Network Synchronization with an Adaptive Coupling Strength
  In this paper, new schemes to synchronize linearly or nonlinearly coupled chaotic systems with an adaptive coupling strength are proposed. Unlike other adaptive schemes, which synchronize coupled chaotic systems to a special trajectory (or an equilibrium point) of the uncoupled node by adding negative feedbacks adaptively; here, adaptive schemes for the coupling strength are used to synchronize coupled chaotic systems without knowing the synchronization trajectory. Moreover, in many applications, the state variables are not observable; instead, some functions of the states can be observed. How to synchronize coupled systems with the observed data is of great significance. In this paper, synchronization of nonlinearly coupled chaotic systems with an adaptive coupling strength is also discussed. The validity of those schemes are proved rigorously. Moreover, simulations show that by choosing some proper parameter $\alpha$, the coupling strength obtained by adaptation could be much smaller. It means that chaos oscillators can be easily synchronized with a very weak coupling. 
Xiwei Liu Tianping Chen