(a) The red particles have attached most recently to the cluster and are concentrated at the tips of the growing branches. By contrast, relatively few particles penetrate deeply into the "fjords." (b) The lines represent the successive equipotentials of random walker probability densities for a two-dimensional DLA cluster growing from a single line. Clearly the random walker probability declines precipitously as one progresses down a fjord, leading to very small growth probabilities at the bottom compared with the growing tips of the cluster. (Adapted from ref. 10, Mandelbrot and Evertsz.)

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© 2001 American Institute of Physics