The KLU faculty, post-docs, and PhD candidates regularly publish the results of their research in scientific journals. You will find a complete overview of all KLU publications below (e.g. articles in peer-reviewed journals, professional journals, books, working papers, and conference proceedings). Search for relevant terms and keywords, or filter the list by name, year of publication or type of publication. The references include DOIs and abstracts where available, and you can download them to your own reference database or platform. We regularly update the database with new publications.

Selected Publications

Copy reference link   DOI: 10.1016/j.ejor.2011.06.033

Abstract: We develop an approximate dynamic programming approach to network revenue management models with customer choice that approximates the value function of the Markov decision process with a non-linear function which is separable across resource inventory levels. This approximation can exhibit significantly improved accuracy compared to currently available methods. It further allows for arbitrary aggregation of inventory units and thereby reduction of computational workload, yields upper bounds on the optimal expected revenue that are provably at least as tight as those obtained from previous approaches. Computational experiments for the multinomial logit choice model with distinct consideration sets show that policies derived from our approach can outperform some recently proposed alternatives, and we demonstrate how aggregation can be used to balance solution quality and runtime.

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Copy reference link   DOI: 10.1016/j.cor.2011.12.016

Abstract: In Canada transport companies must ensure that truck drivers can comply with Canadian Commercial Vehicle Drivers Hours of Service Regulations. Canadian regulations comprise the provisions found in US hours of service regulations as well as additional constraints on the maximum amount of driving and the minimum amount of off-duty time on each day. This paper presents a mixed integer programming formulation and an iterative dynamic programming approach for minimising the duration of truck driver schedules complying with Canadian hours of service regulations. Computational experiments show that schedule durations can be significantly reduced compared with a previously presented approach which only focuses on feasibility.

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Copy reference link   DOI: 10.15358/0344-1369-2012-2-140

Abstract: Brand extension and co-branding are two brand strategies with numerous similarities, but also distinct differences. So far, the existing literature has analyzed these strategies without making a detailed comparison between them. That is why this study discusses the joint and differing opportunities and risks of these two strategies. Spill-over effects, cost synergies, image transfers, coordination and independence issues are assessed in detail. In addition, the study considers the critical success factors for each strategy, which is necessary for a final assessment of the different strategy benefits. These success factors include characteristics of the parent brand, product and brand fit as well as consumer and company characteristics. In this context, the study elaborates under which general conditions which strategy may be more preferable. In the end, it becomes clear that there are some advantages related to a co-branding strategy, which cannot be realized by pursuing a brand extension strategy.

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Abstract: The repeated execution of workflow logic is usually modeled with loop constructs in the workflow model. But there are cases where it is not known at design time that a subset of activities has to be rerun during workflow execution. For instance in e-Science, scientists might have to spontaneously repeat a part of an experiment modeled and executed as workflow in order to gain meaningful results. In general, a manually triggered ad hoc rerun enables users reacting to unforeseen problems and thus improves workflow robustness. It allows natural scientists steering the convergence of scientific results, business analysts controlling their analyses results, and it facilitates an explorative workflow development as required in scientific workflows. In this paper, two operations are formalized for a manually enforced repeated enactment of activities, the iteration and the re-execution. The focus thereby lies on an arbitrary, user-selected activity as a starting point of the rerun. Important topics discussed in this context are handling of data, rerun of activities in activity sequences as well as in parallel and alternative branches, implications on the communication with partners/services and the application of the concept to workflow languages with hierarchically nested activities. Since the operations are defined on a meta-model level, they can be implemented for different workflow languages and engines.

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Abstract: The performance of business processes is measured and monitored in terms of Key Performance Indicators (KPIs). If the monitoring results show that the KPI targets are violated, the underlying reasons have to be identified and the process should be adapted accordingly to address the violations. In this paper we propose an integrated monitoring, prediction and adaptation approach for preventing KPI violations of business process instances. KPIs are monitored continuously while the process is executed. Additionally, based on KPI measurements of historical process instances we use decision tree learning to construct classification models which are then used to predict the KPI value of an instance while it is still running. If a KPI violation is predicted, we identify adaptation requirements and adaptation strategies in order to prevent the violation.

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Copy reference link   DOI: 10.1007/s11761-011-0095-6

Abstract: Service composition is a well-established field of research in the service community. Services are commonly regarded as black boxes with well-defined interfaces that can be recursively aggregated into new services. The black-box nature of services does not only include the service implementation but also implies the use of middleware and hardware to run the services. Thus, service composition techniques are typically limited to choosing between a set of available services. In this paper, we keep the black-box nature and the principle of information hiding of services, but in addition we break up services vertically. By introducing vertical service composition, we allow services to be provisioned on demand using the middleware and runtime environment that specifically meets user-required quality of services. Therefore, a service is setup individually for services requestors instead of providing them with a pre-determined list of available services to choose from. We introduce the concept of vertical service composition and present an extension to an enterprise service bus that implements the concept of vertical service composition by combining concepts from provisioning with those of (dynamic) service binding.

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Copy reference link   DOI: 10.1111/j.1937-5956.2011.01251.x

Abstract: Supply chain risk management (SCRM) is a nascent area emerging from a growing appreciation for supply chain risk by practitioners and by researchers. However, there is diverse perception of research in supply chain risk because these researchers have approached this area from different domains. This paper presents our study of this diversity from the perspectives of operations and supply chain management scholars: First, we reviewed the researchers' output, i.e., the recent research literature. Next, we surveyed two focus groups (members of Supply Chain Thought Leaders and International SCRM groups) with open-ended questions. Finally, we surveyed operations and supply chain management researchers during the 2009 INFORMS meeting in San Diego. Our findings characterize the diversity in terms of three “gaps”: a definition gap in how researchers define SCRM, a process gap in terms of inadequate coverage of response to risk incidents, and a methodology gap in terms of inadequate use of empirical methods. We also list ways to close these gaps as suggested by the researchers.

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Copy reference link   DOI: 10.1016/j.ejor.2011.09.028

Abstract: One of the latest developments in network revenue management (RM) is the incorporation of customer purchase behavior via discrete choice models. Many authors presented control policies for the booking process that are expressed in terms of which combination of products to offer at a given point in time and given resource inventories. However, in many implemented RM systems—most notably in the hotel industry—bid price control is being used, and this entails the problem that the recommended combination of products as identified by these policies might not be representable through bid price control. If demand were independent from available product alternatives, an optimal choice of bid prices is to use the marginal value of capacity for each resource in the network. But under dependent demand, this is not necessarily the case. In fact, it seems that these bid prices are typically not restrictive enough and result in buy-down effects.We propose (1) a simple and fast heuristic that iteratively improves on an initial guess for the bid price vector; this first guess could be, for example, dynamic estimates of the marginal value of capacity. Moreover, (2) we demonstrate that using these dynamic marginal capacity values directly as bid prices can lead to significant revenue loss as compared to using our heuristic to improve them. Finally, (3) we investigate numerically how much revenue performance is lost due to the confinement to product combinations that can be represented by a bid price.The heuristic is not restricted to a particular choice model and can be combined with any method that provides us with estimates of the marginal values of capacity. In our numerical experiments, we test the heuristic on some popular networks examples taken from peer literature. We use a multinomial logit choice model which allows customers from different segments to have products in common that they consider to purchase. In most problem instances, our heuristic policy results in significant revenue gains over some currently available alternatives at low computational cost.

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Copy reference link   DOI: 10.1287/trsc.1110.0382

Abstract: The U.S. truck driver scheduling problem (US-TDSP) is the problem of visiting a sequence of λ locations within given time windows in such a way that driving and working activities of truck drivers comply with U.S. hours-of-service regulations. In the case of single time windows it is known that the US-TDSP can be solved in O(λ3) time. In this paper, we present a scheduling method for the US-TDSP that solves the single time window problem in O(λ2) time. We show that in the case of multiple time windows the same complexity can be achieved if the gap between subsequent time windows is at least 10 hours. This situation occurs, for example, if, because of opening hours of docks, handling operations can only be performed between 8.00 a.m. and 10.00 p.m. Furthermore, we empirically show that for a wide range of other problem instances the computational effort is not much higher if multiple time windows are considered.

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Copy reference link   DOI: doi:10.1007/s10696-011-9086-3

Abstract: This paper studies the problem of scheduling working hours of team drivers in European road freight transport where a sequence of lambda locations must be visited within given time windows. Since April 2007 working hours of truck drivers in the European Union must comply with regulation (EC) No 561/2006. These regulations impose standard limits on the daily driving times of truck drivers and extended daily limits that may only be used twice a week for each driver. We present a depth-first-breadth-second search method which can find a feasible schedule complying with standard daily driving time limits in O(lambda^2) time, if such a schedule exists. Furthermore, we show that this method can also be used to find schedules complying with regulation (EC) No 561/2006 if daily driving times may exceed the standard limit.

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Copy reference link   DOI: doi:http://dx.doi.org/10.1016/j.obhdp.2011.07.004

Abstract: The better-than-average effect describes the tendency of people to perceive their skills and virtues as being above average. We derive a new experimental paradigm to distinguish between two possible explanations for the effect, namely rational information processing and overconfidence. Experiment participants evaluate their relative position within the population by stating their complete belief distribution. This approach sidesteps recent methodology concerns associated with previous research. We find that people hold beliefs about their abilities in different domains and tasks which are inconsistent with rational information processing. Both on an aggregated and an individual level, they show considerable overplacement. We conclude that overconfidence is not only apparent overconfidence but rather the consequence of a psychological bias.

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Copy reference link   DOI: 10.1016/j.ijpe.2011.01.022

Abstract: Lot-sizing and capacity planning are important supply chain decisions, and competition and cooperation affect the performance of these decisions. In this paper, we look into the dynamic lot-sizing and resource competition problem of an industry consisting of multiple firms. A capacity competition model combining the complexity of time-varying demand with cost functions and economies of scale arising from dynamic lot-sizing costs is developed. Each firm can replenish inventory at the beginning of each period in a finite planning horizon. Fixed as well as variable production costs incur for each production setup, along with inventory carrying costs. The individual production lots of each firm are limited by a constant capacity restriction, which is purchased up front for the planning horizon. The capacity can be purchased from a spot market, and the capacity acquisition cost fluctuates with the total capacity demand of all the competing firms. We solve the competition model and establish the existence of a capacity equilibrium over the firms and the associated optimal dynamic lot-sizing plan for each firm under mild conditions.

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Copy reference link   DOI: 10.1080/15213269.2011.620541

Abstract: Conventional wisdom suggests that variations in vertical picture angle cause the subject to appear more powerful when depicted from below and less powerful when depicted from above. However, do the media actually use such associations to represent individual differences in power? We argue that the diverse perspectives of evolutionary, social learning, and embodiment theories all suggest that the association between verticality and power is relatively automatic and should, therefore, be visible in the portrayal of powerful and powerless individuals in the media. Four archival studies (with six samples) provide empirical evidence for this hypothesis and indicate that a salience power context reinforces this effect. In addition, two experimental studies confirm these effects for individuals producing media content. We discuss potential implications of this effect.

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Copy reference link   DOI: 10.1016/j.leaqua.2011.02.011

Abstract: Leader categorization theory suggests that subordinates implicitly compare their leaders with a cognitively represented ideal image of a leader, i.e., an ideal leader prototype. The better the match, the more favorable subordinates' attitudes toward their leaders will be. We suggest, however, that subordinates not only perceive their leaders against the backdrop of a leader prototype but also themselves. Based on socio-cognitive research, we hypothesize that these self-perceptions in turn should lend more weight to the leader prototype as a benchmark. Three field studies with employees (N = 87; N = 265; N = 385) were undertaken to test our hypothesis. Results confirm that subordinates' perceptions of their leaders against an ideal leader prototype are related to subordinates' respect for their leaders and leadership effectiveness perceptions, and that these relationships are moderated by subordinates' self-perceptions against the ideal leader prototype. This study therefore extends current follower-centric perspectives on leadership and strengthens its ties with fundamental socio-cognitive research.

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Copy reference link   DOI: 10.1080/00207543.2010.518991

Abstract: One of the fundamental problems in operations management is determining the optimal investment in capacity. Capacity investment consumes resources and the decision, once made, is often irreversible. Moreover, the available capacity level affects the action space for production and inventory planning decisions directly. In this article, we address the joint capacitated lot-sizing and capacity-acquisition problems. The firm can produce goods in each of the finite periods into which the production season is partitioned. Fixed as well as variable production costs are incurred for each production batch, along with inventory carrying costs. The production per period is limited by a capacity restriction. The underlying capacity must be purchased up front for the upcoming season and remains constant over the entire season. We assume that the capacity acquisition cost is smooth and convex. For this situation, we develop a model which combines the complexity of time-varying demand and cost functions and of scale economies arising from dynamic lot-sizing costs with the purchase cost of capacity. We propose a heuristic algorithm that runs in polynomial time to determine a good capacity level and corresponding lot-sizing plan simultaneously. Numerical experiments show that our method is a good trade-off between solution quality and running time.

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Copy reference link   DOI: 10.1177/1368430210391311

Abstract: Contemporary so called follower-centric leadership theories often argue that “good leadership is in the eye of the beholder”. Leader categorization theory, for instance, suggests that subordinates use their cognitive representation of an ideal leader (ideal leader prototype) as an implicit “benchmark” to determine their openness towards the target’s leadership, i.e., influence. With the present study, we extend this rationale by hypothesizing that such benchmarking processes are subject to follower individual differences. In particular, we argue that the process of leader categorization plays a bigger role for subordinates who perceive themselves as ideal (potential) leaders. Moreover, this two-way moderation is proposed to be further qualified by subordinates’ disposition to engage in social comparison orientation. Results of two field samples with employees (N = 140; N = 287) confirm our hypotheses. In integrating the leader categorization perspective with an individual difference perspective, we not only expand the scope of follower-centric theorizing on social influence, but also support its validity.

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Copy reference link   DOI: 10.1016/j.ejor.2011.02.013

Abstract: In this paper, we consider a continuous review inventory system of a slow moving item for which the demand rate drops to a lower level at a known future time instance. The inventory system is controlled according to a one-for-one replenishment policy with a fixed lead time. Adapting to lower demand is achieved by changing the control policy in advance and letting the demand take away the excess stocks. We show that the timing of the control policy change primarily determines the tradeoff between backordering penalties and obsolescence costs. We propose an approximate solution for the optimal time to shift to the new control policy minimizing the expected total cost during the transient period. We find that the advance policy change results in significant cost savings and the approximation yields near optimal expected total costs.

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Copy reference link   DOI: 10.1016/j.tre.2010.07.007

Abstract: This paper presents the results of nine independent studies that link a seaport container terminal’s long-run average quay crane rate to various strategic and tactical decisions made by the terminal operating company. New numerical results on yard capacity, fleet composition, truck substitutability, and terminal scalability issues are obtained using a fully-integrated, discrete event simulation model of a vessel-to-vessel transshipment terminal that is designed to reproduce the microscopic, stochastic, real-time environment at a multiple-berth facility. These are the first such studies to be conducted using a fully-integrated simulation model of a non-automated container terminal.

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Copy reference link   DOI: 10.1080/00207543.2010.532910

Abstract: Tailored for a complex application in the process industry, this article examines a multi-product production planning and scheduling problem with sequence-dependent setup cost and times. The manufacturing process is characterised by a two-stage structure where the sequencing problem occurs on the first level and contribution margin, holding cost, penalty cost are accounted on the second level. We present a hybrid mixed-binary optimisation model based on the general lot-sizing and scheduling problem [Fleischmann, B. and Meyr, H. 1997. The general lotsizing and scheduling problem. OR Spectrum, 19 (1), 11–21], which combines discrete and continuous-time elements within a standard inventory and lot-size (I&L) formulation. Since the I&L formulation does not provide sharp linear programming-relaxation bounds, we present two alternative reformulations based on a transportation problem. In a numerical study inspired by real industry data, we show that on average, both reformulations yield significant improvements in computation time and integrality gap.

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Abstract: Dem deutschen Einkommensteuergesetz wird häufig vorgeworfen, es sei aufgrund seiner zahlreichen Ausnahmeregelungen zu komplex. In der hier beschriebenen Online-Studie (N = 742) wurden 82 Ausnahmen aus dem Einkommensteuergesetz auf ihre Gerechtigkeit und Wichtigkeit sowie die Angemessenheit der angesetzten Freibeträge und Freigrenzen beurteilt. Zusätzlich wurde erhoben, für welche gesellschaftlichen Gruppen Ausnahmeregelungen als gerecht empfunden werden. Es zeigt sich, dass nur wenige Ausnahmen als ungerecht und unwichtig (M < 3) eingeschätzt werden. Allerdings findet sich auch eine Beurteilung als eindeutig gerecht und wichtig (M > 4) nur in einer überschaubaren Fallzahl. Gerechtigkeits- und Wichtigkeitseinschätzungen hängen dabei eng zusammen. Als generell begünstigenswert gelten in erster Linie bedürftige, abhängige und leistungsschwache Gruppen wie Menschen mit Behinderung, Familien oder Kleinunternehmer. Über die verschiedenen Ausnahmen hinweg lässt sich allerdings keine entsprechende klare Struktur in der Bewertung der einzelnen Ausnahmen auffinden. Dabei besteht auch kein korrelationsstatistischer Zusammenhang zwischen sozioökonomischen Daten und der Bewertung der Ausnahmen bzw. den Angaben zu den zu begünstigenden Gruppen. Diese Erkenntnisse ermöglichen Hinweise für zukünftige Modifikationen des Gesetzes.

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Copy reference link   DOI: 10.1007/s10551-011-0897-7

Abstract: Traditionally, conceptualizations of human values are based on the assumption that individuals possess a single integrated value system comprising those values that people are attracted by and strive for. Recently, however, van Quaquebeke et al. (in J Bus Ethics 93:293–305, 2010) proposed that a value system might consist of two largely independent value orientations—an orientation of ideal values and an orientation of counter-ideal values (values that individuals are repelled by), and that both orientations exhibit antithetic effects on people’s responses to the social world. Following a call for further research on this distinction, we conducted two studies to assess the independent effects of ideal and counter-ideal values in leadership settings. Study 1 (N = 131) finds both value orientations to explain unique variance in followers’ vertical respect for their leaders. Study 2 (N = 136) confirms these results and additionally shows an analogous effect for followers’ identification with their leaders. Most importantly, we find that both value orientations exhibit their effects only independently when the content of the two orientations pertain to different value types in Schwartz’s (in J Soc Issues 50:19–46, 1994) circumplex model. Implications for theory and practice are discussed.

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Copy reference link   DOI: 10.1007/s11573-011-0490-7

Abstract: For companies, online communities (OCs) have become a potent means of rapidly and easily identifying user needs as a result of the social and technological changes within the Web 2.0. Some OCs even are suited ideally for integration into NPD as they frequently have innovative members. Despite their growing relevance, however, user innovation activities within OCs still are underexplored. The members’ motivations to innovate and contribute to OCs in particular are part of a young line of research requiring further investigation. This research provides an in-depth netnographic analysis of innovative, privately operated OCs dedicated to tangible consumer products. Most fundamentally, we differentiate 1) motives to join OCs, 2) motives to innovate, and 3) motives to publish innovations in OCs. This is the first study to categorize the motives of innovative OC members depending on the stages of their membership as well as situational factors. Our results support companies in understanding and classifying the members’ motives in independent customer OCs. This is a precondition for the development of specific incentives that stimulate innovative user activities in OCs and contribute to customer integration.

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Copy reference link   DOI: 10.1016/j.ejor.2011.06.019

Abstract: Lee et al. (1997) advocated the idea of sharing demand and order information among different supply chain entities to mitigate the bullwhip effect. Even with full supply chain visibility afforded by IT systems with requirements planning and with no information distortion, we identify a “core” bullwhip effect inherent to any supply chain because of the underlying demand characteristics and replenishment lead times. In addition, we quantify an incremental bullwhip effect as various operational deviations (inaccurate order placements, batching, lag in sharing demand forecast) contribute incrementally to the variance of the order quantity not only at the node where the deviation is taking place but also at all upstream supply chain nodes. We discuss some managerial implications of our results in the context of a UK manufacturer.

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