1,720,956 research outputs found
The cluster distribution as a test of dark matter models - III. The cluster velocity field
No full textWe study the large-scale velocity fields traced by galaxy clusters in numerical simulations of a box of side 960 h(-1) h(-1), and compare them with available data on real clusters. In order to test the reliability of the simulations, which are based on an optimized version of the Zel'dovich approximation, we compare their cluster velocities with those of 'exact' N-body simulations, and find a remarkable agreement between the two according to a variety of statistical tests. We analyse cold dark matter (CDM) models with density parameter in the range 0.2 less than or equal to Ohm(0) less than or equal to 1, both with and without the cosmological constant term to provide a flat geometry. We also simulate a cold+hot dark matter (CHDM) model, with 30 per cent provided by the hot component. Comparison with real data is performed by applying tests based on the cumulative velocity frequency distribution (CVFD) and bulk flow statistics. For the CVFD, we use observational velocity data from different authors, and find that results based on different data sets are contradictory. In particular, the recent infrared Tully-Fisher (IRTF) data of Giovanelli yield smaller velocities with smaller errors than both the IRTF and D-n-sigma data of Hudson. It turns out that the Giovanelli data are only only consistent with the open Ohm(0) = 0.4 and the flat Omega(0) = 0.2 models, while the Hudson data, though less discriminatory because of their larger errors, appear to exclude open models with Ohm(0) less than or equal to 0.4 and hat models with Ohm(0) = 0.2. This latter conclusion also holds if one pools all the data into a single sample regardless of the systematic differences in the two different sources. Furthermore, CVFD and bulk flow analyses of the Branchini et al. reconstructed velocity data again disfavour precisely those models accepted on the grounds of Giovanelli's sample. Finally, we confirm that the Lauer & Postman reported bulk flow determination would be a rare event in the cosmological models we have analysed
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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