1,721,030 research outputs found
Thermal expansion of C3S and Mg-doped alite
No full textThe lattice thermal expansion coefficients were measured using in situ high temperature x-ray powder diffraction on triclinic tricalcium silicate (C3S) in the temperature range 25-970 degrees C and on monoclinic alite of composition Ca(2.879)Mg(0.112)Al(0.0439)Si(0.971)O5 in the temperature range 30-1150 degrees C. Full profile refinements were performed using the Rietveld method. The structural model of Mumme [1] was adopted for the alite crystal structure, implying a space group Cm and cell constants a=12.18, b=7.04, c=9.25 Angstrom, beta=116.11 degrees at 25 degrees C. All three lattice parameters show similar temperature behaviour and relative thermal expansion coefficients. There is a clear change in slope at about 900 degrees C, which is assumed to be related to the phase change between two monoclinic forms of alite. Refinements of C3S were conducted using the structural model of Golovastikov et al. [2] implying a space group and cell constants a=11.67, b=14.28, c=13.72 Angstrom, alpha=105.3, beta=94.2, gamma=90.0 degrees at 25 degrees C. The C3S lattice parameter b shows a different trend in temperature with respect to a and c. The same behaviour is reproduced by the relative thermal expansion coefficient alpha. Three clear changes in slope are found and regarded as phase transition points between triclinic modifications of C3S. Integrated intensity analysis for selected peaks, together with TG/DTA in the temperature range 25-1150 degrees C, were also used in order to preliminarly characterize the phase transitions
The nature of disorder in montmorillonite by simulation of X-ray powder patterns
No full textThe planar disorder of Ca-montmorillonite (Fuller's earth) has been investigated using structural simulations of X-ray powder patterns. A standard sample was fully characterized using chemical, microscopic, and diffraction methods. Earlier models of disorder taken front the literature and newly formulated combined models were used to generate simulated powder patterns to be compared with the experimental spectrum. A new model of disorder with random shifts of -a/3 and +/-b/3, with a total density of defects of 75%. gives the best fit to the observed data. Thus, the sample cannot be classified as a turbostratic structure (fully disordered) and consequently turbostratic disorder does not invariably apply to all smectite samples. These findings open a debate on the nature and application of turbostratic disorder: is it possible for smectite samples to have intermediate degrees of disorder between a fully disordered stacking (turbostratic) and a highly faulted but well-defined stacking or is the result obtained for the Ca-montmorillonite Just an exception? This model of disorder is useful for the quantitative phase analysis by X-ray powder diffraction based on the Rietveld method, which can now benefit from a more reliable initial Structure model for Ca-montmorillonite and which will improve the accuracy of the weight-fraction estimates
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
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
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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