1,720,955 research outputs found
Crystal structure refinements and compositional control of Mn-Mg-Ca ardennites from the Belgian Ardennes, Greece, and the Western Alps
No full textThe As5+ - V5+-bearing silicate ardennite is commonly present in highly oxidized, manganiferous metasediments that were affected by low- to high-pressure metamorphism in the T range from ca. 300 to 600-degrees-C. Electron microprobe analyses of ardennite from the Belgian Ardennes, Greece, and the Western Alps combined with the results from structure refinements on four ardennite crystals from Andros, Greece; Haute-Maurienne, French Western Alps; and Lago di Cignana, Valtournanche, Italy (two specimens of different composition), suggest the general formula VI(A1)2 (VII)(A2)2 (VI)(M1-M3)6 [(IV)T4(O,OH)4/(SiO4)2/Si3O10/(OH,O)6], where Al = Mn2+, Mg; A2 = Mn2+, Ca; Ml = Al, +/- Fe3+; M2 = Al; M3 = Al, Mg, +/- Fe3+, +/- Mn3+, +/- Cu2+, +/- Ni2, ; and T4 = As5+, V5+, P5+, Si4+. Least squares refinements of the four structures (space group Pnmm, a = 8.710(6)-8.767(3) Å, b = 5.803(4)-5.846(2) Å, c = 18.542(9)-18.613(6) Å) converged with R = 0.036-0.083 and allowed to locate the hydrogen atoms in ardennite from Haute-Maurienne. Mn3+ Al-1 substitution (up to 1.1 Mn3+ per 16 total cations) principally occurs in the M3 octahedron which is larger ([M3 - O] = 2.006 - 2.018 Å) and more distorted (two long and four short cation-oxygen distances) than the M1 (1.918 - 1.941 angstrom) and the M2 octahedron (1.897-1.906 angstrom). Within the range from zero to 0.4 Mn3+ p.f.u., obtained for the refined structures, however, the degree of distortion of the M3 octahedra is unrelated to the Mn3+. content. Fe3+ (up to 0.4 atoms p.f.u. in microprobe analyses) may enter either the M1 or, in Mn3+-free ardennite, the M3 site. Mg2+ is partitioned between the M3 octahedron (0.5 - 0.95 atoms p.f.u.) and the irregular (6 + 1)-coordinated A1 polyhedron (0 - 1.6 atoms p.f.u.). Ca has a strong preference for the larger 7-coordinated A2 site, where it substitutes for up to 77 mol% of the Mn2+ in Mn3+-rich ardennites from low-grade assemblages. Besides As5+ and/or V5+, the isolated T4 tetrahedron may incorporate significant Si4+ commonly up to 40 mol%) as well as up to 28 mol% P5+ in ultrahigh-pressure metamorphic ardennites. The [T4-O] distances range from 1.688 angstrom to 1.659 angstrom and reflect the variable extent of substitution of Si4+ and P5+ for As5+ and V5+. The chemical analyses suggest that charge balance for Al3+-Mg2+ substitution in M3 and Si4+-(As, V, P)5+ substitution in T4 is maintained by variations in the overall hydrogen content. During prograde high-pressure metamorphism, Mg (in A1 sites) and P5+ gradually increases as the result of multivariant reactions of ardennite with coexisting garnet, apatite, phengite, clinochlore/talc, quartz/coesite and piemontite. Ca, Mn3+ and Fe3+ contents in ardennite vary i) with T and P by virtue of Mn3+Al-I and Mn3+Fe-13+ exchange with braunite, hematite and piemontite and ii) as a result of different mineral assemblages in closely associated rocks
Graulichite-(Ce), a new arsenate mineral from the Stavelot Massif, Belgium
Full text linkpeer reviewedGraulichite-(Ce), ideally CeFe33+(AsO4)(2)(OH)(6), is a new mineral species from Hourt, Stavelot Massif, Belgium. It occurs in the most altered parts of a Devillian quartzite (Lower to Middle Cambrian), in close association with arsenopyrite, scorodite, mimetite, pharmacosiderite, and goethite. Graulichite-(Ce) forms 80 to 150 mum spherical aggregates of rhombohedral crystals, 50 to 80 mum length, which show the forms {10 (1) over bar2} and {10 (11) over bar}. The mineral is transparent and exhibits a light-green to brownish colour, with a resinous lustre. It is non-fluorescent and shows an irregular fracture, without any perceptible cleavage. The calculated density is 4.42 g/cm(3). Graulichite-(Ce) is uniaxial negative, with a mean refractive index close to 1.97(1) (lambda=590 nm), pleochroic from light green to yellowish. Electron microprobe analyses gave As2O5 31.20, P2O5 0.03, SO3 0.06, SiO2 0.03, Al2O3 3.09, Fe2O3 30.65, SrO 0.24, PbO 0.07, BaO 3.95, CaO 0.03, La2O3 2.26, Ce2O3 15.73, Nd2O3 2.08, H2O (calc.) 8.37, total 97.79 wt. %. The resulting empirical formula, calculated on the basis of 6 cations, is (Ce0.67Ba0.18La0.10Nd0.09Sr0.02)(Sigma1.06) (Fe2.683+Al0.42)(Sigma3.10)[(As(1.89)S(.001)square(0.10))(Sigma2.00)O-8][(OH)(5.57)(H2O)(0.43)](Sigma6.00). The single-crystal unit-cell parameters are a=7.288(2) and c=16.812(9) Angstrom, space group R (3) over barm. The seven strongest lines in the X-ray powder-diffraction pattern [d(in Angstrom)(I)(hkil)] are: 3.052(100)(11 (2) over bar3), 3.636(40)(11 (2) over bar0), 2.239(35)(10 (1) over bar7), 1.817(35)(22 (4) over bar0), 2.792(30)(0006), 5.906(25)(10 (1) over bar1), 1.968(25)(30 (3) over bar3). Graulichite-(Ce) is the iron analogue of arsenoflorencite-(Ce), and belongs to the crandallite mineral group, with the alunite-type structure. The crystal structure of graulichite-(Ce) has been refined, based on single-crystal X-ray diffraction data, to R=0.048
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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