1,721,069 research outputs found
Chemical evolution of the intra-cluster medium
Full text linkThe high metallicity of the intra–cluster medium (ICM) is
generally interpreted on the basis of the galactic wind scenario for
elliptical galaxies. In this framework, we develop a toy model to follow
the chemical evolution of the ICM, formulated in
analogy to chemical models for individual galaxies.
The model computes the galaxy formation history (GFH)
of cluster galaxies, connecting the final luminosity function (LF)
to the corresponding metal enrichment history of the ICM.
The observed LF can be reproduced with a smooth, Madau–plot like GFH
peaking at ,
plus a “burst” of formation of dwarf galaxies at high redshift.
The model is used to test the response of the predicted
metal content and abundance evolution of the ICM to varying input
galactic models.
The chemical enrichment is
computed from “galactic yields” based on models of elliptical
galaxies with a variable initial mass function (IMF), favouring
the formation of massive stars at high redshift and/or
in more massive galaxies. For a given final galactic luminosity, these model
ellipticals eject into the ICM a larger quantity of gas and of metals
than do standard models based on the Salpeter IMF.
However, a scenario in which the IMF varies with redshift as a consequence
of the
effect of the cosmic background temperature on the Jeans mass scale
appears to be
too mild to account for the observed metal production in clusters.
The high iron–mass–to–luminosity–ratio
of the ICM
can be reproduced only by assuming a more dramatic variation of the typical
stellar mass, in line with other recent findings. The mass
in the wind–ejected gas is predicted to exceed the mass in galaxies by
a factor of 1.5–2 and to constitute roughly half of the intra–cluster gas
Can a "standard" initial mass function explain the metal enrichment in clusters of galaxies ?
No full textPhysical Processes in Fragmentation and Star Formation
No full textThe present workshop on the physical processes in fragmentation and star formation discusses atomic and molecular processes, turbulence, and magnetic field in fragmentation, star formation in different astrophysical environments, hydrodynamical and dynamical models, the initial mass function, star clusters, and the low mass end of the initial mass function (IMF). Attention is given to molecular cloud chemistry with mixing, the collapse and fragmentation of molecular clouds, supersonic turbulent fragmentation of giant molecular clouds, and turbulence in the frame of the evolution of a self-gravitating protocloud. Topics addressed include the interstellar structure, interstellar gas cycling powered by star formation, observations of fragmentation, and extrasolar planetary material. Also discussed are protostellar core instabilities, the evolution of the first protostellar core, the multimodality of star formation, fragmentation theories and the IMF, and star clusters in the LMC
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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