This paper presents a novel yokeless and segmented armature (YASA) axial-flux in-wheel motor with amorphous magnetic material (AMM) stator cores for a solar-powered electric vehicle. Although this new axial-flux in-wheel motor has many advantages such as high efficiency, shorter axial length, and high power density, its working condition is complicated. In-wheel motors are usually operated in electromagnetic, thermal, and other multiphysics environments. Increasing the performance requirements of in-wheel motors, such as power density, efficiency, and reliability, requires a multiphysics design approach. The focus of this paper is on the analysis of electromagnetic characteristics, losses, temperature distribution, mechanical behavior and other characteristics of the axial-flux in-wheel motor. The back electromotive force (EMF) and electromagnetic torque of the motor with harmonic current are obtained by the 3-D finite element method (FEM). The permanent magnet (PM) eddy-current losses when using different PM shapes are studied. The equivalent thermal model of the tape-wound AMM stator segments and the windings are established, and the temperature distribution of the motor is obtained. The mechanical behavior of the stator segments and the rotor disks when the motor is eccentric and axially offset is analyzed, and the structural strength of the motor is evaluated. Finally, a prototype of the motor is fabricated, and the electromagnetic performance and temperature of the motor are tested to verify the accuracy of the multiphysics design approach.

In order to solve the contradiction between the opening and closing time of the high speed on/off valve for space propulsion systems of the liquid rocket engine, a pneumatic pilot-operated high speed on/off valve is proposed and multiobjective optimization for the opening and closing time of the valve is carried out in this paper. Based on the analysis of the working mechanism of the valve, the mathematical models for the pilot valve and the main valves are established respectively. The Plackett-Burman design is used to select the optimization variables which influence the performance of the response time significantly. The central composite design is used to obtain the sample points and establish second-order response surface models of the response time. The NSGA-II is used to obtain the Pareto front of the optimization objectives. The optimized opening and closing time can be reduced by 17.7% and 37.4% respectively. A prototype based on the optimized parameters is manufactured and tested to verify the accuracy of the multiobjective optimization results. The test results verify the validity of the optimization approach for the proposed valve in this paper.

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Background：The relationship between season and the risk of preterm birth is not consistent. Importantly, the role of environmental factors in it is not clear. Methods：Based on the baseline of the Jinan birth cohort, our study focused on seasons of conception to examine the relationship. The mothers from the birth cohort were the subjects, and they were interviewed face-to-face by the questionnaire. The average exposure levels of temperature and humidity during the first 30 days of pregnancy were calculated, and those of air pollutants were assessed by an inverse distance weighting method. Results: A total of 4.4 % (263/5984) of mothers had premature babies. The rates of preterm birth were higher in winter (6.0 %) and summer (4.5 %) than that in spring (3.1 %) at the 0.05 significant level. In the multivariate logistic regression model, the adjusted odds ratio (OR) and 95 % confidence interval (CI) for the risk of preterm birth at conception in winter and summer were 2.228 (1.512-3.316) and1.541 (1.055-2.277). However, after further adjustment for humidity, only the association between winter conception and preterm birth remained statistically significant (OR: 2.353, 95% CI: 1.594-3.511). Moreover, the humidity partially mediated the relationship (41.2 %) between conception in winter and preterm birth, and humidity in winter was negatively associated with the risk of preterm birth (indirect effect = -0.007, P < 0.001). Conclusions: For women living in the temperate regions, conception in summer and winter may increase the risk of preterm birth, and this association persisted in winter after adjusting for environmental factors. During the first 30 days of pregnancy, lower levels of humidity exposure in winter contributed to and mediated the relationship. The results may provide epidemiological evidence for pregnancy planning and care of women from the perspective of environmental factors.