In this paper, the formation control of unmanned surface vehicles (USVs) is addressed considering actuator saturation and unknown nonlinear items. The algorithm can be divided into two parts; one is steering the leader USV to trace along the desired path and the other is steering the follower USV to follow the leader in the desired formation. In the proposed formation control framework, a virtual USV is first constructed so that the leader USV can be guided to the desired path. To solve the input constraint problem, an auxiliary is introduced, and the adaptive fuzzy method is used to estimate the unknown nonlinear items in the USV. To keep the desired formation, the desired velocities of follower USVs are deduced by using geometry and Lyapunov stability theories. The stability of the closed-loop system is also proved. Finally, the effectiveness of the proposed approach is demonstrated by the simulation and experimental results.

Cryptography is one of the most important areas in information security. Cryptography ensures secure communication and data privacy, and it is increasingly being applied in healthcare and related fields. As an important classical cryptographic method, the Hill cipher has always been closely studied by experts and scholars. In order to enhance the security of the conventional Hill cipher (CHC), a novel dynamic Hill cipher (NDHC) is proposed in this work. The proposed NDHC not only replaces the static key matrix of the CHC with a time-varying dynamic key matrix (TVDKM) to change the image pixel values over time t, but also uses the Logistic chaos sequence scrambling the image pixel positions, which greatly enhances the security of the CHC. However, how to effectively obtain the dynamic inversion key matrix (DIKM) of the TVDKM becomes an urgent issue in the NDHC decryption. In order to quickly find the DIKM, a fixed-time convergence fuzzy Zeroing neural network (FTCF-ZNN) model is constructed, and the convergence and robustness of the FTCF-ZNN model for solving the DIKM are verified through theoretical analysis and comparative experimental results. Moreover, the effectiveness and security of the proposed NDHC for medical images encryption and decryption are also validated by experiments.

Chaotic systems with memristor are favored by academia because of diversity of dynamics. This paper reports a novel two-memristor-based 4D chaotic system. Numerical simulation shows that the system can yield infinite coexisting attractors. The generation mode of infinite coexisting attractors is investigated as well. Finally, the circuit and microcontroller-based implementation of two-memristor-based chaotic system are also given, corresponding experimental results fit well with numerical simulations.

As an effective tool for solving dynamic complex value problems, especially dynamic complex value matrix inversion (DCVMI), the complex value zeroing neural network (CVZNN) has been widely applied in various practical industrial fields. However, previous complex value zeroing neural network (PCVZNN) models only achieve unsatisfactory exponential or finite time convergence, which usually does not conform to actual practical situation. Different from PCVZNN models, a complex-valued variant parameter robust ZNN model (CVVPRZNN) with both fixed-time convergence and robustness for solving DCVMI is proposed in this paper. The fixed-time convergence and noise suppression ability of the CVVPRZNN model for solving DCVMI are strictly deduced. Then, three comparative numerical experiments for DCVMI solving, dynamic circuit currents computing and manipulator trajectory tracking of the proposed CVVPRZNN model with other existing PCVZNN models are provided for demonstrating its better solution performances and higher practical application value. It should be noted that the experimental results indicate that regardless of whether it is disturbed by noise or not, the CVVPRZNN model only requires about 0.01 s to complete the corresponding solving task. However, in the same experimental environment, other models either cannot complete the solving task at all, or require about 8 s which is almost 800 times the solving time of the CVVPRZNN model to complete the corresponding dynamic problem solving.