基于混合型Chopper电路的MMC-UPFC故障渡越方案

当交流系统发生短路时,基于模块化多电平控制器的统一潮流控制器(MMC-UPFC)串、并联侧MMC均会受到故障冲击,存在两侧换流器过流闭锁,MMC-UPFC完全退出运行的风险.对此,以交流系统发生最严重的三相短路故障为例,分析了MMC-UPFC串、并联侧MMC故障特性;在此基础上,借鉴风电场交流故障渡越的Chopper电...     

斜群代数的倾斜维数

基于倾斜理论引入了倾斜投射模的概念.讨论了它的基本性质,并进一步引入了模的倾斜投射维数以及Artin代数的倾斜整体维数.令G是有限群,研究了Artin R-代数Λ和斜群代数ΛG的倾斜整体维数之间的关系,得到等式t.gl.dim(Λ)=t.gl.dim(ΛG).     

Alone or together: examples from history research

Individualistic nature of research in the humanities is a common fact, as well as the notion that boundaries in humanities are poorly defined. Using citation analysis we have to take into account differences in citation practices not only between humanities and sciences but also within narrower fields of humanities. In the current study we observe differences between publication behaviour of historians and archaeologists, examine some aspects of citation practices in those fields, and show their effect on visibility.     

Influence of deposited metal structures on the failure mechanisms of silicon-based components

Miniaturised silicon-based multilayer chips are nowadays widespread as semiconductor components for the mobile device technology. The use of special processing and integration procedures requires such materials to possess a definite mechanical strength to ensure the functionality of the entire device. The strength and mechanical reliability of such components can be described by the Weibull theory, and is highly influenced by the geometry of the metallisation and other near-surface functional layers. In this work, we attempt to clarify the mechanisms leading to the failure of the metallised side of Si-chip components. The combined use of Finite Elements (FE) and Focused Ion Beam (FIB) analyses allowed recognising that cracks are induced in the metal-oxide-silicon interfacial area well before complete failure of the component. Such cracks have a crucial role in the lower strength and higher Weibull modulus observed on the metallised side.     

The Popov criterion and the inverse Nyquist method†

Kosonbrock's inverse Nyquist array (I.N.A.) theory for linear multivariable control Bystema with constant feedback elements is extended, to include systems lip to m nonlinear feedback elements, where the system has m inputs and m outputs. This extension is achieved by considering the Popov criterion for the most general case and through two further theorems. It shows that, as in the ease of Rosenbrock's I.N.A. theory, when certain auxiliary conditions are met with the help of suitable controllers, the design of multivariable controllers containing many non-linear feedbacks, can be based on the m frequency response loci corresponding to the diagonal entries of the open-loop inverse transfer function matrix. This leads to a simple design technique identical to the I.N.A. design method, suitable for use with a computer-aided design facility which permits a designer to use his intuitive understanding of transfer functions based on classical theory. The I.N.A. theory has been extended by Rosenbrock to cover systems having non-linear, time-varying feedback elements very recently.     

SOME OBSERVATIONS ON AIR MOVEMENTS IN CLEAN ROOMS WITH UNIDIRECTIONAL AIR FLOW

ABSTRACT

To avoid particle contamination in clean process production, unidirectional air flow with HEPA-filtered air is used, either in the entire room or partly in the critical process region (clean air zones), the purpose of this presentation is to describe a number of observations in unidirectional air flow and to discuss the interaction between air movements and the dispersion of airborne contaminants, it has been shown, by using smoke photography technique, that wake regions and vortex streets can easily be formed behind the working operator and objects. If a contaminant is emitted in the region of a vortex an accumulation can occur. It is important for the user to investigate that such vortices do not occur in the clean working zone.     

Environmental fatigue behavior of non‐crimp,E‐glass fiber reinforced polyester composites for marine applications

This study is aimed to find the fatigue behavior of Glass Reinforced Plastics, a material which is a widely preferred material for small marine crafts, as well as several other applications. The type of composite tested is hand‐laid E‐glass non‐crimp reinforcements with an polyester resin matrix. The specimens were produced in two standard thicknesses and with these material directions and were tested both under atmospheric and simulated seawater environments for fatigue. It was seen that the results of fatigue lifetime obtained by testing the material in seawater is much lower than the results obtained from testing similar specimens under atmospheric conditions. However, the stress curves indicate the same slope, suggesting that the fatigue failure mechanism of both testing conditions is the same and the fiber‐related factors dominate. It was found that the thickness and material direction did not have a significant effect on the fatigue behavior of the material.     

ARTIFICIAL INTELLIGENCE GOES MOBILE

New mobile computing technologies require new paradigms for infrastructure and interaction with mobile and networked devices. For building smart mobile companions for new intelligent services, a number of challenges have to be addressed. We argue that artificial intelligence is a key to a new generation of mobile systems. In this introduction to AI in mobile systems, we present some of the challenges and solutions in this exciting field of research.     

Diagonal stabilization of linear multivariable systems

A new procedure is presented for the synthesis of diagonal compensators for N × N linear multivariable systems that are free of fixed modes with respect to constant diagonal output feedbacks. The synthesis procedure employs simple polynomial algebra and it is in the form of an N-step algorithm. The geometric configurations 2N- and 2^N-cells in N-space are shown to be especially suitable for visualizing diagonal feedback and aiding the application of the synthesis algorithm.