1,721,364 research outputs found
The jets and disc of SS 433 at super-Eddington luminosities
No full textWe examine the jets and the disc of SS 433 at super-Eddington luminosities with by time-dependent two-dimensional radiation hydrodynamical calculations, assuming an α-model for the viscosity. One-dimensional supercritical accretion disc models with mass loss or advection are used as the initial configurations of the disc. As a result, from the initial advective disc models with α = 0.001 and 0.1, we obtain total luminosities ~2.5 × 1040 and 2.0 × 1040ergs-1. The total mass-outflow rates are ~4 × 10-5 and 10-4Msolaryr-1, and the rates of the relativistic axial outflows in a small half opening angle of ~1° are about 10-6Msolaryr-1: the values are generally consistent with the corresponding observed rates of the wind and the jets, respectively. From the initial models with mass loss but without advection, we obtain total mass-outflow and axial outflow rates smaller than or comparable to the observed rates of the wind and the jets, respectively, depending on α. In the advective disc model with α = 0.1, the initially radiation-pressure-dominant, optically thick disc evolves to a gas-pressure-dominated, optically thin state in the inner region of the disc, and the inner disc is unstable. Consequently, we find remarkable modulations of the disc luminosity and the accretion rate through the inner edge. These modulations manifest themselves as recurrent hot blobs with high temperatures and low densities at the disc plane, which develop outwards and upwards and produce quasi-periodic oscillations (QPOs) of the total luminosity with an amplitude of a factor of ~2 and quasi-periods of ~10-25 s. This may explain the massive jet ejection and the QPO phenomena observed in SS 433
Radiative Shocks in Rotating Accretion Flows around Black Holes
No full textIt is well known that the rotating inviscid accretion flows with adequate injection parameters around black holes could form shock waves close to the black holes, after the flow passes through the outer sonic point and can be virtually stopped by the centrifugal force.
We examine numerically such shock waves in 1D and 2D accretion flows, taking account of cooling and heating of the gas and radiation transport.
The numerical results show that the shock location shifts outward compared with that in the adiabatic solutions and that the more rarefied ambient density leads to the more outward shock location.
In the 2D-flow, we find an intermediate frequency QPO behavior of the shock location as is observed in the black hole candidate
GRS 1915+105
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
QPOs expected in rotating accretion flows around a supermassive black hole
No full textIt is well known that rotating inviscid accretion flows with adequate injection parameters around black holes could form shock waves close to the black holes, after the flow passes through the outer sonic point and can be virtually stopped by the centrifugal force. We numerically examine such shock waves in 2D accretion flows with 10−5 to 106 Eddington critical accretion rates around a supermassive black hole with 106 M. As the results, the luminosities show QPO phenomena with modulations of a factor 2–3 and with quasi-periods of a few to several hours
Shock oscillation model for quasi-periodic oscillations in stellar mass and supermassive black holes
Get PDFWe numerically examine centrifugally supported shock waves in 2D rotating accretion flows
around a stellar mass (10 M) and a supermassive (106 M) black holes over a wide range of
input accretion rates of 107 M ̇ /M ̇ E 10−4. The resultant 2D shocks are unstable with time
and the luminosities show quasi-periodic oscillations (QPOs) with modulations of a factor of
2–3 and with periods of a tenth of a second to several hours, depending on the black hole
masses. The shock oscillation model may explain the intermediate frequency QPOs with 1–
10 Hz observed in the stellar mass black hole candidates and also suggest the existence of
QPOs with the period of hours in active galactic nuclei. When the accretion rate M ̇ is low, the
luminosity increases in proportion to the accretion rate. However, when M ̇ greatly exceeds
the Eddington critical rate M ̇ E, the luminosity is insensitive to the accretion rate and is kept
constantly around ∼3LE. On the other hand, the mass-outflow rate M ̇ loss increases in proportion
to M ̇ and it amounts to about a few per cent of the input mass-flow rat
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
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