ner_tags: O O O O O O O O O O B-Person I-Person O O O O O O B-Person O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Organization I-Organization B-Grant I-Grant I-Grant O B-Organization I-Organization I-Organization B-Organization O B-Organization I-Organization I-Organization I-Organization O B-Location O O B-Grant O O O O O O O O O O O O O O O O O O
tokens: This paper is dedicated to the memory of our co-author James Caswell who passed away January 14th 2015. James was a leading figure in maser astronomy for more than three decades and his work in this field represents a peerless legacy to future researchers. Funding assistance was provided in part by Sigma Xi Grants-in-Aid of research, the Deutscher Akademischer Austauschdienst (DAAD), and National Natural Science Foundation of China (Grant No. 11133008). The authors would like to thank the referee for their detailed analysis and comments in reviewing this paper.