65 research outputs found
Disorder-induced mechanism for positive exchange bias fields
We propose a mechanism to explain the phenomenon of positive exchange bias on
magnetic bilayered systems. The mechanism is based on the formation of a domain
wall at a disordered interface during field cooling (FC) which induces a
symmetry breaking of the antiferromagnet, without relying on any ad hoc
assumption about the coupling between the ferromagnetic (FM) and
antiferromagnetic (AFM) layers. The domain wall is a result of the disorder at
the interface between FM and AFM, which reduces the effective anisotropy in the
region. We show that the proposed mechanism explains several known experimental
facts within a single theoretical framework. This result is supported by Monte
Carlo simulations on a microscopic Heisenberg model, by micromagnetic
calculations at zero temperature and by mean field analysis of an effective
Ising like phenomenological model.Comment: 5 pages, 4 figure
Stability as a natural selection mechanism on interacting networks
Biological networks of interacting agents exhibit similar topological
properties for a wide range of scales, from cellular to ecological levels,
suggesting the existence of a common evolutionary origin. A general
evolutionary mechanism based on global stability has been proposed recently [J
I Perotti, O V Billoni, F A Tamarit, D R Chialvo, S A Cannas, Phys. Rev. Lett.
103, 108701 (2009)]. This mechanism is incorporated into a model of a growing
network of interacting agents in which each new agent's membership in the
network is determined by the agent's effect on the network's global stability.
We show that, out of this stability constraint, several topological properties
observed in biological networks emerge in a self organized manner. The
influence of the stability selection mechanism on the dynamics associated to
the resulting network is analyzed as well.Comment: 10 pages, 9 figure
A scale-free neural network for modelling neurogenesis
In this work we introduce a neural network model for associative memory based on a diluted Hopfield model, which grows through a neurogenesis algorithm that guarantees that the final network is a small-world and scale-free one. We also analyze the storage capacity of the network and prove that its performance is larger than that measured in a randomly dilute network with the same connectivity
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