bow tie structure
http://plosone.org/article/info:doi/10.1371/journal.pone.0010137#article1.body1.sec1.p5
Bow tie structures, where a network can be divided into four main regions (a strongly connected component, links in, links out and other components and tendrils) of more or less equal size, are commonly found in biological networks (see [56]). Whilst, prior to analysis, we do not know the proportions of each part of the graph, the graph is directed and does include cycles as well as disjoint sections. This implies that it is reasonable to expect to see the basic bow tie structure of a central cyclic component, in components, out components and smaller disjoint clusters in this graph. In fact, all four components were successfully extracted from this graph.
