next up previous
Next: Application to hypermeander Up: Deterministic Brownian motion Previous: Mathematical background

Example: deterministic diffusion in R1

This theorem can be directly applied to the case of chaos-driven walk along a straight line, as recently described by Coullet and Emilsson [11]. This is Ising-Bloch wall dynamics in a modified Complex Ginzburg-Landau Equation:

  eqnarray133

for tex2html_wrap_inline876 and tex2html_wrap_inline878 .

At some parameter values, there are two stable equilibria tex2html_wrap_inline880 in the spatially homogeneous system tex2html_wrap_inline882 , and solutions are considered which asymptotically approach one equilibrium at tex2html_wrap_inline884 and the other at tex2html_wrap_inline886 . This equation is invariant under the group of translations along the x axis. Reduction by this group, in the same style as we did it for reaction-diffusion system (1) and Euclidean group tex2html_wrap_inline826 , yields the quotient system

  eqnarray141

for dynamic variables v and c, where

equation144

and tex2html_wrap_inline896 could be chosen, say tex2html_wrap_inline898 or tex2html_wrap_inline900 . X can be considered as the wall coordinate, then drift along the group is the wall motion, and is described simply by

equation149

Coullet and Emilsson [11] simulated the dynamics of the wall solutions and analyzed them in terms of the quantity M(t) defined as

equation154

which is invariant under the group, i.e. is a functional of the quotient system (13). At some parameter values, they have found that time-delay plots M(t) vs tex2html_wrap_inline908 showed pictures typical for chaotic attractors. Assuming that this implies invariant measure, ergodicity and decaying correlation functions, we can apply the Theorem, by identifying the semiflow generated by (13) with tex2html_wrap_inline840 of the Theorem, X with q and c with V. In accordance with the statement of the Theorem, in the case of even distribution of the velocity, which took place in a region of parameters, Coullet and Emilsson observed `diffusive' motion with a root mean squared displacement that scaled as tex2html_wrap_inline920 . In the case of non-even distribution which happened in between the `diffusive' parameter range, the root mean squared displacement scaled as t, which might correspond to the superposition of directed and Brownian motion.


next up previous
Next: Application to hypermeander Up: Deterministic Brownian motion Previous: Mathematical background

Vadim Biktashev
Tue Nov 25 16:48:21 GMT 1997