1,721,094 research outputs found
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
The galaxy velocity dispersion - X-ray temperature relation in galaxy clusters
No full textUsing a large and well-controlled sample of clusters of galaxies, we investigate the relation between cluster velocity dispersions and X-ray temperatures of intra-cluster gas. The cluster selection is based on nonparametric methods. In particular, we present the 2-D optical maps of our sample clusters, obtained via the kernel adaptive technique, using an optimized smoothing parameter. In order to obtain a reliable estimate of the total velocity dispersion of a cluster, independent of the level of anisotropies in galaxy orbits, we analyze the integrated velocity dispersion profiles over increasing distances from the cluster centers. Both increasing and decreasing integrated profiles are found, but the general trend is a flattening of the integrated velocity dispersion profile at the largest radii, thus enabling us to take the asymptotic value of the integrated profile as an estimate of the total velocity dispersion which is independent of possible anisotropies. Distortions in the velocity fields, the effect of close clusters, the presence of substructures, and the presence of a population of (spiral) galaxies not in virial equilibrium
with the cluster potential, are taken into account for reducing the errors in the estimate of the cluster velocity dispersions. Using our final sample of 37 clusters, for which a reliable estimate of the velocity dispersion could be obtained, we derive a relation between the velocity dispersions and the X-ray temperatures, with a scatter reduced by more than with respect to previous works. A chi^2 fit to the temperature-velocity dispersion relation does not exclude the hypothesis that the ratio between galaxy and gas energy density (the so-called beta_spec) is a constant for all clusters. In particular, the value of beta_spec=1, corresponding to energy equipartition, is acceptable. However, the large data scatter in sigma-T relation may suggest the presence of intrinsic dispersion. This intrinsic dispersion may be due to spurious effects (we consider the effect of cluster ellipticity), as well as to physical reasons, different values of beta_spec pertaining to clusters with different properties
Probing modified gravity theories with ISW and CMB lensing
No full textWe use the optimized skew-spectrum as well as the skew-spectra associated with the Minkowski functionals to test the possibility of using the cross-correlation of the integrated Sachs-Wolfe effect (ISW) and lensing of the cosmic microwave background (CMB) radiation to detect deviations in the theory of gravity away from General Relativity (GR). We find that the although both statistics can put constraints on modified gravity, the optimized skewspectra are especially sensitive to the parameter B0 that denotes the Compton wavelength of the scalaron at the present epoch. We investigate three modified gravity theories, namely the post-parametrized Friedmann formalism; the Hu-Sawicki model and the Bertschinger-Zukin (BZ) formalism. Employing a likelihood analysis for an experimental setup similar to ESA's Planck mission, we find that, assuming GR to be the correct model, we expect the constraints from the first two skew-spectra, S (0)l and S (1)l, to be the same: B0 < 0.45 at 95 per cent confidence level (CL) and B0 < 0.67 at 99 per cent CL in the BZ model. The third skew-spectrum does not give any meaningful constraint. We find that the optimal skew-spectrum provides much more powerful constraint, giving B0 < 0.071 at 95 per cent CL and B0 < 0.15 at 99 per cent CL, which is essentially identical to what can be achieved using the full bispectrum. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society
Skewness as a Test of Non-Gaussian Primordial Density Fluctuations
No full textWe investigate the evolution of the skewness of the distribution of density fluctuations in CDM models with both Gaussian and non-Gaussian initial fluctuations. We show that the skewness of galaxy counts is a potentially powerful test of the hypothesis of Gaussian primordial density fluctuations. We find, as expected, that the skewness of the mass distribution in models with initially non-Gaussian fluctuations shows systematic departures from the corresponding behaviour for Gaussian fluctuations on intermediate to large scales. We investigate the effect of peculiar velocity distortions and normalization upon the relationship between skewness and variance. These effects are generally small for the models we consider. Comparing our results to the QDOT measurements of the skewness, we find that our initially positive-skew models are clearly excluded by this analysis, but the available data do not rule out the negative-skew models
Modelling Galaxy Clustering at High Redshift
No full textWe discuss the theoretical interpretation of observational data concerning the clustering of galaxies at high redshifts. Building on the theoretical machinery developed by Matarrese et al., we make detailed quantitative predictions of galaxy clustering statistics for a variety of cosmological models, taking into account differences in spatial geometry and initial fluctuation spectra and exploring the role of bias as a complicating factor in these calculations. We demonstrate that the usual description of evolution (in terms of the parameters epsilon and r_0) is not useful for realistic galaxy clustering models. We compare the detailed predictions of the variation of correlation functions with redshift against current observational data to constrain available models of structure formation. Theories that fit the present-day abundance of rich clusters are generally compatible with the observed redshift evolution of galaxy clustering if galaxies are no more than slightly biased at z~1. We also discuss the interpretation of a concentration of Lyman-break galaxies found by Steidel et al., coming to the conclusion that such concentrations are not unexpected in `standard' models of structure formation
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