The middle layer represents the research articles (circles) selected for the study. Upper and lower layers represent authors of the articles (triangles) and bibliographic references cited in the articles (diamonds), respectively. Linking the three layers together gives rise to two bipartite networks. The architecture of the authorship network (upper network) was analysed to assess the extent to which the scientists collaborated. The architecture of the citation network (lower network) was analysed to quantify to which extent the knowledge circulates among them. In this example, two distinct collaborative groups (yellow, dotted lines) establish their research from different sets of cited literature (blue, continuous lines). Authors having published once (j) and their corresponding articles (i) were removed from the authorship network. Likewise references that were cited only once (j') and the corresponding citing articles (i') were removed from the citation network. Articles i and i' were considered to be articles “isolated” from the authorship and citation networks, respectively.