1,720,956 research outputs found
Quantitative phase analysis of natural raw materials containing montmorillonite
No full textOne of the limits of quantitative phase analysis of natural clays using the Rietveld method is the lack of an applicable structure model for the highly disordered phases such as montmorillonite. The description of disorder of montmorillonite, the main dioctrahedral smectite, was accomplished using the DIFFaX program [1] which allows the calculation of simulated powder patterns. We followed the strategy successfully used for kaolinite [2] in which simulated powder patterns calculated using different models of disorder are compared to the observed one. Since DIFFaX is bases upon a recursive method and produces a statistical crystal, a super-cell composed of n layers describing the average disordered structure was re-defined to be used in the codes which apply the deterministic Rietveld algorithm. Therefore, a working structure composed of 4 layers (an ideal layer, a b/3 shifted layer, a -b/3 shifted layer, and a -a/3 shifted layer) was described and used in GSAS [3] to fit a natural international standard of Ca-montmorillonite.One of the limits of quantitative phase analysis of natural clays using the Rietveld method is the lack of an applicable structure model for the highly disordered phases such as montmorillonite. The description of disorder of montmorillonite, the main dioctrahedral smectite, was accomplished using the DIFFaX program [1] which allows the calculation of simulated powder patterns. We followed the strategy successfully used for kaolinite [2] in which simulated powder patterns calculated using different models of disorder are compared to the observed one. Since DIFFaX is bases upon a recursive method and produces a statistical crystal, a super-cell composed of n layers describing the average disordered structure was re-defined to be used in the codes which apply the deterministic Rietveld algorithm. Therefore, a working structure composed of 4 layers (an ideal layer, a b/3 shifted layer, a -b/3 shifted layer, and a -a/3 shifted layer) was described and used in GSAS [3] to fit a natural international standard of Ca-montmorillonite
Optimization of the strategy for the quantitative phase analysis of ceramic materials using the rietveld method
No full textIn this space of work we describe the optimization of the strategy and times for the quantitative phase analysis of ceramic materials using the Rietveld method in order to accomplish a routinary technique for ceramic laboratories equipped with an X-ray powder diffraction instrumentation. We reduced the data collection, reduction and processing times. The time of the data collection was significantly shortened although the statistics was kept good enough to give reliable estimates on the calculated weights of the crystalline phases. The sinergy between the Rietveld method and the chemical analysis results in a full characterization of the ceramic raw materials and products. This work is the outcome of a partnership project involving an academic institution (The University of Modena and Reggio Emilia) and an industrial Laboratory (the "Modena Centro Prove")
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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