Fault detectability analysis for linear systems within a set-based framework

This paper investigates the fault detectability issue for linear systems within a set-based framework. A set-based fault detectability analysis method is developed based on the geometric approach-based fault detection observer and zonotopes. Three concepts of fault detectability are established according to the relationship between the observer output sets in the presence and absence of faults. Necessary and sufficient conditions are derived corresponding to different detectability concepts. It can be found that the obtained conditions are related to system inputs in open-loop systems and system controllers in closed-loop systems. The impact of both system inputs and system controllers on fault detectability is analyzed. A numerical simulation is presented to illustrate the validity of the conclusions.     

Matrix approach to detectability of discrete event systems

This paper studies the detectability problem of discrete event systems (DESs), and devotes to providing a synthetical method to cope with multiple cases, including (partial) event observation and/or partial state observation. By using the semi-tensor product method, two equivalent types of algebraic expressions are presented for DESs, based on which reachability of DESs is investigated in detail and a new tool called detection matrix is defined. Then, four matrix-based necessary and sufficient conditions are derived for checking different kinds of detectability. Finally, for better presentation, two examples are shown to demonstrate that the theoretical results are efficient.     

Active fault tolerant control design for reusable launch vehicle using adaptive sliding mode technique

In this paper, the problem of active fault tolerant control for a reusable launch vehicle (RLV) with actuator fault using both adaptive and sliding mode techniques is investigated. Firstly, the kinematic equations and dynamic equations of RLV are given, which represent the characteristics of RLV in reentry flight phase. For the dynamic model of RLV in faulty case, a fault detection scheme is proposed by designing a nonlinear fault detection observer. Then, an active fault tolerant tracking strategy for RLV attitude control systems is presented by making use of both adaptive control and sliding mode control techniques, which can guarantee the asymptotic output tracking of the closed-loop attitude control systems in spite of actuator fault. Finally, simulation results are given to demonstrate the effectiveness of the developed fault tolerant control scheme.     

Intermittent fault detection for delayed stochastic systems over sensor networks

This paper is concerned with the intermittent fault (IF) detection problem for a class of linear discrete-time stochastic systems over sensor networks with constant time delay. By utilizing the lifting method, the distributed decoupled observers are proposed based on the output information of neighbor nodes and the node itself. In order to detect the appearing time and disappearing time of the IF, the truncated residuals are designed by introducing a sliding-time window. Furthermore, the IF detection and location thresholds are determined based on the hypothesis testing technique and the detectability of the IF is analyzed in the framework of stochastic analysis. Finally, a simulation example is presented to illustrate the effectiveness of the derived results.     

A quantitative causal diagram based optimal sensor allocation strategy considering the propagation of fault risk

Optimal sensor allocation can substantially reduce the life cycle maintenance costs of engineering systems. Considerable effort has been exerted to model the causal relationship between sensors and faults, but without considering the propagation of fault risk. In this paper, a grey relational analysis (GRA) based quantitative causal diagram (QCD) sensor allocation strategy is proposed that can take account of the influence of the propagation of fault risk. QCD is used to describe both the fault-sensor causal relationship and the fault-to-fault causal relationship. A data-driven-based GRA is applied in QCD to calculate the coefficients of the propagation of fault risk. To achieve an accurate relationship between faults and sensors, an improved quantitative analytic hierarchy process is proposed to calculate the coefficients between faults and sensors that is defined as sensor detectability in this paper. An optimal sensor allocation strategy is then developed using an improved particle swarm optimization (IPSO) algorithm under the constraint on sensor detectability to minimize fault unobservability and total cost. The proposed strategy is demonstrated by a case study on a single-phase inverter system. Compared with two other sensor allocation strategies, the results show that the proposed strategy can obtain the lowest fault unobservability of per unit cost (?0.242) for sensor allocation under the propagation of fault risk.     

Resilient strategy design for cyber-physical system under active eavesdropping attack

We consider a remote state estimation process under an active eavesdropper for cyber-physical system. A smart sensor transmits its local state estimates to a remote estimator over an unreliable network, which is eavesdropped by an adversary. The intelligent adversary can work in passive eavesdropping mode and active jamming mode. An active jamming mode enables the adversary to interfere the data transmission from sensor to estimator, and meanwhile improve the data reception of itself. To protect the transmission data from being wiretapped, the sensor with two antennas injects noise to the eavesdropping link with different power levels. Aiming at minimizing the estimation error covariance and power cost of themselves while maximizing the estimation error covariance of their opponents, a two-player nonzero-sum game is constructed for sensor and active eavesdropper. For an open-loop case, the mixed Nash equilibrium is obtained by solving an one-stage nonzero-sum game. For a long term consideration, a Markov stochastic game is introduced and a Nash Q-learning method is given to find the Nash equilibrium strategies for two players. Numerical results are provided to show the effectiveness of our theoretical conclusions.     

Decentralized fault tolerant model predictive control of discrete-time interconnected nonlinear systems

This paper presents a novel approach to address the decentralized fault tolerant model predictive control of discrete-time interconnected nonlinear systems. The overall system is composed of a number of discrete-time interconnected nonlinear subsystems at the presence of multiple faults occurring at unknown time-instants. In order to deal with the unknown interconnection effects and changes in model dynamics due to multiple faults, both passive and active fault tolerant control design are considered. In the Active fault tolerant case an online approximation algorithm is applied to estimate the unknown interconnection effects and changes in model dynamics due to multiple faults. Besides, the decentralized control strategy is implemented for each subsystem with the model predictive control algorithm subject to some constraints. It is showed that the proposed method guarantees input-to-state stability characterization for both local subsystems and the global system under some predetermined assumptions. The simulation results are exploited to illustrate the applicability of the proposed method.     

欠驱动漂浮基空间多体系统的递推动力学

针对欠驱动漂浮基空间多体系统,将欠驱动关节分解为主动和被动关节,研究用李群和李代数表示其动力学问题.将牛顿-欧拉反向动力学方法推广到适合于含主被动关节的形式,同时得到了漂浮基空间多体系统的主被动关节递推动力学建模方法.该方法可以用于对链式、树形拓扑结构的空间系统建模,也可用于对采用有限段方法建立的柔性梁式构件的离散模型进行高效率递推计算.结果表明,用李群李代数理论中的方法和符号更有助于形成递推的高效动力学建模,得到的动力学公式简明、清晰.     

Circuit state analysis using chaotic signal excitation

A new testing method for analog circuit is proposed in this paper. A low-pass Butterworth filter is taken as the typical system under test (SUT) since the analog circuits in different types of electronic systems can be regarded as the low-, band- or high-pass active (passive) filters. The chaotic signal, which is generated by an improved Chua's circuit, is employed as the excitation signal of SUT. The SUT is a “narrowband” system compared with the bandwidth of input signal, whose state is analyzed with an error-tracking approach. The experimental result depicts that this testing method can efficiently detect the change of the circuit parameter. Besides, another eight features are extracted from the output signal of SUT for analyzing the SUT states. A discussion is made for comparing the effectiveness of each feature according to the testing results.     

Synthesis of biquadratic impedances with at most four passive elements

In this paper, we consider the passive network synthesis problem of biquadratic impedances with at most four elements, motivated by the passive mechanical control. In order to solve this problem, a necessary and sufficient realizability condition for no more than three elements is obtained by some topological properties derived previously. Furthermore, the constraints on the possible realizations are used to derive the networks which can cover all the cases, and they are classified as several quartets. Through investigating one of the networks in each quartet, we obtain a necessary and sufficient condition for any biquadratic impedance to be realizable with at most four elements. Finally, the interlocking conditions are illustrated graphically, and numerical examples are given.     

Active fault diagnosis for a class of closed-loop systems via parameter estimation

This paper addresses an active fault diagnosis problem for a class of discrete-time closed-loop system with stochastic noise. By introducing the theories of system identification, a novel active fault diagnosis method is developed to detect and isolate the faults. An important advantage of the proposed method is that there is no need to cut off the original input signal, which is necessary in most active fault diagnosis methods. Firstly, due to the features of the faults, we transform the problem of fault diagnosis into a problem of model selection by estimating model parameters. Then, the sufficient condition for active fault diagnosability is analysed, and the property that auxiliary input signal can enhance the fault diagnosability is given. Finally, simulation studies are carried out to demonstrate the effectiveness and applicability of the proposed method.     

Data-driven fault diagnosis for an automobile suspension system by using a clustering based method

This paper concerns the issues of fault diagnosis and monitoring for an automobile suspension system where only accelerator sensors in the four corners of the car body are available. A clustering based method is proposed to detect the fault happened in the spring, and the Fisher discriminant analysis is applied to isolate the root factor for the fault. Different from most of the existing approaches, the pure data-driven characteristic enables this method to serve as an on-line fault diagnosis and monitoring tool without suspension model or fault features known as a prior. Moreover, this method can classify different reductions in the spring coefficient into one fault rather than different faults. The effectiveness of the proposed method is finally illustrated on an automobile suspension benchmark.     

A unified approach to the realization of canonic RC-active,single as well as variable,frequency oscillators using operational amplifiers

A general, unified and systematic approach is employed to study realization of operational amplifier (OA) based sinusoidal RC-active oscillators. Both single frequency and variable frequency operations are investigated. A set of circuits is found for each case. The sets consist of 12 and 16 circuits respectively. The circuits are canonic, that is, they require the minimum number of active and passive components. For each circuit, the single frequency set requires one OA, two capacitors and four resistors, while the variable frequency set needs one OA, two capacitors and five resistors. Both sets are shown to be complete in that generation of any additional canonic circuit is not possible. Variable frequency oscillators are all single resistor controlled. They are classified into four groups according to the nature of their dependence on the variable resistor. All the circuits are laboratory tested. Experimental results agree closely with the theoretical analysis. Representative test results are included.     

“互联网+”情境下商业模式创新与企业跨界成长：模型构建及跨案例分析

互联网信息技术的发展推动了产业的融合,模糊了产业之间的边界,日益成为商业模式创新的基本时代背景,同时越来越多的企业通过商业模式创新实现跨界成长,甚至颠覆产业竞争格局,但国内外文献尚未对此进行应有研究和探讨。本文立足于“互联网+”情境,结合商业模式创新视角（要素创新和价值创新）和企业跨界成长方式（内生式和外生式）两个维度,从理论上剖析商业模式创新与企业跨界成长动态影响关系,并构建具有四种不同情景的分类模型。在此基础上,采用多案例比较分析法,选取四种不同情境的典型企业（包括荣昌洗衣、尚品宅配、腾讯、携程）作为案例对象,分别探讨“互联网+”情境下案例企业商业模式创新对跨界成长的影响作用及其发生机理,然后通过案例间横向对比分析,识别了驱动企业跨界成长的客户价值、战略合作关系、价值共创三项关键性因素,并总结出分类模型演化规律。本文研究结论能够对深化企业跨界成长战略的研究思路和视野,拓宽商业模式创新的应用范围以及优化变量动态关系模型等方面提供积极的启示和借鉴作用。     

Neural network-based sensor fault estimation and active fault-tolerant control for uncertain nonlinear systems

In this work, we developed a novel active fault-tolerant control (FTC) design scheme for a class of nonlinear dynamic systems subjected simultaneously to modelling imperfections, parametric uncertainties and sensor faults. Modelling imperfections and parametric uncertainties are dealt with using an adaptive radial basis function neural network (RBFNN) that estimates the uncertain part of the system dynamics. For sensor fault estimation (FE), a nonlinear observer based on the estimated dynamics is designed. A scheme to estimate sensor faults in real-time using the nonlinear observer and an additional RBFNN is developed. The convergence properties of the RBFNN, used in the fault FE part, are improved by using a sliding surface function. For FTC design, a sliding surface is designed that incorporates the real-time sensor FE. The resulting sliding mode control (SMC) technique-based FTC law uses the estimated dynamics and real-time sensor FE. A double power-reaching law is adopted to design the switching part of the control law to improve the convergence and mitigate the chattering associated with the SMC. The FTC works well in the presence and absence of sensor faults without the requirement for controller reconfiguration. The stability of the proposed active FTC law is proved using the Lyapunov method. The developed scheme is implemented on a nonlinear simulation of an unmanned aerial vehicle (UAV). The results show good performance of the proposed unified FE and the FTC framework.     

Current/voltage-mode universal filter using FTFNs

A new configuration realizing current/voltage-mode (CM/VM) universal filter using two four terminal floating nullors (FTFN) and four passive components is presented. The current-mode configuration has single input and three outputs and realises simultaneously lowpass (LP), bandpass (BP) and highpass (HP) responses from which allpass (AP) and notch functions can also be implemented. The voltage-mode filter has three inputs and two outputs and can be configured to realise all the five filtering functions. The circuit in current-mode uses grounded capacitors which are ideal for monolithic integration. Besides using a bare minimum number of passive components, the topology enjoys low active and passive sensitivity figures. Experimental and PSPICE simulation results are also included.     

Four challenges for a theory of informational privacy

In this article, I summarise the ontological theory of informational privacy (an approach based on information ethics) and then discuss four types of interesting challenges confronting any theory of informational privacy: (1) parochial ontologies and non-Western approaches to informational privacy; (2) individualism and the anthropology of informational privacy; (3) the scope and limits of informational privacy; and (4) public, passive and active informational privacy. I argue that the ontological theory of informational privacy can cope with such challenges fairly successfully. In the conclusion, I discuss some of the work that lies ahead.     

互联网开放式创新社区用户画像构建及用户创新需求识别

本文通过分析互联网开放式创新社区用户参与创新行为，采集用户知识共享的不同特征数据，构建用户画像，从而识别不同类别用户参与平台知识创新的功能和角色。此外，基于用户的异质性，分析不同用户群体的创新需求差异和需求点的分布。通过对小米社区的实证研究识别出了核心用户、积极创新用户、积极社交用户、潜在创意用户、边缘用户这5个类型用户并进行画像，同时从必备型需求、魅力型需求、期望型需求、沉默型需求这4个角度对不同类型用户的创新需求点进行分析，体现了不同类型用户的不同创新需求差异。通过用户画像构建以及用户创新需求识别，达到社区管理与用户之间的高匹配度及用户的创新需求与企业产品创新方向之间的一致性。     

Can the inerter be a successful shock-absorber? The case of a ball-screw inerter with a variable thread lead

This paper investigates an application of a ball-screw inerter for mitigation of impact loadings. The problem of impact absorption is to provide a minimum reaction force that optimally decelerates and eventually stops an impacting object within the available absorber stroke. It significantly differs from vibration mitigation problems which are typical application of inerters. The paper demonstrates that the optimum absorption can be achieved by fully passive means. For known values of the object mass and inerter parameters, the obtained solution is independent of the impact velocity. The optimum passive absorption is achieved by employing a variable thread lead. As a result, two force components emerge, the typical inertance-related force and a damping-like term, and sum up to provide the optimum constant deceleration force. This result is relatively unique: conventional absorbers do not provide a constant force even with complex active control systems. Finally, an optimization problem is formulated to reduce the influence of process uncertainties (range of possible mass values, unknown friction). The results are verified and analyzed in a numerical example.     

随机通达理论与英语课外阅读

随机通达教学的核心是对同一内容的学习要在不同时间、不同情境,以不同目的、从不同角度多次进行,从而获得对同一事物更为全面的认识与理解.从随机通达理论的角度探讨课外阅读在增加英语词汇量和促进消极词汇向积极词汇转化两个方面的意义,并且就培养课外阅读习惯提出建议:转变阅读观念、选择感兴趣的题材、把握材料的合适难度、合理安排阅读时间等.