Fig. 2From: Particulate matter and atherosclerosis: a bibliometric analysis of original research articles published in 1973–2014Collaborative relationship network of the top 50 researchers. The size of the nodes represents the number of papers. The size of the lines represents the close degree of co-authors. The shapes of the nodes represent different countries (circle represents the US, down-triangle represents Germany, box represents Canada, up-triangle represents Finland, and diamond represents UK)Back to article page