With rapid urbanization and increase in car ownership, ambient noise pollution resulting from diversified sources (e.g., road traffic, railway, commercial services) has become a severe environmental problem in the populated areas in China. However, research on the spatial variation of noise pollution and its potential effects on urban residents’ mental health has to date been quite scarce in developing countries like China. Using a health survey conducted in Beijing in 2017, we for the first time investigated the spatial distributions of multiple noise pollution perceived by residents in Beijing, including road traffic noise, railway (or subway) noise, commercial noise, and housing renovation (or construction) noise. Our results indicate that there is geographic variability in noise pollution at the neighborhood scale, and road traffic and housing renovation/construction are the principal sources of noise pollution in Beijing. We then employed Bayesian multilevel logistic models to examine the associations between diversified noise pollution and urban residents’ mental health symptoms, including anxiety, stress, fatigue, headache, and sleep disturbance, while controlling for a wide range of confounding factors such as socio-demographics, objective built environment characteristics, social environment and geographic context. The results show that perceived higher noise-pollution exposure is significantly associated with worse mental health, while physical environment variables seem to contribute little to variations in self-reported mental disorders, except for proximity to the main road. Social factors or socio-demographic attributes, such as age and income, are significant covariates of urban residents’ mental health, while the social environment (i.e., community attachment) and housing satisfaction are significantly correlated with anxiety and stress. This study provides empirical evidence on the noise-health relationships in the Chinese context and sheds light on the policy implications for environmental pollution mitigation and healthy city development in China.

Most prior studies adopted a static residence-based approach in the assessment of noise exposure, which may lead to biased exposure estimates and misleading findings in noise-health relationships. Relatively little is known about personal noise exposure based on individuals' space-time behavior and its effect on mental health. This study aims to analyze and geo-visualize personal exposure to noise in various microenvironments based on individuals' space-time trajectories at a very fine resolution and to further investigate the relationships between mental health and personal noise exposure at both the activity/travel episode level and the entire day level. Individual-level real-time data were collected with portable noise sensors and GPS trackers from a sample of 117 residents aged 18-60 years old from December 2017 to February 2018 in Beijing, China. Descriptive statistics and geo-visualization methods were used to examine how personal noise exposure varied across different activity types, travel modes, and among residents living in the same residential neighborhood on workdays and weekends based on individuals' space-time behaviors. Logistic regression models were applied to examine the relationships between personal noise exposure and self-reported mental health. We observed substantial differences in personal noise exposure across different activity types. The equivalent sound levels (Leq, dB(A)) for sleeping were the lowest, while the average Leq for work-related activities was the highest in indoor environments. The noise exposure levels for activities in outdoor environments were higher than indoor noise levels but differed between workdays and weekends. Variations in noise exposure associated with different travel modes were also evident, with the average Leq for public transport being much higher than that of other travel modes. A-weighted equivalent sound pressure level measured over 24 h for each individual (Leq,24h, dB(A)) varied significantly for residents living in the same residential neighborhood, ranging from 36 to 97 dB(A), with the majority of respondents being exposed to noise levels above 55 dB(A) on both workdays and weekends. Regarding the noise-health relationships, the modeling results showed that individual-level objective noise exposure based on space-time behaviors measured over a 24-h period (Leq,24h) was strongly associated with residents' self-reported mental health. Higher exposure to noise was significantly associated with worse mental health. However, personal noise exposure at the activity/travel episode level (Leq) was not significantly associated with mental health on weekdays, but this link turned out to be significant in the weekend model. There were large variations in personal noise exposure associated with different activity types and travel modes, and the individual-level noise exposure varied significantly across time of day and between residents living in the same residential neighborhood. Variations in personal exposure strongly depend on different space-time behaviors and individual-specific microenvironments experienced in daily life, and they were significantly correlated with mental health.

Many scholars have conducted in-depth analysis on relevant factors that affect the accuracy of jet dispensing. However, research on the influence of needle impact velocity on jetting performance is limited. Thus, a piezoelectric needle-collision dispenser for micro-droplet jetting is designed in this study, and the influence of the needle impact velocity on jetting effect is deeply analyzed. Initially, the principle of droplet formation and injection is analyzed by Fluent simulation. Thereafter, the mathematical model of the droplet velocity in the nozzle orifice is derived, and the influence of the needle impact velocity on the jetting performance is simulated and analyzed. Results show that the needle impact velocity has an influence on the jetting effect. A prototype of the jetting dispenser is subsequently fabricated, and the needle impact velocity is tested with laser micrometer. The relationship between the needle impact velocity and droplet weight and its corresponding ejected effect are obtained through experimental research. Finally, a UV glue with viscosity of 5,000 cps can be ejected with a minimum average diameter of 272.1 μm by using a needle with a radius of 0.5 mm, a nozzle with a diameter of 50 μm, a taper angle of 90°, a supply pressure of 0.2 Mpa, and a needle impact velocity of 0.13 m/s. The variation of the droplet diameter is within ±2.5%.