An atmosphere-vegetation interaction model (AVIM) has been coupled with a nine-layer General Cir culation Model (GCM) of Institute of Atmospheic Physics / State Key Laboratory of Numerical Modeling for Atmospheric Sci...An atmosphere-vegetation interaction model (AVIM) has been coupled with a nine-layer General Cir culation Model (GCM) of Institute of Atmospheic Physics / State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (IAP/ LASG), which is rhomboidally truncated at zonal wave number 15, to simulate global climatic mean states. AVIM is a model having inter-feedback between land surface processes and eco-physiological processes on land. As the first step to couple land with atmosphere completely, the physiological processes are fixed and only the physical part (generally named the SVAT (soil-vegetation-atmosphere-transfer scheme) model) of AVIM is nested into IAP/ LASG L9R15 GCM. The ocean part of GCM is prescribed and its monthly sea surface temperature (SST) is the climatic mean value. With respect to the low resolution of GCM, i.e., each grid cell having lon gitude 7.5?and latitude 4.5? the vegetation is given a high resolution of 1.5?by 1.5?to nest and couple the fine grid cells of land with the coarse grid cells of atmosphere. The coupling model has been integrated for 15 years and its last ten-year mean of outputs was chosen for analysis.Compared with observed data and NCEP reanalysis, the coupled model simulates the main characteris tics of global atmospheric circulation and the fields of temperature and moisture. In particular, the simu lated precipitation and surface air temperature have sound results. The work creates a solid base on coupling climate models with the biosphere.展开更多
The high-pressure phase diagram of the Nb-Ti binary system at 0 K is explored by systematic crystal structure prediction.The results highlight a novel niobium-rich bcc phase,Nb_(7)Ti,which is the only dynamically stab...The high-pressure phase diagram of the Nb-Ti binary system at 0 K is explored by systematic crystal structure prediction.The results highlight a novel niobium-rich bcc phase,Nb_(7)Ti,which is the only dynamically stable ordered Nb-Ti compound under ambient pressure.Extensive first-principles calculations have provided insights into the electronic structure,bonding and superconducting properties of Nb_(7)Ti.The superconducting transition temperature(T_(c))for Nb_(7)Ti at ambient pressure is estimated within the framework of BCS theory to be about 17.5 K,which is significantly higher—nearly double—that of the widely utilized NbTi alloy.Furthermore,the results unveil that the high T_(c) is mainly attributed to the unique ordered lattice along with the strong electron-phonon coupling driven by interatomic interactions at mid-frequency and phonon softening induced by low-frequency Fermi surface nesting.Valuable insights are provided for the subsequent synthesis of application-oriented superconductors at low pressure.展开更多
Brushless Doubly-Fed Machine has attracted considerable attention in recent years due to its advantages. It has the robustness of the squirrel cage induction machine, and the speed and power factor controllability of ...Brushless Doubly-Fed Machine has attracted considerable attention in recent years due to its advantages. It has the robustness of the squirrel cage induction machine, and the speed and power factor controllability of the synchronous machine as well as the absence of brushes and slip rings, and using a fractionally rated frequency converter. Hence, there are considerable benefits over the conventional machines, when the machine is applied to applications such as a wind turbine generator or high power adjustable speed drive. However, these benefits are obtained in slightly more complex structure, higher cost and larger dimensions in comparison to the conventional induction machine. This paper presents fundamental aspects of the three modes of operation of brushless doubly fed machine, i.e. simple induction mode, cascade induction mode, and synchronous mode. The investigation is performed by analyzing the spatial harmonic contents of the rotor magnetic flux density. The direct cross couplings between stator and rotor fields as well as, indirect cross coupling between stator fields by the special rotor of this machine is described. Furthermore, loss analysis of the machine in various modes is presented and the torque-speed curves for asynchronous modes are obtained. A 2-D magnetodynamic finite element model based on the D-180 4/8 pole prototype machine is extracted and simulated to verify the results.展开更多
为了减小阵元之间的互耦效应,首先提出一种阵元间距可调节的互素嵌套阵列。这种阵列由2个不同的嵌套子阵列组成,2个子阵的最小阵元间距由一对互素的正整数确定。只要这对正整数足够大,2个子阵的最小阵元间距便可远超过入射信号的半个波...为了减小阵元之间的互耦效应,首先提出一种阵元间距可调节的互素嵌套阵列。这种阵列由2个不同的嵌套子阵列组成,2个子阵的最小阵元间距由一对互素的正整数确定。只要这对正整数足够大,2个子阵的最小阵元间距便可远超过入射信号的半个波长,从而将阵元间的互耦效应减小到可忽略的程度。然后,为了解决大间距阵列所引起的角度模糊问题,提出了一种基于四阶累积量的无模糊波达方向(DOA,direction of arrival)估计算法。仿真实验表明,此算法具有较好的估计性能,相比一些经典的自校正DOA估计算法,此算法具有更高的角度分辨力和估计精确度。展开更多
基金This paper is financially supported by the NKBRSF(National Key Basic Research Special Funds)project ofChina(G1999043400).the Key Project of Knowledge Innovation Engineering of Chinese Academy of Sciences(ZKCX2-SW-210),and the Lead Project of Innovation
文摘An atmosphere-vegetation interaction model (AVIM) has been coupled with a nine-layer General Cir culation Model (GCM) of Institute of Atmospheic Physics / State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (IAP/ LASG), which is rhomboidally truncated at zonal wave number 15, to simulate global climatic mean states. AVIM is a model having inter-feedback between land surface processes and eco-physiological processes on land. As the first step to couple land with atmosphere completely, the physiological processes are fixed and only the physical part (generally named the SVAT (soil-vegetation-atmosphere-transfer scheme) model) of AVIM is nested into IAP/ LASG L9R15 GCM. The ocean part of GCM is prescribed and its monthly sea surface temperature (SST) is the climatic mean value. With respect to the low resolution of GCM, i.e., each grid cell having lon gitude 7.5?and latitude 4.5? the vegetation is given a high resolution of 1.5?by 1.5?to nest and couple the fine grid cells of land with the coarse grid cells of atmosphere. The coupling model has been integrated for 15 years and its last ten-year mean of outputs was chosen for analysis.Compared with observed data and NCEP reanalysis, the coupled model simulates the main characteris tics of global atmospheric circulation and the fields of temperature and moisture. In particular, the simu lated precipitation and surface air temperature have sound results. The work creates a solid base on coupling climate models with the biosphere.
基金supported by the National Natural Science Foundation of China(Grant Nos.12122405,12274169,and 11574109)the Fundamental Research Funds for the Central Universities。
文摘The high-pressure phase diagram of the Nb-Ti binary system at 0 K is explored by systematic crystal structure prediction.The results highlight a novel niobium-rich bcc phase,Nb_(7)Ti,which is the only dynamically stable ordered Nb-Ti compound under ambient pressure.Extensive first-principles calculations have provided insights into the electronic structure,bonding and superconducting properties of Nb_(7)Ti.The superconducting transition temperature(T_(c))for Nb_(7)Ti at ambient pressure is estimated within the framework of BCS theory to be about 17.5 K,which is significantly higher—nearly double—that of the widely utilized NbTi alloy.Furthermore,the results unveil that the high T_(c) is mainly attributed to the unique ordered lattice along with the strong electron-phonon coupling driven by interatomic interactions at mid-frequency and phonon softening induced by low-frequency Fermi surface nesting.Valuable insights are provided for the subsequent synthesis of application-oriented superconductors at low pressure.
文摘Brushless Doubly-Fed Machine has attracted considerable attention in recent years due to its advantages. It has the robustness of the squirrel cage induction machine, and the speed and power factor controllability of the synchronous machine as well as the absence of brushes and slip rings, and using a fractionally rated frequency converter. Hence, there are considerable benefits over the conventional machines, when the machine is applied to applications such as a wind turbine generator or high power adjustable speed drive. However, these benefits are obtained in slightly more complex structure, higher cost and larger dimensions in comparison to the conventional induction machine. This paper presents fundamental aspects of the three modes of operation of brushless doubly fed machine, i.e. simple induction mode, cascade induction mode, and synchronous mode. The investigation is performed by analyzing the spatial harmonic contents of the rotor magnetic flux density. The direct cross couplings between stator and rotor fields as well as, indirect cross coupling between stator fields by the special rotor of this machine is described. Furthermore, loss analysis of the machine in various modes is presented and the torque-speed curves for asynchronous modes are obtained. A 2-D magnetodynamic finite element model based on the D-180 4/8 pole prototype machine is extracted and simulated to verify the results.
文摘为了减小阵元之间的互耦效应,首先提出一种阵元间距可调节的互素嵌套阵列。这种阵列由2个不同的嵌套子阵列组成,2个子阵的最小阵元间距由一对互素的正整数确定。只要这对正整数足够大,2个子阵的最小阵元间距便可远超过入射信号的半个波长,从而将阵元间的互耦效应减小到可忽略的程度。然后,为了解决大间距阵列所引起的角度模糊问题,提出了一种基于四阶累积量的无模糊波达方向(DOA,direction of arrival)估计算法。仿真实验表明,此算法具有较好的估计性能,相比一些经典的自校正DOA估计算法,此算法具有更高的角度分辨力和估计精确度。
