1,721,016 research outputs found
Uncertainties in the modeling of old stellar populations
No full textWe compare three recent models of the spectral evolution of stellar populations to assess the origin of serious discrepancies in the colors predicted for greater than or similar to 1 Gyr old populations of the same input age and metallicity. To isolate the source of these discrepancies, we investigate separately the two main characteristics of each model: the underlying stellar evolution prescription and the spectral calibrations used to transform the theoretical Hertzsprung-Russell diagram into observables. A 0.05 mag discrepancy in B - V color is caused almost entirely by a known limitation of theoretical spectra. Differences in spectral calibrations are found to account for only a small fraction of the 0.25 mag discrepancies in V - K color and of the 25% dispersion in mass-to-visual light ratio among the models considered here. The main source of disagreement for these quantities in the underlying stellar evolution prescription. For idealized galaxies containing a single generation of stars and no dust, properties derived from broadband colors using population synthesis models are found to be accurate by roughly +/-35% in age at fixed metallicity, 25% in metallicity at fixed age if the heavy-element mixture is assumed to be scaled-solar, and 35% in mass at fixed metallicity and fixed initial mass function. These indicative uncertainties are based on the dispersion in the predictions of the models investigated here. There appear to be persistent problems in virtually every ingredient of population synthesis models. The most serious are the lifetimes and luminosities of stars in post-main-sequence evolutionary stages; the temperature of the red giant branch and color-temperature relation for cool stars; and the lack of accurate libraries of stellar spectra, especially for cool stars and for nonsolar metallicities. These problems have profound causes. The main one is the high sensitivity of stellar evolution models on the efficiency of several critical factors which are either not sufficiently understood or cannot yet be determined uniquely from comparisons with observations (opacities, heavy-element mixture, helium content, convection, diffusion, mass loss, rotational mixing). Other major limitations are the difficult spectral modeling of cool stars and the unavailability of calibration stars for metal-rich populations and populations with altered chemical mixes
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
The role of the environment and the merging activity in the evolution of star formation up to z~1.6
Full text linkVariations 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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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