18,615 research outputs found
Radiative non-isothermal Bondi accretion onto a massive black hole
In this paper, we present the classical Bondi accretion theory for the case
of non-isothermal accretion processes onto a supermassive black hole (SMBH),
including the effects of X-ray heating and the radiation force due to electron
scattering and spectral lines. The radiation field is calculated by considering
an optically thick, geometrically thin, standard accretion disk as the emitter
of UV photons and a spherical central object as a source of X-ray emission. In
the present analysis, the UV emission from the accretion disk is assumed to
have an angular dependence, while the X-ray/central object radiation is assumed
to be isotropic. This allows us to build streamlines in any angular direction
we need to. The influence of both types of radiation is evaluated for different
flux fractions of the X-ray and UV emissions with and without the effects of
spectral line driving. We find that the radiation emitted near the SMBH
interacts with the infalling matter and modifies the accretion dynamics. In the
presence of line driving, a transition resembles from pure type 1 & 2 to type 5
solutions (see Fig2.1 of Frank etal. 2002), which takes place regardless of
whether or not the UV emission dominates over the X-ray emission. We compute
the radiative factors at which this transition occurs, and discard type 5
solution from all our models. Estimated values of the accretion radius and
accretion rate in terms of the classical Bondi values are also given. The
results are useful for the construction of proper initial conditions for
time-dependent hydrodynamical simulations of accretion flows onto SMBH at the
centre of galaxies.Comment: 10 pages, 10 figures, Accepted to be published in A&
Comment on "Feynman Effective Classical Potential in the Schrodinger Formulation"
We comment on the paper "Feynman Effective Classical Potential in the
Schrodinger Formulation"[Phys. Rev. Lett. 81, 3303 (1998)]. We show that the
results in this paper about the time evolution of a wave packet in a double
well potential can be properly explained by resorting to a variational
principle for the effective action. A way to improve on these results is also
discussed.Comment: 1 page, 2eps figures, Revte
Continuity of Local Time: An applied perspective
Continuity of local time for Brownian motion ranks among the most notable
mathematical results in the theory of stochastic processes. This article
addresses its implications from the point of view of applications. In
particular an extension of previous results on an explicit role of continuity
of (natural) local time is obtained for applications to recent classes of
problems in physics, biology and finance involving discontinuities in a
dispersion coefficient. The main theorem and its corollary provide physical
principles that relate macro scale continuity of deterministic quantities to
micro scale continuity of the (stochastic) local time.Comment: To appear in: "The fascination of Probability, Statistics and Their
Applications. In honour of Ole E. Barndorff-Nielsen on his 80th birthday
Reproductive capacity of the red cusk-eel genypterus chilensis (Guichenot, 1848) in captivity
Indexación: Scopus.This work was supported by the FONDEF Project D06I 1024 “Development of technologies for the production of red cusk-eel fingerlings (Genypterus chilensis)”.Genypterus chilensis is a marine fish of high gastronomic demand, whose capture has declined in recent years due to overfishing. In the development of the farming technology, high mortalities were obtained during egg incubation. The objective of this study is to contribute to the knowledge of fecundity and eggs viability of G. chilensis in captivity. The spawns of G. chilensis were analyzed over a period of 2 years and 3 months. The total fecundity was estimated by counting the masses and eggs produced monthly throughout the period. The results confirm that G. chilensis is a partial spawner, since a female may more than two masses of eggs per day, due to a large amount of mass spawned per season (621 average). The total production of masses of the Farming Centre during the period was 2,290; of these, only 7% (166) corresponding to 15,330,517 eggs were incubated. Because of its high fecundity, G. chilensis produces numerous masses of eggs, of which only a small percentage reaches incubation, as well as it occurs in other marine fish. © 2018, Escuela de Ciencias del Mar. All rights reserved.https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-560X201800020048
- …