Shakuntla, M., S. Kalal, A. Lal, S. Bhatia, and J. Singh. “Availability Analysis of Polytube Industry When Two Sub-System Are Simultaneous Fail”. Bangladesh Journal of Scientific and Industrial Research, vol. 46, no. 4, Jan. 2012, pp. 475-80, doi:10.3329/bjsir.v46i4.9594.