23,290 research outputs found
Role of shocked accretion flows in regulating the QPO of galactic black hole candidates
Using a generalized non-spherical, multi-transonic accretion flow model, we
analytically calculate the normalized QPO frequency
of galactic black hole candidates in terms of dynamical flow variables and
self-consistently study the dependence of on such
variables. Our results are in fairly close agreement with the observed QPO
frequencies of GRS 1915+105. We find that is quite
sensitive to various parameters describing the black hole accretion flow
containing dissipative and non-dissipative shock waves. Thus the QPO phenomena
is, {\it indeed}, regulated by `shocked' black hole accretion, and, for the
first time, we establish a definitive connection between the QPO frequency and
the properties of advective BH accretion flows. This information may provide
the explanation of some important observations of galactic micro quasars.Comment: Final version accepted for publication in the Astrophysical Journal
Letters (ApJL). A considerable part of the paper is almost completely
re-written, though the results and the final conclussions are the same. One
can now ignore the previous version. 8 pages with four black and white
figures. For high resolution Fig. 3, please mail the author
<[email protected]
Why Two Renormalization Groups are Better than One
The advantages of using more than one renormalization group (RG) in problems
with more than one important length scale are discussed. It is shown that: i)
using different RG's can lead to complementary information, i.e. what is very
difficult to calculate with an RG based on one flow parameter may be much more
accessible using another; ii) using more than one RG requires less physical
input in order to describe via RG methods the theory as a function of its
parameters; iii) using more than one RG allows one to solve problems with more
than one diverging length scale. The above points are illustrated concretely in
the context of both particle physics and statistical physics using the
techniques of environmentally friendly renormalization. Specifically, finite
temperature theory, an Ising-type system in a film geometry, an
Ising-type system in a transverse magnetic field, the QCD coupling constant at
finite temperature and the crossover between bulk and surface critical
behaviour in a semi-infinite geometry are considered.Comment: 17 pages LaTex; to be published in the Proceedings of RG '96, Dubn
New Kinetic Equation for Pair-annihilating Particles: Generalization of the Boltzmann Equation
A convenient form of kinetic equation is derived for pair annihilation of
heavy stable particles relevant to the dark matter problem in cosmology. The
kinetic equation thus derived extends the on-shell Boltzmann equation in a most
straightforward way, including the off-shell effect. A detailed balance
equation for the equilibrium abundance is further analyzed. Perturbative
analysis of this equation supports a previous result for the equilibrium
abundance using the thermal field theory, and gives the temperature power
dependence of equilibrium value at low temperatures. Estimate of the relic
abundance is possible using this new equilibrium abundance in the sudden
freeze-out approximation.Comment: 19 pages, LATEX file with 2 PS figure
Three-Dimensional Evolution of the Parker Instability under a Uniform Gravity
Using an isothermal MHD code, we have performed three-dimensional,
high-resolution simulations of the Parker instability. The initial equilibrium
system is composed of exponentially-decreasing isothermal gas and magnetic
field (along the azimuthal direction) under a uniform gravity. The evolution of
the instability can be divided into three phases: linear, nonlinear, and
relaxed. During the linear phase, the perturbations grow exponentially with a
preferred scale along the azimuthal direction but with smallest possible scale
along the radial direction, as predicted from linear analyses. During the
nonlinear phase, the growth of the instability is saturated and flow motion
becomes chaotic. Magnetic reconnection occurs, which allows gas to cross field
lines. This, in turn, results in the redistribution of gas and magnetic field.
The system approaches a new equilibrium in the relaxed phase, which is
different from the one seen in two-dimensional works. The structures formed
during the evolution are sheet-like or filamentary, whose shortest dimension is
radial. Their maximum density enhancement factor relative to the initial value
is less than 2. Since the radial dimension is too small and the density
enhancement is too low, it is difficult to regard the Parker instability alone
as a viable mechanism for the formation of giant molecular clouds.Comment: 8 pages of text, 4 figures (figure 2 in degraded gif format), to
appear in The Astrophysical Journal Letters, original quality figures
available via anonymous ftp at
ftp://ftp.msi.umn.edu/pub/users/twj/parker3d.uu or
ftp://canopus.chungnam.ac.kr/ryu/parker3d.u
Generalized -conformal change and special Finsler spaces
In this paper, we investigate the change of Finslr metrics which we refer to as a
generalized -conformal change. Under this change, we study some special
Finsler spaces, namely, quasi C-reducible, semi C-reducible, C-reducible,
-like, -like and -like Finsler spaces. We also obtain the
transformation of the T-tensor under this change and study some interesting
special cases. We then impose a certain condition on the generalized
-conformal change, which we call the b-condition, and investigate the
geometric consequences of such condition. Finally, we give the conditions under
which a generalized -conformal change is projective and generalize some
known results in the literature.Comment: References added, some modifications are performed, LateX file, 24
page
Temporal 1/f^\alpha Fluctuations from Fractal Magnetic Fields in Black Hole Accretion Flow
Rapid fluctuation with a frequency dependence of (with ) is characteristic of radiation from black-hole objects. Its
origin remains poorly understood. We examine the three-dimensional
magnetohydrodynamical (MHD) simulation data, finding that a magnetized
accretion disk exhibits both fluctuation (with )
and a fractal magnetic structure (with the fractal dimension of ).
The fractal field configuration leads reconnection events with a variety of
released energy and of duration, thereby producing fluctuations.Comment: 5 pages, 4 figures. Accepted for publication in PASJ Letters, vol. 52
No.1 (Feb 2000
Universal entanglement concentration
We propose a new protocol of \textit{universal} entanglement concentration,
which converts many copies of an \textit{unknown} pure state to an \textit{%
exact} maximally entangled state. The yield of the protocol, which is outputted
as a classical information, is probabilistic, and achives the entropy rate with
high probability, just as non-universal entanglement concentration protocols
do.
Our protocol is optimal among all similar protocols in terms of wide
varieties of measures either up to higher orders or non-asymptotically,
depending on the choice of the measure. The key of the proof of optimality is
the following fact, which is a consequence of the symmetry-based construction
of the protocol: For any invariant measures, optimal protocols are found out in
modifications of the protocol only in its classical output, or the claim on the
product.
We also observe that the classical part of the output of the protocol gives a
natural estimate of the entropy of entanglement, and prove that that estimate
achieves the better asymptotic performance than any other (potentially global)
measurements.Comment: Revised a lot, especially proofs, though no change in theorems,
lemmas itself. Very long, but essential part is from Sec.I to Sec IV-C. Some
of the appendces are almost independent of the main bod
A Multi-dimensional Code for Isothermal Magnetohydrodynamic Flows in Astrophysics
We present a multi-dimensional numerical code to solve isothermal
magnetohydrodynamic (IMHD) equations for use in modeling astrophysical flows.
First, we have built a one-dimensional code which is based on an explicit
finite-difference method on an Eulerian grid, called the total variation
diminishing (TVD) scheme. Recipes for building the one-dimensional IMHD code,
including the normalized right and left eigenvectors of the IMHD Jacobian
matrix, are presented. Then, we have extended the one-dimensional code to a
multi-dimensional IMHD code through a Strang-type dimensional splitting. In the
multi-dimensional code, an explicit cleaning step has been included to
eliminate non-zero at every time step. To estimate the
proformance of the code, one- and two-dimensional IMHD shock tube tests, and
the decay test of a two-dimensional Alfv\'{e}n wave have been done. As an
example of astrophysical applications, we have simulated the nonlinear
evolution of the two-dimensional Parker instability under a uniform gravity.Comment: Accepted for publication in ApJ, using aaspp4.sty, 22 text pages with
10 figure
- âŠ