7,168 research outputs found

### Depinning exponents of the driven long-range elastic string

We perform a high-precision calculation of the critical exponents for the
long-range elastic string driven through quenched disorder at the depinning
transition, at zero temperature. Large-scale simulations are used to avoid
finite-size effects and to enable high precision. The roughness, growth, and
velocity exponents are calculated independently, and the dynamic and
correlation length exponents are derived. The critical exponents satisfy known
scaling relations and agree well with analytical predictions.Comment: 6 pages, 5 figure

### Noise versus chaos in a causal Fisher-Shannon plane

We revisit the Fisher-Shannon representation plane ${\mathcal H} \times
{\mathcal F}$, evaluated using the Bandt and Pompe recipe to assign a
probability distribution to a time series. Several stochastic dynamical (noises
with $f^{-k}$, $k \geq 0$, power spectrum) and chaotic processes (27 chaotic
maps) are analyzed so as to illustrate the approach. Our main achievement is
uncovering the informational properties of the planar location.Comment: 6 pages, 1 figure. arXiv admin note: text overlap with
arXiv:1401.213

### Non-equilibrium relaxation of an elastic string in random media

We study the relaxation of an elastic string in a two dimensional pinning
landscape using Langevin dynamics simulations. The relaxation of a line,
initially flat, is characterized by a growing length, $L(t)$, separating the
equilibrated short length scales from the flat long distance geometry that keep
memory of the initial condition. We find that, in the long time limit, $L(t)$
has a non--algebraic growth, consistent with thermally activated jumps over
barriers with power law scaling, $U(L) \sim L^\theta$.Comment: 2 pages, 1 figure, Proceedings of ECRYS-2005 International Workshop
on Electronic Crysta

### Frictional dynamics of viscoelastic solids driven on a rough surface

We study the effect of viscoelastic dynamics on the frictional properties of
a (mean field) spring-block system pulled on a rough surface by an external
drive. When the drive moves at constant velocity V, two dynamical regimes are
observed: at fast driving, above a critical threshold Vc, the system slides at
the drive velocity and displays a friction force with velocity weakening. Below
Vc the steady sliding becomes unstable and a stick-slip regime sets in. In the
slide-hold-slide driving protocol, a peak of the friction force appears after
the hold time and its amplitude increases with the hold duration. These
observations are consistent with the frictional force encoded
phenomenologically in the rate-and-state equations. Our model gives a
microscopical basis for such macroscopic description.Comment: 10 figures, 7 pages, +4 pages of appendi

### Uniqueness of the thermodynamic limit for driven disordered elastic interfaces

We study the finite size fluctuations at the depinning transition for a
one-dimensional elastic interface of size $L$ displacing in a disordered medium
of transverse size $M=k L^\zeta$ with periodic boundary conditions, where
$\zeta$ is the depinning roughness exponent and $k$ is a finite aspect ratio
parameter. We focus on the crossover from the infinitely narrow ($k\to 0$) to
the infinitely wide ($k\to \infty$) medium. We find that at the thermodynamic
limit both the value of the critical force and the precise behavior of the
velocity-force characteristics are {\it unique} and $k$-independent. We also
show that the finite size fluctuations of the critical force (bias and
variance) as well as the global width of the interface cross over from a
power-law to a logarithm as a function of $k$. Our results are relevant for
understanding anisotropic size-effects in force-driven and velocity-driven
interfaces.Comment: 10 pages, 12 figure

### Efficiency characterization of a large neuronal network: a causal information approach

When inhibitory neurons constitute about 40% of neurons they could have an
important antinociceptive role, as they would easily regulate the level of
activity of other neurons. We consider a simple network of cortical spiking
neurons with axonal conduction delays and spike timing dependent plasticity,
representative of a cortical column or hypercolumn with large proportion of
inhibitory neurons. Each neuron fires following a Hodgkin-Huxley like dynamics
and it is interconnected randomly to other neurons. The network dynamics is
investigated estimating Bandt and Pompe probability distribution function
associated to the interspike intervals and taking different degrees of
inter-connectivity across neurons. More specifically we take into account the
fine temporal ``structures'' of the complex neuronal signals not just by using
the probability distributions associated to the inter spike intervals, but
instead considering much more subtle measures accounting for their causal
information: the Shannon permutation entropy, Fisher permutation information
and permutation statistical complexity. This allows us to investigate how the
information of the system might saturate to a finite value as the degree of
inter-connectivity across neurons grows, inferring the emergent dynamical
properties of the system.Comment: 26 pages, 3 Figures; Physica A, in pres

### Classification and Verification of Online Handwritten Signatures with Time Causal Information Theory Quantifiers

We present a new approach for online handwritten signature classification and
verification based on descriptors stemming from Information Theory. The
proposal uses the Shannon Entropy, the Statistical Complexity, and the Fisher
Information evaluated over the Bandt and Pompe symbolization of the horizontal
and vertical coordinates of signatures. These six features are easy and fast to
compute, and they are the input to an One-Class Support Vector Machine
classifier. The results produced surpass state-of-the-art techniques that
employ higher-dimensional feature spaces which often require specialized
software and hardware. We assess the consistency of our proposal with respect
to the size of the training sample, and we also use it to classify the
signatures into meaningful groups.Comment: Submitted to PLOS On

### Tuning spreading and avalanche-size exponents in directed percolation with modified activation probabilities

We consider the directed percolation process as a prototype of systems
displaying a nonequilibrium phase transition into an absorbing state. The model
is in a critical state when the activation probability is adjusted at some
precise value p_c. Criticality is lost as soon as the probability to activate
sites at the first attempt, p1, is changed. We show here that criticality can
be restored by "compensating" the change in p1 by an appropriate change of the
second time activation probability p2 in the opposite direction. At
compensation, we observe that the bulk exponents of the process coincide with
those of the normal directed percolation process. However, the spreading
exponents are changed, and take values that depend continuously on the pair
(p1, p2). We interpret this situation by acknowledging that the model with
modified initial probabilities has an infinite number of absorbing states.Comment: 9 pages, 11 figure

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