7Mark S.Granovetter,The Strength of Weak Ties,The American Journal of Sociology,Vol.78,No.6(May,1973), pp.1360-1380.
8JP Onnela,etc,structure and tie strengths in mobile communication networks,Proceedings of the National Academy of Sciences of the United States of America, http://www.hks.harvard. edu/davidlazer/files/papers/Lazer PNAS_2007 .pdf.