1,720,982 research outputs found
Experimentally determined compositions and thermodynamic modeling of coexisting clinopyroxene and orthopyroxene on the enstatite and jadeite join at 25 Kbar
Get PDFSolid solutions of clinopyroxene (Cpx) and orthopyroxene (Opx) on the enstatite (En, Mg₂Si₂O₆) - jadeite (Jd, NaAISi₂O₆) join were studied experimentally at 25 Kbar and different temperatures using a piston-cylinder apparatus. Starting materials were about 1:1 molar mixtures of En and Jd plus 5 weight % Na₂Si₂O₅ flux. Typical run duration was 6 days. The compositions of coexisting Cpx and Opx were determined by electron microprobe analysis. The present results indicate that for a 1:1 molar starting mixture, solid solutions of Cpx and Opx coexist below 1200 °C at 25 Kbar and above this temperature, Cpx disappears. The concentrations of Mg₂Si₂O₆ in Cpx increase substantially with increasing temperatures whereas the concentrations of NaAISi₂O₆ in Opx have little dependence on temperature. Mg-Tschermak (MgTs) component exists in both Cpx and Opx that varies from 0.33 to 13.5% mole in Opx and does not exceed 3% in mole in Cpx. From the compositions of coexisting Opx and Cpx, a thermodynamic model was developed which in turn is used to formulate a geothermometer based on compositions of Na-bearing Cpx-Opx pairs
Investigations of Na gas-melt interactions of melt droplets and precursors: Implications for chondrule formation
No full textChondrules contain higher concentrations of volatiles (Na) than expected for melt
droplets in the solar nebula. Recent studies have proposed that chondrules may have formed
under non-canonical nebular conditions such as in particle/gas-rich clumps. Such chondrule
formation areas may have contained significant Na vapor. To test the hypothesis of whether a
Na-rich vapor would minimize Na volatilization reaction rates in a chondrule analog and
maintain the Na value of the melt, experiments were designed where a Na-rich vapor could be
maintained around the sample. The Knippa basalt, a MgO-rich alkali olivine basalt with a
melting temperature of 1325°±5°C and a Na2O content of 3.05 wt.%, was used as the
chondrule analog. Experiments were conducted in a one-atmosphere, gas-mixing furnace with
the ID2 controlled by a CO/CO2 gas mixture and fixed at the 1-W buffer curve. To determine
the extent of Na loss from the sample initial experiments were conducted at high temperatures
(1300° - 1350°C) for duration of up to 72 hours without a Na-rich vapor present. Almost all
(up to 98%) Na was volatilized in runs of 72 hours. Subsequent trials were conducted at
1330°C for 16 hours in the presence of a Na-rich vapor, supplied by a NaCl-filled crucible
placed in the bottom of the furnace. Succeeding Knudsen cell weight-loss mass-spectrometry
analysis of NaCl determined the PNa for these experimental conditions to be in the 10⁻⁶ atm
range. In these trials the Na2O content of the glass was maintained or in some cases
increased; Na2O values ranged from 2.62 % to 4.37 % wt.
The Na content of chondrules may be controlled by the Na vapor pressure in the
chondrule formation region. Most heating events capable of producing chondrules are
sufficient to volatilize Na. Sodium volatilization reaction rates will be reduced to varying
degrees from melt droplets, depending on the magnitude of the PNa generated. A combination
of Na vapor during, and Na diffusion back into chondrules after, formation could maintain
and/or enrich Na concentrations in chondrules
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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