Negacyclic codes of length 4p^s over F_p^m + uF_p^m and their duals

For any odd prime p, negacyclic codes of length 4p^s over the finite commutative chain ring F_p^m + uF_p^m are investigated. The algebraic structures of such codes are classified and completely determined. As an application, the number of codewords and the dual of each negacyclic code are obtained. Simpler structure of cyclic codes of length 4p^s over F_p^m + uF_p^m is also noted. Among others, some self-dual negacyclic and cyclic codes of length 4p^s over F_p^m + uF_p^m are provided.