1,721,400 research outputs found
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
The Relevance of Macerals In the Combustion of A Coal Char In the Chemical Kinetic Regime
No full textA Fractal Approach To the Analysis of Low-temperature Combustion-rate of A Coal Char .1. Experimental Results
No full textThe combustion reactivity of char obtained by devolatilization of South African bituminous coal has been investigated by thermogravimetric analysis in the temperature range of 653 to 733 K at oxygen partial pressures from 0.21 to 1 bar. Samples of the same char, either unreacted or preburned in a fixed bed reactor to given levels of carbon burn-off, have been characterized from the standpoints of their surface area and of their volume and size distribution of pores. Different experimental techniques, namely mercury porosimetry and adsorption of either carbon dioxide or nitrogen, and models for the interpretation of porosimetric data have been used. Analysis of meso- and macropore size distributions, and of adsorption isotherms in the low relative pressure region, has been directed to check whether the topological structure of the porous matrix of the char might be described as a fractal
The influence of char surface oxidation on thermal annealing and loss of combustion reactivity
No full textThermal annealing associated with heat treatment of coal chars affects gasification reactivity and levels of unburned carbon in residual ash from coal-fired furnaces. The present study addresses the effect of char surface oxidation, occurring upon exposure to oxygen, on the course of thermal annealing, and related loss of combustion reactivity. This goal is pursued by comparing the extent of thermal annealing suffered by coal char upon heat treatment in a nitrogen atmosphere with that of chars that underwent oxidation prior to or during heat treatment. Oxidation of char was accomplished by supplying single or multiple pulses of air during the heat treatment, which were sufficient to oxidize the char surface but small enough to limit carbon gasification to less than 5%. The extent of thermal annealing was characterized both in terms of the loss of combustion reactivity and of the development of structural anisotropy of char samples, investigated by HRTEM. Results of the present study confirm that heat treatment reduces oxyreactivity of char samples, the effect being more pronounced at temperatures exceeding 1200 degrees C. Oxidation of samples mitigates the effects of heat treatment, as demonstrated by the smaller loss of gasification reactivity and by the more limited development of structural anisotropy of oxidized samples. Correspondingly, elemental analysis of samples indicates the formation of stable surface oxides upon oxidation, that are subsequently desorbed upon heat treatment. At temperatures exceeding 1200 degrees C, the effect of oxidation vanishes. Results are analysed and discussed in the light of the possible hindrance of thermal annealing due to the formation of stable surface oxides and of the parallel modifications occurring to the ash constituents. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved
Heat treatment-induced loss of combustion reactivity of a coal char: the effect of exposure to oxygen
No full textA South African bituminous coal was heat treated at different temperatures in the range 500-1300 degreesC under inert conditions with or without exposure to pulses of air. The effect of the heat treatment conditions on the reactivity of the resulting char towards oxygen under chemical kinetic controlled regime was assessed. The oxygen content of chars subjected to different heat treatment conditions was also measured by elemental analysis. Results indicated that exposure to pulses of air during the early stages of heat treatment at temperatures up to 1200 degreesC mitigates the effects of thermal annealing as far as the loss of combustion reactivity of the resulting char is concerned. Beyond about 1200 degreesC, exposure to air is ineffective to mitigate the effects of thermal annealing on combustion reactivity. Altogether, it appears that mutual interactions exist between modifications of the carbon structure induced by thermal annealing, uptake of oxygen during heat treatment and the oxy-reactivity of the resulting char. The preliminary findings of this work would suggest that the loss of carbon combustion reactivity cannot be assessed on the basis of its time-temperature history only, but modes and extent of carbon interaction with oxygen come into play. A speculative explanation of the phenomenology is presented and discussed. (C) 2004 Elsevier Inc. All rights reserved
Assessment of thermodeactivation during gasification of a bituminous coal char
No full textThe annealing-induced loss of gasification reactivity of a bituminous coal char with respect to carbon dioxide was studied by means of a combination of experimental techniques. Heat treatment of coal samples under inert atmosphere for different time intervals was accomplished at temperatures as high as 2000 degrees C by means of thermogravimetric analyzers and of a specially designed heated-strip reactor. Gasification reactivities of untreated and heat-treated coal samples were determined by isothermal thermogravimetric analysis in carbon dioxide atmospheres. The influence of the time-temperature history of the coal sample on the parameters of the apparent gasification kinetics (preexponential factor, activation energy) has been assessed. Results were further analyzed in the framework of a simple annealing kinetic model suitable for implementation in gasification modeling
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