Sparse, Dense, and Attentional Representations for Text Retrieval Yi Luan author Jacob Eisenstein author Kristina Toutanova author Michael Collins author 2021 text journal article Transactions of the Association for Computational Linguistics continuing MIT Press Cambridge, MA periodical academic journal luan-etal-2021-sparse 10.1162/tacl_a_00369 https://aclanthology.org/2021.tacl-1.20/ 2021 9 329 345