The paper developed a dynamic network model to capture the director-company network involving the leading Irish companies on the Irish stock exchange.
The authors were particularly interested in the process of so-called "company interlocks", where a company director may sit on multiple boards of directors. The paper showed that the level of interlocking increased up until the financial crash and has more or less stayed at the same level ever since.

More information can be found here:

http://www.ucd.ie/newsandopinion/news/2016/june/02/impendingfinancialstabilitysignaledbyriseinsamedirectors/

Full paper is available here:

http://www.pnas.org/content/early/2016/05/25/1606295113.full.pdf