1,720,961 research outputs found
Weathering sequence of rhyolitic minerals: the kaolin deposit of Torniella (Italy)
No full textThe Torniella mine (Southern Tuscany, Italy) represents one of the most important Italian deposit of kaolin, formed by hydrothermal weathering of primary rhyolites. Raw material is currently exploited for the ceramic industry. The mining area is heterogeneous, ranging from preserved rhyolites to completely weathered rocks; all the different lithologies have been sampled and investigated by XRPD, XRF and SEM-EDS techniques, to reconstruct the overall weathering sequence.
Early weathering, characterized by low fluid/rock ratios, first affects plagioclase and biotite, replaced by crystalline kaolinite (possibly associated with poorly-crystalline halloysite) along cleavage planes and crystal edges; later, weathering affects the glassy groundmass, which is replaced by a microgranular association of silica and kaolin. The last weathering stage, characterized by high fluid/rock ratios, pervasive fluid circulation and fast reactions, produces a nearly-pure kaolin material, consisting of kaolinite and halloysite, in variable proportions; kinetically-favoured, fluid-enhanced halloysite occurs only in most weathered samples. Sanidine is completely replaced, whereas quartz relics may persist. Fine-grained pseudocubic crystals of alunite are commonly associated to feldspars weathering; alunite occurrence and whole-rock sulfur content (increasing with weathering extent) suggest circulation of sulfur-rich hydrothermal fluids
A new chaotic algorithm for video encryption
No full textWe present a new encryption algorithm for the video signal that, employing suitably arranged chaotic functions, allows to increase the security level while maintaining acceptable processing times. We analyze the performance of the new scheme either though simulation or via practical implementation, thus demonstrating its efficiency, also in comparison with previous proposals
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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