In current researches on spectrum leasing, Common model and Property-right model are two main approaches to dynamic spectrum sharing. However, Common model does not consider the obligation of Primary System (PS) and i...In current researches on spectrum leasing, Common model and Property-right model are two main approaches to dynamic spectrum sharing. However, Common model does not consider the obligation of Primary System (PS) and is unfair to Secondary System (SS), while the cooperation based on Property-rights model has problems on its feasibility. This paper proposes a novel system model, in which a Cost-Prediction scheme for Spectrum Leasing (CPSL scheme) is designed to forecast the cost that PS would pay for leasing spectrum. Cost Function is introduced as a criterion to evaluate the potential cost of spectrum leasing for PS. The simulation results show that compared with Common model based scheme, CPSL scheme substantially improves the QoS of the delay-sensitive traffic in SS at the cost of a small degradation of PS performance.展开更多
Competitive use of transboundary freshwater resources is becoming one of the key factors influencing regional peace and political relationship among states.In China, 18 major international river basins are concentrate...Competitive use of transboundary freshwater resources is becoming one of the key factors influencing regional peace and political relationship among states.In China, 18 major international river basins are concentrated in three regions, of which the total annual outflow at the border is 7320×108 m3, occupying 26.8% of the total annual runoff of China, and the inflow at the border is only 172×108 m3.In this paper, we analyzed the major drivers affecting shared water vulnerability in China, namely:(1) changes in physical conditions affecting the availability of water;(2) competing objectives between economic development and ecological conservation;(3) lack of emergency response mechanisms;(4) unsound administrative institutions;and(5) shortcomings in the development of regional cooperation based on transboundary waters.We concluded by identifying four pathways for reducing vulnerability:(1) encouraging scientific research cooperation;(2) constructing information-sharing channels;(3) establishing early-warning mechanisms;and(4) promoting further coordination and negotia-tion.展开更多
A straightforward technique has been developed to quickly determine the wall contour of super/hypersonic nozzles working at multiply Mach number which share a common throat section.Mach number distribution along the c...A straightforward technique has been developed to quickly determine the wall contour of super/hypersonic nozzles working at multiply Mach number which share a common throat section.Mach number distribution along the centerline of the nozzle is specified in advance and divided into two sections,both of which are described by the b-spline function.The first section is shared by different exit Mach number nozzles.The nozzle contour is determined by the method of characteristics plus boundary layer correction.An example of this design method is employed to illustrate the technique with a computational fluid dynamics calculation.The simulation results indicate that desired Mach numbers are obtained at the nozzle exit,and the good flow quality is attained for different nozzles within δMa/Ma<±0.56% in the flow core region.This technique improves the design precision of the converging-diverging nozzle,cancels waves completely,and achieves nozzles with multiple Mach number exiting which share a common throat section.展开更多
基金supported by the National High Technology Research and Development Program of China ('863' Program, No.2009AA01Z242)National Natural Science Foundation of China (60972080)
文摘In current researches on spectrum leasing, Common model and Property-right model are two main approaches to dynamic spectrum sharing. However, Common model does not consider the obligation of Primary System (PS) and is unfair to Secondary System (SS), while the cooperation based on Property-rights model has problems on its feasibility. This paper proposes a novel system model, in which a Cost-Prediction scheme for Spectrum Leasing (CPSL scheme) is designed to forecast the cost that PS would pay for leasing spectrum. Cost Function is introduced as a criterion to evaluate the potential cost of spectrum leasing for PS. The simulation results show that compared with Common model based scheme, CPSL scheme substantially improves the QoS of the delay-sensitive traffic in SS at the cost of a small degradation of PS performance.
基金The National Key Project for Basic Research on Ecosystem Changes in Longitudinal Range-Gorge Region and Transboundary Eco-security of Southwest China,No.2003CB415105
文摘Competitive use of transboundary freshwater resources is becoming one of the key factors influencing regional peace and political relationship among states.In China, 18 major international river basins are concentrated in three regions, of which the total annual outflow at the border is 7320×108 m3, occupying 26.8% of the total annual runoff of China, and the inflow at the border is only 172×108 m3.In this paper, we analyzed the major drivers affecting shared water vulnerability in China, namely:(1) changes in physical conditions affecting the availability of water;(2) competing objectives between economic development and ecological conservation;(3) lack of emergency response mechanisms;(4) unsound administrative institutions;and(5) shortcomings in the development of regional cooperation based on transboundary waters.We concluded by identifying four pathways for reducing vulnerability:(1) encouraging scientific research cooperation;(2) constructing information-sharing channels;(3) establishing early-warning mechanisms;and(4) promoting further coordination and negotia-tion.
基金Project(11072264) supported by the National Natural Science Foundation of China
文摘A straightforward technique has been developed to quickly determine the wall contour of super/hypersonic nozzles working at multiply Mach number which share a common throat section.Mach number distribution along the centerline of the nozzle is specified in advance and divided into two sections,both of which are described by the b-spline function.The first section is shared by different exit Mach number nozzles.The nozzle contour is determined by the method of characteristics plus boundary layer correction.An example of this design method is employed to illustrate the technique with a computational fluid dynamics calculation.The simulation results indicate that desired Mach numbers are obtained at the nozzle exit,and the good flow quality is attained for different nozzles within δMa/Ma<±0.56% in the flow core region.This technique improves the design precision of the converging-diverging nozzle,cancels waves completely,and achieves nozzles with multiple Mach number exiting which share a common throat section.
