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Peptidomimetics Inspired by α-Synuclein or Its Chaperone αB-Crystallin Differentially Modulate α-Synuclein Aggregation
No full textInternational audienceAggregation of the α-Synuclein (αSyn) protein in neurons is responsible for synucleinopathies such as Parkinson's disease. In healthy cells, αSyn is primarily present as monomers. Under pathological conditions, oligomers and fibrils are formed, leading to neuronal toxicity and death. No treatment prevents fatal synucleinopathies. We designed small peptidomimetics based on the structure of αSyn aggregates and on its chaperone protein αB-Crystallin. Interestingly, a relationship between the impact of peptidomimetics on the αSyn aggregation process, their sequences, and secondary conformation has been evidenced. In vitro and in cellular assays demonstrated that one compound based on αB-Crystallin was able to interfere with αSyn folding and aggregation by reducing the formation of oligomers and promoting off-pathway aggregation. The demonstration that physiological chaperone proteins can be mimicked by small peptide derivatives paves the way for new strategies to design inhibitors of amyloid protein aggregation, a hallmark of around 50 neurodegenerative and systemic amyloid diseases.</div
A Riemann-Roch formula for singular reductions by circle actions
No full textWe compute a Riemann-Roch formula for the invariant Riemann-Roch number of a quantizable Hamiltonian S^1-manifold (M,\omega,\mathcal{J}) in terms of the geometry of its symplectic quotient, allowing 0 to be a singular value of the moment map \mathcal{J}:M\to\mathbb{R}. The formula involves a new explicit local invariant of the singularities. Our approach relies on a complete singular stationary phase expansion of the associated Witten integral
Partial Bergman kernels and determinantal point processes on Kähler manifolds
No full textWe compute the full off-diagonal asymptotics of the equivariant and partial Bergman kernels associated with a circle action on a prequantized Kähler manifold with bounded geometry at infinity, then use these results to compute the asymptotics of the linear statistics of the associated determinantal point process as the number of points grows to infinity, showing that its distribution converges to a centered normal variable with variance given by the sum of an -norm squared in the bulk and an -norm squared on the boundary of the associated droplet
Maths en classe : la confiance en soi, une clé de la réussite ?
No full textL’article montre que la réussite en mathématiques ne dépend pas uniquement des connaissances ou des programmes, mais aussi du rapport émotionnel des élèves à la discipline. Le stress, la peur de l’erreur ou le sentiment de ne pas être « fait pour les maths » peuvent freiner les apprentissages et accentuer les inégalités, notamment entre filles et garçons.Des recherches récentes soulignent que l’anxiété mathématique est corrélée à de moins bons résultats, et que la confiance en soi et le sentiment d’efficacité jouent un rôle déterminant dans la réussite.L’auteure s’appuie sur une expérimentation menée en collège autour de jeux mathématiques (situations de recherche pour la classe). Dans ces dispositifs, les élèves explorent, testent des stratégies, argumentent et construisent progressivement les savoirs, sans pression immédiate de la bonne réponse.Ces pratiques favorisent trois dimensions du bien-être :émotionnelle : diminution du stress, droit à l’erreur, plaisir d’apprendrecognitive : engagement, sentiment de progresser, développement du raisonnementrelationnelle : échanges entre élèves, coopération, sentiment d’appartenanceL’article conclut que le bien-être n’est pas secondaire, mais constitue une condition essentielle de l’apprentissage des mathématiques. Créer un climat de sécurité émotionnelle permet aux élèves d’oser chercher, se tromper et apprendre, sans diminuer les exigences disciplinaires
Vers une étude de la coordination dans un grand corpus d'écrits scolaires
No full textInternational audienceThis article represents an alternative to teaching coordination as a memorization of a list of conjunctions. It traces the evolutions in school grammar that have led to this state of affairs and hypothesizes that it is possible to propose a progression in the conceptualization of coordination starting from conjunctions that share all the defining criteria of coordination, but with great differences in frequency in their use: et (and), ou (or) and ni (nor). The study of their distribution in a large corpus of school writings, supplemented on an exploratory basis by a reference corpus, makes it possible to compare the uses in argumentative and narrative texts and to point out the places where didactic intervention is expected.Cet article propose une alternative à un enseignement de la coordination se résumant à la mémorisation d'une liste de conjonctions. Il retrace les évolutions de la grammaire scolaire qui ont conduit à cet état de fait et pose l'hypothèse qu'il est possible de proposer une progression dans la conceptualisation de la coordination en partant des conjonctions qui partagent tous les critères définitoires de la coordination, mais avec de grandes différences de fréquence dans leur emploi : et, ou et ni. L'étude de leur répartition dans un grand corpus d'écrits scolaires, complété à titre exploratoire par un corpus de référence, permet de comparer les usages dans les textes argumentatifs et narratifs et de pointer les lieux où l'intervention didactique est attendue
Crustal-Scale Signatures of Steady-State Thermal Inheritance: Insights from the South China Sea
No full textInternational audienceLong-lived lateral variations in radiogenic heat production create persistent thermal heterogeneities that shape continental lithosphere over geological timescales. We introduce a steady-state concept of thermal inheritance, linking these variations to crustal-scale strain localization and tectonic architecture. Using numerical models, we explore both crustal-and lithospheric-scale consequences of heterogeneous heat production. A key finding is that lateral variations in heat production leave a distinct crustal-scale tectonic signature, controlling patterns of strain localization.The South China Sea serves as a proof-of-concept: the segmented, oblique extension observed there aligns with zones of mechanically weaker crust, reflecting the underlying inherited thermal heterogeneity. These results highlight that crustal-scale tectonic features can emerge from steady-state thermal conditions, independently of transient anomalies. They provide a quantitative framework linking inherited thermal structure to observable deformation patterns. More broadly, our study suggests that laterally heterogeneous heat production offers a physically motivated alternative to traditional exponential-decay models, better capturing the spatial complexity and persistence of lithospheric thermal structure. By emphasizing the crustal imprint of thermal inheritance, we demonstrate that radiogenic heat variations are a fundamental control on strain localization and tectonic segmentation. This approach opens a new perspective on how long-lived thermal heterogeneities shape continental deformation and the architecture of lithospheric structures over hundreds of millions of years
ADRC-based dual-loop control and stability analysis of stacked interleaved DC–DC buck converter for hydrogen production using PEM electrolyzer
No full textInternational audienceHydrogen production via water electrolysis, particularly using Proton Exchange Membrane (PEM) electrolyzers, is a key technology for advancing renewable energy integration. Ensuring a stable and efficient supply requires DC–DC converters capable of precise regulation under disturbances. This paper proposes a dual-loop Active Disturbance Rejection Control (ADRC) strategy for a stacked interleaved DC–DC converter supplying a PEM electrolyzer. The proposed ADRC enhances robustness against disturbances and improves system stability under dynamic conditions typical of RES-based microgrids. Simulation results demonstrate that the approach significantly improves voltage regulation and overall performance—achieving a settling time of 10 ms and limiting overshoot to 20.06%—thereby ensuring a reliable and efficient power supply for PEM electrolyzers in renewable energy applications
Impact of charge transfer inefficiency on transit light curves: A correction strategy for PLATO
No full textInternational audienceContext. PLATO is designed to detect Earth-sized exoplanets orbiting solar-type stars and to measure their radii (relative to the star radii) with an accuracy better than 2% via the transit method. Charge transfer inefficiency (CTI), a by-product of radiation damage to charge-coupled devices (CCDs), can jeopardise this accuracy constraint and therefore must be corrected to reach scientific requirements.Aims. We assessed and quantified the impact of CTI on transit depth measurements. Our objective was to demonstrate the need for CTI correction and to develop a correction strategy that restores CTI-biased transit depths with an acceptable residual within the accuracy budget.Methods. Using a calibration dataset generated with PLATOSim to simulate a realistic stellar field, we modelled the parallel overscan signal as the sum of exponential decays and used least-squares fitting to infer the number of trap species and initial estimates for the release times (τr,k). Smearing was then modelled with an exponential-plus-constant function and removed on a column-wise basis. We modelled the spatial variation in the trap density with a quadratic polynomial function of the radial distance from the centre of the focal plane. The polynomial coefficients (ap,k) of this model, the well-fill power index (β), and the release times (τr,k) were subsequently adjusted via an iterative application of the extended pixel edge response method combined with a CTI correction algorithm. This yielded the final calibration model that underpins our correction strategy.Results. In the worst-case scenario (8-year mission, high CTI impact zone), we found that CTI induced a bias of approximately 4% in the measured transit depth. The polynomial coefficients from our trap density model were then used to correct the CTI-affected transit depths. Our correction reduced the bias to a residual of 0.06%, which is comfortably within PLATO’s accuracy requirements.Conclusions. We quantified the CTI-induced bias in transit depth measurements and implemented a calibration strategy that incorporates spatial variations in trap density. From the calibrated parameters, we derived a correction scheme that brought the photometric measurements within PLATO’s noise budget, ensuring that the mission’s precision requirements are met
Four high resolution solar atlases of the 3000 Å - 9900 Å range
No full textWe present a set of useful high resolution atlases of the Sun in FITS format, originally produced by Delbouille et al (1972), Kurucz et al (1972) at disk centre, Gandorfer (2000, 2002, 2005) and Stenflo (2014, 2015) close to the limb (respectively for μ = cosθ = 0.1 for Gandorfer and 0.145 for Stenflo). The ZIP file contains the FITS data (wavelength and intensity) together with derived sets of PNG spectral images of 100 Å bandwidth
Electrocaloric cooling efficiency: Comparative insights on P(VDF-TrFE-CFE) polymer and BSTM ceramics
No full textInternational audienceIn response to the increasing demand for efficient and compact refrigeration and energy conversion devices, research has focused on identifying optimal electrocaloric (EC) materials among ferroelectric ceramics and polymers. This study investigates the EC properties of the Poly [(Vinylidene Fluoride) 0.664 -(Trifluoroethylene) 0.245 -(Chlorofluoroethylene) 0.091 ] terpolymer and multi-layer Ba 0.6 Sr 0.4 Ti 0.998 Mn 0.002 O 3 (BSTM) ceramics, comparing various parameters to assess their suitability for advanced energy applications.The multilayer ceramic capacitor contains a large amount of inactive material, which hinders the performance of the capacitor both in terms of ΔT ad and efficiency. Finite-element modeling with direct temperature measurement was therefore employed to extract intrinsic electrocaloric response from geometric and diffusion effects, providing the ΔT ad and diffusion-related energy losses required for evaluating the cooling efficiency. Adiabatic temperature change (ΔT ad ) obtained in an electric field representing long-term operation, reaches 4.91 • C for Terpo at 100 V/ μm and 3.0 • C for BSTM at 30 • C. The loss in ferroelectric hysteresis is observed to be much lower in BSTM than in PVDF Terpolymer. Hence, the cooling efficiency relative to Carnot reveals that the PVDF Terpolymer achieves a relative cooling efficiency upper bound of 4.5% at 100 V/μm, whereas BSTM ceramics reach nearly 14 times, being 62.1% at 30 V/μm. The PVDF Terpolymer outperforms BSTM ceramics in terms of adiabatic temperature change and flexibility, but not in terms of expected cooling efficiency. Considering these complementary strengths, both BSTM ceramics and PVDF terpolymers emerge as promising electrocaloric materials for advanced energy applications, including solid-state cooling and energy harvesting