Random walk in an eddy and tube formation from fine particles.

Tubular shape formation of an ensemble of ultrafine particles, captured by microscopic eddies in a fluid or gaseous medium, is investigated. In the circulation flow of the eddy, the small particles are driven by the deterministic hydrodynamical forces and the random forces of Brownian motion. The conditions for dynamically/statistically stable tube formation and the resulting tube parameters are obtained by analytic calculations and computer simulations, respectively. The model yields striking similarities to the characteristics of nanotube formation observed in turbulent media such as the carbon arc, and throws some light on tubular formation observed in fluid media. (c) 2001 American Institute of Physics.