“…The methods for synchronization of the chaotic systems have been widely studied in recent years, and many different methods have been applied theoretically and experimentally to synchronize chaotic systems, such as feedback control [4][5][6][7][8][9][10], adaptive control [11][12][13][14][15], backstepping [16] and sliding mode control [17][18][19][20][21]. One of the most attractive dynamical systems is the second-order systems which capture the dynamic behaviour of many natural phenomena, and have found applications in many fields, such as vibration and structural analysis, spacecraft control, electrical networks, robotics control and, hence, have attracted much attention (see, for instance, [22][23][24][25][26][27][28][29][30][31][32]). It has been proved that in special situations a second-order system may show chaotic dynamics.…”