554 research outputs found
Crossover from Intermittent to Continuum Dynamics for Locally Driven Colloids
We simulate a colloid with charge q_d driven through a disordered assembly of
interacting colloids with charge q and show that, for q_d \approx q, the
velocity-force relation is nonlinear and the velocity fluctuations of the
driven particle are highly intermittent with a 1/f characteristic. When q_d >>
q, the average velocity ddrops, the velocity force relation becomes linear, and
the velocity fluctuations are Gaussian. We discuss the results in terms of a
crossover from strongly intermittent heterogeneous dynamics to continuum
dynamics. We also make several predictions for the transient response in the
different regimes.Comment: 4 pages, 5 postscript figures. Version to appear in Physical Review
Letter
Shear Banding and Spatiotemporal Oscillations in Vortex Matter in Nanostructured Superconductors
We propose a simple nanostructured pinning array geometry where a rich
variety of complex vortex shear banding phenomena can be realized. A single row
of pinning sites is removed from a square pinning array. Shear banding effects
arise when vortex motion in the pin-free channel nucleates motion of vortices
in the surrounding pinned regions, creating discrete steps in the vortex
velocity profile away from the channel. Near the global depinning transition,
the width of the band of moving vortices undergoes oscillations or fluctuations
that can span the entire system. We use simulations to show that these effects
should be observable in the transport properties of the system. Similar large
oscillations and shear banding effects are known to occur for sheared complex
fluids in which different dynamical phases coexist.Comment: 4 pages, 4 postscript figure
Noise at the Wigner Glass Transition
Using a simple model for interacting electrons in two dimensions with random
disorder, we show that a crossover from a Wigner liquid to a Wigner glass
occurs as a function of charge density. The noise power increases strongly at
the transition and the characteristics of the 1/f^alpha noise change. When the
temperature is increased, the noise power decreases. We compare these results
with recent noise measurements in systems with two-dimensional metal-insulator
transitions.Comment: 4 pages, 5 postscript figure
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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