Minimizing the expected variation of waiting times in stochastic flow shop

We consider the problem of scheduling n jobs on a 2-machine flow shop. Under the assumption that the processing times of a job on different machines are identically distributed random variables, several properties of optimal sequences for minimizing the expected variation of waiting times on each machine are established when jobs can be stochastically ordered. We also show that, if the machines are subject to stochastic breakdowns, under appropriate conditions, the properties also hold