Pammolli, Fabio and Buldyrev, Sergey V. and Riccaboni, Massimo and Yamasaki, Kazuko and Fu, Dongfeng and Matia, Kaushik and Stanley, H. Eugene A generalized preferential attachment model for business firms growth rates: II. Mathematical treatment. The European Physical Journal B, 57 (2). pp. 131-138. ISSN 1434-6028 (2007)