1,721,390 research outputs found
Transient modeling of thermal degradation in non-charring solids
No full textFor a more extensive investigation of polymers, a better understanding of its gasification process is extremely essential. Especially compared with the extensive studies in the gas phase, the solid phase received rather little attention. Thus, the purpose of this paper is in its comparison of several modeling approaches for thermal degradation and systematic demonstration of the effects of basic assumptions on the model results, while taking account of in-depth radiation. For this object, this study has examined in more detail the degradation for a horizontally positioned polymer which is exposed to external radiation. After a preliminary study, three different solid degradation models were chosen from the literature, and their corresponding mass and energy conservation equations and boundary conditions were assembled. The in-depth non-gray as well as gray radiation was taken into account by solving relevant radiative transfer equation. In order to concentrate on the fundamental mechanisms of polymer degradation, gas phase reactions and subsequent heal feedback from the gas were neglected. This corresponds to a nitrogen environment. Various other parameters such as the polymer refractive index, polymer absorption coefficient, convective heat loss, solid fuel thickness and external radiative heat flux were changed to discuss their effects on the quantitative as well as qualitative change in the mass loss rate. While the effect of the solid fuel thickness on the mass loss rate was negligible for a thick sample, each parameter among the polymer refractive index, polymer absorption coefficient, convective heat loss, and external radiative heat flux incurred a non-negligible change in the results. Furthermore, the convection term in the energy equation, which is usually neglected in the in-depth pyrolysis by many other works, was shown to account for 29% decrease in the mass loss rate. Finally, depending on the solid degradation model used, the addition of gray radiation to the energy equation was shown to augment or diminish the mass loss rate. It was further enhanced by taking account of the non-gray radiation. This results from the fact that the inner solid is more quickly heated due to the far-reaching effects of radiation from the surface
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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