An integrated modelling approach for the representation and embodiment of engineering systems with standard components

In todays global markets the commercial success of a product, however defined, is highly dependent upon the rapid and efficient transformation of an engineering system from a design schema to a fully embodied optimal solution. The ability of the designer to achieve this is severely frustrated by the analytically intensive and time-consuming aspects of embodying a concept. This is particularly the case where standard components have to be considered. This paper presents a new modelling approach that supports the designer during the transformation of a concept to an embodied solution. This modelling approach provides for the representation of conceptual schemas and their subsequent embodiment with standard components from third-party electronic representations. The modelling strategies and associated software issues for representing a mechanical system, handling the interactions between components and incorporating the governing representations for the design and selection of individual components are discussed. The process of constructing a system model, specifying the desired performance characteristics and the process of system resolution are also described. The paper concludes with an industrial case study which is used to demonstrate the capabilities and potential of the new approach for supporting the embodiment of systems and the important task of design synthesis.     

Distributed Streams Algorithms for Sliding Windows

Massive data sets often arise as physically distributed, parallel data streams, and it is important to estimate various aggregates and statistics on the union of these streams. This paper presents algorithms for estimating aggregate functions over a “sliding window” of the N most recent data items in one or more streams. Our results include: 1. For a single stream,we present the first ε-approximation scheme for the number of 1’s in a sliding window that is optimal in both worst case time and space. We also present the first ε-approximation scheme for the sum of integers in [0..R] in a sliding window that is optimal in both worst case time and space (assuming R is at most polynomial in N). Both algorithms are deterministic and use only logarithmic memory words. 2. In contrast, we show that any deterministic algorithm that estimates, to within a small constant relative error, the number of 1’s (or the sum of integers) in a sliding window on the union of distributed streams requires Ω(N) space. 3. We present the first (randomized) (ε, δ)-approximation scheme for the number of 1’s in a sliding window on the union of distributed streams that uses only logarithmic memory words. We also present the first (ε, δ)-approximation scheme for the number of distinct values in a sliding window on distributed streams that uses only logarithmic memory words. Our results are obtained using a novel family of synopsis data structures called waves.     

The compatibility of structural adhesives with wood

An evaluation procedure, based on simple test methods, was developed in order to assess the compatibility with wood adherents of some new types of structural adhesives.Zusammenfassung Ein Bewertungsprozess wurde aufgrund einfacher Testmethoden entwickelt, um die Kompatibilität einiger neuer Typen von Klebern für Bauholz einzuschätzen.

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Die Kompatibilität von Klebern für Bauholz

     

Aurora: a new model and architecture for data stream management

This paper describes the basic processing model and architecture of Aurora, a new system to manage data streams for monitoring applications. Monitoring applications differ substantially from conventional business data processing. The fact that a software system must process and react to continual inputs from many sources (e.g., sensors) rather than from human operators requires one to rethink the fundamental architecture of a DBMS for this application area. In this paper, we present Aurora, a new DBMS currently under construction at Brandeis University, Brown University, and M.I.T. We first provide an overview of the basic Aurora model and architecture and then describe in detail a stream-oriented set of operators.Received: 12 September 2002, Accepted: 26 March 2003, Published online: 21 July 2003Edited by Y. Ioannidis     

Agent-based simulation of electricity markets: a survey of tools

Agent-based simulation has been a popular technique in modeling and analyzing electricity markets in recent years. The main objective of this paper is to study existing agent-based simulation packages for electricity markets. We first provide an overview of electricity markets and briefly introduce the agent-based simulation technique. We then investigate several general-purpose agent-based simulation tools. Next, we review four popular agent-based simulation packages developed for electricity markets and several agent-based simulation models reported in the literature. We compare all the reviewed packages and models and identify their common features and design issues. Based on the study, we describe an agent-based simulation framework for electricity markets to facilitate the development of future models for electricity markets.     

用有机掺杂硅酸盐法制备稳定的pH传感膜

采用溶胶-凝胶法制备基于染料吸收原理的光纤化学pH传感膜.通过有机掺杂,获得了对溶液pH具有宽范围动态响应的敏感膜.将四乙氧基硅烷和有机硅单体水解后加入pH指示剂,铺成溶胶-凝胶薄膜.该pH传感器的pH感应范围可达到pH3～11,响应速度3 min,一个月稳定性在RSD＜18%.     

换流站直流刀闸发热改造

就两起换流站直流刀闸发热的问题进行技术分析,从技术、经济及工程施工难易程度方面进行方案比较,在回路电阻计算的基础上提出了增加旁路导电带的改造方案.实施改造后在实际运行中测量结果表明改造结果良好.     

三维压电陶瓷的断裂

基于三维压电陶瓷中的一般平片裂纹前沿的位移，应力和应力强度因子的表达式，求得局部机械能率，以此建立了压电陶瓷的断裂准则。作为特例，将此准则应用于二维问题，所得结果与已有结果基本一致。     

我国缺水风险分布状况及其对策

在对风险理论及水资源风险研究进展回顾与展望的基础上，探讨了水资源短缺风险主导因子的辨识方法，提出了采用缺水率、人均缺水量和缺水边际损失3个指标的缺水风险评价指标体系，采用模糊层次分析评价方法对全国二级水资源分区的缺水风险进行了综合评价。评价结果表明，全国现状情况下有33个二级水资源分区面临着不同程度的水资源短缺风险，必须采取工程和非工程等防范措施和有效调控，方可减轻缺水风险对我国经济社会发展的危害程度。