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Papers by W. van der Weij

Research paper thumbnail of Local application of a competitive NMDA antagonist in the medial prefrontal cortex increases in vivo DA but not NA release

Research paper thumbnail of On Tandem Queues with Threadpool Sharing

Nowadays many application servers need to handle huge amounts of transactions within a reasonable... more Nowadays many application servers need to handle huge amounts of transactions within a reasonable time frame. The performance of these servers is a complex interplay between software and hardware contention, which naturally leads to the formulation of multi-layered queueing models. This paper provides several explorative contributions, providing initial insight into the performance of a class of multi-layered queueing models. To this end, we study perhaps one of the simplest non-trivial multi-layered queueing models: a tandem of two multi-server stations with c i servers at station i (i = 1, 2), with Poisson arrivals at station 1 and with general service time distributions at both stations. At any moment in time, the servers (throughout referred to as threads) that are busy share an underlying resource in a processor-sharing (PS) fashion; that is, if k i (0 < k i ≤ c i ) threads are busy at station i (i = 1, 2), then each thread processes jobs at rate 1/(k 1 + k 2 ). In this paper we (1) investigate the possibility of analytic or approximate expressions for the mean sojourn times in case the numbers of threads at both stations are fixed (referred to as the uncontrolled case), and (2) obtain good thread-allocation rules for both the uncontrolled case and the controlled case, where the numbers of threads per station may change dynamically.

Research paper thumbnail of Product-form results for two-station networks with shared resources

Performance Evaluation, 2012

ABSTRACT Queueing networks are studied with two stations: either in tandem or in parallel, and wi... more ABSTRACT Queueing networks are studied with two stations: either in tandem or in parallel, and with a common service resource shared among the two stations. First, a necessary and sufficient criterion, called adjoint reversibility, is provided to decide whether the system possesses a product form or not. This criterion unifies both the parallel (a reversible) and the tandem (a non-reversible) system in one product-form theorem. Next, the criterion is applied separately for the parallel and tandem system to obtain a number of new product-form examples which also includes non-balanced capacity sharing. Despite, but also due to, the different parallel and tandem mechanisms we observe that for certain examples the product form has the same structure, while for others there are essential differences. In addition, it is also proven that several models cannot have a product-form result. The results provide new insights and a step forward in understanding the behavior of multi-layered queueing networks in which resources are shared among stations.

Research paper thumbnail of Rate stability and output rates in queueing networks with shared resources

Performance Evaluation, 2010

Motivated by a variety of applications in information and communication systems, we consider queu... more Motivated by a variety of applications in information and communication systems, we consider queueing networks in which the service rate at each of the individual nodes depends on the state of the entire system. The asymptotic behaviour of this type of networks is fundamentally different from classical queueing networks, where the service rate at each node is usually assumed to be independent of the state of the other nodes. We study the per-node rate stability and output rates for a class networks with a general capacity allocation function. More specifically, we derive necessary conditions of per-node rate stability, and give bounds for the per-node output rate and asymptotic growth rates, under mild assumptions on the allocation function. For a set of parallel nodes, we further prove the convergence of the output rates for most parameters and give a sharp characterization of the per-node rate stability. The results provide new intuition and fundamental insight in the stability and throughput behavior of queueing networks with shared resources.

Research paper thumbnail of Concentration-dependent dual action of locally applied N-methyl-d-aspartate on extracellular dopamine in the rat prefrontal cortex in vivo

Neuroscience Letters, 1995

Using microdialysis, the glutamate agonist N-methyl-D-aspartate (NMDA) was perfused for 20 min th... more Using microdialysis, the glutamate agonist N-methyl-D-aspartate (NMDA) was perfused for 20 min through the medial prefrontal cortex of freely moving rats, and its effects on extracellular concentrations of dopamine (DA) were determined. NMDA (1 mM) increased DA to 170--1500%, depending on the intensity and duration of the clonic forelimb jerks and convulsions that were induced. NMDA (0.1 mM), however, decreased DA to 61%. Metabolites of DA were decreased after both concentrations of NMDA. The effects of both 0.1 mM and 1 mM NMDA were blocked by 0.5 mM of the competitive NMDA-antagonist D-AP-5. The NMDA-induced decrease in release and metabolism possibly results from an indirect action via an inhibitory local intemeuron or polysynaptic circuit.

Research paper thumbnail of Sojourn times in a two-layered tandem queue with limited service positions and a shared processor

... The ambience at TNO Telecom was very pleasant; I have enjoined the music-in, the table tennis... more ... The ambience at TNO Telecom was very pleasant; I have enjoined the music-in, the table tennis tournament, the Big Band, the KIC division trip and other ... In Zhi-Long Chen&amp;#x27;s paper a column generation based branch and bound method for finding optimal solutions is presented. ...

Research paper thumbnail of Report PNA-R0712 December 2007

Research paper thumbnail of Stability and throughput in a two-layered network of multi-server queues

We study stability and throughput in a two-layered queueing network consisting of two multiserver... more We study stability and throughput in a two-layered queueing network consisting of two multiserver nodes, where at any time the busy servers share a common underlying resource in a processor-sharing fashion. We assume general arrival processes, general service-time distributions, arbitrary numbers of servers at both queues, and multiple customer classes, each with a class-specific arrival rate and visit order. For this model we derive a full characterization of the per-queue stability and the per-class throughput, considered as a function of the arrival rates, in a general paramenter setting. The results provide intuition and new fundamental insights into the behavior of queueing networks with this multi-layered structure.

Research paper thumbnail of Local application of a competitive NMDA antagonist in the medial prefrontal cortex increases in vivo DA but not NA release

Research paper thumbnail of On Tandem Queues with Threadpool Sharing

Nowadays many application servers need to handle huge amounts of transactions within a reasonable... more Nowadays many application servers need to handle huge amounts of transactions within a reasonable time frame. The performance of these servers is a complex interplay between software and hardware contention, which naturally leads to the formulation of multi-layered queueing models. This paper provides several explorative contributions, providing initial insight into the performance of a class of multi-layered queueing models. To this end, we study perhaps one of the simplest non-trivial multi-layered queueing models: a tandem of two multi-server stations with c i servers at station i (i = 1, 2), with Poisson arrivals at station 1 and with general service time distributions at both stations. At any moment in time, the servers (throughout referred to as threads) that are busy share an underlying resource in a processor-sharing (PS) fashion; that is, if k i (0 < k i ≤ c i ) threads are busy at station i (i = 1, 2), then each thread processes jobs at rate 1/(k 1 + k 2 ). In this paper we (1) investigate the possibility of analytic or approximate expressions for the mean sojourn times in case the numbers of threads at both stations are fixed (referred to as the uncontrolled case), and (2) obtain good thread-allocation rules for both the uncontrolled case and the controlled case, where the numbers of threads per station may change dynamically.

Research paper thumbnail of Product-form results for two-station networks with shared resources

Performance Evaluation, 2012

ABSTRACT Queueing networks are studied with two stations: either in tandem or in parallel, and wi... more ABSTRACT Queueing networks are studied with two stations: either in tandem or in parallel, and with a common service resource shared among the two stations. First, a necessary and sufficient criterion, called adjoint reversibility, is provided to decide whether the system possesses a product form or not. This criterion unifies both the parallel (a reversible) and the tandem (a non-reversible) system in one product-form theorem. Next, the criterion is applied separately for the parallel and tandem system to obtain a number of new product-form examples which also includes non-balanced capacity sharing. Despite, but also due to, the different parallel and tandem mechanisms we observe that for certain examples the product form has the same structure, while for others there are essential differences. In addition, it is also proven that several models cannot have a product-form result. The results provide new insights and a step forward in understanding the behavior of multi-layered queueing networks in which resources are shared among stations.

Research paper thumbnail of Rate stability and output rates in queueing networks with shared resources

Performance Evaluation, 2010

Motivated by a variety of applications in information and communication systems, we consider queu... more Motivated by a variety of applications in information and communication systems, we consider queueing networks in which the service rate at each of the individual nodes depends on the state of the entire system. The asymptotic behaviour of this type of networks is fundamentally different from classical queueing networks, where the service rate at each node is usually assumed to be independent of the state of the other nodes. We study the per-node rate stability and output rates for a class networks with a general capacity allocation function. More specifically, we derive necessary conditions of per-node rate stability, and give bounds for the per-node output rate and asymptotic growth rates, under mild assumptions on the allocation function. For a set of parallel nodes, we further prove the convergence of the output rates for most parameters and give a sharp characterization of the per-node rate stability. The results provide new intuition and fundamental insight in the stability and throughput behavior of queueing networks with shared resources.

Research paper thumbnail of Concentration-dependent dual action of locally applied N-methyl-d-aspartate on extracellular dopamine in the rat prefrontal cortex in vivo

Neuroscience Letters, 1995

Using microdialysis, the glutamate agonist N-methyl-D-aspartate (NMDA) was perfused for 20 min th... more Using microdialysis, the glutamate agonist N-methyl-D-aspartate (NMDA) was perfused for 20 min through the medial prefrontal cortex of freely moving rats, and its effects on extracellular concentrations of dopamine (DA) were determined. NMDA (1 mM) increased DA to 170--1500%, depending on the intensity and duration of the clonic forelimb jerks and convulsions that were induced. NMDA (0.1 mM), however, decreased DA to 61%. Metabolites of DA were decreased after both concentrations of NMDA. The effects of both 0.1 mM and 1 mM NMDA were blocked by 0.5 mM of the competitive NMDA-antagonist D-AP-5. The NMDA-induced decrease in release and metabolism possibly results from an indirect action via an inhibitory local intemeuron or polysynaptic circuit.

Research paper thumbnail of Sojourn times in a two-layered tandem queue with limited service positions and a shared processor

... The ambience at TNO Telecom was very pleasant; I have enjoined the music-in, the table tennis... more ... The ambience at TNO Telecom was very pleasant; I have enjoined the music-in, the table tennis tournament, the Big Band, the KIC division trip and other ... In Zhi-Long Chen&amp;#x27;s paper a column generation based branch and bound method for finding optimal solutions is presented. ...

Research paper thumbnail of Report PNA-R0712 December 2007

Research paper thumbnail of Stability and throughput in a two-layered network of multi-server queues

We study stability and throughput in a two-layered queueing network consisting of two multiserver... more We study stability and throughput in a two-layered queueing network consisting of two multiserver nodes, where at any time the busy servers share a common underlying resource in a processor-sharing fashion. We assume general arrival processes, general service-time distributions, arbitrary numbers of servers at both queues, and multiple customer classes, each with a class-specific arrival rate and visit order. For this model we derive a full characterization of the per-queue stability and the per-class throughput, considered as a function of the arrival rates, in a general paramenter setting. The results provide intuition and new fundamental insights into the behavior of queueing networks with this multi-layered structure.