The seasonal generation and evolution of eddies in the region of the North Pacific Subtropical Countercurrent remain poorly understood due to the scarcity of available data.We used TOPEX/POSEIDON altimetry data from 1...The seasonal generation and evolution of eddies in the region of the North Pacific Subtropical Countercurrent remain poorly understood due to the scarcity of available data.We used TOPEX/POSEIDON altimetry data from 1992 to 2007 to study the eddy field in this zone.We found that velocity shear between this region and the neighboring North Equatorial Current contributes greatly to the eddy generation.Furthermore,the eddy kinetic energy level(EKE) shows an annual cycle,maximum in April/May and minimum in December/January.Analyses of the temporal and spatial distributions of the eddy field revealed clearly that the velocity shear closely related to baroclinic instability processes.The eddy field seems to be more zonal than meridional,and the energy containing length scale shows a surprising lag of 2-3 months in comparison with the 1-D and 2-D EKE level.A similar phenomenon is observed in individual eddies in this zone.The results show that in this eddy field band,the velocity shear may drive the EKE level change so that the eddy field takes another 2-3 months to grow and interact to reach a relatively stable state.This explains the seasonal evolution of identifiable eddies.展开更多
The deformation mechanism of C5191 phosphor bronze sheet under ultra-high-speed blanking was investigated.By virtue of a DOBBY-OMEGA F1 ultra-high-speed press,the ultra-high-speed blanking test was conducted on C5191 ...The deformation mechanism of C5191 phosphor bronze sheet under ultra-high-speed blanking was investigated.By virtue of a DOBBY-OMEGA F1 ultra-high-speed press,the ultra-high-speed blanking test was conducted on C5191 phosphor bronze sheets with a thickness of 0.12 mm at 3000 strokes per minute.The microstructures of the blanked edges were characterized and analyzed separately by electron back-scatter diffraction(EBSD)and transmission electron microscopy(TEM).The results show that grains in the blanked edges are stretched along the blanking direction.Strong{001}<100>cube textures(maximum pole densities of 9 and 12,respectively)and secondarily strong{011}<011>textures(maximum pole densities of 4 and 7,respectively)are formed in local zones.Additionally,deformation twins are found in the shear zone of the blanked edges which are rotated and coarsened due to the blanking-induced extrusion and local thermal effect which can further form into sub-grains with clear and high-angle boundaries.The C5191 phosphor bronze sheet is subjected to adiabatic shear during ultra-high-speed blanking,accompanied with dynamic recrystallization.展开更多
The hemodynamics of intracranial aneurysm(IA)comprises complex transient flow patterns that affect its growth and rupture.Owing to the combined effects of geometrical factors and pulsatile flow conditions,the transien...The hemodynamics of intracranial aneurysm(IA)comprises complex transient flow patterns that affect its growth and rupture.Owing to the combined effects of geometrical factors and pulsatile flow conditions,the transient flow patterns in the IA are still unclear.The purpose of this work is to reveal the effect of the aspect ratio(AR,sac height/neck width)on the evolution of the internal flow patterns and the hemodynamics of the IA.We proposed an easy method to fabricate three simplified elastic IA models and measured the transient flow characteristics by using particle image velocimetry(PIV).Transient vortex structures in the IA modes during a cardiac cycle were systemically measured and many new flow phenomena were found,including the vortex morphology(size,structure,and core location),a high-speed jet,wall compliance effects,and three flow modes during retrograde flow phase.The results show that the AR of the IA affects the transient flow patterns as well as the wall shear stress(WSS)in complex ways.The results could deepen our understanding of the transient flow behaviors in IA and guide related clinical studies.展开更多
基金Supported by the Key Program of the Knowledge Innovation Program of the Chinese Academy of Sciences (No.KZCX1-YW-12-04)the National Basic Research Program (973 Program) (No.2006CB403601)
文摘The seasonal generation and evolution of eddies in the region of the North Pacific Subtropical Countercurrent remain poorly understood due to the scarcity of available data.We used TOPEX/POSEIDON altimetry data from 1992 to 2007 to study the eddy field in this zone.We found that velocity shear between this region and the neighboring North Equatorial Current contributes greatly to the eddy generation.Furthermore,the eddy kinetic energy level(EKE) shows an annual cycle,maximum in April/May and minimum in December/January.Analyses of the temporal and spatial distributions of the eddy field revealed clearly that the velocity shear closely related to baroclinic instability processes.The eddy field seems to be more zonal than meridional,and the energy containing length scale shows a surprising lag of 2-3 months in comparison with the 1-D and 2-D EKE level.A similar phenomenon is observed in individual eddies in this zone.The results show that in this eddy field band,the velocity shear may drive the EKE level change so that the eddy field takes another 2-3 months to grow and interact to reach a relatively stable state.This explains the seasonal evolution of identifiable eddies.
基金The authors are grateful for the financial supports from Jiangsu Key Laboratory of Precision and Micro-manufacturing Technology of China(JSJMYWX2020-01)Zhejiang Provincial Natural Science Foundation of China(LY18E050005)the Startup Foundation for Introducing Talent of Nanjing Institute of Industry Technology(YK18-13-02)of China.
文摘The deformation mechanism of C5191 phosphor bronze sheet under ultra-high-speed blanking was investigated.By virtue of a DOBBY-OMEGA F1 ultra-high-speed press,the ultra-high-speed blanking test was conducted on C5191 phosphor bronze sheets with a thickness of 0.12 mm at 3000 strokes per minute.The microstructures of the blanked edges were characterized and analyzed separately by electron back-scatter diffraction(EBSD)and transmission electron microscopy(TEM).The results show that grains in the blanked edges are stretched along the blanking direction.Strong{001}<100>cube textures(maximum pole densities of 9 and 12,respectively)and secondarily strong{011}<011>textures(maximum pole densities of 4 and 7,respectively)are formed in local zones.Additionally,deformation twins are found in the shear zone of the blanked edges which are rotated and coarsened due to the blanking-induced extrusion and local thermal effect which can further form into sub-grains with clear and high-angle boundaries.The C5191 phosphor bronze sheet is subjected to adiabatic shear during ultra-high-speed blanking,accompanied with dynamic recrystallization.
基金supported by the National Natural Science Foundation of China(Grant Nos:12172017 and 11872083)Project of Beijing Municipal Education Commission(Grant Nos.KZ202210005006 and KZ202110005007).
文摘The hemodynamics of intracranial aneurysm(IA)comprises complex transient flow patterns that affect its growth and rupture.Owing to the combined effects of geometrical factors and pulsatile flow conditions,the transient flow patterns in the IA are still unclear.The purpose of this work is to reveal the effect of the aspect ratio(AR,sac height/neck width)on the evolution of the internal flow patterns and the hemodynamics of the IA.We proposed an easy method to fabricate three simplified elastic IA models and measured the transient flow characteristics by using particle image velocimetry(PIV).Transient vortex structures in the IA modes during a cardiac cycle were systemically measured and many new flow phenomena were found,including the vortex morphology(size,structure,and core location),a high-speed jet,wall compliance effects,and three flow modes during retrograde flow phase.The results show that the AR of the IA affects the transient flow patterns as well as the wall shear stress(WSS)in complex ways.The results could deepen our understanding of the transient flow behaviors in IA and guide related clinical studies.
