Sri V. Sridharan

Early/tardy scheduling with sequence dependent setups on uniform parallel machines

Abstract We consider the problem of scheduling N jobs on M parallel machines that operate at different speeds (known as uniform parallel machines), to minimize the sum of earliness and tardiness costs. Jobs are assumed to arrive in a dynamic albeit deterministic manner, and have nonidentical due dates. Violations of due dates result in earliness or tardiness penalties that may be different for different jobs. Setup times are job-sequence dependent and may be different on different machines based on the characteristics of the machines. For this problem, we present a mixed integer formulation that has substantially fewer zero–one variables than typical formulations for scheduling problems of this type. We present our computational experience in using this model to solve small sized problems, and discuss solution approaches for solving larger problems. Scope and purpose In JIT environments, firms face the need to complete jobs as close to their due dates as possible. Failure to do so would result in earliness and/or tardiness costs and the optimum schedule would seek to minimize functions of these costs. In many real-world situations, the problem is greatly complicated by the presence of disparate issues such as: (i) uniform parallel machines that are capable of processing these jobs at different speeds; (ii) sequence-dependent setup times; (iii) distinct job due dates; (iv) distinct job ready dates; and (v) distinct earliness and/or tardiness costs for each job. For this complex problem, we present a compact mathematical model and describe our computational experience in using this model to solve small sized problems.

Managing capacity in tightly constrained systems

Abstract Many make-to-order firms face total expected demand in excess of available capacity. This is particularly true, in the short range, for capital intensive firms such as those in the flow process industry, firms making short life cycle products such as those in high-fashion apparel industry, and printing-shops. In such situations the manager is left with the difficult task of allocating the available capacity between competing classes of products and/or customers. At the same time the manager is faced with the challenge of achieving delivery dependability and speed in order to stay competitive. In this paper, I describe the problem, contrast it with a class of problems known as perishable asset revenue management problems, review recent literature that presents alternative approaches for managing capacity such as capacity rationing, improved coordination mechanisms, and subcontracting, and discuss fruitful avenues for future research.

Mapping the Critical Links between Supply Chain Evaluation System and Supply Chain Integration Sustainability: An Empirical Study

Supply Chain Integration is widely advocated as an important factor to attain superior supply chain performance. While firms are able to achieve integration, they find it hard to sustain integration. In this paper, the authors argue that to sustain integration partner firms must establish a formal system to evaluate supply chain-wide performance. The authors draw on theories from a number of management disciplines to map the critical links between supply chain evaluation capability and supply chain integration sustainability. The authors develop and test the research model by conducting an empirical study involving 102 firms. The results of the study show that supply chains can sustain integration by establishing a supply chain wide evaluation system.

Dynamic non-preemptive single machine scheduling

Abstract Considering a dynamic single machine problem in which operations cannot be split, we first develop a decision theory based heuristic called DT-TD (Decision Theory-Tactically Delayed) of computational complexity O ( n 2 ). Using a simple look-ahead procedure, it produces, actically delayed (TD) schedules. We then develop a branch-and-bound (BB) algorithm (which uses DT-TD to obtain the initial upper bound) to obtain the optimum schedule. The optimum schedules are examined to identify conditions where TD schedules are necessary. Results based on 540 test problems suggest that TD schedules are important, for job shop scheduling under the range of conditions examined, when due dates are arbitrary and utilization is low. Additional test results indicate that the difference between the optimum schedule and the optimum non-delay schedule could be substantial. Finally, the performance of the DT-TD heuristic is analyzed by comparing its solution to the optimum solution obtained using the BB algorithm. The results indicate that the DT-TD heuristic is effective.

Applying confirmatory factor analysis multi-trait multi-method approach in supply chain management research

Supply chain integration (SCI) is considered as one of the important critical success factors for firms. Both academic researchers and business managers have attempted to understand the impact of supply chain integration for buyer and supplier firms. To date, the answer still remains unclear and is fuelled by debates that there could be an asymmetric distribution of benefits to buyer and supplier firms. One way to assess the impact of SCI is to assess the joint capabilities of buyer-supplier dyad. It calls for data collection of joint capabilities from the stand point of both the buyer and the supplier firms. When we deal with empirical research involving multiple traits (capability factors) and multiple methods (in this case, buyer and supplier firms), confirmatory factor analysis multi-trait multi-method approach can be applied to assess the construct validity. We provide a methodological review of this approach and provide a detailed empirical illustration by examining the ‘capabilities of buyer-supplier dyad’ construct.

Adapting traditional breakeven analysis to modern production economics: Simultaneously modeling economies of scale and scope

Abstract Although sophisticated models exists for the justification of advanced manufacturing technologies, practitioners often rely on simple tools, such as cost volume breakeven analysis (CVBA), to make initial comparisons between equipment alternatives. In the case of expensive automation technologies this initial comparisons may be followed by further attempts, using more sophisticated models, to define the costs and benefits of the alternatives remaining after CVBA. Ultimately, a leap of faith based upon some “intangible” benefits may underlie the actual adoption of new manufacturing technology (NMT). Finally, the implementation process determines the actual costs incurred and benefits derived from NMT. In this paper, we provide a historical perspective and show that CVBA is inadequate in the context of the process of justification for modern automation technologies. We also introduce an alternative to CVBA, cost volume flexibility breakeven analysis (CVFBA) and use examples to demonstrate its usefulness, particularly in the context of modern manufacturing technologies. CVFBA provides an approach which allows both economies of scale and economies of scope to be considered in initial comparisons between equipment alternatives. It may be applied at various levels of the managerial decision hierarchy.

Extending Cost-Volume Breakeven Analysis to Include Flexibility

Recently many manufacturers have emphasized the enhancement of customer service through increased manufacturing flexibility. Sophisticated models exist for the justification of modern automation technologies which could have an impact on manufacturing flexibility, but practitioners are more likely to utilize a simple tool such as cost‐volume break even analysis. Indeed, much of the difficulty that managers have in justifying modern automation technologies may be due to the shortsightedness of cost‐volume break even analysis. In this paper, we introduce an equally simple justification tool, cost‐volume‐flexibility break even analysis, and explain its use and the benefits accompanying its use.