1,721,003 research outputs found
Structural parameters of chromite included in diamond and kimberlites from Siberia: A new tool for discriminating ultramafic source
No full textSiberian chromite included in diamond, kimberlite, and spinel peridotite as well as Cr-spinel from garnet-spinel peridotite have been studied by single-crystal X-ray diffraction and electron microprobe analysis. Cell edges and oxygen positional parameters, u, of chromite in diamond and in kimberlite are comparable (cell edge, 8.3249–8.3390 Å; u, 0.26175–0.26213). The structural parameters of chromite in the spinel peridotite are similar to those of chromite grains from ophiolitic complexes, and those of Cr-spinel from garnet-spinel peridotite are comparable to those of Cr-spinel in lherzolitic mantle xenoliths. With the exception of the chromite in garnet-spinel peridotite, all analyzed spinels have a high Cr content. Recasting the chemical analyses according to spinel stoichiometry reveals negligible or no Fe3+. Chrome spinel may be present in heavy concentrates derived from serpentinized mafic and ultramafic rocks as the sole surviving primary mineral and, as such, their particular structural and chemical parameters may represent a new prospecting tool for discriminating the ultramafic source
Major and trace element composition of chromian diopsides from the Zagadochnaya kimberlite (Yakutia, Russia): Metasomatic processes, thermobarometry and diamond potential
No full textThe major and trace element composition of chromian diopsides and associate minerals from concentrates of the diamond-free Zagadochnaya kimberlite have been studied to gain an insight into the lithological variability of the underlying mantle and explore the possible reasons for the different diamond potential of contiguous portions of the Yakutian lithosphere.
A few (Al. Cr, Na)-poor chromian diopsides (group I) have a megacrystic signature and are interpreted as spinel-facies magmatic segregates from melts related to the host kimberlite. Other (Al, Cr, Na)-rich chromian diopsides (groups II and III) originated from variously metasomatized garnet peridotites and, possibly, pyroxenites from relatively shallow mantle depths (<130-160 km). Two main metasomatic stages are distinguished, which led to strong enrichments in LILE and LREE. The metasomatic processes recorded by group II diopsides are broadly similar to those shown by garnet peridotite xenoliths from the nearby, highly diamondiferous Udachnaya kimberlite. Group III diopsides document a peculiar, subsequent modification after reaction with ultra-alkaline melts, which led to variable enrichments in Na, Al, Cr and Fe and was probably related to the magmatic stage connected with the eruption of the host kimberlite. It is suggested that the barren nature of the Zagadochnaya kimberlite is primarily a consequence of the relatively shallow depth of mantle sampling. Extensive melt-peridotite interaction at shallow levels may have played a significant role in controlling the high-Mg, low-Ti composition of this kimberlite
Fe3+/Fetot ratio in the mantle: A micro-Mössbauer study of chromites included in diamond and kimberlites
No full textCongresso Associazione Internazionale di Mineralogia, Budapest 21-27 agosto 201
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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