128 research outputs found
The risk of extinction - the mutational meltdown or the overpopulation
The phase diagrams survival-extinction for the Penna model with parameters:
(mutations rate)-(birth rate), (mutation rate)-(harmful mutations threshold),
(harmful mutation threshold)-(minimal reproduction age) are presented. The
extinction phase may be caused by either mutational meltdown or overpopulation.
When the Verhulst factor is responsible for removing only newly born babies and
does not act on adults the overpopulation is avoided and only genetic factors
may lead to species extinction.Comment: RevTex4, 5 pages, 4 figures (8 eps files
Ferromagnetic Ising spin systems on the growing random tree
We analyze the ferromagnetic Ising model on a scale-free tree; the growing
random network model with the linear attachment kernel
introduced by [Krapivsky et al.: Phys. Rev. Lett. {\bf 85} (2000) 4629-4632].
We derive an estimate of the divergent temperature below which the
zero-field susceptibility of the system diverges. Our result shows that
is related to as , where is the
ferromagnetic interaction. An analysis of exactly solvable limit for the model
and numerical calculation support the validity of this estimate.Comment: 15 pages, 5 figure
Memory effect in growing trees
We show that the structure of a growing tree preserves an information on the
shape of an initial graph. For the exponential trees, evidence of this kind of
memory is provided by means of the iterative equations, derived for the moments
of the node-node distance distribution. Numerical calculations confirm the
result and allow to extend the conclusion to the Barabasi--Albert scale-free
trees. The memory effect almost disappears, if subsequent nodes are connected
to the network with more than one link.Comment: 9 pages, 9 figure
The Sznajd dynamics on a directed clustered network
The Sznajd model is investigated in the directed Erdos--Renyi network with
the clusterization coefficient enhanced to 0.3 by the method of Holme and Kim
(Phys. Rev. E65 (2002) 026107). Within additional triangles, all six links are
present. In this network, some nodes preserve the minority opinion. The time
tau of getting equilibrium is found to follow the log-normal distribution and
it increases linearly with the system size. Its dependence on the initial
opinion distribution is different from the analytical results for fully
connected networks.Comment: dedicated to Dietrich Stauffer for his 65-th birthda
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