1,721,043 research outputs found
Calcified Fungal Filaments in the Petrocalcic Horizon of Eutrochrepts in Beauce, France
No full textAry Bruand : Present Address : Institut des Sciences de la Terre d'OrléansInternational audienceCalcified filaments could be responsible for the induration of petrocalcic horizons, although they are absent or very rare in petrocalcic horizons with a porosity filled by needle-fiber and micro-rod calcite. The aim of this study was to show that calcified filaments were also numerous in these petrocalcic horizons, thus ensuring their high cohesion. Samples were collected in petrocalcic horizons of Eutrochrepts in Beauce, France. They were studied by scanning electron microscopy, and chemical analyses were performed using an energy dispersion spectrometer microprobe. Observations of fragments in the secondary electron mode showed a close packing of needle-fiber calcite with micro-rod calcite without any visible calcified filament. In the backscattered electron mode, observations showed numerous rounded voids, 0.5 to 1.0 µm in diameter within the packing of microrods. These voids and their walls exhibited similar morphological characteristics to those of the calcified filaments described earlier and interpreted as the remains of fungal hyphae. Chemical analysis of the rounded voids' walls, needle-fiber calcite, and micro-rod calcite revealed the presence of C and Ca as main elements and secondarily of Al and Si, but their respective compositions were not significantly different (P = 0.05). The C/Ca atomic ratio indicated that the analyses did not avoid resin, and that they cannot be used for discussion of calcite or calcium oxalate presence
Tendance à la lapidification de sols sableux (hardé du Nord-Cameroun) Une évolution naturelle sous climat semi-aride à fort pouvoir évaporant
No full textAry Bruand : Present Adress Institut des Sciences de la Terre d'OrléansInternational audienceEn région semi-aride, la désertification succède fréquemment à une dégradation des propriétés physiques des sols. Pour les sols sableux, milieux meubles et filtrants, la dégradation qui consiste en l'apparition d'une forte cohésion et d'une faible perméabilité est due au mode d'assemblage des constituants : une faible quantité d'argile fine revêt et relie systématiquement les grains du squelette. Ce mode d'assemblage résulte d'une évolution naturelle en relation étroite avec le fonctionnement hydrique, lui-même favorisé par des conditions lithologiques et climatiques. Sans que l'homme n'intervienne nécessairement, des formations supergènes peuvent ainsi perdre les caractéristiques qui en faisaient des sols, à savoir des matériaux meubles, hydratés et biotiques
Nature et mode d'assemblage des constituants minéraux et organiques dans des Ferralsols de la région des Cerrados (Brésil). Evolution après mise en culture
No full textM. François LIEUTIER - Professeur, Université d'Orléans Président du juryM. Ary BRUAND - Professeur, Université d'Orléans Directeur de thèseM. Francis ANDREUX - Professeur, Université de Dijon RapporteurM. Michel GRIMALDI - Directeur de Recherche, IRD, Bondy RapporteurM. Michel BROSSARD - Chargé de Recherche, IRD, Montpellier ExaminateurM. Jean-Robert DISNAR - Directeur de Recherche, CNRS, Orléans ExaminateurFerralsols are characterized by a very well developed microstructure of which the fertility depends closely. This microstructure consists of highly stable microaggregates 50 to 800 µm in diameter. Under native vegetation and pasture, the analysis of the soil bulk density, the microaggregates size and assemblage, as well as the organic matter, highlight significant variations according to depth. We established a typology of microaggregate assemblage as well as a model relating structure development to porosity. The organic matter is characterized in pyrolysis by a component of high temperature, of conjectural origin probably due to a mineral matrix effect. The whole of the differences recorded between the soils studied cannot be explained a priori by soil use alone, but more probably by a difference of activity of the social insects which would be at the origin of the microaggregates.Les Ferralsols se caractérisent par une microstructure très développée dont dépend étroitement leur fertilité. Cette microstructure repose sur des microagrégats très stables, de 50 à 800 µm de diamètre. Sous végétation naturelle comme sous pâturage, la densité apparente des sols, la taille et le mode d'assemblage des microagrégats, ainsi que la caractérisation de la matière organique, ont permis de mettre en évidence d'importantes variations avec la profondeur. Nous avons établi une typologie du mode d'assemblage des microagrégats ainsi qu'un modèle mettant en relation structure et porosité. La matière organique se singularise, en pyrolyse, par une composante de haute température, d'origine conjecturale, mais très probablement due à un effet de matrice minérale. L'ensemble des variations observées ne peuvent a priori s'expliquer par des différences d'usage du sol, mais plutôt grâce à l'activité des insectes sociaux qui sont vraisemblablement à l'origine des microagrégats
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Backscattered Electron Scanning Images of Soil Porosity for Analyzing Soil Compaction around Roots
No full textAry Bruand : Present Address : Institut des Sciences de la Terre d'OrléansInternational audienceThin sections of soil surrounding maize roots were studied in scanning electron microscopy using the backscattered electron mode. The soil is a fine-loamy, mixed, mesic, Typic Eutrochrept. Backscattered electron scanning images (BESI) of the porosity surrounding a selected maize (Zea mays L.) root were studied by image analysis at the scale of micro- and mesopores. Image analysis of BESI revealed that the porosity was 22 to 24% less within the soil surrounding the root than in the bulk soil. The bulk density increased up to 1.80 Mg m−3 close by the root-soil interface, although it was 1.54 Mg m−3 in the bulk soil. The porosity reduction consisted of a removal of the mesopores and a decrease in micropores, which resulted from the packing of skeleton grains with the porous clayey phase. The micropores were affected, although they are usually thought to be altered only with difficulty under natural conditions. A model which was developed earlier for soil compression around roots of plants growing on remolded soils was fitted to the experimental data by nonlinear regression analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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