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Objective During off-peak hours, large train departure interval is adopted for off-peak urban rail transit passenger flow, however, it is commonly faced with issues of low seat occupancy rates and high energy consumption. To enhance the operational service level of urban rail transit, it is necessary to conduct in-depth research on flexible formation train reconnection functionality. Method Based on the development situation of flexible train operation mode in urban rail transit in China, referring to some concepts from high-speed railway EMU (electric multiple units), the main design contents of flexible formation train reconnection are elaborated from aspects of coupler reconnection, vehicle hard-wired circuit reconnection, TCMS (train control and monitoring system) reconnection, and train signal interface requirements. Additionally, the primary verification contents of flexible train formation are introduced from two dimensions: vehicle reconnection form tests and vehicle reconnection routine tests. Result & Conclusion The operation plan of 3-car or 3+3 car train formations on Shanghai Rail Transit Line 16, tailored to peak and off-peak passenger flow demands, can achieve train coupling or decoupling within 3 minutes, which demonstrates the feasibility of the proposed plan.

Recurrent pregnancy loss (RPL) has become an important reproductive health issue worldwide. RPL affects about 2%–3% of reproductive-aged women, and makes serious threats to women’s physical and mental health. However, the etiology of approximately 50% of RPL cases remains unknown (unexplained RPL), which poses a big challenge for clinical management of these patients. RPL has been widely regarded as a complex disease where its etiology has been attributed to numerous factors. Heretofore, various risk factors for RPL have been identified, such as maternal ages, genetic factors, anatomical structural abnormalities, endocrine dysfunction, prethrombotic state, immunological factors, and infection. More importantly, development and applications of next generation sequencing technology have significantly expanded opportunities to discover chromosomal aberrations and single gene variants responsible for RPL, which provides new insight into its pathogenic mechanisms. Furthermore, based upon patients’ diagnostic evaluation and etiologic diagnosis, specific therapeutic recommendations have been established. This review will highlight current understanding and recent advances on RPL, with a special focus on the immunological and genetic etiologies, clinical diagnosis and therapeutic management.