1,721,092 research outputs found
A model for the viscosity of rhyolite as a function of H2O -content and pressure: a calibration based on centrifuge piston cylinder experiments
No full textThe Newtonian viscosity of synthetic rhyolitic liquids with 0.15–5.24 wt% dissolved water was determined in the interval between 580 and 1640 °C and pressures of 1 atm and 5–25 kbar. Measurements were performed by combining static and accelerated (up to 1000g) falling sphere experiments on water-bearing samples, with high temperature concentric cylinder experiments on 0.15 wt% H2O melts. These methods allowed viscosity determinations between 102 and 107 Pa s, and cover the complete range of naturally occurring magmatic temperatures, pressures, and H2O-contents for rhyolites. Our viscosity data, combined with those from previous studies, were modeled by an expression based on the empirical Vogel–Fulcher–Tammann equation, which describes viscosities and derivative properties (glass transition temperature Tg, fragility m, and activation volume of viscous flow Va) of silicic liquids as a function of P-T-X(H2O). The fitted expressions do not account for composition-dependent parameters other than X(H2O) and reproduce the entire viscosity database for silicic liquids to within 3.0% average relative error on log g (i.e. std. error of estimate of 0.26 log units). The results yield the expected strong decrease of viscosity with temperature and water content, but show variable pressure dependencies. Viscosity results to be strongly affected by pressure at low pressures; an effect amplified at low temperatures and water contents. Fragility, as a measure for the deviation from Arrhenian behavior, decreases with H2O-content but is insensitive to pressure. Activation volumes are always largely negative (e.g., less than -10 cm3/mol) and increase strongly with H2O-content. Variations in melt structure that may account for the observed property variations are discussed
Effect of fO2 on Eu partitioning between clinopyroxene, orthopyroxene and basaltic melt: Development of a Eu3+/Eu2+ oxybarometer
No full textWe present partition coefficients for Cs, Li, Sr, Ba, Zn, Mn, Co, Ni, Sc, Ga, Y, La, Nd, Sm, Eu, Tb, Yb, Lu, Ti, Zr, Hf, Ta, Nb and P for synthetic clinopyroxene and orthopyroxene crystallized from a Fe-free basalt at 1.5 GPa and four different oxygen fugacities (fO2) ranging from 6 log units above the quartz-fayalite-magnetite oxygen buffer (QFM + 6) to QFM-5 at temperatures of 1275–1300 °C. Partition coefficients for the rare earth elements (REE) vary as a function of their ionic radii, in agreement with lattice strain theory. We use the lattice strain model to evaluate partition coefficients for Eu2+ and Eu3+. Our results suggest that fO2 exerts a primary and important control on Eu, Ni and Co partitioning in clinopyroxene whereas fO2 seemingly has no recognizable effect on the partitioning behavior of these elements in orthopyroxene. However Eu anomalies in orthopyroxene, orthopyroxene Onuma diagrams and calculated proportions of Eu2+ in melts all show evidence that fO2 influence Eu partitioning also in orthopyroxene. We combined our results, available experimental data and predictive models for divalent and trivalent Eu clinopyroxene-melt and orthopyroxene-melt partitioning to parameterize fO2-dependent Eu partitioning models. The reported models reproduce measured Eu partition coefficients within a factor of two. Our model can be applied as clinopyroxene-melt and orthopyroxene-melt oxybarometers if Eu equilibrium partitioning between melt and pyroxene can be demonstrated
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
The dependence of Nb and Ta rutile-melt partitioning on melt composition and Nb/Ta fractionation during subduction processes
No full textVariations on the Author
Full text link“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
Full text linkWe 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
Full text linkWe 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
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