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Objectives: To investigate the prevalence of molar-incisor hypomineralization (MIH) in children aged 12 to 15 years in Beijing, China. Materials and methods: A cross-sectional study was performed to recruit children aged 12 to 15 years old based on the method of multi-stage cluster random sampling during the Fourth National Oral Health Survey in Beijing, China, from September 2015 to March 2016. The first permanent molars (FPMs) and permanent incisors were examined for the presence of MIH by a single-calibrated examiner according to the European Academy of Paediatric Dentistry (EAPD) criteria. Results: Of the 6523 children recruited, 655 (10.0%) had MIH. The average number of affected MIH teeth in children was 2.68 ± 1.51. There was no gender-specific difference. With respect to the distribution of MIH in the mandible and maxilla, the most common condition was the simultaneous involvement of both the upper and lower FPMs. The severity of MIH was positively correlated with the number of affected teeth. The prevalence of MIH was lower in children who resided in the central districts and whose mothers had received higher education. Conclusion: MIH was relatively prevalent among children aged 12 to 15 years old in Beijing, China. Clinical relevance: This study is the first epidemiological survey on the prevalence of MIH in the pediatric population in North China. Some demographic and sociological factors were associated with the presence of MIH. [ABSTRACT FROM AUTHOR]

A meteorological model, RAMS, and a commercial computational fluid dynamics (CFD) model, FLUENT are combined as a one-way off-line nested modeling system, namely, RAMS/FLUENT system. The system is experimentally applied in the wind simulation over a complex terrain, with which numerical simulations of wind field over Foyeding weather station located in the northwest mountainous area of Beijing metropolis are performed. The results show that the method of combining a meteorological model and a CFD model as a modeling system is reasonable. In RAMS/FLUENT system, more realistic boundary conditions are provided for FLUENT rather than idealized vertical wind profiles, and the finite volume method (FVM) of FLUENT ensures the capability of the modeling system on describing complex terrain in the simulation. Thus, RAMS/FLUENT can provide fine-scale realistic wind data over complex terrains. [ABSTRACT FROM AUTHOR]