1. Recent reviews are: A. Blumen, J. Klafter and G. Zumofen, in Optical Spectroscopy of Glasses, edited by I. Zschokke D. Reidel Pub. Co., 1986); V. Kuzovkov and E. Kotomin, Rep. Prog. Phys. 51, 1479 (1988);
2. A. S. Mikhailov, Phys. Rep. 184, 307 (1989);
3. D. ben-Avraham, M. A. Burschka and Ch. R. Doering, J. Stat. Phys. 60, 695 (1990);
4. K. Lindenberg, B. J. West and R. Kopelman, in it Noise and Chaos in Nonlinear Dynamical Systems, edited by F. Moss, L. A. Lugiato and W. Schleich, (Cambridge U. P., Cambridge, 1990).
5. L. W. Anacker and R. Kopelman, Phys. Rev. Lett. 58, 289 (1987).