Browsing by Subject "service level"

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Open Access
A hybrid inventory control policy for medical supplies in hospitals
(2010) Akın, Gökçe
In this thesis, we consider the inventory control problem of medical supplies that arises in a particular hospital environment. The items are stored in nursing stations from where they are retrieved by the nurses and used for the needs of in-patients or out-patients. The nursing stations are replenished from a central warehouse. Items are moved between the hospital’s central warehouse and the nursing stations by a capacitated porter cart. In the representative nursing station that we analyze, the need for the medical supplies by the in-patients can arise at any time during day or night. It is possible to replenish the nursing stations during the day time on a continuous scale; however, this is not possible after-hours because the warehouse operates only during regular working hours. For this particular setting, we propose a hybrid inventory control policy which consists of a continuous review joint replenishment policy to manage the day time demand and a periodic review policy to manage the night time demand. The prior performance measure is set to satisfy the target service levels in the nursing stations. For a special case of the problem with a single item, we develop exact expressions to estimate the policy parameters. For the multi-item case, we analyze the impact of the policy parameters on the service level targets by simulating a representative system under different scenarios. Finally, we analyze a sample data collected from a nursing station and prescribe methods to determine the policy parameters
Open Access
Robust airline scheduling with controllable cruise times and chance constraints
(2012) Duran, Aslıgül Serasu
This is a study on robust airline scheduling where flight block times are considered in two parts as cruise time and non-cruise time. Cruise times are controllable and non-cruise times are random variables. Cruise time controllability is used together with idle time insertion to handle uncertainty to guarantee passenger connection service levels while ensuring minimum costs. The nonlinearity of these cost functions are handled by representing them via second order conic inequalities. The uncertainty in non-cruise times are modeled through chance constraints on passenger connection service levels, which are expressed using second order conic inequalities using the closed form equations. Congestion levels of origin and destination airports are used to decide variability for each flight. Computational study shows exact solutions can be obtained by commercial solvers in seconds for a single hub schedule and in minutes for a 4-hub daily schedule of a major US carrie