Free Boson Representation of $q$-Vertex Operators and their Correlation   Functions
  A bosonization scheme of the $q$-vertex operators of $\uqa$ for arbitrary level is obtained. They act as intertwiners among the highest weight modules constructed in a bosonic Fock space. An integral formula is proposed for $N$-point functions and explicit calculation for two-point function is presented. 
Akishi Kato, Yas-Hiro Quano and Jun'ichi Shiraishi