An Analysis of Scheduling Policies In Multiechelon Production Systems

Results of a simulation study of the economics of frequency of rescheduling Material Requirements Planning (MRP) systems are presented for a single-product, two-stage system in which demand is uncertain. The results indicate that for systems with moderate demand uncertainty, frequent rescheduling to maintain customer service may be uneconomical when compared with the alternative of more stable schedules in conjunction with safety stock. This result arises primarily because the cost of “emergency” production setups which occur when rescheduling is frequent exceeds the cost of safety stock required to “protect” stable schedules.     

A System for Measurement of Isokinetic Strength for Estimation of Load Handling Capacity

This note describes a method for measurement of isokinetic strength for prediction of manual materials handling capacity of individuals. The apparatus used in this methodology and measurement technique are illustrated in detail.     

Fast approximate analysis for token passing LAN protocol with asymmetrically distributed traffic loads

A new approximate analytical expression for the mean packet delay for a non-exhaustive token passing LAN is derived and compared with discrete event computer simulation. The computational problems associated with the exact and other approximate treatments are avoided because the need to solve a system of simultaneous equations is removed.<>     

Modeling Chirp and Phase Inversion in Wavelength Converters based on Symmetrical MZI-SOAs for use in All-Optical Networks

All-optical wavelength conversion based on multi-section semiconductor optical amplifiers (SOAs) in a symmetrical Mach-Zehnder interferometer (SMZI) is modeled for use in optical networks. It incorporates an enhanced SOA model that is implemented using the time domain transfer matrix approach and hence the overall numerical model determines simultaneously the wavelength and gain parameters for the wavelength converter. The overall model accurately predicts the optimal conditions for the SMZI arrangement in order to achieve the best results for the chirp, the phase inversion and the converted probe signal power. It is also demonstrated that large chirp and mismatch of the phase inversion reduces the eye opening ratio (EOR) which can seriously affect the performance of the wavelength converter to be used as a sub-system component in all-optical networks.     

New modelling strategy for representing asymmetric traffic loads on LANs

A new technique for modelling asymmetric traffic load distributions on local area networks (LANs) is presented. The traffic model which is analytical and easy to implement into discrete event computer simulations also has the benefit of providing expressions for the higher mathematical moments of the traffic load distribution.<>     

Higher order impedance and absorbing boundary conditions

Traditionally, generalized impedance boundary conditions (GIBCs) have been used to model dielectrics and coated surfaces, and absorbing boundary conditions (ABCs) have been used to simulate nonreflecting surfaces. The two types have the same mathematical form and, in most instances, a higher order condition involving higher order field derivatives has a better accuracy. We demonstrate that there is a close connection between the two and this enables us to use a systematic method which is available for generating GIBCs of any desired order to derive new two- and three-dimensional ABCs. The method is applicable to curvilinear/doubly-curved surfaces and examples are given. Finally, curves are presented that quantify the accuracy of two-dimensional ABCs up to the fourth order, and show how higher order ABCs can improve the efficiency of large scale partial differential equation (PDE) solutions     

邮电通信对信息化适应问题浅析

信息化是社会发展的必然要求，适应信息化的要注是邮电通信发展的一个基本目标。本文采取国际上较为通用的分析方法研究了中国邮电通信对信息化的适应程度，并结合通信发展中现存问题对今后发展提出应引以注意的方面。     

在帧中继骨干网上传送话音的技术

在帧中继网上传送话音（ＶｏＦＲ）是帧中继网上的一项增值业务。本文提出该业务的主要障碍是话音分组的时延和丢弃；接着又介绍了克服这些障碍的技术，包括话音压缩、采用回波消除器和抖动缓冲器以及优先级技术等；最后又探讨了ＶｏＦＲ的兼容性和标准化问题。     

迅速崛起的亚太光纤市场

本文归纳分析出亚太光纤市场的两个显著特点，介绍了亚太地区光通信发展水平，以及亚太各国和地区间的光通信合作，指出亚太光纤市场得以迅速发展的主要原因。