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1/f Noise in Sea-level Elevations
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We have analyzed a 101 year record of sea-level elevations. The data
consist of hourly recordings of sea-level elevations from
1889 to 1990 for the port of Esbjerg in Denmark. Power spectra analysis shows
three distinct regimes.
In the frequency range from 1/2 Hour to 1/3 Days the
spectrum shows 1/f behavior. This is then followed by a region with
clear 1/f noise, followed by a crossover to white
noise at the frequency 1/3 Years. This record is one of the rare
examples where a lower cutoff to 1/f noise is found. In addition
intermittent behavior is suggested by stretched exponential probability
density distributions. By using methods based on the correlation integral
both the 1/f noise and the high frequency part of the spectrum
have been checked for low-dimensionality.
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(H. Svensmark), (J.D. Pietrzak) and P. Dimon
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Recurrent Epidemics in a Cellular Automaton
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We investigate an extended version of the * Forest-Fire model
conceived as a model of disease spreading. In contrast to previous
claims, we show that the model self-organizes spatially and temporally
from random initial conditions into a well-defined non-trivial state
with a characteristic length and time scale. The time scale has a
power law dependence on the correlation length , i.e., with in d=2. We show that stochastic
recovery is essential for this behaviour. The aim of the investigation
is primarily to investigate sufficient conditions for obtaining recurrent
epidemic behaviour and propagation of fronts.
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A. Johansen
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Studies of Granular Flow
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When small beads flow through a narrow channel, fluctuations in
the flow rate and density are observed. We can measure the local
density anywhere in the flow with light transmission.
In particular, it has been observed that as the angle of the channel walls
is decreased so they become nearly parallel, there appears to be a critical
angle at which the flow rate is a maximum and the fluctuations are
strongly intermittent.
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C. Veje and P. Dimon
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Distributions of Self-Interactions and Voids
in (1+1)-d Directed Percolation
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We investigate the scaling of self-interactions
and voids in -d directed percolation clusters and backbones.
We verify that the meandering of the
backbone scales like the directed cluster.
A geometric relation between the size distribution
and the fractal dimensions of a set of objects
is applied to find the scaling properties of
self-interactions in directed percolation.
Lastly we connect the geometric properties
of the backbone with the avalanche distribution
generated by interface
dynamics at the depinning transition.
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(G. Huber), M.H. Jensen and K. Sneppen
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Intermittent Activity, Multiscaling and Self-Organized Criticality
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We characterize the spatio-temporal behavior of all self-organized
critical phenomena by means of an activity function. The activity
function is equivalent to a roughening front and shows intermittent
behavior in space and time. Due to the intermittency, the moments of
the activity function exhibits multiscaling in time with a continuous
spectrum of exponents. This spectrum of exponents can for SOC dynamics
be estimated analytically in terms of the roughness exponent for the
activity function whereas for dynamics generated by Levy flights we
have not been able to express the spectrum analytically.
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M.H. Jensen, K. Sneppen and (M. Sellitto)
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Self-Organized Criticality, Stochastic Cellular Automata, and the
Game of Life
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The question of self-organized criticality in Conway's game of life
is studied in the broader context of stochastic cellular automata.
We are particularly interested in the directed percolation type of
phase transitions observed.
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P. Alstrøm, J. Nordfalk and C. Veje
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Mon Mar 6 19:42:06 MET 1995