49 research outputs found
Surrogates with random Fourier Phases
The method of surrogates is widely used in the field of nonlinear data
analysis for testing for weak nonlinearities. The two most commonly used
algorithms for generating surrogates are the amplitude adjusted Fourier
transform (AAFT) and the iterated amplitude adjusted Fourier transfom (IAAFT)
algorithm. Both the AAFT and IAAFT algorithm conserve the amplitude
distribution in real space and reproduce the power spectrum (PS) of the
original data set very accurately. The basic assumption in both algorithms is
that higher-order correlations can be wiped out using a Fourier phase
randomization procedure. In both cases, however, the randomness of the Fourier
phases is only imposed before the (first) Fourier back tranformation. Until
now, it has not been studied how the subsequent remapping and iteration steps
may affect the randomness of the phases. Using the Lorenz system as an example,
we show that both algorithms may create surrogate realizations containing
Fourier phase correlations. We present two new iterative surrogate data
generating methods being able to control the randomization of Fourier phases at
every iteration step. The resulting surrogate realizations which are truly
linear by construction display all properties needed for surrogate data.Comment: To appear in: "Topics on Chaotic Systems: Selected Papers from Chaos
2008 International Conference", World Scientifi
Long term persistence in the sea surface temperature fluctuations
We study the temporal correlations in the sea surface temperature (SST)
fluctuations around the seasonal mean values in the Atlantic and Pacific
oceans. We apply a method that systematically overcome possible trends in the
data. We find that the SST persistence, characterized by the correlation
of temperature fluctuations separated by a time period , displays two
different regimes. In the short-time regime which extends up to roughly 10
months, the temperature fluctuations display a nonstationary behavior for both
oceans, while in the asymptotic regime it becomes stationary. The long term
correlations decay as with for both
oceans which is different from found for atmospheric land
temperature.Comment: 14 pages, 5 fiure
Application of a renormalization group algorithm to nonequilibrium cellular automata with one absorbing state
We improve a recently proposed dynamically driven renormalization group
algorithm for cellular automata systems with one absorbing state, introducing
spatial correlations in the expression for the transition probabilities. We
implement the renormalization group scheme considering three different
approximations which take into account correlations in the stationary
probability distribution. The improved scheme is applied to a probabilistic
cellular automaton already introduced in the literature.Comment: 7 pages, 4 figures, to be published in Phys. Rev.
Study of the one-dimensional off-lattice hot-monomer reaction model
Hot monomers are particles having a transient mobility (a ballistic flight)
prior to being definitely absorbed on a surface. After arriving at a surface,
the excess energy coming from the kinetic energy in the gas phase is dissipated
through degrees of freedom parallel to the surface plane. In this paper we
study the hot monomer-monomer adsorption-reaction process on a continuum
(off-lattice) one-dimensional space by means of Monte Carlo simulations. The
system exhibits second-order irreversible phase transition between a reactive
and saturated (absorbing) phases which belong to the directed percolation (DP)
universality class. This result is interpreted by means of a coarse-grained
Langevin description which allows as to extend the DP conjecture to transitions
occurring in continuous media.Comment: 13 pages, 5 figures, final version to appear in J. Phys.
Critical behavior of a one-dimensional monomer-dimer reaction model with lateral interactions
A monomer-dimer reaction lattice model with lateral repulsion among the same
species is studied using a mean-field analysis and Monte Carlo simulations. For
weak repulsions, the model exhibits a first-order irreversible phase transition
between two absorbing states saturated by each different species. Increasing
the repulsion, a reactive stationary state appears in addition to the saturated
states. The irreversible phase transitions from the reactive phase to any of
the saturated states are continuous and belong to the directed percolation
universality class. However, a different critical behavior is found at the
point where the directed percolation phase boundaries meet. The values of the
critical exponents calculated at the bicritical point are in good agreement
with the exponents corresponding to the parity-conserving universality class.
Since the adsorption-reaction processes does not lead to a non-trivial local
parity-conserving dynamics, this result confirms that the twofold symmetry
between absorbing states plays a relevant role in determining the universality
class. The value of the exponent , which characterizes the
fluctuations of an interface at the bicritical point, supports the
Bassler-Brown's conjecture which states that this is a new exponent in the
parity-conserving universality class.Comment: 19 pages, 22 figures, to be published in Phys. Rev