1,720,983 research outputs found
Hydrothermal sulphides from the Broken Spur Vent Field, 29,10’N Mid-Atlantic Ridge: Preliminary observations
No full textTrace metal distributions in Broken Spur sulphides revealed by laser ablation ICPMS techniques
No full textMineralogy, sulphur isotope geochemistry and the development of sulphide structures at the Broken Spur hydrothermal vent site, 29°10'N, Mid-Atlantic ridge
No full textA large collection of hydrothermal sulphides from the Broken Spur hydrothermal vent site, including representative samples of mound sulphide materials, has been characterized using optical mineralogy and sulphur isotope analysis. Young mound sulphides from Broken Spur have a pyrrhotite-dominated mineralogy unusual for bare ridge vent systems. However, pyrrhotite is metastable and is ultimately converted to iron disulphides. Mature sulphides are indurated, recrystallized and contain abundant quartz. Sulphide mound materials are developed by three major processes: (i) coalescing of chimney structures; (ii) accumulation of talus from mass wasting and (iii) precipitation and growth in response to hydrothermal flow. Progressive maturation of mound materials is by modification of primary textures, development of mineralogical zoning and replacement of metastable phases. Sulphur isotope analysis of 35 mineral separates returned δ34S values of – 0.5 to +3.2‰. These values are similar to those previously measured for Broken Spur and Snakepit, but are distinctly 32S enriched compared to the TAG active mound and some Pacific sites. Seawater entrainment and sulphate reduction within the subsurface feeder zone below Broken Spur mounds do not appear to be important processes at Broken Spur, in contrast to the TAG active mound
Trace element distributions in the chalcopyrite wall of a black smoker chimney: insights from laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS)
No full textThe thin walls of young black smoker chimneys experience steep physico-chemical gradients during active venting of hydrothermal fluid, and these gradients control trace element precipitation within those walls. Here, we utilise a combination of high sensitivity ICPMS and UV laser ablation (resolution of better than 30 ?m) to demonstrate the existence of non-random V, Ag, In, Te, Ba, Au, Pb and U distributions within the chalcopyrite wall of an immature black smoker chimney. The data are the first of their kind to be produced for black smoker chimney walls. Distributions of In and Te are attributed to preferential incorporation into lattices at elevated temperature. Enrichments of U and V derived from seawater are the product of redox immobilisation on sulphide surfaces. The distributions of Au, Ag, Pb and Ba may be related to interactions at the hydrothermal fluid–seawater mixing front; however, comparison of distribution data with reaction-transport models of chimney walls suggest a possible pH control on precipitation. These data illustrate the power of the LA–ICP–MS method, and such spatially resolved data have the potential to constrain models of element precipitation both in chimneys and in associated mounds
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
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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