@techreport{oai:tsukuba.repo.nii.ac.jp:00022888,
 author = {Sumita, Ushio and Namikawa, Atsushi},
 month = {Nov},
 title = {Danger of Exclusive Reliance on Ergodic Analysis for a Class of Preventive Maintenance Policies : Dynamic Semi-Markov Process Approach},
 year = {2008}
}