Photoluminescence (PL) polarization of a spin ensemble was examined over a wide excitation wavelength range from 520 nm to 700 nm and a temperature range from 3.5 K to 300 K after it transfers from a (AlGa)As barrier ...Photoluminescence (PL) polarization of a spin ensemble was examined over a wide excitation wavelength range from 520 nm to 700 nm and a temperature range from 3.5 K to 300 K after it transfers from a (AlGa)As barrier layer and eventually quenches irradiatively in a GaAs quantum well (QW).A highest PL circular polarization of 30% can be kept at temperatures up to 120 K,while its room temperature value reaches about 17%.It is found that the main features of the optical spin orientation in bulk Al 0.27 Ga 0.73 As materials can be reproduced in terms of the wavelength dependence of PL polarization degree,as the spin polarized ensemble transfers and relaxes into GaAs QW.The transient of PL polarization degree also indicates that a dense spin ensemble collected from the barrier region is in favor of conserving its polarization in GaAs QW as evidenced by a rising temporal response.展开更多
This study established a 3D finite element model for 15# hydropower house of the Three Gorges Project (TGP) and performed a nonlinear dynamic analysis under pressure fluctuation. In this numerical model, the stiffness...This study established a 3D finite element model for 15# hydropower house of the Three Gorges Project (TGP) and performed a nonlinear dynamic analysis under pressure fluctuation. In this numerical model, the stiffness degradation in tension for concrete was considered on the basis of the continuum isotropic damage theory. Natural vibration frequencies of the damaged and undamaged structures were compared after static water pressure was applied. Then a study was further conducted on forced vibration of the powerhouse with pre-existing damages under pressure fluctuation that acts on the flow passage; displacement, velocity and acceleration of the important structural members were afterwards presented and checked. Numerical results show that tensile damages in concrete surrounding the spiral case only exert significant impact upon the dynamic characteristics of substructure but show little effect on the superstructure. Nevertheless vibrations of the powerhouse are still under the recommended vibration limits.展开更多
The stochastic stability of the harmonically and randomly excited Duffing oscillator with damping modeled by a fractional derivative of Caputo's definition is analyzed.First,the system state is approximately descr...The stochastic stability of the harmonically and randomly excited Duffing oscillator with damping modeled by a fractional derivative of Caputo's definition is analyzed.First,the system state is approximately described by It equations through the stochastic averaging method based on the generalized harmonic function.Then,the associated expression for the largest Lyapunov exponent of the linearized averaged It is derived,and the necessary and sufficient condition for the asymptotic stability with probability one of the trivial solution of the original system is obtained approximately by letting the largest Lyapunov exponent be negative.The effects of fractional orders and random excitation intensities on the asymptotic stability with probability one determined by the largest Lyapunov exponent are shown graphically.展开更多
基金supported by the National Basic Research Program of China (Grant Nos.2007CB924904 and 2011CB932901)
文摘Photoluminescence (PL) polarization of a spin ensemble was examined over a wide excitation wavelength range from 520 nm to 700 nm and a temperature range from 3.5 K to 300 K after it transfers from a (AlGa)As barrier layer and eventually quenches irradiatively in a GaAs quantum well (QW).A highest PL circular polarization of 30% can be kept at temperatures up to 120 K,while its room temperature value reaches about 17%.It is found that the main features of the optical spin orientation in bulk Al 0.27 Ga 0.73 As materials can be reproduced in terms of the wavelength dependence of PL polarization degree,as the spin polarized ensemble transfers and relaxes into GaAs QW.The transient of PL polarization degree also indicates that a dense spin ensemble collected from the barrier region is in favor of conserving its polarization in GaAs QW as evidenced by a rising temporal response.
基金Project (No. 50809013) supported by the National Natural Science Foundation of China
文摘This study established a 3D finite element model for 15# hydropower house of the Three Gorges Project (TGP) and performed a nonlinear dynamic analysis under pressure fluctuation. In this numerical model, the stiffness degradation in tension for concrete was considered on the basis of the continuum isotropic damage theory. Natural vibration frequencies of the damaged and undamaged structures were compared after static water pressure was applied. Then a study was further conducted on forced vibration of the powerhouse with pre-existing damages under pressure fluctuation that acts on the flow passage; displacement, velocity and acceleration of the important structural members were afterwards presented and checked. Numerical results show that tensile damages in concrete surrounding the spiral case only exert significant impact upon the dynamic characteristics of substructure but show little effect on the superstructure. Nevertheless vibrations of the powerhouse are still under the recommended vibration limits.
基金supported by the National Natural Science Foundation of China(Grant Nos.10932009,11072212 and 11002059)the Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20103501120003)+2 种基金the Natural Science Foundation of Fujian Province (Grant No.2010J05006)the Fundamental Research Funds for Huaqiao University(Grant No.JB-SJ1010)the Research & Development Start Funds of Huaqiao University(Grant No.09BS622)
文摘The stochastic stability of the harmonically and randomly excited Duffing oscillator with damping modeled by a fractional derivative of Caputo's definition is analyzed.First,the system state is approximately described by It equations through the stochastic averaging method based on the generalized harmonic function.Then,the associated expression for the largest Lyapunov exponent of the linearized averaged It is derived,and the necessary and sufficient condition for the asymptotic stability with probability one of the trivial solution of the original system is obtained approximately by letting the largest Lyapunov exponent be negative.The effects of fractional orders and random excitation intensities on the asymptotic stability with probability one determined by the largest Lyapunov exponent are shown graphically.
