The work functions of the （110） and （10（3） surfaces of LaB6 are determined from ambient pressure to 39.1 GPa. The work function of the （110） surface slowly decreases but that of the （100） surface remains at a...The work functions of the （110） and （10（3） surfaces of LaB6 are determined from ambient pressure to 39.1 GPa. The work function of the （110） surface slowly decreases but that of the （100） surface remains at a relatively constant value. To determine the reason for this difference, the electron density distribution （EDD） is determined from high-pressure single-crystal x-ray diffraction data by the maximum entropy method. The EDD results show that the chemical bond properties in LaB6 play a key role also investigated by single-crystal x-ray diffraction. In observed from ambient pressure to 39.1 GPa. The structural stability of LaB6 under high pressure is this study, no structural or electronic phase transition is展开更多
The employment quality of college graduates in China is a topic of widespread concern.This paper uses authoritative data sources,including the China Labor Statistics Yearbook,China Statistical Yearbook,and data from p...The employment quality of college graduates in China is a topic of widespread concern.This paper uses authoritative data sources,including the China Labor Statistics Yearbook,China Statistical Yearbook,and data from provincial statistical bureaus,to examine the employment quality of college graduates in different regions of China.Specifically,the paper explores three aspects:salary level,job intensity,and job stability.The research results indicate that undergraduate graduates experience lower job intensity than college counterparts.However,while North,East,and South China show high salary levels and job stability,issues such as high work intensity,high cost of living,and small living space exist.Therefore,this paper offers policy development recommendations to promote job market reform and improve employment quality.These recommendations aim to address the challenges faced by college graduates in various regions of China and to promote the stability of the country’s social and economic development.By examining the employment quality of college graduates in different regions of China,this paper provides valuable insights for scholars,policymakers,and practitioners.展开更多
Concentrated photovoltaic(CPV)has been identified as an effective method to further enhance the efficiency of photovoltaic cells.Previous studies on CPV mainly focused on III-V multi-junction cells.Nevertheless,Ⅲ-ⅤC...Concentrated photovoltaic(CPV)has been identified as an effective method to further enhance the efficiency of photovoltaic cells.Previous studies on CPV mainly focused on III-V multi-junction cells.Nevertheless,Ⅲ-ⅤCPV technology is mainly used in niche applications due to its high cost.Here,we use metal-halide perovskite solar cell(PSC)to demonstrate a concentrated photovoltaic-thermoelectric tandem device.The thermoelectric generator(TEG)is utilized to reduce the effect of heat generation under concentrated solar irradiance.Our tandem system achieved a peak power conversion efficiency(PCE)of 25.0%at a solar concentration of 3 suns.This efficiency exceeded that of the single PSC by~4.7%.Our work proves that by controlling the heat flow in concentrated PSC-TEG tandem system,the redundant heat produced by upper PSC can be effectively reused.This tandem structure provides a promising approach to improve the efficiency and stability of PSC under low-concentrated solar irradiation.展开更多
Ducted fans have been widely used in VTOL aircraft due to the high propulsion efficiency and safety.The efficiency and stability of ducted fans deteriorate in some flight conditions such as hovering in crosswinds or g...Ducted fans have been widely used in VTOL aircraft due to the high propulsion efficiency and safety.The efficiency and stability of ducted fans deteriorate in some flight conditions such as hovering in crosswinds or ground effect.It is necessary to optimize the ducted fan’s structures or apply flow control methods for better adaptions to the typical conditions.This paper presents a detailed review on the ducted fan technology for VTOL applications,especially the methods for improving its efficiency and stability.We first simplified the classification categories based on boundary conditions instead of flight conditions,since the new classification method covers more situations and is easier to distinguish flow field characteristics.The flow characteristics,thrust properties and the optimal structures under different boundary conditions were summarized and discussed.Finally,new configurations and flow control methods for increasing the efficiency and stability were introduced.The newly proposed integration design between the ducted fan and the motor was emphasized for increasing the power density of the ducted fans.This review would be helpful to improve our understanding of the relationship between the structures,flow characteristics and thrust properties of ducted fans under different flight conditions,and inspires scientists to design high-efficiency and high-stability propulsion systems with ducted fans.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 11274030 and 11474281
文摘The work functions of the （110） and （10（3） surfaces of LaB6 are determined from ambient pressure to 39.1 GPa. The work function of the （110） surface slowly decreases but that of the （100） surface remains at a relatively constant value. To determine the reason for this difference, the electron density distribution （EDD） is determined from high-pressure single-crystal x-ray diffraction data by the maximum entropy method. The EDD results show that the chemical bond properties in LaB6 play a key role also investigated by single-crystal x-ray diffraction. In observed from ambient pressure to 39.1 GPa. The structural stability of LaB6 under high pressure is this study, no structural or electronic phase transition is
文摘The employment quality of college graduates in China is a topic of widespread concern.This paper uses authoritative data sources,including the China Labor Statistics Yearbook,China Statistical Yearbook,and data from provincial statistical bureaus,to examine the employment quality of college graduates in different regions of China.Specifically,the paper explores three aspects:salary level,job intensity,and job stability.The research results indicate that undergraduate graduates experience lower job intensity than college counterparts.However,while North,East,and South China show high salary levels and job stability,issues such as high work intensity,high cost of living,and small living space exist.Therefore,this paper offers policy development recommendations to promote job market reform and improve employment quality.These recommendations aim to address the challenges faced by college graduates in various regions of China and to promote the stability of the country’s social and economic development.By examining the employment quality of college graduates in different regions of China,this paper provides valuable insights for scholars,policymakers,and practitioners.
基金supported by Tsinghua University Initiative Scientific Research Programthe National Natural Science Foundation of China(NSFC,51772166,52072207)。
文摘Concentrated photovoltaic(CPV)has been identified as an effective method to further enhance the efficiency of photovoltaic cells.Previous studies on CPV mainly focused on III-V multi-junction cells.Nevertheless,Ⅲ-ⅤCPV technology is mainly used in niche applications due to its high cost.Here,we use metal-halide perovskite solar cell(PSC)to demonstrate a concentrated photovoltaic-thermoelectric tandem device.The thermoelectric generator(TEG)is utilized to reduce the effect of heat generation under concentrated solar irradiance.Our tandem system achieved a peak power conversion efficiency(PCE)of 25.0%at a solar concentration of 3 suns.This efficiency exceeded that of the single PSC by~4.7%.Our work proves that by controlling the heat flow in concentrated PSC-TEG tandem system,the redundant heat produced by upper PSC can be effectively reused.This tandem structure provides a promising approach to improve the efficiency and stability of PSC under low-concentrated solar irradiation.
基金supported by the National Key Research and Development Program of China(Grant No.2020YFC1512500)the Advanced Aviation Power Innovation Institution,the Aero Engine Academy of ChinaTsinghua University Initiative Scientific Research Program。
文摘Ducted fans have been widely used in VTOL aircraft due to the high propulsion efficiency and safety.The efficiency and stability of ducted fans deteriorate in some flight conditions such as hovering in crosswinds or ground effect.It is necessary to optimize the ducted fan’s structures or apply flow control methods for better adaptions to the typical conditions.This paper presents a detailed review on the ducted fan technology for VTOL applications,especially the methods for improving its efficiency and stability.We first simplified the classification categories based on boundary conditions instead of flight conditions,since the new classification method covers more situations and is easier to distinguish flow field characteristics.The flow characteristics,thrust properties and the optimal structures under different boundary conditions were summarized and discussed.Finally,new configurations and flow control methods for increasing the efficiency and stability were introduced.The newly proposed integration design between the ducted fan and the motor was emphasized for increasing the power density of the ducted fans.This review would be helpful to improve our understanding of the relationship between the structures,flow characteristics and thrust properties of ducted fans under different flight conditions,and inspires scientists to design high-efficiency and high-stability propulsion systems with ducted fans.
