1,360 research outputs found
On Damage Spreading Transitions
We study the damage spreading transition in a generic one-dimensional
stochastic cellular automata with two inputs (Domany-Kinzel model) Using an
original formalism for the description of the microscopic dynamics of the
model, we are able to show analitically that the evolution of the damage
between two systems driven by the same noise has the same structure of a
directed percolation problem. By means of a mean field approximation, we map
the density phase transition into the damage phase transition, obtaining a
reliable phase diagram. We extend this analysis to all symmetric cellular
automata with two inputs, including the Ising model with heath-bath dynamics.Comment: 12 pages LaTeX, 2 PostScript figures, tar+gzip+u
Small world effects in evolution
For asexual organisms point mutations correspond to local displacements in
the genotypic space, while other genotypic rearrangements represent long-range
jumps. We investigate the spreading properties of an initially homogeneous
population in a flat fitness landscape, and the equilibrium properties on a
smooth fitness landscape. We show that a small-world effect is present: even a
small fraction of quenched long-range jumps makes the results indistinguishable
from those obtained by assuming all mutations equiprobable. Moreover, we find
that the equilibrium distribution is a Boltzmann one, in which the fitness
plays the role of an energy, and mutations that of a temperature.Comment: 13 pages and 5 figures. New revised versio
Control of cellular automata
We study the problem of master-slave synchronization and control of
totalistic cellular automata (CA) by putting a fraction of sites of the slave
equal to those of the master and finding the distance between both as a
function of this fraction. We present three control strategies that exploit
local information about the CA, mainly, the number of nonzero Boolean
derivatives. When no local information is used, we speak of synchronization. We
find the critical properties of control and discuss the best control strategy
compared with synchronization
Age-Dependent Regulation of Notch Family Members in the Neuronal Stem Cell Niches of the Short-Lived Killifish Nothobranchius furzeri
Background: The annual killifish Nothobranchius furzeri is a new experimental model organism in biology, since it represents the vertebrate species with the shortest captive life span and also shows the fastest maturation and senescence recorded in the laboratory. Here, we use this model to investigate the age-dependent decay of neurogenesis in the telencephalon (brain region sharing the same embryonic origin with the mammalian adult niches), focusing on the expression of the Notch pathway genes. Results: We observed that the major ligands/receptors of the pathway showed a negative correlation with age, indicating age-dependent downregulation of the Notch pathway. Moreover, expression of notch1a was clearly limited to active neurogenic niches and declined during aging, without changing its regional patterning. Expression of notch3 is not visibly influenced by aging. Conclusion: Both expression pattern and regulation differ between notch1a and notch3, with the former being limited to mitotically active regions and reduced by aging and the latter being present in all cells with a neurogenic potential, regardless of the level of their actual mitotic activity, and so is less influenced by age. This finally suggests a possible differential role of the two receptors in the regulation of the niche proliferative potential throughout the entire fish life
Study of Water Speed Sensitivity in a Multifunctional Thick-film Sensor by Analytical Thermal Simulations and Experiments
The present paper deals with an application of the analytical thermal
simulator DJOSER. It consist of the characterization of a water speed sensor
realized in hybrid technology. The capability of the thermal solver to manage
the convection heat exchange and the effects of the passivating layers make the
simulation work easy and fast.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Quasispecies evolution in general mean-field landscapes
I consider a class of fitness landscapes, in which the fitness is a function
of a finite number of phenotypic "traits", which are themselves linear
functions of the genotype. I show that the stationary trait distribution in
such a landscape can be explicitly evaluated in a suitably defined
"thermodynamic limit", which is a combination of infinite-genome and strong
selection limits. These considerations can be applied in particular to identify
relevant features of the evolution of promoter binding sites, in spite of the
shortness of the corresponding sequences.Comment: 6 pages, 2 figures, Europhysics Letters style (included) Finite-size
scaling analysis sketched. To appear in Europhysics Letter
Phase diagram of a probabilistic cellular automaton with three-site interactions
We study a (1+1) dimensional probabilistic cellular automaton that is closely
related to the Domany-Kinzel (DKCA), but in which the update of a given site
depends on the state of {\it three} sites at the previous time step. Thus,
compared with the DKCA, there is an additional parameter, , representing
the probability for a site to be active at time , given that its nearest
neighbors and itself were active at time . We study phase transitions and
critical behavior for the activity {\it and} for damage spreading, using one-
and two-site mean-field approximations, and simulations, for and
. We find evidence for a line of tricritical points in the () parameter space, obtained using a mean-field approximation at pair level.
To construct the phase diagram in simulations we employ the growth-exponent
method in an interface representation. For , the phase diagram is
similar to the DKCA, but the damage spreading transition exhibits a reentrant
phase. For , the growth-exponent method reproduces the two absorbing
states, first and second-order phase transitions, bicritical point, and damage
spreading transition recently identified by Bagnoli {\it et al.} [Phys. Rev.
E{\bf 63}, 046116 (2001)].Comment: 15 pages, 7 figures, submited to PR
Towards generalized measures grasping CA dynamics
In this paper we conceive Lyapunov exponents, measuring the rate of separation between two initially close configurations, and Jacobians, expressing the sensitivity of a CA's transition function to its inputs, for cellular automata (CA) based upon irregular tessellations of the n-dimensional Euclidean space. Further, we establish a relationship between both that enables us to derive a mean-field approximation of the upper bound of an irregular CA's maximum Lyapunov exponent. The soundness and usability of these measures is illustrated for a family of 2-state irregular totalistic CA
Short period attractors and non-ergodic behavior in the deterministic fixed energy sandpile model
We study the asymptotic behaviour of the Bak, Tang, Wiesenfeld sandpile
automata as a closed system with fixed energy.
We explore the full range of energies characterizing the active phase. The
model exhibits strong non-ergodic features by settling into limit-cycles whose
period depends on the energy and initial conditions. The asymptotic activity
(topplings density) shows, as a function of energy density , a
devil's staircase behaviour defining a symmetric energy interval-set over which
also the period lengths remain constant. The properties of -
phase diagram can be traced back to the basic symmetries underlying the model's
dynamics.Comment: EPL-style, 7 pages, 3 eps figures, revised versio
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