James D. Blocher

Online/In-Store Integration and Customer Retention

Reducing the risks believed to be associated with product availability can be critical to increasing consumer retention rates. This study considers the role that perceptions of channel integration have on such beliefs and their impact on purchasing decisions. Surveys distributed to purchasers of specific goods both online and in-store provide data used in the analysis of these effects. The findings suggest that firms simultaneously managing both online and in-store channels should not only reassess the repercussions of availability failures but also consider efforts that encourage the transparency of channel integration.

Measurement of Firm Diversification: Is It Robust?

This study investigated the convergent validity of Rumelt’s categorical classification of types of business diversification across different data sources and variations from Rumelt’s method. The st...

The customer order lead-time problem on parallel machines

We consider the problem of scheduling customer orders, each consisting of one or more individual jobs, on a set of parallel processors with the objective of minimizing average order completion time. We provide simple intuitive heuristics to guide managers in this environment and introduce lower bounds that show that these heuristics are effective for a wide variety of problems.

A forward branch-and-search algorithm and forecast horizon results for the changeover scheduling problem☆

Abstract This paper considers the problem of minimizing the total schedule changeover cost when faced with scheduling multiple products on a finite capacity resource. Several new analytical results are presented for this problem. These results are then used in developing a forward-time branch-and-search algorithm and forecast horizon results for the problem. We also present computational results to investigate the effectiveness of the forecast horizon results.

Minimizing customer order lead-time in a two-stage assembly supply chain

Abstract Coordination across different process stages of the supply chain is becoming more common as the information needed for this coordination is easier to obtain and share. With the availability of this information, managers are beginning to recognize that there can be benefits to scheduling processes in a coordinated fashion. Thus, finding good schedules for the entire supply chain has added importance to today’s managers. Coordination of the material as it moves from one stage to the next should lead to improved customer order lead-time performance for the whole chain and thus better customer service overall. We look at a two-stage assembly supply chain with the objective of minimizing the average customer order lead-time. Minimizing lead-time is becoming increasingly important as customers demand quicker response. But beyond this better customer service objective, minimizing lead-time is consistent with keeping inventory costs low. We introduce a number of properties of optimal solutions, results for special problem cases, and a series of lower bounds. We also provide a number of intuitive heuristics for coordinated supply chain scheduling and test them to determine their effectiveness.

A note on the Coffman---Sethi bound for LPT scheduling

Makespan minimization on a set of parallel machines is one of the most widely studied problems in scheduling theory. A new result is presented which improves on the classical Coffman–Sethi a posteriori bound on the relative error of the LPT algorithm. It is shown that the ratio of these two bounds (the old one to the new one) can be arbitrarily large.

Optimal single machine scheduling of products with components and changeover cost

We consider the problem of scheduling products with components on a single machine, where changeovers incur fixed costs. The objective is to minimize the weighted sum of total flow time and changeover cost. We provide properties of optimal solutions and develop an explicit characterization of optimal sequences, while showing that this characterization has recurrent properties. Our structural results have interesting implications for practitioners, primarily that the structure of optimal sequences is robust to changes in demand.

An efficient network-based formulation for sequence dependent setup scheduling on parallel identical machines

Abstract This paper compares the efficacy of a newly developed network-based mixed-integer programming (MIP) formulation with three existing formulations for the sequence dependent setup scheduling problem with earliness/tardiness penalties. This research shows that the new model is more efficient in terms of computation time for larger multi-machine problems than the existing formulations of these problems. The mixed-integer nature of the formulation allows companies to solve this class of problems with any one of many commonly available integer programming software packages. The presented MIP formulation provides a unique and useful method of conceptualizing and modeling a practical, yet difficult, problem within industry.

An Improved Lower Bound for the Changeover Scheduling Problem

In a multi-product, discrete-item manufacturing environment, it is often more economical to produce several products on one flexible machine than to have a dedicated machine for each product. In this paper, we consider the changeover scheduling problem (CSP). The CSP minimizes the cost consequences of changing over limited-capacity resources when two or more products are produced on them. We consider scheduling multiple products on a single machine where demand is dynamic, deterministic, and is to be met without backlogging. We develop analytical results for a lower bound on this problem and give computational results using this lower bound in a branch-and-bound algorithm.

Scheduling products with subassemblies and changeover time

We revisit the problem, previously studied by Coffman et al, of scheduling products with two subassemblies on a common resource, where changeovers consume time, under the objective of flow-time minimization. We derive some previously unidentified structural properties that could be important to researchers working on similar batch scheduling problems. We show that there exists a series of base schedules from which optimal schedules can be easily derived. As these base schedules build on each other, they are easy to construct as well. We also show that the structure of these base schedules is such that batch sizes decrease over time in a well-defined manner. These insights about the general form of the schedules might also be important to practitioners wanting some intuition about the schedule structure that they are implementing.