Time-varying exponential stabilization of a rigid spacecraft withtwo control torques

Rigid body models with two controls cannot be locally asymptotically stabilized by continuous feedbacks which are functions of the state only. This impossibility no longer holds when the feedback is also a function of time, and time-varying asymptotically stabilizing feedbacks have already been proposed. However, due to the smoothness of the feedbacks, the convergence rate is only polynomial. In this paper, exponential convergence is obtained by considering time-varying feedbacks which are only continuous     

Multivariable dead-beat control

The problem of forcing the state of a linear, multivariable, sampled-data system to zero in a minimum number of time steps is discussed. The solution to the posed problem is given as linear state feedbacks. Numerical aspects of the algorithms for computing these feedbacks are presented. The methods are successfully used to control the temperature profile of a diffusion process in the laboratory.     

Design of a single-input system for specified roots using output feedback

A method is given for choosing feedbacks from an output vector of smaller dimension than the state vector in such a way that a subset of the roots assume desired values. A sufficient condition for arbitrary placement of as many roots as there are feedbacks is proved. It is also proved that a root corresponding to a mode which is either uncontrollable or unobservable cannot be altered. It may be desired to place more roots than there are feedbacks, and it is shown that the method can be extended to give an approximate solution of this problem.     

Point-to-point regulation of a robot with flexible joints includingelectrical effects of actuator dynamics

This paper considers the set-point tracking problem in rigid and flexible-joint robots when both the mechanical as well as the electrical effects of the actuator dynamics are taken into account. The suggested controllers are based on state and output feedbacks. The current approach demonstrates that for every given desired operating point, linear state and output feedbacks with constant feedforwards can be constructed such that the closed-loop system is globally asymptotically stable     

An incentive mechanism to reinforce truthful reports in reputation systems

The success of current trust and reputation systems is on the premise that the truthful feedbacks are obtained. However, without appropriate mechanisms, in most reputation systems, silent and lying strategies usually yield higher payoffs for peers than truthful feedback strategies. Thus, to ensure trustworthiness, incentive mechanisms are highly needed for a reputation system to encourage rational peers to provide truthful feedbacks. In this paper, we model the feedback reporting process in a reputation system as a reporting game. We propose a wage-based incentive mechanism for enforcing truthful report for non-verifiable information in self-interested P2P networks. A set of incentive compatibility constraint rules including participation constraint and self-selection constraints are formulated. We design, implement, and analyze incentive mechanisms and players’ strategies. The extensive simulation results demonstrate that the proposed incentive mechanisms reinforce truthful feedbacks and achieve optimal welfare.     

稳定反馈空间的拓扑结构

本文讨论控制系统反馈空间的拓扑结构.首先讨论线性情况.然后,将其结果推广到非 线性的情况.赋予线性反馈集合以Rn×m拓扑(其中n为状态空间维数,m为输入维数),在这 个拓扑下研究完全能控系统稳定反馈集合的几何结构.文中证明了稳定反馈集合的拓扑结构 与具体系统无关.并且,对较小维数的系统(n≤5)给出了具体的拓扑结构.     

带两控制器刚体飞行器的姿态镇定

已知带两控制器的刚体飞行器系统不能被连续的纯状态反馈局部渐近镇定.有效的解 决方法包括时变反馈镇定方法和非连续反馈镇定方法.现有的时变反馈镇定方法设计均较为复 杂.已有的光滑时变反馈方法是非指数收敛的.本文通过引入辅助变量以及采用反馈线性化技术 设计出光滑时变的控制器.该方法设计简单且保证闭环系统状态是指数收敛的.仿真结果证明了 本文方法的有效性.     

时滞反馈Liu系统的动力学行为

研究了具有时滞反馈项作用的Liu系统.文中针对两种典型的时滞反馈情形,着重分析了时滞参数对系统动力学行为的影响.研究结果表明,当Liu系统存有时滞反馈时,其动力学行为将变得异常丰富;时滞参数的改变可引起系统复杂的动力学演化.此外,数值计算还发现了时滞Liu系统的虫洞吸引子.     

Analysis of fragmented time directionality in time series to elucidate feedbacks in climate data

Identifying and characterizing feedbacks in environmental processes may help in improving predictions for some environmental systems. The statistical study of time series is a manner to approach these feedbacks. Here, we consider feedbacks that are induced by occasional extreme events and that locally disturb the probabilistic behavior of climate time series. For example, intense rainfalls may induce bio-physical feedback processes and, consequently, influence the occurrence or intensity of daily rainfalls afterwards. In this article, we associate such eventual perturbations in time series to the concept of fragmented time directionality, and we present the R package FeedbackTS that contains a statistical exploratory toolbox for investigating fragmented time directionality. The toolbox mostly consists of simple randomization tests. The use of the package is illustrated with historical Australian rainfall data: we show the existence of feedback and identify temporal and spatial variation in feedback.     

采用排名反馈的P2P名誉评价模型

P2P网络中的节点很可能从另外的节点那里收到质量很差的服务和信息,名誉评价是解决该问题的常见方法.基于评分反馈的P2P名誉计算机制存在下述缺点:无法区分恶意评价和诚实节点给出错误评价间的差别;需要对评分可信度进行二次评价,使名誉计算速度减慢;用数字来表示节点名誉的方式不够自然.实际上,名誉评价的用途是确定节点可信度的相...     

一种新的P2P系统中基于双ratings的声誉管理机制

声誉系统的效率取决于回馈的质量,现有P2P系统中的声誉模型不能处理合谋、不递交ratings等攻击,并且对无过失节点还存在不公平性,针对这些问题,提出了一个新的基于双ratings的声誉管理机制,采用两个度量来评价节点:服务信任和回馈信任,服务信任反映server提供服务的可靠性;回馈信任反映consumer汇报ratings的可信度.一次交易后,要求服务双方都递交ratings,依据这两个ratings对server的服务信任和consumer的回馈信任进行更新,并且server的服务信任更新与consumer的回馈信任紧密相关.为了防止恶意节点反复实施恶意行为或不递交rating,还提出了一个惩罚机制,作为对声誉模型的补充,仿真表明,提出的声誉管理机制能够抵制上述恶意攻击,减少不公平性.     

Securing decentralized reputation management using TrustGuard

Reputation systems have been popular in estimating the trustworthiness and predicting the future behavior of nodes in a large-scale distributed system where nodes may transact with one another without prior knowledge or experience. One of the fundamental challenges in distributed reputation management is to understand vulnerabilities and develop mechanisms that can minimize the potential damages to a system by malicious nodes. In this paper, we identify three vulnerabilities that are detrimental to decentralized reputation management and propose TrustGuard—a safeguard framework for providing a highly dependable and yet efficient reputation system. First, we provide a dependable trust model and a set of formal methods to handle strategic malicious nodes that continuously change their behavior to gain unfair advantages in the system. Second, a transaction-based reputation system must cope with the vulnerability that malicious nodes may misuse the system by flooding feedbacks with fake transactions. Third, but not the least, we identify the importance of filtering out dishonest feedbacks when computing reputation-based trust of a node, including the feedbacks filed by malicious nodes through collusion. Our experiments show that, comparing with existing reputation systems, our framework is highly dependable and effective in countering malicious nodes regarding strategic oscillating behavior, flooding malevolent feedbacks with fake transactions, and dishonest feedbacks.     

Lyapunov functions and discontinuous stabilizing feedback

We study the controllability and stability of control systems that are nonlinear, and for which, for whatever reason, linearization fails. We begin by motivating the need for two seemingly exotic tools: nonsmooth control-Lyapunov functions, and discontinuous feedbacks. With the aid of nonsmooth analysis, we build a theory around these tools. We proceed to apply it in various contexts, focusing principally on the design of discontinuous stabilizing feedbacks.     

基于不满意度的网络安全模型

提出了一种基于不满意度的网络安全模型,主要功能是帮助用户在网络环境中正确地选择交易对象,屏蔽恶意节点,基于不满意度(degree of dissatisfaction,DoD)对交易节点进行分类控制.节点的不满意度定义为该节点属于恶意节点集的概率.a)使用粗糙集(rough set)模块与Bayesian学习器计算节点的不满意度,依据节点的交易历史记录计算节点的本地不满意度(local DoD,LDoD),依据反馈推荐意见计算推荐不满意度(recom-mended DoD,RDoD),基于不满意度将节点划分为可信任节点、陌生节点、恶意节点等不同的类型;b)基于推荐意见的信息熵(information entropy)计算其可信度,对反馈推荐意见进行综合.实验表明,与已有的安全模型相比,提出的安全管理模型对恶意节点具有更高的检测率,具有更满意的交易成功率.     

基于保局投影的相关反馈算法

在原有保局投影算法中引入用户反馈,用其更新构建降维映射的特征向量,从而得到一个更能够反映语义属性的图像表示子空间.该算法利用用户反馈迅速优化图像表示,使它具有长期学习的能力.实验结果表明:该算法可以提高检索的准确度,而且在经过长期学习后可以获得一个近似最优的图像降维子空间.     

非完整移动机器人的有限时间跟踪控制算法研究

对非完整移动机器人的有限时间轨迹跟踪控制问题进行讨论．与基于非连续状态反馈的传统有限时间控制算法相比，基于连续状态反馈的有限时间控制算法更适合于控制工程应用．利用该连续系统有限时间控制技术，设计一种连续的状态反馈跟踪控制算法．使得对角速度为非零常数的期望轨迹，非完整移动机器人能够实现全局跟踪，并能在有限时间内完全跟踪上期望轨迹．仿真结果表明了该方法的有效性．     

基于神经网络的交互式图像检索

提出了基于神经网络的交互式图像检索方法,系统根据用户对检索结果的评价,动态构造神经网络,描述图像之间的相似性;图像间的这种相似性以及本次检索结果可以作为以后检索的历史信息保存在神经网络中,从而提高下一次检索的效率。实验表明,该方法嵌入到典型的图像检索系统中,改善了图像检索性能。     

面向冷启动用户偏好获取的自适应物品询问列表生成方法

新用户进入系统之初,由于缺少必要的行为信息,推荐系统无法给出高质量的推荐,为了提高推荐精度,可以使用主动学习技术,使系统主动向用户发起相关物品的评分请求,从而通过用户的交互信息了解用户的偏好信息.现有的主动学习方法基于不确定性、熵等信息选择物品让用户提供反馈.然而由于用户的差异性,其适合的最佳策略是不一样的.因此,本文针对新用户冷启动问题,将要向用户发起询问的物品分阶段产生,通过用户对上一阶段问题的不同反馈,通过决策树模型个性化的动态选择下一阶段适合的策略来生成物品列表以征求其评价.同时,采用遗传算法来优化各个阶段的最优物品个数.在实际数据集上的实验表明,通过这种自适应生成询问物品列表的方法能够改进推荐效果.     

Autonomous takeoff and landing control for a prototype unmanned helicopter

In this paper, an autonomous takeoff and landing control strategy is designed and implemented for a prototype coaxial unmanned helicopter with ducted fan configuration. The control strategy is designed such that longitudinal and lateral controls use ground forces, attitude and drifting feedbacks. Vertical control employs takeoff and landing decision and vertical velocity control is based on altitude tracking. Ground forces feedback is used to balance longitudinal forces and moments during liftoff effectively cancelling all ground forces. Attitude and drifting feedbacks are used to balance the longitudinal and lateral movements of the helicopter during takeoff and landing. The flight control strategy is successfully verified during flight tests.     

Remarks on output feedback stabilization of two-species chemostat models

We consider a class of output feedback stabilization problems for chemostats with two species. We design dilution rate feedbacks that stabilize a componentwise positive equilibrium. Our feedbacks only depend on the sum of the species levels. The novelty of our treatment is in our dropping the usual condition on the relative sizes of the growth yield constants.