Publication list  Call centers  Health care  Monotonicity  other  all PhD students Call center book Suggested reading Alpinism Art ger.koole@vu.nl ger@gerkoole.com +31624922626 address

Submitted papers: Call center routing policy using call waiting and agent idle times (with Wyean Chan and Pierre L'Ecuyer). Performance indicators for call centers with impatience (with Oualid Jouini and Alex Roubos). Flexible staffing for call centers with non-stationary arrival rates (with Alex Roubos and Sandjai Bhulai). Evaluating extraordinarily large requests in a revenue management network (with Alwin Haensel). Capacity management for a diagnostic medical facility (with Arnoud de Boer, Rob van der Mei and Bert Zwart). Optimization of overflow policies in call centers (with Bo Nielsen and Thomas Nielsen). Waiting time dependent multi-server priority queues (with Bo Nielsen and Thomas Nielsen). Bed reservation, earmarking and merging of clinical wards (with René Bekker and Dennis Roubos). Fairness in the aircraft landing problem (with Maarten Soomer). Waiting times of scheduled patients in the presence of emergency requests (with Dieter Fiems and Philippe Nain). Redefining the service level in call centers. Refereed papers: Optimal outpatient appointment scheduling with emergency arrivals and general service times (with Paulien Koeleman). To appear in IIE Transactions on Healthcare Systems Engineering, 2012. Service level variability of inbound call centers (with Alex Roubos and Raik Stolletz). To appear in Manufacturing & Service Operations Management, 2012. Staffing a call center with uncertain non-stationary arrival rate and flexibility (with Shuangqing Liao, Christian van Delft and Oualid Jouini). To appear in OR Spectrum, 2011 (published online 23 May 2010). Estimating unconstrained customer choice set demand: A case study on airline reservation data (with Alwin Haensel and Jeroen Erdman). Journal of Choice Modelling 4(3):75-87, 2011. A note on profit maximization and monotonicity for inbound call centers (with Auke Pot). Operations Research 59(5):1304-1308, 2011. Improving CT scan capabilities with a new trauma workflow concept: Simulation of hospital logistics using different CT scanner scenarios (with Korik Alons, Marcel Dijkgraaf, P.H.P. Fung Kon Jin, C. van Kuijk, L.F.M. Beenen, and Carel Goslings). European Journal of Radiology 80(2):504-509, 2011. Analyzing completion times in an academic Emergency Department: Coordination of care is the weakest link (with Annemieke van Dongen and 6 others). The Netherlands Journal of Medicine 69(9):392-398, 2011. Queues with waiting time dependent service (with René Bekker, Thomas Nielsen and Bo Nielsen). Queueing Systems 68(1):61-78, 2011. Estimating unconstrained demand rate functions using customer choice sets (with Alwin Haensel). Journal of Revenue & Pricing Management 10(5):438-454, 2011. Booking horizon forecasting with dynamic updating: A case study of hotel reservation data (with Alwin Haensel). International Journal of Forecasting 27:942-960, 2011. Dynamic control of a single-server system with abandonments (with Doug Down and Mark Lewis). Queueing Systems 67(1):63-90, 2011. Optimising a general repair kit problem with a service constraint (with Marco Bijvank and Iris Vis). European Journal of Operational Research 204:76-85, 2010. Dimensioning hospital wards using the Erlang loss model (with Arnoud de Bruin, René Bekker, and Lillian van Zanten). Annals of Operations Research 178:23-43, 2010. Online scheduling policies for multiclass call centers with impatient customers (with Oualid Jouini, Auke Pot, and Yves Dallery). European Journal of Operational Research 207:258-268, 2010. Dynamic Load Balancing and Job Replication in a Global-Scale Grid Environment: a Comparison (with Menno Dobber and Rob van der Mei). IEEE Transactions on Parallel and Distributed Systems 20:207-218, 2009. Resource allocation in grid computing (with Rhonda Righter). Journal of Scheduling 11:163-173, 2008. A simple staffing method for multi-skill call centers (with Auke Pot and Sandjai Bhulai). Manufacturing & Service Operations Management 10:421-428, 2008. Simple methods for shift scheduling in multi-skill call centers (with Sandjai Bhulai and Auke Pot). Manufacturing & Service Operations Management 10:411-420, 2008. Modeling "Just-in-Time" communication in distributed real-time multimedia applications (with Ran Yang, Rob van der Mei, Dennis Roubos, Frank Seinstra, and Henri Bal). Proceedings of CCGrid, Lyon, pages 518-525, IEEE Computer Society Press, 2008. On the optimization of resource utilization in distributed multimedia applications (with Ran Yang, Rob van der Mei, Dennis Roubos, and Frank Seinstra). Proceedings of CCGrid, Lyon, pages 358-365, IEEE Computer Society Press, 2008. Optimal outpatient appointment scheduling (with Guido Kaandorp). Health Care Management Science 10:217-229, 2007. A Prediction Method for Job Runtimes on Shared Processors: Survey, Statistical Analysis and New Avenues (with Menno Dobber and Rob van der Mei). Performance Evaluation 64:755-781, 2007. Modeling the emergency cardiac in-patient flow: An application of queueing theory (with Arnoud de Bruin, Bert van Rossum, and Marieke Visser). Health Care Management Science 10:125-137, 2007. Monotonicity in Markov reward and decision chains: Theory and applications. Foundations and Trends in Stochastic Systems 1:1-76, 2006. Statistical properties of task running times in a global-scale grid environment (with Menno Dobber and Rob van der Mei). Proceedings of CCGrid, Singapore, pages 150-153, IEEE Computer Society Press, 2006. Approximating multi-skill blocking systems by hyperexponential decomposition (with Geert Jan Franx and Auke Pot). Performance Evaluation 63:799-824, 2006. Workload minimization in re-entrant lines (with Auke Pot). European Journal of Operational Research 174:216-233, 2006. The effect of service time variability on maximum queue lengths in MX/G/1 queues (with Misja Nuyens and Rhonda Righter). Journal of Applied Probability 42:883-891, 2005. Dynamic load balancing experiments in a grid (with Menno Dobber and Rob van der Mei). Proceedings of CCGrid, Cardiff, pages 1063-1070, IEEE Computer Society Press, 2005. Message delay in Mobile Ad Hoc Networks (with Robin Groenevelt and Philippe Nain). Performance Evaluation 62:210-228, 2005. Dynamic load balancing for a grid application (with Menno Dobber and Rob van der Mei). In Proceedings of HiCP 2004, Bangalore, pages 342-352, Springer LNCS 3296, 2004. Scaling and comparison of fluid limits of queues applied to call centers with time-varying parameters (with Tania Jiménez). OR Spectrum 26:413-422, 2004. An explicit solution for the value function of a priority queue (with Philippe Nain). Queueing Systems 47:251-282, 2004. A formula for tail probabilities of Cox distributions. Journal of Applied Probability 41:935-938, 2004. Convexity in tandem queues. Probability in the Engineering and Informational Sciences 18:13-31, 2004. Telephone call centers: Tutorial, review, and research prospects (with Noah Gans and Avishai Mandelbaum). Manufacturing and Service Operations Management 5:79-141, 2003. On the structure of value functions for threshold policies in queueing models (with Sandjai Bhulai). Journal of Applied Probability 40:613-622, 2003. Optimal shift scheduling with a global service level constraint (with Erik van der Sluis). IIE Transactions 35:1049-1055, 2003. A queueing model for call blending in call centers (with Sandjai Bhulai). IEEE Transactions on Automatic Control 48:1434-1438, 2003. Queueing models of call centers: An introduction (with Avishai Mandelbaum). Annals of Operations Research 113:41-59, 2002. On the bias vector of a two-class preemptive priority queue (with Robin Groenevelt and Philippe Nain). Mathematical Methods of Operations Research 55:107-120, 2002. Managing uncertainty in call centres using Poisson mixtures (with Geurt Jongbloed). Applied Stochastic Models in Business and Industry 17:307-318, 2001. On optimal call admission control in a resource-sharing system (with Eitan Altman and Tania Jiménez). IEEE Transactions on Communications 49:1659-1668, 2001. A stochastic batching and scheduling problem (with Rhonda Righter). Probability in the Engineering and Informational Sciences 15:465-479, 2001. Optimal transmission policies for noisy channels (with Zhen Liu and Rhonda Righter). Operations Research 49:892-899, 2001. On deviation matrices for birth-death processes (with Floske Spieksma). Probability in the Engineering and Informational Sciences 15:239-258, 2001. On the comparison of queueing systems with their fluid limits (with Eitan Altman and Tania Jiménez). Probability in the Engineering and Informational Sciences 15:165-178, 2001. On the value of learning for Bernoulli bandits with unknown parameters (with Sandjai Bhulai). IEEE Transactions on Automatic Control 45:2135-2140, 2000. On the convergence of the power series algorithm (with Gerard Hooghiemstra). Performance Evaluation 42:21-39, 2000. On the value function of a priority queue with an application to a controlled polling model (with Philippe Nain). Queueing Systems 34:199-214, 2000. Stochastic scheduling with event-based dynamic programming. Mathematical Methods of Operations Research 51:249-261, 2000. Minimizing response times and queue lengths in systems of parallel queues (with Panayotis Sparaggis and Don Towsley). Journal of Applied Probability 36:1185-1193, 1999. On the static assignment to parallel servers. IEEE Transactions on Automatic Control 44:1588-1592, 1999. A transformation method for stochastic control problems with partial observations. Systems and Control Letters 35:301-308, 1998. Structural results for the control of queueing systems using event-based dynamic programming. Queueing Systems 30:323-339, 1998. On submodular value functions and complex dynamic programming (with Eitan Altman). Stochastic Models 14:1051-1072, 1998. Optimal control of tandem reentrant queues (with Rhonda Righter). Queueing Systems 28:337-347, 1998. Stochastic bounds for queueing systems with multiple on-off sources (with Zhen Liu). Probability in the Engineering and Informational Sciences 12:25-48, 1998. Optimal control in light traffic Markov decision processes (with Olaf Passchier). Mathematical Methods of Operations Research 45:63-79, 1997. Assigning a single server to inhomogeneous queues with switching costs. Theoretical Computer Science 182:203-216, 1997. On the use of the power series algorithm for general Markov processes, with an application to a Petri net. INFORMS Journal on Computing 9:51-56, 1997. On suboptimal policies in multi-class tandem models (with Arie Hordijk). Probability in the Engineering and Informational Sciences 10:29-39, 1996. Scheduling a repairman in a finite source system (with Martin Vrijenhoek). Mathematical Methods of Operations Research 44:333-344, 1996. On the pathwise optimal Bernoulli routing policy for homogeneous parallel servers. Mathematics of Operations Research 21:469-476, 1996. A simple proof of the optimality of a threshold policy in a two-server queueing system. Systems and Control Letters 26:301-303, 1995. Optimal repairman assignment in two symmetric maintenance models. European Journal of Operations Research 82:295-301, 1995. Control of a random walk with noisy delayed information (with Eitan Altman). Systems and Control Letters 24:207-213, 1995. Analysis of a customer assignment model with no state information (with Arie Hordijk and Anneke Loeve). Probability in the Engineering and Informational Sciences 8:419-429, 1994. Stochastic scheduling games with Markov decision arrival processes (with Eitan Altman). Computers and Mathematics with Applications 26(6):141-148, 1993. Optimal server assignment in the case of service times with monotone failure rates. Systems and Control Letters 20:233-238, 1993. On the optimality of LEPT and $\mu c$ rules for parallel processors and dependent arrival processes (with Arie Hordijk). Advances in Applied Probability 25:979-996, 1993. Marked point processes as limits of Markovian arrival streams (with Sören Asmussen). Journal of Applied Probability 30:365-372, 1993. On the assignment of customers to parallel queues (with Arie Hordijk). Probability in the Engineering and Informational Sciences 6:495-511, 1992. The $\mu c$-rule is not optimal in the second node of the tandem queue: a counterexample (with Arie Hordijk). Advances in Applied Probability 24:234-237, 1992. On the shortest queue policy for the tandem parallel queue (with Arie Hordijk). Probability in the Engineering and Informational Sciences 6:63-79, 1992. On the optimality of the generalized shortest queue policy (with Arie Hordijk). Probability in the Engineering and Informational Sciences 4:477-487, 1990. Other scientific papers: Call center capacity allocation with random workload (with Shuangqing Liao, Christian van Delft, Yves Dallery, and Oualid Jouini). Proceedings of the 2009 International Conference on Computers & Industrial Engineering, July 6-8, Troyes, France. An evaluation of a Shockroom located CT scanner: a Randomized study of Early Assessment by CT scanning in Trauma patients in the bi-located Trauma center North-West Netherlands (REACT trial) (with 13 others). BMC Emergency Medicine 8(10), 2008. Bottleneck analysis of emergency cardiac in-patient flow in a university setting: an application of queueing theory (with Arnoud de Bruin and Marieke Visser). Clinical and Investigative Medicine 28(6): 316-317, 2005. Approximate dynamic programming in multi-skill call centers (with Auke Pot). Proceedings of the 2005 Winter Simulation Conference. Routing to parallel homogeneous queues. Presented at the Lorentz Center workshop in honor of Arie Hordijk, March 2005. Performance analysis and optimization in customer contact centers. Proceedings of QEST 04, Enschede, pages 2-5, 2004. Routing heuristics for multi-skill call centers (with Auke Pot and Jérôme Talim). Proceedings of the 2003 Winter Simulation Conference, New Orleans, pages 1813-1816, 2003. The mathematics of call centers. ``Research highlight'', Biennual report Stieltjes Institute, pages 31-35, 2000/2001. Exponential approximation of multi-skill call centers architecture (with Jérôme Talim). In Proceedings of QNETs 2000, Ilkley (UK), pages 23/1-10, 2000. Comparing queueing systems with heterogeneous on-off sources (with Zhen Liu and Don Towsley). Technical Report WS-533, Vrije Universiteit Amsterdam, 1999. Optimal admission, routing and service assignment control: the case of single buffer queues (with Eitan Altman, Bruno Gaujal, and Arie Hordijk). In Proceedings of the 37th IEEE CDC, Tampa, pages 2119-2124, 1998. The deviation matrix of the M/M/1 and M/M/1/N queue, with applications to controlled queueing models. In Proceedings of the 37th IEEE CDC, Tampa, pages 56-59, 1998. Nonconservative service for minimizing cell loss in ATM networks (with Zhen Liu). In Proceedings of WATM '95, Paris, pages 123-130, 1995. On scheduling and routing problems with a partially observed environment (with Olaf Passchier). Technical Report TW-95-13, Leiden University, 1995. Polling models with threshold switching (with Onno Boxma and Isi Mitrani). In Quantative Methods in Parallel Systems, pages 129-140, Springer-Verlag (Esprit Basic Research Series), 1995. Queueing-theoretic solution methods for models of parallel and distributed systems (with Onno Boxma and Zhen Liu). In Performance Evaluation of Parallel and Distributed Systems - Solution Methods, CWI Tract 105 & 106, CWI, Amsterdam, 1994. On the optimality of FCFS for networks of multi-server queues. Technical Report BS-R9235, CWI, Amsterdam, 1992. Assigning customers of multiple classes to parallel servers. Technical Report TW-91-07, Leiden University, 1991. Popular-scientific articles: Ehealth verhoogt efficiëntie en kwaliteit van gezondheidszorg. Reformatorisch Dagblad 24 February 2011, pages 7-8. De wiskunde van het wachten. Pythagoras 43(1):30-32, 2003. Met wiskunde naar de zon. Pythagoras 42(5):12-15, 2003. Eurodiffusie: een model voor je portemonnee. STAtOR 3(4):13-15, 2002. Het modelleren van de Eurodiffusie. Nieuwe Wiskrant 21(4):24-26, 2002. The Euro Diffusion Project (with Piet van Blokland, Lorna Booth, Kirankumar Hiremath, Michiel Hochstenbach, Sorin Pop, Marieke Quant, and Djoko Wirosoetisno). Proceedings of the 42nd European Study Group with Industry, CWI syllabus 51, pages 41-57, 2002. Stochastisch dynamisch programmeren. Nieuwe Wiskrant 21(3):23-26, 2002. Virtuele wetenschap. STAtOR 2(3): 27-28, 2001. Over wiskundig modelleren en call centers. Nieuwe Wiskrant 20(3):8-12, 2001. Wiskunde tussen model en werkelijkheid. Public lecture, Vrije Universiteit Amsterdam, 30 November 2000. An optimal dice rolling policy for Risk. Nieuw Archief voor Wiskunde 12:49-52, 1994. Publications in the professional literature: Kwantitatieve methoden voor zorglogistiek (with René Bekker). Part 2 of Logistiek in de Zorg - P2 Capaciteit en Aanbod, LogiZ, pages 79-122, 2011. Parkeeromzet verhogen met Revenue Management (with Maarten Soomer, Kevin Pak, and Rob van der Mei). Parkeer Magazine 5(1):16-17, 2009. Grootte van Zorgeenheden (with Arnoud de Bruin, Ben Nijman, Rien Caljouw, and Marieke Visser). Zorgvisie 37(4):29, 2007. Logistiek in de gezondheidszorg: Een bedrijfskundige benadering (with Jan Jurriens). Technologie in de Gezondheidszorg 22(3):5-7, 2006. WFM - Kosten, winst, SL en klanttevredenheid (with Annemiek van Moorst). Call Center Magazine 11(6):14-16, 2005. WFM en de kwaliteit van data (with Annemiek van Moorst). Call Center Magazine 11(4):14-16, 2005. Schaalvoordeel en skills bijten elkaar (with Annemiek van Moorst). Call Center Magazine 11(2):14-15, 2005. WFM: goede voorspelling noodzakelijk maar niet voldoende (with Annemiek van Moorst). Call Center Magazine 11(1):16-18, 2005. Interviews: Waarheid met kans nul (with Gerard Alberts and Jaap Molenaar). Nieuw Archief voor Wiskunde (fifth series) 6:215-220, 2005. Gele dingen die kunnen drijven (with Laurens Gelling and Jaap Molenaar). Nieuw Archief voor Wiskunde (fifth series) 6:47-50, 2005. Managementpotentieel (with Jaap Top and Roel Verstappen). Nieuw Archief voor Wiskunde (fifth series) 5:232-236, 2004. Tussen wetenschap en commercie (with Gerard Alberts and Hans Melissen). Nieuw Archief voor Wiskunde (fifth series) 4:327-331, 2003. Twee seconden is hier een eeuwigheid (with Gerard Alberts and Jaap Molenaar). Nieuw Archief voor Wiskunde (fifth series) 4:224-228, 2003. Het wiskunde B1,2-examen (with Alex van den Brandhof). Nieuw Archief voor Wiskunde (fifth series) 4:165-166, 2003. Behoud de keuzevrijheid - Wiskunde en politiek bij G. Zoutendijk (with Gerard Alberts). Nieuw Archief voor Wiskunde (fifth series) 2:36-41, 2001. Books: Call center optimization. In preparation. Optimization of business processes. Lecture notes. Stochastic scheduling and dynamic programming. PhD thesis, Leiden University, 1992. Editorial work: Special issue on call center management. Management Science 54(2), 2008. Special issue in honor of Arie Hordijk (with Lodewijk Kallenberg and Floske Spieksma). Mathematical Methods of Operations Research 62(3), 2005. Proceedings of the fifty-second European study group with industry (with Jan Bouwe van den Berg, Sandjai Bhulai, Joost Hulshof, Corrie Quant, JF Williams). CWI Tract, CWI, Amsterdam, 2005. Performance evaluation of parallel and distributed systems - solution methods (with Onno Boxma). CWI Tract 105 & 106, CWI, Amsterdam, 1994. Press articles: Zwaarder geschut op planning nodig. Telecommerce Magazine 06, 2011. Sneldiagnose kanker: Hogere wiskunde in de zorg. Synaps 76:14-15, December 2009. Wiskunde toepassen. Business Process Magazine 15(3):20-25, May 2009. Pilot met diagnostische zorgpaden van start. VUmc Tracer 10:7, 4 June 2009. Een emmer vol slome eurocenten. Volkskrant, 4 January 2003.