A note on controllability of deterministic context-free systems

In this paper, we prove that the most important concept of supervisory control of discrete-event systems, the controllability property, is undecidable for two deterministic context-free languages $K$ and $L$, where $L$ is prefix closed, even though $K$ is a subset of $L$. If $K$ is not a subset of $L$, the undecidability follows from the work by Sreenivas. However, the case where $K$ is a subset of $L$ does not follow from that work because it is decidable whether $K$ and $L$ are equivalent as shown by Sénizergues. Thus, our result completes this study. The problem is also mentioned as open in the Ph.D. thesis by Griffin, who extended the supervisory control framework so that the specification language is modeled as a deterministic context-free language (compared to the classical approach where the specification is regular) and the plant language is regular. This approach is of interest because it brings an opportunity for more concise representations of the specification (as discussed, e.g., in the work by Geffert et al.) and, therefore, in some sense it treats the most interesting problem of current supervisory control theory, the state-space explosion problem.     

旋转式电场仪测量交流电场的研究

基于高斯定理,对旋转式电场仪在特高压交流输电线下交流电场中产生的感应信号进行了详细的理论推导,同时在实验室模拟了旋转式电场仪测量交流电场的工作过程,验证了该电场仪测量交流电场的可行性。这样,可以实现对特高压交直流同走廊输电线路下交流电场和直流电场同时进行实时测量,具有较高的实际应用价值和广阔的应用前景。     

模糊群决策环境下的实物期权模型

在实物期权B-S模型框架下,采用正态模糊数刻画模糊群决策环境下决策者的行为特征,并利用格贴进度理论构建了决策变量关系矩阵进行决策信息的赋权和归集,建立了在模糊群决策环境下利用实物期权方法进行大型项目投资决策的分析框架.模型解决了在模糊群决策环境中难以利用传统实物期权方法进行大型项目投资决策的问题,更加贴近实际决策情景.最后通过数值实例对模型的应用进行了说明.     

一种基于自适应框架的Web服务选择算法

在服务组合中,动态环境的变化可能导致参与组合的Web服务行为发生变化。为此,提出基于自适应框架的Web服务选择算法,用于获取公共服务注册处的信息,并将其记录在本地绑定库中,利用链接分析算法获得绑定库某一时刻高链接度的Web服务,实现服务选择。实验结果证明,该算法可在服务组合中动态选择高质量的Web服务,降低由服务质量变化造成的服务组合失败率。     

A new method for measurement of harmonic groups in power systems using wavelet analysis in the IEC standard framework

The paper presents a new method based on the wavelet-packet transform for the analysis of harmonic groups in power systems, compatible with the standards of the International Electrotechnical Commission. The paper studies the performance of the new method in the analysis of harmonic groups and the spectral leakage associated with the presence of interharmonic components, synchronized and non-synchronized with the fundamental component, and also due to the loss of synchronization between the sampling window width and the fundamental frequency. Finally, the results obtained in the application of this method to different test waveforms are compared with the results obtained using the IEC method.     

On the a-priori error analysis and convergence of meshless BEM

This paper deals with the a-priori error analysis and convergence of meshless boundary element methods. The paper investigates the convergence of the particular solution method (PSM) in conjunction with the boundary element method (BEM) as well as the method of fundamental solutions (MFS) and the radial basis functions (RBF)—type techniques. A-priori error estimates for meshless BEMs are also provided, and several illustrating numerical experiments are derived.     

A study on type II structures. Part I:: a modified one-dimensional mass–spring model

Most impact energy-absorbing structures can be classified into one of two types in terms of the shape of the overall quasi-static load–displacement curve in the early stages of deformation. Type I has a relatively “flat-topped” curve, while type II has an initial peak load followed by a “steeply falling” curve. The previous work showed that the deformation of type II specimens is much more sensitive to the impact velocity than that of type I specimens. That is, when the total kinetic energy remains the same for all specimens, smaller final deformations result from higher impact velocities; and this phenomenon is much more significant for type II specimens than for type I specimens. In order to explain this characteristic of type II structures, a one-dimensional mass–spring model with variable mass is proposed for a typical type II structure (i.e., a pair of pre-bent plates), and used to examine the effects of the lateral inertia of the structure under impact. Unlike conventional mass–spring models, our system contains an equivalent variable mass, which is a function of the rotational angle at plastic hinges and comes into effect during the second phase of the dynamic response. Predictions of this analytical model agree very well with an ABAQUS FE simulation of the dynamic response of the pre-bent plates to impact; and this verifies the validity of the mass–spring model proposed.