Formaliser l'activité de recherche d'information : les modèles et modélisations à l'épreuve des pratiques effectives

International audienceThis article proposes to assess the relevance of French social objects reference for the teaching of information retrieval. After analyzing these works of authority, constituting a professional culture, and their impact on the training practices of the teacher librarians, a study of information retrieval activity developed in the non-formal sphere is proposed.Cet article propose d'évaluer la pertinence des objets sociaux de référence français pour l'enseignement de la recherche d'information. Après une analyse de ces objets d'autorité, constitutifs d'une culture professionnelle, et de leur impact sur les pratiques de formation des enseignants documentalistes, est proposée une étude de l'activité de recherche d'information développée dans la sphère non formelle. Peut ainsi être mesurée la compatibilité entre les pratiques formelles et les pratiques non formelles, socialement légitimées

A new fast method for ceramic foam impregnation: Application to the CCVD synthesis of carbon nanotubes

A new process that allows preparing, in a single step, good washcoats of catalytic materials for the catalytic chemical vapour deposition (CCVD) synthesis of carbon nanotubes (CNTs) in reticulated ceramic foams is reported. It is shown that the washcoats, obtained by impregnation using viscous slurries made of finely divided powders dispersed in different media, cover the total surface of foams with good adhesions. The catalytic activity with regards to the CNT synthesis is finally verified, showing that our new fast impregnation process makes possible to get materials with final architectures suitable for heterogeneous catalysis applications

In situ CCVD synthesis of carbon nanotubes within a commercial ceramic foam

Consolidated nanocomposite foams containing a large quantity of carbon nanotubes (CNTs) within millimetre-sized pores are prepared for the first time. A commercial ceramic foam is impregnated by a 60 g L21 slurry of a (Mg(12x)(Co0.75Mo0.25)xO solid solution (x = 0.01, 0.05, 0.1 and 0.2) powder in ethanol. Three successive impregnations led to deposits several tens of mm thick, with a good coverage of the commercial-ceramic pore walls but without closing the pores. The materials were submitted to a CCVD treatment in H2–CH4 atmosphere in order to synthesise the CNTs. When using attrition-milled powders, the carbon is mostly in the form of nanofibres or disordered carbon rather than CNTs. Using non-milled powders produces a less-compact deposit of catalytic material with a higher adherence to the walls of the ceramic foam. After CCVD, the carbon is mostly in the form of high-quality CNTs, as when using powder beds, their quantity being 2.5 times higher. The so-obtained consolidated nanocomposite materials show a multi-scale pore structuration

Catalytic chemical vapor deposition synthesis of single- and double-walled carbon nanotubes from α-(Al1−xFex)2O3 powders and self-supported foams

An investigation of the potential interest of α-alumina–hematite foams, as opposed to powders, as starting materials for the synthesis of carbon nanotubes (CNTs) by catalytic chemical vapor deposition method was performed. The oxide powders and foams as well as the corresponding CNT–Fe–Al2O3 composite powders and foams are studied by X-ray diffraction, specific surface area measurements, electron microscopy, Raman spectroscopy and Mössbauer spectroscopy. The latter technique revealed that four components (corresponding to α-Fe, Fe3C, γ-Fe-C and Fe3+) were present in the Mössbauer spectra of the composite powders, and that an additional sextet, possibly due to an Fe1−yCy alloy, is also present in the Mössbauer spectra of the composite foams. Contrary to some expectations, using foams do not lead to an easier reduction and thus to the formation of more α-Fe, Fe3C and/or γ-Fe–C potentially active particles for the formation of CNTs, and hence to no gain in the quantity of CNTs. However, using foams as starting materials strongly favors the selectivity of the method towards SWCNTs (60% SWCNTs and 40% DWCNTs) compared to what is obtained using powders (5% SWCNTs, 65% DWCNTs and 30% MWCNTs)

Le chercheur confronté au duo pratique-imaginaire

L’objectif de cet article est de montrer la pertinence d’une conjugaison, dans un même cadre d’analyse, des notions de pratique et imaginaire. Après avoir défini ces deux notions complexes, notre démarche de recherche, fondée sur une approche interactionniste, sera explicitée. L’article se conclut par l’analyse des implications méthodologiques liées à cette préoccupation scientifique. Il s’agit ici de montrer la pertinence de cette conjugaison pour proposer un modèle explicatif des conduites documentaires formelles et non formelles.The purpose of this paper is to show the relevance of associating the concepts of practice and imagination in the same analytical framework. After defining these two complex notions, we will then explain our research method based on an interactionist approach. The paper ends with an analysis of the methodological implications linked to this research topic. The objective is to show the value of such a combination in providing an explanatory model of both formal and non-formal information-seeking behaviors

Enquêter auprès de publics enfantins : questions de méthodes

Offrir un regard nouveau sur les enfants à travers la compréhension de leur rapport au numérique dans leur vie quotidienne comme à l’école : voilà ce qui fédère l’équipe-projet ELN depuis janvier 2020. Depuis cette date, une vaste recherche de terrain à travers la France a été engagée, permettant de recueillir des données variées auprès d’enfants, de parents et de professionnel·les de l’éducation sur leurs représentations et leurs usages du numérique dans et hors l’école. Pour ce faire, des choix méthodologiques ont été effectués, choix loin d’être anodins tant dans la conception de l’objet qu’ils témoignent que dans leur impact sur les résultats obtenus. Petite synthèse des réflexions qui ont animé les chercheuses et les chercheurs du groupe

Culture numériques enfantines : un impensé de l\u27EMI ?

Diaporama de l\u27intervention d\u27Anne Cordier, enseignante-chercheuse en sciences de l\u27information et de la communication à l\u27Université de Lorraine, spécialiste des usages et pratiques numériques, particulièrement des jeunes, ainsi que de leurs usages et pratiques de l\u27information et des médias

Modes d’appréhension et de dissémination des cultures de l’information dans l’École

À partir d’études de terrain, portant sur les pratiques informationnelles d’acteurs différenciés, jeunes adultes et conducteurs de travaux, nous cherchons à saisir comment l’École peut favoriser de manière effective la culture des liens entre des univers différents, dépassant les cloisonnements disciplinaires, pour atteindre une véritable dissémination des cultures de l’information. Après avoir présenté le croisement conceptuel au cœur de cette contribution – cultures de l’information et reliance – nous nous attacherons à proposer des pistes pour que les cultures de l’information soient mises en lien au sein de l’École.From field researches about informative practices of various actors, young adults and foremen, we try to grasp how school can promote in an effective way the culture of links between different universes, beyond disciplinary partitioning, to reach a real scattering of the information cultures. This paper states the conceptual crossing of cultures of information and “reliance” [eng. rebinding]. Then, it proposes ways to create links at school between information cultures

Time scales of melt extraction revealed by distribution of lava composition across a ridge axis

International audienceTemporal fluctuations of magmatic processes during the last 800 kyr have been investigated for the slow spreading Central Indian Ridge. The fluctuations are recorded by variations in lava chemistry along a 40 km long profile across the ridge. The temporal relations of the basalts were accurately restored using magnetic microanomalies. We report on the occurrence of ancient lavas enriched in incompatible elements whereas on-axis samples are typical normal mid-ocean ridge basalts. The enriched lavas are symmetrically distributed on either side of the ridge, implying that enriched melts reached the seafloor at intervals of about 150–200 kyr. This periodicity is viewed as a characteristic time scale in the aggregation processes of the melts produced from a heterogeneous mantle source. Geochemical variations of zero-age mid-ocean ridge basalts may primarily reflect such periodic processes rather than the spatial distribution of mantle heterogeneities

Melilite-bearing lavas in Mayotte (France): An insight into the mantle source below the Comores

International audienceOcean island basalts (OIB) from the Comores archipelago (Indian Ocean) display mineralogical and geochemical features different from the other Indian OIB. We present here new geochronological data (40Ar/39Ar), major and trace element compositions and isotopic (Sr, Nd, Pb) ratios of silica-undersaturated alkaline rocks from Mayotte, the oldest island of the Comores. Two trends are defined using major element composition: (1) a highly silica-undersaturated trend which includes basanites, (melilite-bearing) nephelinites, intermediate lavas and phonolites from the southern part of the island and (2) a moderately silica-undersaturated trend which is mainly represented by alkali basalts, basanites, intermediate lavas and phonolites from the northern part of the island. Both trends could be explained, to some extent, by variable degrees of partial melting. Normative larnite-bearing olivine melilitites and nephelinites exhibit, in addition to their high silica-undersaturation, elevated concentrations in CaO (>12wt.%) and P2O5 (up to 1.35wt.%). These exceptional rocks would result from low degree deep partial melting of a CO2-metasomatized source in the presence of carbonate (probably dolomite) and apatite. Igneous rocks from southern and northwestern shield volcanoes are characterized by a radiogenic Pb composition, revealing the existence of a HIMU (high μ=238U/204Pb) component in their source. Its influence decreases from the main building stage (>10.6-~3.0Ma) to the post-shield stage for the benefit of a depleted MORB-mantle (DMM) component, especially in the north central rocks. This feature would reflect increasing melting degrees of the depleted dominant source, bearing small-scale HIMU heterogeneities progressively consumed with time. The HIMU signature might have been introduced in the Comorian lithospheric mantle by thermal erosion or delamination of a continental lithosphere during the Gondwana break-up. The other islands of the Comores archipelago (Moheli, Anjouan and "La Grille" type lavas from Grande Comore) display also a DMM-HIMU mixing trend. Only a few lavas from Grande Comore ("Karthala" type) and one sample from Mayotte show the clear EM1 contribution (87Sr/86Sr>0.7035) of the Comorian plume