1,721,044 research outputs found
Phosphoric acid fractionation factors for smithsonite and cerussite between 25 and 72°C.
No full textStable isotope geochemistry of carbonate minerals in in supergene oxidation zones of Zn-Pb deposits
No full textThe O-18/O-16 and C-13/C-12 ratios of carbonate minerals formed by supergene oxidation of Zn-Pb deposits and submarine alteration of ancient slags were studied in order to constrain isotope fractionation factors for smithsonite, cerussite, and phosgenite, and to characterize conditions of nonsulfide ore formation. We present new isotope data of carbonate-hosted ores from the lglesiente district (Sardinia, Italy) and Vila Ruiva (Portugal), as well as from the silicate-hosted ores of the Broken Hill district, New South Wales (Australia) and Freihung (Germany) and review previously published isotope data. The temperature dependence of oxygen isotope fractionation between Pb and Zn carbonate minerals and water below 240 degrees C for cerussite and below 100 degrees C for smithsonite and phosgenite can be expressed as
10001n alpha(cerussite-water) = 2.29(10(6)/T-2)-3.56
10001n alpha(smithsonite-water) = 3.10(10(6)/T-2)-3.50
10001n alpha(phosgenite-water) = 2.55(10(6)/T-2)-3.50
with Tin Kelvin. The carbon isotope fractionation between smithsonite, phosgenite, hydrozincite and calcite is less than about 2 parts per thousand, while cerussites are strongly depleted in C-13 by about 10 parts per thousand as compared to the former minerals. Oxygen isotope variations of individual carbonate minerals within a deposit are relatively small indicating constant formation temperatures and a single, meteoric fluid source. Average formation temperatures of the studied deposits are calculated at 20 +/- 5 degrees C using the estimated isotope compositions of local paleometeoric waters. We observe a linear relationship between the isotope values of estimated paleometcoric waters and supergene carbonates. Thus, base metal carbonate minerals from supergene deposits may provide paleoclimatic information. The carbon isotope values are in most carbonate-hosted deposits highly variable (more than 10 parts per thousand) suggesting at least two isotopically distinct carbon sources. The isotopically light component can be related to oxidation of C3 plants (soil-derived carbon) and/or microbes that take active part in sulfide oxidation, while the isotopically heavy component originates from carbonate carbon from wall rocks and/or atmospheric carbon. The C-13-enriched component is less dominant in silicate-hosted deposits
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
Variations 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
Stable isotopes of Nonsulphide Zn-Pb ores in Britain and Ireland: fluid characteristics and paleoclimatic variability
No full text
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
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