Chen, Kehui
Zhang, Xiaoke
Petersen, Alexander
Müller, Hans-Georg
Funding for this research was provided by:
National Science Foundation (DMS-1228369)
National Science Foundation (DMS-1407852)
Article History
Received: 20 June 2015
Revised: 4 September 2015
Accepted: 30 October 2015
First Online: 20 November 2015