2018-09-102018-09-102008http://www.scopus.com/inward/record.url?eid=2-s2.0-47249141258&partnerID=MN8TOARShttp://scholars.lib.ntu.edu.tw/handle/123456789/340415Minimal open stringsjournal article10.1088/1126-6708/2008/06/029