LaPraDoR: Unsupervised Pretrained Dense Retriever for Zero-Shot Text Retrieval Canwen Xu author Daya Guo author Nan Duan author Julian McAuley author 2022-05 text Findings of the Association for Computational Linguistics: ACL 2022 Smaranda Muresan editor Preslav Nakov editor Aline Villavicencio editor Association for Computational Linguistics Dublin, Ireland conference publication xu-etal-2022-laprador 10.18653/v1/2022.findings-acl.281 https://aclanthology.org/2022.findings-acl.281/ 2022-05 3557 3569