## Søk

Viser treff 1-10 av 37

#### Evidence of low-dimensional chaos in magnetized plasma turbulence

(Working paper; Arbeidsnotat, 2008-03-10)

We analyze probe data obtained from a toroidal magnetized plasma configuration
suitable for studies of low-frequency gradient-driven instabilities. These instabilities give
rise to field-aligned convection rolls analogous to Rayleigh-Benard cells in neutral fluids,
and may theoretically develop similar routes to chaos. When using mean-field dimension
analysis, we observe low dimensionality, but ...

#### Modeling temporal fluctuations in avalanching system

(Working paper; Arbeidsnotat, 2008-07-22)

We demonstrate how to model the toppling activity in avalanching systems by stochastic differential
equations (SDEs). The theory is developed as a generalization of the classical mean field
approach to sandpile dynamics by formulating it as a generalization of Itoh’s SDE. This equation
contains a fractional Gaussian noise term representing the branching of an avalanche into small
active clusters, ...

#### Stretched-exponential decay functions from a self-consistent model of dielectric relaxation

(Working paper; Arbeidsnotat, 2007-07-22)

There are many materials whose dielectric properties are described by a stretched
exponential, the so-called Kohlrausch-Williams-Watts (KWW) relaxation function.
Its physical origin and statistical-mechanical foundation have been a matter of debate
in the literature. In this paper we suggest a model of dielectric relaxation,
which naturally leads to a stretched exponential decay function. Some ...

#### E-pile model of self-organized criticality

(Working paper; Arbeidsnotat, 2007-11-28)

The concept of percolation is combined with a self-consistent treatment of the interaction between
the dynamics on a lattice and the external drive. Such a treatment can provide a mechanism by which
the system evolves to criticality without fine tuning, thus offering a route to self-organized criticality
(SOC) which in many cases is more natural than the weak random drive combined with ...

#### Scale-free vortex cascade emerging from random forcing in a strongly coupled system

(Working paper; Arbeidsnotat, 2008-03-04)

The notions of self-organised criticality (SOC) and turbulence are traditionally considered to be applicable to disjoint classes of phenomena. Nevertheless, scale-free burst statistics is a feature shared by turbulent as well as self-organised critical dynamics. It has also been suggested that another shared feature is universal non-gaussian probability density functions (PDFs) of global fluctuations. ...

#### A stochastic theory for temporal fluctuations in self-organized critical systems

(Working paper; Arbeidsnotat, 2008-07-22)

A stochastic theory for the toppling activity in sandpile models is
developed, based on a simple mean-field assumption about the toppling process. The
theory describes the process as an anti-persistent Gaussian walk, where the diffusion
coefficient is proportional to the activity. It is formulated as a generalization of the Itˆo
stochastic differential equation with an anti-persistent fractional ...

#### Burst statistics of fluctuations in a simple magnetized torus configuration

(Working paper; Arbeidsnotat, 2009-04-19)

In a toroidal plasma confined by a purely toroidal magnetic field the plasma transport is governed by electrostatic turbulence driven by the flute interchange instability on the low-field side of the torus cross section. In this paper we revisit experimental data obtained from the Blaamann torus at the University of Tromso. On time-scales shorter than the poloidal rotation time, the time series of ...

#### Klimakrisen og økonomisk politikk

(Chronicle; Kronikk, 2015-11-14)

#### Low-dimensionality and predictability of solar wind and global magnetosphere during magnetic storms

(Journal article; Tidsskriftartikkel; Peer reviewed, 2011)

The storm index SYM-H, the solar wind velocity v, and interplanetary magnetic field Bz show no signatures of low-dimensional dynamics in quiet periods, but tests for determinism in the time series indicate that SYM-H exhibits a significant low-dimensional component during storm time, suggesting that self-organization takes place during magnetic storms. Even though our analysis yields no discernible ...

#### Organization of the magnetosphere during substorms

(Journal article; Tidsskriftartikkel; Peer reviewed, 2012)

The change in degree of organization of the magnetosphere during substorms is investigated by analyzing various geomagnetic indices, as well as interplanetary magnetic field z-component and solar wind velocity x-component. We conclude that the magnetosphere self-organizes globally during substorms, but neither the magnetosphere nor the solar wind become more predictable in the course of a substorm. ...