Data-driven preventive maintenance for a heterogeneous machine portfolio

in Operations Research Letters (2023)

The Decay Vendor: Timing Medical Radioisotope Production to Meet a Fixed Delivery Schedule

E-print/Working paper (2022)

Over 85% of nuclear medicine procedures are conducted with Technetium-99m (Tc-99m), a decay product of Molybdenum-99 (Mo-99). Mo-99 has a half-life of 66.7 hours and is primarily produced by irradiating ... [more ▼]

Over 85% of nuclear medicine procedures are conducted with Technetium-99m (Tc-99m), a decay product of Molybdenum-99 (Mo-99). Mo-99 has a half-life of 66.7 hours and is primarily produced by irradiating uranium in a nuclear research reactor. Due to its continuous decay the alignment of the supply chain’s just-in-time processes are critical. We present a basic structure to model and analyze this unique type of perishable supply chain. We consider how to integrate a production timing decision with a fixed delivery schedule. The objective is to maximize the viable amount of Mo-99 that makes it to the delivery given a stochastic lead time and departure. We compare a naïve approach for determining a production time to a greedy heuristic and show significant improvement potential of 5% on average and up to 22% in our test bed. We also investigate how different delivery schedules allow more viable Mo-99 to reach market [less ▲]

A column-and-constraint generation algorithm for two-stage stochastic programming problems

in TOP (2021), 29

Projected Inventory Level Policies for Lost Sales Inventory Systems: Asymptotic Optimality in Two Regimes

E-print/Working paper (2021)

The stochastic maintenance location routing allocation problem for rolling stock

in International Journal of Production Economics (2020), 230

maintenance service logistics

in Operations Logistics and Supply Chain Management (2019)

Economies of scale in recoverable robust maintenance location routing for rolling stock

in Transportation Research. Part B, Methodological (2018), 117

We consider the problem of locating maintenance facilities in a railway setting. Different facility sizes can be chosen for each candidate location and for each size there is an associated annual facility ... [more ▼]

We consider the problem of locating maintenance facilities in a railway setting. Different facility sizes can be chosen for each candidate location and for each size there is an associated annual facility costs that can capture economies of scale in facility size. Because of the strategic nature of facility location, the opened facilities should be able to handle the current maintenance demand, but also the demand for any of the scenarios that can occur in the future. These scenarios capture changes such as changes to the line plan and the introduction of new rolling stock types. We allow recovery in the form of opening additional facilities, closing facilities, and increasing the facility size for each scenario. We provide a two-stage robust programming formulation. In the first-stage, we decide where to open what size of facility. In the second-stage, we solve a NP-hard maintenance location routing problem. We reformulate the problem as a mixed integer program that can be used to make an efficient column-and-constraint generation algorithm. To show that our algorithm works on practical sized instances, and to gain managerial insights, we perform a case study with instances from the Netherlands Railways. A counter intuitive insight is that economies of scale only play a limited role and that it is more important to reduce the transportation cost by building many small facilities, rather than a few large ones to profit from economies of scale. [less ▲]

The asymptotic hazard rate of sums of discrete random variables

in Statistics and Probability Letters (2017), 125

Repairable stocking and expediting in a fluctuating demand environment: Optimal policy and heuristics

in Operations Research (2016), 64(6), 1285-1301

Spare parts planning and control for maintenance operations

in Civil-Comp Proceedings (2014), 104