Asia-Pacific Journal of Operational Research

This paper, analyzes the allocation problem of customers in a discrete-time multi-server queueing system and considers two criteria for routing customers' selections: equilibrium and social optimization. As far as we know, there is no literature concerning the discrete-time multi-server models on the subject of equilibrium behaviors of customers and servers. Comparing the results of customers' distribution at the servers under the two criteria, we show that the servers used in equilibrium are no more than those used in the socially optimal outcome, that is, the individual's decision deviates from the socially preferred one. Furthermore, we also clearly show the mutative trend of several important performance measures for various values of arrival rate numerically to verify the theoretical results.

In this paper, we consider the parallel machine scheduling with a simultaneity constraint and unit-length jobs. The problem can be described as follows. There are given m parallel machines and a graph G, whose vertices represent jobs. Simultaneity constraint means that we can process a vertex job v if and only if there exists at least d_G(v) idle machines, where d_G(v) is the degree of vertex v in graph G. Once a vertex job is completed, we delete the vertex and its incident edges from the graph. The number of machines that a vertex job needing depends on its degree in current graph. Changes of graph result in changes of vertex degree. Here, we consider a special case that all jobs in the original graph are unit-length. Let p_v denote the processing time of vertex job v, we define p_v = 0 if d(v) = 0, and p_v = 1, otherwise. The objective is to minimize the time by which each vertex job is completed, i.e., the time by which the graph becomes an empty graph. We show that this problem is strongly NP-hard and provide a -approximation algorithm.

This paper introduces a new multiple pivot shortest path simplex method by choosing a subset of non-basic arcs to simultaneously enter into the basis. It is shown that the proposed shortest path simplex method requires O(n) multiple pivots and its running time is O(nm). Results from a computational study comparing the proposed method from previously known methods are reported. The experimental show that the proposed rule is more efficient than the considered shortest path simplex pivot rules.

This study develops a mathematical inventory model for deteriorating item taking into account a vertical integration of a three-echelon supply chain (one supplier, one distributor, and one retailer) through strategic alliances. The objective is to minimize the joint total relevant cost for the integrated inventory model. A simple but efficient heuristic technique is used to derive the optimal solution. A numerical example and sensitivity analysis on the optimal results are presented to validate the results of the proposed integrated model. The proposed mathematical model has demonstrated how an integrated approach to decision making can achieve a global optimum and outperform three typically individual models (i.e., independent model, dominant supplier's model and dominant retailer's model).

In this paper, we have proposed a hybrid permutation-coded steady-state genetic algorithm for a single machine scheduling problem with earliness and tardiness costs and no machine idle time. The steady-state genetic algorithm generates schedules, which are further improved by successive applications of an adjacent pairwise interchange procedure. We have compared our approach against the best approaches reported in the literature. Computational results show the effectiveness of our approach, since it obtained better quality solutions in shorter time.

We consider a single server retrial queueing system in which arrivals occur according to a Markovian arrival process. An arriving customer finding an idle server will get service immediately; otherwise the customer enters into a retrial orbit. The system is subject to catastrophic failures at which time all customers in the system (the one in service as well as the customers, if any, in the orbit) are lost. The system undergoes a repair and after completion of a repair the server in the system will be available for service. The customers in the orbit try to reach the server by sending a signal at random times and get service if the server is idle at those times. While customers are waiting in the orbit, they may become impatient and leave the system after a random amount of time. Any arrival finding the server unavailable (due to busy or under repair) and cannot enter the orbit due to the buffer being full (in the case of finite buffer only) is considered lost. Under exponential assumption for all except for the arrivals, the queueing model (for both finite and infinite orbit sizes) is studied using matrix-analytic methods and the qualitative nature of the model is brought out through some illustrative numerical examples.

In today's increasingly competitive business world, selecting and evaluating the suppliers is one of the most important activities of a company. In the Taiwanese TV industry, selecting optimal suppliers of programs is also vital. But few attempts have so far been made to address this specific point. After reviewing the literature, we collect criteria for the selection of a program supplier. Considering the interdependence among the selection criteria, the analytic network process (ANP) is applied to help Taiwanese TV companies to effectively select optimal program suppliers. To avoid the complicated computing process from additional pairwise comparisons of the ANP, we retain the 12 critical criteria according to the opinions of the 44 senior executives about the importance of criteria: Quality, On-time, Marketability, Reputation, Rating, Finance, Relationship, Attitude, Communication, Creativity, Price and Time. Subsequently, we discuss with senior executives to group these criteria into 4 perspectives to structure the hierarchy for the selection of program suppliers. According to the hierarchy based on 4 perspectives and 12 vital criteria, Taiwanese TV companies could select optimal program suppliers more effectively. Moreover, the practical application of the ANP presented in Section 4 is generic and also suitable to be exploited for Taiwanese TV companies.