Ger Koole - Profile on Academia.edu (original) (raw)

Papers by Ger Koole

De overval : Twee seconden is hier een eeuwigheid

KNAW Narcis. Back to search results. Publication De overval : Twee seconden is hier een eeuwighei... more KNAW Narcis. Back to search results. Publication De overval : Twee seconden is hier een eeuwigheid (2003). Pagina-navigatie: Main. Title, De overval : Twee seconden is hier een eeuwigheid. Published in, Nieuw Archief voor Wiskunde, Vol. 5/4, No. 3, p.224-. ...

European Study Group with Industry

... nl Leila Mohammadi Universiteit Leiden leila@ math. leidenuniv. nl Jaap Molenaar Technische U... more ... nl Leila Mohammadi Universiteit Leiden leila@ math. leidenuniv. nl Jaap Molenaar Technische Universiteit Eindhoven j. molenaar1@ tue. nl Jeroen Mulder KLM, Amstelveen jeroen. mulder@ klm. ... dlo. nl Nienke Valkhoff Universiteit van Amsterdam nienke@ science. uva. ...

De overval bij het Nederlands Forensisch Instituut : waarheid met kans nul

KNAW Narcis. Back to search results. Publication De overval bij het Nederlands Forensisch Institu... more KNAW Narcis. Back to search results. Publication De overval bij het Nederlands Forensisch Instituut : waarheid met kans nul (2005). Pagina-navigatie: Main. ...

Care workers account for a significant proportion of the total health expenditure in nursing home... more Care workers account for a significant proportion of the total health expenditure in nursing homes and are by far the largest controllable resource. Therefore, determining the appropriate number and type of care workers required plays an important role in the search for more efficiency. This study provides insights into how and why ‘scale of scheduling’ and the enlargement of care workers’ jobs (blending tasks of different qualification levels (QLs)) affect the number and type of staff required to meet the preferences (in terms of day and time) of nursing home residents. The scheduling data for plannable care activities of three separate decision-making units within a single Dutch nursing home have been analyzed. The results show that in >85% of the examined cases, substantial scale and skillmix economies can be achieved. We also found that the correlation between the demand patterns of different types of care tasks is of considerable importance when it comes to possible scale and skill-mix efficiencies.

In this study, we analyze a task scheduling problem with small time windows and care workers with... more In this study, we analyze a task scheduling problem with small time windows and care workers with different levels of qualification in a nursing home. A set of care tasks has to be assigned to a given number of care workers, so that the total earliness and tardiness from the nursing home residents’ preferred time is minimized.

To optimally solve this scheduling problem, we formulate a mixed integer program (MIP) and develop a dynamic programming (DP) approach. The numerical analysis shows the reliability of this optimization approach as well as of a heuristic DP approach. A sensitivity analysis with real-world demand data shows the impact of hierarchical qualification levels and large-scale scheduling.

Queueing systems, Jan 1, 1998

We consider optimal policies for reentrant queues in which customers may be served several times ... more We consider optimal policies for reentrant queues in which customers may be served several times at the same station. We show that for tandem reentrant queues the lastbuffer-first-served (LBFS) policy stochastically maximizes the departure process. 0

We are concerned with the minimization of multimodular functions. We show that for these function... more We are concerned with the minimization of multimodular functions. We show that for these functions local search gives the global optimum for a well-de ned nite neighborhood. We apply this to a problem arising from manpower scheduling in call centers which has a multimodular objective function.

Optimal repairman assignment in two symmetric maintenance models

European journal of operational research, Jan 1, 1995

Lecture notes, Jan 1, 2009

INFORMS Journal on Computing, Jan 1, 1997

The power series algorithm has been developed as a numerical procedure for solving queueing model... more The power series algorithm has been developed as a numerical procedure for solving queueing models. This paper shows that it can be used for each Markov process with a single recurrent class. This applies in particular to finite state processes, which is illustrated with the analysis of a bounded stochastic Petri net model.

… Computing, 2006 15th …, Jan 1, 2006

Grid applications that use a considerable number of processors for their computations need effect... more Grid applications that use a considerable number of processors for their computations need effective predictions of the expected computation times on the different nodes. Currently, there are no effective prediction methods available that satisfactorily cope with those ever-changing dynamics of computation times in a grid environment. Motivated by this, in this paper we develop the Dynamic Exponential Smoothing (DES) method to predict job processing times in a grid environment. To compare predictions of DES to those of the existing prediction methods, we have performed extensive experiments in a real large-scale grid environment. The results illustrate a strong and consistent improvement of DES in comparison with the existing prediction methods.

Stochastic scheduling with event-based dynamic programming

Mathematical Methods of Operations Research, Jan 1, 2000

… Conference, 2005 Proceedings of the Winter, Jan 1, 2005

We consider a multi-skill call center consisting of specialists and fully cross-trained agents. A... more We consider a multi-skill call center consisting of specialists and fully cross-trained agents. All traffic is inbound and there is a waiting queue for each skill type. Our objective is to obtain good call routing policies. In this paper we use the so-called policy iteration (PI) method. It is applied in the context of approximate dynamic programming (ADP). The standard PI method requires the exact value function, which is well known from dynamic programming. We remark that standard methods to obtain the value function suffer from the curse of dimensionality, i.e., the number of states grows exponentially with the size of the call center. Therefore, we replace the real value function by an approximation and we use techniques from ADP. The value function is approximated by simulating the system. We apply this method to our call routing problem, yielding very good results.

Probability in the Engineering and Informational …, Jan 1, 2001

We consider a batch scheduling problem in which the processing time of a batch of jobs equals the... more We consider a batch scheduling problem in which the processing time of a batch of jobs equals the maximum of the processing times of all jobs in the batch. This is the case, for example, for burn-in operations in semiconductor manufacturing, and other testing operations. Processing times are assumed to be random, and we consider minimizing the makespan and the flowtime. The problem is much more difficult than the corresponding deterministic problem, and the optimal policy may have many counterintuitive properties. We prove various structural properties of the optimal policy, and use these to develop a polynomial-time algorithm to compute the optimal policy. 0

A note on profit maximization and monotonicity for inbound call centers

Statistical properties of task running times in a global-scale grid environment

Cluster Computing and the …, Jan 1, 2006

European journal of operational research, Jan 1, 2006

This paper is concerned with workload minimization in re-entrant lines with exponential service t... more This paper is concerned with workload minimization in re-entrant lines with exponential service times and preemptive control policies. Using a numerical algorithm called the power series algorithm we obtain nearly optimal policies for systems with up to 8 queues. We also improve considerably the implementation of the power series algorithm.

BMC emergency …, Jan 1, 2008

Background: Trauma is a major source of morbidity and mortality, especially in people below the a... more Background: Trauma is a major source of morbidity and mortality, especially in people below the age of 50 years. For the evaluation of trauma patients CT scanning has gained wide acceptance in and provides detailed information on location and severity of injuries. However, CT scanning is frequently time consuming due to logistical (location of CT scanner elsewhere in the hospital) and technical issues. An innovative and unique infrastructural change has been made in the AMC in which the CT scanner is transported to the patient instead of the patient to the CT scanner. As a consequence, early shockroom CT scanning provides an all-inclusive multifocal diagnostic modality that can detect (potentially life-threatening) injuries in an earlier stage, so that therapy can be directed based on these findings.

Parallel and Distributed …, Jan 1, 2009

Global-scale grids provide a massive source of processing power, providing the means to support p... more Global-scale grids provide a massive source of processing power, providing the means to support processor intensive parallel applications. The strong burstiness and unpredictability of the available processing and network resources raise the strong need to make applications robust against the dynamics of grid environments. The two main techniques that are most suitable to cope with the dynamic nature of the grid are Dynamic Load Balancing (DLB) and job replication (JR). In this paper, we analyze and compare the effectiveness of these two approaches by means of trace-driven simulations. We observe that there exists an easy-tomeasure statistic Y and a corresponding threshold value Y Ã , such that DLB consistently outperforms JR when Y > Y Ã , whereas the reverse is true for Y < Y Ã . Based on this observation, we propose a simple and easy-to-implement approach, throughout referred to as the DLB/JR method, that can make dynamic decisions about whether to use DLB or JR. Extensive simulations based on a large set of real data monitored in a global-scale grid show that our DLB/JR method consistently performs at least as good as both DLB and JR in all circumstances, which makes our DLB/JR method highly robust against the unpredictable nature of global-scale grids.

Manufacturing & Service …, Jan 1, 2003

T elephone call centers are an integral part of many businesses, and their economic role is signi... more T elephone call centers are an integral part of many businesses, and their economic role is significant and growing. They are also fascinating sociotechnical systems in which the behavior of customers and employees is closely intertwined with physical performance measures. In these environments traditional operational models are of great value-and at the same time fundamentally limited-in their ability to characterize system performance.