HR: 1340h
AN: NG43A-0560    [Abstracts]
TI: The Dynamics of SOC Systems with Diffusion
AU: * Newman, D E
EM: ffden@uaf.edu
AF: Geophysical Institute/Physics Department, University of Alaska Fairbanks, Physics Department P.O. Box 755920, Fairbanks, AK 99775-5920 United States
AU: Sanchez, R
EM: rsanchez@fis.uc3m.es
AF: Universidad Carlos III de Madrid, Departamento de Fˇsica. Office 4.0C07., Madrid, 30 28911 Spain
AU: Carreras, B A
EM: carreras@fed.ornl.gov
AF: Oak Ridge National Laboratory, P.O. Box 2008 MS6169, Oak Ridge, TN 37831-6169 United States
AB: A number of models based on the idea of self-organized-criticality (SOC) have been proposed in the last decade. While these models have often successfully reproduced much of the underlying dynamics of the very different physical systems they have been applied to: from traffic jams and earthquakes to accretion disks, solar flare dynamics and turbulent transport of plasmas, they are often criticized for leaving out important physics. This criticism is sometimes justified, for example, a number of these systems have secondary relaxation mechanisms, in addition to the intermittent avalanches characteristic of SOC. Diffusion and avalanche transport are examples of two transport mechanisms that frequently coexist. Understanding the dynamical interaction between these varied mechanisms is important if we are to understand both the proposed robustness of the SOC paradigm and the real behavior of the physical systems being modeled. Diffusion, or diffusion like processes, are common in many physical systems. For example, in addition to the dominant ``discrete'' earthquakes, other mechanisms are available to relax tectonic stress such as plastic deformation and creep. While in solar flare or accretion disk dynamics, diffusion and/or convection of energy or mass can provide alternative transport mechanisms whose role is often ignored. We show that neglecting the diffusion processes, or other similar transport mechanisms, can lead to a reduction of the range of dynamics found in the SOC like models and therefore a narrowing of the relevance of these models for physical systems. We show how diffusion can strongly modify the SOC dynamics while remaining a very subdominant transport mechanism. A dynamical transition is shown to take place in the system as the relative importance of diffusive transport increases beyond a critical threshold. The role of the avalanche-like transport events characteristic of the self-similar SOC state is then abruptly taken over by quasi-periodic constant-size edge-triggered events. As a result, the system loses its "Self Organized Critical" properties. The mechanism for this change will be explored and we show that the required diffusion for this to happen is remarkably small. These results while perhaps suggesting a reduction of the robustness of the SOC paradigm actually broaden the dynamics available though such simple models. The possible implications for relevant systems such as earthquake dynamics will be discussed.
DE: 3235 Persistence, memory, correlations, clustering (3265, 7857)
DE: 4425 Critical phenomena
DE: 4430 Complex systems
DE: 4475 Scaling: spatial and temporal (1872, 3270, 4277)
DE: 4480 Self-organized criticality
SC: Nonlinear Geophysics [NG]
MN: Fall Meeting 2005