1,721,263 research outputs found
The crystal structure of vurroite, Pb20Sn2(Bi,As)22S54Cl6: OD-character, polytypism, twinning, and modular description
No full textThe crystal structure of the type specimen of vurroite from Vulcano (Aeolian Islands, Italy) has been solved and refined using single-crystal X-ray diffraction data collected at the Elettra synchrotron facility (Basovizza, Trieste). Vurroite has an OD (order-disorder) structure belonging to the category III of OD structures composed of equivalent layers. The OD-groupoid family (λ and σ partial operations) and MDO structures were derived by means of the application of the OD theory. The two theoretically possible polytypes with maximum degree of order (MDO polytypes) have pseudo-orthorhombic metric, with lattice parameters a ≈ 45.6, b ≈ 8.4, c ≈ 54 Å, and a ≈ 22.8, b ≈ 8.4, c ≈ 54 Å, and space group symmetries F2/d11 and A2/d11, respectively. Only the former polytype (MDO1) could be identified in the analyzed crystals. The MDO1 structure was solved and refined to R = 6.26% for 4968 reflections with Fo > 4σ(Fo). In the standard C2/c setting of the space group the unit-cell parameters of MDO1 are a = 8.371(2), b = 45.502(9), c = 27.273(6) Å, β = 98.83(3)°, V = 10265(4) Å3, Z = 4. Frequent twinning with (001) as the twin plane, together with the occurrence of disordered domains in the structure, was observed.
The crystal structure of vurroite contains lozenge-shaped composite rods made of coordination polyhedra of Pb and Sn, interconnected into layers parallel to (010) of the standard monoclinic setting. These layers are separated by ribbons of As and Bi, each in distorted octahedral coordination. The ribbons form wavy, discontinuous double layers of PbS archetype. Lone electron pairs of As and Bi are accommodated in the central portions of the PbS-like layers. The structure of vurroite contains building blocks topologically similar to those found in the zinckenite group and in the structure of kirkiite. It can be considered a box-work structure containing the smallest possible pseudo-hexagonal block in the form of a sole octahedron
On pavonite, cupropavonite, benjaminite and «oversubstituted » gustavite
No full textSpecimens described by Karup-Møller (1972) were re-studied by means of microprobe analyses, single-crystal X-ray studies and ore microscopy.
«Typical pavonites » follow closely the formula Cu3xPb2xAg1-yBi3-yS5 with 5 x ~ 2 y. The substitution coefficient y varies from 0.18 to 0.32. The substitution interval is centered on Cu0.33Ag0.75Bi2.75Pb0.20S5, y = 0.25, Σ Me = 4.03, i.e. Cu1.33Ag3Bi11Pb0.99Sb20 (Me16S20) in a unit cell with c = 16.4 Å. Cupropavonite, a new mineral from Alaska Mine, Colorado has the formula Cu0.90Ag0.50Bi2.50Pb0.60S5 (y = 0.50, Σ Me = 4.5), i. e. Cu7.2Ag4Bi20Pb4.8S40 (Me32+4S4O) in a monoclinic unit cell with a = 13.45, b = 4.02, c = 33.06 Å (= 2 x 16.53 Å), β = 93. 50°, space group C2/m or Cm. It forms an exsolution pair with Pb-rich pavonite Cu0.27Ag0.78Bi2.78Pb0.33S5. Both phases contain copper interstitial to the pavonite structural motif. Benjaminites are spread on both the Pb-richer and Bi-richer sides of the CuaPbbAg1.5-yBi3.5-y line (idealized y = 0.13-0.44). Benjaminite from Manhattan, Nevada has structural formula Cu0.25Pb0.20Ag1.15Bi3.40S6 with unequal substitution of Ag and Bi (Ag1.5-yBi3.5-z, y > z).
Formulae for determination of the order number, NP, of pavonite homologues from chemical analyses were devised for the cases y = z and y > z, applied to the present and published data. A number of published phases were redetermined in this way and potential new phases pointed out. Benjaminite from Manhattan, Nevada and Old Laut's Mine, Colorado forms oriented intergrowths with gustavite (presumably exsolution). «Oversubstituted gustavite» 3.8Gu79,6 --> 3.4Gu114.1 from Old Laut's Mine is interpreted as a gustavite (80) - pavonite intergrowth.Nous avons ré-étudié les échantillons de Karup-Moller (1972) par microsonde électronique, par diffraction de rayons X sur monocristaux et par observation optique de sections polies. La composition des «pavonites typiques » approche la formule idéale Cu3xPb2xAg1-yBi3-yS5) avec 5 x ~ 2 y.
Le coefficient de substitution y, varie entre 0,18 et 0,32. L'intervalle de substitution est centré sur la composition Cu0,33Ag0,75Bi2,75Pb0,20S5, y = 0,25, Σ Me = 4,03, c'est-à-dire Cu0,33Ag3Bi11Pb0,80S20 (Me16S20) dans une maille avec c = 16,4 Å. La cupropavonite, un nouveau minéral de la mine d'Alaska, Colorado, avec la formule chimique Cu0,90Ag0,50Bi2,50Pb0,50S5 (y = 0,50, Σ Me = 4,5), donc Cu7,2Ag4Bi20Pb4,8S40 (Me32+4S40) dans une maille monoclinique avec a = 13,45, b = 4,02, c = 33,06 (= 2 x 16,53) Å, β = 93,50°, groupe spatial C2/m ou Cm. Elle se trouve en exsolution avec la pavonite riche en Pb, Cu0,27Ag0,78Bi2,78Pb0,33S5. Les deux phases contiennent Cu dans les lacunes de la structure de la pavonite. Les benjaminites sont groupées autour de la ligne CuaPbbAg1,5-yBi3,5-y (y idéalisé ~ 0,13-0,44). La formule structurale de la benjaminite de Manhattan, Nevada, est Cu0,25Pb0,20Ag1,15Bi3,40S6, avec une substitution inégale de Ag et de Bi (Ag1,5-yBi3,5-z, y > z).
Dans les cas ou y = z et y > z nous avons dérivé des formules pour estimer le numéro d'ordre, NP, des homologues de la pavonite en fonction de leur composition chimique. Appliqué aux analyses publiées, on a redéterminé quelques phases et dégagé quelques nouveaux minéraux potentiels. Les benjaminites de Manhattan, Nevada et de la Mine d'Old Laut, Colorado, forment des intercroissances orientées avec la gustavite (probablement, des produits d'exsolution). Nous interprétons la gustavite «sur-substituée », 3,8Gu79,6 -> 3,4Gu114,1 de la mine d'Old Laut comme une intercroissance de gustavite (80) avec de la pavonite.Karup-Møller Sven, Makovicky Emil. On pavonite, cupropavonite, benjaminite and «oversubstituted » gustavite. In: Bulletin de Minéralogie, volume 102, 4, 1979. pp. 351-367
Tsygankoite, Mn8Tl8Hg2(Sb21Pb2Tl)Σ24S48, a New Sulfosalt from the Vorontsovskoe Gold Deposit, Northern Urals, Russia
Full text linkTsygankoite, ideally Mn8Tl8Hg2(Sb21Pb2Tl)Σ24S48, is a new sulfosalt discovered at the Vorontsovskoe gold deposit, Northern Urals, Russia. It occurs as lath-like elongated crystals up to 0.2 mm embedded in calcite–dolomite–clinochlore matrix. The associated minerals also include aktashite, alabandite, arsenopyrite, barite, cinnabar, fluorapatite, orpiment, pyrite, realgar, routhierite, sphalerite, tilasite, and titanite. The new mineral is non-fluorescent, black, and opaque with a metallic lustre and black streak. It is brittle with an uneven fracture and no obvious parting and cleavage. Its Vickers hardness (VHN10) is 144 kg/mm2 (range 131–167 kg/mm2) and its calculated density is 5.450 g cm. In reflected light, tsygankoite is white; between crossed polars it is dark grey to black. It is strongly anisotropic: rotation tints vary from light grey to dark grey to black. Pleochroism and internal reflections are not observed. The chemical composition of tsygankoite (wt %, electron-microprobe data) is: Mn 6.29, Hg 5.42, Tl 26.05, Pb 5.84, As 3.39, Sb 30.89, S 21.87, total 99.75. The empirical formula, calculated on the basis of 90 atoms pfu, is: Mn8.06Tl8.00Hg1.90(Sb17.87As3.19Pb1.99Tl0.97)Σ24.02S48.03. Tsygankoite is monoclinic, space group C2/m, a = 21.362(4) Å, b = 3.8579(10) Å, c = 27.135(4) Å, β = 106.944(14)°, V = 2139.19(17) Å3 and Z = 1. The five strongest diffraction peaks from X-ray powder pattern (listed as (d,Å(I)(hkl)) are: 3.587(100)(112), 3.353(70)(−114), 3.204(88)(405), 2.841(72)(−513), and 2.786(99)(−514). The crystal structure of tsygankoite was refined from single-crystal X-ray diffraction data to R = 0.0607 and consists of an alternation of two thick layer-like arrays, one based on PbS-archetype and the second on SnS-archetype. Tsygankoite has been approved by the IMA-CNMNC under the number 2017-088. It is named for Mikhail V. Tsyganko, a mineral collector from Severouralsk, Northern Urals, Russia, who collected the samples where the new mineral was discovered
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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