Copyright 2005 Society of Photo-Optical Instrumentation Engineers. This paper was published in Noise in Complex Systems and Stochastic Dynamics III, edited by L. B. Kish, K. Lindenberg, and Z. Gingl, Proc. of SPIE Vol. 5845 (SPIE, Bellingham, WA, 2005) 12 - 26, and is made available as an electronic preprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.