Before revision:  It can be regarded as a generalization of the one used by Steffen Liepelt and Reinhard Lipowsky (PRL 98, 258102 (2007)) . The method used in this research is similar as the one used by Michael E.
After revision:  It can be regarded as a generalization of the recently work of Liepelt and Lipowsky (PRL 98, 258102 (2007)) . The method used in this research is similar as the one used by Michael E.