1,721,110 research outputs found
Analysis of rotation curves in the framework of Rn gravity
Full text linkWe present an analysis of a devised sample of rotation curves (RCs), with the aim of checking the consequences of a modified f(R) gravity on galactic scales. Originally motivated by the mystery of dark energy, this theory may explain the observed non-Keplerian profiles of galactic RCs in terms of a breakdown of Einstein general relativity. We show that, in general, the power-law f(R) version could fit the observations well, with reasonable values for the mass model parameters. This could encourage further investigation into Rn gravity from both observational and theoretical points of view. © 2007 RAS
Analysis of rotation curves in the framework of the gravitational suppression model
No full textWe present an analysis of suitable rotation curves (RCs) of eight galaxies, aimed at checking the consistency and universality of the gravitational suppression (GraS) hypothesis, a phenomenological model for a new interaction between dark matter and baryons. Motivated by the puzzle of the core versus cusp distribution of dark matter in the center of halos, this hypothesis claims to reconcile the predictions from N-body \Lambda cold dark matter simulations with kinematic observations. The GraS model improves the kinematic fitting residuals, but the mass parameters are unphysical and put the theory in difficulty
The local dark matter density
Full text linkWe present the recent robust determination of the value of the Dark Matter density at the Sun’s location (ρ) with a technique that does not rely on a global mass-modeling of the Galaxy. The method is based on the local equation of centrifugal equilibrium and depends on local and quite well known quantities such as the angular Sun’s velocity, the disk to dark contribution to the circular velocity at the Sun, and the thin stellar disk scale length. This determination is independent of the shape of the dark matter density profile, the knowledge of the rotation curve at any radius, and the very uncertain bulge/disk/dark-halo mass decomposition. The result is: ρ = 0.43(0.11)(0.10)GeV/cm3, where the quoted uncertainties are due to the uncertainty a) in the slope of the circular-velocity at the Sun location and b) in the ratio between this radius and the exponential length scale of the stellar disk. The devised technique is also able to take into account any future improvement in the data relevant for the estimate
R-n gravity is kicking and alive: the cases of Orion and NGC 3198
Full text linkWe analyzed the Rotation Curves (RCs) of two crucial objects, the dwarf galaxy Orion and the low luminosity Spiral NGC 3198, in the framework of Rn gravity. We surprisingly found that the no dark matter (DM) power-law F(R) case fits them well, performing much better than LCDM halo models. The level of this unexpected success can be a boost for Rn gravity. 2014 World Scientific Publishing Company
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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