Illustration of a co-authorship network.

<p>(a) <i>author-paper</i> network for three papers written by four authors; (b) corresponding co-authorship network; and (c) co-authorship network showing same network attributes for each author. <i>Au</i> stands for <i>Author</i>, <i>P</i> stands for <i>Paper</i> and <i>At</i> stands for network attribute (e.g., <i>degree centrality</i>) of authors. Although in this figure we consider two attributes (i.e., <i>At1</i> and <i>At2</i>) for illustration, we consider network attributes of <i>degree centrality</i>, <i>closeness centrality</i> and <i>betweenness centrality</i> of all authors for research analysis in this study.