On the Jordan decomposition of tensored matrices of Jordan canonical   forms
  Let k be an algebraically closed field of characteristic p \ge 0. We shall consider the problem of finding out a Jordan canonical form of J(\alpha,s) \otimes_{k} J(\beta,t), where J(\alpha,s) means the Jordan block with eigenvalue \alpha \in k and size s. 
Kei-ichiro Iima, Ryo Iwamatsu