Extensions of vector bundles and rationality of certain moduli spaces of   stable bundles
  In this paper, it is proved that certain stable rank-3 vector bundles can be written as extensions of line bundles and stable rank-2 bundles. As an application, we show the rationality of certain moduli spaces of stable rank-3 bundles over the projective plane P^2. 
Wei-ping Li, Zhenbo Qin