[1] Huberman B A and Lukose R M 1997 Science 277 535

[2] Guimer\'a R, D\'\i az-Guilera A, Vega-Redondo F,
Cabrales A and Arenas A 2002 Phys. Rev. Lett. 89 248701

[3] Moreno Y, Pastor-Satorras R, Vazquez A and Vespignani A 2003
Europhys. Lett. 62 292

[4] Echenique P Gomez-Gardenes J and Moreno Y 2004 cond-mat/0412053

[5] Echenique P Gomez-Gardenes J and Moreno Y 2004 Phys.
Rev. E 70 056105

[6] Zhao L, Lai Y, Park K and Ye N 2005 Phys. Rev. E 71 026125

[7] Yin C, Wang B, Wang W, Zhou T and Yang H 2006 Phys. Lett. A
351 220

[8] Wang W, Wang B, Yin C, Xie Y and Zhou T 2006 Phys. Rev.
E 73 026111

[9] Liu Z, Ma W, Zhang H, Sun Y and Hui P 2006 Physica A
370 843

[10] Echenique P, Gomez-Gardenes J and Moreno Y 2004 Phys.
Rev. E 70 056105

[11] Echenique P, Gomez-Gardenes J and Moreno Y 2005
Europhys. Lett. 71 325

[12] Zhang H, Liu Z, Tang M and Hui P 2007 Phys. Lett. A
364 177

[13] Peng C, Buldyrev S V, Havlin S, Simons M, Stanley H E and
Goldberger A L 1994 Phys. Rev. E 49 1685

[14] Peng C, Havlin S, Stanley H E and Goldberger A L 1995
Chaos 5 82

[15] Liu Y, Gopikrishnan P, Cizeau P, Meyer M, Peng C and Stanley H E
1999 Phys. Rev. E 60 1390

[16] Yang H, Zhao F, Qi L and Hu B 2004 Phys. Rev. E
69 066104

[17] Chen Z, Hu K, Carpena P, Bernaola-Galvan P, Stanley H E and
Ivanov P 2005 Phys. Rev. E 71 011104

[18] Liu Z, Lai Y, Ye N and Dasgupta P 2002 Phys. Lett. A
303 337