1,721,000 research outputs found
Study and fabrication of the La2SiO5/SiO2 diffusion couple for the elaboration of textured and optimized silicate oxyapatite layers for the energy field
No full textCes travaux de thèse sont consacrés à l'étude de différents procédés de mise en forme en vue d'obtenir un matériau polycristallin, dense et texturé d’oxyapatite (La9,33+x/3(SiO4)6O2+x/2). De par leurs propriétés de conduction ionique, ces matériaux ont des applications potentielles en tant qu’électrolyte de pile à combustible SOFC. Une orientation préférentielle des cristallites dans le matériau d’oxyapatite améliore considérablement les performances de conduction. Ce dernier est obtenu par frittage réactif entre des couches alternées de précurseurs : La2SiO5 et SiO2. Le précurseur La2SiO5 a dû être synthétisé au laboratoire, par voie solide, en utilisant des poudres de La2O3 et SiO2. Cette voie de synthèse a été optimisée en prenant en compte l’influence de la nature cristalline et la taille des particules de silice. Nous avons ainsi pu mettre en évidence les mécanismes réactionnels mis en jeu dans la formation des différents silicates de lanthane du pseudo-binaire La2O3-SiO2 selon les caractéristiques de la silice. Différents procédés ont ensuite été étudiés (coulage en bande, pressage uniaxial et électrophorèse) pour la mise en forme de matériaux bicouches et multicouches alternant le couple de diffusion La2SiO5 / SiO2. L’influence de divers paramètres, tels que la température et le palier de frittage réactif, le taux de porosité des couches, sur les mécanismes de germination/croissance des cristaux d’apatite, à chacune des interfaces de précurseurs, ont ainsi été étudiés. Ces travaux ont également permis de tester la faisabilité du coulage en bande et de l’électrophorèse pour l’élaboration de fines couches de réactifs en vue d’obtenir des matériaux orientés par diffusion réactive. Le bilan dressé à l’issu de ces différents essais montre que le mécanisme de germination des cristaux d’apatite est conditionné par l’apparition d'une phase liquide à l'interface La2SiO5 / SiO2 (sur les grains de silice), propice à la diffuse du lanthane La+III, et qui engendre la précipitation d’une couche La2Si2O7, support à la croissance des cristaux d’apatite.This thesis work is focused on the study of different shaping processes in order to obtain a polycrystalline, dense and textured oxyapatite material (La9,33+x/3(SiO4)6O2+x/2). Due to their ionic conduction properties, these materials have potential applications as SOFC fuel cell electrolyte. A preferential orientation along the c-axis of oxyapatite crystallites considerably improves the conduction performances. This material is obtained by reactive sintering between layers of precursors: La2SiO5 and SiO2. The La2SiO5 precursor was synthesized by solid-state reaction, using La2O3 and SiO2 as raw materials. This synthesis route was optimized evaluating the influence of the crystalline nature and the particle size of silica. Thus, the reaction mechanisms involved in the formation of the different lanthanum silicates from the La2O3-SiO2 phase diagram in relation with the silica characteristics were identified. Several shaping processes were studied (tape casting, uniaxial pressing and electrophoretic deposition) for the fabrication of bi-layer and multi-layer materials using the diffusion couple La2SiO5 / SiO2. The influence of different reactive sintering parameters (temperature and holding time) and the porosity of layers on the mechanisms of oxyapatite crystal growth were studied. This work also made it possible to evaluate the feasibility of tape casting and electrophoretic deposition for the elaboration of thin layers of reagents in order to obtain textured materials by reactive diffusion. The results of these studies show that the mechanism of oxyapatite crystal growth is conditioned by the appearance of a liquid phase at the La2SiO5 / SiO2 interface (on the silica grains), which enables the diffusion of lanthanum La+III, and leads to the precipitation of a La2Si2O7 layer, that is the basis for the oxyapatite crystal growth
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
Elaboration, characterization and modelling of conduction mechanisms in anionic and protonic conducting ceramic materials
No full textDans ce travail, le composé de structure apatite La9,33(SiO4)6O2+3x/2 (-0,2<x<0,27) a été synthétisé et caractérisé en vue d’applications comme matériau d’électrolyte dans les piles à combustible à conduction anionique (IT-SOFC) et potentiellement protonique (PC-SOFC).Des pastilles et membranes denses d’oxyapatite pure ont été élaborées à partir de poudres synthétisées par voie solide, mises en forme par pressage isostatique ou coulage en bande et thermocompression, et frittées à 1550°C. Les échantillons ont été caractérisés électrochimiquement par spectroscopie d’impédance complexe et semi-perméation à l’oxygène et à l’hydrogène. Les phases La2SiO5 et La2Si2O7, qui peuvent apparaître lors de la synthèse de l’oxyapatite, ont été élaborées selon un protocole similaire, afin de caractériser leurs propriétés de conduction anionique. Ces phases ont d’autre part été utilisées lors d’essais d’élaboration d’oxyapatite à microstructure orientée le long de l’axe c, par frittage réactif d’échantillons d’architecture multicouche composés initialement d’une alternance de bandes La2SiO5 et La2Si2O7.Des tests de protonation en autoclave, à 550°C et 50 bars de pression de vapeur d’eau, ont été réalisés afin d’étudier le mécanisme d’insertion des protons dans la structure de l’oxyapatite. Des analyses thermogravimétriques, effectuées sur les échantillons protonés, ont permis de localiser les espèces protoniques insérées (surface/cœur) et de faire une analyse semi-quantitative de ces dernières. Les pertes de masses observées sont d’autant plus importantes que le temps de protonation et la stœchiométrie en oxygène des échantillons sont élevés. Des caractérisations structurales par diffraction des rayons X et spectroscopie Raman ont mis en évidence une augmentation conséquente du volume de la maille et un élargissement des grands canaux de la structure, ainsi qu’un changement de symétrie et une augmentation du désordre au sein de ces derniers. Ainsi, il semble que l’insertion des protons dans l’oxyapatite se fasse de manière préférentielle à l’intérieur des grands canaux de la structure.This work is devoted to the synthesis and characterization of apatite-type La9,33(SiO4)6O2+3x/2 (-0,2<x<0,27), as electrolyte material for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) and potentially Proton Conducting SOFC (PC-SOFC).Pure and dense oxyapatite pellets and membranes were prepared from powders synthetized by solid-state reaction and shaped by isostatic pressing or tape-casting process and thermocompression, then sintered at 1550�C. The electrochemical properties of the samples were characterized by complex impedance spectroscopy and O2 and H2 semi-permeation. La2SiO5 et La2Si2O7 phases, which may appear during the oxyapatite synthesis, were prepared following a similar process, in order to study their electrochemical properties. Theses phases were also used in an experiment whose purpose was to elaborate highly c-axis-oriented apatite-type lanthanum silicate polycrystals by combined use of tape casting and reactive diffusion between La2SiO5 and La2Si2O7.In order to study the protonation process of oxyapatite, tests were performed in autoclave with water at 550�C and 50 bars. Thermogravimetric analyses enabled to locate (surface/bulk) and to make a semi-quantitative analysis of inserted protonic species. The longer the protonation time and the higher the oxygen stoichiometry are, the greater the mass loss is. Moreover, structural studies by X ray diffraction and Raman spectroscopy revealed that the cell volume was increased and the channels of the structure enlarged, while the symmetry was modified and the disorder increased inside them. Thus, it appears that the protonic species insertion in oxyapatite takes place preferentially inside the channels of the structure
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
