5,644 research outputs found

### Platelet Collapse Model of Pulsar Glitches

A platelet collapse model of starquakes is introduced. It displays
self-organized criticality with a robust power-law behavior. The simulations
indicate a near-constant exponent, whenever scaling is present.Comment: Figures available by sending request to Ivan Schmidt:
[email protected]

### Noncommutative Vortex Solitons

We consider the noncommutative Abelian-Higgs theory and investigate general
static vortex configurations including recently found exact multi-vortex
solutions. In particular, we prove that the self-dual BPS solutions cease to
exist once the noncommutativity scale exceeds a critical value. We then study
the fluctuation spectra about the static configuration and show that the exact
non BPS solutions are unstable below the critical value. We have identified the
tachyonic degrees as well as massless moduli degrees. We then discuss the
physical meaning of the moduli degrees and construct exact time-dependent
vortex configurations where each vortex moves independently. We finally give
the moduli description of the vortices and show that the matrix nature of
moduli coordinates naturally emerges.Comment: 22 pages, 1 figure, typos corrected, a comment on the soliton size is
adde

### Elliptic supertube and a Bogomol'nyi-Prasad-Sommerfield D2-brane--anti-D2-brane Pair

An exact solution, in which a D2-brane and an anti-D2-brane are connected by
an elliptically tubular D2-brane, is obtained without any junction condition.
The solution is shown to preserve one quarter of the supersymmetries of the
type-IIA Minkowski vacuum. We show that the configuration cannot be obtained by
"blowing-up" from some inhomogeneously D0-charged superstrings. The BPS bound
tells us that it is rather composed of D0-charged D2-brane-anti-D2-brane pair
and a strip of superstrings connecting them. We obtain the correction to the
charges of the string end points in the constant magnetic background.Comment: v3. 12 pages, journal version; title changed, length trimmed to fit
for Rapid Communication forma

### Exact Results for the One-Dimensional Self-Organized Critical Forest-Fire Model

We present the analytic solution of the self-organized critical (SOC)
forest-fire model in one dimension proving SOC in systems without conservation
laws by analytic means. Under the condition that the system is in the steady
state and very close to the critical point, we calculate the probability that a
string of $n$ neighboring sites is occupied by a given configuration of trees.
The critical exponent describing the size distribution of forest clusters is
exactly $\tau = 2$ and does not change under certain changes of the model
rules. Computer simulations confirm the analytic results.Comment: 12 pages REVTEX, 2 figures upon request, dro/93/

### The Moduli Space of Noncommutative Vortices

The abelian Higgs model on the noncommutative plane admits both BPS vortices
and non-BPS fluxons. After reviewing the properties of these solitons, we
discuss several new aspects of the former. We solve the Bogomoln'yi equations
perturbatively, to all orders in the inverse noncommutivity parameter, and show
that the metric on the moduli space of k vortices reduces to the computation of
the trace of a k-dimensional matrix. In the limit of large noncommutivity, we
present an explicit expression for this metric.Comment: Invited contribution to special issue of J.Math.Phys. on
"Integrability, Topological Solitons and Beyond"; 10 Pages, 1 Figure. v2:
revision of history in introductio

### A Heavenly Example of Scale Free Networks and Self-Organized Criticality

The sun provides an explosive, heavenly example of self-organized
criticality. Sudden bursts of intense radiation emanate from rapid
rearrangements of the magnetic field network in the corona. Avalanches are
triggered by loops of flux that reconnect or snap into lower energy
configurations when they are overly stressed. Our recent analysis of
observational data reveals that the loops (links) and footpoints (nodes), where
they attach on the photosphere, embody a scale free network. The statistics of
the avalanches and of the network structure are unified through a simple
dynamical model where the avalanches and network co-generate each other into a
complex, critical state. This particular example points toward a general
dynamical mechanism for self-generation of complex networks.Comment: Submitted to proceedings for the Latin American Workshop on Nonlinear
Phenomena, Salvador, Brazil (2003

### Intelligent systems in the context of surrounding environment

We investigate the behavioral patterns of a population of agents, each controlled by a simple biologically motivated neural network model, when they are set in competition against each other in the Minority Model of Challet and Zhang. We explore the effects of changing agent characteristics, demonstrating that crowding behavior takes place among agents of similar memory, and show how this allows unique `rogue' agents with higher memory values to take advantage of a majority population. We also show that agents' analytic capability is largely determined by the size of the intermediary layer of neurons.
In the context of these results, we discuss the general nature of natural and artificial intelligence systems, and suggest intelligence only exists in the context of the surrounding environment (embodiment).
Source code for the programs used can be found at http://neuro.webdrake.net/

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