Synchronous Bidirectional Neural Machine Translation Long Zhou author Jiajun Zhang author Chengqing Zong author 2019 text journal article Transactions of the Association for Computational Linguistics continuing MIT Press Cambridge, MA periodical academic journal zhou-etal-2019-synchronous 10.1162/tacl_a_00256 https://aclanthology.org/Q19-1006/ 2019 7 91 105