1,721,189 research outputs found
Unravelling combustion mechanisms through a quantitative understanding of elementary reactions
No full textThis review of the role of reaction kinetics in combustion chemistry traces the historical evolution and present state of qualitative and quantitative understanding of a number of reaction systems. Starting from the H(2)-O(2) system, in particular from the reaction between H and O(2), mechanisms and key reactions for soot formation, for the appearance of NO,, and for processes of peroxy radicals in hydrocarbon oxidation are illustrated. The struggle for precise rate constants on the experimental and theoretical side is demonstrated for the example of the reaction H + O(2) -> OH + O. The intrinsic complexity of complex-forming bimolecular reactions, such as observed even in this reaction, also dominates most other key reactions of the systems considered and can be unravelled only with the help of quantum-chemical methods. The multi-channel character of these reactions often also requires the combination with master equation codes. Although kinetics provides an already impressive database for quantitative modelling of simple combustion systems, considerable effort is still required to quantitatively account for the complexities of more complicated fuel oxidation processes. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved
When do actively controlled visual events guide our attention?
Get PDFVisual attention and action seem to be interdependent. In a recent study (Pilling & Barrett, 2017), participants performed a visual search task, searching for non-tilted target ellipses, periodically changing orientation from left to right, amongst left-or-right tilted distractor ellipses, also changing orientation. Participants were substantially better at locating the target during active-control trials in which they controlled the target’s orientation change, than in passive-control trials, where the change was computer controlled. However, it was unclear whether this action-control advantage only occurs under the specific conditions of the original study, where the rate at which distractors changed orientation was kept constant and the number of distractors (set size) varied. The present study identified whether this action-control advantage was more prominent under certain conditions by varying the rate at which distractors change orientation, whilst keeping set size constant, on participants’ attention to active and computer-controlled visual stimuli. The distractor orientation change occurred in a regular or random-change-pattern and target orientation change was participant or computer controlled. Twelve participants performed a visual search task on a computer. The search-displays consisted of 20 coloured ellipses (1 target and 19 distractors). During active- and passive-control trials, the target stimulus changed orientation horizontally/vertically, which participants had to report. The results showed participants were quicker at locating target stimuli in active-control trials, when distractors changed orientation at a slow or moderate rate. This was found regardless of change-pattern. The results demonstrate the importance of action-attention relationships, showing the limits of the conditions under which such effects are prevalent
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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