1. M Bianucci, R Manella, B J West and P Grigolini, Phys. Rev. E51, 3002 (1995)
2. V L Berdichevsky and M V Alberti, Phys. Rev. A44, 858 (1991)
3. V M Bannur, P K Kaw and J C Parikh, Phys. Rev. E55, 2525 (1997)
4. V M Bannur, Phys. Rev. E58, 407 (1998)
5. H H Rugh, Phys. Rev. Lett. 78, 772 (1997)