IIE Transactions Research Articles

Promoting electric automobiles: supply chain analysis under a government’s subsidy incentive scheme

This article analyzes a Fuel Automobile (FA) supply chain and an electric-and-fuel automobile supply chain in a duopoly setting, under a government’s subsidy incentive scheme that is implemented to promote the use of Electric Automobiles (EAs) for the control of air pollution. Benefiting from such a scheme, each EA consumer can enjoy a subsidy from the government. It is shown that the incentive scheme is more effective in increasing the sales of EAs when consumers’ bargaining power is stronger. The impact of the incentive scheme on consumers’ net surplus is the largest among all components in the social welfare. A higher subsidy may not result in a greater reduction in the environmental hazard. Moreover, a larger number of service and charging stations can reduce the negative impact of the incentive scheme on the FA market while enhancing its positive impact on the EA market. An incentive scheme with the centralized control with no subsidy is also considered and it is found that the incentive scheme is more effective in promoting EAs and protecting the environment. [Supplementary materials are available for this article. Go to the publisher's online edition of IIE Transactions for the Appendices to this article.]

Modified EWMA controller subject to metrology delay

The resource and capacity limitations of the metrology equipment used in the creation of integrated circuits result in delay being a common issue for the practical implementation of run-to-run control scheme. In the literature, several papers have provided the means of using metrology delay data or Virtual Metrology (VM) prediction models on the transient behavior and asymptotic stability of Exponentially Weighted Moving Average (EWMA) controllers. However, these procedures still suffer from large bias and/or variation of the process response variable. To overcome this difficulty, a modified EWMA controller is proposed that adjusts the process by using both the metrology delay data and VM information. The analytical expression of the process output of this developed controller and its long-term stability along with short-term output performance are derived. Furthermore, under some specific parameter settings, a more comprehensive study is presented to illustrate that the proposed controller has the capability to reduce the total mean square error of process response variable compared with existing controllers. [Supplementary materials are available for this article. Go to the publisher's online edition of IIE Transactions for the Appendices to this article.]

The call for equity: simulation optimization models to minimize the range of waiting times

Providing equal access to public service resources is a fundamental goal of democratic societies. Growing research interest in public services (e.g., health care, humanitarian relief, elections) has increased the importance of considering objective functions related to equity. This article studies discrete resource allocation problems where the decision maker is concerned with maintaining equity between some defined subgroups of a customer population and where non-closed-form functions of equity are allowed. Simulation optimization techniques are used to develop rigorous algorithms to allocate resources equitably among these subgroups. The presented solutions are associated with probabilistic bounds on solution quality. A full-factorial experimental design demonstrates that the proposed algorithm outperforms competing heuristics and is robust over various inequity metrics. Additionally, the algorithm is applied to a case study of allocating voting machines to election precincts in Franklin County, Ohio. [Supplementary material is available for this article. Go to the publisher’s online edition of IIE Transactions for the Appendices to the article.]

A distribution inventory model with transshipments from a support warehouse

This article considers a distribution inventory system consisting of N retailers and a regional support warehouse, all being replenished from a central warehouse/outside supplier. For the case where stock-outs occur, the retailers receive transshipments from the support warehouse at an extra cost. A model is presented for cost evaluation and optimization of the reorder points in the system under fill rate constraints. The solution method is designed to handle large real-life systems and is fast enough to be directly implemented in practice. A numerical study illustrates that (i) the model renders near-optimal solutions; (ii) the value of using a support warehouse can be significant even for large transshipment costs; and (iii) significant cost savings can be obtained using the proposed model. Using real data for a sample of 50 representative products, the proposed model reduces the expected holding and transshipment costs by 29% while still meeting target fill rates. [Supplemental materials are available for this article. Go to the publisher's online edition of IIE Transactions to view the supplemental file.]

Interpolation approximations for queues in series

Tandem queues constitute a fundamental structure of queueing networks. However, exact queue times in tandem queues are notoriously difficult to compute except for some special cases. Several approximation schemes that are based on mathematical assumptions that enable approximate analyses of tandem queues have been reported in the literature. This article proposes an approximation approach that is based on observed properties of the behavior of tandem queues: the intrinsic gap and intrinsic ratio. The approach exploits the nearly linear and heavy-traffic properties of the intrinsic ratio, which appear to hold in realistic production situations. The proposed approach outperforms existing approximation methods across a broad range of examined cases. It is also demonstrated that the proposed approach has the potential when applied to historical data to achieve accurate mean queue time estimates in practical production environments. [Supplemental materials are available for this article. Go to the publisher's online edition of IIE Transactions to view the supplemental file.]

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From group work to teamwork: A case study of “Lean” rapid process improvement in the ThedaCare Information Technology Department

This paper presents a mixed-methods case study of process improvement at the information technology (IT) Department of ThedaCare, a Northeast Wisconsin community health system. As part of its broader goal to improve care, ThedaCare launched a “Lean” improvement project directed at IT support or “fix work” services. IT Department staff, IT support service customers, and a Lean facilitator participated in a weeklong rapid improvement event. Participants identified opportunities for process improvement, collected baseline measures on how (and how well) the IT Department was providing support services, and jointly developed a preliminary solution centered on a new team-based organization of support services. Rather than forwarding service requests to groups of support staff organized by IT application type, service requests would now be resolved on-the-spot by a team with distributed knowledge of multiple applications. Six and twelve months post-intervention, there was some evidence of success, including performance improvement and staff buy-in. We use realistic evaluation as an organizing framework to describe potential links between the intervention content and process, the surrounding context, and the outcomes of the intervention. We hypothesize four mechanisms that mediate this link: work standardization; connections between people; seamless flow; and participatory problem solving. We conclude that other organizations can learn as much from ThedaCare's participatory rapid improvement process and Lean approach to transformational change as from the actual implemented changes. Supplemental materials are available for this article. Go to the publisher's online edition of IIE Transactions on Healthcare Systems Engineering to view the free supplemental file.

Optimal design of the synthetic chart for the process mean based on median run length

Control charts are usually designed using average run length as the criterion to be optimized. The shape of the run length distribution changes according to the shift in the mean, from highly skewed for an in-control process to approximately symmetric when the mean shift is large. Since the shape of the run length distribution changes with the mean shift, the Median Run Length (MRL) provides a more meaningful interpretation for in-control and out-of-control performances of the charts, and it is readily understood by practitioners. This article presents an optimal design procedure for a synthetic chart able to monitor the mean based on the MRL under the zero- and steady-state modes. The synthetic chart integrates and conforming run length charts. Pseudocodes and Mathematica programs are presented for the computation of the optimal parameters of the synthetic chart based on a desired in-control MRL (MRL(0)), a given sample size, and a specified mean shift for which a quick detection is needed. [Supplementary materials are available for this article. Go to the publisher's online edition of IIE Transactions for additional example, additional performance study, proof, tables, and figures.]

텍스트마이닝을 활용한 산업공학 학술지의 논문 주제어간 연관관계 연구

Identification of meaningful patterns and trends in large volumes of text data is an important task in various research areas. In the present study we crawled the keywords from the abstracts in IIE Transactions, one of the representative journals in the field of Industrial Engineering from 1969 to 2011. We applied low-dimensional embedding method, clustering analysis, association rule, and social network analysis to find meaningful associative patterns of key words frequently appeared in the paper.

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Creating clear designs: a graph-based algorithm and a catalog of clear compromise plans

A graph-based algorithm is proposed for creating regular fractional factorial designs with two-level factors such that a pre-specified set of two-factor interactions is clear of aliasing with any main effects or two-factor interactions (clear design). The Clear Interactions Graph (CIG) used in the algorithm is unique for each design and different in nature from the well-known Taguchi linear graph. Based on published catalogs of two-level fractional factorials, enhanced by the CIG, a search algorithm finds an appropriate clear design or declares its non-existence. The approach is applied to the creation of a catalog of minimum aberration clear compromise plans, which is also of interest in its own right. [Supplementary materials are available for this article. Go to the publisher’s online edition of IIE Transactions for additional discussions on run times and implementation of the algorithm for larger designs.]

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The “W” network and the dynamic control of unreliable flexible servers

This article addresses the problem of effectively assigning partially flexible resources to various jobs in Markovian parallel queueing systems with heterogeneous and unreliable servers. Attention is focused on a structure forming a “W” and it is found that this design is highly efficient; it requires only a small amount of cross-training but often performs almost as well as a fully cross-trained system. It is shown that (even allowing disruptions) a version of the cμ rule, which prioritizes serving the “fixed task before the shared,” is optimal under some conditions. Since the optimal policy is complex in general, a powerful and yet simple control policy is developed. This policy (which is implementable in any parallel queueing system) defines a simple measure of workload costs and assigns each server to the queue with the Largest Expected Workload Cost (LEWC). Thus, it effectively combines the intuition underlying two widely used policies: (i) the load-balancing objective in serving the Longest Queue (LQ); and (ii) the greedy cost minimization emphasis of the cμ rule. Extensive numerical tests show that LEWC performs well in comparison with four key policies: optimal, LQ, cμ, and generalized cμ (Gcμ). The stability of the LEWC, LQ, and Gcμ policies is proved. [Supplementary materials are available for this article. Go to the publisher's online edition of IIE Transactions for additional appendices (detailed proofs, additional analyses, data sets, etc.).]

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Setting planned lead times for a make-to-order production system with master schedule smoothing

This article considers a make-to-order manufacturing environment with fixed guaranteed delivery lead times and multiple product families, each with a stochastic demand process. The primary challenge in this environment is how to meet the quoted delivery times subject to fluctuating workload and capacity limits. The tactical planning parameters are considered, namely, the planning windows and planned lead times. The planning process that is modeled is the one in which the demand represents a dynamic input into the master production schedule. A planning window for each product family controls how the schedule of each product family is translated into a job release. It can be thought of as the slack that exists when the fixed quoted delivery lead time is longer than the total planned production lead time. Furthermore, the planned lead time of each station regulates the workflow within a multi-station shop. The model has underlying discrete time periods to allow the modeling of the planning process that is typically defined in time buckets; within each time period, the intra-period workflow that permits multiple job movements within the time period is modeled. The presented model characterizes key performance measures for the shop as functions of the planning windows and planned lead times. An optimization model is formulated that is able to determine the values of these planning parameters that minimize the relevant production-related costs. [Supplementary materials are available for this article. Go to the publisher's online edition of IIE Transactions for additional results of the simulation study in Section 6 of this manuscript.]