Issue
EPL
Volume 87, Number 2, July 2009
Article Number 20001
Number of page(s) 5
Section General
DOI http://dx.doi.org/10.1209/0295-5075/87/20001
Published online 16 July 2009
EPL, 87 (2009) 20001
DOI: 10.1209/0295-5075/87/20001

The harmonic measure of diffusion-limited aggregates including rare events

D. A. Adams1, L. M. Sander1, 2, E. Somfai3 and R. M. Ziff2, 4, 5

1   Department of Physics, University of Michigan - Ann Arbor, MI, 48109-1040, USA
2   Michigan Center for Theoretical Physics, University of Michigan - Ann Arbor, MI, 48109-1040, USA
3   Department of Physics and Centre for Complexity Science, University of Warwick - Coventry CV4 7AL, UK, EU
4   Center for the Study of Complex Systems, University of Michigan - Ann Arbor, MI, 48109-1040, USA
5   Department of Chemical Engineering, University of Michigan - Ann Arbor, MI, 48109-2136, USA

davidada@umich.edu

received 2 June 2009; accepted in final form by P. Ch. Ivanov on 29 June 2009; published July 2009
published online 16 July 2009

Abstract
We obtain the harmonic measure of diffusion-limited aggregate (DLA) clusters using a biased random-walk sampling technique which allows us to measure probabilities of random walkers hitting sections of clusters with unprecedented accuracy; our results include probabilities as small as 10- 80. We find the multifractal D(q) spectrum including regions of small and negative q. Our algorithm allows us to obtain the harmonic measure for clusters more than an order of magnitude larger than those achieved using the method of iterative conformal maps, which is the previous best method. We find a phase transition in the singularity spectrum $f (\alpha)$ at $\alpha$ $\approx$ 14 and also find a minimum q of D(q), qmin = 0.9 $\pm$ 0.05.

PACS
05.45.Df - Fractals.
61.43.Hv - Fractals; macroscopic aggregates (including diffusion-limited aggregates).
64.60.al - Fractal and multifractal systems.

© EPLA 2009