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Sustainable scheduling of manufacturing and transportation systems
JID: EOR
ARTICLE IN PRESS
[m5G;October 1, 2015;8:59]
European Journal of Operational Research 000 (2015) 1–3
Contents lists available at ScienceDirect
European Journal of Operational Research journal homepage: www.elsevier.com/locate/ejor
Editorial
Sustainable scheduling of manufacturing and transportation systems
1. Introduction Scheduling has long been an active field in Operations Research (OR) due to its theoretical value for combinatorial optimisation and its practical relevance in the industrial and service sectors. Broadly speaking, scheduling concerns the allocation of limited resources to a number of competing agents in a way that certain performance measures are optimised for the system considered. Manufacturing and transportation represent two areas in which scheduling techniques have been most extensively used. Typical problems that have been widely studied in the literature include the job shop scheduling problem (for manufacturing) and the vehicle routing problem (for transportation). In the context of job shops, the order of processing jobs on each machine needs to be decided, while in the context of vehicle routing, decisions to be made include the allocation of orders to vehicles and also the delivery route for each vehicle. Traditional scheduling models focus on profit-driven performance indicators (e.g., the cycle time of a manufacturing system or distribution cost of a transportation system) while neglecting the negative externalities generated by manufacturing and transportation operations, such as excessive carbon emissions and other undesirable by-products threatening our environment. In recent years, natural resource deficiency, environmental deterioration and regulatory pressure have urged relevant companies or organisations to pay more attention to the sustainability aspects of manufacturing and transportation systems. In some manufacturing firms, for example, the performance indicator of greatest concern is related to energy consumption simply because of high electricity prices charged during peak hours or seasons. Appropriate scheduling of the manufacturing process plays an important role in improving energy efficiency besides the adoption of new production equipment. In the transportation sector, a recent trend is to employ alternative fuel vehicles (e.g., hybrid electric vehicles) with the aim of reducing the emission of greenhouse gases and toxic air pollutants. Scheduling the new types of vehicles considering their specific refuelling requirements can directly help to control the carbon footprint of transportation. This recent shift from economic profit to sustainability has resulted in a noticeable gap between theoretical scheduling assumptions and real-world scenarios. To bridge the gap, we solicited original and high-quality papers that present the latest research on manufacturing and transportation scheduling with explicit consideration of sustainability. Our endeavour attracted considerable attention and we received 59 submissions in total. A rigorous two-round review process was carried out, in which each submission was evaluated by at least three independent reviewers. The rigorous review process
resulted in 10 papers being accepted for inclusion in the current feature cluster, of which four are associated with manufacturing, four are related to transportation and the remaining two deal with supply chain problems. 2. Sustainable manufacturing scheduling The first paper by Gahm, Denz, Dirr, and Tuma (2015) develops a research framework for “energy-efficient scheduling” (EES) in manufacturing companies and provides a systematic review of the relevant publications. Since the manufacturing sector is a major energy consumer, production scheduling with the function of improving energy efficiency is essential for sustainable development of the manufacturing industry. It is encouraging to see that the number of publications related to EES approaches is growing rapidly in recent years. However, the interdisciplinary nature of EES has resulted in a very heterogeneous research field with a lot of ambiguous terms and definitions, making it challenging for one to evaluate or compare the scopes and conditions of different EES approaches. Therefore, a unified framework would potentially be helpful for the future research on EES. Applying an iterative methodology, Gahm et al. (2015) review, analyse and synthesise the current literature and propose a new framework to characterise the research field. Three dimensions, namely “energetic coverage”, “energy supply” and “energy demand”, are introduced to classify the problems studied in the literature. Each dimension contains categories and attributes to specify energy-related characteristics that are relevant for EES. The paper also highlights the benefits that can be achieved by EES in real-world applications, demonstrating that EES can make substantial contributions to the realisation of sustainable manufacturing. In the second paper, Ding, Song, and Wu (2015) study a permutation flow shop scheduling problem with the objectives of minimising the makespan and carbon emission. The processing speed of each machine can be adjusted: higher speed implies shorter processing time but leads to increasing energy consumption. After a preliminary investigation, the authors discover some structural properties of non-dominated solutions for this bi-objective optimisation problem. Inspired by these, they develop an extended Nawaz–Enscore– Ham (NEH)-Insertion procedure with energy-saving capability. Incorporating and utilising this procedure, a constructive heuristic method (i.e., the multi-objective NEH algorithm) and a meta-heuristic optimisation approach (i.e., the modified multi-objective iterated greedy algorithm) are proposed for solving the scheduling problem. Computational experiments show that the energy-saving function of the extended NEH-Insertion procedure remarkably helps both algorithms
http://dx.doi.org/10.1016/j.ejor.2015.09.019 0377-2217/© 2015 Elsevier B.V. and Association of European Operational Research Societies (EURO) within the International Federation of Operational Research Societies (IFORS). All rights reserved.
JID: EOR 2
ARTICLE IN PRESS
[m5G;October 1, 2015;8:59]
Editorial / European Journal of Operational Research 000 (2015) 1–3
in finding high-quality non-dominated solutions. Systematic comparisons suggest that the proposed algorithms can outperform some state-of-the-art meta-heuristics in the literature. In the next paper, Mansouri, Aktas, and Besikci (2015) study a similar scheduling problem but with two distinctive factors. First, the considered flow shop involves only two machines, and second, sequence-dependent setup time has been taken into account. A mixed-integer linear multi-objective optimisation model incorporating machine speed is developed to find the Pareto frontier comprised of the makespan and total energy consumption. Since it is not possible to solve this mathematical model in a reasonable timeframe for medium- and large-sized instances, the authors propose a constructive heuristic to assist shop floor operations managers in their daily scheduling tasks. They also define lower bounds for the two objectives under some non-restrictive conditions and compare the performance of the constructive heuristic with CPLEX by a design of experiments approach. It is found that the proposed heuristic performs better than CPLEX on most of the test instances. The following paper by Urban and Chiang (2015) is concerned with energy-efficient design of serial production lines. The design of production lines determines the required number of workstations and the relative length of idle time, both of which can directly affect energy efficiency of a production system. A traditional method of designing serial production lines is the balancing of paced synchronous lines. Line balancing is an effective tool for achieving sustainable manufacturing as it minimises the number of workstations. This, in turn, reduces the space requirement and idle time. The effectiveness of line-balancing procedures, however, is compromised when the task time is not known with certainty. The authors propose the use of unpaced synchronous lines as an alternative to paced lines when there is considerable variability in the task time. Rather than having a fixed cycle time, an unpaced synchronous production line advances only when all of the stations have completed their tasks. The paper shows that unpaced lines generally provide more energyefficient production processes than their paced counterparts.
studies flourish along this line of research, focusing on how to locate a given number of refuelling stations in a road network. The authors of this paper provide an enhanced compact model based on a combination of existing models from the literature for this location problem, and then extend the problem by adding the routing aspect of individual drivers. A branch and price algorithm is proposed as an exact solution methodology, and the results show that it requires significantly less computational time compared to existing models and adapts very well to more realistic network dimensions. Next in the line, the paper by Guépet, Briant, Gayon, and AcunaAgost (2015) deals with aircraft ground routing, i.e., the scheduling of aircraft movements between runways and parking positions under operational and safety constraints. Aircraft ground movements constitute a significant source of NOx emissions in airports, and therefore ground routing is a key component of the airport carbon footprint. The authors present a mixed-integer programming formulation for aircraft routing along a predetermined path for each flight, and then generalise the model to consider a set of possible paths for each flight. Their model takes into account four performance measures, of which the average taxi time is a direct indicator of aircraft fuel consumption and thus pollution emissions. Based on numerical results, the authors conclude that the punctuality indicators (the average delay and on-time performance) are in contradiction with the objective of reducing taxi time and emission. Qian and Eglese (2015) consider a vehicle routing problem that minimises fuel emissions in a road network with time-varying speeds. The route for each vehicle and the speeds of the vehicles along each road in their paths are treated as decision variables in the model. The objective is to minimise the total emissions in terms of the amount of greenhouse gases produced. To solve the problem, the paper presents a column generation based Tabu search algorithm, which is then used for modelling a distribution problem using real traffic data from a road network located in London. It is found that the proposed algorithm can achieve a reduction in greenhouse gas emissions of about 3% compared to an approach where the objective is to minimise the total time.
3. Sustainable transportation scheduling 4. Sustainable supply chain scheduling The first paper in this section by Passchyn, Briskorn, and Spieksma (2015) addresses a lock scheduling problem, which finds applications in the context of canal and waterway transportation systems. The authors consider the scheduling of a series of consecutive locks arranged in sequence along a canal. In the problem studied, ships travel in both directions and each lock acts as a single server that handles both the upstream and downstream traffic. Besides minimising the total flow time (i.e., the total time ships spend in the canal), another objective considered in the paper is to minimise fuel consumption (and the related emission of greenhouse gases) for ships passing through the waterway system. As ships are allowed to travel at different speeds, both fuel consumption and emissions per kilometre travelled increase at higher ship speed. Therefore, there is clearly a trade-off between reducing emissions and shortening ships’ flow times. The authors provide two mathematical programming formulations for the problem and compare them empirically. By computational evaluations, they confirm that the integrated scheduling of locks is more effective than a heuristic that schedules each lock individually. In the following paper, Yıldız, Arslan, and Karasan ¸ (2015) investigate the refuelling station location problem with routing considerations. As we have mentioned earlier, the use of alternative fuel vehicles in transportation is on the rise due to environmental concerns associated with fossil fuels and greenhouse gas emissions. However, this new generation of vehicles heavily relies on the availability of refuelling stations for alternative fuels. The lack of these stations is identified as one of the foremost barriers to widespread adoption of alternative fuel vehicles. To tackle the problem, several
The paper by Absi, Dauzère-Pérès, Kedad-Sidhoum, Penz, and Rapine (2015) addresses an emission-constrained single-item lot sizing problem, which concerns optimising the supply plan (when and how much to supply) of an item to satisfy deterministic timedependent demand over a planning horizon of several periods. In each period, the carbon emission constraint defines an upper limit on the average emission per product. Different supply modes are available, and fixed carbon emission is incurred at each period when a mode is selected. The problem deals with selecting the modes to use for each period and the quantities to order such that the supplying and inventory costs are minimised, while a carbon emission constraint per product in each period is satisfied. The authors present several dominant properties and two dynamic programming algorithms for this NP-hard problem. It is also established that the problem can be solved in polynomial time under specific assumptions. The final paper by Zhu, Wang, Chen, and Chen (2015) focuses on closed-loop supply chains, in particular, the application of tradein strategies in the remanufacturing industry. Remanufacturing has been regarded as an effective way to achieve environmental sustainability, but a fundamental challenge is to motivate consumers to return their used products and thereby ensure continuous input. As a special means of collection, trade-in not only takes back used products but also brings additional benefits, such as promotion of new product sales. The authors of this paper investigate the optimal production and trade-in pricing decisions for profit-maximising firms that sell a durable and remanufacturable product. To explain why
JID: EOR
ARTICLE IN PRESS Editorial / European Journal of Operational Research 000 (2015) 1–3
firms should be widely encouraged to implement trade-in and when to take action, they construct a duopoly competition model to explore the possible reasons from both the firm and the consumer perspectives. They develop a framework to model each customer’s purchasing or returning choices, and then focus on the decisions of the firms in the presence of duopoly competition both in the new product market and in the trade-in market. The optimal decisions for the firms and the threshold of implementing trade-in are derived under different scenarios according to the range of salvage values and government subsidies. 5. Conclusion To conclude, we would like to thank the authors for their highquality contributions relevant to the featured topics on sustainable scheduling. We also wish to acknowledge the reviewers involved for their constructive and timely feedback. A special note of thanks is extended to the co-ordinating editor, Roman Slowinski, for giving us the opportunity to guest-edit this feature cluster. We hope the papers in this feature cluster will provide readers a glimpse of the fast-growing research on “OR for sustainability” and attract more researchers to contribute to the field. References Absi, N., Dauzère-Pérès, S., Kedad-Sidhoum, S., Penz, B., & Rapine, C. (2015). The singleitem green lot-sizing problem with fixed carbon emissions. European Journal of Operational Research. doi:10.1016/j.ejor.2015.07.052. Ding, J.-Y., Song, S., & Wu, C. (2015). Carbon-efficient scheduling of flow shops by multi-objective optimization. European Journal of Operational Research. doi:10.1016/j.ejor.2015.05.019. Gahm, C., Denz, F., Dirr, M., & Tuma, A. (2015). Energy-efficient scheduling in manufacturing companies: a review and research framework. European Journal of Operational Research. doi:10.1016/j.ejor.2015.07.017. Guépet, J., Briant, O., Gayon, J. P., & Acuna-Agost, R. (2015). The aircraft ground routing problem: analysis of industry punctuality indicators in a sustainable perspective. European Journal of Operational Research. doi:10.1016/j.ejor.2015.08.041.
[m5G;October 1, 2015;8:59] 3
Mansouri, S. A., Aktas, E., & Besikci, U. (2015). Green scheduling of a two-machine flowshop: trade-off between makespan and energy consumption. European Journal of Operational Research. doi:10.1016/j.ejor.2015.08.064. Passchyn, W., Briskorn, D., & Spieksma, F. C. R. (2015). Mathematical programming models for lock scheduling with an emission objective. European Journal of Operational Research. doi:10.1016/j.ejor.2015.09.012. Qian, J., & Eglese, R. (2015). Fuel emissions optimization in vehicle routing problems with time-varying speeds. European Journal of Operational Research. doi:10.1016/j.ejor.2015.09.009. Urban, T. L., & Chiang, W.-C. (2015). Designing energy-efficient serial production lines: the unpaced synchronous line-balancing problem. European Journal of Operational Research. doi:10.1016/j.ejor.2015.07.015. Yıldız, B., Arslan, O., & Karasan, ¸ O. E. (2015). A branch and price approach for routing and refueling station location model. European Journal of Operational Research. doi:10.1016/j.ejor.2015.05.021. Zhu, X., Wang, M., Chen, G., & Chen, X. (2015). The effect of implementing tradein strategy on duopoly competition. European Journal of Operational Research. doi:10.1016/j.ejor.2015.07.053.
Rui Zhang School of Management, Xiamen University of Technology, Xiamen 361024, PR China Raymond Chiong Faculty of Science and Information Technology, The University of Newcastle, Callaghan, NSW 2308, Australia Zbigniew Michalewicz School of Computer Science, The University of Adelaide, Adelaide, SA 5005, Australia Pei-Chann Chang Department of Information Management, Yuan Ze University, Chungli, Taoyuan 32003, Taiwan E-mail addresses: [email protected] (R. Zhang), [email protected] (R. Chiong), [email protected] (Z. Michalewicz), [email protected] (P.-C. Chang)
ARTICLE IN PRESS
[m5G;October 1, 2015;8:59]
European Journal of Operational Research 000 (2015) 1–3
Contents lists available at ScienceDirect
European Journal of Operational Research journal homepage: www.elsevier.com/locate/ejor
Editorial
Sustainable scheduling of manufacturing and transportation systems
1. Introduction Scheduling has long been an active field in Operations Research (OR) due to its theoretical value for combinatorial optimisation and its practical relevance in the industrial and service sectors. Broadly speaking, scheduling concerns the allocation of limited resources to a number of competing agents in a way that certain performance measures are optimised for the system considered. Manufacturing and transportation represent two areas in which scheduling techniques have been most extensively used. Typical problems that have been widely studied in the literature include the job shop scheduling problem (for manufacturing) and the vehicle routing problem (for transportation). In the context of job shops, the order of processing jobs on each machine needs to be decided, while in the context of vehicle routing, decisions to be made include the allocation of orders to vehicles and also the delivery route for each vehicle. Traditional scheduling models focus on profit-driven performance indicators (e.g., the cycle time of a manufacturing system or distribution cost of a transportation system) while neglecting the negative externalities generated by manufacturing and transportation operations, such as excessive carbon emissions and other undesirable by-products threatening our environment. In recent years, natural resource deficiency, environmental deterioration and regulatory pressure have urged relevant companies or organisations to pay more attention to the sustainability aspects of manufacturing and transportation systems. In some manufacturing firms, for example, the performance indicator of greatest concern is related to energy consumption simply because of high electricity prices charged during peak hours or seasons. Appropriate scheduling of the manufacturing process plays an important role in improving energy efficiency besides the adoption of new production equipment. In the transportation sector, a recent trend is to employ alternative fuel vehicles (e.g., hybrid electric vehicles) with the aim of reducing the emission of greenhouse gases and toxic air pollutants. Scheduling the new types of vehicles considering their specific refuelling requirements can directly help to control the carbon footprint of transportation. This recent shift from economic profit to sustainability has resulted in a noticeable gap between theoretical scheduling assumptions and real-world scenarios. To bridge the gap, we solicited original and high-quality papers that present the latest research on manufacturing and transportation scheduling with explicit consideration of sustainability. Our endeavour attracted considerable attention and we received 59 submissions in total. A rigorous two-round review process was carried out, in which each submission was evaluated by at least three independent reviewers. The rigorous review process
resulted in 10 papers being accepted for inclusion in the current feature cluster, of which four are associated with manufacturing, four are related to transportation and the remaining two deal with supply chain problems. 2. Sustainable manufacturing scheduling The first paper by Gahm, Denz, Dirr, and Tuma (2015) develops a research framework for “energy-efficient scheduling” (EES) in manufacturing companies and provides a systematic review of the relevant publications. Since the manufacturing sector is a major energy consumer, production scheduling with the function of improving energy efficiency is essential for sustainable development of the manufacturing industry. It is encouraging to see that the number of publications related to EES approaches is growing rapidly in recent years. However, the interdisciplinary nature of EES has resulted in a very heterogeneous research field with a lot of ambiguous terms and definitions, making it challenging for one to evaluate or compare the scopes and conditions of different EES approaches. Therefore, a unified framework would potentially be helpful for the future research on EES. Applying an iterative methodology, Gahm et al. (2015) review, analyse and synthesise the current literature and propose a new framework to characterise the research field. Three dimensions, namely “energetic coverage”, “energy supply” and “energy demand”, are introduced to classify the problems studied in the literature. Each dimension contains categories and attributes to specify energy-related characteristics that are relevant for EES. The paper also highlights the benefits that can be achieved by EES in real-world applications, demonstrating that EES can make substantial contributions to the realisation of sustainable manufacturing. In the second paper, Ding, Song, and Wu (2015) study a permutation flow shop scheduling problem with the objectives of minimising the makespan and carbon emission. The processing speed of each machine can be adjusted: higher speed implies shorter processing time but leads to increasing energy consumption. After a preliminary investigation, the authors discover some structural properties of non-dominated solutions for this bi-objective optimisation problem. Inspired by these, they develop an extended Nawaz–Enscore– Ham (NEH)-Insertion procedure with energy-saving capability. Incorporating and utilising this procedure, a constructive heuristic method (i.e., the multi-objective NEH algorithm) and a meta-heuristic optimisation approach (i.e., the modified multi-objective iterated greedy algorithm) are proposed for solving the scheduling problem. Computational experiments show that the energy-saving function of the extended NEH-Insertion procedure remarkably helps both algorithms
http://dx.doi.org/10.1016/j.ejor.2015.09.019 0377-2217/© 2015 Elsevier B.V. and Association of European Operational Research Societies (EURO) within the International Federation of Operational Research Societies (IFORS). All rights reserved.
JID: EOR 2
ARTICLE IN PRESS
[m5G;October 1, 2015;8:59]
Editorial / European Journal of Operational Research 000 (2015) 1–3
in finding high-quality non-dominated solutions. Systematic comparisons suggest that the proposed algorithms can outperform some state-of-the-art meta-heuristics in the literature. In the next paper, Mansouri, Aktas, and Besikci (2015) study a similar scheduling problem but with two distinctive factors. First, the considered flow shop involves only two machines, and second, sequence-dependent setup time has been taken into account. A mixed-integer linear multi-objective optimisation model incorporating machine speed is developed to find the Pareto frontier comprised of the makespan and total energy consumption. Since it is not possible to solve this mathematical model in a reasonable timeframe for medium- and large-sized instances, the authors propose a constructive heuristic to assist shop floor operations managers in their daily scheduling tasks. They also define lower bounds for the two objectives under some non-restrictive conditions and compare the performance of the constructive heuristic with CPLEX by a design of experiments approach. It is found that the proposed heuristic performs better than CPLEX on most of the test instances. The following paper by Urban and Chiang (2015) is concerned with energy-efficient design of serial production lines. The design of production lines determines the required number of workstations and the relative length of idle time, both of which can directly affect energy efficiency of a production system. A traditional method of designing serial production lines is the balancing of paced synchronous lines. Line balancing is an effective tool for achieving sustainable manufacturing as it minimises the number of workstations. This, in turn, reduces the space requirement and idle time. The effectiveness of line-balancing procedures, however, is compromised when the task time is not known with certainty. The authors propose the use of unpaced synchronous lines as an alternative to paced lines when there is considerable variability in the task time. Rather than having a fixed cycle time, an unpaced synchronous production line advances only when all of the stations have completed their tasks. The paper shows that unpaced lines generally provide more energyefficient production processes than their paced counterparts.
studies flourish along this line of research, focusing on how to locate a given number of refuelling stations in a road network. The authors of this paper provide an enhanced compact model based on a combination of existing models from the literature for this location problem, and then extend the problem by adding the routing aspect of individual drivers. A branch and price algorithm is proposed as an exact solution methodology, and the results show that it requires significantly less computational time compared to existing models and adapts very well to more realistic network dimensions. Next in the line, the paper by Guépet, Briant, Gayon, and AcunaAgost (2015) deals with aircraft ground routing, i.e., the scheduling of aircraft movements between runways and parking positions under operational and safety constraints. Aircraft ground movements constitute a significant source of NOx emissions in airports, and therefore ground routing is a key component of the airport carbon footprint. The authors present a mixed-integer programming formulation for aircraft routing along a predetermined path for each flight, and then generalise the model to consider a set of possible paths for each flight. Their model takes into account four performance measures, of which the average taxi time is a direct indicator of aircraft fuel consumption and thus pollution emissions. Based on numerical results, the authors conclude that the punctuality indicators (the average delay and on-time performance) are in contradiction with the objective of reducing taxi time and emission. Qian and Eglese (2015) consider a vehicle routing problem that minimises fuel emissions in a road network with time-varying speeds. The route for each vehicle and the speeds of the vehicles along each road in their paths are treated as decision variables in the model. The objective is to minimise the total emissions in terms of the amount of greenhouse gases produced. To solve the problem, the paper presents a column generation based Tabu search algorithm, which is then used for modelling a distribution problem using real traffic data from a road network located in London. It is found that the proposed algorithm can achieve a reduction in greenhouse gas emissions of about 3% compared to an approach where the objective is to minimise the total time.
3. Sustainable transportation scheduling 4. Sustainable supply chain scheduling The first paper in this section by Passchyn, Briskorn, and Spieksma (2015) addresses a lock scheduling problem, which finds applications in the context of canal and waterway transportation systems. The authors consider the scheduling of a series of consecutive locks arranged in sequence along a canal. In the problem studied, ships travel in both directions and each lock acts as a single server that handles both the upstream and downstream traffic. Besides minimising the total flow time (i.e., the total time ships spend in the canal), another objective considered in the paper is to minimise fuel consumption (and the related emission of greenhouse gases) for ships passing through the waterway system. As ships are allowed to travel at different speeds, both fuel consumption and emissions per kilometre travelled increase at higher ship speed. Therefore, there is clearly a trade-off between reducing emissions and shortening ships’ flow times. The authors provide two mathematical programming formulations for the problem and compare them empirically. By computational evaluations, they confirm that the integrated scheduling of locks is more effective than a heuristic that schedules each lock individually. In the following paper, Yıldız, Arslan, and Karasan ¸ (2015) investigate the refuelling station location problem with routing considerations. As we have mentioned earlier, the use of alternative fuel vehicles in transportation is on the rise due to environmental concerns associated with fossil fuels and greenhouse gas emissions. However, this new generation of vehicles heavily relies on the availability of refuelling stations for alternative fuels. The lack of these stations is identified as one of the foremost barriers to widespread adoption of alternative fuel vehicles. To tackle the problem, several
The paper by Absi, Dauzère-Pérès, Kedad-Sidhoum, Penz, and Rapine (2015) addresses an emission-constrained single-item lot sizing problem, which concerns optimising the supply plan (when and how much to supply) of an item to satisfy deterministic timedependent demand over a planning horizon of several periods. In each period, the carbon emission constraint defines an upper limit on the average emission per product. Different supply modes are available, and fixed carbon emission is incurred at each period when a mode is selected. The problem deals with selecting the modes to use for each period and the quantities to order such that the supplying and inventory costs are minimised, while a carbon emission constraint per product in each period is satisfied. The authors present several dominant properties and two dynamic programming algorithms for this NP-hard problem. It is also established that the problem can be solved in polynomial time under specific assumptions. The final paper by Zhu, Wang, Chen, and Chen (2015) focuses on closed-loop supply chains, in particular, the application of tradein strategies in the remanufacturing industry. Remanufacturing has been regarded as an effective way to achieve environmental sustainability, but a fundamental challenge is to motivate consumers to return their used products and thereby ensure continuous input. As a special means of collection, trade-in not only takes back used products but also brings additional benefits, such as promotion of new product sales. The authors of this paper investigate the optimal production and trade-in pricing decisions for profit-maximising firms that sell a durable and remanufacturable product. To explain why
JID: EOR
ARTICLE IN PRESS Editorial / European Journal of Operational Research 000 (2015) 1–3
firms should be widely encouraged to implement trade-in and when to take action, they construct a duopoly competition model to explore the possible reasons from both the firm and the consumer perspectives. They develop a framework to model each customer’s purchasing or returning choices, and then focus on the decisions of the firms in the presence of duopoly competition both in the new product market and in the trade-in market. The optimal decisions for the firms and the threshold of implementing trade-in are derived under different scenarios according to the range of salvage values and government subsidies. 5. Conclusion To conclude, we would like to thank the authors for their highquality contributions relevant to the featured topics on sustainable scheduling. We also wish to acknowledge the reviewers involved for their constructive and timely feedback. A special note of thanks is extended to the co-ordinating editor, Roman Slowinski, for giving us the opportunity to guest-edit this feature cluster. We hope the papers in this feature cluster will provide readers a glimpse of the fast-growing research on “OR for sustainability” and attract more researchers to contribute to the field. References Absi, N., Dauzère-Pérès, S., Kedad-Sidhoum, S., Penz, B., & Rapine, C. (2015). The singleitem green lot-sizing problem with fixed carbon emissions. European Journal of Operational Research. doi:10.1016/j.ejor.2015.07.052. Ding, J.-Y., Song, S., & Wu, C. (2015). Carbon-efficient scheduling of flow shops by multi-objective optimization. European Journal of Operational Research. doi:10.1016/j.ejor.2015.05.019. Gahm, C., Denz, F., Dirr, M., & Tuma, A. (2015). Energy-efficient scheduling in manufacturing companies: a review and research framework. European Journal of Operational Research. doi:10.1016/j.ejor.2015.07.017. Guépet, J., Briant, O., Gayon, J. P., & Acuna-Agost, R. (2015). The aircraft ground routing problem: analysis of industry punctuality indicators in a sustainable perspective. European Journal of Operational Research. doi:10.1016/j.ejor.2015.08.041.
[m5G;October 1, 2015;8:59] 3
Mansouri, S. A., Aktas, E., & Besikci, U. (2015). Green scheduling of a two-machine flowshop: trade-off between makespan and energy consumption. European Journal of Operational Research. doi:10.1016/j.ejor.2015.08.064. Passchyn, W., Briskorn, D., & Spieksma, F. C. R. (2015). Mathematical programming models for lock scheduling with an emission objective. European Journal of Operational Research. doi:10.1016/j.ejor.2015.09.012. Qian, J., & Eglese, R. (2015). Fuel emissions optimization in vehicle routing problems with time-varying speeds. European Journal of Operational Research. doi:10.1016/j.ejor.2015.09.009. Urban, T. L., & Chiang, W.-C. (2015). Designing energy-efficient serial production lines: the unpaced synchronous line-balancing problem. European Journal of Operational Research. doi:10.1016/j.ejor.2015.07.015. Yıldız, B., Arslan, O., & Karasan, ¸ O. E. (2015). A branch and price approach for routing and refueling station location model. European Journal of Operational Research. doi:10.1016/j.ejor.2015.05.021. Zhu, X., Wang, M., Chen, G., & Chen, X. (2015). The effect of implementing tradein strategy on duopoly competition. European Journal of Operational Research. doi:10.1016/j.ejor.2015.07.053.
Rui Zhang School of Management, Xiamen University of Technology, Xiamen 361024, PR China Raymond Chiong Faculty of Science and Information Technology, The University of Newcastle, Callaghan, NSW 2308, Australia Zbigniew Michalewicz School of Computer Science, The University of Adelaide, Adelaide, SA 5005, Australia Pei-Chann Chang Department of Information Management, Yuan Ze University, Chungli, Taoyuan 32003, Taiwan E-mail addresses: [email protected] (R. Zhang), [email protected] (R. Chiong), [email protected] (Z. Michalewicz), [email protected] (P.-C. Chang)