnetisation (20.6 emu/g) under optimal conditions, attributed to increased super-exchange interactions. The optical bandgap was modulated by more than 11% (2.04 to 2.30 eV) by adjusting pH-mediated surface chemistry and subsequent defect states. The sample synthesised at pH 9 exhibited the highest values of ε’, ε”, and σac. These results conclusively demonstrate that accurate control of synthesis pH and annealing enables the design of multifunctional properties in MgFe2O4 nanoparticles, providing a solid foundation for their application in high-end magnetic, optical, and electronic devices
“Poètes d’aujourd’hui” et l’École de Rochefort : une tentative de patrimonialisation collective ?
No full textInternational audienceThe remarkable longevity of the "Poètes d'aujourd'hui" collection (1944-2007) has produced a complex catalog featuring a multiplicity of internal series. The collection thus progresses by gradually investing linguistic fields, geographical areas, extra-poetic and sometimes political themes or poetic genres. Among the series that can be identified, the case of literary circles is illustrated by the École de Rochefort, in which Jean-Yves Debreuille sees an "area of influence" for Seghers, who found authors and critics for various collections there. From 1941 onwards, this circle brought together some thirty poets born between around 1900 and 1920, belonging to a generation to which Seghers (1906-1987) also belonged. They gradually entered the catalog, probably through the intermediary of René Lacôte (1913-1971) and René Guy Cadou (1920-1951), with whom Pierre Seghers had been in contact since 1940, and occupied several complementary roles (poet, critic, literary historian, collection director). Even though it integrates them into a larger whole, the catalog bears the trace of the group's earlier social contacts and cohesion; its bibliographic organization reveals a school effect that reflects a convergence of interests: the poets of Rochefort made Editions Seghers a tool in the service of their own patrimonialization, while the publisher used these connexions to strengthen his own network.La remarquable longévité de la collection « Poètes d’aujourd’hui » (1944-2007) a produit un catalogue complexe, comportant une multiplicité de séries internes. La collection progresse ainsi en investissant progressivement des domaines linguistiques, des aires géographiques, des thématiques extra-poétiques et parfois politiques ou des genres poétiques. Parmi les séries repérables, le cas des cercles littéraires est illustré entre autres par l’École de Rochefort, dans laquelle Jean-Yves Debreuille voit une « aire d’influence » pour Seghers, qui y trouve des auteurs et des critiques pour différentes collections. Ce cercle réunit à partir de 1941 une trentaine de poètes nés entre 1900 et 1920 environ, appartenant donc à une génération dont Seghers (1906-1987) fait aussi partie. Ceux-ci entrent peu à peu dans le catalogue, probablement grâce à l’entremise de René Lacôte (1913-1971) et de René Guy Cadou (1920-1951), avec qui Pierre Seghers est en contact dès l’année 1940, et y occupent plusieurs rôles complémentaires (poète, critique, historien de la littérature, directeur de collection). Même s’il les intègre à un ensemble plus vaste, le catalogue porte la trace des sociabilités antérieures et de la cohésion de ce groupe ; il laisse apparaître dans son organisation bibliographique un effet école qui traduit une convergence d’intérêts : les poètes de Rochefort ont fait des éditions Seghers un outil au service de leur propre patrimonialisation tandis que l’éditeur a mis à profit ce réseau pour renforcer le sien
A CNN encoder for modal phase reconstruction in Adaptive Optics systems
No full textPyramid wavefront sensing (pWFS) offers some of the best sensitivity for adaptive optics, but suffers from strong non-linearity. Modulation can extend linear range at the expense of sensitivity. Operating the pyramid without modulation is therefore attractive, but remains challenging. We develop a non-linear CNN reconstructor for pyramid wavefront sensing that maps pWFS images directly to a modal phase representation, and we assess simple hybrid methods combining it with a standard linear least-squares (LS) reconstructor. Using the end-to-end COMPASS simulator, we generate a large open-loop dataset spanning wide ranges of RMS and power spectra to train a compact CNN encoder. We then compare the CNN against an LS baseline and evaluate hybrid schemes in closed-loop simulations over a grid of guide-star magnitudes and Fried parameters, reporting long-exposure Strehl at lambda=1.6 um with controller gain re-optimized per method and bin. We also report preliminary offline bench tests on SCExAO. The CNN reduces open-loop reconstruction error and, in closed loop, outperforms LS across most (magnitude, r_0) conditions, with the largest gains for faint stars where it often closes the loop while LS does not. In very strong turbulence, LS can exceed the CNN; in these cases the hybrid methods are necessary to surpass LS, with a second-stage NN performing best. Inference is real-time capable and the hybrid overhead is negligible. Bench snapshots on SCExAO show successful correction of small static/slow perturbations, with instability for stronger/faster cases. A compact CNN can be trained to perform modal reconstruction for a non-modulated pWFS and improves performance over a classical linear reconstructor in most regimes. When the CNN alone is not optimal, simple hybrid methods achieve the best performance, suggesting a practical way to exploit the pyramid’s sensitivity without modulation
2013-2023 : retour sur les programmes PatrimEph et ThesaurEph
No full texthttps://ephemera.hypotheses.org/category/actualite
Entropic Fluctuation Theorems for the Spin-Fermion Model
No full textInternational audienceWe study entropic fluctuations in the Spin–Fermion model describing an N -level quantum system coupled to several independent thermal free Fermi gas reservoirs. We establish the quantum Evans–Searlesand Gallavotti–Cohen fluctuation theorems and identify their link with entropic ancilla state tomography and quantum phase space contraction of non-equilibrium steady state. The method of proof involves the spectral resonance theory of quantum transfer operators developed by the authors in previous works
Le modèle de la confluence : les formations professionnelles en France.
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José Antonio Kast au pouvoir au Chili : un tournant symptomatique d’une radicalisation droitière en Amérique latine
No full textBergman kernels and Poincaré series
No full textWe show that the Bergman kernel of a finite-volume quotient of a Hermitian manifold with bounded geometry by a discrete group of its isometries is the same as the average of the Bergman kernel upstairs. We then use these results when is a Hermitian symmetric space to show that a large class of relative Poincaré series does not vanish. This extends the results of Borthwick-Paul-Uribe and Barron (formerly Foth) to the case of general locally symmetric spaces of finite volume