220 research outputs found
Long Range Hops and the Pair Annihilation Reaction A+A->0: Renormalization Group and Simulation
A simple example of a non-equilibrium system for which fluctuations are
important is a system of particles which diffuse and may annihilate in pairs on
contact. The renormalization group can be used to calculate the time dependence
of the density of particles, and provides both an exact value for the exponent
governing the decay of particles and an epsilon-expansion for the amplitude of
this power law. When the diffusion is anomalous, as when the particles perform
Levy flights, the critical dimension depends continuously on the control
parameter for the Levy distribution. The epsilon-expansion can then become an
expansion in a small parameter. We present a renormalization group calculation
and compare these results with those of a simulation.Comment: As-published version; two significant errors fixed, two references
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Sand stirred by chaotic advection
We study the spatial structure of a granular material, N particles subject to
inelastic mutual collisions, when it is stirred by a bidimensional smooth
chaotic flow. A simple dynamical model is introduced where four different time
scales are explicitly considered: i) the Stokes time, accounting for the
inertia of the particles, ii) the mean collision time among the grains, iii)
the typical time scale of the flow, and iv) the inverse of the Lyapunov
exponent of the chaotic flow, which gives a typical time for the separation of
two initially close parcels of fluid. Depending on the relative values of these
different times a complex scenario appears for the long-time steady spatial
distribution of particles, where clusters of particles may or not appear.Comment: 4 pages, 3 figure
The iron limitation mosaic in the California Current System: Factors governing Fe availability in the shelf/near-shelf region
The California Current System is a productive eastern boundary region off the coasts of Washington, Oregon, and California. There is strong seasonality to the region, with high levels of rainfall and river input to the coastal ocean during the winter season, and coastal and Ekman upwelling during the spring and summer. Iron (Fe) input to the coastal ocean during the winter months can be stored in the continental shelf mud belts and then be delivered to the surface ocean by upwelling in the spring and summer. There have been a number of studies providing strong evidence of Fe-limitation of diatom growth occurring in regions of the California Current System off of California, and the occurrence of Fe-limitation has been linked with narrow continental shelf mud belt width and low river input. We provide evidence for potential Fe-limitation of diatoms off the southern coast of Oregon in July 2014, just off the shelf break near Cape Blanco in a region with moderate shelf width and river input. Since eastern boundary regions account for a disproportionally large amount of global primary production, this observation of potential Fe-limitation in an unexpected near-shore region of the California Current System has implications for global models of primary productivity. In order to re-evaluate the factors impacting Fe availability, we utilize satellite imagery to compare with historical datasets, and show that unexpected levels of Fe can often be explained by eddies, plumes of upwelled water moving offshore, or lack of recent upwelling
Fractional Langevin equation
We investigate fractional Brownian motion with a microscopic random-matrix
model and introduce a fractional Langevin equation. We use the latter to study
both sub- and superdiffusion of a free particle coupled to a fractal heat bath.
We further compare fractional Brownian motion with the fractal time process.
The respective mean-square displacements of these two forms of anomalous
diffusion exhibit the same power-law behavior. Here we show that their lowest
moments are actually all identical, except the second moment of the velocity.
This provides a simple criterion which enables to distinguish these two
non-Markovian processes.Comment: 4 page
Classical Infinite-Range-Interaction Heisenberg Ferromagnetic Model: Metastability and Sensitivity to Initial Conditions
A N-sized inertial classical Heisenberg ferromagnet, which consists in a
modification of the well-known standard model, where the spins are replaced by
classical rotators, is studied in the limit of infinite-range interactions. The
usual canonical-ensemble mean-field solution of the inertial classical
-vector ferromagnet (for which recovers the particular Heisenberg
model considered herein) is briefly reviewed, showing the well-known
second-order phase transition. This Heisenberg model is studied numerically
within the microcanonical ensemble, through molecular dynamics.Comment: 18 pages text, and 7 EPS figure
Exponential Ergodicity of stochastic Burgers equations driven by -stable processes
In this work, we prove the strong Feller property and the exponential
ergodicity of stochastic Burgers equations driven by -subordinated
cylindrical Brownian motions with . To prove the results, we
truncate the nonlinearity and use the derivative formula for SDEs driven by
-stable noises established in Zhang (arXiv:1204.2630v2).Comment: 17p
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