1,721,007 research outputs found
Diffusion across the glass transition in silicate melts: Systematic correlations, new experimental data for Sr and Ba in calcium-aluminosilicate glasses and general mechanisms of ionic transport
No full textViscosity and diffusivity of silicate melts and glasses are related to each other through relaxation timescales. The systematic is explored based on published data. Diffusion coefficients for Sr and Ba were measured in calcium aluminosilicate glasses at conditions near the glass/supercooled liquid boundary in temperature - time space making use of thin film technology and Rutherford Backscattering Spectroscopy (RBS) to measure concentration profiles on nanoscales. These data extend the range of published diffusion coefficients and combined with the systematic noted above allow the nature of change of diffusion coefficients across the glass transition region to be studied. Activation energies for diffusion in the glassy state (similar to 360 kJ/mol) are higher than in the molten liquid (similar to 213 kJ/mol). A defect based model of glass transition derived by Ojovan and coworkers, where attainment of a percolation threshold of configuron-type defects accounts for the glass - liquid transition, can explain the observed diffusion behaviour. Data treatment using this model yields a defect formation enthalpy of similar to 146 kJ/mol and a migration enthalpy of similar to 213 kJ/mol. The results of this study provide generalized expressions for the prediction of diffusion coefficients of cations in silicate melts for any composition at any temperature. (C) 2016 Published by Elsevier B.V
New experimental approach to study aqueous alteration of amorphous silicates at low reaction rates
Get PDFUnderstanding the kinetics of silicate alteration in aqueous media is central to the study of oceanic hydrothermal systems, nuclear glass durability or carbonaceous asteroids from which chondrites are coming. We present a new experimental approach in combination with an integrated analytical protocol designed to study alteration processes at low temperatures ( 50%) and H2 formation, whose quantifications are crucial to understand terrestrial serpentinization processes. Interfacial precipitation-dissolution seems to be the rate controlling mechanisms. In addition, we investigated a crystallized film reacted at 190°C (2 hours), which transformation rate is ten times slower than that of the amorphous silicate but is nevertheless readily observable. This approach can be used to understand alteration in terrestrial and extraterrestrial samples. In particular, we reproduced several features observed in carbonaceous chondrites (amorphous and oxidized hydrated silicates) and show that, at 90°C, alteration may be faster than usually considered. It should allow us in the future to constrain the temperatures and timescales of alteration in chondrites
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
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
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