1,720,958 research outputs found
Detection of ionized gas in the globular cluster 47 Tucanae
No full textWe report the detection of ionized intracluster gas in the globular cluster 47 Tucanae. Pulsars in this cluster with a negative period derivative, which must lie in the distant half of the cluster, have significantly higher measured integrated electron column densities than the pulsars with a positive period derivative. We derive the plasma density within the central few parsecs of the cluster using two different methods that yield consistent values. Our best estimate of n(e) = 0.067 +/- 0.015 cm(-3) is about 100 times the free electron density of the interstellar medium in the vicinity of 47 Tucanae, and the ionized gas is probably the dominant component of the intracluster medium
Timing the millisecond pulsars in 47 Tucanae
No full textIn the last ten years, 20 millisecond pulsars have been discovered in the globular cluster 47 Tucanae. Hitherto, only three of these pulsars had published timing solutions. Here we improve upon these three and present 12 new solutions. These measurements can be used to determine a variety of physical properties of the pulsars and of the cluster. The positions of the 15 pulsars have been determined with typical errors of only a few mas and they are all located within 1.2 arcmin of the cluster centre. Their spatial density within that region is consistent with a distribution of the type n(r) proportional to r(-2), with a sudden cut-off outside four core radii. Two pulsars have a projected separation of only 0.12 arcsec, and could be part of a triple system containing two observable pulsars. We have measured the proper motions of five of the pulsars: the weighted mean of these, mu (alpha) = (6.6 +/- 1.9) mas yr(-1) and mu (delta) = (-3.4 +/- 0.6) mas yr(-1), is in agreement with the proper motion of 47 Tucanae based on Hipparcos satellite data. The period derivatives measured for many of the pulsars are dominated by the dynamical effects of the cluster gravitational field, and are used to constrain the surface mass density of the cluster. The pulsar accelerations inferred from the observed period derivatives are consistent with those predicted by a King model using accepted cluster parameters. We derive limits on intrinsic pulsar parameters: all the pulsars have characteristic ages greater than 170 Myr and have magnetic fields smaller than 2.4 x 10(9) Gauss; their average characteristic age is greater than similar to1 Gyr. We have also measured the rate of advance of periastron for the binary pulsar J0024-7204H, (omega) over dot = (0.059 +/- 0.012)degrees yr(-1), implying a total system mass of 1.4(-0.8)(+0.9) M. with 95 per cent confidence
Further results from the timing of the millisecond pulsars in 47 Tucanae
No full textWe have been observing the millisecond pulsars in the globular cluster 47 Tucanae (47 Tuc) at the Parkes radio telescope since 1999 August with threefold higher time-resolution than hitherto possible. We present the results in this paper, including: improved 1400-MHz pulse profiles; one new timing solution, for PSR J0024-7204S, which imposes stringent constraints on the acceleration model for 47 Tucanae and implies a projected mass-to-light ratio >1.4 M-circle dot/L-circle dot at the centre of the cluster; refined estimates for the five previously determined proper motions; and newly determined proper motions for six pulsars. We have detected, for the first time, relative motions between the pulsars. We have detected a second period derivative for the pulsar in the PSR J0024-7204H binary system, which could indicate the presence of a third nearby object, and improved measurement of the rate of advance of periastron of this pulsar, which yields a total system mass of 1.61+/-0.04 M-circle dot. We also have determined upper limits for the masses of any hypothetical planets orbiting the pulsars in 47 Tuc. PSR J0023-7203J shows variations of dispersion measure (DM) as a function of orbital phase with a total column density at superior conjunction of about 1.7x10(16) cm(-2), 10 times smaller than observed for a similar system in the Galaxy. We interpret the small value as being due to a smaller inclination of the orbit of PSR J0023-7203J. We find that the DM variation with orbital phase changes with time, and we detect material at more than 90degrees (in orbital phase) from the companion. PSR J0024-7204O also shows variations of DM with orbital phase, but these are restricted to phases near the eclipse. This binary system displays significant monotonic variation of its orbital period: (P)over dot(b)=(9+/-1)x10(-12). This is probably due to spin-orbit coupling; this effect seems to be significantly smaller for PSR J0023-7203J
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
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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