基于轮廓系数的参数无关空中交通轨迹聚类方法

为消除专家经验的主观性、避免依赖轨迹特征并且减轻实验调参的负担,提出一种基于轮廓系数的参数无关聚类分析（PICBASIC）算法。首先,比较了现有基于欧氏距离的航迹配对方法,并且建立基于动态时间弯曲（DWT）距离和高斯核函数的轨迹相似度计算模型;其次,利用谱聚类对空中交通轨迹进行聚类划分;最后,提出一种基于轮廓系数的最佳簇数寻优方法,并且其具有对聚类结果量化评价功能。利用真实进场轨迹进行实验验证,PICBASIC判断将28L跑道的365条轨迹聚为5个簇,28R跑道的530条轨迹聚为6个簇时聚类质量最佳,平均轮廓系数分别为0.8099和0.8056。相同实验数据条件下,PICBASIC与MeanShift聚类的平均轮廓系数差异率分别为-1.23%和0.19%。实验结果表明：PICBASIC包容轨迹的速度和长度差异,全程无需人工指导或实验调参,而且能够筛除异常轨迹对聚类质量的不利影响。     

Intersecting a freeform surface with a general swept surface

We present efficient and robust algorithms for intersecting a rational parametric freeform surface with a general swept surface. A swept surface is given as a one-parameter family of cross-sectional curves. By computing the intersection between a freeform surface and each cross-sectional curve in the family, we can solve the intersection problem. We propose two approaches, which are closely related to each other. The first approach detects certain critical points on the intersection curve, and then connects them in a correct topology. The second approach converts the intersection problem to that of finding the zero-set of polynomial equations in the parameter space. We first present these algorithms for the special case of intersecting a freeform surface with a ruled surface or a ringed surface. We then consider the intersection with a general swept surface, where each cross-sectional curve may be defined as a rational parametric curve or as an implicit algebraic curve.     

A rational model of the surface swept by a curve*

This paper shows how to construct a rational Bezier model of a swept surface that interpolates N frames (i.e., N position/orientation pairs) of a fixed rational space curve c(s) and maintains the shape of the curve at all intermediate points of the sweep. Thus, the surface models an exact sweep of the curve, consistent with the given data. The primary novelty of the method is that this exact modeling of the sweep is achieved without sacrificing a rational representation for the surface. Through a simple extension, we also allow the sweeping curve to change its size through the sweep. The position, orientation, and size of the sweeping curve can change with arbitrary continuity (we use C² continuity in this paper). Our interpolation between frames has the classical properties of Bezier interpolation, such as the convex hull property and linear precision. This swept surface is a useful primitive for geometric design. It encompasses the surface of revolution and extruded surface, but extends them to arbitrary sweeps. It is a useful modeling primitive for robotics and CAD/CAM, using frames generated automatically by a moving robot or tool.     

Boundary of the volume swept by a free-form solid in screw motion

The swept volume of a moving solid is a powerful computational and visualization concept. It provides an excellent aid for path and accessibility planning in robotics and for simulating various manufacturing operations. It has proven difficult to evaluate the boundary of the volume swept by a solid bounded by trimmed parametric surfaces undergoing an arbitrary analytic motion. Hence, prior solutions use one or several of the following simplifications: (1) approximate the volume by the union of a finite set of solid instances sampled along the motion; (2) approximate the curved solid by a polyhedron; and (3) approximate the motion by a sequence of simpler motions. The approach proposed here is based on the third type of simplification: it uses a polyscrew (continuous, piecewise-helical) approximation of the motion. This approach leads to a simple algorithm that generates candidate faces, computes the two-cells of their arrangement, and uses a new point-in-sweep test to select the correct cells whose union forms the boundary of the swept volume.     

Efficient topology determination of implicitly defined algebraic plane curves

This paper is devoted to present a new algorithm computing in a very efficient way the topology of a real algebraic plane curve defined implicitly. This algorithm proceeds in a seminumerical way by performing a symbolic preprocessing which allows later to accomplish the numerical computations in a very accurate way.     

Determination of the topology of a directed network

We consider strongly-connected, directed networks of identical synchronous, finite-state processors with in- and out-degree uniformly bounded by a network constant. Via a straightforward extension of Ostrovsky and Wilkerson's Backwards Communication Algorithm [Proc. 14th Annual Symp. on Principles of Distributed Computing, 1995], we exhibit a protocol which solves the Global Topology Determination Problem, the problem of having a root processor map the global topology of a network of unknown size and topology, with running time O(ND) where N represents the number of processors and D represents the diameter of the network. A simple counting argument suffices to show that the Global Topology Determination Problem has time-complexity which makes the protocol presented asymptotically time-optimal for many large networks.     

Complete swept volume generation, Part I: Swept volume of a piecewise C-continuous cutter at five-axis milling via Gauss map

In this paper, we present a methodology to generate swept volume of prevailing cutting tools undergoing multi-axis motion and it is proved to be robust and amenable for practical purposes with the help of a series of tests. The exact and complete SV, which is closed from the tool bottom to the top of the shaft, is generated by stitching up envelope profiles calculated by Gauss map.The novel approach finds the swept volume boundary for five-axis milling by extending the basic idea behind Gauss map. It takes piecewise C¹-continuous tool shape into account. At first, the tool shape is transformed from Euclidean space into Tool map (T-Map) on the unit sphere and the velocity vector of a cutter is transformed into Contact map (C-Map) using Gauss map. Then, closed intersection curve is found between T-Map and C-Map on the Gaussian sphere. At last, the inverse Gauss map is exploited to get envelope profile in Euclidean space from the closed curve in the range. To demonstrate its validity, a cutting simulation kernel for five-axis machining has been implemented and applied to mold and die machining.     

模拟透视云成像的调色板映射方法研究

利用基于ＨＶＳ成像方法的含水汽大气自然景观的亮度模型,建立透视云的离散模型,确定ＲＧＢ显示方式中Ｒ,Ｇ,Ｂ三参量与亮度间的转换关系,并提出基于ＲＧＢ显示方式的高速云中透视成像方法。该方法具有速度快,透视同效果良好的特点。     

A tool to minimize the time costs of parallel computations through optimal processing power allocation

In this paper, we present a software system, OPAS (Optimal Allocation System), that incorporates the optimal allocation policy in the analysis of the time-cost behaviour of parallel computations. OPAS assumes that the underlying system which supports the executions of parallel computations has a finite number of processors, that all the processors have the same speed and that the communication is achieved through a shared memory. OPAS defines the time cost as a function of the input, the algorithm, the data structure, the processor speed, the number of processors and the processing power allocation. In analysing the time cost of a computation, OPAS first uses the optimal allocation policy that we developed previously to determine the amount of processing power each node receives and then derives the computation's time cost. OPAS can evaluate different time-cost behaviours, such as the minimum time cost, the maximum time cost, the average time cost and the time-cost variance. It can also determine the speed-up and efficiency, and plot the time-cost curve and time-cost distribution.     

一类复杂系统非建模控制方法的研究

以石油化工中加热炉、反应器、蒸馏塔等为背景，讨论复杂系统的控制问题，目的是寻求对复杂系统的有效控制方法。对复杂系统进行稳定控制，必须考虑诸如非线性、大时滞、时交和强耦合的控制问题。给出了这类问题的一种解决途径，并给出了成功应用的实例。     

具有非线性时变滑模面的变结构控制系统设计

以二阶系统为研究对象,提出一种具有非线性连续时变滑模面的变结构控制器设计方法.用该方法设计的变结构控制系统,系统的初始状态位于滑模面上,通过滑模面斜率的连续变化,能消除系统状态变量到达滑模面的过程,极大地提高对参数摄动和外部干扰的鲁棒性,应用Lyapunov法证明时变滑模面的存在,计算机仿真结果证明该方法的正确性.     

Topology optimization of heat conduction problems using the finite volume method

This note addresses the use of the finite volume method (FVM) for topology optimization of a heat conduction problem. Issues pertaining to the proper choice of cost functions, sensitivity analysis, and example test problems are used to illustrate the effect of applying the FVM as an analysis tool for design optimization. This involves an application of the FVM to problems with nonhomogeneous material distributions, and the arithmetic and harmonic averages have here been used to provide a unique value for the conductivity at element boundaries. It is observed that when using the harmonic average, checkerboards do not form during the topology optimization process. Preliminary results of the work reported here were presented at the WCSMO 6 in Rio de Janeiro 2005, see Gersborg-Hansen et al. (2005b).     

基于知识图的观点句识别算法研究

针对观点句的特点提出了适合观点句识别的特征抽取规则.在此基础上,融合图论中最小割原理和机器学习分类方法,引入知识图的概念,并提出了基于知识图的观点句识别算法.以公开评测语料、自建语料和开放语料进行了相关实验,结果表明:基于知识图的观点句识别算法的分类性能和稳定性有明显优势.     

无线传感网络中通用传感器节点硬件结构设计

无线传感网络是当前国内外传感器技术领域的热点研究课题。提出了一种构建无线传感网络节点实验平台的方法;基于该设计方案实现的无线传感网络节点可以有效地组建网络拓扑结构及多种传感数据采集传输。它还可以用于实现声音空间定位系统。关键词:无线传感网络;节点;拓扑结构;数据采集;声音空间定位     

从单幅透视投影灰度图象识别和复原旋转体

基于旋转体的三维模型研究了透视投影下的旋转体剖节线和侧轮廓线的几何性质及其计算方法，并在此基础上成功地开发了一个从单幅透视投影灰度图象识别和复原旋转体的三维视觉信息的新技术。大量的实验表明该技术是精确、有效和可靠的。     

Generating cutter swept envelopes in five-axis milling by two-parameter families of spheres

This paper presents an efficient parametric approach of determining the shape of the envelope surface by a generalized cutter that follows five-axis tool path during NC machining. In this approach the cutter is modeled as a canal surface. By considering the tool motions the cutter is decomposed into a set of characteristic and great circles which are generated by two-parameter families of spheres. The center of a sphere from these families is described by two parameters which represent the spine curve and the tool path, and the radius of the sphere is described by one parameter representing the spine curve. Considering the relationship between characteristic and great circles the grazing points on the tool surface are identified. Analytically it is proven for the NC cutter geometries that any point on the envelope surface is located at the intersection of the characteristic and great circles. Then based on the proofs a closed-form solution for computing the grazing points generated by a surface of revolution is presented. The presented methodology is reduced to a simpler parametric form when the NC cutters are described by pipe surfaces.     

Periodic output feedback stabilization of single-input single-output continuous-time systems with odd relative degree

The paper considers the long-standing open problem of static output feedback stabilization with periodic output feedback. Extending the tools from vibrational control theory, we are able to derive some original results for this problem. We provide some sufficient conditions for stabilization with periodic output feedback. The proposed approach is constructive, and for some low dimensional cases, the sufficient conditions that we present are also necessary.     

Global robust stability of delayed neural networks with a class of general activation functions

In this paper, the global robust stability is discussed for delayed neural networks with a class of general activation functions. By constructing new Lyapunov functionals, several novel conditions are derived to guarantee the existence, uniqueness and global robust stability of the equilibrium of neural networks with time delays. These conditions do not require the activation functions to be differentiable, bounded or monotonically nondecreasing. The results obtained here are generalizations of some earlier results reported in the literature for neural networks with time delays. In addition, two examples are given to illustrate our proposed results.