Reliability study of series and parallel systems of heterogeneous   component lifetimes under proportional odds model
  In this paper, we investigate various stochastic orderings for series and parallel systems with independent and heterogeneous components having lifetimes following the proportional odds model. We also investigate comparisons between system with heterogeneous components and that with homogeneous components. This paper also studies relative ageing orders for two systems in the framework of components having lifetimes following the proportional odds model. 
Pradip Kundu, Nil Kamal Hazra and Asok K. Nanda
math.ST stat.TH