Operations & Supply Chain Management

In many important combinatorial optimization problems, such as bin packing, allocating customer classes to queueing facilities, vehicle routing, multi-item inventory replenishment and combined routing/inventory control, an optimal partition into groups needs to be determined for a finite collection of objects; each is characterized by a single attribute. The cost is often separable in the groups and the group cost often depends on the cardinality and some aggregate measure of the attributes, such as the sum or the maximum element.

We empirically explore the accuracy of an easily computed approximation for long run, average performance measures such as expected delay and probability of delay in multiserver queueing systems with exponential service times and periodic (sinusoidal) Poisson arrival processes. The pointwise stationary approximation is computed by integrating over time (that is taking the expectation of) the formula for the stationary performance measure with the arrival rate that applies at each point in time.

We examine the effects of nonstationarity on the performance of multiserver queueing systems withe exponential service times and sinusoidal Poisson input streams. Our primary objective is to determine when and how a stationary model may be used as an approximation for a nonstationary system. We focus on a particular quesion: How nonstationary can an arrival process be before a simple stationary approximation fails? Our analysis reveals that stationary models can seriously underestimate delays when the actual system is only modestly nonstationary.

Similarity scaling often requires subjects to produce such a large number of judgments that fatigue may become a problem. Yet it remains unclear just how respondent fatigue affects similarity perceptions and resulting judgments. The present study uses a categorization perspective to examine the effects of fatigue on similarity judgments. The results suggest that subjects rely increasingly on category membership as they progress through a similarity judgment task.

A central assumption of meta-analysis is that the sample of studies fairly represents all work done in the field, published and unpublished. However, if studies with "poor" results are less likely to be published, a potential publication bias is present. The authors propose a maximum likelihood approach to estimating publication bias for the situation in which censorship based on effect size may occur. An explicit hypothesis test is provided for testing whether or not censorship is present.

In most vehicle routing problems, a given set of customers is to be partitioned into a collection of regions each of which is assigned to a single vehicle starting at a depot and returning there after visiting all of the region's customers exactly once in a route. In this paper we consider problem settings where the cost of a route may depend on its length ϑ as well as m, the number of points on the route, according to some general function f(ϑ,m), assumed to be nondecreasing and concave in ϑ.

The ultimate success of new product R&D depends as much on customer acceptance as on technological breakthroughs. In this article, Susan Holak and Donald Lehmann focus on customer acceptance by exploring the manner in which the general attributes of Rogers (relative advantage, compatibility, complexity, divisibility and communicability) plus perceived risk combine to form the intention to buy an innovation. Results demonstrate a causal structure among these attributes and lead to various implications for R&D guidelines and product design.

We consider a single-server queueing system with Poisson arrivals and general service times. While the server is up, it is subject to breakdowns according to a Poisson process. When the server breaks down, we need to repair the server immediately by initiating one of two available repair operations. The operating costs of the system include customer holding costs, repair costs and running costs. The objective is to find a corrective maintenance policy that minimizes the long-run average operating costs of the system. The problem is formulated as a semi-Markov decision process.