科研成果

Teflon bag chambers have long been used for investigating atmospheric chemical processes, including secondary organic aerosol formation. The wall-loss process of gas-phase species in Teflon bag chambers has typically been investigated at around room temperature. Recent laboratory studies started employing Teflon bag chambers at sub-273 K conditions for simulating wintertime and upper-tropospheric environments. However, temperature dependence in vapor-wall-loss processes of semi-volatile organic compounds (SVOCs) in a Teflon bag chamber has not been well investigated. In this study, we experimentally investigated wall-loss processes of C14–C19 n-alkanes in a 1 m3 Teflon bag for the temperature range of 262 to 298 K. Enhanced wall losses of the tested n-alkanes were observed following the decrease in temperature. For instance, 65 %​​​​​​​ of C14 n-alkane was lost to the wall 15 h after injection at room temperature, while the corresponding value was 95 % at 262 K. The experimental data were analyzed using a two-layer kinetic model, which considers both absorption of gas-phase species to the surface layer of the Teflon wall and diffusion to the inner layer. The experimental data demonstrated that absorption of gas-phase species by the surface layer was enhanced at lower temperatures. The temperature dependence in absorption was well accounted for using the equilibrium-dissolution model of organic compounds to the Teflon surface by considering reduced saturation vapor pressure at lower temperatures. On the contrary, diffusion of n-alkanes from the surface to the inner layer slowed down at reduced temperatures. Mechanistic studies on these processes will need to be conducted in the future to quantitatively predict the influence of temperature-dependent wall-loss processes of SVOCs on laboratory experimental results.

The reactions between CO2 slugs and crude oil induce a substantial amount of asphaltene precipitation and adsorption on the rock surface during the CO2 alternative water flooding process. When the subsequent water slug passes through the core pores after asphaltene adsorption, it will displace the previous CO2 slug. The wettability of water and CO2 on the asphaltene-adsorbed rock surface will directly determine the magnitude and direction of the capillary force of the two media, which in turn affects their flow resistance and flow pattern analysis. In this paper, the systems of CO2/water/sandstone and CO2/water/asphaltene adsorption sandstone were established by molecular dynamics simulation technology. The effects of asphaltene adsorption, thickness of the asphaltene adsorption layer, CO2 density, mass fraction and type of salt in water on the wettability of water on sandstone surfaces were studied. The results reveal that asphaltene adsorption significantly reduces the wettability of water on the original powerful water-wetting sandstone surface, making it easier to see how CO2 density affects the wettability of water on the asphaltene-adsorbed sandstone surface. The increased CO2 density will continue to lower the wettability of water on the asphaltene-adsorbed sandstone surface, even causing it to become wet with CO2. The adsorption thickness of asphaltene does not affect the wettability of water and CO2 on the asphaltene-adsorbed sandstone surface, and just a layer of 5A-thick asphaltene adsorption can significantly reduce the wettability of water on sandstone surfaces. Furthermore, a rise in salinity in water has a detrimental impact on the wettability of water on the asphaltene-adsorbed sandstone surface, with divalent salts having a stronger negative effect than monovalent salts.

Rural households contend with numerous uninsured risks that hinder their ability to leverage profitable yet risky opportunities. We study whether the provision of insurance coverage for medical expenditure, one of the most substantial and unpredictable risk, can stimulate entrepreneurship and other risky financial decisions among rural households. We leverage the progressive nationwide rollout of a universal public health insurance program in rural China. We find that the introduction of health insurance led to a substantial increase in rural households engagement in entrepreneurship. This increase is mainly driven by the risk sharing of health insurance, rather than a reduction in realized medical expenses. The entrepreneurship-promoting effect is also evident at an aggregate level, fostering the growth of smallholder businesses in rural counties. Our findings shed light on the understudied, favorable impact of health insurance on household’s risk taking in rural markets of developing countries.

This book analyzes the wealth management of mid-high net worth individuals and families. As China's economy develops and people's living standards improve, more and more families are becoming well-off and the middle-income group continues to expand. After creating wealth and becoming rich, better guarding, spreading and enjoying wealth is not only an urgent challenge faced by more and more micro-families, but also an inevitable need to enrich and energize people's livelihood and the connotation of a good life. Mid-high net worth people are an organic part of China's middle-income group, as well as the future coordinates of many families that have just crossed into the middle-income group. An accurate portrait of this group and an in-depth study of the needs, habits, ways and effects of their family wealth management and distribution are conducive to better responding to the demands of affluent families to "keep, pass on and enjoy wealth," as well as exploring the path of solidly promoting common prosperity at the micro-family level. From this perspective, Institute of Social Science Survey of Peking University has conducted a panoramic analysis on mid-high net worth people from panel survey with more 16,000 households in China after 10 years of tracking and investigation, from six aspects: behavioral patterns, financial asset allocation, non-financial asset allocation, commercial insurance allocation, children's commercial medical insurance allocation and pension insurance allocation, the importance of which is self-evident. As the first systematic work on asset allocation and insurance protection of Chinese middle and high net worth families, although part of the purpose is to explore the demand for insurance protection and develop the commercial insurance market, there is no doubt that this study is an important reference for the government to formulate social security policies and for financial institutions to optimize the supply of family wealth services.