65,155 research outputs found
Magnetic connection and current distribution in black hole accretion discs
We discuss one of the possible origins of large-scale magnetic fields based
on a continuous distribution of toroidal electric current flowing in the inner
region of the disc around a Kerr black hole (BH) in the framework of general
relativity. It turns out that four types of configuration of the magnetic
connection (MC) are generated, i.e., MC of the BH with the remote astrophysical
load (MCHL), MC of the BH with the disc (MCHD), MC of the plunging region with
the disc (MCPD) and MC of the inner and outer disc regions (MCDD). It turns out
that the Blandford-Znajek (BZ) process can be regarded as one type of MC, i.e.,
MCHL. In addition, we propose a scenario for fitting the quasi-periodic
oscillations in BH binaries based on MCDD associated with the magnetic
reconnection.Comment: 5 pages, 4 figures, 2 tables. Accepted by MNRAS, 05/05/200
An investigation of strain softening phenomenon in Al-0.1% Mg alloy during high-pressure torsion processing
An Al-0.1% Mg alloy was processed by high-pressure torsion (HPT) at room temperature. The Al-0.1% Mg alloy displays strain softening phenomenon through hardness evolution: the hardness values in the disc centre area are higher than at the disc edge area after 1/2, 1 and 3 turns, and the size of the hard region in the disc centre gradually reduces as the numbers of turns increases from 1/2 to 3 turns. The hardness values evolve towards homogeneity along the disc diameters after 5 and 10 turns. Electron backscatter diffraction (EBSD) and X-ray line profile analysis suggest that the lower hardness values at the disc edge area in the Al-0.1% Mg alloy are related to a recovery / recrystallization mechanism where the material is subjected to heavy straining
An Analytic Model for left invertible Weighted Translation Semigroups
M. Embry and A. Lambert initiated the study of a semigroup of operators
indexed by a non-negative real number and termed it as weighted
translation semigroup. The operators are defined on by
using a weight function. The operator can be thought of as a continuous
analogue of a weighted shift operator. In this paper, we show that every left
invertible operator can be modeled as a multiplication by on a
reproducing kernel Hilbert space of vector-valued analytic functions
on a certain disc centered at the origin and the reproducing kernel associated
with is a diagonal operator. As it turns out that every hyperexpansive
weighted translation semigroup is left invertile, the model applies to these
semigroups. We also describe the spectral picture for the left invertible
weighted translation semigroup. In the process, we point out the similarities
and differences between a weighted shift operator and an operator Comment: 14 page
Outward migration of a giant planet with a gravitationally unstable gap edge
We present numerical simulations of disc-planet interactions where the planet
opens a gravitationally unstable gap in an otherwise gravitationally stable
disc. In our disc models, where the outer gap edge can be unstable to global
spiral modes, we find that as we increase the surface density scale the gap
becomes more unstable and the planet migrates outwards more rapidly. We show
that the positive torque is provided by material brought into the planet's
coorbital region by the spiral arms. This material is expected to execute
horseshoe turns upon approaching the planet and hence torque it. Our results
suggest that standard type II migration, applicable to giant planets in
non-self-gravitating viscous discs, is likely to be significantly modified in
massive discs when gravitational instabilities associated with the gap occur.Comment: 9 pages, 11 figures, accepted by MNRA
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