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De quelques enjeux psychiques du co-enseignement
No full textInternational audienceCet article propose une nouvelle analyse d’un corpus issu d’une recherche menée dans des classes uniques situées dans un milieu rural isolé du département de l’Ardèche. Ces classes ont comme point commun d’avoir été choisies par les instances rectorales pour la mise en place d’un dispositif de co-enseignement. À partir de l’analyse clinique de plusieurs entretiens couplés avec des observations d’enseignant·es en poste dans ces classes, l’auteur dégage quelques pistes d’appréhension des possibles mouvements psychiques à l’œuvre pour des enseignant·es exerçant dans un tel dispositif. L’analyse d’un corpus concernant trois binômes d’enseignantes permet de fournir des hypothèses à propos des remaniements du lien au savoir et du lien aux élèves de chaque enseignante, induits par le co-enseignement. L’article s’interroge également sur les conditions d’extension de la notion de transfert didactique à des situations d’enseignement à deux. Enfin, en appui sur des recherches sur la co-animation de groupes de formation, l’auteur invite à considérer, dans les situations de co-enseignement, la dimension intertransférentielle du lien entre les enseignant·es
Regular singular Mahler equations and Newton polygons
No full textInternational audienceThough Mahler equations have been introduced nearly one century ago, the study of their solutions is still a fruitful topic for research. In particular, the Galois theory of Mahler equations has been the subject of many recent papers. Nevertheless, long is the way to a complete understanding of relations between solutions of Mahler equations. One step along this way is the study of singularities. Mahler equations with a regular singularity at 0 have rather "nice" solutions: they can be expressed with the help of Puiseux series and solutions of equations with constant coefficients. In a previous paper, the authors described an algorithm to determinewhether an equation is regular singular at 0 or not. Exploiting information from the Frobenius method and Newton polygons, we improve this algorithm by significantly reducing its complexity, by providing some simple criterion for an equation to be regular singular at 0, and by extending its scope to equations with Puiseux coefficients
Les logiques de consécration et de diffusion des savoirs scientifiques se transforment-elles ? Une sociologie de conférences 'prédatrices'
No full textInternational audienc
Modules cuspidaux pour les algebres superconformes de rang ≥ 1
No full textAccording to V. Kac and J. van de Leur, the superconformal algebras are the simple Z-graded Lie superalgebras of growth one which contains the Witt algebra. We describe an explicit classification of all cuspidal modules over the known supercuspidal algebras of rank ≥ 1, and their central extensions.Our approach reveals some unnoticed phenomena. Indeed the central charge of cuspidal modules is trivial, except for one specific central extension of the contact algebra K(4). As shown in the paper, this fact also impacts the representation theory of K(3), CK(6) and K (2) (4).Besides these four cases, the classification relies on general methods based on highest weight theory.Suivant V. Kac et J. van de Leur, une algèbre superconforme est une superalgèbre de Lie Z-graduee simple de croissance un contenant l’algèbre de Witt. Nous décrivons de manière explicite la classification des modules cuspidaux pour toutes les algèbres superconformes connues et leurs extensions centrales.Notre approche montre des phénomènes nouveaux. En fait la charge centrale d'un module cuspidal est triviale, sauf pour une extensioncentrale spécifique de l’algèbre de contact K(4). Ce fait impacte la théorie des représentations de K(3), CK(6) et K(2)(4). Mis a part ces quatre cas, la classification est utilise sur des méthodes générales basées sur la théorie du plus haut poids
Effect of Polyols Absorption onto Cellulose Nanocrystals (CNC) on Melt and Mechanical Strengthening Through Reactive Extruded Vitrimerization.
No full textInternational audienceIn this research, PLA based closed loop upcycling ‘foam to foam’ concept was proposed. An innovative and upcycling cellulose-reinforced PLA vitrimeric composites were prepared through a two-step reactive processing, in which CNC was ingeniously coated by polyols glycerol as the vitrimer composition by the freeze-drying method with water as the solvent and glycerol-coating. Well-dispersed CNC obtained by freeze-drying and glycerol coating was observed as good dispersion as evidenced as 200 nm in mean length as a reference of CNC powder in several micrometers. Subsequently, well-dispersed CNC remarkably reinforced melt strength, mechanical stiffness and thermal resistance on basis of neat vitrimer as evidenced by a pronounced strain hardening behavior, an around 20% increase in storage modulus and 3.7 ºC of increase in Vicat softening temperature. Consequently, CNC reinforced vitrimeric system achieved best foamability with 25-fold foam expansion with the assistance of effect of CNC on foaming nucleating. Most importantly, these foamed materials are recyclable, reprocessed. This ‘foam to foam’ concept
Connaissance par les gouffres. Jean-Marie Massou et le devenir signe des pierres
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Peuplement du parc social et inégalités socio-spatiales. Une approche statistique dans six agglomérations françaises
No full textInternational audienceLe peuplement du parc locatif social a fait l’objet de nombreux travaux fondés sur des enquêtes qualitatives qui mettent en évidence les processus de catégorisation, de tri et de sélection des ménages, susceptibles de produire des discriminations et des inégalités de traitement dans l’accès au logement social. Les approches quantitatives étant plus rares, les recherches existantes peinent à saisir les relations entre le peuplement du parc social, sa structure et les caractéristiques de la demande et des attributions. Cet article propose une approche statistique originale permettant de caractériser le peuplement du parc social et de le mettre en rapport avec, d’une part, la structure du parc et, d’autre part, les caractéristiques des demandeurs et des attributaires. Testée sur six intercommunalités françaises, cette méthodologie permet d’abord de montrer que la structure du parc locatif social ne rend pas entièrement compte du peuplement du parc social. Elle révèle ensuite que certains profils de demandeurs sont globalement sous-représentés dans les attributions au regard de leur poids dans la demande. Enfin, elle montre, à l’échelle intercommunale, que les attributions récentes continuent de loger les ménages à bas revenus dans les quartiers prioritaires de la politique de la ville, sans que cela ne s’explique toujours par les niveaux de loyer observés
Plasmacytoid dendritic cell sensing of hepatitis E virus is shaped by both viral and host factors
No full textInternational audienceType I and III interferons critically protect the host against viral infection. Previous studies showed that IFN responses are suppressed in cells infected by hepatitis E virus (HEV). Here, we studied the anti-HEV function of IFN secreted by plasmacytoid dendritic cells (pDCs), specialized producers of IFNs. We showed that pDCs co-cultured with HEV-replicating cells secreted IFN in a cell contact–dependent manner. This pDC response required the endosomal nucleic acid sensor TLR7 and adhesion molecules. IFNs secreted by pDCs reduced viral spread. Intriguingly, ORF2, the capsid protein of HEV, can be produced in various forms by the infected cells, and we wanted to study their role in anti-HEV immune response. During infection, a fraction of ORF2 localizes into the nucleus, and glycosylated forms of ORF2 are massively secreted by infected cells. We showed that glycosylated ORF2 potentiates the recognition of infected cells by pDCs, by regulating cell contacts. On the other hand, nuclear ORF2 triggers immune response by IRF3 activation. Together, our results suggest that pDCs may be essential to control HEV replication
Plant volatile organic compounds: Emission and perception in a changing world
No full textInternational audienceVolatile organic compounds (VOCs) are produced by all kingdoms of life and play crucial roles in mediating the communication between organisms and their environment through emission and perception. Plants, in particular, produce and emit an exceptional variety of VOCs that together serve as a complex chemical language facilitating intra-plant, inter-plant, plant-animal, and plant-microbe interactions. VOC signals are perceived and decrypted by receiver plants; however, the emission, composition, distribution and effective range, as well as uptake of these infochemicals depend on temperature and atmospheric chemistry in addition to their physicochemical properties. Since both emission and perception are directly affected by ongoing climate change, research into these processes is urgently needed to develop mitigation strategies against this threat to plant communication networks. In this brief review, we highlight the recent advances about plant VOC emission and perception, emphasizing the effect of the current climate crisis on these processes. Despite some progress in understanding VOC emission and perception, significant gaps remain in elucidating their molecular mechanisms in plants
In-situ (Nano) fibrillation of biopolymer blends based on poly(butylene-adipate-co-terephtalate)/poly(lactic acid) (PBAT/PLA) : effect of ethan-1-aminium ionic liquids on rheological, mechanical and barrier properties
No full textInternational audienceThe ionic liquids based on ethan-1-aminium salts associated with inorganic (perchlorate (ClO4−), tetrafluoroborate (BF4−) and dicyanamide (Dca)) anions have been used as new compatibilizers of biopolymer blends based on poly(butylene-adipate-co-terephtalate)/poly(lactic acid) (PBAT/PLA). To highlight the effect of the nature of the anions, 2wt% of ionic liquids (ILs) have been introduced within a PBAT/PLA blend (60/40 wt%) and the corresponding compositions have been processed in melt by twin-screw extrusion and injection molding at a processing temperature which was above the melting temperature of the PBAT matrix and below the peak melting temperature of the PLA dispersed phase. Under these conditions, the PBAT matrix remained as a melt, whereas the dispersed phase with the higher melting temperature (PLA phase) could deform into fibrous structure under the elongational flow. The thermal, rheological, mechanical and barrier properties of PBAT/PLA/ILs were systematically investigated to elucidate structure–rheology–properties relationships. Transmission electron microscopy (TEM) analyses revealed the presence of stable nanofibrillar morphology in the case of PBAT/PLA/ILs blends. The aspect ratio of PLA fibrils increased when ILs were used, especially with the presence of BF4– and Dca anions. The latter resulted in the greatest improvement of the rheological response of the blends due to their high aspect ratios and the ionic liquids induced network structure [1]. The mechanical properties analyses showed that the use of ethan-1-aminium ILs in PLA/PBAT blends induced a self-reinforcing effect with an excellent compromise between stiffness (Young's modulus) and ability to sustain large deformation (strain at break), especially for BF4– and dCa based anions. More interestingly, the addition of 2 wt% of ethan-1-aminium-based ILs induced a high decrease in water vapor permeability of self-reinforced PBAT/PLA/ILs nanofibrillar composites with a reduction factor of 10 in the case of BF4– anions. On the other hand, the oxygen permeability values were reduced in all PBSA/PLA/ILs blends, reaching reduction rates between 35 and 73 %. The results found in the present study highlight the potential role of ethan-1-aminium ILs as compatibilizers of polyester-based blends allowing to design PBAT/PLA blends displaying improved gaz barrier, rheological and mechanical performances, i.e. combining the intrinsic properties of PBAT and PLA coexisting phases.References[1]M. Yousfi, S. Livi, J. Duchet-Rumeau, Ionic liquids: A new way for the compatibilization of thermoplastic blends. 255 (2014) 1391–1398. https://doi.org/10.1016/j.cej.2014.06.080