Yael Perlman

Setting expediting repair policy in a multi-echelon repairable-item inventory system with limited repair capacity

Inventory systems with limited repair capacity are affected by congestion externalities, caused by use of a shared service. There is incompatibility between individual and system optimisation in considering congestion externalities. Three models are described that investigate the congestion effect in a multi-echelon inventory system which has two modes of repair, each with a limited repair capacity. An expanding repair policy employed by the bases in order to choose which repair mode to use is described and compared with different expediting policies related to congestion externalities. The expanding repair policy that considers congestion externalities was found to lead to better system performance measurement than an expanding policy with no congestion. The results of the numerical experiment indicate that the model that ignores congestion externalities—that is, the model that measures each base as an individual—leads to poorer performance measurement for every expediting repair policy, and particularly for the optimal expediting repair policy.

Economic design of offline inspections for a batch production process

We consider a batch production process that can be either stable or unstable, in which inspection is performed offline after production of the batch is completed. The quality of a batch can be estimated with a desired level of certainty by inspecting only a sample of its units. In order to minimise the expected total cost per batch, which includes the costs of inspection, of false acceptance and of false rejection, we propose an economic inspection plan in which only a fraction of the batches, rather than each batch, is inspected. We prove that the expected total cost is a strictly quasiconvex function of the inspection interval. We establish necessary and sufficient conditions for the optimal inspection interval to be finite and propose an efficient algorithm to obtain its value. We demonstrate for the case of a single-sampling plan where the proposed economic approach outperforms the common procedure of inspecting every batch, and the proposed algorithm is very efficient.

The effect of risk aversion on product family design under uncertain consumer segments

A product family refers to a group of products that have been derived from a common product platform and which are specifically designed to satisfy a variety of market segments. In this paper, we consider a firm utilising product family design in order to respond to the requirements of two consumer segments, each characterised by different quality valuations. Although the total number of consumers in the market is known, the proportions each segment share are random, with known mean and variance. We show how the uncertainty of the market segmentation affects the firms decision whether to use common rather than unique components. Motivated by a problem faced by a major automotive manufacturer, we study the consequence of low and high uncertainty, various product quality levels and the difference of marginal valuation on the best configuration.

Reducing Shoplifting by Investment in Security

We consider a single retailer with a given potential revenue, who sells a product that is subject to shoplifting. In order to decrease losses due to shoplifting and to maximize his profit, the retailer can invest in security measures. In particular, we assume that the retailer purchases security services from a single security supplier. The security supplier decides which price to charge the retailer for these services, with the purpose of maximizing his own profit, and the retailer decides on the quantity of security services to purchase. We address this problem using a game theoretic approach, where the retailer competes with the supplier—the leader—who specifies first the service price. The retailer responds by deciding how much to invest in security. We study the conditions under which both players are profitable and the extent to which double marginalization affects the supply chain performance.

Mergers and acquisitions between risk-averse parties

This paper evaluates mergers and acquisitions (MA however, it may yield a higher price for the consumer. Moreover, we show that a decentralized supply chain can be more beneficial for the parties than a centralized supply chain (formed by acquisition).

Production Planning and WIP Assignment for Wafer Fabrication Tools With Availability Constraints

This paper deals with a short-term production plan of a single toolset during a shift at a semiconductor fabrication plant. We propose a cost-based optimization model that seeks to minimize the cost of the shift while meeting the following conditions: 1) the shift produces its required output, measured in work-in-process (WIP) levels; 2) preventive maintenance (PM) tasks are carried out in compliance with the manufacturers recommended PM policy; and 3) the equipment undergoes cleaning operations, as recommended by the manufacturer, in a way that minimizes the production of blank wafers (a by-product of the cleaning process). A linear programming model is formulated and a practical procedure is provided to solve this production plan problem. Data from a real fab are used to demonstrate the optimality and applicability of the proposed approach. Results of various sensitivity analyzes further demonstrate how the model can be used to analyze the impact of changes in cost parameters, WIP levels and production rate parameters on the optimal solution.

Centralized decision of internal transfer-prices with congestion externalities for two modes of repair with limited repair capacity

The internal transfer-prices set by an organization are what an organizations bases ‘pay’ its service centre, the depot, for its services. Since each base has a limited budget, these transfer-prices control and motivate the bases usage of two types of repair services: normal and expedited. In this paper, we implement a unique approach—transfer-prices with congestion externalities—to determine the optimal transfer-price for the expedited repair service. Inventory systems with limited repair capacity are affected by congestion externalities, which reflect the negative externalities caused by the use of a shared service. We also describe different models that develop transfer prices schemas, and which differ in the way they consider congestion externalities. Numerical illustrations based on data from an air force display the incompatibility between two optimization models. One model ignores congestion externalities, while another considers congestion externalities. In the case of congestion externalities, the base must pay extra for the expedited repair service. The increased costs are due to expanded usage of the limited repair capacity which a particular base is imposing on the rest of the system in the form of longer queues that degrade service quality.

Economic design of control charts for monitoring batch manufacturing processes

The issue of economic design of an control chart is addressed for a batch manufacturing process, subject to Markovian failure characteristics. The objective of this design is to minimise the expected total quality cost per batch. To find the optimal sample size and control limits, a Markov chain model is formulated. There is no analytical solution to the optimisation problem, so to avoid an exhaustive search, a heuristic approach, based on a regression model with the Cobb–Douglas function, is proposed. The impact of the model parameters and their interactions on the optimal solution is explored by conducting analysis of variance on 6561 numerical examples in a factorial design. Finally, an example of a real application demonstrates the effectiveness of the proposed model and heuristic.

Dynamic allocation of stochastically-arriving flexible resources to random streams of objects with application to kidney cross-transplantation

Abstract Two distinct random streams of discrete objects flow into a system and queue in two separate lines. Concurrently, two distinct types of resources arrive stochastically over time. Upon arrival, each resource unit is matched with a waiting object. One resource type is ʻflexible’ and can be allocated to either one of the object types. However, units of the other, non-flexible, resource type can be allocated only to units of one specific object type. The allocation probabilities are not fixed and may depend on both queue sizes of the two objects. If a resource unit is not allocated immediately, it is lost. The goal is to find an optimal state-dependent probabilistic dynamic allocation policy. We formulate the system as a two-dimensional Markov process, analyze its probabilistic behavior, and derive its performance measures. We then apply the model to the problem of kidney cross-transplantation and propose a new measure of system effectiveness, called Expected Value of Transplantation (EVT), based on the histocompatibility between kidneys and candidates. We further show that it is possible to balance the objectives of achieving equity in candidates’ expected waiting times (EW) and maximizing EVT by equating the value of EW/EVT between the two groups.

Part-time practice in healthcare: Impact on operational versus medical performance

Abstract We explore how reliance on part-time medical staff affects operational and medical outcome performance in two general surgery departments Whereas prior research has indicated that operational performance is positively associated with medical performance, we find that heavier reliance on part-time practice may deteriorate operational performance but not necessarily medical-outcome performance. For so-called “complex” patients, reliance on part-time practice may even override the effect of patients’ characteristics on medical-outcome performance. This result calls into question common perceptions in behavior marketing literature regarding part-time employees’ working patterns and efficiency, and thereby provides a new perspective regarding current labor-market trends.