基于逆向超图的从关系模式到“改进的第三范式”的分解

本文以逆向超图为工具, 讨论了非必要和非基本属性在超图中的性质, 给出了基于逆向超图的泛关系模式到改进的３ＮＦ的分解算法     

PANORAMA多数据库系统的后处理查询策略

分析不同的模式集成语义 ,从而得出后处理查询的两种主要运算 :场地间联接和外联接运算 .运用规则把后处理查询先转换成普通表达式 ,再转换成析取条件范式 ,并讨论了其内部树结构的实现机制 ,生成实际用于调度的全局查询超图集 ,并给出了具体的算法 .在此基础上 ,根据超图集的特点 ,给出后处理查询的三级调度     

基于分层超图的可重构体系结构模型

计算机应用领域的广泛性导致了应用任务的多样性,同一种体系结构难以适应差异巨大的应用任务。通过分析应用任务的计算、存储和通信资源需求,对实现应用问题的程序结构进行理论分析和关键算粒的提取,形成具有独立功能的子算法簇。利用分层超图对应用程序结构和体系结构进行可视化描述,使用感知算法得到应用程序结构和部件忙闲信息等系统状态,利用体系结构的可重构性,使用决策算法完成子结构对子算法簇的合理配对。通过一个计算实例分析验证了可重构结构的有效性。图同构理论表明,这种可变体系结构是合理的,在解决不同复杂应用问题时,具有高效率、低功耗的特点。     

基于混合系统模型的非线性系统最大可控不变集求解

针对非线性系统线性化在状态约束下最优鲁棒控制求解问题,提出了一种基于混合系统的分段仿射系统(PWA)建模,通过多次优化迭代的方法求解系统的最大鲁棒控制不变集的方法,并求得不变集内的最优控制器,解决系统的状态约束问题.通过一个非线性系统实例进行建模、仿真,证明了本方法的可行性.     

Direct control method for improving stability and reliability of nonlinear stochastic dynamical systems

Optimal control for improving the stability and reliability of nonlinear stochastic dynamical systems is of great significance for enhancing system performances. However, it has not been adequately investigated because the evaluation indicators for stability (e.g. maximal Lyapunov exponent) and for reliability (e.g. mean first-passage time) cannot be explicitly expressed as the functions of system states. Here, a unified procedure is established to derive optimal control strategies for improving system stability and reliability, in which a physical intuition-inspired separation technique is adopted to split feedback control forces into conservative components and dissipative components, the stochastic averaging is then utilized to express the evaluation indicators of performances of controlled system, the optimal control strategies are finally derived by minimizing the performance indexes constituted by the sigmoid function of maximal Lyapunov exponent (for stability-based control)/the reciprocal of mean first-passage time (for reliability-based control), and the mean value of quadratic form of control force. The unified procedure converts the original functional extreme problem of optimal control into an extremum value problem of multivariable function which can be solved by optimization algorithms. A numerical example is worked out to illustrate the efficacy of the optimal control strategies for enhancing system performance.     

Optimal subcarrier pairing scheme for maximal ratio combining in OFDM power line communications

Power line communication (PLC) networks for a smart grid require high reliability for data communications. In order to improve the reliability of PLC networks, we consider a maximal ratio combining (MRC) diversity scheme for a power line orthogonal frequency division multiplexing (OFDM) system. An optimal subcarrier pairing scheme is proposed to maximize the MRC gain. Numerical results are presented to verify that the proposed scheme provides enhanced performance.     

利用邻接结构熵确定超网络关键节点

识别网络中的关键节点对研究网络的拓扑结构及功能特性具有重要的实际应用价值.基于超图的超网络拓扑结构为超图,由于超图中的超边可以包含任意数量的节点,使得超网络能够清晰明了地表达出多元、多维、多准则的复杂关系.为了更好地挖掘超网络中的关键节点,基于超图理论及性质,提出超图中的邻接结构熵识别超网络中的关键节点,该方法通过研究...     

Constant false alarm rate detector based on the maximal reference cell

In order to improve the detection performance of constant false alarm rate (CFAR) detectors in multiple targets situations, a CFAR detector based on the maximal reference cell (MRC) named MRC-CFAR is proposed. In MRC-CFAR, a comparison threshold is generated by multiplying the amplitude of MRC by a scaling factor. The number of the reference cells left, whose amplitudes are smaller than the comparison threshold, is counted and compared with a threshold integer. Based on the comparison result, proper reference cells are selected for detection threshold computation. A closed-form analysis for MRC-CFAR in both homogeneous and non-homogeneous environments is presented. The performance of MRC-CFAR is evaluated and compared with other CFAR detectors. MRC-CFAR exhibits a very low CFAR loss in a homogeneous environment and performs robustly during clutter power transitions. In multiple targets situations, MRC-CFAR achieves a much better detection performance than switching CFAR (S-CFAR) and order-statistic CFAR (OS-CFAR). Experiment results from an X-band linear frequency modulated continuous wave radar system are given to demonstrate the efficiency of MRC-CFAR. Because ranking reference cells is not required for MRC-CFAR, the computation load of MRC-CFAR is low; it is easy to implement the detector in radar system in practice.     

基于分布式路径计算单元的多域光网络组密钥管理方案

针对分布式路径计算单元（PCE）架构下多域光网络的通信特点和密钥管理需求，提出一种该架构下的组密钥管理方案。首先使用超图理论对分布式PCE架构下的多域光网络密钥关系进行建模得到两层式密钥超图；然后在自治域层采用基于自认证公钥密码体制和成员过滤技术的密钥管理方法，在PCE层采用基于椭圆曲线密码体制的组密钥协商方法；最后完成密钥的产生、分发、更新和动态管理，较好地解决了成员的私钥保密性问题和第三方节点的冒充问题，减少了密钥更新时的计算开销。性能分析显示，该方案具有前向安全性、后向安全性、密钥保密性和抗合谋攻击等特点，与典型的分散式方案相比，在密钥存储量、加解密次数和通信开销等方面取得了较优的性能。