4,300 research outputs found
Numerical simulations of winds driven by radiation force from the corona above a thin disk
Observations show that winds can be driven from the innermost region (inside
a 50 Schwarschild radius) of a thin disk. It is interesting to study the winds
launched from the innermost region. A hot corona above the black hole (BH) thin
disk is irradiated by the disk. We perform two-dimensional hydrodynamical
simulations to study the winds driven by radiation force from the corona in the
innermost regions. The hard X-ray spectrum from active galactic nuclei (AGNs)
suggests that the corona temperature is about K, so that we mainly
analyze the properties of winds (or outflows) from the K corona. The
disk luminosity plays an important role in driving the outflows. The more
luminous the disk, the stronger the outflows. Mass outflow rate () at a 90 Schwarschild radius depends on disk luminosity, which can be
described as ( is the ratio
of the disk luminosity to the Eddington luminosity). In the case of high
luminosity (e.g. ), the supersonic outflows with maximum speed
Km s are launched at -- and
-- away from the pole axis. The Bernoulli parameter keeps
increasing with the outward propagation of outflows. The radiation force keeps
accelerating the outflows when outflows move outward. Therefore, we can expect
the outflows to escape from the BH gravity and go to the galactic scale. The
interaction between outflows and interstellar medium may be an important AGN
feedback process.Comment: 9 pages, 12 figures, accepted for publication in Ap
Trees with the most subtrees -- an algorithmic approach
When considering the number of subtrees of trees, the extremal structures
which maximize this number among binary trees and trees with a given maximum
degree lead to some interesting facts that correlate to other graphical indices
in applications. The number of subtrees in the extremal cases constitute
sequences which are of interest to number theorists. The structures which
maximize or minimize the number of subtrees among general trees, binary trees
and trees with a given maximum degree have been identified previously. Most
recently, results of this nature are generalized to trees with a given degree
sequence. In this note, we characterize the trees which maximize the number of
subtrees among trees of a given order and degree sequence. Instead of using
theoretical arguments, we take an algorithmic approach that explicitly
describes the process of achieving an extremal tree from any random tree. The
result also leads to some interesting questions and provides insight on finding
the trees close to extremal and their numbers of subtrees.Comment: 12 pages, 7 figures; Journal of combinatorics, 201
Disease Considerations for 2011 Soybean Variety Selection
As producers plan for the 2011 soybean growing season, many will make disease management a high priority because of the outbreaks of sudden death syndrome (SDS) in 2010. Some soybean producers will select soybean varieties for the coming season according to what happened during the last season. While picking up SDS resistant or tolerance varieties may seem to be a good decision, the risk of white mold should be considered as well, particularly in northern Iowa where white mold was wide spread in 2009. It is too early to say what disease may have outbreaks for the coming season
Lower Bound of Concurrence Based on Positive Maps
We study the concurrence of arbitrary dimensional bipartite quantum systems.
An explicit analytical lower bound of concurrence is obtained, which detects
entanglement for some quantum states better than some well-known separability
criteria, and improves the lower bounds such as from the PPT, realignment
criteria and the Breuer's entanglement witness.Comment: 8 pages, 1 figur
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