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Phase Separation in Lead-Saponified Drying Oils: Implications for Historical Painting Techniques and Paint Stability
No full textInternational audienceRenaissance Masters often prepared siccative oils by heating linseed oil with siccatives, particularly lead oxide, inducing partial saponification and altering its properties. Our reconstructions show that lead-saponified oils naturally separate into two phases. In this study, we investigate the differences between these two phases through a comprehensive set of analytical methods, from macro-level assessments (rheology) to micro-level characterizations (SAXS, WAXS, optical microscopy, SEM), and chemical analyses (FTIR, GC-MS and SFC-HRMS, TGA and DSC).The lower phase is enriched in free fatty acids and lead carboxylates, especially saturated species-both as free acids and metal soaps-prone to self-organization. As a result, the lower phase displays a pronounced lamellar organization with partial crystallization, and exhibits viscoelastic and shear-thinning properties. In contrast, the unstructured upper phase behaves as a Newtonian fluid. The observed phenomena share similarities with the formation of soap-related defects such as protrusions, linked to saturated lead soaps. Teaser Spontaneous phenomenon of phase separation in saponified oils influences the structure and behavior of historical paint systems
Modélisation des Court-circuits entre Spires dans les Machines Synchrones Multiphasées utilisant des Capacités de Partage de Puissance
No full textInternational audienceThis paper explores the modeling of interturn short circuits in segmented permanent magnet synchronous machines, with a focus on highly coupled segmentation and multi-sector segmentation of its winding. It introduces a specific approach, providing a consistent framework for analyzing this phenomenon when the segmented drive operates in power sharing mode. The study presents a comprehensive model for analyzing inter-turn short circuits faults regardless of the segmentation technology implemented. This model is compared with data extracted from an experimental bench designed in the laboratory for this study. The analysis shows an excellent fit of the model to the experiment. Also, the analytical structure implemented enables comparing the impact of power sharing on segmented structures. The main results reveal that, contrary to highly coupled segmentation, multi-sector segmentation configurations exhibit greater sensitivity to power sharing variations, particularly depending on the degrees of freedom of the segment where inter-turn short circuit fault occurs.Ce document étudie la modélisation des courts-circuits entre spires dans les machines synchrones à aimants permanents fractionnées, en mettant l’accent sur le fractionnement fortement couplé et le fractionnement multisecteur de leur enroulement. Il présente une approche spécifique, offrant un cadre cohérent pour analyser ce phénomène lorsque l’entraînement fractionné fonctionne en mode de partage de puissance. L’étude propose un modèle complet pour analyser les défauts de courts-circuits entre spires, indépendamment de la technologie de fractionnement mise en œuvre. Ce modèle est comparé aux données issues d’un banc d’essai expérimental conçu en laboratoire pour cette étude. L’analyse montre une excellente adéquation entre le modèle et les résultats expérimentaux. De plus, la structure analytique développée permet de comparer l’impact du partage de puissance sur les structures fractionnées. Les principaux résultats révèlent que, contrairement au fractionnement fortement couplé, les configurations de fractionnement multisecteur présentent une sensibilité accrue aux variations de partage de puissance, notamment en fonction des degrés de liberté du segment où survient le défaut de court-circuit entre spires
Enhancing Soil Moisture Statistical Retrieval from SMOS using Partial Convolutions and Localization Strategies
No full textInternational audienceNeural networks have been used for the retrieval of soil moisture (SM) from microwave observations over the last 20 years. The exploitation of the SMOS (Soil Moisture and Ocean Salinity) observations has largely benefited from such statistical models. However, these retrievals are currently done at the pixel level, ignoring spatial context and using a constant incidence angle configuration approach. While pixels are seen with a varying number of angles from the SMOS instrument, only pixels monitored by a fixed pre-selected angle configuration are considered. These two limitations can have a negative impact on the quality of the retrievals. This paper introduces a new NN architecture that combines two powerful innovations. Firstly, the new model is image-based: it ingests entire SMOS orbit swath and thus leverages the strong spatial pattern present in the satellite observations. Secondly, a “partial convolutional layer” is tested. It allows being flexible, in the retrieval, on the angle configuration: more incidence angles can be exploited when they are available. Finally, a concept called “Localization” is also exploited, helping the NN retrieval to adapt his behaviour to specific local conditions Experiments are conducted at SMOS orbit scale over the contiguous united states (CONUS) region using five years of SMOS data (2016–2019). A temporal correlation of 0.74 (unit-less) with respect to ERA5 reanalysis and 0.62 with respect to in situ SM measurements network are obtained (to be compared to respectively 0.63 and 0.60 with the legacy pixel and fixed angle based approach). Furthermore, the use of partial convolutions results in enlarging the retrieval domain by +240% versus legacy retrieval, and by +140% versus the operational SMOS Level-2 product
Technical status report on plasma components and systems in the context of EuPRAXIA
No full textInternational audienceThe EuPRAXIA project [Walker et al., J. Phys.: Conf. Ser. 874, 012029 (2017)] aims to construct two state-of-the-art accelerator facilities based on plasma accelerator technology. Plasma-based accelerators offer the possibility of a significant reduction in facility size and cost savings over current radio frequency (RF) accelerators. The two facilities—one laser-driven, one a beam-driven—are envisioned to provide electron beams with an energy in the range of 1–5 GeV and beam quality comparable to existing RF machines. This will enable a versatile portfolio of applications from compact free-electron laser drivers to sources for medical and industrial imaging. At the heart of both facilities is the use of plasma-based accelerator components and systems, which encompass not only the accelerating medium itself but also a range of auxiliary systems such as plasma-based electron beam optics and plasma-based mirrors for high-intensity lasers. From a technical standpoint, a high-degree of control over these plasma devices will be essential for EuPRAXIA to achieve its target performance goals. The ability to diagnose and characterize these plasma devices and to simulate their operation will be further essential success factors. Additionally, compatibility with extended operation at high-repetition rates and integration into the accelerator beamline will also prove crucial. In this work, we aim to review the current status of plasma components and related systems for both laser-driven and beam-driven plasma accelerators and to assess challenges to be addressed regarding implementation at future EuPRAXIA facilities
Temperature-Dependent Coarse-Grained Model for Simulations of Intrinsically Disordered Protein LCST and UCST Liquid–Liquid Phase Separations
No full textInternational audienceMany intrinsically disordered proteins (IDPs) can undergo a liquid-liquid phase separation (LLPS) in water, depending on the solution conditions (temperature, pH, ionic strength). There are two types of LLPS that are controlled by temperature, those occurring above a lower critical solution temperature (LCST) and those occurring below an upper critical solution temperature (UCST). IDP coarse-grained (CG) models are particularly well appropriate for investigating the physical chemical factors that govern their LLPS and supramolecular organization. However, the development of CG models allowing simulations of both LCST and UCST behavior of temperature-sensitive IDPs is still in its infancy. In this context, we present here a novel temperature-dependent (TD) CG model for IDP simulations based on MARTINI 3 force field. The model was developed by modifying the Lennard-Jones potentials between the apolar or charged solute beads and water with a TD rescaling factor. It was parametrized to fit the TD potentials of mean force (PMF) between two apolar or two charged molecules computed using all-atom (AA) simulations. We show that the TD CG model is able to 1 reproduce the experimentally known LLPS of both LCST and UCST low-complexity sequences, and to estimate phase transition temperatures comparable to experimental measurements
Visualisation graphique sur le web : enjeux créatifs et usages pédagogiques
No full textInternational audienceIn this article, we explore the web both as a medium and a technical platform through its creative and pedagogical uses. Adopting an empirical approach inspired by research-creation, we examine the technical and graphical challenges of the web based on a case study focused on the visualization of the most popular YouTube videos. A second part of the text addresses the creative and pedagogical implications of automated graphic tools. We discuss the impact of AI tools on students' technical proficiency and their ability to experiment with new visual forms, emphasizing the development of concrete projects, the creation of functional prototypes, and the exploration of innovative discursive forms.Dans cet article, nous explorons le web comme média et support technique à travers ses usages créatifs et pédagogiques. En adoptant une approche empirique inspirée de la recherche-création, nous interrogeons les enjeux techniques et graphiques du web à partir d'un cas d'étude portant sur la visualisation des vidéos les plus populaires de YouTube. Une deuxième partie du texte s'intéresse aux implications créatives et pédagogiques liées aux outils graphiques automatisés. Nous discutons l'impact des outils IA sur la maîtrise technique des étudiants ainsi que sur leur capacité à expérimenter de nouvelles formes visuelles, en mettant l'accent sur la réalisation de projets concrets, la conception de prototypes fonctionnels et l'exploration de nouvelles formes discursives
Unlocking the mystery of strontium synthesis in the early Galaxy through analysis of barium isotopes in very metal-poor stars
No full textInternational audienceAims . We determine the contributions of the rapid (r) and slow (s) neutron capture processes to the Ba isotope mixture, along with Ba, Eu, and Sr NLTE abundances, in a sample of very metal-poor stars. The selected stars formed before the contribution from the main s-process in low- and intermediate-mass stars became significant. Some of our sample stars are enhanced in Sr, with [Sr/Ba] reaching up to 0.7. These stars gained their high Sr abundance from a poorly understood process, sometimes referred to in the literature as a light element primary process, which may appear to be a weak s-process or a weak r-process. Our aim is to uncover the nature of this additional Sr source. Methods . The abundances derived from the resonance Ba II 4554 and 4934 Å lines are influenced by the adopted Ba isotope mixture. We computed Ba isotope mixtures corresponding to different r- to s-process contributions (pure r-process, 80%/20%, 50%/50% and 12%/88%, i.e. solar ratio) and determined the corresponding abundances from the Ba II resonance lines in each sample star. Additionally, we determined Ba abundances from weak subordinate Ba II lines, which are unaffected by the adopted Ba isotope mixture. We then compared the Ba abundances derived from the subordinate lines with those from the Ba II resonance lines. Results . We find a higher s-process contribution to Ba isotopes in stars with greater [Sr/Eu] and [Sr/Ba] overabundances, suggesting that the additional Sr synthesis was due to the early s-process occurring in massive stars. Using Sr-enhanced stars, we estimate the [Sr/Ba] ratio produced by the early s-process and obtain [Sr/Ba] earlyS = 1.1 ± 0.2. The derived value should be regarded as an upper limit, as we cannot definitively exclude the possibility of a contribution to Sr from the weak r-process, which produces Sr but not Ba. Regarding the potential synthesis of Sr and Ba in the i-process in massive stars, our results for Ba isotopes and element abundances argue that there was no detectable contribution from this process within the error bars in our sample stars. Conclusions . In the early Galaxy, before significant main s-process enrichment, barium and strontium were produced primarily by the main r-process and the early s-process, which occurred in rapidly rotating massive stars
Ondes élastiques guidées dans un tube gaine en alliage de zirconium chromé
No full textUltrasons laser, interaction son-lumière; GAPSUS - Acoustique Physique, Sous-Marine et Ultra-SonoreNational audienceLes ondes élastiques guidées sont utilisées pour le contrôle des tubes, notamment pour la détection de fissures ou la mesure d'épaisseur. Ces ondes sont engendrées efficacement par impact laser et peuvent être détectées par interférométrie laser, offrant des mesures à large bande et sans contact. Cette étude exploite les ondes guidées, engendrées et détectées par ultrasons laser, pour évaluer les propriétés mécaniques d’un revêtement de chrome déposé sur un tube en alliage de zirconium (M5). La dispersion ainsi que l’observabilité des modes par notre dispositf ultrasons-laser, sont calculées pour différentes épaisseurs de revêtements à l’aide du code GEWtool (1). Dans un tube non-revêtu, les premier et second modes longitudinaux L(0,1) et L(0,2), respectivement analogues aux modes A0 et S0 dans une plaque, convergent vers le mode Rayleigh. Un dépôt de chrome modifie la dispersion et l’observabilité des modes, notamment celles du mode L(0,2). Ce mode est bien observé et particulièrement sensible à l’épaisseur du revêtement dans une gamme de fréquences bornée par la fréquence de coupure du mode de surface existant pour une même épaisseur de chrome déposée sur un substrat semi-infini en M5 (2). En revanche, en haute fréquence, la vitesse de phase de ce mode converge vers la vitesse de cisaillement du M5 et il n’est plus observable. Nous concluons que l'utilisation du mode L(0,2) est limitée aux couches très fines. Ces prédictions théoriques sont comparées à des mesures réalisées par ultrasons laser sur différents tubes. (1) D. A. Kiefer (2023). GEWtool. https://doi.org/10.5281/zenodo.10114243 (https://github.com/dakiefer/GEWtool) (2) G.W. Farnell and E.L. Adler. “Elastic Wave Propagation in Thin Layers”. 9 (1972). Physical Acoustics Elsevier, pp. 35–127
The most metal-poor stars
No full textInternational audienceThe most metal-poor stars found in the Galaxy and in nearby galaxies are witnesses of the early evolution of the Universe. In a general picture in which we expect the metallicity to increase monotonically with time, as a result of the metal production in stars, we also expect the most metal-poor stars to be the most primitive objects accessible to our observations. The abundance ratios in these stars provide us important information on the first generations of stars that synthesised the nuclei that we observe in these stars. Because they are so primitive the modelling of their chemical inventory can be often satisfactorily achieved by assuming that all the metals were produced in a single supernova, or just a few. This is simpler than modelling the full chemical evolution, using different sources, that is necessary at higher metallicity. The price to pay for this relative ease of interpretation is that these stars are extremely rare and require specifically tailored observational strategies in order to assemble statistically significant samples of stars. In this review we try to summarise the main observational results that have been obtained in the last ten years
