1,720,969 research outputs found
Contrasting chemical compositions in associated lizardite and chrysotile in veins from Elba, Italy
No full textSerpentinitic veins consisting of associated chrysotile and well crystallized lizardite were extensively sampled in the Monte Fico quarries, Elba Island, Italy. The veins are mostly formed of euhedral lizardite-1T. After optical, IR and X-ray characterization, the specimens were studied by transmission electron microscopy. TEM provides evidence for the occurrence of chrysotile, polygonal serpentine and lizardite, with microstructural relations pointing to a continuous recrystallization from chrysotile to polygonal serpentine and to lizardite. No major fault structure occurs in lizardite. Chemical data indicate the existence of a compositional gap between lizardite [mean composition (Mg2.79Fe2+ 0.09 Fe3+ 0.07Al0.07)Σ=3.02(Si 1.91Al0.09)Σ=2.00 O5 (OH)3.90] and chrysotile [mean composition (Mg2.80Fe0.11Al0.06) Σ=2.97Si2.00 O5 (OH)4] with lizardite systematically enriched in aluminum and iron with respect to chrysotile. Therefore, the two minerals should no longer be considered as polymorphs
Vein antigorites from Elba Island, Italy
No full textAntigorite in veins from Elba Island, Italy, appears as light-green splintery fibers, discontinuously surrounding the massive dark serpentinite, extending along fractures and deformed by compressive shearing.
The chemical compositions cluster around Mg2.66Fe0.12Al0.02Si2.00O5(OH)(3.60) with the exact value depending upon the polysomatic structural modulations. Electron diffraction shows superperiodicities variable from 33 to 49 Angstrom and changing from vein to vein, with no relation with the metamorphic grade of the surrounding rocks.
Common polysomatic faulting, (001) twinning and parallel association with polygonal serpentine as well as with anomalous (thin wall tubes) chrysotile are the most evident microstructural features.
A complete set of X-ray diffraction, IR, NMR and thermal analyses results is presented for a selected number of specimens.
With respect to massive antigorite serpentinites, antigorite veins show periodicities shorter than expected; this feature is interpreted as due to shearing stress and/or favourable kynetics able to accelerate the sluggish chrysotile-antigorite transformations
Microtexture and microchemistry of glaze and pigments in Italian Renaissance pottery from Gubbio and Deruta
No full textRenaissance ceramic shards from Gubbio and Deruta (Italy) were investigated by scanning and transmission electron microscopy, coupled with energy dispersive spectrometry. The study mainly focuses on the glaze layer, which was applied over the main ceramic body in a second firing process. The glaze contains several inclusions, such as K-feldspar, cassiterite, calcium phosphate and quartz. Most of the shards have blue and yellow decorations, which correspond to the so-called Blue Smalt and Naples Yellow. Overall evidence (glaze bulk-chemistry, the number and type of inclusions, pigment characteristics and the microtextural-microchemical relationships among glaze, inclusions and the main ceramic body) constrains the nature and provenance of raw materials and can be used to estimate firing temperatures in the different processing steps
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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