Funding for this research was provided by:
National Science Foundation (DMS-1304999)
National Security Agency (H98230-14-1-0130)
Romanian Ministry of National Education (PN-II-ID-PCE-2012-4- 0156)
Deutsche Forschungsgemeinschaft (SFB 878)
Grants-in-Aid for Scientific Research (Kakenhi 15K04816)
Romanian Ministry of National Education (PN-III-P4-ID-PCE-2016-0030)
Article History
Received: 23 March 2017
Revised: 16 August 2018
First Online: 28 August 2018