This network of tight co-authorship is further revealed in a network analysis based on the University affiliation (Figure 6). Korea University (Yong Sik Ok) and Hongkong Polytechnic (Dan Tsang)  drive the group of authors in producing these highly cited papers. In particular Korea and Hong Kong Poltechnic becomes the center of papers mass producer. They supplied to King Abdullah Azizm Sejong University, Tsinghua University etc. University of Florida also has its own cluster.