1,720,955 research outputs found
Platinum-group-element distribution in subcontinental mantle: evidence from the Ivrea zone (Italy) and the Betic-rifean cordillera (Spain and Morocco)
No full textThe six platinum-group elements (PGE’s) Os, Ir, Ru, Rh, Pt, and Pd and Au were analyzed by instrumental neutron-activation analysis after nickel sulfide fire assay, in peridotites and dyke rocks from the orogenic ultramafic massifs of the Ivrea Zone in the Italian western Alps (Baldissero, Balmuccia, Finero) and the Betico—Rifean cordillera in southern Spain and northern Morocco (Ronda, Beni Bousera). The peridotites are considered as variably depleted, and reenriched low lithosphere, whereas the dyke rocks represent polybaric derivatives of basaltic melts (pyroxenites and gabbros), most coming from the underlying asthenosphere. The peridotites have total PGE content in the range 8.6—54.7 ppb, while mantle-normalized patterns generally grade from nearly flat and PGE rich, in less depleted lherzolites, to negative and PGE poor, in residual harzburgites and dunites. Dyke rocks have total PGE’s in the range 5.4—250 ppb and positive mantle-normalized patterns. Negative anomalies of Ir—Pt are frequently observed in dykes, indicating that both metals were probably retained in the mantle source of these melts. Most of the peridotites display positive anomaly of Au, and in some case are enriched in Ru, Rh, and Pd, but exhibit the same negative anomalies in Ir and Pt as the dykes. These features are ascribed to réintroduction of noble metals into the residual mantle by reaction with the basaltic melts that generated the dykes, or alternatively by recycling of “dyke material” during further partial melting of the host mantle. The role of the sulfide phase as carrier of the recycled PGE is stressed by clear interelemental correlation in peridotites from the Ivrea Zone. Present data provide evidence that zones of PGE enrichment can originate this way in the subcontinental mantle, and may constitute a potential reservoir for noble metal fertile volcanism in continental rift systems
Neutron Activation analysis of Platinum Group Elements and Gold in Reference Materials: A comparison of two methods
No full textNAA of Platinum Group Elements and Gold in Reference Materials: A comparison of two methods
No full textTwo methods have been developed for the determination of platinum group elements (PGEs) and gold in four geological reference materials: one using radiochemical neutron activation analysis and the other using nickel sulphide fire assay, followed by instrumental neutron activation analysis. The results from ten multiplicate measurements have been discussed in terms of precision and accuracy. The average precision for both methods is about 5%, Comparing the reported data with existing values in the literature, the accuracy of the proposed methods is good agreement in most cases. Detection limits in the range 0,001 -0,015 ng have been derived for both methods under the operational conditions
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
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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