1,720,978 research outputs found
Gabrielsonite revisited: crystal-structure determination and redefinition of chemical formula
Full text linkA reinvestigation of gabrielsonite from the holotype specimen from Långban, central Sweden, using single-crystal
synchrotron diffraction, electron-microprobe techniques and Fourier-transform infrared (FTIR) spectroscopy, Raman and Mo ̈ssbauer
spectroscopies show that the mineral is an anhydrous Fe3+-bearing arsenite and not a hydrous Fe2+-bearing arsenate, as originally
proposed. The revised ideal chemical formula of gabrielsonite is PbFe3+(As3+O3)O. The mineral is related to the descloizite
supergroup, but it differs through the valencies of the non-Pb cations Fe (M3+ vs. M2+) and As (3 + vs. 4 +) and through lower
coordination of Pb (4 vs. 7–8) and As (3 vs. 4). The redefinition of gabrielsonite (proposal 17-G) has been approved by the
Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association
On the Crystal-Chemistry of Rosasite and Parádsasvárite
Full text linkWe report the results of mineralogical and structural studies of para ́dsasva ́rite from Rudaba ́nya, Hungary, and rosasite from
Hayden, Arizona (USA). A preliminary investigation of the two minerals, which belong to the rosasite–malachite group, was
conducted using Raman spectroscopy, X-ray diffraction, and EPMA. Para ́dsasva ́rite has the chemical formula
(Zn1.91Cu0.06Mg0.02)R1.99(CO3)(OH)2, ideally Zn2(CO3)(OH)2, and rosasite has the formula (Cu1.14Zn0.84Mg0.02)R2(CO)3(OH)2,
matching the general formula CuZn(CO3)(OH)2.
The first single-crystal full structural study of rosasite from Hayden, based on synchrotron X-ray data, is reported here and
fully confirms the results obtained by Perchiazzi (2006) on the basis of X-ray powder data. The presence of structural disorder
in Cu-Zn distribution in these minerals is indicated by the streaking of reflections along c*. Rosasite is monoclinic, P21/a, a
12.2436(29) A, ̊ b 9.3555(19) A, ̊ c 3.1535(6) A, ̊ b1⁄498.69(3)8, and its crystal structure was refined to R11⁄412.4%, wR21⁄435.5%.
The presence of Cu2þ causes a Jahn-Teller distortion of coordination polyhedra, a major feature of the rosasite crystal structure,
particularly evident in the Me1 coordination polyhedron, which is fully occupied by Cu.
A Rietveld study of para ́dsasva ́rite, based on synchrotron radiation data, shows it is isostructural with rosasite, monoclinic
P21/a, a 12.253(4) A, ̊ b 9.348(3) A, ̊ c 3.167(1) A, ̊ b 1⁄4 97.700(4)8, and its crystal structure was refined to R1 1⁄4 1.45%, wR2 1⁄4
2.45%. The Me1 and Me2 coordination polyhedra in para ́dsasva ́rite, the former hosting Zn with a minor presence of Cu, the
latter fully occupied by Zn, are as expected both more regular than the corresponding polyhedra in rosasite.
Crystal-chemical considerations, based on literature chemical data for rosasite and Zn-rich malachite, indicate that a
minimum Cu content of 0.4–0.5 apfu is necessary to stabilize the malachite-type structure
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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