Based on the daily rainfall datasets from 740 stations in China from 1954 to 2005 and the NCEP/NCAR reanalysis data, the relationship between the north-south anti-phase distribution(APD) of rainfall during Meiyu perio...Based on the daily rainfall datasets from 740 stations in China from 1954 to 2005 and the NCEP/NCAR reanalysis data, the relationship between the north-south anti-phase distribution(APD) of rainfall during Meiyu periods and the Quasi-Biweekly Oscillation(QBWO) in the atmosphere was analyzed. Diagnostic results are as follows:(1) there was significant north-south oscillation of Meiyu rainfall during the 16 years from 1954 to 2005. Since the 1990 s, the APD enhanced significantly and showed 2- and 4-6-year period. In the region with more rainfall, the QBWO was always more active.(2) The APD of Meiyu and north-south movements of precipitation in eastern China belong to the same phase.(3) The 10-25 day filtered water vapor flux could spread to the area north of 30°N in 1991. The divergence of the water vapor flux which propagated from middle- and higher- latitudes to the of Yangtze-Huaihe River Basins(YHRB) was significant in 1991, but the latitudes that the water vapor flux could reach were further southward and there was no southward propagation of divergence in 1993.(4) The locations of Western Pacific Subtropical High(WPSH) and 10-25 day anti-cyclone, which modulated WPSH's advancement in and out of the South China Sea, were relatively northward in 1991. Furthermore, the vertical circulation showed north-south deviation between 1991 and 1993, just as other elements of the circulation did.展开更多
In this paper, we consider a model system with two identical time-delayed coupled layers. Synchronization and anti-phase synchronization are exhibited in the reactive system without diffusion term. New segmented spira...In this paper, we consider a model system with two identical time-delayed coupled layers. Synchronization and anti-phase synchronization are exhibited in the reactive system without diffusion term. New segmented spiral waves, which are constituted by many thin trips, are found in each layer of two identical time-delayed coupled layers, and are different from the segmented spiral waves in a water-in-oil aerosol sodium bis（2-ethylhexyl） sulfosuccinate （AOT） microemulsion （ME） （BZ-AOT system）, which consists of many small segments. ＂Anti-phase spiral wave synchronization＂ can be realized between the first layer and the second one. For different excitable parameters, we also give the minimum values of the coupling strength to generate segmented spiral waves and the tip orbits of spiral waves in the whole bilayer.展开更多
This paper suggests a scheme of electromagnetic chirality-induced negative refraction utilizing magneto-lectric cross coupling in a four-level atomic system. The negative refraction can be achieved with the two chiral...This paper suggests a scheme of electromagnetic chirality-induced negative refraction utilizing magneto-lectric cross coupling in a four-level atomic system. The negative refraction can be achieved with the two chirality coefficients having the same amplitude but the opposite phase, without requiring the simultaneous presence of an electric-dipole and a magnetic-dipole transition near the same transition frequency.展开更多
Transition of flows past a pair of side-by-side circular cylinders are investigated by numerical simulations and the bifurcation analysis of the numerical results. Various flow patterns behind the cylinder-pair have b...Transition of flows past a pair of side-by-side circular cylinders are investigated by numerical simulations and the bifurcation analysis of the numerical results. Various flow patterns behind the cylinder-pair have been identified by the gap ratio (G) and Reynolds number (Re). This study focus on transition of in-phase and anti-phase vortex shedding synchronized forms. A nested Cartesian-grid formulation, in combination with an effective immersed boundary method and a two-step fractional-step procedure, has been adopted to simulate the flows. Numerical results reveal that the in-phase and anti-phase vortex shedding flows at Re = 100 can co-exist at 2.08 ≤G≤ 2.58. Hysteresis loop with increasing/decreasing G at constant Reynolds number Re = 100 is reported.展开更多
随着数字化技术和雷达系统的发展,针对合成孔径雷达(Synthetic Aperture Radar,SAR)的干扰对抗技术不断进步,尤其是基于数字射频存储技术(Digital Radio Frequency Memory,DRFM)产生的有源欺骗干扰为SAR成像系统带来了前所未有的考验。...随着数字化技术和雷达系统的发展,针对合成孔径雷达(Synthetic Aperture Radar,SAR)的干扰对抗技术不断进步,尤其是基于数字射频存储技术(Digital Radio Frequency Memory,DRFM)产生的有源欺骗干扰为SAR成像系统带来了前所未有的考验。针对欺骗干扰开展SAR成像抗干扰方法研究,本文基于相位编码波形与带有循环前缀的正交频分复用(Cyclic Prefix Orthogonal Frequency Division Multiplexing,CP-OFDM)波形进行正交波形设计,提出了相位编码CP-OFDM正交波形。基于CP-OFDM波形的循环前缀(Cyclic Prefix,CP)特征,引入基于线性模型的脉冲压缩方法对相位编码CP-OFDM正交波形的SAR成像回波进行距离向处理,能够实现无旁瓣干扰的自相关脉冲压缩。通过对相位编码CP-OFDM波形的时域相位进行编码优化设计,可以实现不同相位编码CP-OFDM波形之间良好的互相关性能。基于线性模型脉冲压缩方法改善了一种p范数多波形加权循环(p-norm Weighted Cyclic Algorithm,p-WeCAN)波形优化算法,采用该算法对相位编码CP-OFDM波形集的相位编码序列进行优化设计,优化后波形的互相关脉冲压缩结果的峰值水平(Peak Sidelobe Level,PSL)相比于随机相位编码CP-OFDM波形的互相关PSL改善了2 dB左右。CP特性赋予了相位编码CP-OFDM波形良好的自相关脉冲压缩结果,相位编码优化设计提供了良好的互相关脉冲压缩结果,采用该正交波形集进行SAR成像,能够实现对欺骗干扰的抑制。进行了点目标、面目标和基于GF-3回波数据反演的半实测数据的抗欺骗干扰SAR成像仿真,与基于线性调频(Linear Frequency Modulation,LFM)波形的欺骗干扰条件下的成像结果进行对比,验证了相位编码CP-OFDM对欺骗干扰的抑制能力。展开更多
Single crystal(SX)superalloys are required for full-operating-temperature mechanical properties.How-ever,the quest for intermediate temperature(IT)resistance often encounters a perplexing phenomenon:anomalous yielding...Single crystal(SX)superalloys are required for full-operating-temperature mechanical properties.How-ever,the quest for intermediate temperature(IT)resistance often encounters a perplexing phenomenon:anomalous yielding behavior coupled with an unexpected loss of ductility.This study delved into the tensile behavior of a[111]-oriented SX superalloy from room temperature(RT)to 1150℃,uncover-ing temperature-dependent tensile mechanisms where the interplay among phases and deferent de-fects governs plastic deformation.Desirable high strength-ductility properties were observed at IT,show-casing comparable strength with increased ductility.Microstructural evidences show that the primary strengthening effects stem from coupled interface boundary strengthening and anti-phase boundary(APB)strengthening,while the plasticity arises from planer defects transitioning from the stacking fault(SF)withinγphase at small strains,to superlattice SFs,ultimately to the erasure of superlattice SFs,leaving cutting dislocation pairs inγʹphase.Energy analysis of APB and SF,along with adherence to Schmid laws,reinforce the plausibility of such intricate defect interactions.The strength-ductility balance can be ascribed to the collective effect of preferentially generated dislocations and prompt formation of SF.This strategy of sequential defects’competition provides a new route for solving the strength-ductility trade-offof alloys.展开更多
Overcoming the tradeoffbetween mechanical strength and electrical conductivity is a long-standing chal-lenge in developing advanced copper alloys for industrial applications.Herein,we report a new strategy to obtain h...Overcoming the tradeoffbetween mechanical strength and electrical conductivity is a long-standing chal-lenge in developing advanced copper alloys for industrial applications.Herein,we report a new strategy to obtain high strength and good conductivity of Cu-Ni-Si-Ca alloy by introducing and regulating the discontinuous precipitation(DP)and continuous precipitation(CP)behaviors.The DP process combined with thermomechanical treatment was exploited to expedite the precipitation kinetics,whilst the com-petition between DP and CP was utilized to inhibit the nucleation and growth of continuous precipitation phase(CPP).The resultant copper alloy exhibits superior comprehensive properties with a yield strength of 956 MPa,fracture strength of 989 MPa,and electrical conductivity of 34.1%IACS.The improved elec-trical conductivity is attributed to the heterogeneous-nucleation dominant DP,while the high strength stems from the combination of strain hardening and precipitation strengthening of δ-Ni2 Si and t-Ni3 Si precipitates.Notably,the precipitation strengthening arises from both the dislocation passing and cutting mechanisms,with the strongly ordered DO22-type(t-Ni3 Si)phase contributing approximately 202 MPa to the overall strength through the cutting mechanism.This work offers a new pathway for alloy design of high-strength and high-electrical-conductivity copper alloys,by regulating coherent ordered nanoprecip-itates through DP and CP.展开更多
基金Beijing Excellent Talents Cultivation ProjectOceanography Science Foundation for Youth Scholars of State Oceanic Administration(2013256)
文摘Based on the daily rainfall datasets from 740 stations in China from 1954 to 2005 and the NCEP/NCAR reanalysis data, the relationship between the north-south anti-phase distribution(APD) of rainfall during Meiyu periods and the Quasi-Biweekly Oscillation(QBWO) in the atmosphere was analyzed. Diagnostic results are as follows:(1) there was significant north-south oscillation of Meiyu rainfall during the 16 years from 1954 to 2005. Since the 1990 s, the APD enhanced significantly and showed 2- and 4-6-year period. In the region with more rainfall, the QBWO was always more active.(2) The APD of Meiyu and north-south movements of precipitation in eastern China belong to the same phase.(3) The 10-25 day filtered water vapor flux could spread to the area north of 30°N in 1991. The divergence of the water vapor flux which propagated from middle- and higher- latitudes to the of Yangtze-Huaihe River Basins(YHRB) was significant in 1991, but the latitudes that the water vapor flux could reach were further southward and there was no southward propagation of divergence in 1993.(4) The locations of Western Pacific Subtropical High(WPSH) and 10-25 day anti-cyclone, which modulated WPSH's advancement in and out of the South China Sea, were relatively northward in 1991. Furthermore, the vertical circulation showed north-south deviation between 1991 and 1993, just as other elements of the circulation did.
基金The project supported by National Natural Science Foundation of China under Grant No.10647127National Natural Science Foundation of China for Major Projects under Grant No.10335010the Natural Science Foundation of Hebei Province of China under Grant No.A2006000128
文摘In this paper, we consider a model system with two identical time-delayed coupled layers. Synchronization and anti-phase synchronization are exhibited in the reactive system without diffusion term. New segmented spiral waves, which are constituted by many thin trips, are found in each layer of two identical time-delayed coupled layers, and are different from the segmented spiral waves in a water-in-oil aerosol sodium bis（2-ethylhexyl） sulfosuccinate （AOT） microemulsion （ME） （BZ-AOT system）, which consists of many small segments. ＂Anti-phase spiral wave synchronization＂ can be realized between the first layer and the second one. For different excitable parameters, we also give the minimum values of the coupling strength to generate segmented spiral waves and the tip orbits of spiral waves in the whole bilayer.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60768001 and 10464002)
文摘This paper suggests a scheme of electromagnetic chirality-induced negative refraction utilizing magneto-lectric cross coupling in a four-level atomic system. The negative refraction can be achieved with the two chirality coefficients having the same amplitude but the opposite phase, without requiring the simultaneous presence of an electric-dipole and a magnetic-dipole transition near the same transition frequency.
文摘Transition of flows past a pair of side-by-side circular cylinders are investigated by numerical simulations and the bifurcation analysis of the numerical results. Various flow patterns behind the cylinder-pair have been identified by the gap ratio (G) and Reynolds number (Re). This study focus on transition of in-phase and anti-phase vortex shedding synchronized forms. A nested Cartesian-grid formulation, in combination with an effective immersed boundary method and a two-step fractional-step procedure, has been adopted to simulate the flows. Numerical results reveal that the in-phase and anti-phase vortex shedding flows at Re = 100 can co-exist at 2.08 ≤G≤ 2.58. Hysteresis loop with increasing/decreasing G at constant Reynolds number Re = 100 is reported.
文摘随着数字化技术和雷达系统的发展,针对合成孔径雷达(Synthetic Aperture Radar,SAR)的干扰对抗技术不断进步,尤其是基于数字射频存储技术(Digital Radio Frequency Memory,DRFM)产生的有源欺骗干扰为SAR成像系统带来了前所未有的考验。针对欺骗干扰开展SAR成像抗干扰方法研究,本文基于相位编码波形与带有循环前缀的正交频分复用(Cyclic Prefix Orthogonal Frequency Division Multiplexing,CP-OFDM)波形进行正交波形设计,提出了相位编码CP-OFDM正交波形。基于CP-OFDM波形的循环前缀(Cyclic Prefix,CP)特征,引入基于线性模型的脉冲压缩方法对相位编码CP-OFDM正交波形的SAR成像回波进行距离向处理,能够实现无旁瓣干扰的自相关脉冲压缩。通过对相位编码CP-OFDM波形的时域相位进行编码优化设计,可以实现不同相位编码CP-OFDM波形之间良好的互相关性能。基于线性模型脉冲压缩方法改善了一种p范数多波形加权循环(p-norm Weighted Cyclic Algorithm,p-WeCAN)波形优化算法,采用该算法对相位编码CP-OFDM波形集的相位编码序列进行优化设计,优化后波形的互相关脉冲压缩结果的峰值水平(Peak Sidelobe Level,PSL)相比于随机相位编码CP-OFDM波形的互相关PSL改善了2 dB左右。CP特性赋予了相位编码CP-OFDM波形良好的自相关脉冲压缩结果,相位编码优化设计提供了良好的互相关脉冲压缩结果,采用该正交波形集进行SAR成像,能够实现对欺骗干扰的抑制。进行了点目标、面目标和基于GF-3回波数据反演的半实测数据的抗欺骗干扰SAR成像仿真,与基于线性调频(Linear Frequency Modulation,LFM)波形的欺骗干扰条件下的成像结果进行对比,验证了相位编码CP-OFDM对欺骗干扰的抑制能力。
基金sponsored by the National Natural Science Foundations of China(Nos.52101116,52301126,and 92360302)the Science Center for Gas Turbine Project(Nos.P2022-A-I-001-001 and P2022-A-Ⅰ-002-002)+2 种基金the National Science and Technology Major Project(No.2019-Ⅵ-0016-0131)the Beijing Nova Program(No.20230484318)the Key R&D Program of Zhejiang(No.2024SSYS0076).
文摘Single crystal(SX)superalloys are required for full-operating-temperature mechanical properties.How-ever,the quest for intermediate temperature(IT)resistance often encounters a perplexing phenomenon:anomalous yielding behavior coupled with an unexpected loss of ductility.This study delved into the tensile behavior of a[111]-oriented SX superalloy from room temperature(RT)to 1150℃,uncover-ing temperature-dependent tensile mechanisms where the interplay among phases and deferent de-fects governs plastic deformation.Desirable high strength-ductility properties were observed at IT,show-casing comparable strength with increased ductility.Microstructural evidences show that the primary strengthening effects stem from coupled interface boundary strengthening and anti-phase boundary(APB)strengthening,while the plasticity arises from planer defects transitioning from the stacking fault(SF)withinγphase at small strains,to superlattice SFs,ultimately to the erasure of superlattice SFs,leaving cutting dislocation pairs inγʹphase.Energy analysis of APB and SF,along with adherence to Schmid laws,reinforce the plausibility of such intricate defect interactions.The strength-ductility balance can be ascribed to the collective effect of preferentially generated dislocations and prompt formation of SF.This strategy of sequential defects’competition provides a new route for solving the strength-ductility trade-offof alloys.
基金supported by the Funds for Cre-ative Research Groups of China(No.51921001)the National Natural Science Foundation of China Major Research Program Integration Project(No.92266301)+2 种基金the Natural Science Foundation for Distinguished Young Scholars of China(No.51925401)the National Key Research and Development Programme of China(No.2023YFB3812601)the Youth Foundation of National Natural Science Foundation China(No.52001020).
文摘Overcoming the tradeoffbetween mechanical strength and electrical conductivity is a long-standing chal-lenge in developing advanced copper alloys for industrial applications.Herein,we report a new strategy to obtain high strength and good conductivity of Cu-Ni-Si-Ca alloy by introducing and regulating the discontinuous precipitation(DP)and continuous precipitation(CP)behaviors.The DP process combined with thermomechanical treatment was exploited to expedite the precipitation kinetics,whilst the com-petition between DP and CP was utilized to inhibit the nucleation and growth of continuous precipitation phase(CPP).The resultant copper alloy exhibits superior comprehensive properties with a yield strength of 956 MPa,fracture strength of 989 MPa,and electrical conductivity of 34.1%IACS.The improved elec-trical conductivity is attributed to the heterogeneous-nucleation dominant DP,while the high strength stems from the combination of strain hardening and precipitation strengthening of δ-Ni2 Si and t-Ni3 Si precipitates.Notably,the precipitation strengthening arises from both the dislocation passing and cutting mechanisms,with the strongly ordered DO22-type(t-Ni3 Si)phase contributing approximately 202 MPa to the overall strength through the cutting mechanism.This work offers a new pathway for alloy design of high-strength and high-electrical-conductivity copper alloys,by regulating coherent ordered nanoprecip-itates through DP and CP.
