Quantum dynamical semigroups and non-decomposable positive maps
  We study dynamical semigroups of positive, but not completely positive maps on finite-dimensional bipartite systems and analyze properties of their generators in relation to non-decomposability and bound-entanglement. An example of non-decomposable semigroup leading to a 4x4-dimensional bound-entangled density matrix is explicitly obtained. 
F. Benatti, R. Floreanini, M. Piani