We use antagonistic stochastic games and fluctuation analysis to examine a single-server queue with bulk input and secondary work during server's multiple vacations. When the buffer contents become exhausted the server leaves the system to perform some diagnostic service of a minimum ofLjobs clustered in packets of random sizes (event A). The server is not supposed to stay longer thanTunits of time (event B). The server returns to the system when A or B occurs, whichever comes first. On the other hand, he may not break service of a packet in a middle even if A or B occurs. Furthermore, the server waits for batches of customers to arrive if upon his return the queue is still empty. We obtain a compact and explicit form functional for the queueing process in equilibrium.

We use semi-regenerative, fluctuations methods, and sequential games to examine a queueing system with server performing a secondary maintenance work. When the buffer becomes empty, the server leaves the system to service packets of jobs at a maintenance facility where his time there is restricted by T (a random time). He returns to the system when his sojourn time expires and if the last packet is fully processed. If the buffer contents is below N , the server departs from the system again to continue with maintenance; this time rendering just one packet at a time until the buffer is replenished. We obtain compact and explicit functionals for the queueing process in equilibrium for both discrete and continuous time parameter processes.

We use optimal control theory to determine the optimal manufacturing, remanufacturing, and disposal rates in a closed-loop supply chain. The returned items are of different quality levels. The firm grades the returned items according to their quality. Each class of returned items is remanufactured and stocked separately. Also, all items are subject to deterioration and the deterioration rate depends on the class. Finally, each class of items is sold to a different segment of customers. An illustrative example is presented along with a sensitivity analysis on some of the system parameters.

This work deals with two models of a single machine subject to breakdowns. The first model is a binary-state model while the second one is a multi-state model. Breakdowns are followed by repairs. The systems under study are of the tracking type. We use nonlinear model predictive control to determine the optimal repair rates that keep the variables as close as possible to their target. Numerical illustrations with sensitivity analysis are used to assess the effect of the system parameters on the optimal solution.

This study explores individual differences and the effects of these differences on usage of a statistics website, especially in combination with new platforms, such as mobile devices (i.e. smart phones and iPods). This study looks to assist in the improvement of a website for both computer and mobile device usage, and propose suggestions for similar websites.