共享内存技术在Radius服务端应用中的研究

随着上网用户的激增，电信级的Radius应用服务器的性能问题越来越受到关注，研究一种软件实现的稳定、高效多进程通讯的同步机制，解决可靠提升接入认证服务器整体性能的问题，现实中采用了共享内存结合可靠信号量和原子变量技术，实现共享内存锁机制，应用于Radius服务中，深入细致剖析共享内存锁机制是如何避免访问冲突的，提供了新的思路。在实践中满足了百万级用户的认证授权要求，在服务端性能调优方面起着重要的作用。     

On the realization of periodic functions

In this article, canonical and spectrally minimal infinite-dimensional state space realizations for periodic functions are considered. It is shown that the periodic functions having ℓ₁ Fourier coefficients are precisely those realizable by a Riesz spectral system (RSS) in which the system operator generates a periodic strongly continuous semigroup and the observation operator is bounded. This realization can easily be converted to a canonical and spectrally minimal form. It is shown how the use of RSS and Cesáro sums of Fourier series allows the construction of a state space realization for a given periodic function merely integrable over its period. Simple finite-dimensional approximations with error bounds are derived for the RSS realization. Regular well-posed linear systems (WPLS) are used to construct a Fuhrmann-type realization for a given periodic function integrable over its period. It is shown that the RSS realizations and WPLS realizations are precisely equally good at coping with the possible ill behavior of a given bounded periodic function integrable over its period, but the WPLS realization is not always spectrally minimal or canonical.     

Consistency analysis of some closed-loop subspace identification methods

We study statistical consistency of two recently proposed subspace identification algorithms for closed-loop systems. These algorithms may be seen as implementations of an abstract state-space construction procedure described by the authors in previous work on stochastic realization of closed-loop systems. A detailed error analysis is undertaken which shows that both algorithms are biased due to an unavoidable mishandling of initial conditions which occurs in closed-loop identification. Instability of the open loop system may also be a cause of trouble.     

雷达组网中的IP实时可靠多播

随着Internet的发展,要求一对多或多对多通信形式的网络应用迅速增长,IP多播服务为该类网络应用提供了一种有效的通信手段。但是基于IP的多播是一种无连接的数据传输方式(UDP),UDP数据传输是一种“尽力而为”的方式,因此在传输过程中存在丢包和乱序现象。对于某些应用,该传输的不可靠性是不允许的,因此出现了可靠多播技术。可靠多播协议的应用针对性很强,不同的应用场合对可靠多播的要求以及实现方法也大不相同。文中分析了雷达组网对多播及其实时性和可靠性的需求,参考现有的解决可靠多播主要问题的方法,初步提出了一种适合于小批量数据分发的实时可靠多播通信协议的设计方案。     

Issues related to the computer realization of a multidisciplinary and multiobjective optimization system

Issues and novel ideas to be considered when developing computer realizations of complex multidisciplinary and multiobjective optimization systems are introduced. The aim is to discuss computer realizations that make possible both computationally efficient multidisciplinary analysis and multiobjective optimization of real world problems. We introduce software tools that make typically very time-consuming simulation processes more effective and, thus, enable even interactive multiobjective optimization with a real decision maker. In this paper, we first define a multidisciplinary and multiobjective optimization system and after that present an implementation overview of such problems including basic components participating in the solution process. Furthermore, interfaces and data flows between the components are described. A couple of important features related to the implementation are discussed in detail, for example, the usage of automatic differentiation. Finally, the ideas presented are illustrated with an industrial multiobjective optimization problem, when we describe numerical experiments related to quality properties in paper making.     

容错节能无线传感器网络中可靠覆盖问题的解决方案

基于生成最小覆盖的k集合覆盖启发式算法,提出了分簇结构下解决簇内观测区域可靠覆盖问题的高效节能方案,即可靠覆盖方案.最小覆盖是一个可以完全覆盖观测区域的传感器节点最小集合,可靠覆盖方案使用的1-损毁最小覆盖拓扑结构是两个最小覆盖的迭加.通过1-损毁最小覆盖间的轮流工作延长网络可用时间,体现节能效果;通过增加一个冗余最小覆盖,屏蔽来自单个最小覆盖的节点失效,体现容错效果.在该方案中,介绍簇头节点和簇内成员的交互协议,并使用快速覆盖替换算法处理可能的节点失效.仿真实验显示,该方案能够高效地利用有限的能量,显著延长网络工作时间,同时将由节点失效而产生的漏测次数保持在较低值.     

一个移动智能体位置管理与可靠通信的算法

对于移动智能体应用环境下的可靠通信问题,已有的支撑系统和相关研究或不能满足要求或存在缺陷.提出了一个面向移动智能体位置管理与可靠通信的新算法,它保证在智能体的移动行为不可预测的情况下,能可靠的完成消息传递,并承诺消息传递的exactly-once语义.     

RMTP协议的时延分析

RMTP(reliable multicast transport protocol)是一种通过修复服务器(repair server)本地恢复来提供可靠性的组播协议.对改进的RMTP协议的时延性能进行建模分析.推导了数据包自发送主机发出到成功地被一个随机选择的接收主机接收之间的平均时延公式.分析表明,随着丢失率的增长,RMTP的时延性能恶化点将迅速下降;随着每个修复服务器下连接尾链路数量的增加,RMTP的时延性能恶化点也将下降.但是,随着尾链路总数量的增加而保持每个修复服务器连接的尾链路数量不变,RMTP的时延性能的变化很小.仿真结果较好地验证了分析的有效性.     

位图的转向算法及其实现

多媒体编辑中图形的操作占据着重要的地位，尤其是位图的平面旋转和立体翻转更是其中的主要部分，也更具复杂性和多样化。本文给出其中的一种算法，并经Delphi5.0调试通过，仅供同行们参考。