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A novel image encryption scheme employing the memristive hyperchaotic system, cellular automata (CA) and DNA sequence operations is presented, which consists of diffusion process. SHA 256 hash function is used to give the secret key and compute the initial values of the chaotic system. Moreover, a dynamic DNA encoding scheme is introduced. Two DNA rule matrices for encoding the plain image and two-dimensional (2D) CA are generated from chaotic sequences, and they are controlled by the plain image, so that there are different DNA encoding rules for different original image. Besides, we manipulate block diffusion encryption method to the plain image in order to save time. The previous diffused block image and 2D CA are combined to affect the encryption effect of the current block image. Among them, 2D CA is updated by the local rule computed from the previous diffused sub image, and its initial configuration is determined by the chaotic sequences. Simulation results and security analyses both confirm that the proposed image encryption scheme not only demonstrates extraordinary encryption performance, but also resists various attacks. It can be applied in secure image and video communication fields.

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In this paper, a new linear primary permanent magnet vernier (LPPMV) machine is developed for direct-drive wave energy conversion. Owing to the magnetic gearing effect, the LPPMV machine possesses the advantages of high thrust force and low speed motion. After describing the machine structure, the operation principle of the machine is analysed and compared using two methods, namely, the magnetic gearing principle and the straightforward magnetic path. Then the characteristics are analysed by using the finite element method. Considering the unbalance of the no-load flux linkage and the inductance among the three phases, the mathematical model of the proposed machine is established, which is significantly different to that of the traditional permanent magnet machine. Finally, the machine is prototyped and tested so as to experimentally verify the theoretical analysis.

This paper presents the comparison of linear primary permanent magnet vernier (LPPMV) machine and linear vernier hybrid (LVH) machine. The LPPMV machine and the LVH machine both operate based on the magnetic gear principle, hence possessing the advantages of low speed and high thrust force density. In addition, both machines employ similar configurations between which the key difference is that a one-piece primary iron core is employed in the LPPMV machine instead of the modular cores in the LVH machine. Using the finite element method (FEM), the characteristics and performances of two machines are analyzed and compared. The results show that the LPPMV machine exhibits higher thrust force and lower cogging force. Finally, the FEM results are validated by experiments based on a prototype of the LPPMV machine.Index Terms-Comparative study, high thrust force, linear machine, low speed, primary PM machine, vernier machine.

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