9,746 research outputs found
25 Years of Self-Organized Criticality: Solar and Astrophysics
Shortly after the seminal paper {\sl "Self-Organized Criticality: An
explanation of 1/f noise"} by Bak, Tang, and Wiesenfeld (1987), the idea has
been applied to solar physics, in {\sl "Avalanches and the Distribution of
Solar Flares"} by Lu and Hamilton (1991). In the following years, an inspiring
cross-fertilization from complexity theory to solar and astrophysics took
place, where the SOC concept was initially applied to solar flares, stellar
flares, and magnetospheric substorms, and later extended to the radiation belt,
the heliosphere, lunar craters, the asteroid belt, the Saturn ring, pulsar
glitches, soft X-ray repeaters, blazars, black-hole objects, cosmic rays, and
boson clouds. The application of SOC concepts has been performed by numerical
cellular automaton simulations, by analytical calculations of statistical
(powerlaw-like) distributions based on physical scaling laws, and by
observational tests of theoretically predicted size distributions and waiting
time distributions. Attempts have been undertaken to import physical models
into the numerical SOC toy models, such as the discretization of
magneto-hydrodynamics (MHD) processes. The novel applications stimulated also
vigorous debates about the discrimination between SOC models, SOC-like, and
non-SOC processes, such as phase transitions, turbulence, random-walk
diffusion, percolation, branching processes, network theory, chaos theory,
fractality, multi-scale, and other complexity phenomena. We review SOC studies
from the last 25 years and highlight new trends, open questions, and future
challenges, as discussed during two recent ISSI workshops on this theme.Comment: 139 pages, 28 figures, Review based on ISSI workshops "Self-Organized
Criticality and Turbulence" (2012, 2013, Bern, Switzerland
Non Asymptotic Properties of Transport and Mixing
We study relative dispersion of passive scalar in non-ideal cases, i.e. in
situations in which asymptotic techniques cannot be applied; typically when the
characteristic length scale of the Eulerian velocity field is not much smaller
than the domain size. Of course, in such a situation usual asymptotic
quantities (the diffusion coefficients) do not give any relevant information
about the transport mechanisms. On the other hand, we shall show that the
Finite Size Lyapunov Exponent, originally introduced for the predictability
problem, appears to be rather powerful in approaching the non-asymptotic
transport properties. This technique is applied in a series of numerical
experiments in simple flows with chaotic behaviors, in experimental data
analysis of drifter and to study relative dispersion in fully developed
turbulence.Comment: 19 RevTeX pages + 8 figures included, submitted on Chaos special
issue on Transport and Mixin
A renormalisation approach to excitable reaction-diffusion waves in fractal media
Of fundamental importance to wave propagation in a wide range of physical phenomena is the structural geometry of the supporting medium. Recently, there have been several investigations on wave propagation in fractal media. We present here a renormalization approach to the study of reaction-diffusion (RD) wave propagation on finitely ramified fractal structures. In particular we will study a Rinzel-Keller (RK) type model, supporting travelling waves on a Sierpinski gasket (SG), lattice
A Review of Micro-Contact Physics for Microelectromechanical Systems (MEMS) Metal Contact Switches
Innovations in relevant micro-contact areas are highlighted, these include, design, contact resistance modeling, contact materials, performance and reliability. For each area the basic theory and relevant innovations are explored. A brief comparison of actuation methods is provided to show why electrostatic actuation is most commonly used by radio frequency microelectromechanical systems designers. An examination of the important characteristics of the contact interface such as modeling and material choice is discussed. Micro-contact resistance models based on plastic, elastic-plastic and elastic deformations are reviewed. Much of the modeling for metal contact micro-switches centers around contact area and surface roughness. Surface roughness and its effect on contact area is stressed when considering micro-contact resistance modeling. Finite element models and various approaches for describing surface roughness are compared. Different contact materials to include gold, gold alloys, carbon nanotubes, composite gold-carbon nanotubes, ruthenium, ruthenium oxide, as well as tungsten have been shown to enhance contact performance and reliability with distinct trade offs for each. Finally, a review of physical and electrical failure modes witnessed by researchers are detailed and examined
Nonlinear Hamiltonian dynamics of Lagrangian transport and mixing in the ocean
Methods of dynamical system's theory are used for numerical study of
transport and mixing of passive particles (water masses, temperature, salinity,
pollutants, etc.) in simple kinematic ocean models composed with the main
Eulerian coherent structures in a randomly fluctuating ocean -- a jet-like
current and an eddy. Advection of passive tracers in a periodically-driven flow
consisting of a background stream and an eddy (the model inspired by the
phenomenon of topographic eddies over mountains in the ocean and atmosphere) is
analyzed as an example of chaotic particle's scattering and transport. A
numerical analysis reveals a nonattracting chaotic invariant set that
determines scattering and trapping of particles from the incoming flow. It is
shown that both the trapping time for particles in the mixing region and the
number of times their trajectories wind around the vortex have hierarchical
fractal structure as functions of the initial particle's coordinates.
Scattering functions are singular on a Cantor set of initial conditions, and
this property should manifest itself by strong fluctuations of quantities
measured in experiments. The Lagrangian structures in our numerical experiments
are shown to be similar to those found in a recent laboratory dye experiment at
Woods Hole. Transport and mixing of passive particles is studied in the
kinematic model inspired by the interaction of a jet current (like the Gulf
Stream or the Kuroshio) with an eddy in a noisy environment. We demonstrate a
non-trivial phenomenon of noise-induced clustering of passive particles and
propose a method to find such clusters in numerical experiments. These clusters
are patches of advected particles which can move together in a random velocity
field for comparatively long time
Fractal-cluster theory and thermodynamic principles of the control and analysis for the self-organizing systems
The theory of resource distribution in self-organizing systems on the basis
of the fractal-cluster method has been presented. This theory consists of two
parts: determined and probable. The first part includes the static and dynamic
criteria, the fractal-cluster dynamic equations which are based on the
fractal-cluster correlations and Fibonacci's range characteristics. The second
part of the one includes the foundations of the probable characteristics of the
fractal-cluster system. This part includes the dynamic equations of the
probable evolution of these systems. By using the numerical researches of these
equations for the stationary case the random state field of the one in the
phase space of the , , criteria have been obtained. For the
socio-economical and biological systems this theory has been tested.Comment: 37 pages, 20 figures, 4 table
Review of Some Promising Fractional Physical Models
Fractional dynamics is a field of study in physics and mechanics
investigating the behavior of objects and systems that are characterized by
power-law non-locality, power-law long-term memory or fractal properties by
using integrations and differentiation of non-integer orders, i.e., by methods
of the fractional calculus. This paper is a review of physical models that look
very promising for future development of fractional dynamics. We suggest a
short introduction to fractional calculus as a theory of integration and
differentiation of non-integer order. Some applications of
integro-differentiations of fractional orders in physics are discussed. Models
of discrete systems with memory, lattice with long-range inter-particle
interaction, dynamics of fractal media are presented. Quantum analogs of
fractional derivatives and model of open nano-system systems with memory are
also discussed.Comment: 38 pages, LaTe
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