459 research outputs found
Formaliser l'activité de recherche d'information : les modÚles 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'Ă©valuer la pertinence des objets sociaux de rĂ©fĂ©rence français pour l'enseignement de la recherche d'information. AprĂšs une analyse de ces objets d'autoritĂ©, constitutifs d'une culture professionnelle, et de leur impact sur les pratiques de formation des enseignants documentalistes, est proposĂ©e une Ă©tude de l'activitĂ© de recherche d'information dĂ©veloppĂ©e dans la sphĂšre non formelle. Peut ainsi ĂȘtre mesurĂ©e la compatibilitĂ© entre les pratiques formelles et les pratiques non formelles, socialement lĂ©gitimĂ©es
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 H2âCH4 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-(Al1âxFex)2O3 powders and self-supported foams
An investigation of the potential interest of α-aluminaâhematite 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 CNTâFeâAl2O3 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, Îł-Fe-C and Fe3+) were present in the Mössbauer spectra of the composite powders, and that an additional sextet, possibly due to an Fe1âyCy 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 Îł-FeâC 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
Lâobjectif de cet article est de montrer la pertinence dâune conjugaison, dans un mĂȘme cadre dâanalyse, des notions de pratique et imaginaire. AprĂšs avoir dĂ©fini ces deux notions complexes, notre dĂ©marche de recherche, fondĂ©e sur une approche interactionniste, sera explicitĂ©e. Lâarticle se conclut par lâanalyse des implications mĂ©thodologiques liĂ©es Ă cette prĂ©occupation scientifique. Il sâagit ici de montrer la pertinence de cette conjugaison pour proposer un modĂšle 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
EnquĂȘter auprĂšs de publics enfantins : questions de mĂ©thodes
Offrir un regard nouveau sur les enfants Ă travers la comprĂ©hension de leur rapport au numĂ©rique dans leur vie quotidienne comme Ă lâĂ©cole : voilĂ ce qui fĂ©dĂšre lâĂ©quipe-projet ELN depuis janvier 2020. Depuis cette date, une vaste recherche de terrain Ă travers la France a Ă©tĂ© engagĂ©e, permettant de recueillir des donnĂ©es variĂ©es auprĂšs dâenfants, de parents et de professionnel·les de lâĂ©ducation sur leurs reprĂ©sentations et leurs usages du numĂ©rique dans
et hors lâĂ©cole. Pour ce faire, des choix mĂ©thodologiques ont Ă©tĂ© effectuĂ©s, choix loin dâĂȘtre anodins tant dans la conception de lâobjet quâils tĂ©moignent que dans leur impact sur les rĂ©sultats obtenus. Petite synthĂšse des rĂ©flexions qui ont animĂ© 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, particuliÚrement des jeunes, ainsi que de leurs usages et pratiques de l\u27information et des médias
Modes dâapprĂ©hension et de dissĂ©mination des cultures de lâinformation dans lâĂcole
Ă partir dâĂ©tudes de terrain, portant sur les pratiques informationnelles dâacteurs diffĂ©renciĂ©s, jeunes adultes et conducteurs de travaux, nous cherchons Ă saisir comment lâĂcole peut favoriser de maniĂšre effective la culture des liens entre des univers diffĂ©rents, dĂ©passant les cloisonnements disciplinaires, pour atteindre une vĂ©ritable dissĂ©mination des cultures de lâinformation. AprĂšs avoir prĂ©sentĂ© le croisement conceptuel au cĆur de cette contribution â cultures de lâinformation et reliance â nous nous attacherons Ă proposer des pistes pour que les cultures de lâinformation soient mises en lien au sein de lâĂcole.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 ârelianceâ [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 150â200 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 Ό=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
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