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Stratifying quiver Schur algebras via ersatz parity sheaves
No full text41 pagesWe propose an extension of the theory of parity sheaves, which allows for non-locally constant sheaves along strata. Our definition is tailored for proving the existence of (proper, quasihereditary, etc) stratifications of Ext-algebras. We use this to study quiver Schur algebras A(α) for the cyclic quiver of length 2. We find a polynomial quasihereditary structure on A(α) compatible with the categorified PBW basis of McNamara and Kleshchev-Muth, and sharpen their results to arbitrary characteristic. We also prove that semicuspidal algebras of A(nδ) are polynomial quasihereditary covers of semicuspidal algebras of the corresponding KLR algebra R(nδ), and compute them diagrammatically
La babélisation de la pratique réflexive dans la formation initiale des enseignants : une étude qualitative multiniveau
No full textInternational audienceLa pratique réflexive (PR) est une compétence clé pour la professionnalisation des enseignants (Cornejo, 2003; Tardif & Núñez-Moscoso, 2018). Cependant, son concept demeure polysémique, étant associé à des outils pédagogiques, des compétences professionnelles, des fonctions critiques ou des concepts théoriques (Chouinard & Caron, 2015). La littérature n’éclaire pas clairement comment la PR est comprise par les différents acteurs de la formation initiale des enseignants (FIE), notamment au Chili. À partir d’une approche inductive (Zemelman, 2005 ; Nunez-Moscoso, 2013), cette étude explore les conceptions de la PR à différents niveaux : transnational (OCDE, UNESCO), national (documents éducatifs chiliens), institutionnel (programmes de formation de trois centres au Chili) et individuel (entretiens avec directeurs, coordinateurs, formateurs et enseignants en formation). L’analyse met en évidence quatre tensions dans les conceptions de PR : 1) vision appliquée vs spéculative, 2) espaces effectifs vs idéalistes, 3) outils de documentation vs déploiement, et 4) développement individuel vs collectif. Ces résultats montrent des divergences entre institutions et acteurs, mais révèlent aussi des défis communs, tels que clarifier les fonctions et outils de la PR. L’étude recommande une collaboration visant à intégrer des conceptions partagées et des approches opérationnelles de la PR dans les programmes de formation
Spectro-photometry of Phobos simulants, II: Effects of porosity and texture
No full textInternational audienceSurface porosity and texture has been found to be an important property for small bodies. Some asteroids and comets can exhibit an extremely high surface porosity in the first millimeter layer. This layer may be produced by various processes and maintained by the lack of an atmosphere. However, the influence of porosity on the spectro-photometric properties of small body surfaces is not yet fully understood.In this study, we looked into the effect of the texture on the spectro-photometric properties of Phobos regolith spectroscopic simulants. Macro- and micro-porosity were created by mixing the simulants with ultra-pure water, producing ice-dust particles, and then sublimating the water. The sublimation of the water ice enabled the production of porous and rough powdered simulants with significant micro- and macro-porosity associated with macro-roughness. The reflectance spectroscopic properties in the visible and near-infrared (0.5–4.2m) demonstrate a brightening of the porous samples in comparison to the compact ones. One simulant exhibits a bluing of the spectral slope after increasing porosity, which is likely linked to the presence of expandable phyllosilicates. In the mid-infrared range, a contrast increase of the 10 m emissivity-related plateau due to silicates is observed. This spectral feature is typically observed as a 10m emissivity plateau on some asteroids, making the mid-infrared region important for assessing mineralogy and surface texture.Photometry reveals a modification of the phase reddening behavior between the compact powder and the sublimation residue for both simulants. However, the observed behavior is different between the simulants, suggesting that the phase reddening may be dependent on the composition of the simulants. The phase curves of the sublimation residues exhibit a higher contribution of forward scattering. The derivation of the Hapke parameters indicates an increase in roughness for the porous sample, but no significant modification of the opposition effect. The modifications of the spectrophotometric properties observed in this experiment are definitely due to the textural changes obtained after sublimation, which depend on the initial composition of the simulants.This study aims to provide new insights into the understanding of porosity by using two Phobos simulants in the context of the upcoming JAXA/Martian Moons eXploration mission. We suggest that the Phobos blue unit may be due to the presence of a highly porous layer, rather than only to space-weathering processes, as often postulated
The atmosphere of Titan in late northern summer from JWST and Keck observations
No full textInternational audienceSaturn's moon Titan undergoes a long annual cycle of 29.45 Earth years. Titan's northern winter and spring were investigated in detail by the Cassini-Huygens spacecraft (2004-2017), but the northern summer season remains sparsely studied. Here we present new observations from the James Webb Space Telescope (JWST) and Keck II telescope made in 2022 and 2023 during Titan's late northern summer. With JWST's Mid-Infrared Instrument we spectroscopically detected the methyl radical, the primary product of methane breakup and key to the formation of ethane and heavier molecules. With JWST's Near Infrared Spectrograph we detected several non-LTE CO and CO2 emission bands that allow measurement of these species over a wide altitude range. Lastly, with JWST's Near Infrared Camera and Keck II we imaged northern hemisphere tropospheric clouds evolving in altitude, providing new insights and constraints on seasonal convection patterns. These observations pave the way for new observations and modeling of Titan's climate and meteorology as it progresses through northern Fall equinox, when its atmosphere is expected to show dramatic seasonal changes
Postal horse relays and roads in France, from the 17th to the 19th centuries
No full textInternational audienceThe database presented here results from a collective work that involved researchers in geography, historical geography and geomatics over the last twenty years, focusing on one of the first rapid transportation and communication network created in France, the postal horse relay. The research's goals evolved through this period of time, as we will show in this paper, but were constantly based on the exploration of this database resulting from the digitalization of the relays in a geographical information system (GIS). It provides information allowing the modeling of the postal horse roads and their relays (where horses were changed) in a Historical GIS from 1632 to 1833, at seven different dates. Different datasets can be downloaded*: the location and the name of the postal relays and of the current commune** in which they are located in 1632, 1708, 1733, 1758, 1783, 1810 and 1833 (digitized from a 1632 historical map and from historical Post Books); the roads digitized in the GIS as the crow flies between two adjacent relays according to the historical sources, with different attributes (length in number of "posts", which was the historical count unit of the time, length in kilometers, estimation of the speed travel according to a model integrating the average slope and the evolution of horse speed during the two centuries); the population of the relays for 1600, 1700, 1750, 1780, 1809 and 1831 (when the information is available in historical sources); the historical boundaries of France in 1632, 1708, 1733, 1758, 1783, 1810 and 1833 (digitized from historical maps).*. [Online]. URL: https://doi.org/10.5281/zenodo.11196161**. The commune is the French name for the administrative level of municipalities.Se presenta una base de datos que emana de un trabajo colectivo realizado en los últimos veinte años por parte de geógrafos, geohistoriadores y geomáticos, para la red del correo tirado por caballos, una de las primeras redes de transporte rápido creadas en Francia. Los objetivos de la investigación han variado a lo largo de los años -como es expresado en el texto- pero siempre se han sostenido en el desarrollo de una base en sistema de información geográfica (SIG) que captura la red en diferentes fechas. Tal geodatabase histórica proporciona información que permite modelizar la red de caminos de postas tirados por caballos y sus paradas (donde se cambiaban las monturas), desde 1632 a 1833 en siete fechas. Permite la descarga cuatro archivos: la localización y el número de los relevos y municipios actuales en los que se encuentran para 1632, 1708, 1733, 1758, 1783, 1810 y 1833 (digitalizados a partir de un mapa de 1632 y de los Libros de Correos); las rutas digitalizadss en línea recta entre dos postas adyacentes, con diferentes atributos (longitud en número de "postas", que corresponde a la unidad de conteo en la época, longitud en kilómetros, estimación de la velocidad de viaje según un modelo que integra la pendiente media en el tramo de carretera y la evolución histórica de la velocidad media a caballo durante estos dos siglos); la población de relevos en 1600, 1700, 1750, 1780, 1809 y 1831 (según fuentes disponibles); Las fronteras históricas de Francia para 1632, 1708, 1733, 1758, 1783, 1810 y 1833 (digitalizadas a partir de mapas históricos).La base de données présentée ici résulte d’un travail collectif mené depuis une vingtaine d’années, réunissant géographes, géohistoriens et géomaticiens, autour d’un des premiers réseaux de transport rapide créé en France, celui de la poste à cheval. Les objectifs de recherche ont varié au cours des années, comme nous le montrons dans cet article, mais se sont constamment appuyés sur l’exploitation de la saisie du réseau à différentes dates dans un système d’information géographique (SIG). La base fournit les informations permettant la modélisation du réseau des routes de la poste à cheval et leur relais (où les montures étaient changées) sur ce SIG Historique, de 1632 à 1833, à sept dates. Quatre fichiers peuvent être téléchargés : la localisation et le nom des relais et des communes actuelles dans lesquels ils sont localisés en 1632, 1708, 1733, 1758, 1783, 1810 et 1833 (numérisés à partir d’une carte de 1632 et des Livres de Poste) ; les routes numérisées selon une distance à vol d’oiseau entre deux relais de poste adjacents, avec différents attributs (longueur en nombre de "postes", qui est l’unité de compte de l’époque, longueur en kilomètres, estimation de la vitesse de parcours selon un modèle intégrant la pente moyenne sur le segment routier et l’évolution historique de la vitesse moyenne du cheval sur ces deux siècles) ; la population des relais en 1600, 1700, 1750, 1780, 1809 and 1831 (quand les sources sont disponibles) ; les frontières historiques de la France en 1632, 1708, 1733, 1758, 1783, 1810 et 1833 (numérisées à partir de cartes anciennes)
Euclid preparation: TBD. Cosmic Dawn Survey: evolution of the galaxy stellar mass function across 0.2<z<6.5 measured over 10 square degrees
No full textInternational audienceThe Cosmic Dawn Survey Pre-launch (PL) catalogues cover an effective 10.13 deg area with uniform deep Spitzer/IRAC data ( mag, 5), the largest area covered to these depths in the infrared. These data are used to gain new insight into the growth of stellar mass across cosmic history by characterising the evolution of the galaxy stellar mass function (GSMF) through and significantly reduces cosmic variance, yielding strong constraints on the abundance of massive galaxies. Results are generally consistent with the literature but now provide firm estimates of number density where only upper limits were previously available. Contrasting the GSMF with the dark matter halo mass function suggests that massive galaxies ( M) at required integrated star-formation efficiencies of 0.25--0.5, in excess of the commonly-held view of ``universal peak efficiency" from studies on the stellar-to-halo mass relation (SHMR). Such increased efficiencies imply an evolving peak in the SHMR at which can be maintained if feedback mechanisms from active galactic nuclei and stellar processes are ineffective at early times. In addition, a significant fraction of the most massive quiescent galaxies are observed to be in place already by --3. The apparent lack in change of their number density by is consistent with relatively little mass growth from mergers. Utilising the unique volume, evidence for an environmental dependence of the galaxy stellar mass function is found all the way through for the first time, though a more careful characterisation of the density field is ultimately required for confirmation
Between liberalization and public service obligation: evidence from France and Japan
No full textInternational audienc
Online Clustering of Massive Text Data Streams
No full textInternational audienceClustering large text data streams is a complex and computationally demanding task due to its unique challenges including high dimensionality, data sparsity, evolving data distributions, and the curse of dimensionality. Traditional clustering techniques often struggle to keep up with these dynamic changes and high-velocity nature of streaming text data while maintaining efficiency and accuracy. In this paper, we introduce OMTStream, a novel approach that combines an adaptive text representation technique with an online clustering based CluStream. Our method continuously learns meaningful semantic representations of text while reducing dimensionality, allowing for fast and efficient real-time clustering. By leveraging micro-clusters that evolve over time, OMTStream can track emerging patterns and adapt to shifting data distributions without the need for retraining from scratch.We evaluate our approach on real-world datasets, demonstrating its superior performance compared to existing techniques. Through a comprehensive set of experiments, we also validate the effectiveness of OMTStream across various scenarios, highlighting its robustness, adaptability, and computational efficiency in handling large, continuously evolving text data streams
On the presence of a fifth force at the Galactic Center
No full textInternational audienceAims: The presence of a Yukawa-like correction to Newtonian gravity is investigated at the Galactic Center, leading to a new upper limit for the intensity of such a correction. Methods: We perform a Markov Chain Monte Carlo analysis using the astrometric and spectroscopic data of star S collected at the Very Large Telescope by GRAVITY, NACO and SINFONI instruments, covering the period from to . Results: The precision of the GRAVITY instrument allows us to derive the most stringent upper limit at the Galactic Center for the intensity of the Yukawa contribution () to be for a scale length . This improves by roughly one order of magnitude all estimates obtained in previous works
Application of modular isoxazoline-βamino acid-based peptidomimetics as chemical model systems for studying the tau misfolding
No full textInternational audienceTau is a microtubule-associated protein essential for regulating microtubule dynamics and axonal transport in neurons. In tauopathies, the transition of tau from a physiological to a pathological form remains unclear, though the hexapeptides PHF6 and PHF6∗ are key in triggering aggregation. These sequences are shielded by a β-hairpin structure in the native state but expose hydrophobic residues during misfolding, promoting self-assembly. This study employs a non-natural β2-amino acid to induce PHF6 and PHF6∗ into either extended or β-hairpin conformations. The extended form triggers tau aggregation without additives, acting as a seed-competent monomer model system. Conversely, the β-hairpin preserves tau in a soluble monomeric state. Additionally, a β-hairpin mimic inspired by Hsp90 showed potential as a chaperone mimic and inhibitor of tau aggregation, offering insights into corrective folding and aggregation modulation in neuronal environments