A new distributed approximation algorithm for constructing minimum connected dominating set in wireless ad hoc networks

In recent years, constructing a virtual backbone by nodes in a connected dominating set (CDS) has been proposed to improve the performance of ad hoc wireless networks. In general, a dominating set satisfies that every vertex in the graph is either in the set or adjacent to a vertex in the set. A CDS is a dominating set that also induces a connected sub‐graph. However, finding the minimum connected dominating set (MCDS) is a well‐known NP‐hard problem in graph theory. Approximation algorithms for MCDS have been proposed in the literature. Most of these algorithms suffer from a poor approximation ratio, and from high time complexity and message complexity. In this paper, we present a new distributed approximation algorithm that constructs a MCDS for wireless ad hoc networks based on a maximal independent set (MIS). Our algorithm, which is fully localized, has a constant approximation ratio, and O(n) time and O(n) message complexity. In this algorithm, each node only requires the knowledge of its one‐hop neighbours and there is only one shortest path connecting two dominators that are at most three hops away. We not only give theoretical performance analysis for our algorithm, but also conduct extensive simulation to compare our algorithm with other algorithms in the literature. Simulation results and theoretical analysis show that our algorithm has better efficiency and performance than others. Copyright © 2005 John Wiley & Sons, Ltd.     

WSNs中基于能量代价的最小权和支配集拓扑控制算法

该文针对无线传感器网络中最小连通支配集拓扑并非网络耗能最小拓扑的问题,定义由节点剩余能量,邻居个数和通信代价构建的能量代价函数综合反映支配节点的能量效率以及对降低网络整体能耗的贡献,进而以其作为拓扑权值,提出一种基于能量代价的最小权和连通支配集拓扑控制算法。算法选取局部最小权值节点担负支配任务,搭建整体权和最小的支配集,最小化网络整体能耗。实验结果表明,算法不仅具有节能的特点,还确保了通信链路的可靠性,有效延长了网络生命周期。     

宽带激光二倍频特性的理论分析

在激光核聚变(ICF)物理实验中,采用相干度较小的宽带倍频激光,能有效抑制高阶非线性效应和提高靶的激光辐照均匀性。根据不同频率成分和频耦合原理,建立了宽带二倍频转换的物理模型,作了理论计算分析,发现二倍频光的光谱变窄,结果对宽带三倍频研究具有一定应用价值。     

风电并网对电力系统暂态稳定的影响

随着社会经济的快速发展,作为一种重要的可再生资源,风力发电已成为当前发电技术最成熟、最具开发潜力的发电技术.在实际应用中,由于大规模开发风力资源、单一风电场装机容量不断提高,电网系统中风电占比日益增加.随着风电的不断接入,电网系统原潮流分布发生了变化,受风速随机与间歇性影响,其输出功率有一定的波动性,严重影响到电网电压的稳定.因此,在开发与规划风电场建设中,风电并网对电力系统电压稳定性的影响做深入研究,意义深远.     

Distributed Construction of Connected Dominating Set in Wireless Ad Hoc Networks

Connected dominating set (CDS) has been proposed as virtual backbone or spine of wireless ad hoc networks. Three distributed approximation algorithms have been proposed in the literature for minimum CDS. In this paper, we first reinvestigate their performances. None of these algorithms have constant approximation factors. Thus these algorithms cannot guarantee to generate a CDS of small size. Their message complexities can be as high as O(n ²), and their time complexities may also be as large as O(n ²) and O(n ³). We then present our own distributed algorithm that outperforms the existing algorithms. This algorithm has an approximation factor of at most 8, O(n) time complexity and O(nlogn) message complexity. By establishing the (nlogn) lower bound on the message complexity of any distributed algorithm for nontrivial CDS, our algorithm is thus message-optimal.     

超薄氧化铝模板的制备及应用

基板上大面积的有序纳米阵列,在电子学、光电子学、传感器、催化剂、太阳能电池、高密度储存、场发射设备和超薄显示设备等领域具有广阔的应用前景.综述了一种构造表面有序纳米结构的新方法--超薄氧化铝模板法.根据超薄氧化铝模板的制备方法又分为附着型和结合型.还总结了近年来该方法的应用.     

Energy‐efficient power control for uplink spectrum‐sharing heterogeneous networks

This article considers energy‐efficient power control schemes for interference management in uplink spectrum‐sharing heterogeneous networks that maximize the energy efficiency of users, protect the macro base station, and support users with QoS consideration. In the first scenario, we define the objective function as the weighted sum of the energy efficiencies and develop an efficient global optimization algorithm with global linear and local quadratic rate of convergence to solve the considered problem. To ensure fairness among individual user equipments (UEs) in terms of energy efficiency, we consider the max‐min problem, where the objective is defined as the weighted minimum of the energy efficiencies, and a fractional programming theory and the dual decomposition method are jointly used to solve the problem and investigate an iterative algorithm. As by‐products, we further discuss the global energy efficiency problem and consider near‐optimal schemes. Numerical examples are provided to demonstrate significant improvements of the proposed algorithms over existing interference management schemes.     

两步动态编程识别连续单词的算法实现

传统的DTW算法大多用来识别孤立单词,并已极具实用价值,但是这种方法不适用于连续单词的识别。利用两步动态编程算法解决了连续单词的识别问题。两步动态编程算法首先把每个参考模型与测试串的一部分匹配,然后根据获得两者间最小距离的次序将参考模型个体拼接起来当作辨识解。给出了两步动态编程算法的基本实现方法,并进行了实验验证。     

利用 Free Search 算法推求作物水分 响应 Jensen 模型参数

依据最小二乘法原理推求作物水分响应模型参数时可能存在参数不合理、模型模拟精度尚可提升、试验处理少而难于估计模型参数等问题。针对这些问题,以Jensen模型参数推求为例,引入自由搜索(Free Search,FS)算法率定作物水分响应模型参数,将FS单个动物每步探查行走的位置向量作为参数的一组潜在解,利用FS算法的动物群体迁移行为推求一组最优参数,从而改善作物水分响应模型的适用性。三个实例研究结果表明:FS算法概念清晰,操作便捷,可以直接率定作物水分响应模型参数,不需转换作物水分响应模型的数学形式,能够有效避免参数出现负值或大于1等不合理现象,并提升作物水分响应模型的模拟精度;当难于采用线性回归方法时,可以考虑利用FS算法推求作物水分响应模型参数。     

基于三角划分的多连通域图形匹配研究

由若干个多边形通过组合产生的具有多个连通域的多连通域图形识别问题是工程图纸识别与理解所要解决的重要问题。首先,通过建立包围多边形、连通多边形概念,完成对多连通域图形的表示;然后,依据最近距离、无遮挡、包含原则添加辅助线,实现三角划分,解决了包含连通的定位问题。在匹配过程中,首先通过匹配包围多边形实现多连通域图形的外轮廓定位;然后通过匹配连通多边形删除连通域,逐步收缩图形,实现图形匹配。应用此方法,解决了多连通域图形的旋转、缩放匹配问题,在汽车线束图纸识别中取得了良好的应用效果。