1,720,997 research outputs found
The stellar Initial Mass Function of the solar neighbourhood revealed by Gaia
Full text linkI use a sample of more than 120,000 stars in the solar neighbourhood with
parallaxes, magnitudes and colours estimated with unprecedented accuracy by the
second data release of the Gaia mission to derive the initial mass function of
the Galactic disc. A full-forward technique is used to take into account for
the population of unresolved binaries, the metallicity distribution, the star
formation history and their variation across the Galactic disk as well as all
the observational effects. The shape of the initial mass function is well
represented by a segmented power-law with two breaks at characteristic masses.
It has a maximum at M~0.15 Ms with significant flattening (possibly a
depletion) at lower masses and a slope of alpha=-1.34 +/- 0.07 in the range
0.25<M/Ms<1. Above 1 Ms the IMF shows an abrupt decline with a slope ranging
from alpha=-2.68 +/- 0.09 to alpha=-2.41 +/- 0.11 depending on the adopted
resolution of the star formation history
The eye of Gaia on globular clusters structure: tidal tails
Full text linkI analyse the projected density distribution of member stars over a wide area
surrounding 18 Galactic globular clusters using the photometric and astrometric
information provided by the second data release of the Gaia mission. A 5D
mixture modelling technique has been employed to optimally isolate the signal
of the cluster stellar population from the contamination of the Galactic field,
taking advantage of its different distribution in the space formed by colours,
magnitudes, parallaxes and proper motions. In 7 clusters I detect collimated
overdensities at a >3 sigma level above the background density extending well
beyond the cluster tidal radius, consistent with the distortion expected as a
result of the tidal interaction with the Milky Way potential. In five of these
clusters (NGC288, NGC2298, NGC5139, NGC6341 and NGC7099) spectacular tidal
tails extend up to the border of the analysed field of view at 5 degrees from
the centre. At large distances from the cluster centre, the orientation of the
detected overdensities appears to be systematically aligned with the cluster
orbital path, in agreement with the predictions of N-body simulations. The
fraction of stars contained in the tidal tails of these clusters is also used
to determine the first observational estimate of their present-day destruction
rates
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 global mass functions of 35 Galactic globular clusters - II. Clues on the initial mass function and black hole retention fraction
Full text linkIn this paper, we compare the mass function slopes of Galactic globular clusters recently determined by Sollima & Baumgardt with a set of dedicated N-body simulations of star clusters containing between 65 000 and 200 000 stars. We study clusters starting with a range of initial mass functions (IMFs), black hole retention fractions and orbital parameters in the parent galaxy. We find that the present-day mass functions of globular clusters agree well with those expected for star clusters starting with Kroupa or Chabrier IMFs, and are incompatible with clusters starting with single power-law mass functions for the low-mass stars. The amount of mass segregation seen in the globular clusters studied by Sollima & Baumgardt can be fully explained by two-body relaxation driven mass segregation from initially unsegregated star clusters. Based on the present-day global mass functions, we expect that a typical globular cluster in our sample has lost about 75 per cent of its mass since formation, while the most evolved clusters have already lost more than 90 per cent of their initial mass and should dissolve within the next 1-2 Gyr. Most clusters studied by Sollima & Baumgardt also show a large difference between their central and global mass function (MF) slopes, implying that the majority of Galactic globular clusters are either near or already past core collapse. The strong mass segregation seen in most clusters also implies that only a small fraction of all black holes formed in globular clusters still reside in them. <P /
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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