1,721,001 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
S-process nucleosynthesis in massive stars and the weak component. II - Carbon burning and galactic enrichment
No full textThe s-process that occurs in the shell carbon-burning phase of a typical
massive star of 25 solar masses is examined. It is shown that neutron
captures during shell C-burning can significantly change the
s-abundances. The composition of the s-processed material ejected by a
25 solar mass model is evaluated, and the contributions of massive stars
to the chemical enrichment of the Galaxy in s-isotopes are estimated.
The s-contributions to the solar composition from low-mass stars are
then taken into account, and possibility of matching the solar
distribution of the s-isotopes produced by the weak component is
investigated. It is found that the s-process in massive stars can
completely account for the weak component observed in the solar system
and can put important constraints on the scenario of the chemical
evolution of the Galaxy
Are s-elements really produced during thermal pulses in intermediate-mass stars?
No full textThe problem of n-capture nucleosynthesis in intermediate-mass stars
during the thermal instabilities of the He shell is reanalyzed in the
light of an updated set of cross sections for n-captures and of reaction
rates for alpha reactions. The reaction network used in the calculations
is sketched and inserted into models of thermal phases derived from new
evolutionary computations for a Population II star developing an
H-exhausted core of 1.07 solar mass and from published data on
Population I He-shell instabilities. The computations invariably lead to
strongly nonsolar distributions of s-elements. In the majority of cases,
high neutron densities are found, implying the saturation of many
s-branches and the production of r-isotopes. The reaction Ne-22 (alpha,
n) Mg-25 probably cannot give rise to a solar distribution of s-nuclei
The influence of revised nuclear reaction rates on s-element production in intermediate mass stars of pop. I and pop. II
No full textThe authors estimate the influence of the recent revisions in many
reaction rates on the s-element production both in Pop. I and Pop. II
intermediate mass stars during the thermally pulsing He-burning phases.
In Pop. I stars, the resulting s-element distribution turns out to be
clearly non solar. In order to explore the production of s-nuclei in
Pop. II stars, the authors employ a new stellar model of initially 5
M_sun;, with Z = 10-4 and Y = 0.20, whose thermally unstable
He-shell phases are followed up to the sixteenth pulse. In this case the
situation is even worse than in the Pop. I case. Indeed, together with
the increased poisoning by light nuclei due to the revised cross
sections, the authors find also a very small neutron flux, owing to the
low temperature reached at the bottom of the convective He-shell
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
Nucleosynthesis by N-14 depletion during shell He burning in massive stars
No full textNew computations of He shell nucleosynthesis occurring during both
radiative and convective phases are presented for stars in the range 8 -
25 M_sun;, taking in account the recent changes proposed for many cross
sections. While the internal zones, swept by the radiative shell, are
shown to efficiently produce elements up to A = 70 - 80 only in the most
massive stellar models, the intermediate convective regions can be an
important source for elements like 12C, 18O,
22Ne and Mg isotopes
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