20,638 research outputs found
Simulations of Noise in Disordered Systems
We use particle dynamics simulations to probe the correlations between noise
and dynamics in a variety of disordered systems, including superconducting
vortices, 2D electron liquid crystals, colloids, domain walls, and granular
media. The noise measurements offer an experimentally accessible link to the
microscopic dynamics, such as plastic versus elastic flow during transport, and
can provide a signature of dynamical reordering transitions in the system. We
consider broad and narrow band noise in transport systems, as well as the
fluctuations of dislocation density in a system near the melting transition.Comment: 12 pages, 9 postscript figures, requires spie.cls. SPIE Conference on
Fluctuations and Noise 2003, invited contributio
Disordering Transitions and Peak Effect in Polydisperse Particle Systems
We show numerically that in a binary system of Yukawa particles, a dispersity
driven disordering transition occurs. In the presence of quenched disorder this
disordering transition coincides with a marked increase in the depinning
threshold, known as a peak effect. We find that the addition of poorly pinned
particles can increase the overall pinning in the sample by increasing the
amount of topological disorder present. If the quenched disorder is strong
enough to create a significant amount of topological disorder in the
monodisperse system, addition of a poorly pinned species generates further
disorder but does not produce a peak in the depinning force. Our results
indicate that for binary mixtures, optimal pinning occurs for topological
defect fraction densities of 0.2 to 0.25. For defect densities below this
range, the system retains orientational order. We determine the effect of the
pinning density, strength, and radius on the depinning peak and find that the
peak effect is more pronounced in weakly pinning systems.Comment: 8 pages, 8 postscript figures. Version to appear in PR
Fluctuations, Jamming, and Yielding for a Driven Probe Particle in Disordered Disk Assemblies
Using numerical simulations we examine the velocity fluctuations of a probe
particle driven with constant force through a two-dimensional disordered
assembly of disks which has a well-defined jamming point J at a density of
\phi_J=0.843. As \phi increases toward \phi_J, the average velocity of the
probe particle decreases and the velocity fluctuations show an increasingly
intermittent or avalanchelike behavior. When the system is within a few percent
of the jamming density, the velocity distributions are exponential, while when
the system is less than a percent away from jamming, the velocity distributions
have a non-exponential or power law character. The velocity power spectra
exhibit a crossover from a Lorentzian form to a 1/f shape near jamming. We
extract a correlation exponent \nu which is in good agreement with recent shear
simulations. For \phi > \phi_J, there is a critical threshold force F_c that
must be applied for the probe particle to move through the sample which
increases with increasing \phi. The onset of the probe motion above \phi_J
occurs via a local yielding of the particles around the probe particle which we
term a local shear banding effect.Comment: 11 pages, 20 postscript figure
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