1,720,967 research outputs found
Afghanite from Mount Vesuvius: A rediscovery
No full textAfghanite is a member of the cancrinite group first described in 1968 as a new species from the Sar-e-Sang lazurite deposit in Afghanistan. However, specimens of the mineral were first collected more than a century earlier from the Mount Vesuvius area. The material was partially described and named "natrodavyne" in 1910, but was then lost until being recently re-identified
Potassium-fluor-richterite from San Vito, Monte Somma, Campania, Italy
No full textPotassium-fluor-richterite occurs as euhedral crystals, light-grey in colour, in a skarn ejectum from a pyroclastic deposit near S. Vito, Monte Somma, Naples. It is associated with diopside and calcite. The strongest X-ray diffraction lines are (d- spacing in Å): 3.166, 8.49, 3.288, 2.831, 1.918 and 1.633. The cell parameters (in Å, space groupC2/m) are:a = 9.978 (1);b = 17.991(2);c = 5.269 (1); ß(°) = 104.90 (2);V = 914.2 (3). Potassium-fluor-richterite is biaxial negative with (± 0.004) nX = 1.613; nY = 1.623; nZ = 1.630. The crystal-chemical formula is:
(K0.67Na0.34) (Ca1.09Na0.91) (Mg40.976Fe0.017Mn0.002) (Si7.94Al0.04Ti0.007) O22 (F1.35OH0.65).
The FTIR spectrum in the OH-stretching region is discussed.
La potassium-fluor-richterite si rinviene in proietti carbonatici metamorfosati e metasomatizzati contenuti in un deposito piroclastico affiorante vicino al Comune di S. Vito, Monte Somma, Napoli. È associata con diopside e calcite. I riflessi più intensi nello spettro misurato ai raggi X sono (distanze interplanari in Å): 3.166, 8.49, 3.288, 2.831, 1.918 e 1.633. I parametri di cella sono (in Å):a = 9.978 (1);b = 17.991 (2);c = 5.269 (1); ß(°)= 104.90 (2);V = 914.2 (3). La potassium-fluor-richterite è biassica negativa. Gli indici di rifrazione sono (± 0.004): nX = 1.613; nY = 1.623; nZ = 1.630. La formula cristallochimica è: (K0.67Na0.34) (Ca1.09Na0.91) (Mg40.976Fe0.017Mn0.002) (Si7.94Al0.04Ti0.007) O22 (F1.35OH0.65). Lo spettro FTIR nella regione di stiramento dell’OH viene discusso
Vicanite-(Ce): a new Ca-Th-REE borosilicate from the Vico volcanic district (Latium, Italy)
No full textVicanite-(Ce), ideally (Ca, REE, Th) As-15(5+) (As0.53+Na0.5Fe3+ Si-6 B-4 O-40 F-7, was found inside a volcanic ejectum collected from a pyroclastic formation of the Vice volcanic complex at Tre Croci, Vetralla (north of Rome), Viterbo province, Italy. The host rock is composed of K-feldspar (high sanidine), plagioclase, clinopyroxene plus minor quantities of magnetite and clinoamphibole. Vicanite-(Ce) occurs in small myarolitic cavities in association with zircon, thorite, thorian uraninite, betafite, thorian hellandite, titanite, antimonian asbecasite, apatite, stillwellite-(Ce), and other unidentified phases. It is found as rare euhedral crystals up to 0.3 mm across, yellowish green in colour; uniaxial (-), epsilon 1.722(2), omega 1.757(2), non pleochroic. The streak is white, and the mineral shows no fluorescence under UV radiation. The crystal chemical formula calculated from electron microprobe analyses, on the basis of 47(O+F) and B fixed to 4 atoms, is: (Ca-8.03 Ce-2.32 La-1.95 Th-1.82 Pr-0.44 Nd-0.28 U-0.19)(Sigma 15.06) (As-0.86(5+) P-0.14)(Sigma 1.00) (As-0.34(3+) Na-0.12)(Sigma 0.46) (Fe0.573+Ti0.05Al0.08)(Sigma 0.67) Si6.07B4 (O-36.57 F-10.43)(Sigma 47). Density is higher than 4.2. The mineral is trigonal and crystallizes in the non-centrosymmetric R3m space group. The refined unit-cell parameters are: a = 10.795(1), and c = 27.336(4) Angstrom, Z = 3 (hexagonal cell). The eight strongest X-ray diffraction lines are [d in Angstrom (I) (hkl)]: 7.70 (50) (012), 4.42 (50) (202), 3.13 (50) (214), 2.993 (100) (027), 2.950 (70) (303), 2.698 (50) (220), 1.839 (50) (3,0,12), 1.802 (50) (2,0,14). The main feature of the structure is the presence of a new polyanion (Si-3 B-3 O-18)(15-). The cell dimensions of vicanite-(Ce) are very close to those of okanoganite-(Y), but the chemical composition is rather different as no Y, Gd, Dy, Sm and Er are present in vicanite-(Ce). The name is for the Vican volcanic complex where the mineral was found. Holotype is deposited in Museo di Mineralogia, Universita di Roma ''La Sapienza'' (MMUR)
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
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