955 research outputs found
Non-Gaussian Resistance Noise near Electrical Breakdown in Granular Materials
The distribution of resistance fluctuations of conducting thin films with
granular structure near electrical breakdown is studied by numerical
simulations. The film is modeled as a resistor network in a steady state
determined by the competition between two biased processes, breaking and
recovery. Systems of different sizes and with different levels of internal
disorder are considered. Sharp deviations from a Gaussian distribution are
found near breakdown and the effect increases with the degree of internal
disorder. However, we show that in general this non-Gaussianity is related to
the finite size of the system and vanishes in the large size limit.
Nevertheless, near the critical point of the conductor-insulator transition,
deviations from Gaussianity persist when the size is increased and the
distribution of resistance fluctuations is well fitted by the universal
Bramwell-Holdsworth-Pinton distribution.Comment: 8 pages, 6 figures; accepted for publication on Physica
Statistics of Extreme Values in Time Series with Intermediate-Term Correlations
It will be discussed the statistics of the extreme values in time series
characterized by finite-term correlations with non-exponential decay.
Precisely, it will be considered the results of numerical analyses concerning
the return intervals of extreme values of the fluctuations of resistance and
defect-fraction displayed by a resistor with granular structure in a
nonequilibrium stationary state. The resistance and defect-fraction are
calculated as a function of time by Monte Carlo simulations using a resistor
network approach. It will be shown that when the auto-correlation function of
the fluctuations displays a non-exponential and non-power-law decay, the
distribution of the return intervals of extreme values is a stretched
exponential, with exponent largely independent of the threshold. Recently, a
stretched exponential distribution of the return intervals of extreme values
has been identified in long-term correlated time series by Bunde et al. (2003)
and Altmann and Kantz (2005). Thus, the present results show that the stretched
exponential distribution of the return intervals is not an exclusive feature of
long-term correlated time series.Comment: 6 pages, 7 figures, conference paper, in Noise and Stochastics in
Complex Systems and Finance, ed. by J. Kertez, S. Bornhold, R. N. Mantegna,
Procs. of SPIE, vol. 6601, 19, 200
Distribution of Return Intervals of Extreme Events
The distribution of return intervals of extreme events is studied in time
series characterized by finite-term correlations with non-exponential decay.
Precisely, it has been analyzed the statistics of the return intervals of
extreme values of the resistance fluctuations displayed by resistors with
granular structure in nonequilibrium stationary states. The resistance
fluctuations are calculated by Monte Carlo simulations using a resistor network
approach. It has been found that for highly disordered networks, when the
auto-correlation function displays a non-exponential and non-power-law decay,
the distribution of return intervals of the extreme values is a stretched
exponential, with exponent independent of the threshold.Comment: 10 pages, 6 figures, Next-SigmaPhi Int. Conference, News Expectations
and Trends in Statistical Physics, 13-18 August 2005, Kolymbari - Crete
(Greece
Distribution of Return Periods of Rare Events in Correlated Time Series
We study the effect on the distribution of return periods of rare events of
the presence in a time series of finite-term correlations with non-exponential
decay. Precisely, we analyze the auto-correlation function and the statistics
of the return intervals of extreme values of the resistance fluctuations
displayed by a resistor with granular structure in a nonequilibrium stationary
state. The resistance fluctuations, , are calculated by Monte Carlo
simulations using the SBRN model introduced some years ago by Pennetta,
Tref\'an and Reggiani and based on a resistor network approach. A rare event
occurs when overcomes a threshold value significantly higher
than the average value of the resistance. We have found that for highly
disordered networks, when the auto-correlation function displays a
non-exponential decay but yet the resistance fluctuations are characterized by
a finite correlation time, the distribution of return intervals of the extreme
values is well described by a stretched exponential, with exponent largely
independent of the threshold . We discuss this result and some of the main
open questions related to it, also in connection with very recent findings by
other authors concerning the observation of stretched exponential distributions
of return intervals of extreme events in long-term correlated time series.Comment: 10 pages, 8 figures, Procs. of 4th. Int. Conf. on Unsolved Problems
on Noise and Fluctuations in Physics, Biology and High Technology (UPoN05),
6-10 June 2005, Gallipoli (Italy), AIP Conf. Procs. (in print
Trapping-detrapping fluctuations in organic space-charge layers
A trapping-detrapping model is proposed for explaining the current
fluctuation behavior in organic semiconductors (polyacenes) operating under
current-injection conditions. The fraction of ionized traps obtained from the
current-voltage characteristics, is related to the relative current noise
spectral density at the trap-filling transition. The agreement between theory
and experiments validates the model and provides an estimate of the
concentration and energy level of deep traps
A Percolative Model of Soft Breakdown in Ultrathin Oxides
The degradation of ultrathin oxide layers in the presence of a stress voltage
is modeled in terms of two antagonist percolation processes taking place in a
random resistor network. The resistance and leakage current fluctuations are
studied by MonteCarlo simulations for voltages below the breakdown threshold.
An increase of excess noise together with a noticeable non-Gaussian behavior is
found in the pre-breakdown regime in agreement with experimental results.Comment: accepted for publication on Physica
Universality and Scaling Behaviour of Injected Power in Elastic Turbulence in Worm-like Micellar Gel
We study the statistical properties of spatially averaged global injected
power fluctuations for Taylor-Couette flow of a worm-like micellar gel formed
by surfactant CTAT. At sufficiently high Weissenberg numbers (Wi) the shear
rate and hence the injected power p(t) at a constant applied stress shows large
irregular fluctuations in time. The nature of the probability distribution
function (pdf) of p(t) and the power-law decay of its power spectrum are very
similar to that observed in recent studies of elastic turbulence for polymer
solutions. Remarkably, these non-Gaussian pdfs can be well described by an
universal large deviation functional form given by the Generalized Gumbel (GG)
distribution observed in the context of spatially averaged global measures in
diverse classes of highly correlated systems. We show by in-situ rheology and
polarized light scattering experiments that in the elastic turbulent regime the
flow is spatially smooth but random in time, in agreement with a recent
hypothesis for elastic turbulence.Comment: 8 pages, 3 figure
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