A Spatiotemporal-chaos-based Encryption Having Overall Properties Considerably Better Than Advanced Encryption Standard

Spatiotemporal chaos of a two-dimensional one-way coupled map lattice is used for chaotic cryptography. The chaotic outputs of many space units are used for encryption simultaneously. This system shows satisfactory cryptographic properties of high security; fast encryption (decryption) speed; and robustness against noise disturbances in communication channel. The overall features of this spatiotemporal-chaos-based cryptosystem are better than chaotic cryptosystems known so far, and also than currently used conventional cryptosystems, such as the Advanced Encryption Standard (AES).Comment: 11 pages, 3 figure

Analysis of wide-band oscillation of hybrid MMC interfacing weak AC power system

The wide-band oscillation of the hybrid MMC induced by excessive power infeed under weak AC power system integration is analyzed in this paper. A closed-loop state-space-based time-domain small-signal model is firstly established to investigate the instability problem. Different from the findings in two-level VSCs or half-bridge MMCs, the root locus analysis and participation factor analysis in this paper reveals that the oscillation frequency and involved control loops are highly related to the operation status. When hybrid MMC operates as a rectifier, a low-frequency oscillation is observed with the d-channel control loop mainly participated. In contrast, a high-frequency oscillation occurs with a q-channel control loop mainly involved when the hybrid MMC operates as an inverter. This wide-band oscillation phenomenon is explored with the aid of two simplified loop-gain-based s-domain models, which are derived referring to the selective modal analysis approach. To suppress the oscillation, sensitivity analysis regarding the impact of parameters on the phase margin is conducted to recognize effective parameter adjustment methods. The analysis results are validated by detailed electromagnetic simulations

Comparative study of small-signal stability under weak AC system integration for different VSCs

Voltage source converters (VSCs) with self-commutation ability are suitable to interconnect weak AC systems. This paper conducts a comparative study of the small-signal stability characteristics for three typical VSCs, namely, the two-level VSCs (TL-VSCs), the half-bridge modular multilevel converters (HB-MMCs) and the hybrid MMCs (HY-MMCs),underweak AC system integration with special consideration on both inverter and rectifier operation. The frequency responses based on impedance models are compared using the frequency-domain analysis. The oscillation frequencies and mainly participated state variables of the unstable modes are compared using root locus and participation factor analysis in time-domain. Proper parameter retuning approaches for stability enhancement are proposed. The above analysis is adequately validated by electromagnetic simulations

A Study on the Correlation Between Sleep Quality and Accidental Injuries Among University Students in Hainan

Objective: To analyze the correlation between sleep quality and accidental injuries among university students in Hainan, and to provide reference for improving injury prevention among university students. Methods: A total of 1100 college students from freshman to Senior Students in three universities in Hainan were selected by multilevel random sampling method, and investigated by Pittsburgh Sleep Quality Index (PSQI) and injury questionnaire. Results: The average PSQI score of Hainan university students was 7.645. In the five dimensions of sleep latency, sleep efficiency, sleep disturbances, sleep medication, and daytime dysfunction, as well as the PSQI total score, the differences between the accidental injury group and the non-accidental injury group were statistically significant (P＜0.01), except for sleep quality and sleep time, all other dimensions and PSIQ total score were higher in the accidental injury group than in the non-accidental injury group. Conclusion: The problem of poor sleep quality among university students in Hainan were widespread, and the occurrence of accidental injuries among university students were related to the sleep quality