Kenneth Sörensen

University of Antwerp | UA · ANT/OR - University of Antwerp Operations Research Group

This paper compares the current generation of ventilation systems: natural ventilation, exhaust ventilation, and balanced ventilation, and weighs them against an ideal benchmark case. To achieve this, a transparent, selfdeveloped evaluation framework is constructed. This assessment framework is used to calculate three different and distinct perform...

In this work we analyze the performance of integrating a large-scale on-demand bus system with a high-frequency fixed line public transport network in an urban context. Given are a high-speed metro network, a set of real-time requests, a set of bus station locations and a fleet of fixed capacity minibuses. Requests have a set of possible departure/...

Deep convolutional neural networks (DCNNs) are able to partially predict brain activity during object categorization tasks, but factors contributing to this predictive power are not fully understood. Our study aimed to investigate the factors contributing to the predictive power of DCNNs in object categorization tasks. We compared the activity of f...

Public transportation out of suburban or rural areas is crucial. Feeder transportation services offer a solution by transporting passengers to areas where more options for public transport are available. On one hand, fully flexible demand-responsive feeder services (DRFSs) efficiently tailor their service to the needs of the passengers. On the othe...

On the one hand, fully flexible demand-responsive feeder services efficiently tailor their service to passengers' needs. Traditional services , on the other hand, offer predictability and easier cost control. This paper considers a semi-flexible feeder service that combines positive characteristics of both traditional and fully flexible services. T...

Humans can quickly recognize objects in a dynamically changing world. This ability is showcased by the fact that observers succeed at recognizing objects in rapidly changing image sequences, at up to 13 ms/image. To date, the mechanisms that govern dynamic object recognition remain poorly understood. Here, we developed deep learning models for dyna...

Deep convolutional neural networks (DCNNs) are able to predict brain activity during object categorization tasks, but factors contributing to this predictive power are not fully understood. Our study aimed to investigate the factors contributing to the predictive power of DCNNs in object categorization tasks. We compared the activity of four DCNN a...

The real-time on-demand bus routing problem (ODBRP) supports the online routing of buses in a large-scale ride-sharing system. Given are a set of buses with fixed capacity, a set of bus stations and a set of transportation requests, only part of which are known before the planning horizon. A request consists of a set of possible departure and arriv...

Humans recognize objects in a dynamically changing world integrating evidence across a vast variety of timescales. This ability is showcased by performance on rapid serial visual presentation (RSVP) tasks in which observers succeed at recognizing objects in rapid sequences of natural scenes, at up to 13 ms/image. To date, the computational mechanis...

Arousal levels strongly affect task performance. Yet, what arousal level is optimal for a task depends on its difficulty. Easy task performance peaks at higher arousal levels, whereas performance on difficult tasks displays an inverted U-shape relationship with arousal, peaking at medium arousal levels, an observation first made by Yerkes and Dodso...

When demand for transportation is low or highly variable, traditional public bus services tend to lose their efficiency and typically frustrate (potential) passengers. In the literature, a large number of demand-responsive systems, that promise improved flexibility, have therefore been developed. At present, however, a comprehensive survey of these...

Facility planning is one of the critical decisions faced by humanitarian managers. Some managerial implications have been offered in the literature, but these are commonly derived from simple sensitivity analyses on individual instance characteristics and/or using a single case study, and as such can be misleading as they ignore important interacti...

With the rise of smart cities, relevant passenger data can be collected to improve the quality of transport services. In this article, a demand-responsive feeder service is presented. A feeder service transports passengers from a low-demand area, like a sub-urban area, to a transportation hub, like a city center. The feeder service modeled in this...

Following decades of sustained improvement, metaheuristics are one of the great success stories of optimization research. However, in order for research in metaheuristics to avoid fragmentation and a lack of reproducibility, there is a pressing need for stronger scientific and computational infrastructure to support the development, analysis and co...

We introduce a novel optimization problem to support the planning and routing of on‐demand buses in an urban context. We call this problem the on‐demand bus routing problem (ODBRP). Given are a fleet of buses with fixed capacity, a set of bus stations and travel times between them, and a set of transportation requests. Each transportation request c...

In this paper, we describe a matheuristic to solve the stochastic facility location problem which determines the location and size of storage facilities, the quantities of various types of supplies stored in each facility, and the assignment of demand locations to the open facilities, which minimize unmet demand and response time in lexicographic o...

The gravity fed water distribution network design (WDND) optimization problem consists in determining the pipe diameters of a water network such that hydraulic constraints are satisfied and the total cost is minimized. Traditionally, such design decisions are made on the basis of expert experience. When networks increase in size, however, rules of...

Real-world problems are becoming highly complex and therefore have to be solved with combinatorial optimization (CO) techniques. Motivated by the strong increase in publications on CO, 8393 articles from this research field are subjected to a bibliometric analysis. The corpus of literature is examined using mathematical methods and a novel algorith...

Feeder services are public transit services that transport people from a low demand, typically suburban, area to a high demand area, such as a transportation hub or a city. Here, passengers continue their journey using traditional forms of public transport. On the one hand, on-demand feeder services have been a topic of discussion in a number of re...

We introduce pattern injection local search (PILS), an optimization strategy that uses pattern mining to explore high-order local-search neighborhoods, and illustrate its application on the vehicle routing problem. PILS operates by storing a limited number of frequent patterns from elite solutions. During the local search, each pattern is used to d...

Spatial attention enhances sensory processing of goal-relevant information and improves perceptual sensitivity. The specific mechanisms linking neural changes to changes in performance are still contested. Here, we examine different attention mechanisms in spiking deep convolutional neural networks. We directly contrast effects of noise suppression...

Real-world problems are becoming highly complex and, therefore, have to be solved with combinatorial optimisation (CO) techniques. Motivated by the strong increase of publications on CO, 8,393 articles from this research field are subjected to a bibliometric analysis. The corpus of literature is examined using mathematical methods and a novel algor...

The location–routing problem (LRP) unites two important challenges in the design of distribution systems: planning the delivery of goods to customers (i.e., the routing of the delivery vehicles) and determining the locations of the depots from where these deliveries are executed. In this paper, we design an efficient and effective heuristic for the...

Following decades of sustained improvement, metaheuristics are one of the great success stories of optimization research. However, in order for research in metaheuristics to avoid fragmentation and a lack of reproducibility, there is a pressing need for stronger scientific and computational infrastructure to support the development, analysis and co...

Research on metaheuristics has focused on (novel) algorithmic development and on competitive testing, both of which have been frequently argued to yield little generalizable knowledge. The main goal of this paper is to promote meta-analysis — a systematic statistical examination that combines the results of several independent studies — as a more s...

The gravity fed water distribution network design (WDND) optimization problem consists in determining the pipe diameters of a water network such that hydraulic constraints are satisfied and the total cost is minimized. Traditionally, such design decisions are made on the basis of expert experience. When networks increase in size, however, rules of...

This special issue of the International Transactions in Operational Research focuses on Matheuristics and Metaheuristics and is the largest published to date, highlighting the importance of the field and the broad scope of these methods and the reach of their applications. Academicians and practitioners responded with enthusiasm to three parallel c...

We introduce pattern injection local search (PILS), an optimization strategy that uses pattern mining to explore high-order local-search neighborhoods, and illustrate its application on the vehicle routing problem. PILS operates by storing a limited number of frequent patterns from elite solutions. During the local search, each pattern is used to d...

The number of people affected by natural disasters or displaced by conflict, persecution, violence or human rights violations has been steadily increasing, doubling in a decade and reaching 141.1 million in 2017 (United Nations Office for the Coordination of Humanitarian Affairs (OCHA) in Global humanitarian overview 2017 (June status report), 2017...

Significance Understanding the computational principles that underlie human vision is a key challenge for neuroscience and could help improve machine vision. Feedforward neural network models process their input through a deep cascade of computations. These models can recognize objects in images and explain aspects of human rapid recognition. Howev...

Purpose Despite a growing body of research on the problem of increasing disaster preparedness by pre-positioning relief supplies at strategic locations, there is a lack of a benchmark set of problem instances that hinders thorough hypotheses testing, sensitivity analysis, model validation or solution procedure evaluation. The purpose of this paper...

This paper introduces an efficient algorithm for the bike request scheduling problem (BRSP). The BRSP is built around the concept of request, defined as the pickup or dropoff of a number of identical items (bikes) at a specific station, within a certain time window, and with a certain priority. The aim of the BRSP is to sequence requests on (and he...

Record companies invest billions of dollars in new talent around the globe each year. Gaining insight into what actually makes a hit song would provide tremendous benefits for the music industry. In this research we tackle this question by focussing on the dance hit song classification problem. A database of dance hit songs from 1985 until 2013 is...

In this paper, we develop an intelligent solution to a complex, real-life vehicle routing problem in the waste management sector. Waste management companies deliver various types of empty waste containers to industrial customers, to be filled with different types of waste, after which the containers are picked up again. The full containers are tran...

Local search has been established as a successful cornerstone to tackle the Vehicle Routing Problem, and is included in many state-of-the-art heuristics. In this paper we aim to demonstrate that a well-implemented local search on its own suffices to create a heuristic that computes high-quality solutions in a short time. To this end we combine thre...

A method is proposed to analyze the effect of the algorithmic parameters and instance characteristics on the quality of a Pareto front produced by a multiobjective algorithm. This method is applied to a variable neighborhood tabu search that is used to solve a multiobjective microzone-based vehicle routing problem. Our method can accommodate many d...

The vehicle routing problem is among the most-studied and practically relevant problems in combinatorial optimization. Yet, almost all research thus far has been targeted at solving problems with not more than a few hundred customers. In this paper, we explore how to design a local search heuristic that computes good solutions for very large-scale...

In collaborative logistics, carriers form coalitions in order to perform parts of their operational business jointly. Combinatorial auctions can be used to exchange transportation requests without having to reveal critical information. Collaborators submit requests for exchange to a common pool. The requests in the pool are then grouped into bundle...

The field of combinatorial optimization has inspired the development of a large number of heuristic solution procedures. These methods are commonly assessed using a competitive evaluation methodology that may give an indication of which algorithm has a better performance. A next step in the experimental analysis is to uncover “why” one algorithm pe...

A method is proposed to analyze the effect of the algorithmic parameters and instance characteristics on the quality of a Pareto front produced by a multiobjective algorithm. This method is applied to a variable neighborhood tabu search that is used to solve a multi-objective microzone-based vehicle routing problem. Our method can accommodate many...

In this paper, a general solution framework is presented for optimising decisions in a horizontal logistics cooperation. The framework distinguishes between the objective of the group and the objectives of the individual partners in the coalition. Although the importance of the individual partner interests is often acknowledged in the literature, t...

This chapter describes the history of metaheuristics in five distinct periods, starting long before the first use of the term and ending a long time in the future. The field of metaheuristics has undergone several paradigm shifts that have changed the way researchers look upon the development of heuristic methods. Most notably, there has been a shi...

For the last decades, metaheuristics have become ever more popular as a tool to solve a large class of difficult optimization problems. However, determining the best configuration of a metaheuristic, which includes the program flow and the parameter settings, remains a difficult task. Adaptive metaheuristics (that change their configuration during...

In a previous study using transcranial alternating current stimulation (tACS), we found preliminary evidence that phase coherence in the alpha band (8–12 Hz) within the fronto-parietal network may critically support top-down control of spatial attention (van Schouwenburg et al., 2017). Specifically, synchronous alpha-band stimulation over the right...

Centralized air distribution systems in non-residential buildings are characterized by an extensive air distribution network, that has to be built in a building environment with finite degrees of freedom. The ductwork layout, i.e., the network structure of the ducts, as well as the number and location of the fans, has a large impact on the total co...

This paper considers a horizontal logistics cooperation in which multiple companies jointly solve their logistics optimisation problem. To capture the individual partner interests in the logistics optimisation model, we allow each individual partner to set its own set of objectives. In such a situation, the question arises whether only these indivi...

In most heating, ventilation and air conditioning systems, the ductwork layout, i.e., the network structure of the ducts, as well as the number and location of the fans, is an important determinant of the installation's cost and performance. The network layout is especially important in large, non-residential buildings with an extensive air distrib...

Heuristics are the weapon of choice when it comes to solving complex combinatorial optimization problems. Even though a large amount of research focuses on tuning heuristics on a specific problem, little research has been done to investigate structural characteristics of the problem itself. We argue that knowledge about the structural characterist...

The growth of e-commerce is accompanied by an increasing distribution of parcels in cities resulting in externalities like traffic congestion or emissions. As a consequence, different delivery concepts like bike deliveries or delivery points have been suggested. Naturally, companies will only accept these changes, if they do not result in higher co...

The vehicle routing problem is one of the most-studied and practically relevant problems in combinatorial optimization. However, even though some applications like waste collection and parcel distributions can require thousands or even tens of thousands of customer visits, almost all research thus far has been targeted at solving problems of not mo...

In their paper “An improved Clarke and Wright savings algorithm for the capacitated vehicle routing problem,” published in ScienceAsia (38, 3, 307–318, 2012), Pichpibul and Kawtummachai developed a simple stochastic extension of the well-known Clarke and Wright savings heuristic for the capacitated vehicle routing problem. Notwithstanding the simpl...

Two-stratum experiments are widely used in case a complete randomization is not possible. In some experimental scenarios, there are constraints that limit the number of observations that can be made under homogeneous conditions. In other scenarios, there are factors whose levels are hard or expensive to change. In both of these scenarios, it is nec...

A piano fingering indicates which finger should play each note in a piece. Such a guideline is very helpful for both amateur and experienced players in order to play a piece fluently. In this paper, we propose a variable neighborhood search algorithm to generate piano fingerings for complex polyphonic music, a frequently encountered case that was i...

In most heating, ventilation and air conditioning systems, the ductwork layout, i.e., the network structure of the ducts, as well as the number and locations of the fans, is an important determinant of the installation's cost and performance. Nevertheless, the layout is not explicitly taken into account in existing duct design methods. Most methods...

This chapter describes the history of metaheuristics in five distinct periods, starting long before the first use of the term and ending a long time in the future.

Stated choice experiments are conducted to identify the attributes that drive people’s preferences when choosing between competing options. They are widely used in transportation in order to support the decision making of companies and governmental authorities. A large number of attributes might increase the complexity of the choice task in a choic...

Does paracetamol alleviate pain? The answer to that question is an unambiguous yes. Yes: on average, in most people, if one does not die from overdosing on it, paracetamol does alleviate pain, and its effect is stronger than that of a placebo. Apparently, the medical sciences have succeeded in gathering so much evidence for the pain-relieving quali...

Water distribution networks consist of different components, such as reservoirs and pipes, and exist to provide users (households, agriculture, industry) with high-quality water at adequate pressure and flow. Water distribution network design optimization aims to find optimal diameters for every pipe, chosen from a limited set of commercially avail...

We focus on the D-optimal design of screening experiments involving main-effects regression models, especially with large numbers of factors and observations. We propose a new selection strategy for the coordinate-exchange algorithm based on an orthogonality measure of the design. Computational experiments show that this strategy finds better desig...

In this paper, we propose a new metaheuristic to solve the Risk constrained Cash-in-Transit Vehicle Routing Problem (Rctvrp). The Rctvrp is a variant of the well-known capacitated vehicle routing problem and models the problem of routing vehicles in the cash-in-transit sector. In the Rctvrp, the risk associated with a robbery represents a critical...

Real-life utility networks such as smart grids, pipelines, and water networks can be exposed to safety- and security-related risk. To mitigate the risks that might result in service interruptions for the users of these networks, countermeasures can be applied. In this paper, a decision model is proposed that assumes that all edges (e.g., pipes, cab...

Horizontal logistic collaboration offers a great opportunity for companies to reduce their distribution costs. By forming a coalition and carrying out a joint operational plan, companies are able to achieve a larger profit. The extent of this profit is, however, highly dependent on the partners that form the coalition and the characteristics of the...

HydroGen instances of single-period, gravity-fed water distribution networks. Usable as input instances for water distribution network design optimization. Available in EPANET and GraphML format.