1,721,143 research outputs found
Comptonization of low-frequency radiation in accretion disks Angular distribution and polarization of hard radiation
No full textIn accretion disks the angular distribution and polarization of hard radiation forming via Comptonization, i.e., multiple scatterings in the disk, depend only on the optical thickness of the disk and are independent of either the photon frequency or the geometric distribution of low-frequency photons. This paper presents calculations of the angular distribution and polarization made for several values of the optical thickness of disks, for the case of the Thomson scattering. The method of successive approximations over the number of scatterings was employed in the calculations, without taking into account the frequency dependence of the scattering cross-section and indicatrix. Specific astrophysical applications of the results obtained are discussed. A simplified theory of electron temperature dependence on the vertical coordinate in the disk is given. The density distribution over the vertical coordinate in the radiation-dominated disks is derived
MODELING X-RAY DATA OF BLACK HOLE BINARIES
Full text linkWe test the truncated disc models using multiwavelength (optical/UV/X-ray) data from the 2005 hard state outburst of the black hole SWIFT J1753.5-0127. This system is both fairly bright and has fairly low interstellar absorption, so gives one of the best datasets to study the weak, cool disc emission in this state. We fit these data using models of an X-ray illuminated disc to constrain the inner
disc radius throughout the outburst. Close to the peak, the observed soft X-ray component is consistent with being produced by the inner disc, with its intrinsic emission enhanced in temperature and luminosity by reprocessing of hard X-ray illumination in an overlap region between the disc and corona. This disc emission provides the seed photons for Compton scattering to produce the hard X-ray
spectrum, and these hard X-rays also illuminate the outer disc, producing the optical emission by reprocessing.
However, towards the end of the outburst, all these conclusions may change. The optical points clearly lie on an extrapolation of the hard X-ray flux, which may indicate that the seed photons for Compton scattering are now self-generated in the flow by Cyclo-Synchrotron radiation rather than being from the disc. The weak soft X-ray emission implies a small disc radius, unchanged from the outburst peak, in conflict with the expectations of the truncated disc model. However, this also requires that the energy to power the corona is advected vertically and radially in a dissipationless fashion from the disc. Thus it seems more likely that the soft X-ray component is not direct emission from the disc itself. We show that a similarly dim low/hard state spectrum from XTE J1118+480 puts similar constraints on the soft X-ray emission region, but here the very low interstellar absorption (an order of magnitude smaller than in SWIFT J1753.5-0127) allows detection of a much larger, cooler, UV component which is well fit by a truncated disc. Thus whatever the origin of the additional weak soft X-ray emission (irradiation of the inner face as opposed to the top surface of the inner edge of the disc, residual inner disc left from evaporation, ionised reflection, jet etc), its existence as a clearly separate component from the truncated disc in XTE J1118+480 shows that it does not trace the inner disc radius, so cannot be used to constrain the truncated disc models
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
Disentangling the Galactic centre X-ray reflection signal using XMM-Newton data
No full textAims. We investigate the X-ray emission from the Galactic centre (GC) region, focusing on the 6.4 keV fluorescent line of neutral or weakly ionised iron, which is commonly attributed to X-ray reflection from dense molecular clouds. Our goal is to separate the reflection signal from other physical X-ray components. We aim to produce a clean map of the 6.4 keV emission, thus providing a better understanding of the X-ray reflection processes in the GC. Methods. We utilised a deep mosaic of all available XMM-Newton observations, encompassing the central 40 square degrees of the Galaxy. This dataset integrates information from 503 individual observations, resulting in a total clean exposure time of 7.5 Ms. The mosaics of two narrow bands centred at 6.7 keV and 6.4 keV, and a broader continuum band at lower energies (5-6.1 keV), provided valuable spatial and spectral information on the X-ray emission. These combined with the stellar mass distribution of our Galaxy enabled us to decompose the observed signal into physically meaningful components. Results. Our analysis shows that the cleaned 6.4 keV band map, free from the contribution of bright and unresolved point sources, is predominantly shaped by X-ray reflection from dense molecular clouds. The spatial distribution of this emission, which strongly correlates with the molecular gas distribution in the central molecular zone (CMZ), supports the interpretation that this map provides the best estimate of the X-ray reflection signal averaged over the last two decades. This cleaned reflection map could serve as a tool for future studies aiming to quantify upper limits on the reflection contribution from low-energy cosmic rays in unilluminated regions. Moreover, we estimate that, on average, within the CMZ, approximately 65% of the ridge emission contributes to the observed emission in the 6.4 keV band, a factor that should be incorporated into upcoming investigations of the GC, such as polarisation studies of the reflected X-ray continuum from molecular clouds and statistical assessments of the reflection surface brightness
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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