1,721,015 research outputs found
On the nature of the X-ray absorption in the Seyfert 2 galaxy NGC 4507
No full textWe present results of the ASCA observation of the Seyfert 2 galaxy NGC 4507. The 0.5-10 keV spectrum is rather complex and consists of several components: (i) a hard X-ray power law heavily absorbed by a column density of about 3 x 10(23) cm(-2), (ii) a narrow Fe K alpha line at 6.4 keV, () soft continuum emission well above the extrapolation of the absorbed hard power law and (iv) a narrow emission line at similar to 0.9 keV. The line energy, consistent with highly ionized neon (Ne IX), may indicate that the soft X-ray emission is derived from a combination of resonant scattering and fluorescence in a photoionized gas. Some contribution to the soft X-ray spectrum from thermal emission, as a blend of Fe L lines, by a starburst component in the host galaxy cannot be ruled out with the present data
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
X-ray emission from faint galaxies and quasars
Get PDFIn this thesis a study of faint X-ray sources is undertaken to understand the nature and origin of the Cosmic X-ray Background (XRB). A study of the X-ray variability characteristics of the QSO population is also presented. The optical identification of faint ROSAT sources is described. A large fraction of these sources are identified as QSOs. A number of the remaining sources appear to be associated with faint galaxies with a range of morphological types. The discovery of a rare, high redshift obscured QSO is also described and discussed. A method is developed to study the X-ray variability of faint QSOs. Low amplitude variability (~ 25% rms) on timescales of hours to days appears to be characteristic. Contrary to the trends apparent in local AGN, the QSO population show no evidence for a decrease in variability amplitude with luminosity. There is also no trend in variability with redshift, which may favour a short lived model for QSO evolution. A bright, highly variable Seyfert galaxy is analysed in detail. To constrain the galaxy contribution to the XRB a cross-correlation analysis is presented. Cross-correlating faint galaxy catalogues with unidentified X-ray sources suggests that faint b(_i) < 23 galaxies account for ~ 21 ± 6% of all X-ray sources to a flux limit S(0.5 - 2.0 keV) ~ 4 x l0(^-15)ergs(^-1)cm(^-2). Galaxies are then cross-correlated with the remaining unresolved XRB. A highly significant signal is obtained on 3 deep ROSAT fields. Using a formalism to model the galaxy population and its clustering, an estimate of the local X-ray volume emissivity is obtained. The results suggest that b(_j) < 23 galaxies contribute ~ 20% of the unresolved XRB. Comparing the cross-correlation of faint and bright galaxies with theoretical models reveals strong evolution in the X-ray luminosity of galaxies with the form L(_x) oc (1 + z)(^3±1). Extrapolation to high redshift suggests that faint galaxies contribute 50 - 100% of the unresolved XRB. Finally, a study of the X-ray spectra of faint ROSAT sources is presented. The mean source spectra harden significantly at lower flux. Separating the QSOs from the unidentified sources and galaxies, we find no trend in the 0.5 - 2 keV spectra of QSOs. The remaining population produces the spectral hardening. Taking a subset of the most probable X-ray luminous galaxies, these show significantly harder spectra than QSOs with a mean photon index of Γ ~ 1.5 ± 0.1. X-ray luminous galaxies could therefore account for the missing component of the XRB
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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