1,222 research outputs found
Phase transitions of extended-range probabilistic cellular automata with two absorbing states
We study phase transitions in a long-range one-dimensional cellular automaton
with two symmetric absorbing states. It includes and extends several other
models, like the Ising and Domany-Kinzel ones. It is characterized by a
competing ferromagnetic linear coupling and an antiferromagnetic nonlinear one.
Despite its simplicity, this model exhibits an extremely rich phase diagram. We
present numerical results and mean-field approximations.Comment: New and expanded versio
Synchronization universality classes and stability of smooth, coupled map lattices
We study two problems related to spatially extended systems: the dynamical
stability and the universality classes of the replica synchronization
transition. We use a simple model of one dimensional coupled map lattices and
show that chaotic behavior implies that the synchronization transition belongs
to the multiplicative noise universality class, while stable chaos implies that
the synchronization transition belongs to the directed percolation universality
class.Comment: 6 pages, 7 figure
The Hot-Spot Phenomenon and its Countermeasures in Bipolar Power Transistors by Analytical Electro-Thermal Simulation
This communication deals with a theoretical study of the hot spot onset (HSO)
in cellular bipolar power transistors. This well-known phenomenon consists of a
current crowding within few cells occurring for high power conditions, which
significantly decreases the forward safe operating area (FSOA) of the device.
The study was performed on a virtual sample by means of a fast, fully
analytical electro-thermal simulator operating in the steady state regime and
under the condition of imposed input base current. The purpose was to study the
dependence of the phenomenon on several thermal and geometrical factors and to
test suitable countermeasures able to impinge this phenomenon at higher biases
or to completely eliminate it. The power threshold of HSO and its localization
within the silicon die were observed as a function of the electrical bias
conditions as for instance the collector voltage, the equivalent thermal
resistance of the assembling structure underlying the silicon die, the value of
the ballasting resistances purposely added in the emitter metal
interconnections and the thickness of the copper heat spreader placed on the
die top just to the aim of making more uniform the temperature of the silicon
surface.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
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
Noise and nonlinearities in high-throughput data
High-throughput data analyses are becoming common in biology, communications,
economics and sociology. The vast amounts of data are usually represented in
the form of matrices and can be considered as knowledge networks. Spectra-based
approaches have proved useful in extracting hidden information within such
networks and for estimating missing data, but these methods are based
essentially on linear assumptions. The physical models of matching, when
applicable, often suggest non-linear mechanisms, that may sometimes be
identified as noise. The use of non-linear models in data analysis, however,
may require the introduction of many parameters, which lowers the statistical
weight of the model. According to the quality of data, a simpler linear
analysis may be more convenient than more complex approaches.
In this paper, we show how a simple non-parametric Bayesian model may be used
to explore the role of non-linearities and noise in synthetic and experimental
data sets.Comment: 12 pages, 3 figure
A Self-Organized Method for Computing the Epidemic Threshold in Computer Networks
In many cases, tainted information in a computer network can spread in a way
similar to an epidemics in the human world. On the other had, information
processing paths are often redundant, so a single infection occurrence can be
easily "reabsorbed". Randomly checking the information with a central server is
equivalent to lowering the infection probability but with a certain cost (for
instance processing time), so it is important to quickly evaluate the epidemic
threshold for each node. We present a method for getting such information
without resorting to repeated simulations. As for human epidemics, the local
information about the infection level (risk perception) can be an important
factor, and we show that our method can be applied to this case, too. Finally,
when the process to be monitored is more complex and includes "disruptive
interference", one has to use actual simulations, which however can be carried
out "in parallel" for many possible infection probabilities
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
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