1,436 research outputs found
Damage spreading in the Bak-Sneppen model: Sensitivity to the initial conditions and equilibration dynamics
The short-time and long-time dynamics of the Bak-Sneppen model of biological
evolution are investigated using the damage spreading technique. By defining a
proper Hamming distance measure, we are able to make it exhibits an initial
power-law growth which, for finite size systems, is followed by a decay towards
equilibrium. In this sense, the dynamics of self-organized critical states is
shown to be similar to the one observed at the usual critical point of
continuous phase-transitions and at the onset of chaos of non-linear
low-dimensional dynamical maps. The transient, pre-asymptotic and asymptotic
exponential relaxation of the Hamming distance between two initially
uncorrelated equilibrium configurations is also shown to be fitted within a
single mathematical framework. A connection with nonextensive statistical
mechanics is exhibited.Comment: 6 pages, 4 figs, revised version, accepted for publication in
Int.J.Mod.Phys.C 14 (2003
Effect of the Canting of Local Anisotropy Axes on Ground-State Properties of a Ferrimagnetic Chain with Regularly Alternating Ising and Heisenberg Spins
The effect of the canting of local anisotropy axes on the ground-state phase
diagram and magnetization of a ferrimagnetic chain with regularly alternating
Ising and Heisenberg spins is exactly examined in an arbitrarily oriented
magnetic field. It is shown that individual contributions of Ising and
Heisenberg spins to the total magnetization basically depend on the spatial
orientation of the magnetic field and the canting angle between two different
local anisotropy axes of the Ising spins.Comment: 3 pages, 3 figure
Formation of sharp eccentric rings in debris disks with gas but without planets
‘Debris disks’ around young stars (analogues of the Kuiper Belt in
our Solar System) show a variety of non-trivial structures attributed
to planetary perturbations and used to constrain the properties
of those planets. However, these analyses have largely
ignored the fact that some debris disks are found to contain small
quantities of gas, a component that all such disks should contain
at some level. Several debris disks have been measured with a
dust-to-gas ratio of about unity, at which the effect of hydrodynamics
on the structure of the disk cannot be ignored. Here
we report linear and nonlinear modelling that shows that dust–gas
interactions can produce some of the key patterns attributed to
planets. We find a robust clumping instability that organizes the
dust into narrow, eccentric rings, similar to the Fomalhaut debris
disk. The conclusion that such disks might contain planets is not
necessarily required to explain these systems
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