Construction and performance analysis of a Petri net model based on a functional model in a CIM system

The so-called functional models, such as IDEF0, are useful tools for describing, designing and analysing the functional aspects of a complex manufacturing system, for example a CIM (computer integrated manufacturing) System. Though it involves considerable time and cost to build a sound functional model, the model usually cannot be used directly in further systems analysis procedures, such as quantitative performance analyses, due to its informal nature. To overcome this problem, we suggest a Petri net based procedure. First, we build a Petri net model from the IDEF0 and IDEF3 models, both of which are functional modelling tools widely used in real applications. Then, employing steady-state analysis for the Petri net, we propose a method to obtain performance measures such as the production rate. Since the analytical ability of a Petri net diminishes with increasing manufacturing system size, we develop a technique to aggregate and consolidate the Petri net to alleviate this problem that is associated with increasing complexity. An example problem is included to show the viability of our method for constructing a Petri net from a functional model and to evaluate the performance of the Petri net in an analytic manner.     

从日、韩低碳型生态城市探讨相关生态城规划实践

随着全球对气候变化和生态环境的重视,最近国内外的城市发展政策都将焦点集中到低碳生态城市的规划建设上.于是,实现现有城市发展模式向低碳生态城市空间结构的转变就成为城市领域共同探讨的新课题.目前,我国正在积极与新加坡和欧洲国家共同对生态城规划建设进行实践研究,在此背景下,首先对生态规划建设起步较早的日本和韩国的典型低碳型生态城市进行案例分析,然后利用归纳总结的规划要素构想出适合低碳生态城市建设的紧凑型城市空间结构,最后针对中新天津生态城与日本和韩国的低碳生态城市比较分析中得出的问题提出相应的改善建议.     

Design of class-based storage racks for minimizing travel time in a three-dimensional storage system

This paper deals with a new storage structure layout method called ‘cubic-in-time’, for minimizing the travel time of selected handling equipment in a three-dimensional palletized storage system. Storage-system design algorithms for minimizing travel times are described, the results are analysed, and some general conclusions are drawn.     

Electrical Properties of Sputter-deposited ZrO2-based Pt/ZrO2/Si Capacitors

Pt/ZrO2/Si sandwich structures where ZrO2 is deposited by radio frequency （r.f.） magnetron sputtering using a Zr target in an atmosphere of O2/Ar gas mixture, were fabricated and the effects of the O2/Ar flow ratio in the reactive sputtering process, the annealing temperature, the ZrO2 film thickness on the structure, the surface roughness of ZrO2 films and the electric properties of Pt/ZrO2/Si metal-oxide-semiconductor （MOS） capacitors were investigated. The optimum process parameters of the Pt/ZrO2/Si capacitor based on reactively sputtered-ZrO2 determined in such a way as the capacitance is maximized and the leakage current, the oxide charge, and the interface trap density are minimized that is the O2/Ar flow ratio of 1.5, the annealing temperature of 800℃, and the film thickness of 10 nm. Also the conduction mechanism in the Pt/ZrO2/Si capacitor has been discussed.     

Processing, microstructure and mechanical properties of hot-pressed SiC continuous fibre/SiC composites

SiC (SCS-6TM) continuous fibre/SiC composites were fabricated by hot-pressing at 1700°C in vacuum using an Al sintering additive. Analytical transmission electron microscopy was used to investigate the microstructure of the composites. The room-temperature mechanical and high-temperature creep properties of the composites were investigated by four-point bending. The SiC powders used were sintered at a relatively low sintering temperature to high density (97% of theoretical density) with the addition of the Al sintering additive. It is believed that the Al additive is very efficient for the densification of SiC. The SiC fibres maintained their original form and microstructure during fabrication. The SiC matrix reacted with the outermost carbon sublayer in the fibre, forming a thin (1.8–4.8m) interfacial layer, which was composed of Al4C3, Si–Al–C, and Si–Al–O phases. The incorporation of SiC fibre into a dense SiC matrix significantly increased the room-temperature failure strain and improved the high-temperature creep properties. In addition, the incorporation of SiC fibre into a porous SiC matrix increased the room-temperature failure strain, but did not contribute to the high-temperature creep properties.     

Grain growth of copper films prepared by chemical vapour deposition

Copper films having thickness 600 nm were prepared on TiN using chemical vapour deposition (CVD). The deposited films were annealed at various temperatures (350–550°C) in Ar and H₂(10%)-Ar ambients. The changes in the grain size of the films upon annealing were investigated. Annealing in an H₂(10%)-Ar ambient produced normal grain growth; annealing in an Ar ambient caused grain growth to stop at 550°C. The grain size followed a monomodal distribution and the mean size increased in proportion to the square root of the annealing time, indicating the curvature of the grain is the main driving force for grain growth. Upon annealing at 450°C for 30 min in an H₂(10%)-Ar ambient, the average grain size of the film increased from 122 nm to 219 nm, and the resistivity decreased from 2.35 μΩ cm to 2.12 μΩ cm at a film thickness of 600 nm. This revised version was published online in July 2006 with corrections to the Cover Date.     

The concept of directional binding energy and analysis of the phenomena involving surface and grain boundary: Part I Theory

The concept of directional binding energy (DBE) is proposed to describe the binding energy of the crystal and the ideal direction of the antiaction force against the surface tension, which derives the grain-boundary energy and also energy ratio (γ_gb/γ_s). It may provide a simple and lucid way to analyse the surface energy, grain-boundary energy and energy ratio from the correlative view point. It has been found that the grain-boundary energy can be derived only from the conceptual approach of DBE, irrespective of the dislocation model, which also makes it possible to determine the energy ratio with the misorientation angle. That is, the energy ratio (γ_gb/γ_s) is proportional to the misorientation angle, 2 sin (k′θ/2) where k′ is a constant and θ is the misorientation angle. This revised version was published online in November 2006 with corrections to the Cover Date.     

Differential Scanning Calorimetry of Fish Muscle: The Effect of Processing and Species Variation

Differential Scanning Calorimetry (DSC) has been used to study the thermal properties of fish muscle proteins and to measure the extent of their denaturation under various processing conditions. Fish myosin was susceptible to denaturation by frozen storage and dehydration. Denaturation of certain fish proteins was partially reversible. Although fish myosin was very unstable, its thermal stability was found to increase in species adapted, to higher environmental temperatures.     

Optimal number of minor failures before replacement

This paper extends a replacement model based on failure number to include a repair-cost limit for general failure distributions. The stochastic behaviour of failures and repair costs are modelled by a non-homogeneous Poisson process. An efficient marginal analysis algorithm is presented for finding the optimal failure number for replacement that minimizes the average cost rate.     

A Modification of the Coates Gain Formula for the Analysis of Linear Systems

In this paper, the Coates flow-graph gain formula is modified by the introduction of the loop-set and the two-loop-set, baaed on the concepts of the tree and the two-tree in network topology. The analogy is evident by observing that the two-trees T _ij of a given graph G can be obtained by coalescing vertices i and j of G and thon removing the self-loops. In a similar manner, the two-loop-sets can be obtained from the flow graph by first modifying the graph and then obtaining the loop-sets of tho modified graph. Because of such modification, the derivation of tho gain formula is considerably simplified. Consequently, the evaluation of the terms in the formula becomes easier. Finally, a simple method of determining the number of terms in the formula is derived as a check against possible omission of terms due to carelessness.