1,721,104 research outputs found
Fluidization of solids with CO2 at pressures and temperatures ranging from ambient to nearly critical conditions
No full textEffect of system pressure on char combustion in Fluidized Beds. Model predictions
No full textAlthough Pressurized Fluidized Bed Combustion is already at the demonstration stage, fundamental studies on the effect of system pressure on the many aspects of the process are still under way. In this paper the effect of system pressure on fluidized bed char combustion is considered from a theoretical standpoint. Char combustion in bubbling fluidized bed is controlled by the oxygen transfer from bubbles to emulsion phase and from this latter to char particle surface, oxygen diffusion in the pore network and char intrinsic reactivity. According to previous indications this study confirms that the actual influence of system pressure on char combustion can only be deduced by means of a comprehensive mathematical model which accounts for the controlling steps altogether. The extention of a model previously developed by the authors to a pressure higher than atmospheric is finalized to this objective. This model is based on a char particle population balance and considers particle combustion, attrition and elutriation under simple bed fluid dynamics. With reference to a pre-pilot combustor, from which experimental data at atmospheric pressure were available, bed carbon loading, specific carbon combustion rate, characteristics resistances of the combustion mechanism and combustion efficiency have been calculated at a pressure of 12 bar and compared with results at 1 bar. In model evaluations, the excess air has been considered the main parametric variable. Different assumptions concerning bed fluid dynamics as well as combustion kinetics have been tested. Model results clearly indicate that bed carbon loading increases with pressure even though char combustion rate is faster due to higher oxygen partial pressure
Comparison of Models for Supercritical Fluids Extraction of Seed and Essential Oils in Relation to the Mass Transfer Rate
No full textA general dimensionless model was developed for a sensitivity analysis of the supercritical extraction process of vegetable oils and essential oils. Two dimensionless parameters, Gamma, a dimensionless partition coefficient, and Theta, a dimensionless characteristic time, appeared as the most important parameters to monitor the evolution of the extraction process. Some Limiting values of these two parameters within the general model yielded simpler models which are often used in the literature. The numerical solutions of both the complete model and the simpler cases were compared to assess the range of relevance of the simpler models in terms of Gamma and Theta values. These results were compared with the experimental data found in the literature to assess the correctness of the assumption used to model supercritical fluid extraction in single eases. The implications of this analysis on the development of scale-up procedures were also discussed
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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