Sun Hur

Performance analysis of automatic storage/retrieval systems by stochastic modelling

This study considers an automated storage/retrieval system that performs either single or dual commands and analyses it as a queuing system with two waiting spaces and one server. It is assumed that the storage and retrieval commands arrive at the system according to Poisson processes with different rates and that the service times of single and dual commands are distributed differently. The steady-state probability distribution of the number of commands in the system at the service completion epochs is derived; subsequently, the semi-Markov process is employed to obtain the distribution at an arbitrary time. Several performance measures are derived and include the expected number of commands in the system, the expected waiting time, the probability that an arbitrary command cannot enter the system (the ‘blocking probability’) and the utilization of the storage/retrieval machine.

Performance computation methods for composition of tasks with multiple patterns in cloud manufacturing

Task composition in cloud manufacturing involves the selection of appropriate services from the cloud manufacturing platform and combining them to process the task with the purpose of achieving its expected performance. Calculation methods for achieving the performance expected by customers when the task has two or more composition patterns (e.g. sequential and switching pattern) are necessary because most tasks have multiple composition patterns in cloud manufacturing. Previous studies, however, have focused only on a single composition pattern. In this paper, we regard a task as a directed acyclic graph, and propose graph-based algorithms to obtain cost, execution time, quality and reliability of a task having multiple composition patterns. In addition, we model the task composition problem by introducing cost and execution time as performance attributes, and quality and reliability as basic attributes in the Kano model. Finally, an experiment to compare the performances of three metaheuristic algorithms (namely, variable neighbourhood search, genetic, and simulated annealing) is conducted to solve the problem. The experimental result shows that the variable neighbourhood search algorithm yields better and more stable solutions than the genetic algorithm and simulated annealing algorithms.

A Preventive Maintenance Scheduling Model of the Cluster Tool

This paper considers the preventive maintenance scheduling problem of the cluster tool which is one of the most important manufacturing equipments in the next-generation semiconductor production environment. We define a random process that expresses the successive amount of chemicals accumulating inside the tool. Based on the renewal theory, we find the expected value and probability distribution of the time that the amount of accumulated chemicals exceeds a predetermined level. For a given probability that the accumulated chemicals exceeds the predetermined level we present a method to obtain the number of chamber operations to perform the preventive maintenance of that chamber. In addition, a method to get the preventive maintenance schedule for the whole cluster tool is presented. A numerical example is provided to illustrate our method.

An Evaluation Model of Multimedia Composition Processes

Recent advances in developing smart devices, fast and reliable wireless communication, and mobile computing technologies offer rich information services to humans and machines by delivering multi-modal multimedia contents. As mobile contents are mostly composed of heterogeneous data delivered from multiple sources, these advances have significantly changed the way humans and machines interact from a content delivery perspective. How multiple devices communicate to provide useful content to users and how computing resources can be effectively exploited are critical issues in mobile computing. In this paper, a formal information composition process model is presented, and an analytical model based on a queueing theory approach is developed to address important challenges in the composition of multimedia information and the evaluation of content delivery in mobile computing. An illustrative application is also provided to demonstrate the effectiveness of the proposed model.

A real-time scheduling method for the cluster tool with wafer transfer delay

In this study, we propose an effective real-time scheduling method based on the timetabling technique for the cluster tool. Instead of considering the no-wait assumption generally adopted in almost all of the previous literature, we take wafer transfer delay into consideration, which implies that a wafer can stay at the current chamber for a certain, limited time before proceeding to the next chamber. In order to improve the total cycle time, an additional pulling procedure to the timetabling is introduced and applied. Numerical examples show that the proposed method gives effective schedules in real time even for practical-sized problems.

Mathematical model for performance analysis of a context-aware device with composite service

Abstract Recent advances in the development of smart devices and wireless network infrastructures have made it possible to provide a variety of rich services to diverse user groups. In order to make the best use of these technological benefits, the services provided by the device need to be developed and supplied with consideration for the user context that contains information about the environments with which the device and the user interact. The user context is mostly inferred based on the data that are dispersed in the user’s environment and can trigger a service when enough data are gathered to infer a certain degree of user context. A service provided by the device usually consists of one or more smaller services taking the form of a composite service. In this regard, we investigate a context-aware composite service provision process and present an analytical tool for assessing the performance of the process by means of a mathematical model. The results from extensive experimental simulations indicate that a performance assessment based on the proposed mean value analysis model effectively confirms the characteristics of the composite service systems.

Performance Analysis of Context-Aware Composite Device Services

Recent rich services provided by mobile devices take a form of composite services consisting of several constituent atomic services and they are gaining popularity due to technological advances and wireless network infrastructures. To make the best use of these technological benefits, the services given by the device need to be developed and provided with consideration of user context that contains information about environments. We regard these pieces of information as data segments that can trigger a service when they are gathered enough to infer a certain degree of the user context. In this regard, we investigate a context-aware composite service provision process and present an analytical tool for assessing the performance of the service provision process by means of a mathematical model. Based on the results from extensive experimental simulations, it is observed that the performance assessment based on the proposed mean value analysis (MVA) model effectively confirms the characteristics of the composite service systems.

An analytical model for delivery evaluation of multimodal contents in pervasive computing

Recent advance of mobile and interactive devices, such as smart phones, PDAs, and handheld computers, enables to deliver multimodal contents based on users and their environments. In pervasive computing, multimodal contents are mainly composed of multiple components which are often delivered from distributed multiple sources. Therefore, how appropriate contents can be provided to users and how computing resources can be effectively exploited are critical issues. In this paper, an analytical model for multimodal contents is developed based on a queueing theory for the purpose of delivery evaluation of the contents. The model can be applied to estimate how delivery parameters of multimodal contents, such as arrival rates, drop rates, and the number of packets, can impact overall the quality of services in terms of temporal aspects. A numerical example of weather information delivery is provided to illustrate the effectiveness of the proposed model.

An ECA-based Mechanism of Non-blocking Device Coordination for a Ubiquitous Environment

Recent advances in ubiquitous computing offer a variety of rich services to users using multiple devices. Since multiple devices operate concurrently to provide services to users, it is desirable to coordinate them in an effective manner. In particular, potential conflicts among devices need to be prevented while anticipated services are guaranteed to be delivered to users at the same time. In this paper, we present a novel mechanism to coordinate devices in a ubiquitous environment with formal methodologies. It ensures non-blocking service provision in consideration of deadlock- and livelock-free properties. An ECA-based framework is developed and the non- blocking property is proved using finite state automata. An illustrative example is provided and an application system is demonstrated.