Baruch Halachmi, William R. Franta. A closed, cyclic, two-stage multiprogrammed system model and its diffusion approximation solution. In John H. Howard Jr., Philip J. Kiviat, James D. Connell, Stuart Trask, J. William Atwood, editors, Proceedings of the 1974 ACM SIGMETRICS conference on Measurement and evaluation, SIGMETRICS 1974, USA, 1974. pages 54-64, ACM, 1974. [doi]