Niobium- and antimony-doped tin dioxide aerogels as new catalyst supports for PEM fuel cells

The final publication is available at Springer via http://dx.doi.org/10.1007/s10853-016-9833-7International audienceIn order to tackle the problem of low durability, tin dioxide was studied to replace carbon black as a catalyst support in proton exchange membrane fuel cells (PEMFCs). SnO2 is a well-known n-type semi-conductor whose electronic conductivity can be improved by doping with hypervalent cations such as Nb5+ or Sb5+. In addition, as a catalyst support, this material has to develop a high specific surface area with an adequate mesoporous morphology to allow both good dispersion and activity of the catalyst (Pt). To this end, our objective was to develop doped SnO2 aerogels in order to gather in a same material both a high electronic conductivity and an adapted morphology. In this study, SnO2 xerogels and aerogels were successfully synthesized following an acid-catalyzed sol–gel route starting with metal alkoxides as precursors. Dried gels were calcined for 5 h at 600 °C in flowing air. The effect on both the structure and the morphology of the material resulting from doping with niobium or antimony was investigated by XRD, SEM, and nitrogen sorption. The electronic conductivity of pure and doped SnO2 materials was obtained from impedance spectroscopy and resistance measurements. Our materials showed a very interesting airy morphology adapted for the foreseen application: a reasonable specific surface area (80–90 m2/g) with a bimodal pore size distribution centered on around 25 and 45 nm. Moreover, all Sb-doped samples exhibited significant improvement in electronic conductivity. 5 at.% Sb-doped SnO2 even showed an electronic conductivity of 1 S/cm, very similar to that of Vulcan XC-72 (4 S/cm) and representing a 5 orders of magnitude increase compared to that of pure SnO2

Circonscriptions et réseaux de voies : un angle mort de la Géographie Historique

International audienceThis paper examines two aspects of the relation to space and territory : networks and grids. Over the past one hundred and fifty years, historigraphy has focused either on constituencies or on means of communication and transport, but has largely overlooked the relationship between the two. A detailed examination of historical practices reveals that the introduction of the planimetry of ditstricts (between 1680 and 1850 in the case of France) coincided with the construction of both objects. Based on several case studies at the level of cantons, the findings suggest that there are a number of significant links between district boundaries and means of transport. This raises the question of common or separate histories (or temporalities) and the importance of mapping ond planimetrics conceived as the combination or association of different objects in the 18th century.L'objectif de cet article est de proposer la mise en place de réflexions articulant maillages et treillages, alors que l'historiographie dominante sépare ces deux aspects de la relation aux territoires. En effet, une lecture de l'historiographie des 150 dernières années montre que les réflexions dominantes portent soit sur les circonscriptions, soit sur les voies de communication, mais n'essayent pas, en règle générale de penser leur relation. Pourtant, une observation soucieuse des pratiques anciennes montre que la période de mise en place d'une planimétrie des circonscriptions, soit pour la France une période qui court de 1680 à 1850, est celle d'une co-construction de ces objets sur le terrain. Une série de cas pris à l'échelle cantonale permet de démontrer diverses formes d'association sur le long terme entre voies de communication et limites de circonscription. Se posent alors des questions de différentes natures, d'une part sur les temporalités communes ou disjointes entre voies et circonscriptions, d'autre part sur l'importance de la planimétrie en tant que mise en cohérence d'objets différents au XVIIIe siècle

Karyological analysis of three strains of the African catfish, Clarias gariepinus (Clariidae), used in aquaculture

A karyological analysis of three strains of #Clarias gariepinus used in fish culture, originating from different localities in Africa and Asia Minor, and thus representing populations from the distribution limits of this species, revealed an identical karyotype, 2n = 56 with a pair of heteromorphic sex chromosomes (ZW) and a nucleolus organizer (NOR) location in a single pair of chromosomes, for all strains. These results confirm the synonymy between #C. gariepinus, #C. lazera and #C. mossambicus as introduced by Teugels in 1982. (D'après résumé d'auteur

Le canton d'hier à aujourd'hui : étude cartographique d'un maillage

Between 1800 and 1999, the number of canton passes from 3043 to 3694 cantons. At the same time, the average surface of these districts passes from 178 to 48 km2. If we accumulate all the modifications which know the cantonal limits during these two hundred years we find more than 3000. The canton is thus an eminently changeable district, what allows to return on the image of fixedness which is attached to it. Maps present the set of these transformations. Beyond these results, the survey presented here aimed at understanding better the spatial nature of the modifications which affect the cantonal weft, as long within the framework of a relation in the big balances of the national territory, that in that of the relationship in the other level of district, or in that of the relations between the city and the countryside.Entre 1800 et 1999, le nombre de canton passe de 3043 à 3694 cantons. Dans le même temps, la superficie moyenne de ces circonscriptions passe de 178 à 48 km2. Si l'on cumule l'ensemble des modifications que connaissent les limites cantonales durant ces deux cents années on en trouve plus de 3000. Le canton est donc une circonscription éminemment changeante, ce qui permet de revenir sur l'image de fixité qui lui est attachée. Des cartes présentent l'ensemble des ces mutations. Au-delà de ces résultats, l'enquête présentée ici a visé à mieux comprendre la nature spatiale des modifications qui affectent la trame cantonale, tant dans le cadre d'une relation aux grands équilibres du territoire national, que dans celui du rapport aux autres circonscriptions, ou dans celui des relations ville-campagne

Genomics of an ancient sex chromosome in Tilapia. W633

We have developed important genomic tools and methods of comparative genomics in the Nile tilapia, Oreochromis niloticus. The physical comparative map generated with BACs allowed us to calculate that there were about one rearrangement of intra-chromosomal every 3 Mb. For most chromosomes (about 40-48 Mb) there were about 16 breakpoints with ie eight inversions per chromosome. When extrapolated to the large bivalent chromosome Chr 1-LG3 (about 100-120 Mb), we estimate probably 40 breakpoints and 20 inversions. Our work suggests that intrachromosomal rearrangements with 160 inversions have occurred since the divergence of tilapia with stickleback, the species found to be closely related to tilapia. We have also developed a high resolution RH map containing 1296 markers distributed over the 22 chromosomes, that are now identifiable by cytogenetic analysis. The linkage groups of the genetic map were anchored with 149 microsatellites to chromosomes. A inverted zone was found by BAC-FISH close to the centromere in one of the Chr1-LG3 chromosomes of XY males and in 2 Chr1-LG3 chromosomes of YY males, but absent in XX females. This inversion is not in the region where recombination is suppressed. These results suggest that the Chr1-LG3 chromosome is still acting as a sex chromosome. The Nile tilapia appears to be in the midst of a transition between ZW to XY systems. In the Chr1-LG3 chromosome, 515 protein-encoding genes were found with 152 being tilapia-specific, while in the inversed region 19 genes were found including the gene dmrtA1. Highly conserved and ordered syntenies have been identified with the genes of the inversion zone, not only with the stickleback (Chr 7 and Chr9) but also with the chicken Z chromosome, the platypus X5 Chr and also with human Chr9, in which genes involved in sex determination are located. (Texte integral

Données nouvelles sur l’origine du lintage des grèzes : implications paléoclimatiques

À partir de l'étude détaillée d'une grèze litée répondant à la définition granulo-métrique proposée par Guillien, les différentes hypothèses avancées concernant les processus de mise en place de ces dépôts ont été ré-examinées. Les données recueillies lors des observations de terrain, les résultats des analyses sédimentologiques et ceux de l'analyse micromorphologique ont permis de cerner le processus dominant conduisant à la stratification des grèzes. Le rôle majeur attribué au ruissellement par Guillien est remis en question par l'absence de figures d'incision, de granoclassements longitudinaux, de structures obliques ou entrecroisées. L'hypothèse congélifluxion-ruissellement de Journaux ne permet pas d'expliquer les granoclassements verticaux; par ailleurs, le ruissellement diffus ne peut seul aboutir à la formation d'une « table » bien marquée au sommet des lits gras. En revanche, Journaux et Francou font appel à la solifluxion pour la mise en place des lits gras. Le modèle andin de Francou qui privilégie la cryoreptation nous semble le mieux adapté pour expliquer le litage des grèzes charentaises. Les granoclassements verticaux, les contacts entre les lits, les figures sedimentaires observés dans le milieu andin ont été retrouvés dans les grèzes litées charentaises. Le mécanisme de la nappe-coulée a donc été retenu comme moteur essentiel de la stratogénèse. De ce fait, le contexte climatique d'élaboration des grèzes est caractérisé par la grande fréquence de cycles gel-dégel brefs, superficiels et des apports de neige faibles mais renouvelés fournissant l'eau nécessaire à une cryoclastie et à une cryoreptation actives. La formation des grèzes litées se situerait donc pendant les phases froides et humides qui ont été les plus durables au cours du dernier cycle glaciaire, la phase plus froide et plus sèche terminale ayant provoqué le remaniement du sommet de la grèze (fauchages, cryoturbations).Following a detailed study of a "grèze litée" which presents the granulometric characteristics defined by Guillien, we have reviewed the various assumptions concerning the processes of deposition of these materials. The field data and the results of the sedimentological and the micromorphological analyses make it possible to better determine the main processes involved in the deposition of the "grèzes". The dominant role assigned to slopewash by Guillien is not supported by sedimentary structures such as longitudinal graded beddings and oblique or cross beddings. The congelifluxion-slopewash hypothesis of Journaux does not explain vertical graded beddings and the washing alone cannot lead to the formation of a well defined table at the top of the diamicton or "lit gras". However, Journaux and Francou consider that solifluction may explain the "lit gras". The Andean model by Francou which favours frost-creep seems to be the best explanation for the bedding of the "grèzes charentaises". Vertical graded beddings, contacts between layers, sedimentary features observed in the Andean environment have been recognized in the "grèzes litées charentaises". The mecanism of solifluction sheet (nappe-coulée) seems to be the essential process of the stra-togenesis. Thereby the climatic context of development of the "grèzes" is characterized by a great frequency of short and superficial freezing and thawing cycles and the contribution of short-lived and renewed snow cover or patches providing the water required for active frost shattering and frost creep. The development of the "grèzes litées" probably occurred during the dominant cold and humid periods of the last glacial cycle. The cold and dry terminal period is responsible for the reworking of the top of the "grèze" (bendings and cryoturbations).Ausgehend von einer detaillierten Studie einer gréze litée, welche der von Guillien vorgeschlagenen granu-lometrischen Definition entspricht, werden die verschiedenen Hypothesen zum AbIa-gerungsprozeB dieser Materialien nochmals ûberprùft. Die bei Terrainbeobachtungen gesammelten Daten und die Ergebnisse der sedimentologischen und mikromorphologis-chen Analysen ermôglichen es, den dominie-renden Vorgang, der zur Stratifizierung der grèzes fùhrte, nàher zu bestimmen. Die domi-nierende RoIIe, die Guillien der Regenspulung zuspricht, wird wegen des Fehlens von Einschnittformen und Sedimentstrukturen wie Làngs-, Schràg- und Kreuzschichtung in Frage gestellt. Die Gelifluktion-Regenspulung-Hypothese von Journaux erlaubt nicht, die vertikalen Komschichtungen zu erklàren; auBerden kann die diffuse Regenspulung allein nicht zu der Bildung einer klar erkenn-baren "Tafel" auf dem Gipfel der lits gras fùhren. Dagegen meinen Journaux und Francou, daB BodenflieBen die lits gras herbeigefùhrt hat. Das Anden-Modell von Francou, welches dem Frostkriechen den Vorzug gibt, scheint uns am ehesten geeignet, die Schichtung der grèzes charentaises zu erklàren. Die vertikalen Komschichtungen, die Kontakte zwischen den Betten und die Ablagerungsformen, die im Anden-Milieu beobachtet wurden, hat man in den grèzes litées charentaises wiederge-funden. Der Mechanismus der geflossenen Flâche wurde also als hauptsàchlicher Motor der Stratogénèse festgehalten. Auf Grund dieser Tatsache zeichnet sich der klimatische Kontext der Ausbildung der grèzes durch die groBe Hâufigkeit kurzer, oberf lâchlicher Vereisungs-Enteisungs-Zyklen aus, sowie durch schwache aber wiederholte Schneebeitràge, welche das fur aktive Frostsprengung und aktives Frostkriechen notwendige Wasser lieferten. Die Bildung der "grèzes litées" fand wohl wâhrend der kalten und feuchten Phasen statt welche im letzten glazialen Zyklus am dauerhaftesten waren

How collective participation impacts social identity: a longitudinal study from India

A key issue for political psychology concerns the processes whereby people come to psychologically invest in socially and politically significant group identities. Since Durkheim, it has been assumed that participation in group-relevant collective events increases one’s investment in such group identities. However, little empirical research explicitly addresses this or the processes involved. We investigated these issues in a longitudinal questionnaire study conducted at one of the world’s largest collective events – a month-long Hindu festival in north India (the Magh Mela). Data gathered from pilgrims and comparable others who did not attend the event show that one month after the event, those who had participated (but not the controls) exhibited heightened social identification as Hindu and increased frequency of prayer rituals. Data gathered from pilgrims during the festival predicted these outcomes. Specifically, perceptions of sharing a common identity with other pilgrims, and of being able to enact their social identity in this event, helped predict changes in participants’ identification and behavior. The wider significance of these data for political psychology is discussed

Les enseignants: à la recherche de leur profession

Les Enseignants: à la recherche de leur profession reprend les idées centrales présentées à la Conférence donnée, sur l'invitation de l'ATEE, au Séminaire de Barcelone, en 1993. Cet article est la reproduction du texte de support à la Conférence. Étant donné l'espace disponible, il n'a pas été possible de le travailler dans le sens d'une plus grande problématisation et élaboration théorique