No abstract

There are various uncertain factors such as parameter perturbation and external disturbance during the steering process of a permanent magnet slip clutch electronically controlled hydraulic power steering system (P-ECHPS) of medium and heavy duty vehicles, which is an electronically controlled hydraulic power steering system based on a permanent magnetic slip clutch (PMSC). In order to avoid the immutable single assistance characteristic of a hydraulic power steering system, a PMSC speed-controlled model and P-ECHPS of each subsystem model were studied. Combined with non-singular terminal sliding mode and fast terminal sliding mode, an Adaptive Non-singular Fast Terminal Sliding (ANFTS) mode control strategy was proposed to control precisely the rotor speed of the PMSC in P-ECHPS, thus achieving better power control for the entire P-ECHPS system. The simulation results show that adaptive nonsingular fast terminal sliding mode control enables PMSC output speed to track the target speed. Compared with the non-singular terminal sliding mode control and the ordinary sliding mode control, the convergence speed has been improved by 66.7% and 84.2%, respectively. The rapid control prototype test of PMSC based on dSPACE (dSPACE is a development and verification platform based on MATLAB/Simulink software.) was carried out. The validity of the adaptive NFTSM algorithm and the correctness of the offline simulation results are validated. The adaptive NFTSM algorithm have better robustness and can realize variable assist characteristics and save energy.

Through the network teaching platform, distance teaching provides relevant distance technical support services for adult education, and evaluates teaching results of the teaching method, relying on modern network technology and integrating educational resources. It has become a consistent pursuit in the field of education to change the learning mode of distance learners, to cultivate higher-order sustained thinking ability, and to promote sustained learning so that learners’ knowledge transferability becomes more obvious. The results show that Cronbach’s á coefficient and KMO values of the questionnaire are 0.879 and 0.850, indicating that the reliability and validity of the questionnaire are good. Sustained learning, which consists of learning engagement, learning motivation and learning strategy, can significantly improve knowledge transferability. Distance learning duration and age of learners have significant differences in knowledge transferability. Gender and specialty have no significant difference in knowledge transferability. Conclusions have very important reference value for improving sustained learning effect of learners in distance teaching, promoting the occurrence of learners’ multiple interaction behaviors in distance teaching, and realizing cooperative knowledge construction of learners in distance teaching.

Background: Currently, China is carrying forward “Healthy China” construction. Thus, health investment has gradually become an important issue concerned by the Chinese government. Exploring the influence of health investment on economic growth under this background is of great theoretical and realistic significance for realizing economic transformation and upgrading in China. Methods: Thirty-one provincial regions in China were selected as research objects. Based on the panel data during 2000-2017, difference-generalized method of moment (D-GMM) and system-generalized method of moment (S-GMM) were comprehensively used to estimate the dynamic panel model from the national perspective, combining the fixed effects model (FE) estimation method to estimate the static panel model from the regional perspective, so as to investigate the relationships among governmental, residential health investment, and economic growth. Results: First, the governmental and residential health investments have positive effects on economic growth. Second, from the perspective of different regions, the governmental and residential health investments present positive correlations with economic growth, but the correlations present a progressively decreasing trend from the east to west. Conclusion: The Chinese government needs to steadily increase governmental health investment, elevate the level of residents' health expenditure, promote the development of the health industry, and finally facilitate sustainable economic growth in China.

Simultaneous localization and mapping (SLAM) is one of the core technologies to realize automated valet parking (AVP). Currently, advanced visual feature-based SLAM systems suffer from feature extraction failure and tracking loss due to the constraints of textureless scenes, unclear illumination, and dynamic conditions. To address these problems, this paper proposes a visual SLAM algorithm based on a semantic closed-loop detection algorithm using surround-view cameras and inertial measurement units (IMU) as sensors. The algorithm combines semantic features and the idea of inverse index to improve the traditional keyframes selection methods and the closed-loop detection algorithms, effectively avoiding the tedious and complicated feature point matching and improving the computational efficiency of the computer. Experiments show that the algorithm in this paper achieves better results in terms of precision and recall, absolute trajectory error (ATE), and relative pose error (RPE), and can meet the demand for SLAM and subsequent navigation in indoor parking lots.