1,720,981 research outputs found
The tensor virial theorem for subsystems. II
No full textIn an earlier paper (Brosche et al, 1983), a tensor virial theorem has been formulated for subsystems and the special case of two concentric and copolar homogeneous oblate spheroids, one lying completely within the other, has been evaluated. Some special cases are considered, and possible applications to elliptical galaxies and spiral bulges are discussed in detail
Mutual sensitivity of halo and disk parameters in a two-component model
No full textThe tensor virial theorem for two components is used here to analyze a simplified model for the Galaxy approximated by a dark halo and a bright disk. The two components are modeled by concentric and coaxial spheroidal subsystems, one lying completely within the other. Special attention is given to the numerical interdependence between the present parameters of the visible Galaxy and the ones of dark matter and to the dependence of the bright component evolution on the characteristics of the dark halo
The tensor virial theorem for subsystems
No full textThe tensor virial theory extension presently formulated for subsystems has novel terms that are evaluated for the special case of two homogeneous oblate spheroids, of which one lies completely within the other. Attention is given to the possibility of applying this theorem extension to elliptical rotation and shape
Dark halos in virialized two-component systems of galactic mass.
No full textThe authors propose an application of the tensor virial theorem to two-component galactic systems, which could suggest a possible range for the mass and flatness of the dark halo in which the bright component is likely embedded
A simple model for the manifold of galaxies.
No full textThe authors assume an initial protogalaxy to consist of a few independently moving clouds. As driving process of its early evolution they have the collisions of clouds. This process dissipates energy, but slowly enough such that the evolution can be considered as quasi-static. The retarding process is star formation which the authors model with a phenomenological formula depending on the density and the random velocities of the clouds. Star formation diminishes the substrate of the driving process and therefore may bring the evolution to a "halt" if there is not new delivery. If this condition does not act, then a further "halt" occurs if the energetically deepest state permitted under conservation of angular momentum is arrived at. The authors' semi-quantitative model permits to understand besides of other details: 1. The fact that the observed number of dimensions of the manifold of galaxies is two (amongst other possibilities, one may choose mass and angular momentum as two independent parameters). 2. The appearance of galaxies of different morphological type at constant mass. Here the authors identify the Hubble sequence by the axis ratio and by the fraction of nonstellar mass left at the end of the early evolution. 3. The occurrence of an extremal oblateness at an intermediate type - due to the competition of the driving and the retarding processes. 4. The formation of the type scale at varying masses within an acceptable time scale - due to the scaling laws inherent to the model
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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