Cross-regional tourism expenditure can stimulate market activity and meet the increasing demand for high-quality tourism experiences.Using UnionPay offline transaction data matched with flight route information from 2...Cross-regional tourism expenditure can stimulate market activity and meet the increasing demand for high-quality tourism experiences.Using UnionPay offline transaction data matched with flight route information from 2013 to 2018 in China,this study applied a difference-in-differences model to investigate the impact of direct flights on cross-city tourism expenditure.It found that,after the opening of new routes,the cross-city tourism expenditure between city pairs increased by approximately 3.2 percent.Direct flights also increased tourism expenditure on sightseeing,lodging,catering,and shopping,with the larger effects for city pairs separated by more than 400 km.Destinations with high-quality cultural and natural assets,such as national 5A-level tourist attractions,world cultural and natural heritage sites,and national tourist resorts,tended to experience increased tourist expenditure.Direct flights also produced spillover effects on expenditure in surrounding cities,which decreased with distance,and these effects occurred mainly in hub cities and origin nonhub cities.These findings have implications for urban growth policy.展开更多
A direct drive actuator （DDA） with direct drive valves （DDVs） as the control device is an ideal solution for a flight actuation system. This paper presents a novel triple-redundant voice coil motor （TRVCM） used ...A direct drive actuator （DDA） with direct drive valves （DDVs） as the control device is an ideal solution for a flight actuation system. This paper presents a novel triple-redundant voice coil motor （TRVCM） used for redundant DDVs. The TRVCM features electrical/mechanical hybrid triple-redundancy by securing three stators along with three moving coils in the same frame. A permanent magnet （PM） Halbach array is employed in each redundant VCM to simplify the system structure. A back-to-back design between neighborly redundancies is adopted to decouple the magnetic flux linkage. The particle swarm optimization （PSO） method is implemented to optimize design parameters based on the analytical magnetic circuit model. The optimization objective function is defined as the acceleration capacity of the motor to achieve high dynamic performance. The optimal geometric parameters are verified with 3D magnetic field finite element analysis （FEA）. A research prototype has been developed for experimental purpose. The experimental results of magnetic field density and force output show that the proposed TRVCM has great potential of applications in DDA systems.展开更多
In recent times,the use of vertical take-off and landing(VTOL)multi-rotor Unmanned Aerial Vehicle(UAVs)for spraying chemical pesticides against weeds and pests has recently become popular.The current aerial spray appl...In recent times,the use of vertical take-off and landing(VTOL)multi-rotor Unmanned Aerial Vehicle(UAVs)for spraying chemical pesticides against weeds and pests has recently become popular.The current aerial spray application research is primarily focused on examining the influence of UAV spraying parameters such as flight height,travel speed,rotor configuration,droplet size,payload and wind velocity.The downwash airflow velocity generated by the UAV rotor propeller has a significant impact on the droplet deposition process.A test rig was developed to measure the downwash airflow pattern generated by the rotor propeller of a UAV.In this investigation,a six-rotor electric autonomous UAV sprayer was used to investigate the parameters and distribution laws of downwash airflow velocity.The downwash airflow velocity was measured using portable anemometers mounted on the test rig at radial positions viz.,0 m,0.5 m,1 m,1.5 m and 2 m,perpendicular to(X)and parallel to the UAV’s flight direction(Y).The experiment was conducted at three levels of hover height,viz.,1 m,2 m and 3 m(Z)and three levels of payload,viz.,0 kg,5 kg,and 10 kg.The special downwash airflow distribution pattern was analysed using the Python programming language(Version 3.7).Results show that the downwash airflow velocity generated by the radial position of the UAV rotor is evenly distributed on the rotating loop and the standard deviation of the downwash airflow velocity is less than 0.5 m/s.The maximum downwash airflow velocity of 13.8 m/s was observed below the rotor at 10 kg payload capacity,1 m hover height(Z),and 0.5 m in the X-direction.The minimum downwash wind field of 0.3 m/s was observed at 0 kg pay load capacity,1 m height,and 2 m in the X-direction.The downwash airflow velocity along each position in the radial direction of the rotor increases initially and then decreases.This downwash airflow distribution results helps in mounting of spray nozzle configuration to drone sprayer which helps to understanding spray liquid distribution and other spray operational parameters.The influence of downwash airflow distribution combined with the spray operational parameters of the UAV sprayer viz.,flight height,travel speed,rotor configuration,payload and wind velocity on spray volume distribution was studied.A field experiment was conducted to study the effect of UAV sprayer downwash airflow distribution on spray droplet deposition characteristics in a rice crop compared with manual knapsack sprayer.展开更多
基金supported by the National Natural Science Foundation of China(Nos.72233002 , 72173104)the Major Program of National Fund of Philosophy and Social Science of China(No.24ZDA087)the Postdoctoral Fellowship Program of CPSF(No.GZC20233140).
文摘Cross-regional tourism expenditure can stimulate market activity and meet the increasing demand for high-quality tourism experiences.Using UnionPay offline transaction data matched with flight route information from 2013 to 2018 in China,this study applied a difference-in-differences model to investigate the impact of direct flights on cross-city tourism expenditure.It found that,after the opening of new routes,the cross-city tourism expenditure between city pairs increased by approximately 3.2 percent.Direct flights also increased tourism expenditure on sightseeing,lodging,catering,and shopping,with the larger effects for city pairs separated by more than 400 km.Destinations with high-quality cultural and natural assets,such as national 5A-level tourist attractions,world cultural and natural heritage sites,and national tourist resorts,tended to experience increased tourist expenditure.Direct flights also produced spillover effects on expenditure in surrounding cities,which decreased with distance,and these effects occurred mainly in hub cities and origin nonhub cities.These findings have implications for urban growth policy.
基金supported by National Science Foundation for Distinguished Young Scholars of China(No.50825502)National Natural Science Foundation of China(No.51105016)
文摘A direct drive actuator （DDA） with direct drive valves （DDVs） as the control device is an ideal solution for a flight actuation system. This paper presents a novel triple-redundant voice coil motor （TRVCM） used for redundant DDVs. The TRVCM features electrical/mechanical hybrid triple-redundancy by securing three stators along with three moving coils in the same frame. A permanent magnet （PM） Halbach array is employed in each redundant VCM to simplify the system structure. A back-to-back design between neighborly redundancies is adopted to decouple the magnetic flux linkage. The particle swarm optimization （PSO） method is implemented to optimize design parameters based on the analytical magnetic circuit model. The optimization objective function is defined as the acceleration capacity of the motor to achieve high dynamic performance. The optimal geometric parameters are verified with 3D magnetic field finite element analysis （FEA）. A research prototype has been developed for experimental purpose. The experimental results of magnetic field density and force output show that the proposed TRVCM has great potential of applications in DDA systems.
文摘In recent times,the use of vertical take-off and landing(VTOL)multi-rotor Unmanned Aerial Vehicle(UAVs)for spraying chemical pesticides against weeds and pests has recently become popular.The current aerial spray application research is primarily focused on examining the influence of UAV spraying parameters such as flight height,travel speed,rotor configuration,droplet size,payload and wind velocity.The downwash airflow velocity generated by the UAV rotor propeller has a significant impact on the droplet deposition process.A test rig was developed to measure the downwash airflow pattern generated by the rotor propeller of a UAV.In this investigation,a six-rotor electric autonomous UAV sprayer was used to investigate the parameters and distribution laws of downwash airflow velocity.The downwash airflow velocity was measured using portable anemometers mounted on the test rig at radial positions viz.,0 m,0.5 m,1 m,1.5 m and 2 m,perpendicular to(X)and parallel to the UAV’s flight direction(Y).The experiment was conducted at three levels of hover height,viz.,1 m,2 m and 3 m(Z)and three levels of payload,viz.,0 kg,5 kg,and 10 kg.The special downwash airflow distribution pattern was analysed using the Python programming language(Version 3.7).Results show that the downwash airflow velocity generated by the radial position of the UAV rotor is evenly distributed on the rotating loop and the standard deviation of the downwash airflow velocity is less than 0.5 m/s.The maximum downwash airflow velocity of 13.8 m/s was observed below the rotor at 10 kg payload capacity,1 m hover height(Z),and 0.5 m in the X-direction.The minimum downwash wind field of 0.3 m/s was observed at 0 kg pay load capacity,1 m height,and 2 m in the X-direction.The downwash airflow velocity along each position in the radial direction of the rotor increases initially and then decreases.This downwash airflow distribution results helps in mounting of spray nozzle configuration to drone sprayer which helps to understanding spray liquid distribution and other spray operational parameters.The influence of downwash airflow distribution combined with the spray operational parameters of the UAV sprayer viz.,flight height,travel speed,rotor configuration,payload and wind velocity on spray volume distribution was studied.A field experiment was conducted to study the effect of UAV sprayer downwash airflow distribution on spray droplet deposition characteristics in a rice crop compared with manual knapsack sprayer.
