1,720,960 research outputs found
Jets: black holes and beyond
No full textWe review the topic of jets in the universe, starting with the early history. We focus on jets from X-ray binaries, discussing the contrasts between the jets seen from black holes and from neutron stars. We then show the implications of results on X-ray binaries for studies of active galactic nuclei, and other black holes not in binary systems, such as stellar-mass black holes accreting from molecular clouds, and intermediate-mass black holes accreting from the interstellar medium in globular clusters. We close by listing some open issues on the topic
Jet-dominated advective systems: radio and x-ray luminosity dependence on the accretion rate
No full textWe present a novel method to measure the accretion rate of radio emitting x-ray binaries (XRBs) and active galactic nuclei (AGN) independently of the x-ray luminosity. The radio emission of the jet is used as a tracer for the accretion rate and is normalised using sources of known accretion rates: island state neutron stars and efficiently radiating black holes close to a state transition. We show that the radio power in black holes and neutron stars is comparable for a given mass accretion rate and verify empirically the assumed analytic scaling of the radio luminosity with accretion rate. As our accretion measure is independent of the x-ray luminosities, we can search for radiatively inefficient accretion in black holes by comparing the x-ray luminosities with the accretion rate in XRBs and AGN. While the x-ray luminosity of efficiently radiating objects scales linearly with accretion rate, the scaling of hard state black holes is quadratical, in agreement with theoretical models. We show that the turnover from the inefficient quadratic scaling to the linear scaling has to occur at accretion rates of 1-10 % Eddington both in XRBs and AGN. The comparison of both accretion states supports the idea that in a black hole in the hard state some accretion power is advected into the black hole while the jet power exceeds the x-ray luminosity: these are therefore jet-dominated advective systems
Accretion states and radio loudness in active galactic nuclei: analogies with X-ray binaries
No full textHardness-intensity diagrams (HIDs) have been used with great success to study the accretion states and their connection to radio jets in x-ray binaries (XRBs). The analogy between XRBs and active galactic nuclei (AGN) suggests that similar diagrams may help to understand and identify accretion states in AGN and their connection to radio loudness. We construct "disc-fraction luminosity diagrams" (DFLDs) as a generalization of HIDs, which plot the intensity against the fraction of the disc contribution in the overall spectral energy distribution (SED). Using a sample of 4963 Sloan Digital Sky Survey (SDSS) quasars with ROSAT matches, we show empirically that an AGN is more likely to have a high radio:optical flux ratio when it has a high total luminosity or a large non-thermal contribution to the SED. We find that one has to consider at least two-dimensional diagrams to understand the radio loudness of AGN. To extend our DFLD to lower luminosities we also include a sample of low-luminosity AGN. Using a simulated population of XRBs we show that stellar and supermassive BHs populate similar regions in the DFLD and show similar radio/jet properties. This supports the idea the AGN and XRBs have the same accretion states and associated jet properties
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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