About
23
Publications
6,919
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
230
Citations
Introduction
I am a researcher in the field mathematical modelling, in particular queueing systems and operations research.
Publications
Publications (23)
We investigate a fundamental model from open-pit mining, which is a cyclic system consisting of a shovel, traveling loaded, unloading facility, and traveling back empty. The interaction of these subsystem determines the capacity of the shovel, which is the fundamental quantity of interest. To determine this capacity one needs the stationary probabi...
We consider exponential single server queues with state-dependent arrival and service rates that evolve under influences of external environments. The transitions of the queues are influenced by the environment’s state and the movements of the environment depend on the status of the queues (bidirectional interaction). The environment is constructed...
How well can social scientists predict societal change, and what processes
underlie their predictions? To answer these questions, we ran two
forecasting tournaments testing the accuracy of predictions of societal
change in domains commonly studied in the social sciences: ideological
preferences, political polarization, life satisfaction, sentiment...
How well can social scientists predict societal change, and what processes underlie their predictions? To answer these questions, we ran two forecasting tournaments testing accuracy of predictions of societal change in domains commonly studied in the social sciences: ideological preferences, political polarization, life satisfaction, sentiment on s...
We consider exponential single server queues with state-dependent arrival and service rates which evolve under influences of external environments. The transitions of the queues are influenced by the environment’s state and the movements of the environment depend on the status of the queues (bi-directional interaction). The environment is construct...
In robotic mobile fulfillment systems, human pickers don’t go to the inventory area to search for and pick the ordered items. Instead, robots carry shelves (called “pods”) containing ordered items from the inventory area to picking stations. At the picking stations, pickers put ordered items into totes; then these items are transported to the packi...
We present models for performance analysis of IPTV services. The main topic is to model the interplay of the restricted number of channels, the larger number of available programs to be transmitted over the channels, and the concurrent access of many users to the same program, resp. channel (multicast services). In a simple Engset-like model we com...
We investigate a new class of separable systems which exhibit a product-form stationary distribution. These systems consist of parallel production systems (servers) at several locations, each with a local inventory under base stock policy, connected with a common supplier network. Demand of customers arrives at each production system according to a...
We consider a semi-open queueing network (SOQN), where a customer requires exactly one resource from the resource pool for service. If there is a resource available, the customer is immediately served and the resource enters an inner network. If there is no resource available, the new customer has to wait in an external queue until one becomes avai...
Robotic mobile fulfillment systems (RMFSs) are a new type of warehousing system, which has received more attention recently, due to increasing growth in the e-commerce sector. Instead of sending pickers to the inventory area to search for and pick the ordered items, robots carry shelves (called "pods") including ordered items from the inventory are...
In a robotic mobile fulfillment system, robots bring shelves, called pods, with storage items from the storage area to pick stations. At every pick station there is a person-the picker-who takes parts from the pod and packs them into boxes according to orders. Usually there are multiple shelves at the pick station. In this case, they build a queue...
Presentation for OR2018 conference.
We investigate a fundamental model from open-pit mining which is a cyclic system consisting of an (unreliable) shovel, trucks travelling loaded, unloading facility, and trucks travelling back empty. The interaction of these subsystems determines the mean number of trucks loaded per time unit - the capacity of the shovel, which is a fundamental quan...
We investigate queueing networks in a random environment. The impact of the evolving environment on the network is by changing service capacities (upgrading and/or degrading, breakdown, repair) when the environment changes its state. On the other side, customers departing from the network may enforce the environment to jump immediately. This means...
We consider a two-echelon production-inventory system with a central supplier connected to production systems (servers) at several locations, each with a local inventory. Demand of customers arrives at each production system according to a Poisson process and is lost if the local inventory is depleted. To satisfy a customer’s demand, a server at th...
We consider a single server system with infinite waiting room in a random environment. The service system and the environment interact in both directions. Whenever the environment enters a prespecified subset of its state space the service process is completely blocked: Service is interrupted and newly arriving customers are lost. We prove a produc...
We develop randomized modifications of Markov chains and apply these
modifications to the routing chains of customers in Jacksonian stochastic
networks. The aim of our investigations is to find new rerouting schemes for
non standard Jackson networks which hitherto resist computing explicitly the
stationary distribution.
The non standard properties...
We develop a separable model for a referenced node in a fault tolerant (disruption tolerant) wireless sensor network, which encompasses the message queue of the node and an inner and an outer environment for describing details of the transmission protocols. We prove that the system has steady state of product form for the queue and its environment....
We consider a single server system with infinite waiting room in a random
environment. The service system and the environment interact in both
directions. Whenever the environment enters a prespecified subset of its state
space the service process is completely blocked: Service is interrupted and
newly arriving customers are lost. We prove an if-an...
We consider a single server system with infinite waiting room in a random environment. The service system and the environment interact in both directions. Whenever the environment enters a specific subset of its state space the service process is completely blocked: Service is interrupted and newly arriving customers are lost. We prove an if-and-on...