Portail HAL-PSL
Not a member yet
293219 research outputs found
Sort by
Wadsley-Roth FeNb11O29 as negative electrode material for lithium solid-state batteries
No full textInternational audienceFeNb 11 O 29 and Li 6 PS 5 Cl but revealed an interfacial degradation, with a resistive Li 2 S/oxide-rich interface, consistent with impedance growth. These findings highlight the critical role of microstructural and interfacial optimisation in the electrode composites and establish FeNb 11 O 29 as a promising candidate for high-rate solidstate batteries.</div
Hydration mechanisms in Roman seawater concrete: Archaeological analogue for validation of long-term ageing reactive transport model
No full textInternational audienceCement-based materials are considered for sealing plugs in deep geological disposal of radioactive waste. Ensuring their long-term durability is critical for safety over millennia. The Roman Concrete (RoC) project uses ancient Roman underwater concretes as analogues to validate reactive transport models for long-term ageing.This study focuses on hydration mechanisms in Roman concrete made with Phlegrean pozzolan, slaked lime, and seawater. Various techniques (XRD, SEM-EDS, NMR, nanoindentation, microtomography, ICP-OES, ion chromatography) were used to characterize hydration products. Casting underwater led to aragonite and brucite layers with a 60 GPa Young's modulus, protecting the concrete from further degradation. In the core, pozzolanicreactions produce C-(A)-S-H phases (Ca/Si = 1.2; Al/Si = 0.2) with a modulus of 12 GPa. HYTEC modeling confirmed the mechanism: incongruent pozzolan dissolution releases ions (K+, SiO₄ 4− , Al3+, Na+), promoting C-(A)-S-H formation and portlandite consumption
Toward an alternative to the EU migration policy : hospitality as ethics
No full textInternational audienc
Sull’edizione di Bartolomeo Anglico, o della collazione a campione di manoscritti digitalizzati
No full textInternational audienc
Comment Hélinand de Froidmont travaillait-il ? Découvrir ses notes grâce à des collections d’exempla cisterciennes
No full textInternational audienc
Evolutionarily stable cleistogamy
No full textInternational audienceCleistogamy, the production of closed flowers providing obligatory selfed seeds, has evolved repeatedly in more than 50 botanical families. Usually associated with chasmogamy, open flowers producing potentially outcrossed seeds in various proportion is an iconic example of mixed self-fertilization.Here, I develop an analytical Evolutionarily Stable Strategies (ESS) model for the evolution of cleistogamy. The model considers the role of inbreeding depression and the dependence of pollen export to chasmogamous flowers. Three generic functional relationships between pollen export and cleistogamy are considered. The model reveals that the classical inbreeding depression threshold of 0.5 no longer applies in the evolution of cleistogamy. Evolutionarily stable mixed cleistogamy is possible when inbreeding depression is low (below 0.5) and when pollen export per flower decreases with the rate of chasmogamy, consistent with the higher physiological cost of open flowers relative to closed flowers. Beyond the cost of flower types, the model points out the major impact of cleistogamy rate on gene transmission through pollen in the evolution of cleistogamy
Reconstruct Anything Model: a lightweight foundation model for computational imaging
No full textInternational audienceMost existing learning-based methods for solving imaging inverse problems can be roughly divided into two classes: iterative algorithms, such as plug-and-play and diffusion methods leveraging pretrained denoisers, and unrolled architectures that are trained end-to-end for specific imaging problems. Iterative methods in the first class are computationally costly and often yield suboptimal reconstruction performance, whereas unrolled architectures are generally problem-specific and require expensive training. In this work, we propose a novel non-iterative, lightweight architecture that incorporates knowledge about the forward operator (acquisition physics and noise parameters) without relying on unrolling. Our model is trained to solve a wide range of inverse problems, such as deblurring, magnetic resonance imaging, computed tomography, inpainting, and super-resolution, and handles arbitrary image sizes and channels, such as grayscale, complex, and color data. The proposed model can be easily adapted to unseen inverse problems or datasets with a few fine-tuning steps (up to a few images) in a self-supervised way, without ground-truth references. Throughout a series of experiments, we demonstrate state-of-the-art performance from medical imaging to low-photon imaging and microscopy. Our code is available at https://github.com/matthieutrs/ram
Broad Iron Line as a Relativistic Reflection from Warm Corona in AGN
No full textInternational audienceWe present that the broad feature usually observed in X-ray spectra can be explained by a ray-traced emission from a two-slab system containing a dissipative, warm corona on top of an accretion disk in an AGN. Such an accretion flow is externally illuminated by X-ray radiation from a lamp located above a central SMBH. Thermal lines from highly ionized iron ions (FeXXV and FeXXVI), caused by both internal heating and reflection from the warm corona, can be integrated into an observed broad line profile due to the close vicinity of the SMBH. We investigate the dependence of the broad line profile by varying the SMBH spin parameter, viewing angle, lamp height, and dissipation factor. Our results introduce a new method to probe properties of the warm corona using high-resolution spectroscopic measurements. We use the photoionization code TITAN to compute local ion populations and emission line profiles, and the ray-tracing code GYOTO to include relativistic effects on the outgoing X-ray spectrum. In our models, the temperature of the inner atmosphere covering the disk can reach values of 10^7 - 10^8 K due to internal warm corona dissipation and external illumination, which is adequate for generating the highly ionized iron lines. These lines can undergo significant gravitational redshift near the black hole, leading to a prominent spectral feature centered around 6.4 keV. For all computed models, the relativistic corrections shift highly ionized iron lines to the X-ray region, usually attributed to fluorescent emission from the illuminated skin of an accretion disk. Hence, in the case of a warm corona covering the inner disk regions, the resulting theoretical line profile under strong gravity is a sum of different iron line transitions, and those originating from highly ionized iron contribute the most to the observed total line profile in AGN
Investigating the Influence of Training Difficulty on the Learning Outcomes of Medical Students
No full textInternational audienceBackground: Determining an optimal training difficulty level for the best learning outcome is a crucial goal for adaptive educational systems. The literature supports the Inverted U-shape Hypothesis, suggesting that the ideal challenge level for learning is neither too easy nor too difficult. However, this optimal point depends on the type of training and response modality and may vary across domains, necessitating thorough examination before implementing adaptive learning procedures.Objectives: This study aimed to investigate the influence of training difficulty on the learning outcomes of French medical students.Methods: Using data from a national educational platform, we explored the influence of the mean question difficulty encountered during training, relative to individual student ability, on the learning outcomes of medical students across diverse medical specialties. Importantly, the mean difficulty level varied randomly between students on this platform, mirroring a quasi-experimental design and enabling a thorough exploration of these effects. We first employed the Elo rating system to estimate the difficulty of platform questions and the evolution of students’ abilities. A linear mixed-effects model was then used, with final exam performance as the main outcome and mean relative question difficulty during training (linear and quadratic terms) as the main predictor.Results and Conclusions: Results showed a significant negative quadratic effect of mean relative difficulty on final exam performance, revealing optimal difficulty levels for each medical specialty. Additionally, the analysis demonstrated that students with high abilities displayed a more pronounced inverted U-shaped relationship between training difficulty and final exam scores. This study advances our understanding of optimal training difficulty in the complex realm of medical education by emphasizing the need to acknowledge variability across medical specialties and student abilities