1,720,968 research outputs found
Accretion and jets from stellar-mass to supermassive black holes
Get PDFAccretion and jets occur in many astrophysical systems across a multitude of size and mass scales, and environments. As such, the study of accretion and jet physics has for decades been, and still remains, a hot topic in astrophysics. Accretion onto black holes has particular significance for many reasons, not least because supermassive black holes likely exist at the centres of every galaxy in the universe. The energetic impact of black hole accretion is therefore key to furthering our understanding of the universe as a whole. Over the past few decades we have learned that black hole accretion seems to be a scale-invariant process: despite the orders of magnitude difference in black hole mass, and the diversity of astrophysical environments accretion occurs within, the efficiency and power budget associated with the accretion process appears ignorant to these variables. However, the physical explanation for this scaling is lacking, due to the degeneracy in broadband spectral modelling. In this thesis I show work I have done, alongside many collaborators, to address these modelling degeneracies. I focus on the outflow-dominated states of accreting black holes, from the stellar-mass components of X-ray binaries in the Milky Way, to their supermassive analogues in low-luminosity active galactic nuclei. In addition, I show how this concept of scale-invariance can be used to make predictions about the existence of the more controversial primordial black holes
Radiatively inefficient accretion in short-period black hole low mass X-ray binaries
No full textThere is statistical evidence for a dearth of short-period (Porb < 4h) black hole (BH) low mass X-ray binaries (LMXBs) in the Galaxy. At short periods accretion onto the central object (be it a BH) may become inefficient because the cooling timescale of the gas is greater than the accretion timescale (this is the well known ADAF model). The nature of the switch is important in terms of the outburst timescales of transient sources. The switch may be sharp or occur smoothly over time. I show that the dearth can be explained if the switch to inefficiency occurs sharply at some fraction of the Eddington luminosity of the BH (fLEdd )
Accretion and jets from stellar-mass to supermassive black holes
Get PDFAccretion and jets occur in many astrophysical systems across a multitude of size and mass scales, and environments. As such, the study of accretion and jet physics has for decades been, and still remains, a hot topic in astrophysics. Accretion onto black holes has particular significance for many reasons, not least because supermassive black holes likely exist at the centres of every galaxy in the universe. The energetic impact of black hole accretion is therefore key to furthering our understanding of the universe as a whole. Over the past few decades we have learned that black hole accretion seems to be a scale-invariant process: despite the orders of magnitude difference in black hole mass, and the diversity of astrophysical environments accretion occurs within, the efficiency and power budget associated with the accretion process appears ignorant to these variables. However, the physical explanation for this scaling is lacking, due to the degeneracy in broadband spectral modelling. In this thesis I show work I have done, alongside many collaborators, to address these modelling degeneracies. I focus on the outflow-dominated states of accreting black holes, from the stellar-mass components of X-ray binaries in the Milky Way, to their supermassive analogues in low-luminosity active galactic nuclei. In addition, I show how this concept of scale-invariance can be used to make predictions about the existence of the more controversial primordial black holes
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
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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