Aggregation growth in a gas of finite density: Velocity selection via fractal dimension of diffusion-limited aggregation

The structure and dynamics of an aggregation have been studied when the aggregate grows from a lattice gas with a nonzero gas density n₆. At low n₆ and for a short length scale up to, the structure of the aggregation is fractal and similar to the diffusion-limited aggregation (DLA). For a large length scale it is compact and has a nonzero asymptotic density. The steady growth rate V in d-dimensional space is inversely proportional to the characteristic length, and depends on the density as V^-1n₆^1/ (d-{D₅) }, with D₅ being the fractal dimension of DLA. Extensive Monte Carlo simulations in two dimensions confirm the above theoretical hypothesis of the velocity selection mechanism with D₅=1. 71. The interfacial width w is also found to be compatible with the expectation wn₆^-1/2 (d-{D₅) }. . AE