http://repub.eur.nl/res/aut/26109/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/37193/ 2012-09-07T00:00:00Z The Orienteering Problem (OP) is a generalization of the well-known traveling salesman problem and has many interesting applications in logistics, tourism and defense. To reflect real-life situations, we focus on an uncertain variant of the OP. Two main approaches that deal with optimization under uncertainty are stochastic programming and robust optimization. We will explore the potentialities and bottlenecks of these two approaches applied to the uncertain OP. We will compare the known robust approach for the uncertain OP (the robust orienteering problem) to the new stochastic programming counterpart (the two-stage orienteering problem). The application of both approaches will be explored in terms of their suitability in practice. http://repub.eur.nl/res/pub/22802/ 2011-02-25T00:00:00Z Unmanned Areal Vehicles (UAVs) can provide significant contributions to information gathering in military missions. UAVs can be used to capture both full motion video and still imagery of specific target locations within the area of interest. In order to improve the effectiveness of a reconnaissance mission, it is important to visit the largest number of interesting target locations possible, taking into consideration operational constraints related to fuel usage between target locations, weather conditions and endurance of the UAV. We model this planning problem as the well-known orienteering problem, which is a generalization of the traveling salesman problem. Given the uncertainty in the military operational environment, robust planning solutions are required. As such, our model takes into account uncertainty in the fuel usage between targets (for instance due to weather conditions) as well as uncertainty in the importance of visiting specific target locations. We report results using different uncertainty sets that specify the degree of uncertainty against which any feasible solution will be protected. We also compare the probability that a solution is feasible for the robust solution on one hand and the solution found with average fuel usage and expected value of information on the other. In doing so, we show how the sustainability of a UAV mission can be significantly improved. http://repub.eur.nl/res/pub/21241/ 2010-11-01T00:00:00Z Scheduling surgical patients is one of the complex organizational tasks hospitals face daily. Master surgical scheduling is one way to optimize utilization of scarce resources and to create a more predictable outflow from the operating room towards subsequent hospital departments. The paper addresses two aims. First, we investigate the effect of the length of the planning horizon and other planning parameters in a master surgical scheduling approach on patients ́ waiting time, schedule stability and hospital efficiency. Second, the master surgical scheduling approach is compared with a standard operating room planning approach on levelled bed occupancy. The assignment of patients to a master surgical schedule is carefully described. Using real case data from a regional hospital in the Netherlands a simulation study is performed. The approach is applicable to any other hospital. Results show that only the planning horizon has substantial influence on outcome parameters waiting time, schedule stability and hospital efficiency. We found that increasing the planning horizon increases patients’ waiting time on the one hand, but also increases schedule stability and hospital efficiency on the other hand. Regarding our second aim, we found that using an MSS substantially decreases variability in bed occupancy levels.