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Based on the viewpoint of friction self-excited vibration, the formation mechanism of wheel polygonal wear in high-speed train and related influence factors are studied in this study. Firstly, a field investigation of the Chengdu-Chongqing high-speed railway is conducted. The wheel polygon characteristics of the section is mastered, and the vibration frequencies excited by high-order OOR is obtained. A finite element model considering the brake system and the wheel-rail system is proposed. The unstable vibration frequency distribution and the system stability are studied by complex eigenvalue analysis. Results show that when the high-speed train runs at 300 km/h, the unstable vibration of frequency 652.8 Hz is excited. The unstable vibration will cause periodic fluctuation of wheel-rail friction work, leading to 22–23 order polygonal wear of the trailer wheel. The consistency of simulation results and Field research situation proves the correctness of the proposed method. In addition, the influence factors on the wheel polygonal wear are investigated. The pad with a high damping coefficient can effectively inhibit the 22–23order wheel polygonal wear. Increasing the Young's modulus of the pad will cause the self-excited vibration frequency increases, and the system is prone to higher-order wheel polygonal wear. The Poisson's ratio of brake pad has little effect on wheel polygonal. In addition, the brake pad structure also has a great influence on the self-excited vibration of the system. The brake pads with groove surface can decrease the self-excited vibration frequency and reduce the polygon order. • An investigation into the polygonal wheel wear characteristics of the Chengdu-Chongqing high-speed railway was carried out. • It is pointed out that the frictional self-excited vibration of the braking system is the main reason for the generation of 22–23 order polygonal wheel wear. • The influence of braking parameters and brake pad properties on the polygonal wear of wheels was investigated, the corresponding measures to mitigate the generation of polygonal wheel wear are proposed. [ABSTRACT FROM AUTHOR]

Objective: To investigate whether implementation of a universal salt iodization (USI) programme has sufficient effects on pregnant women in Chongqing, the present study evaluated the iodine nutritional status of pregnant women living in Chongqing by spot urinary iodine concentration (UIC), to provide scientific suggestions to better meet the specific iodine needs of this vulnerable group.Design: Cross-sectional design.Setting: A random spot urine sample and household table salt sample were provided by each participant.Participants: A total of 2607 pregnant women from twenty-six of thirty-nine districts/counties in Chongqing participated.Results: The overall median UIC of pregnant women was 171·80 μg/l (interquartile range (IQR) = 113·85-247·00 μg/l) and 40·97 % (n 1057) of participants were iodine insufficient. The median iodine in table salt samples was 25·40 mg/kg (IQR = 23·10-28·30 mg/kg); 93·26 % (n 2406) of samples examined were found to be adequately iodized. Iodine nutritional status was not significantly different according to table salt iodization category. Trimester was identified to be statistically associated with UIC (P < 0·01). Seven districts/counties had median UIC below 150 μg/l and one district had median UIC of 277·40 μg/l.Conclusions: The USI programme in Chongqing prevents iodine deficiency generally, but does not maintain iodine status within adequate and recommended ranges throughout pregnancy. Usage of non-iodized or unqualified iodized salt and the slight change of dietary habits of iodized salt in Chongqing may present a substantial challenge to fight iodine-deficiency disorders; more efforts are needed to ensure adequate iodine intake during pregnancy besides the USI programme. [ABSTRACT FROM AUTHOR]