Optimal clustering of frequency-constrained maintenance jobs with shared set-ups

Since maintenance jobs often require one or more set-up activities, joint execution or clustering of maintenance jobs is a powerful instrument to reduce shut-down costs. We consider a clustering problem for frequency-constrained maintenance jobs, i.e. maintenance jobs that must be carried out with a prescribed (or higher) frequency. For the clustering of maintenance jobs with identical, so-called common set-ups, several strong dominance rules are provided. These dominance rules are used in an efficient dynamic programming algorithm which solves the problem in polynomial time. For the clustering of maintenance jobs with partially identical, so-called shared set-ups, similar but less strong dominance rules are available. Nevertheless, a surprisingly well-performing greedy heuristic and a branch and bound procedure have been developed to solve this problem. For randomly generated test problems with 10 set-ups and 30 maintenance jobs, the heuristic was optimal in 47 out of 100 test problems, with an average deviation of 0.24% from the optimal solution. In addition, the branch and bound method found an optimal solution in only a few seconds computation time on average

Agent-based transportation planning compared with scheduling heuristics

Here we consider the problem of dynamically assigning vehicles to transportation orders that have di¤erent time windows and should be handled in real time. We introduce a new agent-based system for the planning and scheduling of these transportation networks. Intelligent vehicle agents schedule their own routes. They interact with job agents, who strive for minimum transportation costs, using a Vickrey auction for each incoming order. We use simulation to compare the on-time delivery percentage and the vehicle utilization of an agent-based planning system to a traditional system based on OR heuristics (look-ahead rules, serial scheduling). Numerical experiments show that a properly designed multi-agent system may perform as good as or even better than traditional methods

Model based decision support for planning of road maintenance

In this article we describe a Decision Support Model, based on Operational Research methods, for the multi-period planning of maintenance of bituminous pavements. This model is a tool for the road manager to assist in generating an optimal maintenance plan for a road. Optimal means: minimising the Net Present Value of maintenance costs, while the plan is acceptable in terms of technical admissibility, resulting quality, etc. Global restrictions such as budget restrictions can also be imposed.\ud \ud Adequate grouping of maintenance activities in view of quantity discounts is an important aspect of our model. Our approach is to reduce the complexity of the optimisation by hierarchical structuring in four levels. In the lowest two levels maintenance per lane sector is considered, first with an unbounded planning horizon and next with a bounded planning horizon and time-windows for maintenance. The grouping of maintenance activities for a specific road is the topic of the third level. At the fourth level, which we will not consider in this article, the problem of optimal assignment of the available maintenance budgets over a set of roads or road sections takes place. Here, some results are presented to demonstrate the effects of grouping and to show that this hierarchical approach gives rise to improvements compared with previous work

Comparison of agent-based scheduling to look-ahead heuristics for real-time transportation problems

We consider the real-time scheduling of full truckload transportation orders with time windows that arrive during schedule execution. Because a fast scheduling method is required, look-ahead heuristics are traditionally used to solve these kinds of problems. As an alternative, we introduce an agent-based approach where intelligent vehicle agents schedule their own routes. They interact with job agents, who strive for minimum transportation costs, using a Vickrey auction for each incoming order. This approach offers several advantages: it is fast, requires relatively little information and facilitates easy schedule adjustments in reaction to information updates. We compare the agent-based approach to more traditional hierarchical heuristics in an extensive simulation experiment. We find that a properly designed multiagent approach performs as good as or even better than traditional methods. Particularly, the multi-agent approach yields less empty miles and a more stable service level

Reinforcement learning for Order Acceptance on a shared resource

Order acceptance (OA) is one of the main functions in business control. Basically, OA involves for each order a reject/accept decision. Always accepting an order when capacity is available could disable the system to accept more convenient orders in the future with opportunity losses as a consequence. Another important aspect is the availability of information to the decision-maker. We use the stochastic modeling approach, Markov decision theory and learning methods from artificial intelligence to find decision policies, even under uncertain information. Reinforcement learning (RL) is a quite new approach in OA. It is capable of learning both the decision policy and incomplete information, simultaneously. It is shown here that RL works well compared with heuristics. Finding good heuristics in a complex situation is a delicate art. It is demonstrated that a RL trained agent can be used to support the detection of good heuristics

Trends in kwaliteitsmanagement in de gezondheidszorg: breder, van intern naar extern en op weg naar houdbaarheid...

In de jaren tachtig van de vorige eeuw ontstond expliciet belangstelling voor de kwaliteit van de gezondheidszorg in het licht van een enorme en tot dan toe verwelkomde kostenexplosie in de gezondheidszorg. Vanwege de grote kostenstijging ten opzichte van het bruto nationaal product werden toenemend vragen gesteld bij de toegevoegde waarde voor de maatschappij. Tevens bleek uit met name het werk van Wennberg en anderen, dat er grote verschillen in medische consumptie tussen regio’s en landen bestonden, zonder dat dit een relatie had met gemeten behandelresultaat of gemiddelde levensduur. In een aantal stappen – soms worden die ook als generaties aangeduid – is vervolgens de weg van kwaliteitsmanagement ingeslagen

Polarization properties of real aluminum mirrors; I. Influence of the aluminum oxide layer

In polarimetry it is important to characterize the polarization properties of the instrument itself to disentangle real astrophysical signals from instrumental effects. This article deals with the accurate measurement and modeling of the polarization properties of real aluminum mirrors, as used in astronomical telescopes. Main goals are the characterization of the aluminum oxide layer thickness at different times after evaporation and its influence on the polarization properties of the mirror. The full polarization properties of an aluminum mirror are measured with Mueller matrix ellipsometry at different incidence angles and wavelengths. The best fit of theoretical Mueller matrices to all measurements simultaneously is obtained by taking into account a model of bulk aluminum with a thin aluminum oxide film on top of it. Full Mueller matrix measurements of a mirror are obtained with an absolute accuracy of ~1% after calibration. The determined layer thicknesses indicate logarithmic growth in the first few hours after evaporation, but it remains stable at a value of 4.12+/-0.08 nm on the long term. Although the aluminum oxide layer is established to be thin, it is necessary to consider it to accurately describe the mirror's polarization properties.Comment: accepted for publication in PAS

Wie vecht er mee tegen de bierkaai?

Het Antoni van Leeuwenhoek onderging in de laatste twaalf maanden zes inspecties van de overheid, zes visitaties van medisch specialistische opleidingen en vier kwaliteitsaudits waaronder voor hygiëne en stamceltransplantaties.\ud \ud Voor alle klinische trials – waar zo'n 25 procent van onze nieuwe patiënten aan mee doet – worden nauwgezet alle bijwerkingen bijgehouden. Er moesten meer dan honderd extra interne registratiechecks worden gedaan om de Nederlandse Zorgautoriteit, accountant en verzekeraars gerust te stellen over onze interne administratie en daaruit voortkomende facturen. Het jaar ervoor had ons instituut één van de laagste scores van het aantal geconstateerde afwijkingen in de Nederlandse ziekenhuizen.\ud \ud Uit preventieve overwegingen en ten behoeve van dezelfde instanties werden ons vorig jaar rond de vijftig interne audits opgelegd. Voor de Dutch Institute for Clinical Auditing wordt een tiental kwaliteitsregistraties bijgehouden en voor ons veiligheidssysteem zijn er minstens tien interne projectregistraties. Voor 2016 staat de teller van de interne planning alweer op meer dan zestig audits. Veel is nuttig, maar een aantal zouden we niet zelf verzonnen hebben, en… ik neem niet aan dat iemand denkt dat de raad van bestuur al deze scores zelf invult