Separation of synchronous and asynchronous communication via testing

One of the early results concerning the asynchronous π$\pi$-calculus which significantly contributed to its popularity is the capability of encoding the output prefix of the (choiceless) π$\pi$-calculus in a natural and elegant way. Encodings of this kind were proposed by Honda and Tokoro, by Nestmann and (independently) by Boudol. We investigate whether the above encodings preserve De Nicola and Hennessy’s testing semantics. In this sense, it turns out that, under some general conditions, no encoding of the output prefix is able to preserve the must testing. This negative result is due to (a) the non-atomicity of the sequences of steps which are necessary in the asynchronous π$\pi$-calculus to mimic synchronous communication, and (b) testing semantics’ sensitivity to divergence.     

基于译文的英汉双语句子自动对齐

本文利用英汉互译译文间的内在联系,提出了基于译文的方法,通过使用一部翻译较完整的词典作为桥梁,将英汉句子间的对应关系连结起来,根据英语文本中的单词,在词典中找其对应的译文,并以译文到汉语句子中去匹配,根据评价函数和动态规划算法找到对齐句对,实验结果证明这种对齐方法消除了基于长度做法中错误蔓延的情况。并且普遍适用于任何文本,它大大地提高了对齐的精度,其效果是令人满意的。     

轮廓字网格编织带修饰效果的实现

利用计算机进行设计各种字形修饰效果一直是计算机图形学的重要内容之一.本文给出了在轮廓字表面上构造网格点,基于这些网格点进行Delaunay三角剖分,并转换为3-4网格,最后在网格上实现编织带修饰效果的具体实现方法.其中3-4网格由良构的四边形单元和少量辅助三角形单元构成,在其上实现了较好的编织带修饰的效果.     

MPEG—4视频的实时传输

MPEG－4是一个全新的多媒体标准,采用了基于对象和模型的编码方法。简要总结了MPEG－4视频编码的各种特点,对网络实时传输MPEG－4视频提出了各种评估标准,并针对面临的困难介绍了相应的解决方案。     

A reactive GRASP and path relinking for a combined production–distribution problem

An NP-hard production–distribution problem for one product over a multi-period horizon is investigated. The aim is to minimize total cost taking production setups, inventory levels and distribution into account. An integer linear model is proposed as a compact problem specification but it cannot be solved to optimality for large instances. Instead of using a classical two-phase approach (production planning and then route construction for each day), metaheuristics that simultaneously tackle production and routing decisions are developed: a GRASP (greedy randomized adaptive search procedure) and two improved versions using either a reactive mechanism or a path-relinking process. These algorithms are evaluated on 90 randomly generated instances with 50, 100 and 200 customers and 20 periods. The results confirm the interest of integrating production and distribution decisions, compared to classical two-phase methods. Moreover, reaction and path-relinking give better results than the GRASP alone.     

Real-time 2D to 3D video conversion

We present a real-time implementation of 2D to 3D video conversion using compressed video. In our method, compressed 2D video is analyzed by extracting motion vectors. Using the motion vector maps, depth maps are built for each frame and the frames are segmented to provide object-wise depth ordering. These data are then used to synthesize stereo pairs. 3D video synthesized in this fashion can be viewed using any stereoscopic display. In our implementation, anaglyph projection was selected as the 3D visualization method, because it is mostly suited to standard displays.

Limitations of nonlinear discrete periodic control for disturbance attenuation and robust stabilization

This paper presents a performance analysis of nonlinear periodically time-varying discrete controllers acting upon a linear time-invariant discrete plant. Time-invariant controllers are distinguished from strictly periodically time-varying controllers. For a given nonlinear periodic controller, a time-invariant controller is constructed. Necessary and sufficient conditions are given under which the time-invariant controller gives strictly better control performance than the time-invariant controller from which it was obtained, for the attenuation of l_p exogenous disturbances and the robust stabilization of l_p unstructured perturbations, for all p[1,∞].     

A method of predicting the number of clusters using Rand's statistic

Distributional and asymptotic results on the moment of Rand's C_k statistic were derived by DuBien and Warde [1981. Some distributional results concerning a comparative statistic used in cluster analysis. ASA Proceedings of the Social Statistics Section, 309–313.]. Based on those results, a method to predict the number of clusters is suggested by applying various agglomerative clustering algorithms. In the procedure, the methods using different indexes are examined and compared based on the concept of agreement (or, disagreement) between clusterings generated by different clustering algorithms on the set of data. Our method having practical generality works better than the other methods and assigns statistical meaning to C_k values in determining the number of clusters from the comparison.     

Simplifying the weft hierarchy

We give simple, self-contained proofs of the basic hardness results for the classes W[t]$W[t]$ of the weft hierarchy. We extend these proofs to higher levels of the hierarchy and illuminate the distinctions among its classes. The anti-monotone collapse at W[1,s]$W[1,s]$ and the normalization of weft-t$t$ formulas arise as by-products of the proofs.     

超混沌系统自周期轨道链接式控制

基于混沌同步和周期轨道理论提出一种超混沌系统自周期轨道链接式控制法。从超混沌系统状态变量的时间序列中提取周期轨道并用于对系统的实时控制,可使混沌系统稳定运行于某一周期轨道。将提周期轨道经链接组合后用于系统控制,可得到大量的大周期轨道。对4阶蔡氏电路进行数字仿真实验,获得了满意的结果。