COMPUTING MAXIMUM CLIQUES OF CIRCULAR ARCS IN PARALLEL*

Given a set S of n proper circular arcs, it is required to identify a largest cardinality subset K[S] of S each two of whose members intersect. This paper describes an optimal parallel algorithm to compute K[S]. The algorithm is not based on any previously known sequential solution, and is designed for the CREW PRAM model of computation. It uses 0(n/logn) processors and runs in O(logn) time. An interesting feature of the algorithm is that it transforms the computational geometric problem at hand, to a problem involving computations on 0-1 matrices, and then transforms the latter back into a ray shooting problem in computational geometry.     

概念格中多层次的属性约简理论

提出了形式背景的子概念格及形式背景关于概念、子概念格(包括概念格)的属性约简概念;定义了概念、子概念格(包括概念格)的特征函数,并以此为基础提出了属性约简定理,得出了具体的属性约简方法,同时研究了不同约简下属性间的关系,进一步完善了概念格属性约简理论,也为概念格用于数据处理及知识发现提供了新的工具.     

Universal instability modes in internal and external flows

Two prototypical external and internal flows have been studied which display linear temporal instability followed by nonlinear saturation taking the flows to a new equilibrium state. Direct simulation results are obtained using a specific formulation and numerical methods with very high accuracy. These results are analyzed via proper orthogonal decomposition (POD), which reveal similar modes for flow past a circular cylinder and flow inside a lid-driven cavity, indicating universality of such modes. Unlike many other efforts on reduced order modeling via POD, here the emphasis has been on understanding the physical aspect of the flow instability which requires very high accuracy of the simulation. Then, the obtained POD modes are related to the instability modes (in the classical sense of defining the latter) and new generic types of instability modes are identified in the studied external and internal flows. These new modes have been reported for flow past a circular cylinder [Sengupta TK, Singh N, Suman VK. Dynamical system approach to instability of flow past a circular cylinder. J Fluid Mech 2010;656:82–115] which help one in understanding the instability sequence and the relative importance of these modes in the flow evolution starting from an impulsive start. Present comparative study, furthermore, reveals universality of such instability modes by showing their presence for the flow inside a lid-driven cavity as well. Despite seeming dissimilarities between these two flows, similarities between the instability portrait of these two flows suggest universality of such modes. From the equilibrium amplitude of vorticity time-series, we establish the presence of multiple modes and multiple bifurcation sequences for these flows in parameter space. Existing theory due to Landau and Stuart that considers only a single dominant mode and its self-interaction does not explain all these features. We invoke a multi-modal interaction model in the cited reference above, termed as Landau–Stuart–Eckhaus (LSE) equation in recognition of Eckhaus’ work in modifying the classical Stuart–Landau equation. We also show that the new instability modes do not follow either the classical Stuart–Landau or the newly proposed LSE model equations and for this reason we call these as anomalous modes. Two specific classes of anomalous modes are identified and classified in the present work. Empirical expressions for the evolution of these anomalous modes are presented and their unambiguous role during instabilities is discussed.     

粗集中粗元的结构及其拓广

1 引言在决策过程中,如何处理不确定性,已吸引了不少学者的注意,对此,人们提出了各种各样关于不确定性信息的表示模型,及不确定性推理方法,如Shortliffe和Buchanan的不确定因子法,Duda的概率逻辑,Dempster和shafer提出的证据理论方法,Zadeh的模糊集理论,Dubois和Prade提出的可能度推理方法等。近年来,波兰人Pawlak建立的粗集理论在学术界影响很大,这是因为粗集理论为数据挖掘和知识发现领     

Two-stage iterations based on composite splittings for rectangular linear systems

In this paper, we introduce a two-stage method to solve rectangular linear systems that exhibits faster convergence than typical stationary iterative methods. Under suitable conditions, we prove convergence of the new method. The number of outer iterations can be reduced by using a few significant number of inner iterations for efficient computations. Further, we perform a comparison analysis, and establish that a higher number of inner iterations ensures a smaller spectral radius of the global iteration matrix. We also discuss the uniqueness of a proper splitting, and illustrate different comparison theorems for different subclasses of proper splittings.     

Using projection pursuit and proper orthogonal decomposition to identify independent flow mechanisms

In this paper, we develop a new dimension reduction technique, using the projection pursuit approach, to identify underlying physical mechanisms of the flow. By first applying the standard dimension reduction technique-proper orthogonal decomposition (POD), a low-dimensional subspace is defined. POD models of pressure fields have, in the past, been challenged with questions of interpretation in terms of flow mechanisms. To address this issue, the projection criterion is applied to decompose independent physical mechanisms in the non-Gaussian pressure field. This procedure leads to a non-orthogonal subspace decomposition that provides a suitable subspace for identification of physical mechanisms in intermittent flows. This approach provides a new tool to further our understanding of the fundamental nature of intermittent and independent phenomena in fluid flows. Finally, this technique is tested with experimental data collected at Texas Tech University's Wind Engineering Research Field Laboratory.     

汉语未登录词识别现状及一种新识别方法介绍

未登录词的识别对于各种汉语处理系统不仅有直接的实用意义,而且起到基础性的作用.在大规模中文文本的自动分词中,未被识别的未登录词是造成分词错误的一个重要原因,也成为许多自动分词系统走向应用的瓶颈.首先对未登录词的研究现状及现有方法做了一个综合的介绍,分析了目前方案的利弊.在此基础上提出了一个基于框架结构的未登录词专有名词识别方法.     

Compensation of high-frequency components of wind load by wind tunnel testing

To analyze the wind-induced response of structures, wind tunnel tests are often carried out to determine the wind loads on structures. However, due to the influence of similarity requirements in wind tunnel tests, the resulting data from the model test still needs to be translated by similarity rules for predicting the real loads on prototype structures. During this process, an inevitable result is that the high-frequency components of fluctuating wind loads get lost, which leads to some unexpected errors in the subsequent wind-induced response analysis. To solve this problem, a frequency compensation method is put forward. The purpose of this method is to reconstruct the high-frequency part of fluctuating wind loads based on experimental data and some basic principles of the aerodynamics of bluff bodies. The causes and effects of the frequency compensation problem are discussed first, then a practical method of frequency compensation is proposed by combining the fluctuating wind energy spectrum theory and the Proper Orthogonal Decomposition technique. Based on this method, the wind-induced response of a single-layer reticulated shell is analyzed to show the validity and necessity of this method.