1,721,559 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
Compact objects in active galactic nuclei and X-ray binaries
No full textIn this thesis I study the inner-most regions of Active Galactic Nuclei (AGN) using
the reverberation mapping technique, and neutron star low-mass X-ray binaries in
quiescence using X-ray observations.
Using the 13-year optical monitoring data for the AGN NGC 5548, the luminosity dependence
of the Hβ emitting radius was modelled using a delay map, finding that
the radius scales with luminosity as predicted by recent theoretical models. Time-delays
between the continuum at different wavelengths in AGN can be used to probe the accretion
disc. Here, continuum time-delays in a sample of 14 AGN were used to measure the radial
temperature profile of the accretion discs, determine the nuclear extinction, and measure
distances to the objects. However, the distances measured correspond to a value for
Hubble's constant that is a factor of ~2 lower than the accepted value. The implications
of this on the thermal disc reprocessing model are discussed.
I present two Chandra observations of the neutron star transient in the globular
cluster NGC 6440 in quiescence, where the power-law component to the spectrum is seen
to be variable between the observations, suggesting that there is ongoing residual accretion.
From a Chandra observation of the globular cluster Terzan 1, I have identifed the likely
quiescent counterpart to a transient previously observed in outburst, and discuss the other
sources within the cluster. Using Chandra and XMM-Newton monitoring observations of
two neutron star transients (KS 1731-260 and MXB 1659-29) in quiescence I have found
that the neutron star crusts in both sources have now returned to thermal equilibrium
with the core. These observations also indicate that the crusts in both sources may have
a high thermal conductivity and that enhanced neutrino emission may be occurring in the
core. Finally, the discovery of an X-ray transient with XMM-Newton is presented, and the
other sources in this observation 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 patchy accretion disc in HT Cassiopeiae
No full textWe reconstruct the temperatures and surface densities in the quiescent accretion disc in HT Cas by performing a Physical Parameter Eclipse Mapping analysis of archival UBVR observations. Using a simple hydrogen slab model and demanding a smooth, maximally artefact-free reconstruction, we derive a formal distance to HT Cas of 207 +/- 10 pc, significantly larger than the 133 +/- 14 pc we derive from a re-analysis of the data in the literature.The accretion disc is small (0.3-0.4 R-L1 ) and moderately optically thin, but becomes nearly optically thick near the white dwarf. The temperatures and surface densities in the disc range from 9500 K and 0.013 g cm(-2) in the centre to about 4000 K and 0.04 g cm(-2) at the disc edge. The mass-accretion rate in the disc is roughly constant but - at the derived distance - uncomfortably close to the rate that would prohibit the dwarf nova eruptions.We argue that the larger derived distance is probably incorrect but is not produced by inaccuracies in our spectral model or optimization method. The discrepancy can be resolved if the emission regions on the disc are patchy with a filling factor of about 40 per cent of the disc's surface. This solves the problem with the high effective temperatures in the disc - reducing them to around 6500 K within a radius of 0.2 R-L1 - and reduces the derived temperature of the white dwarf and/or boundary layer from 22 600 to 15 500 K.The viscosity parameters alpha derived from all reconstructed temperatures and surface densities are of order 10-100 and cannot be lowered significantly by invoking a lower distance or the filling factor. This situation is easily explained using the same patchy nature of the emitting material, since the quiescent disc cannot consist of optically thin regions alone, but also of a dark and hence cold and dense disc which could easily contain most of the matter. If we require global values of alpha of order 0.1, the implied total surface densities are 1-100 g cm(-2) - just like those expected for quiescent discs awaiting the next eruption.We discuss several possible sources of the chromospheric emission and its patchiness, including irradiation of the disc, thermal instabilities, spiral-wave-like global structures, and magnetically active regions associated with dynamo action and/or Balbus-Hawley instabilities.</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
Space telescope and optical reverberation mapping project. II. Swift and HST reverberation mapping of the accretion disk of NGC 5548
No full textRecent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over 125 days across six UV/optical bands and the X-rays. This is the densest extended active galactic nucleus (AGN) UV/optical continuum sampling ever obtained, with a mean sampling rate <0.5 day. Approximately daily Hubble Space Telescope UV sampling was also obtained. The UV/optical light curves show strong correlations () and the clearest measurement to date of interband lags. These lags are well-fit by a wavelength dependence, with a normalization that indicates an unexpectedly large disk radius of lt-day at 1367 Å, assuming a simple face-on model. The U band shows a marginally larger lag than expected from the fit and surrounding bands, which could be due to Balmer continuum emission from the broad-line region as suggested by Korista and Goad. The UV/X-ray correlation is weaker () and less consistent over time. This indicates that while Swift is beginning to measure UV/optical lags in general agreement with accretion disk theory (although the derived size is larger than predicted), the relationship with X-ray variability is less well understood. Combining this accretion disk size estimate with those from quasar microlensing studies suggests that AGN disk sizes scale approximately linearly with central black hole mass over a wide range of masses
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