This paper deals with inventory control in a class of M/G/1 queueing systems. At each point of time the system can be switched from one of two possible stages to another. The rate of arrival process and the service rate depend on the stage of the system. The cost structure imposed on the model...

A machine consists of two stochastically failing units. Failure of either of the units causes a failure of the machine and the failed unit has to be replaced immediately. Associated with the units are running costs which increase with the age of the unit because of increasing maintenance costs,...

In a previous paper [1] we have proved the optimality of a control limit policy for certain two-unit systems with running costs. Under such a policy when either of theunits fails we also replace the other unit if its age exceeds a predetermined control limit. In this work we develop a procedure...