6,529 research outputs found
Self-organized critical earthquake model with moving boundary
A globally driven self-organized critical model of earthquakes with
conservative dynamics has been studied. An open but moving boundary condition
has been used so that the origin (epicenter) of every avalanche (earthquake) is
at the center of the boundary. As a result, all avalanches grow in equivalent
conditions and the avalanche size distribution obeys finite size scaling
excellent. Though the recurrence time distribution of the time series of
avalanche sizes obeys well both the scaling forms recently observed in analysis
of the real data of earthquakes, it is found that the scaling function decays
only exponentially in contrast to a generalized gamma distribution observed in
the real data analysis. The non-conservative version of the model shows
periodicity even with open boundary.Comment: 5 pages, 4 figures, accepted version in EPJ
Wealth redistribution with finite resources
We present a simplified model for the exploitation of finite resources by
interacting agents, where each agent receives a random fraction of the
available resources. An extremal dynamics ensures that the poorest agent has a
chance to change its economic welfare. After a long transient, the system
self-organizes into a critical state that maximizes the average performance of
each participant. Our model exhibits a new kind of wealth condensation, where
very few extremely rich agents are stable in time and the rest stays in the
middle class.Comment: 4 pages, 3 figures, RevTeX 4 styl
Sandpile model on a quenched substrate generated by kinetic self-avoiding trails
Kinetic self-avoiding trails are introduced and used to generate a substrate
of randomly quenched flow vectors. Sandpile model is studied on such a
substrate with asymmetric toppling matrices where the precise balance between
the net outflow of grains from a toppling site and the total inflow of grains
to the same site when all its neighbors topple once is maintained at all sites.
Within numerical accuracy this model behaves in the same way as the
multiscaling BTW model.Comment: Four pages, five figure
d_c=4 is the upper critical dimension for the Bak-Sneppen model
Numerical results are presented indicating d_c=4 as the upper critical
dimension for the Bak-Sneppen evolution model. This finding agrees with
previous theoretical arguments, but contradicts a recent Letter [Phys. Rev.
Lett. 80, 5746-5749 (1998)] that placed d_c as high as d=8. In particular, we
find that avalanches are compact for all dimensions d<=4, and are fractal for
d>4. Under those conditions, scaling arguments predict a d_c=4, where
hyperscaling relations hold for d<=4. Other properties of avalanches, studied
for 1<=d<=6, corroborate this result. To this end, an improved numerical
algorithm is presented that is based on the equivalent branching process.Comment: 4 pages, RevTex4, as to appear in Phys. Rev. Lett., related papers
available at http://userwww.service.emory.edu/~sboettc
Noncommutative Electrodynamics with covariant coordinates
We study Noncommutative Electrodynamics using the concept of covariant
coordinates. We propose a scheme for interpreting the formalism and construct
two basic examples, a constant field and a plane wave. Superposing these two,
we find a modification of the dispersion relation. Our results differ from
those obtained via the Seiberg-Witten map.Comment: 5 pages, published versio
Coronal Mass Ejections Associated with Slow Long Duration Flares
It is well known that there is temporal relationship between coronal mass
ejections (CMEs) and associated flares. The duration of the acceleration phase
is related to the duration of the rise phase of a flare. We investigate CMEs
associated with slow long duration events (LDEs), i.e. flares with the long
rising phase. We determined the relationships between flares and CMEs and
analyzed the CME kinematics in detail. The parameters of the flares (GOES flux,
duration of the rising phase) show strong correlations with the CME parameters
(velocity, acceleration during main acceleration phase and duration of the CME
acceleration phase). These correlations confirm the strong relation between
slow LDEs and CMEs. We also analyzed the relation between the parameters of the
CMEs, i.e. a velocity, an acceleration during the main acceleration phase, a
duration of the acceleration phase, and a height of a CME at the end of the
acceleration phase. The CMEs associated with the slow LDEs are characterized by
high velocity during the propagation phase, with the median equal 1423 km/s. In
half of the analyzed cases, the main acceleration was low (a<300 m/s^2), which
suggests that the high velocity is caused by the prolongated acceleration phase
(the median for the duration of the acceleration phase is equal 90 minutes).
The CMEs were accelerated up to several solar radii (with the median 7 Rsun),
which is much higher than in typical impulsive CMEs. Therefore, slow LDEs may
potentially precede extremely strong geomagnetic storms. The analysis of slow
LDEs and associated CMEs may give important information for developing more
accurate space weather forecasts, especially for extreme events.Comment: Solar Physics, accepte
Exact equqations and scaling relations for f-avalanche in the Bak-Sneppen evolution model
Infinite hierarchy of exact equations are derived for the newly-observed
f-avalanche in the Bak-Sneppen evolution model. By solving the first order
exact equation, we found that the critical exponent which governs the
divergence of the average avalanche size, is exactly 1 (for all dimensions),
confirmed by the simulations. Solution of the gap equation yields another
universal exponent, denoting the the relaxation to the attractor, is exactly 1.
We also establish some scaling relations among the critical exponents of the
new avalanche.Comment: 5 pages, 1 figur
A model for the emergence of cooperation, interdependence and structure in evolving networks
Evolution produces complex and structured networks of interacting components
in chemical, biological, and social systems. We describe a simple mathematical
model for the evolution of an idealized chemical system to study how a network
of cooperative molecular species arises and evolves to become more complex and
structured. The network is modeled by a directed weighted graph whose positive
and negative links represent `catalytic' and `inhibitory' interactions among
the molecular species, and which evolves as the least populated species
(typically those that go extinct) are replaced by new ones. A small
autocatalytic set (ACS), appearing by chance, provides the seed for the
spontaneous growth of connectivity and cooperation in the graph. A highly
structured chemical organization arises inevitably as the ACS enlarges and
percolates through the network in a short, analytically determined time scale.
This self-organization does not require the presence of self-replicating
species. The network also exhibits catastrophes over long time scales triggered
by the chance elimination of `keystone' species, followed by recoveries.Comment: 8 pages, 4 figure
Chaos in Sandpile Models
We have investigated the "weak chaos" exponent to see if it can be considered
as a classification parameter of different sandpile models. Simulation results
show that "weak chaos" exponent may be one of the characteristic exponents of
the attractor of \textit{deterministic} models. We have shown that the
(abelian) BTW sandpile model and the (non abelian) Zhang model posses different
"weak chaos" exponents, so they may belong to different universality classes.
We have also shown that \textit{stochasticity} destroys "weak chaos" exponents'
effectiveness so it slows down the divergence of nearby configurations. Finally
we show that getting off the critical point destroys this behavior of
deterministic models.Comment: 5 pages, 6 figure
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