1,720,964 research outputs found
In situ U-Pb and Nd-Hf-(Sr) isotopic investigations of zirconolite and calzirtite
No full textAlthough the calcium- and titanium-bearing zirconsilicates, zirconolite and calzirtite, are common minerals in carbonatites little is known regarding their trace element or isotopic characteristics. Available data indicate that they can have significant contents of U. Pb, Nb, Ta, Zr, Hf, rare earth elements (REEs), minor Sr and low Rb/Sr and Lu/Hf ratios. Their compositions indicate that they have potential for U Pb age determination together with Nd Hf and possibly Sr isotopic analyses. In this study, zirconolite and calzirtite from carbonatites occurring at Phalaborwa (South Africa), Prairie Lake (Canada), Afrikanda and Kovdor (Kola, Russia), Gull (Siberia, Russia) and Jacupiranga (Brazil) were selected for an isotopic analysis by in situ techniques. Ion microprobe analyses using a CAMECA 1280 ion microprobe show that reliable Pb Pb ages can be obtained from these minerals as they have extremely high U concentrations, coupled with negligible common Pb. Although these minerals have low Rb/Sr ratios, their low Sr concentrations, in most cases, render in situ Sr isotopic analyses difficult. In contrast, their high Sm, Nd and Hf concentrations, with generally low Lu/Hf ratios, permit precise in situ isotopic analysis of Nd and Hf
Vlasovite, Na2Zr(Si4O11), from the Kipawa alkaline complex, Quebec, Canada: crystal-structure refinement and polarized infrared spectroscopy
No full textThe crystal structure of vlasovite, Na-2 Zr (Si4O11), from the Kipawa alkaline complex, Quebec, Canada, monoclinic, a 11.0390(5), b 10.0980(3), c 8.5677(4) angstrom, beta 100.313(1)degrees, V 939.6(1) angstrom(3), space group 4,72/c. Z = 4, D (calc.) = 3.008 g.cm(-3), was refined to all R, index of 1.9% based oil 1352 observed [F-o > 4 sigma F] unique reflections measured with MoK alpha X-radiation on a Broker P4 diffractometer equipped with a 4K CCD detector. An electron-microprobe analysis gave the composition Na-1.98 Zr-1.00 (Si4O11) based on 11 O apfit. In the crystal structure, there ire two tetrahedrally coordinated Si sites with a grand distance of 1.612 angstrom, and one octahedrally coordinated Zr site with = 2.085 angstrom. There are two Na sites: the Na(1) site is [7]-coordinated with = 2.620 angstrom, The Na(2) site is split into two subsites, Na(2A) and Na(2B), with a separation of 0.829 angstrom, and the symmetry-related Na(2B) sites are separated by 1.525 angstrom. Na(2A) is octahedrally coordinated, and No(2B) is [5]-coordinated, and their occupancies are 0.826(8) and 0.092(4) Na, respectively. Thus the Na(1) and aggregate Na(2) sites are each fully Occupied. In the crystal structure of vlasovite, four-membered rings of (SiO4) tetrahedra link together to form an [Si4O11](6-) chain. Chains of tetrahedra and Zr octahedra link together to form a heteropolyhedral framework with channels extending along [001]. Three channels contain the Na atoms, which are bonded to O atoms of the octahedron-tetrahedron framework. Vlasovite is not significantly damaged by exposure to X-rays. Infrared spectro;copy shows that vlasovite can be free of H2O or can contain variable amounts of H2O; single crystals can be anhydrous in so ne regions and hydrous in other regions. Moreover, the H2O content and its spectral response are unaffected by exposure of crystals to X-rays
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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