Funding for this research was provided by:
the Project of Gansu Province for Industrial and Information Development (23051358)
Gansu Province for Guiding Scientific and Technological Innovation and Development (2018ZX-05)
National Natural Science Foundation of China (61603420)
Received: 15 February 2019
Accepted: 15 May 2019
First Online: 10 June 2019
: The authors declare that they have no competing interests.