Publications

A systematic design methodology for integrating fuzzy modeling and adaptive control is proposed and developed in this paper. This design procedure provides a real-time system identification scheme using less fuzzy rules than that of the other existing methods due to a new sliding-mode learning mechanism embedded in the identified model, which has robust stability not only for stabilization of the identified system but also for trajectory tracking control. The integration of the identification and the adaptive control schemes ensures the suggested methodology overall advantageous and more attractive as compared to the other existing, usually separated, design approaches. Two typical complex systems are simulated, showing some convincing stabilization and tracking performance of the proposed integrated fuzzy system.

No abstract is provided for this article.

A time-delayed feedback control (TDFC) system is by nature a rather special version of the familiar autoregressive moving-average (ARMA) control, or the canonical state-space control systems. Despite some of its inherent limitations, TDFC can be quite successful in many chaos control applications. To understand to what extent the TDFC method is useful, some analytic (sufficient) conditions for chaos control from the TDFC approach are derived in this paper, for both stabilization and tracking problems. A gradient descent based search algorithm is incorporated with the TDFC to estimate the time delay constant for tracking unstable periodic orbits. The established theoretical results and estimation method are further clarified via a case study of the typical chaotic Rossler system with computer simulations.

In this paper, the bidirectional associative memory (BAM) neural network with axonal signal transmission delay is considered. This model is also referred to as a delayed dynamic BAM model. By combining a number of different Lyapunov functionals with the Razumikhin technique, some sufficient conditions for the existence of a unique equilibrium and global asymptotic stability of the network are derived. These results are fairly general and can be easily verified. Besides, the approach for the analysis allows one to consider several different types of activation functions, including piecewise linear sigmoids with bounded activations as well as C 1 ‐smooth sigmoids. It is believed that these results are significant and convenient in the design and applications of BAM neural networks. Copyright © 2002 John Wiley & Sons, Ltd.

Rewiring is a common strategy for enhancing the controllability robustness of complex networks. In this brief, rewiring strategies including the degree-preserving strategy, underlying-topology-preserving strategy, and unconstrained-rewiring strategy, are compared and analyzed. Since measuring the true controllability-robustness values by simulations is time-consuming hence impractical, three surrogates are proposed for improvement, namely initial controllability, critical nodes exposure, and network heterogeneity. Combinations of rewiring strategies and objective functions are compared to the random edge-rectification strategy. Extensive simulations show that the random-edge rectification outperforms all the other strategies in enhancing the controllability robustness, but significantly changes the resulting network topology. In effect, the degree-preserving rewiring strategy performs as well as the unconstrained-rewiring strategy on homogeneous networks. The results also show the effectiveness of using the critical nodes exposure as a surrogate for the true controllability robustness.

In this paper, based on the discrete-time delayed impulsive system theory, exponential synchronization of discrete-time complex networks with both time-varying delays and stochastic disturbances is investigated. By applying an iterative Lyapunov function in combination with the linear matrix inequality (LMI) technique, a new synchronization criterion based on topology matrices and impulsive conditions is developed. Some numerical simulations are provided to verify the theoretical results.

Critical transition, a phenomenon that a system shifts suddenly from one state to another, occurs in many real-world complex networks. We propose an analytical framework for exactly predicting the critical transition in a complex networked system subjected to noise effects. Our prediction is based on the characteristic return time of a simple one-dimensional system derived from the original higher-dimensional system. This characteristic time, which can be easily calculated using network data, allows us to systematically separate the respective roles of dynamics, noise and topology of the underlying networked system. We find that the noise can either prevent or enhance critical transitions, playing a key role in compensating the network structural defect which suffers from either internal failures or environmental changes, or both. Our analysis of realistic or artificial examples reveals that the characteristic return time is an effective indicator for forecasting the sudden deterioration of complex networks.

A differential chaos shift keying cooperative communication (DCSK-CC) system with two users is proposed in this paper, which has an orthogonal subchannel in broadcast phase and cooperative phase through orthogonal Walsh code sequences as its multiaccess scheme. The single relay cooperative network with decode-and-forward relay is investigated in the proposed system according to two cooperation protocols, namely, conventional cooperation and space-time cooperation. Unlike conventional CDMA cooperative communication (CDMA-CC) systems, quite surprisingly power control devices that consume more energy to mitigate near-far effects can be avoided in the proposed system, which is of great importance to energy-constrained networks such as wireless sensor networks. Simulation results demonstrate that, through a conventional cooperation mechanism, the proposed system has a prominent advantage of good bit-error-probability (BEP) performance over the CDMA-CC systems that have a single path correlation receiver, at the same data rate with a high SNR range over multipath Rayleigh fading channels. Meanwhile, it is found that conventional cooperation is a better cooperation strategy relative to space-time cooperation in the proposed system. In addition, a lower bound of BEP performance is derived and verified by simulations over independent three-ray Rayleigh fading channels.

No abstract is provided for this article.

This Letter introduces a relatively simple three-dimensional continuous autonomous chaotic system, which can display complex 2- and 4-scroll attractors in simulations. Its generation and basic dynamical behaviors are briefly described.

While the majority of methods for community detection produce disjoint communities of nodes, most real-world networks naturally involve overlapping communities. In this paper, a scalable method for the detection of overlapping communities in large networks is proposed. The method is based on an extension of the notion of normalized cut to cope with overlapping communities. A spectral clustering algorithm is formulated to solve the related cut minimization problem. When available, the algorithm may take into account prior information about the likelihood for each node to belong to several communities. This information can either be extracted from the available metadata or from node centrality measures. We also introduce a hierarchical version of the algorithm to automatically detect the number of communities. In addition, a new benchmark model extending the stochastic blockmodel for graphs with overlapping communities is formulated. Our experiments show that the proposed spectral method outperforms the state-of-the-art algorithms in terms of computational complexity and accuracy on our benchmark graph model and on five real-world networks, including a lexical network and large-scale social networks. The scalability of the proposed algorithm is also demonstrated on large synthetic graphs with millions of nodes and edges.

This paper develops a theory of global exponential synchronization using two Chua circuits as the platform, for which five theorems are established by constructing new Lyapunov functions and employing the comparison principle in conjunction with the stability theory with respect to partial components.