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NP-complete problems such as the traveling salesman problem (TSP) play a prominent role in most advanced undergrad/graduate courses in discrete optimization modeling. Teaching such an important topic from a purely mathematical perspective without discussing specific applications may result in reduced student interest and motivation. The DeLand Crayon Company case introduces students to an application of the TSP to a practical production-planning scenario with realistic data. In crayon production, proper sequencing of colors in production can result in significant savings in total production time. The primary objective of the case is to provide students with hands-on experience in applying the TSP model. The case requires the students to consider variations of the basic model with the goal of encouraging them to think logically through the process of mathematical modeling and to consider the decision-making implications of their models. This case study can be used in undergraduate- and graduate-level courses in linear/integer programming or in production planning. It was implemented as part of a term project in a graduate operations research course with overwhelmingly positive feedback.

DeLand Crayon Company (DCC) is a large manufacturer of molded wax crayons. DCC sells three sizes of crayons, namely standard, large and jumbo. Standard-sized crayons, which account for most of the demand, include nine basic colors (red, blue, green, yellow, orange, violet, brown, black, and white), seven popular combination colors (red-orange, yellow-orange, yellow-green, red-violet, blue-green, blue-violet, and pink), 16 fluorescent colors, and four metallic colors. DCC also manufactures several specialty crayons, such as reduced length, hexagonal shaped, golden glitter, glow-in-the-dark, wipe-off, washable, and keno. Demand for non–standard-size crayons, fluorescent, and metallic-colored standard crayons and the specialty crayons is low and uneven, but DCC believes that they must be maintained to create the perception of a broad product line.

Combining the study of queuing with inventory is very common and such systems are referred to as queuing-inventory systems in the literature. These systems occur naturally in practice and have been studied extensively in the literature. The inventory systems considered in the literature generally include (s,S)-type. However, in this paper we look at opportunistic-type inventory replenishment in which there is an independent point process that is used to model events that are called opportunistic for replenishing inventory. When an opportunity (to replenish) occurs, a probabilistic rule that depends on the inventory level is used to determine whether to avail it or not. Assuming that the customers arrive according to a Markovian arrival process, the demands for inventory occur in batches of varying size, the demands require random service times that are modeled using a continuous-time phase-type distribution, and the point process for the opportunistic replenishment is a Poisson process, we apply matrix-analytic methods to study two of such models. In one of the models, the customers are lost when at arrivals there is no inventory and in the other model, the customers can enter into the system even if the inventory is zero but the server has to be busy at that moment. However, the customers are lost at arrivals when the server is idle with zero inventory or at service completion epochs that leave the inventory to be zero. Illustrative numerical examples are presented, and some possible future work is highlighted.

This paper analyzes the stochastic process generated by unit failures, and the corresponding cash flows, for products with cumulative warranties where the seller offers warranty on the total useful life of a batch of units rather than the lifetimes of individual units. Relative to individual warranties, cumulative warranties reduce administrative cost to seller as well as buyer, and are expected to lead to lower selling price due to reduced cost of warranty to the seller. For products with phase type lifetime distributions, matrix-analytic methodology is used to develop algorithms to compute economic measures such as cost of warranty. Results indicate that savings in cost of warranty due to a cumulative warranty relative to individual warranties, increase with increasing product lifetime variability, and that the marginal savings in cost of warranty decrease with increasing batch size. Economic measures are proposed to establish the amounts of discounts that the seller may be willing to offer, or the buyer expects, in order to change from individual warranties to a cumulative warranty.

A comprehensive case study to introduce students to several concepts from linear, integer, and goal programming in an integrative manner is presented. Starting with a relatively simple production planning decision problem, the case progressively incorporates generalizations to introduce various modeling principles. Each variation to the case enables the teacher to engage in insightful discussion into the nature of the optimal solutions; the effect on the optimum solution of changes to the objective function or to key constraints. The case article also describes several ways in which the case can be used, ranging from a comprehensive introduction to a concluding capstone case in an undergraduate or graduate course in linear programming. Case Teaching Note: Interested Instructors please see the Instructor Materials page for access to the restricted materials. To maintain the integrity and usefulness of cases published in ITE, unapproved distribution of the case teaching notes and other restricted materials to any other party is prohibited.

This paper addresses the question of servicing warranties for repairable items. Each time a unit under warranty fails, the manufacturer is obliged to restore it to operating condition either by repairing it or by replacing it with a new unit. The decision to replace or repair depends on a variety of factors such as cost of immediate repair, age of the unit, the extent of usage, the condition of the unit, and the remaining warranty period. We consider products with phase type lifetime distributions, where the phase describes the condition of the unit, and develop a decision support system (DSS) for the repair/replace decisions in servicing the warranty using the criterion of expected cost of servicing the remaining warranty. A comprehensive example is presented to illustrate the DSS. Effectiveness of the proposed DSS is verified by simulation.

This paper proposes an OR modelling approach to study the effect of managing queue reneging by providing amenities to improve customers' queueing experience. We evaluate quantitatively the changes in the servers' utilization and customers' satisfaction when the size and quality of the amenities are varied. We find that when the size of the amenities is increased to cover more and more customers, the incremental return in benefits will eventually diminish. So is the case when the quality of the amenities is improved to higher and higher standards for systems with sufficiently heavy workload. However, for systems with light workload, the models show that improving the quality of the amenities has an increasing incremental return in benefits.

Total quality management (TQM) is widely accepted as a means of obtaining and sustaining competitive edge. This study finds support for the proposition that TQM implementation correlates with quality performance. Behavioral factors (role of top management leadership, customer focus, human resource focus, and quality focus) as well as TQM tools and techniques (corporate planning, process focus, and information and analysis) contribute to the successful implementation of TQM. Also, the study finds that the size of the company (big or small), the company’s adoption of TQM, and the duration of a company’s experience with TQM affect the rigor of implementation and the resulting level of quality performance. However, the nature of the company (manufacturing or service) does not seem to have a significant effect on the rigor of quality management implementation and level of quality performance.

This paper focuses on gaining insight into the impact of TQM on the business performance of the service sector of the economy. The study yields clear evidence that TQM implementation improved business performance in the service sector of Singapore. Success of TQM implementations appears to be attributable more to the rigor of its implementation rather than the duration. The study finds that while accrued benefits can be attributed to some of the tools of TQM, such as, customer focus and quality improvement rewards, the key to the success of TQM lies in its intangible and behavioral features such as top management support, employee empowerment and employee involvement.

Investigates the state of benchmarking in the manufacturing and service sectors of Singapore. Our aim is to understand the state of benchmarking in Singapore as well as the expectations and motivation of non‐benchmarking companies. Our approach to the adoption of benchmarking is to view it as a major organisational change. We seek to understand the many dimensions of the transformation process. In addition, we examine the role of factors such as motivation, objectives, driving force, top management’s commitment, preconditions, process, company culture, employee participation, presence of pitfalls, and the potential benefits in determining the success of a benchmarking project. We identify driving forces, preconditions and effectiveness of implementation as the major facilitators of benchmarking. Also, we establish the importance of these facilitators towards the achievement of benefits and success of benchmarking. Moreover, the study emphasises the importance of preconditions and effectiveness of implementation for the success and benefits of benchmarking.

We consider a system of single user workstations connected to a file server over a local network. Users arrive at random intervals and occupy a workstation if one is available otherwise leave the system. Upon arrival, the user issues a request for file transfer from the server to the workstation local memory. Subsequent requests for additional transfers are issued in a random manner as needed. We consider two priority schemes for scheduling the two types of requests at the file server. Assuming that all relevant intervals are exponentially distributed, we propose two queueing models for the two scheduling schemes and develop computational procedures to analyze the performance of the system. Illustrative examples are presented to study the system behavior under various load conditions and to compare the performance of the two scheduling disciplines.

Falcon Die Casting Company (FDC) is an automotive parts manufacturer based in Ohio. FDC recently patented an innovative method of high volume die casting using traditional die casting machines. This patent was instrumental in FDC receiving a long term contract from a major automobile manufacturer for the bulk of its requirements for five key die cast items used in most of its automobiles. The customer provides FDC with an indication of the possible demand for the next 12 weeks with the understanding that demand beyond Week 2 is tentative and subject to change depending on auto sales during the preceding weeks. Table 1 shows the projected demand for the next 12 weeks. FDC can produce the parts on five die casting machines, each of which is capable of producing a subset of the parts as indicated in Table 2. For example, Part 1 can be produced only on Machines 1 and 2.

Most undergraduate curriculums in CS include at least a one semester study of data base management systems. In this paper, we take a closer look at a DBMS course we have offered recently and elaborate on a world wide web based database project in this course; it integrates a number of ideas not only from within DBMS but across other CS areas. We discuss the objectives underlying the design of the project and the ways in which these projects provide students with a feel for the organization and use of contemporary commercial database applications.